A physically based constitutive model for predicting surface and subsurface changes induced by orthogonal dry machining of hardened AISI 52100 steel

The modification of surface and subsurface characteristics in mechanical components, such as microstructure, hardness variation and phase content, is crucial due to their significant impact on the functional performance and reliability of engineered products. Additionally, a deeper understanding of the relationship between mechanical behaviour and physical phenomena (such as recovery and dynamic recrystallization) under dynamic loading is required. In this context, accurate physically based numerical models that can simulate material behaviour during orthogonal machining and predict surface integrity by modelling thermal and mechanical aspects are necessary. In the present work, metallurgical changes during dry orthogonal machining of AISI 52100 steel with three different initial hardness levels are modelled using a customised 2D finite element (FE) model with a physically based constitutive law for material behaviour. A user subroutine has been developed and implemented in commercial FE software to predict grain refinement, hardness variation and dislocation density evolution induced by the process. Furthermore, the developed numerical model evaluates the martensite volume fraction transformation within the workpiece affected layer, considering the influences of (i) plastic deformation, (ii) cooling rate and (iii) austenitizing temperature under the effects of stress and strain. The numerical prediction strategy was calibrated and validated by analysing experimental results at different initial workpiece hardness levels, tool geometries, feed rates and cutting speeds. The outcomes demonstrated the effectiveness of the proposed strategy and its utility in studying metallurgical phenomena (both thermally and mechanically induced), predicting grain size change, microhardness evolution, machining-affected layers, phase contents and formation mechanisms.