Microstructure Characterization for P92 Steels Subjected to Short Term Overheating above Critical Transformation Temperatures

Abstract

Advanced ferritic steels containing 9 wt% Cr are widely used for nuclear and fossil energy applications, especially in the construction of supercritical and ultra supercritical boiler components. The microstructure of the as supplied 92 materials consists of a tempered martensite matrix, a fine dispersion of intergranular chromium rich M23C6 precipitates and intragranular carbonitrides MX particles rich in V and Nb. This steel requires post weld heat treatment (PWHT) to produce a tempered microstructure after welding to develop excellent creep strength for high temperature service. The short excursion to high temperature beyond Ac1 and Ac3 would have resulted in the formation of deleterious phases, for example, soft α-ferrite which has a poor creep strength and hard martensite which has a low toughness. In this study, the microstructure evolution as a result of short exposure to various peak temperatures above Ac1 and Ac3 is analyzed. Creep rupture database for overheated condition will be established after the completion of uninterrupted creep testing.