Wear behavior in turning high hardness alloy steel by CBN tool

Tool wear mechanisms in turning of high hardness alloy steels by CBN tools under various speeds are investigated by experimental studies. In low speed cutting, the binder of the hard particles of the cutting tool is found to be removed from the substrate due to a high cutting force, resulting from low cutting temperature, and abrasion dominates tool wear. When the cutting speed is increased, a protective layer resulting from the diffusion of the bond material of the cutting tool starts to form on the chip-tool interface. This layer works as a diffusion barrier. Hence, tool wear rate is reduced and the usable life of the CBN tool is prolonged. However, when the cutting speed is further increased, cutting temperature becomes the dominant factor instead of the cutting force. The high cutting speed causes inhomogeneous shear strain, and a transition from continuous chip to saw-tooth chip occurs. The friction force is found to increase because of the very irregular chip-tool contact. This would remove the protective layer. In addition, the bond between tool particles is weakened due to serious diffusion between the work material and the cutting tool under high cutting temperature. Subsequently, hard particles are detached, and tool life is reduced. Hence, it is concluded that there exists an optimal cutting speed of CBN tool in turning of high hardness alloy steels. (c) 2007 Elsevier B.V. All rights reserved.