PRODUCTION OF HOT ROLLED HIGH TENSILE STEEL PLATE OR HIGH FORMING PROPERTY

摘要

PURPOSE:To obtain a high tensile steel plate of low yield ratios having excellent balance of strength and ductility by desirable combinations of controlling the austenite grain sizes in the stage of hot rolling adequately and controlling cooling conditions after the end of finish rolling. CONSTITUTION:The steel contg. 0.05-0.15% C, 0.4-1.5% Si, 1.0-2.5% Mn, =0.005% S, and, if necessary, =1 kind of =0.5% Cr, and =0.3% Mo is prepared as a blank material. In the stage of hot rolling of this steel, it is screwed down to =40% total drafts in a temp. region of =35mum austenite grain aizes at = 880 deg.C and is finished at =Ar3 point. The steel plate after the finishing is cooled quickly to the Ar3 point - (Ar3-100) deg.C within 2 seconds and is held at around these temp. for 1sec, after which it is cooled quickly down to =40 deg.C/S cooling rates. The coiling temp. of this time is kept at =250 deg.C. As a result, the hot rolled high tensile steel plate of high forming property is obtained stably and accurately.