Study Of Submicron Grain Cemented Carbide In Low-pressure Sintering Technique

In this thesis, some test methods, such as Heating Microscope, DTA-TG, Thermal Dialation Testing, were used to research the sintering properties of cemented carbide in submicron grain, systematically. It is found with Heating Microscop that the granularity, carbon content, cobalt content of tungsten carbide are related to the temperature of liquid phase emerging and eutectic point. It is shown that the finer the granularity, the higher the carbon content and cobalt content for carbide tungsten, the lower the liquid phase temperature of hard alloy, contrarily, the higher of liquid phase temperature.It is found that the weight loss of submicron grain of cemented carbide can be divided into four phases, as follows: the water in the sample evaporates at 33.9℃, paraffine begin to decompose in 294.3℃ ~ 369℃, the oxygen content of WC and Co decreases in 369℃-710.9℃, carbon-riched chains of paraffin cracke in 710.9℃ ~ 840.5 ℃. And, it is found through the Differential thermal Analysis(DTA) that liquid phase temperature of cemented carbide in submicron grain is 1256.2 ℃, the eutectic point temperature is 1325.3 ℃.It is also found with Thermal Dialation Testing that temperature at starting shrinkage and the sintering temperature at maximum shrinkage of cemented carbide in submicron grain are related to granularity and carbon content of tungsten carbide. The granularity and carbon content of tungsten carbide have effects on the temperature for starting and ending shrinkage, which are the finer the granularity of tungsten carbide or the higher the carbon content, the lower the starting temperature and ending temperature.The experimental results show that vacuum sintering is not benefit to the production of cemented carbide in submicron grain and overpressure sintering can guarantee the production of excellent cemented carbide in submicron grain.In the research, the JZ13U cemented carbide at 1350℃,1370℃,1390℃,1420oC with the overpressure sintering were sintered respectively, effects of sintering temperature on the microscopic structure, hardness and bending strength were analyzed. The experimental results show that the opitimum sintering temperature of JZ13U cemented carbide is 1370 ℃.In the research, the JZ06S, JZ08U, JZ10U, JZ10S, JZ13U, JZ10 alloy samples were sintered in the ALD low-pressure-sintering furnace (made in Germany). Theexperimental results show as follows: low-pressure sintering is valid to eliminate the pore of submicron carbide cemented, and is related to the cobalt content and granularity of tungsten carbide. It can effectively close pores in the carbide cemented by increasing the sintering pressure and granularity of tungsten carbide. The more the cobalt content in the pore, the better close effect in the same granularity of tungsten carbide and sintering pressure. When the cobalt content keeps unchanged, the finer granularity of alloy, the larger pressure is needed to close pores, pores in carbide cemented of brand JZ10S, JZ10U, JZ13U can be closed in 8.0xl06Pa, however, JZ06S, JZ08U can not be closed in the same pressure, they need to be processed in HIP.It worked effectively when applyed the submicron grain hard alloy SMI3 to three-roller bits, but the manufacture technique should be controlled strictly in order to assure no crack and no cobalt lake and no abnormally large size grain in tungsten carbide alloy.