Machinability of FLC-4608 powder metallurgy steel compacts in cured green, pre-sintered and sinter-hardened states: A comparative analysis

FLC-4608 (denomination by Metal Powder Industries Federation) sinter-hardened steel is a difficult-to-cut material; however, machining powder compacts before sinter-hardening of this material is a viable solution to deal with the machining difficulties. Earlier studies have separately discussed the machinability of green and pre-sintered FLC-4608 compacts without comparing their machinability outcomes. Further, correlating the microstructures of these compacts with their respective machinability outcomes has also received scarce attention. In this view, the present study is novel because it compares the machinability of FLC-4608 powder compacts in their cured green versus pre-sintered (at 800 °C) versus sinter-hardened states with respect to the microstructural attributes of these compacts. In this study, the compacts were machined at a fixed level of spindle speed (1185 r/min), feed rate (0.045 mm/rev), and depth of cut (0.5 mm). The cutting force, machined surface roughness, and exit-edge-breakout area, that is, the broken area at the edge from where the cutting tool leaves the workpiece at the end of the machining, were considered as machinability outcomes. The results indicated that cured green compacts exhibit nearly 80% less and pre-sintered compacts exhibit nearly 59% less cutting force compared to sinter-hardened compacts. Conversely, compared to cured green compacts, pre-sintered compacts exhibit nearly 92% reduction and sinter-hardened compacts exhibit nearly 94% reduction in the machined surface roughness. Sinter-hardened compacts were found to be free from exit-edge-breakout, whereas nearly 176% higher breakout was observed in pre-sintered compacts compared to cured green compacts. In light of these results, a hybrid production sequence that includes machining green or pre-sintered compacts for material removal and re-machining post-sinter-hardening for finishing is found to be a pertinent approach for fabricating FLC-4608 sinter-hardened steel components.