Microstructural characterization of coarse grain heat affected zone (CGHAZ) of as-welded carbon steel in MIG welding

Abstract

Metal Inert Gas (MIG) welding is a versatile and one of the arc welding processes commonly used to join metal. The high temperature due to welding arc causes a metal to fuse and formed a weld bead, and the un-melted area along the weld bead that metallurgically affected known as heat affected zone. The presence of thermal gradient at the area due to the difference in cooling rate affects the grain growth, in which the closest area to the fusion line witnesses the coarsened grain, thus deteriorates the joint property. In this experiment, the microstructure at the coarsened area is characterized based on the two main factors: heat input and the carbon content of the base metal. The heat input is controlled through variation of welding speed, and carbon content (low and medium carbon steel). As a result, it was found that the increase in heat input delays the solidification process and contributes to the transformation of high temperature microstructure (bainite) with higher energy absorption. Moreover, the specimen with lower carbon content shows higher energy absorption. These two conditions are confirmed to contributes to the mechanical property at the area.