Influence of thermal flow and predicting phase transformation on various welding positions

This study performed computational fluid dynamics (CFD) simulation to investigate the flow patterns of molten pool during welding with a transient heat transfer. The influence of gravity changed the flow patterns of the molten pool, which determined the molten pool length and cooling time from 800℃ to 500℃(t 8/5 ) under the same heat input. In the flat position, the upward flow caused by arc forces and the inward flow generated by Marangoni convection resulted in a conflict between flows, and a molten pool length of 12.1 mm. In the overhead position, the volume of the molten pool was continuously drawn by gravity, eliminating the conflict between the inward and the upward flow. Therefore, convective heat transfer accelerated toward the edge of the molten pool, leading to an increased molten pool length (15 mm). In the vertical downward position, gravity pushed the molten pool toward the welding direction. The resultant flow pattern resulted in a rapid cooling rate and reduced the upward flow of the molten pool, leading to a short molten pool length (8.8 mm). The t 8/5 obtained from the CFD were coupled with thermodynamic simulations to predict the microstructures of the coarse-grain heat-affected zone.