The primary objectives of this study were: (1) to verify the effectiveness of ECAE to induce equal amounts of strain and grain refinement in bars of different cross-sectional areas, (2) to determine the effectiveness of ECAE in breaking down the as-cast macrostructure in CDA 101 Cu and in producing a homogeneous material containing micron-scale grains upon recrystallization, and (3) to determine a thermomechanical processing (TMP) schedule (from the ones examined) that produces the best microstructure in terms of grain size and uniformity. The effects of extrus ion route, levels of strain and intermediate heat treatment were investigated. To achieve the first objective, bars having square cross-sections of three different sizes, 19 mm, 25 mm and 50 mm, were processed up to eight ECAE passes through routes A, B, C and E. To achieve the second and third objectives, bars were processed up to eight ECAE passes with and without intermediate heat treatments through routes Bc, C, E and F. ECAE processing was carried out in a 90o extrusion die with sliding walls at an extrusion speed of 2.5 mm/s. Recrystallization studies were carried out on the processed material to evaluate the recrystallization behavior and thermal stability of the material. The as-worked and recrystallized materials were characterized by Vickers microhardness, optical microscopy (OM) and transmission electron microscopy (TEM). Results indicate that similar hardness values, sub-grain morphology and recrystallized grain size are generated in the three bars having different cross-sectional sizes processed through ECAE. ECAE is shown to induce uniform strain in all three billet sizes. ECAE is therefore shown to be effective in scale-up to a size of at least 50 mm, with larger billets giving better load efficiency. Results from the later parts of this study indicate that eight extrusion passes via route Bc produces the best microstructure in terms of grain size and microstructural uniformity. The routes can be arranged in the sequence Bc> E, F> C for their ability to produce a uniform recrystallized microstructure with small average grain size. Macroscopic shear bands are sometimes generated during extrusion depending upon the initial grain morphology and texture of the material.

Made available in DSpace on 2016-12-08T17:19:37Z (GMT). No. of bitstreams: 1 Resumo.pdf: 10956 bytes, checksum: b3ab8ff2ededda1434fbc70325d132f4 (MD5) Previous issue date: 2010-12-07 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Semi-processed electrical steels require annealing after processing in the motors manufactures to improve motors efficiency by reducing losses and increasing permeability. Annealing in fully processed electrical steel is performed to relax the residual stress and promote recovery or recrystallization of distorted parts. Commercial samples from different steels with different chemical compositions were selected to evaluate the influence of final annealing heat treatment temperature and dew point on the magnetic properties, the carbon content and grain size increase. Were performed with annealing atmosphere without steam and with dew point of 5, 10, 20 and 25°C at temperatures of 760 and 790°C. Magnetic losses, relative permeability, carbon content, grain size and mechanical properties measurements were made in addition to the evaluation of the microstructure to determine this influence. It was observed in the semi-processed steel with 300 ppm carbon content, which with dew point increase the carbon content reduce the grain size increase and improve magnetic properties. In the other steels studied, reducing the dew point improved the magnetic properties, but the atmosphere without steam has improved only fully processed steel with 2% silicon. It was found that in fully processed steels the best results were obtained with annealing temperature of 790°C. / Aços elétricos semiprocessados necessitam de recozimento após a sua manufatura para melhorar o rendimento dos motores com a redução das perdas magnéticas e aumento da permeabilidade. os aços totalmente processados o recozimento é realizado para relaxar as tensões residuais e promover a recuperação ou recristalização das partes deformadas. Amostras comerciais de diferentes aços com variadas composições químicas foram selecionadas para avaliar a influência do ponto de orvalho e temperatura de recozimento final nas propriedades magnéticas, no teor de carbono e no aumento do tamanho de grão. Foram realizados recozimentos com atmosfera sem vapor e com ponto de orvalho de 5, 10, 20 e 25°C, nas temperaturas de 760 e 790°C. Medições de perdas magnéticas, permeabilidade, teor de carbono, tamanho de grão e propriedades mecânicas, além da avaliação da microestrutura, foram efetuados para determinar esta influência. Foi verificado no aço com 300 ppm de carbono, que com aumento do ponto de orvalho reduziu o teor de carbono, aumentou o tamanho de grão e melhorou as propriedades magnéticas. Nos demais aços estudados, a redução do ponto de orvalho melhorou as propriedades magnéticas, porém com ausência de umidade somente houve melhora no aço totalmente processado com 2% de silício. Foi verificado ainda que nos aços totalmente processados os melhores resultados foram obtidos com a temperatura de recozimento de 790°C.