2.2 Composition and structure of corundum-spinel castable after use
The thickness of the original working layer is 230～250mm, and the apparent morphology of the impact area at the bottom of the 8# ladle after 91 times of use. The residual thickness of the corundum-spinel castable is about 120mm, and the hot end metamorphic layer is thin. There are obvious through cracks parallel to the hot surface at about 20 and 80 mm away from the hot end, and there is a phenomenon of slag penetration along the crack in the crack.
In order to analyze the interaction between the molten slag and the corundum-spinel castable and understand the damage mechanism of the material, the area A was taken to make a light sheet. Scanning electron microscope and energy spectrometer were used to observe the microstructure of the area and determine the components of the micro area. The microstructure of the hot surface of the A area of the residue after use from the slag layer to the quasi-protoplasmic layer
It can be seen that the area A of the residual material after use can be clearly divided into 3 layers: the slag layer (about 0.5mm), the permeable layer (6-8mm) and the protoplasmic layer. The elements in the slag react with the castable matrix to form a low-melting phase (see the infiltration layer in Figure 2), and penetrate into the castable through the matrix, which promotes the sintering and densification of the matrix. There are a large number of pores in the protoplasmic layer, the structure is loose, the thermal expansion coefficient between the permeable layer and the protoplasmic layer does not match, and through cracks occur between the two. In the permeable layer, FeO, CaO and SiO₂ in the slag penetrate into the castable matrix. With further penetration, its content gradually decreases.
In order to further analyze the influence of slag penetration on the microstructure and micro-area composition of the castable, each area in Figure 2 was enlarged to observe and EDS analysis was performed. In area a of the slag layer, the microstructure of the castable matrix of the working face is destroyed, the matrix is infiltrated by a large amount of liquid phase, and the structure is dense. The main phases are MgO-CaO-Al₂O₃-SiO₂-FeO low melting point phase and CaO-Al₂O₃- SiO₂-FeO low melting phase). In areas b and c in the infiltration layer, a large amount of CaO, SiO₂, and FeO in the slag penetrate into the castable, resulting in densification of the matrix. Magnesium aluminum spinel phase. In the area d of the protoplasmic layer, there are a large number of pores in the matrix and the structure is loose, mainly magnesium-aluminum spinel phase, CaO-Al₂O₃ phase and corundum phase. In addition to infiltrating into the castable through the matrix, the slag also spreads into the castable along the cracks.
2.3 Damage mechanism of corundum-spinel castable
The main damage factors of the bottom working layer of the ladle are: thermal shock, mechanical stress, erosion and penetration of slag. On the working face, the main phases of the original castable are magnesium aluminum spinel, CaO-Al₂O₃ and corundum. With the erosion and penetration of the slag into the castable, the magnesium-aluminum spinel phase in the matrix absorbs the FeO in the slag, and the corundum reacts with CaO and SiO₂ in the slag to form a calcium-aluminum-silicon low-melting phase:
As the content of SiO2, FeO and CaO in the slag decreases, the relative content of the slag decreases, so that the amount of slag that further erodes and penetrates into the castable is reduced.
At the working surface, the liquid phase in the slag and the liquid phase formed by the reaction penetrate into the castable. Due to the temperature gradient, the sintering densification of the hot surface is caused, and the matrix bonding phase is destroyed at the same time. Due to mechanical stress and thermal stress, cracks are formed in the dense layer and spread through the interface between the reaction layer and the permeable layer, resulting in the peeling of the reaction layer. In addition, the slag corrodes and penetrates into the castable along the cracks, which accelerates the peeling of the reaction layer from the refractory. The repetition of this situation during service led to the destruction of refractory materials.
in conclusion
(1) Corundum-spinel castables are used to replace magnesia-aluminum-carbon bricks at the bottom of the ladle, which can meet the smelting process of the electric furnace round billet production line. Using integral castables, the melting loss rate of the bottom working layer of the ladle is small, the integrity and air tightness are strengthened, and the probability of cold steel infiltration along the brick joints and offline due to abnormal ventilating bricks is reduced, and the safety of ladle operation is significantly improved and optimized The maintenance mode is improved and the consumption of refractory materials is reduced.
(2) The damage of the corundum-spinel castable is mainly caused by the reaction of slag and refractory materials. At the same time, thermal stress and mechanical stress also play an important role; in addition, the slag corrodes and penetrates into the castable along the crack, accelerating The reaction layer peeled off from the refractory material. The repetition of this process during service has led to the destruction of refractory materials.
