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<p>This work focuses on the effect Cu content on precipitates, prior austenite grains (PAGs) growth, and impact toughness in coarse-grained heat-affected zone (CGHAZ) of Ca-Ti deoxidized high-strength low-alloy (HSLA) steels. Two steels with the Cu contents of 0.069 and 0.22&#xa0;wt&#xa0;pct contain three types of nano-precipitates: Type I: (Ti,Nb)(C,N), Type II: Cu<sub>2</sub>S(+MnS)+(Ti,Nb)(C,N), and Type III: <i>γ</i>-Al<sub>2</sub>O<sub>3</sub>(+Cu<sub>2</sub>S)+(Ti,Nb)(C,N). In CGHAZ, 220Cu steel contains Types I and II nano-precipitates, whereas 69Cu steel contains Types I, II, and III nano-precipitates. Based on theoretical calculations, Cu<sub>2</sub>S precipitates on the substrate of TiN or MnS to form Type II nano-precipitate, and TiN or Cu<sub>2</sub>S precipitate on the substrate of <i>γ</i>-Al<sub>2</sub>O<sub>3</sub> to form Type III nano-precipitate. With the increase of Cu content, the number densities of Type I and Type II nano-precipitates increase from 3.07 and 0.69&#xa0;<i>μ</i>m<sup>−2</sup> to 5.33 and 2.24&#xa0;<i>μ</i>m<sup>−2</sup>, respectively, which results in an increase in their effective pinning force from 0.0031 to 0.0055&#xa0;MPa, especially with Type II nano-precipitate accounting for half of the effective pinning force in 220Cu steel. The aggregation growth of Type III nano-precipitate formed only in 69Cu steel and their location within PAGs render them ineffective for pinning PAG boundaries, contributing to abnormal growth PAGs in 69Cu steel. Meanwhile, the irregular micro-precipitates with low MnS content at PAGs boundaries in 220Cu steel exert stronger pinning effect on PAG boundaries than the long strip-shaped micron-precipitates with high MnS content at PAGs boundaries in 69Cu steel. Above combined effects reduce average PAGs size from 254&#xa0;<i>μ</i>m of 69Cu steel to 196&#xa0;<i>μ</i>m of 220Cu steel, thereby forming coarsening and inhomogeneous microstructures in 69Cu steel. As a result, the impact toughness in CGHAZ increases significantly from 14&#xa0;J of 69Cu steel to 199&#xa0;J of 220 Cu steel at −&#xa0;20&#xa0;°C.</p>

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Insight into Cu on Precipitates, PAG Growth, and Impact Toughness of CGHAZ for Ca-Ti Deoxidized HSLA Steels After HHIW

  • 期刊论文

  • 发表日期：

    2025年8月8日

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  • Liang Wang,
  • Jian Yang,
  • Yinhui Zhang,
  • Yuqi Zhang,
  • Yanli Chen

摘要

This work focuses on the effect Cu content on precipitates, prior austenite grains (PAGs) growth, and impact toughness in coarse-grained heat-affected zone (CGHAZ) of Ca-Ti deoxidized high-strength low-alloy (HSLA) steels. Two steels with the Cu contents of 0.069 and 0.22 wt pct contain three types of nano-precipitates: Type I: (Ti,Nb)(C,N), Type II: Cu2S(+MnS)+(Ti,Nb)(C,N), and Type III: γ-Al2O3(+Cu2S)+(Ti,Nb)(C,N). In CGHAZ, 220Cu steel contains Types I and II nano-precipitates, whereas 69Cu steel contains Types I, II, and III nano-precipitates. Based on theoretical calculations, Cu2S precipitates on the substrate of TiN or MnS to form Type II nano-precipitate, and TiN or Cu2S precipitate on the substrate of γ-Al2O3 to form Type III nano-precipitate. With the increase of Cu content, the number densities of Type I and Type II nano-precipitates increase from 3.07 and 0.69 μm−2 to 5.33 and 2.24 μm−2, respectively, which results in an increase in their effective pinning force from 0.0031 to 0.0055 MPa, especially with Type II nano-precipitate accounting for half of the effective pinning force in 220Cu steel. The aggregation growth of Type III nano-precipitate formed only in 69Cu steel and their location within PAGs render them ineffective for pinning PAG boundaries, contributing to abnormal growth PAGs in 69Cu steel. Meanwhile, the irregular micro-precipitates with low MnS content at PAGs boundaries in 220Cu steel exert stronger pinning effect on PAG boundaries than the long strip-shaped micron-precipitates with high MnS content at PAGs boundaries in 69Cu steel. Above combined effects reduce average PAGs size from 254 μm of 69Cu steel to 196 μm of 220Cu steel, thereby forming coarsening and inhomogeneous microstructures in 69Cu steel. As a result, the impact toughness in CGHAZ increases significantly from 14 J of 69Cu steel to 199 J of 220 Cu steel at − 20 °C.