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<p>The underutilization of steelmaking slags stems from instability, predominantly due to complex phase structures. Addressing this challenge is crucial for improving resource recovery and promoting sustainable practices in the steel industry. Despite known benefits of rapid cooling in reducing <i>f</i>-CaO, the influence of cooling methods on the elemental distribution within the RO (MgO–FeO solid solution) and its impact on slag stability has been insufficiently explored. This study systematically investigates how different cooling methods and MgO concentrations affect the phase composition and microstructure of steelmaking slag, with a focus on improving its stability. The principal phases in steelmaking slag, namely Ca<sub>2</sub>SiO<sub>4</sub> (C<sub>2</sub>S), RO, and Ca<sub>2</sub>Fe<sub>2</sub>O<sub>5</sub> (C<sub>2</sub>F) were identified by XRD and SEM–EDS. Ca<sub>3</sub>SiO<sub>5</sub> (C<sub>3</sub>S) was precipitated in the steelmaking slag with 10 and 14 mass pct MgO under slow cooling. The C<sub>2</sub>S exists in the <i>α</i>′ + <i>β</i> structure in the steelmaking slag obtained at different cooling methods with varying MgO concentrations. The presence of CaO and SiO<sub>2</sub> in the slag system has the effect of lowering the solidus temperature of the system, which results in the MgO concentration in the RO being as high as 58.30 and 71.03 mass pct for water quenching slag with 6 to 14 mass pct MgO, respectively. Conversely, slow cooling reduced MgO concentration in the RO to 20.50 and 40.32 pct. Although rapid cooling effectively lowers <i>f</i>-CaO content (below 1 pct), it also introduces stability concerns through high-MgO RO formation. These findings emphasize the importance of balancing MgO concentration and cooling strategies to optimize slag properties. By clarifying the mechanisms behind slag instability, this study contributes to improving slag recovery efficiency, enhancing long-term stability, and guiding the design of advanced slag treatment processes. The results provide theoretical foundations for the utilization of steelmaking slag in sustainable metallurgical operations and circular material flows.</p>

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Effects of Cooling Methods on Phase Evolution, Microstructure, and Stability of Steelmaking Slag

  • 期刊论文

  • 发表日期：

    2025年6月2日

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  • Wen-Feng Gu,
  • Jiang Diao,
  • Hao-Ran Tao,
  • Jun-Yi Deng,
  • Hua-Fang Yu,
  • Takayuki Iwama,
  • Cheremisina Elizaveta,
  • Hong-Yi Li,
  • Bing Xie,
  • Shigeru Ueda

摘要

The underutilization of steelmaking slags stems from instability, predominantly due to complex phase structures. Addressing this challenge is crucial for improving resource recovery and promoting sustainable practices in the steel industry. Despite known benefits of rapid cooling in reducing f-CaO, the influence of cooling methods on the elemental distribution within the RO (MgO–FeO solid solution) and its impact on slag stability has been insufficiently explored. This study systematically investigates how different cooling methods and MgO concentrations affect the phase composition and microstructure of steelmaking slag, with a focus on improving its stability. The principal phases in steelmaking slag, namely Ca2SiO4 (C2S), RO, and Ca2Fe2O5 (C2F) were identified by XRD and SEM–EDS. Ca3SiO5 (C3S) was precipitated in the steelmaking slag with 10 and 14 mass pct MgO under slow cooling. The C2S exists in the α′ + β structure in the steelmaking slag obtained at different cooling methods with varying MgO concentrations. The presence of CaO and SiO2 in the slag system has the effect of lowering the solidus temperature of the system, which results in the MgO concentration in the RO being as high as 58.30 and 71.03 mass pct for water quenching slag with 6 to 14 mass pct MgO, respectively. Conversely, slow cooling reduced MgO concentration in the RO to 20.50 and 40.32 pct. Although rapid cooling effectively lowers f-CaO content (below 1 pct), it also introduces stability concerns through high-MgO RO formation. These findings emphasize the importance of balancing MgO concentration and cooling strategies to optimize slag properties. By clarifying the mechanisms behind slag instability, this study contributes to improving slag recovery efficiency, enhancing long-term stability, and guiding the design of advanced slag treatment processes. The results provide theoretical foundations for the utilization of steelmaking slag in sustainable metallurgical operations and circular material flows.