Cementite dissolution at 860 °C in an Fe-Cr-C steel

摘要

In this work, cementite dissolution at 860 °C in SAE 52100 Fe-Cr-C steel is experimentally investigated using optical microscopy and dilatometry, and numerically simulated based on a model proposed to solve a vector-valued Stefan problem with a finite size of austenite cell. It is found that cementite particles are dissolved very rapidly in the initial stage and then the dissolution gradually slows as a result of the change of the concentration slope at the interface of both carbon and chromium. At the end of the dissolution process, carbon is homogeneously distributed over the austenite grain, while the chromium distribution is inhomogeneous. Nevertheless, it is also found from image analysis that during the later stage of the dissolution, the size and particle density do not decrease simultaneously, which is not taken into account by the numerical model. When applied to a thermal treatment for bainitic transformation at 230 °C, cementite dissolution at 860 °C is found to increase the incubation time and to decrease the transformation rate.