Abstract: In this paper the experimental analysis is conducted regarding the failure of the T23/12Cr1MoV dissimilar steel welded joints on the specimen of the platen superheater in a 1 000-MW ultra supercritical (USC) boiler. Macroscopic and microscopic examinations indicate that the crack is distributed along the fusion line and occurs in the heat affected zone of the 12Cr1MoV steel. The crack initiates in the coarse grained heat affected zone(CGHAZ) of the tube inner wall, propagates into the weld metal at the 1/3 thickness of the wall, and terminates at the tube outer wall. Mechanical performance tests conclude that the higher hardness and lower ductility in the heat affected zone (HAZ) and weld metal are the major reasons for cracking. Post welding heat treatment(PWHT) is suggested to improve the ductility and reduce the welding residual stress for the welded joints.

Key words: T23 steel, 12Cr1MoV steel, dissimilar steel welding, failure analysis, boiler