Distinguishing between Chi and Sigma phases in duplex stainless steels using potentiostatic etching

Jackson, Eric M.; Visser, P.E.de; Cornish, L.A.

doi:10.1016/1044-5803(93)90061-y

Cited by 32 publications

(18 citation statements)

References 6 publications

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“…The morphology of r-phase often shows an allotriomorphic appearance due to its preferential growth along phase boundaries and towards ferrite grain interiors [57]. The surrounding regions are then depleted in Cr and Mo, resulting in the formation to secondary austenite [4,16,57]. The eutectoid secondary austenite can have a similar appearance to that of r-phase, as can be seen in Figs.…”

Section: Ebsd Microstructure Characterisationmentioning

confidence: 59%

“…The eutectoid reaction mainly takes place at d/c-interphase boundaries due to increased diffusion rates, leading to segregation of Cr and Mo resulting in r-phase formation [4,12,16,26,30,32,34]. The morphology of r-phase often shows an allotriomorphic appearance due to its preferential growth along phase boundaries and towards ferrite grain interiors [57]. The surrounding regions are then depleted in Cr and Mo, resulting in the formation to secondary austenite [4,16,57].…”

Section: Ebsd Microstructure Characterisationmentioning

confidence: 99%

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Correlative EBSD and SKPFM characterisation of microstructure development to assist determination of corrosion propensity in grade 2205 duplex stainless steel

Örnek

Engelberg

2015

J Mater Sci

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Correlative electron backscatter diffraction (EBSD) and scanning Kelvin probe force microscopy (SKPFM) analysis has been carried out to characterise microstructure development and associated corrosion behaviour of as-received and 750°C heat-treated grade 2205 duplex stainless steel. High-resolution EBSD analysis revealed the presence of r-and v-phase, secondary austenite, Cr 2 N, and CrN after ageing treatment. SKPFM Volta potential measurements confirmed the formation of discrete reactive sites, indicating local corrosion propensity in the microstructure. Cr 2 N, r-phase, and inter-granular v-phase had the largest net cathodic activity, followed by CrN and intra-granular v-phase showing medium electrochemical activity, with ferrite and austenite (including secondary austenite) showing net anodic activity. Corrosion screening confirmed selective corrosion of ferrite in the as-received and 750°C-aged conditions with the corrosion propensity of secondary phases staying in-line with SKPFM observations. Stress corrosion micro-cracks were also observed and are discussed in light of microstructure corrosion propensity.

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Section: Ebsd Microstructure Characterisationmentioning

confidence: 59%

Section: Ebsd Microstructure Characterisationmentioning

confidence: 99%

Correlative EBSD and SKPFM characterisation of microstructure development to assist determination of corrosion propensity in grade 2205 duplex stainless steel

Örnek

Engelberg

2015

J Mater Sci

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“…Foi então realizado ataque eletrolítico com solução de NaOH 40%, com 0,2 V por 300 segundos com objetivo de se obter uma melhor diferenciação entre as fases secundárias formadas. É interessante mencionar que este ataque foi desenvolvido a partir do princípio de ataque eletrolítico e tem como importante característica a capacidade de distinguir, por microscopia ótica em campo claro, fases deletérias como sigma e chi, além das fases principais ferrita e austenita [5]. Assim, este tipo de ataque seletivo se caracteriza como uma importante ferramenta para identificação de diferentes fases num mesmo material, pois possibilita que cada fase se revele com uma coloração diferente e distinta das outras fases componentes.…”

Section: Preparação Metalográfica E Análise Microestruturalunclassified

“…Nas amostras tratadas termicamente, além da ferrita e austenita características, também se pode observar uma fase de tonalidade marrom, sendo esta provavelmente a fase sigma (). Estas observações estão de acordo com os resultados obtidos por JACKSON et al [5] para o ataque seletivo das fases em questão. Pela observação destas mesmas amostras no MEV (figura 2) e pela análise de EDS (tabela 2) dos pontos em que se detecta a fase de coloração marrom no ótico e coloração mais escura no MEV, nota-se a elevada concentração de cromo e ferro dessa fase.…”

Section: Micrografiasunclassified

Caracterização De Um Aço Lean Duplex Por Técnicas Analíticas

Santos¹,

Rocha²,

Pereira³

2018

ABM Proceedings

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ResumoNeste trabalho, amostras de aço Lean Duplex UNS S32304 foram submetidas à temperatura de 800°C em um forno acoplado a um difratômetro de raios-x durante intervalos de tempo de 30, 60 e 90 minutos. Com o objetivo de analisar em tempo real a transformação das fases constituintes, foram realizadas várias varreduras insitu durante os diferentes tempos de permanência em 800°C deste material. Assim, observou-se a formação da fase sigma neste aço, tanto nos contornos de grão da ferrita como nas interfaces ferrita/austenita. Os valores de fase sigma obtidos para cada tempo de exposição foram calculados através do método de Rietveld sobre cada difratograma obtido e variaram de 11% a 17%. Notou-se que a fase sigma exibiu crescimento contínuo até 60 minutos e variação após este período. Todavia, observou-se que a formação de fase sigma a 800°C ocorre de forma significativa neste material após 30 minutos de aquecimento, o que pode comprometer as propriedades do mesmo. Palavras-chave: Aço lean duplex; Difração de raios-x in-situ; Microestrutura; Fase sigma. LEAN DUPLEX STEEL CHARACTERIZATION BY ANALYTICAL METHODS AbstractIn this work, samples from a Lean Duplex Steel UNS S32304 were subjected to a temperature of 800°C for different intervals of time, being 30min, 60min and 90 min. All samples were allocated inside a small high temperature furnace attached to an xray diffractor. The goal of the work was to analyze the phase transformations occurring in those samples in real time. Formation of sigma phase was observed both in the ferrite grain boundaries as in the ferrite/austenite interface. The amount of sigma phase formed was measured by quantitative phase analysis using the Rietveld method and result values ranged from 11% to 17 % in volume. It was also noticed that the sigma phase exhibit a continuous growth up to 60 minutes, become stable for a few minutes to then grow again. In any case, it was observed that sigma phase formed significantly in the material after 30 minutes soaking, which can lead to a decrease in the material properties.

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“…Samples have been electrochemically etched at 0.5 V for 90 s at 40 • C in a sodium hydroxide solution (10 g NaOH in 100 mL H 2 O) This electrochemical etching highlights the microstructure of the investigated alloy, coloring differently the constituent phases. Compared to other etchants, this electrochemical etching does not completely dissolve the aluminum and the aluminum compounds [29,30]. Afterwards, following the standards ASTM E1245-13 and ASTM E1382-10 (ASTM International, West Conshohocken, PA, USA), the quantitative metallographic analysis has been performed.…”

Section: Methodsmentioning

confidence: 99%

Hot-Dip Aluminizing on AISI F55–UNS S32760 Super Duplex Stainless Steel Properties: Effect of Thermal Treatments

Ciuffini

Barella

Cecca

et al. 2017

Metals

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Abstract:The behavior of super duplex stainless steels AISI F55-UNS S32760 in hot-dip aluminizing process has been studied, investigating the influence of cold working and of different initial microstructures obtained through a preliminary thermal treatment. The microstructural features examined are the secondary austenite precipitation, the static recovery of ferrite and the thermal dissolution of austenite within ferritic matrix. The hot-dip aluminizing temperature has been optimized through sessile drop tests. The treatment has been performed at 1100 • C for 300 s, 900 s and 2700 s. A strong chemical interaction occurs, generating intermetallic compounds at the interface. Molten aluminum interacts exclusively with the ferritic phase due to its much higher diffusivity in this phase coupled with its marked ferrite-stabilizer behavior. Thus, the influence of cold working is not remarkable, since the strains are mainly allocated by austenitic phase. The diffusivity of aluminum increases due to lattice defects thermally generated and, mainly, to influence given by grain boundaries, multiplied by secondary austenite precipitation, which act as short-circuit diffusion paths. Ni and Cr contents in the ferritic matrix have an influence but not highly relevant. Then, the best starting condition of the super duplex stainless steel substrates, to obtain a thick interfacial layer, are the thermal annealing at 1080 • C for 360 s/mm after a solution thermal treatment at 1300 • C for 60 s/mm.

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Distinguishing between Chi and Sigma phases in duplex stainless steels using potentiostatic etching

Cited by 32 publications

References 6 publications

Correlative EBSD and SKPFM characterisation of microstructure development to assist determination of corrosion propensity in grade 2205 duplex stainless steel

Correlative EBSD and SKPFM characterisation of microstructure development to assist determination of corrosion propensity in grade 2205 duplex stainless steel

Caracterização De Um Aço Lean Duplex Por Técnicas Analíticas

Hot-Dip Aluminizing on AISI F55–UNS S32760 Super Duplex Stainless Steel Properties: Effect of Thermal Treatments

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