Abstract The narrow gap multi-pass laser welding with filler wire addition of 30-mm-thick S275 ferritic steel was investigated in this paper. The purpose of this paper is to understand the formation mechanism and influencing factors of laser welding defects, in order to optimize the welding process and avoid the formation of cracks, lack of fusion, porosity and other defects. The experimental results show that, properly increasing the heat input can reduce the cooling rate of molten pool and restrain the generation of welding cracks. When the heat input is 0.9 kJ/mm, the longitudinal surface crack is 2.3 mm deep. When the heat input increases to 1.05 kJ/mm, the depth of longitudinal surface crack decreases to 0.8 mm. When the heat input reaches 1.2 kJ/mm, no crack is found in the joint. Choosing a smaller distance between the laser and wire can ensure the contact between the molten metal and the weld pool, and avoid the lack of fusion on the side wall. When the distance between the smooth wires is 1mm, no fusion or splashing is found on the groove side wall. When the distance between the laser and wire is 3 mm, the side wall is not fused. When the distance between the laser and wire 5 mm, the deposited metal is found above the side wall of the welding groove. When a 15 mm diameter pipe is used to transport protective gas at the top of the groove, a large number of air holes can be avoided. The welding joint with better mechanical properties can be obtained by using 6 m/min wire feeding speed.
ZHANG Hong. Defect formation mechanism and influence factors of narrow gap multi-pass fiber laser welding of S275 ferritic steel sheets[J]. Materials Science and Engineering of Powder Metallurgy, 2020, 25(2): 112-117.
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2020, Vol. 25 
