Overview of powder metallurgy high speed steel tools with excellent performance (3)
The disadvantage of powder metallurgy high-speed steel is that it is more expensive, about 2 to 5 times that of ordinary high-speed steel (different grades are different). Therefore, tool manufacturers must balance the increase in tool performance with the additional tool manufacturing costs. For small and complex tools, the use of powder metallurgy high-speed steel is very cost-effective because the material cost is only a small part of the total cost of the tool. For large-size simple tools, the choice of powder metallurgy high-speed steel requires careful consideration. However, significant improvements in the grindability of powder metallurgy high speed steels often result in partial (or total) compensation for increased material costs.
The main factor affecting the grindability of steel is the content of vanadium carbide in steel. Since the hardness of vanadium carbide is higher than the hardness of alumina abrasive grains in the grinding wheel, when grinding ordinary high-speed steel with high vanadium content, abrasive grains It is easy to passivate, resulting in more grinding heat, faster grinding wheel wear and longer grinding time. The powder metallurgy high-speed steel has fine carbides and uniform distribution. Compared with ordinary high-speed steel, the loss of the grinding wheel is small, which can greatly shorten the grinding man-hour and save the grinding processing cost. Small and complex tools usually require a large number of precision grinding processes, ie their grinding/to-material-cost ratio is high, so the increased material costs are easily recovered in the grinding process (even There may be a surplus). While larger size tools require less grinding and a lower grinding/material cost ratio, improvements in material grindability typically only partially compensate for material cost increases. Although the economics of using powder metallurgy high speed steel varies depending on the manufacturing process of different tool manufacturers, in general, the improvement of the grindability of the tool material can reduce the grinding time by about 30%.
Today, powder metallurgy high speed steel tools have become a strong contender for solid carbide tools. Although the solid carbide tool has a high hardness and is brittle, it is often used for turning, and is not suitable for machining and roughing with large cutting impact. Because powder metallurgy high-speed steel contains a lot of hard carbide, its wear resistance can reach the level equivalent to the whole cemented carbide, and its toughness is better than the whole hard alloy, and it is more suitable for the tool and wear resistance. And tough cutting (such as tapping, end milling, etc.).
The latest advances in powder metallurgy high speed steel preparation technology have further enhanced its competitiveness. The application of electro-slag heating (ESH) refining process has great significance for powder metallurgy high-speed steel. The process removes almost all of the impurities in the steel, further improving the toughness of the material and significantly improving the chip's resistance to chipping. In addition, due to the reduction of impurities in the steel, the manufacturer can further increase the alloy content of the steel. For example, the vanadium carbide content of a certain powder metallurgy high-speed steel grade can reach 14%, while the maximum content of ordinary high-speed steel grade vanadium carbide is only about 4%. Although a large amount of alloy is added to the steel, it does not affect its toughness and grindability.
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