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The stainless steel two-way pressure butterfly valve is rusted during use. After metallographic analysis, dyeing test face, heat treatment test face, SEM and other experimental analysis, the key factor of material corrosion was found because the carbide precipitation along the grain boundary formed a chromium-depleted zone, which caused the stainless steel two-way pressure butterfly valve to rust.
The stainless steel two-way pressure butterfly valve made of CF8M has rust during use. After normal heat treatment of austenitic stainless steel, the microstructure should be austenite at room temperature, and the corrosion resistance is very good. In order to analyze the cause of the rust of the butterfly valve, a sample was taken for analysis. Two-way pressure butterfly valve 1. Test method Sampling for chemical composition analysis (to judge whether it meets the standard requirements), metallographic examination, heat treatment process test and SEM analysis.
2. Test results and analysis 2.1. Chemical composition The results of chemical composition analysis and standard components.
2.2. Metallographic analysis The metallographic sample was cut from the butterfly valve with rust phenomenon. After grinding and polishing, it was etched with aqueous solution of ferric chloride and observed on Neophot-32 metallographic mirror. The metallographic structure was The body is composed of another precipitate. In theory, austenitic stainless steel should obtain a uniform austenite structure after normal heat treatment. There is two kinds of judgments as to which organization of another precipitate appearing in the organization: one is σ phase and the other is carbide. The σ phase is different from the carbide formation conditions, but all have a common feature, which is the sensitivity of the austenitic stainless steel to intergranular corrosion.
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