A METHOD FOR MANUFACTURING HIGH TS 50kgf/㎟ GRADE TEMPERATURE FIRE RESISTANT STEEL

摘要

PURPOSE: A method for manufacturing fire resistance steel having superior tensile strength (50kgf/mm2) is provided to produce a fire resistant steel having superior yield strength at 700deg.C in comparison with conventional 600°C-grade fire resistant steel for the application to structure material of high buildings. CONSTITUTION: The manufacturing method for the fire resistance steel comprises the processes of reheating a steel slab comprising C 0.05-0.15wt.%, Si 0.55wt.% or less, Mn 1.6wt.% or less, Cr 0.70wt.% or less, Mo 0.3-0.9wt.%, V 0.05-0.10wt.%, 0.003wt.%=N= 2.64/V, P 0.03wt.% or less, S 0.025wt.% or less, sol Al 0.01-0.06wt.%, a balance of Fe, and other inevitable impurities to the temperature range of 1000 to 1300deg.C; finishing hot rolling at over 900deg.C under a hard reduction ratio of at least 15%; water-cooling to the temperature range of 500 to 600deg.C at a cooling rate of 6°C/sec or more; and the air-cooling.