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By Dagoberto Brandão Santos, Kairo de Barros Guimarães, Túlio Magno Füzessy de Melo

The effect of the cooling conditions on the microstructure and hardness of a Dual Phase hot-rolled steel 800 MPa strength was investigated. Simulations of the cooling conditions using a dilatometer were carried out from samples of a hot rolled coil with variations of the intermediary temperature from 620 to 740°C, isothermal holding time between 1 and 10 s and coiling temperature between 50 and 400°C. In addition, two CCT (Continuous Cooling Transformation) diagrams were developed to evaluate the effect of the isothermal holding time on the phase transformations of the remaining austenite. It was observed that the intermediary temperature has a strong influence on the kinetics of the phase transformation, as well as the isothermal holding time influences the amount of ferrite formed and, consequently, the final microstructure and hardness of the material. The coiling temperature did not cause significant changes in the amount and morphology of the ferrite, but a gradual replacement of martensite with bainite was observed, which, in addition to the self-tempering effect, contributed to the hardness reduction.

Oct 1, 2019

By Joachiim Lehner

The application of post-combustion (secondary oxygen) to avoid skull formation on BOF lances was tested in industrial trials. The main findings are that no negative impact on the metallurgical targets (i.e. carbon, temperature and phosphorus at end of blow as well as iron–oxide in the slag) could be observed. The technology is capable of avoiding the buildup of lance skull and consequently increasing the average life of lance tips. The application of post-combustion not only affects the skull formation, there are also interactions with the refractory lining, especially thermal wear, and the utilization of the process gases (CO Recovery) that have to be considered. Special attention has to be paid to the parameters determining the use of secondary oxygen because rather small changes can strongly affect the points mentioned above. Since August 2016, the PCD (Post-CombustionDistributor) lances are used on a daily basis in the steelplant LD3 in Linz.

Oct 30, 2017

By J. Bas A. F. Smeulders

Traditional laboratory lubrication tests, including those for cold rolling lubricants often involve measurement of neat oils. To achieve increased levels of test severity, such tests are often carried out at high temperatures and prolonged durations. However, we found that the levels of lubricant degradation and wear in these tests can be much higher than in the field. Moreover, steel rolling is not done with neat oils, but with emulsions, where the presence of water influences film formation, surface chemistry and oil composition in the roll bite. To better approach the situation in the field, and thus to be able to develop rolling oils with improved lubrication performance, several lubrication tests were developed for emulsions: direct measurement of film formation and measurement of Stribeck curves, in which the emulsions can be assessed in terms of their boundary lubrication and elastohydrodynamic behaviour. The key innovation is that also another test method was developed, which focuses on boundary lubrication and wear, and the role of extreme pressure and anti-wear additives. Realistic levels of test severity are achieved in the tribometer by mimicking frictional power intensities and flash temperatures for typical cold rolling or tinplate mills. Test conditions can be adapted according to the mill stand or pass number and other cold rolling process parameters. The emulsions are kept at normal operational temperature. Clear differences could be observed between emulsions of various concentration and composition. The viability of the method is illustrated by a number of field cases, in which a good correlation is demonstrated between the laboratory tests and the performance in a pilot or production mill.

Jul 30, 2018

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 Daniel Wild, Tobias Scheffer, Marvin Laugwitz, Martin Jochum

Leveling is a standard process in the rolling mill to eliminate flatness deviations. The process layout is based on models and the leveling result depends on the accuracy of the material parameters in these models. Even small deviations from the correct assumptions can have a major effect on the final flatness. Thus, after leveling the products may look optically flat, but subsequent to a final cutting process springback occurs due to residual stresses. The objective of this work is to analyze the influence of material parameters and gravity on the flatness after leveling. To evaluate the sensitivity of the process, an FE parameter study is exerted that reveals the influence of fluctuations in material properties in the case that the leveling setup is fixed. Gravity is neglected to not conceal flatness deviations. Examples of this study are rerun in a further step under consideration of gravity to also analyze its influence on the resulting flatness and residual stresses. Finally, to analyze the consequence of the residual stresses, all information of the plate from the previous step are transferred while gravity is suppressed to prompt springback. This study revealed that slight deviations of the material properties can lead to uneven plates in simulations where gravity is not considered. If gravity is taken into account, the unevenness is concealed and the plate seems flat. A springback simulation of the same plate shows that strong residual stresses are still present and would lead to unevenness if e.g. the plate were cut.

Oct 1, 2019

By Hormando Leocadio, CWM van der Geld, Julio Cesar Passos

Impinging water jets promote high heat flux extraction rate. Steel industry widely employs the process for accurate temperature control to improve the microstructure and to ensure adequate mechanical properties. The range of surface temperatures, heat fluxes and cooling rates are very large, which makes it important to obtain an accurate value of the heat transfer coefficient. This paper presents an experimental and numerical study of the heat transfer behavior of a high temperature (450°C - 900°C) steel plate cooled by a water jet at 20°C to 70°C. High-speed imaging (up to 20,000 fps) within water jet impingement zone allowed the characterization of the boiling regimes in the early stages of cooling. The effects of initial temperature, water jet temperature and velocity on the heat transfer coefficient were analyzed by inverse heat conduction method that predicts the heat flux and temperature on the top surface from temperatures measured with thermocouples inserted in test plate. Heat transfer is strongly affected by the initial temperature of the hot steel, water jet temperature and, less intensely, by jet velocity. High cooling rates start when liquid water is in direct contact with surface temperatures above 700°C.The results will contribute to the enhancement of the temperature cooling control on the runout table and cooling model employed at Usiminas Hot Strip Mill.

Oct 1, 2019

By Gerhard Finstermann, Ichiro Maeno, Takehiko Saito, Hironori Shimogama, Konrad Krimpelstätter

Automobile manufacturers are developing Electrified Vehicles with light steel body structure designs that reduce mass and therefore greenhouse gas emissions over the vehicle’s entire life cycle. This raises the demand for the production and development of Advanced and Ultra High-Strength Steels (AHSS / UHSS) and Electrical Steels with increased permeability and reduced core loss to improve energy conversion efficiency. To meet this requirements the steel market is tending towards new generations of AHSS with improved formability (3rd generation AHSS) and high-silicon steels with higher strength and thinner products. With this growing demand for advanced high-strength steels and electrical steels, producers are faced with a unique and interesting challenge in producing materials that strain or exceed the capabilities of existing mill equipment and automation designed to produce low- to medium-carbon sheet. While specialty steel producers have known for decades how to process special high-strength steels and thinner gauges, this equipment typically does not offer the yield and productivity desired by the market, necessitating innovation in re-engineering existing equipment to meet the market demands more economically than new construction. In the case of cold rolling, this can be supported through variable roll geometries, more effective roll-gap lubrication technologies, application of strip heaters (Warm Rolling) to reduce risk for edge crack propagation and strip breaks as well as continuous rolling managed by state-of-the-art automation technologies.

Oct 1, 2019

By Paolo Demetlika

In this paper it is shown how the “Zero Operator” concept on the casting floor has been reached by adoption of a standard 6 axis industrial anthropomorphic robot coupled with the most innovative machine vision technology. This has been achieved by automating all the operations related to the ladle and tundish activities, including shroud manipulation, powder addition, ladle nozzle identification, nozzle opening by lancing, temperature measurement and chemical sampling. Q–Robot CAST family products are the result of the successful alliance between industrial robotics and the most advanced technology in process automation. This led, for each production area, to the introduction of flexible automation in dangerous places, even where some degree of human intervention is still necessary. By using anthropomorphic robots, human operators can be reassigned to safer environments. Furthermore, robots are suited to deal with repetitive and labor intensive tasks thus guaranteeing a high process quality.

Oct 30, 2017

By Karl Berger

The paper gives a comprehensive overview of the historical development of various metal rolling technologies and also describes the influence to industrial and socio-economic developments. The rolling of steel, in particular of rails, beams, rebar, strip and plate has enabled the large scale transport and travel, the building of bridges and buildings, the manufacturing of ships and cars. All this has changed the face of the world significantly. Further the paper approaches technological highlights in the design, manufacturing, drive and control of modern mills and the various types developed to create industrial economic units for the different markets and customers’ requirements. An outlook of future challenges is as well discussed in the paper. Various solution approaches for the rolling technologies, from continuous improvement of existing plants to more radical new concepts like endless rolling, near net-shape casting and rolling are approached. A positive conclusion is drawn that rolling technologies will remain a valuable area for engineers with scientific and economic challenges, but also a clear vision for positive contribution to further industrial and social development.

Jul 30, 2018

By Wolfgang Oberaigner

Primetals Technologies has always been a driver of innovation in steelmaking, especially by providing sophisticated process expert models for continuous casting machines. This capability is demonstrated by recent advancements in automation solutions that include: DynaPhase, Dynacs 3D, and DynaGap. This state-of-the-art suite of dynamic secondary cooling and soft-reduction packages take into account thermodynamic effects such as shrinkage and phase transitions, and thereby significantly contribute to direct quality improvements during the solidification phase in the continuous casting process. Speed Expert calculates an optimum casting speed for every casting situation, and additionally recommends a strand speed so that the point of final solidification is positioned at the end of a segment for optimum soft reduction. In the case of steel grade changes, the Intermix Expert precisely calculates the chemical properties of the mixed steel, thereby minimizing losses due to deviations from required specifications. The Nozzle Expert is a new model that detects clogged nozzles and broken hoses in secondary cooling systems. The first installations were highly successful and customers are pleased with impressive reductions in maintenance costs and improved steel quality. This paper describes these innovative process automation solutions and gives an overview about the successful results achieved within the first installations.

Aug 16, 2017

By Kazuya Nakabo

In this article, influences of restraint and MgO content on densification of alumina-magnesia castable during heating were experimentally studied. High thermal expansion-alumina-magnesia castable specimens were surrounded by low thermal expansion-alumina-silica castables, and heated in an electric furnace. Doing so allows restrained heating of alumina-magnesia castable. According to the results of simple calculations, the restraint stresses were estimated to be between 2 to 20 MPa, so the experimental conditions were considered reasonable. As a result of the experiments, it was verified that restraint densifies alumina-magnesia castable, resulting in an increase in modulus of rupture and modulus of elasticity. The densification effect of restraint became larger as the MgO content increased. The effects are attributable to an in-situ spinel forming reaction, which improves corrosion resistance.Taking the temperature distribution in the castable lining into account, large restraint stress is expected for the hot face while only a little effect is expected for back end. Thus, excessive difference in material property in the thickness direction, which is undesirable in terms of structural spalling, is a concern.Hence, the MgO content of alumina-magnesia castable should be determined carefully, taking not only corrosion resistance but also spalling resistance into consideration.

Oct 30, 2017

By Dr. Steven G. Jansto

The market demand for reduced fuel consumption and CO2 emissions in the automotive, energy and construction sectors have further increased the demand for new and advanced higher quality microalloyed grades produced via TMCP. The technological integration of the process and physical metallurgical advancements of value-added niobium (Nb) microalloyed thermo-mechanical controlled process (TMCP) steels continue to be developed and is an important element for these more demanding end user requirements and cost-effective steel production. The reheat furnace process step has a profound effect on the TMCP performance, final hot rolled steel quality and mechanical property consistency during the production of hot rolled steels. The uniformity of heating applied across the entire width, thickness and length of the slab or billet is essential in the successful achievement of consistent customer properties regardless of the chemistry. The resultant ferrite grain size in the final hot rolled product is significantly governed by the initial prior austenite grain size. However, the transition from laboratory melted and TMCP hot rolled heats to the production scale is often quite challenging. Aberrations in the reheating process step at the industrial furnace are often the root cause of mechanical property quality issues. These combustion process metallurgy parameters connect directly to the resultant TMCP product quality and is defined as Combustion Metallurgy

Oct 1, 2019

By Massimilinao Svetina

In 2010 Danieli & C. S.p.A. put into operation a new Pickling Tandem Mill in Cremona (Italy) at Acciaieria Arvedi, the last Pickling line coupled Tandem Cold Mill (PLTCM) in Europe. The plant was tailor-made to suit the specific requirements of this customer; a very broad range of sizes and grades (IF to AHSS as well as DP and TRIP1000) including ultra-thin hot band can be processed, achieving a total capacity of 1.6 Mt/y. The Danieli & C. S.p.A. Turboflo® process was selected because of its proven efficiency and ability to handle ultra-thin gauges at speeds exceeding 400 mpm in the pickling tanks. All the equipment, i.e. pickling section and rolling mills was provided with the last generation of Danieli market-oriented technologies. Danieli & C. S.p.A. - with the support of Arvedi and feedback from the field - is continuously improving its technical design solutions and optimizing plant operations.

Aug 16, 2017

By Alberto Nei Carvalho Costa

Devido às novas tendências de design de carrocerias de automóveis, as peças pertencentes a estas carrocerias apresentam características de fabricações cada vez mais críticas, principalmente relacionadas ao processo de estampagem. Uma forma de atuar neste processo para evitar perdas de produtividade, principalmente com o rompimento do material, é atuar na lubricidade entre o material e o ferramental do equipamento. A aplicação do óleo lubrificante na bobina de aço é uma forma de atuar na lubricidade, mas devido à criticidade de estampagem que determinadas peças apresentam, somente o óleo lubrificante não é suficiente para este fim. Visando atender essa necessidade, a CSN e seus fornecedores desenvolveram um sistema de lubrificante para seus aços, conhecida como tecnologia de pré-fosfato. Este trabalho tem como objetivo apresentar as vantagens fornecidas pelo aço pré-fosfatizado no que se refere a estampagem crítica de peças automotivas, bem como avaliar o seu impacto no processo de pintura automotiva. Como resultado verificou-se que a camada de pré-fosfato impactou na redução do coeficiente de atrito do aço zincado de forma suficiente para confecção de peças críticas de carrocerias de automóveis. Verificou-se também que o filme de pré-fosfato é totalmente removido na etapa de desengraxe do processo pintura automotivo, não prejudicando as etapas subseqüentes do processo: fosfatização e pintura.

Jul 30, 2018

By Gilmar Zacca Batista

Este trabalho analisa a tenacidade e dureza do metal de solda e ZAC da solda circunferencial de tubos X65, X70 e X80 para serviço ácido. Os tubos de elevada resistência, fabricados para serviço ácido, apresentam grande desafio para a soldagem. Os consumíveis e processos devem ser capazes de produzir uma junta soldada de alta resistência, baixa dureza e elevada tenacidade. O objetivo deste estudo foi identificar problemas de amolecimento ou fragilização da ZAC e verificar se a elevada resistência não prejudica a tenacidade e dureza do metal de solda. A metodologia incluiu a soldagem circunferencial e ensaios de dureza e CTOD. Os resultados mostraram que o metal de solda e a ZAC do X65 e X70, são adequadas para o emprego em dutos terrestres. Observou-se um amolecimento na ZAC do X70 e X80 que, de acordo com a literatura, não é crítico para projetos baseados em tensão. Para o X80, o CTOD da ZAC ficou abaixo do valor mínimo desejado, indicando que pode ter ocorrido a formação de zonas frágeis localizadas e resultando na necessidade de estudos complementares para ajustar os parâmetros de soldagem. Os resultados deste estudo servem como base para uma futura aplicação destes materiais em campo.

Aug 16, 2017

By Alexandre de Aparecida Morais

No processo de lingotamento contínuo a secagem e o pré-aquecimento do refratário do distribuidor são de fundamental importância. Estes são realizados visando: reduzir a perda de calor do aço líquido, reduzir as bolhas nas primeiras placas, evitar respingos de aço (reações) ocasionados pela umidade e prevenir a degradação refratário por choque térmico. Para aços planos, os sistemas para promover a secagem e pré-aquecimento podem ser do tipo a "quente" (mais usual) ou a "frio". É denominado "partida a quente" quando se realiza a secagem e o pré-aquecimento; e de “partida a frio”, quando apenas a secagem é realizada. Têm-se como características distintas entre os processos: - A Quente: maior consumo de gás; forte degradação do refratário; temperatura de trabalho do distribuidor mais elevada, deteriorando as condições do ambiente; - A Frio: menor consumo de gás; redução da degradação do refratário; no entanto, exige um controle rigoroso da curva de secagem, o que implica maior investimento inicial no equipamento de secagem. Em 2002, após uma análise de viabilidades a ArcelorMittal Tubarão implementou o sistema de frio. Este artigo mostra a evolução deste sistema após a sua implementação, analisando a correlação com defeitos, a implementação de melhorias e os ganhos obtidos.

Jul 30, 2018

By Carlos Gonzalo Alvarez Rosario

O presente trabalho avaliou a capacidade de degradação bacteriana de cianeto da cepa Bacillus pumilus em efluentes contaminados. Para isso foram realizados estudos de degradação bacteriana de cianeto em frascos agitados e incubados em agitador orbital durante 120 horas. Os ensaios aconteceram em três etapas; a primeira etapa consistiu na ativação e crescimento da bactéria em meio Luria Bertani, seguida da adaptação a ambientes alcalinos e por ultimo a etapa de degradação de cianeto. A proporção de inoculo foi de 1:500. Utilizou-se tampão CAPS para manter o pH alcalino. Para avaliação da degradação de cianeto foi preparada uma solução sintética contendo 500mgL-1 de cianeto de potássio pH 10. Foi avaliada a influencia da temperatura na degradação bacteriana (27, 32 e 37oC). O controle do crescimento celular foi realizado por medidas de densidade óptica com comprimento de onda ?=600nm. A quantificação do cianeto livre foi realziada por polarografia utilizando-se o analisador voltamétrico (computrace control 797 Metrohm). Dos resultados obtidos foi possível determinar que a cepa B. pumilus obteve melhor desempenho na degradação de cianeto a temperatura de 27oC conseguindo degradar 100% do cianeto livre presente na solução. O tempo empregado para a degradação total do cianeto foi de 3 dias.

Oct 30, 2017

By Tainan Ferreira Muniz

O presente trabalho estudou a influência de alguns tratamentos térmicos sobre a microestrutura e as propriedades mecânicas de um aço microligado visando à adequação de parâmetros que o classifiquem como um ao do tipo API X65 paraaplicação na prospecção e condução de óleo e gás. Diferentes ciclos de tratamentos térmicos envolvendo normalização, têmpera e revenimento foram aplicados a amostras deste aço. Estas foram submetidas a ensaios de tração, dureza Vickers e impacto Charpy, além de terem sido microestruturalmente caracterizadas com o auxílio de microscopia ótica e eletrônica de varredura. Observou-se que as microestruturas e propriedades mecânicas foram fortemente influenciadas pelos tratamentos estudados. Entretanto, apenas a amostra temperada e revenida atendeu integralmente aosrequisitos para o grau API X65no que diz respeito às propriedades mecânicas.Estaamostratambémapresentou maior a tenacidade ao impacto, o que está associado ao alívio de tensões e à decomposição da martensitae da bainita em carbonetos de ferro e ferrita. A amostra normalizada apresentou microestrutura constituída por perlita e ferrita, possuindo assim os menores limites de resistência mecânica e a maior ductilidade. Já nas espécies normalizada-temperada, assim como na simplesmente temperada, observou-semartensita e bainitacomo principais constituintes, supondo-se a presença de uma pequena fração de constituinte MA.

Aug 16, 2017

By Robson Aguiar de Macedo

O estudo de ligas livres de Pb envolvendo o emprego de junções metálicas sob altas temperaturas tem recebido atenção especial, sendo desenvolvidas novas ligas com qualidade e desempenho adequados. Ligas Bi-Ag consistem em alternativas promissoras para a substituição das ligas de solda contendo Pb para tais aplicações, por isso devem ser melhor caracterizadas sob o aspecto de estruturas brutas de fusão. Assim, o presente trabalho objetiva investigar a liga hipoeutética Bi-1,5%Ag (%em peso) solidificada unidirecionalmente sob regime transitório de fluxo de calor. Será analisada a influência dos parâmetros térmicos de solidificação como velocidade de solidificação (VL), taxa de resfriamento (?) gradiente de temperatura (G) na microestrutura e na evolução de dureza da liga citada. Para determinação do perfil de dureza, foram realizados ensaios de dureza Vickers. Para obtenção e caracterização das microestruturas presentes no fundido Bi-1,5%Ag, fez-se o uso da microscopia ótica e da fluorescência de raios-x. Uma estrutura de dendritas facetadas de Bi circundadas pelo eutético Bi-Ag prevaleceu ao longo do lingote Bi-1,5%Ag. Verificou-se um aumento gradativo dos espaçamentos dendríticos primário (?1) e secundário (?2) à medida que a distância da base refrigerada foi aumentada. Em geral, os valores de dureza diminuíram para maiores valores de ?1 e ?2.

Aug 7, 2018

By Tatiane Suelen Santos Silveira, Dagoberto Santos Brandão, Dalila Chaves Sicupira, Graziele Gianini Braga Maria, Marcos Vinícius Fonseca Ferreira, Daniela Barçante Perasoli

O aço inoxidável duplex combina as propriedades mecânicas da ferrita e a resistência à corrosão da austenita, sendo muito utilizado em aplicações industriais que requerem um bom desempenho. Quando submetido a deformações intensas, a austenita transforma-se parcialmente em martensita, aumentando a resistência do aço. Quando o aço é recozido, essa transformação é revertida e a martensita se transforma em austenita, ocasionando um refino de grão do material. Fases secundárias formadas durante o recozimento podem prejudicar suas propriedades mecânicas e corrosivas. Nesse sentido, o objetivo desse trabalho foi avaliar o efeito da temperatura de recozimento na resistência à corrosão do aço inoxidável duplex UNS S32304 laminado a frio. O aço foi submetido à laminação a frio, com deformação de 60%, e posteriormente recozido nas temperaturas de 600°C, 700°C, 800°C e 900°C por um tempo de 0,5 h. A resistência à corrosão foi estudada através da técnica de polarização potenciodinâmica. A laminação a frio promoveu a formação de martensita induzida por deformação (SIM) e a reversão parcial começou a ser observada após recozimento a 600ºC. A ocorrência de SIM promoveu significativa diminuição do potencial de pite e o aumento da temperatura de recozimento aumentou a resistência à corrosão localizada.

Mar 1, 2019