| 摘要 |
PROBLEM TO BE SOLVED: To increase high temp. strength of a steel and to simplify and eliminate fireproofing coatings according to the Building Standards Act, by specifying its compsn., executing controlled cooling after hot rolling and precipitating an optimum amt. of VN into the structure. SOLUTION: The steel contains, by weight, 0.01 to 0.15%C, <=0.6% Si, 0.5 to 1.5% Mn <=0.030% P, <=0.030% S, 0.005 to 0.05$ Al, 0.2 to 0.7% Mo, 0.01 to0.15% V and 0.0050 to 0.0120% N, contg. one or >= two kinds among 0.001 to 0.15% Ti, 0.001 to 0.030% rare earth metals, 0.0005 to 0.0030% B, 0.0005 to 0.0030% Ca and 0.001 to 0.05% Zr and preferably contg. one or >= two kinds among 0.05 to 0.5% Cu, 0.05 to 0.5% Ni, 0.05 to 0.5% Cr and 0.005 to 0.3% Nb as well. This steel is subjected to hot rolling and is thereafter subjected to cooling in such a manner that the average cooling rate is regulated to <=αdefined by the formula I and the cooling stopping temp. is regulated to >=(Ar3-200 deg.C) based on Ar3 defined by the formula II.
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