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<p>With the advancement of pipeline systems towards high-pressure, high-efficiency transportation and deployment in increasingly complex environments,&#xa0;linepipe steel&#xa0;is required to meet stringent requirements including high strength, toughness, strain capacity, and thick-wall. This study investigates a 33&#xa0;mm thick-walled high-performance linepipe steel to explore the optimal microstructure and associated fracture behavior using&#xa0;mechanical property testing, microstructural analysis (SEM, TEM, EBSD), finite element simulation, and in-situ characterization. A systematic comparison is conducted between a&#xa0;multiphase composite microstructure&#xa0;(containing ~ 30% polygonal ferrite, acicular ferrite, granular bainite, and minor lath bainite) and a&#xa0;dual-phase microstructure&#xa0;(~70% polygonal ferrite and lath bainite). Results show that the&#xa0;multiphase composite microstructure&#xa0;exhibits better fracture resistance. The synergistic interactions and transitional interfaces among its constituent phases reduce strength and hardness&#xa0;gradients, resulting in a high fraction (86%) of low&#xa0;kernel average misorientation (KAM)&#xa0;grains (0–1°). This structure also contains more &lt; 111 &gt; -oriented grains&#xa0;(~4.3&#xa0;μm average diameter), improving fracture resistance. In contrast, the&#xa0;dual-phase microstructure, while having better strain accommodation, shows a lower fraction (~62%) of low KAM grains, higher stress concentration, and pronounced banding of lath bainite. These features weaken phase boundary cohesion, leading to more severe drop-weight tear test (DWTT) fracture separation.</p>

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Research on Microstructure and Fracture Behavior of Thick-Walled High-Performance Linepipe Steel

  • 期刊论文

  • 发表日期：

    2026年3月9日

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  • Shuai Zhang,
  • Jing Li,
  • Hong Gao,
  • Shuang Wang,
  • Fu-yue Wang,
  • Zhe-rui Zhang

摘要

With the advancement of pipeline systems towards high-pressure, high-efficiency transportation and deployment in increasingly complex environments, linepipe steel is required to meet stringent requirements including high strength, toughness, strain capacity, and thick-wall. This study investigates a 33 mm thick-walled high-performance linepipe steel to explore the optimal microstructure and associated fracture behavior using mechanical property testing, microstructural analysis (SEM, TEM, EBSD), finite element simulation, and in-situ characterization. A systematic comparison is conducted between a multiphase composite microstructure (containing ~ 30% polygonal ferrite, acicular ferrite, granular bainite, and minor lath bainite) and a dual-phase microstructure (~70% polygonal ferrite and lath bainite). Results show that the multiphase composite microstructure exhibits better fracture resistance. The synergistic interactions and transitional interfaces among its constituent phases reduce strength and hardness gradients, resulting in a high fraction (86%) of low kernel average misorientation (KAM) grains (0–1°). This structure also contains more < 111 > -oriented grains (~4.3 μm average diameter), improving fracture resistance. In contrast, the dual-phase microstructure, while having better strain accommodation, shows a lower fraction (~62%) of low KAM grains, higher stress concentration, and pronounced banding of lath bainite. These features weaken phase boundary cohesion, leading to more severe drop-weight tear test (DWTT) fracture separation.