Abstract: This case hardening steel has a chemical composition including, by mass %: C: 0.1 to 0.6%; Si: 0.02 to 1.5%; Mn: 0.3 to 1.8%; P: 0.025% or less; S: 0.001 to 0.15%; Al: over 0.05 to 1.0%; Ti: 0.05 to 0.2%; N: 0.01% or less; and O: 0.0025% or less, and further including, by mass %, one or more of Cr: 0.4 to 2.0%, Mo: 0.02 to 1.5%, Ni: 0.1 to 3.5%, V: 0.02 to 0.5%, and B: 0.0002 to 0.005%, and the balance consisting of iron and unavoidable impurities.

Abstract: The present invention provides a steel for nitriding with a composition including, by mass %: C: 0.10% to 0.20%; Si: 0.01% to 0.7%; Mn: 0.2% to 2.0%; Cr: 0.2% to 2.5%; Al: 0.01% to less than 0.19%; V: over 0.2% to 1.0%; Mo: 0% to 0.54%; N: 0.001% to 0.01%; P limited to not more than 0.05%; S limited to not less than 0.2%; and a balance including Fe and inevitable impurities, the composition satisfying 2?[V]/[C]?10, where [V] is an amount of V by mass % and [C] is an amount of C by mass %, in which the steel for nitriding has a microstructure containing bainite of 50% or more in terms of an area percentage.

Abstract: The present invention provides spring use heat treated steel which is cold coiled, can achieve both sufficient atmospheric strength and coilability, has a tensile strength of 2000 MPa or more, and can improve the performance as a spring by heat treatment after spring fabrication, that is, high strength spring-use heat treated steel characterized by containing, by mass %, C: 0.45 to 0.9%, Si: 1.7 to 3.0%, and Mn: 0.1 to 2.0%, restricting N: to 0.007% or less, having a balance of Fe and unavoidable impurities, and satisfying, in terms of the analyzed value of the extracted residue after heat treatment, [amount of Fe in residue on 0.2 ?m filter/[steel electrolysis amount]×100?1.1.

Abstract: A bearing steel includes, as a metallographic structure, inclusions which contain complex oxysulfides including Rare Earth Metal, Ca, O, S, and Al, TiN, MnS, Al2O3, and complex oxides including Al and Ca, wherein, a number fraction of the complex oxysulfides in a total number of the inclusions is 50% to less than 100% and a number of complex oxysulfides having a major axis of 5 ?m or more is 0.001 pieces to 2 pieces in an observed section of 1 mm2, and a number of TiN existing independently from the complex oxysulfides and having a major axis of 5 ?m or more is 0.001 pieces to less than 1.0 piece in an observed section of 1 mm2.

Abstract: The present invention is steel for surface hardening for machine structural use which contains, by mass %, C: 0.3 to 0.6%, Si: 0.02 to 2.0%, Mn: 0.35 to less than 1.5%, and Al: 0.01 to 0.5%, is restricted to B: less than 0.0003%, S: 0.0001 to 0.021%, N: 0.003 to 0.0055%, P: 0.0001 to 0.03%, and 0:0.0001 to 0.0050%, has a ratio Mn/S of Mn and S satisfying 70 to 30,000, has a balance of Fe and unavoidable impurities, and, when nitrided, then induction hardened, has a surface hardenability of a Vicker's hardness when tempered at 300° C. of 650 or more.

Abstract: The present invention is steel for surface hardening for machine structural use which contains, by mass %, C: 0.3 to 0.6%, Si: 0.02 to 2.0%, Mn: 0.35 to less than 1.5%, and Al: 0.01 to 0.5%, is restricted to B: less than 0.0003%, S: 0.0001 to 0.021%, N: 0.003 to 0.0055%, P: 0.0001 to 0.03%, and O: 0.0001 to 0.0050%, has a ratio Mn/S of Mn and S satisfying 70 to 30,000, has a balance of Fe and unavoidable impurities, and, when nitrided, then induction hardened, has a surface hardenability of a Vicker's hardness when tempered at 300° C. of 650 or more.

Abstract: High strength steel wire for spring containing, by mass %, C: 0.67% to less than 0.75%, Si: 2.0 to 2.5%, Mn: 0.5 to 1.2%, Cr: 0.8 to 1.3%, V: 0.03 to 0.20%, Mo: 0.05 to 0.25%, W: 0.05 to 0.30%, and N: 0.003 to 0.007%, having a total of contents of Mn and V of 0.70%?Mn+V?1.27% and a total of contents of Mo and W of 0.13%?Mo+W?0.35%, limiting P: 0.025% or less, S: 0.025% or less, and Al: 0.003% or less, and having a balance of iron and unavoidable impurities, having a microstructure comprised of, by volume percent, over 6% to 15% of retained austenite and tempered martensite, having a prior-austenite grain size number of 10 or more, having a density of presence of spheroidal carbides with a circle equivalent diameter of 0.2 to 0.5 ?m of 0.06 particles/?m2 or less, having a density of presence of spheroidal carbides with a circle equivalent diameter of over 0.5 ?m of 0.01 particles/?m2 or less, and having a tensile strength of 2100 to 2350 MPa.

Abstract: A case hardening steel includes by mass %, C: 0.1% to 0.5%, Si: 0.01% to 1.5%, Mn: 0.3% to 1.8%, S: 0.001% to 0.15%, Cr: 0.4% to 2.0%, Ti: 0.05% to 0.2%, Al: limited to 0.2% or less, N: limited to 0.0050% or less, P: limited to 0.025% or less, O: limited to 0.0025% or less, and the balance of Fe and inevitable impurities, wherein the number d of sulfide having an equivalent circle diameter more than 5 ?m per 1 mm2 and a mass percentage [S] of S satisfy: d?500×[S]+1.

Abstract: Steel for machine structure use for surface hardening containing, by mass %, C: 0.3 to 0.6%, Si: 0.02 to 2.0%, Mn: 1.5% to 3.0%, W: 0.0025 to 0.5%, Al: 0.001 to 0.5%, N: 0.003 to 0.02%, S: 0.0001 to 0.025%, P: 0.0001 to 0.03%, and O: 0.0001 to 0.0050%, having an Mn/S of 70 to 30000, and having a balance of substantially Fe and unavoidable impurities.

Abstract: The present invention provides a steel for nitriding with a composition including, by mass %: C: 0.10% to 0.20%; Si: 0.01% to 0.7%; Mn: 0.2% to 2.0%; Cr: 0.2% to 2.5%; Al: 0.01% to less than 0.19%; V: over 0.2% to 1.0%; Mo: 0% to 0.54%; N: 0.001% to 0.01%; P limited to not more than 0.05%; S limited to not less than 0.2%; and a balance including Fe and inevitable impurities, the composition satisfying 2?[V]/[C]?10, where [V] is an amount of V by mass % and [C] is an amount of C by mass %, in which the steel for nitriding has a microstructure containing bainite of 50% or more in terms of an area percentage.

Abstract: A case hardening steel includes by mass %, C: 0.1% to 0.5%, Si: 0.01% to 1.5%, Mn: 0.3% to 1.8%, S: 0.001% to 0.15%, Cr: 0.4% to 2.0%, Ti: 0.05% to 0.2%, Al: limited to 0.2% or less, N: limited to 0.0050% or less, P: limited to 0.025% or less, O: limited to 0.0025% or less, and the balance of Fe and inevitable impurities, wherein the number d of sulfide having an equivalent circle diameter more than 5 ?m per 1 mm2 and a mass percentage [S] of S satisfy: d 500×[S]+1.

Abstract: Drawn heat treated steel wire for high strength spring use is provided containing, by mass %, C: 0.67% to less than 0.9%, Si: 2.0 to 3.5%, Mn: 0.5 to 1.2%, Cr: 1.3 to 2.5%, N: 0.003 to 0.007%, and Al: 0.0005% to 0.003%, having Si and Cr satisfying the following formula: 0.3%?Si?Cr?1.2%, and having a balance of iron and unavoidable impurities, having as impurities, P: 0.025% or less and S: 0.025% or less, furthermore having a circle equivalent diameter of undissolved spherical carbides of less than 0.2 ?m, further having, as a metal structure, at least residual austenite in a volume rate of over 6% to 15%, having a prior austenite grain size number of #10 or more, and having a circle equivalent diameter of undissolved spherical carbides of less than 0.2 ?m.

Abstract: High strength steel wire for spring containing, by mass %, C: 0.67% to less than 0.75%, Si: 2.0 to 2.5%, Mn: 0.5 to 1.2%, Cr: 0.8 to 1.3%, V: 0.03 to 0.20%, Mo: 0.05 to 0.25%, W: 0.05 to 0.30%, and N: 0.003 to 0.007%, having a total of contents of Mn and V of 0.70%?Mn+V?1.27% and a total of contents of Mo and W of 0.13%?Mo+W?0.35%, limiting P: 0.025% or less, S: 0.025% or less, and Al: 0.003% or less, and having a balance of iron and unavoidable impurities, having a microstructure comprised of, by volume percent, over 6% to 15% of retained austenite and tempered martensite, having a prior-austenite grain size number of 10 or more, having a density of presence of spheroidal carbides with a circle equivalent diameter of 0.2 to 0.5 ?m of 0.06 particles/?m2 or less, having a density of presence of spheroidal carbides with a circle equivalent diameter of over 0.5 ?m of 0.01 particles/?m2 or less, and having a tensile strength of 2100 to 2350 MPa.

Abstract: The present invention provides steel superior in machinability comprised of, by wt %, C: 0.005 to 0.2%, Si: 0.001 to 0.5%, Mn: 0.2 to 3.0%, P: 0.001 to 0.2%, S: 0.03 to 1.0%, T.N: 0.002 to 0.02%, T.O: 0.0005 to 0.035%, and the balance of Fe and unavoidable impurities, said steel satisfying one or both of Mn/S in the steel being 1.2 to 2.8 or an area ratio of pearlite over a grain size of 1 ?m in a microstructure of the steel being not more than 5%.

Abstract: Cold worked, machined, and carburized quenched case-hardened steel prevented from formation of coarse grains, that is, case-hardened steel superior in cold workability, machinability, and fatigue characteristics after carburized quenching characterized by limiting, by mass %, S: 0.001 to 0.15%, Ti: 0.05 to 0.2%, Al: 0.04% or less, and N: 0.0050% or less, containing other specific ingredients in specific ranges, furthermore containing one or more of Mg: 0.003% or less, Zr: 0.01% or less, and Ca: 0.005% or less, limiting the amount of precipitation of AlN to 0.01% or less, and having a density d (/mm2) of sulfides with a equivalent circle diameter of over 20 ?m and an aspect ratio of over 3 and a content of S [S] (mass %) satisfying d?1700[S]+20.

Abstract: The present invention provides high strength spring and high strength spring steel wire superior in corrosion fatigue characteristics and methods of production of the same, that is, a high strength spring steel wire and high strength spring containing, by mass %, C: 0.35 to 0.50%, Si: 1.00 to 3.00%, and Mn: 0.10 to 2.00%, restricting P to 0.015% or less and S to 0.015% or less, having a balance of Fe and unavoidable impurities, and, when raising the temperature in the range from 50° C. to 600° C. by 0.25° C./s and measuring the differential scanning calories, having the only peak of the exothermic reaction present at 450° C. or more. A method of production of high strength spring characterized by tempering under conditions where the tempering temperature T[K], tempering time t[s], and content Si % [mass %] of Si satisfy the following: 16000?(T?40×[Si %])×(31.7+log t)?23000.

Abstract: The present invention is steel for surface hardening for machine structural use which contains, by mass %, C: 0.3 to 0.6%, Si: 0.02 to 2.0%, Mn: 0.35 to less than 1.5%, and Al: 0.01 to 0.5%, is restricted to B: less than 0.0003%, S: 0.0001 to 0.021%, N: 0.003 to 0.0055%, P: 0.0001 to 0.03%, and O: 0.0001 to 0.0050%, has a ratio Mn/S of Mn and S satisfying 70 to 30,000, has a balance of Fe and unavoidable impurities, and, when nitrided, then induction hardened, has a surface hardenability of a Vicker's hardness when tempered at 300° C. of 650 or more.

Abstract: This case hardening steel has a chemical composition including, by mass %: C: 0.1 to 0.6%; Si: 0.02 to 1.5%; Mn: 0.3 to 1.8%; P: 0.025% or less; S: 0.001 to 0.15%; Al: over 0.05 to 1.0%; Ti: 0.05 to 0.2%; N: 0.01% or less; and O: 0.0025% or less, and further including, by mass %, one or more of Cr: 0.4 to 2.0%, Mo: 0.02 to 1.5%, Ni: 0.1 to 3.5%, V: 0.02 to 0.5%, and B: 0.0002 to 0.005%, and the balance consisting of iron and unavoidable impurities.

Abstract: Steel for machine structure use for surface hardening containing, by mass %, C: 0.3 to 0.6%, Si: 0.02 to 2.0%, Mn: 1.5% to 3.0%, W: 0.0025 to 0.5%, Al: 0.001 to 0.5%, N: 0.003 to 0.02%, S: 0.0001 to 0.025%, P: 0.0001 to 0.03%, and O: 0.0001 to 0.0050%, having an Mn/S of 70 to 30000, and having a balance of substantially Fe and unavoidable impurities.

Abstract: This steel for induction hardening includes: in terms of mass %, C: 0.40% or more to 0.75% or less; Si: 0.002% or more to 3.0% or less; Mn: 0.20% or more to 2.0% or less; S: 0.002% or more to 0.1% or less; Al: more than 0.10% to 3.0% or less; P: 0.030% or less; and N: 0.035% or less, with the remainder being Fe and inevitable impurities.