| 摘要 |
PURPOSE:To ensure base wetal strength, to lower preheating temp. for welding, and to improve toughness at large heat input welded zone, by using Cr together with B or V, further adding Ti, rare earth element or Ca in low C and extremely thick steel plate for boiler, etc. CONSTITUTION:Extremely thick steel plate is composed of, by weight %, 0.12-0.22 C, <=0.40 Si, 0.8-1.50 Mn, 0.01-0.10 Al, 0.4-0.8 Cr, 0.1-0.3 Mo, further 0.03-0.1 V, and or 0.0003-0.0015 B, if necessary <=0.5 Cu and or <=0.5 Ni, further >= one kind among 0.002-0.020 Ti, 0.003-0.050 rare earth element, 0.0001-0.0100 Ca, and the balance Fe, under <=0.33%PCM value prescribed by a formula. The steel plate is superior in weldability and toughness at large heat input weld zone, in extremely thick steel plate having the thickness in which average cooling rate at center part in plate thickness between 800-400 deg.C is <=10 deg.C/min especially at normalizing time.
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