DMA2022 Microscopic mechanism of cyclic hardening/softening of a TRIP-aided duplex stainless steel

Abstract

Abstract To further promote high performance transformation-induced plasticity (TRIP) duplex stainless steel’s industrial application in lightweight design of automotive structural parts, the cyclic softening/hardening properties and its microscopic mechanism of a TRIP duplex stainless steel Fe-19.33Cr-1.92Ni-2.7Mn-1.8Si is studied. Symmetrical cyclic loading tests with different strain amplitudes under strain control were conducted. The variation curves of the hysteresis loop and stress amplitude with cycles are obtained, and its cyclic hardening/softening characteristics is analyzed. An experimental study on the microstructure observation of a typical strain amplitude of 1.1% under quasi-in-situ cyclic loading was carried out by Electron Backscattered Diffraction (EBSD) and Transmission Electron Microscope (TEM). The combination of macroscopic mechanical properties and microstructure observation found that the entanglement of dislocations, dislocation interaction and grain boundaries' hindrance to dislocations are the main reasons for the initial cyclic hardening of the test steel. The formation of dislocation walls and dislocation cells leads to subsequent cyclic softening. At the secondary hardening stage, stable low-energy dislocation cells have little effect on the test steel's cyclic hardening/softening properties. The secondary cyclic hardening is mainly dominated by strain-induced ε martensite and α' martensite.