Abstract: A method produces a steel sheet having a microstructure including, in area fraction, 20% to 50% intercritical ferrite, 10% to 20% retained austenite, 25% to 45% tempered martensite, 10% to 20% fresh martensite, and bainite. The sum of tempered martensite and bainite is between 30% and 60%. A cold-rolled steel sheet provided includes 0.18% ?C?0.25%, 0.9% ?Si?1.8%, 0.02% ?Al?1.0%, with 1.00% ?Si+Al?2.35%, 1.5% ?Mn?2.5%, 0.010% ?Nb ?0.035%, 0.10% ?Cr?0.40%. The steel sheet is annealed to obtain 50% to 80% austenite and 20% to 50% of ferrite, quenched at a cooling rate between 20° C/s and 50° C/s to between Ms-50° C. and Ms-5° C., heated to a partitioning temperature between 375° C. and 450° C. and maintained at the partitioning temperature for at least 50s, then immediately cooled to room temperature.

Abstract: Provided are a laminate shaped article made of a maraging steel and having excellent toughness, a method for manufacturing the same, and a metal powder for laminate shaping. The laminate shaped article is made of a maraging steel comprising 0.1-5.0 mass % of Ti. When sis is performed on concentration distribution of Ti in a cross section parallel to a lamination direction of the above laminate shaped article, a length of a linear Ti-rich portion having a Ti concentration B of (1.5×A) or more with respect to an average Ti concentration A in the cross section is 15 ?m or less. In addition, the method for manufacturing the laminate shaped article uses a metal powder made of a maraging steel comprising 0.1-5.0 mass % of Ti, and a heat source output is set to 50-330 W and a scanning speed is set to 480-3000 mm/sec during the laminate shaping.

Abstract: A nitrogen-containing microalloyed spring steel and a preparation method thereof are provided. The chemical components are: 0.45-0.52% of carbon, 0.15-0.35% of silicon, 0.90-1.10% of manganese, 0.90-1.15% of chromium, 0.10-0.25% of molybdenum, 0.10-0.20% of vanadium, 0.025-0.04% of niobium, 0.007-0.012% of nitrogen, less than or equal to 0.03% of lead, tin, zinc, antimony, and bismuth, less than or equal to 25 ppm of oxygen and hydrogen, less than or equal to 0.02% of sulfur and phosphorus, less than or equal to 0.2% of copper, less than or equal to 0.35% nickel, and a balance of iron. The spring steel has significantly improved properties, including high mechanical strength, large elongation, high reduction of area, and good anti-fatigue performance.

Abstract: An abrasion-resistant steel plate comprises: a chemical composition containing, in mass %, C: 0.20% to 0.45%, Si: 0.01% to 1.0%, Mn: 0.3% to 2.5%, P: 0.020% or less, S: 0.01% or less, Cr: 0.01% to 2.0%, Ti: 0.10% to 1.00%, B: 0.0001% to 0.0100%, Al: 0.1% or less, N: 0.01% or less, and a balance consisting of Fe and inevitable impurities; and a microstructure in which a volume fraction of martensite is 90% or more, and a prior austenite grain size is 80 ?m or less, wherein a number density of TiC precipitate having a size of 0.5 ?m or more is 400 particles/mm2 or more, and a Mn content [Mn] and a P content [P] in a plate thickness central segregation area satisfy 0.04[Mn]+[P]<0.50.

Abstract: A method of manufacturing a welded structure of a ferritic heat-resistant steel is provided that prevents Type IV damage and that has good on-site operability without adding a high B concentration. The method includes: the step of preparing a base material including 1.0 to 7.0% Cr, less than 0.005% B and other elements; the step of forming an edge on the base material; a pre-weld heat treatment step in which a region located between a surface of the edge and a position distant from the surface of the edge by a pre-weld heat treatment depth of 10 to 50 mm is heated to a temperature of 950 to 1050° C. and is held at this temperature for 10 to 30 minutes; a welding step in which the edge is welded to form the weld metal; and a post-weld heat treatment step in which a region located between the surface of the edge and a position distant therefrom by a distance not smaller than the pre-weld heat treatment depth and not greater than 100 mm is heated to a temperature of 680 to 750° C.

Abstract: This disclosure is directed at methods for mechanical property improvement in a metallic alloy that has undergone one or more mechanical property losses as a consequence of forming an edge, such as in the formation of an internal hole or an external edge. Methods are disclosed that provide the ability to improve mechanical properties of metallic alloys that have been formed with one or more edges placed in the metallic alloy by a variety of methods which may otherwise serve as a limiting factor for industrial applications.

Abstract: Disclosed herein is a steel composition with improvement in tensile strength and fatigue life, which can be used for a vehicle part such as a vehicle suspension system.

Abstract: A method of manufacturing yield ratio-controlled steel, including the steps of subjecting alloy steel to rolling or wire drawing, thus obtaining a bar material; performing a first heat treatment, in which the material is heated and maintained for a predetermined period of time at a first temperature ranging from Ac1 to Ac3 based on Ac1 and Ac3 transformation temperatures; and cooling the material to a second temperature ranging from Mf to Ms based on a martensite start temperature (Ms) and a martensite finish temperature (Mf), and performing a second heat treatment, in which the material is maintained at the second temperature for a predetermined period of time.

Abstract: A hot-stamped steel according to the present invention has a predetermined chemical composition, satisfies (5×[Si]+[Mn])/[C]>10 when [C] is the amount of C by mass %, [Si] is the amount of Si by mass %, and [Mn] is the amount of Mn by mass %, includes 40% to 95% ferrite and 5% to 60% martensite in area fraction, and optionally further includes 10% or less pearlite in area fraction, 5% or less retained austenite in volume fraction, and less than 40% bainite in area fraction. The total of the area fraction of ferrite and the area fraction of martensite is 60% or more, the hardness of martensite measured with a nanoindenter satisfies H2/H1<1.10 and ?HM<20, and TS×? which is product of tensile strength TS and hole expansion ratio ? is 50000 MPa·% or more.

Abstract: Provided is a high-strength cold-rolled steel sheet having excellent ductility and stretch-flangeability as well as weldability in a range in which a tensile strength is 980 MPa or higher and a 0.2% yield strength is 700 MPa or higher. In the high-strength cold-rolled steel sheet of the present invention, the chemical composition is adjusted as appropriate, and the area ratio of below-mentioned metal structures at a position of ¼ sheet thickness in the steel sheet satisfies following requirements: tempered martensite: 30 area % or more, bainite: 15 area % to 70 area %, total of tempered martensite and bainite: 90 area % or more, ferrite: 0 area % to 5 area %, and retained austenite: 0 area % to 4 area %. The high-strength cold-rolled steel sheet has excellent ductility, stretch-flangeability, and weldability, and has a tensile strength of 980 MPa or higher and a 0.2% yield strength of 700 MPa or higher.

Abstract: This disclosure is directed at methods for mechanical property improvement in a metallic alloy that has undergone one or more mechanical property losses as a consequence of forming an edge, such as in the formation of an internal hole or an external edge. Methods are disclosed that provide the ability to improve mechanical properties of metallic alloys that have been formed with one or more edges placed in the metallic alloy by a variety of methods which may otherwise serve as a limiting factor for industrial applications.

Abstract: The present invention relates to the steel alloy for railway components and the process of manufacturing it, said alloy comprising, in weight percentage, from 0.21 to 0.27 carbon, from 0.80 to 1.20 manganese, from 0.35 to 0.60 silicon, up to 0.02 phosphorus, up to 0.02 sulfur, from 0.55 to 0.65 chromium, from 0.45 to 0.55 molybdenum, from 1.75 to 2.05 nickel and from 0.005 to 0.030 titanium, conferring, with its composition, desirable mechanical properties, hardenability and corrosion resistance for application on railway components.

Abstract: A spring steel includes a predetermined chemical composition and a composite inclusion having a maximum diameter of 2 ?m or more that TiN is adhered to an inclusion containing REM, O and Al, in which the number of the composite inclusion is 0.004 pieces/mm2 to 10 pieces/mm2, the maximum diameter of the composite inclusion is 40 ?m or less, the sum of the number density of an alumina cluster having the maximum diameter of 10 ?m or more, MnS having the maximum diameter of 10 ?m or more and TiN having the maximum diameter of 1 ?m to 10 pieces/mm2.

Abstract: A steel alloy is disclosed that provides a unique combination of strength, toughness, and fatigue life. The steel alloy has the following composition in weight percent: C about 0.15 to about 0.30 Mn about 1.7 to about 2.3 Si about 0.7 to about 1.1 Cr about 1.85 to about 2.35 Ni about 0.5 to about 0.9 Mo+½W about 0.1 to about 0.3 Cu about 0.3 to about 0.7 V+ 5/9×Nb about 0.2 to about 0.5. The balance of the alloy is iron, usual impurities, and residual amounts of other elements added during melting for deoxidizing and/or desulfurizing the alloy. A hardened and tempered steel article made from the alloy is also disclosed.

Abstract: An alloy with tailored hardenability includes carbon, silicon, manganese, nickel, molybdenum, chromium, vanadium, and cobalt. A time and temperature transformation diagram of the alloy has a bainite nose and a ferrite nose that occur at approximately the same time at approximately 4 seconds at temperatures of about 750 K and 950 K, respectively.

Abstract: Method for producing an extrusion die having a functional surface for metal extrusion material, comprising the following steps: providing a die support body, depositing a weldable substance containing cobalt and/or nickel onto a subsection of the die support body by means of an effective bonding application process to produce an inseparable deposition layer, machining the deposition layer in a chipping and/or material removal process to form the functional surface of the extrusion die, and carrying out a CVD coating process with a reaction gas at least on the functional surface.

Abstract: A high-strength spring steel wire is provided which secures excellent hydrogen embrittlement resistance even when the adding amount of alloy elements is suppressed, and has 80 area % or more of tempered martensite and 1,900 MPa or more of the tensile strength, in which a predetermined chemical composition is satisfied, with C and Si satisfying the relation of the expression (1) below, with prior austenite grain size number being No. 10 or more, and with the hydrogen absorption amount being 14.0 ppm or more. 0.73%?[C]+[Si]/8?0.90%??(1) where [C] and [Si] express the content (mass %) of C and Si respectively.

Abstract: A method of forming an earth-boring tool includes introducing metal into a die, rotating the die to generate centrifugal forces on the metal, and cooling the metal in the rotating die. A rotary drill bit may include a unitary, centrifugally cast bit body including an integral shank, at least one blade, and at least one cutting element on the blade. A rotary drill bit or a roller cone may include a first centrifugally cast material and a second centrifugally cast material. Another rotary drill bit includes a bit body comprising a maraging steel alloy. A method of forming a rotary drill bit may include disposing cutting elements on a rotary drill bit comprising maraging steel and aging the rotary drill bit to form at least one intermetallic precipitate phase. Methods of repairing a rotary drill bit include annealing and aging at least a portion of a rotary drill bit.

Abstract: The invention relates to a steel sheet having a tensile strength of 1180 MPa or more, which excels in workability and cold brittleness resistance. The high-strength steel sheet contains 0.10% to 0.30% of C, 1.40% to 3.0% of Si, 0.5% to 3.0% of Mn, 0.1% or less of P, 0.05% or less of S, 0.005% to 0.20% of Al, 0.01% or less of N, 0.01% or less of O, as well as Fe and inevitable impurities. The steel sheet has: (i) a ferrite volume fraction of 5% to 35% and a bainitic ferrite and/or tempered martensite volume fraction of 60% or more; (ii) a MA constituent volume fraction of 6% or less (excluding 0%); and (iii) a retained austenite volume fraction of 5% or more.

Abstract: A rolled steel sheet or blank is provided, the composition of which comprises the elements listed below in percent by weight: C?0.1%; 0.5%?Mn?7%; 0.5%?Si?3.5%; 0.5%<Ti?2%; 2%<Ni?7%; Al?0.10%; Cr?2%; Cu?2%; Co?2%; Mo?2%; S?0.005%; P?0.03%; Nb?0.1%; V?0.1%; B<0.005%; N?0.008%, and the silicon and titanium contents are such that: Si + Ti ? 2.5 ? % , Ti Si ? 0.3 the remainder of the composition consisting of iron and unavoidable impurities resulting from processing. A method for the fabrication of a part for a land motor vehicle from the sheet or blank by hot stamping is also provided. The microstructure of the part consisting essentially of martensite and intermetallic precipitates of type Fe2TiSi with an area percentage between 1 and 5% intermetallic precipitates.

Abstract: The present invention provides a spring steel, which is finally formed into a spring, by making use of, at a maximum, the temper softening resistance effect due to alloying elements while suppressing the formation of hard inclusions of SiO2 and the generation of decarburization, which may cause deterioration of fatigue characteristics of the spring. The spring steel is characterized by comprising, in % by mass, C: 0.50 to 0.70%, Si: 1.00 to 5.00%, Mn: 0.30 to 2.00%, P: 0.0002 to 0.0500%, S: 0.0002 to 0.0500%, Cr: 0.10 to 3.50%, Al: 0.0005 to 0.0500%, and N: 0.0020 to 0.0100%, with the balance being Fe and inevitable impurities, wherein the H-value defined by the following equation (a) is 160 or more, and the C-value defined by the following equation (b) is 3.25 or less: H=33.6[C]+10.0[Si]+5.95[Mn]+11.1[Cr]+90.0??(a), and C=[Si]/[Mn]??(b).

Abstract: A steel sheet, including: as chemical components, by mass %, 0.05% to 0.35% of C; 0.05% to 2.0% of Si; 0.8% to 3.0% of Mn; 0.01% to 2.0% of Al; equal to or less than 0.1% of P; equal to or less than 0.05% of S; equal to or less than 0.01% of N; and the balance including iron and inevitable impurities, wherein the steel sheet comprises 50% or more of a ferrite phase, a bainite phase, and a tempered martensite phase, 3% or more of a retained austenite phase, and 50% or more of the crystal grains of the retained austenite phase satisfy Expression 1, wherein a carbon concentration at a position of center of gravity is Cgc and a carbon concentration at a grain boundary is Cgb.

Abstract: Provided is a hot-working steel excellent in machinability and impact value comprising, in mass %, C: 0.06 to 0.85%, Si: 0.01 to 1.5%, Mn: 0.05 to 2.0%, P: 0.005 to 0.2%, S: 0.001 to 0.35%, and Al: 0.06 to 1.0% and N: 0.016% or less, in contents satisfying Al×N×105?96, and a balance of Fe and unavoidable impurities, total volume of AlN precipitates of a circle-equivalent diameter exceeding 200 nm accounting for 20% or less of total volume of all AlN precipitates.

Abstract: The invention relates to a steel plate, the chemical composition of which comprises, the contents being expressed by weight: 0.010%?C?0.20%, 0.06%?Mn?3%, Si?1.5%, 0.005%?Al?1.5%, S?0.030%, P?0.040%, 2.5%?Ti?7.2%, (0.45×Ti)?0.35%?B?(0.45×Ti)+0.70%, and optionally one or more elements chosen from: Ni?1%, Mo?1%, Cr?3%, Nb?0.1%, V?0.1%, the balance of the composition consisting of iron and inevitable impurities resulting from the smelting.

Abstract: A rolled steel sheet or blank is provided, the composition of which comprises the elements listed below in per cent by weight: C?0.1%; 0.5%?Mn?7%; 0.5%?Si?3.5%; 0.5%<Ti?2%; 2%<Ni?7%; Al?0.10%; Cr?2%; Cu?2%; Co?2%; Mo?2%; S?0.005%; P?0.03%; Nb?0.1%; V?0.1%; B<0.005%; N?0.008%, and the silicon and titanium contents are such that: Si + Ti ? 2.5 ? % , Ti Si ? 0.3 the remainder of the composition consisting of iron and unavoidable impurities resulting from processing. A method for the fabrication of a part for a land motor vehicle from the sheet or blank by hot stamping is also provided. The microstructure of the part consisting essentially of martensite and intermetallic precipitates of type Fe2TiSi with an area percentage between 1 and 5% intermetallic precipitates.

Abstract: A steel for an induction hardening including, by mass %, C: more than 0.75% to 1.20%, Si: 0.002 to 3.00%, Mn: 0.20 to 2.00%, S: 0.002 to 0.100%, Al: more than 0.050% to 3.00%, P: limited to 0.050% or less, N: limited to 0.0200% or less, O: limited to: 0.0030% or less, and the balance composing of iron and unavoidable impurities, wherein an Al content and a N content satisfy, by mass %, Al?(27/14)×N>0.050%.

Abstract: A component composition contains, by % by mass, 0.0016 to 0.01% of C, 0.05 to 0.60% of Mn, and 0.020 to 0.080% of Nb so that the C and Nb contents satisfy the expression, 0.4?(Nb/C)×(12/93)?2.5. In addition, the amount of Nb-based precipitates is 20 to 500 ppm by mass, the average grain diameter of the Nb-based precipitates is 10 to 100 nm, and the average crystal grain diameter of ferrite is 6 to 10 ?m. Nb is added to ultra-low-carbon steel used as a base, and the amount and grain diameter of the Nb-based precipitates are controlled to optimize the pinning effect. Grain refinement of ferrite is achieved by specifying the Mn amount, thereby achieving softening and excellent resistance to surface roughness of steel.

Abstract: A forging heat resistant steel of an embodiment contains in percent by mass C: 0.05-0.2, Si: 0.01-0.1, Mn: 0.01-0.15, Ni: 0.05-1, Cr: 8 or more and less than 10, Mo: 0.05-1, V: 0.05-0.3, Co: 1-5, W: 1-2.2, N: 0.01 or more and less than 0.015, Nb: 0.01-0.15, B: 0.003-0.03, and a remainder comprising Fe and unavoidable impurities.

Abstract: A steel plate has a chemical composition containing, by mass %, C: 0.03% or more and 0.08% or less, Si: 0.01% or more and 1.0% or less, Mn: 1.2% or more and 3.0% or less, P: 0.015% or less, S: 0.005% or less, Al: 0.08% or less, Nb: 0.005% or more and 0.07% or less, Ti: 0.005% or more and 0.025% or less, N: 0.010% or less, O: 0.005% or less and the balance being Fe and inevitable impurities, a structure being a dual-phase structure consisting of a bainite phase and island martensite, wherein the area fraction of the island martensite is 3% to 15%, the equivalent circle diameter of the island martensite is 3.0 ?m or less, and the remainder of the structure is a bainite phase.

Abstract: A hot worked matrix steel consisting of (in weight-%) 0.60-0.85 C, 0.05-0.5 Si, ?0.5 (Si+Al), 0.1-2.0 Mn, 4.5-5.5 Cr, 1.5-2.6 Mo, ?1.0 W, 1.5-2.6 (Mo+W/2), 0.42-0.65 V, ?0.1 Nb, ?0.1 Ti, ?0.1 Zr, ?2.0 Co, ?2.0 Ni, ?0.003 S, optionally, up to 30 ppm B, balance iron and unavoidable impurities. The steel after hardening and tempering at 520-600° C. (2×2 h) has a hardness of 57-63 HRC and an un-notched impact energy in the transverse direction of 20-100 J. The steel consists of tempered martensite. The steel contains 1.04 vol. % or less of primary precipitated vanadium carbides. The steel is void of primary carbides other than primary precipitated vanadium carbides.

Abstract: The present invention relates to high strength cold rolled steel sheet suitable for applications in automobiles, construction materials and the like, specifically high strength steel excellent in formability. In particular, the invention relates to cold rolled steel sheets having a tensile strength of at least 780 MPa.

Abstract: The high strength steel sheet has a chemical composition including 0.08% to 0.20% of C, 0.3% or less of Si, 0.1% to 3.0% of Mn, 0.10% or less of P, 0.030% or less of S, 0.10% or less of Al, 0.010% or less of N, 0.20% to 0.80% of V, and the remainder composed of Fe and incidental impurities on a percent by mass basis, and a microstructure which includes 95% or more of ferrite phase on an area percentage basis, in which fine precipitates are dispersed having a distribution in such a way that the number density of precipitates having a particle size of less than 10 nm is 1.0×105/?m3 or more and the standard deviation of natural logarithm values of precipitate particle sizes with respect to precipitates having a particle size of less than 10 nm is 1.5 or less.

Abstract: Provided are: a boron-added high strength steel for bolt excellent in delayed fracture resistance even having a tensile strength of 1100 MPa or more without addition of large amounts of expensive alloy elements such as Cr and Mo: and a high strength bolt made from the boron-added high strength steel for bolt. The high strength steel for bolt contains C of 0.23% to less than 0.40%, Si of 0.23% to 1.50%, Mn of 0.30% to 1.45%, P of 0.03% or less (excluding 0%), S of 0.03% or less (excluding 0%), Cr of 0.05% to 1.5%, V of 0.02% to 0.30%, Ti of 0.02% to 0.1%, B of 0.0003% to 0.0050%, Al of 0.01% to 0.10%, and N of 0.002% to 0.010%, with the remainder being iron and inevitable impurities. The steel has a ratio ([Si]/[C]) of the Si content [Si] to the C content [C] of 1.0 or more and has a ferrite-pearlite mixed microstructure.

Abstract: The present invention relates to high strength cold rolled steel sheet suitable for applications in automobiles, construction materials and the like, specifically high strength steel excellent in formability. In particular, the invention relates to cold rolled steel sheets having a tensile strength of at least 980 MPa and a method for producing such steel sheet.

Abstract: This gear has a predetermined chemical composition and has, in a surface-layer part, a texture of tempered martensite and/or tempered bainite and a steel material texture in which retained austenite exists in 1-10% by area percentage and in which a carbide is deposited in at least 5% by area percentage, and the nitrogen content at a depth of 20 ?m below the surface is 2.0-6.0%. Thus, a gear that achieves even better seizing resistance in a power transmission part subjected to high rotation and high slippage and using a low-kinematic-viscosity lubricating oil is provided.

Abstract: The invention relates to a steel plate, the chemical composition of which comprises, the contents being expressed by weight: 0.010%?C?0.20%, 0.06%?Mn?3%, Si?1.5%, 0.005%?Al?1.5%, S?0.030%, P?0.040%, 2.5%?Ti?7.2%, (0.45×Ti)?0.35%?B?(0.45×Ti)+0.70%, and optionally one or more elements chosen from: Ni?1%, Mo?1%, Cr?3%, Nb?0.1%, V?0.1%, the balance of the composition consisting of iron and inevitable impurities resulting from the smelting.

Abstract: In the present invention, a press-formed product is manufactured by heating a steel sheet for hot pressing use to a temperature of 900° C. or above and 1,100° C. or below, the steel sheet for hot pressing use having a predetermined chemical component composition, some of Ti-containing precipitates contained in the steel sheet, each of which having an equivalent circle diameter of 30 nm or less, having an average equivalent circle diameter of 6 nm or less, and the precipitated Ti amount and the total Ti amount in the steel fulfilling the relationship represented by formula (1) shown below, thereafter starting press-forming, and holding at the bottom dead point and cooling to a temperature lower than the martensite transformation starting temperature Ms while securing the average cooling rate of 20° C./s or more within a tool. Precipitated Ti amount(mass %)?3.4[N]<0.5×[total Ti amount (mass %)?3.4[N]]??(1) (In the formula (1), [N] represents the content (mass %) of N in the steel.

Abstract: A method of the present invention includes the steps of heating a steel sheet for hot pressing use to a temperature of Ac3 transformation point or above and 950° C. or below, the steel sheet for hot pressing use containing a predetermined chemical component composition, some of Ti-containing precipitates contained in the steel sheet, each of which having an equivalent circle diameter of 30 nm or less, having an average equivalent circle diameter of 3 nm or more, and the precipitated Ti amount and the total Ti amount in the steel fulfilling the relationship represented by formula (1) shown below, thereafter starting press forming, and being held at the bottom dead point and being cooled to a temperature lower than martensite transformation starting temperature Ms while securing the average cooling rate of 20° C./s or more within a tool. Precipitated Ti amount (mass %)?3.4[N]?0.5×[total Ti amount (mass %)?3.4[N]]??(1) (In the formula (1), [N] represents the content (mass %) of N in the steel.

Abstract: The present invention provides a steel part for machine structural use whose fatigue strength and toughness are improved and a manufacturing method thereof. A steel part made of a steel containing, in mass %, C: 0.05 to 0.20%, Si: 0.10 to 1.00%, Mn: 0.75 to 3.00%, P: 0.001 to 0.050%, S: 0.001 to 0.200%, V: exceeding 0.25 to 0.50%, Cr: 0.01 to 1.00%, Al: 0.001 to 0.500%, and N: 0.0080 to 0.0200%, and a balance being composed of Fe and inevitable impurities, in which a steel structure contains a bainite structure having an area ratio of 95% or more, a bainite lath width is 5 ?m or less, V carbide having an average grain diameter of not less than 4 nm nor more than 7 nm dispersedly exists in the bainite structure, and an area ratio of V carbide in the bainite structure is 0.18% or more.

Abstract: Provided is a low yield ratio, high strength and high uniform elongation steel plate having excellent strain ageing resistance equivalent to API 5L X70 Grade or lower and a method for manufacturing the same. In particular, the steel plate contains 0.06% to 0.12% C, 0.01% to 1.0% Si, 1.2% to 3.0% Mn, 0.015% or less P, 0.005% or less S, 0.08% or less Al, 0.005% to 0.07% Nb, 0.005% to 0.025% Ti, 0.010% or less N, and 0.005% or less O on a mass basis, the remainder being Fe and unavoidable impurities. The low yield ratio, high strength and high uniform elongation steel plate has a metallographic microstructure that is a two-phase microstructure consisting of bainite and M-A constituent, the area fraction of the M-A constituent being 3% to 20%, the equivalent circle diameter of the M-A constituent being 3.0 ?m or less.

Abstract: The invention relates to a cold-rolled flat steel product which, despite high strength values, has a high level of deformability characterised by a high elongation at break and a good hole expansion ratio A. For this purpose the flat steel product is produced from a steel that is composed of (in % by weight) C: 0.12-0.19%, Mn: 1.5-2.5%, Si: >0.60-1.0%, Al: ?0.1%, Cr: 0.2-0.6%, Ti: 0.05-0.15% with the remainder being iron and unavoidable impurities caused by the production process, and which comprises a perlite- and bainite-free structure having 4-20% by vol. martensite, 2-15% by vol. residual austenite, remainder ferrite, an elongation at break A80 of at least 15%, a tensile strength Rm of at least 880 MPa, a yield strength ReL of at least 550 MPa and a hole expansion ratio ?M of more than 6%. The invention also relates to a method which easily enables production of a flat steel product according to the invention.

Abstract: The present invention provides a steel part for machine structural use whose fatigue strength and toughness are improved and a manufacturing method thereof. A steel part made of a steel containing, in mass %, C: 0.05 to 0.20%, Si: 0.10 to 1.00%, Mn: 0.75 to 3.00%, P: 0.001 to 0.050%, S: 0.001 to 0.200%, V: 0.05 to 0.20%, Cr: 0.01 to 1.00%, Al: 0.001 to 0.500%, and N: 0.0080 to 0.0200%, and a balance being composed of Fe and inevitable impurities, in which a steel structure contains a bainite structure having an area ratio of 95% or more, a bainite lath width is 5 ?m or less, V carbide having an average grain diameter of not less than 4 nm nor more than 7 nm dispersedly exists in the bainite structure, and an area ratio of V carbide in the bainite structure is 0.18% or more.

Abstract: A low density high strength steel sheet including 0.15% to 0.25% C, 2.5% to 4% Mn, 0.02% or less P, 0.015% or less S, 6% to 9% Al and 0.01% or less N, the balance being iron and inevitable impurities, wherein 1.7·(Mn—Al)+52.7·C is at least 3 and at most 4.5. A method of producing the low density and high strength steel sheet.

Abstract: Disclosed is a spring steel which contains, by mass, 1.2% or less C; 0.1% to 2% Mn; 0.2% to 3% Si; 0.0003% to 0.005% Al; to 8 ppm Li; 30 ppm or less (excluding 0 ppm) Ca; and 10 ppm or less (excluding 0 ppm) Mg. The steel contains oxide inclusions satisfying the following conditions (1) to (3) in a number of 1×10?4 or more per square millimeter: (1) containing a total of 80 percent by mass or more of Al2O3 and SiO2 based on the inclusion composition excluding Li2O; (2) having a ratio by mass of Al2O3 to SiO2 of from 1:4 to 2:3; and (3) containing lithium (Li). The spring steel gives a spring that exhibits superior fatigue properties without strict control of the average composition of inclusions.

Abstract: The present invention relates to a mechanical part, which is obtained by: processing a steel into a shape of a part, the steel having an alloy composition containing, by weight percent, C: 0.10 to 0.30%, Si: 0.50 to 3.00%, Mn: 0.30 to 3.00%, P: 0.030% or less, S: 0.030% or less, Cu: 0.01 to 1.00%, Ni: 0.01 to 3.00%, Cr: 0.20 to 1.00%, Al: 0.20% or less, N: 0.05% or less, and the remainder of Fe and inevitable impurities, and the alloy composition satisfying the following condition: [Si %]+[Ni %]+[Cu %]?[Cr %]>0.50, in which [Si %], [Ni %], [Cu %] and [Cr %] represent the concentration of Si, the concentration of Ni, the concentration of Cu and the concentration of Cr in the alloy composition, respectively; subjecting the steel to a carburizing treatment in a vacuum, followed by gradually cooling the steel; and subsequently subjecting the steel to a high-frequency hardening to thereby harden a surface of the steel.

Abstract: This high-strength steel sheet includes: in terms of percent by mass, 0.03 to 0.10% of C; 0.01 to 1.5% of Si; 1.0 to 2.5% of Mn; 0.1% or less of P; 0.02% or less of S; 0.01 to 1.2% of Al; 0.06 to 0.15% of Ti; and 0.01% or less of N; and contains as the balance, iron and inevitable impurities, wherein a tensile strength is in a range of 590 MPa or more, and a ratio between the tensile strength and a yield strength is in a range of 0.80 or more, a microstructure includes bainite at an area ratio of 40% or more and the balance being either one or both of ferrite and martensite, a density of Ti(C,N) precipitates having sizes of 10 nm or smaller is in a range of 1010 precipitates/mm3 or more, and a ratio (Hvs/Hvc) of a hardness (Hvs) at a depth of 20 ?m from a surface to a hardness (Hvc) at a center of a sheet thickness is in a range of 0.85 or more.

Abstract: A method for manufacturing a precipitation hardening cold-rolled steel sheet with an excellent yield ratio. The method may include the steps of hot rolling a steel slab with finish rolling at a temperature of Ar3 transformation point or more to form a hot-rolled steel sheet, coiling the hot-rolled steel sheet at a temperature of 550-600 ° C., cold rolling the hot-rolled steel sheet at a reduction ratio of 50% or more; and recovery-recrystallization annealing the cold-rolled steel sheet at a line speed of 150-200 mpm and at a temperature of 780-820° C. in a continuous annealing furnace. The recovery-recrystallization annealing may provide a recrystallization ratio of 65-75%. The steel slab includes, by weight %: C: 0.07-0.10%, Mn: 1.41-1.70%, P: 0.05-0.07%, S: 0.005% or less, N: 0.005% or less, acid-soluble Al: 0.10-0.15%, Nb: 0.06-0.09%, B: 0.0008-0.0012%, Sb: 0.02-0.06%, and the balance comprising Fe and other unavoidable impurities.

Abstract: Steel for induction hardening wherein coarsening of austenite crystal grains can be prevented even at a high temperature of over 1100° C. such as which occurs at projecting parts of steel parts at the time of induction hardening, the steel for induction hardening characterized by containing, by mass %, C: 0.35 to 0.6%, Si: 0.01 to 1%, Mn: 0.2 to 1.8%, S: 0.001 to 0.15%, Al: 0.001 to 1%, Ti: 0.05 to 0.2%, and Nb: 0.001 to 0.04%, restricting N: 0.0060% or less, P: 0.025% or less, and O: 0.0025% or less, satisfying Nb/Ti?0.015, and having a balance of iron and unavoidable impurities.

Abstract: A high strength steel, including about 0.05 to about 0.25% of C, less than about 0.5% of Si, about 0.5 to about 3.0% of Mn, not more than about 0.06% of P, not more than about 0.01% of S, about 0.50 to about 3.0% of Sol. Al, not more than about 0.02% of N, about 0.1 to about 0.8% of Mo, about 0.02 to about 0.40% of Ti, and the balance of iron and unavoidable impurities, wherein the steel has a structure formed of at least three phases including a bainite phase, and a retained austenite phase in addition to a ferrite phase having a composite carbide containing Ti and Mo dispersed and precipitated therein, wherein the total volume of the ferrite phase and the bainite phase is not smaller than 80%, the volume of the bainite phase is about 5% to about 60%, and the volume of the retained austenite phase is about 3 to about 20%.

Abstract: The present invention provides steel plate or steel pipe with small occurrence of the Bauschinger effect and methods of production of the same, particularly steel pipe used for steel pipe for oil wells or line pipe with a small drop in the compression strength in the circumferential direction due to the Bauschinger effect when expanded and methods of production of the same, that is steel plate or steel pipe with small occurrence of the Bauschinger effect characterized by having a dual-phase structure substantially comprising a ferrite structure and fine martensite which is dispersed in the ferrite structure. Further, this steel plate or steel pipe contains, by mass %, C: 0.03 to 0.30%, Si: 0.01 to 0.8%, Mn: 0.3 to 2.5%, P: 0.03% or less, S: 0.01% or less, Al: 0.001 to 0.01%, and N: 0.01% or less and a balance of iron and unavoidable impurities.