MANUFACTURE OF DUAL-PHASE HOT ROLLED HIGH TENSILE STRENGTH STEEL SHEET HAVING EXCELLENT SURFACE PROPERTIES AND WORKABILITY

摘要

PURPOSE:To obtain the steel sheet free from cloudy patterns and having excellent workability and tensile strength by subjecting a molten steel having specified compsn. of C, Si, Mn, P, S, H, Al and Fe to continuous casting and rolling under prescribed conditions and thereafter coiling it at a prescribed temp. CONSTITUTION:A steel constituted of, by weight, 0.03 to 0.15% C, 1.1 to 2% Si, 0.5 to 2% Mn, =0.025% P, =0.01% S, =0.0005% H, 0.005 to 0.1% Al and the balance Fe is refined. The molten steel is subjected to continuous casting at the casting temp. TD ( deg.C) shown by the inequality into a slab. Next, the slab is heated by a heating furnace to regulate the surface temp. to =1100 deg.C. At this time, the maximum surface temp. T ( deg.C) in the slab is controlled to =-2.75t+1420 [where the furnace remaining time at =T-60 ( deg.C) is denoted by t(min)]. In the subsequent hot rolling, descaliing is executed for one or more times, and the rolling is ended at 800 to 900 deg.C. Then, the slab is coiled at =250 deg.C.