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<p>P91 steel and its weld joint (WJ) have been selected for the present study with the goal, to investigate the combined effects of fatigue and creep loadings [known as creep–fatigue interaction (CFI)] on the microstructures of the five constituting zones of actual P91 steel WJ when it is subjected to various types of CFI loading waveforms. Experiments were conducted at constant strain rate (3 × 10<sup>−3</sup>&#xa0;s<sup>−1</sup>), temperature (873&#xa0;K), and total strain amplitude (±&#xa0;0.6&#xa0;pct); the CFI loadings comprised of unsymmetrical loadings (short or long tensile/compressive holds) and symmetrical loadings (tensile plus compressive holds/pure fatigue). The hierarchical boundaries within the prior austenite grains and M<sub>23</sub>C<sub>6</sub> carbides at the boundaries are investigated. Under CFI loading, the interrelations between the stabilities of M<sub>23</sub>C<sub>6</sub> carbides at the hierarchical boundaries and the subgrains were found to be dependent upon the microstructural zone of the WJ in consideration, symmetricity/asymmetricity of the applied waveform and the extents of creep/fatigue contributions in the CFI waveform cycles. The subgrains of soft regions (intercritical and fine grain) and base metal were at stake under larger fatigue contributions, whereas the subgrains of hard regions (coarse grain and weld metal) were unaffected by the CFI loadings.</p>

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Impact of Various Creep–Fatigue Interaction Loading Waveforms at 873 K on the Subgrains and M23C6 Carbides Interrelations and Stability in P91 Steel Weld Joints

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  • 发表日期：

    2025年2月9日

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  • P. Vaishali,
  • Vani Shankar

摘要

P91 steel and its weld joint (WJ) have been selected for the present study with the goal, to investigate the combined effects of fatigue and creep loadings [known as creep–fatigue interaction (CFI)] on the microstructures of the five constituting zones of actual P91 steel WJ when it is subjected to various types of CFI loading waveforms. Experiments were conducted at constant strain rate (3 × 10−3 s−1), temperature (873 K), and total strain amplitude (± 0.6 pct); the CFI loadings comprised of unsymmetrical loadings (short or long tensile/compressive holds) and symmetrical loadings (tensile plus compressive holds/pure fatigue). The hierarchical boundaries within the prior austenite grains and M23C6 carbides at the boundaries are investigated. Under CFI loading, the interrelations between the stabilities of M23C6 carbides at the hierarchical boundaries and the subgrains were found to be dependent upon the microstructural zone of the WJ in consideration, symmetricity/asymmetricity of the applied waveform and the extents of creep/fatigue contributions in the CFI waveform cycles. The subgrains of soft regions (intercritical and fine grain) and base metal were at stake under larger fatigue contributions, whereas the subgrains of hard regions (coarse grain and weld metal) were unaffected by the CFI loadings.