Neste trabalho foram estudadas 10 corridas em duas usinas siderúrgicas semi-integradas, de aço baixa liga para uso em construção mecânica. Em cada uma das corridas foram retiradas 9 amostras, cada uma ao final de uma etapa do processo de produção: após a remoção de escória na panela, antes da desgaseificação a vácuo, após a desgaseificação a vácuo, após a adição de arame de Al, após a adição de arame de CaSi, após a adição de arame de S, após o fim da turbulência no distribuidor no lingotamento contínuo, 30 minutos após o fim da turbulência no distribuidor no lingotamento contínuo, e 60 minutos após o fim da turbulência no distribuidor no lingotamento contínuo. As amostras foram preparadas metalograficamente e analisadas ao microscópio eletrônico de varredura (MEV) com espectrometria de dispersão de energia (EDS), a fim de se identificar as inclusões presentes no aço em cada etapa do processo. Com isto pode-se fazer a caracterização das inclusões encontradas em cada etapa do processo e a sua classificação segundo a composição química e morfologia. Através da comparação da composição química das inclusões encontradas ao final do refino e no lingotamento contínuo foi possível verificar uma tendência de formação de inclusões de espinélio, e através da composição química das inclusões encontradas no lingotamento contínuo foi possível identificar em quais das corridas estudadas houve a presença de inclusões de aluminatos de cálcio formados no estado líquido. / In the present work it was studied 10 heats in two steelworks, of low alloyed steel for use in mechanical construction. From each heat were taken 9 samples, each one of them at end of one production stage: after deslagging in the ladle; before vacuum degassing; after vacuum degassing; after Al wire addiction; after CaSi wire addiction; after S wire addiction; after the end of tundish turbulence at continuously casting; 30 minutes after the end of tundish turbulence at continuously casting; and 60 minutes after the end of tundish turbulence at continuously casting. Samples were metallographic prepared and analyzed by scanning electronic microscopic (SEM) with energy dispersive X-ray spectroscopy (EDX), in order to identify the inclusions present in steel in each process stage. This allowed the founded inclusions in each process stage to be characterized and classified according to chemical composition and morphology. By comparing founded inclusions chemical composition at end of refining and continuous casting was possible to observe a tendency of formation of spinel inclusions, and by founded inclusions chemical composition in continuous casting was possible to identify in which studied heats there were presence calcium aluminates inclusions formed in the liquid state.

Neste trabalho foram estudadas 10 corridas em duas usinas siderúrgicas semi-integradas, de aço baixa liga para uso em construção mecânica. Em cada uma das corridas foram retiradas 9 amostras, cada uma ao final de uma etapa do processo de produção: após a remoção de escória na panela, antes da desgaseificação a vácuo, após a desgaseificação a vácuo, após a adição de arame de Al, após a adição de arame de CaSi, após a adição de arame de S, após o fim da turbulência no distribuidor no lingotamento contínuo, 30 minutos após o fim da turbulência no distribuidor no lingotamento contínuo, e 60 minutos após o fim da turbulência no distribuidor no lingotamento contínuo. As amostras foram preparadas metalograficamente e analisadas ao microscópio eletrônico de varredura (MEV) com espectrometria de dispersão de energia (EDS), a fim de se identificar as inclusões presentes no aço em cada etapa do processo. Com isto pode-se fazer a caracterização das inclusões encontradas em cada etapa do processo e a sua classificação segundo a composição química e morfologia. Através da comparação da composição química das inclusões encontradas ao final do refino e no lingotamento contínuo foi possível verificar uma tendência de formação de inclusões de espinélio, e através da composição química das inclusões encontradas no lingotamento contínuo foi possível identificar em quais das corridas estudadas houve a presença de inclusões de aluminatos de cálcio formados no estado líquido. / In the present work it was studied 10 heats in two steelworks, of low alloyed steel for use in mechanical construction. From each heat were taken 9 samples, each one of them at end of one production stage: after deslagging in the ladle; before vacuum degassing; after vacuum degassing; after Al wire addiction; after CaSi wire addiction; after S wire addiction; after the end of tundish turbulence at continuously casting; 30 minutes after the end of tundish turbulence at continuously casting; and 60 minutes after the end of tundish turbulence at continuously casting. Samples were metallographic prepared and analyzed by scanning electronic microscopic (SEM) with energy dispersive X-ray spectroscopy (EDX), in order to identify the inclusions present in steel in each process stage. This allowed the founded inclusions in each process stage to be characterized and classified according to chemical composition and morphology. By comparing founded inclusions chemical composition at end of refining and continuous casting was possible to observe a tendency of formation of spinel inclusions, and by founded inclusions chemical composition in continuous casting was possible to identify in which studied heats there were presence calcium aluminates inclusions formed in the liquid state.

<p>The electric arc furnace (EAF) is a critical steelmaking facility that melts the scrap by the heat produced from electrodes and burners. The migration to EAF steelmaking has accelerated in the steel industry over the past decade owing to the consistent growth of the scrap market and the goal of "green" steel production. The EAF production already hit a new high in 2018, contributing to 67% of total short tons of U.S. crude steel produced. The EAF steelmaking process involves dynamic complex multi-physics, in which electric arc plasma and coherent jets coexist resulting in an environment with local high temperature and velocity. Different heat transfer mechanisms are closely coupled and the phase change caused by melting and re-solidification is accompanied by in-bath chemical reactions and freeboard post-combustion, which further creates a complicated gas-liquid-solid three-phase system in the furnace. Therefore, not all conditions and phenomena within the EAF are well-understood. The traditional experimental approach to study the EAF is expensive, dangerous, and labor-intense. Most of the time, direct measurements and observations are impossible due to the high temperature within the furnace. To this fact, the numerical model has aroused great interest worldwide, which can help to gain fundamental insights and improve product quality and production efficiency, greatly benefiting the steel industry. However, due to the complexity of the entire EAF steelmaking process, the relevant computational fluid dynamics (CFD) modeling and investigations of the whole process have not been reported so far. </p> <p><br></p> <p>The present study was undertaken with the aim of developing the modeling methodologies and the corresponding comprehensive EAF CFD models to simulate the entire EAF steelmaking process. Two state-of-the-art comprehensive EAF CFD models have been established and validated for both the lab-scale direct current (DC) EAF and the industry-scale alternating current (AC) EAF, which were utilized to understand the physical principles, improve the furnace design, optimize the process, and perform the trouble-shootings.</p> <p><br></p> <p>For the lab-scale DC EAF, a direct-coupling methodology was developed for its comprehensive EAF CFD model which includes the solid steel melting model based on the enthalpy-porosity method and the electric arc model (for lab-scale DC arc) based on the Magneto Hydrodynamics (MHD) theory, so that the dynamic simulation of the steel ingot melting by DC arc in the lab-scale furnace can be achieved, which considered the continuous phase changing of solid steel, the ingot surface deformation, and the phase-to-phase interaction. Both stationary DC arc and the arc-solid steel interface heat transfer and force interaction were validated respectively against the experimental data in published literature. For the given lab-scale furnace, the DC arc behavioral characteristics with varying arc lengths generated by the moving electrode were analyzed, and the effects of both the initial arc length and the dynamic electrode movement on the steel ingot melting efficiency were revealed.</p> <p><br></p> <p>For the industry-scale AC EAF, an innovative integration methodology was proposed for its comprehensive EAF CFD model, which relies on the stage-by-stage approach to simulate the entire steelmaking process. Six simulators were developed for simulating sub-processes in the industry-scale AC EAF, and five models were developed for the above four simulators, including the scrap melting model, the electric arc model (for industry-scale AC arc), the coherent jet model, the oxidation model, and the slag foaming model, which can be partially integrated according to the mass, energy, and momentum balance. Specifically, the dual-cell approach and the stack approach were proposed for the scrap melting model to treat the scrap pile as the porous medium and simulate the scrap melting together with its dynamic collapse process. The statistical sampling method, the CFD-compatible Monte Carlo method, and the electrode regulation algorithm were proposed for the electric arc model to estimate the total AC arc power delivery, the arc radiative heat dissipation, and the instantaneous electrode movement. The energetic approach was proposed to determine the penetration of the top-blown jet in the molten bath based on the results from the coherent jet model. The source term approach was proposed in the oxidation model to simulate the in-bath decarburization process, where the oxidation of carbon, iron, and manganese as well as the effect of those exothermic reactions on bath temperature rising was considered. Moreover, corresponding experiments were performed in the industry-scale EAF to validate the proposed simulators. The quantitative investigations and analyses were conducted afterward to explore and understand the coherent jet performance, the AC arc heat dissipation, the burner preheating characteristics, the scrap melting behavior, the in-bath decarburization efficiency, and the freeboard post-combustion status.</p> <p><br></p>