As an industrial tooth, cemented carbide is made of one or more refractory metal carbides (WC, TiC, etc.) as a hard phase, using a transition metal (Co, etc.) as a binder phase, and is produced by powder metallurgy. Multiphase materials. As a tool for cutting carbide tools, common carbides are WC, TiC, TaC, NbC, etc. Common bonding phases are Co, Ni, Fe, etc. The strength of cemented carbide depends mainly on the bonding phase. The content of cemented carbide has the advantages of high strength, high hardness, wear resistance, corrosion resistance, high temperature resistance and small coefficient of linear expansion. It is widely used in many industrial production and processing operations and is one of the most excellent tool materials.
According to the relevant parameters of physics, the mechanical properties of cemented carbide are mainly reflected in the following aspects:
1. Bending strength
The flexural strength of cemented carbide is lower than that of high speed steel. Even the high flexural strength of YG8 hard alloy is only about half of that of high speed steel. The higher the cobalt content in hard alloy, the higher its strength. The cobalt content is the same, the flexural strength of WC-TiC-Co alloy decreases with the increase of TiC content. In addition to the type of carbide, the size of WC grain also has an effect on the strength of cemented carbide. The flexural strength of the alloy is higher than that of the medium grain cemented carbide.
2. Compressive strength
The hardness of cemented carbide is very high, it can be 30%-50% higher than high speed steel, about 3500-5600MPa, and the hot isostatic product can reach 6000MPa. The compressive strength of cemented carbide is related to cobalt content, cobalt content The compressive strength is the highest at 5%. The compressive strength of fine-grained cemented carbide is greater than that of coarse grains. The compressive strength of YT-based cemented carbide is lower than that of YG-based cemented carbide, which decreases with the increase of TiC content. Add A small amount of TaC, NbC, VC, etc. can refine the WC grains, thereby increasing the compressive strength.
Since the compressive strength of cemented carbide is much higher than the flexural strength, when designing the tool structure and selecting the cemented carbide insert, the cutter head should be in the state of compressive stress as much as possible, and less subject to bending moment.
3. Tensile strength
The tensile strength of cemented carbide is 750-1500MPa, which is about 1/4 of compressive strength. Because of the many factors affecting the plasticity of cemented carbide materials, the tensile strength of a certain hard alloy is usually within a certain range. Inside.
4. Impact toughness
The impact toughness of cemented carbide is lower than that of high speed steel. The impact toughness of YG8 alloy with good performance is 30-40KJ/m2, while the impact toughness of W18Cr4V high speed steel is 180-320KJ/m2.
The impact toughness of TiC-containing cemented carbide decreases. When the TiC content increases from 6% to 10%, the impact toughness decreases remarkably. The temperature has a certain influence on the impact toughness of WC-Co cemented carbide at higher temperature. The impact toughness has improved.
Since the impact toughness of cemented carbide is lower than that of high-speed steel, it is not suitable for use in cases with strong impact and vibration. Otherwise, the edge of the hard alloy may be caused. The impact of hard alloy impact toughness is large, and the absolute value is related to the test method. Therefore, when comparing the impact toughness of cemented carbide, the same instrument should be used to compare samples of the same size.
5. Fatigue strength
Since the tool usually works under dynamic conditions, its fatigue strength is very important. The higher the cobalt content in the hard alloy, the higher the fatigue strength. The fatigue strength of the cemented carbide has a great relationship with the surface quality of the sample. The better the smoothness, the higher the fatigue strength.