New carbon‐bonded filters with coatings based on calcium aluminates are developed. The samples are tested for 10 s in contact with a steel melt containing endogenous inclusions at 1650 °C, in order to explore the behavior and impact of these materials on the filtration process. Investigation of the filters after the test is carried out by optical and scanning electron microscopy. In addition, steel samples are analyzed with a special automatic SEM. The population of the detected inclusions is classified in terms of size and chemistry. Both compositions deliver excellent filtration results.

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Carbon-bonded magnesia and magnesia alumina carbon (MAC) bricks have been used in the sidewalls and bottom of steel ladles for over 20 years. Due to the increasing ratio of scrap to steel, higher working temperature, and prolonged refining time, steel producers seek refractories with enhanced service lifetime. Therefore, a new generation of MgO-C bricks with addition of calcium magnesium aluminate (CMA) aggregates is tested in a ladle lining of an integrated steel shop for 138 cycles. The corrosion mechanisms are evaluated by digital light microscopy and with scanning electron microscopy (SEM) equipped with energydispersive X-ray spectroscopy (EDS). The industrial trial tests reveal the formation of a slag coating at the hot face, leading to a much slower corrosion rate compared with a common MgO-C lining. The dissolution of the CMA aggregates and MgO grains results in a significant change of the slag chemistry and viscosity causing a reduced infiltration and corrosion behavior of the ladle slag. Also, the ability of bonding iron plays a major role, leading to the formation of brownmillerite phase in the protective slag coating on top of the bricks.

Refractory monolithics for steel ladle linings are typically products with low porosities and high bulk densities. They achieve high temperature, penetration, and corrosion resistance. Despite the high density of these products, which is due to the low porosity of the aggregates, their matrices still exhibit a high amount of pores. Since calcium magnesium aluminate (CMA) has already proven its resistance to penetration and corrosion as a binder in the matrix, this paper investigated if alumina spinel refractories containing microporous calcium magnesium aluminate aggregates can withstand conditions that occur in a steel ladle wall. The objective was to reduce the castable density with the advantage of a lower material requirement for a ladle lining and reduced heat and energy losses. This was achieved by replacing dense alumina aggregates by up to 38% of porous CMA aggregates (grains with 30 vol% porosity), which resulted in a bulk density reduction from 3.1 g/cm3 for the dense alumina castable to 2.8 g/cm3 for the 38% CMA aggregates containing castable. However, the despite the higher porosity, penetration, and corrosion resistance and thermomechanical properties were not impacted negatively for a model alumina spinel castable. A postmortem investigation was conducted on a newly developed dry-gunning mix that was installed in a steel ladle wall on top of a slag penetrated castable and that achieved a service life of 31 heats versus only 18 heats for the reference mix that contained dense alumina and spinel aggregates. This new repair mix contained the newly designed porous CMA aggregates, which in this case partly replaced the dense alumina and spinel aggregates. These porous aggregates consisted of magnesium aluminate and calcium aluminate micro-crystals. The postmortem study revealed two important phenomena that can explain the improved performance: at the hot face in contact with steel and slag, a thin densified zone was observed that blocked the slag penetration into the porous matrix and the porous aggregates. Iron oxides were almost completely blocked from penetration, and only some manganese oxide was observed in the penetrated zone together with some silica and lime from the slag. Clusters of calcium aluminate (CA6) and magnesium aluminate (MA) spinel build the refractory back-bone on the hot side of the material and gussets filled with mostly glassy calcium aluminum silicates close to the hot face and gehlenite further inside the penetrated zone. Alumina grains had a reaction rim consisting of CA2 or CA6 and a very intimate connection to the surrounding matrix unlike the CMA-free mix that showed micro cracks around the alumina grains. At the colder side, the gunning mix with CMA aggregates showed a very good connection to the substrate, supported by a hercynite formation in the gunning mix resulting from a cross-reaction with remains of iron oxide on the CMA containing repair mix. Furthermore, macroscopic observations of a CMA aggregate containing alumina magnesia castable in the metal zone of a steel ladle revealed that macro cracks developed only very slowly, which resulted in a superior service life.

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Stratlingite is one of the constituent minerals of the bonding matrix of low-cement castables. In this study, the crystallization processes of stratlingite in hydrates of high alumina cement at 60°C and 10°C were analyzed using X-ray diffraction (XRD) and electron probe microanalyzer (EPMA). The stratlingite has crystallized in large quantities in the samples cured at 60°C, while in the samples cured at 10°C, stratlingite was not detected beyond the period of fifteen months.