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<p>Modification of inclusions in pipeline steel melts by Ca treatment and Mg treatment were studied by two heats of industrial trials. Liquid steel was sampled at different times of the BOF-LF→RH→Ca treatment/Mg treatment→tundish process to evaluate changes of cleanliness and inclusions. From LF ending to RH ending, T[O] contents and number density of inclusions in steel reduced obviously from 0.0042 to 0.0020 pct and from 0.0036 to 0.0020 pct. After Ca treatment, inclusions in heat 1 were composed of CaO–MgO–Al<sub>2</sub>O<sub>3</sub>–CaS, and the number density of inclusions increased to 24.16/mm<sup>2</sup>. By contrast, only a few MgO–Al<sub>2</sub>O<sub>3</sub>–CaO inclusions were observed, while MgO-based and MgO–Al<sub>2</sub>O<sub>3</sub> inclusions were mainly produced in heat 2 after Mg treatment, with a number density of inclusions about 8.74/mm<sup>2</sup>. From soft blowing to casting tundish, steel was reoxidized in both heats, witnessing transformations of inclusions from MgO–Al<sub>2</sub>O<sub>3</sub>–CaO–CaS to CaO–MgO–Al<sub>2</sub>O<sub>3</sub> in heat 1 and increased numbers of MgO–Al<sub>2</sub>O<sub>3</sub> inclusions while decreased numbers of MgO inclusions in heat 2. Average size of inclusions in Mg treatment and Ca treatment was within 4 and 3 <i>μ</i>m, respectively, while maximum size of inclusions were both below 10 <i>μ</i>m. Hence, Mg treatment indicated more desirable modifications of inclusions than Ca treatment in this study. Detailed thermodynamic calculations by FactSage 8.1 software were conducted to elucidate formation and changes of inclusions, taking into account of T[Ca], T[Mg], T[O], T[S], and also temperature, which agreed with experimental results.</p>

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Modifications of Inclusions in Ca-Treated and Mg-Treated Pipeline Steel Melts

  • 期刊论文

  • 发表日期：

    2025年6月16日

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  • Huajun Zhong,
  • Min Jiang,
  • Benli Luan,
  • Xuechong Ren,
  • Xinhua Wang

摘要

Modification of inclusions in pipeline steel melts by Ca treatment and Mg treatment were studied by two heats of industrial trials. Liquid steel was sampled at different times of the BOF-LF→RH→Ca treatment/Mg treatment→tundish process to evaluate changes of cleanliness and inclusions. From LF ending to RH ending, T[O] contents and number density of inclusions in steel reduced obviously from 0.0042 to 0.0020 pct and from 0.0036 to 0.0020 pct. After Ca treatment, inclusions in heat 1 were composed of CaO–MgO–Al2O3–CaS, and the number density of inclusions increased to 24.16/mm2. By contrast, only a few MgO–Al2O3–CaO inclusions were observed, while MgO-based and MgO–Al2O3 inclusions were mainly produced in heat 2 after Mg treatment, with a number density of inclusions about 8.74/mm2. From soft blowing to casting tundish, steel was reoxidized in both heats, witnessing transformations of inclusions from MgO–Al2O3–CaO–CaS to CaO–MgO–Al2O3 in heat 1 and increased numbers of MgO–Al2O3 inclusions while decreased numbers of MgO inclusions in heat 2. Average size of inclusions in Mg treatment and Ca treatment was within 4 and 3 μm, respectively, while maximum size of inclusions were both below 10 μm. Hence, Mg treatment indicated more desirable modifications of inclusions than Ca treatment in this study. Detailed thermodynamic calculations by FactSage 8.1 software were conducted to elucidate formation and changes of inclusions, taking into account of T[Ca], T[Mg], T[O], T[S], and also temperature, which agreed with experimental results.