High-speed tool steel is also called wind steel or front steel, also known as white steel. This means that it hardens even when cooled in air during quenching and is sharp. It is an alloy steel with complex composition, containing tungsten, molybdenum, chromium, vanadium, cobalt and other carbide forming elements. The total amount of alloying elements is about 10-25%. It can still maintain high hardness under high heat conditions (about 500 ℃), and HRC can be above 60. This is the main characteristic of high-speed steel-red hardness. After quenching and tempering at low temperature, carbon tool steel has a high hardness at room temperature, but when the temperature is higher than 200 ° C, the hardness decreases sharply, and at 500 ° C, the hardness has dropped to a similar degree to the annealed state , Completely lost the ability to cut metal, which limits the use of carbon tool steel for cutting tools. High-speed steel has good red hardness, which makes up for the fatal shortcomings of carbon tool steel, and can be used to manufacture cutting tools.

High-speed steel is generally not tested for tensile strength, but mainly for metallographic and hardness testing.

Tungsten and molybdenum-based high-speed steels can achieve Rockwell hardness above 63 and cobalt-based high-speed steel above 65 after proper heat treatment. The acid-soaked low magnification tissue of steel shall not have visible shrinkage and peeling. Center loose, generally loose should be less than 1 grade.

The contents of metallographic examination mainly include three items: decarburization layer, microstructure and carbide unevenness.

1. High-speed steel should not have obvious decarburization. The microstructure must be free of fish-bone eutectic leinite.

2. The carbide unevenness in high-speed steel has the greatest impact on quality. Metallurgical and mechanical departments attach great importance to the grade of carbide unevenness. According to the different uses of steel, different grades of carbide non-uniformity can be proposed, which should usually be less than 3 grades.

3. In addition to the high hardness, high wear resistance and sufficient toughness of cutting tools made of high-speed steel, there is also an important factor that is red hardness. (Red rigidity refers to the ability of the blade 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, hold it for 1 hour, and then cool it down, and then measure its hardness value 4 times. The quenching temperature of high-speed steel is generally close to the melting point of the steel. For example, tungsten-based high-speed steel is 1210-1240 ° C, and high-molybdenum-based high-speed steel is 1180-1210 ° C. After quenching, it is generally 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 nitriding, etc.