| 摘要 |
PROBLEM TO BE SOLVED: To maintain the finely precipitated state of the composite precipitates of Nb and Mo with V as nuclei sufficiently effective for strengthening the steel for a relatively short time even at 800 deg.C. SOLUTION: The 800 deg.C high temperature fire resistant steel for building construction has a composition containing, by mass, 0.01 to 0.1% C, 0.2% to 1.2% Si, <=0.5% Mn, >0.05% to 1% Al, 0.4 to 1.5% Mo, 0.05 to 0.2% V and 0.01 to 0.2% Nb, and the balance Fe and inevitable impurities, and of which Ac1 transformation temperature is 800 to 900 deg.C. The steel preferably contains one or more kinds selected from 0.1 to 2% Cu, 0.1 to 0.5% Ni, 0.1 to 1% Cr, 0.01 to 0.1% Ti and 0.0005 to 0.01% B as well. Further, in its production method, a steel slab or a cast iron slab is heated to >=1,100 deg.C and is subjected to hot rolling where the cumulative draft of >=50% is secured to the finishing plate thickness in the temperature region of 830 deg.C to 930 deg.C to form into a thick steel plate.
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