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Previous issue date: 2014-08-05 / This work aimed to evaluate the influence caused by Nb single addition and by Nb-Ti and Nb-Zr combined addition in the high temperature mechanical properties of a centrifugally cast HP alloy. Particular investigation was carried out on creep and hot tensile properties in the temperature range between 900 to 1100 oC. Seamless tubes were casted by horizontal centrifugal process with the following nominal composition 0.50C-25Cr-35Ni, 0.50C-25Cr-35Ni-1Nb, 0.50C- 25Cr-35Ni-1Nb-0.1Ti e 0.50C-25Cr-35Ni-1Nb-0.1Zr. These 04 alloys were evaluated using the following techniques differential scanning calorimetry (DSC), optical and electron microscopy, energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The mechanical characterization was performed by elevated temperature tension tests with 3 different strain rates and constant load creep rupture test in the stress range of 65 to 15 MPa and comprising rupture times between 10 to 2000 hours, with or without extensometer using. The results were interpreted using classical methodologies (Norton, Arrhenius, Monkman-Grant, Larson-Miller, and others). The results shown that these elements addition did not change significantly the macrostructure, but they played an important role on formation, fragmentation, size, quantity, distribution, coarsening and coalescence on the carbides in the microstructure. Additions also refined the dendritic arm space. These microstructural changes led to a different mechanical behavior in each alloy. In the elevated temperature tension tests the Nb addition led to the highest values for mechanical resistance. On the other hand, Nb-Ti and Nb-Zr addition presented the highest time to rupture in creep tests, but in opposite conditions of temperature and stress. / Nesta tese buscou-se avaliar a influencia da adicao do elemento Nb e da adicao conjunta dos elementos Nb-Ti, e Nb-Zr nas propriedades mecanicas a quente da liga HP fundida por centrifugacao. Em especial se investigou a influencia desses elementos nas propriedades de fluencia e tracao a quente, no intervalo de temperatura entre 900 e 1100 oC. Tubos sem costura foram fundidos pelo processo de centrifugacao horizontal com a composicao nominal 0.50C-25Cr-35Ni, 0.50C-25Cr-35Ni-1Nb, 0.50C-25Cr-35Ni-1Nb-0.1Ti e 0.50C- 25Cr-35Ni-1Nb-0.1Zr. Essas 04 ligas foram avaliadas atraves das tecnicas de calorimetria exploratoria de varredura (DSC), microscopia optica e eletronica de varredura, espectroscopia de raios x por dispersao de energia (EDS) e difracao de raios x (DRX). A caracterizacao mecanica foi realizada atraves de ensaios de tracao a quente realizados em 03 taxas de deformacao diferentes, e de ensaios de fluencia do tipo carga constante, com e sem extensometria, no intervalo de tensoes entre 65 e 15 MPa, compreendendo tempos de ruptura entre 10 e 2000 horas. Os dados foram analisados atraves das metodologias classicas (Norton, Arrhenius, Monkman-Grant, Larson-Miller, entre outras). Os resultados indicam que as adicoes destes elementos modificantes nao alteraram significantemente a macroestrutura, porem influenciaram a formacao, fragmentacao, tamanho, quantidade, distribuicao, espessamento e coalescencia dos carbonetos presentes na microestrutura, e refino do braco dendritico da matriz. Essas alteracoes microestruturais conferiram a cada liga diferentes comportamentos mecanicos onde, a adicao de Nb resultou nos maiores incrementos das propriedades de resistencia de tracao a quente. Ja a adicao de Nb-Ti e Nb-Zr originou os maiores tempos de ruptura em fluencia, porem em diferentes regimes de tensao e temperatura.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufscar.br:ufscar/736 |
| Date | 05 August 2014 |
| Creators | Andrade, Antonio Rafael de |
| Contributors | Bolfarini, Claudemiro |
| Publisher | Universidade Federal de São Carlos, Programa de Pós-graduação em Ciência e Engenharia de Materiais, UFSCar, BR |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Format | application/pdf |
| Source | reponame:Repositório Institucional da UFSCAR, instname:Universidade Federal de São Carlos, instacron:UFSCAR |
| Rights | info:eu-repo/semantics/openAccess |
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