Development of Modified 9 Cr-1 Mo Steel for Elevated-Temperature Service

摘要

The status of development and commercialization of a modified 9 Cr-1 Mo alloy is presented. The alloy is modified by the addition of 0.06 to 0.10% Nb and 0.18 to 0.25% V. The alloy is recommended for use in the normalized and tempered condition (1040 exp 0 C for 1 h, air cooled to room temperature; 760 exp 0 C for 1 h, air cooled to room temperature). Heat treatment, Charpy impact, tensile, and creep properties of the alloy are described in detail along with a brief description of other properties. The modified alloy has creep strength that exceeds that of standard 9 Cr-1 Mo and 2 1/4 Cr-1 Mo steels for the temperature range from 427 to 704 exp 0 C. The total-elongation and reduction-of-area values for all test temperatures and rupture times up to 22,500 h exceed 15 and 70%, respectively. The estimated design allowable stresses for this alloy are higher than those for standard 9 Cr-1 Mo and 2 1/4 Cr-1 Mo steel. At 550 exp 0 C and above, these values are twice those of the other alloys. Operating experience on this alloy is being obtained by installing tubes in various steam power plants. 13 figures, 5 tables. (ERA citation 09:006138)