Development of new methods and models to measure and characterise the creep behaviour of refractory materials

The creep behaviour of coarse refractory products at elevated temperature is a complex issue. Operating conditions, such as the temperature, the load and the atmosphere, play a decisive role. The prediction of the creep behaviour of a refractory lining in service based on measurements according to the existing testing standards and equipment cannot mirror the conditions during industrial application of refractory products and are therefore not realistic. Since refractory linings experience unsteady thermal gradients and pressure gradients in practice, an extensive investigation is necessary for a good understanding and sound modelling of the refractory creep behaviour.

The equipment developed within the framework of this project coupled with microstructural examinations was proven to be powerful combination for a comprehensive investigation of the creep behaviour of refractory products.Along with project-specific development and improvements of testing equipment, the proficiency of the testing equipment was verified with measurements on reference materials and by comparison with standard testing equipment. Thanks to a system to control the atmosphere, the creep behaviour of carbon containing refractories, especially used in steel making applications, as well as other materials sensitive to oxidation such as SiC can now be char-acterised.

An exemplary study of the creep behaviour and the reasons for the behaviour of SiC containing castable was performed.The deformation levels at the end of the primary creep regime of the investigated SiC containing castable were found to be higher with increasing temperature and higher initial stress. In contrast, the creep rates in the quasi steady state appeared to be highly dependent of the microstructure obtained after the primary creep regime. High temperature and high initial stress conducted to important densification during the primary creep regime which impeded further creep process in oxidising atmosphere. In inert atmosphere, however, a much looser microstructure was achieved after the primary creep regime, and a relatively high creep rate after 12 hours was observed. The evolution of the refractory microstructure at elevated temperature was thus found to impact the creep behaviour. In addition, the obtained results highlight the necessity of smart control of the atmosphere in combustion plants using SiC containing castables.Finally, the optical dilatometer provided insight and new information about the two-dimensional creep behaviour of refractory product. This information is provided for the first time and should be decisive to support the development and verification of 3-dimensional models.