6th CIRP International Conference on High Performance Cutting, HPC2014 Dissolution of Iron-Chromium Carbides during White Layer Formation induced by Hard Turning of AISI 52100 Steel

Abstract The (Fe, Cr) 3 C carbide morphology in the surface region of hard turned bainitic AISI 52100 steel was investigated using both experimental techniques and simulations, where microstructural analysis was correlated with analytical studies of the carbide dissolution kinetics using DICTRA 1 . The experimental results showed that for both predominantly thermally and mechanically induced white layers no significant carbide dissolution took place down to a depth of 20 μm below the machined surfaces. This was confirmed by the analytical results from DICTRA, which showed that no significant carbide dissolution should take place during hard turning given the short contact times. Within the hard turned surfaces up to ~12% of the carbides were elongated, indicating plastic deformation of the carbides during machining. Keywords: Carbide dissolution, DICTRA simulation, White layer, Hard turning, Surface integrity, AISI 52100 steel, 1. Introduction Historically, grinding has been used as the final machining operation of hardened metallic materials because of high process robustness, small dimensional variations of the workpiece, good surface roughness quality, and generation of compressive residual stresses [1]. Over the last decades, the interest in hard turning has steadily increased. The process enables a high degree of flexibility, comparatively short setup times and environmental compatibility [2]. Also the development of Cubic-Boron-Nitride cutting tool materials and geometries has resulted in a more robust process. Hence, the hard turning process has become both a complementary and a replacing process to grinding. However, even though hard turning can produce comparable surface qualities to grinding, the process is still not widely accepted as the final machining operation in the manufacturing industry. As discussed by Bartarya and Choudhury [3], the major reasons are connected to the tool wear that results in the generation of tensile residual stresses, larger dimensional variations of the final component, and surface induced white layers. The formation mechanisms of white layers during hard turning have been extensively studied over the last decades [4-7]. For example, Chou and Evans [4] concluded that white layer formation in hard turning of AISI 52100 steel was mainly thermally activated and that the high temperatures reached in cutting caused reversed martensitic transformation. Given the short duration of contact between the tool and the workpiece material, the authors concluded that the time was too short to affect the (Fe, Cr)