Impact of Non-Metallic Inclusions and Grain Structures Modified by Fast Heating Annealing on Tensile Properties of a V-Microalloyed High-Mn TWIP Steel

Characterization, classification, and size distribution of non-metallic inclusions (NMIs) in a cast high-Mn TWIP steel (Fe-20Mn-0.6C-1.5Al-0.3V, in wt.%), were studied to explore their interplay with the fracture mode during tensile deformation. NMIs were separated by electrochemical extraction, and subsequent X-ray dispersive analysis was performed to characterize their compositions. Subsequently, 70 % cold rolled TWIP sheets were processed and undergone fast heating annealing (FHA) at a heating rate of 200°C/s to anneal at temperatures 750 - 850 °C for 30 s. The grain structures achieved by FHA were evaluated by EBSD. The mechanical properties were determined by tensile testing. Distinct categories of NMIs, including Al2O3 and Mn (S,Se), and (Ti,V)N nitrides, and intricate combinations of inclusions, were identified. FHA process at low temperatures, 750-800 °C, promoted partially recrystallized microstructures. Fully recrystallized structures were obtained at 850 °C characterized by an average grain size of 2 µm at 850 °C. The structure promoted at FA 850 °C displayed noteworthy elongation of 60% with a yield strength (YS) and tensile strength (TS) of 410 and 830 MPa, respectively. A minimal effect of NMIs in TWIP steel was observed due to activating mechanical twinning mechanism, which overcomes the detrimental impact of NMIs and retard the necking induced by void formation related to NMIs.