Effect of grain size on strain-induced martensitic transformation start temperature in an ultrafine grained metastable austenitic steel

Tensile tests were used to investigate the effect of grain size on the strain-induced martensitic transformation start temperature in metastable austenitic steel with special attention to ultrafine grain size. The austenite grains were refined to submicron size by the strain-induced martensite and its reverse transformations (SIMRT), which occurred during a conventional cold rolling and annealing process. The start temperature of the straininduced martensitic transformation was linearly lowered with a decrease in austenite grain size, even down to submicron grain sizes. This result is due to the decrease in grain size causing an increase in the temperature dependency of the strain-induced martensitic transformation and higher austenite stability brought about by grain refinement.