Creep behaviour of Magnesia Carbon refractory

Abstract

Refractories are widely used as lining material in the steelmaking industry. This class of materials is known for its superior creep resistance. However, creep of refractory linings is a known phenomenon in refractory science. Therefore, knowledge on creep behaviour is critical for furnace lining life predictions and selection of materials. This work, in collaboration with Tata Steel IJmuiden, focuses on creep development in magnesia carbon (MgO-C), a refractory often found in Basic Oxygen Furnaces (BOF). In this research, the influence of binder and aluminium content on creep development in MgO-C was investigated. This was addressed, based on the microstructural changes, phase transformations and thermo-mechanical properties. Microscopy, scanning electron microscopy, X-Ray diffraction, cold crushing strength, hot modulus of rupture, dilatometry, refractoriness under load and hot compressive strength tests were conducted in order to explain creep behaviour. For creep testing, a nonstandardised set-up was designed to be able to retrieve creep data more efficiently. The experimental configuration increased the load every 5 hours (multi-stage). Resulting creep rates were validated against a single-load stage creep measurement. A small difference of 5% in creep rates was observed. This indicated that the multi- and single-stage results are within range of each other. Therefore, the proposed multi-stage creep test can be considered a viable creep testing method. A trend of decreasing creep rates with increasing binder content was found. Increasing the content from 2% to 3% showed a maximum decrease in creep rates of 80%. A further increase of binder content from 3% to 4% showed a maximum decrease in creep rates of 30%. This behaviour was mainly attributed due to volatilisation of the binder and magnesium, and densification due to carbonisation of the binder. Increasing the aluminium content from 0 to 1% resulted in a maximum decrease in creep rates of 70%. This was mainly attributed due to spinel formation. The irreversible volume expansion due to spinel formation, increased the density and the stress state within the material. As a result, micro cracks formed which strengthened the material and improved creep resistance. The outcomes of this work are an important contribution to refractory science. However, further development of refractories is still necessary, especially due to the increasing pressure on the steelmaking sector to make its processes more sustainable.