| 摘要 |
PURPOSE:To produce a steel having high strength at high temp. and excellent in oxidation resistance by subjecting a steel, in which the ranges of the amounts of alloying elements, an OR value, and an MC value are respectively specified, to hot rolling at specific temp., to coiling, and then to holding at a temp. not lower than the Ms point. CONSTITUTION:This steel has a composition which consists of, by weight, 0.3-3.0% Si, 0.02-2% Mn, 3.5-9.9% Cr, 0.01-1.0% Al, <=0.03% C, <=0.03% P, <=0.03% S, <=0.02% N, and the balance Fe with inevitable impurities and in which the OR value given by equation I is regulated to >=6.5. Further, V, Ti, Zr, and Hf are added, and the MC value given by equation II is regulated to >=0. A slab of this high Cr steel is heated to 1100-1300 deg.C, and hot rolling is finished at >=850 deg.C. The resultant steel strip is coiled and then held at a temp. not lower than the Ms point of the steel for >=60min, by which the metallic structure is essentially formed into ferrite. While roll-forming the steel strip into cylindrical state, both ends of the steel strip are welded to form into a steel tube. |
