Microstructural evolution and stress relaxation cracking mechanism for Super304H austenitic stainless steel weld metal.

• Stress relaxation cracking in Super304H austenitic stainless steel weld metal. • The pre-compressed CT technique combined with FEM analysis was successfully used. • The mechanism responsible for stress relaxation cracking formation was illustrated after short-term aging and long-term aging. The pre-compressed CT technique was used to quantitatively investigate the formation of stress relaxation cracks under different tensile residual stresses and aging time in Super304H austenitic stainless steel weld metal. The statistical results revealed that intergranular cracks could occur within 2000 h under 650 °C when the residual stress was applied with greater than 18 KN pre-compression force. Detailed grain interior and boundary analyses showed that the growth of intragranular Cu-rich particles could induce a strong grain interior, and the intergranular Nb(C, N) carbides were one of the causes to crack under short-term aging time. For long-term aging time conditions, the intergranular M 23 C 6 carbides were more susceptible to crack than intergranular Nb(C, N) carbides. Finally, the mechanism responsible for stress relaxation cracking formation was carefully illustrated for the weld metals after short-term aging and long-term aging, respectively. [Display omitted] [ABSTRACT FROM AUTHOR]