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In this paper we have investigated the possibility of increasing the complex mechanical properties of steel strength category X90 by refinement the structure of hot and warm deformation. Were carried out tests to determine the critical points of recrystallization and built thermokinetic curves of austenite decomposition. After that, for produce disperse ferrite in samples has been applied to the processing mode, which is exactly the same mode of controlled rolling, then, to obtain nanoscale state of the metal deformed at temperatures of bainite transformation with varying degrees of deformation at different temperatures. It was shown that the dispersion and morphology of the structure and, consequently, the mechanical properties vary depending on temperature and strain, and samples show satisfactory ductility at high strength.

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Effects of various factors such as the grain size, the morphology of nonmetallic inclusions, and joint microalloying with boron and titanium on the high-temperature ductility of pipe steels are studied. Physical modeling of the conditions of cooling of the skin of a continuous-cast preform in the zone of secondary cooling in a Gleeble facility is performed. Technical recommendations are given for raising the hot ductility of steels under industrial conditions. Key words: hot ductility, continuous casting of steel, physical modeling, pipe steel. INTRODUCTIONReported data on carbon and alloy steels show that ductility drops in continuously cast metal occur in the temperature range of 750 -1050°C [1 -4]. When the crystallization is accompanied by additional impacts on the metal, for example, in the form of thermal or deformation cycles typical for the skin of solidified metal in the zone of secondary cooling in continuous casting machines, the temperature range of the ductility drop widens and deepens [5 -7]. It has been shown in [7,8] that ductility drops typical for the stage of cooling of steel in a continuous casting machine do not manifest themselves during subsequent hot rolling, and the studied pipe steels possess high ductility.The aim of the present work was to test the methods of grain refinement in the process of cooling of the skin of a slab in a continuous casting machine for raising the ductility of the continuously cast metal and to study the changes in the morphology of nonmetallic inclusions in heating for rolling and the effect of microalloying with boron and titanium on the ductility of steels.