High speed steel is also known as wind steel or front steel, also known as white steel. It means that even when it is cooled in air, it can harden and be very sharp. It is a kind of alloy steel with complex composition, containing tungsten, molybdenum, chromium, vanadium, cobalt and other carbide forming elements. The total amount of alloy elements is about 10-25%. It can still maintain high hardness under the condition of high heat generated by high-speed cutting (about 500 ℃), and the HRC can be above 60. This is the main characteristic of high-speed steel - red hardness.
After quenching and low temperature tempering, the carbon tool steel has a high hardness at room temperature, but when the temperature is higher than 200 ℃, the hardness drops sharply. At 500 ℃, the hardness has dropped to a level similar to the annealing state, completely losing the ability to cut metal, which limits the use of carbon tool steel to make cutting tools. High speed steel can be used to manufacture cutting tools because of its good red hardness, which makes up for the fatal shortcomings of carbon tool steel.
Generally, tensile strength test is not conducted for high-speed steel, but metallographic and hardness tests are mainly conducted. After proper heat treatment, the Rockwell hardness of tungsten and molybdenum high speed steels can reach above 63 and cobalt high speed steels above 65. The acid immersed macrostructure of steel shall be free of shrinkage cavity and peeling visible to naked eyes. The center is loose. Generally, the looseness should be less than Grade 1. Metallographic examination mainly includes three items: decarburized layer, microstructure and carbide non-uniformity.
