Carbon-bonded magnesia (MgO-C) is an established lining material in converters, steel casting ladles and electric arc furnaces. With regard to the increasingly desired recycling of refractory materials, the comparison of the thermo-mechanical behavior between MgO-C batches with fresh MgO and with partially recycled MgO-C agglomerates is of high economic relevance. The Refratechnik Steel GmbH provided the MgO-C material used in this study, which is applied in industry. Two batches were provided to evaluate the influence of MgO already used in practice in MgO-C materials: MgO-C consisting of only fresh MgO, as well as MgO-C with recyclates with a proportion of recyclate:fresh material of 1:1.

In this study, the thermo-mechanical properties of the MgO-C materials were determined at temperatures of up to 1300 °C. The focus was on determining the compressive strength, which provided the basis for the subsequent creep and stress relaxation tests. The thermo-mechanical tests were carried out on an electromechanical high-temperature testing machine with an integrated protective gas chamber. This enables testing at temperatures of up to 1500 °C in an inert gas atmosphere.

It was shown that the introduction of recyclates influences the microstructure of the composite material and therefore also its properties. In addition to a change in porosity, density and dynamic Young’s modulus, the use of recyclates also has an effect on compressive strength, stress relaxation and creep behavior. SEM images provide insights into the deformation and damage behavior.