The valve stem is an important part of the valve. It is used for transmission. The actuator or handle is connected to the upper part. The lower part directly drives the valve core to move or rotate to realize the valve switch or adjustment function.


Features
The valve stem is not only a moving part, a force-receiving part, but also a sealing part during the opening and closing process of the valve. At the same time, it is impacted and corroded by the medium, and it also generates friction with the filler. Therefore, when selecting the valve stem material, it must be ensured that it has sufficient strength, good impact toughness, scratch resistance, and corrosion resistance at the specified temperature. The valve stem is a vulnerable part, and attention should be paid to the machining performance and heat treatment performance of the material when selecting it.
Commonly used materials
1. Copper alloy
Generally, the selected grades are QA19-2, HPb59-1-1. It is suitable for low pressure valves with nominal pressure less than or equal to 1.6MPa and temperature less than or equal to 200 degrees.
2. Carbon steel
Generally, A5 and 35 steel are selected, after nitriding treatment, they are suitable for ammonia valves with a nominal pressure less than or equal to 2.5MPa, and low and medium pressure valves for water, steam and other media. A5 steel is suitable for valves whose temperature does not exceed 300 degrees; 35 steel is suitable for valves whose temperature does not exceed 450 degrees. (Note: The actual route proves that the valve stem made of carbon steel nitriding can not solve the corrosion resistance problem well and should be avoided.)
3. Alloy steel
Generally choose 40Cr, 38CrMoA1A, 20CrMo1V1A and other materials. After 40Cr is chrome-plated, it is suitable for water, steam, petroleum and other media with a nominal pressure of 32MPa or less and a temperature of 450 degrees or less. 38CrMoA1A has undergone nitriding treatment and can withstand a pressure of 10MPa at a working temperature of 540 degrees. It is often used in power station valves. After nitriding treatment, 20CrMo1V1A can withstand a pressure of 14MPa at a working temperature of 570 degrees, and is often used in power station valves.
4. Generally, 2Cr13, 3Cr13, 1Cr17Ni2, 1Cr18Ni12Mo2Ti and other materials are used. 2Cr13, 3Cr13 stainless steel is suitable for water, steam and weakly corrosive media with nominal pressure less than or equal to 32MPa and temperature less than or equal to 450 degrees. The surface can be strengthened by methods such as chrome plating and high frequency quenching. The 1Cr17Ni2 stainless steel valve and low temperature valve are resistant to corrosive media. 1Cr18Ni9Ti, 1Cr18Ni12Mo2Ti stainless, acid-resistant steel is used in high temperature valves with a nominal pressure of 6.4MPa or less and a temperature of 600 degrees or less, and can also be used in stainless steel valves and low temperature valves with a temperature of -100 degrees or less. 1Cr18Ni9Ti is resistant to corrosive media such as nitric acid; 1Cr18Ni12Mo2Ti is resistant to corrosive media such as acetic acid. When 1Cr18Ni9Ti and 1Cr18Ni12Mo2Ti are used in high-temperature valves, nitriding treatment can be used to improve scratch resistance.
5. Bearing chrome steel
Select GCr15, which is suitable for ultra-high pressure valves with nominal pressure less than or equal to 300MPa and temperature less than or equal to 300 degrees.
There are many materials used to make valve stems, including 4Cr10Si2Mo martensitic heat-resistant steel, 4Cr14Ni14W2Mo austenitic heat-resistant steel and so on.
The stem nut and the stem are matched with threads to directly bear the axial force of the stem, and the friction between the plate and the bracket and other valve parts. Therefore, in addition to a certain strength, the valve stem nut also requires the properties of low friction coefficient, no corrosion, and no seizure with the valve stem.