Chapter 7 briefly introduces steels, including classification, production processes, microstructure, and properties as well as computational tools for design of steels. Two case studies for S53 and AISI H13 steels are demonstrated. For S53 steel, high strength and good corrosion resistance are needed. For that purpose, plots of thermodynamic driving forces for precipitates were established, guaranteeing the accurate precipitation of M2C strengthener in steels. In addition, a martensite model is developed, designing maximal strengthening effect and appropriate martensite start temperature to maintain an alloy with lath martensite as the matrix. The corrosion resistance was designed by analyzing thermodynamic effects to maximize Cr partitioning in spinel oxide and enhance the grain boundary cohesion. In the case of AISI H13 steel, precipitations of carbides were simulated. Then simulated microstructure was coupled with structure–property models to predict the stress–strain curve and creep properties. Subsequently, those simulated properties were coupled with FEM to predict the relaxation of internal stresses and deformation behavior at the macroscopic scale during tempering of AISI H13