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The article presents the results of a study of the effect of slab thickness on the element segregation of during continuous casting of billets. The process of accumulation of elements on the surface of dendrites during crystallization of steel slabs for various thicknesses is considered. The theoretical dependence of the process of accumulation of elements on the dendrite surface during the crystallization of steel slabs for various thicknesses has been established. It is shown that the efficiency of accumulation of elements on the dendrite surface depends significantly from the crystallization and cooling rate of the slab. The established dependence makes it possible to determine the permissible increased element content in strips, which is equivalent to their content in thick slabs during continuous casting of billets. The element segregation searching shows that at pouring of thin steel strips, an increasing of the element content is possible compared to continuous casting of thick slabs with an identical level of segregation. The elements are arranged as possible to maximize the impurities content in AISI 1006 carbon steel in the following decreasing sequence: S, O, N, P, H. Another sequence is observed for stainless steel AISI 304: O, S, P, H, N. The following sequences are observed in the case of residual elements: for steel AISI 1006 - Pb, Bi, Sn, As, Zn, Sb, Cu; for steel AISI 304 - Cu, Sb, Sn, Bi, Pb, As, Zn. The sequences are as follows for the alloying elements: for steel AISI 1006 - B, Se, Al, Te, Ca, Mg, Ce, C, La, Nb, Ti, Mn, Ni, Si, Cr; for steel AISI 304 - Ca, Te, Al, Ti, Mg, C, La, Ce, Nb, Se, V, B, Si, Cr, Mn.

An analytical dependence of the influence of alloying elements on the equilibrium temperature of vanadium nitride in austenite is established for the main alloying elements based on an analysis of state diagrams, which describe an actual process with an error of 0.9%. As a result of the process analysis is theoretically justified and experimentally confirmed that the precipitation of the secondary phases from the supersaturated solution kinetics is controlled by the thermodynamic activity, diffusion mobility and solubility of the components forming the secondary phase in the solid solution, the deviation degree of the system from the equilibrium state, where the equilibrium state is the formation temperature and dissolution of the secondary phase. The established quantitative regularity shows that the precipitation kinetics of the vanadium nitrides in austenite with a probability of 99.9% and an error of 7.1% is reliably described by the thermodynamic activity of nitrogen and vanadium, the deviation degree of the system from the equilibrium state, and the process time. In this case, the correlation coefficient between experimental and theoretical data is 0.915. An analysis of the obtained analytical equations shows that the influence of the chemical composition on the content of the carbide and nitride-vanadium phases in the solid solution is significant. The elements are arranged according to the degree of increasing influence in the following sequence: the content of vanadium nitrides in austenite increases Si and decreases Mn, C, Cr. As a result of studying the process of converting austenite to ferrite and perlite, martensite, and bainite, it was found that the nonequilibrium critical points of phase transformations are controlled by the equilibrium temperature of austenite and ferrite, the content of secondary phases in them, the diffusion mobility of carbon in austenite, the degree of alloying, and the grain size of austenite and in the case of diffusion transformations by the heating and cooling rate. Quantitative influence laws are determined, which describe the real process with a probability of 95% and an error from 2.3% to 7.1%.

The study showed that the influence of alloying elements on the secondary structure formation of the steels containing from 0.19 to 0.37 wt. % carbon; 0.82-1.82 silicon; 0.63-3.03 manganese; 1.01-3.09 chromium; 0.005-0.031 nitrogen; up to 0.25 wt.% vanadium and austenite grain size is determined by their change in the content of vanadium nitride phase in austenite, its alloying and overheating above tac3, and the dispersion of ferrite-pearlite, martensitic and bainitic structures is determined by austenite grain size and thermal kinetic parameters of phase transformations. Analytical dependencies are defined that describe the experimental data with a probability of 95% and an error of 10% to 18%. An analysis results of studying the structure formation of structural steel during tempering after quenching show that the dispersion and uniformity of the distribution of carbide and nitride phases in ferrite is controlled at complete austenite homogenization by diffusion mobility and the solubility limit of carbon and nitrogen in ferrite, and secondary phase quantity in case of the secondary phase presence in austenite more than 0.04 wt. %. Equations was obtained which, with a probability of 95% and an error of 0.7 to 2.6%, describe the real process.

As a result of the analysis of the formation processes of fluidity and the conditions for feeding the castings during cooling after solidification, a significant effect of the properties of the melt and the dispersion of the primary structure on the fluidity and density of steel was established. It is theoretically substantiated and experimentally confirmed that the level of fluidity and density is determined by the dispersion of the dendritic structure, the magnitude of the melt overheating over the liquidus temperature, as well as the properties of the liquid metal, the thermal conductivity of steel at the solidus temperature, crystallization heat and crystallization interval. The established quantitative laws describe the real process with a probability more than 95% and a high degree of reliability (R = 0,709-0,837; ð = 1,2 – 13,8%). The article shows that in order to increase the effectiveness of the influence of integral factors on the fluidity of structural steels, they can be arranged in the following sequence: thermophysical conditions of solidification, dispersion of the dendritic structure, properties of liquid metal. In this case, an increase in fluidity occurs with an increase in the overheating of the melt above the liquidus temperature, the heat of crystallization and the dispersion of the dendritic structure. An increase in the values of other factors leads to the opposite effect. Alloying elements are arranged in the following sequence: Si, Cr, Mn, C, V, N, V + N according to the specific efficiency of increasing fluidity. The results of the studies performed show that according to the effectiveness of the influence of the considered factors on the steel density, they can be arranged in the following sequence: dispersion of the dendritic structure, properties of liquid metal and thermalphysic conditions of solidification. Alloying elements affect these parameters in such a way that a complex multiextremal change in density is observed during alloying of steel. The general trend is that carbon and chromium decrease, while silicon, manganese, vanadium, nitrogen, and co-alloying with nitrogen and vanadium increase the density of the steel. Alloying elements can be arranged in the following sequence: V, Cr, Mn, Si, N, N + V, C to increase the specific efficiency of changing the density.