Strength at elevated temperature of the basic material and the fire-resistant steel and the production method of being superior in hot ductility of the welding heat-affected zone

摘要

PPROBLEM TO BE SOLVED: To provide a refractory steel used for a steel structure, in which a base material part has 600°C high yield strength and a weld heat-affected zone has 600°C high ductility when exposed to fire, and further the base material part and the weld heat-affected zone have excellent low-temperature toughness, and to provide a production method for the refractory steel. PSOLUTION: The refractory steel has a composition containing 0.005 to 0.050% C, 0.50 to 2.00% Mn, 0.50 to 2.00% Cr, 0.10 to 0.50% V and 0.005 to 0.030% Ti, and has an optical microscope structure in which, by area fraction, ≥80% is composed of a bainitic phase or a martensitic phase. In the production method, a slab having the above composition is heated to 1,100 to 1,300°C and is subjected to hot rolling or working at 800 to 1,000°C at a reduction ratio of ≥50%, and the hot rolling or working is finished at ≥800°C, and thereafter, the slab is subjected to accelerated cooling from an Ar3 point or more to 450°C at a cooling rate of ≥2°C/s. PCOPYRIGHT: (C)2011,JPO&INPIT