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, 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, 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 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: The chemical composition of a steel material according to the present embodiment consists of, in mass %, C: 0.50 to 0.80%, Si: 1.20 to 2.90%, Mn: 0.25 to 1.00%, Cr: 0.40 to 1.90%, V: 0.05 to 0.60%, P: 0.020% or less, S: 0.020% or less, N: 0.0100% or less, Mo: 0 to 0.50%, Nb: 0 to 0.050%, W: 0 to 0.60%, Ni: 0 to 0.50%, Co: 0 to 0.30%, B: 0 to 0.0050%, Cu: 0 to 0.050%, Al: 0 to 0.0050%, and Ti: 0 to 0.050%, with the balance being Fe and impurities. In the microstructure of the steel material, an area fraction of pearlite is 90% or more, and in ferrite in the pearlite, a volumetric number density of V-based precipitates having a maximum diameter of 2 to 20 nm is 3000 to 80000 pieces/?m3.

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 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: 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: There is provided a hot rolled steel according to one aspect of the invention including, as a predetermined chemical composition: Bi: 0.0001 mass % to 0.0050 mass %, in which 90 area % or more of a metallographic structure is configured with a ferrite and a pearlite, and an average number density of Mn sulfides measured on a cross section parallel to a rolling direction having an aspect ratio of more than 10 and 30 or less which is extended along the rolling direction, is 50 pieces/mm2 to 200 pieces/mm2.

Abstract: A steel according to one aspect of the present invention has a chemical composition containing, by unit mass %, C: 0.25 to 0.55%, Si: 0.20 to 1.30%, Mn: 0.50 to 1.50%, P: 0.010 to 0.200%, S: 0.010 to 0.100%, Cr: 0 to 1.20%, V: 0.25 to 0.40%, Ti: 0.010 to 0.070%, Mo: 0 to 0.15%, N: 0.0010 to 0.0060%, Al: 0 to 0.200%, Ca: 0 to 0.005%, Zr: 0 to 0.005%, Mg: 0 to 0.005%, Bi: 0 to 0.0050%, Pb: 0 to 0.50%, Nb: 0 to 0.05%, Cu: 0 to 0.05%, and Ni: 0 to 0.05%, with the balance being Fe and impurities, wherein 0.002<Ti?3.4×N<0.050 is satisfied.

Abstract: A spring steel wire includes, by mass %, C: 0.40% to 0.75%, Si: 1.00% to 5.00%, Mn: 0.20% to 2.00%, P: 0.0001% to 0.0500%, S: 0.0001% to 0.0500%, Cr: 0.50% to 3.50%, Al: 0.0005% to 0.0500%, N: 0.0020% to 0.0100%, Mo: 0% to 2.00%, V: 0% to 0.50%, W: 0% to 0.50%, Nb: 0% to 0.100%, Ti: 0% to 0.100%, Ca: 0% to 0.0100%, Mg: 0% to 0.0100%, Zr: 0% to 0.1000%, B: 0% to 0.0100%, Cu: 0% to 1.00%, Ni: 0% to 3.00%, and a remainder consisting of Fe and impurities. A structure includes, by area radio, tempered martensite of 90% or more. The prior austenite grain size number is No. 12.5 or higher. The presence density of iron-based carbide having an equivalent circle diameter ranging from 0.15 ?m to 0.50 ?m ranges from 0.40 pieces/?m2 to 2.00 pieces/?m2.

Abstract: According to an aspect of the present invention, there is provided a steel containing, by unit mass %, C: 0.08% to 0.12%, Si: 0.05% to 0.50%, Mn: 1.50% to 3.00%, P: 0.040% or less, S: 0.020% or less, V: 0.010% or less, Ti: 0.010% or less, Nb: 0.005% or less, Cr: 1.00% to 2.50%, Cu: 0.01% to 0.50%, Ni: 0.75% to 1.60%, Mo: 0.10% to 0.50%, Al: 0.025% to 0.050%, N: 0.0100% to 0.0200%, Ca: 0% to 0.0100%, Zr: 0% to 0.0100%, Mg: 0% to 0.0100%, and a remainder including Fe and impurities, in which a ratio of an Al content to a N content is 2.6 or less, a ratio of a Mn content to a Ni content is 1.5 or more and 3.0 or less.

Abstract: There is a hot-rolled steel according to one aspect of the invention including predetermined chemical compositions including 0.0001 to 0.0050 mass % of Bi, in which 90 area % or more of a metallographic structure is configured with a ferrite and a pearlite, and an average number density of Mn sulfides extending along a rolling direction and having an aspect ratio exceeding 10 and equal to or smaller than 30, which is measured on a cross section parallel to the rolling direction, is 50 to 200 number/mm2.

Abstract: A rolled steel bar for machine structural use includes a predetermined chemical composition comprising, by mass %, C: 0.45% to 0.65%, Si: higher than 1.00% to 1.50%, Mn: higher than 0.40% to 1.00%, P: 0.005% to 0.050%, S: 0.020% to 0.100%, V: 0.08% to 0.20%, Ti: 0% to 0.050%; Ca: 0% to 0.0030%, Zr: 0% to 0.0030%, Te: 0% to 0.0030%, and a remainder including Fe and impurities, wherein the impurities include: Cr: 0.10% or lower, Al: lower than 0.01%, and N: 0.0060% or lower. In the rolled steel bar for machine structural use, K1 obtained from “K1=C+Si/7+Mn/5+1.54×V” is 0.95 to 1.05, K2 obtained from “K2=139?28.6×Si+105×Mn?833×S?13420×N” is more than 35, a Mn content and a S content satisfy Mn/S?8.0, and a total decarburized depth of a surface layer is 500 ?m or less.

Abstract: A rolled steel bar for machine structural use includes a predetermined chemical composition comprising, by mass %, C: 0.45% to 0.65%, Si: higher than 1.00% to 1.50%, Mn: higher than 0.40% to 1.00%, P: 0.005% to 0.050%, S: 0.020% to 0.100%, V: 0.08% to 0.20%, Ti: 0% to 0.050%; Ca: 0% to 0.0030%, Zr: 0% to 0.0030%, Te: 0% to 0.0030%, and a remainder including Fe and impurities, wherein the impurities include: Cr: 0.10% or lower, Al: lower than 0.01%, and N: 0.0060% or lower. In the rolled steel bar for machine structural use, K1 obtained from “K1=C+Si/7+Mn/5+1.54×V” is 0.95 to 1.05, K2 obtained from “K2=139?28.6×Si+105×Mn?833×S?13420×N” is more than 35, K3 obtained from “K3=137×C?44.0×Si” is 10.7 or more, a Mn content and a S content satisfy Mn/S?8.0, and a total decarburized depth in a surface layer is 500 ?m or less.

Abstract: According to an aspect of the present invention, there is provided a steel containing, by mass %, C: 0.08% to 0.12%, Si: 0.05% to 0.50%, Mn: 1.00% to 3.00%, P: 0.040% or less, S: 0.020% or less, Cr: 1.0% to 2.5%, Cu: 0.01% to 0.50%, Ni: 0.75% to 3.20%, Mo: 0.10% to 0.50%, Nb: 0.005% to 0.050%, Al: 0.010% to 0.100%, N: 0.0050% to 0.0150%, V: 0% to 0.300%, Ca: 0% to 0.0100%, Zr: 0% to 0.0100%, Mg: 0% to 0.0100%, and a remainder including Fe and impurities, in which a number density of Mn sulfides having an equivalent circle diameter of more than 5 m is 0 pieces/mm2 to 10 pieces/mm2, and an average aspect ratio of the Mn sulfides having an equivalent circle diameter of 1.0 m to 5.0 ?m is 1.0 or more and 10.0 or less.

Abstract: A steel according to one aspect of the present invention contains, in unit mass %, C: 0.10% to 0.25%, Si: 0.60% to 1.20%, Mn: 0.60% to 1.00%, P: 0.040% to 0.060%, S: 0.060% to 0.100%, Cr: 0.05% to 0.20%, Bi: 0.0001% to 0.0050%, N: 0.0020% to 0.0150%, V: 0% to 0.010%, Al: 0% to 0.0050%, Ti: 0% to 0.020%, Ca: 0% to 0.005%, Zr: 0% to 0.005%, Mg: 0% to 0.005%, and a remainder including Fe and impurities.

Abstract: This steel component includes, by mass %, C: 0.50% to 0.65%, Si: 0.60% to 1.20%, Mn: 0.60% to 1.00%, P: 0.040% to 0.060%, S: 0.060% to 0.100%, Cr: 0.05% to 0.20%, V: 0.25% to 0.40%, Bi: 0.0001% to 0.0050%, N: 0.0020% to 0.0080%, and a remainder including Fe and impurities, in which a steel structure is a ferrite-pearlite, and an area ratio of a ferrite therein is 20% or more.