| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing a steel by which sufficient toughness can be obtained in a high heat input weld zone of >350 kJ/cm. SOLUTION: A steel stock having a composition containing, by mass, 0.05 to 0.15% C, 0.05 to 0.50% Si, 1.0 to 2.0% Mn, <=0.015% P, <=0.0050% S, 0.005 to 0.06% Al, <=0.05% Nb, 0.006 to 0.02% Ti, 0.0035 to 0.0070% N, 0.0003 to 0.0020% B and 0.0005 to 0.0030% Ca, and in which Ca, O, S, B, N and Ti are contained also so as to satisfy the following equations (1) and (2), and the balance Fe with inevitable impurities is heated to 1,050 to 1,200 deg.C. After that, the stock is hot-rolled so that the cumulative draft in the temperature range of >=950 deg.C is controlled to >=30%, and the cumulative draft in the temperature range of <950 deg.C-40 to 70%, and is cooled at a cooling rate of >=2 deg.C/s by direct quenching or forced cooling.
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