Abstract: A non-heat treated steel for induction hardening contains, in mass %, C: 0.35 to 0.44%, Si: 0.01 to less than 0.30%, Mn: 0.80 to 1.50%, P: 0.030% or less, S: more than 0.010 to 0.095%, Cr: more than 0.10 to 0.30%, V: 0.050 to 0.200%, N: 0.0040 to 0.0200%, O: 0.0024% or less, Cu: 0.05% or less and Ni: 0.05% or less, and for which fn1?50.0, fn2: 0.70 to 1.00, and fn3?1.30. In the steel, a ratio of a number of Mn oxides containing oxygen in an amount of 20.0 mass % or more and Mn in an amount of 10.0 mass % or more to the number of oxides is 10.0% or less fn1=80C2+55C+13Si+4.8Mn+30P+30S+1.5Cr fn2=C+(Si/10)+(Mn/5)?(5S/7)+(5Cr/22)+1.65V fn3=?2C—Si+2.33Mn+0.26Cr+V?1.5Cu?1.5Ni.

Abstract: A non-heat treated steel for induction hardening contains, in mass %, C: 0.35 to 0.44%, Si: 0.01 to less than 0.30%, Mn: 0.80 to 1.50%, P: 0.030% or less, S: more than 0.010 to 0.095%, Cr: more than 0.10 to 0.30%, V: 0.050 to 0.200%, N: 0.0040 to 0.0200%, O: 0.0024% or less, Cu: 0.05% or less and Ni: 0.05% or less, and for which fn1?50.0, fn2: 0.70 to 1.00, and fn3?1.30. In the steel, a ratio of a number of Mn oxides containing oxygen in an amount of 20.0 mass % or more and Mn in an amount of 10.0 mass % or more to the number of oxides is 10.0% or less. fn1=80C2+55C+13Si+4.8Mn+30P+30S+1.5Cr fn2=C+(Si/10)+(Mn/5)?(5S/7)+(5Cr/22)+1.65V fn3=?2C—Si+2.33Mn+0.26Cr+V?1.5Cu?1.

Abstract: Provided is a non-thermal refined soft-nitrided component including chemical composition of a steel material of a base metal containing: in mass %, C: 0.25 to 0.40%; Si: 0.10 to 0.35%; Mn: more than 2.0% to 2.8% or less; N: 0.0030 to 0.0250%; Cu: 0 to 1.0%; Mo: 0 to 0.3%; Ni: 0 to 0.5%; Ti: 0 to 0.020%; and a balance being Fe and impurities, the impurities including P: 0.08% or less; S: 0.10% or less; Al: 0.05% or less; and Cr: less than 0.20%, wherein a Vickers hardness at a position of 0.05 mm from the surface is 400 to 480, a Vickers hardness at a position of 1.0 mm from the surface is 200 or more, and a compound-layer depth at a stress concentrated region is 5 ?m or less. This non-thermal refined soft-nitrided component has an excellent bending straightening property and a high fatigue strength.

Abstract: A non-thermal refined nitrocarburized component with excellent bending straightening and fatigue strength, includes a base metal steel material having a composition consisting of: (mass %), C: 0.35 to 0.50%; Si: 0.10 to 0.35%; Mn: 2.3 to 2.8%; S: 0.01% or less; N: 0.0030 to 0.0250%; Cu: 0 to 1.0%; Mo: 0 to 0.3%; Ni: 0 to 0.5%; Ti: 0 to 0.020%, the balance: Fe, impurities, and 3.10 £ (0.316 C+0.122)·(0.7 Si+1)·(5.1 Mn?1.12)·(0.364 Ni+1)·(2.16 Cr+1)·(3 Mo+1) £ 6.00. Impurities include P: 0.08% or less, Al: 0.05% or less, and Cr: less than 0.20%. In a stress concentrated region, an HV hardness 0.05 mm from a surface is 410 to 480, an HV hardness 1.0 mm from the surface is 200 or more, a compound-layer depth is 5 mm or less, and a base metal micro-structure is bainite.

Abstract: Provided is a non-thermal refined soft-nitrided component including chemical composition of a steel material of a base metal containing: in mass %, C: 0.25 to 0.40%; Si: 0.10 to 0.35%; Mn: more than 2.0% to 2.8% or less; N: 0.0030 to 0.0250%; Cu: 0 to 1.0%; Mo: 0 to 0.3%; Ni: 0 to 0.5%; Ti: 0 to 0.020%; and a balance being Fe and impurities, the impurities including P: 0.08% or less; S: 0.10% or less; Al: 0.05% or less; and Cr: less than 0 20%, wherein a Vickers hardness at a position of 0.05 mm from the surface is 400 to 480, a Vickers hardness at a position of 1.0 mm from the surface is 200 or more, and a compound-layer depth at a stress concentrated region is 5 ?m or less. This non-thermal refined soft-nitrided component has an excellent bending straightening property and a high fatigue strength.