ATOM-PROBE FIELD-ION MICROSCOPY STUDY OF THE PARTITIONING OF SUBSTITUTIONAL ELEMENTS DURING TEMPERING OF A LOW-ALLOY STEEL MARTENSITE

The partitioning behavior of Mn and Si at the cementite/ferrite interf ace during tempering of Fe-C-Si-Mn steel martensite has been studied b y atom probe field-ion microscopy (APFIM). It has been shown that ceme ntite can form without partitioning of Si and Mn during the early temp ering stage at a low temperature. The atom probe compositional analysi s shows no evidence of segregation or of concentration spikes of subst itutional elements at the interface. This suggests that the early stag e of cementite growth occurs by paraequilibrium mode and is controlled only by C diffusion in the matrix. In addition, significant C concent ration fluctuations are measured in the as-quenched condition. The ons et of partitioning of both Si and Mn occurs after prolonged time or by increasing the tempering temperature.