The impact of intercritical annealing in conjunction with warm deformation process on microstructure, mechanical properties and TRIP effect in medium-Mn TRIP steels

We propose here for the first time, warm deformation processing involving intercritical annealing of Fe-8.5Mn-0.2C-3.0Al medium-Mn TRIP steels to obtain outstanding tensile strength-ductility combination. A critical analysis of results demonstrated that warm deformation is characterized by excellent mechanical properties. The multiphase microstructure of warm-deformed steels was relatively ultrafine. The PSE (product of tensile strength and total elongation) approached 27-53 GPa%, and the value was significantly high compared to the previously reported hot-deformed boron steels and medium manganese steels. When the deformation temperature decreased from 770 to 710 degrees C, the austenite volume fraction increased from 35.6% to 53.1%, resulting in high tensile ductility (up to 53.6%). The difference in intercritical annealing temperature had a significant effect on the tensile deformation behavior of warm-deformed steels: at 710 degrees C, the tensile deformation behavior exhibited discontinuous TRIP effect and Eiders band propagation (LBP). While at 730 degrees C, only discontinuous TRIP effect occurred in the whole plastic deformation region. The ductility of warm-deformed parts heated at 690 degrees C was mainly related to the deformation of delta-ferrite. The increase in warm deformation temperature led to significant changes in the characteristics and mode of fracture.