Microstructure and microhardness of fiber laser butt welded joint of stainless steel plates

The butt welding of 304 stainless steel plates with thickness of 3 mm and 6 mm were achieved by YLR-6000 fiber laser under Ar protective gas. The weld appearance, microstructure, composition distribution and microhardness of welded joint were emphatically investigated. The results showed that the narrow and fully penetrated welded joint without marco-defects can be obtained with tightly focused 2 kW fiber laser power and 20 mm/s welding speed. The weld bead was smooth, and various microstructures typically formed at different zones of the welded joint. The fine columnar and equiaxed crystals existed in the edge and center of weld bead, respectively. Both were different with the microstructure of the stainless steel substrate. However, the composition distribution of the welded joint had no obvious changes. Furthermore, the superior microhardness of welded joint over the stainless steel substrate was mainly attributed to its finer microstructure.