MICROSTUCTURAL AND HARDNESS VARIATION IN POST WELD HEAT TREATED FIBER LASER WELDED DUAL PHASE STEELS

The present study is aimed to understand the variation of microstructure and Hardness across the weld bead with varying the Post Weld Heat Treatment temperatures on Dual Phase Steel 590 grade. Nd: YAG fiber laser source was used to produce butt joint with 2.5 kW Laser Beam Power and at a welding speed of 4m/min. Due to the rapid solidification of fusion zone, the liquid metal was transformed into lath martensite upon solidification. The hardness in the fusion zone was increased to 350 HV0.5 from 200 HV0.5 of the base material. This high hardness in the weld zone may be the potential source for the failures. To decrease the hardness of the fusion zone, Post weld Heat Treatments were given to Laser Welded samples.