The heat treatment process of valve body blank is as follows according to different materials:
1. Heat treatment of gray cast iron
In order to achieve different purposes, gray cast iron can be subjected to different heat treatments after casting. In valve production, the heat treatment processes commonly used for gray cast iron valve bodies and other parts after casting are: heat aging to eliminate casting stress and high temperature annealing to eliminate free cementite. Heat aging is a necessary process. High temperature annealing is only used to replace heat aging when primary cementite exists in the structure after casting due to improper control of chemical composition and casting cooling rate during casting.
2. Heat treatment of carbon cast steel
Steel castings have large casting residual stress after casting, and sometimes the structure of steel castings is coarse, and even overheated structure appears. These all affect the dimensional stability of steel castings, reduce the mechanical properties of steel and are not conducive to cutting. In order to eliminate casting stress, refine the structure, improve mechanical properties and improve cutting processability, annealing or normalizing + tempering treatment is often used for carbon steel valve bodies and other parts in valve production after casting.
3. Heat treatment of austenitic stainless acid-resistant steel
The main defect of austenitic stainless acid-resistant steel is that it is easy to produce intergranular corrosion. Generally, certain preventive measures can be taken to apply certain heat treatment to the steel. In valve production, the heat treatment processes commonly used for austenitic stainless acid-resistant steel valve bodies and other parts are: solution treatment (quenching), stabilization treatment and deep cryogenic treatment.
4. Heat treatment of martensitic heat-resistant steel
Martensitic heat-resistant steel should be annealed in time after casting to prevent cracks, and the annealing and heat preservation time should be sufficient (generally 4 to 8 hours). The purpose of annealing martensitic heat-resistant steel is to eliminate stress, recrystallize, refine grains, reduce hardness, improve cutting performance, and prepare the organization for the final heat treatment.
The final heat treatment of martensitic heat-resistant steel adopts normalizing + tempering treatment.
5. Heat treatment of carbon steel
Take the heat treatment of No. 35 forged steel valve body as an example. The No. 35 steel valve body needs to be normalized after forging, and its final heat treatment should be carried out according to the provisions of the valve manufacturing technical documents, and generally requires quenching and tempering.