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 interface during tempering of Fe-C-Si-Mn steel martensite has been studied by atom probe field-ion microscopy (APFIM). It has been shown that cementite can form without partitioning of Si and Mn during the early tempering stage at a low temperature. The atom probe compositional analysis shows no evidence of segregation or of concentration spikes of substitutional elements at the interface. This suggests that the early stage of cementite growth occurs by paraequilibrium mode and is controlled only by C diffusion in the matrix. In addition, significant C concentration fluctuations are measured in the as-quenched condition. The onset of partitioning of both Si and Mn occurs after prolonged time or by increasing the tempering temperature.