Study of Oxide-Layer Adhered on Tool Surface When Machining Ca-Deoxidized Steel (Report 2)

Abstract

The effective range of cutting speed in which a special protective layer is formed on the tool face and prevents tool wear was studied when machining Ca-Si deoxidized steels. The correlation of the composition and location of the adhered layer with the tool wear was also investigated. From the result of the experiment, the following facts were clarified.
At the flank surface of the tool, a layer mainly consisting of CaO, Al₂O₃, and SiO₂ is formed at the cutting speeds of 150 m/min and above. On the contrary, the layer formed at lower cutting speeds mainly consists of MnS and SiO₂. Both layers prevent the tool wear effectively. However, if the tool-life criterion is determined too small, the tool life sometimes becomes short when machined at the speed range between 150 and 210 m/min.
The behaviour of the layer at the rake face is similar to that at the tool flank, and in a higher speed range the layer seems to have such composition and structure as 2CaO·Al₂O₃- SiO₂, which locates at the trailing half of the chip-tool contact zone. At an extremely high cutting speed, the crater wear advances quickly before the protective layer is formed. Therefore, the cutting speed at which the layer acts effectively has an upper limit from the view point of tool life.