A machinability evaluation based on the thermal and mechanical properties of two engine valve steels

Abstract

Iron-based superalloys are difficult to machine because of their thermal and mechanical properties provided by alloying elements as nickel, chromium, titanium, and aluminum. However, parts made with this kind of material has to be machined during their production processes. In this work, two different automotive engine valve steel grades, VAT 30® and VAT 36®, were compared in terms of machinability, considering cutting power consumption, roughness of the machined surface, and tool life, besides the identification of the main tool wear mechanisms that have led to the end of tool life. The main goal of this work is to understand the difference in these machining outputs based on the thermal and mechanical properties of these two materials. In order to reach this goal, turning tests were held using two different cooling conditions, conventional and high-pressure coolant. Also, two PVD-coated carbide inserts were applied, one with negative rake angle and another neutral. Finally, cutting speed was tested in two levels, providing a full 24 factorial planning. Results show that VAT 30® has shown higher machinability in terms of tool life in almost every condition, although this steel presents higher hardness, mechanical strength, and strain hardening coefficient, besides lower thermal conductivity. However, it also presents lower ductility and abrasiveness, features that retarded abrasion and attrition as tool wear mechanisms, in such a way that tool life could have been lengthened.