Experimental Examination for Understanding of Transition Behavior of Oxide Inclusions on Gas Pressure Weld Interface

Gas pressure welding method is often applicable for joining of rails and reinforcing steel bars. However, if bonding work is inferior, a large quantity of oxide inclusions remain at the weld interface and those inclusions will cause the weld defects. In the previous study, the morphologies of oxide inclusions were estimated by the observation of the transition behavior for inclusions on each welding stage during the gas pressure welding.In this study, we traced the morphological change of oxide inclusions and base material in pressure welding process to clarify the transition behavior of oxide inclusions.In the first stage, Fe-O type oxide inclusions were mainly deoxidized by carbon, which exists in base material, and the degree of decomposition was influenced by temperature. Furthermore, oxide inclusions, which contain Si and Mn, emerged from outside region of Fe-O type oxide inclusions due to participation of Si and Mn, which exist in base material. In the final stage, almost of oxide inclusions existed on the weld interface were Si-Mn-O type, and the Si content of these oxide inclusions gradually increased as well as downsizing of oxide inclusions as welding process advanced.