Deformation and Damage Mechanisms of a Novel Mn‐Based 85 GPa% Transformation‐Induced Plasticity/Twinning‐Induced Plasticity‐Assisted Steel

The tensile deformation behavior of a C–Mn–Al–Si alloy system medium Mn steel (MMnS) is investigated in the intercritical annealing (IA) temperature range of 700 °C to 900 °C. The results indicate that MMnS exhibits excellent mechanical properties with an ultimate tensile strength of 1105.62 MPa and a total elongation of 76.87% at an IA temperature of 800 °C. This is attributed to the austenite (γ) → deformation twins (DTs) → martensite (α′) sequential transformation mechanism, which involves both the twinning‐induced plasticity (TWIP) and transformation‐induced plasticity (TRIP) effects. However, the TWIP effect disappears when the IA temperature exceeds 850 °C. A kinetic model and a strength increment model for deformation‐induced martensitic transformation (DIMT) have been developed. Additionally, the fracture mode of the sample undergoes a ductile‐to‐brittle transition as the IA temperature increases. The crack in all the samples occurs at the α′/α interface. However, the martensitic brittleness enhancement alters the crack propagation mode with increasing IA temperature. The transition from interfacial cracking to transgranular cracking through the deformation martensite leads to the occurrence of a ductile‐brittle transition.