It is strong production manner null of the high intensity hot-rolled sheet steel for processing to which fatigue property

摘要

PURPOSE:To produce a high strength hot rolled steel plate for high degree working having high strength and excellent in fatigue characteristics and stretch- flange formability by subjecting a slab of a steel remarkably reduced in C content, having properly regulated proportion between C and P, and containing trace amounts of Cu to hot rolling, to cooling, and to coiling under respectively specified conditions. CONSTITUTION:A slab of a steel having a composition which contains, by weight, 0.0010-0.010% C, 1.0% Si, 0.10-1.5% Mn, 0.04-0.10% P, =0.005% S, 0.010-0.06% Al, =0.0040% N, 0.05-0.50% Cu, and 0.05-0.50% Ni or further contains one or =2 kinds among =0.010% Ca, =0.010% REM, =1.0% Cr, 0.010-0.050% Ti, and 0.010-0.050% Nb and in which C/P is regulated to =0.10 is heated and then continuously hot-rolled under the conditions of 50% cumulative rolling reduction and =Ar3 point finish rolling temp. The resulting hot rolled plate is rapidly cooled at =20 deg.C/sec cooling rate and coiled at =500 deg.C.