What is powder metallurgy HSS, VS general HSS?
High speed steel has a high tungsten content, and it is known for its good high-speed cutting performance in the machining industry. Because of its different tungsten content, high-speed steel is roughly divided into two kinds on the market: one is 18/4/2, its chemical composition is W18C4Mo2, and the other is 6/5/4/2, its chemical composition is W6Cr5Mo4V2, and the latter is gradually replacing the former.
High-speed steel has two common names, one is called front steel, which means that it is sharp, another is called wind steel, that is, it is hard when it is hot, which shows that its quenching performance is extremely fast, but also put forward higher requirements for high-speed steel smelting and heat treatment. If it is slow, it will affect its good performance.
Look at the process of pouring high-speed steel into the ingot mold after smelting: although the ingot mold has been preheated, the maximum is about 300 ° C. When the high speed steel molten steel at 1500℃ is poured on the ingot mold, the molten steel in contact with the inner wall of the ingot mold will quickly cool and harden, and the molten steel in the middle of the ingot mold can only slowly cool because of a layer of high-speed steel around it or has a certain temperature, so its hardness and metallographic structure will be different from the surrounding layer of high-speed steel. Although later re-forging and heat treatment will improve this situation, the problem still exists, and it is difficult to make its organizational structure uniform. That's the problem with traditional high speed steel.
In order to improve this shortcoming of traditional high-speed steel, the world has adopted the method of powder metallurgy, the high-speed steel in the molten state, like the production of milk powder, is blown into small particles with compressed air, and then placed in a mold with a specific shape, the high-speed steel particles are pressed into a cylinder or sheet material with high pressure, and then to manufacture various parts. This high speed steel is called powder metallurgy high speed steel.
Compared with cemented carbide, its normal service life in a very perfect working environment is not better than cemented carbide, but its impact toughness is far better than cemented carbide, so the actual life in use may be better than cemented carbide, because tungsten carbide is very brittle and can not work in case of a collapse. In addition, powder metallurgy high-speed steel has good processability, it can be like ordinary steel, heat treatment and planing, milling, grinding and other mechanical processing, and cemented carbide is not able to do this, which greatly saves the cost of the mold.
The microstructure of powder metallurgy high speed steel and traditional high speed steel under 250 times and 1000 times microscope is very different. Obviously, there are a lot of rough blocks in traditional high-speed steel, and its impact resistance is certainly poor.
