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<p>In duplex stainless steels (DSSs), phase separation of iron and chromium is a well-known phenomenon causing low-temperature embrittlement, which greatly limits the lifetime of components in service conditions at temperatures above 250&#xa0;°C–300&#xa0;°C. Hence, means of mitigating the underlying phase separation causing this embrittlement is highly interesting to extend the service life of DSSs in certain applications. In this work, we investigate the effect of intermediate heat treatments (5&#xa0;minutes annealing at temperatures between 700&#xa0;°C and 900&#xa0;°C), performed after the conventional solution treatment, on the kinetics of phase separation super duplex stainless steel 2507. Using <i>in situ</i> small-angle neutron scattering at accelerated aging conditions (<i>i.e.</i>, aging at 475&#xa0;°C), we show that the application of intermediate heat treatments, which change the “initial state” of the material, can slow down development of the concentration fluctuation amplitude by up to 65 pct during aging inside the miscibility gap. This indicates great potential to delay the embrittlement process of duplex stainless steel. All intermediate heat treatments, conducted prior to aging, change the phase separation kinetics but to different extent. The 800&#xa0;°C intermediate heat treatment shows the largest reduction in phase separation kinetics as compared to the reference sample. This sample also correspondingly shows the lowest hardness increase after aging. These findings show that intermediate heat treatments can be effective to reduce phase separation kinetics in duplex stainless steel and thus mitigate low-temperature embrittlement during service. The origin of the intermediate temperature treatment effect on phase separation kinetics is discussed in relation to the short-range atomic order introduced during intermediate heat treatment, prior to accelerated low-temperature aging.</p>

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Kinetics of Phase Separation in Super Duplex Stainless Steel 2507 Revealed by In Situ Neutron Scattering for Various Intermediate Heat Treatments

  • 期刊论文

  • 出版模式：

    开放获取

  • 发表日期：

    2025年7月11日

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  • Monika Rolinska,
  • Gabriel Spartacus,
  • Alexander Dahlström,
  • Wangzhong Mu,
  • Tristan G. A. Youngs,
  • Joakim Odqvist,
  • Peter Hedström

摘要

In duplex stainless steels (DSSs), phase separation of iron and chromium is a well-known phenomenon causing low-temperature embrittlement, which greatly limits the lifetime of components in service conditions at temperatures above 250 °C–300 °C. Hence, means of mitigating the underlying phase separation causing this embrittlement is highly interesting to extend the service life of DSSs in certain applications. In this work, we investigate the effect of intermediate heat treatments (5 minutes annealing at temperatures between 700 °C and 900 °C), performed after the conventional solution treatment, on the kinetics of phase separation super duplex stainless steel 2507. Using in situ small-angle neutron scattering at accelerated aging conditions (i.e., aging at 475 °C), we show that the application of intermediate heat treatments, which change the “initial state” of the material, can slow down development of the concentration fluctuation amplitude by up to 65 pct during aging inside the miscibility gap. This indicates great potential to delay the embrittlement process of duplex stainless steel. All intermediate heat treatments, conducted prior to aging, change the phase separation kinetics but to different extent. The 800 °C intermediate heat treatment shows the largest reduction in phase separation kinetics as compared to the reference sample. This sample also correspondingly shows the lowest hardness increase after aging. These findings show that intermediate heat treatments can be effective to reduce phase separation kinetics in duplex stainless steel and thus mitigate low-temperature embrittlement during service. The origin of the intermediate temperature treatment effect on phase separation kinetics is discussed in relation to the short-range atomic order introduced during intermediate heat treatment, prior to accelerated low-temperature aging.