Carburization of tungsten powder by carburizing gases. (2nd Report)

Abstract

In the 1st. report, the effect of carburization temperature, carburization time, the specific surface area of W powder, CH4/H2 ratio in volume, and the thickness of W powder on the carburization of W powder by H2-CH4 mixture has been discussed. In this paper, the effect of heating of imperfectly carburized W powder at lower temperatures for 30 min in the temperature range of 1200°C-1400°C in a stream of H2 and H2-CH4 mixture have been studied and the change of lattice constants of residual W with progress fo carburization has been studied. The mechanism of carburization of W powder by H2-CH4 mixture has been also discussed. The results obtained are summarized as follows: (1) The lattice constant of the residual W in gaseously carburized powder is smaller than that of normal W and approaches to normal value with progress of carburization. (2) By heating at higher temperatures the diffracted X-ray of WC in carburized powder becomes sharper. (3) When WC powder which is carburized at lower temperature, is used in popuration of WC-Co alloy, abnormaly grown grains appear and the number of these grains increases with the broadening of the diffracted X-ray of the used WC.