China has used a large number of coated high-speed steel knives and has mastered the coating process, but powder alloy high-speed steel tools are still blank. In industrial advanced countries, powder metallurgy high-speed steel tools have accounted for 10% of the total high-speed steel. Because of its superior performance, it can effectively improve tool life and equipment utilization. Therefore, although the price of such tools is relatively expensive, it can still be overall. Reduce processing costs. In recent years, domestic steel mills and tool factories have been able to manufacture powder metallurgy high-speed steel. If quality and performance are guaranteed, it should be recommended by machinery manufacturers. The author believes that China should vigorously develop powder metallurgy high-speed steel.
2. <br> <br> Carbide Carbide carbide (WC, TiC, etc.) of powder metallurgy products, the following six kinds of new carbide.
1 Adding TaC and NbC cemented carbide: After adding, it can effectively improve the normal temperature hardness, high temperature strength and high temperature hardness, refine the crystal grains, and improve the anti-diffusion and anti-oxidation ability. In addition, it also enhances the ability to resist plastic deformation.
2 Fine-grained and ultra-fine grained cemented carbide: After grain refinement, the hardness and wear resistance of the alloy can be improved, and the flexural strength can be improved by appropriately increasing the cobalt content. The average tool size and alloy average grain size is 2 to 3 mm, the fine grain alloy is 1 to 2 mm, the submicron grain alloy is 0.5 to 1 mm, and the ultrafine grain alloy is 0.5 mm or less. China's cemented carbide tools have reached the level of fine grains and submicron grains.
3TiC-based and Ti(C,N)-based cemented carbide cermets: In YT, YG, YW alloys, WC is the main component and Co is used as the binder; TiC-based alloys are mainly composed of TiC, excluding Or less WC, with Ni-Mo as a binder.
4 Hard alloy with rare earth elements: Adding a small amount of rare earth elements can effectively improve the toughness and flexural strength of the alloy, and the wear resistance is also improved. These alloys are best suited for roughing tool grades and can also be used for semi-finished grades; they also have broad prospects for use in mining tools, top hammers, and hard alloys for wire drawing. China's rare earth elements are rich in resources, and research on the addition of rare earths in cemented carbide is leading. P, M, and K alloys have been developed with grades of rare earth added.
5 Surface-coated cemented carbide: The surface hardness and wear resistance of coated cemented carbide fully reflect the performance of coating materials such as TiC, so it can improve tool life and processing efficiency, reduce cutting force and improve the quality of processed surface. In the past 20 years, coated cemented carbide tools have developed greatly, and in industrial advanced countries, they have accounted for 50-60% of indexable tools.
6 Gradient Cemented Carbide: This is a new variety developed in recent years, and the composition of each layer can be adjusted as needed.
According to the review, all kinds of hard alloys are improving and expanding their range of use. In the 21st century, cemented carbide tool materials will focus on two aspects: first, refine grains, improve toughness and flexural strength, thereby expanding applications and further replacing high-speed steel tools. The grain size is up to the nanometer level, and the flexural strength can reach 2.5 to 3.0 GPa or more. The second is to develop cermets, replace TiC with TiC and Ti (C, N) to save W resources; replace Co with Ni and Mo, and save Co resources. The problem now is that the toughness of cermets is still inferior to that of WC-based cemented carbides. In this regard, it is necessary to strengthen research and strive for breakthroughs.
A ceramic <br> <br> ceramic tool material is divided into three categories: an alumina-based ceramic; silicon nitride-based ceramics; composite silicon nitride - aluminum oxide ceramic. Ceramics have higher temperature performance than hard alloys and are therefore suitable for high speed cutting. Al2O3 based and Si3N4 based composite ceramics are suitable for cutting hardened steel, high hard cast iron and general cast iron; Al2O3 based composite ceramics can also effectively cut unhardened steel, while Si3N4 based ceramics wear rapidly in general steel.
The hardness of ceramics is slightly higher than that of hard alloys, but its brittleness is large, the toughness is insufficient, and the workability is poor, so the application is limited. The future development direction is toughen, and the toughness of the ceramic material can be improved to some extent by using the method of refining the particle size of the raw material and adding ZrO2, TiB2 or SiC whiskers.
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