Aiming at finding the cause of cracks at welded point of T91/HR3C dissimilar heat-resistant steels for high temperature superheater in 1 000 MW unit of a power plant

various tests such as macroscopic examination

material evaluation and welding

heat treatment process analysis were conducted.Results showed that

the cracks are cold crack

and large restraint stress caused by no weld preheating was considered as the main reason.Because the T91 steel is martensitic heat resistant steel

it will form martensite at air cooling condition

while during welding

martensite with high harden quenching tendency will be formed more easily

so the cold crack happens.