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<p>This study utilized thermodynamic approximate calculations to determine the precipitation–time–temperature (PTT) and nucleation rate–temperature (NrT) curves for microalloyed carbide precipitation in Nb-Ti microalloyed high-strength steel used for marine risers. The microstructural characteristics of carbide precipitates at different isothermal temperatures were examined using FE-SEM and HRTEM. To obtain a uniformly fine dispersed carbides to act as an irreversible hydrogen trap, three temperatures with higher nucleation rates (580℃, 630℃, and 650℃) were selected based on the NrT curve for isothermal treatment for 30 min. The obtained microstructures consisted of tempered martensite with precipitates, and these precipitates exhibited a Baker–Nutting (B–N) orientation relationship with the matrix. As the isothermal tempering temperature increased, both microstructural coarsening and a concomitant increase in the particle size of the face-centered cubic (FCC) microalloyed carbides were observed. Furthermore, the precipitation morphology transitioned from planar-interphase precipitation (PIP) with regular lamellar spacing to curved-interphase precipitation (CIP) also characterized by regular lamellar spacing.</p>

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Research on the Isothermal Precipitation Behavior of Carbides in Nb-Ti Microalloyed Offshore Steel

  • 期刊论文

  • 发表日期：

    2026年3月19日

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  • Tingfeng Xu,
  • Dazheng Zhang,
  • Ruifei Xuan,
  • Xingyu Wang

摘要

This study utilized thermodynamic approximate calculations to determine the precipitation–time–temperature (PTT) and nucleation rate–temperature (NrT) curves for microalloyed carbide precipitation in Nb-Ti microalloyed high-strength steel used for marine risers. The microstructural characteristics of carbide precipitates at different isothermal temperatures were examined using FE-SEM and HRTEM. To obtain a uniformly fine dispersed carbides to act as an irreversible hydrogen trap, three temperatures with higher nucleation rates (580℃, 630℃, and 650℃) were selected based on the NrT curve for isothermal treatment for 30 min. The obtained microstructures consisted of tempered martensite with precipitates, and these precipitates exhibited a Baker–Nutting (B–N) orientation relationship with the matrix. As the isothermal tempering temperature increased, both microstructural coarsening and a concomitant increase in the particle size of the face-centered cubic (FCC) microalloyed carbides were observed. Furthermore, the precipitation morphology transitioned from planar-interphase precipitation (PIP) with regular lamellar spacing to curved-interphase precipitation (CIP) also characterized by regular lamellar spacing.