| 摘要 |
PURPOSE:To obtain a titled inexpensive hot-rolled steel plate with ease of operation and of good material quality by hot rolling steel contg. C, Si, Mn, S, sol.Al respectively at prescirbed ratios at prescribed finishing temp., cooling the same in two stages by specifying the respective temp. ranges and residence times and coiling the steel at temps. lower than specific values. CONSTITUTION:Steel contg., by weight, 0.03-0.10% C, <=0.90% Si, 0.80-1.70% Mn, <=0.015% S, and 0.05-0.25% sol.Al, and consisting of the balance substantially Fe is prepared. This steel is hot-rolled at the rolling finishing temp. (FT) in an Ar3-Ar3+80 deg.C range. The hot rolled steel is subjected to primary cooling above the Ar1 and secondary cooling below the Ar1 on the run-out table shown in the figure. In the primary cooling, the residence time in the Ar3-Ar1 2-phase region is set at 2-10sec and in the secondary cooling the cooling rate is set at >=50 deg.C/sec. The steel after the cooling is coiled at <=300 deg.C, whereby the intended hot-rolled steel plate having low yield ratio and high strength hot rolled steel plate is obtained. |
