Kunytska I. Optimization of temperature-deformation parameters of rolling with respect to their influence on structure and properties of special steels.

The research object is the process of structure formation and kinetics recrystallization of austenite at multipass hot deformation of special steels. The research subject is the principles of influence temperature-deformation parameters of rolling on the formation of physical and mechanical properties of rolled section of special steels with combined deformation-heat treatment. The aim of the research is to establish the peculiarity of structure formation and recrystallization kinetics of austenite at multipass hot deformation and to develop the technologies of combined deformation-heat treatment to produce of rolled section of special steels with increased level of physical and mechanical properties. The research methods: metallographic researches were carried out by the optical light microscopy. The structure of grain boundaries, dislocation structure, structure and composition of phase have been researched by methods of electron and scanning microscopy, auger-spectroscopy, micro X-radiation specturm analisis. Kinetics of recrystallization process was studied by quantitative metellography, by measuring the hardness and microhardness. Mechanical properties have been determined at normal temperatures.The results attained: the technologies of combined deformation-heat treatment were developed for structural, corrosion-resistant and bearing steels. Improvement of physical and mechanical properties and shortening of heat treatment time are obtained for rolled section of special steels, as compared to the treatment in thermal workshop. Technological control of dynamic recrystallization decreases the grain size, length and thickness of carbide network, and accelerates the formation of carbide spheroids. For bearing steel with spheroidizing annealing, the technology of combined deformation-heat treatment is introduced in mill 325 at PJSC «Dneprospetsstal». Area of application – metallurgy of special steels.