Fabrication and properties of MgO–C refractories improved with expanded graphite

Abstract

Graphite containing MgO–C refractory system is one of the most important class of consumable refractories in steel making due to their superior chemical inertness to slag, and high thermal shock resistance. However, higher graphite or carbon content leads to reduced hot strength, increases oxidation of graphite in high temperature conditions, and higher thermal conductivity of the refractory lining. Higher conductivity leads to process heat loss and increased metallic shell temperature. Therefore, there is a need to reduce the carbon content in the refractories without sacrificing thermal shock and corrosion resistance. Recent investigations have explored the use of various carbon forms to enhance properties of low graphite containing MgO–C refractories. In the current work, expanded graphite was used as a carbon source to partially replace flaky graphite in 5% graphite containing MgO–C refractories. In the refractory composition 0, 0.2, 0.5 and 0.8% of graphite was replaced with expanded graphite. The specimens were fabricated on a pilot plant scale, and their physical and thermo-mechanical properties were studied. The developed composition showed better bulk density and reduced porosity. 25–30% increase in cold crushing strength could be obtained. Thermal shock resistance improved from 9 cycles to 12 cycles. Additionally, significant improvement in hot strength, more than 100%, was observed for the new composition. The beneficial properties were ascribed to an efficient packing of the fine aggregates, and homogeneous formation of nanostructured high temperature phases throughout the microstructure.