Formation, quantification and morphology of retained austenite in the heat-affected zone of a high-strength steel

This study focuses on the formation, quantification and morphology of retained austenite in the heat-affected zone (HAZ) of a thermomechanically controlled processed high-strength steel. Physical simulation using dilatometry combined with high-energy X-ray diffraction was employed for in situ phase quantification, while various electron microscopy methods were used for microstructural investigation. Compared to the initial state, which contained approximately 1% retained austenite, the content increased by 1.9% in the coarse-grained HAZ and by 3.9% in the intercritically reheated coarse-grained HAZ. Some of the formed retained austenite appears as stand-alone phase in both zones. However, the majority seems to be present within various types of martensite–austenite constituents.