In situ observations of non–equilibrium austenite formation during weld solidification of an Fe–C–Al–Mn low–alloy steel

Abstract

The microstructure and properties of a welded alloy are influenced by the combined effects of solidification and subsequent solid–state transformations that occur during weld cooling. These phase transformations are further influenced by the cooling rate that the weld experiences and thus by the type of welding process that is used. In this research, microstructure development of a low–alloy steel weld was investigated under the high cooling rates produced by stationary arc welds. These welding conditions are different from the slow weld–cooling conditions, where δ–ferrite forms as the primary solidification phase. The cooling rates of the stationary welds used in this study were of the order of 10 3 K s –1 , which were high enough to induce the formation of the non–equilibrium austenite phase during solidification. This non–equilibrium mode of solidification was directly observed using an in situ time–resolved X–ray diffraction technique using synchrotron radiation, and the resulting microstructures were examined using optical microscopy.