Research On Microstructure And Properties Of Molten Aluminum Corrosion Resistant Low-alloy Gray Cast Iron

In the non-ferrous metal aluminum smelting,casting industry,the temperature of the molten aluminum is usually required to be continuously measured.Aluminum liquid is characterized by severe corrosive,permeability,easy to slag.Thermocouple protective sleeve used for measuring temperature is often destroyed by the severe erosion of aluminum liquid.Due to its low price,excellent casting and machining performance,cast iron material has come to the foreground.In general,practical application gray cast iron thermocouple protective sleeve can only be used for about a week.Therefore,the study on the life extension of thermocouple protective sleeve is of great significance.In this paper,less-carbon,less-silicon,more-manganese,less-chromium and nickel-containing low-alloy gray cast irons were designed on the basis of the practical protective sleeve components(application group).The effects of C,Si,Mn,Cr and Ni on the microstructure and mechanical properties of lo w alloy gray cast iron were studied.The effect of composition on the corrosion resistance of low alloy gray cast iron in molten aluminum was studied by using aluminum liquid corrosion test.And the corrosion behavior and corrosion mechanism of low-alloy gray cast iron in molten aluminum were investigated by scanning electron microscopy(SEM),energy dispersive spectrometer(EDS)and X ray diffraction(XRD).The main results obtained were as follows:Mechanical properties of as-cast low-alloy gray cast iron,hardness:less-carbon>more-manganese>less-silicon>nickel-containing>application group>less-chromium;tensile strength:less-carbon>less-silicon>more-manganese>nickel-containing>less-chromium>application group.The main factor affecting the hardness and tensile strength of low-alloy gray cast iron was carbon equivalent.The hardness of the less-carbon group was HBW 224,tensile strength was 359MPa,and the mechanical property was the best.After aluminum liquid corrosion test,hardness:less-carbon>moremanganese>less-silicon>nickel-containing>application group>lesschromium.The hardness of six group samples decreased,and the decrease of nickel-containing specimen was the smallest.The transformation of the matrix from the lamellar pearlite to the granular pearlite and the precipitation of the secondary graphite were the main reasons for its reduced hardness.Corrosion resistance of aluminum liquid:nickel-containing>application group>less-silicon>less-chromium>less-carbon>more-manganese.The corrosion resistance of the nickel-containing group was the best,the composition is(mass fraction/%):3,40%C,2.70%Si,0.7%Mg,1.0%C r.1.2%Ni,0.4%Cu.Due to the small increase in tensile strength,which can be used to manufacture a shorter,lower strength of the protective sleeve.Low-alloy gray cast iron in molten aluminum was a gradual corrosion process,The alloy layer was formed between the substrate and the aluminum liquid,which consisted of two phases,near the matrix was Fe2Al5,near the liquid aluminum was FeAl3.The interface layer can prevent the contact between the aluminum liquid and the matrix,which had the function of protecting the matrix,the thickness of the interface layer was thicker,and the corrosion resistance of the material was better.