Mechanical behaviour of MgO–C refractory bricks evaluated by stress–strain curves

In this work, the mechanical behaviour of a set of resin- and pitch-bonded MgO–C refractories containing metallic additives was evaluated in laboratory tests at high temperature in a non-oxidant atmosphere. Commercial bricks were used for this evaluation, and a comprehensive characterization of the as-received materials was performed using several techniques (mineralogical analysis by X-ray diffraction, density and porosity measurements, differential thermal and thermogravimetric analyses and microstructural analysis by reflected light microscopy coupled with cathodoluminiscence accessory and scanning electron microscopy). Stress–strain curves in compression were obtained at room temperature, 600, 1000 and 1400 °C under flowing N2 gas. An Instron 8501 servo-hydraulic machine was used with a capacitive extensometer suitable for axial strain measurements at high temperatures. A constant displacement of 0.1 mm/min was applied until specimen failure. Several parameters were calculated from the stress–strain curves: failure stress, failure strain, yield stress and secant Young's modulus. Moreover, a comprehensive characterization of the tested specimens was carried out. The analysis of the mechanical behaviour has been based on previous research and the results have been interpreted in terms of the thermal evolution of the brick's microstructure. The resin-based refractory exhibited the higher values of mechanical strength and Young's modulus in the entire range of testing temperatures. Up to 1000 °C, the mechanical behaviour was controlled by the type of binder and the changes in porosity whereas at 1400 °C, the main differences between the responses of resin- and pitch-based refractories were mainly caused by the metallic additive reactions.