Suppression of decarbonization and resource characteristics of carbonated spinel-corundum refractories in steel-ladle lining

Experimental studies of changes in the pore structure and physical and technical properties of carbonated spinel-corundum refractories under different conditions of decarbonization and the formation of a protective regulatory layer on their hot surface, suppressing decarbonization of the refractory material and mass transfer between the lining and the flow of slag melt, are presented. The results of industrial tests of carbonated spinel-corundum refractories in the working layer of the lining of a 400-ton steel-ladle lining, as well as the topography and consumption specific coefficients of refractories for the functional zones of the ladle lining, the amount of refractory destruction products of the lining during its operation are considered.

Corrosion Mechanism of A Density-Reduced Steel Ladle Lining Containing Porous Spinel-Calcium Aluminate Aggregates

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.

Influence of Variation/Response Space Complexity and Variable Completeness on BP-ANN Model Establishment: Case Study of Steel Ladle Lining

Artificial neural network (ANN) is widely applied as a predictive tool to solve complex problems. The performance of an ANN model is significantly affected by the applied architectural parameters such as the node number in a hidden layer, which is largely determined by the complexity of cases, the quality of the dataset, and the sufficiency of variables. In the present study, the impact of variation/response space complexity and variable completeness on backpropagation (BP) ANN model establishment was investigated, with a steel ladle lining from secondary steel metallurgy as the case study. The variation dataset for analysis comprised 160 lining configurations of ten variables. Thermal and thermomechanical responses were obtained via finite element (FE) modeling with elastic material behavior. Guidelines were proposed to define node numbers in the hidden layer for each response as a function of the node number in the input layer weighted with the percent value of the significant variables contributing above 90% to the response, as well as the node number in the output layer. The minimum numbers of input variables required to achieve acceptable prediction performance were three, five, and six for the maximum compressive stress, the end temperature, and the maximum tensile stress.

Life Cycle Assessment Comparison of Two Refractory Brick Product Systems for Ladle Lining in Secondary Steelmaking

This paper aims to compare the environmental performance of two types of refractory bricks for the internal lining of ladles in secondary steelmaking, where the dissolved inclusions coming from the refractory material require fine control to obtain the target steel quality. In this context, magnesia-carbon-based refractories are largely utilized, thanks to the adequate durability of the ladle lining in terms of number of heats before re-lining, but the utilization of organic binders in the mixture (pitch, resins) arises ecological and human health concerns. Concurrently, research efforts in refractory material science look at improving the quality of steel by reducing the content of dissolved carbon due to the release from the bricks, thus focusing on different refractory materials and specifically on alumina-based materials. The European Commission funded the research project “LeanStory”, aiming to promote such new lines of refractories through the cooperation between industrial partners and scholars where different recipes are considered. In the present paper, two representative systems of the refractory types considered, magnesia-carbon and magnesia-alumina, are compared with a preliminary Life Cycle Assessment (LCA). Suppliers and transports for the two product systems have been taken into account, referring to one tonne of refractory material as the functional unit for comparison. Preliminary impact results (adopting the ReCiPe Midpoint–Hierarchist perspective methodology for calculating the impact indicators) show that the new solution performs largely better almost for each indicator. Further investigations are required in order to assess the ecological performance of the two systems, considering the effective consumption of bricks for the production of steel.