Because of the different heating and cooling conditions, precision castings have many heat treatment methods. The following editor introduces its main heat treatment methods: annealing, normalizing, homogenization, quenching, tempering, solution treatment, precipitation hardening, stress relief treatment and hydrogen removal treatment.
1. Annealing: Annealing is to heat the steel castings to 20-30 degrees Celsius above Acs, suitable for all grades of steel castings.
2. Normalizing: Normalizing is a heat treatment process in which the steel castings are heated to a temperature above Ac degrees Celsius, 30-50 degrees Celsius heat preservation, so that they are completely austenitized, and then cooled in still air. Carbon steel for general engineering and some thick and complex alloy steel castings are mostly normalized.
3. Quenching: Quenching is a heat treatment process in which steel castings are heated to austenitization and then kept for a certain period of time and then cooled in an appropriate manner to obtain martensite or bainite structure. Commonly used are water-cooled quenching, oil-cooled quenching and air-cooled quenching. After quenching, steel castings should be tempered in time to eliminate quenching stress and obtain the required comprehensive mechanical properties. .
4. Tempering: Tempering is to heat the steel castings after quenching or normalizing to Ac, one of the following selected temperatures, after holding for a certain period of time, cooling at an appropriate rate to make the unstable structure obtained after quenching or normalizing It is transformed into a heat treatment process that stabilizes the structure, eliminates quenching (or normalizing) stress, and improves the plasticity and toughness of cast steel.
5. Solution treatment: The solution treatment is a heat treatment process in which the casting is heated to an appropriate temperature and kept warm to fully dissolve the excess phase, and then rapidly cooled to obtain a supersaturated solid solution. The main purpose of solution treatment is to dissolve carbides or other precipitated phases in solid solution to obtain a supersaturated single-phase structure.
6. Precipitation hardening treatment: After the casting is solution treated or quenched, it is kept at room temperature or an appropriate temperature higher than room temperature to form a solute atom segregation zone and/or precipitate a dispersed strengthening phase in the supersaturated solid solution to harden the metal The treatment is called precipitation hardening treatment.
7. The purpose of stress relief treatment is to eliminate the stress formed by casting stress, quenching stress and machining, and stabilize the size.
8. The purpose of hydrogen removal treatment is to remove hydrogen and improve the plasticity of cast steel. Heat to 170-200 degrees Celsius or 280-320 degrees Celsius, and keep warm for a long time for treatment. No organizational changes. Mainly used for low alloy steel castings prone to hydrogen embrittlement.