Effect of Si in Workpiece Material on Tool Wear in Hard Turning

The influence of Si content in steel on tool wear in turning of 0.8 mass% C hardened steels with TiAlN coated CBN cutting tools is investigated. The Si contents in the steels are varied between 0.05 and 0.6 mass%. Although these steels have similar microstructure, hardness and volume fraction of retained austenite, the width of the flank wear of the tool increases with increasing the Si content. Adhered oxides are formed on the flank face after cutting, and the amounts, compositions and crystal structures of these oxides are changed as the Si content is varied. The higher Si content results in large amounts of adhered oxides. The crystalline oxide containing a large amount of Fe is mainly formed when cutting the 0.2 mass% Si steel, while the amorphous oxide containing a large amount of Si is mainly formed when cutting the 0.6 mass% Si steel. At the interfaces between the tool coating and the adhered oxides, the Al element of the tool coating tends to diffuse more easily into the Si containing amorphous oxide than into the Fe containing crystal oxide. This indicates that the Si containing amorphous oxide, formed with the higher Si added steel, promotes diffusion wear, resulting in increased tool wear.