Evaluation of Crack Growth Resistance in Low Carbon MgO-C Refractories

摘要

The crack growth resistance of the bricks in MgO-C refractory bricks containing 1.5 %C (Carbon black) was investigated based on the principles of fracture mechanics. R-curves were determined and evaluated based on notch width changes, and the critical stress intensity factor was calculated from the R-curves. The critical stress intensity factor in the reference sample exhibited the highest value, whereas the sample whose aggregate contents were respectively 1.6 times higher than that in the reference sample exhibited the second highest. The bridging stress, which indicates the bridging effect of the aggregate, clearly increased when the aggregate content increased. Based on the roughness analysis, it is predicted that the bridging stress will increase when the ratio of aggregate in the refractory increases because more site for the action of pull-out force and frictional force exist on the crack surface. In conclusion, it was predicted that it will be desirable to increase the content of aggregate in the refractory while keeping the higher strength of matrix force in order to provide the refractory with excellent resistance against dynamic thermal fatigue.