The effect of microstructure on the formation of retained austenite in TRIP assisted steel

The effects of the isothermal austempering conditions were investigated to clarify the mechanism of retained austenite formation in C-Mn-Si steel. The volume fraction of retained austenite increases with increases in the carbon content in the austenite and the volume fraction of austenite during austempering treatment. As the bainite transformation progresses, the carbon content of the austenite increases along with it, while the fraction of austenite that has not been transformed to bainite decreases. As a result, the volume fraction of retained austenite peaks during the austempering treatment. A high austempering temperature and large initial austenite grain size enhance bainite transformation, and the austempering time decreases when the volume fraction of the retained austenite peaks. A small initial austenite grain size leads to increases in the volume fraction of the retained austenite at the same level of the solute carbon content.