Aiming at leakage positions in weld joints of T91 steel

macroscopic inspection

microscopic hardness examination

metallographic analysis

element analysis

and difracted spot analysis of carbides etc.have been carried out.Results show that the cracks in the weld joint is typical Ⅲ-type cracking

the over-high welding temperature makes large amount of M23C6 carbides separated out and coarsening in coarse grain zone of the heat affecting region

leading to deterioration of the grain boundary toughness and weakening the strength of creep rupture resisitance

thereby

resulting in cracks occurred in the weld joint.It is recommended that the welding temperature should be suitably lowered

to avoid separating out of carbide grains and their coarsening.