Adjacent phase-governed stability of retained austenite and hetero-deformation-induced hardening in transformation-induced plasticity-assisted steels

The phase constituents are pivotal in modulating the transformation-induced plasticity (TRIP) effect and hetero-deformation-induced (HDI) hardening, which govern the work-hardening behavior of multiphase TRIP-assisted steels. This study investigated the mechanical stability of retained austenite (RA) and the distinct work-hardening responses of two TRIP-assisted steels with contrasting matrices: a ferrite-based matrix (TRIP-F) and a bainite-based matrix (TRIP-B), both of which have comparable RA volume fractions and characteristics. The results reveal that about 44.6% of RA grains in the TRIP-F sample were surrounded by soft ferrite, which exhibits significantly lower mechanical stability than that in the TRIP-B sample. This is attributed to the diminished hydrostatic constraint provided by the ferrite matrix, which leads to the premature onset of martensitic transformation. Crucially, the pronounced strain partitioning between the soft ferrite matrix and hard strain-induced martensite in the TRIP-F sample triggered substantial HDI hardening. HDI hardening emerged as the dominant mechanism in the later stages of deformation, sustaining a high work-hardening rate even after the exhaustion of the TRIP effect. In contrast, the minimal hardness gradient between the bainite matrix and RA in the TRIP-B sample restricted the development of HDI stress. Thus, the work-hardening behavior of the TRIP-B sample was primarily governed by the TRIP effect. This study provides new insights into tailoring phase constituents to optimize hardening mechanisms and enhance the mechanical properties of advanced steels.