Prevention of σ Phase and Improvement of Anti-Hot Corrosion Properties of High-Chromium-Nickel Cast Steel by Reduction of Silicon and Manganese

One effect of high purification is to delay σ phase formation in high Cr steel. This report presents the application trial of this concept to a practical material, namely 45Cr-30Ni cast steel used for boiler burner parts in fossil power plants, which are exposed to a severe hot-corrosion atmosphere. Conventionally, a Ni content of 30 mass % has been required in order to prevent σ phase formation in this cast steel. However, it is desirable to reduce the amount of Ni in order to improve anti-hot corrosion properties. The research reported here considers the possibility of lowering the amount of Ni in this cast steel through the reduction of silicon and manganese as impurities. Aging and hot-corrosion behavior of 45Cr-30Ni and 45Cr-20Ni cast steels with both conventional and small amounts of silicon and manganese were investigated. It was found that reduction of these impurities greatly impeded the formation of the σ phase, even in 45Cr-20Ni cast steel conventionally characterized by σ phase formation. Also, with the decrease in Ni content, anti-hot corrosion performance was substantially improved in a heavy oil combustion atmosphere