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<p>In this study, three novel low-alloy ultra-high-strength martensitic steels with different chromium contents (1%, 2%, and 3%) were designed to investigate the effect of Cr content on the microstructure and mechanical properties after tempering. The relationship between microstructure and properties was systematically analyzed through tensile, impact, and fracture toughness tests, combined with multi‑scale microstructural characterization via scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy, and X-ray diffraction. The results demonstrate that the steel containing 2% Cr achieves an exceptional combination of strength and toughness, exhibiting a yield strength of 1517&#xa0;MPa, ultimate tensile strength of 2017&#xa0;MPa, and fracture toughness of 66.0&#xa0;MPa·m⁻<sup>1</sup>/<sup>2</sup>, respectively. This superior performance is attributed to a refined and spatially uniform hierarchical microstructure composed of fine tempered martensite, uniformly distributed film‑like retained austenite (RA), and a dense dispersion of refined ε‑carbides. In contrast, increasing the Cr content to 3% fundamentally alters ε‑carbides coarsening and promotes θ‑carbides formation, with the RA content decreasing. This microstructure evolution embrittles the materials and reduces toughness significantly, inducing a mixed ductile–brittle fracture mode. These findings demonstrate that Cr acts as a critical microstructural modulator, where an optimal addition of 2% refines the carbide dispersion and stabilizes the RA, effectively mitigating the classic strength–toughness trade-off.</p>

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Effect of Cr on microstructural evolution and mechanical properties of a low-alloy ultra-high-strength martensitic steel

  • 期刊论文

  • 发表日期：

    2026年6月24日

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  • Mengmei Xu,
  • Chunxu Wang,
  • Yandong Sun,
  • Shun Han,
  • Yuxian Cao,
  • Wuhua Yuan

摘要

In this study, three novel low-alloy ultra-high-strength martensitic steels with different chromium contents (1%, 2%, and 3%) were designed to investigate the effect of Cr content on the microstructure and mechanical properties after tempering. The relationship between microstructure and properties was systematically analyzed through tensile, impact, and fracture toughness tests, combined with multi‑scale microstructural characterization via scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy, and X-ray diffraction. The results demonstrate that the steel containing 2% Cr achieves an exceptional combination of strength and toughness, exhibiting a yield strength of 1517 MPa, ultimate tensile strength of 2017 MPa, and fracture toughness of 66.0 MPa·m⁻1/2, respectively. This superior performance is attributed to a refined and spatially uniform hierarchical microstructure composed of fine tempered martensite, uniformly distributed film‑like retained austenite (RA), and a dense dispersion of refined ε‑carbides. In contrast, increasing the Cr content to 3% fundamentally alters ε‑carbides coarsening and promotes θ‑carbides formation, with the RA content decreasing. This microstructure evolution embrittles the materials and reduces toughness significantly, inducing a mixed ductile–brittle fracture mode. These findings demonstrate that Cr acts as a critical microstructural modulator, where an optimal addition of 2% refines the carbide dispersion and stabilizes the RA, effectively mitigating the classic strength–toughness trade-off.