QUENCHED AND TEMPERED HIGH TENSION STEEL FOR LARGE HEAT INPUT WELDING EXCELLENT IN SITE WELDABILITY AND JIG MARK CRACKING RESISTANCE AND ITS PRODUCTION

摘要

PURPOSE: To improve large heat input weldability for improving the welding efficiency of a large structure and jig mark cracking resistance in a fillet weld zone, to perfectly prevent cracking on the inside of a tank support part, and also to improve site weldability. ;CONSTITUTION: A steel having a composition, which contains ≤0.10% C, ≤0.10% Si, 0.50-2.20% Mn, ≤0.015% P, 0.0008-0.0025% S, 0.010-0.10% Sol.Al, 0.50-2.50% Cu, 0.50-2.00% Ni, 0.005-0.024% Nb, 0.005-0.018% Ti, and ≤0.0002% B as impurity and where (Si+Sol.Al) is regulated to ≤0.13% and also Ceq and Tieq are regulated, respectively, to ≤0.38% and to -0.007 to 0.005%, is provided, by which MnS can form a compound precipitate together with TiON or TiN. At the time when MnS forms a compound precipitate, successively to slight- degree deoxidation by Si at the time of tapping, perfect deoxidation is done by using Al at the time of vacuum degassing.;COPYRIGHT: (C)1994,JPO&Japio