After the correct heat treatment, the Rockwell hardness can reach above 63, and the cobalt-based high-speed steel can reach above 65. The acid leached low-magnification structure of the steel shall not have shrinkage cavities and skin turns visible to the naked eye. The center is loose, and the general looseness should be less than grade 1.
It can still maintain high hardness under high heat 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 quenching and low-temperature tempering, carbon tool steel has high hardness at room temperature, but when the temperature is higher than 200 °C, the hardness drops sharply, and the hardness at 500 °C has dropped to a similar level 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, due to its good red hardness, makes up for the fatal shortcomings of carbon tool steel and can be used to manufacture cutting tools.