HIGH STRENGTH HOT ROLLED STEEL PLATE EXCELLENT IN HOLE SPREADABILITY BY CONTINUOUS HOT ROLLING PROCESS AND ITS PRODUCTION

摘要

PROBLEM TO BE SOLVED: To remove material dispersion in a coil by treating a steel slab of specific composition by a continuous hot rolling process. ;SOLUTION: A steel slab, having a composition consisting of, by weight, 0.02-0.14% C, 0.40-2.00% Si, 0.30-2.00% Mn, ≤0.020% P, ≤0.010% S, 0.005-0.100% Al, and the balance Fe, etc., is treated by means of a continuous hot rolling process, that is, finish rolling is finished at a temp. not lower than Ar₃ and cooling is performed at a cooling rate CR(°C/sec) satisfying log Cr≥2.83-0.44×Mn-6.73×C. Then, coiling is carried out at 350-550°C to form a bainitic structure. By this method, a steel plate excellent in hole spreadability can be obtained. Further, by adopting a continuous hot rolling process, fluctuations in material in a coil can be minimized.;COPYRIGHT: (C)1997,JPO