A new effect of retained austenite on ductility enhancement in high strength bainitic steel

Relation between microstructure and formability of quenching-partitioning-tempering martensitic steel

“…It was further proposed that for the DARA effect to occur, two empirical conditions need to be met [32]: 1) the amount of retained austenite needs to be more than 10% by volume fraction, and 2) the interface between the two phases should be coherent or semi-coherent. These two conditions have been confirmed to exist in low-carbon Q-P-T steel [33], bainitic steel [34] and 6 high-carbon Q-P-T steel [35] when subjected to quasi-static tension, as under these conditions the interface between martensite (or bainite) and retained austenite has a coherent or semi-coherent K-S or N-W orientation. It is therefore reasonable to assume that the formability of high-strength, low-carbon Q-P-T martensitic steels will be improved by a softening of its martensitic matrix and considerable retained austenite, but this has not been yet verified by experiments.…”

Ultrahigh strength-ductility steel treated by a novel quenching–partitioning–tempering process

“…Such a DARA effect availably intensifies the deformation ability of the hard martensite phase at uniform deformation stage, and in turn evidently improves the ductility. Meanwhile, the DARA effect was predicted and verified in a bainitic steel again [24]. We cannot definitely evaluate the degree of plasticity reinforcement caused by DARA effect, however it is clear that this effect is limited based on following two facts: (1) the decrease of micro-strain and dislocation density in martensite/bainitic is limited [23], (2) the absorption of dislocation from neighboring martensite/bainitic laths would deteriorate ductility of the retained austenite.…”

Very high cycle fatigue behaviors of bainite/martensite multiphase steel treated by quenching-partitioning-tempering process

“…In this study, the morphology and size of RA have a significant influence on the [40]. With the accumulation of localized strain, the film-like RA could also transform to martensite and contribute to TRIP effect, which could relieve the stress concentration and postpone plastic localization [41].…”