HIGH STRENGTH HOT ROLLED STEEL PLATE EXCELLENT IN UPSET BUTT WELDABILITY AND FORMABILITY, PRODUCED BY CONTINUOUS HOT ROLLING PROCESS, AND ITS PRODUCTION

摘要

PROBLEM TO BE SOLVED: To secure the uniformity of material in the same coil by producing a steel plate of specific composition by a continuous hot rolling process and providing specific properties. ;SOLUTION: The composition of the steel plate is regulated so that it consists of, by weight, 0.07-0.12% C, 0.1-0.6% Si, 2.0-2.5% Mn, ≤0.02% P, ≤0.01% S, 0.004-0.05% Al, 0.025-0.06% Nb, 0.10-0.15% Ti, and the balance Fe with inevitable impurities. The steel is heated to ≥1230°C, and, in the continuous hot rolling process, the temp. in a finish rolling mill is regulated to Ar₃ to 900°C and the resultant plate is coiled at 500-690°C. By this procedure, a fine- grained ferrite structure having ≤5μm average grain size in an as-rolled state is formed. Moreover, tensile strength and the product of TS and uniform elongation are regulated to ≥780N/mm² and 10000N/mm².%, respectively, and further, the fluctuation of TS in the coil is regulated to 100N/mm². By this method, the amount of discard of the head and the tail end of the steel plate can be reduced, and also yield can be improved.;COPYRIGHT: (C)1997,JPO