The heat treatment of the sealing surface of carbon steel gate valve refers to the heat treatment of the cobalt-chromium-tungsten carbide sealing surface of the carbon steel valve body and the gate plate. After the carbon steel gate valve is welded with the cobalt-chromium-tungsten carbide sealing surface, stress-relieving annealing is required. The main purpose is to remove the residual stress generated by the welding and improve the machining performance.
For the gate valve whose base is carbon steel, surfacing welding CoCrW hard alloy, 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 part, generally 1h/25mm, at least 2h. After heat preservation, it is cooled to 300℃ in the furnace and then air-cooled out of the furnace.
Due to the different media suitable for carbon steel gate valves, different surfacing sealing surface materials can be selected. Suitable for gate valves of water, steam, petroleum and their products. Generally, Cr13 stainless steel is surfacing, but some factories also surfacing chromium-manganese alloy (alloy 85 or 137), copper alloy and iron-based alloy.
Surfacing materials can be divided into two categories according to the effect of heat treatment. One type is represented by cobalt-chromium-tungsten cemented carbide. Generally, its hardness cannot 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 required 38~44HRC) can be achieved by heat treatment.