Influence of tool properties on thermomechanical load and surface morphology when cryogenically turning metastable austenitic steel AISI 347

When cryogenically turning metastable austenitic steels, the microhardness of the workpiece subsurface can be increased by deformation induced phase transformation from austenite to martensite in superposition with strain hardening mechanisms, which leads to an increased wear and fatigue resistance. In this way, a components surface can be hardened during machining, rendering a separate hardening process like shot peening obsolete, thus leading to a more economical and sustainable manufacturing of hardened components made of stainless steel. While the impact of the cutting parameters and the cooling strategy were already investigated, the influence of the tool design on the thermomechanical load and the resulting surface morphology is largely unknown. This paper presents comprehensive investigations regarding the influence of different tool properties on the process forces, the surface temperature, the extent of deformation induced phase transformation, the resulting microhardness as well as the surface topography. The varied tool properties were the cutting edge radius, the chamfer angle, the corner radius and the coating. The causal correlations were evaluated and subsequently recommendations for the tool design were derived.