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Doctoral Thesis
DOI
10.11606/T.3.2008.tde-13052009-084348
Document
Author
Full name
Claudia Regina Serantoni
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2008
Supervisor
Committee
Goldenstein, Hélio (President)
Albertin, Eduardo
Boccalini Júnior, Mário
Caram Junior, Rubens
Martorano, Marcelo de Aquino
Title in Portuguese
Nucleação e crescimento do eutético austenita/VC em ligas do sistema Fe-V-C.
Keywords in Portuguese
Engenharia metalúrgica
Materiais
Abstract in Portuguese
As três famílias de ligas de maior importância comercial para a indústria de fundição apresentam a formação de eutéticos do tipo facetado/não-facetado durante a solidificação: os ferros fundidos com grafita (eutético austenita/grafita), os ferros fundidos brancos (eutético austenita/carboneto) e as ligas Al-Si (eutético alfa/silício). No caso dos ferros fundidos brancos, a morfologia dos carbonetos eutéticos exerce influência decisiva sobre o comportamento mecânico e a resistência à degradação (em função de solicitações como abrasão ou ciclos térmicos e/ou mecânicos) das ligas resistentes a desgaste pertencentes ao sistema Fe-C-X (em que X representa um ou mais dos elementos Cr, V, Mo, W e, mais raramente, Nb). Investigou-se o efeito do potencial nucleante do banho metálico sobre o eutético de ligas do sistema Fe-C-V, e conseqüentemente sobre a morfologia do carboneto. As alterações de morfologia do eutético austentita/carboneto VC em função da adição de alumínio ou titânio foram avaliadas por meio de microscopias óptica e eletrônica de varredura. Observou-se que a adição de alumínio ou titânio, em ligas com teores residuais de oxigênio ou nitrogênio, promoveu alteração do eutético VC de irregular para fibroso (no caso da adição de alumínio) e para divorciado (no caso da adição de titânio). Conclui-se que a presença de partículas nucleantes induziu a nucleação seletiva da fase facetada (carboneto VC) a temperaturas mais elevadas, diminuindo o grau de cooperação durante o crescimento do eutético.
Title in English
Nucleation and growth of austenite/VC eutectic in alloys of the Fe-V-C system.
Keywords in English
Carbides morphology
Eutectic
Nucleation
Abstract in English
The three most commercially important families of alloys for the foundry industry show the formation of faceted/non-faceted eutectics type during solidification: cast irons with graphite (austenite/graphite eutectic), white cast irons (austenite/carbide eutectic) and Al-Si alloys (alfa/silicon eutectic). In the case of white cast irons, the eutectic carbide morphology has decisive influence on mechanical behavior and on degradation resistance (due to solicitation such as abrasion or thermal and/or mechanical cycling) of wearing resistant alloys of the Fe-C-X system (where X stands for one or more of the following elements: Cr, V, Mo, W and, seldom, Nb). The metallic bath nucleant potential on the eutectic of the Fe-C-V system and, thus, on the carbide morphology, were investigated. It was evaluated the nucleant potential for aluminum and titanium addition to the bath. The morphologies changes for the austenite/carbide eutectic were evaluated by optical and scanning electronic microscopy. It was observed that aluminum or titanium addition in alloys with residual content of oxygen or nitrogen promoted VC eutectic morphology change from irregular to fibrous (when aluminum is added) and to divorced (when titanium is added). It is concluded that the presence of nucleant agents in the metallic bath induced the preferred nucleation of the faceted phase at higher temperatures, decreasing the cooperation during the eutectic growth.
 
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Publishing Date
2009-07-06
 
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