Study On Corrosion Behavior Resistance To Sulfates/Chloride Salts Of Three Kinds Of Alloy

The development of ultra-supercritical technology have put forward higher requirements of boiler steel. It has developed Super304H and HR3C as the candidate materials in order to meet the high steam parameters and good oxidation and corrosion resistant properties in widely used high temperature resistance materials. With the development of materials, a new multi principal elements alloy is received extensive attention. It exhibits excellent performance, and can be used as ultra supercritical boiler materials. The high entropy alloy containing Cr or Al has excellent antioxidant properties and gets more attention, therefore CoCrFeNiTio.5is studied in this paper.Ultra-supercritical boiler operation experience shows that pipeline has occurred serious high temperature corrosion problems, directly affect the security of power plant and grid. High temperature corrosion mainly depends on coal with high content of sulfur, chlorine and metallic elements such as Na, K. This results in deposition of sulfates and chloride salts in combustion process. Therefore, we mainly research the high-temperature corrosion behavior of three materials with sulfate corrosion and chloride corrosion.In this article, we simulated sulfate corrosion and chloride corrosion experiments on the three materials. We used a variety of analytical techniques, including dynamic curve in a way of weighing, corrosion products analysis by XRD, sectional morphology and composition distribution by SEM equiped with EDS and combined with EPMA. It was disscused the influence of temperature and different corrosion medium on the corrosion behavior of above three kinds of materials. The corrosion resistence performance of these materials was also be compared.The chloride corrosion results of these materials indicate that, a variety of oxides are formed in the corrosion process, which are closely related to composition and elements of alloys. Because of high Cr content, the corrosion products of HR3C is mainly Cr2O3, while in Super304H the products is mainly iron oxides as the Cr content is low. It also generates a little amount CuFe2O4in the surface of film. CoCrFeNiTi0.5alloy generates various oxides visa different elements, including TiO2, G2O3, Fe2O3and AB2O4type oxides. The three kinds of material all generate little Fe/Ni sulfides in affected zone. The vulcanization makes crack and pore occurred and chlorination can destroy the oxide film of alloy, which accelerates corrosion. The corrosion results of above materials in sulfur atmosphere show that the corrosion products are similar to chloride corrosion. The corrosion products of Super304H are mainly Fe oxides; HR3C is mainly Cr2O3; the products of CoCrFeNiTio.5alloy are a variety of oxides. Corrosion mechanism is distributed to oxidation of the alloy in the early age and subsequent interaction between SO3and oxides, which strengthens sulphuration and increases corrosion.The results of the corrosion properties of CoCrFeNiTi0.5alloy coated with Na2SO4-K2SO4mixed salts show that the corrosion kinetics curves follow segment weight law. The corrosion products are made up of volatile products of Na4(CrO4)(SO4), sulfide and oxides. Micro pores are generated in the matrix/oxide interface as the internal sulfidation.The comparison of three kinds of material corrosion features show that fireside corrosion resistance performance of the CoCrFeNiTi0.5alloy is superior to HR3C, and they all better than that of Super304H under the same corrosion environment.