Vývoj optimalizace metalurgických a technologických parametrů pro minimalizaci vznikajících vad plynule litých bramových ocelových předlitků

Abstract

Continuously cast steel slabs, classified as flat products, find their use across the entire machine-engineering industry. The final products made of continuously cast steel slabs include metal sheets for ship-building industry, bridge structures, transport machines, pressure vessels, flame-cutting shape cuts, and pipelines. High-quality final products production requires the continuous cast steel slabs to be manufactured with accurate chemical composition, precise slab shape, high internal purity, and flawless slab outer surface. Any surface defects of continuously cast steel slabs impact the final surface of metal sheets and their mechanical properties. The surface defects initiated already in the mould may further develop by improperly set secondary cooling. The experimental part of the thesis focuses on the research and development of optimizing the metallurgy and technology parameters in order to minimize the defects occurring in continuously cast steel slabs in single-strand slab machine with 250 mm slab thickness. To narrow down the specification, the S355 steel grade group evaluation has been selected. The complex of theoretical and practical knowledge and skills has been verified at individual technology nodes of continuous casting machine. The efforts resulted in reducing the quantity of defects originating in continuously cast steel slab blanks. The thesis describes the applied designs of tundish internal layout, impacts of steel flowing from tundish to mould through submerged entry nozzle, and new possibilities of mould powders use. In the area of the casting arc it focuses on the options of primary cooling alterations and optimization of secondary cooling setting at the continuous casting machine. As the feedback for checking the tested and implemented changes in the entire slab continuous casting technology served the optimization of surface defects evaluation system and settings of the quality prediction for continuously cast steel slabs.