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<p>Dilatometric experiments were conducted on 20MnTiB steel using a Gleeble-3500 thermal simulation tester to investigate the relationship between isothermal holding time and the transformation products of austenite along with their corresponding quantities during isothermal cooling processes. The maximum transformation quantity of austenite to bainite within the bainitic transformation region was experimentally determined. Furthermore, the JMA equation and KM equation were employed to establish diffusional and diffusionless phase transformation kinetic models for the steel, respectively. Thermal analysis reveals critical phase transition temperatures: Austenitization initiates at 706.1&#xa0;°C (Ac1) and completes at 817.4&#xa0;°C (Ac3), whereas martensitic transformation occurs between 414.6&#xa0;°C (Ms) and 328.4&#xa0;°C (Mf). The time–temperature–transformation (TTT) diagram of 20MnTiB steel exhibits a characteristic “C-curve” profile, with the nose temperature located at 500&#xa0;°C. Isothermal holding in the temperature range of 706.1&#xa0;°C to 575&#xa0;°C results in austenite decomposition into pearlite and ferrite, whereas isothermal treatment between 575&#xa0;°C and 414.6&#xa0;°C promotes bainitic transformation. The isothermal phase transformation rate demonstrates a non-monotonic temperature dependence, initially increasing and subsequently decreasing with lowering temperature. Isothermal cooling treatments at 525&#xa0;°C, 500&#xa0;°C, 475&#xa0;°C, and 425&#xa0;°C yield maximum bainite transformation fractions of 67.4%, 76.3%, 87.1%, and 100%, respectively. The derived kinetic model for 20MnTiB steel demonstrates high predictive accuracy, with correlation coefficients <i>r</i> ≥ 0.95, enabling reliable prediction of microstructural evolution during phase transformation.</p>

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Analysis of Isothermal Transformation Behavior and Phase Transformation Kinetic Model for 20MnTiB Steel

  • 期刊论文

  • 发表日期：

    2025年12月15日

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  • Haonan Liu,
  • Dong Xu,
  • Hongxuan Pang,
  • Xiao Yin,
  • Xiaoying Wang,
  • Bing Zheng

摘要

Dilatometric experiments were conducted on 20MnTiB steel using a Gleeble-3500 thermal simulation tester to investigate the relationship between isothermal holding time and the transformation products of austenite along with their corresponding quantities during isothermal cooling processes. The maximum transformation quantity of austenite to bainite within the bainitic transformation region was experimentally determined. Furthermore, the JMA equation and KM equation were employed to establish diffusional and diffusionless phase transformation kinetic models for the steel, respectively. Thermal analysis reveals critical phase transition temperatures: Austenitization initiates at 706.1 °C (Ac1) and completes at 817.4 °C (Ac3), whereas martensitic transformation occurs between 414.6 °C (Ms) and 328.4 °C (Mf). The time–temperature–transformation (TTT) diagram of 20MnTiB steel exhibits a characteristic “C-curve” profile, with the nose temperature located at 500 °C. Isothermal holding in the temperature range of 706.1 °C to 575 °C results in austenite decomposition into pearlite and ferrite, whereas isothermal treatment between 575 °C and 414.6 °C promotes bainitic transformation. The isothermal phase transformation rate demonstrates a non-monotonic temperature dependence, initially increasing and subsequently decreasing with lowering temperature. Isothermal cooling treatments at 525 °C, 500 °C, 475 °C, and 425 °C yield maximum bainite transformation fractions of 67.4%, 76.3%, 87.1%, and 100%, respectively. The derived kinetic model for 20MnTiB steel demonstrates high predictive accuracy, with correlation coefficients r ≥ 0.95, enabling reliable prediction of microstructural evolution during phase transformation.