Chapter 19 Solidification of Some Casting Alloys of Commercial Significance This chapter will cover the solidification of some alloys of commercial interest as well as selected numerical models developed to describe and predict the microstruc- ture evolution and defect formation in these alloys. The research community and the commercial entities have produced and continue to produce quite an abundance of numerical models for the prediction of defect occurrence and microstructure development of alloys. For metal casting applications, the most commonly used commercial software are ProCAST and Magmasoft. General commercial codes, such as ABAQUS or Fluent, have also been used in conjunction with specialized routines. This chapter will attempt to illustrate the progress, success, and limitation of both research and commercial models in the prediction of microstructure and related features. 19.1 Steel Steel is a Fe–C-based alloy that solidifies without eutectic. Plain carbon (unalloyed) steel is an alloy whose equilibrium phase diagram (the Fe–C diagram) exhibits partial solid solubility with a peritectic reaction (see Fig. 10.20). Consequently, the solidification microstructure of plain carbon and low-alloy steels is made of equiaxed or columnar α or γ dendrites. 19.1.1 Macrostructure As carbon steel solidifies with a peritectic transformation, the primary grain struc- ture of steel is hard to outline through optical metallography because of the post-solidification recrystallization. Sometimes the macrostructure can be observed in shrinkage cavities, which behave similar to interrupted solidification experiments. The typical dendritic structure of steel revealed by such a technique is presented in c  Springer International Publishing Switzerland 2015 435 D. M. Stefanescu, Science and Engineering of Casting Solidification, DOI 10.1007/978-3-319-15693-4 19