304不锈钢局部干法水下激光焊接头成形与性能OA

To address the adverse effects of water environment on weld quality,underwater laser welding of 4 mm thick 304 austenitic stainless steel was conducted using a local dry method.The drainage stability of a double-layer drainage hood was verified within 0-50 mm water depth.The influence of welding speed(0.8-1.2 m/min)on weld formation and porosity was systematically investigated,and the differences in microstructure and mechanical properties between underwater and conven-tional welds were compared.The results show that the local dry method effectively isolates the weld top surface from water,but the backside water environment promotes hydrogen entrapment and reduces keyhole stability.The porosity exhibits a decrease-then-increase trend with welding speed:the minimum of 1.4%is achieved at 1.0 m/min,metallurgical hydrogen po-rosity dominates at 1.2 m/min(7.8%),and process-induced porosity due to keyhole instability rises to 5.9%at 0.8 m/min.Enhanced heat dissipation from the backside water environment significantly refines the underwater weld microstructure and mitigates depression and hump defects under high heat input.Under optimal parameters(laser power 3800 W,welding speed 1.0 m/min,defocusing distance+3 mm),the underwater weld exhibits a tensile strength of 668 MPa and yield strength of 367 MPa,with tensile and bending properties slightly superior to conventional welds.Small-scale pores and minor backside inhomogeneity have negligible effects on mechanical performance.