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<p>Medium-manganese steels are the next-generation advanced high strength steels gaining preferences for automotive applications due to their excellent combination of high strength, ductility and crash performance. The microstructural design of these steels, in terms of major phases of martensite and retained austenite, is crucial to obtain the final mechanical properties. However, the available models in literature to predict the martensitic transformation kinetics in these steels are inadequate, due to unsuitability of the mathematical approaches as well as the deviations introduced by the user-dependent determination of the martensite start transformation temperature. To resolve this issue, six different medium Mn steels, having Mn content 2.5–10 wt pct with two levels of carbon, 0.1 and 0.2 wt pct, are investigated using high-resolution dilatometry. The uncertainties in analysis of dilatometry data while determining the martensite transformation start and finish temperatures (<i>M</i><sub><i>s</i></sub> and <i>M</i><sub><i>f</i></sub>) are analysed in detail and steps to overcome them are proposed. The shortcomings of the available kinetic models from literature with respect to nonuniformity in data analysis and model development are further analysed. Finally, this study presents a new, user-independent alternative to the Koistinen–Marburger equation, with an improved mathematical expression, as well as consideration of the influence of the chemical composition.</p>

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Martensitic Transformation Kinetics in Medium-Manganese Steels: A Dilatometry-Based Transformation Analysis and Determination of Transformation Temperatures

  • 期刊论文

  • 发表日期：

    2025年9月1日

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  • Anindita Chakraborty,
  • Oguz Gulbay,
  • Radhakanta Rana,
  • Carlos Garcia-Mateo,
  • Alexander Gramlich

摘要

Medium-manganese steels are the next-generation advanced high strength steels gaining preferences for automotive applications due to their excellent combination of high strength, ductility and crash performance. The microstructural design of these steels, in terms of major phases of martensite and retained austenite, is crucial to obtain the final mechanical properties. However, the available models in literature to predict the martensitic transformation kinetics in these steels are inadequate, due to unsuitability of the mathematical approaches as well as the deviations introduced by the user-dependent determination of the martensite start transformation temperature. To resolve this issue, six different medium Mn steels, having Mn content 2.5–10 wt pct with two levels of carbon, 0.1 and 0.2 wt pct, are investigated using high-resolution dilatometry. The uncertainties in analysis of dilatometry data while determining the martensite transformation start and finish temperatures (Ms and Mf) are analysed in detail and steps to overcome them are proposed. The shortcomings of the available kinetic models from literature with respect to nonuniformity in data analysis and model development are further analysed. Finally, this study presents a new, user-independent alternative to the Koistinen–Marburger equation, with an improved mathematical expression, as well as consideration of the influence of the chemical composition.