Production method of high-toughness microcrystal hard alloys

[0012] The specific implementation of the present invention will be further described below:

[0013] The process of manufacturing microcrystalline cemented carbide in the present invention is divided into: batching → ball milling → granulation (including sieving drying and wax mixing process) → pressing → low pressure sintering (including dewaxing and pre-sintering process). The vacuum sintering method is different. The pressed product adopts the low-pressure sintering process, which is sintered in an integrated furnace for dewaxing and low pressure sintering. The specific process is: charging→vacuum→heating to 300~500℃ for dewaxing and prefiring → Heat up to 1200°C for heat preservation → heat up to the liquid phase sintering temperature → pressurize with Ar gas → heat preservation and pressurize → pressure-reducing cooling → unloading. At the same time, in the batching process of the present invention, the HCP value of the raw material is (39~41) KA/ m superfine grained WC powder, add 8~12% superfine Co powder, and add 0.2%~0.6% by weight of VC and 0.1%~0.5% by weight of B 4 C. The weight percentage is 0.1%~0.5% NbC, the weight percentage is 0.3%~2.0% TaC, the weight percentage is 0.1%~0.5% Mo2C, and the carbon balance value is (+0.15 ~+0.20)%, the average grain size of WC in the cemented carbide reaches (0.25~0.35)μm. The ball milling process adopts high-energy planetary ball mill ball milling to mix the ball milling medium and each raw material powder in proportion, so that the raw material powder is fully broken and mixed more uniformly, and the sintering activity is increased to a certain extent. In the granulation process (including the sieving drying and wax mixing process), the alloy powder prepared by atomization of inert gas (N2, Ar) is adopted, and the inert gas (N2, Ar) is used to protect the alloy powder in the sieving drying process. The pressing process is an automatic pressing process, which uses automatic pressing to obtain a green body with a uniformly distributed green density, and avoids secondary pollution that may be caused during the pressing process, and uses inert gas (N2, Ar) to protect the pressed product . The described sintering process adopts low pressure sintering process (including dewaxing pre-firing process), adopting dewaxing pre-firing and sintering integrated furnace sintering. It is a relatively advanced technology for densification of hard materials at present. It can work at higher sintering temperature and liquid temperature. In the state of more phasor, the sintered material can be completely compacted by a certain gas pressure to ensure that the relative density reaches more than 99%.

[0014] In the batching process of the present invention, the raw material is ultra-fine grained WC powder with HCP value (39~41) KA/m, 8~12% ultrafine Co powder is added, and the weight percentage is 0.2%~0.6% VC, weight percentage of 0.1%~0.5% B 4 C. The weight percentage is 0.1%~0.5% NbC, the weight percentage is 0.3%~2.0% TaC, the weight percentage is 0.1%~0.5% Mo2C, and the carbon balance value is (+0.15 ~+0.20)%, the average grain size of WC in the cemented carbide reaches (0.25~0.35)μm. Add 0.1%~0.5% by weight of B 4 C can improve the wear resistance and bending strength of cemented carbide.

[0015] Table 1 provides 0.3% by weight of B 4 C. Comparison of the performance of front and back materials. It can be seen from Table 1 that 0.3% by weight of B is added 4 C, the hardness increase is not obvious, and the bending strength is obviously improved. Because boron carbide is a solid harder than tungsten carbide, it has a high melting point. Under the condition of 1000~1100℃, VC transition metal and boron carbide powder react strongly to form metal boride, which can increase the hardness and toughness of the alloy. Therefore, the formula component adds B 4 C can improve the overall performance of cemented carbide.

[0016]

[0017] The ball milling process described in the present invention adopts high-energy planetary ball mill ball milling to mix the ball milling medium and each raw material powder in proportion, so that the raw material powder is fully crushed, and the mixing is more uniform than the traditional process, the mixing efficiency is higher, and the sintering is increased to a certain extent. active. In the granulation process (including the sieving drying and wax mixing process), the alloy powder prepared by inert gas (N2, Ar) atomization is used, and the inert gas (N2, Ar) is used to protect the alloy powder in the sieving drying process to make The alloy powder is separated from other gases to prevent the alloy powder from producing CO or CO 2 Such gases are not conducive to the mechanical properties of the alloy. The pressing process is an automatic pressing process, which uses automatic pressing to obtain a green body with a uniformly distributed green density, and avoids secondary pollution that may be caused during the pressing process, and uses inert gas (N2, Ar) to protect the pressed product , To separate the pressed product from other gases to prevent the pressed product from producing CO or CO 2 Such gases are not conducive to the mechanical properties of the alloy. The described sintering process is a low-pressure sintering process (including dewaxing pre-sintering process). It is sintered in an integrated furnace of dewaxing pre-sintering and low-pressure low sintering. It is currently a relatively advanced technology for densification of hard materials. It can be used at higher sintering temperatures. , When the liquid phase is large, the sintered material can be completely compacted by a certain gas pressure to ensure that the relative density is above 99%. The traditional low-pressure sintering process is to dewax and pre-fire the pressed product in a vacuum sintering furnace, and then sinter it in a low-pressure sintering furnace. During the charging process, the pressed product is likely to produce CO or CO. 2 The gas is not conducive to the mechanical properties of the alloy, and the integrated furnace sintering of dewaxing, pre-sintering and low-pressure sintering avoids this situation. Table 2 provides a comparison of the properties of materials before and after low-pressure sintering. It can be seen from Table 2 that after the low-pressure sintering treatment, the porosity of the alloy is reduced, the hardness is slightly increased, and the bending strength is significantly improved. Therefore, low pressure sintering can significantly improve the overall performance of the alloy.

[0018] The low pressure of low pressure sintering in the present invention is relative to the pressure of hot isostatic pressing. Both are sintered under isostatic pressure, the pressure of the former is less than 10 MPa, and the pressure of the latter is as high as 100 MPa. Low pressure sintering is formed on the basis of vacuum sintering and hot isostatic pressing. Lower pressure at sintering temperature can eliminate pores in the alloy and avoid the defects of "cobalt pool" in the alloy due to high pressure. Low pressure sintering enables the alloy to obtain better comprehensive properties.

[0019] The advantage of using low pressure sintering in the present invention is that it can significantly reduce the microscopic pores in the alloy, and most of the pores in the sintered body have been eliminated in the vacuum sintering stage. The pressing stage is mainly to eliminate microscopic pores. Low porosity is an important sign of high-quality cemented carbide, and the porosity in the alloy should be minimized during production. The densification of cemented carbide is closely related to capillary force, wettability of liquid to solid phase and surface tension of liquid. As the temperature rises during the sintering process, when a liquid phase appears, due to the capillary pressure, the liquid phase moves to the surface of the WC. Because the liquid has good wettability relative to the WC phase, the liquid phase adheres to the WC surface well. Due to the surface tension of the liquid phase, the WC wrapped by the liquid phase is driven to move, and a strong contraction occurs. Under the action of pressure, the WC wrapped in the liquid phase moves, and during the shrinking process, the gas present in it is further discharged, and the degree of densification increases. However, as the shrinkage increases, pressure is generated in the closed pores. When the surface tension is equal to or less than the pressure in the pores, the closed pores are preserved in the alloy and form microscopic pores. Before low-pressure sintering, the WC particles are irregular polygons with sharp corners. There are defects such as holes in the structure, and they are concentrated in the dense areas of WC particles. After low-pressure sintering, the holes in the structure are significantly reduced or refined, which makes the alloy The key factors in the improvement of hardness and bending strength. Although both vacuum sintering and low-pressure sintering have a densification effect, the densification mechanism is different. In the vacuum sintering process, the reduction and spheroidization of pores are the driving force for the reduction and disappearance of pores; while in the low-pressure sintering process In addition to the continued action of this mechanism, the high-pressure environment also exerts an external force on the alloy, resulting in obvious viscoplastic flow, making it easier for atoms to move toward the pores and moving faster. In addition, under the simultaneous action of pressure and temperature, WC dissolves and precipitates in the alloy liquid phase, which makes the sharp corners of individual larger WC particles dull, the boundary becomes smooth, and the shape tends to be rounded. In cemented carbide, the sharp corners of the hard phase will cause stress concentration and have a cutting effect on the matrix. The rounding of the hard phase improves the mechanical properties of the alloy.