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A. Liersch, H. Danninger, R. Ratzi:
"The role of admixed solid lubricants in sintered steels";
Poster: International Symposium on Friction, Wear and Wear Protection, Aachen; 08.04.2008 - 11.04.2008; in: "Friction, wear and wear protection", (2008).

To improve the friction and wear behaviour of sintered ferrous materials, admixing solid lubricants to the base powder is an attractive way, and different inorganic additives can be used for lubrication. To identify the respective effects, iron powder ASC 100.29 (Höganäs AB, Sweden) and different amounts (between 0 - 2wt%) of solid lubricants such as e.g. hexagonal BN, CaF2, MnS, MoS2 or graphite were admixed, pressed and sintered. To study the influence of carbon on these systems partially 0,5wt% graphite was added. After sintering in a laboratory pusher furnace at 1120°C, in flowing hydrogen atmosphere for 60 minutes the samples were characterised by measurements of sintering density, Vickers hardness and impact energy. The microstructures were studied by LOM (light optical microscopy). To get information about the friction and wear behaviour the samples were machined, and dry sliding tests were performed on a pin-on-disc testbed. From these results friction and wear coefficients could be determined.
It can be shown that in particular the chemical stability during sintering has to be considered. The addition of the lubricants to sintered steels affects the wear behaviour in different ways; much more pronounced is the influence on machinability of PM steels and hence on tool life. For this purpose the surface roughness - characterised by Rz and Ra values after machining - was examined by a roughness depth analyser and the surface quality was evaluated and described by LOM.

solid lubricant, BN, MoS2, MnS, Iron powder, pin-on-disc-test, machining