Stas I. Structure formation and properties of steel castings in the conditions of regulated heat removal.

The object of research - crystallization and structure formation processes in carbon steel castings under the regulated heat removal conditions. The aim of the work - establishing patterns of the influence of the parameters of crystallization and subsequent cooling of castings on the formation of the macro- and microstructure, features of the segregation behavior, phase-structural state, physico-mechanical properties of carbon steel castings, as well as the development of methodological approaches of prediction of the structural zones formation processes in the solidifying casting. In the paper, on the basis of the system investigations of the influence of the regulated heat removal conditions on the crystallization processes, structure formation and properties of steel castings the features of the crystallization kinetics of the cast carbon steels with different intervals of crystallization were investigated; quantitative patterns of formation of the macro-and microstructure, fine crystalline structure, phase-structural state, features of the segregation behavior under the normal and intensive heat removal conditions in a wide range of cooling rates (1 - 110 оС/s) were established; the mechanisms change of the solid-phase transformations according to the different thermokinetic conditions of subsequent cooling of castings were experimentally established; the efficiency of the processes of non-equilibrium crystallization and structure formation by increasing the cooling rate from 0.1 - 0.5 °C/s to 100 - 110 °C/s to increase the strength characteristics by 10 - 15%, the ductility by 5 - 10%, the toughness in the range of 25 - 40% according to carbon content in the steels was shown. A new parameter of the quantifying dendritic structure - the coefficient of branching of the dendrites borders - was introduced and its connection with heat removal conditions and the kinetic parameters of crystallization and structure formation, the energy and fractography Failure characteristics were established. On the basis of the system experiments using methods of thermometry, metallographic analysis, physical and mathematical modeling, regression analysis the methodological basis of prediction and control of the length of the structural zones and properties of carbon steel castings were developed. The obtained experimental data and established regularities provide additional opportunities of the purposeful managing crystallization and structure formation of steel products at different stages of the process for their production and treatment.