PRODUCTION OF STEEL TUBE EXCELLENT IN SELECTIVE CORROSION RESISTANCE IN WELD ZONE

摘要

PURPOSE: To provide a weld heat-affected zone with seawater corrosion resistance and to properly secure the toughness, weldability, and wear resistance of a base material by forming a welded steel tube by using a steel sheet prepared by applying controlled rolling and controlled cooling to an extra low C-Cr-Mn type low alloy steel of specific composition. ;CONSTITUTION: A steel, having a composition consisting of, by weight ratio, 0.03-0.07% C, 0.05-0.5% Si, 0.5-2.0% Mn, ≤0.03% P, η0.005% S, 0.1-0.3% Ni, 0.8-1.5% Cr, 0.0005-0.005% Ca, and the balance essentially Fe. Moreover, if necessary, small amounts of Mo, Nb, V, Ti, and B are further added selectively, is used. A slab of steel with this composition is heated to ≥900°C and hot-rolled under the conditions of a draft in an unrecrystallized temp. region of ≥30% and a finishing temp. not lower than the Ar₃ transformation point. Subsequently, the resulting hot rolled steel plate is subjected to accelerated cooling from a temp. of ≥(Ar₃ transformation point -50°C) down to ≤600°C at a rate of 1°C/sec. Then, the steel plate is cold-formed and formed into welded steel tube.;COPYRIGHT: (C)1996,JPO