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By Ana Paula de Andrade Manfridini

A formação de nitretos na superfície de aços Interstitial Free (IF) nitretados a plasma em função da temperatura de tratamento foi investigada. Amostras de aço IF estabilizados ao Ti, laminado a frio e com shot peening foram nitretadas a plasma nas temperaturas de 450°C, 475°C e 500°C durante 4 horas. A camada nitretada resultante foi caracterizada por microscopia eletrônica de varredura (MEV), difração de raios-X (DRX) e método Rietveld. As imagens de MEV revelaram duas principais regiões na camada nitretada formada nas três temperaturas de tratamento: uma camada de compostos constituída de ?-Fe2-3N e ?’-Fe4N e uma camada de difusão apresentando uma matriz ferrítica com finos precipitados de ?’’-Fe16N2. Através da DRX, foi observada uma variação na proporção das fases ?-Fe2-3N e ?’-Fe4N. A partir de análises Rietveld, foi sugerido que a maior temperatura de nitretação facilitou a formação de nitretos ?-Fe2-3N, uma vez que a quantidade dessa fase aumentou de 475°C para 500°C. A presença deste precipitado com maior teor de nitrogênio sugere uma possível maior aplicabilidade dos aços IF.

Aug 16, 2017

By André Carlos Silva

Dewatering stage is among the most important industrial unit operations, and is wide adopted in many different industries, due the fact that a large portion of industrial products is produced using suspensions of solids in liquids. Nowadays the mineral processing tailings disposal is a big problem due the environmental degradation produced. The phosphate rock processing in Anglo American Phosphate Brazil, situated in Catalão/Go/Brazil, generates around 180 t/h of tailings for a plant feed of 480 t/h (approximately 37,5% of the processing plant feed), with 5 to 10% of solids and approximately 14% of P2O5. Nowadays the tailings are sent direct to the tailings dam. The present work proposes the paste production using with the tailings from phosphate rock processing plant divide in two different stages. The first one composed by the free settling of the material in presence of industrial flocculants in a graduated cylinder with 2.0 L of internal volume for one hour, in the same way it must occur in conventional thickeners. After that time, the clarified liquid was drained and the remaining pulp was sent to the second stage consisting in the tailings vacuum filtration. Ten different flocculants and nine different filter media were tested. The found results were satisfactory for paste tailings production with solids percentage around 65%.

Aug 8, 2018

By Haysler Apolinário Amoroso Lima, Francisco Pereira Netto, Vladnilson Peter de Souza Ramos, Bruno Nery Stoco, Gilvan Nascimento de Souza

Em um mercado dominado por tijolos de Al2O3-MgO-C, o revestimento de trabalho de panela de aço monolítico e CarbonFree se apresenta como uma tecnologia disruptiva para um novo patamar de qualidade do aço e eficiência energética. O presente estudo relata a motivação para a implementação do primeiro fundo de panela de aço com revestimento monolítico concretado in situ no Brasil, e apresenta uma análise preliminar dos resultados e vantagens observadas. Uma panela da Ternium Brasil foi revestida com refratários de Al2O3-MgO, e colocada em operação sem nenhuma necessidade de ajuste na operação da aciaria. A partir dos dados de processo e das medições a laser, calculou-se o desgaste do revestimento, bem como verificou-se a garantia de qualidade nos aços IF (interstitial free) e a maior preservação na temperatura do aço durante o refino secundário.

Oct 1, 2019

By Esteban Ruisanchez Rodriguez

In this paper we will discuss the process of the grain size customization of the EBT filler sand in relationship to the technical characteristics of the furnace and its tap hole. By customizing the grain size distribution, the glassy area formed on the top of the tap hole varies and supports differently the metallurgical pressure of the molten steel providing increased free opening speeds. Taylor made sand improves therefore the free opening rate, reduces the tap to tap time and increases the lifespan of the tap

Aug 16, 2017

By Marcos Paulo Kohler Caldas

Após a sanção da RoHS Directive 2002/95/EC que entrou em vigor em 01/07/2006 proibindo a utilização de seis substâncias perigosas, sendo elas: chumbo, mercúrio, cádmio, cromo hexavalente, bifenilos polibromados e éteres difenil-polibromado fabricantes de equipamentos eletroeletrônicos tiveram que restringir os usos de tais substâncias. Com isto, as placas de circuito impresso dos equipamentos passaram a ser identificadas com a sigla RoHS ou outra identificação que indique o atendimento a diretiva. O presente trabalho visa analisar um lote de placas mãe de computadores obsoletos direcionados ao CEDIR-USP (Centro de Descarte e Reuso de Resíduos de Informática) no período de 01/01/2013 a 30/05/2013, identificando-as como “lead free” ou “comuns”, a fim de verificar a relação entre placas livres de substâncias perigosas e placas contendo tais substâncias. O lote possuía quantidade aproximada de 3.230 placas. Após a separação, as placas “lead free” foram classificadas por marca e nacionalidade. O resultado da pesquisa mostrou que mesmo após onze anos da edição da diretiva o percentual de placas livres de substâncias perigosas ainda é muito baixo. Cerca de 97,80% das placas de circuito impresso coletadas ainda possuem em sua composição substâncias perigosas. Verificou-se que todas as placas “lead free” encontradas são de origem chinesa e seus fabricantes são: Gigabayte, Itautec, Intel e CE. O estudo também classifica a origem dos resíduos como: industriais, da própria universidade ou residenciais.

Aug 8, 2018

By Steven George Jansto

The hot ductility behavior of different microalloyed steel chemical compositions was examined simulating the thermal and strain conditions through the straightening or unbending section of the continuous casting machine. All samples were obtained from industrial slab casters ranging from 200 to 300 mm in slab thickness from steel mills throughout the world including China, Brazil, North America and Europe. The slabs were crack-free and hot rolled into prime quality products. No laboratory heats were tested. Although these microalloyed steels exhibit inherently lower hot ductility behavior, as measured by percent reduction in area at elevated temperature, these steels still exhibit sufficient ductility to satisfactorily meet the unbending stress and strain gradients existing in the straightening section of most casters. The majority of the published hot ductility data, as measured by % reduction in area (%RA), were based on laboratory heats and hence, are inaccurate in accessing the propensity for slab cracking on an industrial caster. This situation then results in invalid conclusions for different chemistries. This research has determined the minimum required %RA for crack-free casting is significantly lower than results based upon previously published laboratory generated data. For example, the literature quotes 40% RA minimum for Nb-bearing steels when in fact as low as 10% minimum RA is more than sufficient to assure crack-free casting based upon the extensive testing and analysis performed in this study. Instead of %RA, the measurement of strain energy has been introduced to evaluate hot ductility behavior. It is concluded that strain energy is a better measure of hot ductility behaviour than %RA. There is considerable value in the evaluation of the hot stress and strain curves, process metallurgy parameters and their relationship to slab quality instead of just basing hot ductility decisions on simple %RA measurements.

Aug 16, 2017

By Jetson Lemos Ferreira

A Usiminas vem procurando fornecer aços de menor espessura ao mercado automotivo, com graus de resistência cada vez mais elevados, destacando-se os Advanced High Strength Steels (AHSS). Contudo, até então, a aplicação desses aços tem sido destinada basicamente em aplicações em peças de segurança e de reforço estrutural dos veículos. Visou-se nesse estudo avaliar, em escala laboratorial, a aplicabilidade em painel exposto de um AHSS referente ao grau DP450 em termos de conformabilidade e de desempenho, tendo como referência aços Interstitial Free (EC180) e Interstitial Free High Strength (IFHSS220). Foi verificado que o aço DP450 apresenta características mecânicas favoráveis ao processo de estampagem de componentes automotivos expostos. Para fatores que podem limitar sua utilização, tais como a flangeabilidade e o retorno elástico, foram propostas alternativas de processamento, as quais resultaram na maximização da conformabilidade do material e em melhor fixação de forma. Em termos de aplicação, verificou-se que o aço DP450 exibiu uma resistência à indentação, avaliada pela profundidade da impressão permanente, em torno de 43% e 31% superior à dos aços EC180 e IFHSS220, respectivamente.

Aug 17, 2017

By Nicolás Ariel Zabala

During the make-up and break-out of the connections, threaded joints are exposed to intense mechanical and tribological solicitations. The connection performance is influenced by its geometry, material properties, surface treatments and thread compound. The aim of this work is to evaluate and characterize the tribological behavior of different thread compounds applied on manganese phosphated carbon steel under low speed and high pressure sliding contact. Four thread compounds were evaluated: one containing lead, zinc and graphite; other lead-free, containing copper and finally, the last two lead-free and containing non-metallic solids. The tribological behavior was analyzed by a block-on-ring tribotest. During the test, load varied linearly between 250 N and 7000 N; loading and unloading lasted 14 sec and were performed in opposite directions of rotation to simulate the make-up and break-out operations. Friction force and load as a function of time were registered. Upon completion of the test, wear surfaces were analyzed by SEM, optical microscopy and energy dispersive spectroscopy. The obtained results show that the lead and zinc containing thread compound displayed the best behavior, showing a wear reduction of approximately 20%. These results are in line with previously known oilfield experience. Average COF values around 0.15 were measured and no significant differences between dopes were observed; indicating that the wear behavior was influenced by the additive package.

Jul 31, 2018

By Hui-bin Wu, Rui Yuan, Yang Gu, Peng-cheng Zhang, Zheng-zhi Zhao

The corrosion behavior of three kinds of medium-Cr rolled steel pipeline steels in carbon dioxide collecting and transporting environment at different temperatures was studied. The results shew that the 5Cr sample was most affected by temperature. When the temperature rised from 30 °C to 90 °C, the corrosion rate increased from 0.12 mm/a to 1.87 mm/a, which was increased 15.6 times. The corrosion rate of 7Cr steel at 30 °C was similar to that of 5Cr steel. However, as the temperature increased, the corrosion rate rised slowly, increasing by 2.4 times at 90 °C. The corrosion rate of 9Cr steel was not obvious with temperature, and it was always below 0.06 mm/a. The thickness of the corrosion product film of the three samples gradually increased below 70 °C, and suddenly increased above 70 °C. This was related to the negative temperature coefficient of the solubility of FeCO3, and the thickening of the product film also affected the ion exchange of the cathodic reaction. An increase in the Cr content contributed to grain refinement and increased the proportion of the small-angle grain boundaries. More fine grains mean an increase in the total length of the grain boundaries, which could provide a diffusion channel for the free Cr element; on the other hand, the low-angle grain boundary structure was more orderly, with a lower free volume and lower interface energy. Under the combined effect of both, 9Cr steel and 7Cr steel had high volta potential and better corrosion

Oct 1, 2019

By Francisco Morganti

In order to support hot rolling mill managers in improving the utilization of their plants, SMS group offers well defined Performance Modules. These are technologies, components, automation solutions or services, which can be implemented in existing plants to increase competitiveness in categories of efficiency, productivity, quality and process and product control referred to as “Industry 4.0”. Except the Performance Modules dedicated to the last category, targeting overall process controls, Performance Modules are characterized by quantifiable benefits. Performance Modules related to hot rolling mills are e.g. camber free rolling, modular laminar strip cooling system, new edge masking and intelligent components.

Oct 30, 2017

By Samuel Filgueiras Rodrigues, Clodualdo Aranas Jr., Gedeon Silva Reis, Eden Santos Silva, Fulvio Siciliano

When austenite is deformed above the Ae3 temperature, partial amount of it transforms dynamically into ferrite by a displacive mechanism. After unloading, it retransforms back into the stable austenite by a diffusional process. This influences the rolling load which decreases under isothermal condition or does not increase with decreasing temperature as rapidly as expected under cooling. Plate rolling simulations under isothermal and continuous cooling conditions were carried out on a 0.09 wt.% Nb X-70 steel. Pass strains of 0.2 were employed together with interpass times of 10 s, and 30 s for the cooling conditions and 0.3 with interval of 10 s at 900 °C for the isothermal experiments; strain rate of 1 s-1 was used during the simulations. The mean-flow-stress (MFS`s) behavior of both conditions indicates that dynamic transformation and dynamic recrystallization were taking place during straining. The critical strains for the initiation of dynamic transformation fell around 0.06 while the critical strain for DRX was 0.12. It has been shown that ferrite is formed due to the applied deformation of roughing passes and increases its volume fraction throughout the finishing rolling stage. Under cooling conditions, the ferrite formation is also favored as the temperature approaches the Ae3 line. Such ferrite forms when the driving force for dynamic transformation is higher than the total free energy barrier preventing its formation. This obstacle consists of the free energy difference between austenite and ferrite as well as the lattice dilatation work and shear accommodation work. The addition of Nb retards the retransformation of the ferrite into austenite. Moreover, holding times after rolling increases the amount of austenite available for microstructure control on subsequent stages. The dynamic transformation (DT) mechanism can be used to design improved rolling schedules

Oct 1, 2019

By Wagner Viana Bielefeldt, Felipe Buboltz Ferreira, Antônio Cezar Faria Vilela

The continuous casting machine is one of the most important steel production steps in a melt shop. The tundish, a reservoir between the steelmaking ladle and the mold, has great influence over the steel cleanliness, along with the productivity bid. It must takes into account the quality of the metal and operational safety. Several different variables are related to the tundish process, of inclusionary cleanliness. Some of them are discussed in this paper: the free opening of ladle, tundish inertization, steel temperature in the reservoir and clogging formation, besides a brief topic about castability. Therefore, a critical analysis, with a review from some papers available in literature, is proposed in this study, with its focus on tundish.

Oct 1, 2019

By Sander Mul, Michael Brandner, Armin Paar

Graphitic HSS roll grades such as ESW’s brand VANIMO can be considered as the latest developments for the last finishing stands in hot strip mills. These roll grades are developed on the basis of the alloying concept of (Carbide Enhanced) Indefinite Chill work roll materials. During the development of VANIMO, the amounts and types of carbide forming elements were increased and adjusted into the direction of cast HSS roll grades. The microstructure of graphitic HSS roll grades therefore consists of tempered martensite, cementite and several different carbide types as well as a well-defined amount of free graphite. The main purpose of graphitic HSS roll grades is to combine the high surface quality of Indefinite Chill alloys as well as the high wear resistance of HSS roll grades. Several systematic steps were taken to increase the wear performance from Carbide-Enhanced Indefinite Chill grades to the more advanced VANIC grade and further on to the highest alloyed roll grade VANIMO. In every development step, the surface quality of the roll grades was carefully monitored. The decision to invest in new testing equipment at ESW’s plant was driven by the wish to see microstructural effects of different alloys in a macroscopic dimension. Usually samples are taken from cast rolls and investigation is done in comparably small areas compared to the total surface of a roll. Rolling of strip is done with the entire barrel, so effects of alloy and microstructure can appear anywhere on the barrel surface. To ensure better understanding and deeper knowledge about influences of alloying trials we decided to install the last version of LRI (Lismar Roll Inspection). LRI includes the latest technology of Eddy Current with an enormous resolution. Depending on the formation of carbide precipitations, carbide network as well as matrix and free graphite, the EC test can detect smallest differences. The possibility to analyze the different results of EC and UT surface wave inspection will be discussed. A few examples of surface effects in the mill application will be discussed and improvement strategies explained.

Oct 1, 2019

By Jetson Lemos Ferreira

O presente estudo teve por objetivo verificar a independência tanto da Curva Limite de Tensão (CLT), quanto da Curva Limite de Deformação Plástica Efetiva (CLDPE) em relação à trajetória de deformação. Para tal, foram utilizadas Curvas Limite de Conformação (CLC) de aço livre de intersticiais (Interstitial Free - IF), determinadas, primeiramente, por meio de trajetórias lineares e, posteriormente, por trajetórias bi-lineares estabelecidas por níveis de pré-deformação nos modos de tração uniaxial e estiramento biaxial simétrico. As previsões da CLT e da CLDPE, calculadas a partir das deformações limites da CLC convencional em trajetórias lineares e bi-lineares, mostraram-se independentes em relação à trajetória de deformação. Entretanto, verificou-se que o critério de escoamento adotado tem grande influência na forma e posição destas curvas limites.

Aug 17, 2017

By Helder Keitaro Arçari Ambo

Aços IF (Interstitial Free) são materiais com grande capacidade de serem conformados a frio, normalmente na forma de chapas, utilizados na indústria automobilística na fabricação de carrocerias de automóveis e outros componentes similares. Neste artigo foi realizado ensaio isotérmico de dupla deformação com objetivo de determinar a fração de amaciamento que ocorre no intervalo entre passes e o parâmetro de amaciamento4. O método para obter estes dados foi utilizando software da Instron em conjunto a maquina de torção e o forno de indução. Os resultados obtidos foram de grande importância no estudo para avaliar o comportamento do material quanto aos fenômenos metalúrgicos e termomecânicos envolvidos, ou seja, se ocorre recuperação, recristalização dinâmica entre outros processos de restauração do material quando submetido a forças externas em elevadas temperaturas.

Oct 30, 2017

By Marcos Paulo Kohler Caldas

Após a edição da RoHS Directive 2002/95/EC, diretiva que entrou em vigor em 1º de julho 2006 proibindo a utilização de seis substâncias perigosas: chumbo, mercúrio, cádmio, cromo hexavalente, bifenilos polibromados e éteres difenil-polibromados, fabricantes de equipamentos eletroeletrônicos passaram a utilizar soldas livres de chumbo (lead free) para montagem de suas placas de circuito impresso. A SAC 305 é um tipo de solda muito utilizada pelas empresas fabricantes de placas de circuito impresso. O presente trabalho visa caracterizar este tipo de solda verificando sua composição e identificar se a mesma se encontra livre de elementos perigosos ao ambiente. Avaliou-se a extração de metais como Ag e Sn através de digestão ácida em água-régia e rota HNO3 a temperatura ambiente. A composição do licor lixiviado foi caracterizada por espectrometria de emissão óptica com acoplamento de plasma induzido (ICP-OES). Os resultados indicam que a solda SAC 305 atende a RoHS, possui 2,7% Ag, 96,4% Sn e 0,9% de outros metais e a melhor rota para extração de Ag foi a HNO3 e para Sn foi a água-régia.

Aug 7, 2018

By Alberto Lainati

The Bar Reducing and Sizing Technology has a core function in the value-chain for the production of rolled SBQ (Special Bar Quality) products. The EVO 2+4-roll is based on the compact combination of a 2-roll high-reduction module followed by a 4- roll low-reduction module for precise sizing. The EVO 2+4-roll mill, allows to gain significant technical and economical advantages in the hot- and post-rolling process routes: dimensional and surface accuracy, quick adaptability to processing variances and to small lots requirements, superior technological features of as-rolled product, competitive capex and opex. The EVO 2+4 unit has a very compact design, which makes it suitable both for new mills and upgrade applications.

Aug 17, 2017

By Marco Castenetto

Some of the most significant Danieli innovations in the field of long products are the: i) The EWR® system, through automatic continuous head-to-tail flash welding of billets at reheating furnace exit side, enables uninterrupted production of the mill for endless rolling of straight bars, wire rod and bar in coils. The process is particularly beneficial to wire rod and bar-in-coil mills as it enables production of “customized-size coils” (any coil weight according to specific Customer request) and with extra-high final coil weight, even starting from low-weight billets; ii) The Spooler process is based on twistfree winding of hot-rolled rebars into highly-compact/ultra-heavy coils featuring a unique cobble-free un-coiling capability. This enables high-speed feeding of the downstream cold-processing lines with hot-rolled spooled coils coming directly from the rolling mill without the need of any traditional off-line operation (such as de-coiling, stretching & re-winding). The system results highly beneficial both to bar-in-coil producers and to the downstream lines operators. The latest step forward is the combined application of these two systems that has made it possible for endless rolling of spooled bar in coils, enabling to cumulate the benefits of the two processes, particularly as far as transformation costs are concerned.

Aug 16, 2017

By João Luiz do Vale

In standard wear tests, such as pin on disk (ASTM-G99) or block on ring (ASTM-G77), the apparatus simulates conditions that are often different from a machine element real application. Therefore, for an accurate investigation of a tribological application, it is essential to test the real condition in which there are similarities as: geometry, contact details, force application mode, materials, among others. It emphasizes that for studies involving polymeric materials it becomes extremely relevant. Thus, the Laboratory of Surfaces and Contact (LASC) at UTFPR developed an apparatus for sliding bearing on shaft test. In that equipment, loads are applied by a dead-weight system and the frictional force is measured on a load cell. The apparatus operating ranges for load added to the dead weight system and rotation shaft are from 0.2 to 5.0 kgf and from 260 to 3500 rpm, respectively. This paper presents a detailed evaluation of such apparatus, which includes free-body diagrams analysis and a deduction to obtain an equation for the kinetic friction coefficient. Also, the standard measurement uncertainties of a caliper, an electronic scale, and a cell load were determined. It was verified that the kinetic friction coefficient equation is dependent on the apparatus geometry, the applied load, and the frictional force value. Additionally, through the statistical significance analysis it was concluded that some terms in the equation were not significant. Finally, through the application of the error propagation theory in the kinetic friction coefficient equation, the standard measurement uncertainty of the apparatus which showed a value nearby 0.002 along the operating range of the apparatus was obtained.

Jul 31, 2018

By Marcella Gautê Cavalcante Xavier

As ligas livres de chumbo (Lead-free solder alloys) potencialmente utilizáveis em processos de soldagem branda, tais como as ligas à base de Sn, vêm sendo estudadas como alternativas para substituir as ligas do sistema Sn-Pb. Em vista disto, o presente trabalho, aborda tanto a análise das características microestruturais formadas durante a solidificação transitória das ligas eutética Sn-0,2%Ni e hipereutética Sn-0,5%Ni, quanto a determinação das suas respectivas correlações com os parâmetros térmicos de solidificação: velocidade da isoterma eutética (VE) e taxa de resfriamento (?E). Para tanto, as ligas foram solidificadas unidirecionalmente no sentido vertical ascendente e em regime transiente, e caracterizadas por técnicas de microscopias ótica e eletrônica de varredura. Na liga hipereutética Sn-0,5%Ni, o aumento da quantidade de Ni na liga influenciou tanto o comportamento térmico quanto o espaçamento celular (λC), proporcionando maiores valores de ?E, porém, λC mais grosseiros.O intermetálico NiSn4 formou-se na região eutética de ambas as ligas, enquanto que na liga Sn-0,5%Ni, as fases primárias identificadas por EDS-MEV foram NiSn4 e Ni3Sn4. A transição morfológica celular/dendrítica(?E> 1,2ºC/s) ocorreu apenas para a liga eutética, enquanto que as células regulares da liga hipereutética deram origem as células do tipo placas(?E> 1,4ºC/s).

Oct 30, 2017