High-temperature tensile and fatigue strength properties of stainless steel repaired by laser metal deposition method

Abstract

An overlay welding is widely employed to repair damaged components in aged thermal power plants. However, the overlay welding causes heat-affected zone and tensile residual stress which reduce the high-temperature strength of these components. Our research group has reported that a thermal spray technique can reduce the residual stress, while the bonding strength of the repaired part needs to be improved. This study is focusing on a laser metal deposition (LMD) technique as a repairing technique of the damaged component. In order to identify the high-temperature strength of an austenitic stainless steel repaired by LMD, a tensile test and a fatigue test were conducted at 873 K. The tensile test revealed that the repaired part was not delaminated from the base material until rupture, moreover, the yield stress of the specimen repaired by LMD (LMD specimen) is significantly higher than that of the non-repaired specimen. In contrast, it was found that the fatigue strength of the LMD specimen was lower than that of the non-repaired specimen. A fatigue test using LMD specimens without tapered area in the parallel part and a finite element analysis revealed that the low fatigue strength of the LMD specimen is attributed to the residual stress concentrated at the tapered area in the repaired part. The finite element analysis also indicated that the cutting angle of less than 15 leads to the residual stress of less than 100 MPa normal to the LMD/base material interface.