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<p>The blast furnace remains the most efficient, energy-saving, and environmentally friendly core equipment for ironmaking. The formation of a stable protective layer in the hearth is essential to ensure the safe and long-term operation of blast furnace smelting. In this study, the phase composition and microstructure of the hearth protective layer were systematically investigated to elucidate its formation mechanism based on the nucleation and growth processes. The protective layer samples were analyzed using X-ray fluorescence (XRF), high-frequency infrared carbon/sulfur analyzer (HFC/S), X-ray diffraction (XRD), and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS). The results reveal that the protective layer consists of an interwoven mixture of iron and graphite phases, with a phase ratio maintained between 4.0 and 10.3. Graphite is distributed within the iron matrix in branched or strip-like morphologies, accompanied by cracks within and along graphite boundaries. When the molten iron is cooled to 1304&#xa0;°C or below 1150&#xa0;°C, the ordered graphite and iron will transform into a nucleus when they reach the critical size under a certain degree of undercooling. Graphite grows anisotropically along both planar and axial directions, facilitated by rotational twinning and screw dislocations. Iron forms equiaxed crystals through dendrite growth, and then evolves into columnar crystals due to growth constraints. The mutual growth and integration of graphite and iron ultimately lead to the formation of a dense graphite–iron composite protective layer. The corrosion resistance, stability, uniformity, and rapid formation of the protective layer can be regulated by promoting the formation of the protective layer network structure, the precipitation of heterogeneous nucleation cores, and the increase of artificial nucleation sites.</p>

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Nucleation and Growth Mechanism of Graphite-Iron Protective Layer in Blast Furnace Hearth

  • 期刊论文

  • 发表日期：

    2025年8月11日

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  • Kexin Jiao,
  • Jian Cao,
  • Jianliang Zhang,
  • Cui Wang,
  • Ming Lei,
  • Mingbo Song

摘要

The blast furnace remains the most efficient, energy-saving, and environmentally friendly core equipment for ironmaking. The formation of a stable protective layer in the hearth is essential to ensure the safe and long-term operation of blast furnace smelting. In this study, the phase composition and microstructure of the hearth protective layer were systematically investigated to elucidate its formation mechanism based on the nucleation and growth processes. The protective layer samples were analyzed using X-ray fluorescence (XRF), high-frequency infrared carbon/sulfur analyzer (HFC/S), X-ray diffraction (XRD), and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS). The results reveal that the protective layer consists of an interwoven mixture of iron and graphite phases, with a phase ratio maintained between 4.0 and 10.3. Graphite is distributed within the iron matrix in branched or strip-like morphologies, accompanied by cracks within and along graphite boundaries. When the molten iron is cooled to 1304 °C or below 1150 °C, the ordered graphite and iron will transform into a nucleus when they reach the critical size under a certain degree of undercooling. Graphite grows anisotropically along both planar and axial directions, facilitated by rotational twinning and screw dislocations. Iron forms equiaxed crystals through dendrite growth, and then evolves into columnar crystals due to growth constraints. The mutual growth and integration of graphite and iron ultimately lead to the formation of a dense graphite–iron composite protective layer. The corrosion resistance, stability, uniformity, and rapid formation of the protective layer can be regulated by promoting the formation of the protective layer network structure, the precipitation of heterogeneous nucleation cores, and the increase of artificial nucleation sites.