MANUFACTURING METHOD OF TENSILE STRENGTH 58 kgf/mm¬2 GRADE STEEL FOR BUILDING CONSTRUCTION HAVING HIGH TEMPERATURE STRENGTH PROPERTIES

摘要

PURPOSE: A manufacturing method of tensile strength 58 kgf/mm¬2 grade fire resistant steel for building construction is provided to obtain superior high temperature strength properties without increase of addition quantities of alloy constituents of Cr and Mo or addition of tempering process by accelerated cooling the hot rolled steel after hot rolling a steel composition. CONSTITUTION: The manufacturing method comprises a step of heating a steel slab comprising 0.05 to 0.15 wt.% of C, 0.55 wt.% or less of Si, 1.6 wt.% or less of Mn, 0.70 wt.% or less of Cr, 0.3 to 0.9 wt.% of Mo, 0.06 wt.% or less of Nb, 0.03 wt.% or less of P, 0.025 wt.% or less of S, 0.01 to 0.06 wt.% of soluble Al and a balance of Fe and other inevitable impurities in the temperature range of 1,150 to 1,300 deg.C; a step of finish rolling the heated steel slab at a temperature of 800 deg.C; a step of water cooling the finish rolled steel to the temperature range of 500 to 650 deg.C in a cooling rate of 16 to 50 deg.C/sec; and a step of air cooling the water cooled steel.