On some aspects of creep deformation of low-alloy Cr-Mo-V creep resistant steels

Abstract

Low-alloy steels containing Cr, Mo & V by virtue of their good long-term creep strength have become the most favou-rite materials all r the world in thermal power generation industry for the use in various types of tubes, superhea-ter, headers, main steam pipe and in the nstruction of a number of engineering components viz, rotor, steam chest, bolts, valves etc. In view of the versatility of Cr-Mo- V steels, paper presents a critical assessment of the dependence of their creep deformation behaviour on micro-structural features. After discussing the main shortcomings of the steels viz. poor creep ductility and susceptibility to cracking during post-weld heat atment, the paper dwells on the developmen-tal approach which has mainly centered around (i)additions of alloying elements such as Ti & B, lijeontrolling the V/C ratio and reviews the effectiveness of such measures. Lastly the paper raises the following two important issues in the context of Ti & B addition to the Cr-Mo- V Steels- (i) Is the long. term creep strength of the steels con-taining Ti-B restricted by the presence of Ti (CN)ITIN, type of inclusion? (ii) Whether the addition of Ti & B to conventional 1Cr-1 Mo-1 V rotor steel would be desirable.