Abstract: Microstructural evolution and mechanical properties of hot-extruded 13Cr martensitic stainless steel during austenitizing isothermal holding were investigated. During hot extrusion, Dynamic strain-induced transformation (DSIT) generated only a limited fraction of strain-induced ferrite in 13Cr steel. In contrast, through isothermal static phase transformation at 950 °C, extensive banded ferrite formed, its volume fraction first increasing to a peak value, then decreasing with prolonged holding. At an early stage of static transformation, the elastic energy stored in deformation shear bands provided the driving force for austenite-to-banded ferrite transformation within these localized regions. At a later stage, the formation of ferrite coupled with recrystallization and growth of austenite grains released elastic energy, promoting reversion of ferrite to austenite. Ultimately, elastic energy relaxation governed the morphology and volume fraction of the ferritic/martensitic dual-phase (DP) structure. The fine-banded ferritic/martensitic dual-phase structure developed in 13Cr steel exhibited a tensile strength of 1.77 GPa coupled with a remarkable elongation of 18.9 %. The strength-ductility synergy in 13Cr steel was enabled by stress-partitioning behavior at soft/hard phase interfaces and activation of multiple slip systems under the boundary constraints of banded ferrite.

Key words: Elastic energy relaxation, Static transformation, 13Cr martensitic stainless steel, Banded ferrite, Strength-ductility synergy