ORIGINAL ARTICLE Analytical multi-physics model of microstructure changes in hard turning of AISI 52100 steel: prediction of thicknesses of white and dark layers F. Zemzemi 1 & H. Khochtali 2 & W. Ben Salem 2 & B. Alzahrani 3 & M-L. Bouazizi 3 Received: 19 May 2020 /Accepted: 15 December 2020 # The Author(s), under exclusive licence to Springer-Verlag London Ltd. part of Springer Nature 2020 Abstract Hard turning is more and more considered by the industry as a possible and good option for the process of grinding or pre- grinding. However, it is hurdled to a very great extent by surface integrity problems, to wit, for example, the microstructure transformations and the tensile residual stresses (white layers (WLs) and dark layers (DLs)), which are generally found to have negative effects on the stress corrosion, wear resistance, and fatigue life of machined parts. The optimization of this process has become the focus of experts. This paper presents a thermo-mechanical model able to predict the thicknesses of WLs and DLs during the orthogonal cuts of the hardened steel AISI 52100. The model combines the temperature, stress, and strain effects on the phase transformation mechanism to predict the thicknesses of layers. Unlike a similar model, presented in the literature, our developed approach firstly predicts the cutting forces for each tested condition. Secondly, it evaluates the thermo-mechanical loads on the machined surface. Thirdly, it evaluates the austenite transformation temperature. Therefore, it is possible to predict the WL and DL thicknesses for selected cutting conditions. This multi-physics model provides cutting force and layer thickness results close to those obtained experimentally in the literature. Analyzing the effect of the cutting conditions on the affected layer thickness reveals that the WL thickness increases with the rise in the cutting speed and the feed rate. Moreover, the flank wear has a greater effect on the thicknesses of layers. Keywords Multi-physics model . Hard machining . AISI 52100 . Thicknesses of white and dark layers . Flank wear 1 Introduction During machining, the finished surface and the cutting tool are exposed to extreme thermo-mechanical loads which can reach values higher than 2 GPa and 1000 °C in tool-chip-workpiece interfaces [1, 2]. Moreover, the heating and cooling rates are very high (106 °C/s). All these conditions allow the micro- structural transformations of the finished surface layer into hard-turned materials. Many microstructural alterations can occur during hard turning, such as hardening [3, 4], hardness changes [5, 6], and phase modifications [7, 8]. Some studies have reported surface softening in the near surface of compo- nents by hard turning with a sharp cutting tool [9]. These alterations have a large effect on the surface integrity and the subsurface residual stresses [10, 11]. Thin white layers (WLs) and/or dark layers (DLs) appear on the finished surface and on the formed chip. WLs have high hardness, but they are very brittle, whereas DLs are ductile [12]. Because of its critical effect on the machined part quality in terms of mechanical behavior and dimensional specifications, several experimental studies have been performed to examine these layers during hard turning. According to Barry et al. [13] and Chou et al. [14], the formation of WLs during hard turning was caused by phase transformations. The rapid increase in the contact temperature, combined with extreme high pres- sure, modifies the state of the machined surface to make it austenitic. Rapid cooling, after finishing the operation, con- verts a part of the machined surface into a martensite state. * F. Zemzemi fzemzemi@gmail.com 1 Laboratory of Mechanics of Sousse, National Engineering School of Sousse, University of Sousse, BP 264, Erriadh, 4023 Sousse, Tunisia 2 Mechanical Engineering Laboratory, National Engineering School of Monastir, University of Monastir, Av. Ibn ElJazzar, 5020 Monastir, Tunisia 3 Department of Mechanical Engineering, College of Engineering, Prince Sattam Bin Abdulaziz University, Alkharj 11942, Saudi Arabia https://doi.org/10.1007/s00170-020-06521-1 / Published online: 7 January 2021 The International Journal of Advanced Manufacturing Technology (2021) 112:2755–2771