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Previous issue date: 2016-04-29 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / Os a?os inoxid?veis duplex s?o a?os altamente ligados caracterizados por uma estrutura bif?sica de ferrita-austenita obtida atrav?s de processos de conforma??o a quente ou tratamentos t?rmicos adequados ap?s os processos de conforma??o a frio. A presen?a de fra??es volum?tricas pr?ximas de ferrita e austenita na estrutura dos a?os duplex promove uma boa combina??o entre as propriedades de resist?ncia mec?nica e resist?ncia a corros?o. Uma das classes dos a?os duplex que vem se desenvolvendo nos ?ltimos anos ? o Lean duplex, que apresentam teores mais baixos de Cr, Ni e Mo, o que os torna mais baratos em compara??o com os austen?ticos. Para compensar a redu??o de Ni e Mo, elementos como Mn e N s?o adicionados em maior quantidade para proporcionar uma boa resist?ncia ? corros?o e conferir a estabilidade da austenita no a?o. Nos ?ltimos anos o n?mero de trabalhos relacionados ao a?o Lean duplex cresceu bastante devido ao interesse em se conhecer, desenvolver e aplicar cada vez mais essa classe de a?os. Uma das aplica??es que est? em alta ? a soldagem por difus?o no estado superpl?stico, e os a?os inox duplex possuem o comportamento superpl?stico, que exige microestruturas com gr?os pequenos e baixas taxas de deforma??o. Sendo assim, um estudo de recristaliza??o do a?o inoxid?vel Lean duplex 2101 como m?todo de refino de gr?o ? proposto para este trabalho. Diferentes lamina??es a frio, sendo elas 70, 80 e 90% de redu??o, foram empregadas no material para fornecer potencial termodin?mico para a recristaliza??o nos tratamentos t?rmicos em tr?s temperaturas, 900?C, 1000?C e 1100?C por tempos de 20 minutos, 1 e 2 horas. T?cnicas de microscopia ?ptica, eletr?nica de varredura, EDS, medidas magn?ticas, difra??o de raios-X, EBSD e microdureza foram empregadas para a caracteriza??o. Os resultados de medidas magn?ticas e microscopia ?tica indicam que h? acentuada ocorr?ncia de transforma??o induzida por deforma??o da austenita para martensita CCC, al?m de ind?cios da ocorr?ncia de outros mecanismos de deforma??o como macla??o mec?nica e deslizamento de discord?ncias, bem como ind?cios de zonas de austenita n?o transformada, aparentemente isenta de encruamento, conforme indicado pelos valores de microdureza, mesmo para redu??es de 90% na lamina??o a frio; aparentemente houve precipita??es de fases indesejadas tanto na ferrita quanto na austenita durante os tratamentos t?rmicos e aparente recristaliza??o total das amostras laminadas p?s tratamento t?rmico mesmo para os tempos mais curtos. Nas amostras analisadas por EBSD foram observados ind?cios de refino do gr?o austen?tico e uma tend?ncia de crescimento secund?rio da ferrita. Nas amostras recristalizadas identificou-se que para temperaturas e tempos de tratamento mais baixo as fra??es de ferrita se mostraram levemente maiores, enquanto que para temperaturas e tempos de tratamentos maiores as fra??es de austenita foram maiores. / Duplex Stainless Steel are an alloy based on Fe-Cr-Ni system characterized by biphasic structure of austenite-ferrite obtained through different thermomechanical cycles and they show good combination between mechanical (high tension strength and good tenacity) and corrosion resistance properties (stress corrosion cracking and pitting corrosion), besides good soldability. One of the Duplex Stainless Steel grades that is being developed in the last years is the Lean Duplex (LDSS) which have low addition of Cr, Ni, Mo and, for this, they are cheaper than austenitic and standard duplex stainless steel. To compensate the reduction of Ni and Mo, elements like Mn and N are added in larger quantities to give good corrosion resistance and ensure the stability of austenite. A possibility for application for LDSS is the manufacturing of components that are subjected corrosion conditions lesser severe for petrochemical industries, manufactured by diffusion bonding, taking advantage of superplastic behavior that these steels have since refined grains structure is present and low deformation rate are applied. Therefore, in this work was made a study of recrystallization of LDSS 2101, previously work hardened, as a method to refine grain. The material was subjected to different reduction degree by cold rolling (70, 80 and 90%), different heat treatments of recrystallization annealing in three temperatures (900, 1000 and 1100?C) and different times (20 min, 1 and 2 hours). The techniques of optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy, magnetic saturation measures, X-ray diffraction, Electron Backscattered Diffraction (EBSD) and Vickers micro hardness were employed in the microstructure characterization. The results of magnetic measures and optical microscopy show a sharp occurrence of strain induced martensite BCC (??) on austenite, besides evidences of occurrence of other deformations mechanisms such as deformation twins and dislocation glide, as well evidences of non-transformed austenite without work hardening, according to the hardness values, even for 90% reduction. Evidences of deleterious phases precipitation, as seen in SEM, were not confirmed by X-ray diffraction, which confirms the system thermodynamic simulation, which indicates phase precipitation such as ? and nitrides in temperature smaller than those used in this work. Preliminary analysis of EBSD samples indicates that recrystallization were not complete for 900?C and 20 minutes, as well a refined austenite grain structure and a trend for secondary recrystallization for ferrite. Optical microscopy also shows a trend to increase austenite over ferrite when temperature and time of recrystallization increased.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/21472 |
| Date | 29 April 2016 |
| Creators | Freitas Neto, Ramiro Gomes de |
| Contributors | 94086591634, Buschinelli, Augusto Jos? de Almeida, 30399564853, Castro, Nicolau Apoena, 27783773877, Hupalo, M?rcio Ferreira, 03274154792, Silva, Wanderson Santana da |
| Publisher | PROGRAMA DE P?S-GRADUA??O EM CI?NCIA E ENGENHARIA DE MATERIAIS, UFRN, Brasil |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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