Martensitic Transformation and Its Microscopic Mechanism of TRIP Duplex Stainless Steel Under Cyclic Loading

TRIP duplex stainless steels, characterized by high strength and high plasticity, can achieve light-weighting and contribute to reducing fuel consumption and emissions. To further promote the development and application of lightweight metastable duplex stainless steels, the martensitic transformation and the microscopic mechanism of Mn-N alloyed TRIP duplex stainless steel under cyclic loading were investigated. An in situ measurement platform for martensitic transformation under cyclic loading was constructed using an INSTRON 8801 series servo-hydraulic testing machine (Shanghai Instron Test Equipment Trading Co., Ltd., Shanghai, China) and an FMP30 ferrite measuring instrument (Nantong Fischer Testing Instrument Co., Ltd., Nantong, China). The volume fraction of martensitic transformation under symmetrical cyclic loading for different cycles, with strain amplitudes of 0.5%, 0.7%, 0.9%, 1.1%, and 1.3%, was measured. The transformation law of martensite under cyclic loading was analyzed, and a kinetics model for martensitic transformation under cyclic loading was established. Furthermore, the martensitic transformation law, the influence of austenite grain orientation on martensitic transformation, and the microscopic mechanism of martensitic transformation under cyclic loading were analyzed by means of electron back-scattering diffraction (EBSD) and transmission electron microscopy (TEM).