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<p>The present study investigates the effect of tempering on the microstructural evolution and mechanical properties of a nanostructured bainitic steel produced through a novel thermomechanical treatment. In this study, tempering was applied to separately prepared specimens to reproduce the thermal exposure associated with the anticipated service conditions of the steel, rather than as part of its conventional heat-treatment route. Tempering was carried out at temperatures ranging from 150&#xa0;°C to 600°C for 2&#xa0;h to evaluate the stability and transformation behavior of the nanobainitic microstructure. A combination of synchrotron X-ray diffraction, dilatometric analysis, scanning electron microscopy observation, and mechanical testing was employed to investigate the structural changes and their influence on strength and ductility. At lower tempering temperatures (150–360&#xa0;°C and 450&#xa0;°C), microstructural changes were primarily determined by carbon diffusion within the bainitic ferrite and retained austenite. This led to a decrease in the volume fraction of the retained austenite and an increase in the volume fraction of the bainitic ferrite. Additionally, these temperatures promoted the precipitation of ε-carbides and cementite, as well as bainitic transformation during tempering and martensitic transformation during cooling. At elevated temperatures (500–600&#xa0;°C), the decomposition of retained austenite into ferrite and cementite, indicating further carbon redistribution and phase transformation. The ultimate tensile strength (UTS) and yield strength (YS) of tempered specimens were lower than those of the untempered condition. However, a substantial increase in YS was observed at 450&#xa0;°C, surpassing the untempered value by 131&#xa0;MPa. This phenomenon is presumably attributable to the impeding of dislocation motion by interfacial cementite precipitation.</p>

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The thermal stability of nanobainitic microstructure and its effect on the mechanical properties of a high-carbon steel manufactured by the thermomechanical treatment

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月19日

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  • K. Janus,
  • Ł. Rogal,
  • G. Korpala,
  • A. Góral,
  • R. Chulist,
  • M. Zapf,
  • A. Jarzębska,
  • U. Prahl,
  • W. Maziarz

摘要

The present study investigates the effect of tempering on the microstructural evolution and mechanical properties of a nanostructured bainitic steel produced through a novel thermomechanical treatment. In this study, tempering was applied to separately prepared specimens to reproduce the thermal exposure associated with the anticipated service conditions of the steel, rather than as part of its conventional heat-treatment route. Tempering was carried out at temperatures ranging from 150 °C to 600°C for 2 h to evaluate the stability and transformation behavior of the nanobainitic microstructure. A combination of synchrotron X-ray diffraction, dilatometric analysis, scanning electron microscopy observation, and mechanical testing was employed to investigate the structural changes and their influence on strength and ductility. At lower tempering temperatures (150–360 °C and 450 °C), microstructural changes were primarily determined by carbon diffusion within the bainitic ferrite and retained austenite. This led to a decrease in the volume fraction of the retained austenite and an increase in the volume fraction of the bainitic ferrite. Additionally, these temperatures promoted the precipitation of ε-carbides and cementite, as well as bainitic transformation during tempering and martensitic transformation during cooling. At elevated temperatures (500–600 °C), the decomposition of retained austenite into ferrite and cementite, indicating further carbon redistribution and phase transformation. The ultimate tensile strength (UTS) and yield strength (YS) of tempered specimens were lower than those of the untempered condition. However, a substantial increase in YS was observed at 450 °C, surpassing the untempered value by 131 MPa. This phenomenon is presumably attributable to the impeding of dislocation motion by interfacial cementite precipitation.