Machinability of Powder Metallurgy Steels Using PcBN Inserts

Abstract

Primary manufacturing of steels by powder metallurgy (PM) is of increasing interest for a wide range of industrial applications. Especially in automotive parts and tools, PM materials are utilized, as they show advantageous behavior regarding chemical, mechanical and functional properties as well as resource efficiency. Consequently, machining of these materials is an emerging topic for both, industry and science. This paper addresses the machinability of PM steels. Two PM high speed steels (HSS) were characterized and machined varying the machining parameters and edge preparation (PcBN inserts) in longitudinal and orthogonal hard turning. Furthermore, the influence of manganese sulfides (MnS) in the PM material was analyzed by comparing experiments applying alloys with defined content of MnS. Besides tool life and achievable surface roughness, the surface integrity was assessed. The results reveal that the amount and shape of carbides as well as the porosity of the PM steels play an important role in the wear mechanism when machining this kind of materials. As expected, addition of MnS leads to a decrease of cutting forces and allows for significantly higher tool life. The influence of machining parameters and the tool edge geometry is discussed. Based on the results, suitable cutting conditions for machining of PM steels can be derived.