Study Of Hot Corrosion Behaviors Of Pre-oxidized Fe-Cr Alloys Under KCl Deposits

The study of high temperature corrosion is very important in the development of modern science and technology, especially for the development of industry including energy,chemical and dynamic. This experiment is based on high temperature corrosion in the environment of waste incineration which is found in the industry environment of high temperature chloride corrosion. In recent years, environmental pollution and resource shortage is increasingly serious incineration has been adopted as an effective and hygienic method for disposal of the ever-increasing voluminous industrial and municipal solid waste world-widely. But, in the process of waste incineration, metallic materials usually undergo an aggressive and degrade completely before the end of the designed life due to the complex environment. The development of voluminous industrial has been restricted. Researcher found that chloride corrosion is the most important factor of leading to high temperature corrosion in the environment of waste incineration. In the waste, there is large amount of Cl. These Chloride include Cl₂,HCl and chloride salt deposits, these all lead to alloy corrosion.In the experiment, corrosion behaviors of 5%-80% Fe-Cr alloys under KCl deposits were systematically investigated. Fe-20%Cr was chosen to compare the corrosions of wiping KCl directly and after pre-oxidation at 750℃. The effect of pre-oxidation on corrosion behaviors of Fe-Cr alloys under KCl deposits was discussed. Corrosion behaviors of pre-oxidized 5%-80% Fe-Cr alloys at 750℃and 800℃were investigated to find the effect of Cr content on corrosion behaviors of Fe-Cr alloys under KCl deposits. The reactions of Fe₂O₃ and Cr₂O₃ with KCl at 750℃and 800℃were investigated to explain the damage mechanism of alloys coved with Fe₂O₃ and Cr₂O₃ protective film under KCl deposits at high temperature by analyzing kinetics and products. It provides useful result and testing data for selecting material and protective coating under these conditions.The results of test show that Cr₂O₃ produced by pre-oxidation takes a protective action on the hot corrosion of Fe-Cr alloys under KCl deposits. It can reduce corrosion rate,alleviate damage of corrosion to base alloy and maintain integrity of oxide film. The weight gain and corrosion degree of Fe-Cr alloy both reduce when Cr content increases. The corrosion products of pre-oxidized Fe-Cr alloy under liquid and solid KCl deposits include mainly Fe₂O₃,Cr₂O₃ and few K₂Fe₂O₄,K₂Cr₂O₇. Fe₂O₃ distributes at outer layer while Cr₂O₃ is riched at the scale /substrate interface. Because active oxidation happens at different positions, scales of Fe-Cr alloys with low,middle and high Cr content have different morphologies. Volatile metal chlorides FeCl₂ and CrCl₃ are produced in the reactions of KCl with Fe₂O₃ and Cr₂O₃ at high temperature, which causes obvious weight loss of Fe₂O₃-KCl and Cr₂O₃-KCl systems. K₂O·M₂O_x and metal chlorides are the common products of the reactions of KCl with metal oxides. The reactions of Fe₂O₃ and Cr₂O₃ with KCl are main reasons of fast hot corrosion rate of pre-oxidized Fe-Cr alloy under KCl deposits. The difference of dynamics and thermodynamics of the reactions of two metal oxides with KCl causes the difference of corrosion resistance of Fe-Cr alloys with different Cr content under KCl deposits.