Sigma Phase Formation and Polarization Response of UNS S31803 in Sulfuric Acid

Magnabosco, Rodrigo; Alonso-Falleiros, Neusa

doi:10.5006/1.3278215

Cited by 19 publications

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“…However, at 850°C, some authors 9,10 found that σ phase may form by different mechanisms depending on aging time. So, at 850°C, for aging times up to 10 min, σ phase may form from direct precipitation from ferrite phase, resulting in Cr and Mo depleted α, also denominated secondary ferrite (α 2 ) phase (α→σ+α 2 ).…”

Section: Results Presented By Borba and Magnaboscomentioning

confidence: 99%

Influence of the microstructure on the degree of sensitization of a duplex stainless steel UNS S31803 aged at 650ºC

Melo¹,

Magnabosco²,

Neto³

2013

Mat. Res.

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This work evaluates the phase transformations during aging of an UNS S31803 DSS at 650°C and its influence on the DOS. The material was solution treated at 1175°C and then aged at 650°C for times up to 360 h. SEM-BSC images indicate the formation of Cr 2 N, σ and χ phases in the samples aged at 650°C. The analysis of DL-EPR curves, obtained in a 1 M H 2 SO 4 + 0.25 M NaCl + 0.01 M KSCN solution, shows an increase in DOS values for samples aged at 650°C. Probably, this increase observed in DOS values is mainly related to the presence of Cr-and/or Mo-depleted α, as a result of σ phase, χ phase and/or Cr 2 N formation at 650°C. Moreover, a possible healing up of Cr-and/ or Mo-depleted areas is observed between 1 h and 4 h of aging at 650°C.

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Section: Results Presented By Borba and Magnaboscomentioning

confidence: 99%

Influence of the microstructure on the degree of sensitization of a duplex stainless steel UNS S31803 aged at 650ºC

Melo¹,

Magnabosco²,

Neto³

2013

Mat. Res.

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“…UNS S31803, which presents typical chemical composition Fe-22% Cr-5% Ni-3% Mo-0,15% N-0,02% C [2] , has a microstructure of 40-45% of ferrite and 55-60% austenite, obtained after solution heat treatment at temperatures between 1000 and 1200 °C, followed by water quenching 6 . However, during heating between 700 and 900 °C precipitation of a hard and brittle Cr-rich phase, called sigma, can occur, resulting in brittleness and reduction in corrosion resistance [6][7][8][9][10][11][12][13][14] . There are strong indications that sigma phase formed at 900 °C present isolated particles morphology, precipitated from ferrite; however, between 700 and 800 °C eutectoid decomposition of ferrite is observed, resulting in a lamellar morphology of sigma phase and secondary austenite, impoverished in Cr and Mo if compared to the original austenite present in the duplex structure 15 .…”

Section: Introductionmentioning

confidence: 99%

Kinetics of sigma phase formation in a Duplex Stainless Steel

Magnabosco¹

2009

Mat. Res.

187

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This work determines the kinetics of sigma phase formation in UNS S31803 Duplex Stainless Steel (DSS), describing the phase transformations that occur in isothermal aging between 700 and 900 °C for time periods up to 1032 hours, allowing the determination of the Time-Temperature-Precipitation (TTP) diagram for sigma phase and proposing a model to predict the kinetics of sigma phase formation using a Johnson-Mehl-Avrami (JMA) type expression. The higher kinetics of sigma phase formation occurs at 850 °C. However, isothermal aging between 700 and 900 °C for time periods up to 1032 hours are not sufficient to the establishment of thermodynamic equilibrium. Activation energy for both nucleation and growth of sigma phase is determined (185 kJ.mol -1 ) and its value is equivalent to the activation energy for Cr diffusion in ferrite, indicating that diffusion of Cr is probably the major thermally activated process involved in sigma phase formation. The determined JMA type expression presents good fit with experimental data between 700 and 850 °C.

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“…Os mecanismos de formação de fase sigma em aço inoxidável dúplex UNS S31803 são explorados em alguns trabalhos, (1)(2)(3)(4) onde se constata, de forma geral, que em até 0,1 horas de envelhecimento entre 700°C e 900°C a fase sigma se forma em interfaces ferrita/ferrita ou ferrita/austenita, por meio da transformação da ferrita presente por decomposição eutetóide, gerando também austenita secundária. A partir de 0,1 horas de envelhecimento, as frações volumétricas de ferrita e de austenita decrescem, indicando que o crescimento da http://dx.doi.org/10.4322/tmm.2012.027…”

Section: Introductionunclassified

Influência Do Trabalho a Frio Na Formação De Fase Sigma Em Aço Inoxidável Dúplex

Magnabosco¹,

Ávila²,

Rabechini³

2012

TMM

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ResumoA formação de fase sigma em aços inoxidáveis dúplex durante envelhecimento isotérmico é extensamente relatada na literatura, mas a influência de encruamento prévio ao envelhecimento na cinética de formação dessa fase não foi alvo de estudos sistemáticos até então. Deste modo, o objetivo deste trabalho é estudar a influência do grau de encruamento e do tempo de envelhecimento a 650°C e 850°C, na microestrutura do aço UNS S31803. Foi realizado encruamento em laminador de planos, obtendo-se quatro séries de amostras, com 0%, 10%, 30% e 80% de redução de área transversal. A seguir, conduziu-se envelhecimento isotérmico a 650°C ou 850°C por tempos variando de 10 minutos a 96 horas, seguido de resfriamento em água. Para a quantificação de fase sigma foi utilizado ataque eletrolítico seletivo com solução 10% KOH, e a fração volumétrica de ferrita foi obtida com o auxílio de ferritoscópio. Observa-se que o aumento do encruamento aumenta a possibilidade de nucleação heterogênea de fase sigma no interior dos grãos de ferrita, o que leva a aumento da taxa de formação de sigma e de consumo de ferrita com o aumento do tempo de envelhecimento nas duas temperaturas estudadas. Palavras-chave: Fase sigma; Aço inoxidável dúplex; Cinética de formação. INFLUENCE OF COLD WORK ON SIGMA PHASE FORMATION IN DUPLEX STAINLESS STEEL AbstractThe formation of sigma phase in duplex stainless steels during isothermal aging is widely reported in the literature, but the influence of strain hardening prior to aging on the kinetics of formation of this phase was not a subject of systematic studies so far. The objective of this paper is to study the influence of cold work degree and aging time in aging at 650°C or 850°C of an UNS S31803 steel. Cold rolling was conducted, resulting in four sets of samples with 0%, 10%, 30% or 80% cross sectional area reduction. Those samples were submitted to isothermal aging between 10 minutes and 96 hours, followed by water quenching. Sigma phase quantification is possible after selective electrolytic etching with 10% KOH solution, and the volume fraction of ferrite is obtained with the aid of ferritscope. It is observed that increasing the strain hardening increases the possibility of heterogeneous nucleation of sigma phase within the ferrite grains, leading to increased rate of formation of sigma and consumption of ferrite with increasing aging time at both temperatures studied. Key words: Sigma phase; Duplex stainless steel; Transformation kinetics. INTRODUÇÃOOs mecanismos de formação de fase sigma em aço inoxidável dúplex UNS S31803 são explorados em alguns trabalhos, (1)(2)(3)(4) onde se constata, de forma geral, que em até 0,1 horas de envelhecimento entre 700°C e 900°C a fase sigma se forma em interfaces ferrita/ferrita ou ferrita/austenita, por meio da transformação da ferrita presente por decomposição eutetóide, gerando também austenita secundária. A partir de 0,1 horas de envelhecimento, as frações volumétricas de ferrita e de austenita decrescem, indicando que o crescimento da http://dx

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Sigma Phase Formation and Polarization Response of UNS S31803 in Sulfuric Acid

Cited by 19 publications

References 0 publications

Influence of the microstructure on the degree of sensitization of a duplex stainless steel UNS S31803 aged at 650ºC

Influence of the microstructure on the degree of sensitization of a duplex stainless steel UNS S31803 aged at 650ºC

Kinetics of sigma phase formation in a Duplex Stainless Steel

Influência Do Trabalho a Frio Na Formação De Fase Sigma Em Aço Inoxidável Dúplex

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