Deformation Induced Surface Hardening when Turning Metastable Austenitic Steel AISI 347 with Different Cryogenic Cooling Strategies

In terms of production costs and manufacturing time there is a permanent effort to shorten the process chain by combining different process steps. For metastable austenitic steels there is the opportunity of an integrated surface hardening during machining. This leads to an increase of the wear resistance and fatigue strength of highly loaded components. For this purpose, high deformations combined with low temperatures during the material removal process are needed. To achieve this an insert with a chamfered cutting edge is used to enlarge the passive forces. The central challenge is to keep the temperatures in the cutting zone at a sufficient low level during turning AISI 347. Cryogenic coolants like liquid nitrogen (LN2) or carbon dioxide (CO2) offer an opportunity to keep the process temperature at low values. In this context, the influence of different cryogenic cooling strategies are compared with dry cutting. Additionally, the cutting parameters feed f and cutting speed vc are varied. To detect cause and effect relationships measurements of the passive force, workpiece surface temperature, formed martensite content and micro hardness are performed.