The study of continuously cast steels with different contents of carbon, manganese and silicon is carried out in the work. To determine the features of the structural state of steels, we use microstructural analysis, x-ray microanalysis, and x-ray diffraction method. As shown, depending on the carbon, manganese, and silicon contents in the structure during solidification, the next development is possible as follows: formation of the primary phase of $\delta$-ferrite and, then, formation of $\gamma$-iron according the peritectic reaction; coexistence of $L$-, $\gamma$- and $\delta$-phases, and formation of $\gamma$-iron from the melt. As found, with an increase in the carbon content $\geq$ 0.5 wt.%, manganese content $\geq$ 0.75 wt.% and silicon content $\geq$ 0.45 wt.% in steel, formation of the $\delta$-ferrite primary phase from the melt in the continuous cast steel billet does not occur. At given content of carbon, manganese and silicon in the steel, formation of $\gamma$-iron in the melt and increase in the quantity of inclusions, namely, complex carbides and iron silicides, are observed. Calculations show that, with an increase in the manganese and silicon contents, the peritectic area in the diagram decreases. In the interdendritic space, the segregation of manganese and silicon is detected: in the crust zone and at the 1/2 radius of ingot, the segregation of manganese is up to 0.7 wt.% and the silicon one is up to 0.5 wt.%; in the central part of ingot, the content will be almost the same as in the alloy.