Dispersion Mechanism of Oxide Inclusions at the Interface of Specimens in Upset Butt Welding

Abstract

Dispersing mechanism of oxide inclusions is studied by investigating the behavior of oxide film inserted artificially at the interface of specimens in the upset butt welding process.Applying the concept obtained in the study of flash welding, the authors presume that good mechanical properties can be obtained, if the oxide film which may exist always in the interface, is dispersed by adopting adequate welding conditions.It is obtained that if the temperature of the weld interface is above a certain value, welded joints with good mechanical properties are obtained under rapid heating and cooling as in this experiment. By using the model test pieces with oxide film artificially inserted in the interface, it is made clear that a certain maximum temperature in upset butt welding process is necessary for the dispersion of the oxide film. See Figs.10, 11. Above mentioned critical maximum temperature is measured to be about 1370°C which coincides with the melting point of FeO.Accordingly the mechanism of the dispersion of the oxide film is understood as follows. As the coupling force between Fe and O becomes weak in liquid state of oxide, O can diffuse easily from the oxide film layer in the interface, giving many fine oxide particles in the neighborhood and no trace of oxide film in the interface.It must be noticed that dispersion takes place at temperatures below the melting point of steel. The dispersion has little relation to applied mechanical pressure or the deformation of the test pieces. See Figs.13, 14.