Optimization of deep penetration laser welding of thick stainless steel with a 10 kW fiber laser

• The focal position is a key parameter for high-power fiber laser welding of thick plate.
• Good full penetration weld cannot be obtained just via varying the welding speed without a proper focal position.
• The bottom shielding gas improves the stability of the total welding process.
• The cross section of the optimal butt joint appears “I” shape.
• The joint is ductile fractured far from the weld seam with the tensile strength of 809 MPa.

Deep penetration laser welding of 12 mm thick stainless steel plates was conducted using a 10 kW high-power fiber laser. The effect of the processing parameters on the weld bead geometry was examined, and the microstructure and mechanical properties of the optimal joint were investigated. The results show that the focal position is a key parameter in high-power fiber laser welding of thick plates. There is a critical range of welding speed for achieving good full penetration joint. The type of top shielding gas influences the weld depth. The application of a bottom shielding gas improves the stability of the entire welding process and yields good weld appearances at both the top and bottom surfaces. The maximum tensile stress of the joint is 809 MPa. The joint fails at the base metal far from the weld seam with a typical cup–cone-shaped fracture surface. The excellent welding appearance and mechanical properties indicate that high-power fiber laser welding of a 304 stainless steel thick plate is feasible.