Steels containing high levels of Mn, Si and Al exhibit high plasticity when deformed, owing to twinning-induced plastitity (TWIP) and transformation-induced plasticity (TRIP) effects. In this study, we investigated the microstructural evolution of samples of samples of a 17%Mn steel subjected to war rolling at 700° and 800°C. We also studied the effects of the microstructure of the steel samples on their mechanical behavior. Using a mathematic model the stacking fault energy of the steel was estimated to be 14.5 mJ/m 2 . This value was indicative of a martensitic transformation. The presence of martensite and twinned austenite was verified using optical microscopy, scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) analyses. The presence of austenite and ε-and α'-martensites was confirmed using X-ray diffraction (XRD) analyses and dilatometry. Increasing the rate of cold reduction resulted in the formation of a α'-martensite phase and a decrease in the volume fraction of the ε-martensite phase. The volume fractions of the various phases were measured by integrating the areas under the XRD peaks. The sample subjected to a cold-rolling reduction of 81% and a subsequent annealing treatment did not contain a α'-martensite phase, indicating that it was fully recrystallized. The Vickers microhardness of the samples increased with an increase in the cold-rolling reduction rate. However, the microhardness values of the cold-rolled samples decreased after the annealing treatment.

The steel of this work, 0.06C-25Mn-3Al-2Si-1Ni steel, presenting TWIP effect, was hot and cold rolled and then annealed at temperatures between 600 and 850ºC. The microstructure examination was focused in the recrystallization during annealing for different temperatures through optical and scanning electron microscopy. The volume fraction and recrystallized grain size measurements were performed. Tensile tests were conducted at room temperature. A polycrystalline model, based on micromechanics and working hardening theory, developed by Bouaziz et al., to predict the behavior of TWIP steels under different loading paths, was applied to the current steel. The results from the model are in good agreement with mechanical test and show a total elongation above 60%, uniform elongation up to 55% and a tensile strength greater than 600 MPa, which highlights the potential of this steel for its various applications, mainly automotive industry. The model parameters are discussed and their limitations are presented.

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A pesquisa por aços que combinem altos valores de resistência mecânica e conformabilidade, além de um baixo peso específico, é uma constante na indústria siderúrgica atual. É neste contexto que surge o aço alto Mn, Si e Al capaz de apresentar o efeito TWIP (TWinning Induced Plasticity) devido à baixa energia de falha de empilhamento na estrutura cristalina deste material. No trabalho atual desenvolve-se um modelo físico do encruamento de um aço C-0,06; Mn-25; Al-3; Si-2; Ni-1, apresentando o efeito TWIP, que foi inicialmente laminado a quente, a frio e recozido em temperaturas entre 600°C e 850°C. A fração volumétrica e o tamanho de grão recristalizado foram medidos através de microscopia óptica e eletrônica de varredura (MEV). Para tal modelo foram utilizados resultados de ensaios de tração do material nas várias condições de recozimento. Um modelo considerando a liga policristalina e baseado no comportamento mecânico do aço sob carregamento em tração foi aplicado. Foram utilizadas equações constitutivas formuladas a partir da teoria da plasticidade. Os resultados do modelo mostraram boa compatibilidade com a curva de fluxo obtida no ensaio de tração. palavras-chave: Efeito TWIP; Recozimento; Modelagem matemática; Simulação. pHYsical Model oF deForMation and worK Hardening oF HigH Manganeese and low carbon twip steel abstract The new concepts for building automotive structures with impact resistance, formability, and low specific weight lead to increase in the research for materials with high strength and toughness, combined with low density. The TWIP steel (Twinning Induced Plasticity) can meet these needs and therefore it is essential its development. The material of this work, 0.06C-25Mn-3Al-2Si-1Ni steel, with TWIP effect, was hot and cold rolled and then annealed at temperatures between 600°C and 850°C. The microstructural examination was focused in the recrystallization during annealing for different temperatures through optical and scanning electron microscopy (SEM). For mechanical evaluation tensile tests were performed. A polycrystalline model, based on micromechanics and working hardening theory, developed by Bouaziz et al., to predict the behavior of TWIP steels under tensile tests was applied to current steel. The results from the model are in good agreement.

Resumo O presente trabalho tem como objetivo avaliar as propriedades mecânicas de tubos trefilados à frio em aço microligado ao Vanádio a partir de diferentes rotas de tratamento térmico, sendo elas: normalização, normalização seguida do recozimento subcrítico e apenas o recozimento subcrítico. A realização do recozimento subcrítico após a normalização propiciou resultados para o limite de escoamento superiores aos das amostras somente normalizadas. Este aumento está vinculado principalmente à precipitação de Carbonetos de Vanádio. Já para a rota em que se utilizou somente o recozimento subcrítico foram obtidos os maiores valores de limite de escoamento.