Effect of Density and Composition on Static and Dynamic Properties of Low Alloy Sintered Steels 960386
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. Mean fatigue strength in excess of 85,000 psi (585 MPa) was reached on specimens pressed from low alloy steel powder admixed with 0.3% graphite and 2.0 or 4.0% Ni, sintered, case hardened and tempered.