AN ATOM-PROBE STUDY OF CEMENTITE PRECIPITATION IN AUTOTEMPERED MARTENSITE IN AN FE-MN-C ALLOY

Atom probe field ion microscopy has been used to determine the concent ration profile of the substitutional solute element manganese through cementite particles in martensite in a ternary Fe-3Mn-0.1C (wt%) alloy . The start temperature of the martensite reaction (M(s)) in this allo y has been determined to be 380 degrees C, which is relatively high. T his means that as the specimen is quenched using helium gas, after aus tenitising, cementite particles are able to precipitate within the mar tensite plates which form at or near the M(s) temperature. The atom pr obe results revealed that, in the case of autotempered martensite, the re is no significant partitioning of the manganese between the cementi te and the supersaturated ferrite matrix.