Stress corrosion property of 304 stainless steel and Q345 steel laser-MAG hybrid welded joints

The stress corrosion cracking (SCC) property of laser-MAG hybrid welded 304 stainless steel and Q345 steel was evaluated through cycle-immersion testing in 3.5 wt.% NaCl solution. The average SCC crack propagation rate of different zones under different initial stress intensity factors was calculated, and the SCC fracture and crack propagation path were observed. The microstructure and mechanical properties of the weld joint have also been examined. The result indicates that the fusion zone (FZ) is extremely prone to SCC. The average SCC crack propagation rate in FZ is 5.4489 x 10(-6) mm/h, while no obvious SCC was found in the base metal (BM) and heat-affected zone (HAZ). The steel BM and HAZ may also suffer SCC, but not as fast as in FZ. Grooves caused by SCC were found on the fracture surface with a large amount of corrosion products accumulated close to the interface between the pre-crack section and SCC section. Crystallized-sugar-shaped pattern was found on the SCC zone of FZ. Crack jumping, deflection and crack closure occurred in the crack propagation path. Martensite on the FZ was considered to be the major reason that the FZ has a higher SCC propagation rate.