TRIP deformation mechanism of core–shell austenite in PH17-7 stainless steel

The synergy of high strength and good ductility remains a critical challenge in the development of advanced precipitation-hardened stainless steels. To clarify the relationships between strength and plasticity-toughness in semi-austenitic precipitation-hardened stainless steels, we systematically examined the microstructure evolution behaviors of core–shell austenite structure in PH17-7 stainless steel under RH conditioning and aging treatment, and explored the mechanism how these evolution behaviors governed the deformation behaviors of the steel. Under the aging conditions, fine Cr 23 C 6 carbides (<100 nm) were mainly located at martensite lath boundaries and the interfaces between martensite and retained austenite, accompanied by the local enrichment of Ni and the formation of reverted austenite consisting of a relatively Ni-depleted core and a Ni-enriched shell. EDS line scanning results showed a characteristic double-peak Ni profile in the shell, where the Ni content was enriched to about 15 wt% relative to the matrix (from 7 to 8 wt.% in the matrix), confirming the pronounced chemical gradient. Under tensile deformation, a graded TRIP response emerges: the less stable, Ni-depleted cores transformed to martensite at lower strain levels, whereas the Ni-enriched shells transformed at higher strain levels; After fracture, nearly all austenite transformed to martensite. This stepwise transformation-induced plasticity (TRIP) effect yielded the concurrency of high strength with appreciable plasticity. Our study elucidates the graded TRIP deformation mechanism of core–shell reverted austenite during tensile loading and provides a microstructural basis for achieving the synergy of high strength and good ductility in PH17-7 stainless steels.