Development of prediction of mechanical properties and working stress of materials is unavoidable component in area of materials engineering and steel alloys, as very important materials in area of engineering, have a special importance in area of materials engineering. On the basis of structural features on sub‐micro, micro and macro scale it is possible to predict mechanical properties of materials, i.e. steel alloys. By knowing the effects of processing history on those structural features it is possible to model the mechanical properties of steel alloys and according to exploitation conditions it is possible to select the optimal material and optimal process of manufacturing which significantly reduce the costs of manufacturing processes. In this work, the effects of different processes, like casting, processes of mechanical metallurgy and heat treatment processes, on microstructure and mechanical properties of steel alloys was defined on some unique and original way. Great contribution is achieved in prediction of mechanical properties of steel castings. The trend of development of near net shaping processes, which casting is, make these achievement more significant. Results and experiences given by this work can be quality applied in development of manufacturing processes of irons and non‐ferrous alloys. In this Doctoral Thesis, based on obtained cognition, mathematical models of prediction of mechanical properties of steel and cast steel was developed. Developed models are implemented in existing software, ''Quenching for Windows’’ of author B. Smoljan, by which this software was additionally improved. Those improvements make this software more efficiently in applying in research institutes, in the development of new processes of hardening of alloys, in which heat treatment will be integrated into the process of material forming to increase economic efficiency. Accordingly, this Doctoral Thesis gives appreciable contribution in realization of objectives of project Optimization of Parameters and Prediction of Metals Heat Treatment Results, project of Ministry of Science, Education and Sports of the Republic of Croatia of senior researcher B. Smoljan, under which this Doctoral Thesis is carried out.