| 摘要 |
PURPOSE:To obtain a steel plate excellent in sour-resistant properties, strength and toughness by heating a steel of specific composition to a specific temperature and hot rolling, cooling and naturally cooling it under the specific conditions to form it into a fine bainite structure uniform in its thickness direction. CONSTITUTION:A steel is heated up to 1000-1200 deg.C, which consists of by weight %, as the basic components 0.02-0.15 C, 0.1-0.6 Si, 0.5-1.5 Mn, <=0.0015 P, <=0.01 S, 0.005-0.1 Al, 0.005-0.025 Ti, and one or more kinds of the following groups <=0.1 Nb, <=0.005B, <=1.0 Ni, <=1.0 Cu, <=1.25 Cr, <=0.005 Ca, and the balance Fe with inevitable impurities. The steel is rolled thereafter under the draft of >=60% at <=850 deg.C and at the finishing temperature of >=Ar3 transformation point. Next, the steel is cooled at a cooling speed of >=30 deg.C/sec. from the temperature of >=Ar3 transformation point to the temperature range of 350-550 deg.C and then cooled naturally. In this way, a steel plate excellent in sour-resistant properties having the fine bainite structure uniform in the plate- thickness direction is obtained.
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