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Master's Dissertation
DOI
10.11606/D.88.2016.tde-16092016-111802
Document
Author
Full name
Solange de Souza
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 1997
Supervisor
Committee
Rollo, João Manuel Domingos de Almeida (President)
Rocha Filho, Romeu Cardozo
Sichieri, Eduvaldo Paulo
Title in Portuguese
Aparências metalográficas e corrosão seletiva de fases de aços inoxidáveis fundidos austenítico e martensítico atacados potenciostaticamente
Keywords in Portuguese
Aços inoxidáveis fundidos
Aparência metalográfica
Ataque potenciostático
Corrosão seletiva de fases
Curva de polarização
Abstract in Portuguese
A corrosão seletiva de fases de dois tipos de aços inoxidáveis fundidos foi analisada, ao serem submetidos a vários valores constantes de potencial, a partir da região catódica para a anódica da curva de polarização. Os aços estudados foram: austenítico (ACI CF-3M) solubilizado e martensítico (ACI CA-6NM) normalizado e revenido. As curvas de polarização foram traçadas potenciodinamicamente, a uma velocidade de varredura de 0,16 m.V.s-1 em solução aerada contendo H2SO4 1M e NaCl 1M, pH 0,35, à temperatura ambiente. Vários valores de potencial foram selecionados, previamente localizados nas regiões catódica, ativa, passiva e transpassiva da curva de polarização. Potenciostaticamente, foram atingidos os valores de potencial selecionados, sendo eles mantidos fixos por 1800 s. Após o ataque potenciostático, as aparências metalográficas dos aços foram verificadas, desde a região catódica até a anódica. Por microssonda eletrônica, foram quantificados os elementos químicos presentes nas fases dos aços. Para melhor avaliar o início de propagação de pite, foi determinada a porcentagem de íons liberados para o eletrólito, após a imposição de valores de potencial críticos de pite predeterminados pelas curvas de polarização, pelas aparências metalográficas e pelas curvas de densidade de corrente em função do tempo.
Title in English
Metallographic appearances and selective corrosion of phases of austenitic and martensitic cast stainless steels potentiostatically etched
Keywords in English
Cast stainless steels
Metallography
Polarization curves
Potentiostatic etching
Selective corrosion of phases
Abstract in English
The selective corrosion of phases present in two types of cast stainless steels was analyzed, when submitled to several constant values of potential, starting from the cathodic to the anodic regions of the polarization curve. The cast stainless steels were: austenitic (ACI CF-3M) solubilized and martensitic (ACI CA-6NM) normalized and tempered. The polarization curves were obtained at a scanning rate of 0.16 mV.s-1 in 1M H2S04 and 1M NaCI solution, pH 0.35 and at room temperature. Several potential values were selected, previously located in the cathodic, active, passive and transpassive regions of the polarization curve. The values of the selected potential were maintained fixed for 1800 s. After the potentiostatic etching, the metallographic appearances of the steels were verified, from the cathodic to the anodic region. Through electronic microprobe analysis, the present chemical elements were quantified in the phases of the steels. For betler evaluating the beginning of pitling propagation in the studied steels, liberated ion percentage for the solution was determined, after the imposition of critic pitting potential values predetermined from the polarization curves, through the metallographic appearances obtained after potentiostatic etching of the samples and the current density curves as a function of time.
 
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Publishing Date
2016-09-16
 
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