The Effect Of Aluminum And Chromium On Microstructure And Properties Of Heat Resistant Ductile Cast Iron

Aluminum products are widely used in the construction industry,electronic power industry and transportation industry.As a national basic industry,the electrolytic aluminum industry is related to the development of the national industrial system and the national economy.In the process of electrolytic aluminum production,the aluminum ingot mold is an important consumable part,which needs to withstand the rapid heat and quenching cycle of 25?750?,resulting in fatigue failure and scale peeling of the aluminum ingot mold,reducing the service life of the aluminum ingot mold,affecting the economic benefits of the electrolytic aluminum industry.Therefore,it is necessary to develop heat-resistant ductile iron for aluminum ingot molds with excellent performance.Based on the silicon-molybdenum heat-resistant cast iron,the effects of aluminum and chromium on the microstructure,mechanical properties,oxidation resistance and thermal fatigue resistance of heat-resistant ductile cast iron were investigated by means of OM.SEM.EDS and XRD.The test results show that when the chromium content is 0.2%.0.4%and 0.6%.respectively,the graphite size increases slightly with the increase of aluminum content,the graphite spheroidization rate decreases gradually,the chunky graphite increases gradually,the pearlite content decreases and the ferrite content increases.When the aluminum content is 1.5%and 2.5%,respectively,as the chromium content increases,the graphite morphology remains basically unchanged,the pearlite content increases,and the ferrite content decreases.When the aluminum content is 3.5%.the morphology of the graphite is substantially unchanged,the matrix structure is ferrite.and the ? phase is produced.When the chromium content is 0.4%.the tensile strength of heat-resistant ductile iron increases first and then decreases with the increase of aluminum content,the elongation decreases gradually and the Brinell hardness increases gradually.When the aluminum content is 2.5%,with the increase of chromium content,the tensile strength of heat-resistant ductile iron increases gradually,the elongation decreases gradually and the Brinell hardness decreases first and then increases.All samples at 750? and 850? were oxidation resistant.3.5%AI 0.6%Cr samples at 950? were secondary oxidation resistance levels,and the remaining samples were weak antioxidant levels.When the chromium content is 0.2%.0.4%and 0.6%,respectively,the oxidation resistance of heat-resistant ductile iron increases with the increase of aluminum content,when the aluminum content is 1.5,2.5%and 3.5%,respectively,the oxidation resistance of the heat-resistant ductile iron is enhanced with the increase of chromium content.as the oxidation temperature increases,the oxidation resistance of the heat-resistant ductile iron decreases.The morphology of the oxide film of 1.5%Al 0.4%Cr and 2.5%Al 0.4%Cr at 850? is cell shape,and the cell oxide film is Fe22O3.The surface of the oxide film of 3.5%Al 0.4%Cr is layer.The layered oxide film is a composite oxide of Fe,AI,Si.and Cr.The oxide films of 1.5%Al 0.4%Cr sample,2.5%Al 0.4%Cr sample and 3.5%Al 0.4%Cr sample at 950? are all cellular Fe2O3.The thermal fatigue main crack length of 2.5%Al 0.2%Cr samples is up to 67 mm.and the thermal fatigue main crack length of the 1.5%Al 0.2%Cr samples is at least 12 mm.The main crack did not appear in the 2.5%Al 0.4%Cr sample and 2.5%A1 0.6%Cr sample.The main crack of the thermal fatigue specimen is generally formed at the edge of the specimen,gradually expanding toward the center of the specimen.The edge of the main.crack has local oxidation and crack bifurcation,the graphite sphere changes the direction of crack propagation to some extent.microcracks are generally produced in graphite and the second phase around.In this paper,the effects of aluminum and chromium on the microstructure,mechanical properties,high temperature oxidation resistance and thermal fatigue resistance of heat-resistant ductile cast iron for aluminum ingot mold are analyzed.It is recommended that the optimum content of heat-resistant ductile iron is 2.5%A.0.4%?0.6%Cr.