The present work was carried out in order to investigate systematically the effect of the carbon content and microstructure on the current efficiency and surface roughness of the steel during the electrochemical machining.
The annealed sample had two contrasting characteristics distinguished by being hypereutectoid or hypoeutectoid constitution, and the quenched sample showed a quite different feature from them. One group of the annealed samples consisting of ferrite and pearlite structure has a high current efficiency more than 100% and a rough surface finish. The current efficiency and surface roughness increases with carbon content. Another group of annealed samples consisting of networked cementite and pearlite structure has a poor efficiency abut 60 to 75% and also a rough surface finish. On the other hand, every quenched sample, which consists of homogeneous martensite phase, has almost the theoretical current efficiency and a good surface finish. When quenching condition changed so as to give the networked cementite and the martensite together, the quenched sample showed the poor current efficiency. Further investigation by EPMA into machined surfaces proved that these characteristics were attributed to the appearance of networked cementite, to the increase in the carbide phase and to the carbon state in the iron phase.