Damage Evolution Mechanism Around AlN Non-Metallic Inclusions in Fe-8.5Mn–3Al-0.2C Lightweight Medium-Mn Steel During Warm Forming

Based on the tensile test in two-phase region, the damage evolution mechanism around AlN non-metallic inclusions in Fe-8.5Mn–3Al-0.2C lightweight medium-Mn steel during warm forming was elucidated. The findings indicate that voids primarily originate from the bonding interfaces between AlN non-metallic inclusions and ferrite. According to the numerical simulation results, strain eventually concentrates at the bonding interface where the AlN inclusion is connected to the high-strain ferrite in the direction parallel to the load, which is in good agreement with the experimental results. TEM analysis reveals the semi-coherent interface between AlN and austenite as well as the incoherent interface between AlN and ferrite. The incoherent interface between AlN and ferrite exhibits higher interfacial energy and worse mechanical stability, accelerating the separation of the bonding interface between AlN and ferrite.