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Microstructure and Mechanical Properties of P91 Steel during Heat Treatment: The Effect of the Cooling Speed during the Normalization Stage

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Abstract

The evolution of the microstructure and mechanical properties of P91 steel during heat treatments at different cooling speeds during the normalization stage was investigated. Results showed that normalized martensite with high hardness and strength was obtained over a wide range of cooling rates (higher than 200 °C/h) during the normalization stage of P91 steel. Within this cooling rate range, twin martensite gradually generated as the cooling rate decreased, which enhanced the brittleness of the normalized P91 steel. When the cooling rate was decreased to 25 °C/h, the P91 steel exhibited completely annealed microstructures consisting mainly of bulk α-Fe grains, with the formation of continuous M23C6 carbides at the grain boundaries. As a result, the annealed P91 steel had poor hardness and strength, as well as demonstrating increased brittleness. Notably, after tempering, the hardness and strength of normalized martensite were greatly weakened, while the toughness of tempered martensite greatly increased. After the tempering process, the continuous M23C6 GBs in the completely annealed P91 steel partly dissolved, which also remarkably enhanced the toughness.

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Acknowledgments

The authors would like to express their gratitude for projects supported by the National Natural Science Foundation of China (51574181 and 51374153) and Supported by Sichuan Science and Technology Program (2018JY0668). The help from Meng Ruan of Wuhan University was also appreciated.

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Authors and Affiliations

  1. Da Tang East China Electric Power Test and Research Institute, Hefei, 230000, China

    Mansheng Ni, Jiaqing Wang & Junjian Liu

  2. School of Power and Mechanical Engineering, Wuhan University, Wuhan, 430072, China

    Xue Wang, Kai Zhang & Chengchao Du

  3. School of Materials Science and Engineering, Jiangsu University, Zhenjiang, 212013, China

    Chengchao Du

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  1. Mansheng Ni
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  2. Jiaqing Wang
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Correspondence to Xue Wang or Chengchao Du.

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Ni, M., Wang, J., Liu, J. et al. Microstructure and Mechanical Properties of P91 Steel during Heat Treatment: The Effect of the Cooling Speed during the Normalization Stage. J. of Materi Eng and Perform 30, 2329–2340 (2021). https://doi.org/10.1007/s11665-021-05534-5

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