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<p>The static continuous cooling transformation curve (CCT) of the test steel was measured using a thermal expansion testing machine. By analyzing the phase transformation process of the test steel during continuous cooling at different rates, the influence of Nb and W alloy elements on the microstructure transformation characteristics of 25MnCrNiMo steel was studied. The results showed that when 0.015 wt.% of Nb and W was added, the critical cooling rate of the test steel increased from 5°C/s to 10°C/s; the bainite phase zone expanded, and bainite/martensite was obtained within a wider cooling rate range. After the cooling rate exceeded 10°C/s, the transformation temperature of martensite decreased. Through the heat treatment process of 950°C quenching and 600°C reheat, the yield strength of the test steel was 1314.45&#xa0;MPa, the impact energy was 76.95&#xa0;J, and the hardness was 359 HBW. Compared with the cast steel without adding alloy elements, it was increased by 14%, 80%, and 9.8% respectively. The reasons for this are that Nb and W refined the original austenite grains, and the average grain size decreased from 41.36&#xa0;μm to 8.93&#xa0;μm, forming a fine lamellar martensite structure. At the same time, due to the precipitation of fine dispersed carbides, its comprehensive performance was improved.</p>

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Effects of Nb-W Microalloying on Continuous Cooling Transformation Behavior and Microstructure Evolution in Low-Alloy Steel

  • 期刊论文

  • 发表日期：

    2025年8月25日

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  • Shiting Zhu,
  • Huiqin Chen,
  • Fang Wang,
  • Hua Hou,
  • Ning Li,
  • Xiangxiang Liang

摘要

The static continuous cooling transformation curve (CCT) of the test steel was measured using a thermal expansion testing machine. By analyzing the phase transformation process of the test steel during continuous cooling at different rates, the influence of Nb and W alloy elements on the microstructure transformation characteristics of 25MnCrNiMo steel was studied. The results showed that when 0.015 wt.% of Nb and W was added, the critical cooling rate of the test steel increased from 5°C/s to 10°C/s; the bainite phase zone expanded, and bainite/martensite was obtained within a wider cooling rate range. After the cooling rate exceeded 10°C/s, the transformation temperature of martensite decreased. Through the heat treatment process of 950°C quenching and 600°C reheat, the yield strength of the test steel was 1314.45 MPa, the impact energy was 76.95 J, and the hardness was 359 HBW. Compared with the cast steel without adding alloy elements, it was increased by 14%, 80%, and 9.8% respectively. The reasons for this are that Nb and W refined the original austenite grains, and the average grain size decreased from 41.36 μm to 8.93 μm, forming a fine lamellar martensite structure. At the same time, due to the precipitation of fine dispersed carbides, its comprehensive performance was improved.