Abstract
•A high precision prototype lathe is adapted to machining hard steel.•The achieved surface roughness is in the range of 0.1–0.2μm (Ra).•Precision hard turning generates homogeneous microstructure and induces compressive residual stresses at surface and in subsurface.
Frequently, strict conditions are imposed for high precision components manufacture such as high dimensional precision, accurate geometrical form and good surface finish. High precision machining allows industry to dispense with successive operations such as turning, grinding and polishing to attain these objectives. In this paper, precision hard turning is proposed for the finishing of AISI 52100 bearing components. Several developments were carried out on the prototype lathe in order to adapt it to machining hard steel AISI 52100. To ensure high stability and stiffness during machining, the performances of hydrostatic X and Z-axis slides-ways were investigated. Machined surfaces were characterized in terms of roughness, microstructure analysis, quantitative phase composition and residual stress measurements. The achieved surface roughness Ra is in the range of 0.1–0.2μm. Microstructural investigations revealed metallurgical transformations, such as the presence of a very fine white layer (<1μm) on the top surface and a thermal affected zone (transition zone) of 35–50μm in the sub-surface. Energy dispersive X-ray diffraction analyses show that the percentage of the different phases is not quantitatively affected and the material remains in the martensite phase. X-ray measurements show that Full Width at Half-Maximum (FWHM) is lower in the transition zone than in the bulk material. This decrease of FWHM may be associated to a decrease of dislocation rate. Precision hard turning induces compressive residual stresses at the surface and in the subsurface, which corresponds to the transition zone. Moreover, increasing cutting speed leads to increase the level of compressive residual stresses.