Abstract
This work studies the high temperature corrosion behavior of new heat-resistant steel with salt coating method of 75%Na2SO4+25%NaCl coating on the steel surface at 700℃. The chemical composition of corrosion products and surface morphology of the corrosion layer were analyzed using X-ray diffractometer (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and investigate the effect of Cu content on high temperature corrosion behavior of heat resistant steel. The results show that the thermal corrosion kinetics curve of tested steel follows the parabolic law and the surface is composed of Fe2O3 and FeCr2O4. The corrosion layer were divided into two layers, the outer layer was loose and porous while the inner layer was dense and continuous. The structure of the oxide film consists of various protective oxide films; with increasing of Cu content, the high-temperature corrosion resistance of heat-resistant steel was improved and the thickness of the corrosion layer was decreased which led to improving the bonding strength between the inner layer and the matrix. The results of EDS analysis shows that Cu elements can promote the outward diffusion of Cr elements to oxidation of the steel to form a Cr2O3 protective oxide film for preventing the diffusion of chlorine elements, oxygen elements into the interior toward the steel with slow down the process of activation oxidation, reduce the sensitivity of intergranular corrosion and achieve the function of protecting materials. Keywords: Heat-resistant steel. Thermal corrosion. Molten salt. Corrosion layer.
Highlights
The super supercritical unit with high steam parameters has the advantages of high efficiency, cleanliness, economy, safety and so on
The results show that the thermal corrosion kinetics curve of tested steel follows the parabolic law and the surface is composed of Fe2O3 and FeCr2O4
It is shown that the heat-resistant steel had certain high temperature corrosion resistance
Summary
The super supercritical unit with high steam parameters has the advantages of high efficiency, cleanliness, economy, safety and so on. It has become the main development direction of the thermal power unit in the world [1]. Ferritic heat-resistant steel for boiler is widely used in supercritical generating units with high steam parameters because of its excellent comprehensive performance [3-6] and T91 as the representative of this steel, it has been become the most extensive steel grade in the world supercritical power plant at the same time, it is used as a benchmark for developing high steam parameter steel [7, 8]. Relevant studies have shown that [11-16]: corrosion is significantly accelerated above the melting point of the molten salt, and below the melting point, oxidation is accelerated; under the melting condition, NaCl will destroy the protective oxide film, which is the main reason for accelerating the alloy corrosion, especially under the effect of chlorine salt and sulphate, the protective oxide
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