Using Eddy Current Technology for the Determination of Subsurface Hardening during Machining

Surface integrity is an important property of all workpieces. Each manufacturing process influences the condition of the subsurface of a component. A hardened subsurface is advantageous to withstand high mechanical loads by simultaneously maintaining a ductile workpiece core. Cryogenic external longitudinal turning can harden metastable austenitic stainless steel using deformation-induced martensitic transformation, which leads to a martensitic subsurface and, thus, increased wear resistance. The mechanism of the martensitic transformation was analysed to improve this kind of hardening process. Eddy current testing can be used to determine the martensite content of metastable austenitic steel even within the cutting process. To improve the understanding of the martensite on the eddy current testing signals, finite element simulations were conducted. This thesis presents a method to enable the generation of hardened subsurfaces by cryogenic turning.