Degradation mechanisms of magnesia-chromite refractories in vecuum-oxygen decarburisation ladles during production of stainless steel

摘要

Magnesia-chromite brick are used as refractories for the refining of stainless steel in vacuum-oxygen decarburisation (VOD) ladles. Refractory wear is not uniform. In the present work, worn bricks from different zones in the ladle have been analysed, and a set of interdependent degradation mechanisms is proposed. Refractory wear as a function of position in the ladle is discussed. Slag infiltration and MgO dissolution from the refractory were observed in all samples, whereas FeO_x decomposition was seen at two levels in the high wear samples. First partial decomposition of primary chromite crystals ((Mg)(Fe~(3+), Cr, Al)_2O_4) occurred at the hot face of the brick. Three layers were distinguished in the reacted chromite crystals and a reaction mechanism is presented. Second, a decrease in the FeO_x content of the magnesia phase occurred at the hot face of the brick. The negative effect of the presence of FeO_x in magnesia-chromite refractories is discussed and the influence of the ferrostatic pressure is demonstrated. Finally, the consequences of the following phenomena are discussed: increase in brick porosity, slag infiltration, corrosion, erosion of the partially liquid bonded refractory system, and spalling and cracking.