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<p>The electrochemical behaviour of ASTM A890 grade 6A cast superduplex stainless steel aged at 475&#xa0;°C was investigated using cyclic polarisation, chronoamperometry, electrochemical impedance spectroscopy, galvanic corrosion tests, and Mott-Schottky analysis in a NaCl aqueous solution with 60&#xa0;g/kg salinity. Exposure to 475&#xa0;°C induces spinodal decomposition in the ferritic phase, resulting in the formation of chromium-enriched (α′) and iron-enriched (α) regions, which progressively affect the alloy’s properties. A substantial increase in ferrite hardness (from 333 to 482 HV) occurred within the first 2&#xa0;h of ageing, while electrochemical degradation became significant only after 100&#xa0;h. Galvanic tests showed a rise in galvanic current density to − 68&#xa0;nA·cm<sup>−2</sup> for specimens aged for 100&#xa0;h, evidencing enhanced galvanic susceptibility. Overall, the results demonstrate that early ageing enhances mechanical strength without impairing corrosion resistance, whereas prolonged exposure promotes localised electrochemical heterogeneity that accelerates passive film breakdown. These findings clarify the ageing-dependent evolution of passivity and galvanic interactions in 6A superduplex stainless steel under highly saline conditions.</p>

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Electrochemical Characterisation of 6a Superduplex Stainless Steel After Thermal Ageing at 475 °C

  • 期刊论文

  • 发表日期：

    2025年12月19日

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  • H. M. L. F. de Lima,
  • W. S. Araújo,
  • I. N. Bastos

摘要

The electrochemical behaviour of ASTM A890 grade 6A cast superduplex stainless steel aged at 475 °C was investigated using cyclic polarisation, chronoamperometry, electrochemical impedance spectroscopy, galvanic corrosion tests, and Mott-Schottky analysis in a NaCl aqueous solution with 60 g/kg salinity. Exposure to 475 °C induces spinodal decomposition in the ferritic phase, resulting in the formation of chromium-enriched (α′) and iron-enriched (α) regions, which progressively affect the alloy’s properties. A substantial increase in ferrite hardness (from 333 to 482 HV) occurred within the first 2 h of ageing, while electrochemical degradation became significant only after 100 h. Galvanic tests showed a rise in galvanic current density to − 68 nA·cm−2 for specimens aged for 100 h, evidencing enhanced galvanic susceptibility. Overall, the results demonstrate that early ageing enhances mechanical strength without impairing corrosion resistance, whereas prolonged exposure promotes localised electrochemical heterogeneity that accelerates passive film breakdown. These findings clarify the ageing-dependent evolution of passivity and galvanic interactions in 6A superduplex stainless steel under highly saline conditions.