Method of manufacturing a good welding structural steel of high heat input welding heat-affected zone toughness

摘要

PURPOSE: To produce a steel material for welded structure excellent in toughness in a large heat input weld heat-affected zone by deoxidizing a molten steel, into which specific amounts of C, Si, Mn, P, S, and N are incorporated and in which the amount of dissolved oxygen is regulated, with specific amounts of Ti, successively adding specific amounts of Al, and subjecting the molten steel to casting and to rolling. ;CONSTITUTION: Ti is added, by 0.005-0.020% final content, to a molten steel, in which the amount of dissolved oxygen is regulated to 20-100ppm, to deoxidize the molten steel. Then, within five minutes, Al is added to the molten steel by 0.005-0.030% final content. This molten steel has a composition consisting of, besides the above, 0.09-0.18%, by weight, C, ≤0.50% Si, 0.50-1.80% Mn, ≤0.020% P, 0.0010-0.0050% S, 0.0020-0.0060% N, and the balance Fe with inevitable impurities and further containing, if necessary, one or more kinds among ≤1.0% Cu, ≤2.0% Ni, ≤0.030% Nb, ≤0.1% V, ≤0.6% Cr, and ≤0.6% Mo. This molten steel is cast and rolled. By this method, both of Ti nitride and Ti oxide are utilized, and the structure in the vicinity of a weld zone can be improved.;COPYRIGHT: (C)1994,JPO