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<p>The creep behavior of AISI 316L stainless steel in the 1/8 hard initial condition was examined following friction stir welding (FSW) at temperatures ranging from 550 to 650&#xa0;°C. For comparison, a limited number of tests were also performed on unwelded samples. Microstructural analysis revealed that FSW produced a structure densely populated with finely spaced twins. The hardness of both the initial 1/8 hard and FSWed states was significantly higher than that of the annealed condition. The minimum creep rates observed in the FSWed material were slightly lower than those measured in the annealed state under very-high-stress conditions. However, under the lowest stress levels used in this study, the FSWed material exhibited minimum creep rates approximately an order of magnitude lower than those of the annealed steel. This behavior was interpreted using a physically based constitutive model that accurately captured the dependence of the minimum creep rate on applied stress and temperature, as established by literature data for annealed material. The model accounted for the dominant strengthening mechanisms across different regimes: in the high-stress/low-temperature regime, dislocation motion is impeded by dense dislocation cell walls formed during loading; in the low-stress/high-temperature regime, dislocation mobility is limited by interactions with precipitates. While the same model provided a qualitative understanding of the creep response of FSWed AISI 316L, the absence of a reliable physical model to quantify the strengthening effect of twinning during creep precludes accurate predictions of the minimum strain rate without relying on empirical fitting procedures.</p>

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The effect of initial microstructure on the creep response of austenitic stainless steels: the case of annealed and friction stir welded AISI 316L tested between 550 and 650 °C

  • 期刊论文

  • 发表日期：

    2025年5月22日

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  • S. Spigarelli,
  • M. Cabibbo,
  • D. Ciccarelli,
  • A. Santoni,
  • M. Regev

摘要

The creep behavior of AISI 316L stainless steel in the 1/8 hard initial condition was examined following friction stir welding (FSW) at temperatures ranging from 550 to 650 °C. For comparison, a limited number of tests were also performed on unwelded samples. Microstructural analysis revealed that FSW produced a structure densely populated with finely spaced twins. The hardness of both the initial 1/8 hard and FSWed states was significantly higher than that of the annealed condition. The minimum creep rates observed in the FSWed material were slightly lower than those measured in the annealed state under very-high-stress conditions. However, under the lowest stress levels used in this study, the FSWed material exhibited minimum creep rates approximately an order of magnitude lower than those of the annealed steel. This behavior was interpreted using a physically based constitutive model that accurately captured the dependence of the minimum creep rate on applied stress and temperature, as established by literature data for annealed material. The model accounted for the dominant strengthening mechanisms across different regimes: in the high-stress/low-temperature regime, dislocation motion is impeded by dense dislocation cell walls formed during loading; in the low-stress/high-temperature regime, dislocation mobility is limited by interactions with precipitates. While the same model provided a qualitative understanding of the creep response of FSWed AISI 316L, the absence of a reliable physical model to quantify the strengthening effect of twinning during creep precludes accurate predictions of the minimum strain rate without relying on empirical fitting procedures.