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By Bruno Deves Flores, Guilherme Liziero Ruggio da Silva, Eduardo Osório, Anderson Azevedo Agra, Jamile Guarda, Antônio Cezar Faria Vilela, Anderson Nicolodi

Na literatura são descritos basicamente dois modelos de relações entre resistência mecânica e parâmetros microestruturais: (1) relações entre parâmetros microestruturais médios do coque e índices de ensaios mecânicos e (2) quantificação dos poros mais críticos a resistência mecânica, a partir de determinados critérios que levam em conta o tamanho e a forma dos poros. Nesse trabalho coques laboratoriais produzidos a partir de carvões com propriedades distintas foram caracterizados pela associação das técnicas de microscopia ótica e análise de imagens. Os principais modelos da literatura de relação entre resistência mecânica e parâmetros microestruturais foram avaliados. Foi demonstrado que nenhuma das relações estudadas conseguem descrever o comportamento mecânico de coques produzidos a partir de carvões de alto teor de componentes inertes (>40%). A partir desses resultados duas novas abordagens foram realizadas a fim de obter modelos que contemplem tais coques: (1) introdução de uma nova relação entre resistência mecânica e os parâmetros microestruturais e (2) um novo critério de classificação das regiões derivadas de componentes inertes como críticas a resistência mecânica.

Oct 1, 2019

By Pedro Cunha Alves, Wagner Viana Bielefeldt, Vinicius Cardoso da Rocha, Julio Aníbal Morales Pereira, Antônio Cezar Faria Vilela

A limpeza e a reoxidação de um aço SAE 1055 modificado foram avaliadas durante a sua produção em uma aciaria elétrica. Escória A no sistema óxido CaO-SiO2-MgO-Al2O3-CaF2 (CSMA-F) e escórias B e C no sistema óxido CaO-SiO2-MgO-Al2O3 (CSMA) foram analisadas. Duas amostras de aço foram coletadas em ambiente industrial: forno panela e barra laminada. ASPEX Explorer foi utilizado para obter informações sobre as inclusões, organizando-as por composição química, tamanho, densidade e tipo. FactSage v7.2 calculou as inclusões formadas durante a solidificação do aço, fração líquida e sólida das escórias e viscosidade da fração líquida. Após o refino secundário, o tipo mais comum de inclusão encontrada foram os aluminatos de cálcio. Na barra laminada, o espinélio foi o tipo de inclusão mais frequente, indicando um possível produto de reoxidação. Sua formação pode ser causada devido a interação com os materiais utilizados no distribuidor e molde. A redução da temperatura também favorece a formação de espinélios, como demonstrado pelo FactSage. As inclusões de espinélio foram analisadas pelo método Função de Densidade Populacional (PDF), que identificou que as corridas A1, A2, C1 e C2 apresentavam inclusões de espinélio formadas por reoxidação. Uso de escória no sistema CSMA é indicado já que eventos de reoxidação foram diminuídos nas corridas B1 e B2. No entanto, é necessária uma análise mais profunda dos materiais utilizados no distribuidor e molde para melhorar a limpeza do aço SAE 1055.

Oct 1, 2019

By Fábio Dian Murari, Antônio Adel dos Santos

The effect of reheating temperature of slabs on the precipitates dissolution and mechanical properties of Ti-Nb microalloyed steel was investigated in pilot scale. It was verified, by means of transmission electron microscopy, a significant decrease in precipitates formed during the solidification of the steel as the reheating temperature increased from 1100°C to 1200°C. No significant changes in size and shape of the precipitates were observed with further temperature increase up to 1280°C. In line with the precipitates dissolution behavior, an increase in strength was observed with the elevation of the reheating temperature up to 1200°C, due in part to the reprecipitation of fine Nb-rich precipitates during the hot rolling. At 1200°C the presence of deformed ferrite on the microstructure contributed to the additional increase in strength. After reheating above 1200°C up to 1280°C, a decrease in strength of the rolled plates was noticed. This effect has been credited to the absence of deformed ferrite grains and also to a small increase in the low angle grain boundaries size. The results were in agreement with Thermo-Calc and Dictra simulations.

Oct 1, 2019

By Zhisong Chai, Wei Xu

Q&P steels undergo continuous multiple processes, including hot rolling, intermediate heat treatment, cold rolling and continuous annealing etc. The inheritant effect of initial microstructure could affect the final microstructure and mechanical properties of Q&P steels. In this work, effects of different hot rolled microstructure/texture on the final microstructure and properties subjected to Q&P process were investigated in Fe-0.38C-1.58Mn-1.6Si system. Different initial microstructures were generated combing different TMCP and cooling strategies. The microstructure and texture of hot rolled materials were characterized in detail. The hot rolled material was subsequently processed by intermediate annealing, cold rolling and continuous annealing. The comparison reveals great effects of the initial hot rolled microstructures, i.e. inheritance effect. The faster reverse transformation would lead to more sufficient austenitization and it would greatly weaken the inheritant effect of the initial microstructure. Although the difference of final phase fraction for different initial microstructures was not significant, the inheritance effect was mainly reflected in the effect on austenite morphology. For the mechanical properties, no obvious difference in strength was shown for the samples with different initial microstructures after Q&P heat treatment, but there was fluctuation in elongation.

Oct 1, 2019

By Andrew Slifka, Pello Uranga, Douglas Glenn Stalheim

Structural steel final mechanical properties of strength and ductility are predominately generated by the final ferrite grain size/packet size and homogeneity of that ferrite grain size/packet size through the cross-sectional area. Forty to seventy percent of the strength components come from how fine the final cross-sectional ferrite grain size/packet size that can be produced.[1] All the ductility properties of structural steels for a given microstructure are predominately driven by how fine AND homogenous the final cross-sectional ferrite grain size/packet size can be refined.[2,3,4] One key ductility property of structural steels used in construction and energy transmission applications is fatigue. Both low and high cycle fatigue can be realized in these end applications, however, low cycle fatigue is typically the predominate mechanism. In construction applications the environment for fatigue is typically air, such as in wind towers or high-rise building construction. In energy applications, there is an interest in high pressure (5.5 – 21 MPa, 800-3000 psi) gaseous hydrogen as an alternative fuel source to fossil fuels. A project to study the effect of the cross-sectional grain size/homogeneity of a relatively pure polygonal ferrite microstructure on the fatigue performance in air and high-pressure gaseous hydrogen has been developed. This paper will discuss the project strategy, microstructure developed for the project and initial test results.

Oct 1, 2019

By João Domingos Guimarães de Athayde Junior, Luiz Fernando Andrade de Castro, Willian Facundes, Marlon José dos Anjos Silva

O aumento da demanda por aços com baixos teores de enxofre tem levado algumas indústrias siderúrgicas a estudar formas de otimizar o tratamento de dessulfuração no aço, visando reduzir o consumo de agentes dessulfurantes, o teor de enxofre e o tempo de tratamento no refino secundário. Neste trabalho, foi analisada a evolução do enxofre durante o tratamento de dessulfuração de duas classes de aço no forno panela, nas 30 corridas experimentais utilizou-se uma mistura micropulverizada contendo cal e fluorita. Após avaliação dos resultados e das condições termodinâmicas e cinéticas, foram desenvolvidas equações para cálculo da mistura a ser injetada em função do teor de enxofre inicial e objetivado. O uso da mistura proposta no processo resultou na redução de 1,1 kg/t de mistura micropulverizada, 0,22 kg/t de alumínio, 3,3 kWh/t de energia, 0,034 kg/t de eletrodo e 2 minutos de tratamento.

Oct 1, 2019

By F. D. Rodriguez, J. Ramirez Cuellar, J. Salinas Reyes, C. Gómez-de-la Garza

The Pickling Line and Tandem Continuous Mill (PLTCM) at Ternium Pesquería Facility with a Five Stands, Six High configuration started in 2013. Manufactured by PRIMETALS, to produce steel to exposed automotive market, Turnkey project, with supervision of best practices from Nippon Steel. The main equipment that the process has are; Laser welding machine, 3 loopers, Scale Breaker, jet Pickling tanks, Inspection Station and COGNEX System Side Trimmer (flying width change), Type of Mill: UCMW(S) Carrousel, 2 Tension Reels. The principals goals are, Simulate production programs, validate materials for thin thicknesses before processing, low Re-welds, optimization use Cognex, good performance in Thickness, flatness and productivity.

Oct 1, 2019

By Wenting Zhu, Liqing Chen, Junjun Cui, Zhenye Chen

In this presentation, a low carbon high strength steel microalloyed with Nb and Ti was processed by thermo-mechanical controlled process (TMCP) containing two stages of controlled rolling. The austenite with various grain sizes was obtained by austenitizing this hot-rolled steel at different temperatures. And the effect of austenite grain size on bainitic transformation was investigated in a dilatometer to reveal microstructural change. The results showed that the microstructure of the hot-rolled steel was mainly composed of granular bainite, lath-like bainite, and martenite/austenite constituents (M-A constituents). With increasing the austenitizing temperature, or increasing the austenite grain size, the microstructure was changed from granular bainite to lath bainite. When the steel was reheated to a lower temperature of 860 ºC, a relatively higher start temperature (Bs) was measured for bainitic transformation. This was mainly caused by the formation of solute-depleted region in the austenite and the promotion of the granular bainitic nucleation. The highest reaction rate occurred at austenitizing temperature of 1000 ºC with fine grain size, while the coarse austenite grain can lead to a sharp increase in the amount of bainite. An analysis was made on the kinetics of bainite transformation which was controlled by the volume diffusion of C atom.

Oct 1, 2019

By Deusdedit Motta, Marcos de Oliveira Fonseca, Marlon Rosa de Gouvea

A Transformação Digital é a palavra de ordem em todo o mercado mundial e na indústria não é diferente, principalmente no que se refere à Gestão de Ativos de produção. Dentre as diversas técnicas de Analítica Preditiva disponíveis, algumas se destacam pela sua capacidade de facilmente aprenderem o comportamento dos ativos a partir dos dados históricos, assim como monitorarem pequenos desvios que estejam relacionados aos mecanismos de falhas de interesse. O presente trabalho apresenta como estender uma das técnicas de Inteligência Artificial para Modelamento Baseado em Similaridade para aplicação em ativos que possuem uma dinâmica rápida de funcionamento ou de operação para seus estados estacionários. São demonstrados os resultados dessa abordagem em aplicações práticas que exemplificam como aumentar o resultado proporcionado por essa técnica na obtenção de ganhos para o desempenho dos ativos e resultados do negócio.

Oct 1, 2019

By Eduardo Gimenes Jabes, Thiago Pires Nagasima, João Ricardo Filipini da Silveira, João Batista Ferreira Neto, Marcelo de Aquino Martorano

Foi implementado um modelo matemático para simular a solidificação de ligas do sistema Nd-Fe-B no processo de lingotamento de tiras. O modelo foi baseado na aplicação da equação de condução de calor unidimensional através da espessura da tira e da parede do rolo refrigerado da máquina de lingotamento. A resolução numérica dessas equações permitiu o cálculo do perfil de fração de sólido através da espessura da tira e dos perfis de temperatura através da tira e da parede do rolo. A temperatura de um ponto da superfície do rolo oscila em ciclos formados pelo contato com o metal líquido (vazamento) e pelo destacamento de um pedaço da tira. A temperatura média do rolo aumenta continuamente, diminuindo a taxa de resfriamento nas tiras. Mesmo no início do processo, os pedaços de tiras que se destacam ainda não estão completamente sólidos.

Oct 1, 2019

By Breno T. Maia, Débora C. O. Silveira, Mariana A. Ribeiro, Daniel A. G. de Carvalho, Roberto P. Tavares, Raissa S. Salgado

Mixing time is an important parameter when considering chemical and thermal homogenization in steelmaking reactors. It can also be relevant in the kinetics of chemical reactions. Different methods have been used to estimate mixing times in physical models of steelmaking reactors. In the present work a new method to estimate mixing times in physical models has been proposed. This method can be used when transparent fluids are used to simulate the liquid steel and the slag. Results of mixing times in a physical model of a BOF obtained with different techniques were compared. It was shown that the new method is more reliable and consistent than the common methods based on electrical conductivity measurements and colorimetric analysis.

Oct 1, 2019

By Michael Breuer, Christian Mengel, Luis Acainas Caballero, Olaf Jepsen

Stability of the hot strip mill rolling process remains a main topic when it comes to processing thin and hard materials. Strip steering especially at the end of rolling and tail out rips are a main source of unscheduled down times in a hot strip mill. Main focus of this paper is the new X-Roll® Guide system to improve mill stability and quality. An overview of SMS group developments in the recent years regarding equipment and control strategies is given. The new side guiding system in the entry area of the finishing mill is introduced and explained with operational examples. The system provides reproducible conditions for the threading process and during rolling. Steering control has a direct benefit on the availability of the mill. New developments of the roll alignment control strategies based on roll force and mill stand entry guide force measurement will be presented. Additionally a camera based measuring system is introduced that generates a direct process feedback of the strip position. It provides together with the roll alignment control the necessary control parameters for adjusting the roll gap and guiding the strip correct centered through the mill. As a summary the SMS group system is explained combining all features.

Oct 1, 2019

By Glaucon Medeiros Silva

Este trabalho técnico tem por finalidade apresentar a evolução dos ensaios de porosidade em pelotas de minério de ferro. Apresentando as diversas formas de realização deste tipo de ensaio a não correlação entre eles, pois cada método possui uma finalidade distinta e como se ocorreu a evolução do método volumétrico (ótico) desde sua realização manual, na década de 1980, início de medições automatizadas na década de noventa e sua total automatização a partir da década de 2010 até o ano de 2019.

Oct 1, 2019

By Alexandre José Ramos Valentim, Valéria da Silva Guandelini, Fausto Kunioshi

Em um mercado cada vez mais competitivo, garantir serviços com qualidade em ambientes mais produtivos e de custos reduzidos são valores fundamentais para aumentar a eficiência das organizações. Baseada no modelo de gestão de centro de serviços compartilhados, a Diretoria de Suprimentos da Companhia Siderúrgica Nacional criou o BackOffice como uma das formas de dar foco ao core business e tornar estes valores sustentáveis. Este artigo tem como objetivo apresentar a metodologia utilizada para o planejamento, implementação e aprimoramento da área e compartilhar os ganhos de qualidade, performance e custos com a reorganização e padronização de processos que estavam fragmentados e sendo executados em diferentes departamentos.

Oct 1, 2019

By Mingyu Ma, Lingling Liu, Liqing Chen, Houlong Liu

In this article, a 444-type heat-resistant ferritic stainless steel containing 0.05wt% Ce and 2wt% (Mo+W) was used as an experimental material and a study was carried out on the effect of rolling processes on the microstructures and texture evolution as well as on the mechanical properties and formability. The rolling processes contain hot rolling at different hot rolling finish temperatures, annealing after hot rolling, cold rolling and subsequent annealing. As for the hot rolling process, two hot rolling finish temperatures, 860 C and 770 C, were adopted, and their influence on the microstructures and mechanical properties was comparatively studied. The results showed that the microstructures after hot rolling and subsequent annealing could be refined by lowering the hot rolling finish temperature. The resultant microstructures after cold rolling and annealing were hereditarily refined. Lowering the hot rolling finish temperature can weaken the -fiber texture in hot rolled or cold rolled ferritic stainless steel strip. However, the -fiber texture was homogeneously strengthened by annealing the cold rolled ferritic stainless steel strip. Enhanced mechanical property and formability in terms of strength and average plastic strain ratio could be obtained by lowering the hot rolling finish temperature of ferritic stainless steel.

Oct 1, 2019

By Alexandre Gonçalves Andrade, Crisley Dellaqua Pacheco, Gabriel Miranda Teixeira, Aline Maria Santoro Nasaré, Tatiane Ferreira Alvarenga

Diffuse emissions are that directly related to particulate matter suspended from civil structures, materials disposed in conveyor belts carried out by wind, stack e reclaimers operations and that one where dust collectors are not able to act correctly. Vale implemented in the last years a unique system capable to measure this kind of dust, called RAMPs (Dust Monitoring Automatic Network), which creates an analytical net in Tubarao industrial site, located in Vitória, ES. In order to prevent diffuse emissions in Tubarao’s pellets stockyard, it was proposed and developed a predictive model based on operational and climate variables available on the site, using big data and advanced analytics tools. The models developed shows to be adherent to the real emissions rates measured by the RAMPs and proved to be an efficient tool to predict emissions over the internal target with 4 hours of precedence.

Oct 1, 2019

By Priscilla Messias Pereira, Wellington Bonelar dos Santos, Alex Dalapicola Veronez, Maurício do Santos Rocha Junior, Leandro Resinentti Zanon

The pelletizing process allows inputs to be added to the mixture resulting in better control of the physical, chemical and metallurgical characteristics desired by the pellet. Anthracite is incorporated as input of the pellets as an alternative form of fuel, making the burning more homogeneous, "from the inside out", benefiting the physical resistance of the burned pellets and aiming to reduce the cost of natural gas during the stage of hardening. However, the amount of anthracite should not exceed an optimum value, which may cause an adverse effect on the physical quality of the pellets. Hence, it is very important an accurate control of the coal dosage. Based on that, the present study presents the implementation of a control using advanced control system that applies, using linear regression of historical data, the optimum relationship between anthracite and ore (respecting the physical quality of the pellets during processing in pelletizing furnaces). After the implementation of this control, it was possible to adjust the anthracite dosage automatically, measured in percentage of fixed carbon in the mixture, when the process is able, thus reducing the specific consumption of natural gas.

Oct 1, 2019

By Miguel Araújo Vasconcelos Filho, Ulisses Tetti

In order to determine the influence of the number of increments of the sinter sample on the variability of the chemical composition obtained in Sinter Plant production, a variographic study was carried out. It was performed with two series of samples. The first series was composed of 40 samples with a 6-second interval, with the objective of obtaining the so-called minimum practical error, resulting from the extraction processes of the sample of the conveyor belt and preparation and analysis in the laboratory and the second series composed of 60 samples with a range of 4 minutes, which points to the sample selection error. The results obtained showed that the minimization of the sample selection error occurs for increments spaced in 15 minutes, being in agreement with ISO 3082, but with significantly better results than those currently practiced for intervals between 1hour increments. It was then decided on the suitability of the sampler to allow hourly increments to be collected and on a second opportunity to install a sampling tower with primary and secondary samplers to collect increments every 15 minutes including sample size reduction.

Oct 1, 2019

By Olivier Lacroix, Dubé Mathieu, Guylaine Laforest

The reduction behavior of iron ore pellets in gas-based DR shaft processes has been studied at COREM since the late 80s. At that time, a new DR characterization test called COREM R180 was developped in collaboration with ArcelorMittal Mines Canada (former Quebec Cartier Mining) and ArcelorMittal Long Products Canada (former ISPAT Sidbec Inc.). This paper describes COREM’s approach to improve its understanding of the relations between iron ore pellet microstructure and pellet quality. The differences between the DR90 and the R180 tests are discussed. The evolution of the microstructure during reduction of both tests is also described. The reduction steps during the two tests are put forward as an important factor impacting the microstructural changes as well as the test results.

Oct 1, 2019

By Luiz Afonso Andrade, Pablo Amâncio de Freitas, Ana Patrícia Andrade Jaccard, Eduardo Cezar Ribeiro, Ana Christina Pitard Lima, Rodrigo Ribeiro de Souza

A análise dos carvões em mistura é de suma importância para redução dos custos e controle de qualidade de uma coqueria, esse trabalho trata da influência da cominuição comum de carvões de diferentes ranks, assim como suas implicações no processo de amostragem e consequentes desvios nas análises. O processo de produção da mistura de carvões na Ternium Brasil possuía um desvio não rastreado entre matéria volátil resultante da amostragem automática da mistura de carvões e a matéria volátil esperada pelo resultado da média ponderada dos carvões individuais no recebimento, para tal foram estudadas todas as etapas do processo de produção da mistura de carvões desde a variação dos carvões em pilha, escoamento em silos e na etapa anterior e posterior a britagem. Os dados foram comparados e foi feito um plano de ação para redução do desvio.

Oct 1, 2019