Abstract: Provided are a high-strength hot-rolled steel sheet and a method for manufacturing the steel sheet. The steel sheet includes C: 0.060% or more and 0.140% or less, Si: 1.00% or less, Mn: 1.30% or more and 2.50% or less, P: 0.030% or less, S: 0.0050% or less, Al: 0.070% or less, N: 0.010% or less, Ti: 0.060% or more and 0.140% or less, Cr: 0.10% or more and 0.50% or less, B: 0.0002% or more and 0.0020% or less, and the balance being Fe and inevitable impurities, in which the relationship 5.0?18C+Mn+1.3Cr+1500B?6.0 is obtained. The microstructure includes a bainite phase in an amount of more than 90% one, two, or all of a ferrite phase, a martensite phase, and a retained austenite phase in an amount of less than 10%.

Abstract: A high-carbon hot-rolled steel sheet having a chemical composition containing, by mass %, C: more than 0.40% and 0.63% or less, Si: 0.10% or less, Mn: 0.50% or less, P: 0.03% or less, S: 0.010% or less, sol.Al: 0.10% or less, N: 0.0050% or less, B: 0.0005% or more and 0.0050% or less, and at least one of Sb, Sn, Bi, Ge, Te, and Se in an amount of 0.002% or more and 0.030% or less in total. The steel sheet has a microstructure including ferrite and cementite, in which the density of cementite in ferrite grains is 0.13 pieces/?m2 or less. Additionally, the steel sheet has a hardness of 81 or less in terms of HRB and a total elongation of 33% or more.

Abstract: Disclosed is a high-strength steel sheet having a tensile strength (TS) of 780 MPa or more and excellent in ductility, fatigue properties, balance between high strength and ductility, surface characteristics, and sheet passage ability that can be obtained by providing a predetermined chemical composition and a steel microstructure that contains, by area, 20-50% of ferrite, 5-25% of bainitic ferrite, and 5-20% of martensite, and that contains, by volume, 10% or more of retained austenite, in which the retained austenite has a mean grain size of 2 ?m or less, a mean Mn content in the retained austenite in mass % is at least 1.2 times the Mn content in the steel sheet in mass %, and the retained austenite has a mean free path of 1.2 ?m or less.

Abstract: Disclosed is a high-strength steel sheet having a tensile strength (TS) of 780 MPa or more and excellent in ductility, fatigue properties, stretch flangeability, surface characteristics, and sheet passage ability that can be obtained by providing a predetermined chemical composition and a steel microstructure that contains, by area, 20-50% of ferrite, 5-25% of bainitic ferrite, 1-10% of martensite, and 5-15% of tempered martensite, and that contains, by volume, 10% or more of retained austenite, in which the retained austenite has a mean grain size of 2 ?m or less, a mean Mn content in the retained austenite in mass % is at least 1.2 times the Mn content in the steel sheet in mass %, the retained austenite has a mean free path of 1.2 ?m or less, and the tempered martensite has a mean free path of 1.2 ?m or less.

Abstract: There is provided is a high-carbon hot-rolled steel sheet and method for producing the same. The steel sheet has excellent hardenability consistently, even when annealed in a nitrogen atmosphere, and excellent formability. The steel sheet has a hardness in the range of 83 HRB or less and a total elongation of 30% or more before being subjected to a quenching treatment.

Abstract: A high strength steel sheet is formed of steel having the composition containing by mass % over 0.015% and less than 0.100% C, less than 0.50% Si, over 1.0% and less than 2.0% Mn, 0.05% or less P, 0.03% or less S, 0.01% or more and 0.3% or less sol. Al, 0.005% or less N, less than 0.35% Cr, 0.0010% or more and 0.0050% or less B, less than 0.15% Mo, less than 0.030% Ti, and iron and unavoidable impurities as a balance, wherein the steel satisfies 2.1?[Mneq]?3.1, the microstructure of the steel includes a ferrite and a second phase, a volume fraction of the second phase is set to 2.0 to 12.0%, a total ratio of a volume fraction of martensite and a volume fraction of retained ? to the volume fraction of second phase is 60% or more, and the number of carbides which are present within ferrite particles, have an aspect ratio of 3.0 or less and have a diameter of 0.25 to 0.90 ?m is set to 10000 pieces/mm2 or less.

Abstract: Disclosed is a high-strength steel sheet having a tensile strength (TS) of 780 MPa or more and excellent in ductility, fatigue properties, stretch flangeability, surface characteristics, and sheet passage ability that can be obtained by providing a predetermined chemical composition and a steel microstructure that contains, by area, 20-50% of ferrite, 5-25% of bainitic ferrite, 1-10% of martensite, and 5-15% of tempered martensite, and that contains, by volume, 10% or more of retained austenite, in which the retained austenite has a mean grain size of 2 ?m or less, a mean Mn content in the retained austenite in mass % is at least 1.2 times the Mn content in the steel sheet in mass %, the retained austenite has a mean free path of 1.2 ?m or less, and the tempered martensite has a mean free path of 1.2 ?m or less.

Abstract: Disclosed is a high-strength steel sheet having a tensile strength (TS) of 780 MPa or more and excellent in ductility, fatigue properties, balance between high strength and ductility, surface characteristics, and sheet passage ability that can be obtained by providing a predetermined chemical composition and a steel microstructure that contains, by area, 20-50% of ferrite, 5-25% of bainitic ferrite, and 5-20% of martensite, and that contains, by volume, 10% or more of retained austenite, in which the retained austenite has a mean grain size of 2 ?m or less, a mean Mn content in the retained austenite in mass % is at least 1.2 times the Mn content in the steel sheet in mass %, and the retained austenite has a mean free path of 1.2 ?m or less.

Abstract: A high-carbon hot-rolled steel sheet having a chemical composition containing, by mass %, C: more than 0.40% and 0.63% or less, Si: 0.10% or less, Mn: 0.50% or less, P: 0.03% or less, S: 0.010% or less, sol.Al: 0.10% or less, N: 0.0050% or less, B: 0.0005% or more and 0.0050% or less, and at least one of Sb, Sn, Bi, Ge, Te, and Se in an amount of 0.002% or more and 0.030% or less in total. The steel sheet has a microstructure including ferrite and cementite, in which the density of cementite in ferrite grains is 0.13 pieces/?m2 or less. Additionally, the steel sheet has a hardness of 81 or less in terms of HRB and a total elongation of 33% or more.

Abstract: A high-carbon hot-rolled steel sheet having a chemical composition containing, by mass %, C: 0.20% or more and 0.40% or less, Si: 0.10% or less, Mn: 0.50% or less, P: 0.03% or less, S: 0.010% or less, sol.A1: 0.10% or less, N: 0.0050% or less, B: 0.0005% or more and 0.0050% or less, and at least one of Sb, Sn, Bi, Ge, Te, and Se in an amount of 0.002% or more and 0.030% or less in total. The steel sheet has a microstructure including ferrite and cementite, in which the density of cementite in the ferrite grains is 0.08 pieces/m2 or less. Additionally, the steel sheet has a hardness of 73 or less in terms of HRB and a total elongation of 39% or more.

Abstract: A high-strength galvanized steel sheet contains C: 0.010% or more and 0.06% or less, Si: more than 0.5% and 1.5% or less, Mn: 1.0% or more and 3.0% or less, P: 0.005% or more and 0.1% or less, S: 0.01% or less, sol.Al: 0.005% or more and 0.5% or less, N: 0.01% or less, Nb: 0.010% or more and 0.090% or less, and Ti: 0.015% or more and 0.15% or less, on a mass percent basis. The Nb and C contents of the steel satisfy the relation of (Nb/93)/(C/12)<0.20. C* satisfies 0.005?C*?0.025. Ferrite constitutes 70% by area ratio or more of the steel sheet. Martensite constitutes 3% by area ratio or more of the steel sheet. C*=C?(12/93)Nb?(12/48){Ti?(48/14)N}, wherein C, Nb, Ti, and N denote the C, Nb, Ti, and N contents of the steel.

Abstract: Provided are a high-strength hot-rolled steel sheet and a method for manufacturing the steel sheet. The steel sheet includes C: 0.060% or more and 0.140% or less, Si: 1.00% or less, Mn: 1.30% or more and 2.50% or less, P: 0.030% or less, S: 0.0050% or less, Al: 0.070% or less, N: 0.010% or less, Ti: 0.060% or more and 0.140% or less, Cr: 0.10% or more and 0.50% or less, B: 0.0002% or more and 0.0020% or less, and the balance being Fe and inevitable impurities, in which the relationship 5.0?18C+Mn+1.3Cr+1500B?6.0 is obtained. The microstructure includes a bainite phase in an amount of more than 90% one, two, or all of a ferrite phase, a martensite phase, and a retained austenite phase in an amount of less than 10%.

Abstract: A method of manufacturing a high strength cold rolled steel sheet includes hot-rolling and cold-rolling a steel slab annealing the steel sheet at an annealing temperature of 750° C. to 830° C.; subjecting the steel sheet to first cooling at an average cooling rate of 3° C./sec to 40° C./sec in a temperature range from the annealing temperature to 480° C.; subjecting the steel sheet to second cooling at an average cooling rate of 8° C./sec to 80° C./sec in a temperature range from 480° C. to Tc (° C.) given by formula (6): Tc=435?40×[% Mn]?30×[% Cr]?30×[% V]??(6) wherein [% A] is the content (% by mass) of alloying element A; and subjecting the steel sheet to third cooling at an average cooling rate of 0.3° C./sec to 30° C./sec in a temperature range from Tc (° C.) to 200° C.

Abstract: A vehicle collision energy absorbing member is excellent in collision energy absorbing performance in the axial direction upon collision. The vehicle collision energy absorbing member is formed of a high strength thin steel sheet having TS of at least 980 MPa and having an n-value and a limit bending radius Rc satisfying the following Formula: Rc/t?1.31×ln(n)+5.21.

Abstract: There is provided is a high-carbon hot-rolled steel sheet and method for producing the same. The steel sheet has excellent hardenability consistently, even when annealed in a nitrogen atmosphere, and excellent formability. The steel sheet has a hardness in the range of 83 HRB or less and a total elongation of 30% or more before being subjected to a quenching treatment.

Abstract: A high strength cold rolled steel sheet includes a chemical composition containing, by mass %, C: 0.010% or more and 0.060% or less, Si: more than 0.5% and 1.5% or less, Mn: 1.0% or more and 3.0% or less, P: 0.005% or more and 0.100% or less, S: 0.010% or less, sol.Al: 0.005% or more and 0.500% or less, N: 0.0100% or less, Nb: 0.010% or more and 0.100% or less, Ti: 0.015% or more and 0.150% or less and the balance comprising Fe and inevitable impurities. The microstructure includes, in area fraction, 70% or more of a ferrite phase and 3% or more of a martensite phase. The tensile strength is 440 MPa or more and an average r value is 1.20 or more.

Abstract: The high strength galvanized steel sheet contains C: more than 0.015% and lower than 0.100%, Si: 0.3% or lower, Mn: lower than 1.90%, P: 0.015% or more and 0.05% or lower, S: 0.03% or lower, sol.Al: 0.01% or more and 0.5% or lower, N: 0.005% or lower, Cr: lower than 0.30%, B: 0.0003% or more and 0.005% or lower, and Ti: lower than 0.014% in terms of mass %, and satisfies 2.2?[Mneq]?3.1 and 0.42?8[% P]+150B*?0.73. The steel microstructure contains ferrite and a second phase, in which the second phase area ratio is 3 to 15%, the ratio of the area ratio of martensite and retained ? to the second phase area ratio is more than 70%, and 50% or more of the area ratio of the second phase exists in the grain boundary triple point.

Abstract: A high-strength galvanized steel sheet has a low YP, good stretch flangeability, and excellent corrosion resistance and contains, on a percent by mass basis, more than 0.015% to less than 0.10% of C, 0.5% or less of Si, 1.0% to 1.9% of Mn, 0.015% to 0.050% of P, 0.03% or less of S, 0.01% to 0.5% of sol. Al, 0.005% or less of N, less than 0.40% of Cr, 0.005% or less of B, less than 0.15% of Mo, 0.4% or less of V, and less than 0.020% of Ti, in which 2.2?[Mneq]?3.1 and [% Mn]+3.3[% Mo]?1.9, and [% Mn]+3.3[% Mo])/(1.3[% Cr]+8[% P]+150B*)<3.5 are satisfied.

Abstract: A high strength hot-dip galvanized steel sheet has TS of 440 MPa or more and an average r value of 1.30 or more, where the absolute value of the planar anisotropy of the r value (?r) is 0.20 or less. A chemical composition contains C: 0.010% or more and 0.04% or less, Si: more than 1.0% and 1.5% or less, Mn: 1.0% or more and 3.0% or less, P: 0.005% or more and 0.1% or less, S: 0.01% or less, sol. Al: 0.005% or more and 0.5% or less, N: 0.01% or less, Nb: 0.010% or more and less than 0.05%, Ti: 0.015% or more and 0.120% or less, and the remainder composed of Fe and incidental impurities, wherein (Nb/93)/(C/12) 0.20 and 0.005<C*?0.020 are satisfied.

Abstract: The present invention provides a vehicle collision energy absorbing member formed by shaping a thin steel sheet. At least one of the thin steel sheet and the vehicle collision energy absorbing member has tensile properties of a tensile strength TS of 980 MPa or more and a yield point elongation Y-El of 2% or more.