摘要 |
PROBLEM TO BE SOLVED: To provide a fire-resistant steel material which shows high yield strength in each base metal part at 600°C, also has high ductility in a weld heat-affected zone, and is superior in the toughness of the base metal part and the weld heat-affected zone. SOLUTION: The fire-resistant steel material includes 0.005-0.050% C, 0.01-0.50% Si, 0.50-2.00% Mn, 0.50-2.00% Cr, 0.001-0.030% Ti, 0.005-0.10% Al, 0.001-0.006% N, less than 0.01% Mo, less than 0.03% V, 0.0003% or less B, less than 0.02% P, less than 0.01% S, less than 0.01% O and the balance Fe with unavoidable impurities; and has a steel material structure in which one or more of a bainite structure, a martensite structure or a ferrite structure formed of grains with circle equivalent grain sizes of 20μm or less when measured with a EBSP method occupy 80% or more by an area rate, and the balance is a ferrite or MA structure with unavoidable phases. COPYRIGHT: (C)2011,JPO&INPIT |