The Primary Modes of Damage to Runner Brick(Pouring brick) and Factors Affecting Their Refractoriness

1,Composition of Runner Brick from Different Batches

As indicated by the inspection data, the primary constituent of Runner Brick is alumina, followed by silica; they also contain minor amounts of iron oxide and other substances. Consequently, the physicochemical properties of steel pouring bricks are significantly correlated with the proportions of these major constituents; indeed, variations in these primary components exert a substantial influence on the physicochemical parameters of the bricks.

2,The Primary Forms of Damage to Runner Brick During Steel-Refractory Reactions

During the contact between a Runner Brick and molten steel, the interactions between the molten metal and the refractory material encompass several aspects. First, there is the erosive scouring of the refractory by the molten steel, which leads to spalling—where entire sections of the refractory material detach and fall into the molten bath. This constitutes a physical process, which typically occurs when the refractory contains localized points of instability, such as low-melting-point inclusions or voids. Second, chemical reactions take place between the refractory's constituents—such as oxides, carbon, and nitrides—and elements present in the molten steel, such as Al, Si, Mn, and Fe. Although the surface area of ​​this reaction interface is substantial, the thickness of the resulting chemical reaction layer remains relatively thin. Moreover, this chemical interaction persists throughout the entire duration of the refractory's contact with the molten steel. However, since the physical process of dissolution typically precedes the chemical reaction process—and because the rate of material loss due to physical dissolution is significantly faster than that of chemical reaction—it can be concluded that the primary mechanism responsible for the degradation of steel-pouring bricks in contact with molten steel is physical dissolution.

The interaction between a Runner Brick and molten steel proceeds in a sequence: physical dissolution occurs first, followed by chemical decomposition reactions. The reaction interface layer associated with this decomposition is extremely thin, and the rate of these chemical reactions is relatively slow. Consequently, characterizing the refractoriness of Runner Brick based on their melting point is a scientifically sound approach, and the method for calculating this parameter is comparatively straightforward.

3,The Calculation Process of the Chemical Composition Method

3.1 Chemical Composition of a Specific Batch of Runner Brick
Upon receipt of a specific batch of Runner Brick at the plant, samples were collected to verify their chemical composition.

As indicated by the data in Table 1, the chemical composition appears relatively normal, with a distinct disparity between the mass fractions of the major and minor constituents.
3.2 Calculation of the Liquidus Temperature for a Specific Batch of Runner Brick
The formula for calculating the molar amount of an oxide MxOy is:
aMxOy = XMxOy / AMxOy  (1)
Where: aMxOy represents the molar amount of the oxide MxOy; XMxOy represents the mass fraction of the oxide MxOy (in %); and AMxOy represents the molecular weight of the oxide MxOy.
During the contact between the reaction layer of the steel-teeming brick and the high-temperature molten steel, the oxides within the reaction layer invariably tend to undergo chemical reactions to form lower-melting-point phases.

When calculating based solely on constituents such as Al₂O₃, SiO₂, CaO, MgO, and Fe₂O₃, the liquidus temperature for a Runner Brick with an Al₂O₃ content of 65.29% is determined to be 1854°C. In addition to the oxides that form mullite—such as Al₂O₃ and SiO₂—the high-alumina bauxite raw material used for these bricks also contains a certain amount of impurities. Among these impurities, oxides such as Fe₂O₃, K₂O, and Na₂O possess relatively low melting points; consequently, during the interaction between the molten steel and the refractory surface, the high-temperature molten steel readily dissolves these impurities on the surface, thereby creating liquid channels that infiltrate the interior of the refractory material. Therefore, the presence of these low-melting-point oxides effectively lowers the refractoriness of the steel-teeming bricks. The actual liquidus temperature for a Runner Brick with an Al₂O₃ content of 65.29% should, in reality, be lower than 1854°C.

4,The Mineral Phase Composition of Pouring Refractory Bricks Formed During High-Temperature Reaction Processes

From a thermodynamic perspective, during the contact between molten steel and the refractory pouring brick, the various oxides within the brick invariably tend to undergo chemical reactions to form complex oxides with lower melting points. As the pouring brick reacts with the high-temperature molten steel, complex compounds are continuously generated within the brick's reaction layer. When the reaction temperature of the molten steel exceeds the melting point of these complex oxides, a partial liquid phase of complex oxides forms within the reaction layer; these liquid-phase complex oxides are generated at the reaction interface and subsequently entrained into the molten steel by the flowing stream. Adhering to the principle that complex oxides with lower melting points form preferentially—and based on the molecular counts of the various constituent oxides—it is possible to deduce the molecular formulas and quantities of the various complex compounds present within the reaction layer of the pouring brick.

Specifically, there are 46 molecules of SiO₂, 64 molecules of Al₂O₃, and only one molecule each of CaO and Fe₂O₃; consequently, SiO₂ and Al₂O₃ will preferentially combine. As indicated in Table 6, the complex compound with the highest priority for formation is mullite, followed by calcium aluminate; both of these compounds possess very low melting points. Although Fe₂O₃ has the lowest melting point, the single Fe₂O₃ molecule will persist in the form of a standalone oxide. Given that the Al₂O₃-to-SiO₂ ratio in mullite (3Al₂O₃·2SiO₂) is 3:2, approximately 64 molecules of Al₂O₃ and 43 molecules of SiO₂ will combine to form mullite, leaving a remainder of 3 SiO₂ molecules. Furthermore, with only one molecule each of CaO and Fe₂O₃ available, one molecule of CaO, one of Al₂O₃, and one of SiO₂ will combine to form a single molecule of CaO·FeO·SiO₂; ultimately, this leaves a remainder of two SiO₂ molecules.

5, Conclusion

(1) The primary form of erosion occurring during the contact between a refractory pouring brick and molten steel is a physical dissolution process; the interfacial layer associated with the decomposition reactions of oxides is relatively thin, and the reaction rate is slow. The melting points and corresponding mass fractions of the various oxides present in the refractory pouring brick collectively determine the liquidus temperature of the reaction system formed between the brick and the molten steel.

(2) When interfacial reactions occur between a runner brick and molten steel, the reaction mechanism involves the formation of a single complex oxide from multiple individual oxides. Furthermore, the lower the melting point of the resulting complex oxide, the more favorable the reaction kinetics for its formation; conversely, the higher the mass fraction of a specific individual oxide, the more readily that oxide participates in chemical combination reactions.

(3) The method for deriving refractoriness based on chemical composition calculations involves utilizing the mass fractions and melting points of the various constituent components to compute a precise value for the liquidus temperature.