| 摘要 |
PURPOSE:To obtain a high-strength steel excellent in surface toughness, by carrying out rolling with specifying the finishing temp. of rolling as well as the maximum reduction shape ratio per pass at a specific temp. or below, hardening at a temp. of Ar3 point or above, and tempering at a temp. of Ac1 point or below at the time of hot-rolling a steel ingot in which Ti/N among principal components is particularly specified. CONSTITUTION:The steel ingot has a composition containing, by weight, 0.05-0.25% C, 0.03-0.75% Si, 0.30-1.80% Mn, 0.20-1.50% Cr, 0.05-0.75% Mo, 0.0003-0.0035% B, 0.003-0.075% Sol. Al, and <=0.0040% N and satisfying Ti/N=2.5-6.0. This steel ingot is treated so that, at the time of hot-rolling by heating up to 550-1,200 deg.C, the maximum reduction shape ratio per pass at <=900 deg.C defined by an equation is limited to <=3. Moreover, the above steel is rolled at the finishing temp. of rolling of 875-700 deg.C, hardened from the Ar3 point or above, and tempered at the Ac1 point or below. In this way, the titled high-strength steel, particularly a high-strength steel of 11T80-100 class excellent in surface toughness, can be obtained.
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