Effect of plasma flow in plasma MIG welding process to the microstructure refinement at heat affected zone of as-welded carbon steel

Abstract

The use of plasma MIG welding which consists of plasma flow in surrounding of the MIG wire causes the divergence of MIG current from MIG wire to outside. The divergence then disperses the heat and force to the upper side of MIG wire, thus reduces the droplet temperature and affects the droplet size as well as metal transfer frequency. In this study, the effects of plasma flow in plasma MIG welding to the refinement of microstructure at heat affected zone (HAZ) is investigated. The microstructure evaluation is carried out by means of electron backscattered diffraction (EBSD). As a result, it was found that the microstructure refined at HAZ especially at coarse grain HAZ. The difference in grain size at coarse grain HAZ area and fine grain HAZ area was almost eliminated. This result was compared with the one with conventional MIG welding, which shows the clear difference in grain size at coarse grain HAZ and fine grain HAZ area. It is suggested that, the presence of plasma flow in plasma MIG welding process refines the microstructure at HAZ area, thus improves the mechanical property at the area.