| 摘要 |
PROBLEM TO BE SOLVED: To produce a soft-nitriding steel for structural purpose having good machinability and excellent fatigue strength and small in heat treating strains. SOLUTION: This soft-nitriding steel for structural purpose has a compsn. contg., by weight, 0.20 to 0.50% C, 0.03 to 0.50% Si, 0.30 to 3.00% Mn, 0.10 to 1.00% Cr, 0.03 to 1.00% Mo, 0.01 to 0.10% Al, 0.03 to 0.50% V, 0.015 to 0.070% S, 0 to 0.040% Pb, <=15ppm 0, and the balance Fe with inevitable impurities and is excellent in fatigue strength and machinability for use after being subjected to soft-nitriding treatment and shot peening after machining as-rolled, as-cast, as-normalized or the like, and satisfies the following two inequalities: the inequality I; 1.5S(%)+Pb(%) >= (9/10000)×objective stock hardness (HB)-0.22, where the objective stock hardness: 240 to 330 HB and the inequality II; 0.5S(%)+Pb(%)+40 oxygen(%) <= (8/10000)×objective core part hardness (HV)-0.11, where the objective core part hardness: 250 to 350HV.
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