Effect of Alloying Elements on Thermal Contraction and Crack Susceptibility during In-Mold Solidification

A study has been performed on the microstructural properties of steels in the dendritic region with the scope of defining some key parameters denoting the tendency to form cracks during the solidification process, depending on the alloy composition. This study has been coupled to the thermomechanical modeling of the steel solidification inside the mold in order to explain the generation of stresses in the brittle dendritic region. The study has been carried out with the aid of data from round billet casting at Tenaris Siderca, Tamsa, and Dalmine. The linear thermal expansion coefficient calculated at the solidus temperature and the brittle zone width have been defined as the two parameters giving information about the tendency of an alloy to form cracks. The linear thermal expansion coefficient at the solidus temperature, above which steels have peritectic behavior, has also been specified. Some real cases of problems related to cracks and breakouts have been analyzed by means of coupled modeling, and solutions are proposed in terms of alloy composition and mold taper optimization.