Murashkin A. Improvement of quality characteristics of microalloyed steel plate in controlled roll-ing

The thesis aims to study the possibilities of further strengthening low-carbon micro-alloyed steels in heat treatment and deformation regimes. The author has developed the methodology of steel grade selection for designing high-duty building structures using complex criterion that includes strength, plasticity and price fluctuations. To estimate and correct heating and roughing schedules, the thesis provides methodology of defining austenite grain size by final bainite-martensite metal structure. Application of electron mi-croscopy of thin foils allowed to identify that a developed subgrain structure is formed in austenite during repeated hot deformation, the dependence of maximum subgrain-boundary angle value and total degree of deformation being defined. Based on the comprehensive research, an advanced hot rolling heat deformation regime for low-carbon microalloyed steel plate has been developed, which passed performance test at OJSC"Ilyich Iron and Steel Works of Mariupol". The thesis contains recommendations for the usage of 10G2FB steel as a material for high-duty welded metal structures in service in open air conditions.