METHOD FOR PRODUCING CONTINUOUS-CAST SLAB AND HIGH-TENSION HOT ROLLED STEEL PLATE, HIGH-TENSION COLD ROLLED STEEL SHEET, AND HIGH-TENSION GALVANIZED STEEL SHEET

摘要

PROBLEM TO BE SOLVED: To produce a continuous-cast slab as a blank for high-tension steel sheet having ≥590 MPa tensile strength with high productivity without causing surface cracking.;SOLUTION: Molten steel composed of, by mass%, 0.03-0.10% C, ≤1.0% Si, 0.5-3.0% Mn, ≤0.1% P, ≤0.02% S, ≤0.2% Al, ≤0.006% N, where (14/27)×(%Al/%N) is equal to or less than 50, and the balance Fe with inevitable impurities, is cast at casting speed (Vc:m/min) satisfying following formula (1) regulated by Al content and N content and also, a secondary cooling zone is spray-cooled with specific water flow-rate (Q:L/kg) satisfying following formula (2) regulated by a casting speed (Vc). Where, 1.5≤Vc≤4.0-0.68×log[(14/27)×(%Al/%N)]...(1), and 1.0≤Q≤2.5+Vc/1.5...(2).;COPYRIGHT: (C)2007,JPO&INPIT