The intention of final heat treatment of die steel is to improve the mechanical properties such as hardness, wear resistance and strength. So how is the final heat treatment?
1. Quenching includes surface quenching and whole quenching. External quenching is widely used because of less deformation, oxidation and decarburization, and has the advantages of high external strength, good wear resistance, and excellent internal resistance and impact resistance.
In order to improve the mechanical properties of surface quenched parts, heat treatment such as quenching and tempering or normalizing is often required as preparation heat treatment. Its general technological process is: blanking casting normalizing (annealing) - rough machining quenching and tempering semi finishing surface quenching finishing.
2. Carburizing and quenching is suitable for low carbon steel and low alloy steel. The carbon content in the surface layer of the parts is advanced. After quenching, the surface layer can obtain high hardness, while the core still maintains certain strength and high resistance and plasticity. Carburizing consists of whole carburizing and partial carburizing.
The carburizing method should not be used for part of the material. Because of the large deformation of carburizing and quenching, and the carburizing depth is generally between 0.5 ~ 2mm, the carburizing process is generally arranged between semi finishing and finishing.
The process is generally as follows: blanking casting normalizing rough and semi finishing carburizing quenching finishing. When the non carburized part of some carburized parts adopts the process plan of cutting off the extra carburized layer after increasing the allowance, the process of cutting the extra carburized layer should be arranged after carburizing and before quenching.
3. Nitriding treatment nitriding is a treatment method to make nitrogen atoms enter the surface of metal to obtain a layer of nitrogen-containing compounds. Nitriding layer can improve the hardness, wear resistance, fatigue strength and corrosion resistance of parts.
Because the nitriding temperature is low, the deformation is small, and the nitriding layer is thin (generally not more than 0.6 ~ 0.7mm), the nitriding process should be arranged as far back as possible. In order to reduce the deformation during nitriding, high temperature tempering with stress relief is generally required after cutting.