Modeling of chemical wear in ferrous alloys/ silicon nitride contacts during high speed cutting

Abstract

The wear resistance of Si3N4 in machining of iron alloys can be surprisingly low due to chemical affinity for dissolution in the metal. This limits the use of Si3N4 inserts in high speed machining of steels, while Si3N4 retains the best performance of all cutting materials in turning of grey cast iron, a different ferrous alloy. The chemical wear of several ceramics has been investigated on the basis of dissolution in pure iron by Kramer and Suh. Nevertheless, the influence of alloy elements was not studied. In the present work, solid solution thermodynamics is applied to predict chemical wear of Si3N4 by setting the influence of interaction coefficients of the alloy elements in the Henrian activity of Si and N in austenite. The model predicts the relative order of magnitude of the crater wear of Si3N4 inserts in machining of tool steels, carbon steels and grey cast iron.