Why Does Stainless Steel Butterfly Valve Rust When In Use?

Stainless steel butterfly valves will appear rusty when they are in use. Many friends don't know what caused it. Today the butterfly valve manufacturer will tell you about this problem. Let's learn about it with the Butterfly Valve Supplier.

Stainless steel butterfly valve will rust during use. Through metallographic analysis, dyeing test, heat treatment test, SEM and other tests, it is found that the key factor for material corrosion is the precipitation of carbides along the grain boundaries to form chromium-depleted areas, which causes the stainless steel butterfly valve to rust. Material CF8M stainless steel butterfly valve rusts during use. After austenitic stainless steel undergoes normal heat treatment, its structure should be austenite at room temperature, and its corrosion resistance is very good. Analyze the cause of butterfly valve corrosion.

Butterfly Valve

The stainless steel butterfly valve material is nickel-chromium austenitic stainless steel, which is usually used in a solid solution state. Austenitic stainless steel has good corrosion resistance in a wide range of corrosive media, especially in the atmosphere.

Analysis of the cause of corrosion of stainless steel butterfly valve: Comprehensive test results show that the precipitated phase in the butterfly valve material structure is not σ phase, so the rust phenomenon of the butterfly valve is not caused by σ phase; through SEM observation, it is confirmed that the precipitated phase in the butterfly valve structure is chromium Mainly carbides, this eutectic structure is distributed along the grain boundaries.

EDS analysis results show that the content of chromium carbide on the grain boundary is significantly higher than that on the substrate. The carbide is M23C6 type. With the precipitation of carbides, the diffusion of chromium cannot be supplemented, and it precipitates along the austenite grain boundaries in the form of chromium carbides, forming a chromium-depleted zone around the carbides, making the grain boundaries of austenitic stainless steel easy to form. Corroded.

Carbide precipitated along the grain boundary is the main cause of butterfly valve corrosion. The austenitic stainless steel after solution treatment, because most of the carbides are dissolved when heated at high temperature, the austenite is saturated with a large amount of carbon and chromium, and is fixed due to the subsequent rapid cooling, so the material has a good The corrosion resistance. Therefore, the heat treatment process should be strictly controlled. During the solution treatment, the workpiece should be heated to a higher height to completely dissolve the carbides, and then quickly cooled to obtain a uniform austenite structure. After solution treatment, if slow cooling is used, chromium carbide will precipitate along the grain boundary during the cooling process, thereby reducing the corrosion resistance of the material. Our company also has Butterfly Valve on sale, welcome to contact us.