MANUFACTURE OF UNNORMALIZED HIGH TENSION STEEL OF HIGHER WELDABILITY CLASS THAN 50KG/MM2 WITH SUPERIOR QUALITATIVE CHARACTERISTIC IN Z DIRECTION

摘要

PURPOSE:To obtain the titled steel equal or superior to a conventional steel in toughness and much superior to it in weldability even if cooled intensely after controlled rolling by specially combining the composition of a steel with the heating temp. of the slab, the slight controlled rolling and the cooling stopping temp. CONSTITUTION:A steel consisting of 0.03-0.20% C, 0.05-0.60% Si, 0.6-2.5% Mn, 0.005-0.1% T.Al and the balance Fe with inevitable impurities or further contg. one or more among =0.1% Nb, =0.1% V, =0.15% Ti and =0.5% each of Ni, Mo, Cu and Cr and having =0.4Ceq is heated to 900-1,200 deg.C and hot rolled at =60% total draft in the temp. range of 900 deg.C- the Ar3 point. The hot rolled steel is acceleratedly cooled from a temp. above the Ar3 point at =15 deg.C/ sec cooling rate, the accelerated cooling is stopped at 400-600 deg.C, and the steel is allowed to cool. The Ceq value is obtd. by the equation.