HIGH TENSILE STRENGTH STEEL PLATE EXCELLENT IN CRACK PROPAGATING ARREST CHARACTERISTIC AND ITS PRODUCTION

摘要

PROBLEM TO BE SOLVED: To produce a high tensile strength steel plate having excellent low temp. toughness and crack propagating arrest characteristics at a low cost by subjecting a low carbon-low alloy slab having a specified compsn. to primary and secondary hot rolling under specified temp. conditions and thereafter executing hardening and tempering. ;SOLUTION: A slab contg., by weight, 0.02 to 0.15% C, 0.4 to 1.5% Mn, 0.50 to 0.60% Ni, and the balance small amounts of Cr, Mo, Nb, V, B, Ti or the like is subjected to primary hot rolling and is cooled from 950°C surface temp. of the hot rolled steel sheet to the temp. range of 350°C to (the Ar₃ point-25°C) at the average cooling rate of ≥15°C/sec. Then, in a stage in which the surface of the steel sheet is recuperated to an intermediate temp. of the AC1 point to the AC3 point or above, secondary rolling is executed at ≥50% cumulative draft from the stop of the cooling to the completion of the recuperation, the surface layer part of the steel plate is rolled in the austenite non-recrystallized temp. region and the center part to ≥20% respectively in the up and down directions from the center of the plate thickness is rolled at a temp. in an austenite non-recrystallized region to regulate its plate thickness into a prescribed one, which is thereafter quenched and is tempered at a temp. of the AC1 point or below.;COPYRIGHT: (C)1997,JPO