| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel sheet having uniform nitriding hardening in the sheet thickness direction, excellent in weldability after nitriding and further having high strength and toughness, and to provide its producing method. SOLUTION: Steel having a composition containing, by mass, 0.02 to 0.1% C, <=0.1% Si, 0.6 to 1.5% Mn, <=0.1% P, <=0.02% S, 0.01 to 0.1% sol.Al and <=0.0050% N, further containing, at need, 0.003 to 0.02% Ti, and the balance substantially Fe with inevitable impurities is heated at 1,100 to 1,290 deg.C preferably directly or by reheating, is hot-rolled so as to control the finishing temperature to Ar3 to 890 deg.C, is rapidly cooled to 700 deg.C at the average cooling rate of 20 deg.C/sec preferably directly after that and is subsequently subjected to cold rolling and continuous annealing or batch annealing.
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