METHOD FOR PRODUCING SURFACE HARDENED STEEL

To provide a method for producing surface hardened steel capable of preventing grain coarsening during a carburizing treatment.SOLUTION: A surface hardened steel has a chemical composition comprising, in mass%, C: 0.10% or more and 0.30% or less, Si: 0.05% or more and 1.20% or less, Mn: 0.30% or more and 2.00% or less, P: 0.03% or less, S: 0.03% or less, Cu: 1.00% or less, Ni: 3.00% or less, Mo: 0.50% or less, Cr: 0.30% or more and 1.50% or less, Al: 0.030% or more and 0.060% or less, N: 0.015% or more and 0.030% or less, and Nb: 0.010% or more and 0.050% or less, with the balance being Fe and inevitable impurities. A method for producing the surface hardened steel comprises a step of preparing a steel material having an initial austenite grain size number of 9.0 or less, and a step of performing hot forging on a condition that a metallic structure after hot forging is composed of a ferrite structure and a pearlite structure and that the Z factor of the steel material is less than 1.0×1014S-1.SELECTED DRAWING: Figure 5 【課題】浸炭処理時の結晶粒粗大化を防止できる肌焼鋼の製造方法を提供する。【解決手段】質量％で、Ｃ：０．１０％以上０．３０％以下、Ｓｉ：０．０５％以上１．２０％以下、Ｍｎ：０．３０％以上２．００％以下、Ｐ：０．０３％以下、Ｓ：０．０３％以下、Ｃｕ：１．００％以下、Ｎｉ：３．００％以下、Ｍｏ：０．５０％以下、Ｃｒ：０．３０％以上１．５０％以下、Ａｌ：０．０３０％以上０．０６０％以下、Ｎ：０．０１５％以上０．０３０％以下、および、Ｎｂ：０．０１０％以上０．０５０％以下、を含み、残部がＦｅ及び不可避的不純物である化学組成を有し、初期オーステナイト結晶粒度番号が、９．０以下である鋼材を準備する工程と、熱間鍛造後の金属組織がフェライト組織とパーライト組織で構成され、前記鋼材に対して、Ｚ因子が１．０×１０１４Ｓ－１未満となる条件で熱間鍛造を行う工程と、を備える、肌焼鋼の製造方法。【選択図】図５