EFFECT OF AUSTENITE PRE-DEFORMATION ON ISOTHERMAL MARTENSITE-TRANSFORMATION IN AN FE-2B.5NI-4.8MN ALLOY

With electron microscopy the investigation on isothermal martensite tr ansformation in an Fe-20.5Ni-4.8Mn alloy has been carried out to clari fy the effect of austenite state on the transformation, by applying pr e-deformation to austenite before isothermal holding. Under the condit ion without pre-deformation, the isothermal martensite products are la th martensite with {111}(f) habit planes. Dislocations in austenite se em to contribute to nucleation of martensite, and in this nascent stag e austenite substructure has no obvious effect on martensite growth. T he consequent thickening of martensite laths is apparently influenced by local austenite states, resulting in the changes in orientation, mo rphology as well as substructure of martensite lath. The kinetics of i sothermal martensite transformation is controlled by interface disloca tion determined nucleation of martensite in primary stage, but to a la rger extent, by the austenite accommodation for the shape strain of ma rtensite in the thickening stage.