The Research Of Corrosion Behavior Of Q235Steel In Molten Cryolite

Q235steel is one of the most common low carbon steel inindustrial production, widely used in chemical industry, metallurgy,construction, machinery, etc.In the electrolytic aluminium industry,Q235, with its low prices, excellent welding performance and easy to get,become aluminium electrolytic cell, crust hammer head, the first choiceof materials such as special tools. In electrolytic cell, the workingenvironment temperature about100℃~500℃, the molten cryoliteelectrolyte temperature as high as950℃, Q235susceptible to hightemperature corrosion of cryolite, so as to make the material of Q235work failure, reduce the restrain its service life.At present the corrosion mechanism of Q235has done a lot ofresearch, but in the electrolytic aluminium industry of the corrosionmechanism of Q235steel in the electrolytic aluminium troughenvironment research is very few.At present, the electrolytic aluminiumindustry of excess capacity, research on the corrosion mechanism of Q235cryolite for electrolytic aluminium industry has very importantsignificance. Can be the choice of material for electrolytic aluminumindustry, reduce cost, improving the quality of aluminum liquid, reducelabor intensity for reference.This article on how to pre oxidationtreatment of Q235steel, seek a kind of test method on the surface ofQ235to generate a layer of oxide layer of corrosion resistance to moltencryolite, evaluation of corrosion rate by using weight-loss method.UsingXRD, SEM and EDS analysis with the result of oxidation morphologyand metallographic experiment phenomenon, and from the aspects ofthermodynamics and kinetics research the Q235steel pre oxidationcorrosion resistance, and conclusions are as follows:(1) The Q235steel after550℃heat preservation for30minutes,generated on the surface of oxide layer consists only of Fe3O4and Fe2O3,does not generate FeO.Order of the scale and structure outside-in isFe2O3, Fe3O4and Fe2O3oxide layer is dense, but the thickness is thinner,connected to the matrix performance is not good, easy to fall off.Fe3O4thickness, distribution rule, continuous dense and well connected to thematrix is not easy to fall off.(2) The Q235steel with high temperature molten cryolite bond, asthe extension of heat preservation time, cryolite adhesive with increasingthe thickness of the steel surface, and not easy to peel, and by550℃pre oxidation treatment of Q235, rarely electrolyte. (3) In molten cryolite, after550℃oxidation treatment of Q235steel, as the extension of heat preservation time the surface of Fe2O3dissolved in cryolite, Fe3O4with inverse spinel structure, due to itsbelong to cubic crystal system, have excellent thermal stability.(4) The Q235steel with pre-oxidation of Q235steel in moltencryolite insulation after3hours, Q235bare steel corrosion weight lossrate is greater than the550℃oxidation treated Q235steel.Naked by thethermodynamic analysis of Q235steel in molten cryolite, Fe willcombine with the AlF3in cryolite oxygen generated fluoride salt FeF3,low melting point of1000℃in the volatile, promoted the chemicalreaction to the right, make bare steel Q235continuous corrosion inmolten cryolite.(5) Preoxidation generated on the surface of Q235steel Fe3O4oxidefilm on the hot corrosion of Q235steel in molten cryolite environmenthas certain protective effect, can reduce the corrosion rate, reducemolten salt damage to the substrate and maintain the integrity of theoxide film.This method can be for the application of Q235steel in theelectrolytic aluminium industry provides an economic and feasiblemethod.