The Physics of Weldpool Formation: Phase Transition Process In Gas Metal Arc Welding Of Mild Steel Electrodes

Abstract

The phase transition process which takes place during weldpool formation is examined. The phase transition processes occur in three zone determined stages. The fusion zone, the mushy zone, and the heat affected zone (HAZ) are greatly affected by the amount of heat input. The phase change model was used to determine the state of the transition process. From the application of this model, it was found that at the obtained phase change of 0.5, the liquid metal has already cooled, and transited into the mushy zone at a temperature of 1489^oC. A Biot number of 0.0073, which is much less than 1.0 was obtained. This indicates that the heat flow in the weld pool is convective and further shows that the formation of molten weldmetal droplets that form the weldpool are under the influence of the arc heat and this makes the flow turbulent. From the findings and the microstructural analysis, it can be found that during the melting process, phase transition took place but did not significantly alter the microstructure of the weldment. This study also supports the claims made by different investigators about the different heat treatments given to metals to determine a particular hardenability level. This heat treatment process is an indicator of phase change.