The strength of tungsten carbide has a great influence on the green processing. Only when the strength is greater than 30Mpa, it can be processed. In the pre-sintering process, the strength directly depends on the pre-sintering temperature, so the temperature must be strictly controlled.

 

Effects of pre-sintering temperature on the green strength as shown below. From the figure, when the pre sintering temperature higher than 720℃, the strength increased with increasing the pre-sintering temperature. Given that tungsten carbide is hard particles and mechanical meshing force is very small, the strength mainly depends on the forming agent of bonding between particles.

 

 

According to the thermogravimetric curve, the forming agent basically evaporated at 500℃. The strength depends on the coupling force between the powder particles and the particles disappeared, the coupling force mainly depends on the diffusion of surface atoms, atomic particles surface preliminary formed by sintering the attraction between. At this time, the atomic surface diffusion rate is low, the binding force between atoms is difficult to provide enough strength.

 

Therefore, the apparent strength of pre-sintered compacts is relatively low under sintering at 720℃. With the increase of temperature, the rate of atomic diffusion is further improved. When the temperature is above 720, the welding phenomenon occurs between the cobalt powder particles and the particles. In this stage the green began some contraction strength began to increase. From the apparent point of view, the sintering strength of the pre-sintered compacts increases significantly.

 

According to the sintering mechanism of cemented carbide, with the increase of sintering temperature, the forming agent will gradually volatilize, and the strength of pre-sintered billet will inevitably decrease from lower to higher. For hard alloy pre-sintering green, only when the sintering temperature is over 800 ℃, pre sintering strength was greater than 30Mpa.

 

When the sintering temperature of pre sintered compacts is greater than 950℃, the strength will increase to 80Mpa, which means that the diffusion of atoms is very fast and the sintering neck tends to be perfect. If machining is carried out at this time, the tool will contact tungsten carbide directly, resulting in the reduction of tool cutting times, even cutting edge of tool.