Stainless steel butterfly valve door in the process of using the corrosion analysis

In the course of using the stainless steel butterfly valve gate for corrosion phenomenon. After dyeing try face, heat treatment, microstructure analysis, face, such as SEM test analysis, found the key factors for material corrosion because of materials along the grain boundary carbide precipitation form poor chrome area, resulting in stainless steel butterfly valve door not rust. Material for CF8M stainless steel butterfly gate for corrosion phenomena appeared in the process of use. Austenitic stainless steel after normal heat treatment, the organization shall be the austenite at room temperature, corrosion resistant performance is very good. In order to analyze the corrosion cause of butterfly valve door, on which the sample is analyzed. Stainless steel butterfly valve door materials for austenitic stainless steel, nickel chromium this kind of material is generally used in solid solution state. At room temperature, its organization for austenitic austenitic stainless steel in a wide range of corrosive medium, especially the atmosphere with good corrosion resistance. The cause analysis: synthesis of stainless steel butterfly valve door corrosion test results, can determine butterfly valve door materials organization not precipitate phase in & sigma; Phase, therefore, the butterfly valve gate corrosion phenomenon not by & sigma; Phase; Through SEM observation, confirming the organization of the butterfly valve gate of chromium carbides precipitate phase in the, this kind of eutectic organization along the grain boundary. EDS analysis results show that this kind of distribution on the grain boundary carbides chromium content is significantly higher than the substrate. This kind of carbide M23C6 type. With the precipitation of carbide, and lack of chromium diffusion added, in the form of chromium carbide along the austenite grain boundary precipitation, form poor chrome area around carbide, austenitic stainless steel grain boundaries are easy to corrode. Along the grain boundary precipitation of carbide is the main cause of butterfly valve gate corrosion; After solid solution treatment of austenitic stainless steel, because most of the carbide was dissolved in high temperature heating, austenitic saturation in a large amount of carbon and chromium, and fixed by the subsequent rapid cooling, the corrosion resistance of material has a business. So should strictly control the heat treatment process, the solid solution treatment when the workpiece heated to a high return, the carbide dissolved in full, and then rapidly cooling, to get uniform austenite organization. After solid solution treatment, if use the slow cooling, the cooling process of chromium carbide along the grain boundary precipitates, which results in the decrease of the corrosion resistance of materials.