Study on Factors of Tool Wear in Diamond Turning of Carburized Steel using Decision Trees

抄録

Diamond tools wear extremely in single point turning of steels. It is thought that carbon atoms in diamond diffuse into iron. Characteristics of steels can be widely changed by heat treatment and surface modification. In our past work, we have focused on heat treatment and have changed the microstructure to suppress the tool wear. We have found carbides precipitated in α-phase suppress the tool wear. Then, we have studied on carburized steels. Tool wear was examined in comparison with element concentration, hardness, and carbide area ratio of carburized steels. Accordingly, large-size and high-circularity carbides precipitated on grain boundaries were related to increase the tool wear. However, it was not clear which factors may suppress the tool wear. In this study, past experimental data was used to examine relation between tool wear and microstructure of carburized steels. We used 21 sets of data, which contains element concentration, hardness, and carbide area ratio of carburized JIS SKD61 steels. Based on it, a decision tree which explains tool wear was made by using C4.5 classification algorithm. The decision tree revealed carburized steels without carbides whose area is ranging from 1 to 3 μm² and whose circularity is less than 0.5 tend to increase the tool wear. On the other hand, carburized steels with above-mentioned carbides, and with carbides whose area is ranging from 0.07 to 1 μm² and whose circularity is less than 0.5 suppress tool wear the best. Those results suggest that the decision tree can be used to predict microstructure which may suppress tool wear effectively.