Noise and vibration damping of Fe-Cr-x alloys

The aim of the present work is to study the noise and vibration damping capacity of ferromagnetic Fe-16%Cr base alloys (before and after heat treatment) with different Al and Mo contents. The noise damping was evaluated by the level of sound emission after an impact. The vibration damping was studied using a cantilever device. In addition to these tests, the magnetic structure of the materials was also investigated by Kerr effect. It was verified that the materials can decrease noise level in the frequency range of human earring. The vibration damping is influenced by heat treatment and chemical composition of the alloy. The improvement of vibration damping after heat treatment is ascribed to the decrease of internal stresses in materials and changes in magnetic domain structures.115122Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

The Effect Of The Microstructure On The Superplasticity Of A Duplex Stainless Steel

The aim of this work is to study the effect of the microstructure on the superplasticity of 22% Cr-5% Ni-3% Mo-0.18% N ferrite (α)-austenite (γ) duplex stainless steel. To obtain different microstructures several thermo-mechanical treatments were employed. Superplasticity was evaluated at 1253 K by m-value measurements, elongation to failure, deformation homogeneity, and changes in microstructure after tensile tests. A maximum elongation of 1510% was reached with an initial strain rate of 3 × 10-4/s. For this condition, the m-value attained 0.64 and necking was not verified. Higher degrees of superplasticity are obtained when the initial microstructure of the material is fine and homogeneous. Such microstructure can be obtained by a solution treatment in the α-single phase field, followed by a heavy cold rolling operation and a new solution treatment in the α/γ dual phase field. The precipitation of σ-phase during superplastic deformation promotes cavitation and decreases the deformation homogeneity and the elongation to failure. © 1998 Acta Metallurgica Inc.461138573862Hayden, H.W., Gibson, R.C., Brophy, J.H., (1969) Scient. Am., 220, p. 28Smith, C.I., Norgate, B., Ridley, N., (1976) Metals Sci., 10, p. 182Ridley, N., (1990) Mater. Sci. Technol., 6, p. 1145Maehara, Y., (1985) Trans. Iron Steel Inst. Japan., 25, p. 69Maehara, Y., (1987) Trans. Iron Steel Inst. Japan., 27, p. 705Maehara, Y., Ohmori, Y., (1987) Metall. Trans., 18 A, p. 663Osada, K., Ueko, S., Ebato, K., (1987) Trans. Iron Steel Inst. Japan., 28, p. 713Osada, K., Uekoh, S., Tohge, T., Noda, M., Ebato, K., (1988) Trans. Iron Steel Inst. Japan., 28, p. 16Maehara, Y., (1991) Metall. Trans., 22 A, p. 1083Tsuzaki, K., Matsuyama, H., Nagao, M., Maki, T., (1990) Mater. Trans. JIM, 31, p. 983Han, Y.S., Hong, S.H., (1997) Scripta Mater., 36, p. 557Charles, J., (1991) Proc. 5th Conf. on Duplex Stainless Steel, pp. 3-48. , BeauneJosefsson, B., Nilsson, J.O., Wilson, A., (1991) Proc. 5th Conf. on Duplex Stainless Steel, pp. 67-78. , BeaunePulino-Sagradi, D., Nazar, A.M.M., Ammann, J.J., Medrano, R.E., (1997) Acta Mater., 45, p. 4663Backofen, W.A., Turner, I.R., Avery, D.H., (1964) Trans. Am. Soc. Metals, 57, p. 981Krauss, G., (1990) Steels: Heat Treatment and Processing Principles, , ASM, Materials Par

Efeito da microestrutura na superplasticidade de um aço inoxidavel duplex

Orientadores: Ana Maria Martinez Nazar, Ricardo E. MedranoDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecanicaResumo: Materiais superplásticos podem sofrer altos níveis de deformação de maneira homogênea quando submetidos a condições de processamento específicas (alta temperatura e baixa taxa de deformação). Os aços inoxidáveis duplex podem ser superplásticos, contudo isto só é possível para materiais com estrutura refinada, ou seja, é necessário que o tamanho de grão seja inferior a 10 µm. O objetivo deste trabalho é desenvolver e estudar, em função da microestrutura de partida, o comportamento superplástico do aço inoxidável duplex 2205 (21,13% Cr; 4,73% Ni; 2,75% Mo; 0.18N). Para atingir este propósito, um material não superplástico foi submetido a diversos tratamentos termomecânicos, incluindo laminação a quente (80% de redução de área) no campo bifásico, laminação a frio (vários graus de redução) após um tratamento de solubilização no campo monofásico (ferrítico) e um tratamento de solubilização após cada processo de deformação. Desta forma, fabricaram-se duas categorias de materiais: os materiais brutos de laminação e os materiais solubilizados. Para avaliar a superplasticidade, todos os materiais listados acima foram submetidos ao ensaio de tração à temperatura de 980°C com mudança de taxa de deformação. Tal procedimento permitiu a determinação do expoente de sensibilidade à taxa de deformação (m) em função da taxa de deformação. Para verificar a correlação existente entre os resultados obtidos pelos ensaios e a microestrutura de partida, em alguns casos, realizaram-se ensaios de tração até a fratura com uma taxa de 3 x I0-4 s-1 na mesma temperatura. Foi feita ainda uma análise metalográfica em cada corpo-de-prova após cada ensaio de tração. O trabalho permitiu concluir que, como o processo de deformação a frio produz microestruturas mais refinadas, este é mais indicado para tornar o aço estudado superplástico. O tratamento mais efetivo foi a laminação do material a frio com uma redução de 80% após uma solubilização a 1380°C, o que resultou em tamanhos de grão da ordem de 5 µm. Neste caso, o valor máximo encontrado para o alongamento foi de 1500%, para uma taxa de 3 x I0-4 s-1, onde o valor de m é de 0,64. Taxas de deformação menores não melhoraram a superplasticidade do material, devido à precipitação de fase sigma em ensaios mais lentos. Acredita-se que a fase sigma nucleia cavidades, promovendo a falha prematura do materialAbstract: Superplastic materials can undergo high deformation levels with high uniformity when submitted to specific conditions (high temperature and slow strain rate). Duplex stainless steel may exhibit superplastic behavior. However, this is only possible to fine-grained materials, in other words, a grain size less than 10 µm is required. The purpose of this work is to develop and study as a function of prior microstructure the superplastic behavior of the 2205 duplex stainless steel (21.13% Cr, 4.73% Ni, 2.75% Mo, 0.18N). To reach this goal, a non-superplastic material was submitted to several thermomechanical treatments, including hot rolling (80% of area reduction) in the dual-phase field, cold rolling (several levels of area reduction) after a solution treatment in the single phase field (ferritic) and a solution treatment after each deformation process Therefore, it was made two categories of materials: the as rolled materials and the solution treated ones. To evaluate the superplasticity, all materials listed were tested by means of the tensile strain rate change test at 980°C. This allowed the determination of the strain rate sensitivity exponent (m) as a function of strain rate. To verify the correlation between the results of the tensile strain rate change tests and the prior microstructure, in some cases hot tensile tests were performed at 980°C with a strain rate of 3 x I0-4 s-1. The final microstructure of each hot tensile test sample was also analyzed. The main conclusions are listed as follows as the cold work processes produce more refined microstructures, they are more suitable to impair a superplastic behavior to the steel studied. The most effective treatment was cold rolling the material (80%) after a solution treatment at 1380°C. This treatment produced materials whose grain size was about 5 µm. In this case, for a strain rate of 3 x I0-4 s-1the elongation reached 1500% and m value obtained was 0.64. Lower values of strain rate do not increase the material superplasticity. This is related to sigma phase precipitation in the slower test. It was believed that sigma phase nucleates cavities and then promotes premature failure of the materialMestradoMestre em Engenharia Mecânic

Superplasticidade de um aço inoxidavel duplex

Orientadores: Ana Maria Martinez Nazar, Ricardo E. MedranoTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecanicaResumo: Não informadoAbstract: Superplasticity is the ability of certain materials to deform homogeneously with high elongations (several hundreds or thousands percent) at elevated temperatures and low strain rates. This subject of scientific and teclinological interest is not well slablished yet. The purpose of present work is to characterize and to study the superplastic behavior of a 22.5%Cr-6.4%Ni-3.0%Mo-0.16%N duplex stainless steel. Therefore, samples from sheets of the material were examined at 950°C and 98CFC by means of tensile, strain rate change and stress relaxation tests. Moreover, microstructures and cavitation process under main conditions were also analyzed. Tensile tests provided informations about elongation and deformation homogeneity. On the other hand, the strain rate change and stress relaxation tests were more suitable to determine the strain rate sensitivity. The superplastic behavior analysis was based on whole results from elongation, strain rate sensitivity and deformation uniformity. According to these criteria, the material exhibits superplastic deformation at 980X with strain rates ranging from 10 s" to ! 0' s". Under these conditions the deformation was homogeneous (without necking), the strain rate sensitivity coefficient attained 0.7 and elongation achieved 900%. During deformation: (i) the initial microstructure composed of oriented phases change to an equiaxed stable structure and (ii) cavitation process occurs. These observations suggest the grain boundary sliding as the main superplastic deformation mechanism. Key Words: super-plasticity, duplex stainless steel, tensile test, strain rate change test, stress relaxationDoutoradoMateriais e Processos de FabricaçãoDoutor em Engenharia Mecânic

Superplastic Deformation Of A Duplex Stainless Steel

Superplastic behavior of a duplex stainless steel has been studied at 1223 K (950°C) and 1253 K (980°C) for initial strain-rates ranging from 2×10-4 s-1 to 8×10-3 s-1. In the given range of temperature, it was observed that the elongation increased as the strain rate decreased. The best superplastic conditions were obtained at 1253 K where the samples presented homogeneous deformation along the gage length. Under this temperature the maximum elongation (900%) was obtained for an initial strain-rate of 4×10-4 s-1. Those results were also confirmed by determination of the strain-rate sensitivity coefficient, m, which presented the highest value at 1253 K and clearly increased with decreasing strain-rate. Microstructure studies and previous information about the amount of cavities suggest that the deformation process occurs by a superplastic grain boundary sliding mechanism.357-359199204Nilsson, J.O., (1992) Mater. Sci. Tech., 8, pp. 685-700Maehara, Y., (1985) Trans. ISIJ, 25, pp. 69-76Maehara, Y., Ohmori, Y., (1987) Metall. Trans., 18 A, pp. 663-672Maehara, Y., (1987) Trans. ISIJ, 27, pp. 705-712Osada, K., Ueko, S., Ebato, K., (1987) Trans. ISIJ, 28, pp. 713-718Osada, K., Ueko, S., Tohge, T., Noda, M., Ebato, K., (1988) Trans. ISIJ, 28, pp. 16-22Tsuzaki, K., Matsuyama, H., Nagao, M., Maki, T., (1990) Mater. Trans. JIM, 31, pp. 983-994Khaleel, M.A., Johnson, K.I., Lavender, C.A., Smith, M.T., Hamilton, C.H., (1996) Scripta Materialia, 34, pp. 1417-1423Pulino-Sagradi, D., (1996) "Superplasticity of a Duplex Stainless Steel"(in Portuguese), , Ph.D. Thesis, UNICAMP, Campinas, BrazilBackofen, W.A., Turner, I.R., Avery, D.H., (1964) Trans. ASM, 57, pp. 981-990Pulino-Sagradi, D., Nazar, A.M.M., Amann, J.-J., Medrano, R.E., (1997) Acta Materialia, 45, pp. 4663-4666Sagradi, M., Pulino-Sagradi, D., Medrano, R.E., (1998) Acta Materialia, 46, pp. 3857-3862Hart, E.W., (1970) Acta Metallurgica, 18, pp. 599-61

Effect Of Small Amounts Of Elements On Shapes Of Potentiodynamic And Potentiostatic Curves Of Aisi 304l And Aisi 316l Stainless Steels In Chloride Media

Samples of high purity grade and commercial purity grade type AISI 304L and AISI 316L steels were studied by the potentiodynamic and potentiostatic techniques in a naturally aerated 3.5% NaCl aqueous solution at a controlled temperature of (23±2)°C. The anodic polarization curves of the potentiodynamic technique showed that not always is it possible to determine pitting potential: most of the curves of commercial purity grade steels displayed a smooth curvature in the region where the current density should increase sharply. The density current versus time potentiostatic curves also showed different shapes according to the purity grade steels: for the commercial purity grade steels, the current density showed large oscillations with time (related to unstable pits), whereas for the high purity grade steels, a regular behavior of current density as a function of time was found (related to stable pits).14210311