Although the tap hole mix which includes large amount of Si3N4 was markedly corroded by metal, remarkable improvement was achieved by adding Al-containing components as Al powders or Al2O3 powders. The microstructure observation after the corrosion test indicated that, Si3N4 reacted with matrix oxide around the grain and diffused into the matrix followed by Si-O-N glassy phase formation. In the process, Si-Al-O-N glassy phase is formed by addition of Al-containing components resulting in improvement of metal corrosion resistance. Furthermore, influence of the corrosion behavior of tap hole mix, that is, corroded only by metal or only by slag, on slag level in blast furnace and tapping time were evaluated by mathematical calculation and almost the same results were obtained.

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