Heat treatment of high-speed steel
High-speed steel (HSS) is a non-exclusive term for specific materials with a combination of properties which include high hardness, wear resistance, toughness, and the ability to maintain this combination of properties in the presence of heat. HSS is commonly used in cutting tools, cold and hot work applications, and is suitable for any application that requires a high degree of wear and toughness.
Heat treatment of HSS is a complex process involving many different stages and individual temperatures. The main goal of heat treatment is to increase the hardness and wear resistance of the steel. There are two main categories of heat treatment used for HSS: austenitization and martensitization.
Austenitization is the first step of heat treatment for HSS. During this process, the steel is heated to temperatures above its transformation range where austenite is formed and the material is softened. This is done by increasing the temperature of the part until it reaches what is known as the austenitizing temperature. This temperature is determined by the grade of steel being used and the desired hardness and wear resistance. During this heating stage, grain growth can be suppressed by controlling the rate and total energy added to the part.
The next stage in heat treatment of HSS is martensitization. This process transforms austenite into martensite, a hard, stable structure with high defects resistance. This process requires heating the material to temperatures just below the eutectoid point and then rapidly cooling it. The rate of cooling must be rapid enough to ensure that the steel does not re-austenite and retain its high hardness and wear resistance.
The final stage of heat treatment for HSS is tempering. Tempering is a stress relief and homogenization process which reduces residual stresses and further increases hardness and wear resistance of the material. During tempering the part is heated to a specific temperature and held at that temperature for the required duration. The effect of tempering has a direct relationship with the amount of time spent at the selected temperature and must be tailored to the specific application.
Heat treatment of HSS is an extremely complex process but it is essential in order to achieve the desired characteristics. Heat treating HSS correctly is critical in order to optimize the cutting tools, cold and hot work applications, and thus achieve the required hardness and wear resistance.
In conclusion, heat treatment of high-speed steel is necessary in order to achieve the desired properties. This process involves austenitization, martensitization, and tempering. The selection of temperatures and cooling rates are important in order to achieve the desired hardness and wear resistance. Heat treatment of HSS can be complex but with proper knowledge and understanding, optimal results can be achieved.
