Manufacturing method of steel materials, forged heat-treated products, and forged heat-treated products

摘要

It has high machinability, yield strength and fatigue strength, and excellent cracking property can be obtained. Steel material is mass%, C: 0.10 to 0.60%, Si: 0.05 to 1.00%, Mn: 0.30 to 1.50%, P: 0.1000% or less, S: 0 It is composed of 3000% or less, Al: 0.003 to 0.100%, N: 0.0200% or less, and the balance: Fe and impurities, and has a chemical composition satisfying the formula (1). Al2O3 is contained in an amount of more than 70.0% by mass, and the number density of inclusions having √AREA of 3 μm or more is 0.05 to 1.00 pieces / mm2. 9 ≦ 7.6√C × (1 + 0.6Si) × (1 + 4Mn) × (1-0.6S) × (1 + 0.3Cu) × (1 + 0.5Ni) × (1 + 2Cr) × (1 + 3Mo) × (1 + (1) .5 × (0.9-C) × fB)) ≦ 130 (1) The fB in equation (1) is “0” when the B content (mass%) is 0%, and when it exceeds 0%. It is "1".