Fracture behaviour and microstructure of refractory materials for steel ladle purging plugs in the system Al2O3-MgO-CaO

Abstract This paper completes the investigations performed on cement- and no-cement bonded refractory materials for steel ladle purging plugs. In addition to the thermodynamic evaluations and detailed material descriptions given in a previous paper, this paper focuses on the fracture behaviour of the materials. The influence of low and high pre-firing temperatures on the fracture behaviour is investigated. Differences in the microstructure of cement- and hydratable alumina-bonded castables with and without spinel can explain their different mechanical properties and fracture behaviour especially after pre-firing at elevated temperatures. When comparing cement- with no-cement bonded materials for applications in steel ladle purge plugs, both concepts have advantages and disadvantages. The much higher hot modulus of rupture of the cement bonded materials, especially in combination with spinel, is advantageous for the required erosion resistance in this application. With regard to corrosion resistance against the iron oxide-rich slag created during the oxygen lancing of the purging plugs, the calcia-free no-cement bonded materials would be advantageous. The more ductile, less brittle fracture behaviour of the no-cement system even after high temperature pre-firing should provide advantages with respect to the cracking and spalling behaviour of the hot face during use. Based on this investigation it would appear to be worthwhile testing hydratable alumina bonded corundum-spinel materials in industrial applications for steel ladle purging plugs.