| 摘要 |
PURPOSE: To produce a rolled steel material for welded structure, reduced in the width between the upper and the lower value of yield point. CONSTITUTION: A steel, having a composition consisting of, by weight, 0.01-0.20% C, 0.05-0.60% Si, 0.50-2.00% Mn, 0.010-0.100% Al, <=0.005% Nb, <=0.05% Mo, and the balance Fe with inevitable impurities and further containing, if necessary, one or more kinds among 0.05-1.00% Cu, 0.05-1.00% Ni, 0.05-1.00% Cr, 0.005-0.10% V, 0.005-0.020% Ti in the range satisfying Ti <=3.4×N+0.005, 0.0005-0.0050% Ca, 0.003-0.050% Zr, and 0.002-0.020% REM, is used. A slab of this steel is rolled by >=2 passes at <=1050 deg.C maximum temp. in the inner part of steel plate and at a draft of >=1.5 by logarithmic strain (ε) and then subjected to final rolling at >=820 deg.C maximum temp. in the inner part of steel plate and at a draft of >=0.20 by (ε), and further, the average draft in the final three passes is regulated to <=0.35.
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