Retention of austenite in the welded microstructure of a 0.16C–1.6Mn–1.5Si (wt.%) TRIP steel

In this work, the retention of austenite in post-welded microstructures of a 0.16C–1.6Mn–1.5Si (wt.%) TRIP steel is investigated. Fully penetrated welds are produced by means of gas tungsten arc (GTA) welding and laser beam (LB) welding. The microstructure, particularly retained austenite, is analyzed using optical microscopy, Vickers hardness measurements, X-ray diffraction and saturation magnetization. It is found that the GTA welded TRIP steel contains a relatively large fraction of retained austenite, which may benefit the weldability of this steel. A minimum hardness is found in the heat-affected zone (HAZ) next to a high hardness plateau after both LB and GTA welding as a result of a large fraction of ferrite. It is suggested that for TRIP steels, proper control of the formation and decomposition of retained austenite in the HAZ is important to prevent weld failure. The hardness is therefore not a sufficient indicator for the weldability.