Effect of plasma flow in plasma metal inert gas welding process to microstructure formation at heat affected zone of as welded carbon steel

The application of plasma MIG welding that consist of plasma flow in surrounding of MIG wire causes a divergence of MIG current from the MIG wire to outside. Thedivergence then disperse heat and force to the upper side of MIG wire and thus reduce its droplet temperature. This situation affects the droplet size as well as the frequency of metal transfer. In this study, the effect of plasma flow in plasma MIG welding to the refinement of microstructure at heat affected zone is investigated. The microstructure evaluation is carried out by means of Optical Microscopy and Electron Backscattered Diffraction. As for results, it found that the microstructure turn to be refined at HAZ area especially at the coarse grain HAZ. The difference in grain size at CGHAZ and FGHAZ region was almost eliminated. This result was compared with the one with conventional MIG welding where it shows a clear difference in grain size structure at CGHAZ and FGHAZ. The refinement of microstructure also gives an effect to the mechanical property at the area. According to Micro Vickers Hardness test that has been done, the CGHAZ region in conventional MIG welding has higher value of hardness than plasma MIG welding. It is suggested that, the presence of plasma flow in plasma MIG welding process able to refine the microstructure at HAZ region.