Avaliação da Técnica de Voltametria Linear para Determinação Quantitativa de Fase Sigma no Aço Inoxidável Duplex UNS S31803

Abstract

Este é um artigo publicado em acesso aberto (Open Access) sob a licença Creative Commons Attribution Non-Commercial, que permite uso, distribuição e reprodução em qualquer meio, sem restrições desde que sem fins comerciais e que o trabalho original seja corretamente citado. Linear Voltammetry Assessment to Quantitative Determination of the Sigma Phase in Duplex Stainless Steel UNS S31803Abstract: Precipitation of intermetallic phases in duplex stainless steels constitute a problem regarding the use of such materials in certain temperature ranges, in this way, are necessary methods to quantify, non-destructively, the presence of microstructural changes due to thermal contribution. In this work, electrochemical tests of linear voltammetry, tensile and Vickers hardness were performed in duplex stainless steel UNS S31803 for evaluation of the intermetallic sigma phase presence in the microstructure of the material. Samples of this steel were isothermally aged at 870 °C for times up to 3600 seconds to induce the precipitation of different grades of this phase. Linear voltametry tests were conducted in 5% KOH electrolyte solution in an electrochemical cell 3.3.10 -6 m 2 , with a reference electrode of the type Saturated Calomel and auxiliary electrode of platinum wire. The results of this technique showed sensitivity to detect sigma phase content greater than 1% in the material enabling its application as a Non-Destructive Testing (NDT).Key-words: Duplex steel; Deleterious phases; Sigma phase; Linear voltammetry. IntroduçãoOs aços inoxidáveis duplex foram estudados extensivamente ao longo dos anos por apresentarem boas características em relação à resistência mecânica e a corrosão. Estas características se devem a sua microestrutura balanceada de ferrita e austenita, onde a resistência mecânica se deve a boa correlação das propriedades individuais destas fases, e a resistência à corrosão ao cromo em sua estrutura, formando um filme passivador [1].No entanto, componentes fabricados a partir deste material que operem em determinadas faixas de temperatura ou que sejam submetidos a algum gradiente térmico durante a fabricação, tal como ocorre na conformação a quente ou durante o processo de soldagem, podem sofrer alterações metalúrgicas em sua microestrutura e, consequentemente, perda das propriedades originais [2][3][4]. Estas alterações metalúrgicas dizem respeito à precipitação de fases intermetálicas, como a fase sigma, que se presente, mesmo em pequenas quantidades, leva a efeitos deletérios em relação às propriedades

Evaluation of voltametric profiles for quantitative estimation of sigma phase (σ) content in duplex stainless steel UNS S31803: an ohmic and layers porous resistance models (LPRM) analysis

“…The KOH concentration used for this analysis confirm the suitable condition (pH 13.97), as already described by (HASKEL et al, 2015;HASKEL et al, 2019;DE SAMPAIO et al, 2020), for a selective interaction with the intermetallic phase.…”

“…Related to the precipitation of the σ phase, (MAGNABOSCO, 2009) reports three mechanisms have been described, which involve the decrease of Cr in the surrounding metallic matrix of this secondary phase: nucleation and growth from ferrite, eutectoid decomposition of ferrite, with formation of secondary austenite (γ 2 ), and growth from austenite This author by The Time -Temperature -Precipitation (TTP) diagram, for analysis of the σ phase in the UNS S31803 interval of 700-900°C, shows that, for 850°C, there is a higher precipitation kinetics of the σ phase with preferential nucleation in δ/γ interface and growth strongly linked to the consumption of δ. (HASKEL et al, 2015) analyzed the presence of deleterious phases in UNS S31803 steel by the linear scan voltammetry (LSV) technique and it was observed that with increases of the precipitate contents, the voltammograms showed changes for the current density peaks, 𝐽 𝑝 , allowing the determination of 0.9% of σ phase, a value below of the critical range which is between 1 and 2%.…”

A New methodology of Nondestructive Testing for Quantitative Evaluation of Sigma Phase in Duplex Stainless Steels

“…The decrease in charge density for samples 1 and 2 has already been discussed previously and refers to the rebalancing between the ferrite and austenite fractions in DSSs structure. 25 This behavior difference can be observed by the charge density profiles for the concentration of 0.3 and 2 mol /L alone as shown in Figure 9 b) and c). In this way, it was possible to consider that by employing higher concentrations such as 3 mol/L it could be detected very low deleterious phase contents (less than 1%) by means of charge density parameter, as is the case of sample 4 (0.9% of sigma phase).…”

“…The potential of the linear voltammetry technique for the detection of intermetallic phases in DSS UNS S31803 has already been analyzed in a previous work 25 and the best parameters of analysis were the peak current density and its corresponding charge density, the latter being possible to correlate directly with the mechanical properties.…”

DL‐EPR and AFM study of sensitization of a 17%Cr multiphase stainless steel

“…[15][16][17][18][19][20][21][22] Electrochemical techniques have been employed to analyze the sensitization process in many types of stainless steel. Among the most used electrochemistry techniques are linear sweep voltammetry [23][24][25][26] and the classical doubleloop electrochemical potentiodynamic reactivation (DL-EPR). [20][21][22][27][28][29][30][31][32] The degree of sensitization (DOS) obtained in this test is a measure of Cr-depleted areas.…”