High temperature mechanical behavior of MgO-C refractories. Stress-strain curv

G.ROHR; A.TOMBA; A.CAVALIERI; L.MARTORELLO; GALLIANO PABLO

Dresden, Alemania

Congreso; Biennial Worldwide Congress on Refractories UNITECR?07; 2007

UNITECR

MgO-C refractory bricks are widely used for steelmaking vessel working lining. This is due to a set of advantageous specific properties such as high resistance to slag corrosion and thermal spalling, and high temperature mechanical resistance, among others. Although they have been successfully used for more than twenty years in ladle and furnace linings, a deeper understanding of their high temperature behaviour is still required in order to optimize their performance.     A suitable tool for that purpose is the determination of stress-strain curves at in-service temperatures and under controlled atmosphere. The information that is provided through these laboratory tests is essential to understand the in-service materials behaviour during the vessel campaign. Furthermore, the obtained thermomechanical data of MgO-C refractories is need for the calculation of the stresses and strains that are developed in both the refractory lining and the vessel shell during the equipment campaign. Finally, the stress-strain curves at different temperatures can provide information about the in-service structural thermal evolution and the degradation that takes place during their in-plant performance.     High temperature stress-strain curves of MgO-C bricks can be obtained through compressive tests at high temperatures. Although this test is a specially suitable one for this kind of materials, there are not so many published reports on this topic in the open literature.       The aim of this work is to evaluate the thermomechanical behaviour of a set of MgO-C refractory bricks that are used in the working lining of steelmaking vessels by means of compressive stress-strain curves obtained at different temperatures under controlled atmosphere. Analysis of microstructure and composition of the evaluated materials were also done  Results showed that compressive stress-strain curves of the tested MgO-C commercial materials between room temperature and 1000°C are mainly determined by the type of carbon bond (pitch or resin) and its thermal evolution.    Resin bond materials exhibit higher elastic modulus and mechanical resistance than pitch bond ones at both RT and high temperatures (600°C and 1000°C). The higher stiffness and mechanical resistance of the resin bond refractories leads to more fragile fracture.     At 600°C the mechanical strength, the elastic limit and the Young modulus reach minima values in all the specimens, as well as maxima values of parameters measuring deformations. The weakness of the materials at this temperature is attributed to structural changes that take place in both pitch and resin bond phases by thermal effect. Finally, at 1000°C, the MgO-C refractories recover the stiffness and other fractomechanical properties. At this temperature, more stable carbon structures are developed in the matrix of both type of materials. Other incipient processes such as sintering and chemical reactions can also contribute to this phenomenon