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Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

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Carbide Blade Vacuum Sintering

The sintering of cemented carbide is liquid phase sintering, that is, under the condition that the bonding phase is in the liquid phase. The compact is heated to 1350°C-1600°C in a vacuum furnace. The linear shrinkage rate of the compact during sintering is about 18%, and the volume shrinkage is about 50%. The exact value of the shrinkage depends on the particle size of the powder and the composition of the alloy.

The sintering of cemented carbide is a complex physical and chemical process. This process includes plasticizer removal, degassing, solid phase sintering, liquid phase sintering, alloying, densification, and dissolution. The compact forms a product with a certain chemical composition, structure, performance and shape and size under specific sintering conditions. These process conditions vary greatly depending on different sintering devices.

Vacuum sintering can generally be divided into four stages, namely, plasticizer removal stage, pre-sintering stage, high-temperature sintering stage, and cooling stage.

The plasticizer removal stage starts from room temperature to about 200°C. The gas adsorbed on the surface of the powder particles in the compact is released from the surface of the particles under the action of heat and continuously escapes from the compact. The plasticizer in the compact is heated and escapes from the compact. Maintaining a high degree of vacuum is conducive to the release and escape of gas. Different types of plasticizers have different performances due to heat changes, and the development of plasticizer removal technology should be tested and determined according to specific conditions. Generally, the gasification temperature of plasticizers is below 550°C.

The pre-sintering stage refers to the pre-sintering before high-temperature sintering, so that the oxygen and carbon in the powder particles will undergo a reduction reaction to generate carbon monoxide gas and leave the compact. If this gas cannot be eliminated when the liquid phase appears, it will become a closed pore and remain in the compact. In the alloy, even if pressure sintering, it is difficult to eliminate. On the other hand, the presence of oxidation will seriously affect the wettability of the liquid relative to the hard phase, and ultimately affect the densification process of the cemented carbide. Before the liquid phase appears, fully degas and use the highest possible vacuum.

The high-temperature sintering stage is the key stage for the densification of cemented carbide compacts, and the sintering temperature and sintering time are important process parameters for compacting the compacts, forming a uniform structure, and obtaining the required performance. The sintering temperature and sintering time depend on factors such as alloy composition, powder particle size, and grinding strength of the mixture, and are also restricted by the overall design of the material.

In the cooling stage, the cooling rate affects the composition and structure of the alloy’s bonding phase, resulting in internal stress. The cooling rate should be under control. Sintering hot isostatic pressing is a new sintering technology, also called low pressure sintering. After degassing is completed, the pores on the surface of the compact have been closed, and the bonding phase is still liquid, pressurized with a certain pressure of gas to promote The product is densified.

Examples of cemented carbide blade sintering:

Hydrogen sintered cemented carbide blades often carburize and absorb alumina on the surface, resulting in poor wetting between the blade and the flux. The blades of vacuum sintered cemented carbide blades can be joined by ordinary welding methods without special surface treatment.

The process of vacuum sintering is: dewaxing (glue), pre-sintering → sintering and cooling out of the furnace

Dewaxing (gluing) is generally carried out at 350~400℃ for 3~4 hours. It can be carried out under vacuum or in hydrogen.

Pre-sintering is generally carried out at about 700°C for 1 hour

Sintering is generally carried out at 1350~1460°C, the whole sintering process is 3~5 hours, and the highest temperature is generally held for 0.5~1 hour.

Dewaxing (glue) pre-sintering is usually carried out separately from sintering in another furnace, but it can also be carried out in one furnace chamber.