Studies on the Carbon Impregnation during Hot Pressing in WC-Co Alloys

Abstract

It is said that the hot pressing gives better properties to WC-Co alloys than the cold presssinter method. At present time, graphite is mainly used as the die material for the hot pressing of WC-Co alloys. In this paper, the carbon impregnation to the sintered body which is caused by the contact of the powder (sintered body) and the graphite die was studied. The results obtained are as follows.(1) The layer depth of carbon impregnation increased parabolically with the increase of keeping time. However, it was assumed that the carbon impregnation which results in the excess carbon precipitation does not to occur during heating and also at the initial stage of keeping time, but assumed to begin to occur after the.sintering is completed. (2) The layer depth of carbon impregnation increased with an increase of hot press temperature. (3) The layer depth of carbon impregnation depended upon the property of the graphite used for the die. (4) The hot press pressure did not have a definite relation to the layer depth of carbon impregnation, but was affected by the behavior of metal which was squeezed from the die and other factors. (5) The metal which was squeezed from the die during hot pressing was mainly composed of cobalt and the WC content involved in it was by far lesser than that corresponding to Co-WC eutectic.