Mechanical and thermal characterization of MgO-C bricks and thermomechanical stress resistance analysis

E.BENAVIDEZ; Y.LAGORIO; P. GALLIANO; A.TOMBA

Aachen

Congreso; 59th International Colloquium on Refractories - Aachen 2016; 2016

EUROGRESS

MgO-C bricks are widely used in the steelmaking industry, the main consumerof refractory materials. Steelmaking processes proceed in chemical, thermal,and mechanical extreme conditions leading to refractory wear by several relatedmechanisms.Magnesia-carbon bricks used in ladle and converter furnaces linings suffercyclic temperature changes causing thermal stresses. By far, the mechanical andthermal properties involved in the material response depend on the percentage,size, and quality of the raw materials from which they are manufactured, andalso on their textural characteristics. Thus, a complete characterization ofthe brick combined with the use of thermal shock paramters [1, 2] allows aprevision about the behavior of a set of MgO-C materials under thermal stress. On the other hand,the thermal shock resistance of MgO-C refractories are determined by differentmethodologies, being common a cyclic tests in which the refractory samples aresubmerged in a metal liquid bath at 1600°C and then cooled in water or air [3].However, failure by thermal shock occurs at temperaturesbelow that from which the mechanical behavior of the material is visco-plasticand allow the thermal stress relief. This temperatures are generally <1400°C for MgO-C refractories. Taking this in mind, an alternative thermalshock evaluation based on previously reported tests [4, 5]  has been considered in order to determined thebehavior of MgO-C bricks under thermal stresses. It is a rather simple test whichconsist in the cooling of disks in oil (to prevent material oxidation); theresidual strength measured by diametral compression is used as a quantitativeindicator of the resistance to thermal shock. Besides, mechanical and thermalproperties of commercial MgO-C bricks at room temperature and 1200°C weremeasured. From these values, two thermal shock parameters werecalculated in order to predict the resistances to crack initiation and todamage (crack propagation) by thermal stresses. The influence of the brickscompositions (magnesia, antioxidants, and carbon content) on the thermal andmechanical properties is also discussed