HOT STAMPED BODY

- NIPPON STEEL CORPORATION

Provided is a hot stamped body having a predetermined chemical composition and a microstructure comprising, by area ratio, at least one of martensite, bainite, and tempered martensite: 90% or more in total, wherein a standard deviation in grain size distribution of former austenite grains is 5.0 μm or less, and a total amount of segregation of at least one of Mo, W, Ta, Re, Os, Ir, and Tc at the former austenite grain boundaries is 0.10 atm % or more.

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Description
FIELD

The present invention relates to a hot stamped body.

BACKGROUND

In recent years, in the automobile industry, lighter weight of car bodies has been sought from the viewpoint of improvement of fuel economy. To achieve both lighter weight of car bodies and collision safety, one effective method is to increase the strength of the steel sheet used. A high strength steel sheet is being developed due to such a background.

If making a steel sheet high in strength, the formability falls, and therefore it is generally difficult to achieve both strength and formability in the steel sheet. Hot stamping (hot pressing) is known as a technique for press-forming a material, which is difficult to form, such as a high strength steel sheet. Hot stamping is a technique of hot forming which heats then forms a material to be formed. This technique heats then forms the material, and therefore at the time of forming, the steel material is soft and has good formability. Therefore, even a high strength steel material can be formed into a complex shape with a good precision. Further, it is hardened at the same time as being formed by the press dies, and therefore a formed steel material is known to have sufficient strength.

In relation to this, PTL 1 describes a hot stamped body characterized by having a predetermined chemical composition and a microstructure containing former austenite with an average grain size of 3 μm or less and, further, containing at least one of lower bainite, martensite, and tempered martensite in an area ratio of 90% or more, wherein a grain boundary solid solution ratio Z, defined by Z=(mass % of one or both of Nb and Mo at the grain boundaries)/(mass % of one or both of Nb and Mo at time of melting), is 0.3 or more. Further, PTL 1 describes that the hot stamped body has a tensile strength of 2000 MPa or more.

CITATIONS LIST Patent Literature

    • [PTL 1] WO 2019/186928

SUMMARY Technical Problem

If the strength of a steel material becomes higher, in general, the phenomenon of the steel material fracturing before reaching its maximum stress (early fracture) easily arises. For this reason, there is a high need for a steel material enabling suppression of such early fracture. In relation to this, PTL 1 teaches that in a hot stamped body having the above feature, there will be a high tensile strength of 2000 MPa or more and, in addition, early fracture will be suppressed. On the other hand, in the automobile industry, etc., further reduction of weight of the steel material is sought. To achieve such lighter weight, a need arises to raise the strength more than the past. Therefore, there is still a great need for a steel material, more specifically a hot stamped body, able to solve the problem of early fracture even if raising the strength equal to the past or more than the same.

Therefore, the present invention has as its object to provide a hot stamped body which is high in strength and able to suppress early fracture by a novel constitution.

Solution to Problem

The inventors discovered that, to achieve the above object, it is possible to reduce the variation in former austenite grain size in the microstructure of a hot stamped body so as to suppress the rise in local hardness acting as starting points of fracture and in addition possible to make specific elements segregate at the grain boundaries to reinforce the grain boundaries and further discovered that by the combination of such suppression of rise of local hardness and grain boundary strengthening, it is possible to sufficiently suppress early fracture regardless of the hot stamped body having a high tensile strength, and thereby completed the present invention.

The present invention able to achieve this object is as follows:

    • (1) A hot stamped body having a chemical composition comprising, by mass %,
      • C: 0.40 to 0.70%,
      • Si: 0.010 to 3.00%,
      • Mn: 0.50 to 3.00%,
      • P: 0.100% or less,
      • S: 0.0100% or less,
      • N: 0.0200% or less,
      • O: 0.0200% or less,
      • Al: 0.0010 to 0.500%,
      • Nb: 0.0010 to 0.100%,
      • Ti: 0.010 to 0.200%,
      • Cr: 0.010 to 1.00%,
      • Mo: 0.0010 to 1.000%,
      • B: 0.0005 to 0.0200%,
      • Co: 0 to 4.00%,
      • Ni: 0 to 3.00%,
      • Cu: 0 to 3.00%,
      • V: 0 to 3.00%,
      • Ca: 0 to 1.000%,
      • Mg: 0 to 1.000%,
      • REM: 0 to 1.000%,
      • Sb: 0 to 1.00%,
      • Sn: 0 to 1.00%,
      • Zr: 0 to 1.00%,
      • As: 0 to 0.100%,
      • at least one of W, Ta, Re, Os, Ir, and Tc: 0 to 1.00% in total, and balance: Fe and impurities, and
      • a microstructure comprising, by area ratio, at least one of martensite, bainite, and tempered martensite: 90% or more in total, wherein
      • a standard deviation in grain size distribution of former austenite grains is 5.0 μm or less, and
      • a total amount of segregation of at least one of Mo, W, Ta, Re, Os, Ir, and Tc at former austenite grain boundaries is 0.10 atm % or more.
    • (2) The hot stamped body according to the above (1), wherein the amount of segregation of Mo at the former austenite grain boundaries is 0.10 atm % or more.
    • (3) The hot stamped body according to the above (1) or (2), wherein the total amount of segregation is 0.15 atm % or more.

Advantageous Effects of Invention

According to the present invention, it is possible to provide a hot stamped body which is high in strength and able to suppress early fracture.

DESCRIPTION OF EMBODIMENTS <Hot Stamped Body>

The hot stamped body according to an embodiment of the present invention has a chemical composition comprising, by mass %,

    • C: 0.40 to 0.70%,
    • Si: 0.010 to 3.00%,
    • Mn: 0.50 to 3.00%,
    • P: 0.100% or less,
    • S: 0.0100% or less,
    • N: 0.0200% or less,
    • O: 0.0200% or less,
    • Al: 0.0010 to 0.500%,
    • Nb: 0.0010 to 0.100%,
    • Ti: 0.010 to 0.200%,
    • Cr: 0.010 to 1.00%,
    • Mo: 0.0010 to 1.000%,
    • B: 0.0005 to 0.0200%,
    • Co: 0 to 4.00%,
    • Ni: 0 to 3.00%,
    • Cu: 0 to 3.00%,
    • V: 0 to 3.00%,
    • Ca: 0 to 1.000%,
    • Mg: 0 to 1.000%,
    • REM: 0 to 1.000%,
    • Sb: 0 to 1.00%,
    • Sn: 0 to 1.00%,
    • Zr: 0 to 1.00%,
    • As: 0 to 0.100%,
    • at least one of W, Ta, Re, Os, Ir, and Tc: 0 to 1.00% in total, and balance: Fe and impurities, and
    • a microstructure comprising, by area ratio, at least one of martensite, bainite, and tempered martensite: 90% or more in total, wherein
    • a standard deviation in grain size distribution of former austenite grains is 5.0 μm or less, and
    • a total amount of segregation of at least one of Mo, W, Ta, Re, Os, Ir, and Tc at former austenite grain boundaries is 0.10 atm % or more.

As explained above, there is the problem that if the strength of a steel material becomes higher, in general, the phenomenon of the steel material fracturing before reaching the maximum stress (early fracture) easily occurs. Therefore, the inventors conducted studies focusing on the two viewpoints of the viewpoint of reducing hard regions able to become starting points for fracture and the viewpoint of strengthening the grain boundaries for preventing or suppressing fracture. More specifically, the inventors first discovered that if there is a large variation in former austenite grain size in the microstructure, the hardness becomes higher in a region with a smaller former austenite grain size and that such a local high hardness region can become a starting point of early fracture. As opposed to this, the inventors discovered that by controlling the standard deviation in a grain size distribution of former austenite grains to 5.0 μm or less, it is possible to reliably suppress such a rise in local hardness.

While not intending to be bound to any specific theory, it is believed that at the time of hot stamping, the starting temperature of martensite transformation changes in accordance with the size of the austenite grains. If explained in more detail, it is believed that austenite grains having larger size are higher in starting temperature of martensite transformation compared with austenite grains having smaller size, and therefore the hardness becomes lower. Austenite grains having smaller size rise in hardness since martensite transformation occurs at a lower temperature than large grains. Therefore, to suppress or reduce the rise in such local hardness, it becomes important to reduce the variation in the austenite grain size before martensite transformation. Due to such a reason, it is believed that by controlling the standard deviation in the grain size distribution of the former austenite grains to 5.0 μm or less to reduce the variation in former austenite grain size, it would become possible to remarkably suppress the rise in local hardness due to differences in timing of martensite transformation. If there is locally a region of a high hardness, it is believed that there will be a high possibility of such a region acting as a starting point triggering early fracture, and therefore reducing the variation in former austenite grain size would be extremely effective in suppressing early fracture.

In relation to this, as explained later in detail regarding the method of production of the hot stamped body, the inventors focused on the microstructure of a hot rolled steel sheet and discovered that by evenly dispersing the pearlite in the microstructure, it is possible to control the standard deviation of former austenite grains in the final microstructure of the hot stamped body to 5.0 μm or less. Along with the increasingly higher strength of steel materials, sometimes a relatively large amount of Mn is added so as to improve the hardenability of the steel material, but in the research by the inventors this time, it was learned that with such a high Mn content (for example, 0.50 mass % or more), pearlite is relatively easily formed and therefore compared with the case of a low Mn content, it is extremely difficult to evenly disperse the pearlite formed in large amounts in the microstructure of the hot rolled steel sheet. However, the inventors discovered that to deal with such a problem, it is possible to uniformly disperse the pearlite in the microstructure of the hot rolled steel sheet by relatively high reduction at the final stage of finish rolling and that as a result it is possible to remarkably reduce the variation in former austenite grain size in the final microstructure of the hot stamped body. On the other hand, with just reducing the variation in former austenite grain size and reducing the regions which can act as starting points of early fracture, there is a possibility that if a crack occurs, it will not be possible to reliably suppress its progression and prevent early fracture.

Therefore, next, the inventors engaged in further studies from the viewpoint of suppressing progression of cracks along the grain boundaries and discovered that by causing specific elements, more specifically at least one of Mo, W, Ta, Re, Os, Ir, and Tc, to segregate at the former austenite grain boundaries in a total amount of segregation of these of 0.10 atm % or more, it is possible to strengthen the former austenite grain boundaries at the microstructure of the hot stamped body. As a result, the inventors discovered that by the combination of suppression of the rise in local hardness explained above and the strengthening of former austenite grain boundaries by such specific grain boundary strengthening elements, despite the hot stamped body having a high tensile strength, it is possible to sufficiently suppress early fracture. In the past, the fact that, for example, from the viewpoint of improvement of the hardenability, etc., while it is known to add some of these elements to a steel sheet for hot stamping use, it is possible to add at least one of Mo, W, Ta, Re, Os, Ir, and Tc in a predetermined total amount and, further, control the heat treatment conditions to make them segregate at the former austenite grain boundaries and possible to strengthen the former austenite grain boundaries in a superhigh strength steel material containing 0.40 mas % or more of carbon and thereby suppress the progression of cracks along the grain boundaries was clarified the first time by the inventors this time. In the hot stamped body according to an embodiment of the present invention, by combining the suppression of rise of local hardness and grain boundary strengthening by grain boundary segregation of such specific elements, it is possible to reduce the regions which act as starting points of early fracture and reliably suppress the progression of cracks along the grain boundaries even in the case of occurrence of cracks at the hot stamped body. For this reason, according to the hot stamped body according to an embodiment of the present invention, early fracture can be suppressed regardless of having a high tensile strength, for example, a high tensile strength of 2200 MPa or more.

Below, the hot stamped body according to the embodiment of the present invention will be explained in more detail. In the following explanation, the “%” of the units of content of the elements, unless otherwise indicated, means “mass %”. Further, in this Description, “to” showing a numerical range, unless otherwise indicated, is used in the sense including the numerical values described before and after it as the upper limit value and lower limit value.

[C: 0.40 to 0.70%]

C is an element improving the strength of a hot stamped body. If the C content is less than 0.40%, it is not possible to obtain the desired strength at the hot stamped body. For this reason, the C content is 0.40% or more. The C content is preferably 0.42% or more, 0.44% or more, or 0.45% or more.

On the other hand, if the C content is more than 0.70%, the toughness of the martensite is too low and an excellent early fracture resistance cannot be obtained. For this reason, the C content is 0.70% or less. Preferably, the C content is 0.67% or less, 0.65% or less, or 0.60% or less.

[Si: 0.010 to 3.00%]

Si is an element improving the strength of a hot stamped body by solid solution strengthening. If the Si content is less than 0.010%, it is not possible to obtain the desired strength. For this reason, the Si content is 0.010% or more. The Si content is preferably 0.05% or more, 0.10% or more, 0.15% or more, or 0.20% or more.

On the other hand, if the Si content is more than 3.00%, the amount of ferrite increases and the desired metallographic structure cannot be obtained. For this reason, the Si content is 3.00% or less. The Si content is preferably 2.50% or less, 2.00% or less, 1.00% or less, or 0.70% or less.

[Mn: 0.50 to 3.00%]

Mn is an element which promotes the transformation from austenite to pearlite in a hot rolled steel sheet in the process of production of a hot stamped body according to the present embodiment and contributes to control of the former austenite grain size distribution of a hot stamped body. To make the standard deviation in the grain size distribution of former austenite grains the desired range, the Mn content is 0.50% or more. The Mn content is preferably 0.70% or more, 1.00% or more, or 1.30% or more.

On the other hand, if the Mn content is more than 3.00%, transformation from austenite to pearlite in a hot rolled steel sheet is promoted too much and the standard deviation in the grain size distribution of former austenite grains in a hot stamped body cannot be controlled to a desired range. For this reason, the Mn content is 3.00% or less. Preferably, the Mn content is 2.70% or less, 2.50% or less, 2.30% or less, or 2.00% or less.

[P: 0.100% or Less]

P is an impurity element and segregates at the grain boundaries to form starting points of fracture and cause the early fracture resistance to deteriorate. For this reason, the P content is 0.100% or less. The P content is preferably 0.050% or less or 0.010% or less. The lower limit of the P content is not particularly prescribed, but if less than 0.0001%, the dephosphorization cost greatly rises making this not preferable economically. For this reason, the P content may also be 0.0001% or more.

[S: 0.0100% or Less]

S is an impurity element and forms inclusions in the steel. The inclusions become starting points of fracture and cause the early fracture resistance to deteriorate, therefore the S content is 0.0100% or less. The S content is preferably 0.0080% or less, 0.0050% or less, or 0.0030% or less.

The lower limit of the S content is not particularly prescribed, but if less than 0.0001%, the desulfurization cost greatly rises making this not preferable economically. For this reason, the S content may also be 0.0001% or more.

[N: 0.0200% or Less]

N is an impurity element and forms inclusions in the steel. The inclusions become starting points of fracture and cause the early fracture resistance to deteriorate, therefore the N content is 0.0200% or less. The N content is preferably 0.0150% or less, 0.0100% or less, 0.0060% or less, or 0.0040% or less.

The lower limit of the N content is not particularly prescribed, but if less than 0.0001%, the denitridation cost greatly rises making this not preferable economically. For this reason, the N content may also be 0.0001% or more.

[O: 0.0200% or Less]

O, if contained in a large amount in the steel, forms coarse oxides acting as starting points of fracture and causes the early fracture resistance of a hot stamped body to deteriorate. For this reason, the O content is 0.0200% or less. The O content is preferably 0.0100% or less, 0.0070% or less, or 0.0040% or less.

From the viewpoint of reducing the refining costs, the O content may also be 0.0001% or more. To make a large number of fine oxides disperse at the time of deoxidation of the molten steel, the O content may be 0.0005% or more.

[Al: 0.0010 to 0.500%]

Al is an element having the action of deoxidizing the molten steel and making the steel sounder. If the Al content is less than 0.0010%, deoxidation will not sufficiently proceed and coarse oxides will be formed causing the early fracture resistance to deteriorate. For this reason, the Al content is 0.0010% or more. The Al content is preferably 0.005% or more, 0.010% or more, or 0.030% or more.

On the other hand, if the Al content is more than 0.500%, coarse oxides will form in the steel causing the early fracture resistance of a hot stamped body to fall. For this reason, the Al content is 0.500% or less. The Al content is preferably 0.400% or less, 0.300% or less, 0.200% or less, or 0.100% or less.

[Nb: 0.0010 to 0.100%]

Nb is an element forming carbonitrides in steel and improving the strength of a hot stamped body by precipitation strengthening. If the Nb content is less than 0.0010%, the desired strength cannot be obtained. For this reason, the Nb content is 0.0010% or more. The Nb content is preferably 0.005% or more, 0.009% or more, or 0.015% or more.

On the other hand, if the Nb content is more than 0.100%, a large amount of coarse carbonitrides are formed in the steel and the early fracture resistance of a hot stamped body deteriorates. For this reason, the Nb content is 0.100% or less. The Nb content is preferably 0.080% or less, 0.060% or less, or 0.050% or less.

[Ti: 0.010 to 0.200%]

Ti is an element forming carbonitrides in steel and improving the strength of a hot stamped body by precipitation strengthening. If the Ti content is less than 0.010%, the desired strength cannot be obtained. For this reason, the Ti content is 0.010% or more. The Ti content is preferably 0.015% or more, 0.020% or more, or 0.025% or more. On the other hand, if the Ti content is more than 0.200%, a large amount of coarse carbonitrides are formed in the steel and the early fracture resistance of a hot stamped body deteriorates. For this reason, the Ti content is 0.200% or less. The Ti content is preferably 0.150% or less, 0.100% or less, 0.080% or less, 0.060% or less, or 0.050% or less.

[Cr: 0.010 to 1.00%]

Cr is an element dissolving in the former austenite grains at the time of heating before hot stamping and thereby raising the strength of a hot stamped body. If the Cr content is less than 0.010%, it is not possible to obtain the desired strength. For this reason, the Cr content is 0.010% or more. The Cr content is preferably 0.10% or more, 0.15% or more, or 0.20% or more. On the other hand, if the Cr content is more than 1.00%, in a hot stamped body, coarse intermetallic compounds are formed and the early fracture resistance deteriorates. For this reason, the Cr content is 1.00% or less. The Cr content is preferably 0.80% or less, 0.70% or less, 0.50% or less, or 0.40% or less.

[Mo: 0.010 to 1.000%]

Mo is an element segregating at the austenite grain boundaries at the time of heating in the hot stamping step to thereby make the strength of the former austenite grain boundaries rise and raise the early fracture resistance in the hot stamped body. If the Mo content is less than 0.0010%, the desired early fracture resistance cannot be obtained. For this reason, the Mo content is 0.0010% or more. The Mo content is preferably 0.010% or more, 0.050% or more, or 0.100% or more.

On the other hand, if the Mo content is more than 1.000%, in a hot stamped body, coarse intermetallic compounds are formed and the early fracture resistance deteriorates. For this reason, the Mo content is 1.000% or less. The Mo content is preferably 0.800% or less, 0.600% or less, or 0.400% or less.

[B: 0.0005 to 0.0200%]

B is an element improving the hardenability of steel. If the B content is less than 0.0005%, the desired strength cannot be obtained. For this reason, the B content is 0.0005% or more. The B content is preferably 0.0010% or more, 0.0015% or more, or 0.0020% or more. On the other hand, if the B content is more than 0.0200%, coarse intermetallic compounds are formed at a hot stamped body and the early fracture resistance of the hot stamped body falls. For this reason, the B content is 0.0200% or less. The B content is preferably 0.0150% or less, 0.0100% or less, 0.0080% or less, 0.0060% or less, or 0.0040% or less.

The basic chemical composition of a hot stamped body according to an embodiment of the present invention is as explained above. Furthermore, the hot stamped body may, if necessary, contain at least one of the following optional elements in place of part of the Fe of the balance. For example, the hot stamped body may contain at least one element selected from the group comprising Co: 0 to 4.00%, Ni: 0 to 3.00%, Cu: 0 to 3.00%, and V: 0 to 3.00%. Further, the hot stamped body may contain at least one element selected from the group comprising Ca: 0 to 1.000%, Mg: 0 to 1.000%, and REM: 0 to 1.000%. Further, the hot stamped body may also have at least one element selected from the group comprising Sb: 0 to 1.00%, Sn: 0 to 1.00%, and Zr: 0 to 1.00%. Further, the hot stamped body may contain As: 0 to 0.100%. Further, the hot stamped body may contain at least one element of W, Ta, Re, Os, Ir, and Tc in a total of 0 to 1.00%. Below, these optional elements will be explained in detail.

[Co: 0 to 4.00%]

Co is an element improving the strength of a hot stamped body by solid solution strengthening. The Co content may be 0.001% or more, but to reliably obtain this effect, the Co content is preferably 0.01% or more or 0.05% or more.

On the other hand, even if made to be contained in a large amount, the effect becomes saturated, therefore the Co content is preferably 4.00% or less. The Co content may also be 3.00% or less, 2.50% or less, 2.00% or less, or 1.50%% or less.

[Ni: 0 to 3.00%]

Ni has the action of dissolving in the austenite grains at the time of heating in the hot stamping step and thereby raising the strength of a hot stamped body. The Ni content may be 0.001% or more, but to reliably obtain this effect, the Ni content is preferably 0.01% or more.

On the other hand, even if made to be contained in a large amount, the effect becomes saturated, therefore the Ni content is preferably 3.00% or less. The Ni content may also be 2.50% or less, 2.00% or less, 1.50% or less, 1.00% or less, or 0.80% or less.

[Cu: 0 to 3.00%]

Cu has the action of dissolving in the austenite grains at the time of heating in the hot stamping step and thereby raising the strength of a hot stamped body. The Cu content may be 0.001% or more, but to reliably obtain this effect, the Cu content is preferably 0.01% or more or 0.05% or more.

On the other hand, even if made to be contained in a large amount, the effect becomes saturated, therefore the Cu content is preferably 3.00% or less. The Cu content may also be 2.50% or less, 2.00% or less, 1.50% or less, 1.00% or less, or 0.80% or less.

[V: 0 to 3.00%]

V has the effect of forming carbonitrides in the steel to thereby improve the strength of the hot stamped body by precipitation strengthening. The V content may be 0.001% or more, but to reliably obtain this effect, the V content is preferably 0.01% or more or 0.05% or more. On the other hand, the V content is more than 3.00%, sometimes a large amount of carbonitrides are formed in the steel and the early fracture resistance of the hot stamped body deteriorates. For this reason, the V content is preferably 3.00% or less. The V content may also be 2.50% or less, 2.00% or less, 1.50% or less, 1.00% or less, or 0.80% or less.

[Ca: 0 to 1.000%]

Ca suppresses the formation of oxides acting as starting points of fracture and contributes to improvement of the early fracture resistance. The Ca content may be 0.0001% or more, but to reliably obtain this effect, the Ca content is preferably 0.0005% or more or 0.001% or more. On the other hand, even if made to be contained in a large amount, the effect becomes saturated, therefore the Ca content is preferably 1.000% or less. The Ca content may also be 0.100% or less, 0.050% or less, 0.010% or less, 0.005% or less, or 0.002% or less.

[Mg: 0 to 1.000%]

Mg forms oxides and sulfides in the molten steel to suppress the formation of coarse MnS, causes dispersion of large number of fine oxides, and contributes to increased fineness of the metallographic structure and improvement of the early fracture resistance. The Mg content may be 0.0001% or more, but to reliably obtain this effect, the Mg content is preferably 0.0005% or more or 0.001% or more.

On the other hand, even if made to be contained in a large amount, the effect becomes saturated, therefore the Mg content is preferably 1.000% or less. The Mg content may also be 0.100% or less, 0.050% or less, 0.010% or less, 0.005% or less, or 0.002% or less.

[REM: 0 to 1.000%]

REM suppresses the formation of oxides acting as starting points of fracture and contributes to improvement of the early fracture resistance. The REM content may be 0.0001% or more, but to reliably obtain this effect, the REM content is preferably 0.0005% or more or 0.001% or more.

On the other hand, even if made to be contained in a large amount, the effect becomes saturated, therefore the REM content is preferably 1.000% or less. The REM content may be 0.100% or less, 0.050% or less, 0.010% or less, 0.005% or less, or 0.002% or less.

In the present embodiment, “REM” is the general term for the 17 elements of atomic number 21 scandium (Sc), atomic number 39 yttrium (Y), and the lanthanoids of atomic number 57 lanthanum (La) to atomic number 71 lutetium (Lu). The REM content is the total content of these elements.

[Sb: 0 to 1.00%]

Sb suppresses the formation of oxides acting as starting points of fracture and contributes to improvement of the early fracture resistance. To reliably obtain this effect, the Sb content is preferably 0.001% or more.

On the other hand, even if made to be contained in a large amount, the effect becomes saturated, therefore the Sb content is preferably 1.00% or less. The Sb content may also be 0.80% or less, 0.50% or less, 0.20% or less, or 0.10% or less.

[Sn: 0 to 1.00%]

Sn suppresses the formation of oxides which act as starting points of fracture and contributes to the improvement of the early fracture resistance. To reliably obtain this effect, the Sn content is preferably 0.001% or more.

On the other hand, even if contained in a large amount, the above effect is saturated, therefore the Sn content is preferably 1.00% or less. The Sn content may also be 0.80% or less, 0.50% or less, 0.20% or less, or 0.10% or less.

[Zr: 0 to 1.00%]

Zr suppresses the formation of oxides which act as starting points of fracture and contributes to the improvement of the early fracture resistance. To reliably obtain this effect, the Zr content is preferably 0.001% or more.

On the other hand, even if contained in a large amount, the above effect is saturated, therefore the Zr content is preferably 1.00% or less. The Zr content may also be 0.80% or less, 0.50% or less, 0.20% or less, or 0.10% or less.

[As: 0 to 0.100%]

As causes the temperature for forming an austenite single phase to fall and thereby refines the former austenite grains and contributes to improvement of the early fracture resistance. If reliably obtaining this effect, the As content is preferably 0.001% or more. On the other hand, even if contained in a large amount, the above effect is saturated, therefore the As content is preferably 0.100% or less. The As content may be 0.080% or less, 0.050% or less, 0.020% or less, or 0.010% or less.

[At Least One of W, Ta, Re, Os, Ir, and Tc: 0 to 1.00% in Total]

W, Ta, Re, Os, Ir, and Tc are elements segregating at the former austenite grain boundaries in the same way as Mo to raise the strength of the grain boundaries. The total of the content of the at least one element of W, Ta, Re, Os, Ir, and Tc may be 0%, but to obtain such an effect, is preferably 0.001% or more. The total of the content of the at least one element of W, Ta, Re, Os, Ir, and Tc is preferably 0.01% or more, more preferably 0.10% or more, still more preferably 0.15% or more. On the other hand, even if excessively containing these elements, the effect becomes saturated. Therefore, including these elements in the steel material more than necessary is liable to invite a rise in the production costs. Therefore, the total of the contents of the at least one of W, Ta, Re, Os, Ir, and Tc is preferably 1.00% or less and may also be 0.80% or less, 0.60% or less, or 0.40% or less.

The chemical composition of the above hot stamped body may be measured by a general analysis method. For example, it may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). C and S may be measured using the combustion-infrared absorption method, N may be measured using the inert gas melting-thermal conductivity method, and O may be measured by the inert gas melting-nondispersion type infrared absorption method.

If the surface of the hot stamped body is provided with a plating layer, mechanical polishing may be used to remove the plating layer, then the chemical composition may be analyzed.

In a hot stamped body according to an embodiment of the present invention, the balance besides the above elements is comprised of Fe and impurities. The “impurities” are constituents, etc., entering due to various factors in the production process starting from materials such as ore and scrap, etc., when industrially producing hot stamped bodies.

[At Least One of Martensite, Bainite, and Tempered Martensite: 90% or More in Total]

The microstructure of the hot stamped body preferably includes, by area ratio, at least one of martensite, bainite, and tempered martensite in a total of 90% or more. The remaining structure is not particularly limited, but may also be comprised of at least one of 10% or less of ferrite, retained austenite, and pearlite. Martensite, bainite, and tempered martensite are extremely hard structures, therefore by the hot stamped body containing at least one of martensite, bainite, and tempered martensite in an area ratio of a total of 90% or more, a high tensile strength, specifically a tensile strength of 2200 MPa or more, can be achieved. The total of the area ratios of the least one of martensite, bainite, and tempered martensite is preferably 94% or more, more preferably 97% or more. The upper limit of the total of the area ratios of the at least one of martensite, bainite, and tempered martensite is not particularly prescribed and may also be 100%.

The microstructure in a hot stamped body is identified and the area ratios are calculated in the following way.

A sample is cut out from any position 50 mm or more away from the ends of a hot stamped body (if not possible to obtain a sample from this position, a position away from the ends) so as to enable a cross-section of thickness vertical to the surface to be examined. The size of the sample depends on the measurement device, but is a size enabling 10 mm or so to be examined in a direction vertical to the thickness direction.

The cross-section of the sample is polished using #600 to #1500 silicon carbide paper, then a liquid comprised of particle size 1 to 6 μm diamond powder dispersed in alcohol or other diluent or pure water is used to polish the surface to a mirror finish. Next, the examined surface is finished by electrolytic polishing. An area of a length 50 μm and 50 μm in the sheet thickness direction centered at a ¼ depth position of the sheet thickness at any position in the long direction of the sample cross-section is measured at 0.1 μm measurement intervals by electron backscatter diffraction to obtain crystal orientation information. For the measurement, an EBSD analysis apparatus comprised of a thermal field emission type scan electron microscope and EBSD detector may be used. For example, an EBSD analysis apparatus comprised of a JSM-7001F made by JEOL and a DVC5 model detector made by TSL may be used. At that time, the vacuum degree inside the EBSD analysis apparatus may be 9.6×10−5 Pa or less, the acceleration voltage may be 15 kV, and the beam current level may be made 13.

The obtained crystal orientation information is analyzed using the “Phase Map” function included in the software “OIM Analysis®” attached to the EBSD analysis apparatus. Structures with fcc crystal structures are judged to be retained austenite. The area ratio of the retained austenite is obtained by calculating the area ratio of this retained austenite. Next, regions with bcc crystal structures are judged to be bainite, tempered martensite, martensite, and ferrite. In these regions, using the “Grain Average Misorientation” function included in the software “OIM Analysis®” attached to the EBSD analysis apparatus, under conditions deeming a 5° grain boundary as a crystal grain boundary, a region having a “Grain Average Misorientation” of 0.5° or less is extracted as ferrite. The area ratio of ferrite is obtained by calculating the area ratio of the extracted ferrite.

Next, the remaining region (region with “Grain Average Misorientation” of more than 0.5°) is made the area ratio of the total of martensite, tempered martensite, and bainite. The area ratio of pearlite is calculated by subtracting from 100% the area ratio of the retained austenite and the area ratios of the bainite, tempered martensite, martensite, and ferrite.

[Standard Deviation at Grain Size Distribution of Former Austenite Grains: 5.0 μm or Less]

In an embodiment of the present invention, the standard deviation at the grain size distribution of the former austenite grains is 5.0 μm or less. If the variation of the former austenite grain size is large, sometimes a rise in the local hardness is invited and early fracture is caused. According to an embodiment of the present invention, by controlling the standard deviation at the grain size distribution of the former austenite grains to 5.0 μm or less to reduce the variation in former austenite grain size, it is possible to reliably suppress the rise in local hardness acting as the starting points of early fracture. Preferably, the standard deviation is 4.0 μm or less, 3.0 μm or less, or 2.5 μm or less. From the viewpoint of suppressing the rise in local hardness acting as the starting points of early fracture, the smaller the standard deviation at the grain size distribution of the former austenite grains, the better. For this reason, the lower limit does not particularly have to be prescribed. For example, the standard deviation at the grain size distribution of the former austenite grains may be 0.1 μm or more and may be 0.5 μm or more, 1.0 μm or more, 1.2 μm or more, 1.5 μm or more, or 1.7 μm or more.

In an embodiment of the present invention, as explained above, it is important to control the standard deviation at the grain size distribution of the former austenite grains to 5.0 μm or less to reduce the variation of the former austenite grain size. For this reason, it is not necessary to control the former austenite grain size itself to a specific range. Therefore, the former austenite grain size is not particularly limited, but for example may be 10 μm or less. The “former austenite grain size” means the average crystal grain size of former austenite grains in the measurement of the standard deviation explained below.

The standard deviation at the grain size distribution of the former austenite grains can be obtained by the following method.

A sample is cut out from any position 50 mm or more away from the ends of the hot stamped body (if not possible to obtain a sample from this position, a position away from the ends) so as to enable a cross-section of thickness vertical to the surface to be examined. The size of the sample depends on the measurement device, but is a size enabling 10 mm or so to be examined in a direction vertical to the thickness direction.

The cross-section of the sample is polished using #600 to #1500 silicon carbide paper, then a liquid comprised of particle size 1 to 6 μm diamond powder dispersed in alcohol or other diluent or pure water is used to polish the surface to a mirror finish. Next, the examined surface is finished by electrolytic polishing. An area of a length 50 μm and 50 μm in the sheet thickness direction centered at a ¼ depth position of the sheet thickness at any position in the long direction of the sample cross-section is measured at 0.1 μm measurement intervals by electron backscatter diffraction to obtain crystal orientation information. For the measurement, an EBSD analysis apparatus comprised of a thermal field emission type scan electron microscope and EBSD detector may be used. For example, an EBSD analysis apparatus comprised of a JSM-7001F made by JEOL and a DVC5 model detector made by TSL may be used. At that time, the vacuum degree inside the EBSD analysis apparatus may be 9.6×10−5 Pa or less, the acceleration voltage may be 15 kV, and the beam current level may be made 13.

The obtained crystal orientation information is used to calculate the crystal orientation of the former austenite grains from the relationship of crystal orientation between general former austenite grains and crystal grains having bcc structures after transformation. This is used to calculate the average crystal grain size of the former austenite grains.

For the method of calculating the crystal orientations of the former austenite grains, the following method is used. First, a crystal orientation map of the former austenite grains is prepared by the method described in Acta Materialia, 58(2010), 6393-6403. The average value between the shortest diameter and the longest diameter of one former austenite grain included in the examined field is calculated. That average value is made the size of the former austenite grain. The above operation is performed for all of the former austenite grains except for the former austenite grains where the crystal grains as a whole are not included in the captured field, such as at the end parts of the captured field, to find the sizes of all of the former austenite grains in the captured field. From the obtained sizes of all former austenite grains, the average size is calculated whereupon the standard deviation at the grain size distribution of the former austenite grains is obtained.

[Total Amount of Segregation of at Least One of Mo, W, Ta, Re, Os, Ir, and Tc at Former Austenite Grain Boundaries: 0.10 Atm % or More]

In an embodiment of the present invention, the total amount of segregation of at least one of Mo, W, Ta, Re, Os, Ir, and Tc at the former austenite grain boundaries is 0.10 atm % or more. By making at least one of Mo, W, Ta, Re, Os, Ir, and Tc segregate at the former austenite grain boundaries to give a total amount of segregation of 0.10 atm % or more, it is possible to strengthen the former austenite grain boundaries at the microstructure of the hot stamped body. It is possible to not only suppress variation of the former austenite grain size to reduce the regions able to act as the starting points of early fracture, it is also possible to suppress the progression of cracks when they occur and thereby prevent early fracture. According to an embodiment of the present invention, by combining the suppression of the rise of local hardness and grain boundary strengthening by grain boundary segregation of such specific elements, it is possible to reduce the regions able to act as the starting points of early fracture and suppress the progression of cracks along the grain boundary even in the case of occurrence of cracks at the hot stamped bodies. For this reason, despite having a high tensile strength, for example, a high tensile strength of 2200 MPa or more, it is possible to suppress early fracture. The total amount of segregation of the at least one element of Mo, W, Ta, Re, Os, Ir, and Tc at the former austenite grain boundaries is preferably 0.13 atm % or more, more preferably 0.15 atm % or more, still more preferably 0.18 atm % or more, or 0.20 atm % or more. From the viewpoint of grain boundary strengthening, the higher the total amount of segregation of the at least one of Mo, W, Ta, Re, Os, Ir, and Tc at the former austenite grain boundaries, the more preferable. For this reason, the upper limit of the above total content is not particularly limited, but for example the total amount of segregation may be 3.00 atm % or less and may also be 2.00 atm % or less, 1.50 atm % or less, 1.00 atm % or less, 0.80 atm % or less, 0.60 atm % or less, 0.40 atm % or less, or 0.30 atm % or less.

In one embodiment, the amount of segregation of Mo at the former austenite grain boundaries may be 0.10 atm % or more, 0.13 atm % or more, 0.15 atm % or more, 0.18 atm % or more, or 0.20 atm % or more. Similarly, the amount of segregation of Mo at the former austenite grain boundaries may be 3.00 atm % or less, 2.00 atm % or less, 1.50 atm % or less, 1.00 atm % or less, 0.80 atm % or less, 0.60 atm % or less, 0.40 atm % or less, or 0.30 atm % or less. In another embodiment, the total amount of segregation of the amount of segregation of Mo and the amount of segregation of at least one of W, Ta, Re, Os, Ir and Tc at the former austenite grain boundaries may be 0.10 atm % or more, 0.13 atm % or more, 0.15 atm % or more, 0.18 atm % or more, or 0.20 atm % or more and/or may be 3.00 atm % or less, 2.00 atm % or less, 1.50 atm % or less, 1.00 atm % or less, 0.80 atm % or less, 0.60 atm % or less, 0.40 atm % or less, or 0.30 atm % or less.

The total amount of segregation of the at least one of Mo, W, Ta, Re, Os, Ir, and Tc at the former austenite grain boundaries is determined as follows: First, a test piece is taken from a position 50 mm or more away from the end faces of the hot stamped body. At that time, the front and back surfaces of the test piece are finished by machine polishing. Further, if there is a plating layer at the steel sheet surface, the plating layer is removed and then the front and back surfaces of the test piece of the steel sheet are finished by machine polishing. At that time, the sheet thickness is not particularly designated if the ¼ depth position of the sheet thickness can be measured, but the same amounts of the front and back surfaces of the test piece may also be removed by machine grinding so that the sheet thickness becomes 1.2 mm. The test piece is worked to a length of 20 mm and a width of 3.2 mm and formed with a V-notch of an angle of 450 at a position of a length of 11.5 mm. The test piece is dipped in a 20%-ammonium thiocyanate solution. At this time, the dipping time is not particularly limited. It is sufficient that the former austenite grain boundaries are exposed when set inside an Auger electron emission spectrometer and fracturing. For example, it may be 48 hours. The front and back surfaces of the test piece are galvanized within 10 minutes after ending the dipping. After plating, the test piece is quickly subjected to Auger electron emission spectrometry and fractured. At that time, the time after plating to fracture of the test piece is preferably within 1.5 hours, more preferably within 0.5 hour. The test piece is set within the Auger electron emission spectrometer and fractures from the notch portion of the test piece to expose the former austenite grain boundaries. At this time, the apparatus may be an Auger electron emission spectrometer. The model is not particularly limited, but a PHI680 made by ULVAC-PHI may be used. As the measurement conditions, the accelerating voltage may be 10 keV and the beam current may be 10 nA. An electron beam is fired at the exposed former austenite grain boundaries by a 1 to 30 kV accelerating voltage and the atm % of specific elements at the grain boundaries (specifically at least one of Mo, W, Ta, Re, Os, Ir, and Tc) are measured. The measurement is performed at the former austenite grain boundaries at 10 locations at a position of ¼ depth of the sheet thickness from the surface. To prevent contamination of the grain boundaries, quickly ending the measurement after fracture is preferable. The measurement should be ended within 30 minutes. The average value of the atm % of the obtained specific elements is calculated and determined as the total value of segregation of the at least one of Mo, W, Ta, Re, Os, Ir, and Tc.

[Plating]

The hot stamped body according to the present embodiment may having a plating layer at its surface. By having a plating layer at the surface, after the hot stamping, the corrosion resistance can be improved. As the plating layer, an aluminum plating layer, aluminum-zinc plating layer, aluminum-silicon plating layer, hot dip galvanized layer, electrogalvanized layer, hot dip galvannealed layer, zinc-nickel plating layer, aluminum-magnesium-zinc based plating layer, etc., may be illustrated.

[Mechanical Properties]

According to the hot stamped body of an embodiment of the present invention, excellent mechanical properties, for example, a tensile strength of 2200 MPa or more, can be achieved. The tensile strength is preferably 2300 MPa or more, more preferably 2400 MPa or more, most preferably 2500 MPa or more. The upper limit is not particularly prescribed, but, for example, the tensile strength may be 3500 MPa or less, 3300 MPa or less, or 3000 MPa or less. The tensile strength of the hot stamped body is measured by preparing a No. 5 test piece and conducting a tensile test based on JIS Z 2241: 2011. At this time, for the purpose of removing roughness at the surface of the test piece, the surface layer parts of the front and back surfaces may be removed by machining or chemical polishing.

The hot stamped body according to an embodiment of the present invention, despite as explained above having, for example, a high tensile strength of 2200 MPa or more, can reliably suppress early fracture, and therefore is extremely useful for use as, for example, a frame member or bumper of an automobile or other structural member and reinforcing member where strength is required.

<Method of Production of Hot Stamped Body>

Next, a preferable method of production of the hot stamped body according to an embodiment of the present invention will be explained. The following explanation is intended to illustrate the characteristic method for producing the hot stamped body according to the embodiment of the present invention and is not intended to limit the hot stamped body to one produced by the method of production such as explained below.

In the method of production of the hot stamped body according to an embodiment of the present invention, in particular controlling the finish rolling conditions and preheating conditions is effective. Specifically, the method of production of the hot stamped body according to an embodiment of the present invention comprises:

    • hot rolling a slab having a chemical composition explained above relating to the hot stamped body, wherein the hot rolling includes heating the slab, then finish rolling it, and a rolling reduction of a final stage of the finish rolling is 40% or more (hot rolling step),
    • coiling the obtained steel sheet at a temperature of 750° C. or less (coiling step),
    • preheating the steel sheet to a temperature of more than 1200° C., then cooling it by an average cooling speed of 10° C./s or more down to less than 350° C. (preheating step), and
    • hot stamping the steel sheet, wherein the hot stamping includes heating the steel sheet to a temperature region of 800 to 1000° C. and then holding it there for 60 to 600 seconds (hot stamping step). Below, the steps will be explained in detail.

[Hot Rolling Step] [Heating of Slab]

First, a slab having the chemical composition explained above in relation to the hot stamped body is heated. The method of casting the molten steel is not particularly limited. The slab may be produced by continuous casting, ingot forming, or thin slab casting. The heating before the hot rolling is not particularly limited, but the slab used contains a relatively large amount of alloying elements for obtaining a high strength steel sheet. For this reason, the slab may also be heated before being sent on for hot rolling. For the purpose of making the alloying elements dissolve in the slab, the heating temperature may be 1100° C. or more.

[Rough Rolling]

In the present method, for example, the heated slab may be adjusted in thickness, etc., by rough rolling before finish rolling. The rough rolling need only secure the desired sheet bar dimensions. The conditions are not particularly limited.

[Finish Rolling]

The heated slab or the slab additionally rough rolled as needed is next finish rolled. In the present method, it is important that the rolling reduction of the final stage in the finish rolling be 40% or more. By making the rolling reduction of the final stage in the finish rolling 40% or more, the pearlite is evenly dispersed in the hot rolled steel sheet after rolling. This pearlite becomes starting points of austenite at the time of heating in the preheating step explained later in detail. For this reason, if the pearlite is evenly dispersed, at the hot stamped body, the standard deviation at the grain size distribution of the former austenite grains becomes smaller. As a result, the early fracture resistance of the hot stamped body can be improved. More preferably, the rolling reduction of the final stage in the finish rolling is 43% or more or 50% or more.

In a hot stamped body, for the purpose of securing a high hardenability, the amount of Mn added tends to be raised. For example, 0.50% or more of Mn is added. In relation to this, in research by the inventors, it was learned that with such a high Mn content, pearlite tends to be arranged relatively connected in a hot rolled steel sheet, and therefore compared with the case of low Mn content, it is extremely difficult to evenly disperse pearlite in the microstructure of a hot rolled steel sheet. Therefore, if finish rolling a steel material with such a high Mn content by a relatively low rolling reduction of less than 40%, it is believed that the presence of a part of connected pearlite at the microstructure becomes particularly prominent.

However, by making the rolling reduction of the final stage of finish rolling 40% or more, despite a high Mn content of 0.50% or more, it is possible to arrange pearlite sufficiently dispersed at the microstructure of the hot rolled steel sheet after the hot rolling step and coiling step. Therefore, in the microstructure of the hot rolled steel sheet rolled in this way, either there are no parts where pearlite is present connected or they are sufficiently reduced, therefore in the structure after the preheating step and hot stamping step, it is possible to reduce variation in the former austenite grain size. The upper limit of the rolling reduction in the final stage of the finish rolling is not particularly prescribed. Even in a steel material having such a high Mn content, in particular by suitable controlling the rolling reduction in the final stage of the finish rolling, it is possible to arrange the pearlite sufficiently dispersed in the microstructure of the hot rolled steel sheet and in turn possible to reduce the variation in the former austenite grain size and suppress a local rise in hardness.

The dominating factors in the morphology of this microstructure are the rolling reduction in the final stage of the finish rolling and the heating in the preheating step. The morphology is not particularly greatly affected by for example the heating in the hot stamping step after the preheating step, the optional cold rolling before the preheating step, the subsequent annealing, etc. This is because by forming the hot rolled steel sheet by a rolling reduction in the final stage of the finish rolling of 40% or more, even if the hot rolled steel sheet is cold rolled and then annealed at a relatively high temperature, there is a high tendency for formation of a microstructure where the carbides, grain boundaries, and retained austenite forming starting points of austenite after cooling are arranged dispersed. In general, if the rolling reduction in the final stage of the finish rolling is too high, fracture of the steel sheet at the time of rolling becomes a concern. Further, the preheating step explained in detail later is performed at an extremely high temperature compared with the hot stamping step, more specifically is performed at a temperature of more than 1200° C., and therefore generally this becomes a factor behind increased costs. Therefore, in particular the technical idea that by making the rolling reduction in the final stage of the finish rolling 40% or more and further by combining more than 1200° C. preheating before the stamping step, the variation in former austenite grain size is reduced and a local rise in hardness is suppressed has not existed up to now and was first discovered this time by the inventors.

[Coiling Step]

Next, the finish rolled hot rolled steel sheet is coiled at a temperature of 750° C. or less. By making the coiling temperature 750° C. or less, it is possible to keep the ferrite from being arranged connected at the hot rolled steel sheet after rolling and the pearlite evenly disperses. This pearlite acts as starting points for austenite at the time of heating in the preheating step. For this reason, if the pearlite evenly disperses, in the hot stamped body, the standard deviation at the grain size distribution of the former austenite grains becomes smaller. As a result, the early fracture resistance of the hot stamped body can be improved.

Further, for the purpose of softening the hot rolled steel sheet, the coil after coiling may be heat treated to soften it. The method of heat treatment for softening is not particularly limited and may be made general conditions.

[Pickling Step]

After the coiling step and before the cold rolling step, optionally, pickling may be performed for removing the oxide scale formed on the surface of the hot rolled steel sheet. The pickling may be formed under conditions suitable for removing oxide scale. It may be performed at one time or may be performed divided into several times so as to reliably remove the oxide scale.

[Cold Rolling Step]

After the coiling step, the steel sheet may be optionally cold rolled. The cold rolling is not particularly limited and may be performed under any suitable conditions. For example, the rolling reduction of the cold rolling may be 30 to 80%. The number of rolling passes and the rolling reduction per pass are not particularly limited and may be suitable set so that the rolling reduction of the cold rolling as a whole becomes the above range.

[Annealing Step]

For example, after the cold rolling step, annealing may optionally be performed to adjust the microstructure and/or properties. The heating temperature of the annealing step is not particularly limited, but may for example be 800° C. or less.

[Plating Step]

For the purpose of improving the corrosion resistance, etc., the surface of the hot rolled steel sheet or cold rolled steel sheet may also be plated. The plating may be hot dip coating, alloyed hot dip coating, electroplating, or other treatment. For example, as the plating, the steel sheet may be hot dip galvanized. After hot dip galvanization, alloying treatment may be performed. As the plating layer, an aluminum plating layer, aluminum-zinc plating layer, aluminum-silicon plating layer, hot dip galvanized layer, electrogalvanized layer, hot dip galvannealed layer, zinc-nickel plating layer, aluminum-magnesium-zinc based plating layer, etc., may be illustrated. The specific conditions of the plating and alloying treatment are not particularly limited and may be any suitable conditions known to persons skilled in the art.

[Temper Rolling Step]

To correct the shape of the steel sheet or adjust the surface roughness, etc., it is possible, for example, to temper roll the steel sheet after the annealing step, or after the plating step.

[Preheating Step]

In the present method, the obtained hot rolled steel sheet or cold rolled steel sheet is preheated to a temperature of more than 1200° C. before the hot stamping step, then is cooled by an average cooling speed of 10° C./s or more down to less than 350° C. In the hot stamped body according to an embodiment of the present invention, it is extremely important to make specific grain boundary strengthening elements, more specifically at least one type of Mo, W, Ta, Re, Os, Ir, and Tc, segregate at the former austenite grain boundaries in predetermined amounts. However, in the hot rolled steel sheet after the hot rolling step or in the cold rolled steel sheet after the optional cold rolling step or annealing step, these grain boundary strengthening elements are present as carbides and/or intermetallic compounds. Therefore, even if subjecting such steel sheet to the hot stamping step for usual heating and shaping without the preheating step, these grain boundary strengthening elements cannot be made to sufficiently segregate at the former austenite grain boundaries. In this case, it is no longer possible to sufficiently manifest the grain boundary strengthening action based on the grain boundary segregation of these elements. For this reason, in this method, it is extremely important to preheat the steel sheet before the hot stamping step to a relatively high temperature of more than 1200° C. to thereby make the carbides and/or intermetallic compounds of the grain boundary strengthening elements sufficiently melt and make the grain boundary strengthening elements dissolve in the steel sheet. The upper limit of the heating temperature of the preheating is not particularly prescribed, but the heating temperature may for example be 1400° C. or less. Further, after heating, the steel sheet is cooled by an average cooling speed of 10° C./s or more down to less than 350° C. By cooling by an average cooling speed of 10° C./s or more down to less than 350° C., it is possible to keep the grain boundary strengthening elements dissolved in the steel sheet from precipitating as compounds. The upper limit of the average cooling speed is not particularly prescribed, but for example the average cooling speed may be 3000° C./s or less, 1500° C./s or less, or 1200° C./s or less. The upper limit of the cooling speed is not particularly prescribed. The cooling method is also not particularly limited and may be die cooling, water cooling, oil cooling, or gas cooling. In particular, even with an extremely high average cooling speed, cooling can be relatively easily realized by utilizing die cooling or water cooled die cooling.

[Hot Stamping Step]

Finally, the preheated steel sheet is hot stamped in the hot stamping step to produce a hot stamped body having the desired chemical composition and microstructure. In particular, the grain boundary strengthening elements dissolved in the steel sheet in the previous preheating step disperse to the austenite grain boundaries and segregate there at the time of heating in the hot stamping step. For this reason, due to the following shaping and cooling operation, it is possible to achieve the desired total amount of segregation of the grain boundary strengthening elements at the former austenite grain boundaries after the martensite transformation. The dispersion and segregation of the grain boundary strengthening elements can be achieved by the usual heating, shaping, and cooling operations in the hot stamping step. Therefore, from the viewpoint of the dispersion and segregation of the grain boundary strengthening elements, these operations may be performed under suitable conditions known to persons skilled in the art. However, in particular from the viewpoint of obtaining the desired area ratio of the hard structures and former austenite grain size distribution, the steel sheet for hot stamping use is preferably heated to a temperature region of 800° C. to 1000° C. and held at that temperature region for 60 to 600 seconds. If the heating temperature is less than 800° C., sometimes the austenization becomes insufficient and the area ratio of the desired hard structures (at least one of martensite, bainite, and tempered martensite) and former austenite grain size distribution cannot be obtained and the tensile strength and early fracture resistance deteriorate. On the other hand, if the heating temperature is more than 1000° C., sometimes the austenite grains excessively grow, the desired former austenite grain size distribution cannot be obtained, and the early fracture resistance deteriorates. If the holding time is less than 60 seconds, sometimes the austenization becomes insufficient, the desired former austenite grain size distribution cannot be obtained, and the early fracture resistance deteriorates. If the holding time is more than 600 seconds, sometimes the austenite grains excessively grow, the desired former austenite grain size distribution cannot be obtained, and the early fracture resistance deteriorates.

The heating atmosphere is not particularly limited. Usual conditions are enough. For example, it may be an air atmosphere, a gas combustion atmosphere controlled in ratio of air and fuel, and a nitrogen atmosphere. The dew points may also be controlled in these gases.

The steel sheet is held at a temperature region of 800° C. to 1000° C., then hot stamped. After hot stamping, it may be cooled down to a temperature region of 250° C. or less by an average cooling speed of 20° C./s or more.

As the heating method, for example, furnace heating by an electric furnace, gas furnace, etc., flame heating, ohmic heating, high frequency heating, induction heating, etc., may be mentioned.

The hot stamped body according to the present embodiment is obtained by the above method. After hot stamping, it may be tempered at 130 to 600° C. or coated, then bake hardened (BH). Further, part of the hot stamped body may be tempered by being irradiated by a laser, etc., to partially form softened regions.

Below, examples will be used to explain the present invention in more detail, but the present invention is not limited to these examples in any way.

Examples

In the following examples, hot stamped bodies according to an embodiment of the present invention were produced under various conditions and the obtained tensile strengths and early fracture resistances of the hot stamped bodies were investigated.

First, molten steels having the chemical compositions shown in Table 1 were cast by continuous casting to produce slabs. The balances besides the constituents shown in Table 1 were Fe and impurities. These slabs were heated to a 1100° C. or more temperature and rough rolled under predetermined conditions, then were finish rolled and coiled under the conditions shown in Table 2. After the coiling, some of the hot rolled steel sheets were subjected to predetermined heat treatment for softening. Next, the obtained hot rolled steel sheets were pickled to remove the oxide scale cold rolled by 30 to 80% predetermined rolling reductions. (In Invention Example 337, cold rolling was not performed.) Next, some of the steel sheets were subjected to annealing, plating, or temper rolling under predetermined conditions. Next, the obtained steel sheets were preheated under the conditions shown in Table 2, then were cooled and finally were similarly hot stamped under the conditions shown in Table 2. The heating atmosphere and heating method in the hot stamping step, except when clearly indicated otherwise, were a gas combustion atmosphere (air-fuel ratio 0.85) and furnace heating. After the hot stamping, some of the hot stamped bodies were tempered or partially softened.

TABLE 1 Chemical composition (mass %), bal.: Fe and impurities Steel C Si Mn P S N O Al Nb Ti Cr Mo B Co Ni A1 0.37 0.44 1.32 0.007 0.0006 0.0024 0.0032 0.042 0.042 0.046 0.27 0.220 0.0019 A2 0.41 0.44 1.23 0.008 0.0007 0.0023 0.0014 0.041 0.040 0.027 0.33 0.149 0.0028 A3 0.43 0.45 1.32 0.006 0.0005 0.0032 0.0033 0.042 0.040 0.027 0.27 0.227 0.0023 A4 0.44 0.41 1.22 0.006 0.0016 0.0019 0.0033 0.039 0.034 0.040 0.25 0.217 0.0028 A5 0.45 0.44 1.34 0.009 0.0015 0.0027 0.0034 0.040 0.026 0.045 0.30 0.190 0.0024 A6 0.46 0.42 1.22 0.005 0.0009 0.0025 0.0022 0.049 0.031 0.031 0.23 0.174 0.0020 A7 0.47 0.44 1.24 0.007 0.0018 0.0030 0.0017 0.046 0.027 0.035 0.27 0.187 0.0028 A8 0.48 0.45 1.22 0.008 0.0015 0.0034 0.0035 0.040 0.024 0.025 0.31 0.150 0.0028 A9 0.53 0.44 1.21 0.006 0.0003 0.0024 0.0022 0.044 0.042 0.030 0.29 0.174 0.0031 A10 0.57 0.44 1.35 0.008 0.0008 0.0032 0.0021 0.039 0.018 0.040 0.31 0.196 0.0029 A11 0.58 0.41 1.29 0.005 0.0015 0.0021 0.0023 0.049 0.036 0.034 0.30 0.172 0.0019 A12 0.62 0.44 1.23 0.005 0.0012 0.0022 0.0025 0.043 0.028 0.041 0.27 0.178 0.0027 A13 0.67 0.40 1.34 0.007 0.0007 0.0029 0.0028 0.044 0.032 0.044 0.30 0.168 0.0025 A14 0.73 0.41 1.28 0.007 0.0019 0.0028 0.0018 0.044 0.020 0.038 0.25 0.181 0.0018 B1 0.47 0.006 1.30 0.005 0.0019 0.0032 0.0027 0.045 0.034 0.032 0.27 0.223 0.0025 B2 0.46 0.012 1.24 0.005 0.0019 0.0030 0.0025 0.041 0.035 0.045 0.28 0.214 0.0032 B3 0.45 0.04 1.31 0.009 0.0019 0.0023 0.0026 0.045 0.040 0.027 0.31 0.144 0.0018 B4 0.45 0.07 1.28 0.007 0.0018 0.0034 0.0024 0.046 0.028 0.042 0.31 0.177 0.0028 B5 0.47 0.12 1.26 0.004 0.0021 0.0024 0.0015 0.041 0.036 0.031 0.34 0.198 0.0018 B6 0.46 0.22 1.24 0.004 0.0016 0.0021 0.0023 0.040 0.023 0.044 0.24 0.199 0.0023 B7 0.47 0.26 1.33 0.008 0.0007 0.0022 0.0032 0.041 0.026 0.031 0.26 0.140 0.0032 B8 0.45 0.34 1.26 0.007 0.0016 0.0021 0.0025 0.045 0.029 0.033 0.28 0.179 0.0030 B9 0.46 0.41 1.35 0.009 0.0003 0.0019 0.0035 0.046 0.018 0.046 0.23 0.172 0.0025 B10 0.46 0.64 1.34 0.005 0.0017 0.0030 0.0018 0.049 0.032 0.034 0.32 0.179 0.0024 B11 0.46 0.83 1.25 0.004 0.0011 0.0032 0.0030 0.039 0.024 0.040 0.24 0.160 0.0019 B12 0.45 1.72 1.32 0.006 0.0020 0.0031 0.0019 0.040 0.019 0.034 0.28 0.149 0.0020 B13 0.46 2.37 1.22 0.005 0.0016 0.0023 0.0033 0.040 0.023 0.045 0.27 0.188 0.0028 B14 0.47 2.81 1.25 0.007 0.0006 0.0024 0.0026 0.042 0.031 0.036 0.25 0.145 0.0026 B15 0.45 3.20 1.24 0.009 0.0018 0.0033 0.0028 0.044 0.030 0.044 0.24 0.131 0.0033 C1 0.45 0.42 0.45 0.008 0.0017 0.0033 0.0026 0.045 0.024 0.046 0.33 0.162 0.0020 C2 0.45 0.40 0.52 0.005 0.0019 0.0030 0.0021 0.042 0.031 0.040 0.30 0.210 0.0033 C3 0.46 0.44 0.64 0.009 0.0003 0.0024 0.0016 0.044 0.034 0.031 0.25 0.224 0.0024 C4 0.46 0.41 0.81 0.007 0.0008 0.0029 0.0018 0.050 0.031 0.045 0.31 0.149 0.0030 C5 0.47 0.43 1.21 0.004 0.0008 0.0028 0.0018 0.050 0.019 0.044 0.25 0.176 0.0030 C6 0.47 0.40 1.32 0.006 0.0016 0.0023 0.0033 0.045 0.039 0.044 0.27 0.167 0.0032 C7 0.45 0.45 1.59 0.005 0.0016 0.0023 0.0016 0.049 0.018 0.031 0.26 0.204 0.0018 C8 0.47 0.40 1.82 0.009 0.0018 0.0024 0.0022 0.040 0.018 0.026 0.26 0.161 0.0033 C9 0.47 0.45 2.1 0.008 0.0022 0.0027 0.0027 0.043 0.028 0.044 0.31 0.210 0.0020 C10 0.47 0.45 2.29 0.008 0.0022 0.0027 0.0023 0.047 0.030 0.029 0.31 0.145 0.0032 C11 0.45 0.44 2.42 0.007 0.0017 0.0019 0.0019 0.047 0.030 0.032 0.33 0.198 0.0028 C12 0.45 0.44 2.67 0.007 0.0011 0.0019 0.0017 0.041 0.026 0.030 0.33 0.213 0.0028 C13 0.47 0.45 2.91 0.006 0.0017 0.0026 0.0035 0.050 0.040 0.043 0.29 0.173 0.0018 C14 0.45 0.43 3.12 0.004 0.0004 0.0022 0.0019 0.046 0.030 0.035 0.25 0.186 0.0029 D1 0.47 0.42 1.23 0.0006 0.0008 0.0034 0.0034 0.050 0.026 0.036 0.30 0.194 0.0022 D2 0.47 0.42 1.25 0.004 0.0013 0.0029 0.0022 0.050 0.036 0.030 0.33 0.134 0.0020 D3 0.46 0.45 1.25 0.006 0.0020 0.0027 0.0016 0.050 0.026 0.044 0.30 0.229 0.0021 D4 0.46 0.45 1.35 0.008 0.0005 0.0031 0.0014 0.046 0.036 0.031 0.24 0.130 0.0033 D5 0.45 0.41 1.23 0.011 0.0003 0.0026 0.0031 0.050 0.018 0.032 0.25 0.173 0.0018 D6 0.46 0.39 1.27 0.042 0.0009 0.0026 0.0017 0.042 0.030 0.046 0.25 0.165 0.0020 D7 0.46 0.41 1.29 0.069 0.0013 0.0028 0.0021 0.044 0.041 0.027 0.25 0.144 0.0030 D8 0.45 0.39 1.22 0.087 0.0008 0.0024 0.0030 0.046 0.040 0.038 0.31 0.228 0.0030 D9 0.47 0.45 1.35 0.120 0.0016 0.0031 0.0028 0.047 0.032 0.045 0.27 0.193 0.0020 E1 0.45 0.42 1.25 0.007 0.0001 0.0034 0.0017 0.045 0.038 0.031 0.27 0.226 0.0020 E2 0.45 0.40 1.24 0.009 0.0003 0.0032 0.0026 0.043 0.038 0.042 0.31 0.133 0.0026 E3 0.47 0.45 1.25 0.009 0.0008 0.0020 0.0014 0.050 0.018 0.032 0.23 0.175 0.0020 E4 0.47 0.42 1.29 0.007 0.0011 0.0030 0.0030 0.047 0.028 0.033 0.29 0.203 0.0019 E5 0.46 0.42 1.33 0.005 0.0021 0.0032 0.0024 0.041 0.038 0.035 0.34 0.137 0.0028 E6 0.47 0.42 1.21 0.009 0.0045 0.0033 0.0027 0.048 0.034 0.033 0.25 0.201 0.0022 E7 0.47 0.45 1.34 0.006 0.0065 0.0020 0.0024 0.040 0.023 0.045 0.30 0.215 0.0031 E8 0.46 0.43 1.31 0.004 0.0091 0.0033 0.0019 0.044 0.037 0.031 0.28 0.161 0.0030 E9 0.46 0.44 1.35 0.008 0.0151 0.0019 0.0034 0.039 0.038 0.045 0.24 0.224 0.0022 F1 0.45 0.42 1.27 0.007 0.0006 0.0002 0.0025 0.039 0.028 0.036 0.29 0.175 0.0019 F2 0.47 0.41 1.31 0.005 0.0015 0.0008 0.0022 0.049 0.035 0.027 0.32 0.199 0.0021 F3 0.45 0.45 1.32 0.004 0.0004 0.0018 0.0035 0.045 0.030 0.028 0.23 0.139 0.0021 F4 0.46 0.42 1.33 0.005 0.0021 0.0031 0.0035 0.045 0.040 0.044 0.28 0.153 0.0022 F5 0.47 0.41 1.33 0.005 0.0003 0.0047 0.0021 0.046 0.021 0.033 0.33 0.168 0.0028 F6 0.45 0.39 1.28 0.004 0.0008 0.0067 0.0024 0.041 0.041 0.042 0.31 0.147 0.0021 F7 0.45 0.41 1.31 0.009 0.0004 0.0102 0.0028 0.043 0.038 0.042 0.30 0.177 0.0029 F8 0.47 0.45 1.35 0.004 0.0016 0.0179 0.0021 0.045 0.026 0.038 0.23 0.173 0.0031 F9 0.47 0.40 1.25 0.007 0.0003 0.0211 0.0033 0.044 0.040 0.033 0.26 0.197 0.0023 G1 0.47 0.42 1.30 0.004 0.0015 0.0030 0.0006 0.043 0.036 0.026 0.29 0.207 0.0020 G2 0.46 0.42 1.32 0.007 0.0008 0.0023 0.0013 0.050 0.038 0.043 0.23 0.180 0.0020 G3 0.46 0.43 1.25 0.007 0.0012 0.0020 0.0022 0.045 0.039 0.039 0.32 0.196 0.0022 G4 0.45 0.42 1.27 0.005 0.0021 0.0026 0.0034 0.049 0.024 0.026 0.32 0.203 0.0032 G5 0.45 0.45 1.28 0.007 0.0013 0.0019 0.0051 0.044 0.022 0.029 0.27 0.156 0.0026 G6 0.45 0.45 1.34 0.008 0.0013 0.0028 0.0083 0.049 0.036 0.043 0.28 0.171 0.0020 G7 0.47 0.43 1.26 0.004 0.0003 0.0020 0.0197 0.045 0.032 0.041 0.26 0.149 0.0022 G8 0.46 0.40 1.23 0.009 0.0012 0.0023 0.0237 0.039 0.038 0.041 0.26 0.147 0.0029 H1 0.46 0.43 1.24 0.004 0.0004 0.0024 0.0034 0.0007 0.037 0.028 0.32 0.198 0.0030 H2 0.46 0.44 1.35 0.005 0.0016 0.0024 0.0034 0.001 0.026 0.035 0.26 0.177 0.0024 H3 0.46 0.43 1.26 0.006 0.0007 0.0021 0.0030 0.005 0.030 0.046 0.32 0.151 0.0019 H4 0.46 0.39 1.23 0.009 0.0012 0.0024 0.0015 0.016 0.042 0.041 0.32 0.220 0.0028 H5 0.46 0.43 1.30 0.006 0.0020 0.0021 0.0025 0.025 0.032 0.041 0.25 0.143 0.0030 H6 0.45 0.41 1.25 0.008 0.0011 0.0022 0.0031 0.039 0.037 0.032 0.29 0.210 0.0020 H7 0.46 0.43 1.35 0.009 0.0005 0.0026 0.0018 0.049 0.029 0.037 0.31 0.197 0.0020 H8 0.45 0.39 1.27 0.006 0.0015 0.0027 0.0024 0.068 0.027 0.046 0.28 0.139 0.0028 H9 0.47 0.44 1.32 0.006 0.0004 0.0027 0.0015 0.082 0.019 0.038 0.34 0.144 0.0032 H10 0.47 0.39 1.27 0.006 0.0007 0.0021 0.0021 0.126 0.024 0.045 0.28 0.178 0.0032 H11 0.46 0.43 1.33 0.008 0.0018 0.0019 0.0020 0.264 0.034 0.040 0.33 0.190 0.0032 H12 0.47 0.44 1.24 0.009 0.0006 0.0019 0.0033 0.369 0.026 0.033 0.29 0.218 0.0022 H13 0.46 0.39 1.23 0.007 0.0005 0.0024 0.0033 0.491 0.035 0.031 0.32 0.153 0.0023 H14 0.45 0.45 1.30 0.006 0.0013 0.0029 0.0029 0.511 0.032 0.039 0.31 0.149 0.0028 I1 0.46 0.40 1.22 0.009 0.0007 0.0024 0.0018 0.050 0.0006 0.036 0.33 0.133 0.0018 I2 0.45 0.43 1.34 0.008 0.0015 0.0034 0.0031 0.045 0.0012 0.037 0.24 0.225 0.0019 I3 0.46 0.43 1.30 0.005 0.0017 0.0025 0.0032 0.049 0.004 0.029 0.25 0.228 0.0020 I4 0.47 0.45 1.34 0.005 0.0015 0.0028 0.0016 0.044 0.007 0.043 0.31 0.211 0.0030 I5 0.45 0.40 1.31 0.005 0.0008 0.0034 0.0016 0.045 0.012 0.041 0.27 0.218 0.0029 I6 0.47 0.39 1.30 0.008 0.0010 0.0025 0.0034 0.040 0.018 0.034 0.30 0.143 0.0030 I7 0.46 0.40 1.25 0.005 0.0012 0.0021 0.0022 0.046 0.025 0.036 0.33 0.136 0.0029 I8 0.47 0.43 1.26 0.004 0.0010 0.0029 0.0019 0.043 0.037 0.037 0.27 0.183 0.0018 I9 0.45 0.41 1.30 0.004 0.0017 0.0028 0.0023 0.041 0.041 0.029 0.29 0.140 0.0027 I10 0.45 0.44 1.22 0.004 0.0006 0.0020 0.0029 0.050 0.056 0.025 0.26 0.158 0.0032 I11 0.47 0.42 1.34 0.009 0.0021 0.0024 0.0027 0.043 0.065 0.042 0.28 0.228 0.0024 I12 0.47 0.40 1.24 0.004 0.0021 0.0019 0.0014 0.047 0.081 0.045 0.31 0.199 0.0023 I13 0.47 0.39 1.32 0.004 0.0009 0.0019 0.0030 0.040 0.091 0.033 0.31 0.146 0.0019 I14 0.47 0.44 1.28 0.004 0.0010 0.0034 0.0028 0.049 0.126 0.037 0.29 0.156 0.0024 J1 0.46 0.40 1.26 0.006 0.0016 0.0022 0.0027 0.049 0.042 0.007 0.29 0.206 0.0032 J2 0.46 0.42 1.26 0.005 0.0013 0.0022 0.0026 0.048 0.032 0.011 0.31 0.189 0.0026 J3 0.45 0.41 1.25 0.005 0.0017 0.0030 0.0022 0.047 0.042 0.017 0.27 0.194 0.0026 J4 0.45 0.42 1.27 0.005 0.0014 0.0019 0.0019 0.049 0.021 0.023 0.31 0.210 0.0030 J5 0.47 0.39 1.34 0.008 0.0008 0.0032 0.0029 0.042 0.023 0.027 0.25 0.134 0.0025 J6 0.46 0.43 1.33 0.004 0.0022 0.0030 0.0017 0.047 0.030 0.031 0.25 0.170 0.0027 J7 0.46 0.39 1.21 0.008 0.0003 0.0029 0.0014 0.047 0.028 0.048 0.34 0.136 0.0019 J8 0.46 0.43 1.21 0.008 0.0019 0.0027 0.0033 0.048 0.034 0.055 0.27 0.194 0.0020 J9 0.46 0.45 1.34 0.008 0.0014 0.0028 0.0025 0.049 0.041 0.077 0.23 0.140 0.0024 J10 0.47 0.43 1.23 0.005 0.0014 0.0023 0.0020 0.045 0.023 0.111 0.28 0.224 0.0027 J11 0.45 0.44 1.23 0.008 0.0013 0.0019 0.0026 0.050 0.041 0.181 0.30 0.132 0.0023 J12 0.45 0.40 1.28 0.008 0.0009 0.0021 0.0018 0.041 0.024 0.211 0.29 0.175 0.0027 K1 0.47 0.43 1.29 0.004 0.0007 0.0032 0.0020 0.041 0.038 0.045 0.008 0.188 0.0021 K2 0.47 0.41 1.27 0.004 0.0006 0.0027 0.0023 0.039 0.024 0.030 0.012 0.211 0.0024 K3 0.46 0.40 1.34 0.004 0.0006 0.0021 0.0022 0.039 0.039 0.037 0.049 0.229 0.0019 K4 0.45 0.41 1.30 0.009 0.0012 0.0027 0.0019 0.039 0.026 0.035 0.081 0.133 0.0033 K5 0.45 0.40 1.31 0.007 0.0015 0.0019 0.0016 0.050 0.031 0.032 0.13 0.229 0.0018 K6 0.46 0.40 1.35 0.004 0.0015 0.0021 0.0017 0.043 0.039 0.037 0.19 0.183 0.0024 K7 0.47 0.45 1.24 0.008 0.0018 0.0031 0.0034 0.045 0.022 0.034 0.21 0.186 0.0025 K8 0.45 0.42 1.35 0.008 0.0022 0.0019 0.0024 0.044 0.038 0.030 0.27 0.181 0.0025 K9 0.45 0.43 1.34 0.004 0.0010 0.0027 0.0021 0.049 0.038 0.039 0.33 0.215 0.0026 K10 0.45 0.40 1.31 0.006 0.0003 0.0032 0.0019 0.050 0.022 0.043 0.42 0.221 0.0019 K11 0.46 0.43 1.31 0.007 0.0005 0.0030 0.0029 0.039 0.031 0.033 0.61 0.170 0.0031 K12 0.45 0.40 1.25 0.006 0.0004 0.0023 0.0029 0.050 0.041 0.034 0.78 0.204 0.0029 K13 0.47 0.43 1.30 0.006 0.0011 0.0027 0.0022 0.043 0.028 0.038 0.92 0.132 0.0020 K14 0.45 0.45 1.32 0.006 0.0012 0.0032 0.0033 0.049 0.039 0.036 1.12 0.204 0.0022 L1 0.47 0.41 1.22 0.009 0.0003 0.0025 0.0035 0.039 0.019 0.036 0.33 0.0009 0.0018 L2 0.45 0.43 1.28 0.004 0.0014 0.0026 0.0028 0.050 0.029 0.035 0.26 0.0012 0.0032 L3 0.46 0.43 1.29 0.004 0.0015 0.0022 0.0025 0.050 0.036 0.039 0.32 0.0051 0.0027 L4 0.47 0.44 1.31 0.004 0.0008 0.0033 0.0035 0.039 0.019 0.041 0.25 0.023 0.0025 L5 0.46 0.41 1.34 0.005 0.0008 0.0021 0.0023 0.039 0.030 0.028 0.31 0.072 0.0031 L6 0.45 0.41 1.22 0.009 0.0015 0.0022 0.0034 0.041 0.025 0.029 0.29 0.137 0.0024 L7 0.45 0.44 1.35 0.007 0.0008 0.0028 0.0023 0.046 0.036 0.029 0.31 0.193 0.0026 L8 0.45 0.39 1.21 0.004 0.0022 0.0024 0.0028 0.040 0.038 0.026 0.23 0.231 0.0029 L9 0.47 0.43 1.34 0.007 0.0009 0.0025 0.0017 0.050 0.020 0.041 0.28 0.351 0.0024 L10 0.45 0.44 1.23 0.008 0.0020 0.0030 0.0035 0.044 0.040 0.040 0.28 0.496 0.0018 L11 0.47 0.39 1.29 0.005 0.0019 0.0033 0.0016 0.042 0.032 0.031 0.26 0.673 0.0019 L12 0.45 0.41 1.32 0.009 0.0010 0.0028 0.0022 0.050 0.037 0.028 0.28 0.877 0.0030 L13 0.46 0.40 1.28 0.006 0.0022 0.0032 0.0033 0.046 0.028 0.025 0.25 1.236 0.0019 M1 0.47 0.42 1.26 0.007 0.0018 0.0032 0.0031 0.047 0.019 0.028 0.34 0.130 0.0002 M2 0.46 0.40 1.24 0.007 0.0016 0.0020 0.0022 0.050 0.036 0.025 0.32 0.180 0.0006 M3 0.46 0.42 1.21 0.008 0.0018 0.0024 0.0034 0.041 0.023 0.033 0.27 0.188 0.0011 M4 0.47 0.40 1.24 0.004 0.0013 0.0027 0.0033 0.049 0.034 0.033 0.25 0.213 0.0017 M5 0.47 0.42 1.25 0.006 0.0020 0.0020 0.0034 0.044 0.031 0.044 0.34 0.174 0.0022 M6 0.46 0.45 1.21 0.005 0.0012 0.0020 0.0023 0.050 0.025 0.044 0.32 0.149 0.0031 M7 0.45 0.39 1.29 0.004 0.0009 0.0024 0.0032 0.043 0.024 0.025 0.32 0.134 0.0045 M8 0.45 0.45 1.35 0.007 0.0022 0.0021 0.0018 0.044 0.032 0.043 0.24 0.192 0.0072 M9 0.45 0.42 1.21 0.008 0.0009 0.0034 0.0034 0.040 0.034 0.040 0.31 0.136 0.0119 M10 0.45 0.45 1.33 0.007 0.0009 0.0023 0.0034 0.041 0.041 0.034 0.25 0.135 0.0178 M11 0.45 0.44 1.30 0.009 0.0015 0.0030 0.0031 0.049 0.021 0.044 0.27 0.180 0.0221 N1 0.45 0.44 1.27 0.007 0.0006 0.0029 0.0019 0.043 0.019 0.037 0.29 0.132 0.0033 0.05 N2 0.45 0.45 1.27 0.004 0.0006 0.0024 0.0023 0.050 0.039 0.029 0.28 0.172 0.0018 0.12 N3 0.46 0.40 1.29 0.005 0.0021 0.0031 0.0015 0.049 0.018 0.030 0.28 0.155 0.0032 0.22 N4 0.47 0.39 1.34 0.005 0.0020 0.0032 0.0014 0.049 0.036 0.027 0.32 0.131 0.0033 0.42 N5 0.46 0.42 1.21 0.007 0.0019 0.0032 0.0016 0.043 0.029 0.038 0.25 0.167 0.0023 0.61 N6 0.45 0.41 1.21 0.006 0.0008 0.0027 0.0023 0.050 0.041 0.038 0.31 0.198 0.0024 0.85 N7 0.47 0.45 1.27 0.007 0.0018 0.0029 0.0021 0.040 0.037 0.029 0.28 0.221 0.0025 1.11 N8 0.46 0.40 1.35 0.006 0.0013 0.0033 0.0019 0.049 0.033 0.032 0.27 0.131 0.0020 1.35 N9 0.46 0.45 1.35 0.005 0.0004 0.0031 0.0018 0.050 0.037 0.042 0.28 0.211 0.0031 1.57 N10 0.47 0.44 1.27 0.004 0.0008 0.0031 0.0026 0.046 0.025 0.041 0.24 0.152 0.0019 1.72 N11 0.47 0.40 1.31 0.007 0.0006 0.0027 0.0025 0.050 0.038 0.027 0.28 0.210 0.0022 1.91 N12 0.47 0.40 1.35 0.004 0.0015 0.0022 0.0028 0.045 0.028 0.034 0.32 0.191 0.0029 2.56 N13 0.47 0.44 1.23 0.008 0.0018 0.0020 0.0027 0.040 0.026 0.028 0.25 0.181 0.0027 3.55 O1 0.46 0.43 1.22 0.006 0.0015 0.0030 0.0030 0.043 0.019 0.029 0.28 0.153 0.0026 0.02 O2 0.46 0.41 1.26 0.006 0.0015 0.0026 0.0032 0.047 0.035 0.041 0.31 0.130 0.0027 0.13 O3 0.46 0.39 1.27 0.004 0.0013 0.0030 0.0021 0.049 0.022 0.038 0.32 0.155 0.0021 0.23 O4 0.45 0.42 1.34 0.006 0.0017 0.0019 0.0026 0.048 0.026 0.043 0.26 0.150 0.0022 0.41 O5 0.46 0.45 1.25 0.004 0.0019 0.0033 0.0031 0.049 0.041 0.029 0.25 0.151 0.0027 0.84 O6 0.47 0.41 1.35 0.008 0.0022 0.0024 0.0025 0.043 0.019 0.045 0.27 0.200 0.0030 1.21 O7 0.46 0.44 1.21 0.005 0.0017 0.0021 0.0014 0.044 0.031 0.026 0.32 0.162 0.0028 1.62 O8 0.45 0.40 1.35 0.004 0.0011 0.0024 0.0028 0.045 0.041 0.035 0.30 0.168 0.0025 1.92 O9 0.45 0.40 1.30 0.009 0.0005 0.0023 0.0018 0.049 0.030 0.033 0.28 0.176 0.0030 2.11 O10 0.45 0.44 1.23 0.009 0.0018 0.0019 0.0024 0.039 0.020 0.036 0.32 0.164 0.0028 2.56 O11 0.47 0.39 1.35 0.008 0.0010 0.0025 0.0017 0.040 0.029 0.027 0.33 0.154 0.0030 2.79 O12 0.47 0.43 1.25 0.006 0.0018 0.0027 0.0033 0.047 0.022 0.026 0.33 0.220 0.0028 2.91 P1 0.47 0.42 1.26 0.005 0.0015 0.0032 0.0025 0.040 0.022 0.041 0.28 0.135 0.0032 P2 0.45 0.40 1.33 0.005 0.0020 0.0029 0.0021 0.040 0.025 0.027 0.23 0.163 0.0026 P3 0.45 0.45 1.27 0.006 0.0008 0.0028 0.0020 0.042 0.018 0.034 0.34 0.153 0.0021 P4 0.46 0.39 1.35 0.004 0.0006 0.0033 0.0017 0.050 0.024 0.030 0.31 0.136 0.0025 P5 0.45 0.45 1.33 0.007 0.0016 0.0024 0.0016 0.047 0.026 0.040 0.26 0.176 0.0021 P6 0.45 0.39 1.24 0.008 0.0013 0.0027 0.0022 0.043 0.022 0.030 0.31 0.164 0.0024 P7 0.45 0.43 1.25 0.006 0.0009 0.0029 0.0019 0.044 0.022 0.041 0.23 0.229 0.0027 P8 0.45 0.45 1.26 0.007 0.0008 0.0019 0.0029 0.047 0.023 0.031 0.33 0.221 0.0022 P9 0.45 0.44 1.28 0.008 0.0016 0.0033 0.0023 0.047 0.034 0.039 0.24 0.188 0.0032 P10 0.46 0.45 1.22 0.008 0.0012 0.0022 0.0030 0.044 0.026 0.028 0.25 0.188 0.0022 P11 0.46 0.44 1.22 0.004 0.0013 0.0034 0.0035 0.044 0.037 0.032 0.23 0.181 0.0019 P12 0.45 0.42 1.27 0.009 0.0003 0.0025 0.0019 0.049 0.021 0.031 0.28 0.132 0.0023 Q1 0.47 0.45 1.34 0.006 0.0017 0.0026 0.0026 0.040 0.027 0.040 0.34 0.182 0.0027 Q2 0.45 0.45 1.35 0.008 0.0003 0.0033 0.0028 0.045 0.020 0.027 0.30 0.136 0.0022 Q3 0.47 0.39 1.24 0.009 0.0013 0.0019 0.0032 0.045 0.029 0.046 0.27 0.215 0.0020 Q4 0.45 0.39 1.32 0.005 0.0012 0.0025 0.0017 0.048 0.019 0.032 0.23 0.230 0.0029 Q5 0.46 0.43 1.32 0.007 0.0015 0.0021 0.0024 0.041 0.023 0.041 0.28 0.191 0.0032 Q6 0.47 0.42 1.31 0.005 0.0022 0.0027 0.0025 0.048 0.034 0.026 0.26 0.203 0.0024 Q7 0.47 0.43 1.32 0.005 0.0016 0.0029 0.0030 0.039 0.022 0.033 0.32 0.215 0.0027 Q8 0.47 0.45 1.27 0.006 0.0007 0.0019 0.0031 0.049 0.021 0.035 0.29 0.141 0.0020 Q9 0.47 0.41 1.29 0.004 0.0007 0.0034 0.0020 0.045 0.041 0.034 0.24 0.154 0.0030 Q10 0.46 0.43 1.23 0.008 0.0010 0.0030 0.0015 0.042 0.028 0.026 0.26 0.154 0.0019 Q11 0.45 0.44 1.26 0.006 0.0017 0.0019 0.0023 0.039 0.025 0.031 0.34 0.152 0.0029 Q12 0.46 0.41 1.30 0.004 0.0007 0.0021 0.0023 0.045 0.035 0.042 0.27 0.148 0.0029 R1 0.46 0.39 1.31 0.004 0.0008 0.0028 0.0026 0.047 0.030 0.030 0.34 0.165 0.0031 R2 0.45 0.42 1.30 0.008 0.0009 0.0033 0.0025 0.044 0.026 0.042 0.26 0.140 0.0031 R3 0.45 0.41 1.26 0.008 0.0005 0.0028 0.0020 0.040 0.037 0.028 0.30 0.178 0.0027 R4 0.47 0.45 1.26 0.006 0.0009 0.0031 0.0032 0.044 0.038 0.036 0.27 0.218 0.0018 R5 0.47 0.40 1.26 0.006 0.0022 0.0021 0.0022 0.048 0.026 0.033 0.29 0.161 0.0033 R6 0.47 0.40 1.21 0.008 0.0018 0.0020 0.0021 0.042 0.042 0.035 0.30 0.152 0.0021 R7 0.46 0.42 1.32 0.008 0.0008 0.0031 0.0016 0.043 0.034 0.028 0.30 0.162 0.0031 R8 0.45 0.43 1.30 0.008 0.0019 0.0033 0.0033 0.039 0.036 0.044 0.30 0.219 0.0031 S1 0.45 0.45 1.22 0.007 0.0003 0.0028 0.0017 0.046 0.025 0.040 0.32 0.161 0.0021 S2 0.47 0.43 1.30 0.009 0.0014 0.0024 0.0029 0.039 0.028 0.031 0.25 0.173 0.0026 S3 0.45 0.40 1.35 0.004 0.0013 0.0030 0.0032 0.042 0.029 0.043 0.24 0.180 0.0023 S4 0.46 0.44 1.25 0.008 0.0020 0.0029 0.0014 0.049 0.036 0.046 0.30 0.148 0.0025 S5 0.47 0.44 1.22 0.004 0.0003 0.0021 0.0017 0.043 0.041 0.046 0.32 0.148 0.0026 S6 0.45 0.41 1.25 0.005 0.0012 0.0024 0.0029 0.044 0.026 0.046 0.30 0.209 0.0029 S7 0.46 0.45 1.32 0.009 0.0021 0.0032 0.0032 0.040 0.039 0.033 0.28 0.145 0.0025 S8 0.45 0.43 1.25 0.004 0.0017 0.0030 0.0014 0.049 0.036 0.029 0.27 0.161 0.0027 T1 0.46 0.45 1.27 0.004 0.0021 0.0026 0.0021 0.042 0.030 0.025 0.32 0.204 0.0024 T2 0.46 0.42 1.34 0.009 0.0004 0.0021 0.0035 0.040 0.021 0.034 0.26 0.217 0.0020 T3 0.46 0.39 1.21 0.007 0.0022 0.0023 0.0032 0.044 0.031 0.038 0.27 0.177 0.0025 T4 0.45 0.41 1.29 0.007 0.0009 0.0023 0.0034 0.039 0.018 0.033 0.24 0.181 0.0033 T5 0.47 0.42 1.30 0.004 0.0006 0.0027 0.0016 0.048 0.028 0.038 0.26 0.206 0.0019 T6 0.45 0.45 1.24 0.005 0.0019 0.0032 0.0014 0.045 0.031 0.043 0.23 0.227 0.0020 T7 0.47 0.41 1.29 0.009 0.0003 0.0030 0.0029 0.050 0.034 0.031 0.34 0.159 0.0032 T8 0.45 0.42 1.25 0.008 0.0009 0.0025 0.0027 0.040 0.034 0.040 0.31 0.138 0.0022 U1 0.46 0.45 1.23 0.008 0.0014 0.0029 0.0021 0.045 0.024 0.034 0.34 0.203 0.0022 U2 0.47 0.42 1.33 0.004 0.0017 0.0020 0.0035 0.042 0.024 0.039 0.27 0.193 0.0032 U3 0.47 0.39 1.32 0.009 0.0015 0.0029 0.0014 0.043 0.029 0.032 0.28 0.172 0.0024 U4 0.45 0.40 1.28 0.006 0.0014 0.0028 0.0025 0.041 0.037 0.033 0.34 0.181 0.0029 U5 0.46 0.45 1.32 0.005 0.0021 0.0030 0.0021 0.039 0.036 0.036 0.27 0.158 0.0023 U6 0.46 0.40 1.31 0.006 0.0020 0.0023 0.0034 0.041 0.021 0.041 0.26 0.165 0.0030 U7 0.45 0.43 1.28 0.005 0.0008 0.0032 0.0028 0.043 0.031 0.041 0.23 0.209 0.0022 U8 0.46 0.43 1.32 0.004 0.0007 0.0021 0.0025 0.050 0.039 0.035 0.26 0.149 0.0023 V1 0.45 0.45 1.35 0.006 0.0017 0.0032 0.0014 0.047 0.021 0.032 0.31 0.150 0.0021 V2 0.47 0.41 1.32 0.007 0.0004 0.0022 0.0022 0.046 0.020 0.043 0.31 0.203 0.0028 V3 0.45 0.44 1.34 0.009 0.0016 0.0032 0.0031 0.047 0.035 0.046 0.28 0.210 0.0025 V4 0.46 0.45 1.35 0.009 0.0017 0.0025 0.0033 0.040 0.039 0.042 0.27 0.228 0.0023 V5 0.47 0.42 1.31 0.007 0.0010 0.0028 0.0032 0.049 0.023 0.029 0.33 0.159 0.0021 V6 0.46 0.43 1.33 0.005 0.0021 0.0028 0.0022 0.044 0.028 0.033 0.33 0.203 0.0025 V7 0.46 0.45 1.25 0.009 0.0006 0.0026 0.0018 0.047 0.035 0.039 0.33 0.189 0.0024 V8 0.46 0.40 1.22 0.004 0.0006 0.0025 0.0028 0.047 0.041 0.044 0.27 0.230 0.0031 W1 0.46 0.45 1.35 0.008 0.0006 0.0025 0.0021 0.046 0.034 0.034 0.32 0.175 0.0028 W2 0.46 0.41 1.23 0.007 0.0009 0.0032 0.0032 0.049 0.031 0.030 0.30 0.152 0.0023 W3 0.46 0.41 1.30 0.005 0.0007 0.0026 0.0033 0.047 0.024 0.037 0.32 0.174 0.0023 W4 0.46 0.41 1.34 0.007 0.0020 0.0032 0.0023 0.050 0.018 0.032 0.34 0.230 0.0033 W5 0.45 0.42 1.24 0.005 0.0003 0.0023 0.0025 0.044 0.038 0.030 0.30 0.148 0.0024 W6 0.47 0.45 1.24 0.009 0.0017 0.0024 0.0014 0.047 0.024 0.026 0.30 0.203 0.0028 W7 0.46 0.40 1.32 0.005 0.0004 0.0025 0.0014 0.050 0.023 0.040 0.30 0.228 0.0019 W8 0.46 0.44 1.31 0.006 0.0009 0.0030 0.0022 0.048 0.019 0.042 0.29 0.178 0.0018 X1 0.45 0.40 1.21 0.006 0.0016 0.0030 0.0025 0.046 0.027 0.025 0.34 0.207 0.0021 X2 0.46 0.39 1.22 0.008 0.0010 0.0028 0.0018 0.048 0.031 0.037 0.30 0.132 0.0024 X3 0.46 0.45 1.24 0.006 0.0020 0.0022 0.0031 0.043 0.022 0.039 0.32 0.212 0.0033 Y1 0.47 0.40 1.24 0.009 0.0007 0.0019 0.0019 0.040 0.038 0.026 0.33 0.202 0.0029 Y2 0.46 0.44 1.21 0.007 0.0008 0.0026 0.0030 0.049 0.035 0.031 0.31 0.142 0.0018 Y3 0.45 0.39 1.28 0.009 0.0013 0.0032 0.0024 0.043 0.039 0.041 0.29 0.161 0.0029 Y4 0.46 0.39 1.32 0.008 0.0004 0.0019 0.0028 0.041 0.021 0.039 0.29 0.147 0.0021 Y5 0.46 0.43 1.31 0.005 0.0013 0.0022 0.0020 0.041 0.042 0.027 0.33 0.174 0.0028 Y6 0.46 0.41 1.35 0.004 0.0020 0.0031 0.0021 0.046 0.025 0.036 0.31 0.216 0.0033 Y7 0.45 0.40 1.22 0.004 0.0005 0.0023 0.0020 0.045 0.039 0.037 0.31 0.173 0.0032 Y8 0.47 0.42 1.31 0.006 0.0015 0.0031 0.0026 0.049 0.036 0.027 0.31 0.142 0.0025 Y9 0.46 0.45 1.28 0.004 0.0017 0.0033 0.0018 0.045 0.029 0.030 0.24 0.170 0.0031 Y10 0.45 0.42 1.34 0.004 0.0018 0.0022 0.0014 0.050 0.019 0.035 0.33 0.180 0.0029 Z1 0.46 0.45 1.28 0.006 0.0020 0.0025 0.0020 0.039 0.021 0.037 0.24 0.147 0.0022 Z2 0.45 0.40 1.35 0.005 0.0015 0.0019 0.0035 0.043 0.026 0.032 0.27 0.223 0.0026 Z3 0.46 0.39 1.25 0.004 0.0019 0.0023 0.0031 0.042 0.035 0.041 0.32 0.206 0.0018 74 0.47 0.43 1.24 0.005 0.0006 0.0019 0.0017 0.050 0.026 0.044 0.26 0.195 0.0032 Z5 0.47 0.45 1.21 0.005 0.0008 0.0030 0.0033 0.048 0.030 0.026 0.32 0.138 0.0032 Z6 0.46 0.44 1.23 0.007 0.0014 0.0032 0.0015 0.045 0.038 0.025 0.25 0.145 0.0026 Z7 0.47 0.41 1.33 0.009 0.0016 0.0022 0.0015 0.044 0.026 0.036 0.33 0.224 0.0018 Z8 0.46 0.42 1.26 0.006 0.0009 0.0029 0.0024 0.050 0.034 0.036 0.32 0.145 0.0031 Z9 0.45 0.39 1.26 0.004 0.0006 0.0031 0.0017 0.046 0.034 0.037 0.24 0.208 0.0023 Z10 0.46 0.44 1.35 0.006 0.0005 0.0029 0.0024 0.043 0.027 0.032 0.29 0.171 0.0031 AA1 0.46 0.44 1.28 0.005 0.0020 0.0020 0.0030 0.048 0.018 0.026 0.25 0.181 0.0022 AA2 0.47 0.43 1.23 0.004 0.0015 0.0027 0.0029 0.045 0.028 0.043 0.27 0.212 0.0022 AA3 0.46 0.44 1.35 0.008 0.0015 0.0033 0.0019 0.043 0.023 0.030 0.23 0.148 0.0022 AA4 0.47 0.45 1.26 0.004 0.0007 0.0028 0.0027 0.043 0.040 0.042 0.30 0.173 0.0019 AA5 0.46 0.44 1.24 0.005 0.0009 0.0020 0.0020 0.046 0.031 0.040 0.34 0.174 0.0022 AA6 0.47 0.45 1.24 0.005 0.0015 0.0027 0.0020 0.042 0.019 0.044 0.24 0.203 0.0020 AA7 0.45 0.44 1.31 0.005 0.0004 0.0023 0.0025 0.044 0.029 0.029 0.25 0.191 0.0033 AA8 0.47 0.41 1.24 0.006 0.0005 0.0028 0.0023 0.040 0.030 0.044 0.24 0.163 0.0025 AA9 0.46 0.44 1.27 0.004 0.0013 0.0022 0.0018 0.039 0.028 0.032 0.27 0.182 0.0019 AA10 0.47 0.42 1.34 0.009 0.0013 0.0022 0.0023 0.042 0.034 0.032 0.28 0.191 0.0023 BB1 0.46 0.44 1.33 0.007 0.0009 0.0030 0.0032 0.041 0.019 0.034 0.26 0.145 0.0032 BB2 0.47 0.43 1.24 0.008 0.0007 0.0029 0.0023 0.041 0.028 0.041 0.31 0.151 0.0022 BB3 0.46 0.39 1.30 0.004 0.0014 0.0020 0.0030 0.048 0.025 0.040 0.31 0.171 0.0024 BB4 0.45 0.40 1.24 0.008 0.0014 0.0019 0.0024 0.044 0.029 0.035 0.29 0.184 0.0019 BB5 0.47 0.39 1.21 0.008 0.0018 0.0027 0.0017 0.044 0.039 0.031 0.34 0.219 0.0033 BB6 0.46 0.42 1.31 0.006 0.0015 0.0030 0.0033 0.042 0.029 0.033 0.25 0.196 0.0032 BB7 0.47 0.43 1.33 0.009 0.0017 0.0019 0.0023 0.039 0.035 0.045 0.30 0.225 0.0028 BB8 0.47 0.44 1.27 0.006 0.0014 0.0019 0.0031 0.040 0.027 0.025 0.27 0.227 0.0024 BB9 0.46 0.41 1.22 0.007 0.0009 0.0024 0.0031 0.050 0.029 0.043 0.34 0.162 0.0018 BB10 0.45 0.45 1.34 0.008 0.0007 0.0027 0.0034 0.044 0.042 0.043 0.25 0.141 0.0022 CC1 0.46 0.44 1.21 0.005 0.0013 0.0026 0.0015 0.047 0.020 0.043 0.34 0.140 0.0033 CC2 0.45 0.40 1.24 0.009 0.0019 0.0025 0.0027 0.049 0.025 0.035 0.33 0.173 0.0031 CC3 0.46 0.42 1.30 0.005 0.0006 0.0021 0.0031 0.039 0.025 0.046 0.25 0.230 0.0024 CC4 0.47 0.41 1.31 0.007 0.0022 0.0021 0.0024 0.044 0.026 0.032 0.28 0.167 0.0021 CC5 0.46 0.45 1.24 0.007 0.0022 0.0024 0.0034 0.048 0.040 0.025 0.25 0.148 0.0032 CC6 0.47 0.39 1.22 0.006 0.0013 0.0027 0.0026 0.042 0.026 0.027 0.23 0.171 0.0033 CC7 0.46 0.39 1.29 0.008 0.0021 0.0022 0.0030 0.043 0.026 0.040 0.27 0.200 0.0022 CC8 0.46 0.39 1.22 0.008 0.0009 0.0020 0.0030 0.044 0.032 0.029 0.29 0.203 0.0018 CC9 0.45 0.40 1.22 0.004 0.0005 0.0029 0.0028 0.044 0.030 0.038 0.25 0.148 0.0033 CC10 0.47 0.43 1.28 0.009 0.0008 0.0031 0.0029 0.041 0.032 0.037 0.25 0.160 0.0020 DD1 0.46 0.41 1.25 0.006 0.0011 0.0025 0.0029 0.048 0.025 0.025 0.23 0.192 0.0033 DD2 0.46 0.42 1.26 0.007 0.0006 0.0033 0.0026 0.044 0.027 0.038 0.34 0.148 0.0027 DD3 0.46 0.39 1.24 0.004 0.0017 0.0033 0.0023 0.047 0.018 0.026 0.32 0.141 0.0027 DD4 0.45 0.45 1.22 0.007 0.0013 0.0026 0.0015 0.049 0.031 0.026 0.30 0.131 0.0022 DD5 0.47 0.43 1.25 0.009 0.0012 0.0023 0.0019 0.045 0.019 0.035 0.24 0.230 0.0022 DD6 0.46 0.41 1.26 0.006 0.0022 0.0023 0.0024 0.043 0.034 0.030 0.27 0.147 0.0027 DD7 0.46 0.39 1.30 0.007 0.0014 0.0022 0.0026 0.044 0.028 0.040 0.24 0.168 0.0024 DD8 0.45 0.44 1.35 0.008 0.0017 0.0021 0.0035 0.047 0.018 0.037 0.25 0.181 0.0020 DD9 0.47 0.42 1.24 0.004 0.0014 0.0032 0.0032 0.050 0.032 0.041 0.29 0.194 0.0020 DD10 0.46 0.39 1.26 0.008 0.0016 0.0024 0.0015 0.050 0.027 0.034 0.31 0.209 0.0020 EE1 0.46 0.40 1.22 0.007 0.0022 0.0030 0.0028 0.054 0.021 0.036 0.32 0.157 0.0028 0.08 EE2 0.48 0.41 1.21 0.004 0.0024 0.0019 0.0023 0.046 0.032 0.045 0.35 0.136 0.0026 EE3 0.47 0.41 1.29 0.003 0.0008 0.0032 0.0020 0.057 0.033 0.042 0.33 0.222 0.0020 1.02 EE4 0.45 0.45 1.30 0.009 0.0021 0.0023 0.0019 0.053 0.030 0.034 0.35 0.204 0.0035 0.05 EE5 0.46 0.45 0.81 0.007 0.0011 0.0020 0.0017 0.045 0.032 0.042 0.24 0.213 0.0033 EE6 0.47 0.45 1.30 0.006 0.0005 0.0029 0.0015 0.048 0.020 0.029 0.27 0.190 0.0021 EE7 0.45 0.43 2.05 0.003 0.0011 0.0022 0.0027 0.046 0.040 0.031 0.27 0.159 0.0027 EE8 0.46 0.44 2.24 0.004 0.0005 0.0032 0.0035 0.040 0.023 0.029 0.32 0.210 0.0026 Chemical composition (mass %), bal.: Fe and impurities Steel Cu V Ca Mg REM Sb Zr Sn As W Ta Re Os Ir Tc Remarks A1 Comp. steel A2 Inv. steel A3 Inv. steel A4 Inv. steel A5 Inv. steel A6 Inv. steel A7 Inv. steel A8 Inv. steel A9 Inv. steel A10 Inv. steel A11 Inv. steel A12 Inv. steel A13 Inv. steel A14 Comp. steel B1 Comp. steel B2 Inv. steel B3 Inv. steel B4 Inv. steel B5 Inv. steel B6 Inv. steel B7 Inv. steel B8 Inv. steel B9 Inv. steel B10 Inv. steel B11 Inv. steel B12 Inv. steel B13 Inv. steel B14 Inv. steel B15 Comp. steel C1 Comp. steel C2 Inv. steel C3 Inv. steel C4 Inv. steel C5 Inv. steel C6 Inv. steel C7 Inv. steel C8 Inv. steel C9 Inv. steel C10 Inv. steel C11 Inv. steel C12 Inv. steel C13 Inv. steel C14 Comp. steel D1 Inv. steel D2 Inv. steel D3 Inv. steel D4 Inv. steel D5 Inv. steel D6 Inv. steel D7 Inv. steel D8 Inv. steel D9 Comp. steel E1 Inv. steel E2 Inv. steel E3 Inv. steel E4 Inv. steel E5 Inv. steel E6 Inv. steel E7 Inv. steel E8 Inv. steel E9 Comp. steel F1 Inv. steel F2 Inv. steel F3 Inv. steel F4 Inv. steel F5 Inv. steel F6 Inv. steel F7 Inv. steel F8 Inv. steel F9 Comp. steel G1 Inv. steel G2 Inv. steel G3 Inv. steel G4 Inv. steel G5 Inv. steel G6 Inv. steel G7 Inv. steel G8 Comp. steel H1 Comp. steel H2 Inv. steel H3 Inv. steel H4 Inv. steel H5 Inv. steel H6 Inv. steel H7 Inv. steel H8 Inv. steel H9 Inv. steel H10 Inv. steel H11 Inv. steel H12 Inv. steel H13 Inv. steel H14 Comp. steel I1 Comp. steel I2 Inv. steel I3 Inv. steel I4 Inv. steel I5 Inv. steel I6 Inv. steel I7 Inv. steel I8 Inv. steel I9 Inv. steel I10 Inv. steel I11 Inv. steel I12 Inv. steel I13 Inv. steel I14 Comp. steel J1 Comp. steel J2 Inv. steel J3 Inv. steel J4 Inv. steel J5 Inv. steel J6 Inv. steel J7 Inv. steel J8 Inv. steel J9 Inv. steel J10 Inv. steel J11 Inv. steel J12 Comp. steel K1 Comp. steel K2 Inv. steel K3 Inv. steel K4 Inv. steel K5 Inv. steel K6 Inv. steel K7 Inv. steel K8 Inv. steel K9 Inv. steel K10 Inv. steel K11 Inv. steel K12 Inv. steel K13 Inv. steel K14 Comp. steel LI Comp. steel L2 Inv. steel L3 Inv. steel L4 Inv. steel L5 Inv. steel L6 Inv. steel L7 Inv. steel L8 Inv. steel L9 Inv. steel L10 Inv. steel L11 Inv. steel L12 Inv. steel L13 Comp. steel M1 Comp. steel M2 Inv. steel M3 Inv. steel M4 Inv. steel M5 Inv. steel M6 Inv. steel M7 Inv. steel M8 Inv. steel M9 Inv. steel M10 Inv. steel M11 Comp. steel N1 Inv. steel N2 Inv. steel N3 Inv. steel N4 Inv. steel N5 Inv. steel N6 Inv. steel N7 Inv. steel N8 Inv. steel N9 Inv. steel N10 Inv. steel N11 Inv. steel N12 Inv. steel N13 Inv. steel O1 Inv. steel O2 Inv. steel O3 Inv. steel O4 Inv. steel O5 Inv. steel O6 Inv. steel O7 Inv. steel O8 Inv. steel O9 Inv. steel O10 Inv. steel O11 Inv. steel O12 Inv. steel P1 0.05 Inv. steel P2 0.11 Inv. steel P3 0.23 Inv. steel P4 0.42 Inv. steel P5 0.83 Inv. steel P6 1.32 Inv. steel P7 1.63 Inv. steel P8 1.84 Inv. steel P9 2.21 Inv. steel P10 2.45 Inv. steel P11 2.74 Inv. steel P12 2.91 Inv. steel Q1 0.05 Inv. steel Q2 0.11 Inv. steel Q3 0.21 Inv. steel Q4 0.47 Inv. steel Q5 0.84 Inv. steel Q6 1.29 Inv. steel Q7 1.55 Inv. steel Q8 1.81 Inv. steel Q9 2.21 Inv. steel Q10 2.46 Inv. steel Q11 2.63 Inv. steel Q12 2.88 Inv. steel R1 0.001 Inv. steel R2 0.01 Inv. steel R3 0.13 Inv. steel R4 0.27 Inv. steel R5 0.41 Inv. steel R6 0.65 Inv. steel R7 0.75 Inv. steel R8 0.91 Inv. steel S1 0.003 Inv. steel S2 0.02 Inv. steel S3 0.12 Inv. steel S4 0.25 Inv. steel S5 0.47 Inv. steel S6 0.63 Inv. steel S7 0.74 Inv. steel S8 0.96 Inv. steel T1 0.001 Inv. steel T2 0.04 Inv. steel T3 0.12 Inv. steel T4 0.25 Inv. steel T5 0.39 Inv. steel T6 0.63 Inv. steel T7 0.75 Inv. steel T8 0.91 Inv. steel U1 0.002 Inv. steel U2 0.03 Inv. steel U3 0.13 Inv. steel U4 0.25 Inv. steel U5 0.41 Inv. steel U6 0.64 Inv. steel U7 0.71 Inv. steel U8 0.92 Inv. steel V1 0.002 Inv. steel V2 0.04 Inv. steel V3 0.14 Inv. steel V4 0.25 Inv. steel V5 0.39 Inv. steel V6 0.57 Inv. steel V7 0.76 Inv. steel V8 0.93 Inv. steel W1 0.002 Inv. steel W2 0.03 Inv. steel W3 0.12 Inv. steel W4 0.27 Inv. steel W5 0.44 Inv. steel W6 0.64 Inv. steel W7 0.75 Inv. steel W8 0.92 Inv. steel X1 0.004 Inv. steel X2 0.021 Inv. steel X3 0.077 Inv. steel Y1 0.002 Inv. steel Y2 0.008 Inv. steel Y3 0.02 Inv. steel Y4 0.06 Inv. steel Y5 0.12 Inv. steel Y6 0.17 Inv. steel Y7 0.28 Inv. steel Y8 0.51 Inv. steel Y9 0.71 Inv. steel Y10 0.88 Inv. steel Z1 0.002 Inv. steel Z2 0.007 Inv. steel Z3 0.03 Inv. steel Z4 0.06 Inv. steel Z5 0.14 Inv. steel Z6 0.18 Inv. steel Z7 0.28 Inv. steel Z8 0.52 Inv. steel Z9 0.69 Inv. steel Z10 0.87 Inv. steel AA1 0.002 Inv. steel AA2 0.006 Inv. steel AA3 0.04 Inv. steel AA4 0.07 Inv. steel AA5 0.12 Inv. steel AA6 0.19 Inv. steel AA7 0.25 Inv. steel AA8 0.51 Inv. steel AA9 0.65 Inv. steel AA10 0.84 Inv. steel BB1 0.003 Inv. steel BB2 0.006 Inv. steel BB3 0.05 Inv. steel BB4 0.07 Inv. steel BB5 0.15 Inv. steel BB6 0.18 Inv. steel BB7 0.25 Inv. steel BB8 0.49 Inv. steel BB9 0.63 Inv. steel BB10 0.88 Inv. steel CC1 0.002 Inv. steel CC2 0.005 Inv. steel CC3 0.04 Inv. steel CC4 0.08 Inv. steel CC5 0.15 Inv. steel CC6 0.17 Inv. steel CC7 0.21 Inv. steel CC8 0.46 Inv. steel CC9 0.66 Inv. steel CC10 0.91 Inv. steel DD1 0.002 Inv. steel DD2 0.007 Inv. steel DD3 0.03 Inv. steel DD4 0.08 Inv. steel DD5 0.11 Inv. steel DD6 0.17 Inv. steel DD7 0.23 Inv. steel DD8 0.49 Inv. steel DD9 0.61 Inv. steel DD10 0.92 Inv. steel EE1 0.24 Inv. steel EE2 Inv. steel EE3 Inv. steel EE4 0.27 0.122 Inv. steel EE5 Inv. steel EE6 Inv. steel EE7 Inv. steel EE8 Inv. steel Underlines show outside scope of present invention.

TABLE 2 Preheating step Hot rolling step Average Finish rolling Coiling cooling final stage step speed down Hot stamping step rolling Coiling Heating to less than Heating Holding Test reduction temp. temp 350° C. temp. time No. Steel % ° C. ° C. ° C./s ° C. s Others Remarks 1 A1 54 583 1288 473 912 366 Comp. ex. 2 A2 55 655 1279 591 910 348 Inv. ex. 3 A3 51 679 1266 525 903 368 Inv. ex. 4 A4 55 643 1275 518 913 373 Inv. ex. 5 A5 54 646 1265 444 912 358 Inv. ex. 6 A6 52 669 1253 561 922 350 Inv. ex. 7 A7 54 645 1246 411 924 366 Inv. ex. 8 A8 51 648 1248 539 922 368 Inv. ex. 9 A9 54 683 1276 507 908 357 Inv. ex. 10 A10 51 651 1288 539 897 374 Inv. ex. 11 A11 51 616 1263 666 901 370 Inv. ex. 12 A12 54 606 1262 648 911 371 Inv. ex. 13 A13 52 655 1259 625 915 366 Inv. ex. 14 A14 51 694 1276 629 910 351 Comp. ex 15 B1 51 568 1279 445 912 358 Comp. ex. 16 B2 54 619 1283 421 919 350 Inv. ex. 17 B3 51 610 1256 504 912 366 Inv. ex. 18 B4 55 658 1272 560 915 355 Inv. ex 19 B5 54 665 1265 507 920 355 Inv. ex. 20 B6 54 677 1261 610 899 375 Inv. ex. 21 B7 51 604 1249 532 897 373 Inv. ex. 22 B8 55 643 1249 434 910 373 Inv. ex. 23 B9 51 641 1281 575 897 372 Inv. ex. 24 B10 55 624 1288 618 910 364 Inv. ex. 25 B11 53 717 1252 660 912 345 Inv. ex. 26 B12 53 577 1261 422 897 360 Inv. ex. 27 B13 53 593 1280 685 902 365 Inv. ex. 28 B14 51 662 1255 697 920 353 Inv. ex. 29 B15 55 705 1251 411 915 361 Comp. ex. 30 C1 51 684 1254 491 915 346 Comp. ex. 31 C2 55 699 1251 645 898 375 Inv. ex. 32 C3 53 717 1286 679 902 368 Inv. ex. 33 C4 51 717 1249 474 913 369 Inv. ex. 34 C5 55 562 1250 502 918 365 Inv. ex. 35 C6 53 725 1244 502 905 354 Inv. ex. 36 C7 51 688 1270 595 909 366 Inv. ex. 37 C8 55 713 1261 697 898 371 Inv. ex. 38 C9 54 693 1271 670 911 364 Inv. ex. 39 C10 55 612 1283 499 898 370 Inv. ex. 40 C11 55 712 1270 462 923 369 Inv. ex. 41 C12 55 568 1259 527 901 349 Inv. ex. 42 C13 55 687 1290 677 901 346 Inv. ex. 43 C14 51 554 1244 688 895 372 Comp. ex. 44 D1 54 643 1243 458 910 368 Inv. ex. 45 D2 51 626 1268 686 919 374 Inv. ex. 46 D3 54 707 1274 611 925 368 Inv. ex. 47 D4 55 605 1271 618 925 372 Inv. ex. 48 D5 53 719 1247 421 916 357 Inv. ex. 49 D6 51 677 1256 655 901 372 Inv. ex. 50 D7 52 551 1286 623 925 362 Inv. ex. 51 D8 55 575 1246 406 900 361 Inv. ex. Preheating step Hot rolling step Average Finish rolling Coiling cooling final stage step speed down Hot stamping step rolling Coiling Heating to less than Heating Holding Test reduction temp. temp. 350° C. temp. time no Steel % ° C. ° C. ° C./s ° C. s Others Remarks 52 D9 55 703 1271 481 905 355 Comp. ex. 53 E1 52 585 1242 684 921 355 Inv. ex. 54 E2 51 653 1249 438 918 375 Inv. ex. 55 E3 54 591 1289 539 911 348 Inv. ex. 56 E4 54 589 1250 496 916 357 Inv. ex. 57 E5 55 580 1245 640 918 374 Inv. ex. 58 E6 53 619 1253 402 915 373 Inv. ex. 59 E7 52 585 1253 538 907 361 Inv. ex. 60 E8 52 630 1281 467 897 356 Inv. ex. 61 E9 54 627 1273 515 904 346 Comp. ex. 62 F1 54 571 1287 680 922 348 Inv. ex. 63 F2 55 710 1254 424 904 367 Inv. ex. 64 F3 53 566 1258 570 905 357 Inv. ex. 65 F4 52 627 1275 599 900 369 Inv. ex. 66 F5 55 721 1279 609 914 353 Inv. ex. 67 F6 51 675 1271 593 911 362 Inv. ex. 68 F7 53 602 1274 586 902 361 Inv. ex. 69 F8 51 679 1287 406 906 359 Inv. ex. 70 F9 55 580 1278 499 920 354 Comp. ex. 71 G1 55 619 1244 646 916 348 Inv. ex. 72 G2 52 650 1264 485 921 359 Inv. ex. 73 G3 52 675 1279 699 913 354 Inv. ex. 74 G4 51 696 1265 608 910 354 Inv. ex. 75 G5 52 587 1265 415 916 364 Inv. ex. 76 G6 54 590 1290 582 915 355 Inv. ex. 77 G7 54 595 1269 438 902 348 Inv. ex. 78 G8 55 623 1268 649 901 364 Comp. ex. 79 H1 51 586 1287 641 914 346 Comp. ex. 80 H2 52 674 1281 457 925 366 Inv. ex. 81 H3 54 690 1278 687 905 359 Inv. ex. 82 H4 55 701 1270 416 904 362 Inv. ex. 83 H5 54 603 1270 443 916 347 Inv. ex. 84 H6 51 607 1269 622 901 345 Inv. ex. 85 H7 51 591 1271 680 916 345 Inv. ex. 86 H8 53 701 1262 636 914 345 Inv. ex 87 H9 51 552 1252 651 899 345 Inv. ex. 88 H10 55 672 1283 483 909 367 Inv. ex. 89 H11 54 612 1259 490 920 350 Inv. ex. 90 H12 51 648 1253 645 903 372 Inv. ex. 91 H13 53 558 1281 466 925 362 Inv. ex. 92 H14 51 585 1266 559 920 372 Comp. ex. 93 I1 53 717 1266 526 924 355 Comp. ex. 94 I2 51 702 1264 556 897 367 Inv. ex. 95 I3 51 611 1269 527 901 366 Inv. ex. 96 I4 52 721 1274 556 895 374 Inv. ex. 97 I5 55 708 1282 698 897 346 Inv. ex. 98 I6 53 559 1272 491 896 363 Inv. ex. 99 I7 51 715 1254 576 907 363 Inv. ex. 100 18 51 653 1262 579 903 374 Inv. ex. 101 I9 52 662 1263 466 911 361 Inv. ex. 102 I10 53 714 1269 678 923 375 Inv. ex. Preheating step Hot rolling step Average Finish rolling Coiling cooling final stage step speed down Hot stamping step rolling Coiling Heating to less than Heating Holding Test reduction temp. temp. 350° C. temp. time no. Steel % ° C. ° C. 0° C./s ° C. s Others Remarks 103 I11 54 671 1248 471 921 368 Inv. ex. 104 I12 52 566 1241 430 911 346 Inv. ex. 105 I13 55 629 1281 593 898 347 Inv. ex. 106 I14 52 637 1252 687 903 351 Comp. ex. 107 J1 51 650 1284 613 914 348 Comp. ex. 108 J2 51 714 1267 651 910 375 Inv. ex. 109 J3 53 726 1255 665 923 369 Inv. ex. 110 J4 51 557 1277 418 903 354 Inv. ex. 111 J5 53 601 1282 571 920 349 Inv. ex. 112 J6 55 695 1255 553 923 365 Inv. ex. 113 J7 51 673 1267 575 910 355 Inv. ex. 114 J8 55 691 1280 474 922 357 Inv. ex 115 J9 55 682 1264 510 925 356 Inv. ex. 116 J10 51 671 1265 541 924 346 Inv. ex. 117 J11 54 638 1285 631 910 368 Inv. ex. 118 J12 54 724 1244 503 904 375 Comp. ex. 119 K1 51 652 1272 569 906 347 Comp. ex. 120 K2 53 642 1249 637 917 363 Inv. ex. 121 K3 52 724 1284 471 897 353 Inv. ex. 122 K4 52 660 1240 689 921 360 Inv. ex. 123 KS 51 652 1280 417 902 350 Inv. ex 124 K6 55 696 1247 671 919 348 Inv. ex. 125 K7 55 551 1259 566 921 372 Inv. ex. 126 K8 55 588 1256 596 912 372 Inv. ex. 127 K9 54 694 1242 664 915 368 Inv. ex. 128 K10 53 658 1284 529 899 362 Inv. ex. 129 K11 53 674 1263 696 925 352 Inv. ex 130 K12 53 593 1289 493 897 374 Inv. ex. 131 K13 51 720 1258 636 896 359 Inv. ex. 132 K14 51 689 1268 501 895 359 Comp. ex. 133 L1 53 645 1254 410 913 355 Comp. ex. 134 L2 51 627 1260 628 925 353 Inv. ex. 135 L3 55 691 1282 679 905 352 Inv. ex 136 L4 52 572 1257 559 913 365 Inv. ex. 137 L5 52 714 1259 562 917 358 Inv. ex. 138 L6 54 657 1264 443 917 367 Inv. ex 139 L7 52 653 1281 433 917 368 Inv. ex. 140 L8 52 559 1273 454 897 354 Inv. ex. 141 L9 55 722 1265 565 912 362 Inv. ex. 142 L10 55 669 1250 476 919 349 Inv. ex. 143 L11 51 676 1286 541 915 365 Inv. ex. 144 L12 53 708 1243 676 904 363 Inv. ex 145 L13 53 606 1259 556 898 356 Comp. ex. 146 M1 52 720 1289 414 896 372 Comp. ex. 147 M2 53 608 1272 514 918 347 Inv. ex. 148 M3 54 627 1267 464 914 348 Inv. ex. 149 M4 55 586 1275 589 921 361 Inv. ex. 150 M5 51 575 1266 571 899 350 Inv. ex 151 M6 51 670 1259 427 921 353 Inv. ex. 152 M7 54 624 1267 433 919 358 Inv. ex. 153 M8 51 595 1276 462 915 359 Inv. ex. Preheating step Hot rolling step Average Finish rolling Coiling cooling final stage step speed down Hot stamping step rolling Coiling Heating to less than Heating Holding Test reduction temp. temp. 350° C. temp. time no. Steel % ° C. ° C. ° C./s ° C. s Others Remarks 154 M9 55 652 1277 630 909 358 Inv. ex. 155 M10 52 643 1256 662 912 357 Inv. ex. 156 M11 53 667 1251 516 896 372 Comp. ex. 157 N1 52 642 1256 552 915 354 Inv. ex. 158 N2 51 652 1276 439 908 364 Inv. ex. 159 N3 54 722 1278 663 898 370 Inv. ex. 160 N4 55 687 1288 469 909 368 Inv. ex. 161 N5 54 561 1265 504 918 374 Inv. ex. 162 N6 55 583 1279 492 895 366 Inv. ex. 163 N7 54 618 1284 668 909 364 Inv. ex. 164 N8 55 567 1270 490 912 357 Inv. ex. 165 N9 53 719 1269 685 920 360 Inv. ex. 166 N10 55 635 1262 578 906 366 Inv. ex. 167 N11 52 616 1273 466 921 357 Inv. ex. 168 N12 54 673 1272 521 921 359 Inv. ex. 169 N13 54 629 1282 442 909 366 Inv. ex. 170 O1 54 694 1290 434 919 356 Inv. ex. 171 O2 54 581 1263 648 905 357 Inv. ex. 172 O3 52 612 1279 495 923 348 Inv. ex. 173 O4 52 609 1278 563 896 364 Inv. ex. 174 O5 51 599 1266 466 920 371 Inv. ex. 175 O6 52 654 1249 695 913 365 Inv. ex. 176 O7 52 658 1256 544 899 375 Inv. ex. 177 O8 53 601 1248 587 924 369 Inv. ex. 178 O9 51 601 1274 403 908 345 Inv. ex. 179 O10 54 716 1268 424 912 371 Inv. ex. 180 O11 55 581 1251 476 898 351 Inv. ex. 181 O12 53 633 1271 642 901 372 Inv. ex. 182 P1 54 672 1289 434 901 347 Inv. ex. 183 P2 52 728 1249 420 899 357 Inv. ex. 184 P3 51 668 1281 525 904 370 Inv. ex. 185 P4 51 584 1283 690 913 370 Inv. ex. 186 P5 54 587 1275 420 910 356 Inv. ex. 187 P6 55 570 1286 524 896 348 Inv. ex. 188 P7 51 649 1267 485 924 369 Inv. ex. 189 P8 52 710 1240 611 909 356 Inv. ex. 190 P9 54 554 1276 697 916 360 Inv. ex. 191 P10 51 715 1273 586 924 350 Inv. ex. 192 P11 51 617 1280 677 906 371 Inv. ex. 193 P12 51 612 1266 636 896 347 Inv. ex. 194 Q1 52 567 1287 672 896 351 Inv. ex. 195 Q2 53 625 1258 596 905 358 Inv. ex. 196 Q3 53 713 1288 615 914 348 Inv. ex. 197 Q4 54 667 1270 410 897 354 Inv. ex. 198 Q5 53 642 1288 565 899 349 Inv. ex. 199 Q6 54 689 1288 693 922 361 Inv. ex. 200 Q7 53 647 1268 463 922 366 Inv. ex. 201 Q8 51 616 1284 503 906 362 Inv. ex. 202 Q9 54 612 1280 472 922 352 Inv. ex. 203 Q10 52 716 1289 415 897 347 Inv. ex. 204 Q11 51 681 1259 471 912 345 Inv. ex. Preheating step Hot rolling step Average Finish rolling Coiling cooling final stage step speed down Hot stamping step rolling Coiling Heating to less than Heating Holding Test reduction temp. temp. 350° C. temp. time no. Steel % ° C. ° C. ° C./s ° C. s Others Remarks 205 Q12 51 662 1249 696 906 345 Inv. ex. 206 R1 52 720 1260 492 897 359 Inv. ex. 207 R2 53 612 1261 550 914 370 Inv. ex. 208 R3 51 619 1261 584 912 348 Inv. ex. 209 R4 53 594 1254 487 898 346 Inv. ex. 210 R5 51 611 1259 698 900 355 Inv. ex. 211 R6 54 574 1255 601 901 368 Inv. ex. 212 R7 52 632 1267 503 917 372 Inv. ex. 213 R8 51 613 1244 531 910 349 Inv. ex. 214 S1 55 584 1261 602 916 351 Inv. ex. 215 S2 51 564 1244 554 910 361 Inv. ex. 216 S3 53 677 1249 439 904 372 Inv. ex. 217 S4 55 588 1261 447 911 372 Inv. ex. 218 S5 52 583 1247 519 901 357 Inv. ex. 219 S6 52 664 1275 699 911 350 Inv. ex. 220 S7 52 550 1264 692 916 355 Inv. ex. 221 S8 54 707 1240 466 904 374 Inv. ex. 222 T1 55 728 1256 525 898 374 Inv. ex. 223 T2 54 558 1277 680 906 345 Inv. ex. 224 T3 55 680 1247 490 906 365 Inv. ex. 225 T4 54 574 1271 548 911 345 Inv. ex. 226 T5 55 694 1252 467 922 372 Inv. ex. 227 T6 54 677 1273 621 921 371 Inv. ex. 228 T7 51 588 1253 490 913 352 Inv. ex. 229 T8 51 650 1247 469 912 369 Inv. ex. 230 U1 51 590 1253 448 909 369 Inv. ex. 231 U2 52 556 1264 547 919 373 Inv. ex. 232 U3 55 587 1263 424 919 375 Inv. ex. 233 U4 53 586 1276 581 903 346 Inv. ex. 234 U5 54 646 1282 620 906 352 Inv. ex. 235 U6 51 693 1269 517 915 349 Inv. ex. 236 U7 54 556 1241 650 912 355 Inv. ex. 237 U8 54 645 1277 520 909 364 Inv. ex. 238 V1 52 666 1285 652 911 370 Inv. ex. 239 V2 55 634 1273 574 900 365 Inv. ex. 240 V3 51 568 1252 545 910 354 Inv. ex. 241 V4 54 556 1288 442 897 347 Inv. ex. 242 V5 55 689 1250 404 911 353 Inv. ex. 243 V6 55 571 1288 474 922 359 Inv. ex. 244 V7 51 729 1276 676 897 373 Inv. ex. 245 V8 54 669 1250 569 897 353 Inv. ex. 246 W1 54 696 1274 619 904 346 Inv. ex. 247 W2 53 606 1257 517 914 345 Inv. ex. 248 W3 51 676 1289 456 903 357 Inv. ex. 249 W4 53 642 1253 653 907 354 Inv. ex. 250 W5 51 671 1256 510 913 373 Inv. ex. 251 W6 54 660 1287 692 897 357 Inv. ex. 252 W7 55 610 1270 694 909 374 Inv. ex. 253 W8 54 555 1269 698 896 358 Inv. ex. 254 X1 54 663 1246 629 903 368 Inv. ex. 255 X2 54 628 1240 473 918 375 Inv. ex. Preheating step Hot rolling step Average Finish rolling Coiling cooling final stage step speed down Hot stamping step rolling Coiling Heating to less than Heating Holding Test reduction temp. temp. 350° C. temp. time no. Steel % ° C. ° C. ° C./s ° C. s Others Remarks 256 X3 52 624 1282 508 895 356 Inv. ex. 257 Y1 55 657 1249 546 907 361 Inv. ex. 258 Y2 55 672 1277 480 919 358 Inv. ex. 259 Y3 53 667 1250 596 899 370 Inv. ex. 260 Y4 52 685 1243 650 910 349 Inv. ex. 261 Y5 53 555 1248 509 901 358 Inv. ex. 262 Y6 55 639 1288 466 914 350 Inv. ex. 263 Y7 54 644 1255 589 919 356 Inv. ex. 264 Y8 53 631 1266 690 911 366 Inv. ex. 265 Y9 54 653 1264 436 915 349 Inv. ex. 266 Y10 55 639 1265 553 914 364 Inv. ex. 267 Z1 51 653 1280 690 900 367 Inv. ex. 268 Z2 54 603 1253 697 912 369 Inv. ex. 269 Z3 54 620 1273 592 920 366 Inv. ex. 270 Z4 55 700 1277 505 910 373 Inv. ex. 271 Z5 53 601 1275 548 906 351 Inv. ex. 272 Z6 54 615 1242 421 902 365 Inv. ex. 273 Z7 52 650 1264 517 903 356 Inv. ex. 274 Z8 55 645 1256 678 919 374 Inv. ex. 275 Z9 53 568 1283 436 923 358 Inv. ex. 276 Z10 51 698 1245 688 925 371 Inv. ex. 277 AA1 51 656 1260 412 897 375 Inv. ex. 278 AA2 54 724 1261 557 896 375 Inv. ex. 279 AA3 53 627 1262 449 898 373 Inv. ex. 280 AA4 52 565 1263 547 920 355 Inv. ex. 281 AA5 55 612 1261 583 925 354 Inv. ex. 282 AA6 53 727 1284 693 910 373 Inv. ex. 283 AA7 55 682 1286 445 917 347 Inv. ex. 284 AA8 51 579 1257 670 922 361 Inv. ex. 285 AA9 51 648 1270 522 897 364 Inv. ex. 286 AA10 52 704 1242 532 923 346 Inv. ex. 287 BB1 53 581 1243 430 897 356 Inv. ex. 288 BB2 52 710 1257 475 923 356 Inv. ex. 289 BB3 54 622 1288 663 900 359 Inv. ex. 290 BB4 52 564 1245 518 914 349 Inv. ex. 291 BB5 52 724 1286 557 911 371 Inv. ex. 292 BB6 54 606 1267 696 898 367 Inv. ex. 293 BB7 52 639 1277 501 914 348 Inv. ex. 294 BB8 53 707 1248 588 925 365 Inv. ex. 295 BB9 54 553 1277 476 901 370 Inv. ex. 296 BB10 54 632 1284 487 908 359 Inv. ex. 297 CC1 55 676 1251 560 908 354 Inv. ex. 298 CC2 54 627 1241 504 915 371 Inv. ex. 299 CC3 51 668 1264 486 914 364 Inv. ex. 300 CC4 52 672 1272 552 898 361 Inv. ex. 301 CC5 53 608 1266 464 919 354 Inv. ex. 302 CC6 55 607 1252 681 922 351 Inv. ex. 303 CC7 52 607 1253 584 909 349 Inv. ex. 304 CC8 54 647 1279 458 916 358 Inv. ex. 305 CC9 54 727 1256 634 901 371 Inv. ex. 306 CC10 54 668 1258 536 915 361 Inv. ex. Preheating step Hot rolling step Average Finish rolling Coiling cooling final stage step speed down Hot stamping step rolling Coiling Heating to less than Heating Holding Test reduction temp. temp. 350° C. temp. time no. Steel % ° C. ° C. ° C./s ° C. s Others Remarks 307 DD1 55 723 1275 692 920 371 Inv. ex. 308 DD2 51 656 1284 616 916 373 Inv. ex. 309 DD3 53 568 1246 681 901 345 Inv. ex. 310 DD4 52 696 1244 687 917 353 Inv. ex. 311 DD5 55 628 1273 503 917 370 Inv. ex. 312 DD6 55 584 1284 584 925 359 Inv. ex. 313 DD7 54 595 1260 680 895 365 Inv. ex. 314 DD8 52 647 1278 433 910 363 Inv. ex. 315 DD9 52 565 1252 413 896 348 Inv. ex. 316 DD10 55 680 1256 442 901 364 Inv. ex. 317 EE1 53 657 1261 687 925 345 Inv. ex. 318 EE2 51 612 1241 419 909 361 Inv. ex. 319 EE3 54 565 1241 656 911 359 Inv. ex. 320 EE4 51 596 1289 550 922 356 Inv. ex. 321 EE5 53 567 1279 698 895 366 Inv. ex. 322 EE6 51 719 1246 619 924 354 Inv. ex. 323 EE7 51 578 1256 508 898 373 Inv. ex. 324 EE8 51 704 1278 444 904 364 Inv. ex. 325 EE6 16 609 1254 682 915 370 Comp. ex. 326 EE6 43 573 1244 470 914 346 Inv. ex. 327 EE6 50 575 1246 640 914 375 Inv. ex. 328 EE6 54 547 1270 662 920 364 Inv. ex. 329 EE6 55 612 1284 465 918 356 Inv. ex. 330 EE6 52 666 1243 561 902 364 Inv. ex. 331 EE6 55 712 1274 571 922 375 Inv. ex. 332 EE6 51 728 1241 696 901 350 Inv. ex. 333 EE6 54 769 1267 422 919 372 Comp. ex. 334 EE6 52  28 1249 419 915 362 Softening treatment Inv. ex. 335 EE6 51 261 1290 567 909 349 Softening treatment Inv. ex. 336 EE6 54 421 1290 486 896 363 Softening treatment Inv. ex. 337 EE6 55 714 1278 568 916 349 No cold rolling Inv. ex. 338 EE6 55 703 1289 550 902 357 Annealing Inv. ex. 339 EE6 51 612 1268 524 918 366 Al plating Inv. ex. 340 EE6 55 723 1270 584 905 369 Al—Zn plating Inv. ex. 341 EE6 51 582 1245 689 908 368 Al—Si plating Inv. ex. 342 EE6 54 575 1240 552 924 349 Hot dip galvanization Inv. ex. 343 EE6 51 576 1290 485 908 358 Electrogalvanization Inv. ex. 344 EE6 54 720 1257 529 906 349 Hot dip galvannealing Inv. ex. 345 EE6 51 582 1275 677 916 345 Zn—Ni plating Inv. ex. 346 EE6 54 702 1262 669 915 368 Al—Mg—Zn plating Inv. ex. 347 EE6 55 619 1281 455 905 352 Temper rolling Inv. ex. 348 EE6 54 596 1160 617 906 351 Comp. ex. 349 EE6 51 593 1220 657 914 374 Inv. ex. 350 EE6 51 579 1250 665 922 374 Inv. ex. 351 EE6 55 614 1280 639 919 345 Inv. ex. 352 EE6 55 561 1320 418 904 361 Inv. ex. 353 EE6 53 619 1390 686 897 353 Inv. ex. 354 EE6 51 665 1287  6 914 366 Comp. ex. 355 EE6 53 679 1271  12 925 375 Inv. ex. 356 EE6 53 720 1248  53 915 361 Inv. ex. 357 EE6 51 681 1271 110 898 359 Inv. ex. Hot rolling Preheating step step Average Finish cooling rolling Coiling speed final stage step down to Hot stamping step rolling Coiling Heating less than Heating Holding Test reduction temp. temp 350° C. temp. time no. Steel % ° C. ° C. ° C./s ° C. s Others Remarks 358 EE6 52 641 1276 230 906 354 Inv. ex. 359 EE6 55 615 1266 509 920 370 Inv. ex. 360 EE6 55 655 1241 1021 901 355 Inv. ex. 361 EE6 55 599 1275 530 752 370 Comp. ex. 362 EE6 53 579 1279 676 804 353 Inv. ex. 363 EE6 54 583 1266 402 824 374 Inv. ex. 364 EE6 53 617 1272 524 840 371 Inv. ex. 365 EE6 52 713 1279 660 854 362 Inv. ex. 366 EE6 55 577 1280 513 868 347 Inv. ex. 367 EE6 52 593 1290 612 879 358 Inv. ex. 368 EE6 54 633 1274 496 888 359 Inv. ex. 369 EE6 54 690 1269 611 904 359 Inv. ex. 370 EE6 54 619 1269 511 922 350 Inv. ex. 371 EE6 55 728 1251 542 936 364 Inv. ex. 372 EE6 53 607 1277 474 953 347 Inv. ex. 373 EE6 54 602 1290 573 971 370 Inv. ex. 374 EE6 53 616 1245 428 986 357 Inv. ex. 375 EE6 53 629 1275 678 1021  356 Comp. ex. 376 EE6 53 573 1279 468 925  48 Comp. ex. 377 EE6 53 571 1246 493 915  65 Inv. ex. 378 EE6 52 676 1247 679 925  87 Inv. ex. 379 EE6 53 683 1281 685 910 102 Inv. ex. 380 EE6 51 589 1284 430 903 143 Inv. ex. 381 EE6 51 633 1263 625 897 199 Inv. ex 382 EE6 55 566 1287 508 909 241 Inv. ex. 383 EE6 52 643 1267 669 917 297 Inv. ex. 384 EE6 54 605 1276 607 902 337 Inv. ex 385 EE6 55 602 1264 430 920 371 Inv. ex. 386 EE6 54 641 1248 405 897 396 Inv. ex. 387 EE6 53 718 1269 566 921 444 Inv. ex. 388 EE6 53 595 1244 488 918 487 Inv. ex. 389 EE6 51 568 1262 672 909 533 Inv. ex. 390 EE6 51 559 1258 545 896 571 Inv. ex. 391 EE6 53 716 1289 444 920 589 Inv. ex. 392 EE6 52 554 1252 461 922 631 Comp. ex. 393 EE6 54 578 1264 491 907 352 Gas combustion atmosphere Inv. ex. (air-fuel ratio 0.80) 394 EE6 53 600 1255 699 924 369 Gas combustion atmosphere Inv. ex. (air-fuel ratio 0.85) 395 EE6 51 639 1260 432 908 370 Gas combustion atmosphere Inv. ex. (air-fuel ratio 1.1) 396 EE6 54 689 1252 491 909 348 Ambient air Inv. ex. 397 EE6 51 722 1256 628 897 364 Nitrogen gas (dew point −30° C.) Inv. ex. 398 EE6 53 570 1256 577 914 374 Nitrogen gas (dew point 0° C.) Inv. ex. 399 EE6 55 617 1253 582 910 358 Nitrogen gas (dew point +10° C.) Inv. ex. 400 EE6 52 553 1246 532 911 361 Ohmic heating Inv. ex. 401 EE6 51 671 1248 530 901 347 Tempering temp. 152° C. Inv. ex. 402 EE6 53 645 1259 685 901 347 Tempering temp. 170° C. Inv. ex. 403 EE6 54 591 1240 642 907 348 Tempering temp. 201° C. Inv. ex. 404 EE6 51 606 1273 467 920 353 Tempering temp. 341° C. Inv. ex. 405 EE6 51 565 1269 572 906 374 Tempering temp. 433° C. Inv. ex. 406 EE6 53 567 1258 607 913 366 Tempering temp. 521° C. Inv. ex. 407 EE6 52 568 1252 601 919 375 Tempering temp. 591° C. Inv. ex. 408 EE6 55 585 1244 698 901 355 Partial softening treatment Inv. ex. Underlines show values of properties which are not preferable.

The properties of the obtained hot stamped bodies were measured and evaluated by the following methods:

[Tensile Strength (TS)]

The tensile strength (TS) of a hot stamped body was obtained from any position of the hot stamped body by preparing a No. 5 test piece, removing the surface layer parts of the front and back surfaces of the test piece by machine grinding, and conducting a tensile test based on JIS Z 2241: 2011. The crosshead speed was 1 mm/min. If early fracture occurred at the time of the tensile test, i.e., if fracture occurred before reaching the maximum stress, the tensile strength of the hot stamped body was made the stress at the time of fracture.

[Early Fracture Resistance]

The early fracture resistance was evaluated by the value of the tensile strength of the hot stamped body obtained by the above method divided by the value of the Vickers hardness obtained by the following method times 3.3 (tensile strength/(Vickers hardness×3.3)). If this value was 0.80 or more, the hot stamped body was deemed excellent in early fracture resistance and judged as passing while if it was less than 0.80, it was judged as failing. The “value of the Vickers hardness times 3.3” is the tensile strength estimated from the hardness. If the measured value of the tensile strength is 0.80 time or more of the estimated tensile strength, the hot stamped body can be judged to be excellent in early fracture resistance.

The Vickers hardness used for evaluation of early fracture resistance was obtained by the following method. First, a sample was cut out from any position 50 mm or more from the end faces of the hot stamped body so as to enable a cross-section vertical to the surface (sheet thickness cross-section) to be examined. The size of the sample, while depending also on the measuring device, was made a size enabling 10 mm or so to be examined in a direction vertical to the sheet thickness direction. The cross-section of the sample was polished using #600 to #1500 silicon carbide paper, then a liquid comprised of particle size 1 to 6 μm diamond powder dispersed in alcohol or other diluent or pure water was used to polish the surface to a mirror finish. The mirror finished cross-section was measured for hardness at a ¼ depth position of the sheet thickness from the surface in a direction parallel to the sheet surface by a load of 1 kgf at intervals of 3 times or more the indents using a microVickers hardness tester. A total of 20 points were measured and the average value was calculated to thereby obtain the Vickers hardness.

A case where the tensile strength was 2200 MPa or more and the above numerical value relating to the early fracture resistance was 0.80 or more was evaluated as a hot stamped body which is high in strength and able to suppress early fracture. The results are shown in Table 3. The “area ratio of hard structures” in Table 3 means the total of the area ratios of the martensite, bainite, and tempered martensite. Further, the balance of the structures other than the hard structures was comprised of ferrite, retained austenite, and/or pearlite. While not shown in Table 3, when measuring the standard deviation in the grain size distribution of the former austenite grains, the grain size of the former austenite grains of the hot stamped bodies in the invention examples in Table 3 was 10 tm or less in all cases.

TABLE 3 Standard Amount of segregation of Area ratio deviation of grain former γ grain boundaries Early of hard size distribution Amount of Total amount Tensile fracture Test structures of former γ grains segregation of of segregation strength resistance no. Steel % μm Mo atm % atm % MPa evaluation Remarks 1 A1 100  2.2 0.13 0.13 2173 0.93 Comp. ex. 2 A2 100  1.9 0.14 0.14 2251 0.92 Inv. ex. 3 A3 97 2.5 0.14 0.14 2347 0.92 Inv. ex. 4 A4 99 2.1 0.14 0.14 2423 0.94 Inv. ex. 5 A5 97 2.5 0.13 0.13 2472 0.92 Inv. ex. 6 A6 99 1.9 0.13 0.13 2497 0.93 Inv. ex. 7 A7 100  2.1 0.14 0.14 2517 0.94 Inv. ex. 8 A8 97 2.3 0.14 0.14 2600 0.88 Inv. ex. 9 A9 99 2.1 0.14 0.14 2697 0.87 Inv. ex. 10 A10 100  2.1 0.13 0.13 2802 0.88 Inv. ex. 11 A11 99 1.9 0.13 0.13 3001 0.88 Inv. ex. 12 A12 99 2.1 0.13 0.13 3097 0.81 Inv. ex. 13 A13 100  2.0 0.14 0.14 3203 0.80 Inv. ex. 14 A14 100 2.1 0.14 0.14 2517 0.48 Comp. ex. 15 B1 99 1.9 0.13 0.13 2170 0.91 Comp. ex. 16 B2 100  2.1 0.14 0.14 2252 0.94 Inv. ex. 17 B3 97 2.0 0.13 0.13 2289 0.93 Inv. ex. 18 B4 100  2.0 0.14 0.14 2347 0.94 Inv. ex. 19 B5 98 2.0 0.14 0.14 2388 0.91 Inv. ex. 20 B6 100  1.9 0.14 0.14 2417 0.93 Inv. ex. 21 B7 100  2.1 0.13 0.13 2468 0.93 Inv. ex. 22 B8 98 2.2 0.13 0.13 2498 0.90 Inv. ex. 23 B9 99 1.9 0.14 0.14 2518 0.91 Inv. ex. 24 B10 99 2.3 0.14 0.14 2541 0.92 Inv. ex. 25 B11 96 1.9 0.14 0.14 2351 0.87 Inv. ex. 26 B12 93 1.9 0.14 0.14 2290 0.80 Inv. ex. 27 B13 91 2.5 0.13 0.13 2248 0.80 Inv. ex. 28 B14 93 1.9 0.14 0.14 2212 0.85 Inv. ex. 29 B15 74 2.3 0.13 0.13 2172 0.80 Comp. ex. 30 C1 97 6.1 0.14 0.14 2420 0.73 Comp. ex. 31 C2 99 4.4 0.14 0.14 2412 0.81 Inv. ex. 32 C3 99 3.8 0.13 0.13 2464 0.87 Inv. ex. 33 C4 98 3.4 0.13 0.13 2447 0.87 Inv. ex. 34 C5 100  2.1 0.13 0.13 2401 0.92 Inv. ex. 35 C6 99 2.4 0.13 0.13 2528 0.90 Inv. ex. 36 C7 98 2.0 0.14 0.14 2536 0.94 Inv. ex 37 C8 100  1.9 0.13 0.13 2518 0.90 Inv. ex. 38 C9 98 2.1 0.14 0.14 2524 0.90 Inv. ex. 39 C10 97 2.0 0.14 0.14 2410 0.92 Inv. ex. 40 C11 100  2.8 0.14 0.14 2534 0.87 Inv. ex. 41 C12 99 2.9 0.13 0.13 2522 0.88 Inv. ex. 42 C13 98 4.7 0.13 0.13 2476 0.80 Inv. ex. 43 C14 97 5.8 0.13 0.13 2500 0.51 Comp. ex. 44 D1 99 2.3 0.14 0.14 2472 0.93 Inv. ex. 45 D2 97 2.2 0.13 0.13 2438 0.94 Inv. ex. 46 D3 98 2.0 0.14 0.14 2527 0.93 Inv. ex. 47 D4 100  1.9 0.14 0.14 2502 0.91 Inv. ex. 48 D5 97 2.4 0.14 0.14 2422 0.89 Inv. ex. 49 D6 99 2.4 0.14 0.14 2534 0.86 Inv. ex. 50 D7 97 1.9 0.13 0.13 2464 0.88 Inv. ex. 51 D8 97 2.4 0.14 0.14 2439 0.85 Inv. ex. 52 D9 100  2.2 0.13 0.13 2510 0.76 Comp. ex. 53 E1 100  2.0 0.14 0.14 2492 0.90 Inv. ex. 54 E2 99 2.1 0.14 0.14 2469 0.94 Inv. ex. 55 E3 97 2.5 0.13 0.13 2515 0.90 Inv. ex. 56 E4 99 2.5 0.13 0.13 2475 0.93 Inv. ex. 57 E5 98 1.9 0.13 0.13 2467 0.93 Inv. ex. 58 E6 100  2.0 0.14 0.14 2410 0.89 Inv. ex. 59 E7 98 2.1 0.13 0.13 2485 0.87 Inv. ex. 60 E8 100  1.9 0.13 0.13 2522 0.80 Inv. ex. 61 E9 97 2.0 0.14 0.14 2489 0.43 Comp. ex. 62 F1 100  2.5 0.14 0.14 2448 0.93 Inv. ex. 63 F2 97 2.1 0.14 0.14 2457 0.91 Inv. ex. 64 F3 100  2.2 0.14 0.14 2424 0.91 Inv. ex. 65 F4 100  2.1 0.13 0.13 2507 0.94 Inv. ex. 66 F5 97 2.5 0.13 0.13 2474 0.89 Inv. ex. 67 F6 98 2.4 0.13 0.13 2406 0.88 Inv. ex. 68 F7 99 1.9 0.14 0.14 2473 0.80 Inv. ex. 69 F8 97 2.3 0.13 0.13 2417 0.82 Inv. ex. 70 F9 100  2.3 0.14 0.14 2486 0.42 Comp. ex. 71 G1 100  2.1 0.14 0.14 2539 0.91 Inv. ex. 72 G2 97 1.9 0.13 0.13 2459 0.94 Inv. ex. 73 G3 99 2.4 0.13 0.13 2432 0.91 Inv. ex. 74 G4 98 2.3 0.13 0.13 2490 0.93 Inv. ex. 75 G5 99 2.4 0.14 0.14 2452 0.86 Inv. ex. 76 G6 98 2.2 0.14 0.14 2451 0.86 Inv. ex. 77 G7 98 2.4 0.13 0.13 2442 0.85 Inv. ex. 78 G8 98 2.4 0.14 0.14 2540 0.51 Comp. ex. 79 H1 100  2.0 0.14 0.14 2420 0.66 Comp. ex. 80 H2 97 2.4 0.13 0.13 2483 0.85 Inv. ex. 81 H3 98 2.5 0.14 0.14 2540 0.87 Inv. ex. 82 H4 97 2.0 0.13 0.13 2510 0.88 Inv. ex. 83 H5 97 2.5 0.14 0.14 2496 0.88 Inv. ex. 84 H6 97 2.1 0.14 0.14 2405 0.93 Inv. ex. 85 H7 97 1.9 0.14 0.14 2425 0.92 Inv. ex. 86 H8 100  2.2 0.13 0.13 2427 0.90 Inv. ex. 87 H9 97 2.3 0.14 0.14 2500 0.90 Inv. ex. 88 H10 98 2.2 0.13 0.13 2478 0.86 Inv. ex. 89 H11 97 2.5 0.14 0.14 2539 0.88 Inv. ex. 90 H12 98 2.3 0.13 0.13 2452 0.87 Inv. ex. 91 H13 100  2.3 0.13 0.13 2413 0.80 Inv. ex. 92 H14 100  1.9 0.14 0.14 2471 0.50 Comp. ex. 93 I1 98 1.9 0.13 0.13 2093 0.90 Comp. ex. 94 I2 99 2.4 0.13 0.13 2218 0.94 Inv. ex. 95 I3 100  2.0 0.14 0.14 2400 0.94 Inv. ex. 96 I4 98 2.4 0.14 0.14 2318 0.90 Inv. ex. 97 I5 100  2.1 0.14 0.14 2398 0.92 Inv. ex. 98 I6 97 2.3 0.13 0.13 2466 0.94 Inv. ex. 99 I7 97 2.5 0.13 0.13 2488 0.93 Inv. ex. 100 I8 99 2.2 0.13 0.13 2412 0.91 Inv. ex. 101 I9 97 2.1 0.13 0.13 2496 0.90 Inv. ex. 102 I10 99 2.0 0.13 0.13 2434 0.94 Inv. ex. 103 I11 99 2.4 0.13 0.13 2446 0.88 Inv. ex. 104 I12 97 2.3 0.14 0.14 2466 0.89 Inv. ex. 105 I13 97 2.0 0.14 0.14 2480 0.81 Inv. ex. 106 I14 100  2.1 0.14 0.14 2460 0.54 Comp. ex. 107 J1 100  2.5 0.13 0.13 2005 0.92 Comp. ex. 108 J2 98 2.0 0.13 0.13 2230 0.94 Inv. ex. 109 J3 99 2.0 0.13 0.13 2303 0.92 Inv. ex. 110 J4 100  2.1 0.14 0.14 2308 0.91 Inv. ex. 111 J5 98 2.0 0.13 0.13 2535 0.91 Inv. ex. 112 J6 100  2.4 0.13 0.13 2406 0.94 Inv. ex. 113 J7 100  2.3 0.14 0.14 2515 0.92 Inv. ex. 114 J8 98 1.9 0.13 0.13 2413 0.87 Inv. ex 115 J9 97 2.2 0.14 0.14 2546 0.89 Inv. ex. 116 J10 98 1.9 0.13 0.13 2521 0.82 Inv. ex. 117 J11 98 2.4 0.13 0.13 2537 0.80 Inv. ex. 118 J12 97 2.0 0.13 0.13 2523 0.51 Comp. ex. 119 K1 98 2.4 0.14 0.14 2008 0.90 Comp. ex. 120 K2 97 2.3 0.13 0.13 2295 0.92 Inv. ex. 121 K3 100  2.4 0.14 0.14 2337 0.93 Inv. ex. 122 K4 99 1.9 0.13 0.13 2364 0.94 Inv. ex. 123 K5 98 2.0 0.13 0.13 2351 0.92 Inv. ex. 124 K6 100  2.5 0.14 0.14 2321 0.94 Inv. ex. 125 K7 99 2.0 0.14 0.14 2522 0.93 Inv. ex. 126 K8 100  2.1 0.13 0.13 2534 0.90 Inv. ex. 127 K9 100  2.4 0.13 0.13 2407 0.93 Inv. ex. 128 K10 100  1.9 0.13 0.13 2525 0.86 Inv. ex. 129 K11 99 2.2 0.13 0.13 2434 0.86 Inv. ex. 130 K12 98 2.4 0.14 0.14 2450 0.87 Inv. ex. 131 K13 100  1.9 0.14 0.14 2484 0.81 Inv. ex. 132 K14 97 2.3 0.14 0.14 2518 0.52 Comp. ex. 133 L1 100  2.1 0.05 0.05 2522 0.50 Comp. ex. 134 L2 98 2.2 0.11 0.11 2498 0.84 Inv. ex. 135 L3 98 2.3 0.14 0.14 2510 0.87 Inv. ex. 136 L4 99 2.1 0.14 0.14 2452 0.89 Inv. ex. 137 L5 97 2.3 0.14 0.14 2429 0.89 Inv. ex. 138 L6 99 1.9 0.16 0.16 2528 0.94 Inv. ex. 139 L7 99 2.4 0.19 0.19 2467 0.94 Inv. ex. 140 L8 100  2.4 0.15 0.15 2407 0.90 Inv. ex. 141 L9 97 2.5 0.21 0.21 2493 0.88 Inv. ex. 142 L10 98 2.5 0.13 0.13 2521 0.88 Inv. ex. 143 L11 98 2.1 0.13 0.13 2426 0.89 Inv. ex. 144 L12 98 2.3 0.11 0.11 2436 0.84 Inv. ex. 145 L13 97 2.2 0.03 0.03 2446 0.73 Comp. ex. 146 M1 100  2.4 0.14 0.14 2098 0.92 Comp. ex. 147 M2 99 2.4 0.13 0.13 2260 0.94 Inv. ex. 148 M3 99 1.9 0.14 0.14 2395 0.94 Inv. ex. 149 M4 99 1.9 0.13 0.13 2499 0.91 Inv. ex. 150 M5 99 2.3 0.14 0.14 2423 0.92 Inv. ex. 151 M6 97 2.3 0.13 0.13 2474 0.92 Inv. ex. 152 M7 98 2.1 0.13 0.13 2482 0.86 Inv. ex. 153 M8 100  2.4 0.14 0.14 2448 0.89 Inv. ex. 154 M9 98 2.1 0.14 0.14 2436 0.85 Inv. ex. 155 M10 97 2.1 0.13 0.13 2505 0.84 Inv. ex. 156 M11 97 2.5 0.14 0.14 2464 0.66 Comp. ex. 157 N1 97 2.5 0.13 0.13 2726 0.93 Inv. ex. 158 N2 98 2.5 0.13 0.13 2979 0.93 Inv. ex. 159 N3 100  2.1 0.14 0.14 2769 0.93 Inv. ex. 160 N4 99 2.1 0.13 0.13 2796 0.91 Inv. ex. 161 N5 98 1.9 0.14 0.14 2652 0.90 Inv. ex. 162 N6 98 2.2 0.14 0.14 2789 0.90 Inv. ex. 163 N7 100  2.2 0.14 0.14 2965 0.91 Inv. ex. 164 N8 99 2.2 0.14 0.14 2580 0.93 Inv. ex. 165 N9 97 2.0 0.13 0.13 2936 0.91 Inv. ex. 166 N10 99 2.0 0.13 0.13 2910 0.91 Inv. ex. 167 N11 100  2.4 0.14 0.14 2626 0.92 Inv. ex. 168 N12 100  2.2 0.13 0.13 2922 0.93 Inv. ex. 169 N13 100  1.9 0.13 0.13 2708 0.90 Inv. ex. 170 O1 97 2.1 0.14 0.14 2936 0.93 Inv. ex. 171 O2 98 2.2 0.14 0.14 2909 0.93 Inv. ex. 172 O3 99 2.4 0.13 0.13 2822 0.92 Inv. ex. 173 O4 98 2.3 0.13 0.13 2850 0.92 Inv. ex. 174 O5 100  2.5 0.14 0.14 2892 0.90 Inv. ex. 175 O6 98 2.1 0.14 0.14 2648 0.93 Inv. ex. 176 O7 99 2.2 0.13 0.13 2810 0.91 Inv. ex. 177 O8 99 2.0 0.13 0.13 2570 0.90 Inv. ex. 178 O9 99 2.2 0.13 0.13 2682 0.92 Inv. ex. 179 O10 100  2.2 0.13 0.13 2735 0.92 Inv. ex. 180 O11 97 2.5 0.14 0.14 2953 0.91 Inv. ex. 181 O12 98 2.1 0.14 0.14 2770 0.91 Inv. ex. 182 P1 98 2.4 0.13 0.13 2764 0.91 Inv. ex. 183 P2 98 2.1 0.13 0.13 2869 0.93 Inv. ex. 184 P3 100  2.4 0.13 0.13 2739 0.90 Inv. ex. 185 P4 97 1.9 0.14 0.14 2623 0.90 Inv. ex. 186 P5 97 2.5 0.14 0.14 2581 0.92 Inv. ex. 187 P6 100  1.9 0.13 0.13 2880 0.93 Inv. ex. 188 P7 100  2.0 0.14 0.14 2603 0.91 Inv. ex. 189 P8 99 2.4 0.14 0.14 2557 0.94 Inv. ex. 190 P9 100  2.4 0.14 0.14 2789 0.93 Inv. ex. 191 P10 99 2.3 0.14 0.14 2885 0.93 Inv. ex. 192 P11 98 2.0 0.14 0.14 2608 0.91 Inv. ex. 193 P12 98 2.5 0.13 0.13 2562 0.94 Inv. ex. 194 Q1 100  2.1 0.14 0.14 2842 0.92 Inv. ex. 195 Q2 100  2.3 0.14 0.14 2972 0.94 Inv. ex. 196 Q3 97 1.9 0.14 0.14 2593 0.93 Inv. ex. 197 Q4 99 2.5 0.13 0.13 2909 0.91 Inv. ex. 198 Q5 97 2.0 0.14 0.14 2621 0.91 Inv. ex. 199 Q6 98 2.4 0.14 0.14 2875 0.93 Inv. ex. 200 Q7 98 2.4 0.14 0.14 2561 0.91 Inv. ex. 201 Q8 97 2.3 0.13 0.13 2707 0.94 Inv. ex. 202 Q9 97 2.0 0.13 0.13 2946 0.90 Inv. ex. 203 Q10 99 2.3 0.13 0.13 2782 0.94 Inv. ex. 204 Q11 100  2.1 0.13 0.13 2997 0.94 Inv. ex. 205 Q12 99 1.9 0.13 0.13 2677 0.92 Inv. ex. 206 R1 98 2.5 0.14 0.14 2404 0.90 Inv. ex. 207 R2 100  1.9 0.14 0.14 2528 0.92 Inv. ex. 208 R3 99 2.2 0.14 0.14 2465 0.92 Inv. ex. 209 R4 97 1.9 0.13 0.13 2504 0.90 Inv. ex. 210 R5 99 1.9 0.13 0.13 2509 0.90 Inv. ex. 211 R6 99 1.9 0.14 0.14 2433 0.94 Inv. ex. 212 R7 98 2.2 0.14 0.14 2512 0.92 Inv. ex. 213 R8 98 2.4 0.13 0.13 2524 0.93 Inv. ex. 214 S1 98 2.1 0.13 0.13 2491 0.91 Inv. ex. 215 S2 100  2.3 0.14 0.14 2462 0.94 Inv. ex. 216 S3 98 2.4 0.14 0.14 2427 0.90 Inv. ex. 217 S4 98 2.5 0.13 0.13 2513 0.93 Inv. ex. 218 S5 98 2.5 0.13 0.13 2472 0.94 Inv. ex. 219 S6 100  2.5 0.14 0.14 2420 0.92 Inv. ex. 220 S7 98 2.3 0.14 0.14 2490 0.91 Inv. ex. 221 S8 100  2.4 0.13 0.13 2534 0.90 Inv. ex. 222 T1 97 2.1 0.13 0.13 2407 0.92 Inv. ex. 223 T2 100  2.4 0.13 0.13 2411 0.91 Inv. ex. 224 T3 98 2.4 0.14 0.14 2406 0.91 Inv. ex. 225 T4 98 2.5 0.14 0.14 2526 0.93 Inv. ex. 226 T5 100  1.9 0.14 0.14 2481 0.90 Inv. ex. 227 T6 97 2.2 0.13 0.13 2509 0.92 Inv. ex. 228 T7 99 2.0 0.13 0.13 2540 0.92 Inv. ex. 229 T8 98 2.4 0.14 0.14 2413 0.92 Inv. ex. 230 U1 99 2.0 0.14 0.14 2538 0.92 Inv. ex. 231 U2 98 2.3 0.13 0.13 2446 0.92 Inv. ex. 232 U3 97 2.0 0.13 0.13 2541 0.90 Inv. ex. 233 U4 98 1.9 0.13 0.13 2510 0.93 Inv. ex. 234 U5 98 1.9 0.14 0.14 2406 0.94 Inv. ex. 235 U6 98 1.9 0.13 0.13 2407 0.93 Inv. ex. 236 U7 97 2.3 0.14 0.14 2444 0.92 Inv. ex. 237 U8 100  2.0 0.13 0.13 2422 0.91 Inv. ex. 238 V1 98 1.9 0.13 0.13 2413 0.92 Inv. ex. 239 V2 99 2.3 0.14 0.14 2493 0.92 Inv. ex. 240 V3 97 2.1 0.14 0.14 2511 0.90 Inv. ex. 241 V4 99 2.5 0.14 0.14 2488 0.92 Inv. ex. 242 V5 99 2.0 0.13 0.13 2496 0.90 Inv. ex. 243 V6 98 2.1 0.14 0.14 2474 0.93 Inv. ex. 244 V7 97 2.0 0.14 0.14 2548 0.92 Inv. ex. 245 V8 99 2.2 0.14 0.14 2435 0.90 Inv. ex. 246 W1 98 2.3 0.14 0.14 2471 0.90 Inv. ex. 247 W2 99 2.1 0.14 0.14 2446 0.94 Inv. ex. 248 W3 98 2.3 0.13 0.13 2530 0.92 Inv. ex. 249 W4 97 2.0 0.14 0.14 2550 0.92 Inv. ex. 250 W5 99 2.2 0.13 0.13 2537 0.93 Inv. ex. 251 W6 100  2.4 0.13 0.13 2439 0.92 Inv. ex. 252 W7 99 2.5 0.14 0.14 2412 0.92 Inv. ex. 253 W8 97 2.3 0.13 0.13 2470 0.94 Inv. ex. 254 X1 100  2.0 0.13 0.13 2430 0.91 Inv. ex. 255 X2 99 2.1 0.13 0.13 2476 0.93 Inv. ex. 256 X3 97 2.1 0.13 0.13 2522 0.90 Inv. ex. 257 Y1 100  2.0 0.13 0.16 2413 0.98 Inv. ex. 258 Y2 97 2.2 0.14 0.23 2474 0.95 Inv. ex. 259 Y3 99 2.2 0.14 0.19 2537 0.98 Inv. ex. 260 Y4 97 2.4 0.13 0.21 2479 0.96 Inv. ex. 261 Y5 97 2.0 0.13 0.21 2506 0.95 Inv. ex. 262 Y6 99 2.4 0.13 0.17 2501 0.96 Inv. ex. 263 Y7 97 2.2 0.13 0.24 2404 0.99 Inv. ex. 264 Y8 100  2.0 0.14 0.24 2476 0.96 Inv. ex. 265 Y9 98 2.1 0.14 0.23 2416 0.99 Inv. ex. 266 Y10 100  2.5 0.13 0.15 2485 0.96 Inv. ex. 267 Z1 99 2.1 0.14 0.23 2437 0.97 Inv. ex. 268 Z2 98 2.1 0.13 0.22 2543 0.95 Inv. ex. 269 Z3 100  2.3 0.13 0.24 2538 0.98 Inv. ex. 270 Z4 98 2.1 0.13 0.15 2526 0.96 Inv. ex. 271 Z5 99 2.3 0.13 0.21 2427 0.98 Inv. ex. 272 Z6 100  1.9 0.14 0.25 2483 0.96 Inv. ex. 273 Z7 100  2.0 0.14 0.19 2491 0.99 Inv. ex. 274 Z8 100  2.5 0.14 0.25 2497 0.95 Inv. ex. 275 Z9 99 2.1 0.14 0.21 2468 0.97 Inv. ex. 276 Z10 99 2.4 0.14 0.15 2425 0.98 Inv. ex. 277 AA1 98 2.0 0.13 0.25 2463 0.98 Inv. ex. 278 AA2 100  2.0 0.14 0.24 2414 0.97 Inv. ex. 279 AA3 98 2.3 0.14 0.19 2513 0.97 Inv. ex. 280 AA4 99 2.5 0.13 0.23 2477 0.99 Inv. ex. 281 AA5 100  2.5 0.13 0.23 2408 0.98 Inv. ex. 282 AA6 100  2.3 0.13 0.15 2469 0.99 Inv. ex. 283 AA7 98 2.2 0.14 0.16 2496 0.95 Inv. ex. 284 AA8 99 2.2 0.13 0.15 2404 0.98 Inv. ex. 285 AA9 97 2.0 0.14 0.18 2432 0.97 Inv. ex. 286 AA10 99 2.0 0.14 0.21 2432 0.95 Inv. ex. 287 BB1 98 2.1 0.13 0.19 2480 0.97 Inv. ex. 288 BB2 98 2.4 0.13 0.18 2436 0.96 Inv. ex. 289 BB3 100  2.2 0.13 0.20 2471 0.96 Inv. ex. 290 BB4 100  2.4 0.14 0.15 2464 0.95 Inv. ex. 291 BB5 100  2.2 0.14 0.15 2525 0.95 Inv. ex. 292 BB6 100  2.3 0.13 0.17 2531 0.98 Inv. ex. 293 BB7 98 2.0 0.14 0.23 2461 0.99 Inv. ex. 294 BB8 99 2.2 0.14 0.24 2425 0.95 Inv. ex. 295 BB9 97 2.1 0.14 0.17 2528 0.95 Inv. ex. 296 BB10 98 1.9 0.14 0.20 2453 0.99 Inv. ex. 297 CC1 98 2.3 0.14 0.20 2510 0.95 Inv. ex. 298 CC2 98 2.4 0.13 0.16 2425 0.97 Inv. ex. 299 CC3 97 2.0 0.13 0.19 2482 0.99 Inv. ex. 300 CC4 99 2.5 0.14 0.25 2448 0.96 Inv. ex. 301 CC5 98 2.1 0.13 0.18 2538 0.95 Inv. ex. 302 CC6 97 2.0 0.14 0.23 2550 0.95 Inv. ex. 303 CC7 98 2.0 0.13 0.16 2453 0.96 Inv. ex. 304 CC8 98 1.9 0.13 0.21 2410 0.96 Inv. ex. 305 CC9 98 2.1 0.13 0.18 2514 0.95 Inv. ex. 306 CC10 99 2.5 0.14 0.22 2499 0.99 Inv. ex. 307 DD1 97 2.0 0.14 0.16 2503 0.96 Inv. ex. 308 DD2 100  2.0 0.13 0.20 2427 0.97 Inv. ex. 309 DD3 100  2.4 0.14 0.18 2539 0.98 Inv. ex. 310 DD4 100  2.1 0.13 0.15 2538 0.99 Inv. ex. 311 DD5 98 2.1 0.14 0.20 2449 0.97 Inv. ex. 312 DD6 97 2.3 0.14 0.16 2461 0.99 Inv. ex. 313 DD7 97 2.2 0.14 0.23 2419 0.97 Inv. ex. 314 DD8 100  2.4 0.14 0.21 2540 0.98 Inv. ex. 315 DD9 100  2.5 0.14 0.23 2467 0.98 Inv. ex. 316 DD10 100  2.4 0.14 0.22 2468 0.96 Inv. ex. 317 EE1 97 2.3 0.13 0.13 2546 0.91 Inv. ex. 318 EE2 97 2.1 0.14 0.14 2427 0.96 Inv. ex. 319 EE3 97 1.9 0.13 0.13 2516 0.92 Inv. ex. 320 EE4 97 2.1 0.14 0.14 2541 0.94 Inv. ex. 321 EE5 98 3.7 0.14 0.14 2440 0.87 Inv. ex. 322 EE6 99 1.9 0.14 0.14 2419 0.92 Inv. ex. 323 EE7 97 2.3 0.13 0.13 2451 0.91 Inv. ex. 324 EE8 99 2.1 0.13 0.13 2508 0.92 Inv. ex. 325 EE6 99 5.7 0.13 0.13 2417 0.50 Comp. ex. 326 EE6 97 2.8 0.13 0.13 2474 0.88 Inv. ex. 327 EE6 98 2.1 0.14 0.14 2413 0.93 Inv. ex. 328 EE6 100  1.9 0.14 0.14 2477 0.90 Inv. ex. 329 EE6 98 2.4 0.14 0.14 2453 0.90 Inv. ex 330 EE6 98 2.8 0.14 0.14 2431 0.88 Inv. ex. 331 EE6 97 3.4 0.14 0.14 2495 0.88 Inv. ex. 332 EE6 100  4.7 0.14 0.14 2417 0.82 Inv. ex. 333 EE6 99 6.4 0.13 0.13 2495 0.65 Comp. ex. 334 EE6 100  2.0 0.13 0.13 2532 0.94 Inv. ex. 335 EE6 99 2.3 0.13 0.13 2467 0.91 Inv. ex. 336 EE6 97 2.3 0.13 0.13 2536 0.94 Inv. ex. 337 EE6 99 2.3 0.13 0.13 2485 0.94 Inv. ex. 338 EE6 99 2.4 0.13 0.13 2480 0.94 Inv. ex. 339 EE6 99 2.0 0.13 0.13 2491 0.91 Inv. ex. 340 EE6 100  2.2 0.13 0.13 2542 0.94 Inv. ex. 341 EE6 97 2.5 0.13 0.13 2543 0.91 Inv. ex. 342 EE6 99 2.1 0.14 0.14 2548 0.90 Inv. ex. 343 EE6 99 2.2 0.14 0.14 2471 0.94 Inv. ex. 344 EE6 100  1.9 0.14 0.14 2413 0.92 Inv. ex. 345 EE6 100  2.2 0.13 0.13 2424 0.90 Inv. ex. 346 EE6 97 2.0 0.14 0.14 2527 0.90 Inv. ex. 347 EE6 100  2.4 0.14 0.14 2460 0.90 Inv. ex. 348 EE6 99 2.3 0.04 0.04 2457 0.74 Comp. ex. 349 EE6 99 2.2 0.12 0.12 2502 0.84 Inv. ex. 350 EE6 97 2.3 0.13 0.13 2415 0.86 Inv. ex. 351 EE6 100  2.2 0.13 0.13 2454 0.86 Inv. ex. 352 EE6 100  2.5 0.15 0.15 2548 0.98 Inv. ex. 353 EE6 99 2.1 0.25 0.25 2441 0.95 Inv. ex. 354 EE6 100  2.3 0.08 0.08 2493 0.65 Comp. ex. 355 EE6 97 2.2 0.11 0.11 2506 0.83 Inv. ex. 356 EE6 98 1.9 0.14 0.14 2407 0.88 Inv. ex. 357 EE6 99 2.0 0.13 0.13 2507 0.88 Inv. ex. 358 EE6 97 2.4 0.14 0.14 2477 0.86 Inv. ex. 359 EE6 98 2.0 0.21 0.21 2530 0.98 Inv. ex. 360 EE6 100  2.1 0.25 0.25 2458 0.96 Inv. ex. 361 EE6 77 5.2 0.13 0.13 2078 0.42 Comp. ex. 362 EE6 91 1.9 0.13 0.13 2271 0.93 Inv. ex. 363 EE6 94 2.1 0.13 0.13 2396 0.93 Inv. ex. 364 EE6 99 2.5 0.14 0.14 2449 0.94 Inv. ex. 365 EE6 100  2.5 0.13 0.13 2403 0.91 Inv. ex 366 EE6 98 2.4 0.14 0.14 2435 0.91 Inv. ex. 367 EE6 99 2.2 0.13 0.13 2496 0.91 Inv. ex. 368 EE6 100  2.0 0.13 0.13 2531 0.92 Inv. ex. 369 EE6 97 2.2 0.13 0.13 2519 0.90 Inv. ex. 370 EE6 97 2.2 0.14 0.14 2536 0.94 Inv. ex 371 EE6 99 3.6 0.13 0.13 2522 0.88 Inv. ex. 372 EE6 100  2.7 0.14 0.14 2459 0.87 Inv. ex. 373 EE6 100  2.8 0.13 0.13 2523 0.87 Inv. ex. 374 EE6 99 4.1 0.13 0.13 2529 0.85 Inv. ex. 375 EE6 98 5.6 0.13 0.13 2402 0.41 Comp. ex. 376 EE6 100  6.2 0.14 0.14 2488 0.59 Comp. ex. 377 EE6 98 4.9 0.14 0.14 2433 0.83 Inv. ex. 378 EE6 98 3.0 0.14 0.14 2535 0.87 Inv. ex. 379 EE6 97 2.8 0.14 0.14 2418 0.88 Inv. ex. 380 EE6 99 2.2 0.13 0.13 2529 0.92 Inv. ex. 381 EE6 98 2.1 0.13 0.13 2425 0.92 Inv. ex. 382 EE6 99 2.1 0.13 0.13 2426 0.91 Inv. ex. 383 EE6 97 2.3 0.14 0.14 2457 0.92 Inv. ex. 384 EE6 97 2.2 0.14 0.14 2536 0.93 Inv. ex. 385 EE6 97 2.4 0.13 0.13 2425 0.93 Inv. ex. 386 EE6 99 1.9 0.13 0.13 2456 0.91 Inv. ex. 387 EE6 99 2.5 0.14 0.14 2457 0.93 Inv. ex. 388 EE6 97 1.9 0.14 0.14 2503 0.90 Inv. ex. 389 EE6 98 2.7 0.13 0.13 2474 0.87 Inv. ex. 390 EE6 100  3.7 0.13 0.13 2493 0.88 Inv. ex. 391 EE6 99 4.8 0.14 0.14 2497 0.80 Inv. ex. 392 EE6 99 5.6 0.14 0.14 2466 0.48 Comp. ex. 393 EE6 98 2.5 0.13 0.13 2458 0.91 Inv. ex. 394 EE6 98 2.2 0.13 0.13 2547 0.92 Inv. ex. 395 EE6 97 2.1 0.13 0.13 2506 0.91 Inv. ex. 396 EE6 97 2.5 0.14 0.14 2499 0.90 Inv. ex. 397 EE6 100  2.1 0.13 0.13 2495 0.93 Inv. ex. 398 EE6 97 2.4 0.13 0.13 2444 0.93 Inv. ex. 399 EE6 99 2.2 0.13 0.13 2522 0.94 Inv. ex. 400 EE6 99 2.0 0.14 0.14 2550 0.92 Inv. ex. 401 EE6 98 2.5 0.14 0.14 2419 0.93 Inv. ex. 402 EE6 97 2.5 0.14 0.14 2418 0.93 Inv. ex. 403 EE6 97 2.4 0.13 0.13 2351 0.90 Inv. ex. 404 EE6 99 2.0 0.13 0.13 2349 0.90 Inv. ex. 405 EE6 100  1.9 0.14 0.14 2247 0.94 Inv. ex. 406 EE6 99 2.0 0.13 0.13 2250 0.92 Inv. ex. 407 EE6 98 2.2 0.14 0.14 2253 0.94 Inv. ex. 408 EE6 97 2.3 0.13 0.13 2423 0.93 Inv. ex. Underlines show outside scope of present invention or values of properties which are not preferable.

Referring to Table 3, in Comparative Example 1, the C content was low, therefore the tensile strength fell. In Comparative Example 14, the C content was high, therefore the early fracture resistance fell. In Comparative Example 15, the Si content was low, therefore the tensile strength fell. In Comparative Example 29, the Si content was high, therefore the amount of ferrite increased, the desired metallographic structure was not obtained, and as a result the tensile strength similarly fell. In Comparative Example 30, the Mn content was low, therefore the standard deviation at the grain size distribution of the former austenite grains became greater and the early fracture resistance fell. In Comparative Example 43, the Mn content was high, therefore it is believed that in the hot rolled steel sheet, transformation from austenite to pearlite was promoted too much. As a result, in the hot stamped body, the standard deviation in the grain size distribution of the former austenite grains could not be made within the desired range and the early fracture resistance fell. In Comparative Examples 52, 61, 70, 78, 79, and 92, the respective P, S, N, O, or Al contents were not suitable, therefore the early fracture resistances fell. In Comparative Examples 93, 107, and 119, the respective Nb, Ti, and Cr contents were low, therefore the strengths could not be sufficiently improved by precipitation strengthening or solid solution strengthening and the tensile strengths fell. In Comparative Examples 106, 118, and 132, the respective Nb, Ti, and Cr contents were high, therefore it is believed large amounts of carbonitrides were formed or coarse intermetallic compounds were formed and as a result the early fracture resistances fell. In Comparative Example 133, the Mo content was low, therefore the total amount of segregation of the grain boundary strengthening elements at the former austenite grain boundaries become lower and the early fracture resistance fell. In Comparative Examples 145 and 156, the respective Mo and B contents were high, therefore it is believed that coarse intermetallic compounds were formed at the hot stamped bodies and as a result the early fracture resistance fell. In Comparative Example 146, the B content was low, therefore the tensile strength fell.

In Comparative Example 325, the rolling reduction of the final stage in the finish rolling of the hot rolling step was low, therefore it is believed the pearlite could not be evenly dispersed at the hot rolled steel sheet after rolling. As a result, in the hot stamped body, the standard deviation at the grain size distribution of the former austenite grains became greater and the early fracture resistance fell. In Comparative Example 333, the coiling temperature was high, therefore it is believed the ferrite was arranged connected and the pearlite could not be evenly dispersed. As a result, in the hot stamped body, the standard deviation at the grain size distribution of the former austenite grains became larger and the early fracture resistance fell. In Comparative Example 348, the heating temperature at the preheating step was low, therefore it is believed the grain boundary strengthening elements could not sufficiently dissolve in the steel sheet. As a result, the total amount of segregation of the grain boundary strengthening elements at the former austenite grain boundaries became low and the early fracture resistance fell. In Comparative Example 354, the average cooling speed at the preheating step was slow, therefore it is believed the grain boundary strengthening elements dissolved in the steel sheet due to the preheating precipitated as compounds. As a result, the total amount of segregation of the grain boundary strengthening elements at the former austenite grain boundaries became low and the early fracture resistance fell. In Comparative Example 361, the heating temperature at the hot stamping step was low, therefore the austenization became insufficient, the area ratio of the hard structures and the standard deviation at the grain size distribution of the former austenite grains could not be controlled to within the desired ranges, and the tensile strength and early fracture resistance fell. In Comparative Example 375, the heating temperature at the hot stamping step was high, therefore austenite grains excessively grew, the standard deviation at the grain size distribution of the former austenite grains could not be controlled to within the desired range, and the early fracture resistance fell. In Comparative Example 376, the holding time at the hot stamping step was long, therefore austenization became insufficient, the standard deviation at the grain size distribution of the former austenite grains could not be controlled to within the desired range, and the early fracture resistance fell. In Comparative Example 392, the holding time at the hot stamping step was long, therefore austenite grains excessively grew, the standard deviation at the grain size distribution of the former austenite grains could not be controlled to within the desired range, and the early fracture resistance fell.

In contrast to this, the hot stamped bodies according to all of the invention examples have the predetermined chemical compositions and metallographic structures, have standard deviations at the grain size distributions of the former austenite grains controlled to 5.0 μm or less, and have total amounts of segregation of the grain boundary strengthening elements at the former austenite grain boundaries, i.e., at least one of Mo, W, Ta, Re, Os, Ir, and Tc, controlled to 0.10 atm % or more, whereby early fracture can be reliably suppressed regardless of having high tensile strengths of 2200 MPa or more.

Claims

1. A hot stamped body having a chemical composition comprising, by mass %,

C: 0.40 to 0.70%,
Si: 0.010 to 3.00%,
Mn: 0.50 to 3.00%,
P: 0.100% or less,
S: 0.0100% or less,
N: 0.0200% or less,
O: 0.0200% or less,
Al: 0.0010 to 0.500%,
Nb: 0.0010 to 0.100%,
Ti: 0.010 to 0.200%,
Cr: 0.010 to 1.00%,
Mo: 0.0010 to 1.000%,
B: 0.0005 to 0.0200%,
Co: 0 to 4.00%,
Ni: 0 to 3.00%,
Cu: 0 to 3.00%,
V: 0 to 3.00%,
Ca: 0 to 1.000%,
Mg: 0 to 1.000%,
REM: 0 to 1.000%,
Sb: 0 to 1.00%,
Sn: 0 to 1.00%,
Zr: 0 to 1.00%,
As: 0 to 0.100%,
at least one of W, Ta, Re, Os, Ir, and Tc: 0 to 1.00% in total, and
balance: Fe and impurities, and
a microstructure comprising, by area ratio, at least one of martensite, bainite, and tempered martensite: 90% or more in total, wherein
a standard deviation in grain size distribution of former austenite grains is 5.0 μm or less, and
a total amount of segregation of at least one of Mo, W, Ta, Re, Os, Ir, and Tc at former austenite grain boundaries is 0.10 atm % or more.

2. The hot stamped body according to claim 1, wherein the amount of segregation of Mo at the former austenite grain boundaries is 0.10 atm % or more.

3. The hot stamped body according to claim 1, wherein the total amount of segregation is 0.15 atm % or more.

4. The hot stamped body according to claim 2, wherein the total amount of segregation is 0.15 atm % or more.

Patent History
Publication number: 20250034686
Type: Application
Filed: Mar 2, 2023
Publication Date: Jan 30, 2025
Applicant: NIPPON STEEL CORPORATION (Tokyo)
Inventors: Yuri TODA (Tokyo), Kazuma ITO (Tokyo), Yuma ASADA (Tokyo)
Application Number: 18/716,021
Classifications
International Classification: C22C 38/38 (20060101); C22C 38/00 (20060101); C22C 38/02 (20060101); C22C 38/06 (20060101); C22C 38/22 (20060101); C22C 38/26 (20060101); C22C 38/28 (20060101); C22C 38/32 (20060101);