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<p>The current study investigates the influence of dynamic strain aging during ratcheting fatigue and microstructural evolution in SA333 Gr-6 steel. The ratcheting experiments were conducted under a stress-controlled mode with varying the stress rates (20, 115, and 700&#xa0;MPa/s) with a mean stress of 100&#xa0;MPa and a stress amplitude of 350&#xa0;MPa at different temperatures (RT to 350&#xa0;°C). These experimental parameters were selected to simulate an asymmetric cyclic stress which arises in piping systems of power plants during turbulence or seismic occurrences along with temperature fluctuations to evaluate the material’s performance and structural integrity. The ratcheting results indicated that the effect of DSA was dominant in the temperature range of 250-300&#xa0;°C for the stress rates 20 and 115&#xa0;MPa/s. However, at a higher stress rate of 700&#xa0;MPa/s, a dominant DSA effect was observed only at 300&#xa0;°C. Further, the DSA has shown a beneficial effect on ratcheting life due to DSA-induced hardening and reduced strain accumulation. In the sample ratcheted at dominant DSA regime, severe dislocation activities and dislocation tangles signifying DSA-induced hardening behavior, whereas rearrangement of dislocations into well-developed cell structure indicating thermally activated recovery mechanism operating at higher temperature (350&#xa0;°C free of DSA) were revealed through TEM investigation. The dislocation density calculated through XRD analysis correlated well with the ratcheting behavior and TEM observations.</p>

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Ratcheting Fatigue in SA333 Gr-6 Steel: Beneficial Effect of Dynamic Strain Aging and Microstructure Evolution

  • 期刊论文

  • 发表日期：

    2025年9月29日

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  • Girendra Kumar,
  • Avanish Kumar,
  • Himadri Nandan Bar

摘要

The current study investigates the influence of dynamic strain aging during ratcheting fatigue and microstructural evolution in SA333 Gr-6 steel. The ratcheting experiments were conducted under a stress-controlled mode with varying the stress rates (20, 115, and 700 MPa/s) with a mean stress of 100 MPa and a stress amplitude of 350 MPa at different temperatures (RT to 350 °C). These experimental parameters were selected to simulate an asymmetric cyclic stress which arises in piping systems of power plants during turbulence or seismic occurrences along with temperature fluctuations to evaluate the material’s performance and structural integrity. The ratcheting results indicated that the effect of DSA was dominant in the temperature range of 250-300 °C for the stress rates 20 and 115 MPa/s. However, at a higher stress rate of 700 MPa/s, a dominant DSA effect was observed only at 300 °C. Further, the DSA has shown a beneficial effect on ratcheting life due to DSA-induced hardening and reduced strain accumulation. In the sample ratcheted at dominant DSA regime, severe dislocation activities and dislocation tangles signifying DSA-induced hardening behavior, whereas rearrangement of dislocations into well-developed cell structure indicating thermally activated recovery mechanism operating at higher temperature (350 °C free of DSA) were revealed through TEM investigation. The dislocation density calculated through XRD analysis correlated well with the ratcheting behavior and TEM observations.