The valve stem is not only a moving part, a stressed part, but also a sealing part in the process of valve opening and closing. At the same time, it is impacted and corroded by the medium, and has friction with the packing. Therefore, in the selection of stem material, it must be ensured that it has enough strength, good impact toughness, scratch resistance and corrosion resistance at the specified temperature. The valve stem is a vulnerable part, so attention should be paid to the mechanical processing performance and heat treatment performance of the material.
The materials commonly used for valve stem are as follows:
Generally, the selected brands are qa19-2 and 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 ℃.
Generally, A5 and 35 steel are selected, and after nitriding treatment, they are suitable for ammonia valves with nominal pressure less than or equal to 2.5MPa, low and medium pressure valves with water, steam and other media. A5 steel is suitable for valves with temperature not exceeding 300 ℃ and 35 steel is suitable for valves with temperature not exceeding 450 ℃. (Note: the actual route proves that the use of carbon steel nitriding for valve stem can not solve the problem of corrosion resistance, so it should be avoided.)
Generally, 40Cr, 38CrMoA1A, 20crmo1v1a and other materials are selected. After chromium plating, 40Cr is suitable for water, steam, oil and other media with nominal pressure less than or equal to 32Mpa and temperature less than or equal to 450 ℃. 38CrMoA1A can withstand 10MPa pressure at 540 ℃ after nitriding treatment, which is commonly used in power station valves. 20crmo1v1a can withstand 14MPa pressure at 570 ℃ after nitriding treatment, which is commonly used in power station valves.
Generally, 2Cr13, 3Cr13, 1Cr17Ni2, 1cr18ni12mo2ti and other materials are selected. 2Cr13 and 3Cr13 stainless steels are suitable for water, steam and weak corrosive media with nominal pressure less than or equal to 32Mpa and temperature less than or equal to 450 ℃. The surface can be strengthened by chromium plating, high frequency quenching and other methods. 1Cr17Ni2 Stainless steel valve, low temperature valve, can resist corrosive medium. 1Cr18Ni9Ti and 1cr18ni12mo2ti stainless acid resistant steel are used in high temperature valves with nominal pressure less than or equal to 6.4Mpa and temperature less than or equal to 600 ℃. They can also be used in stainless steel valves and low temperature valves with temperature less than or equal to – 100 ℃. 1Cr18Ni9Ti can resist nitric acid and other corrosive media; 1cr18ni12mo2ti can resist acetic acid and other corrosive media. When 1Cr18Ni9Ti and 1cr18ni12mo2ti are used in high temperature valves, nitriding treatment can be used to improve the scratch resistance.
Post time: Apr-13-2021