| 摘要 |
PROBLEM TO BE SOLVED: To provide a thin steel sheet which has excellent impact characteristics after quenching and little variation of properties depending on quenching conditions. SOLUTION: The thin steel sheet having excellent impact characteristics after quenching has a composition containing, by mass, 0.10 to 0.37% C, <=1.0% Si, <=2.5% Mn, <=0.10% P, <=0.03% S, 0.01 to 0.10% sol.Al, 0.0005 to 0.0050% N, 0.005 to 0.05% Ti and 0.0003 to 0.0050% B, or further containing one or more kinds selected from Ni, Cr and Mo by <=1.0% in total, and satisfying B (10.8/14)N*>=0.0005% (N*=N-(14/48)Ti; wherein, in the case of the right side <=0, N*=0). The average grain size of TiN as precipitates in the steel is 0.06 to 0.30μm, and also, the old austenite grain size after quenching is 2 to 25μm.
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