Abstract: A steel wire which has an excellent fatigue limit when made into a spring is provided. A chemical composition of the steel wire according to the present embodiment consists of, in mass %, C: 0.53 to 0.59%, Si: 2.51 to 2.90%, Mn: 0.70 to 0.85%, P: 0.020% or less, S: 0.020% or less, Cr 1.40 to 1.70%, Mo: 0.17 to 0.53%, V: 0.23 to 0.33%, Cu: 0.050% or less, Ni: 0.050% or less, Al: 0.0050% or less, Ti: 0.050% or less, N: 0.0070% or less, Ca: 0 to 0.0050%, and Nb: 0 to 0.020%, with the balance being Fe and impurities. In the steel wire, a number density of V-based precipitates having a maximum diameter ranging from 2 to 10 nm is 500 to 8000 pieces/?m2.

Abstract: A valve spring includes a nitrided layer, and a core portion that is further inward than the nitrided layer. A chemical composition of the core portion consists of, in mass %, C: 0.53 to 0.59%, Si: 2.51 to 2.90%, Mn: 0.70 to 0.85%, P: 0.020% or less, S: 0.020% or less, Cr: 1.40 to 1.70%, Mo: 0.17 to 0.53%, V: 0.23 to 0.33%, Ca: 0.0001 to 0.0050%, Cu: 0.050% or less, Ni: 0.050% or less, Al: 0.0050% or less, Ti: 0.050% or less, and N: 0.0070% or less, with the balance being Fe and impurities. In the core portion, a number density of V-based precipitates having a maximum diameter ranging from 2 to 10 nm is 500 to 8000 per ?m2, and in the core portion, a numerical proportion of Ca sulfides with respect to a total number of oxide-based inclusions and sulfide-based inclusions is 0.20% or less.

Abstract: A steel wire which has an excellent fatigue limit when made into a spring is provided. A chemical composition of the steel wire according to the present embodiment consists of, in mass %, C: 0.53 to 0.59%, Si: 2.51 to 2.90%, Mn: 0.70 to 0.85%, P: 0.020% or less, S: 0.020% or less, Cr 1.40 to 1.70%, Mo: 0.17 to 0.53%, V: 0.23 to 0.33%, Cu: 0.050% or less, Ni: 0.050% or less, Al: 0.0050% or less, Ti: 0.050% or less, N: 0.0070% or less, Ca: 0 to 0.0050%, and Nb: 0 to 0.020%, with the balance being Fe and impurities. In the steel wire, a number density of V-based precipitates having a maximum diameter ranging from 2 to 10 nm is 500 to 8000 pieces/?m2.

Abstract: A damper spring having an excellent fatigue limit is provided. A damper spring according to the present embodiment includes a nitrided layer formed in an outer layer, and a core portion that is further inward than the nitrided layer. The chemical composition of the core portion consists of, in mass%, C: 0.53 to 0.59%, Si: 2.51 to 2.90%, Mn: 0.70 to 0.85%, P: 0.020% or less, 5: 0.020% or less, Cr: 1.40 to 1.70%, Mo: 0.17 to 0.53%, V: 0.23 to 0.33%, Cu: 0.050% or less, Ni: 0.050% or less, Al: 0.0050% or less, Ti: 0.050% or less, N: 0.0070% or less, and Nb: 0 to 0.020%, with the balance being Fe and impurities. In the core portion, a number density of V-based precipitates having a maximum diameter ranging from 2 to 10 nm is 500 to 8000 pieces/?m2.

Abstract: A valve spring which has an excellent fatigue limit is provided. A chemical composition of the valve spring according to the present embodiment contains, in mass %, C: 0.50 to 0.80%, Si: 1.20 to less than 2.50%, Mn: 0.25 to 1.00%, P: 0.020% or less. S: 0.020% or less: Cr: 0.40 to 1.90%, V: 0.05 to 0.60%, Ca: 0.0001 to 0.0050%, and N: 0.0100% or less, with the balance being Fe and impurities. In the valve spring, a number density of V-based precipitates having a maximum diameter ranging from 2 to 10 nm is 5000 to 80000 pieces/?m3, and a numerical proportion of Ca sulfides with respect to a total number of oxide-based inclusions and sulfide-based inclusions is 0.20% or less.

Abstract: A damper spring which has an excellent fatigue limit is provided. A chemical composition of the damper spring according to the present embodiment contains in mass %, C: 0.50 to 0.80%, Si: 1.20 to less than 2.50%, Mn: 0.25 to 1.00%, P: 0.020% or less, S: 0.020% or less, Cr: 0.40 to 1.90%, V: 0.05 to 0.60%, and N: 0.0100% or less, with the balance being Fe and impurities. In the damper spring, a number density of V-based precipitates having a maximum diameter ranging from 2 to 10 nm is 5000 to 80000 pieces/m3.

Abstract: A steel wire which has excellent cold coiling workability, and which has an excellent fatigue limit when made into a spring is provided. A chemical composition of the steel wire according to the present, embodiment containing, in mass %, C: 0.50 to 0.80%, Si: 1.20 to less than 2.50%, Mn: 0.25 to 1.00%, P: 0.020% or less, S: 0.020% or less, Cr: 0.40 to 1.90%, V: 0.05 to 0.60%, and N: 0.0100% or less, with the balance being Fe and impurities. In the steel wire, a number density of V-based precipitates having a maximum diameter ranging from 2 to 10 nm is 5000 to 80000 pieces/?m3.

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: 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 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 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: In the steel for a surface layer hardening which is treated with carburizing in a temperature range of 800° C. to 900° C., chemical composition thereof contains, by mass %, C: 0.10% to 0.60%, Si: 0.01% to 2.50%, Mn: 0.20% to 2.00%, S: 0.0001% to 0.10%, Cr: 2.00% to 5.00%, Al: 0.001% to 0.50%, N: 0.0020% to 0.020%, P: 0.001% to 0.050%, and O: 0.0001% to 0.0030%; the remaining portion thereof includes Fe and unavoidable impurities; and the total amount of Cr, Si, and Mn satisfies, by mass %, 2.0?Cr+Si+Mn?8.0.

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: The present invention provides a gear, continuously variable transmission, constant velocity joint, hub, or other steel part superior in surface fatigue strength compared with the past and method of production of the same, that is, provides a carbonitrided induction hardened steel part made of steel comprised of a specific composition of chemical ingredients and carbonitrided, then treated by induction hardening, the steel part characterized in that a surface N concentration is 0.1 to 0.8 mass %, a sum of an N concentration and C concentration is 1.0 to 2.0 mass %, an amount of surface residual austenite is less than 15 vol %, a depth of the incompletely hardened layer from the surface is less than 5 ?m, and a surface X-ray diffraction half width is 6.0 degrees or more, and a method of production of the same.

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: In the steel for a surface layer hardening which is treated with carburizing in a temperature range of 800° C. to 900° C., chemical composition thereof contains, by mass %, C: 0.10% to 0.60%, Si: 0.01% to 2.50%, Mn: 0.20% to 2.00%, S: 0.0001% to 0.10%, Cr: 2.00% to 5.00%, Al: 0.001% to 0.50%, N: 0.0020% to 0.020%, P: 0.001% to 0.050%, and O: 0.0001% to 0.0030%; the remaining portion thereof includes Fe and unavoidable impurities; and the total amount of Cr, Si, and Mn satisfies, by mass %, 2.0?Cr+Si+Mn?8.0.

Abstract: This invention provides a case-hardening steel excellent in cold forgeability and low carburization distortion property that exhibits low deformation resistance and high limit compressibility when cold, namely, a case-hardening steel excellent in cold forgeability and low carburization distortion property comprising, in mass %, C: 0.07% to 0.3%, Si: 0.01% to 0.15%, Mn: 0.1% to 0.7%, P: 0.03% or less, S: 0.002% to 0.10%, Al: 0.01% to 0.08%, Cr: 0.7% to 1.5%, Ti: 0.01% to 0.15%, B: 0.0005% to 0.005%, N: 0.008% or less, and the balance of Fe and unavoidable impurities, and having a metallographic structure comprising 65% or greater of ferrite and 15% or less of bainite.

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 gear, continuously variable transmission, constant velocity joint, hub, or other steel part superior in surface fatigue strength compared with the past and method of production of the same, that is, provides a carbonitrided induction hardened steel part made of steel comprised of a specific composition of chemical ingredients and carbonitrided, then treated by induction hardening, the steel part characterized in that a surface N concentration is 0.1 to 0.8 mass %, a sum of an N concentration and C concentration is 1.0 to 2.0 mass %, an amount of surface residual austenite is less than 15 vol %, a depth of the incompletely hardened layer from the surface is less than 5 ?m, and a surface X-ray diffraction half width is 6.0 degrees or more, and a method of production of the same.

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.