| 摘要 |
PROBLEM TO BE SOLVED: To improve the long time creep strength and steam oxidation resistance of a steel under supercritical pressure steam conditions by adding specified suitable amounts of carbide forming elements such as Mo, W, Co and Nd into its compsn. and uniformly dispersing and precipitating theμphases of fine Fe7 W6 type carbides into the structure. SOLUTION: This steel has a compsn. contg., by weight, 0.02 to 0.15% C, 0 to 1.0% Si, 0.05 to 1.5% Mn, <=0.030% P, <=0.015% S, 8.0 to 13.0% Cr, 1.5 to 3.5% W, 0 to 1.0% Mo, 2.5 to 6.0% Co, 0.10 to 0.50% V, 0.030 to 0.14% Nb, 0.001 to 0.17% Nd, 0.020 to 0.12% N, 0 to 0.030% B, <=0.010% O and 0.001 to 0.050% acid soluble Al, and the balance Fe with inevitable impurities and satisfying the conditions in the formulae, 0<=PNd <=0.103 and 0.005<=PNb <=0.03 [wherein, PNd =Nd-6.01×0(oxygen), and PNb =0.151×Nb+0.0971×PNd , provided that the element symbols are each content (wt.%) of element in steel]. Furthermore, in a steel pipe or a steel sheet having the above compsn., in a steel pipe or a steel sheet having the above compsn., after normalizing and tempering treatment, as the creep rupture service life at 6150 deg.C under 98MPa, >=1000hr can be secured.
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