MICROMECHANICAL MODELING OF THE BANDED STRUCTURE OF MARTENSITE IN SMALL INCLUSIONS

The stability of austenite against strain induced martensitic transfor mation (SIMT) strongly depends on the grain size of the austenite. Thi s is observed in austenitic steels with grain sizes from several mu m up to several hundred mu m and for much smaller austenitic grains (thr ee orders of magnitude) that are embedded in a non austenitic matrix. fcc Fe-precipitates may be formed in dilute Cu-Fe alloys by a certain heat treatment. These Fe-particles transform only by plastic deformati on of the alloy. The SIMT leads to a banded structure with parallel la yers of martensite. We investigate the influence of the external stres s state on the microstructure (number of twin bands, relative thicknes s of the bands) with the help of a micromechanical model. The grain si ze effect on the austenite's stability against SIMT and on the microst ructure may be explained by a thermodynamic transformation criterion a nd the local mechanical driving force.