Refining and Casting of Steel

Steel has become the most requested material all over the world during the rapid technological evolution of recent centuries. As our civilization grows and its technological development becomes connected with more demanding processes, it is more and more challenging to fit the required physical and mechanical properties for steel in its huge portfolio of grades for each steel producer. It is necessary to improve the refining and casting processes continuously to meet customer requirements and to lower the production costs to remain competitive. New challenges related to both the precise design of steel properties and reduction in production costs are combined with paying special attention to environmental protection. These contradictory demands are the theme of this book

Efficient computational strategies for the control process of continuous casting machines

In continuous casting machineries, monitoring the mold is essential for the safety and quality of the process. Then, the objective of this thesis is to develop mathematical tools for the real-time estimation of the mold-steel heat flux which is the quantity of interest when controlling the mold behaviour. We approach this problem by first considering the mold modelling problem (direct problem). Then, we plant the heat flux estimation problem as the inverse problem of estimating a Neumann boundary condition having as data pointwise temperature measurements in the interior of the mold domain given by the thermocouples that are buried inside the mold plates. In formulating the inverse problem, we consider both the steady and unsteady-state case. For the numerical solution of these problems, we develop several methodologies. We consider traditional methods such as Alifanov's regularization as well as novel methodologies that exploit the parametrization of the sought heat flux. We develop the latter methods to have an offline-online decomposition with a computationally efficient online part. Moreover, in the unsteady-state case, we propose a novel, incremental, data-driven model order reduction technique to achieve the real-time performance of the online phase. Finally, we test all discussed methods on academic and industrial benchmark cases. The results show that the proposed novel numerical tools outclass traditional methods both in performance and computational cost. Moreover, they prove to be robust with respect to the measurements noise and confirm that the computational cost is suitable for real-time estimation of the heat flux

Controlling microalloy interactions on precipitation, hot ductility, and microstructure -- Mechanical property relationships

“One of the main problems faced in the continuous casting of micro-alloy steels is the formation of transverse cracks. Transverse cracks are surface, or near-surface cracks formed perpendicular to the casting direction. The research focuses on using laboratory hot tensile tests methods to determine the low ductility ranges in high strength steel grades with different micro-alloy additions of titanium, niobium, and vanadium. The hot ductility of commercially produced as-cast slab and beam blank samples was evaluated using two experimental methods: tensile testing utilizing a servo-hydraulic load frame with a resistance furnace and thermomechanical testing using rapid Joule heating. The tests were performed at a 3 x 10-3/s strain rate in a temperature window of 650℃ - 950℃ to mimic industrial unbending temperatures during the continuous casting. A ductility trough with a minimum percentage reduction in area (% RA) was observed closer to the Ar3 transformation temperature of the alloys. The ductility drop at this temperature is likely related to the formation of a thin layer of ferrite film along the austenite grain boundaries resulting in minimum ductility and intergranular failure. Both test methods showed similar low ductility trends, but the upper and lower edges of the ductility trough temperature range differed between the two test methods. The differences are attributed to the heating and cooling rates of the two test methods. Future studies are required to perform in-situ-based deformation tests with the aim of directly observing transverse crack formation during solidification and cooling”--Abstract, page iv

Two Phase Flow, Phase Change and Numerical Modeling

The heat transfer and analysis on laser beam, evaporator coils, shell-and-tube condenser, two phase flow, nanofluids, complex fluids, and on phase change are significant issues in a design of wide range of industrial processes and devices. This book includes 25 advanced and revised contributions, and it covers mainly (1) numerical modeling of heat transfer, (2) two phase flow, (3) nanofluids, and (4) phase change. The first section introduces numerical modeling of heat transfer on particles in binary gas-solid fluidization bed, solidification phenomena, thermal approaches to laser damage, and temperature and velocity distribution. The second section covers density wave instability phenomena, gas and spray-water quenching, spray cooling, wettability effect, liquid film thickness, and thermosyphon loop. The third section includes nanofluids for heat transfer, nanofluids in minichannels, potential and engineering strategies on nanofluids, and heat transfer at nanoscale. The forth section presents time-dependent melting and deformation processes of phase change material (PCM), thermal energy storage tanks using PCM, phase change in deep CO2 injector, and thermal storage device of solar hot water system. The advanced idea and information described here will be fruitful for the readers to find a sustainable solution in an industrialized society