Laukhin D. The Theoretical Foundations of the Formation of Substructure, Structure and Properties of the Rolled Plates Made of the Low-Carbon Micro-Alloyed Structural Steels

In this thesis the author presents the theoretical foundations of the controlled rolling that were developed during the investigation of micro- and substructure formation proc-esses at the different stages of the rolled plates production from the low-carbon micro-alloyed steels. In this manuscript it is shown how the controlled rolling parameters affect the me-chanical and operational properties of the steels for modern construction. The formation of highly dispersed state of grain-boundary, structural, substructural and dislocation compo-nents is discussed as one of the possible ways to enhance the properties of the rolled plates. It is shown that the austenite polygonal structure formed during the hot deformation process promotes increasing of the number of nucleation centres of the ferrite phase, due to the fact that the nucleation of new crystals of hypoeutectoid ferrite is taking place not only at the high-anglular but also at the polygonal boundaries of the hot-deformed austen-ite. Stabilization of the subgrain austenite structure initiates formation of the ferrite phase even within the unfavourable liquation areas, thus reducing the ferrite-pearlite banding and enhancing the properties in Z-direction. The presence of low-energy special boundaries in the ferrite component is revealed in the low-pearlite constructional steels; their effect on the mechanical properties of the rolled steel is shown. The domestic rolled plates, pro-duced according to the technology considering the regimes suggested in this thesis, is rec-ommended for the use in the constructional field as a material for the manufacture of frames of the multi-storey buildings and large-span constructions.