The effects of multi-cyclic thermo-mechanical treatment on the grain refinement and tensile properties of a metastable austenitic steel

• The volume fraction of retained austenite increased with the number of SIMRT cycles.
• The multi-cyclic SIMRT process yielded a bimodal UFG structure.
• The reverse transformation kinetics and critical temperatures are related to both grain size of γ and morphology of α′.
• The strengths of bimodal UFG steels were improved by grain refinement.
• The ductility was enhanced by the strain-induced martensitic transformation in relatively coarse grains.

The effects of the multi-cyclic cold rolling and annealing process on the grain refinement and tensile properties of a metastable austenitic steel were investigated. The multi-cyclic thermo-mechanical process yielded the bimodal ultrafine-grained structure through both the reverse transformation and recrystallization during annealing. The kinetics and temperatures of the reverse transformation were related to the average size of coarse grains. Not only yield and tensile strengths but also ductility of the bimodal-grained structure increased with the number of thermo-mechanical cycles.