Understanding effect of ferrite on strength-ductility balance of Fe-Mn-Al-C duplex lightweight steel

Lightweight steel with low density and superior mechanical properties is highly desirable for transportation equipment applications. An Fe-27Mn-10Al-1C (wt.%) lightweight steel with tensile strength of 917 MPa and ductility of 56.6% was prepared via short-time solution treatment. The microstructural evolution during heat treatment and the deformation mechanisms closely associated with strain hardening response were mainly discussed. The coarse intergranular j-carbides detrimental to ductility gradually dissolved with increasing the solution temperature. Meanwhile, the intragranular j-carbides and B2 were precipitated in austenite and ferrite, respectively. Quantitative analysis revealed that the intragranular precipitates contributed approximately ~ 195 MPa to the yield strength. Investigation of deformation behavior revealed that the trans-interface strain transfer by dislocation evolution and pile-up serves as the dominant mediator enabling coordinated deformation between austenite and ferrite. Additionally, it was revealed that the ferrite with deformation ability could dynamically regulate the strain partitioning to inhibit cracks initiation. Such multiscale coordinated defor-mation mechanisms effectively enhanced the strain hardening capacity and the plastic stability.