Solidifacation Simulation Of Spheroidal Graphite Iron Based On Macro-micro Models

Spheroidal graphite cast iron is a very important engineering material alloy. which has good mechanical property and casting property. It plays an important role in casting and mechanical productions. Applications of Spheroidal graphite cast iron continue to increase steadily over the years due to its relatively low cost production. For the spheroidal graphite cast iron castings which must have high quality, shrinkage cavity and porosity are the main defects to be solved. It is required that the research into the rules that the processing parameters affect the shrinkage behavior of spheroidal graphite cast iron castings. Prediction of the position and volume of the shrinkage defects on the spheroidal graphite cast iron castings will reduce the cost . shorten the trial period and enhance the capability of the enterprise.Micro-macro mathematical and physical models which are employed in the solidification simulation of spheroidal graphite cast iron are reviewed and analyzed in this paper. There is not an appropriate model which can predict the porosity distribution of spheroidal graphite cast iron castings correctly. And the nucleation model and latent heat data at hand which should be used in the solidification simulation of the spheroidal graphite cast iron castings processed with different parameters are not reliable. It is necessary to develop the models with floor experiments.The effects of carbon equivalent, inoculation and casting modulus on porosity distribution of spheroidal graphite iron castings has been studied using a series of vertical board castings designed with orthogonal rules. Based on the experiment data. an evaluation mathematical model of porosity calculation model is carried out with the parameters of carbon equivalent, inoculation and cooling rate of the castings. Porosity formation mechanism and process is discussed in this paper. Porosity formation mechanism differs with the type of the spheroidal graphite iron. The existence of the off-eutectic austenite increases the shrinkage volume of the hypoeutectic spheroidal graphite iron and the strong austenite dendrites prevent the liquid melt flow to the shrinkage field which is the position of the porosity after solidification of the castings. For the hypereutectic spheroidal graphite iron, porosity formation is the result of the liquid shrinkage and graphite expansion. Under the condition that the mold is strong enough, the graphite expansion will bring a pressure to the liquid melt and push them to the last solidification field. Based on these analyses, a new spheroidal graphite iron porosity prediction criterion model with the pressure of static liquid pressure and expansion pressure is proposed in this paper.Employed the quantitative metallographic analysis and computer aided cooling curve analysis (CA-CCA). the graphite nucleation density of the spheroidal graphite iron is studied with samples which has different carbon equivalent, inoculation and cooling rate. The nucleation model of the hypoeutectic, eutectic and hypereutectic spheroidal graphite iron is developed considered with their solidification process respectively. At the mean time, a mathematical model of the nucleation temperature calculation is shown by research the undercooling of the castings.The latent heat of spheroidal graphite iron with different carbon equivalent, inoculation and cooling rate is calculated with different heat analysis (DHA) method and different scanning calorimetry (DSC) method. The effects of carbon equivalent, inoculation, cooling rate and microstructure on the latent heat are analyzed. It reveals that the latent heat increase with the increase of carbon equivalent and cooling rate. The latent heat of cast iron is strongly affected by microstructure of graphite.A spheroidal graphite iron solidification simulation software named TMCast-S.G iron is developed based on the Microsoft Visual Studio 6.0 and Windows XP with the program language of Visual C++. The ActiveX Data Objects and DLL technique is used in the software. It can calculate the temperature field, graphite densities of different type spheroidal graphite iron and can predict the cavity and porosity defects on the castings. The software is a powerful tool by comparing the results of the simulation and real castings.