Warm-rolling-induced matrix refinement promotes sustained TRIP-assisted strain hardening in a Q&P martensitic stainless steel

This study investigates how warm-rolling-induced refinement of the martensitic matrix influences retained-austenite transformation kinetics and TRIP-assisted strain hardening in a quenching-and-partitioning (Q&P) martensitic stainless steel. Different warm-rolling reductions followed by an identical Q&P treatment produced comparable retained-austenite fractions and XRD-estimated average carbon contents but distinct martensitic matrix architectures, while the retained-austenite size/morphology descriptors showed no systematic trend. Increasing reduction progressively refined the prior-austenite/martensite structure and altered the strain-induced transformation behavior of retained austenite. In the 90% warm-rolled sample, retained austenite transformed progressively over a broad strain range rather than being rapidly consumed at low strains. This condition achieved a yield strength of 1689 MPa, an ultimate tensile strength of 2091 MPa, and a uniform elongation of 11.0%. Correlative EBSD/HR-DIC revealed that, compared with the 50% warm-rolled sample, the 90% warm-rolled sample exhibited more spatially dispersed high-strain regions, reduced early interconnection of strain-localization paths, and lower relative in-plane surface-strain exposure of initially identified retained-austenite regions. These observations were consistent with its lower early-stage retained-austenite transformation rate and more sustained strain-hardening response. These findings suggest that warm-rolling-induced matrix refinement can promote sustained TRIP-assisted strain hardening by modifying the local deformation environment of retained austenite.