Este trabalho visa analisar a influência das taxas de resfriamento e temperatura no último passe de laminação a quente de fio máquina de um aço DIN 41Cr4 sobre a microestrutura obtida após a laminação e a sua correlação com aquela resultante do tratamento térmico de esferoidização. Foi avaliado a influência da microestrutura prévia de laminação nos tempos e taxa de resfriamento do tratamento térmico necessários para garantir adequada microestrutura do aço DIN 41Cr4. Foram aplicados conceitos de laminação termomecânica através da variação dos parâmetros: temperatura no último passe de laminação (acabador) e após o último passe de laminação (formador de espiras); velocidade das esteiras do “cooling conveyor” e consequente tempo de permanência das espiras sobre a região de ventiladores e alguns parâmetros no ciclo de tratamento térmico: tempo em patamar e taxa de resfriamento durante a produção de fio máquina redondo de bitolas entre 15,88mm e 16,15mm. A avaliação da resposta às variações impostas ao processo foi realizada através de análises metalográficas de microestrutura no material laminado e no material esferoidizado (grau de esferoidização), descarbonetação e de ensaios de propriedades mecânicas como dureza e tração. A partir dos resultados buscou-se determinar a influência dos parâmetros de laminação na microestrutura do material laminado e a influência desta na resposta ao tratamento térmico de esferoidização. Foram analisadas oito diferentes condições e os resultados mostraram que maiores taxas de resfriamento resultam em microestruturas mais refinadas proporcionando uma simplificação no tratamento térmico, atendendo as propriedades desejáveis no produto final (fio máquina redondo esferoidizado). / This work aims to analyze the influence of the cooling rate, the temperature of the finishing pass and at the coil-forming during hot rolling of DIN 41Cr4 steel wire rod on the microstructure and its influence on plateau times and cooling rate during the spheroidizing heat treatment. For this study thermomechanical rolling concepts were applied through the variation of some hot rolling parameters such as: temperature at the finishing pass and at the coils-former, the cooling conveyor belts velocity and some parameters in the heat treatment cycle: soak temperature and cooling rate during the production of round wire rod with 15,88 mm and 16,15 mm diameter. The evaluation response to changes imposed on the process was evaluated by metallographic analysis of microstructure in hot rolled and spheroidized material (spheroidizing degree), hardness, decarburization and tensile test. Eight rolling conditions and cooling rates were analyzed and results showed that higher cooling rates result in finer microstructures allowing a reduction in heat treatment time to achieve the desirable properties in the final product (spheroidized round wire rod).

Seit vielen Jahren wächst die Nachfrage bezüglich sparsamer Fahrzeuge; die Autohersteller konkurrieren miteinander und werben mit neuen Fahrzeugkonzepten, in denen hochmoderne Werkstoffe ihre Anwendung finden. In dieser Arbeit werden Legierungskonzepte und entsprechende Warmwalztechnologien einer ultrahochfesten bainitischen Stahlsorte mit Restaustenit vorgestellt, die der genannten Anwendung angepasst werden können. Der gewählte Werkstoff gehört zu den Stählen mit mittleren Kohlenstoffgehalten, die sich nach der - im Rahmen dieser Arbeit entwickelten - Behandlung durch hohe Zugfestigkeit bei vergleichsweise hoher Bruchdehnung auszeichnen. Es werden erweiterte Modelle zur Beschreibung der Phasenumwandlung von Stählen im Bainitgebiet vorgestellt. Die Ergebnisse aus den Experimenten wurden genutzt, um die Modelle zu ergänzen und zu evaluieren. Dabei wird nicht nur der Warmwalzprozess, sondern auch die chemische Zusammensetzung der Stähle selbst optimiert. Die hier präsentierte Arbeit erstreckt sich über die gesamte Produktionskette und zeigt geeignete Herstellungsbedingungen, die in Betriebsanlagen leicht realisierbar sind und umgesetzt wurden.

Este trabalho visa analisar a influência das taxas de resfriamento e temperatura no último passe de laminação a quente de fio máquina de um aço DIN 41Cr4 sobre a microestrutura obtida após a laminação e a sua correlação com aquela resultante do tratamento térmico de esferoidização. Foi avaliado a influência da microestrutura prévia de laminação nos tempos e taxa de resfriamento do tratamento térmico necessários para garantir adequada microestrutura do aço DIN 41Cr4. Foram aplicados conceitos de laminação termomecânica através da variação dos parâmetros: temperatura no último passe de laminação (acabador) e após o último passe de laminação (formador de espiras); velocidade das esteiras do “cooling conveyor” e consequente tempo de permanência das espiras sobre a região de ventiladores e alguns parâmetros no ciclo de tratamento térmico: tempo em patamar e taxa de resfriamento durante a produção de fio máquina redondo de bitolas entre 15,88mm e 16,15mm. A avaliação da resposta às variações impostas ao processo foi realizada através de análises metalográficas de microestrutura no material laminado e no material esferoidizado (grau de esferoidização), descarbonetação e de ensaios de propriedades mecânicas como dureza e tração. A partir dos resultados buscou-se determinar a influência dos parâmetros de laminação na microestrutura do material laminado e a influência desta na resposta ao tratamento térmico de esferoidização. Foram analisadas oito diferentes condições e os resultados mostraram que maiores taxas de resfriamento resultam em microestruturas mais refinadas proporcionando uma simplificação no tratamento térmico, atendendo as propriedades desejáveis no produto final (fio máquina redondo esferoidizado). / This work aims to analyze the influence of the cooling rate, the temperature of the finishing pass and at the coil-forming during hot rolling of DIN 41Cr4 steel wire rod on the microstructure and its influence on plateau times and cooling rate during the spheroidizing heat treatment. For this study thermomechanical rolling concepts were applied through the variation of some hot rolling parameters such as: temperature at the finishing pass and at the coils-former, the cooling conveyor belts velocity and some parameters in the heat treatment cycle: soak temperature and cooling rate during the production of round wire rod with 15,88 mm and 16,15 mm diameter. The evaluation response to changes imposed on the process was evaluated by metallographic analysis of microstructure in hot rolled and spheroidized material (spheroidizing degree), hardness, decarburization and tensile test. Eight rolling conditions and cooling rates were analyzed and results showed that higher cooling rates result in finer microstructures allowing a reduction in heat treatment time to achieve the desirable properties in the final product (spheroidized round wire rod).

This thesis is dealing with an analysis of thermal and mechanical loads on a work-roll. First, hot rolling focused on work-roll is described in general. A theoretical analysis of roll loads and the mechanisms affecting roll durability are presented here. The thesis is concentrated on creation of a model in FEM program ANSYS. The final model is loaded with different rolling schemes and monitored stresses in a surface layer. The parameters obtained from the measurements performed in a rolling mill are applied as boundary conditions within the model.

The steel quality is deteriorated at a continuous casting start. Therefore, material from the first cast slab is cut off and re-melted in the melt shop. If too little is discarded, the inferior quality in the retained length can cause defects like edge cracks during subsequent hot rolling. This means that manufacturing resources are wasted on processing inferior material which has to be re-melted anyways at a later stage. On the other hand, if an excessive length of the first slab is re-melted, good material is wasted. In either case, optimizing the length of the start-scrap material is both economically and environmentally beneficial. Edge cracks are more common in the beginning of the first slab, even though a part is cut off. It is likely that the edge cracks arise due to reduced hot ductility in the first cast material. The purpose of this project is to optimize where the cut should be made in order to achieve the best yield. The hot ductility was investigated by performing hot tensile- and bending tests. The hot tensile tests indicate high hot ductility for the investigated specimens. The area reduction, which is correlated to the hot ductility, is above 70 % for all the investigated specimens. When considering the average area reduction while neglecting possible differences between the heats, the specimens from one meter tend to have a lower hot ductility compared to the other specimens. However, the differences are small. No difference can be seen between edge and middle specimens when only looking at the tensile tests. The bending tests did not crack without notches, even though the maximum load and a test temperature of 750 °C was used. That strongly indicates high hot ductility as well. By using notches, the bending tests cracked and it was shown that edge specimens and specimens from one meter cracked the most. No edge cracks were found, after hot rolling, on the first cast slabs from the investigated heats. / Vid en stränggjutstart är kvalitén på första slaben sämre. På grund av detta så skärs en bit, av det först gjutna slabet av och smälts om i stålverket. Om för lite material kapas av kan det leda till defekter, såsom kantbrakor, under den efterföljande varmvalsningen. Detta innebär att resurser används i onödan för att tillverka material av otillräcklig kvalitet som sedan ändå måste smältas om i ett senare steg. Skärs istället för mycket material bort så smälts prima material om i onödan. Att optimera startskrotlängden är följaktligen positivt både för miljön och rent ekonomiskt. Under varmvalsningen kan defekten kantbrakor, det vill säga sprickor vid kanterna, uppstå. Trots att en bit av det första gjutna slabet skärs av, så är det första slabet fortfarande mest utsatt för kantbrakor. Detta tros bero på nedsatt varmduktilitet i det första gjutna materialet. Syftet med detta projekt är att optimera längden på startskrotet för att spara så mycket användbart material som möjligt. Varmduktiliteten undersöktes genom drag- och bockprovning. Dragproven indikerar hög varmduktilitet för de undersökta proven. Areakontraktionen, som är ett mått på varmduktiliteten, är över 70 % för alla undersökta prov. Medelareakontraktionen, när man bortser från eventuella skillnader mellan chargerna, visar att prov från en meter generellt har något lägre varmduktilitet än de övriga proven. Det är endast små skillnader som uppfattas. Ingen skillnad kan ses mellan kant- och mittenprov när man enbart tittar på dragprovsresultaten. Bockproven sprack inte trots att maximal last användes och att testtemperaturen var 750 °C. Detta tyder också på hög varmduktilitet. Genom att skapa anvisningar kunde man få bockproven att spricka och det visade sig att kantprov och prov från en meter sprack mest. Inga kantbrakor hade uppstått på de första gjutna slabsen under varmvalsningen av försökschargerna.

This master thesis was done at Swerim AB in cooperation with SSAB and the Technical University of Luleå in the purpose of preventing spalling problems in hot rolling mills. Spallings are a fatigue damage that occurs on the rolls due to extreme loads and unfavorable conditions between the rolls in a mill. This report describes how the roughing mill, which is the first of a series of hot rolling mills is modelled and simulated in order to compute and improve the load distribution between the rolls. The load distribution tells a lot where the spalling problems occurs. By computer aided design and simulations with the finite element method a parametric computational model was created and used to simulate the load distribution between the work roll and backup roll with worn andfresh rolls. These simulations showed what the load distribution looks like when using new rolls and that the load distribution is especially bad when the work roll is worn. The computational model was used to simulate how the load distribution changes with different geometries on the backup roll to provide valuable input and suggest new designs on the backup roll currently used by SSAB Borlänge.

No / A steel hot rolling mill subjects steel slabs to high temperatures and pressures in order to form steel coils. We describe the scheduling problem for a steel hot rolling mill. We detail the operation of a commercial decision support system which provides semi-automatic schedules, comparing its operation with existing, manual planning procedures. This commercial system is currently in use in several steel mills worldwide. The system features a very detailed multiobjective model of the steel hot rolling process. This model is solved using a variety of bespoke local and Tabu search heuristics. We describe both this model and the heuristics used to solve it. The production environment is highly unstable with frequent, unforeseen events interrupting planned production. We describe how the scheduling system's models, algorithms and interfaces have been developed to handle this instability. We consider particularly the impact on existing planning and production systems and the qualitative improvements which result from the system's implementation.

Le laminage est un procédé de mise en forme à chaud permettant d’obtenir des barres de différents diamètres en partant de blooms issus de la coulée continue. Dans les bruts de coulée se répartissent des inclusions qui sont de natures, de formes et de tailles différentes. Le laminage va permettre de réduire le diamètre de la barre et d’agir sur la microstructure du matériau, notamment, en fragmentant et dispersant les inclusions. L’objectif des travaux de thèse est de contribuer à la compréhension des effets du chargement thermomécanique sur l’évolution des défauts de coulée en laminage. Vu la dimension des installations, les investigations expérimentales directes sur les moyens industriels ne sont pas envisageables. L’idée développée dans les travaux de thèse concerne la mise en place et la validation d’un essai de caractérisation à échelle réduite reproduisant le chemin thermomécanique subi par la matière au cours du laminage. Pour ce faire la ligne de laminage industrielle est modélisé afin d’obtenir le chargement thermomécanique de la barre au cours du laminage. Seules les sollicitations ayant un rôle majeur sur le comportement des défauts sont reproduites. Un essai dit de « forgeage libre » a ainsi été conçu, réalisé, mis en place sur les moyens de mise en forme de la plateforme VULCAIN de l’ENSAM. L’essai a été utilisé avec des défauts artificiels présentant des similarités comme la malléabilité avec les défauts réels. Une campagne expérimentale paramétrique a été menée sur les différents types de défauts. Les échantillons forgés ont été analysés par des méthodes non destructives comme les ultrasons, la radiographie et la tomographie X. Ces analyses ont permis de suivre le comportement du défaut et d’observer certains phénomènes mis en évidence dans la littérature comme l’apparition de cavité à l’interface défaut-matrice. / Rolling is a hot forming process dedicated to manufacture bars with different diameters. The initial product is a bloom from the continuous casting. The bloom contains inclusions which have different forms, sizes and distributions. The rolling reduces the diameter of the bar and acts on the material microstructure by fragmenting and dispersing the inclusions. The aim of the thesis work is to understand the behavior of the inclusions with the rolling thermo mechanical loading effects. The direct investigations on the rolling mill are not possible because of the size of the installations. To address this problem, the solution is to develop and validate a small scale characterization test reproducing the thermo mechanical loading of the rolled bar. To achieve this, the rolling mill is modeled. Only the solicitations which have a major role on the behavior of the defects are reproduced. An open-die forging test is designed, manufactured and implemented on the VULCAIN installation of the ENSAM. The artificial defects which have a similar malleability to the real defects are integrated into the sample. A parametric experimental campaign has been conducted on the different defects. The forged samples have been analyzed with non-destructive methods such as ultrasound, radiography and tomography. These analyses allowed to follow the behavior of the defects and to observe certain phenomena illustrated in the literature such as the emergence of a cavity on the defect-matrix interface.

[pt] O advento e consolidação do processo de lingotamento contínuo, hoje dominante no setor siderúrgico, trouxe à tona os crescentes esforços de investigação e análise dos fenômenos relacionados com o comportamento dos aços a elevadas temperaturas. Diferentemente do lingotamento convencional, o lingotamento contínuo é um processo dinâmico no qual ocorre a oscilação do molde enquanto o veio em solidificação é continuamente extraído ao mesmo tempo que é submetido a um segundo resfriamento dito secundário. No Brasil há um parque industrial de empresas que se dedicam à laminação a quente de semiacabados fornecidos por terceiros como placas de aço, as quais são cortadas a quente sob a forma de tarugos de seção quadrada que são então destinados a laminação. A linha de produção dessas empresas compreende basicamente produtos estruturais tais como barras chatas, barras redondas, barras quadradas, cantoneiras e até perfis especiais destinados à indústria automobilística e de máquinas. Uma série catastrófica de eventos de qualidade relacionados com trincas emergiu da laminação de tarugos de aço SAE 1020 oriundos de placas continuamente lingotadas. Essas trincas, porventura preexistentes ou latentes no interior das placas podem ter sido exacerbadas por efeitos de zonas termicamente afetas durante as operações de corte. A solução proposta para superação dessa contingência foi então a de criação de um aço de substituição com teores inferiores de carbono e maior conteúdo de ligas que preservasse as propriedades mecânicas do material laminado. Teores inferiores de carbono não apenas contribuem para a minimização dos efeitos oriundos das transformações peritéticas como também agem favoravelmente sobre as consequências decorrentes de zonas termicamente afetadas. Essa proposta foi bem sucedida e a composição química desse aço de substituição denominado pseudo-1020 passou a ser desde então padrão de laminação. Amostras do SAE 1020 laminado com ocorrências de trincas e do aço de substituição foram obtidas e transformadas em corpos de prova para a realização de ensaios de tração, dureza e impacto. Essa dissertação objetiva apresentar toda a fenomenologia relacionada com a ocorrência de trincas superfícies e internas em aços continuamente lingotados, em especial os submetidos a transformações peritéticas, e as premissas que fundamentaram a criação do aço de substituição e os resultados auferidos. / [en] The advent and consolidation of the continuous casting process, currently dominant in the Steel Industry, raised the increasing investigation and analyses efforts on the phenomena related to the high-temperature behavior of the steels. Unlike the conventional ingot casting process, the continuous casting is a dynamic process in which occurs the mold oscillation while the strand under solidification is continuously withdrawn and submitted to a secondary cooling operation. In Brazil, it can be found an industrial park of companies dedicated to the hot rolling of semis supplied by third parties as steel slabs, which ones are flame cut in the form of square billets for rolling. The production mix of these companies encompasses structural steels such as flat bars, round bars, angles and even special profiles for the machines and automotive industries. A catastrophic series of quality events related to cracking emerged from the rolling of SAE 1020 billets made from continuously cast slabs. These cracks, perhaps pre-existing or latent in the inner parts of the slabs could be exacerbated by thermal affected zones during the flame-cut operations. The propose solution to overcoming this contingency was the creation of a replacement steel grade with lower carbon content and higher alloy content aiming to preserve the mechanical properties of the as rolled material. Lower carbon contents does not only contributes to the minimization of the effects arising from the peritetic transformations as also act in favor on the consequences coming from thermal affected zones. This proposition was well successful and the chemical composition of this replacement steel called pseudo- 1020 since then became a rolling standard. Samples of the rolled SAE 1020 steel with cracks occurrences and of the replacement steel were taken and transformed in specimens for tensile strengths, hardness and impact tests.This paper aims to present all related phenomena to the occurrence of inner and superficial cracks in continuously cast steels, in special the ones submitted to peritetic transformations, and the premises that support the creation of a replacement steel and the related results.

"A Java pre- and post-processing graphical user-oriented interface has been developed by the authors to aid a mill engineer with little or no finite element experience throughout the analysis process of the finishing rolling stands. A case study is presented that uses the commercial finite element code ABAQUS/Explicit to predict roundness and tolerance customer requirements. Other parameters that are determined include spread, crosssectional area, percentage reduction in area, incremental plastic strain, total plastic strain and roll force. All parameters are compared to theoretical models and some are compared to full-scale mill testing."