Numerical Simulation On Solidification Process Of Spheroidal Graphite Cast Iron With Cellular Automaton

Spheroidal Graphite Cast Iron (SGI) is widely used in practice because of its good mechanical and casting properties. The mechanical properties are related with the microstructure formed during solidification process especially the size and morphology of the graphite. The solidification process is affected by several factors such as nodulizer, inoculant, cooling rate and alloy elements and so on. It’s very difficult for people to understand the comprehensive effects of all the factors on microstructure. The present paper is aimed to develop a solidification model based on the simple Fe-C-Si alloy to lay a foundation for further development. Cellular automata(CA) method is a popular tool for growth simulation. CA method can take advantage of the computational efficiency and is physically sound but the defect is the substantial anisotropic influence of the Cartesian grid on the simulation results. Many efforts previously have been taken to reduce the anisotropy to simulate the two phase alloys dendritic growth. However, there are three phases-graphite, liquid, austenite appearing during SGI solidification and the graphite phase grows in spherical shape.In this paper, a new graphite growth model is proposed. The method of composition averaging and geometrical parameter introduced is adopted to make the graphite grow in spherical shape through analyzing the reasons causing anisotropy in the Von Neumann capturing rule. The model can not only eliminate the anisotropy caused by the discontinuous composition distribution but also simulate the effect of dropping roundness because of the different growing environment of interfaces in the same graphite. The proper averaging range, averaging time and geometrical parameter are determined by simulation of single graphite. The confirmed model is used to simulate the interactive growth of two graphite nodules to evaluate the validity of the model.The SGI solidification model is built by coupling the austenite and graphite growth model. The decentered square algorithm cellwise mass balance methods are used to simulate the growth of austenite. The growth model built above is used to simulate the growth of the graphite. The coupled model explains clearly the calculation of thermal and solutal field, growth of austenite and graphite in interface cells and the transition rules of different cells. The C++ language is used on the VS2010 MFC platform to write the simulation programs. To reduce the error caused by computer language, how to calculate the sum of different items and the surface energy anisotropy function are descripted in detail.The coupled model is used to simulate hypereutectic and hypoeutectic SGI to analysis the evolution of composition and microstructure during solidification. The nucleation rate model is estimated and the model can reappear the solidification of SGI reasonably. To evaluate the validity of the model, the solidification of hypereutectic SGI is simulated. The metallography and cooling curves acquired by simulation and experiment are compared and the results are similar.