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A study was conducted to characterize the effect of density and elemental additions of graphite, copper and nickel on static and dynamic properties of low alloy P/M steels prealloyed with 0.85% molybdenum (ATOMET 4401). Each test parameter was studied at three levels: green density at 7.0, 7.2 and 7.4 g/cm3, graphite at 0.30, 0.45 and 0.60%, copper at 0, 0.5 and 1.0% and nickel at 0, 2.0 and 4.0%. Powder mixes were either single or double pressed to the targeted density, sintered at 1120° C in a nitrogen based atmosphere and tempered in air for one hour at 185° C. Specimens were evaluated for tensile, impact and fatigue strengths. The effect of case hardening was also evaluated on a series of FLN2-4400 and FLN4-4400 specimens pressed to 7.4 g/cm3 and carburized to a depth of 1.25 mm. It was confirmed that density is a key variable to improve impact strength, elongation and fatigue strength. Admixed nickel content also contributed to significantly improve fatigue and tensile strengths.

Drastic reduction of costly machining operations is a definite advantage of powder metallurgy. However, due to design constraints, many P/M parts still require some machining. For these applications, the machinability of materials becomes an important parameter of the part manufacturing process. Test programs have been conducted at Quebec Metal Powders Limited to characterize the machinability of ferrous P/M materials. The effects of sintered density and alloying elements, namely carbon, copper and phosphorus, on the drilling thrust force are presented together with those of machinability enhancing additives such as manganese sulphide and boron nitride. Methods to optimize both strength and machinability of P/M materials are also discussed.