On 2018-08-08 14:48:54
valve body material heat treatment analysis
There are many kinds of materials for valve body, which are suitable for different working conditions.
The commonly used materials of valve body are as follows:
1. Gray cast iron, suitable for low pressure valve with working temperature between - 15 ~ + 200 ℃, nominal pressure PN ≤ 1.6Mpa.
2. Black core malleable iron, suitable for medium and low pressure valves with working temperature of - 15 ~ + 250 ℃ and nominal pressure of PN ≤ 2.5MPa.
3. Ductile iron, suitable for medium and low pressure valves with working temperature of - 30 ~ + 350 ℃ and nominal pressure of PN ≤ 4.0Mpa.
4. Carbon steel (WCA, WCB, WCC) is suitable for medium and high pressure valves with operating temperature between - 29 ℃ and - 425 ℃, among which 16Mn and 30mn are used to replace astma105 with operating temperature between - 40 ℃ and + 450 ℃.
5. Low temperature carbon steel (LCB), suitable for low temperature valve with working temperature between - 46 ℃ and + 345 ℃.
6. Alloy steel (wc6, wc9) is suitable for high temperature and high pressure valve of non corrosive medium with working temperature of - 29 ~ + 595 ℃; wc5, wc12 are suitable for high temperature and high pressure valve of corrosive medium with working temperature of - 29 ~ + 650 ℃.
7. Austenitic stainless steel, suitable for valves with corrosive medium operating temperature between - 196 ℃ and + 600 ℃.
8. Monel alloy is mainly suitable for valves with hydrofluoride medium.
9. Cast copper alloy, mainly suitable for oxygen pipeline valves with working temperature between - 273 ℃ and + 200 ℃.
The above listed are the major categories of commonly used materials for valve body. In each category of materials, there are many different brands, which are applicable to different pressure grades. Therefore, when selecting the valve body material, the valve body material suitable for the working condition should be determined according to different purposes 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), etc.
According to different materials, the heat treatment process of valve body blank is as follows:
1. Heat treatment of grey cast iron.
In order to achieve different purposes, different heat treatment can be carried out for gray cast iron after casting. In the production of valve, the heat treatment processes often used for the parts such as gray cast iron valve body 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 can only be used to replace thermal aging when there is primary cementite in the structure after casting due to improper control of chemical composition and cooling rate.
2. Heat treatment of carbon cast steel.
After casting, the steel casting has a large residual stress, sometimes the structure of the steel casting is coarse and even overheated. All of these affect the dimensional stability of steel castings, reduce the mechanical properties of steel and are not conducive to cutting. In order to eliminate the casting stress, refine the structure, improve the mechanical properties and improve the machinability, annealing or normalizing + tempering treatment is often used in the production of valves.
3. Heat treatment of austenitic stainless and acid resistant steel.
The main defect of austenitic stainless and acid resistant steel is easy to produce intergranular corrosion. In the production of valves, the heat treatment processes often used for the valve body and other parts of austenitic stainless and acid resistant steel 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 time should be sufficient (generally 4-8 hours). The purpose of annealing of martensitic heat-resistant steel is to eliminate stress, recrystallize, refine grain, reduce hardness, improve cutting performance, and prepare for final heat treatment.
The final heat treatment of martensitic heat-resistant steel is normalizing + tempering.
5. Heat treatment of high quality carbon steel.
For the heat treatment of high-quality carbon steel, 35 forged steel valve body is taken as an example. After forging, 35 steel valve body shall be normalized, and its final heat treatment shall be carried out according to the provisions of the valve manufacturing technical documents, generally requiring tempering treatment.