New Types of Cemented Carbide
New Types of Cemented Carbide
1. Fine grain and ultra-fine grain carbide
After the grain refinement of cemented carbide, the size of the cemented carbide phase becomes smaller, and the bonding phase is more evenly distributed around the cemented carbide phase, which can improve the hardness and wear resistance of cemented carbide. But the bending strength is decreased. The bending strength can be improved by increasing the content of cobalt in binder appropriately. Grain size: common grade tool alloys YT15, YG6, etc. are medium grain, the average grain size is 2 ~ 3μm；the average grain size of fine grain alloy is 1.5 ~ 2μm, and that of micron grain carbide is 1.0 ~ 1.3μm. Submicrograin carbide is 0.6 ~ 0.9μm；the ultra-fine crystal carbide is 0.4 ~ 0.5μm; The nano-series microcrystalline carbide is 0.1 ~ 0.3μm; China's carbide cutting tools have reached the level of fine grain and sub-fine grain.
2.TiC base carbide
TiC as the main body, accounting for more than 60% to 80%, with Ni ~ Mo as a binder, and add a small amount of other carbides of the alloy, containing no or less WC. Compared with WC base alloy, TiC has the highest hardness in carbide, so the alloy hardness is as high as HRA90 ~ 94, it also has high wear resistance, anti-crescentless wear ability, heat resistance, oxidation resistance and chemical stability, and the affinity with the workpiece material is small, the friction factor is small, the adhesion resistance is strong, the tool durability is several times higher than WC, so it can be processed steel and cast iron. Compared with YT30, the hardness of YN10 is close, the weldability and sharpness are good, and it can basically replace YT30. But the bending strength is not up to WC, mainly used for finishing and semi-finishing. Due to its poor resistance to plastic deformation and falling edge, it is not suitable for heavy cutting and intermittent cutting.
3.Cemented carbide with rare earth elements added
Rare earth cemented carbide is in a variety of cemented carbide tool materials, adding a small amount of rare earth elements (atomic numbers in the periodic table of chemical elements are 57-71 (from La to Lu), plus 21 and 39(Sc and Y) elements, a total of 17 elements), rare earth elements exist in (W, Ti)C or (W, Ti, Ta, Nb)C solid solution. It can strengthen the hard phase, inhibit the uneven growth of WC grains and make them more uniform, and the grain size is reduced. A small amount of rare earth elements are also solidly dissolved in the bonding phase Co, which strengthens the bonding phase and makes the structure more dense. Rare earth elements are enriched at the interface of WC/Co and between the interface of (W, Ti)C, (W, Ti)C, etc., and often combine with impurities S, O, etc., to form compounds such as RE2O2S, which improves the cleanliness of the interface and enhances the wettability of the hard phase and the bonded phase. As a result, the impact toughness, bending strength and impact resistance of the rare earth cemented carbide have been significantly improved. Its room temperature and high temperature hardness, wear resistance and the ability of anti-diffusion and anti-oxidation on the surface of the tool have also been improved. During cutting, the cobalt-rich phenomenon of the surface layer of the rare earth cemented carbide blade can effectively reduce the friction factor between the chip, the workpiece and the tool, and reduce the cutting force. Therefore, the mechanical properties and cutting properties are effectively improved. China is rich in rare earth element resources, and the research and development of rare earth cemented carbide is ahead of other countries. P, M, K alloys have been developed to add rare earth grades.
4.Coated with cemented carbide
Due to the hardness and wear resistance of cemented carbide is good, toughness is poor, through chemical vapor deposition (CVD) and other methods, on the surface of cemented carbide coated with a layer (5 ~ 12μm) of good hardness, high wear resistance of the substance (TiC, TiN, Al2O3), the formation of coated cemented carbide, so that it has both high hardness and high wear resistance of the surface, and a strong matrix; Therefore, it can improve the tool life and processing efficiency, reduce the cutting force and cutting temperature, improve the quality of the machined surface, and greatly improve the tool durability at the same cutting speed. In the past 20 years, coated carbide knives have developed greatly, and have accounted for more than 50% to 60% of index-able tools in advanced industrial countries. Coated blades are best suited for continuous turning and are used for finishing, semi-finishing and lighter load roughing of various carbon structural steels, alloy structural steels (including normalizing and tempering), easy cutting steels, tool steels, martensitic stainless steels and gray cast iron.
5. Graded carbide
Carbide in some cases, in addition to the requirement of very high surface hardness and wear resistance, but also need to have a good impact toughness. Ordinary cemented carbide hardness and strength, toughness and wear resistance between the mutual constraints, the two can not be both. The functional gradient material solves the above problems existing in cemented carbide, such alloys show a gradient distribution of Co in the structure, that is, the outermost layer of the alloy is lower than the nominal Co content of the alloy cobalt-poor layer, the middle layer is higher than the nominal Co content of the alloy cobalt-rich layer, and the core is the WC-Co-η three-phase microstructure. Due to the high WC content on the surface, it has high hardness and good wear resistance; the middle layer has high Co content and good toughness. Therefore, its service life is 3 to 5 times that of similar traditional cemented carbide, and the composition of each layer can be adjusted according to needs.
To sum up，through the classification and refinement of cemented carbide, we can see that the new type of cemented carbide tool has been greatly improved for the traditional tool, on the one hand, the use of fine particles and ultra-fine particle materials of cemented carbide, with a perfect combination of hardness and strength. In addition, new processes such as pressure sintering can further improve the internal quality of cemented carbide. On the other hand, the universal tool developed by the high-quality integral carbide tool makes the cutting speed, cutting efficiency and tool life several times higher than that of high-speed steel. The production of these new tools will largely fill the defects of cemented carbide. The development of carbide tool materials, so that it from its unique application in the performance of the expansion of the development of modern tool material technology in the complementary advantages of materials, materials to replace the supplement. Let it be applied to a higher and wider range of cutting fields.
Hope this article can help you to better understand cemented carbide to some extent. Apart from this one, please read the first half part of “Classification and Study on Cemented Carbide Cutting Tools”. Contact us if you have any question or requirement about carbide products.