Experimental and Numerical Study of C Electromigration in Iron During Ferrite-to-Austenite Transformation

The influence of the electric current on the diffusion of carbon in an ARMCO iron sample is studied. The sample, placed between two graphite punches, is heated in the intercritical domain (between 736 & DEG;C and 912 & DEG;C) thanks to Joule heating. The diffusion of C in ferrite induces its transformation into austenite. After cooling, the microstructure of the sample gives information on the transformation fronts positions and C concentration profiles. The transformation front velocity is higher in the direction of the electric current and lower in the opposite direction. To understand and predict this phenomenon, a new model accounting both for the allotropic phase change and the electromigration of C in iron is proposed. Some model parameters are fitted comparing the predicted and the measured interface positions. With these parameters, the simulated C concentration profile is in good agreement with the experimental one.