| Coal power is one of the key technique that promise the West-East electricity transmission project for Xinjiang province due to its abundant resources and high calorific value of coal. However, it is a major limited factor for severe high temperatuer oxidation/corrosion of heat resisting steels in power plant that the plant was not up to the design life for Xinjiang coal combustion because of its lower sulfur but higher chlorine content. In this work, based on the heat resisting steel T91 uesed in coal power plant, three novel heat resisting steels will be developed by adjusting to increase Cr or Al contents in the T91 alloys. at the same time, aluminizing protective coating, will also be propared on the T91 alloys by chemical thermal diffusion method.the high temperature oxidtion/corrosion behavior and mechanism of the novel steels and the aluminizing coating exposed to laboratory simulation coal combustion atmosphere and ash will be investigated by the thermo gravimetric analysis tests and oxidation/corrosion products were analyzed by XRD, SEM/EDX and so on. The results are as follows:1) 1# 2 # 3 # heat-resisting steels were developed in vacuum melting furnace, among which the Cr content in 2 # steel is close to T91, and the Cr content in 3 # is increased to 14.9%, and the Al content in 1 # was raised to 3.67%.2) An aluminized coating was prepared in the surface of six kinds of heat-resistant steel. No transverse and longitudinal cracks are found on the surface of the coatings,and the coatings are well combined with the matrix steels. Thickness of the coatings are about 100μm, and they are a phase of Al Fe.3) After 300 h oxidation at 600 and 650 ℃ in air, six heat-resistance steels and aluminized coating show good oxidation resistance that no obvious oxidation behaviors is on their surface. When the oxidation temperature is increased to 800 and850 ℃, a thick, no protective oxidation products that are composed of a mixed of iron and chromium oxides on the surface of T91, 2 #, 3 #, which contain lower chromium content. Higher temperaure results thicker oxidation layers. With high chromium content of the S304, 2520 surface is formed protective Cr2O3 oxide film that the oxidation weight gain is small at both temperatures. 1 # and aluminized coating surface can form a single, continuous, uniform and compact, Al2O3 oxide film with high temperature protective combined well with the matrix alloys and coatings,therefore, the oxidation weight gain is fewest. After the corrosion of the typical coal-combustion atmosphere 300 h at 600 and 650 ℃, the significant corrosion of the six species steel and aluminized coating in such an atmosphere containing sulfur and chlorine occurre, contrast to at the same temperature in the air oxidation is not obvious, indicating that the interaction of sulfur and chlorine accelerate the corrosion process of material, and no obvious inner sulfidation and chlorination phenomenon take place. For the heat-resistant steel 2 #, 3 #, and T91 with less content of Cr, the thick, iron and chromium mixed oxide layer is formed on the surface at two temperatures, which lead to insufficient high temperature protective, for the S304 and2520 with higher chromium contents, a protective Cr2O3 oxide film is formed on the surface, 1 # and aluminized coating surface can form a single, continuous, uniform and compact, Al2O3 oxide film with high temperature protective combined well with the matrix alloys and coatings.4)At a typical coal-ash deposition salt of a temperature of 600 and 650 ℃ in air,sulfate and chloride-induced hot corrosion of high temperature obviously is occurred in six kinds of steel and aluminized coating,which produce very thickly corrosion products.The surface corrosion products, with increasing Cr composition,easily is exfoliated off in the six heat-resistant steels. Aluminized coating is not formed a single surface of the protective oxide film Al2O3, but thicker aluminum-rich corrosion products,which results in poor hot corrosion resistance. Inner sulfur attack is occurred in only T91 steel. |
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