Abstract: A steel according to an aspect of the present invention includes, as a chemical composition, by unit mass %, C: 0.15% to 0.40%, Mn: 0.10% to 1.50%, S: 0.002% to 0.020%, Ti: 0.005% to 0.050%, B: 0.0005% to 0.0050%, Bi: 0.0010% to 0.0100%, P: 0.020% or less, N: 0.0100% or less, Si: 0% or more and less than 0.30%, Cr: 0% to 1.50%, Al: 0% to 0.050%, Mo: 0% to 0.20%, Cu: 0% to 0.20%, Ni: 0% to 0.20%, Nb: 0% to 0.030%, and a remainder including Fe and impurities.

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: In this steel component, the concentration of C in a surface layer is 0.85 mass % or more to 1.2 mass % or less, which is higher than the concentration of C in a starting material steel, the surface layer has a volume ratio of a retained-austenite structure higher than 0% and lower than 10%, the remainder of the surface layer is a martensitic structure, the area fraction of grain boundary carbides in the surface layer is lower than 2%, a layer inside the surface layer is higher than the surface layer in a volume ratio of a retained-austenite structure, and in the layer inside the surface layer, the remainder is a martensitic structure.

Abstract: A production method of a carburized steel, which improves a gas carburizing property of a steel having a high Si content and suppress deterioration of productivity, includes preliminary and main gas carburizing processes. In the preliminary gas carburizing process, a steel having a chemical composition that contains C, Si, Mn, and Cr and, in mass %, satisfies Formula (1) is subjected to a gas carburizing treatment at a carburizing temperature Tp° C. that satisfies Formula (A) for 10 minutes to less than 20 hours. In the main gas carburizing process, a gas carburizing treatment is performed at a carburizing temperature Tr(° C.) that satisfies Formula (B) for a carburizing time tr minutes. 6.5<3.5[Si %]+[Mn %]+3[Cr %]?18??(1) 800?Tp<163×ln(CP+0.6)?41×ln(3.5×[Si %]+[Mn %]+3×[Cr %])+950??(A) 4<13340/(Tr+273.15)?ln(tr)<7??(B) Where, CP in the formula is substituted by a carbon potential during carburization in the preliminary carburizing process.

Abstract: Steel for nitrocarburizing includes, by mass %, C: 0% to less than 0.15%; Si: 0.01% to 1.00%; Mn: 0.01% to 1.00%; S: 0.0001% to 0.050%; Al: 0.0001% to 0.050%; Ti: more than 0.50% to 1.50%; N: 0.0005% to 0.0100%; and the balance consisting of Fe and inevitable impurities, in which P is limited to 0.050% or less; O is limited to 0.0060% or less; and the amount of Ti [Ti %], the amount of C [C %], the amount of N [N %], and the amount of S [S %] satisfy 0.48<[Ti %]?47.9×([C %]/12+[N %]/14+[S %]/32)?1.20.

Abstract: A steel according to an aspect of the present invention has a chemical composition within a predetermined range, in which a hardenability index Ceq ranges from greater than 7.5 to smaller than 44.0, a metallographic structure includes ferrite ranging from 85 to 100 area %, an average distance between sulfides, which are observed in a cross section parallel to a rolling direction of the steel and have an equivalent circle diameter ranging from 1 ?m or greater to smaller than 2 ?m, is shorter than 30.0 ?m, and a presence density of the sulfides, which are observed in the cross section parallel to the rolling direction of the steel and have an equivalent circle diameter ranging from 1 ?m or greater to smaller than 2 ?m, is 300 pieces/mm2 or more.

Abstract: The present invention adopts a hot rolled bar or hot rolled wire rod including a chemical composition including, by mass %, C: 0.05 to 0.30%, Si: 0.30 to 0.60%, Mn: 0.40 to 1.0%, S: 0.008 to less than 0.040%, Cr: 1.60 to 2.00%, Mo: 0.1% or less, Al: 0.025 to 0.05%, N: 0.010 to 0.025%, Ti: 0.003% or less, Bi: 0.0001 to 0.0050%, and a remainder including Fe and impurities, in which amounts of P and O in the impurities are respectively P: 0.025% or less and O: 0.002% or less; in which a microstructure includes ferrite-pearlite or ferrite-pearlite-bainite, and an Expression (1) is satisfied. 1.70?Cr+2×Mo?2.

Abstract: A steel according to an aspect of the present invention has a chemical composition within a predetermined range, in which a hardenability index Ceq ranges from greater than 7.5 to smaller than 44.0, an AlN precipitation index IAlN ranges from greater than 0.00030 to smaller than 0.00110, a metallographic structure includes ferrite ranging from 85 to 100 area %, an average distance between sulfides, which are observed in a cross section parallel to a rolling direction of the steel and have an equivalent circle diameter ranging from 1 ?m or greater to smaller than 2 ?m, is shorter than 30.0 ?m, and a presence density of the sulfides, which are observed in the cross section parallel to the rolling direction of the steel and have an equivalent circle diameter ranging from 1 ?m or greater to smaller than 2 ?m, is 300 pieces/mm2 or more.

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: There is provided a hot forging steel including, by mass %, C: more than 0.30% and less than 0.60%, Si: 0.10% to 0.90%, Mn: 0.50% to 2.00%, S: 0.010% to 0.100%, Cr: 0.01% to 1.00%, Al: more than 0.005% and 0.100% or less, N: 0.0030% to 0.0200%, Bi: more than 0.0001% and 0.0050% or less, Ti: 0% or more and less than 0.040%, V: 0% to 0.30%, Ca: 0% to 0.0040%, Pb: 0% to 0.40%, and a remainder including Fe and impurities, in which P and O in the impurities are respectively P: 0.050% or less and O: 0.0050% or less, an expression d+3?<20 is satisfied, and a presence density of MnS having an equivalent circle diameter of smaller than 2.0 ?m is 300 pieces/mm2 or more in a cross section parallel to a rolling direction of a steel.

Abstract: Steel for a suspension spring including, as a chemical composition, by % by mass: C: more than 0.40% and 0.65% or less; Si: 1.00% to 3.50%; Mn: more than 2.00% and 3.00% or less; Cr: 0.01% to 2.00%; V: 0.02% to 0.50%; P: 0.020% or less; S: 0.020% or less: N: 0.0100% or less; and a remainder of Fe and impurities, in which Kf is 280 or more, in which a structure contains a tempered martensite of which an area ratio is 90% or more, in which a Fe-based carbide precipitated in the tempered martensite is a cementite, and in which an average of an area ratios of prior austenite grains which stretch in a longitudinal direction of the steel and of which an aspect ratio exceeds 3.0, is 80% or more in a case of depths of 0.1 mm, 0.2 mm, and 0.3 mm in a sheet thickness direction from a surface of the steel.

Abstract: A non-heat treated steel according to the present invention includes, as steel composition, by mass %, 0.20 to 0.60% of C, 0.50 to 2.0% of Si, 0.20 to 2.0% of Mn, 0.010 to 0.15% of P, 0.010 to 0.15% of S, 0.10 to 0.50% of V. 0.002 to 0.02% of N, and a balance consisting of Fe and impurities, in which, when a ratio of a maximum value of a V content in the steel to an average value of the V content in the steel in a cross section of the steel is defined as a segregation ratio of V, the segregation ratio of V is 1.0 or more and less than 3.0.

Abstract: Spring steel includes: as a chemical composition, by mass %, C: 0.40% to 0.60%, Si: 0.90% to 2.50%, Mn: 0.20% to 1.20%, Cr: 0.15% to 2.00%, Ni: 0.10% to 1.00%, Ti: 0.030% to 0.100%, B: 0.0010% to 0.0060%, N: 0.0010% to 0.0070%, Cu: 0% to 0.50%, Mo: 0% to 1.00%, V: 0% to 0.50%, Nb: 0% to 0.10%, P: limited to less than 0.020%, S: limited to less than 0.020%, Al: limited to less than 0.050%, and a remainder including Fe and impurities, in a case where [Ti] represents a Ti content and [N] represents a N content by mass %, the chemical composition satisfies ([Ti]-3.43×[N])>0.03, and a total number density of a Ti carbide and a Ti carbonitride having a diameter of 5 nm to 100 nm is more than 50 piece/?m3.

Abstract: A case-hardened steel component includes a base metal and a carburized layer, the base metal has a predetermined chemical composition, a number density of Ti-based precipitates having an equivalent circle diameter of 5 to 50 nm in a surface region from a surface to a depth of 0.1 mm is 0.5 pieces/?m2 or more, and in the surface region, a number density of AlN having an equivalent circle diameter of 50 nm or more and 100 nm or less is 0.5 pieces/?m2 or less.

Abstract: A steel for an induction hardening including, by mass %, C: more than 0.75% to 1.20%, Si: 0.002 to 3.00%, Mn: 0.20 to 2.00%, S: 0.002 to 0.100%, Al: more than 0.050% to 3.00%. P: limited to 0.050% or less, N: limited to 0.0200% or less, O: limited to: 0.0030% or less, and the balance composing of iron and unavoidable impurities, wherein an Al content and a N content satisfy, by mass %, Al?(27/14)×N>0.050%.

Abstract: A steel for a carburizing and a carburized steel component having a steel portion and a carburized layer with a thickness of more than 0.4 mm to less than 2 mm which is formed on an outside of the steel portion. A chemical composition of the steel for the carburizing and the steel portion of the carburized steel component satisfies simultaneously equations of a hardness parameter, a hardenability parameter, and a TiC precipitation parameter.

Abstract: A steel for a carburizing and a carburized steel component having a steel portion and a carburized layer with a thickness of more than 0.4 mm to less than 2 mm which is formed on an outside of the steel portion. A chemical composition of the steel for the carburizing and the steel portion of the carburized steel component satisfies simultaneously equations of a hardness parameter, a hardenability parameter, and an AlN precipitation parameter.

Abstract: A steel for a carburizing and a carburized steel component having a steel portion and a carburized layer with a thickness of more than 0.4 mm to less than 2 mm which is formed on an outside of the steel portion. A chemical composition of the steel for the carburizing and the steel portion of the carburized steel component satisfies simultaneously equations of a hardness parameter, a hardenability parameter, and a TiC precipitation parameter.

Abstract: A steel for a carburizing and a carburized steel component having a steel portion and a carburized layer with a thickness of more than 0.4 mm to less than 2 mm which is formed on an outside of the steel portion. A chemical composition of the steel for the carburizing and the steel portion of the carburized steel component satisfies simultaneously equations of a hardness parameter, a hardenability parameter, and an AlN precipitation parameter.

Abstract: The present invention provides a spring steel, which is finally formed into a spring, by making use of, at a maximum, the temper softening resistance effect due to alloying elements while suppressing the formation of hard inclusions of SiO2 and the generation of decarburization, which may cause deterioration of fatigue characteristics of the spring. The spring steel is characterized by comprising, in % by mass, C: 0.50 to 0.70%, Si: 1.00 to 5.00%, Mn: 0.30 to 2.00%, P: 0.0002 to 0.0500%, S: 0.0002 to 0.0500%, Cr: 0.10 to 3.50%, Al: 0.0005 to 0.0500%, and N: 0.0020 to 0.0100%, with the balance being Fe and inevitable impurities, wherein the H-value defined by the following equation (a) is 160 or more, and the C-value defined by the following equation (b) is 3.25 or less: H=33.6[C]+10.0[Si]+5.95[Mn]+11.1[Cr]+90.0??(a), and C=[Si]/[Mn]??(b).