Intermediate package high-performance magnesium-aluminum-lanthanum carbon-free dry material and preparation and use method thereof

Abstract

The application discloses a high-performance intermediate ladle magnesia-alumina-lanthanum carbon-free dry material and a preparation and use method thereof, which is prepared from the following raw materials in parts by weight: magnesia ≤3mm, ≥1mm: 30-40 parts; magnesia ≤1mm: 25-35 parts; fused magnesia powder: 10-25 parts; calcined alumina micro powder D50 ≤5um: 5-10 parts; lanthanum oxide micro powder-325 mesh: 1-3 parts; sulfamic acid: 2-8 parts; sodium thiosulfate pentahydrate: 1-5 parts; boric acid: 1-3 parts. The application has the advantages of carbon-free combination, environmental protection, no toxic and harmful gas substances such as formaldehyde and acetaldehyde generated by decomposition of phenolic resin, low residual carbon content in a steel mill, and reduction of residual carbon inclusions in molten steel. The application significantly improves the low-temperature strength of the high-performance intermediate ladle magnesia-alumina-lanthanum carbon-free dry material, improves the bonding performance, and provides good sintering performance at medium and high temperatures.

Description

Technical Field

[0001] This invention belongs to the field of refractory materials technology for steelmaking tundishes, specifically relating to a high-performance magnesium-aluminum lanthanum-based carbon-free dry refractory for tundishes and its preparation and application methods. Background Technology

[0002] Existing continuous casting intermediate carbon-containing dry materials primarily use phenolic resin, glucose, and other additives as medium- and low-temperature binders. During temperature increases, the carbonization and solidification of the carbon-containing materials provide a certain strength. However, as the temperature rises (200℃–800℃), the resin decomposes, releasing irritating and harmful gases such as cresol and formaldehyde, leaving residual carbon. These toxic and harmful gases cause significant environmental pollution and harm human health; residual carbon also increases the carbon content in molten steel, especially when producing low-carbon clean steel, reducing steel quality. Therefore, new carbon-free dry materials are the optimal choice for steel mills producing low-carbon clean steel.

[0003] Existing carbon-free dry billets for continuous casting tundishes are mostly made from magnesia, using inorganic acids, alkalis, and salts as medium- and low-temperature binders to achieve a certain strength, and are used in the smelting of low-carbon clean steel. However, during testing and use, existing carbon-free dry billet technology suffers from low medium- and low-temperature bonding strength and large high-temperature shrinkage. Furthermore, due to the use of inorganic acids, alkalis, and salts, the refractory properties of the carbon-free dry billet are severely reduced, making it susceptible to corrosion and erosion. Consequently, existing carbon-free dry billets fail to meet application requirements and are not widely used.

[0004] Chinese patent application CN200810050143.8, published on October 29, 2008, discloses an environmentally friendly dry vibratory binder for tundishes. This vibratory binder, by weight percentage, contains 10-80% sodium phosphate or borosilicate, 15-85% magnesium salt, and 0.01-5% alkali metal silicate or borate. This invention uses inorganic salts as a composite binder for carbon-free dry materials, without introducing carbon or increasing the carbon and hydrogen content of the molten steel, thus meeting the needs of smelting steels with relatively low carbon content. It exhibits good corrosion resistance, is easy to disintegrate, and its bonding strength and mid-temperature strength meet demolding and usage requirements. It also improves the service life of the tundish, enabling the average service life of dry materials using fused magnesia and sintered magnesia as main raw materials to exceed 29 hours. However, this scheme uses alkali metal silicates as one of the binders, resulting in a lot of pores in the formed dry material and poor resistance to penetration; it also has large high-temperature shrinkage and is prone to cracking; and the use of phosphates can easily cause phosphorus accumulation in molten steel.

[0005] Application No.: CN202110750675.8, Application Date: 2021-07-01. This invention provides a carbon-free dry feedstock for continuous casting tundishes, comprising the following raw materials by mass fraction: 5-3mm olivine sand: 9%–18%, 3-1mm 91 magnesia: 25%–35%, 1-0mm 91 magnesia: 20%–30%, 200-mesh 91 magnesia: 20%–30%, sodium metasilicate nonhydrate: 2.5%–4.5%, sodium hexametaphosphate: 1.2%–2%, and low-melting-point glass powder: 0.3%–0.8%. This dry feedstock is carbon-free and does not produce harmful volatile gases during ladle baking and use, thus improving the workshop environment and working conditions for operators; it meets production requirements at low, medium, and high temperatures. However, in practical applications, dry-type refractories using sodium metasilicate nonahydrate (2.5%–4.5%), sodium hexametaphosphate (1.2%–2%), and low-melting-point glass powder (0.3%–0.8%) as medium- and low-temperature binders exhibit very low low-temperature strength, severely impacting high-temperature refractory performance and exhibiting low resistance to slag erosion. Furthermore, the low-melting-point glass powder described in this invention has an initial melting temperature of 255°C and a coefficient of linear expansion of 108 × 10⁻⁶. -7 (0~300℃), pH value 7.9, average mesh size 2000 mesh. This glass powder is not widely available on the market, which is not conducive to its widespread application. It also has low strength at medium and low temperatures and poor erosion resistance.

[0006] Chinese patent document CN111362670A (application number: CN202010135953.4) discloses an environmentally friendly carbon-free dry charge comprising sintered magnesia, hydrated sodium metasilicate, hydrated magnesium sulfate, and borides. This dry charge exhibits low erosion and permeability indices, improving the cleanliness of molten steel and reducing carbon contamination. However, this document also suffers from problems such as low high-temperature strength and excessive high-temperature linear shrinkage.

[0007] Chinese patent application CN202111036191.3, published on October 8, 2021, discloses a resource-saving, lightweight, and environmentally friendly tundish lining and its preparation method. The tundish lining, by weight, comprises the following components: 20-120 parts of magnesite and forsterite, 5-30 parts of finely calcined magnesia powder, 1-20 parts of binder, 0.1-3 parts of paper fiber, and 1-10 parts of modifier. The binder is a mixture of three of the following: magnesium sulfate, sulfamic acid, magnesium chloride, sodium metasilicate, and sodium silicate. The modifier is a mixture of graphite and SiC. Although this dry-material tundish lining is called a resource-saving, lightweight, and environmentally friendly tundish lining, the modifier contains carbon, therefore it cannot be used with steels with very low carbon content. Furthermore, the binder uses a mixture of three components, which easily leads to severe sintering. It is not easy to disintegrate after use, and its high-temperature refractory performance is poor, making it susceptible to slag erosion and scouring. Summary of the Invention

[0008] The purpose of this invention is to provide a high-performance lanthanum-based carbon-free dry tundish material for tundishes, along with its preparation and application methods. This material features carbon-free bonding, is environmentally friendly and pollution-free, and does not produce toxic or harmful gases such as formaldehyde and acetaldehyde from the decomposition of phenolic resins. It also has a low residual carbon content during steelmaking, reducing residual carbon inclusions in molten steel. Furthermore, it significantly improves the low-temperature strength and bonding performance of the high-performance lanthanum-based carbon-free dry tundish material, and provides better sintering performance at medium and high temperatures.

[0009] To achieve the above objectives, the present invention employs the following technical solution: This invention provides a clean, environmentally friendly, and pollution-free carbon-free dry feedstock, offering a better option for the production of low-carbon clean steel. This high-performance magnesium-aluminum-lanthanum carbon-free dry feedstock for tundishes is prepared from the following raw materials in parts by weight: magnesia ≤3mm, ≥1mm: 30-40 parts; magnesia ≤1mm: 25-35 parts; fused magnesia powder: 10-25 parts; calcined alumina micro powder D50≤5µm: 5-10 parts; lanthanum oxide micro powder -325 mesh: 1-3 parts; aminosulfonic acid: 2-8 parts; sodium thiosulfate pentahydrate: 1-5 parts; boric acid: 1-3 parts.

[0010] The magnesium oxide content in the magnesia is ≥88wt%.

[0011] The fused magnesia powder contains ≥97.5wt% magnesium oxide, ≤0.5wt% silicon dioxide, and has a particle size of -200 mesh.

[0012] The lanthanum oxide micro powder contains ≥99% lanthanum oxide; the binder aminosulfonic acid is -60 mesh; the binder sodium thiosulfate pentahydrate is -60 mesh; the binder boric acid is -60 mesh.

[0013] The chemical composition of the carbon-free dry material is as follows: by weight percentage, MgO≥72%, Al2O3≥5%, La2O3≥2.5%.

[0014] The physicochemical properties of carbon-free dry feedstock are: bulk density 1.8–2.2 g / cm³. 3 Flexural strength ≥ 1.5 MPa at 230℃*3h, flexural strength ≥ 2.0 MPa at 1550℃*3h, linear change at 1550℃*3h: -1.5%~0.

[0015] A method for preparing a high-performance magnesium-aluminum lanthanum-based carbon-free dry feedstock for intermediate packaging specifically includes the following steps: 1) Weigh each raw material according to the weight ratio, mix them using a sand mixer, and add them in the following order: coarse aggregate - fine powder - admixture. Dry mix for 5-10 minutes until evenly mixed. The coarse aggregate is magnesia, and the fine powder is fused magnesia powder, calcined alumina micro powder, and lanthanum oxide micro powder. The admixtures are aminosulfonic acid, sodium thiosulfate pentahydrate, and boric acid.

[0016] 2) The well-mixed intermediate high-performance magnesium-aluminum lanthanum carbon-free dry material is packaged in sealed woven bags and stored in a dry place.

[0017] A method for using a high-performance magnesium-aluminum lanthanum carbon-free dry intermediate pack: During construction, the mixed high-performance magnesium-aluminum lanthanum carbon-free dry intermediate pack is placed into a pre-installed mold, vibrated and compacted, and baked at a temperature of 200-300℃ for 2-3 hours until it is ready for use.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention, based on the usage and effects of tundish dry refractory materials, innovatively selects raw materials to improve the refractory performance of high-performance magnesium-aluminum lanthanum-based carbon-free dry refractory materials for tundishes. Calcined alumina micropowder and lanthanum oxide micropowder are used as additives to the dry refractory material. The calcined alumina micropowder contains ≥99% aluminum oxide and has a median particle size ≤5 μm, while the lanthanum oxide micropowder contains ≥99% lanthanum oxide and has a particle size of -325 mesh. The addition of calcined alumina micropowder and magnesia forms a magnesium-aluminum spinel phase at high temperatures, compensating for the shrinkage caused by high-temperature linear changes and forming in-situ spinel grains, thus improving the erosion resistance of the dry refractory material. Furthermore, the volume increase caused by the formation of magnesium-aluminum spinel at high temperatures reduces the strength of the dry refractory material, improving its disintegration resistance. The addition of lanthanum oxide micropowder fills the spaces between magnesium oxide particles, inhibiting abnormal growth of magnesium oxide particles, refining the microstructure, absorbing impurities, reducing the content of low-melting phases, increasing high-temperature strength, improving the erosion and scour resistance of the dry refractory material, and reducing permeability.

[0019] 2. This invention provides a high-performance carbon-free dry binder for tundishes, using non-carbon-containing materials. It innovatively selects and combines binders, specifically aminosulfonic acid, sodium thiosulfate pentahydrate, and boric acid in the aforementioned high-performance carbon-free dry binder. This combination significantly improves the low-temperature strength and bonding performance of the high-performance carbon-free dry binder at medium and high temperatures, and provides better sintering performance.

[0020] 3. The high-performance magnesia-alumina lanthanum carbon-free dry refractory provided by this invention, due to the addition of calcined alumina micro powder and lanthanum oxide micro powder, allows for diversification in the selection of the main aggregate magnesia. That is, using lower-grade magnesia will not significantly reduce the refractory performance of the dry refractory, which can reduce raw material costs and improve economic efficiency; while selecting higher-grade magnesia can improve the refractory performance of the dry refractory and increase its service life. Detailed Implementation

[0021] The specific embodiments of the present invention will be further described below with reference to examples: The physicochemical properties of the main raw materials used in the examples, such as magnesia, low-silicon 975 fused magnesia fine powder, calcined alumina micro powder, and lanthanum oxide micro powder-325 mesh, are shown in Table 1.

[0022] Table 1 shows the physicochemical properties (typical values) of the high-performance magnesium-aluminum lanthanum carbon-free dry feedstock in the intermediate jar example.

[0023] Table 1 Table 2 shows several best examples and comparative examples of the high-performance magnesium-aluminum lanthanum carbon-free dry feed for intermediate tundishes of the present invention.

[0024] Table 2 Note: The proportions in Table 2 are by weight.

[0025] Table 3 below shows the test indicators of several best examples of the high-performance magnesium-aluminum lanthanum carbon-free dry feed for intermediate ladles of the present invention.

[0026] Table 3 Examples 1, 2, and 3 and Comparative Examples 1, 2, and 3 are produced as shown in Table 3 for the production of dry intermediate bag materials. Each raw material is weighed according to the weight ratio, and mixed using a sand mixer. The order of adding materials is coarse aggregate - fine powder - admixture, and the mixture is dry-mixed for 5 to 10 minutes.

[0027] The mixed intermediate high-performance magnesium-aluminum lanthanum carbon-free dry material was placed into a pre-installed mold and baked at 230℃ for 3 hours as required. The molded samples were then tested for their properties, and the results are shown in Table 3.

[0028] Examples 1, 2, and 3 show that the test results meet the physical and chemical requirements. The high-performance magnesium-aluminum lanthanum carbon-free dry material in the tundish was transported to the steel plant, stored in a dry place, and awaited use.

[0029] Table 4 shows the effects of using high-performance magnesium-aluminum lanthanum-based carbon-free dry feedstock in the tundishes of Examples 1, 2, and 3 at a steel plant, and the dry feedstock produced by another manufacturer.

[0030] Table 4 Examples 1, 2, and 3 show that high-performance magnesium-aluminum lanthanum carbon-free dry billets and carbon-containing dry billets used in tundishes under the same conditions have good results in terms of the number of ladles, continuous casting time, and residual wall thickness after use, fully meeting the requirements of steel mills.

[0031] The experimental and usage results from the examples show that the high-performance magnesium-aluminum lanthanum carbon-free dry tundish provided by this invention has carbon-free bonding, is environmentally friendly and pollution-free, and does not contain toxic and harmful gases such as formaldehyde and acetaldehyde produced by the decomposition of phenolic resins. It also results in low residual carbon content in steelmaking plants, reducing residual carbon inclusions in molten steel. This invention provides a high-performance magnesium-aluminum lanthanum carbon-free dry tundish by adding calcined alumina micropowder and magnesia to form a magnesium-aluminum spinel phase at high temperatures. This compensates for the shrinkage caused by high-temperature linear changes, forming in-situ spinel grains, improving the erosion resistance of the dry tundish. Furthermore, the volume increase at high temperatures reduces the strength of the dry tundish, improving its disintegration resistance. The addition of lanthanum oxide micropowder fills the spaces between magnesium oxide particles, inhibiting abnormal growth of magnesium oxide particles, refining the microstructure, absorbing impurities, reducing the content of low-melting phases, increasing high-temperature strength, improving the erosion and scour resistance of the dry tundish, and reducing permeability. This invention uses a composite combination of aminosulfonic acid agent, sodium thiosulfate pentahydrate, and boric acid to significantly improve the low-temperature strength of high-performance magnesium-aluminum lanthanum carbon-free dry tundish, enhance bonding performance, and provide better sintering performance at medium and high temperatures.

[0032] Furthermore, by adding calcined alumina powder and lanthanum oxide powder, this invention allows for diversification in the selection of the main aggregate magnesia. That is, using lower-grade magnesia will not significantly reduce the refractory performance of the dry aggregate, which can reduce raw material costs and improve economic efficiency; while selecting higher-grade magnesia can improve the refractory performance of the dry aggregate and increase its service life.

Claims

1. A high-performance magnesium-aluminum lanthanum-based carbon-free dry feedstock for intermediate ladles, characterized in that, It is prepared from the following raw materials in parts by weight: Magnesia ≤3mm, ≥1mm: 30-40 parts; Magnesia <1mm: 25-35 parts; Fused magnesia powder: 10-25 parts; Calcined alumina micro powder D50≤5µm: 5-10 parts; Lanthanum oxide micro powder -325 mesh: 1-3 parts; Aminosulfonic acid: 2-8 parts; Sodium thiosulfate pentahydrate: 1-5 parts; Boric acid: 1-3 parts; The chemical composition of the carbon-free dry material is as follows: by weight percentage, MgO≥72%, Al2O3≥5%, La2O3≥2.5%; The preparation method of high-performance magnesium-aluminum lanthanum-based carbon-free dry feed for intermediate ladles specifically includes: Weigh each raw material according to the weight ratio, mix them using a sand mixer, and add them in the following order: coarse aggregate - fine powder - admixture. Mix until homogeneous. The coarse aggregate is magnesia, and the fine powder is fused magnesia powder, calcined alumina micro powder, and lanthanum oxide micro powder. The admixtures are aminosulfonic acid, sodium thiosulfate pentahydrate, and boric acid.

2. The high-performance magnesium-aluminum lanthanum-based carbon-free dry feedstock for intermediate ladles according to claim 1, characterized in that, The magnesium oxide content in the magnesia is ≥88wt%.

3. The high-performance magnesium-aluminum-lanthanum carbon-free dry feedstock for intermediate ladles according to claim 1, characterized in that, The fused magnesia powder contains ≥97.5wt% magnesium oxide, ≤0.5wt% silicon dioxide, and has a particle size of -200 mesh.

4. A method of using the high-performance magnesium-aluminum lanthanum-based carbon-free dry feedstock as described in claim 1, characterized in that, The baking temperature is 200-300℃, and the baking time is 2-3 hours.

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