WHICH RAW MATERIALS AFFECT THE SLAG RESISTANCE OF ALUMINUM-MAGNESIUM LADLE CASTABLES

Now, the ladle has become an important refining equipment, so alkaline bricks have become an important refractory material for the lining of the ladle, and they are used in conjunction with different construction methods, such as Mg OC bricks for the slag line, and aluminum-magnesium for the bottom and wall of the ladle. Castable. The use conditions of the slag line are particularly harsh, and the damage of the inner lining is also the most serious. In practical applications, special attention should be paid to the damage of steel slag to refractory materials.
The damage of steel slag to refractory materials is mainly divided into two aspects, one is erosion, and the other is penetration. When the slag penetrates into the brick, a metamorphic layer is formed in the brick, and the metamorphic layer and the unmodified layer are continuously exchanged between cold and heat during use, and the difference in expansion coefficient causes cracks and structural peeling. Therefore, the ladle castable is mainly to strengthen the matrix, reduce the penetration of slag, and weaken the formation of metamorphic layer.
1 test
1.1 Raw materials and test plan
The aggregate used is fused white corundum with grain size 8～5, 5～3, 3～1 and ≤1 mm, w(Al2O3)=98.5%; 1～0 mm plate corundum, w(Al2O3)=98.5% ; ≤0.074 mm magnesium aluminum spinel powder, w(Al2O3)=78.5%, w(Mg O)=20%; ≤0.088 mm fused magnesia powder, w(Mg O)=96.5%; ≤3μm α -Al2O3 fine powder, w(Al2O3)=98.5%; pure calcium aluminate cement, w(Al2O3)=70%, w(CaO)=29%.
According to fused white corundum aggregate 55%(w), tabular corundum aggregate 10%(w), fine corundum powder, magnesia powder, magnesia-aluminum spinel powder and α-Al2O3 powder 32%(w), aluminum Calcium acid cement 3% (w) is mixed to change the content of magnesia and spinel.
1.2 Test process and performance test
The prepared sample was vibrated and poured into a mold of 40 mm×40 mm×160 mm, and it was demoulded by natural curing for 24 h. After heat treatment at 110°C for 24 h, 1000°C for 3 h, and 1600°C for 3 h, the heat treatment was measured. Performance, using static crucible method for slag corrosion test. Along the sample forming direction, drill holes with a depth of 40 mm and an inner diameter of 38 mm and 33 mm in the center of the top surface of the sample to make crucibles. After vibrating, forming and baking at 110 ℃ for 24 h, the holes are placed in each crucible. Put 50 g of slag (the chemical composition (w) of the slag is: Fe2O3 24.97%, Al2O3 6.63%, CaO 16.13%, Si O2 9.47%, Ti O2 1.1%, MnO2 0.2%, Na2O 0.05%, K2O 0.01%) Sintered in a 1600℃ electric furnace and kept for 3 hours. After natural cooling, cut along the crucible section, measure the slag corrosion area and the penetration area, and calculate the slag corrosion index (slag corrosion area / original groove axial cross-sectional area × 100%) And permeability index (permeation area / cross-sectional area of ​​the original groove axis × 100%).
2 Results and analysis
2.1 Physical properties
With the increase of magnesia and the decrease of spinel powder, the flexural and compressive strengths of samples A and B in each temperature section are higher than those of sample C. The strengths of the three types of samples in the middle and low temperature sections are not much different. The difference is obvious. After firing at 1600℃, the expansion of the three samples gradually increased with the increase of the magnesia content. The residual expansion of the A sample was 0.48%, the porosity was low, and the volume stability was high; while the C sample was 1.13%, The residual expansion is the largest.
2.2 Macro observation and slag corrosion index of the sample after slag erosion
It can be seen that the slag of the three samples has a complete appearance after corrosion, and there is no obvious sign of corrosion. After sintering at 1600°C, the penetration of slag is dominant. The infiltration part of the slag changes from black to brown, and the transition zone gradually becomes shallower from the inside to the outside. The remaining slag in the groove is called cylindrical shrinkage in the middle. Sample A had horizontal and vertical cracks, and the slag gradually penetrated into the cracks under high temperature, and the amount of internal residues was not much, and the corrosion resistance was average. The penetration of sample B slag into the crucible is shallower than that of samples A and C, and the amount of residue is more than that of sample A. Sample C has relatively high internal pores due to its large volume expansion. The slag penetrates into the matrix through the pores and diffuses through the liquid phase at high temperatures, causing cracks and loose structure in the permeable layer. The amount of residue inside the crucible is more than that of samples A and B. .
With the increase of magnesia, the anti-erosion index gradually increases, and the anti-permeability index first decreases and then increases. On the one hand, the Mg O in the magnesia reacts with Al2O3 to generate spinel in situ to produce volume expansion, and the excess magnesia Mg O is solid-dissolved in the spinel. After firing at 1600℃, sample C has a high magnesia content and the largest expansion of synthetic spinel. Excessive expansion will lead to high porosity and low strength of the pouring body, which will cause the slag to easily penetrate into the matrix and cause thermal spalling; another On the one hand, FeO and MnO in the slag can form a solid solution with spinel: FeO+MnO+MA→(Fe,Mn,Mg)O·(Fe,Al)2O3. The Si O2 in the slag becomes abundant and becomes very viscous. Since the slag penetration depth (L) depends on the equation: where σ is the surface tension of the slag, is the porosity radius of the pouring body, t is the slag penetration time, is the contact angle between the pouring body and the slag, and is the slag viscosity. It can be inferred that L is inversely proportional to. The Al2O3 in the matrix can capture CaO in the slag, spinel added to the castable can solidify FeO and MnO in the slag, which can increase the viscosity and melting point of the slag, and inhibit the penetration of the slag. These two effects can make The decrease in slag penetration resistance is suppressed to a minimum; in addition, as the content of MgO increases, the greater the ratio of Mg O to Al2O3 in the synthetic magnesia-aluminum spinel, the higher its corrosion resistance, so sample C The corrosion resistance index is higher than that of samples A and B. The content of Mg O in sample C is relatively high, and the expansion is large. Microcracks caused by proper expansion can organize the expansion of cracks, but excessive expansion will increase the volume and lose the effect of controlling the slag penetration, causing the slag to penetrate into the matrix. Heat spalling occurred, resulting in a high permeability index of sample C.
According to the study of corrosion mechanism [8], due to the reaction of molten slag and ladle working lining to form a protective zone, the inner lining can no longer be corroded by molten slag. In this protective layer belt, most of the iron oxide and manganese oxide in the slag in contact with the lining are dissolved into the spinel lattice structure to form a solid solution. The iron oxide in the slag reacts with Al2O3 to produce iron-aluminum spinel and the expansion caused by it is not significant. Although the CaO in the slag reacts with Al2O3 to produce CA6, it will have a great expansion, but it is balanced by the reaction of CaO and Si O2 in the slag with Al2O3 to produce mayemite or anorthite and other low-melting minerals. Therefore, the combination of high melting point and low melting point minerals generated by the reaction between the ladle working lining and the molten slag provides a hot surface protection layer for the ladle working lining, thereby minimizing the further erosion of the ladle working lining.
In addition, when the chemical composition of the slag penetrates into the refractory material and reacts with it, the main crystal bond of the infiltrated area decreases, and it is easily eroded by the impulse flow, which will cause the refractory material to be further exposed, and the refractory material is not exposed. The infiltrated part is chemically attacked [9]. On the contrary, when there is no mechanical action to eliminate the infiltrated part, the chemical attack will gradually become slower and stop due to the thermal temperature gradient. In the process of thermal cycling, the permeable layer has never been peeled off by the permeable layer, so the ladle castable structure peeling will be limited by the depth of penetration. The requirements for different parts of the ladle castable are also different. The ladle wall castable is controlled by the metal cladding and will not expand freely in practical applications. For a longer service life, it is necessary to select Al2O3-MgO with low linear expansion rate after high temperature treatment. Castable, non-flaking and corrosion-resistant at the same time. The bottom of the bag is different from the wall of the bag, the binding force of the bottom of the bag is small, and the high-expansion material is difficult to be applied here due to the disadvantage of swelling and floating. In order to prevent arching and suppress slag penetration, corundum-spinel castables with high volume stability and good thermal shock have become the first choice for cladding bottom applications. At present, the B-group formula has been successfully applied to the 110t ladle wall of a large domestic steel plant, with an average service life of 180-200 furnaces, of which 30 furnaces are LF refining, and the residual thickness of the ladle wall is 70 mm.
3 Conclusion
The slag erosion resistance and permeability resistance of castables are often contradictory, and the erosion resistance and permeability resistance should be weighed according to the specific conditions of use. In this experiment, when the amount of fused magnesia powder is 4% (w) and the amount of fused magnesia-aluminum spinel powder is 8% (w), the aluminum-magnesium ladle castable has a better slag resistance effect.