| 摘要 |
PROBLEM TO BE SOLVED: To provide non-refining steel for soft-nitriding which enables the production of forged parts in which a normalizing treatment after forging can be eliminated, and has the limit of strains at which a crack is generated on bending-straightening after soft-nitriding higher than the conventional one obtained from the S48C by a annealing treatment after forging and thereafter the soft-nitriding treatment, and which has high fatigue strength as well. SOLUTION: The non-heattreated steel for soft-nitriding has a composition containing, by weight, 0.2 to 0.6% C, 0.05 to 1.0% Si, 0.25 to 1.0% Mn, 0.03 to 0.2% S, <=0.2% Cr, <=0.045% s-Al, 0.002 to 0.010% Ti, 0.005 to 0.025% N and 0.001 to 0.005% O, and in which the conditions of 0.12×Ti%<O%<2.5×Ti% and 0.04×N%<O%<0.7×N% are satisfied, and the balance Fe with inevitable impurities. The steel has a mixed structure of ferrite and pearlite after hot forging.
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