Common Materials Of Valve Body And Various Materials Heat Treatment Analysis

The valve body has a wide variety of materials and is suitable for various working conditions.

 
There are nine commonly used materials for valve bodies as follows:

1. Gray cast iron, suitable for low pressure valves with working temperature between -15 and +200℃ and nominal pressure PN≤1.6MPa.
2. Black core malleable cast iron, suitable for medium and low pressure valves with working temperature between -15 and +250℃ and nominal pressure PN≤2.5MPa.
3. Nodular cast iron, suitable for medium and low pressure valves with operating temperature between -30 and +350°C and nominal pressure PN≤4.0MPa.
4. Carbon steel (WCA, WCB, WCC), suitable for medium and high pressure valves with operating temperature between -29 and +425°C. Among them, 16Mn and 30Mn have operating temperatures between -40 and +450°C. They are often used to replace ASTMA105. .
5. Low-temperature carbon steel (LCB), suitable for low-temperature valves and valves whose working temperature is between -46~+345℃.
6. Alloy steel (WC6, WC9), suitable for high temperature and high pressure valves of non-corrosive medium with working temperature between -29 and +595℃; WC5 and WC12 are suitable for corrosive working temperature between -29 and +650℃ High temperature and high pressure valve for medium.
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 hydrogen and fluorine media.
9. Cast copper alloy, mainly suitable for oxygen pipeline valves whose operating temperature is between -273~+200℃.

The above-listed are the major categories of commonly used materials for valve bodies. In each category of materials, there are many different grades, and various grades are suitable for different pressure levels. Therefore, when selecting the valve body material, the valve body material suitable for the working conditions should be determined according to different uses and different pressure levels.
In addition, the valve body materials include titanium alloy (titanium valve), aluminum alloy (aluminum valve); plastic (plastic valve); ceramic (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 undergo different heat treatments after casting. In the production of valves, the heat treatment processes that are often 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. 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 the chemical composition and casting cooling rate during casting.

2. Heat treatment of carbon cast steel

Steel castings have large residual casting stress after casting, sometimes the structure of the 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 progress of cutting. In order to eliminate casting stress, refine the structure, improve mechanical properties and improve machinability, etc., in valve production, annealing or normalizing + tempering treatments are often used for carbon steel valve bodies and other parts after casting.

3. Heat treatment of austenitic stainless acid-resistant steel

The main defect of austenitic stainless and acid-resistant steel is that it is prone to intergranular corrosion. Generally, a certain amount of heat treatment can be taken to prevent the steel. In the production of valves, the heat treatment processes often used for parts such as the valve body of austenitic stainless and acid-resistant steel are: solution treatment (quenching), stabilization treatment and 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 time should be sufficient (usually 4 to 8 hours). The purpose of martensitic heat-resistant steel annealing is to eliminate stress, recrystallize, refine grains, reduce hardness, improve cutting performance, and prepare for final heat treatment.
The final heat treatment of martensitic heat-resistant steel adopts normalizing + tempering treatment.

5. Heat treatment of high-quality carbon steel

For the heat treatment of high-quality carbon steel, the valve body of No. 35 forged steel is taken as an example. The valve body of No. 35 steel shall be normalized after forging, and the final heat treatment shall be carried out according to the provisions of the valve manufacturing technical documents. Generally, quenching and tempering treatment is required.

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