Also known as Fenggang or Fenggang, also known as white steel. It means that it can be hardened even if it is cooled in the air during quenching, and it is very sharp. It is a complex alloy steel, containing carbide forming elements such as tungsten, molybdenum, chromium, vanadium, and cobalt. The total amount of alloying elements is about 10-25%. It can maintain high hardness even when high heat is generated by high-speed cutting (about 500℃), and the HRC can be above 60. This is the most important characteristic of high-speed steel-red hardness. After being quenched and tempered at low temperature, carbon tool steel has high hardness at room temperature, but when the temperature is higher than 200℃, the hardness drops sharply, and the hardness at 500℃ has dropped to a level similar to the annealed state. , Completely lost the ability to cut metal, which limits the use of carbon tool steel to make cutting tools. High-speed steel, because of its good red hardness, makes up for the fatal shortcomings of carbon tool steel, and can be used to make cutting tools.
High-speed steel generally does not do tensile strength testing, but mainly metallographic and hardness testing.
After the correct heat treatment of tungsten and molybdenum high-speed steels, the Rockwell hardness can reach more than 63, and the cobalt-based high-speed steel can be more than 65. The acid immersion low-power structure of steel shall not have visible shrinkage holes and peeling. The center is loose, generally the looseness should be less than level 1.
The content of metallographic inspection mainly includes 3 items of decarburized layer, microstructure and carbide unevenness.
1. High-speed steel should not have obvious decarburization. The microstructure must not have herringbone eutectic ledeburite.
2. The unevenness of carbides in high-speed steel has the greatest impact on quality, and the metallurgical and mechanical departments attach great importance to the level of unevenness of carbides. According to the different uses of the steel, different grade requirements can be put forward for the unevenness of carbides, which should be less than grade 3 under normal circumstances.
3. In addition to the high hardness, high wear resistance and sufficient toughness of cutting tools made of high-speed steel, there is another important factor that is red hardness. (Red hardness refers to the ability of the cutting edge to resist softening under red heat when the tool is cutting at high speed.)
One way to measure the red hardness is to first heat the steel to 580-650°C, keep it warm for 1 hour, and then cool it, and then measure its hardness value after repeated 4 times. The quenching temperature of high-speed steel is generally close to the melting point of steel, such as 1210～1240℃ for tungsten high-speed steel and 1180～1210℃ for high-molybdenum high-speed steel. After quenching, it generally needs to be tempered 3 times between 540～560℃. Increasing the quenching temperature can increase the red hardness of the steel. In order to improve the service life of high-speed steel tools, the surface can be strengthened, such as low-temperature cyanidation, nitriding, sulfur and nitrogen co-infiltration, etc.
Post time: Jul-17-2021