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<p>A 1000 MPa-grade high-strength steel for crawler crane cantilever beams was investigated by tensile, axial fatigue, SEM/EDS, and EBSD tests at room temperature under a stress ratio of <i>R</i> = 0.1 and a loading frequency of 15 Hz. The steel exhibited a favorable strength–ductility balance, with a yield strength of 1119.5 MPa, an ultimate tensile strength of 1141.5 MPa, and a fracture elongation of 13.44%. The S-N data followed a Basquin-type relation (<i>R</i><sup>2</sup> = 0.73), although scatter increased in the high-cycle regime. Fatigue cracks initiated mainly from surface or near-surface regions, where inclusions, secondary phases, and voids promoted local stress concentration and multi-source crack coalescence. Oxygen-enriched particle/pit-like features in short-life specimens indicated an oxidation-assisted fatigue effect. Stable crack propagation was dominated by Mode I striations, followed by final dimpled ductile overload fracture. EBSD confirmed a lath martensitic matrix. Strong texture and coarse lath bundles produced channelized high-KAM bands that accelerated strain localization and crack coalescence, whereas grain refinement and a more balanced LAGB/MAGB/HAGB distribution (≈&#xa0;36.3%/17.0%/46.8%, average grain size 1.30 μm) dispersed local deformation and delayed surface crack initiation. A two-stage fatigue life model was developed by coupling a threshold-constrained Basquin relation for crack initiation with a short-crack-corrected Paris law for crack propagation, based on Δ<i>K</i>eff = UΔK, a semi-elliptical surface crack geometry (<i>F</i> = 0.65), and the irreversible energy term <i>W</i><sub><i>d</i></sub> ∝ (<i>K</i><sub>eff</sub>)<sup>2</sup>(da/dN)/E<sup>*</sup>. The results show that the overall fatigue life slope within the investigated stress–life window was governed primarily by crack initiation, while increasing stress raised <i>U</i> and <i>W</i><sub><i>d</i></sub> and reduced the fraction of stable crack growth. This framework provides a physically interpretable basis for microstructural optimization and engineering life assessment of critical crane components.</p>

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Surface Crack Initiation, Oxidation-Assisted Effects, and Life Decomposition of a Novel 1000 MPa-Class High-Strength Steel for Cranes

  • 期刊论文

  • 发表日期：

    2026年5月27日

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  • Suqi Xue,
  • Shanglei Yang

摘要

A 1000 MPa-grade high-strength steel for crawler crane cantilever beams was investigated by tensile, axial fatigue, SEM/EDS, and EBSD tests at room temperature under a stress ratio of R = 0.1 and a loading frequency of 15 Hz. The steel exhibited a favorable strength–ductility balance, with a yield strength of 1119.5 MPa, an ultimate tensile strength of 1141.5 MPa, and a fracture elongation of 13.44%. The S-N data followed a Basquin-type relation (R2 = 0.73), although scatter increased in the high-cycle regime. Fatigue cracks initiated mainly from surface or near-surface regions, where inclusions, secondary phases, and voids promoted local stress concentration and multi-source crack coalescence. Oxygen-enriched particle/pit-like features in short-life specimens indicated an oxidation-assisted fatigue effect. Stable crack propagation was dominated by Mode I striations, followed by final dimpled ductile overload fracture. EBSD confirmed a lath martensitic matrix. Strong texture and coarse lath bundles produced channelized high-KAM bands that accelerated strain localization and crack coalescence, whereas grain refinement and a more balanced LAGB/MAGB/HAGB distribution (≈ 36.3%/17.0%/46.8%, average grain size 1.30 μm) dispersed local deformation and delayed surface crack initiation. A two-stage fatigue life model was developed by coupling a threshold-constrained Basquin relation for crack initiation with a short-crack-corrected Paris law for crack propagation, based on ΔKeff = UΔK, a semi-elliptical surface crack geometry (F = 0.65), and the irreversible energy term Wd ∝ (Keff)2(da/dN)/E*. The results show that the overall fatigue life slope within the investigated stress–life window was governed primarily by crack initiation, while increasing stress raised U and Wd and reduced the fraction of stable crack growth. This framework provides a physically interpretable basis for microstructural optimization and engineering life assessment of critical crane components.