JPS55115924A - Production of high toughness high tensile steel plate - Google Patents

Abstract

PURPOSE:To produce the steel plate of tensile strength much higher than that of conventional ones while maintaining superior toughness by rolling-reducing the steel at the specific draft in the non-recrystal temperature region of gamma and the gamma+alpha region of partially transformed gamma then subjecting the same to accelerated cooling at the time of performing controlled rolling of the steel. CONSTITUTION:The steel which contains C; 0.03-0.20%, Si<0.60%, Mn; 0.60- 2.50%, Al; 0.005-0.10%, and further, if necessary, one or two or more kinds of Nb; 0.01-0.10%, V; 0.01-0.05%, Ti; 0.01-0.15%, 0.5% or less of each of Cu, Cr, Ni, Mo is rolled at least below the non-recrystal temperature of gamma and at the draft of 40% or more. Not less than 20% out of this 40% is accomplished in the gamma+alpha region at the Ar3 transformation point or less. In this case, the rolling finishing temperature is kept within the temperature range from 650 deg.C-(Ar3-20) deg.C and after the rolling, the accelerated cooling if started as quickly as possible and the acceleration cooling is done at the cooling rate of the range from 5-20 deg.C/sec., over the temperature width from that cooling start temperature up to at least 80 deg.C or over in such a manner that the cooling stop becomes 500 deg.C or more, after which air cooling is done.