Study On Inoculation Thermal Analysis And Effect Evaluation Of Compacted Graphite Iron

With the increasing demand for high temperature thermal fatigue limit and mechanical properties of high power diesel engine,traditional materials such as aluminum alloy and gray cast iron cannot meet the requirements of key engine components.Compacted cast iron has become the preferred material for high power diesel engines with good thermal conductivity and thermal fatigue resistance.However,the process of preparation of compacted cast iron is complicated.The quality of base iron metallurgy and inoculation of compacted cast iron have important effects on the final quality of castings.In this paper,the eutectic nucleation,graphitization metallurgical parameters and the inoculation effect of vermiculite were studied by thermal analysis.The results show that:There is a linear correlation between activated carbon equivalent of base iron of CGI and initial crystal temperature T_L,and the correlation coefficient R² is 0.874 of the regression equation of initial crystal temperature of white cooling curves,and the prediction error is within 3%.With the increase of the graphitized eutectic temperature by Si E,the regression coefficient R² of the eutectic temperature T_EN and Si E is 0.895,which can control the liquefaction chemical composition of CGI base iron in a small range.according to the indication of eutectic nucleation degree,the ability on nucleation of base iron first increases and then decreases with the extension of holding time,and the form of graphite changes from flake to supercooled graphite.The variation law of oxygen activity of base iron is studied from thermodynamics.The oxygen activity is highly dependent on temperature.Vermicular graphite is produced in large quantities in the medium oxygen level.The lapsed of nucleation level and graphitization ability of base iron can be improved by pretreatment.Fe S₂ can increase S of the base iron,increase the amount of graphite heterogeneous core and graphite,but the amount of magnesium consumed in subsequent vermicularizing treatment increases,so Fe S₂ is not recommended for production.Comparing with 75Si Fe,Si C can realize the bidirectional regulation of carburizing and siliconing,the time on eutectic solidification of molten iron is prolonged,the number of graphite effective core is increased,and the original metallurgical properties of base iron are restored.Inoculation treatment can eliminate the tendency of supercooling caused by vermicularizing treatment.The molten iron’s inoculation level of compacted cast iron can be determined by the difference ofΔT_EU.The inoculation level of molten iron of CGI whoseΔT_EU is less than 2°C is considered to be high.The inoculation decline first decreases the amount of spherical graphite and finally decreases to flake graphite.Through a series of experiments of increasing inoculant step by step in the sample cup by thermal analysis,the requirements of 75Si Fe with different particle sizes to achieve inoculation saturation state were determined.With the amount of 75Si Fe inoculation increased in the cup,the solidification pattern changed from hypoeutectic solidification to low hypereutectic solidification of CGI molten iron,and the graphite morphology changed from vermicular shape to spherical form.The inoculation effect of compacted graphite iron could be evaluated with the increase of T_EUrapidly.