Study of slab quality and tonnage determination for overlapping heats in a continuous casting tundish

Steel is an alloy of iron and carbon that is widely used in construction and other applications because of its high tensile strength and low cost. Carbon, other elements, and inclusions within iron act as hardening agents that prevent the movement of dislocations that naturally exist in the iron atom crystal lattices. The carbon in typical steel alloys may contribute up to 2.1% of its weight. Steel is irrevocable material because of its wider usage area, possibility for hot and cold forming, weld ability, hard, ductile, abrasion resistance features, corrosion resistance, heat and deformation resistance at high temperatures. So that, its usage area could reach variety of engineering subjects. It is common today to talk about "the iron and steel industry" as if it were a single entity, but historically they were separate products. The steel industry is often considered an indicator of economic progress, because of the critical role played by steel in infrastructural and overall economic development. Contemporarily, there are two main methods to produce a steel from iron ore. First one is reduction of iron ore to liquid and warm metal and the other one is reduction to directly iron (DRI-direct reduced iron) in different name sponge iron. In the present day, two common ways are followed to produce and refine the steel as mentioned below. • Blast furnace-converter method, • Electric arc furnace method. In a blast furnace, fuel, ore, and flux (limestone) are continuously supplied through the top of the furnace, while a hot blast of air (sometimes with oxygen enrichment) is blown into the lower section of the furnace through a series of pipes called tuyeres, so that the chemical reactions take place throughout the furnace as the material moves downward. The end products are usually molten metal and slag phases tapped from the bottom, and flue gases exiting from the top of the furnace. The downward flow of the ore and flux in contact with an up flow of hot, carbon monoxide-rich combustion gases is a countercurrent exchange process. Liquid raw iron is gained by using coke and coal as reduction material in a blast furnace and relevant liquid raw iron is refined in a basic oxygen furnace. In an electric arc furnace, the energy and heat to gain molten steel are provided from electric energy. Generally speaking, electric arc furnace is known as it uses both scrap and sponge iron. The electric arc furnace operates as a batch melting process producing batches of molten steel known "heats". The electric arc furnace operating cycle is called the tap-to-tap cycle and is made up of the following operations: • Furnace charging • Melting • Refining • De-slagging • Tapping • Furnace turn-around After the electric arc furnace process, secondary metallurgy processes begin (ladle furnace, vacuum degasser etc.) for molten steel. The molten steel that was processed in secondary metallurgy is casted through the tundish to the molds considering to sales order requirements for shape, dimension and weight. Casting processes are classified as follows; • Continues casting, • Band casting, • Ingot casting. The most common casting method in the world is "Continues Casting" and its application ratio raised up to approximately %90. Continues casting provides more than %95 efficiency, uniform solidification, faster casting speed etc. In a process of continues casting, tundish is the last metallurgical channel to cover and accommodate the melted steel before pouring to the molds and permitting to begin the solidification. There are one or more than one holes at the bottom of tundish and they let to feed the mold with hot steel. In addition, tundish mechanism provides smooth pouring of hot steel. As a common application for many companies in the world and Çolakoğlu Metalurji A.Ş., slab or billet heats which has different quality names so different chemical compositions are produced in the same tundish during continues casting process in case of the tonnage, quality, dimensions (slab width) unsuitableness to optimize the steel plant's production conditions. At the end of relevant application, two different qualities are mixed, overlapped in the same tundish and the borders of this overlapped slab mixing are unknown. So that, because there is a requirement to know the borders and the new chemical composition of relevant mixing steel, "Study of slab quality and tonnage determination for overlapping heats in a continuous casting tundish" work has been done in this thesis. In addition, this study permits to decide the cast id name (quality name) according to Çolakoğlu Metalurji A.Ş. quality and chemical compositions standards and slab lengths according to Çolakoğlu Metalurji A.Ş. slab dimension standards. In practical case, people in Çolakoğlu Metalurji A.Ş. separate overlapped slabs from original heats with their experience and guess without any measurement, calculation and chemical analysis tests. To wrap up, the main purpose of this study is to clarify the quality borders of overlapped slabs so that to calculate the overlapped slab's tonnage and most suitable slab lengths according to the tonnage though. In addition, the main purpose of this study is to name the overlapped slab quality. In order to control the chemical results of relevant modelling study, 3 pieces from head, middle and tail were taken from the overlapped slab that was separated with experiences by Çolakoğlu Metalurji A.Ş. employees. Then 3 different samples from head, middle and tail of overlapped slabs and 3 different chemical analysis were gained from mass spectrometer of Çolakoğlu Metalurji A.Ş. and viewed the change of chemical compositions step by step from head to tail. Then same conditions were entered (the name of overlapped qualities, dimensions etc.) to the modelling study and viewed the results. At the end, results were compared with each other in tables, graphs. Eventually, relevant results of modelling study that has been already compared with experimental results are quite successful except small and negligible deviations. Basically, this study provides opportunity to work with more reliable result instead of the result based on guess and experiments about overlapped heats in Çolakoğlu Metalurji A.Ş. plant.