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 mechanical properties of high-strength low-alloy steels and weld metals. Here, we have studied the stability of retained austenite in a microalloyed, multipass high-strength all-weld metal using in situ high-energy X-ray diffraction phase quantification during tensile loading. Two-dimensional phase maps were acquired before and after testing to reveal the locally resolved distribution of strain-induced austenite transformation. Depending on the position within the unstrained specimen, the amount of retained austenite varied between 1 wt.% and 6 wt.%. During loading, 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 austenite occurred. Plastic deformation was predominantly localized in areas which were not reheated during multipass welding. In regions where reheating occurred, precipitation hardening from microalloying elements produced a microstructure with significantly higher strength levels.