GB637166A - Improvements relating to the manufacture of sintered hard alloys - Google Patents

Abstract

A process for the manufacture of sintered hard alloys comprises mixing in the form of fine powders a reducible compound of a refractory metal, a reducible compound of a more fusible auxiliary metal in such proportion as not to exceed 20 per cent by weight of auxiliary metal in the final sintered hard alloy, and a reducible compound of chromium or of vanadium or of each of these metals, reducing the mixture in a carburizing atmosphere, e.g. town gas, at a temperature, e.g. not exceeding 900 DEG C., and for a period, e.g. not exceeding two hours, insufficient to reduce the chromium and/or vanadium compound(s) to the metallic state, determining the carbon content of the reduced mixture and adding thereto the calculated complement of finely powdered carbon required for carburization of the refactory metal and of the chromium and/or vanadium, firing the resultant mixture at carburizing temperature, and finally sintering the carburized product. Prior to sintering, the carburized product may be intimately mixed with one or more separately prepared finely powdered refractory metal carbides, e.g. a cubic double carbide of titanium and tungsten having the formula Ti3WC4. The reducible starting mixture may consist of tungsten, cobalt, chromium and vanadium. The said mixture may incorporate reducible compounds of two or more auxiliary metals which form an auxiliary metal alloy in the reduced mixture, in such proportions of the auxiliary metal compounds as not to exceed 20 per cent by weight of auxiliary metal alloy in the final sintered hard alloy. Preferably, the final sintered hard alloy formed has a total content of chromium and vanadium not exceeding 5 per cent by weight, e.g. 2 to 3 per cent, a further preference being a ratio by weight of chromium to vanadium of between 0.5 : 1 and 1.5 : 1, and a total content of chromium and vanadium of 1.5 per cent. Specifications 516,227 and 614,053 are referred to.