Improving stress corrosion cracking resistance of stainless steel welded joints by laser shock peening

Because the distribution of temperature field was not uniform during the processing of welding, the stress, microstructure and performances in different regions in the welded joints were different. And there ware residual tensile stress which might cause to stress corrosion cracking (SCC). The 316 austenitic stainless steel welded joints were treated by laser shock peening. In order to protect the welded joints from stress corrosion cracking, the laser shock waves were designed with different strengths in the weld, heat affected zone (HAZ) and the matrix. Under a constant temperature of 90℃, the performance of stress corrosion cracking of 316 stainless steel was studied in FeCl₃ solution. The welded specimens cracked within 112 h. After laser shock peening the crack time was increased by 33.48%. The mechanisms were analyzed from residual stress tests and microstructure observation. It was found that the residual tensile stress was eliminated in HAZ. There were residual compressive stress and the stress gradient was reduced from 54.7 MPa/mm to 11.7 MPa/mm which were beneficial for protecting weldments against SCC. On the other hand, the microstructure and mechanical property of the welded joints after laser shock peening became uniform. The grain refining would delay crack initiation and propagation. All in all, the residual compressive stress and uniform microstructure caused by laser shock peening would protect the welded joints against stress corrosion cracking.