Microstructural features and mechanical properties of the cold-drawn wires of 304 stainless steel processed by flash annealing

This study systematically investigated the microstructural evolution and mechanical properties of the cold-drawn 304 stainless steel wires processed by flash annealing. The wires, cold-drawn from 100 μm to 50 μm in diameter, exhibited a nanostructure consisting of 92 vol.% strain-induced α′-martensite, achieving a tensile strength of 1.8 GPa with a negligible ductility. Flash annealing, characterized by the rapid heating and extremely short soaking time (∼1 second), was conducted at temperatures ranging from 700°C to 950°C. A complete martensite-to-austenite reversion occurred within a narrow temperature window from 700°C to 750°C. The small transformation temperature range, the refined austenite grain size (∼1 μm) and the high dislocation density indicate a reversion mechanism dominated by martensitic shear. Higher annealing temperatures led to limited grain growth (to ∼1.7 μm at 950°C), reorganization of dislocations into cell structures and a reduction of dislocation density. The restoration of macroscopic ductility required complete austenite reversion. Annealing at 750°C resulted in a combination of high strength (1.1 GPa) and moderate uniform elongation (∼0.02). Increasing the annealing temperature further enhanced ductility and strain-hardening capacity by reducing the initial dislocation density. The findings provide novel insight into the microstructure control and the strength-ductility synergy of advanced wire products via flash annealing.