[Object] To provide a steel sheet for carburizing that demonstrates improved extreme deformability prior to carburizing, and a method for manufacturing the same.

[Solution] A steel sheet consisting of, in mass %, C: more than or equal to 0.02%, and less than 0.30%, Si: more than or equal to 0.005%, and less than 0.5%, Mn: more than or equal to 0.01%, and less than 3.0%, P: less than or equal to 0.1%, S: less than or equal to 0.1%, sol. Al: more than or equal to 0.0002%, and less than or equal to 3.0%, N: less than or equal to 0.2%, and the balance: Fe and impurities, in which average value of X-ray random intensity ratio, assignable to an orientation group of ferrite crystal grain ranging from {100}<011> to {223}<110>, is 7.0 or smaller, average equivalent circle diameter of carbide is 5.0 m or smaller, percentage of number of carbides with an aspect ratio of 2.0 or smaller is 80% or larger relative to the total carbides, and percentage of number of carbides present in the ferrite crystal grain is 60% or larger relative to the total carbides.

One embodiment of the present invention provides: a high toughness high carbon cold rolled steel sheet having excellent formability comprising, by weight %, C: 0.80% to 1.25%, Mn: 0.2% to 0.6%, Si: 0.01% to 0.4%, P: 0.005% to 0.02%, S: 0.01% or less, Al: 0.01% to 0.1%, Cr: 0.01% to 1.0%, Sn: 0.05% to 0.5%, the remainder being Fe and other unavoidable impurities, in which a microstructure includes, by area %, retained austenite: 1% to 10%, martensite: 1% to 10%, ferrite: 5% or less (including 0%), the remainder being bainite, and has an average grain size of 3 m to 20 m, and an internal oxide layer formed directly below the surface has a thickness of 10 m or less; and a method for manufacturing same.

One embodiment of the present invention provides: a high toughness high carbon cold rolled steel sheet having excellent formability comprising, by weight %, C: 0.80% to 1.25%, Mn: 0.2% to 0.6%, Si: 0.01% to 0.4%, P: 0.005% to 0.02%, S: 0.01% or less, Al: 0.01% to 0.1%, Cr: 0.01% to 1.0%, Sn: 0.05% to 0.5%, the remainder being Fe and other unavoidable impurities, in which a microstructure includes, by area %, retained austenite: 1% to 10%, martensite: 1% to 10%, ferrite: 5% or less (including 0%), the remainder being bainite, and has an average grain size of 3 m to 20 m, and an internal oxide layer formed directly below the surface has a thickness of 10 m or less; and a method for manufacturing same.

Method of producing a tube of duplex stainless steel is disclosed. The steel comprises the following composition, in weight %: C max 0.03, Si max 1.0, Mn max 1.5, P max 0.05, S max 0.03, Cr 24-26, Ni 6-8, Mo 3.0-4.0, N 0.24-0.32. The method comprises steps of: forming a tube of the duplex stainless steel, cold working the tube obtained from the step of forming a tube, and soft annealing the tube after the step of cold working by subjecting the tube to a temperature, T, within a range of 500-750 C. for a time period, t, of 0.5-5 minutes.

Disclosed is super-high-strength tool steel having high impact toughness, including 0.7 to 0.9 wt % of C, 0.4 to 0.6 wt % of Si, 0.4 to 0.6 wt % of Mn, 7.0 to 9.0 wt % of Cr, 1.5 to 2.5 wt % of Mo, 1.0 wt % or less (excluding 0 wt %) of V, and at least one of 0.1 wt % or less (excluding 0 wt %) of Ti and 0.1 wt % or less (excluding 0 wt %) of Ce, with the remainder of Fe and inevitable impurities. The super-high-strength tool steel having high impact toughness includes at least one of Ti and Ce, thus reducing primary carbide content in an as-cast state and exhibiting improved impact toughness at a high hardness level after solution treatment and tempering. In addition, a method of manufacturing super-high-strength tool steel having improved impact toughness at a high hardness level is provided.

Disclosed is super-high-strength tool steel having high impact toughness, including 0.7 to 0.9 wt % of C, 0.4 to 0.6 wt % of Si, 0.4 to 0.6 wt % of Mn, 7.0 to 9.0 wt % of Cr, 1.5 to 2.5 wt % of Mo, 1.0 wt % or less (excluding 0 wt %) of V, and at least one of 0.1 wt % or less (excluding 0 wt %) of Ti and 0.1 wt % or less (excluding 0 wt %) of Ce, with the remainder of Fe and inevitable impurities. The super-high-strength tool steel having high impact toughness includes at least one of Ti and Ce, thus reducing primary carbide content in an as-cast state and exhibiting improved impact toughness at a high hardness level after solution treatment and tempering. In addition, a method of manufacturing super-high-strength tool steel having improved impact toughness at a high hardness level is provided.

A rolled wire rod for spring steel contains, as a chemical composition, by mass %: C: 0.42% to 0.60%; Si: 0.90% to 3.00%; Mn: 0.10% to 1.50%; Cr: 0.10% to 1.50%; B: 0.0010% to 0.0060%; N: 0.0010% to 0.0070%; Mo: 0% to 1.00%; V: 0% to 1.00%; Ni: 0% to 1.00%; Cu: 0% to 0.50%; Al: 0% to 0.100%; Ti: 0% to 0.100%; Nb: 0% to 0.100%; P: limited to less than 0.020%; S: limited to less than 0.020%; and a remainder including Fe and impurities, the carbon equivalent (Ceq) is 0.75% to 1.00%, the area fraction of tempered martensite and bainite included in a microstructure is 90% or greater, the tensile strength is 1,350 MPa or less, and the reduction of area is 40% or greater.

There is provided a high-strength steel sheet and a method for producing the same. The high-strength steel sheet has a specified chemical composition and a steel microstructure including, by area fraction, 75.0% or more tempered martensite, 1.0% or more and 20.0% or less fresh martensite, and 5.0% or more and 20.0% or less retained austenite. A hardness ratio of the fresh martensite to the tempered martensite is 1.5 or more and 3.0 or less, the ratio of the maximum KAM value in the tempered martensite in the vicinity of the heterophase interface between the tempered martensite and the fresh martensite to the average KAM value in the tempered martensite is 1.5 or more and 30.0 or less, and the average of ratios of grain sizes of prior austenite grains in the rolling direction to those in the thickness direction is 2.0 or less.

A steel contains, in a chemical composition, C, Si, Mn, and Al, and contains pearlite as a metallographic structure, and a value obtained by dividing an Mn content in a cementite in the pearlite in terms of at % by an Mn content in a ferrite in the pearlite in terms of at % is higher than 0 and equal to or lower than 5.0.

A steel contains, in a chemical composition, C, Si, Mn, and Al, and contains pearlite as a metallographic structure, and a value obtained by dividing an Mn content in a cementite in the pearlite in terms of at % by an Mn content in a ferrite in the pearlite in terms of at % is higher than 0 and equal to or lower than 5.0.