Study On Fabricating Process Of Cobalt Gradient Cemented Carbide In Carburizing Atmosphere At Negative Pressure

The carbon-lack cemented carbide with little eta-phase uneven distribution is fabricated and vacuum carburized in this paper. The vacuum furnace is adapted to meet both vacuum sintering and carburizing at negative pressure.The carbon-lack cemented carbide is carburized in the mixing gas CH4/H2 at the temperature of liquid phase. The dual phase structure cemented carbide, in which eta-phase is free in the outer zone and existing in the inner zone, could be obtained successfully. The ratio of CH4/H2, pressure of mixing gas , time of carburizing , carbon content of alloy made importance influence on the cobalt gradient distribution .The results show that the carbon of eta-phase should be well controlled; the sintering temperature would influence the phase content of eta-phase, the higher sintering temperature and the longer sintering time could increase the eta-phase of the powder. The gradient distributed cobalt phase is more obvious with the conditions of carbon content of alloy of 5.33wt%, sintering pressure of 75mmHg, flow ratio of CH4/H2 of 1.4:1, carburizing temperature of 1440C, and carburizing time of 180min.When alloy body is carburized, the capillary Phenomenon and difference of liquid phase of cobalt which come from the reaction ofeta-phase with C make liquid cobalt migration. The pressure force from the difference quantities of liquid phase and the capillary force have different orientation, the migration of cobalt phase is decided by the difference pressure value P.