Austenite in multiphase microstructures quantified by analysis of thermal expansion

A novel approach is proposed to determine the volume fraction of retained austenite (RA) in annealed dilatometer samples. This method is tested by reheating as-formed multiphase microstructures made from a steel of composition Fe–0.29C–2.4Mn–1.8Si. The measured thermal expansion data can be simulated using analytical models according to a rule of mixtures of the individual phase constituents. The volume fractions of RA evaluated from the best fits are in good agreement with X-ray diffraction results.