Tundish coating for rare earth steel

Abstract

The invention discloses a tundish coating for rare earth steel, the tundish coating comprises raw materials and an additive, the raw materials comprise, by mass, 90-95 wt% of magnesite clinker, 1-5 wt% of activated alumina, 1-4 wt% of rare earth oxide, and 1-4 wt% of a magnesium aluminate binder; the additives comprise a water reducing agent, a plasticizer and explosion-proof fibers. Good compactness and thermal shock resistance are obtained; the rare earth corrosion resistance of the tundish coating is greatly improved, and the tundish coating is particularly suitable for smelting rare earth-containing steel; the problems that an existing magnesium coating is high in SiO2 content and prone to reacting with rare earth, and therefore the high-temperature using performance of the coating and the purity of molten steel are reduced are solved.

Description

Technical Field

[0001] This invention belongs to the field of refractory materials technology, specifically relating to an intermediate ladle coating for rare earth steel. Background Technology

[0002] The tundish is the last smelting vessel before molten steel becomes cast billet, and it is a crucial process for ensuring the purity of the steel. The working lining of the tundish is generally made of refractory coating, which has advantages such as easy application and storage. Magnesia-based coatings are widely used in tundish coatings due to their excellent resistance to corrosion and penetration.

[0003] Rare earth steel is produced by adding rare earth elements in alloy form to molten steel, aiming to alter the morphology of inclusions and improve steel performance. Rare earth elements have low melting points and are easily oxidized; during smelting, they readily react with slag, refractory materials, and air. In molten steel, rare earth elements are easily oxidized to form high-melting-point rare earth oxides (RE₂O₃) and oxysulfides (RE₂O₂S). The magnesium coating used in the tundish has a chemical composition of MgO ≥ 60% and SiO₂ ≤ 10%, with SiO₂ primarily existing as fine powder. Rare earth elements react with SiO₂ to form rare earth silicates (RESiO₄) and a high-viscosity glassy phase. These reactions erode and destroy the binding matrix of the magnesium coating, causing melting, peeling, and cracking during use, reducing high-temperature performance, and potentially leading to steel leakage and seepage.

[0004] Chinese patent CN115246733A discloses a high-durability tundish coating and its application, with magnesia and silica powder as the main raw materials and magnesium aluminate as the binder. Although this patented technology has strong corrosion resistance and is beneficial for improving the purity of molten steel and the life of the tundish, it is only applicable to ordinary steel grades. Since the fine powder is still mainly silica powder, it cannot effectively resist the reaction between rare earth elements and SiO2, causing corrosion of the coating.

[0005] Chinese patent CN111484343A discloses a hydration-resistant magnesium-calcium refractory intermediate coating and its preparation method, using recalcined magnesia and dolomite as raw materials. This patent effectively solves the CaO hydration problem by employing a composite calcium source; however, magnesium-calcium refractory materials still suffer from the problem of difficult sintering.

[0006] Chinese patent CN104803687A discloses an ultra-low silica coating that can reduce the oxygen content in the tundish. It is prepared using 70-80 wt% high-purity magnesia and 10-20 wt% high-purity calcium hydroxide as raw materials, with zirconium oxychloride as a binder. While this patent has an extremely low SiO2 content, effectively reducing the oxygen content in the tundish, the calcium hydroxide and zirconium oxychloride used in the raw materials decompose into CaO and ZrO2 at high temperatures. Both have high coefficients of thermal expansion, which can cause the coating to expand in volume, leading to cracks and affecting the safety of tundish production.

[0007] In summary, current ordinary magnesium coatings have a high SiO2 content. Rare earth elements readily react with SiO2 to form rare earth silicates and high-melting-point glass phases, which reduces the high-temperature performance of the coating and the purity of molten steel. Therefore, reducing the SiO2 content in magnesium coatings through compositional adjustments and improving their resistance to rare earth corrosion is an urgent problem to be solved. Summary of the Invention

[0008] The purpose of this invention is to provide a tundish coating for rare earth steel, which solves the problem that existing magnesium coatings have a high SiO2 content and are prone to reacting with rare earths, thereby reducing the coating's high-temperature performance and the purity of molten steel; it can effectively resist the melting and erosion of the tundish coating by rare earths, which is beneficial to improving the number of consecutive castings and the purity of molten steel for rare earth steel.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows:

[0010] An intermediate ladle coating for rare earth steel includes raw materials and additives; wherein,

[0011] The raw materials comprise, by weight percentage: 90-95 wt% sintered magnesia, 1-5 wt% activated alumina, 1-4 wt% rare earth oxides, and 1-4 wt% magnesium aluminate binder.

[0012] Preferably, the sintered magnesia contains ≥94.5 wt% MgO.

[0013] Preferably, the sintered magnesia contains 38-45 wt% coarse sintered magnesia particles with a particle size of 1-3 mm, 45-50 wt% fine sintered magnesia particles with a particle size of 0.088 mm < 1 mm, and 5-10 wt% fine sintered magnesia powder with a particle size of ≤0.088 mm.

[0014] Preferably, the activated alumina contains Al2O3 ≥ 99.5 wt%, d 50 =1.0~3.0μm, preferably d 50 =1.67μm.

[0015] Preferably, the rare earth oxide is one or both of CeO2 and La2O3.50 =30~60nm, preferably d 50 =50nm.

[0016] Preferably, the magnesium aluminate binder contains MgO ≥ 45 wt% and Al2O3 ≥ 15 wt%.

[0017] Preferably, the additives include water-reducing agents, plasticizers, and explosion-proof fibers.

[0018] Preferably, the amount of water-reducing agent added is 0.15 to 0.5% of the total weight of the raw materials, and the water-reducing agent is sodium tripolyphosphate and sodium hexametaphosphate, wherein the mass percentage of sodium tripolyphosphate and sodium hexametaphosphate is 1 to 3: 1 to 3.

[0019] Preferably, the amount of plasticizer added is 0.1 to 0.5% of the total weight of the raw materials, and the plasticizer is one or both of sodium methylcellulose or dextrin.

[0020] Preferably, the amount of explosion-proof fiber added is 0.05% to 0.1% of the total weight of the raw materials.

[0021] The activated alumina micro powder added in this invention plays a role in promoting sintering. On the one hand, the activated alumina has a small particle size and a large contact area, which can promote sintering. On the other hand, at high temperature, the activated alumina micro powder can react with MgO in the raw material sintered magnesia to form in-situ spinel. The slight volume expansion during the formation of in-situ spinel can block the internal pores and promote sintering.

[0022] Nanoscale rare earth oxides can not only improve thermal shock resistance.

[0023] In addition, activated alumina micro powder (Al2O3) and nano-scale rare earth oxides (RE) x O y The two can coordinate with each other and also achieve the following effects:

[0024] (1) The intermediate coating is a multiphase material. The raw materials inevitably contain impurities such as SiO2 and CaO, and the slag contains compounds such as MgO, CaO and SiO2. The addition of rare earth oxides can reduce the eutectic temperature of Al2O3, MgO and CaO, thereby promoting sintering. At the same time, the liquid phase generated by the reaction of rare earth oxides with them fills the gaps between the raw materials through capillary action, thereby promoting sintering densification.

[0025] (2) The activated alumina micro powder and nano-sized rare earth oxides of this invention will form rare earth aluminate (REAlO3) at high temperature. It has good chemical stability and can resist the corrosion of slag and rare earth elements. This allows REAlO3 to maintain its structural and performance stability when casting rare earth steel, thereby improving the service life of the tundish coating; it can also effectively prevent Al2O3 from entering the molten steel and not affect the purity of the molten steel.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] This invention incorporates activated alumina micropowder and nano-sized rare earth oxides into the tundish coating. The nano-sized rare earth oxides lower the sintering temperature of the activated alumina micropowder, promoting coating sintering and improving the density of the sintered tundish coating. Furthermore, the activated alumina micropowder and nano-sized rare earth oxides form rare earth aluminates at high temperatures, ensuring the stability of the tundish coating's structure and properties, extending the tundish's service life, and improving its thermal shock resistance.

[0028] The tundish coating disclosed in this invention achieves excellent density and thermal shock resistance without the addition of large amounts of SiO2, and significantly improves its resistance to rare earth corrosion, making it particularly suitable for smelting rare earth steel. Traditional coatings, due to the addition of large amounts of SiO2, react with rare earth elements during rare earth steel smelting to form rare earth silicates (RESiO4) and a high-viscosity glassy phase. These substances erode and destroy the binding matrix of the magnesium coating, leading to melting, peeling, and cracking during use, thus reducing the coating's corrosion resistance and the purity of the molten steel. Using the tundish coating described in this invention, the corrosion rate during rare earth steel smelting is reduced by more than 36% compared to traditional magnesium coatings. Detailed Implementation

[0029] The present invention will be further described below with reference to the embodiments.

[0030] Prepare the intermediate liner coating according to the composition of Table 1. When applying it on site, add 10-15 wt% water by weight, mix in a high-speed mixer for 10 minutes, and then apply the intermediate liner coating. See Table 2 for specific performance parameters.

[0031] As shown in Table 1, the bulk density, porosity, and room temperature compressive strength of the tundish linings obtained in Examples 1-4 of the present invention are all superior to those in Comparative Examples 1-3. These are all beneficial for resisting the penetration and erosion of molten steel. The average erosion rate of the embodiments of the present invention is significantly lower than that of the comparative examples, and the erosion rate is reduced by more than 36% compared with traditional magnesium coatings.

[0032] In Comparative Example 1, silica powder was added, but activated alumina and rare earth oxides were not added. The resulting strength was lower than that of the present invention, the bulk density was lower, the porosity was higher, and the erosion resistance rate was significantly higher than that of the present invention.

[0033] Comparative Example 2 involved the addition of activated alumina alone, resulting in a lower strength, lower bulk density, and higher porosity compared to the present invention. In particular, its erosion resistance rate was significantly higher than that of the present invention.

[0034] Comparative Example 3, which added nano-CeO2 alone, resulted in a lower strength, lower bulk density, and higher porosity than the present invention, and in particular, a significantly higher erosion resistance rate.

[0035] Therefore, the simultaneous addition of activated alumina micro powder and nano rare earth oxides can both promote the sintering of the coating and improve its strength, and also enable the coating to resist rare earth corrosion effectively.

[0036] In summary, this invention solves the problems of poor sinterability and strength caused by reduced SiO2 content by replacing traditional silicon micropowder with activated alumina micropowder and nano-sized rare earth oxides, and improves resistance to rare earth corrosion. This invention effectively reduces the corrosion and melting loss of rare earth on the tundish coating, which is beneficial for increasing the number of consecutive castings of rare earth steel and the purity of the molten steel.

[0037]

[0038]

Claims

1. A coating for intermediate ladles of rare earth steel, characterized in that, Includes raw materials and additives; among which, The raw materials comprise, by weight percentage: 90-95 wt% sintered magnesia, 1-5 wt% activated alumina, 1-4 wt% rare earth oxides, and 1-4 wt% magnesium aluminate binder.

2. The intermediate ladle coating for rare earth steel as described in claim 1, characterized in that, The sintered magnesia contains ≥94.5 wt% MgO.

3. The intermediate ladle coating for rare earth steel as described in claim 1 or 2, characterized in that, The sintered magnesia contains 38-45 wt% coarse sintered magnesia particles with a particle size of 1-3 mm, 45-50 wt% fine sintered magnesia particles with a particle size of 0.088 mm < 1 mm, and 5-10 wt% fine sintered magnesia powder with a particle size of ≤0.088 mm.

4. The intermediate ladle coating for rare earth steel as described in claim 1, characterized in that, The activated alumina contains Al2O3 ≥ 99.5 wt%, d 50 =1.0~3.0μm, preferably d 50 =1.67μm.

5. The intermediate ladle coating for rare earth steel as described in claim 1, characterized in that, The rare earth oxide is one or both of CeO2 and La2O3. 50 =30~60nm, preferred d 50 =50nm。 6. The intermediate ladle coating for rare earth steel as described in claim 1, characterized in that, The magnesium aluminate binder contains MgO ≥ 45 wt% and Al2O3 ≥ 15 wt%.

7. The intermediate ladle coating for rare earth steel as described in claim 1, characterized in that, The additives include water-reducing agents, plasticizers, and explosion-proof fibers.

8. The intermediate ladle coating for rare earth steel as described in claim 7, characterized in that, The amount of water-reducing agent added is 0.15 to 0.5% of the total weight of the raw materials. The water-reducing agent is sodium tripolyphosphate and sodium hexametaphosphate, and the mass percentage of sodium tripolyphosphate and sodium hexametaphosphate is 1 to 3: 1 to 3.

9. The intermediate ladle coating for rare earth steel as described in claim 7, characterized in that, The amount of plasticizer added is 0.1 to 0.5% of the total weight of the raw materials, and the plasticizer is one or both of sodium methylcellulose or dextrin.

10. The intermediate ladle coating for rare earth steel as described in claim 7, characterized in that, The amount of explosion-proof fiber added is 0.05% to 0.1% of the total weight of the raw materials.

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