The Control Of Solidification Behavior And Microstructure In Cast Iron

As a very important engineering structural material, cast iron palys an important role in the machinery industry and the world economy. However, due to the very complex multi-components structure of cast iron, it is not easy to achieve the stable production process, scientific control method, uniform microstructure and excellent synthetical quality.In order to obtain the cast iron with good properties, the control of metallurgical quality could be used on one hand, and to improve the solidification structure on the other hand.. Therefor, the control of solidification behavior and microstructure in cast iron was studied from this two sides in this paper.The relationship between characteristic value of cooling curve and the chemical composition of gray cast iron had been researched by thermal analysis. The result of regression analysis shown that the sample cup without Telurium could also be used to test the chemical composition of gray cast iron. The temperature of liquidus (TL), temperature of eutectic undercooling (TEU) and temperature of eutectic recalescence (TER) were used to predict the content of carbon and silicon. In this experimental condition, the mathematical model of carbon content could be expressed as follow:C%=-2.60237-0.00616TL+0.02925TEU-0.01739TER, and the mathematical model of silicon content could be expressed as follow:Si%=34.34162+0.00498TL-0.01729TEU-0.01676TER.The cooling curves of ductile cast iron had been measured at workshop by thermal analyzer. Cooling curves and image analysis software were used to describe different samples. Relationships between the nodulizing grade and chracteristic points on cooling curves such as the temperature of eutectic undercooling, temperature of eutectic recalescence and degree of recalescence (△T=TER-TEU) were studied. The study revealed that the nodularity and graphite nodule count decreased linearly as the temperature of eutetic undercooling increased. The nodularity decreased as the degree of undercooling increased. The nodularity can be expressed by the combination of thermal analysis characteristics as follow:y=1168.36587-0.93784TEU-2.84566AT.By treating the gray cast iron melt with high frequency electromagnetic field of50kHz, the effects of high frequency coil turns, electric current and processing time on the solidification structure of gray cast iron was discussed. The result indicated that high frequency electromagnetic field could change the solidification structure in gray cast iron effectively, and the size of eutectic cell reduced evidently, the graphite morphology was transformed from curving and long flake to fine and crimpy flake. The appropriate of coil turns and current could remarkably refine the graphite in a short time. The reasons causing those effects were attributed to electromagnetic stirring caused by electromagnetic force, and high frequency induction heat.