Comparison Of High Temperature Corrosion Of Two Candidate Alloys Of 700℃ Ultra-Supercritical Boiler Superheater

Higher requirements are required for the parameters of thermal power with the implementation of high efficiency clean energy policy,and the performance of the key components of thermal power also become more strict,especially the material of boiler superheater tube.Because of the excellent performance in high temperature creep strength,high temperature corrosion resistance and structure stability,Ni-base superalloys CCA 617 and Inconel 740H have been the the candidate materials for superheater tube of 700℃/35MPa level ultra-supercritical boiler.The performance test of two kinds of alloys is of great significance to the development of the technology of the ultra-supercritical unit.In this articel,the corrosion behavior of CCA 617 and Inconel 740H were evaluated in environments of simulated coal-ash/flue-gas for 5000h at 700 ℃ and 750℃.Electronic balance,scanning electron microscopy(SEM)with Energy Dispersive Spectrometer(EDS)and X-ray diffraction(XRD)were used to characterize the changes of weight and thickness,corrosion products,the morphology of surface and cross section and distribution of elements of the corrosion alloy samples.The corrosion resistance was figured out by extrapolating the degree of corrosion of 5000h to 50000h.The results showed that:As result of two alloys have similarity on the elements,when the external corrosion conditions were same,the corrosion products were also similar,no matter at 700℃ or 750℃.In the environment of coal-ash and flue-gas,the initial corrosion products included Cr2O3,Al2O3,Fe2o3 and so.on,the spinel structure compound was produced by a variety of oxide reactions at a later stage.The high temperature corrosion resistance of two alloy was enhanced by their own elements and the oxidation of elements.In the process of experiment,the protective Cr2o3,AL2O3 were formed on their surface.Two alloys had a similar corrosion mechanism at the different temperature.The process could be divided into two stages:the initial stage and the acceleration stage.In the initial stage,the main corrosion forms were high temperature oxidation,point corrosion of sulfur and internal oxidation;low temperature thermal corrosion occurred at the acceleration stage,and the damage of the alloys were serious.Because of differences in the content of elements,compared with CCA 617,the corrosion layer of Inconel 740H was denser and more shallow at the two temperatures.Through the analysis of the surface and cross-section of the corrosion morphology and the test and extrapolation of corrosion depth,Inconel 740H alloy performance was better in high temperature corrosion resistance.