Flow stress and temperature considerations for orthogonal cutting of an aluminum-alloyed UHC-steel

Abstract

Recently developed aluminum-alloyed ultra-high carbon steels (UHC-steels) show high potential for industrial lightweight applications due to their exceptional mechanical properties at reduced density of 6.7–6.9 g/cm3. However, earlier publications highlighted that machining these steels results in excessive tool wear. The wear behavior was attributed to the intricate three-phase microstructure as well as the thermal properties of the material. This article aims to give further insight into the influence of tool geometry, cutting speed and uncut chip thickness on process forces and tool temperatures. Moreover, the effects on average strains, strain rates, temperatures in the primary shear zone and flow stress are discussed. The temperature load on the tool is calculated and validated via temperature measurements. The results indicate that the flow stress in the primary shear zone is affected by the strain and strain rate rather than by the shear zone temperature resulting in substantial strain hardening. The temperature measurements as well as the used analytical temperature model show consistently that temperatures above 900 °C can be easily exceeded at the rake face in dry machining of aluminum-alloyed UHC-steels and that the temperature is mainly determined by the cutting speed. Based on the results recommendations for the tool and process design are derived.