PRODUCTION OF BUILDING LOW YIELD RATIO STEEL HAVING EXCELLENT FIRE RESISTANCE AND BUILDING STEEL MATERIAL USING SAME STEEL

摘要

PURPOSE:To economically produce the title building low yield ratio steel having excellent fire resisting characteristic by heating a low-C and low-Mn steel contg. a trace amt. of Nb and an appropriate amt. of Mo and having a specified composition to a specified temp., and then hot-rolling the steel at a relatively high temp. CONSTITUTION:A billet contg., by weight, 0.04-0.15% C, =0.6% Si, 0.5-1.6% Mn, 0.005-0.04% Nb, 0.4-0.7% Mo, =0.1% Al, 0.001-0.006% N, =1 kind among 0.005-0.10% Ti, 0.005-0.03% Zr, 0.005-0.10% V, 0.005-0.5% Ni, 0.05-1.0% Cu, 0.05-1.0% Cr, 0.0003-0.002% B, 0.0005-0.005% Ca, and 0.001-0.02% REM, as required, the balance Fe, and inevitable impurities is reheated to 1100-1300 deg.C. The heated slab is then hot-rolled at 800-1000 deg.C, and then allowed to cool in the air to room temp. As a result, the Nb, Mo, etc., are sufficiently solution- treated, and a steel having high-temp. yield strength and toughness is obtained. An excellent fire-resistant structural material is obtained from the steel with a relatively thin refractory coating.