In situ and locally resolved analysis of retained austenite stability during tensile loading in a high-strength weld metal

The transformation of retained austenite under mechanical load has a significant impact on the mechanicalproperties of high-strength low-alloy steels and weld metals. Here, we have studied the stability of retainedaustenite in a microalloyed, multipass high-strength all-weld metal using in situ high-energy X-ray diffractionphase quantification during tensile loading. Two-dimensional phase maps were acquired before and after testingto reveal the locally resolved distribution of strain-induced austenite transformation. Depending on the positionwithin the unstrained specimen, the amount of retained austenite varied between 1 wt.% and 6 wt.%. Duringloading, the retained austenite remained largely mechanically stable within the macroscopic elastic regime.Upon the onset of plastic deformation, a pronounced transformation of the metastable retained austeniteoccurred. Plastic deformation was predominantly localized in areas which were not reheated during multipasswelding. In regions where reheating occurred, precipitation hardening from microalloying elements produced amicrostructure with significantly higher strength levels.