MgO-C refractories with 8 and 13 wt-% Carbon were studied regarding its mechanical and thermo-mechanical properties. The modulus of rupture, the modulus of elasticity, the linear thermal expansion coefficient, the fracture toughness, the total work of fracture, and the parameters expressing the resistance to thermal shock damage, R'''' and Rst, were characterized. Thermal shock damage was investigated by submitting the refractories to a single thermal shock cycle in the temperature range of 200°C to 800°C. The radiant lines, elasto-plastic and energetic methods were applied to obtain the R-curves. The shape and behaviour of the R-curve of these materials were also investigated. Based on the R-curves profiles, the average R values were obtained and compared to those of the total work of fracture, which were assumed as the criterion to evaluate the R-curves reliability. Thus, it was possible to investigate the effect of the carbon content on the level and shape of the R-curve for these refractories, as well as the effect of the different methods used to determine the R-curve. The results clearly indicate that, although an increase of the carbon content in the form of graphite flakes weakens the material in terms of mechanical strength, this same carbon causes a significant increase of total work of fracture and of resistance to thermal shock damage. Lastly, it was concluded that, surprisingly, the radiant lines method to determine the R-curve of MgO-C refractories is the most suitable and reliable one. The importance of this result lies on the simplicity of the radiant lines method since it does not require sophisticated and costly instrumentation and it is based simply on linear elastic mechanics. This suggests a methodology for a suitable and simple thermo-mechanical quality control for these refractories, insofar as resistance to thermal shock damage is concerned.
Refractory; MgO-C; Mechanical Properties; Thermomechanical Properties; R-Curve
