A method for preparing a protective coating for a tundish lining for clean steel smelting

Abstract

The application discloses a preparation method of a protective coating of a tundish lining for clean steel smelting, and belongs to the field of refractory material applications. The protective layer is prepared from slurry with suitable viscosity of different particle sizes of magnesia-yttria stabilized zirconia, a sintering agent, a stabilizer and a binding agent, is sprayed or smeared on the surface of a tundish working lining to form a thin layer with a thickness of 2-5 mm, and can form a protective layer with suitable performance after on-line baking. The protective layer prepared in the way can effectively isolate the direct contact between the working lining dry charge in initial use and molten steel, avoids the formation of inclusions in the molten steel caused by the peeling of the protective layer, reduces the hydrogen and carbon increasing effect of the resin dry charge on the molten steel, improves the cleanliness of the molten steel, improves the non-wetting performance of the refractory material against the molten steel, and is not easy to form inclusions in the molten steel, thereby guaranteeing the quality of the clean steel.

Description

Technical Field

[0001] This invention relates to the field of refractory materials applications, and specifically to a method for preparing a protective coating for tundish linings used in clean steel smelting. Background Technology

[0002] Clean steel refers to molten steel containing extremely low levels of impurity elements such as S, P, N, O, C, H, and non-metallic inclusions. To achieve this, various refining methods, such as LF, RH, VD, VOD, or composite refining, are used to reduce the content of impurity elements in the molten steel. Besides process control, the refractory materials used in smelting are also a crucial factor affecting the quality of molten steel. The tundish is the final process where molten steel and refractory materials come into direct contact, and its working lining has a significant impact on the quality of the molten steel, especially the quality of clean steel. The commonly used tundish working lining is resin-bonded magnesia dry refractory, which has become the mainstream system for tundish linings due to its simple process, convenient construction, and suitable high-temperature performance. However, due to the influence of the supporting carbon-containing materials, magnesia dry charge can only be directly fed into the molten steel after being baked online to 1000-1300℃ before the first furnace. Since the dry charge is not internally burned at this point, its bonding strength is low, making it easily eroded and melted into the molten steel, forming magnesia inclusions. It may also react with alumina in the molten steel to form spinel inclusions, leading to a decrease in the cleanliness and quality of the molten steel. Furthermore, resin-bonded magnesia dry charge releases irritating gases such as formaldehyde and phenols during use, causing a carbon / hydrogen increase effect on the molten steel and reducing its quality.

[0003] Currently, methods to improve the cleanliness of molten steel mainly focus on process control in the refining process and technological improvements to the working lining materials. Traditional coatings primarily address the inherent oxidation and wear resistance of refractory materials, with limited reports on the protective performance of coatings on the molten steel cleanliness of the tundish working lining. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a method for preparing a protective layer for tundish lining in clean steel smelting.

[0005] Technical solution: This invention proposes a protective coating for tundish linings used in clean steel smelting. The protective layer is composed of magnesium yttrium stabilized zirconium oxide of different particle sizes, powdered sintering aid, stabilizer, and liquid binder.

[0006] Furthermore, the magnesium yttrium stabilized zirconium oxide includes zirconium oxide particles, zirconium oxide fine powder, and zirconium oxide micro powder;

[0007] The raw material composition and specific mass ratio of the protective layer are: 40-50% magnesium yttrium stabilized zirconium oxide particles, D 0.9 ≤0.2mm; 30-40% magnesium yttrium stabilized zirconia fine powder, D 0.9≤0.074mm; 5-15% magnesium yttrium stabilized zirconia micro powder, D 0.9 ≤10um; 5-15% magnesium yttrium stabilized zirconia micro powder, D 0.9 ≤3um;

[0008] 1-5% sintering aid, D 0.9 ≤61um, the total weight of the above raw materials is 100%;

[0009] The stabilizer is added externally, accounting for 0.1-0.5% of the total weight of the raw materials;

[0010] The binder is added externally, accounting for 10-20% of the total weight of the raw materials.

[0011] Furthermore, the magnesium yttrium stabilized zirconium oxide is any one of high-purity magnesium stabilized zirconium oxide;

[0012] Among them, 2% (mol) ≤ MgO ≤ 10% (mol), 2% (mol) ≤ Y2O3 ≤ 10% (mol), and ZrO2 ≥ 88% (mol).

[0013] Furthermore, the sintering aid is any one of boric acid, borax, or borosilicate glass powder, wherein D 0.9 ≤61um.

[0014] Furthermore, the stabilizer is any one of polyphosphate, polyethylene glycol condensate, or lignin sulfonate.

[0015] Furthermore, the binder is any one of liquid aluminum dihydrogen phosphate, aluminum sol, and water glass.

[0016] Furthermore, a method for preparing a protective coating for tundish linings used in clean steel smelting includes the following steps: co-milling and premixing all solid raw materials (magnesium yttrium stabilized zirconium oxide, powdered sintering aid, and stabilizer) with zirconium balls, with a material-to-ball mass ratio of 1:1.5 to 2.

[0017] Then, add liquid binder and stir thoroughly to make protective layer slurry. Adjust the slurry to a suitable viscosity and apply it mechanically or manually to the surface of the working lining of the tundish to form a thin layer of 2-5 mm thickness.

[0018] After the slurry has completely solidified, it is immediately baked online for use: the oven is heated to 300℃~350℃ within 0.5h and maintained for 1h, then rapidly heated to 1200℃~1300℃ within 1h and maintained for at least 1.5-2h before being put into use online.

[0019] Beneficial effects: Compared with the prior art, the features of this invention are: 1. This invention utilizes a dry-material protective layer formed at medium and low temperatures, effectively isolating the working lining dry material from direct contact with molten steel during initial use, avoiding inclusions in the molten steel formed due to its own peeling; at the same time, it reduces the hydrogen / carbon increase effect of resin dry material on molten steel, improving the cleanliness of molten steel; 2. This invention uses magnesium yttrium stabilized zirconium oxide as the main raw material for the protective layer, improving the non-wetting performance of the refractory material against molten steel, making it less likely to form inclusions in the molten steel, and ensuring the quality of clean steel; 3. This invention utilizes the self-bonding of materials at medium and low temperatures to form a protective layer with suitable performance, resulting in low energy consumption, which is beneficial to steelmaking cost control and increased economic benefits. Detailed Implementation

[0020] The present invention will be further described below with reference to embodiments.

[0021] The present invention proposes a protective coating for tundish linings used in clean steel smelting. The protective layer is composed of magnesium yttrium stabilized zirconium oxide of different particle sizes, powdered sintering aid, stabilizer and liquid binder.

[0022] Furthermore, the magnesium yttrium stabilized zirconium oxide includes zirconium oxide particles, zirconium oxide fine powder, and zirconium oxide micro powder;

[0023] The raw material composition and specific mass ratio of the protective layer are: 40-50% magnesium yttrium stabilized zirconium oxide particles, D 0.9 ≤0.2mm; 30-40% magnesium yttrium stabilized zirconia fine powder, D 0.9 ≤0.074mm; 5-15% magnesium yttrium stabilized zirconia micro powder, D 0.9 ≤10um; 5-15% magnesium yttrium stabilized zirconia micro powder, D 0.9 ≤3um;

[0024] 1-5% sintering aid, D 0.9 ≤61um, the total weight of the above raw materials is 100%;

[0025] The stabilizer is added externally, accounting for 0.1-0.5% of the total weight of the raw materials;

[0026] The binder is added externally, accounting for 10-20% of the total weight of the raw materials.

[0027] Furthermore, the magnesium yttrium stabilized zirconium oxide is any one of high-purity magnesium stabilized zirconium oxide;

[0028] Among them, 2% (mol) ≤ MgO ≤ 10% (mol), 2% (mol) ≤ Y2O3 ≤ 10% (mol), and ZrO2 ≥ 88% (mol).

[0029] Furthermore, the sintering aid is any one of boric acid, borax, or borosilicate glass powder, wherein D 0.9 ≤61um.

[0030] Furthermore, the stabilizer is any one of polyphosphate, polyethylene glycol condensate, or lignin sulfonate.

[0031] Furthermore, the binder is any one of liquid aluminum dihydrogen phosphate, aluminum sol, and water glass.

[0032] Furthermore, a method for preparing a protective coating for tundish linings used in clean steel smelting includes the following steps: co-milling and premixing all solid raw materials (magnesium yttrium stabilized zirconium oxide, powdered sintering aid, and stabilizer) with zirconium balls, with a material-to-ball mass ratio of 1:1.5 to 2.

[0033] Then, add liquid binder and stir thoroughly to make protective layer slurry. Adjust the slurry to a suitable viscosity and apply it mechanically or manually to the surface of the working lining of the tundish to form a thin layer of 2-5 mm thickness.

[0034] After the slurry has completely solidified, it is immediately baked online for use: the oven is heated to 300℃~350℃ within 0.5h and maintained for 1h, then rapidly heated to 1200℃~1300℃ within 1h and maintained for at least 1.5-2h before being put into use online.

[0035] This invention uses high-refractive-strength yttrium-magnesium composite stabilized zirconium oxide as the main raw material. Firstly, yttrium-magnesium stabilized zirconium oxide has good non-wetting properties relative to molten steel and slag, making it less likely to form inclusions in the molten steel and ensuring the quality of clean steel. Secondly, both yttrium-magnesium stabilized zirconium oxide and magnesia dry charge contain MgO components, exhibiting homogeneity and avoiding interfacial effects between the protective layer and the dry charge, thus facilitating the formation of a continuous, high-strength interfacial bonding phase and reducing the occurrence of protective layer detachment. Thirdly, yttrium-magnesium composite stabilized zirconium oxide has a more stable cubic phase structure, avoiding the volume effect of zirconium oxide due to phase transformation, reducing MgO desolvation caused by the decomposition of ZrO2-MgO solid solution during medium-temperature (i.e., online baking), and minimizing the formation of inclusions in the molten steel caused by the protective layer.

[0036] Adding an appropriate amount of sintering aid helps to promote the formation of liquid bonding in the protective layer under medium and low temperature conditions, thereby achieving rapid sintering of the protective layer. At the same time, it can also promote the full reaction and sintering of the magnesium dry material at the interface, forming magnesium borate, which helps to improve the bonding strength of the dry material, thereby improving the resistance of the working lining to molten steel scouring.

[0037] Adding a liquid binder ensures the bonding performance of the protective layer after solidification, preventing it from peeling off before online baking. The stabilizer ensures the uniformity of the protective layer slurry composition, improves its stability, and prevents delamination.

[0038] Example:

[0039] According to the formulation schemes of the following three embodiments, the viscosity of the slurry was adjusted to 7000-10000 mPa·S (25-30℃); then, after baking at 200℃ / 24H, it was coated on the magnesium dry material with a coating thickness of about 5mm. Afterwards, the two dry materials with and without the coating were heat-treated at 1300℃ / 5H and their strength was compared. The results are shown in Table 1.

[0040] Example 1:

[0041] The protective layer was prepared using a composite stabilized zirconium oxide (92% (mol) ZrO2 + 5% (mol) MgO + 3% (mol) Y2O3) as the main raw material. Its specific composition and mass ratio are as follows:

[0042]

[0043] Example 2:

[0044] The protective layer was prepared using a composite stabilized zirconium oxide (90% (mol) ZrO2 + 8% (mol) MgO + 2% (mol) Y2O3) as the main raw material. Its specific composition and mass ratio are as follows:

[0045]

[0046] Example 3:

[0047] A protective layer was prepared using a composite stabilized zirconium oxide (90% mol ZrO2 + 5% mol MgO + 5% mol Y2O3) as the main raw material. The specific composition and mass ratio are as follows:

[0048]

[0049]

[0050] The specific details are shown in Table 1;

[0051] Table 1 Performance indicators of dry materials in the examples

[0052]

Claims

1. A protective coating for a tundish lining for clean steelmaking, characterized in that, The protective coating comprises magnesium yttrium stabilized zirconia of different particle sizes, a sintering aid, a stabilizer and a binding agent; The magnesium yttrium stabilized zirconia is one of high-purity magnesium stabilized zirconia; 2 mol%≤MgO≤10 mol%, 2 mol%≤Y2O3≤10 mol%, ZrO2≥88 mol%; The mass percentage of the intermediate ladle lining protective coating raw material is: Magnesium yttrium zirconium oxide particles 40-50%, D 0.9 ≤ 0.2 mm; Magnesium yttrium zirconium oxide fine powder 30-40%, D 0.9 ≤0.074 mm; Magnesium yttrium zirconium oxide fine powder 5-15%, D 0.9 ≤ 10 μm; Magnesium yttrium zirconium oxide fine powder 5-15%, D 0.9 ≤ 3 μm; flux 1-5%, D 0.9 ≤ 61 μm, the total weight of the above raw materials is 100%; The stabilizer is added in the form of addition, accounting for 0.1-0.5% of the total weight of the raw material; The binding agent is added in the form of addition, accounting for 10-20% of the total weight of the raw material; The fluxing agent is any one of boric acid, borax, boron glass powder, wherein D 0.9 ≤ 61 μm; The stabilizer is any one of polyphosphate, polyethylene glycol type condensate and lignin sulfonate; The binding agent is any one of liquid aluminum dihydrogen phosphate, aluminum sol and water glass.

2. A method for the production of a protective coating for a tundish lining for the smelting of clean steel according to claim 1, characterized in that The preparation steps are as follows: (1) The prepared mixed solid raw materials of magnesium yttrium stabilized zirconia, sintering aid and stabilizer are co-mixed with zirconia balls according to the proportion, and then the binding agent is added according to the proportion and stirred uniformly to prepare the protective coating slurry, (2) Adjust the slurry to the surface of the intermediate ladle working lining material for mechanical spraying or manual coating of the slurry to form a thin layer of 2-5 mm thick, (3) After the slurry thin layer is completely solidified, online baking is immediately carried out to finally obtain the intermediate ladle lining protective coating, which is ready for use.

3. The preparation method of the intermediate ladle lining protective coating for clean steel smelting according to claim 2, characterized in that, In step (1), the mass ratio of the solid raw material to zirconia ball is 1:1.5-2.

4. The preparation method of the intermediate ladle lining protective coating for clean steel smelting according to claim 2, characterized in that, In step (3), the baking process is: the baking device is raised to 300-350℃ within 0.5h, kept for 1h, then raised to 1200-1300℃ within 1h, kept for 1.5-2h and then waited for online use.

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