Microstructure and Phase of Carbon Brick and Protective Layer of a 2800 m³ Industrial Blast Furnace Hearth

抄録

In this paper, the residual thickness of carbon brick, residual carbon brick and skull of a Chinese 2800 m³ blast furnace hearth were studied in detail and the formation mechanism of skull and brittle layer were proposed. The results show that the remaining thickness of carbon brick is highly inhomogeneous in the height and circumferential direction. In the circumferential direction, the sidewall erosion in the range of 3.6 m under the taphole is more serious. In the height direction, the carbon brick at the distance of 1.0–2.0 m below the central line of the taphole is more obvious. The erosion of hearth bottom is “mumps face+ bowl” type erosion. The minerals of the hot surface of carbon brick used for more than nine years are mainly composed of KAlSiO₄, KAlSi₂O₆, Zn₂SiO₄ and ZnO as well as a small amount of ZnS, KCl and ZnAl₂O₄. Micro cracks resulted from the KAlSiO₄, KAlSi₂O₆, Zn₂SiO₄ and ZnAl₂O₄ are the inducement of formation of brittle layer. The main reason for the formation of macro cracks and brittle layer in carbon brick is the continuous accumulation of ZnO in micro cracks. The brittle layer mainly occurs in the region where the temperature of carbon brick is lower than 950°C. The skull above the central line of the taphole is mainly composed of Ca₂Al₂SiO₇, Ca₂MgSi₂O₇, CaTiO₃ and KAlSiO₄. The skull below the central line of the taphole is primarily comprised of Ca₂Al₂SiO₇, Ca₂MgSi₂O₇, CaS, Fe and Fe₃Si. The blast furnace slag phase in the skull below the central line of taphole is derived from the blast furnace slag that penetrates into the deadman coke. The blast furnace slag can be present below the central line of the taphole and adhere to the hot surface of the carbon brick to isolate the direct contact between the molten iron and carbon brick.