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<p>A Nb-Ti tempered steel with a 700&#xa0;MPa yield strength was designed in this study based on a low-alloying and tempering heat treatment strategy. The impact of coiling and tempering temperatures on microstructural evolution and strength contributions was investigated. Results indicate that after coiling at 550&#xa0;°C and tempering at 650&#xa0;°C, the steel demonstrates a yield strength of 761.28&#xa0;MPa, a tensile strength of 833.64&#xa0;MPa, an elongation of 20.9%, and a product of strength and elongation of 17.45&#xa0;GPa%. Furthermore, as the coiling temperature is elevated from 450 to 600&#xa0;°C, the strength exhibits a gradual rise. In contrast, when the tempering temperature is elevated from 550 to 700&#xa0;°C, the strength initially increases before declining, while the elongation remains relatively stable around 20%. Low-temperature coiling facilitates the retention of high-density dislocations, which provide nucleation sites for the precipitation of (Ti, Nb)C during subsequent tempering while suppressing the formation of coarse (Ti, Nb)C particles. After high-temperature tempering, fine-uniform, and dispersedly distributed (Ti, Nb)C precipitates effectively compensate for the insufficient precipitation induced by low-temperature coiling, thereby contributing significant precipitation strengthening. Quantitative analysis of strength contributions reveals that grain refinement, dislocation, and precipitation strengthening are the primary factors, with precipitation strengthening being dominant. Tailoring the coiling and tempering temperatures allows for direct control of the formation of second-phase precipitates, promoting the dispersion of nano-sized (Ti, Nb)C and achieving a balanced strength–ductility combination.</p>

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Microstructure and Strength in Nb-Ti Tempering Steel: The Role of Coiling and Tempering Temperatures

  • 期刊论文

  • 发表日期：

    2026年2月11日

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  • Linlin Bao,
  • Qing Yuan,
  • Le Xiong,
  • Wen Liang,
  • Qingxiao Zhang,
  • Shaobai Sang,
  • Xiaolong Li,
  • Guang Xu

摘要

A Nb-Ti tempered steel with a 700 MPa yield strength was designed in this study based on a low-alloying and tempering heat treatment strategy. The impact of coiling and tempering temperatures on microstructural evolution and strength contributions was investigated. Results indicate that after coiling at 550 °C and tempering at 650 °C, the steel demonstrates a yield strength of 761.28 MPa, a tensile strength of 833.64 MPa, an elongation of 20.9%, and a product of strength and elongation of 17.45 GPa%. Furthermore, as the coiling temperature is elevated from 450 to 600 °C, the strength exhibits a gradual rise. In contrast, when the tempering temperature is elevated from 550 to 700 °C, the strength initially increases before declining, while the elongation remains relatively stable around 20%. Low-temperature coiling facilitates the retention of high-density dislocations, which provide nucleation sites for the precipitation of (Ti, Nb)C during subsequent tempering while suppressing the formation of coarse (Ti, Nb)C particles. After high-temperature tempering, fine-uniform, and dispersedly distributed (Ti, Nb)C precipitates effectively compensate for the insufficient precipitation induced by low-temperature coiling, thereby contributing significant precipitation strengthening. Quantitative analysis of strength contributions reveals that grain refinement, dislocation, and precipitation strengthening are the primary factors, with precipitation strengthening being dominant. Tailoring the coiling and tempering temperatures allows for direct control of the formation of second-phase precipitates, promoting the dispersion of nano-sized (Ti, Nb)C and achieving a balanced strength–ductility combination.