The mechanical properties, physical properties and chemical composition of cemented carbide have the following changes.
① Hardness The hardness of cemented carbide is generally between HRA86-93, and decreases with the increase of the cobalt content in the cemented carbide. In YT cemented carbide, the hardness increases with the increase of the titanium carbide content. The red hardness of cemented carbide is better. Only when the service temperature is higher than 500℃, the hardness starts to decrease. However, the hardness can still be as high as HRA73-76 at a high temperature of 1000～1100℃.
② Flexural strength The flexural strength of cemented carbide at room temperature is between 90 and 150MPa, and the higher the cobalt content, the higher the flexural strength.
③ Impact toughness The brittleness of cemented carbide is very high, and it is almost independent of temperature. At high temperatures, the impact toughness of steel is hundreds of times greater than that of cemented carbide. When inserting and welding hard alloy tools, it is not allowed to make impact compression on the hard alloy blade. The impact toughness of cemented carbide is related to the amount of cobalt in the alloy. The higher the cobalt content, the higher the impact toughness.
④ Thermal conductivity The thermal conductivity of tungsten-cobalt alloy is 0.58～0.88J/cm.s.℃, which is about twice higher than that of high-speed steel, while the thermal conductivity of tungsten-cobalt alloy is only 0.17～0.21J/cm.s. .℃, lower than high-speed steel. The thermal conductivity of cemented carbide increases with the increase of cobalt content, while the thermal conductivity of tungsten-titanium-cobalt alloy decreases with the increase of titanium carbide content.
⑤ Coefficient of linear expansion The coefficient of linear expansion of cemented carbide is lower than that of high-speed steel, carbon steel and copper. The linear expansion coefficient of tungsten-cobalt alloy is relatively small and increases with the increase of cobalt content; the linear expansion coefficient of tungsten-titanium-cobalt alloy is higher than that of tungsten-cobalt alloy, and it increases slightly with the increase of titanium carbide.
Compared with YG alloys, YT alloys have higher hardness, hot hardness, oxidation resistance, and corrosion resistance, but YG alloys are better in terms of bending strength, compressive strength and thermal conductivity. Adding TiC to the cemented carbide has little effect on the strength, but it significantly improves the thermal hardness of the alloy, which exceeds that of the YT alloy at 900-1000°C.
