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<p>In this paper, a low-carbon TRIP steel was subjected to four distinct heat treatments: isothermal annealing (IA), non-isothermal annealing (NIA), pre-quenched isothermal annealing (Q-IA), and pre-quenched non-isothermal annealing (Q-NIA). The focus was on understanding how these treatments, especially the innovative Q-NIA process, could refine the microstructure and improve mechanical performance. As the traditional process, the IA produced coarse parent austenite grains (3–10&#xa0;<i>μ</i>m) and M/A islands (1–3&#xa0;<i>μ</i>m) with uneven size distribution, yielding strength (YS) of 536&#xa0;MPa, ultimate tensile strength (UTS) of 1007&#xa0;MPa, total elongation (TEL) of 22.5&#xa0;pct, and product of strength-elongation (PSE) of 22.7 GPa· pct. NIA refined austenite to 1–3&#xa0;<i>μ</i>m but retained banded ferrite, achieving YS of 712&#xa0;MPa, UTS of 950&#xa0;MPa, TEL of 28.4 pct, and PSE of 27.0 GPa· pct. In contrast, the application of martensitic starting microstructure in the Q-IA sample significantly refined the parent austenite to ~ 2&#xa0;<i>μ</i>m, increased the retained austenite fraction from ~ 12 pct (IA and NIA samples) to 16.5 pct, accelerated the bainite transformation, and achieved YS of 753&#xa0;MPa, UTS of 1045&#xa0;MPa, TEL of 30.1 pct, and PSE of 31.5 GPa· pct. Critically, Q-NIA eliminated banded structures, achieved ultra-fine parent austenite (&lt;1&#xa0;<i>μ</i>m) with predominantly lath-like morphology, stabilized 18.4&#xa0;pct retained austenite with enhanced mechanical stability, and delivered optimal mechanical properties with YS of 730&#xa0;MPa, UTS of 1016&#xa0;MPa, TEL of 32.6&#xa0;pct, and PSE of 33.1 GPa· pct. This research overcomes limitations of conventional TRIP steels and provides a new approach for the development of advanced high-strength steels with optimized strength–ductility balance.</p>

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Ultra-fine Microstructure Design and Enhanced Mechanical Properties of TRIP Steels via Novel Heat Treatment

  • 期刊论文

  • 发表日期：

    2025年8月26日

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  • Fei Peng,
  • Qi Liu,
  • Jing Tian,
  • Xingli Gu,
  • Weidong Zhang,
  • Zhenggang Wu

摘要

In this paper, a low-carbon TRIP steel was subjected to four distinct heat treatments: isothermal annealing (IA), non-isothermal annealing (NIA), pre-quenched isothermal annealing (Q-IA), and pre-quenched non-isothermal annealing (Q-NIA). The focus was on understanding how these treatments, especially the innovative Q-NIA process, could refine the microstructure and improve mechanical performance. As the traditional process, the IA produced coarse parent austenite grains (3–10 μm) and M/A islands (1–3 μm) with uneven size distribution, yielding strength (YS) of 536 MPa, ultimate tensile strength (UTS) of 1007 MPa, total elongation (TEL) of 22.5 pct, and product of strength-elongation (PSE) of 22.7 GPa· pct. NIA refined austenite to 1–3 μm but retained banded ferrite, achieving YS of 712 MPa, UTS of 950 MPa, TEL of 28.4 pct, and PSE of 27.0 GPa· pct. In contrast, the application of martensitic starting microstructure in the Q-IA sample significantly refined the parent austenite to ~ 2 μm, increased the retained austenite fraction from ~ 12 pct (IA and NIA samples) to 16.5 pct, accelerated the bainite transformation, and achieved YS of 753 MPa, UTS of 1045 MPa, TEL of 30.1 pct, and PSE of 31.5 GPa· pct. Critically, Q-NIA eliminated banded structures, achieved ultra-fine parent austenite (<1 μm) with predominantly lath-like morphology, stabilized 18.4 pct retained austenite with enhanced mechanical stability, and delivered optimal mechanical properties with YS of 730 MPa, UTS of 1016 MPa, TEL of 32.6 pct, and PSE of 33.1 GPa· pct. This research overcomes limitations of conventional TRIP steels and provides a new approach for the development of advanced high-strength steels with optimized strength–ductility balance.