Post-mortem analysis of alumina-magnesia-carbon refractory bricks used in steelmaking ladles

Abstract

Post-mortem studies in secondary steelmaking ladles are an important way to determine the factors related to Alumina-Magnesia-Carbon (AMC) refractory corrosion. AMC refractory bricks installed in the impact zone of a steelmaking ladle bottom were analyzed after 100 castings. X-ray diffraction, X-ray fluorescence chemical analysis, reflected optical light microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry, density and porosity measurements, and mercury porosimetry were used to analyze the chemical and physical characteristics of the slag, the unused refractory and the slag+steel attacked bricks. The corrosion process produced a specific microstructure characterized by: i) a thick discontinuous slag layer composed by secondary spinel+steel+liquid; ii) a thick dense, cracked, and continuous layer consisting of calcium aluminates+steel+liquid at the slag/refractory interface; iii) next to this layer, a wide densified layer with a uniform microstructure in which corundum aggregates and spinel crystals were linked together by elongated CaAl 12 O 19 crystals.The formation of these reaction layers constituted a barrier that effectively suppressed the massive slag penetration and surely reduced the wear rate. Thermodynamic calculations based on simplified and complex condensed phase equilibrium diagrams, were used to further understanding of the corrosion mechanism.During the service of the ladle, when the secondary metallurgy takes place (i.e., the adjustment of the steel composition), refractories of the working lining are exposed to very aggressive conditions: the high temperature of the process, the oxidant atmosphere that prevails because it is an open vessel, and contact with corrosive agents, especially the liquid slag, among others. The refractories are zoned in type and thickness to provide maximum ladle performance at a minimum cost.However, the particular loading of each refractory depends not only on its location in the vessel, but also on the stage of the ladle cycle [6]: the lifetime of the refractory in the impact zone of the bottom is limited by the thermo-mechanical loading, thermal shock and erosion, which are developed during the tapping and the refining of the steel. For this reason, the use of refractories with high mechanical strength and erosion resistance at high temperatures is convenient, which is why alumina is incorporated into the refractory formulation. However this addition makes the brick incompatible with the ladle slag. Nevertheless, liquid slag is in contact with these refractories during the casting stage, giving corrosion a chance to occur before slag solidification. This paper deals with the degradation of AMC bricks used in the impact zone of a steelmaking ladle (post-mortem study) with a focus on slag corrosion, bearing in mind that it undoubtedly contributed to the refractories' wear. The literature on the corrosion of AMC bricks is scarce, and the papers available concern work implemented in lab tests to the study the phenomenon [7-9]. These tests provi...

Microstructure, properties, and application of low carbon Al2O3‐C refractories used as submerged entry nozzles

“…This phenomenon was mainly owing to the great improvement in densification during high-temperature oxidation. 36 , and 4.21 wt% F) was much less pronounced than that for LAC, failing to form a protective layer at the interface. The Al elements showed an obvious graded distribution across the interface as a result of the dissolution of alumina.…”

“…Undoubtedly, the adhesion of this viscous layer to the interface can inhibit the advance of the liquid slag and thus limit the slag corrosion. 36,37 For the traditional Al 2 O 3 -C refractory, however, the enrichment of Al 2 O 3 in the slag near the interface (containing 25.38 wt% CaO, 14.73 wt% Al 2 O 3 , 40.49 wt% SiO 2 , 1.93 wt% MgO, 8.40 wt% Na 2 O, 2.86 wt% Fe 2 O 3 , and 4.21 wt% F) was much less pronounced than that for LAC, failing to form a protective layer at the interface. This difference was mainly caused by the poor wear resistance of the oxidized layer, which would be easily eroded away by the flux.…”

Thermal stress analysis and structural optimization of ladle nozzle based on finite element simulation

“…When the thermal stress exceeds the limit strength of the ladle nozzle, it will form a crack centered on the casting hole, resulting in thermomechanical erosion. Steel and slag will penetrate through the cracks to the ladle nozzle, and react with the ladle nozzle material, causing thermochemical erosion of the ladle nozzle [2]. In order to improve the service life of the ladle nozzle, it must have good overall performance, such as high temperature resistance, excellent high temperature strength, thermal shock resistance and corrosion resistance.…”

Basic slag corrosion of alumina–magnesia–carbon refractory bricks containing Al and Si antioxidants

“…The campaign of a steelmaking ladle lined with AMC refractories can last roughly 100 castings, as it was previously reported. 6 In that post-mortem study of AMC bricks, it was concluded that the wear mechanisms on microscopy scale included the formation of a decarburized layer, the thermomechanical spalling when the liquid steel jet was received (at 1973 K), and the subsequent infiltration of slag in the refractory. Finally, the matrix and the oxide aggregates were degraded by erosion or dissolution due to the slag movement.…”