Modelagem matemática de curvas tensão-deformação

Exportado OPUSMade available in DSpace on 2019-08-13T00:11:19Z (GMT). No. of bitstreams: 1 1287m.pdf: 706778 bytes, checksum: 48f0c1c4f24b0b14704d7128f23b5561 (MD5) Previous issue date: 12Titânio ou outros elementos como, por exemplo, o Nióbio e o Vanádio, quando adicionados como microligantes, exercem um efeito retardador na cinética de recristalização estática provocando panquecamento da austenita quando deformada a temperaturas compatíveis com asde acabamento na laminação comercial. O efeito dessas adições na cinética de recristalização dinâmica é menos conhecido. O objetivo deste trabalho é propor um modelo que represente bem o comportamento de alguns aços na deformação a quente e avaliar se a adição de microligantes seria capaz de igualmente atrasar a cinética de recristalização dinâmica. Adotou-se como metodologia neste trabalho o estudo da forma de curvas tensão versus deformação obtidas de ensaios de torção a quente isotérmicos. Análise das derivadas primeira e segunda da tensão com relação à deformação, quando traçadas em função da tensão, dá claras evidências do início e do final da recristalização dinâmica, podendo a mesma ser acompanhadadurante todo o processo. Para a modelagem das curvas tensão-deformação foram utilizados dois modelos, o de Sellars que já é bem conhecido e divulgado na literatura, e uma adaptaçãodo modelo de Sellars onde empregou-se o modelo de Jonas para acompanhar a recristalização dinâmica. Os resultados indicam que ambos os modelos propostos representam bem o comportamentodos materiais na conformação a quente. Similarmente ao caso da recristalização estática, a recristalização dinâmica é também atrasada significamente pela adição de elementos microligantes. Com os resultados obtidos foi feita uma avaliação da influência de cada elemento microligante presente nas ligas no início e no final do processo de recristalização dinâmica.Ti or other elements as, for instance, Nb or V, when added as microalloying elements, exert a retarding effect on the kinetics of static recrystallization, leading to pancaking of austenite when deformed at temperatures compatible to those in the finishing of commercial hot rolling mills. The effects of these additions on the kinetics of dynamic recrystalization is less known. This work proposes a model that will best represent the behavior of some steels in the hot deformation and assess whether the addition of microalloying elements would be able to alsodelay the kinetics of dynamic recrystallization It was adopted as a methodology in this work the study of the shape of the stress-strain curves obtained from isothermal hot torsion experiments. Analysis of the first and second derivative of the stress with respect to the strain when plotted against the stress gave clear evidence of the start and finish of dynamic recrystallization allowing the kinetics to be followed fully. Forthe modeling of stress-strain curves two models were used, one by Sellarsl which is already well known and disclosed in the literature, and an adaptation of Sellarss model where a model proposed by Jonas to monitor the dynamic recrystallization part was used. The results indicate that both proposed models represented well the behavior of materials inthe hot deformation. Similarly to the case of static recrystallization, dynamic recrystallization is also delayed significantly by the addition of microalloying elements. As a result, an assessment of the influence of each microalloying element at the beginning and end of the processof dynamic recrystallization could be here made

Influence of the chemical composition on steel casting performance

Improving the quality of steel and the steelmaking process has been a matter of routine for metallurgical engineers and steelmaking companies in a demanding market for quality products at highly competitive price. The chemical and temperature adjustment are made during the secondary refining process, as well as the inclusion modification required to product quality, and also the demand for castability accuracy. Continuous casting process is the most used solidification casting process, in which the flow of pouring liquid metal through the submerged entry nozzle is assured by the correct temperature and the formation of liquid inclusion in the casting temperature. Thermocalc and CEQCSI were the software used in this work to assess the effect of carbon, silicon and sulphur in the castability window of the aluminium vs calcium phase diagrams. They have proved to be highly suitable and effective and the results showed that the chemical elements used directly affected the position of the castability window of carbon steel. An analysis of a 0.2%C billet sample using Scanning Electron Microscopy showed that there is a great heterogeneity of inclusions in aluminium-killed and calcium-treated steel