Investigating the effect of chemistry on the flash butt weldability of steels through a combination of experiments and modeling

Flash butt weld process parameters determine the weld quality. The presence of weld defects due to inappropriate process parameters leads to entrapment of oxides in the weld causes premature failure. It was also observed that the flash butt process parameter is dependent on the chemistry of the steel that is processed. The high weight percentage of Mn and Si leads to a higher weight fraction of the oxides during welding. Altering the flashing length and upset length leads to the elimination of weld defects achieving full joint strength. Thermodynamic calculations predict the oxides to be primarily FeO, Fe<inf>2</inf>O<inf>3</inf> (hematite), and SiO<inf>2</inf> (cristobalite) along with the presence of MnO, Mn<inf>2</inf>O<inf>3</inf>, and Cr<inf>2</inf>O<inf>3</inf>. The presence of Mn, Al, and Ti in the oxides at the fractured surface is correlated with the chemical potential of these elements in the liquid steel. It can be inferred from the modeling and experimental results that with an increase in temperature, a more liquid slag phase is formed as compared to solid oxides. Slag is less viscous and can be easily extruded during the upsetting stage as opposed to solid inclusion which can be trapped during the welding operation.