The important component of the valve, used for transmission, it is connected to the actuator or handle at the top, and directly drives the valve core to move or rotate below to achieve the function of valve opening and closing or regulation.
Common materials for valve stems
Carbon steel
Generally, A5 and 35 steel are selected, which are treated with nitriding. They are suitable for ammonia valves with a nominal pressure of less than or equal to 2.5 MPa, as well as low and medium-pressure valves for water, steam and other media.
A5 steel is suitable for valves with a temperature not exceeding 300 degrees; 35 steel is suitable for valves with a temperature not exceeding 450 degrees. (Note: The actual line indicates that using carbon steel nitriding for the valve stem cannot effectively solve the corrosion resistance problem, and it should be avoided.)
Alloy steel
The commonly used materials are 40Cr, 38CrMoA1A, and 20CrMo1V1A. After chrome plating treatment, 40Cr is suitable for water, steam, petroleum and other media with a nominal pressure less than or equal to 32 MPa and a temperature less than or equal to 450 degrees. After nitriding treatment, 38CrMoA1A can withstand a pressure of 10 MPa at a working temperature of 540 degrees, and is often used in power station valves. After nitriding treatment, 20CrMo1V1A can withstand a pressure of 14 MPa at a working temperature of 570 degrees, and is also often used in power station valves.
Valve accessories
Copper alloy
The commonly used grades are QA19-2 and HPb59-1-1. They are suitable for low-pressure valves with a nominal pressure of no more than 1.6 MPa and a temperature of no more than 200 degrees.
Bearing chromium steel
Select GCr15, which is suitable for ultra-high pressure valves with a nominal pressure of less than or equal to 300 MPa and a temperature of less than or equal to 300 degrees. There are many materials used to make the valve stem, including 4Cr10Si2Mo martensitic heat-resistant steel and 4Cr14Ni14W2Mo austenitic heat-resistant steel, etc. The valve stem nut and the valve stem are connected by threads, directly bearing the axial force of the valve stem and the friction between the valve stem and the valve components such as the bracket and the support. Therefore, in addition to having certain strength, the valve stem nut also requires low friction coefficient, corrosion resistance, and the ability to not get stuck with the valve stem.
Stainless steel
The commonly used materials are 2Cr13, 3Cr13, 1Cr17Ni2, and 1Cr18Ni12Mo2Ti. 2Cr13 and 3Cr13 stainless steel are suitable for water, steam and weakly corrosive media with a nominal pressure less than or equal to 32 MPa and a temperature less than or equal to 450 degrees. Their surfaces can be strengthened through methods such as chrome plating and high-frequency quenching. The 1Cr17Ni2 stainless steel valve and the low-temperature valve can resist corrosive media. The 1Cr18Ni9Ti and 1Cr18Ni12Mo2Ti stainless acid-resistant steels are used in high-temperature valves with a nominal pressure less than or equal to 6.4 MPa and a temperature less than or equal to 600 degrees. They can also be used in stainless steel valves with a temperature less than or equal to -100 degrees in low-temperature valves. 1Cr18Ni9Ti can resist corrosive media such as nitric acid; 1Cr18Ni12Mo2Ti can resist corrosive media such as acetic acid. When used in high-temperature valves, 1Cr18Ni9Ti can undergo nitriding treatment to improve its anti-abrasion performance.
What are the characteristics of the valve stem?
During the opening and closing process of the valve, the valve stem not only functions as a moving part and a force-bearing component, but also serves as a sealing element. At the same time, it is subjected to the impact and corrosion of the medium, and also experiences friction with the packing. Therefore, when selecting the material for the valve stem, it is necessary to ensure that it has sufficient strength, good impact toughness, anti-abrasion property, and corrosion resistance at the specified temperature. The valve stem is a wear-prone component, and when choosing it, attention should also be paid to the material's mechanical processing performance and heat treatment performance.
