Microstructure Simulation Of Gray Iron And Prediction Of Porosity And Shrinkage Cavity

Gray iron is one of the most important materials which are essential to our national industry and even the whole world industry as well as one of the most widespread casting materials. Due to its good castability, processability and low price, gray iron plays a fundamental role in machinery manufacture, metallurgy, petrochemical industry, transportation, defense industry and so on. However, companies in our country major in gray iron casting are less specialized, making high energy consumption and pollution to environment. In the aspect of casting technology design, the companies abroad mainly employ computer aided software and simulation software such as CAD/CAM, while those in our country significantly rely on experience of Engineers, which is lack of scientificalness and reliability, leaving the quality of castings much lower than those made abroad. With the aid of solidification simulation technology, Foundry CAE Method can be used to simulate the solidification process, and then predict the position and shape of shrinkage defect, so that can be employed to design and improve casting technique. It can help companies shorten design cycle, and enhance the production efficiency.Based on the solidification theory, heat transfer theory, and solidification characteristics of gray iron, thermodynamics method and dynamic method are combined effectively to build the framework of gray iron simulation. The solidification process is divided into two main stages - precipitation of primary phases and eutectic solidification. At the former stage, the relationship between solidification ratio and temperature is established, while at the later one, solidification ratio is calculated through the nucleation and growth model. Enthalpy method is introduced to calculate the latent heat. In light of different ways to release the latent heat, the latent heat of primary phase and eutectic phase are treated in different methods. The Critical Solidification Fraction Method and Shrinkage Volume method is used to predict the shrinkage cavity, while G/(?) Method calculating pressure is used to predict porosity.After analyzing the impact of carbon equivalent, inoculation and cooling rate on the nucleation of eutectic cell, a series of castings are designed, and the cooling curves of the special points are recorded in the meanwhile. The latent heat of those castings is measured by Differential Scanning Calorimetry. The closer the composition is approaching to the Eutectic Point, the less the latent heat of primary phase is, and the more the latent heat of eutectic phase is. Silicon has great influence over latent heat of hypoeutectic gray iron. As the Silicon increases, the latent heat released by primary phase and eutectic phase is reduced. According to DSC data, the simulation models of primary phase and eutectic phase are established, respectively.On the basis of simulation models brought forth above, TMCast-Gray Iron, a solidification simulation software, is developed by a object-oriented programming language-C++, and successfully predict the shrinkage cavity and porosity. A new Multi-Liquid Pool Distinction Method is proposed to distinct different liquid pools. Instead of iterative algorithm, the new Multi-Liquid Pool Distinction Method can save 20% computation time. TMCast-Gray Iron provides new functions such as the display and output of cooling curves and isothermal curves. Other parameters including eutectic cell number and pressure are unfolded to the users.