PRODUCTION OF LOW YIELD RATIO STEEL PRODUCTS FOR BUILDING HAVING EXCELLENT FIRE RESISTIVITY AND STEEL MATERIAL FOR BUILDING FORMED BY USING THESE STEEL PRODUCTS

摘要

PURPOSE:To obtain the low yield ratio steel products for buildings having excellent high-temp. characteristics and fire resistivity by rolling a low-C low-Mn steel having a specific compsn. added with Mo at a high temp. and subjecting this steel to air cooling, then to water cooling under specific conditions and allowing the steel sheet to cool. CONSTITUTION:A billet consisting, by weight, 0.04 to 0.15% C, =0.6% Si, 0.5 to 1.6% Mn, 0.2 to 0.7% Mo, =0.1% Al, =0.006% Ni, and the balance Fe and inevitable impurities is heated at 1100 to 1300 deg.C and the hot rolling is ended at 800 to 1000 deg.C. This steel sheet is cooled with air down to (Ar3-20 deg.C) to (Ar3-100 deg.C) and is then cooled with water down to an arbitrary temp. below 550 deg.C at 3 to 40 deg.C/sec cooling rate from these temps. The steel sheet is thereafter allowed to cool. Proper ratios of =1 kinds of Nb, Ti, Zr, V, Ni, Cu, Cr, B, Ca and REM are incorporated at need into the above-mentioned steel. The low yield ratio steel products for buildings having the excellent fire resistivity are obtd. in this way. The fibrous refractory thin-layer material of an inorg. system is clad on the heat receiving surface of such steel products, by which the steel material for buildings is obtd.