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Free keywords:
STACKING-FAULT ENERGY; STAINLESS-STEEL; PHASE-TRANSFORMATIONS;
MECHANICAL-PROPERTIES; DEFORMATION-BEHAVIOR; TENSILE DEFORMATION;
EPSILON-MARTENSITE; STRENGTH; CR; DUCTILITYMaterials Science;
Abstract:
We investigated the effects of solute carbon concentration on the mechanical properties of Fe-19Cr-8Ni-0.05C and Fe-19Cr-8Ni-0.14C metastable austenitic steels. These steels showed an FCC(gamma) -> HCP(epsilon) -> BCC(alpha') martensitic transformation, resulting in transformation-induced plasticity (TRIP). The presence of excess solute carbon reduced the transformability because of an increase in the austenite stability. However, the work hardening capability was enhanced by a combined effect of the TRIP and dynamic strain aging (DSA). DSA requires a high diffusivity of carbon. Thus, the FCC (low diffusivity) to BCC (high diffusivity) transformation favors DSA. The hardening capability of BCC-martensite per volume is enhanced by the dislocation pinning and solution hardening effect of the carbon atmosphere, despite a decrease in the transformation rate per strain by carbon addition. Moreover, carbon addition stabilizes the deformation-induced HCP-martensite against the BCC-martensite, improving the hardening capability of the HCP-martensite through suppression of the window effect, which affects the plastic accommodation mechanism. According to our study, the steel with a low carbon content demonstrated extraordinary work hardening rates owing to a high transformation rate per strain. In contrast, the steel with a high carbon content showed sustained and high work hardening rates because of DSA. Both the steels showed approximately the same tensile strength, but completely different work hardening behavior.
