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: Low-oxygen clean steel is provided containing C, Si, Mn, P, and S as chemical components, and further containing, by mass %, 0.005% to 0.20% of Al, greater than 0% to 0.0005% of Ca, 0.00005% to 0.0004% of REM, and greater than 0% to 0.003% of T.O, wherein the REM content, the Ca content, and the T.O content satisfy 0.15?REM/Ca?4.00 and Ca/T.O?0.50, nonmetallic inclusions which have a maximum predicted diameter of 1 ?m to 30 ?m measured using an extreme value statistical method under the condition in which a prediction area is 30,000 mm2, and contain Al2O3 and REM oxide are dispersed in the steel, an average proportion of the Al2O3 in the nonmetallic inclusions is greater than 50%, the REM is one or two or more of rare-earth elements La, Ce, Pr, and Nd, and the steel is Al-deoxidized steel or Al—Si-deoxidized steel.

Abstract: Low-oxygen clean steel is provided containing C, Si, Mn, P, and S as chemical components, and further containing, by mass %, 0.005% to 0.20% of Al, greater than 0% to 0.0005% of Ca, 0.00005% to 0.0004% of REM, and greater than 0% to 0.003% of T.O, wherein the REM content, the Ca content, and the T.O content satisfy 0.15?REM/Ca?4.00 and Ca/T.O?0.50, nonmetallic inclusions which have a maximum predicted diameter of 1 ?m to 30 ?m measured using an extreme value statistical method under the condition in which a prediction area is 30,000 mm2, and contain Al2O3 and REM oxide are dispersed in the steel, an average proportion of the Al2O3 in the nonmetallic inclusions is greater than 50%, the REM is one or two or more of rare-earth elements La, Ce, Pr, and Nd, and the steel is Al-deoxidized steel or Al—Si-deoxidized steel.