There are many kinds of materials for the valve body, suitable for various working conditions
The commonly used materials for the valve body are as follows:
1. Gray cast iron, suitable for low-pressure valves with working temperature between -15~+200℃ and nominal pressure PN≤1.6MPa.
2. Black heart malleable cast iron is suitable for medium and low pressure valves with working temperature between -15~+250℃ and nominal pressure PN≤2.5MPa.
3. Ductile iron, suitable for medium and low pressure valves with working temperature between -30~+350℃ and nominal pressure PN≤4.0MPa.
4. Carbon steel (WCA, WCB, WCC) is suitable for medium and high pressure valves with working temperatures between -29 and +425°C, among which 16Mn and 30Mn have working temperatures between -40 and +450°C and are commonly used for Instead of ASTM A105.
5. Low-temperature carbon steel (LCB), suitable for low-temperature valves with operating temperatures between -46 and +345°C.
6. Alloy steel (WC6, WC9), suitable for high temperature and high pressure valves with non-corrosive medium with working temperature between -29~+595℃; WC5 and WC12 are suitable for valves with working temperature between -29~+650℃ High temperature and high pressure valves for corrosive media.
7. Austenitic stainless steel, suitable for valves with corrosive media whose working temperature is between -196~+600℃.
8. Monel alloy is mainly suitable for valves containing hydrofluoric medium.
9. Cast copper alloy, mainly suitable for valves for oxygen pipelines with working temperature between -273~+200℃. the
The above lists are the major categories of commonly used materials for valve bodies. Specifically, each type of material has many different grades, and various grades are suitable for various pressure levels. Therefore, when selecting the valve body material of the valve, the valve body material suitable for the working conditions should be determined according to different uses and different pressure levels.
In addition, valve body materials include titanium alloy (titanium valve), aluminum alloy (aluminum valve); plastic (plastic valve); ceramics (ceramic valve) and so on.
The heat treatment process of the 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 the production of valves, the heat treatment processes often used for parts such as gray cast iron valve bodies after casting include: thermal aging to eliminate casting stress and high temperature annealing to eliminate free cementite. Thermal aging is a necessary process. High temperature annealing is only used to replace thermal aging when there is primary cementite 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 structures appear. These all affect the dimensional stability of steel castings, reduce the mechanical properties of steel and are not conducive to the cutting process. In order to eliminate casting stress, refine structure, improve mechanical properties and improve machinability, etc., carbon steel valve body and other parts are often annealed or normalized + tempered after casting in valve production.
3. Heat treatment of austenitic stainless and acid-resistant steel.
The main defect of austenitic stainless and acid-resistant steel is that it is prone to intergranular corrosion. Generally, some preventive measures can be taken by applying certain heat treatment to the steel. In the production of valves, the heat treatment processes commonly used for parts such as austenitic stainless acid-resistant steel valve bodies are: solution treatment (quenching), stabilization treatment and cryogenic treatment.
4. Heat treatment of martensitic heat-resistant steel.
The martensitic heat-resistant steel should be annealed in time after casting to prevent cracks, and the annealing and holding 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 for the final heat treatment.
The final heat treatment of martensitic heat-resistant steel adopts normalizing + tempering treatment.
5. Heat treatment of carbon steel.
The heat treatment of carbon steel takes No. 35 forged steel valve body as an example. After forging, the No. 35 steel valve body needs to be normalized, and its final heat treatment should be carried out according to the regulations of the valve manufacturing technical documents, and generally it needs to be quenched and tempered.