HOT STRENGTH AND THERMAL-SHOCK RESISTANCE OF MAGNESIA-CARBON REFRACTORIES

Magnesia-carbon refractories for BOS vessel linings may suffer from thermal shock during initial heating of a cold lining; however, standard tests of thermal shock resistance are not suitable for these materials. A thermal shock test for magnesia-carbon refractories has been developed and applied to a range of these materials, none of which contained antioxidants. The test involved the rapid heating of one face of a tile of test material by the ignition of a measured quantity of Thermit welding powder. Heating rates of between 2500 and 3000 K min(-1) were recorded 3 mm behind the hot face of the testpieces. The severity of the thermal shock generated was sufficient to enable the behaviour of different magnesia-carbon refractories to be compared. Thermal shock susceptibility was characterised by the reduction in room temperature modulus of rupture and dynamic modulus of elasticity and was found to depend son carbon content, type of bond, and coking state. The room temperature strength of the materials was found to decrease with increasing coking temperatures, but for any given coking temperature the strength increased with test temperature, up to the coking temperature. Thermal shock resistance was found to decrease with increasing coking temperature and with decreasing carbon content. Pitch bonded materials of the same nominal carbon content, both as supplied and after coking. Pitch bonded materials were more resistance to thermal shock than the resin bonded refractories. (C) 1995 The Institute of Materials.