PRODUCTION OF TEMPERED TYPE HIGH TENSION HEAVY-GAGE STEEL PLATE

摘要

PURPOSE:To obtain a tempered type high-tension heavy-gage steel plate having particularly excellent strength, toughness and weldability by subjecting a steel which contains N at a low rate, is decreased in the amt. of V and Si to be added to respectively prescribed values or below and is regulated in weld crack sensitivity index to hot rolling after heating then reheating the steel to a specific temp. region and subjecting the heated steel to hardening followed by tempering and water cooling. CONSTITUTION:The steel contg., by wt%, 0.07-0.15 C, =0.15 Si, 0.40-1.20 Mn, 1.00-3.50 Ni, 0.40-1.20 Cr, 0.40-0.80 Mo, 0.01-0.06 V, 0.005-0.030 Nb, =0.0020 B, 0.01-0.10 Sol.Al, =0.0040 N, =0.010 P and = 0.003 S, and having =0.28% Pc (weld crack sensitivity index) M expressed by the formula is prepd. Such steel is reheated to a temp. region of the Ac3 transformation point -1,050 deg.C after hot rolling and is then hardened and tempered at the Ac1 transformation point or below and thereafter the steel is cooled with water. The HT100-class steel having excellent strength and toughness and good weldability is thus obtd. without using a large amt. of costly Ni.