Abstract: The present invention provides a spring steel having both a high strength and a good coiling property after heat treatment, characterized by: containing, in mass, C: 0.4 to 1.2%, Si: 0.9 to 3.0%, Mn: 0.1 to 2.0%, P: 0.015% or less, S: 0.015% or less, Cr: 2.5% or less, and N: 0.001 to 0.015%, with the balance consisting of Fe and unavoidable impurities; and, in the microstructure of the steel after hot rolling, the density of globular cementite carbides 0.2 to 3 ?m in circle-equivalent diameter being 0.5 piece/?m2 or less and the density of globular cementite carbides over 3 ?m in circle-equivalent diameter being 0.005 piece/?m2 or less.

Abstract: The present invention provides hot forging use non heat-treated steel where controlled cooling after shaping by hot forging is used to make the main structure of the steel martensite even without subsequent reheating and heat treatment by quenching and tempering and thereby give a steel part with a high strength and high toughness and superior machineability and a hot forged non heat-treated steel part made of that steel, in particular provides a martensite type hot forging use non heat-treated steel characterized by containing, by mass %, C: 0.10 to 0.20%, Si: 0.10 to 0.50%, Mn: 1.0 to 3.0%, P: 0.001 to 0.1%, S: 0.005 to 0.8%, Cr: 0.10 to 1.50%, Al: over 0.1 to 0.20%, and N: 0.0020 to 0.

Abstract: The invention provides a machine structural steel excellent in machinability and strength properties that has good machinability over a broad range of machining speeds and also has high impact properties and high yield ratio, which machine structural steel comprises, in mass %, C: 0.1 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 0.15%, total Al: greater than 0.05% and not greater than 0.3%, Sb: less than 0.0150% (including 0%), and total N: 0.0035 to 0.020%, solute N being limited to 0.0020% or less, and a balance of Fe and unavoidable impurities.

Abstract: The present invention provides machining steel superior in machinability, accompanied with little melt loss of plate refractories of continuous casting sliding nozzles, and superior in ductility in hot rolling and able to prevent deterioration of the surface properties due to hot rolling, containing, by mass %, C: 0.005 to 0.2%, Si: 0.001 to 0.5%, Mn: 0.3 to 3.0%, P: 0.001 to 0.2%, S: 0.30 to 0.60%, B: 0.0003 to 0.015%, O: 0.005 to 0.012%, Ca: 0.0001 to 0.0010%, and Al?0.01%, having an N content satisfying N?0.0020% and 1.3×B?0.0100?N?1.3×B+0.0034, and having a balance of Fe and unavoidable impurities, wherein, regarding the MnO in the steel, in a cross-section of the steel material perpendicular to the rolling direction, the area of MnO of a circle equivalent diameter of 0.5 ?m or more being 15% or less of the area of the total Mn-based inclusions.

Abstract: This invention provides a forging steel excellent in forgeability, which forging steel comprises, in mass %, C: 0.001 to less than 0.07%, Si: 3.0% or less, Mn: 0.01 to 4.0%, Cr: 5.0% or less, P: 0.2% or less, S: 0.35% or less, Al: 0.0001 to 2.0%, N: 0.03% or less, one or both of Mo: 1.5% or less (including 0%) and Ni: 4.5% or less (including 0%), and a balance of iron and unavoidable impurities; wherein Di given by the following Equation (1) is 60 or greater: Di=5.

Abstract: The present invention provides a high strength heat treated steel wire for spring having a tensile strength of 2000 MPa or more which is coiled in the cold state and can achieve both sufficient atmospheric strength and coilability and spring steel used for that steel wire, that is, a high strength heat treated steel wire for a spring characterized by comprising, by mass %, C: 0.5 to 0.9%, Si: 1.0 to 3.0%, Mn: 0.1 to 1.5%, Cr: 1.0 to 2.5%, V: over 0.15 to 1.0%, and Al: 0.005% or less, controlling N to 0.007% or less, further containing one or two of Nb: 0.001 to less than 0.01% and Ti: 0.001 to less 0.005%, and having a tensile strength of 2000 MPa or more, having cementite-based spheroidal carbides and alloy-based spheroidal carbides in a microscopic visual field satisfying an area percentage of carbides with a circle equivalent diameter of 0.

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 provides a machine structural steel excellent in machinability and strength properties that has good machinability over a broad range of machining speeds and also has high impact properties and high yield ratio, which machine structural steel comprises, in mass %, C: 0.1 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 0.15%, total Al: greater than 0.05% and not greater than 0.3%, Sb: less than 0.0150% (including 0%), and total N: 0.0035 to 0.020%, solute N being limited to 0.0020% or less, and a balance of Fe and unavoidable impurities.

Abstract: The present invention provides spring-use heat treated steel which is cold coiled, can achieve both sufficient atmospheric strength and coiling workability, has a tensile strength of 2000 MPa or more, and can improve the performance as a spring by heat treatment after shaping the spring, that is, heat treated steel for high strength spring containing, by mass %, C: 0.45 to 0.9%, Si: 1.0 to 3.0%, Mn: 0.1 to 2.0%, V: over 0.1 to 1.0%, N: limited to 0.007% or less, and a balance of Fe and unavoidable impurities, and satisfying, in terms of the analyzed value of the extracted residue after heat treatment, [amount of V in filtrate filtered by 0.2 ?m filter (mass %)]?[amount of V in steel (mass %)]×0.4.

Abstract: The present invention provides a steel wire, for springs excellent in coiling property while having a high strength, as a heat treated steel wire for high strength springs, characterized by: comprising, in mass, C: 0.75 to 0.85%, Si: 1.5 to 2.5%, Mn: 0.5 to 1.0%, Cr: 0.3 to 1.0%, P: not more than 0.015%, S: not more than 0.015%, N: 0.001 to 0.007%, W: 0.05 to 0.3%, and the balance consisting of Fe and unavoidable impurities; having a tensile strength of not less than 2,000 MPa; spheroidal carbides, composed of mainly cementite, observed in a microscopic visual field satisfying the area percentage of the spheroidal carbides not less than 0.2 ?m in circle equivalent diameter being not more than 7%, the density of the spheroidal carbides 0.2 to 3 ?m in circle equivalent diameter being not more than 1 piece/?m2, and the density of the spheroidal carbides over 3 ?m in circle equivalent diameter being not more than 0.

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: 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: 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: 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 provides spring steel used for spring steel wire achieving both high strength and cold coilability and spring steel wire, that is, spring steel containing, by mass %, C: 0.45 to 0.70%, Si: 1.0 to 3.0%, Mn: 0.05 to 2.0%, P: 0.015% or less, S: 0.015% or less, N: 0.0015 to 0.0200%, and t-O: 0.0002 to 0.01 and further limiting Al?0.01% and Ti?0.003%. Further, it is characterized by satisfying the following regarding the cementite-based spherical carbides present at an observed plane, an occupied area ratio of grains with a circle equivalent diameter of 0.2 ?m or more of 7% or less, a density of presence of grains with a circle equivalent diameter of 0.2 to 3 ?m of 1/?m2 or less, and a density of presence of grains with a circle equivalent diameter 3 ?m or more of 0.

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: The present invention is a steel, excellent in machinability, wherein forging workability is improved by suppressing the deterioration of mechanical properties in the direction in which the mechanical properties are the lowest, and more specifically, is a steel excellent in forgeability and machinability, characterized in that: the steel contains, in mass, C: 0.1 to 0.85%, Si: 0.01 to 1.5%, Mn: 0.05 to 2.0%, P: 0.003 to 0.2%, S: 0.003 to 0.5%, and Zr: 0.0003 to 0.01%; the following steel components are controlled in the following ranges respectively, in mass, Al: 0.01% or less, total O: 0.02% or less, and total N: 0.02% or less; the average aspect ratio of MnS grains is 10 or less and the maximum aspect ratio of those is 30 or less; and the balance of the steel components consists of Fe and unavoidable impurities.

Abstract: The present invention provides a steel wire, for springs excellent in coiling property while having a high strength, as a heat treated steel wire for high strength springs, characterized by: comprising, in mass, C: 0.75 to 0.85%, Si: 1.5 to 2.5%, Mn: 0.5 to 1.0%, Cr: 0.3 to 1.0%, P: not more than 0.015%, S: not more than 0.015%, N: 0.001 to 0.007%, W: 0.05 to 0.3%, and the balance consisting of Fe and unavoidable impurities; having a tensile strength of not less than 2,000 MPa; spheroidal carbides, composed of mainly cementite, observed in a microscopic visual field satisfying the area percentage of the spheroidal carbides not less than 0.2 &mgr;min circle equivalent diameter being not more than 7%, the density of the spheroidal carbides 0.2 to 3 &mgr;m in circle equivalent diameter being not more than 1 piece/&mgr;2, and the density of the spheroidal carbides over 3 &mgr;m in circle equivalent diameter being not more than 0.

Abstract: The present invention provides a spring steel having both a high strength and a good coiling property after heat treatment, characterized by: containing, in mass, C: 0.4 to 1.2%, Si: 0.9 to 3.0%, Mn: 0.1 to 2.0%, P: 0.015% or less, S: 0.015% or less, Cr: 2.5% or less, and N: 0.001 to 0.015%, with the balance consisting of Fe and unavoidable impurities; and, in the microstructure of the steel after hot rolling, the density of globular cementite carbides 0.2 to 3 &mgr;m in circle-equivalent diameter being 0.5 piece/&mgr;m2 or less and the density of globular cementite carbides over 3 &mgr;m in circle-equivalent diameter being 0.005 piece/&mgr;m2 or less.

Abstract: This invention provides a steel for cold forging, excellent in surface layer hardness and softening properties by annealing, which contains, in terms of wt %, C: 0.1 to 1.0%, Si: 0.1 to 2.0%, Mn: 0.01 to 1.50%, P: not greater than 0.100%, S: not greater than 0.500%, sol. N: not greater than 0.005% and the balance consisting of Fe and unavoidable impurities, wherein a pearlite ratio in the steel structure is not greater than 120×(C %) % and the outermost surface layer hardness is at least 450×(C %)+90 in terms of the Vickers hardness HV, and a production method thereof. The invention provides also a steel for cold forging, which has a structure wherein a ratio of graphite amount to the carbon content in the steel exceeds 20%, a mean grain diameter of graphite is not greater than 10×(C %)⅓ &mgr;m and a maximum grain diameter is not greater than 20 &mgr;m.