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<p>This study explores the microstructure evolution and strengthening mechanisms of microalloyed low-carbon steel under varying quenching temperatures, aiming to achieve a balance between low yield-strength ratio and high strength–ductility product (PSE). Quenching at 850&#xa0;°C in the ferrite–austenite two-phase region keeps homogeneous dispersion of nano-sized TiC precipitates, which leads to an ultimate tensile strength (UTS) of 504.7&#xa0;MPa and a high PSE of 19.63&#xa0;GPa pct <i>via</i> synergistic dislocation pinning and precipitation strengthening. Notably, the metastable <i>ε</i>-Fe<sub>2</sub>C phase formed at 850&#xa0;°C transforms into stable Fe<sub>3</sub>C as the quenching temperature increases to 900&#xa0;°C, providing new insights into phase transition dynamics during quenching. Full austenitization quenching at 1050&#xa0;°C results in a heterogeneous structure of lath martensite and web-like martensite-encapsulated ferrite, increasing the UTS to 703.5&#xa0;MPa. However, the distribution of reticulated martensite along grain boundaries limits the plastic deformation of ferrite, thereby reducing the PSE to 17.59&#xa0;GPa pct. The differential Crussard–Jaoul (DC–J) model analysis reveals that two-phase zone quenching enhances the strain hardening capacity, whereas full austenitization quenching leads to a notable reduction in the strain hardening exponent. The work provides a theoretical basis for the design of advanced high-strength steels (AHSS) with optimized strength–toughness synergy and offers valuable engineering implications for industrial applications.</p>

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C-partitioning Driven the Formation of Heterogeneously Polymorphic Structure for Low-Carbon Steel with High Strength–Ductility Product

  • 期刊论文

  • 发表日期：

    2025年9月16日

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  • Wenlong Zhang,
  • Sheng Yin,
  • Huijuan Wang,
  • Qingchao Tian

摘要

This study explores the microstructure evolution and strengthening mechanisms of microalloyed low-carbon steel under varying quenching temperatures, aiming to achieve a balance between low yield-strength ratio and high strength–ductility product (PSE). Quenching at 850 °C in the ferrite–austenite two-phase region keeps homogeneous dispersion of nano-sized TiC precipitates, which leads to an ultimate tensile strength (UTS) of 504.7 MPa and a high PSE of 19.63 GPa pct via synergistic dislocation pinning and precipitation strengthening. Notably, the metastable ε-Fe2C phase formed at 850 °C transforms into stable Fe3C as the quenching temperature increases to 900 °C, providing new insights into phase transition dynamics during quenching. Full austenitization quenching at 1050 °C results in a heterogeneous structure of lath martensite and web-like martensite-encapsulated ferrite, increasing the UTS to 703.5 MPa. However, the distribution of reticulated martensite along grain boundaries limits the plastic deformation of ferrite, thereby reducing the PSE to 17.59 GPa pct. The differential Crussard–Jaoul (DC–J) model analysis reveals that two-phase zone quenching enhances the strain hardening capacity, whereas full austenitization quenching leads to a notable reduction in the strain hardening exponent. The work provides a theoretical basis for the design of advanced high-strength steels (AHSS) with optimized strength–toughness synergy and offers valuable engineering implications for industrial applications.