ABSTRACT
3 mm thick nitronic-50 stainless steel sheets were successfully butt-joined using a 2 kW fiber laser beam welding. Three weld joints were fabricated for different incident angles, namely, 70°, 80° and 90° for the other constant welding process parameters. The effect of incident angle on the weld bead geometry, microstructure evolution, and strength of the laser beam welded joints was studied in detail. The incident angle significantly affected the bead geometry and its orientation. Lowering the incident angle beyond a limit caused the beam shift near the weld root of the joint, where the bead was formed away from the joint line resulting in improper fusion and a defective weld occurred. The microstructure transformed from columnar to an equiaxed dendritic structure at the center of the weld nugget for lower incident angles. Skeletal and lathy ferrite was observed in the joints' weld zone. However, the fraction of lathy ferrite was higher at lower incident angles due to a faster cooling rate. A higher weld joint strength of 1010 MPa (97% of the base metal UTS) was achieved at an 80° incident angle, owing to the formation of more equiaxed dendritic grains and the absence of the secondary phases. All of the tensile test samples showed evidence of ductile failure, and overall, an acceptable level of elongation was achieved.
