Abnormal TRIP effect on the work hardening behavior of a quenching and partitioning steel at high strain rate

Quenching and partitioning (Q&P) steels possess high strength and good ductility because of the transformation of metastable austenite to martensite, which is referred to transformation-induced plasticity (TRIP) effect. In literature, TRIP effect generally results in an enhancement of work hardening rate during tensile test. Nevertheless, the present work observes an abnormal TRIP effect in a 1500 MPa Q&P steel. Although a considerable amount of retained austenite transformed to martensite during the tensile test at a strain rate of 1000 s(-1), no obvious enhancement of work hardening rate was observed. To explore the underlying mechanisms for such an abnormal TRIP effect, the evolution of dislocation density and martensitic transformation were characterized by synchrotron X-ray diffraction and electron microscopy. Comparing the quasistatic and high-strain-rate results, it is found that the dislocation density in the martensite matrix is suppressed at 1000 s(-1), resulting in a lower work hardening. Furthermore, the transformed martensite deforms plastically at 1000 s(-1). Without the composite-like deformation behavior (elastically in hard transformed martensite and plastically in soft martensite matrix), the corresponding work hardening is reduced. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.