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Doctoral Thesis
DOI
10.11606/T.88.2012.tde-14032012-122709
Document
Author
Full name
Frederico Augusto Pires Fernandes
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 2012
Supervisor
Committee
Casteletti, Luiz Carlos (President)
Bose Filho, Waldek Wladimir
Gallego, Juno
Ishikawa, Tomaz Toshimi
Kuri, Sebastião Elias
Title in Portuguese
Produção e caracterização de camadas nitretadas e nitrocementadas por plasma nos aços UNS S31603, S31254 e S41425
Keywords in Portuguese
Aços inoxidáveis
Corrosão
Desgaste
Fadiga
Nitretação
Nitrocementação
Plasma
Abstract in Portuguese
A produção de superfícies funcionais sobre componentes, para a obtenção de melhores resistências ao desgaste, à corrosão e à fadiga constitui-se num persistente desafio tecnológico. Os processos termoquímicos de nitretação e nitrocementação por plasma são técnicas de engenharia de superfície usadas para aumentar a dureza superficial e resistência ao desgaste de aços inoxidáveis, sem deteriorar suas resistências à corrosão. O presente trabalho teve como objetivo a avaliação da influência das temperaturas de nitretação e nitrocementação por plasma na estrutura das camadas produzidas nos aços inoxidáveis UNS S31603 (austenítico), S31254 (superaustenítico) e S41425 (supermartensítico) e seus desempenhos quanto ao desgaste, à corrosão e à fadiga. Verificou-se que os tratamentos produziram camadas homogêneas e contínuas, sendo mais espessas, para os aços UNS S31603 e S31254 nitrocementados, e para o aço UNS S41425 nitretado, em uma dada temperatura. As microdurezas das camadas cresceram com o aumento da temperatura, para ambos os tratamentos e para os três aços estudados. A difração de raios X indicou que as fases expandidas, fase-S ou α'N, foram obtidas nas temperaturas de tratamento mais baixas (400 e 450ºC). O aumento na temperatura de tratamento promoveu a formação de carbonetos e/ou nitretos, para a nitrocementação e nitretação, respectivamente. Para os aços UNS S31603 e S31254, isto ocorreu devido a decomposição da fase-S, em uma microestrutura tipicamente lamelar composta por ferrita e nitretos de cromo. Já no caso do aço UNS S41425, o aumento na temperatura de tratamento proporcionou um aumento na quantidade de carbonetos e/ou nitretos. Tal aumento na temperatura de tratamento também promoveu um decréscimo nas resistências ao desgaste das camadas dos aços UNS S31603 e S31254. A resistência ao desgaste aumentou com a temperatura de tratamento, para o aço UNS S41425, para ambos os tratamentos. A resistência à corrosão em solução de NaCl diminuiu com o aumento da temperatura de tratamento, para os três aços estudados, devido a presença dos carbonetos e/ou nitretos. Os ensaios de fadiga de contato indicaram que nos aços UNS S31603 e S31254 o aumento na temperatura de tratamento não causou mudanças significativas nas tensões de ruptura das camadas. No aço UNS S41425, tal tensão diminuiu com o aumento da temperatura.
Title in English
Production and characterization of plasma nitrided and nitrocarburized layers on UNS S31603, S31254 and S41425 steels
Keywords in English
Corrosion
Fatigue
Nitriding
Nitrocarburizing
Plasma
Stainless steels
Wear
Abstract in English
The production of functional surfaces on engineering components, in order to obtain improved wear, corrosion and fatigue resistance is a persistent technological challenge. The plasma nitriding and nitrocarburizing thermochemical processes are surface engineering techniques used to improve surface hardness and wear resistance of stainless steels, without compromising its corrosion resistance. The main goal of this study is to evaluate the influence of plasma nitriding and nitrocarburizing temperature on the structure of the layers produced on UNS S31603 (austenitic), S31254 (superaustenitic) and S41425 (supermartensitic) stainless steels and in addition their wear, corrosion and fatigue performance. It was found that both treatments produced homogeneous and continuous layers. Of all the samples in this work, the nitrocarburized UNS S31603 and S31254 steels and the nitrided UNS S41425 steel presented the thickest layers at a given temperature. Regardless of the treatment used, the microhardness of the layers increased with the raising of the temperature for all the samples. The X-ray diffraction indicated that expanded phases, either S-phase or α'N, were obtained at lower treatment temperatures (400 and 450°C). The increase in treatment temperature promoted the formation of carbides and/or nitrides for nitrocarburizing and nitriding, respectively. For the samples of UNS S31603 and S31254 steels, this occurred due to the decomposition of S-phase in a typical lamellar microstructure consisting of ferrite and chromium nitride. In the case of UNS S41425 steel, the increase in treatment temperature caused an increase on the amount of carbides and/or nitrides. This increase in treatment temperature also promoted a decrease of the wear resistance for the layers produced on the UNS S31603 and S31254 steels samples. On the other hand, the wear resistance increased with treatment temperature for the UNS S41425 steel for both treatments. The corrosion resistance in NaCl solution decreased with increasing treatment temperature for all the samples, due to the presence of carbides and/or nitrides. The contact fatigue tests on UNS S31603 and S31254 steels indicated that an increase on treatment temperature did not cause significant changes on rupture stress of the layers. In UNS S41425 steel, such critical stress decreased with increasing temperature.
 
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Publishing Date
2012-08-03
 
WARNING: The material described below relates to works resulting from this thesis or dissertation. The contents of these works are the author's responsibility.
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  • FERNANDES, F.A.P., et al. Decomposition of expanded austenite in AISI 316L stainless steel nitrided at 723K [doi:10.1179/1749514812Z.00000000025]. International Heat Treatment and Surface Engineering [online], 2012, vol. 6, p. 103-106.
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  • FERNANDES, F.A.P., et al. Plasma nitriding and nitrocarburising of a supermartensitic stainless steel [doi:10.1179/1749514811Z.0000000008]. International Heat Treatment & Surface Engineering [online], 2012, vol. 6, n. 1, p. 24-27.
  • FERNANDES, F.A.P., et al. Stainless steel property improvement by ion nitriding and nitrocarburizing. Heat Treating Progress [online], 2008, vol. 8, p. 41-43. [cited 2012-07-06]. Available from : <http://hts.asminternational.org/portal/site/hts/AsmStore/ProductDetails/?vgnextoid=c98858a20cb5b110VgnVCM100000701e010aRCRD>
  • FERNANDES, F.A.P., et al. Wear of plasma nitrided and nitrocarburized AISI 316L austenitic stainless steel. Journal of Achievements in Materials and Manufacturing Engineering [online], 2012, vol. 40, p. 175-179. [cited 2012-07-06]. Available from : <http://www.journalamme.org/papers_vol40_2/4029.pdf>
  • TOTTEN, G.E., et al. Microstructural Characterization of Layers Produced by Plasma Nitriding on Austenitic and Superaustenitic Stainless Steel Grades [doi:10.1520/JAI103564]. Journal of ASTM International [online], 2012, vol. 9, n. 2, p. 103564.
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