Microstructures of electro-carburised mild steels

The molten carbonate salts based electro-carburisation process, as reported here, is non-toxic, environment friendly, cheaper than the cyanide based techniques and highly effective in turning mild steels into a more valuable metal. The effectiveness of the electro-carburisation process was investigated by microstructure analysis. The sample was ground, polished and then etched in a 2 % nital solution. Examinations of the microstructural changes in the etched samples by SEM-BSE and microscope (500X magnification) revealed the distribution of carbon throughout the electrocarburised mild steel. The changes were typically represented by two phases, namely, the brighter areas resulting from the ferrite phase (iron rich), and the darker areas indicating the presence of carbon in the pearlite phase which were consisted of alternate stripes of ferrite and cementite (carbon rich). These microstructural features, particularly the ferrite and pearlite regions, were found to be affected by the cell voltages applied during electro-carburisation and the type of molten salts.