For the gate valve of the base plain steel, CoCrW cemented carbide, SF-4 (137) alloy, spray welding WF330 or Fe30 parts, the stress relief annealing heating temperature is selected according to the base material carbon steel, generally 600~650℃. The holding time depends on the effective thickness of the parts, generally 1h/25mm, at least 2h. After heat preservation, the furnace is cooled to 300 ℃ and then air-cooled.
Due to the different media suitable for carbon steel gate valves, different surfacing sealing surface materials can be selected. It is suitable for gate valves of water, steam, petroleum and its products. Generally, Cr13 stainless steel is surfacing, but there are also chrome-manganese alloys (85 alloys or 137 alloys), copper alloys and iron-based alloys in some factories.
Surfacing materials can be divided into two categories according to the effect of heat treatment. The first type is represented by cobalt-chromium-tungsten cemented carbide, whose hardness cannot generally be changed by heat treatment, and the hardness of the sealing surface is guaranteed by the surfacing material. The other type is represented by Cr13 stainless steel, whose hardness can be changed by heat treatment, and the hardness of the sealing surface (generally 38~44HRC) can be achieved by heat treatment.