A two-dimensional model for the description of the columnar-to-equiaxed transition in competing gray and white iron eutectics and its application to calender rolls

A two-dimensional (2-D) microstructural model has been developed for the de scription of the solidification of gray and white iron eutectics at the sca le of a casting process. The model deals with the competition that can occu r between the white and gray iron microstructures and between the columnar and equiaxed morphologies. The evolution of the volume fraction of gray and white iron and the respective proportions of columnar and equiaxed morphol ogies are calculated at each node of a finite-element (FE) mesh of the cast ing. The model is coupled with the commercial FE software ABAQUS, which pro vides the solution of the heat-flow problem. Columnar solidification is des cribed with a new front tracking algorithm that allows the undercooling at the interface and the non-steady-state stage of growth to be calculated acc urately, Equiaxed solidification is described with a deterministic model ba sed on nucleation and growth laws. The model is first applied to a casting of a simple geometry in order to investigate possible numerical problems as sociated with the front tracking algorithm. The model is then applied to th e solidification of a reduced-scale cast-iron calender roll. The results of the simulation are compared with measurements performed in an instrumented casting of 0.4 m in diameter and 1 m in length. A comparison between calcu lated and measured volume fractions of white and gray iron is presented as a function of the radial position in the casting. It shows that the model i s able to predict properly the transition from white to gray iron, which oc curs at approximately 20 me from the external surface of the roll. Comparis ons between calculated and measured temperature evolutions and equiaxed gra in densities of equiaxed grains are also presented and show satisfactory ag reement.