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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 Mario SINNAEVE, Olivier LEMAIRE, Gisèle WALMAG, Sébastien FLAMENT

Many hot rolling mills worldwide face nowadays bonding zone fatigue problems before reaching scrap diameter of the work rolls. This phenomenon is nowadays known to occur in reversing roughing mills both in stainless steel and in carbon steel rolling. The phenomenon can be explained through longer rolling campaigns, inadequate backup or work roll maintenance, harder steel grades or increased throughput by reduced amount of passes to achieve the same thickness. In order to help users in optimizing the roll use, we developed a numerical tool to evaluate and optimize roll maintenance. This paper will review the influence of roll geometries on stresses generated at the roll surface but also at the bonding zone. We will also show how roll geometries can decrease contact fatigue damages by modifying crowning and chamfering procedures, shell thickness, material design or campaign length

Oct 1, 2019

By Eric Schaub

Hot Blast Stove Systems are an important equipment of a Blast Furnace plant. During the last years, performance requirements and operation practice for the Hot Blast Systems have changed and have a big influence on the Blast Furnace operation. Therefore it is necessary to keep the Hot Blast System in proper condition in order to maintain the production capacity of the Blast Furnace. It is important for operators to know the condition and relevant constrains of a Hot Blast Stove Plant. Assessing its condition on a regular basis, especially in advance of a Blast Furnace relining is therefore advisable. Considering the individual condition of the Hot Blast Stove Plant, improvements in operation, but also specific and dedicated repairs might be implemented. Design improvements can be implemented as well during such repairs. This paper will describe some of these design improvements, will illustrate their implementation in new hot blast stoves but will also describe repair methods for existing stoves. In addition new developments became popular during the last decade, like the so called Dome Combustion Stoves, which was invented already 30 years ago in Western Europe. Paul Wurth’s development in this regard will be discussed in this paper as well.

Oct 30, 2017

By Evan Thomas

It has been shown before that liquids can slip at a solid boundary, which prompted the idea that parallel-surface bearings can be obtained by the use of alternating slip and non-slip regions in the direction of fluid flow. The amount of slip at the wall depends upon the surface tension at the liquid - solid interface, which in turn depends on the chemical composition of the surface and its roughness. In the present study a heterogeneous surface was created by coating half of a circular glass disc with a coating repellent to glycerol. A rotating glass disc was placed at a known distance above the coated stationary surface and the gap was filled with glycerol. With the top surface moving in the direction of slip to non-slip region, a pressure build up can be theoretically predicted. The pressure gradient in the two regions is constant, similar to that in a Rayleigh step bearing, with the maximum pressure at the boundary. In order to accurately measure the force generated by the pressure increase, a load cell was attached to the heterogeneous disc. Experiments were conducted by varying both sliding speed and distance, and the resultant load carrying capacity was measured and compared with theoretical calculations. This allowed the slip coefficient of the coated surface to be evaluated.

Jul 31, 2018

By Jônatas Venancio Barbosa, Dagoberto Brandão Santos, Túlio Magno Füzessy de Melo

In this work, the mechanical and metallurgical behavior of titanium added ultra-low carbon (ULC-Ti) steel under hot and warm working conditions was studied by means of dilatometer compression tests. Double compression schedules were performed at temperatures between 700°C and 1000°C, inter-pass times of 0.5-100 s, and deformations of 0.5 and 0.3 in the first and second stages, respectively, with strain rate of 1 s-1. The analysis of the flow curves obtained allowed the evaluation of the softening characteristics of the steel. The softening and microstructure features indicate different restoration mechanisms depending on the temperature range. Static recrystallization with rapid microstructure restoration is observed at temperatures within the austenitic and intercritical field. Strain induced boundary motion and recovery mechanisms apparently control the restoration process in the ferrite region. In general, flow stress curves showed dynamic recovery behavior. Only the deformation in the intercritical region produced a peak in the flow stress curves. Isothermal holding tests associated with single hit compression indicated the presence of dynamic strain induced transformation, accelerating the softening kinetics at the intercritical region.

Oct 1, 2019

By Andreas Cestonaro

Roll grade evolution in plate mill applications is traditionally following the development in hot strip mills. New grades normally find their way into service only after being successfully implemented in hot strip production. The majority of the plate mills worldwide are using work roll grades that have been invented before the 1980’s. But today the demands in the mills are pushed by sophisticated product mixes and longer rolling campaigns. The result of this development is a higher wear rate on the work rolls and as a consequence roll hardness is increased and advanced roll materials are used. The backup rolls are also affected by this. The wear rate is higher and the mechanical impact in terms of contact pressure and work hardening is increasing. This paper outlines the results of the roll grade development at Gontermann-Peipers and introduces new materials for work and backup rolls for plate mills.

Jul 30, 2018

By Breno Totti Maia, Rubia Teodoro Silva, Daniel A. G. de Carvalho, Aline Lima da Silva, Gilvan Nascimento de Souza

Para a maior eficiência na técnica conhecida como Slag Splashing, empregada com fins de manutenção e reparo de refratários de convertedor LD, a escória deve apresentar características apropriadas em termos de viscosidade e fração de sólidos. No presente trabalho, desenvolveu-se uma metodologia híbrida, combinando a utilização de padrões para a caracterização visual de escórias na planta, baseada em critérios de atribuição de notas, com a simulação termodinâmica usando o software FactSage para determinação das fases presentes na escória, quantificação de fração de sólidos e cálculo da viscosidade efetiva. A metodologia proposta permite identificar os quadrantes ideais de viscosidade efetiva, fração de sólidos e teor de ferro total, de modo que se possa garantir escórias com notas altas, apresentando qualidade apropriada para o processo. Os resultados indicam que as escórias com nota 3 (ótima) são obtidas nas seguintes condições: temperatura de fim de sopro de 1690-1720ºC, viscosidade efetiva na faixa de 0,070-0,650 Pa.s, fração de sólidos de 13-22%, teor de ferro total na escória de 14-17,5%..

Oct 1, 2019

By Daniel Stickel

Current political, economic and ecological guidelines demand the increase of power densities of nearly all machinery parts today. In order to further lower the wear rate towards the ultra-mild sliding wear regime an integral approach is needed, which has to regard contact conditions, surface topography, surface chemistry, as well as sub-surface properties. Still there are no simple parameters to classify the performance of tribosystem. In this study the area and volume affected by tribocontacts are calculated by means of a three dimensional elastic-ideal plastic contact model. The surfaces are generated by means of conventional machining procedures and characterized by scanning white light interferometry. The further input data as to normal and friction forces are derived by ultra-mild sliding wear tests under boundary lubrication conditions of carburized steel against carburized steel and 52100 steel against case-hardened spheroidal cast iron. This contribution will depict the distinct influence of the topography on friction and ultra-mild sliding wear of common Fe-base materials and point on the marked importance of highly localized effects, which govern the acting mechanisms.

Jul 31, 2018

By Eduardo de Oliveira Cabral

O trabalho apresenta uma comparação entre os principais tipos de processo de aglomeração mecânica de pós e lamas, com foco nas tecnologias de tambor e prato rotativo, misturador horizontal e misturador intensivo vertical, destacando as vantagens e desvantagens de cada processo de acordo com o objetivo final.

Oct 30, 2017

By Claudilene Ribeiro Chaves

Nanopartículas de carbono são uma nova classe de nanomateriais fluorescentes que têm atraido bastante interesse por apresentarem alta estabilidade óptica, ajustáveis comprimentos de onda de excitação e emissão além de excelente biocompatibilidade. Neste trabalho, apresentamos um método de síntese de nanopartículas por carbonização hidrotermal de quitosana. O processo de síntese ocorre em solução aquosa, é biocompatível e de baixo custo.

Aug 16, 2017

By Jan Krull

A high productive coke making process in connection with stringent emission control has clearly become a demand of plant operators and stakeholders. Further to this, availability, quality and coal costs are key concerns for the iron and steel industry in its efforts to optimize raw material cost. Today, the optimization of raw material cost in integrated steel works has further gained priority. Coking coal reflects up to 20% of the cost of steel. In top charged batteries coal preparation and blending is one of the concerns to lower coal cost by maximizing the percentage of non-coking coals in the blend. Stamp charging technology is technologically and economically an effective solution in the process of pre-carbonisation. Paul Wurth’s jumbo top charged oven as well as proven stamp charging technology have recently set new benchmarks in Europe, India and Brazil in terms of productivity, stability and emission control.

Aug 1, 2018

By Fabiano Almir Barbosa, Eduardo Alves Machado, Felipe Ferreira Cajano, Bruno Rodrigues Henriques

Spring steels are usually classified as medium to high carbon low alloy steels with very high yield strength, enabling the part to return to its original shape regardless of significant bending or twisting. Despite the fact that plain carbon steels are suitable for small springs, larger and high performance springs usually requires alloy steels such as Cr-V or Si-Mn in order to achieve an even microstructure throughout the cross section. Clutch diaphragm spring is a high performance part that requires very good cleanliness and microstructure homogeneity, thus requiring an alloy steel. In this paper was studied, in an industrial scale, the process parameters and critical characteristics for the development of a Cr and V alloyed high carbon sheet steel for the production of clutch diaphragm spring. The steel was characterized throughout the entire process (casting, hot rolling, cold rolling + batch annealing and heat treated) using tensile test, hardness test, optical microscopy (OM) and scanning electron microscopy (SEM) to assess the mechanical and metallurgical properties of the studied steel. The results have shown the material’s microstructure evolution after each main stage of the process, from a ferrite-bainite/perlite based microstructure as hot band to fully spheroidized as cold-rolled/annealed and then fully martensitic as ready-to-use part.

Oct 1, 2019

By Arcelor Mittal

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Jan 26, 2018

By Božidar Šarler, Umut Hanoglu

A rolling simulation system has been developed to calculate the macroscopic rate of deformation, stress, strain, and temperature fields by using a novel meshless method. The model is based on two-dimensional traveling slice assumption. The slices are aligned towards the rolling direction. The initial size of the billet, bloom or slab and the geometry of the grooves at each rolling stand, the distances between the rolling stands, and continuous or reverse rolling can be arbitrarily considered. The purpose of this paper is to complement these development by predicting and visualizing also the grain size of steel over the strand cross-section for each position in the rolling mill. The grain size models have been in one-way coupled to the macroscopic calculations. First the critical strain for dynamic recrystallization is being checked. If the calculated strain is higher than that, considering also the time for meta-dynamic recrystallization, dynamic or meta-dynamic grain size calculations are carried out. If the strain is too low then only the static recrystallization is considered together with its required time. Finally, austenite grain size and ferrite grain size are calculated respectively as the steel cools down. The listed physical models are based on collection of empirical relations found in literature. The user of the system is free to choose or create the model he wants with his own parameters. The simulation system has been coded as a user friendly computer application for an industrial use based on C# and .NET framework and runs on regular PCs. The computational time for a rolling simulation is usually less than one hour and can thus be straightforwardly used for optimization of the rolling mill design in a reasonable time.

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 Saulo Brinco Diniz

O presente trabalho buscou explorar a aplicação da nanoindentação instrumentada na caracterização microestrutural e mecânica de materiais metálicos. Para isso foi utilizado um ultramicrodurômetro (Shimadzu, modelo DUH–211S) e um microscópio (Olympus, modelo BX51M) a fim de analisar uma chapa laminada a quente de uma liga de alumínio 7475-T7351. De acordo com algumas das possibilidades apresentadas, pode-se concluir que a nanoindentação instrumentada é uma ferramenta poderosa para a caracterização de materiais metálicos.

Aug 16, 2017

By Douglas Batista Mazzinghy

O projeto Minas-Rio iniciou as suas operações no final de 2014 e se encontra na fase de ramp-up buscando a capacidade nominal. O circuito de cominuição inclui três prensas de rolos em circuito aberto com o objetivo de criar micro fissuras no minério e assim reduzir o consumo energético da etapa seguinte, o circuito de moagem de bolas. Este tipo de fluxograma, com prensa de rolos (circuito aberto) seguido de moagem de bolas (circuito fechado), é conhecido como circuito híbrido. A literatura apresenta este circuito híbrido como o de maior eficiência energética. A maior preocupação com relação as prensas de rolos aplicada aos minérios de ferro é a geração excessiva de finos que poderiam elevar o perda de material na etapa de deslamagem, anterior a etapa de concentração por flotação. Os resultados obtidos através de amostragem das prensas mostraram que não houve geração excessiva de finos. Neste trabalho são apresentados os resultados iniciais da operação das prensas de rolos.

Aug 16, 2017

By Rodrigo Ribeiro de Andrade, Túlio César Nogueira, Ed Juarez Mendes Taiss, Nilton José Lucinda de Oliveira

The objective of this study was to determine the effects of an eventual slab central macro-segregation in microalloyed steels with low Mn content (0.80%) and high Nb content (0.08 to 0.10%) on the kinetics of recrystallization of austenite during its rolling, on its critical temperatures, that is, of non-recrystallization (Tnr), start Ar3 and finish Ar1 of ferrite transformation and its response to a simulated industrial thermomechanical processing. The determination of the austenite recrystallization kinetics was made through isothermal double compression tests using a dilatometer, while the critical temperatures were determined through hot torsion tests in a Gleeble® 3800. It was found that austenite recrystallization kinetics, Ar3 and Ar1 temperatures did not present significant changes for the samples extracted both at ¼ of the thickness and at the core of the plate, indicating that, as expected, the central segregation in this type of steel was not intense to the point of affecting this phenomenon. The Tnr values determined for the samples extracted in the core of the plate were, on average, 30°C lower than those obtained from specimens extracted at ¼ thickness, which suggests that a significant portion of the carbonitrides present in the core of the slab are eutectic and coarse, not having completely dissolved during the reheating of the specimens. This occurred despite the fact that the austenitization temperature adopted in this treatment theoretically leads to the total dissolution of Nb, as seems to have occurred in the case of specimens extracted at ¼ of thickness, where carbonitrides have a finer size.

Oct 1, 2019

By Duberney Hincapie-Ladino

No presente trabalho analisou-se a influência de diferentes microestruturas obtidas através de tratamentos térmicos, sobre a resistência à corrosão de um aço microligado, na solução A segundo a norma NACE TM0284-11. Foi utilizada chapa de um aço destinado à conformação de tubo API 5L X65 para confeccionar as amostras. Algumas destas foram submetidas a tratamentos térmicos (Temperado, Temperado seguido de revenimento, esferoidização) e o restante foi utilizado tal como recebido. Os materiais foram submetidos a ensaios de polarização linear, num eletrólito composto por 0,5% ácido acético e 5% cloreto de sódio (solução A, NACE TM0284-11) fazendo-se purga com N2 e injeções de H2S. Foram realizados exames em microscópio óptico. Os valores de resistência de polarização mostraram que a ordem decrescente de resistência à corrosão de acordo com o tratamento térmico foi: (Esferoidizada) > (Tal Como Recebido) > (Temperada, Temperada e Revenida). Tal fato pode ser explicado pela quantidade de interfaces presentes em cada microestrutura (cementita globulizada em matriz ferrítica; ferrita com perlita; martensita e martensita revenida), sendo que quanto menor a área de interfaces, maior o valor para resistência à corrosão.

Aug 7, 2018

By Leandro Ramos Rodrigues, Jorge Emil João da Penha Júnior, Sérgio Valle Júnior

Esse artigo apresenta a estratégia adotada pela ArcelorMittal Tubarão referente extração de dados de pesagens realizadas pelas pás carregadeiras de forma automática. Para isto, foi desenvolvido um hardware que coleta e envia os dados por meio de uma comunicação de dados 3G/4G para o ambiente de nuvem da Microsoft por meio do produto Microsoft Azure IoT Hub, após isto os dados são enviados para o sistema de balanças rodoviárias da ArcelorMittal Tubarão. A Implantação da solução trouxe uma redução de 17% do tempo do recurso da contratada e 9% do tempo do recurso próprio, além de aumentar a confiabilidade do processo de consolidação dos dados de pesagem das pás carregadeiras.

Oct 1, 2019