MODELING OF WHITE AND DARK LAYER FORMATION IN HARD MACHINING OF AISI 52100 BEARING STEEL

In machining of hardened materials, maintaining surface integrity is one of the most critical requirements. Often, the major indicators of surface integrity of machined parts are surface roughness and residual stresses. However, the material microstructure also changes on the surface of machined hardened steels and this must be taken into account for process modeling. Therefore, in order for manufacturers to maximize their gains from utilizing hard finish turning, accurate predictive models for surface integrity are needed, which are capable of predicting both white and dark layer formation as a function of the machining conditions. In this paper, a detailed approach to develop such a finite element (FE) model is presented. In particular, a hardness-based flow stress model was implemented in the FE code and an empirical model was developed for describing the phase transformations that create white and dark layers in AISI 52100 steel. An iterative procedure was utilized for calibrating the proposed empirical model for the microstructural changes associated with white and dark layers in AISI 52100 steel. Finally, the proposed FE model was validated by comparing the predicted results with the experimental evidence found in the published literature.