Deformation coordination and strengthening-ductilization mechanisms in a heterogeneous structure of coarse ferrite, martensite islands, and fine ferrite in 410 stainless steel

This paper demonstrates that annealing commercial 410 ferritic stainless steel (SUS410) at 850°C forms a heterogeneous structure composed of coarse-grained ferrite, martensite islands band (approximately 25.7%), and a fine-grained ferrite band. This unique microstructure achieves a strength-ductility synergy, increasing the ultimate tensile strength (UTS) from 481.06 MPa to 591.36 MPa (an improvement of 110.3 MPa), while the uniform elongation (UE) only slightly decreases from 9.02% to 8.32% (a reduction of merely 0.7%). The performance enhancement is attributed to stable hetero-deformation induced (HDI) hardening and a multi-stage deformation mechanism, where the martensite bears the load, coarse-grained ferrite accommodates macroscopic strain, and fine-grained ferrite accumulates dislocations to sustain work hardening. This paper establishes a practical annealing process at 850°C that achieves an excellent balance of strength and ductility in low-cost stainless steel through heterogeneous design.