Abstract

Alumina-magnesia (Al2O3-MgO) castable refractory has been used in the sidewall of the molten steel ladles at Kashima Steel Works, Nippon Steel & Sumitomo Metal Corporation. The life of the ladles depends on the wear and residual thickness of the sidewall castable in the ladles. According to the observation of the sidewall refractories through the ladle campaigns, it was revealed that the decrease of the sidewall thickness did not become large until reaching about 70 charges, and thereafter, the sidewall thickness decreased stepwise with spalls ranging from 20-50 mm in thickness. It was considered that the sidewall refractories were not seriously damaged by slag corrosion, but the thickness was reduced sharply by spalling. Based on the field observation of the damage condition of the sidewall refractories, and the laboratory investigation of the used refractory materials, the following three modified castables were selected for trial, with the intent of improving the life of the ladle sidewall.

Castable 1. To reduce the thermal spalling, the grain size distribution was changed, which decreased the elastic modulus and thermal expansion coefficient.

Castable 2. To reduce the structural spalling, the dispersing agents were changed and the amount of the water addition was decreased, which decreased the pores in the refractories, and thus decreased the pathways for slag to penetrate into the castable.

Castable 3. To reduce the structural spalling, fine Al2O3 powder was added, and MgO was reduced, which decreased the slag penetration depth.

  These three castables were tested in the ladle sidewall at Kashima Steel Works.  The field results showed that all three castables showed better residual thickness than the castable used previously. The castables tested were mainly damaged by spalling, similar to the previous castable, but the first spalling occurred some charges later, and the average thickness of the spalling layer was about 15% thinner than the previously used castable. Castable1 was selected as the new standard refractory for the ladle sidewall, with an increased average service life of 30 heats.