Dissolution of different graphite grades during sintering of PM steels

The dissolution behaviour of graphite during sintering of Fe–0.8%C and the resulting properties were studied using standard high quality natural graphite and an artificial graphite grade recently developed for ferrous powder metallurgy. Sintering was done in high purity N2 atmosphere for 60 min, the temperature being varied. It showed that dissolution of carbon takes place mainly in the isothermal temperature range 750–950°C, for the artificial graphite the maximum dissolution rate being observed at a temperature about 50° lower than for the natural graphite. This also affects the properties, especially the hardness, of the specimens sintered in this temperature range while at standard sintering temperatures of about 1120°C both graphite grades yield well comparable results. Therefore, selection of the graphite grade seems to be important especially for pre-sintering of specimens prior to further treatment, dissolution of the graphite increasing the hardness but also improving the inter-particle strength.