Thermal characteristics of Al2O3–MgO and Al2O3–spinel castables for steel ladles

The hot properties of the Al2O3–MgO castables containing 5.5 wt.% MgO and 1.36 wt.% CaO with and without the addition of 0.75 wt.% microsilica and the Al2O3–spinel castables containing 20 wt.% Al2O3–rich spinel of 90 wt.% Al2O3 and 1.70 wt.% CaO, respectively, were investigated. The thermal shock damage test using the prism quench into water technique indicated that the retained modulus of rupture of the Al2O3–MgO castables after three cycles was down to 5%, while that of the Al2O3–spinel castables was 51%. The combined test of slag and thermal shock attack on castables using the rotary slag test furnace showed that the Al2O3–MgO castables had 0% penetration and 24% erosion, while the Al2O3–spinel castables had 10% penetration and 30% erosion. The field trials confirmed that Al2O3–MgO castables have better slag resistance and a longer service life for use in steel ladles, compared to Al2O3–spinel castables. The importance of thermal shock damage resistance of castables for use in steel ladles should be de-emphasized, based on the lab and field tests. There is no correlation between hot strengths and slag resistance for castables. The magnitude of specific surface area of pores is more important than pore size and porosity for governing the slag resistance of Al2O3–MgO castables, with and without microsilica addition.