Machinability of a Sinter-Hardened Powder Metallurgy Steel: Combined Analysis of Cutting Force and Chip Characteristics

This study investigates the machining of FLC-4608 (designation by Metal Powder Industries Federation, standard 35) sinter-hardened steel compacts with 90% relative density during turning operation. The objective of the study is to analyze the effect of cutting velocity and feed rate on the cutting force component in the direction of cutting motion using chip characteristics. The results showed that the combination of high cutting velocity and low feed rate is the appropriate condition to obtain a low value of the cutting force component. The results also indicated that the machining configurations considered produce shear-localized segmented chips, also known as saw tooth chips, and that the chip formation process involves almost complete densification of the uncut chip material. Except for chip length, all the investigated chip characteristics, minimum and maximum chip thickness, shear band microstructure, and structure below the tip of the chip segment were consistent with the results of the cutting force component. As the feed rate increased, the minimum and maximum chip thickness increased, which was consistent with the increasing value of the cutting force component. Similarly, through the microstructure of the adiabatic shear band and the structure below the tip of the chip segment, increasing cutting velocity showed the dominance of the thermal softening effect over strain hardening and strain rate hardening, consistent with the decreasing value of the cutting force component. This approach is novel, as chip characteristics have received little attention in previous studies on the machining of PM materials. The present study is potentially helpful to the PM industry in achieving better machining process control through a thorough understanding of the results related to the cutting force component in the direction of the cutting motion. The future scope discussed in this report also has prospects for advancing the science of machining PM materials.