Creep-fatigue Fracture Mechanism and Microscopic Damage Behavior of New Martensitic Heat-resistant Steel

ZHOU Chao; HUANG Jun; MA Dongliang; SU Kailong; DU Jinfeng; ZHAO Lei

doi:10.3969/j.issn.1674-6457.2025.07.013

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Journal of Netshape Forming Engineering ›› 2025, Vol. 17 ›› Issue (7) : 110-118. DOI: 10.3969/j.issn.1674-6457.2025.07.013

Iron and Steel Forming

Creep-fatigue Fracture Mechanism and Microscopic Damage Behavior of New Martensitic Heat-resistant Steel

ZHOU Chao¹, HUANG Jun¹, MA Dongliang², SU Kailong², DU Jinfeng^1,*, ZHAO Lei³

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Abstract

The work aims to investigate the failure behavior of martensitic heat-resistant steel under creep-fatigue loading conditions, to provide theoretical guidance for the high-temperature failure behavior of ultra-supercritical (USC) power plant units. The creep-fatigue behavior of G115 steel at 650 ℃ was systematically investigated. Tests were conducted under a stress-controlled mode with a stress amplitude range of 180-230 MPa and a stress ratio (R) of 0. A hold time ranging from 0 to 3 600 s was applied at the peak tensile stress. During the tests, a constant loading rate of 90 kN/min was employed, and the fracture mechanism and microstructural damage evolution of G115 steel under creep-fatigue loading were investigated. Prolonging the hold time and increasing the hold stress both led to a decrease in the creep-fatigue life of G115 steel. Characterization of the fractured specimens revealed that all fractured surfaces exhibited distinct creep necking characteristics. Statistical analysis of the morphology and quantity of cavities on the fracture cross-sections showed that at lower stress levels, cavities were predominantly coin-shaped and tended to coalesce to form microcracks, while at higher stress levels, isolated creep cavities were dominant. Additionally, the cavity density increased with longer hold time. Precipitates observed in G115 steel during creep-fatigue tests included M₂₃C₆ phase, Laves phase, and Cu-rich phase. The creep-fatigue micro-fracture mode of G115 steel is characterized by martensitic cracking and martensitic fracture. The rapid coarsening of the Laves phase weakens the precipitation strengthening effect, thereby promoting the nucleation and propagation of cavities and microcracks, which constitutes the primary failure mechanism of G115 steel under these conditions.

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G115 steel / creep-fatigue / fracture mechanism / cavities and microcracks / microstructural evolution

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ZHOU Chao, HUANG Jun, MA Dongliang, SU Kailong, DU Jinfeng, ZHAO Lei. Creep-fatigue Fracture Mechanism and Microscopic Damage Behavior of New Martensitic Heat-resistant Steel[J]. Journal of Netshape Forming Engineering. 2025, 17(7): 110-118 https://doi.org/10.3969/j.issn.1674-6457.2025.07.013

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