Machinability of Sinter-hardening PM materials with experimental machining enhancers

Although powder metallurgy is an economical method for production of near net shape components, machining operations are often required to deliver desired geometrical features, dimensional tolerances, and surface finish of PM parts. Machining enhancers are used to improve the machinability of PM components and to increase tool life. MnS is the most common machinability enhancer used for PM steel parts. However, it is less effective for harder materials and, especially, for sinter-hardening grades. It has also shown to stain steel parts and make them susceptible to corrosion. In this study the machinability of sinter-hardening materials with new experimental machining enhancers was investigated. Different additive formulations were evaluated and their performance was compared to that of the materials without machining enhancer and with MnS. Specimens were compacted, sintered, and cooled down at two cooling rates to evaluate the effect of post-sintering cooling rate on sintered properties and machinability. The results of the material characterization including dimensional change, static and dynamic properties, microstructural analysis, and machinability by drilling test are presented in this paper.