A new effect of retained austenite on ductility enhancement in high-strength quenching-partitioning-tempering martensitic steel

Highlights: → Origin of TRIP effect occurring in Q-P-T steel but in Q and T steel is revealed by XRD. → Abnormal variation of dislocation density in martensite is revealed by XLPA. → Dislocation absorption by the retained austenite (DARA) effect is proposed. → TEM observation related to DARA effect is carried out. - Abstract: A high-strength martensitic steel treated by a quenching-partitioning-tempering process is presented to examine the effect of retained austenite on ductility enhancement in martensitic steels. Results from X-ray diffraction line profile analysis (XLPA) indicate that the average dislocation density in martensite during uniform deformation is lower than before deformation, which effectively intensifies the deformation ability. The average dislocation density in retained austenite rapidly increases with increased strain and exceeds that in martensite. Based on the XLPA results, a new effect of austenite on the ductility enhancement is proposed: the austenite phase can continuously absorb ample dislocations from neighbouring martensite laths. This effect is indirectly verified by transmission electron microscopy.