| 摘要 |
PURPOSE:To obtain a high tension steel plate of 50kgf/mm<2> class for high heat input welding by regulating the composition of a steel and restricting the carbon equiv. CONSTITUTION:The composition of a steel is composed of, by weight, 0.03-0.12% C, 0.05-0.4% Si, 0.7-1.6% Mn, <0.015% P, <0.01% S, 0.01-0.06% acid-sol. Al, 0.005-0.02% Ti, 0.0003-0.0012% B, 0.004-0.006% N, <0.004% Ca and the balance Fe with inevitable impurities, the ratio of Ti/N in the composition is regulated to 1.5-3.4, and the carbon equiv. is restricted to <=0.34%. The steel is heated to 900-1,000 deg.C and hot rolled at >=40% total draft in the temp. range of 800-720 deg.C and at >=720 deg.C finishing temp. The hot rolled steel plate is rapidly cooled at once to room temp. and tempered at 200-400 deg.C.
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