China's Refractories

Abstract: Al₂O₃-MgO and Al₂O₃-spinel low cement castables (LCC-AM and LCC-AS) have been extensively used in steel ladles as working linings. Nevertheless, the use of alumina-magnesia gunning mixes has been mainly kept for maintaining these castable linings, because of high rebound loss, poor green strength, high porosity and short life-span. Thanks to a high BET alumina (MC-G), it is now possible to develop a series of high-performance no-cement or low-cement Al₂O₃-MgO gunning mixes (NCG-AM or LCG-AM). The paper focuses on the BOF slag resistance of NCG-AM, LCG-AM, LCC-AM and LCC-AS. The corrosion mechanisms of rotary slag samples were studied by scanning electron microscopy (SEM/EDS). The results reveal different microstructures around MgO particles, depending on the four used compositions. Continuous and thicker spinel phases were formed in NCG-AM, which was proved to have the best corrosion resistance after the dynamic slag test. MC-G can provide a high diffusion flux of Al³⁺ in terms of kinetics and hence inhibits Kirkendall porosity around MgO particles. In addition, a continuous spinel phase acts like a pinning nail to reinforce the matrix and thus decreases erosion by slag. In contrast to NCG-AM, the porous spinel phase was found around unreacted MgO particles and some particles were carried away near the interface of LCC-AM and slag. The NCG-AM containing MC-G had been tested in two steel plants, and it extended the service life of the ladles up to 50%. In addition, this study suggests the potential application of NCG-AM as steel ladle linings.

Key words: reactive alumina, ladle working lining, dynamic slag test, kirkendall effect, no-cement gunning mix