Reverted austenite formation in a cryorolled lean duplex stainless steel

Abstract

© 2026 The Authors.Strain-induced martensite formation and α′-martensite to austenite reversion (α’ → γ) were investigated in a cryorolled UNS S32304 lean duplex steel. The material was rolled at 77 K up to 50 % thickness reduction and annealed up to 800 °C for 1 h. The microstructural evolution of the steel, with focus on α′-martensite to austenite reversion was followed by several characterization techniques, complemented with thermodynamic calculations. For 50 % reduction, practically all austenite has transformed into α′-martensite. From EBSD and magnetization results, the α′-martensite to austenite reversion occurs in the temperature range of 500–800 °C. At 800 °C, the austenite phase is recrystallized, and presents a bimodal grain size distribution, mainly attributed to the fragmentation of α′-martensite prior to reversion. EBSD and EDS results indicate that the α’ → γ mechanism at 600 °C is likely displacive, while between 700 and 800 °C a gradual transition from a displacive to a diffusional mechanism occurs. From magnetic measurements, a comparison between the cryorolled steel and the same material deformed at room temperature up to 80 % reduction, following annealing, was made. Except at the beginning of the α’ → γ transformation (500–600 °C), cryorolling does not accelerate the reversion of α′-martensite to austenite during annealing, contrary to expectations. However, it has a strong effect on the morphology of reverted austenite. This highlights the possibility of using cryorolling to produce a wider variety of microstructures during thermomechanical processing.

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