Steel history and its chronological progress have been reviewed from different aspects on many published papers, and books and it can be found on many websites. However, one historical aspect of this topic, which has received limited attention, is the gradual progress in knowledge of controlling cooling rate to get the desirable thermal and mechanical properties for the steel products. This paper presents some evidence of understanding the effect of cooling rate on the material properties from Iron Age era. It also discusses briefly the importance of determining optimimum cooling rate in enhancing the production rate.

This paper discusses the major sources of residual stress generation in the steel microstructure during cooling process of as-cast steel (slabs, blooms, and billets). The stress configuration of the steel microstructure changes during quenching due to stresses introduced to the microstructure by these sources. The influence of each source in increasing the stress distribution within the microstructure during quenching is explained via corresponding formula and qualitative discussion in separate sections. The stresses accumulated during cooling may introduce the residual stress concentration zones in the microstructure of the steel.
These stress concentration zones may result in flaws, microcracks or voids formation. Consequently, it may lower the soundness of the steel and cause deviation of the thermo-mechanical properties of the cast steel from the initially designed and customer desired specified properties.

The control of non-metallic inclusions is an important tool for steel properties optimization. Most related actions of this control involve the prevision of the slag-metal and inclusion-metal equilibrium, aiming at implementation of operational practices to obtain a more adequate inclusion profile.
Computational thermodynamics has proved to be a powerful tool in the prevision of equilibrium in different metallurgical systems, especially in the metal-oxide system in question. The aim of this work is to present the application of computational thermodynamics in the study of formation and control of non-metallic inclusions in steels, mainly during secondary refining. This work shows that the careful application of computational thermodynamics can drastically reduce the empirics in the process development for the control of non-metallic inclusions in steels, contributing to an increase in the efficiency of the process manufacture, to improve the present product quality and to enable the economic development of new products.

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