Effect of oscillating laser beam offset on the microstructure and mechanical properties of dissimilar stainless steels joints

Laser oscillating welding of AISI 304 austenitic stainless steel (ASS) and AISI 420 martensitic stainless steel (MSS) was carried out. The effect of laser offset (O-L) on the element distribution, grain growth mode, phase composition, and the consequent mechanical properties were investigated. Epitaxial growth or columnar growth was mainly presented neighboring the fusion boundary, which was depended on the crystal similarity of the fusion zone and the base metals. With the laser beam shifting from the martensitic side to the austenitic side, the fraction of misorientation at 60 degrees within the martensite decreased from 22% to 9%. Correspondingly, that at 45 degrees distributed on the phase boundaries first increased to maximum of 38%, accompanied with the formation of austenite when the O-L increased to 0.6 mm, and then linearly decreased to 6% with the formation of pure austenite. The evolutions in phase composition, misorientation and mechanical properties were closely related to the element distribution within the welds, which could be accurately predicted by the proposed energy distribution model of the laser beam. The related mechanisms were discussed according to the martensitic transformation and the crystal orientation.