The paper presents the comparison of optimization-regulation algorithms applied to the secondary cooling zone in continuous steel casting where the semi-product withdraws most of its thermal energy. In steel production, requirements towards obtaining defect-free semi-products are increasing day-by-day and the products, which would satisfy requirements of the consumers a few decades ago, are now far below the minimum required quality. To fulfill the quality demands towards minimum occurrence of defects in secondary cooling as possible, some regulation in the casting process is needed. The main concept of this paper is to analyze and compare the most known metaheuristic optimization approaches applied to the continuous steel casting process. Heat transfer and solidification phenomena are solved by using a fast 2.5D slice numerical model. The objective function is set to minimize the surface temperature differences in secondary cooling zones between calculated and targeted surface temperatures by suitable water flow rates through cooling nozzles. Obtained optimization results are discussed and the most suitable algorithm for this type of optimization problem is identified. Temperature deviations and cooling water flow rates in the secondary cooling zone, together with convergence rate and operation times needed to reach the stop criterium for each optimization approach, are analyzed and compared to target casting conditions based on a required temperature distribution of the strand. The paper also contains a brief description of applied heuristic algorithms. Some of the algorithms exhibited faster convergence rate than others, but the optimal solution was reached in every optimization run by only one algorithm.

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Nowadays, people are increasingly interested in renewable energy sources and accumulation of energy for its efficient use. The use of non-renewable resources is progressively decreasing due to their adverse changes in climate conditions and high production of CO2 emissions. This work deals with the problem of heat accumulation by means of the phase change of a material using the Stefan problem, which serves to describe the temperature distribution in the medium and to determine the location of the interface between the solid and liquid phase. This approach is used to determine desired properties and thermal behaviour of the material under different accumulation requirements. The main objective was to create and solve an optimization model in order to determine heat transfer conditions and other parameters to ensure the extrema of thermal behaviour characterization.

Monitoring and evaluation of temperature distribution in continuous steel casting coupled with optimal temperature intervals providing no defects can be used for the prediction of crack formation in the cast strand. Crack locations can be further specified with the use of mechanical stress-strain distribution model. These crack locations are strongly dependent on the zero ductility temperature (ZDT) and the liquid impenetrable temperature (LIT). To avoid the excessive stress and strain distribution in the steel, parts of the strand where bending and unbending take place should not be in ZDT and LIT intervals. Thus, the casting speed and water flow rates through cooling nozzles have to be modified to avoid these crack sensitive temperature intervals where the stress exceeds its maximum allowable value determined from the crack criteria. In this paper, the thermal solidification and mechanical stress-strain distribution models of billets with sharp and rounded corners for structural steel grades S355 are presented and the results are compared. Further, the idea of coupling between thermal and mechanical models is presented, which serves as a base for a crack predictive model assessing the quality of cast semi-products.