Alkaline ladle filler sand for clean molten steel and preparation method thereof

Abstract

The invention relates to alkaline ladle filler sand for cleaning molten steel and a preparation method thereof. The alkaline ladle filler sand comprises the following components in percentage by weight: 40-60% of magnesia, 35-55% of magnesia-calcium sand and 2-6% of a waste magnesia carbon brick reclaimed material. The content of MgO and CaO in the alkaline ladle filler sand is larger than or equal to 90 wt%, adding of oxides such as Cr2O3, SiO2, Al2O3 and Fe2O3 which can cause oxygenation of molten steel is reduced, oxygenation of tundish molten steel can be reduced, the molten steel is truly cleaned, the quality of a casting blank is improved, and the alkaline ladle filler sand has the high self-casting rate; the raw materials are easily available and low in cost.

Description

Technical Field

[0001] The invention belongs to the technical field of steelmaking, and in particular relates to alkaline ladle drainage sand for clean molten steel and a preparation method thereof. Background Art

[0002] Ladle drainage sand is a drainage agent filled in the water nozzle of the ladle seat brick. It is a mixture of various oxide refractory raw materials and is filled in the water nozzle of the ladle before tapping. After the refining is completed, the ladle is transferred to the top of the tundish and the slide is opened. The drainage sand opens automatically, and the molten steel flows out to the tundish. This process is called automatic pouring and drainage of the ladle.

[0003] With the development of pure steel and special steel making technology, the cleanliness requirements for molten steel and ingot are getting higher and higher. Before continuous casting, drainage sand must be used for drainage and pouring. Its influence on the purity of molten steel has attracted great attention from steelmaking technicians, because the existing drainage sand contains Cr 2 O 3 、SiO 2 、Al 2 O 3 , Fe 2 O 3 If the total amount exceeds 90%, these oxides will cause oxygenation in the molten steel and affect the quality of the steel variety.

[0004] The study of “The influence of ladle drainage sand on the cleanliness of tundish steel liquid” by Anhui University of Technology shows that when the existing chromium drainage sand is automatically poured, more than 50% of the drainage sand will enter the tundish through the nozzle. The oxygen content of the molten steel in equilibrium with the slag formed by the drainage sand is as high as 630×10 -1 , thereby increasing the oxide inclusions in the tundish steel liquid and reducing the cleanliness of the tundish steel liquid.

[0005] In the study "Calculation and Analysis of the Effect of Drainage Sand on Oxygen Content in Liquid Steel" conducted by Northeastern University, it was pointed out that chromium drainage sand was used as the research object to calculate the Cr content in the drainage sand. 2 O 3 、SiO 2 、Al 2 O 3 , Fe 2 O 3Regarding the influence on the oxygen content in molten steel, the oxygen content in the molten steel in this slag equilibrium reaches 0.0742. According to the calculation results, the tapping sand has a great influence on the oxygen content in molten steel. In actual production, the oxygen content in the molten steel in the tundish is lower than this value because the reaction in actual production cannot reach the equilibrium state completely. However, the tapping sand is a material that needs to be added for each furnace of steel, and its quality will accumulate continuously in the tundish, which will inevitably lead to an increase in the oxygen content in the tundish covering agent. It can be said that the tapping sand is a pollution source relative to the molten steel in the tundish. Under the continuous accumulation of quantity and the impact of the molten steel, it will increase the oxygen content in the molten steel, and then increase the inclusions in the steel, which restricts the production of clean steel.

[0006] Therefore, the self-opening rate of the tapping sand and the composition of the material system have the greatest influence on the oxygen increase in molten steel, the cleanliness of molten steel, and the quality of the continuous casting billet. Metallurgical workers have been developing tapping sands with different material systems to better reduce the pollution to molten steel and achieve a higher self-opening rate.

[0007] The existing types of ladle tapping sands used more are: silica tapping sand, chromite tapping sand, and zircon tapping sand. They belong to the acidic tapping sand and neutral tapping sand material systems respectively.

[0008] 1) Silica tapping sand. The main raw material is quartz sand (chemical composition SiO 2 : 94 - 99%), and its melting point is about 1680 - 1700 °C. SiO 2 has a great influence on the oxygen increase in molten steel. It is not suitable for long smelting time and high-quality steel grades. The self-opening rate is about 80%. Silica tapping sand will also reduce the basicity of the top slag in the tundish, exacerbate the erosion of the tundish, and increase the cost per ton of steel. It has been phased out by most steel mills.

[0009] 2) Chromite tapping sand. Using chromite as the main raw material, the self-opening rate reaches over 95% and it is currently widely used in steel mills. The basic chemical composition of chromite sand includes: Cr 2 O 3 : 27 - 45%, Fe 2 O 3 : 15 - 25% and SiO 2 : 10 - 35%, and the melting point is 1730 - 1750 °C. The oxides in chromite tapping sand are likely to cause secondary oxidation of molten steel, increase the inclusions in molten steel, and have an adverse effect on high-quality and high-value-added steel grades.

[0010] 3) Zircon tapping sand. Using zircon as the main raw material, ZrSiO 4 ≥97%, free SiO 2 ≤2%, and other impurities ≤1%. The melting point is higher than 1850 °C. Both the influence on the quality of molten steel and the self-opening rate meet the requirements, but the cost of zircon tapping sand is relatively high, and steel mills only use it for high-grade and high-value-added steel grades.

[0011] In order to ensure the cleanliness of high-quality molten steel, technicians have also developed a lot of "alkaline" ladle drainage sand.

[0012] Chinese patent CN02158570.9 discloses an alkaline drainage sand for ladle and its preparation method: it is an alkaline drainage agent used in the ladle casting of molten steel in the steelmaking industry, which is conducive to removing the alkaline environment of inclusions in the steel adsorption required for smelting special steel and clean steel, ensuring that it does not pollute the molten steel, and promoting the formation of an alkaline environment that is conducive to removing inclusions in the adsorbed steel. The main raw material of the alkaline drainage sand provided by the invention is calcined forsterite sand (2MgO.SiO 2 ), quartz sand (SiO 2 ), magnesia, feldspar and graphite. However, the patent still contains more than 50% SiO 2 The composition is not pure alkaline drainage sand.

[0013] Chinese patent CN200710053110.4 discloses a forsterite ladle drainage sand and its preparation method. 86-96wt% forsterite sand (2MgO.SiO 2 ), 1-6wt% flake graphite, 1-8wt% potassium feldspar powder, 0.5-2wt% carbonaceous micropowder are mixed evenly and then packaged in bags. The invention uses forsterite sand as the base material, and the prepared product has good high temperature resistance, high self-casting rate, low price and convenient use. Since the forsterite sand and potassium feldspar used in the patent are rich in SiO 2 Therefore, the prepared drainage sand will contain a large amount of SiO 2 .

[0014] Chinese patent CN200810246915.5 discloses a "basic" drainage sand for ladle. The weight percentage of the drainage sand is: 30-50% passivated lime, 5-15% calcite, 5-10% corundum (Al 2 O 3 ), 20-40% calcined olivine sand (2MgO.SiO 2 ), 1-5% flake graphite, each component is mixed evenly after being prepared in proportion. The prepared alkaline drainage sand has high refractoriness, high self-casting rate, and does not damage the metallurgical environment of the tundish. This patent contains CaO, which is good for purifying molten steel to a certain extent, but it also contains a large amount of SiO 2 、Al 2 O 3 The probability of oxygenating molten steel is still very high. Calcite decomposes under high temperature molten steel to release CO 2 , which can increase carbon content in molten steel. The introduction of alkaline drainage sand calcium is still easy to cause material pulverization and affect the pouring rate.

[0015] With the increasing complexity of the refining process and the higher purity requirements for high-quality steel, higher requirements are placed on the function of drainage sand. It is necessary to develop a real basic ladle drainage sand to meet the requirements of molten steel cleanliness and ingot quality and appropriate cost requirements. Therefore, new challenges are posed to traditional and existing drainage sand. Summary of the invention

[0016] The object of the present invention is to provide an alkaline ladle drainage sand for cleaning molten steel and a preparation method thereof. The alkaline ladle drainage sand can reduce the oxygenation of molten steel in the tundish, thereby truly cleaning the molten steel and improving the quality of the ingot; and has a higher self-casting rate, which is ≥99.3%; the raw materials are easily available and the cost is low.

[0017] In order to achieve the above object, the present invention provides the following technical solutions:

[0018] The invention discloses alkaline ladle drainage sand for clean molten steel, the components of which include by weight: 40-60% magnesia sand, 35-55% magnesia-calcium sand and 2-6% recycled waste magnesia-carbon bricks.

[0019] Preferably, the MgO content in the magnesia is ≥ 97wt%, Al 2 O 3 Content ≤0.8wt%Fe 2 O 3 Content ≤0.8wt%, SiO 2 Content ≤1.0wt%.

[0020] Preferably, the magnesia sand has a particle size of 1.0 to 0.1 mm and a bulk density of ≥3.3 g / cm 3 .

[0021] Preferably, the MgO content in the magnesium calcium sand is ≥70wt%, the CaO content is ≥20wt%, and the Al 2 O 3 Content ≤0.3wt%, Fe 2 O 3 Content ≤1.0wt%, SiO 2 Content ≤0.8wt%.

[0022] Preferably, the magnesia calcium sand has a particle size of 1.5 to 0.5 mm and a bulk density of ≥3.4 g / cm 3 .

[0023] Preferably, the MgO content in the recycled waste magnesia carbon brick is ≥50wt%, the C content is ≤32wt%, and the Al content is 2 O 3 Content ≤8wt%, SiO 2 Content ≤4wt%.

[0024] Preferably, the particle size of the recycled waste magnesia carbon bricks is ≤0.088 mm.

[0025] Preferably, the MgO+CaO content in the basic ladle drainage sand is ≥90wt%, and the self-casting rate is ≥99.3%.

[0026] The technical design idea of ​​the present invention is to obtain real alkaline ladle drainage sand, which is completely different from the existing acidic and neutral drainage sand technology, mainly considering the following aspects:

[0027] 1) Do not bring in unnecessary Cr 2 O 3 、SiO 2 、Al 2 O 3 , Fe 2 O 3 Composition, the presence of these oxides will increase the oxygen content in the molten steel, thereby increasing the inclusions in the steel;

[0028] 2) The raw materials have high refractoriness and suitable sintering properties under ladle refining conditions, ensuring that the drainage sand has a high self-casting rate; and the selected alkaline calcium-containing raw materials have the best waterproofing performance. The drainage sand has stable performance and does not deteriorate during production and use, which can ensure a high self-casting rate;

[0029] 3) Raw materials are easily available and the production cost is low to meet the various needs of steel mills.

[0030] In the composition design of the basic ladle drainage sand for clean molten steel of the present invention:

[0031] Magnesia is a basic refractory material with good high temperature resistance, good corrosion resistance, convenient manufacturing, large production volume and excellent performance. Its refractoriness is above 1790℃. In the present invention, sintered magnesia or fused magnesia is selected, the addition amount of magnesia is 40-60%, the MgO content in magnesia is ≥97wt%, Al 2 O 3 Content ≤0.8wt%Fe 2 O 3 Content ≤0.8wt%, SiO 2 Content ≤1.0wt%, particle size 1.0~0.1mm, volume density ≥3.3g / cm 3 Moreover, because its expansion is greater than other refractory materials, without the need to add additional expansion agents, the drainage sand has a certain expansion, can be more densely filled in the nozzle and nozzle seat bricks, can prevent the penetration of some molten steel, and improve the self-casting rate.

[0032] Magnesium calcium sand is a basic refractory raw material made by a synthetic method using high calcium magnesite as raw material and lime. Its refractoriness is above 1750℃ and its clean molten steel performance is very good. In the present invention, the addition amount of magnesium calcium sand is 35-55%, the particle size of magnesium calcium sand is 1.5-0.5mm, and the volume density is ≥3.4g / cm 3 , MgO content ≥ 70wt%, CaO content ≥ 20wt%, Al 2 O 3 Content ≤0.3wt%, Fe 2 O 3 Content ≤1.0wt%, SiO 2 The content is ≤0.8wt%. The present invention adds magnesium calcium sand to introduce CaO, while the traditional method is to introduce it by adding calcite or lime. However, calcite or lime is very easy to hydrate and powderize, which is not easy to store and use. In addition, calcite will emit CO during use. 2 , causing the C content of molten steel to increase.

[0033] The present invention also adds waste magnesium carbon brick regeneration material, which is a regeneration material with good refractory obtained by processing waste magnesium carbon bricks through certain processes. Magnesium carbon bricks are usually made of more than 96% magnesia sand and graphite, and antioxidants are added. The antioxidants not only protect the C in the magnesium carbon bricks from being oxidized, but also promote the sintering of the magnesium carbon bricks during use to increase the strength. Therefore, the waste magnesium carbon bricks have recycling value. Waste magnesium carbon bricks are recycled and reused, and through subsequent treatment, waste magnesium carbon brick regeneration materials with good refractory can be obtained. Reusing this waste magnesium carbon brick regeneration material can not only reduce production costs, but also greatly benefit resource conservation and environmental protection.

[0034] The invention adds magnesia carbon brick recycled material fine powder with a particle size of ≤0.088mm, and the addition amount is 2-6%. The MgO content in the waste magnesia carbon brick recycled material is ≥50wt%, the C content is ≤32wt%, and the Al content is ≤10wt%. 2 O 3 Content ≤8wt%, SiO 2 Content ≤ 4wt%, using the material characteristics of containing a large amount of graphite and antioxidants, it plays the following roles:

[0035] 1) The drainage sand of the present invention does not need to be supplemented with high-cost raw materials such as graphite and carbon black as in the prior art;

[0036] 2) Because the antioxidant contained in the recycled material of magnesia carbon bricks has a sintering effect and also protects the C in the alkaline drainage sand from being oxidized, there is no need to add feldspar as a sintering agent as in the prior art.

[0037] The existing drainage sand will become a pollution source after pouring, and enter the tundish, increasing the oxygen content of the molten steel in the tundish, thereby increasing the content of oxidized inclusions in the tundish and reducing the cleanliness of the molten steel in the tundish. According to the results of thermodynamic research on the relationship between the element content of refractory oxides in molten steel and the activity of equilibrium oxygen in molten steel, the order of the oxygen-enhancing effect of refractory oxides on molten steel from large to small is Cr 2 O 3 >SiO 2 >A1 2 O 3 >MgO>ZrO 2 >CaO.

[0038] Therefore, the total amount of MgO and CaO in the drainage sand of the present invention should be ensured to exceed 90wt%, which is very beneficial to reduce the pollution of molten steel and truly play the role of purifying molten steel. The present invention introduces CaO through magnesia-calcium sand, combined with the use of magnesia sand, controls the concentration of useful main components to basically reach the extreme, and at the same time, uses waste magnesia-carbon brick regeneration materials to avoid the introduction of CaO through lime and calcite in the prior art. Calcite or lime is very easy to hydrate and powder, and is not easy to store and use. It also seriously affects the self-casting rate of the drainage sand finished product, and calcite will decompose and discharge CO when used at high temperature. 2 , causing the C content of molten steel to increase, creating a new source of pollution.

[0039] The particle size of the magnesia sand of the present invention is 1.0-0.1mm, the particle size of the magnesia-calcium sand is 1.5-0.5mm, and the particle size of the magnesia-carbon brick recycled material is ≤0.088mm. The different particle size ranges of the three raw materials are to better play the advantages of each raw material and avoid its disadvantages. Magnesia sand has good stability and can be finer in particle size. Too small particles are easy to hydrate and penetrate molten steel, affecting the pouring rate. Magnesia-calcium sand is easy to hydrate and pulverize due to its calcium content. The larger the particles, the better the stability, so it is introduced in the form of larger particles. Magnesia-carbon brick recycled material uses fine powder because it contains C. The finer the C, the better the encapsulation of magnesia sand and magnesia-calcium sand particles, and the higher the distribution coverage rate. Magnesia-carbon brick recycled material contains antioxidants. The finer the antioxidant, the more obvious the sintering property of the drainage sand during use. It is conducive to the rapid formation of a dense sintered thin layer on the upper part of the drainage sand at high temperature, preventing molten steel or liquid slag from penetrating to the lower part of the drainage sand, and further improving the self-casting rate of the drainage sand.

[0040] The present invention also ensures that the drainage sand has high refractory performance, moderate sinterability, good cleanliness of molten steel, and no invariance or degradation during use. The performance of the drainage sand is improved throughout the entire process, ensuring an excellent self-casting rate.

[0041] The drainage sand of the present invention fully utilizes waste recycling resources, reduces carbon emissions, and has high quality, low cost and excellent performance.

[0042] The preparation method of alkaline ladle drainage sand for clean molten steel of the present invention comprises the following steps: magnesia sand and magnesia-calcium sand are evenly mixed, and then fine powder of recycled waste magnesia-carbon bricks is added, and the mixture is stirred to make the surfaces of the magnesia-calcium sand and the magnesia sand evenly coated with the fine powder of recycled waste magnesia-carbon bricks. In this way, C in the fine powder of recycled waste magnesia-carbon bricks is most distributed on the surfaces of the magnesia sand and magnesia-calcium sand particles, so that the drainage sand is not infiltrated by molten steel when in use, the anti-penetration performance is further improved, and the self-casting rate of the drainage sand is improved.

[0043] The obtained basic ladle drainage sand weighs 10-15kg / bag, is vacuum-sealed and packed, and can be transported to the site for use at any time. After vacuum packaging, the drainage sand has excellent waterproof performance and a longer shelf life; vacuum packaging also prevents the drainage sand product from material segregation during transportation and use, making the quality and performance more stable and further improving the self-casting rate of the drainage sand.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The present invention uses magnesia sand (MgO), magnesia calcium sand (MgO.CaO), and waste magnesia carbon brick recycled materials (MgO, C) as raw materials to generate a new type of alkaline drainage sand mainly composed of MgO+CaO. The total amount of MgO and CaO exceeds 90wt%. MgO and CaO can clean molten steel, reduce secondary oxidation of molten steel, and improve the purity of molten steel, thereby reducing inclusions in the casting, which is different from the existing acidic and neutral drainage sand. Reduce Cr that can cause oxygenation of molten steel 2 O 3 、SiO 2 、Al 2 O 3 , Fe 2 O 3 The addition of oxides such as Cr 2 O 3 、SiO 2 、Al 2 O 3 , Fe 2 O 3 The total amount substantially exceeds 90 wt%.

[0046] The present invention introduces CaO by adding magnesia-calcium sand and combines it with magnesia sand. The raw material has high refractoriness and does not change or deteriorate during use, thereby ensuring that the drainage sand has a high self-casting rate. Combined with the use of recycled waste magnesia-carbon bricks, the sintering property of the drainage sand during use is improved, and the self-casting rate of the drainage sand is further improved. Combined with the matching of the particle sizes between the raw materials, the drainage sand is ensured to be densely stacked, molten steel penetration is avoided, and the self-casting rate is improved. The prior art avoids the introduction of CaO by adding lime or calcite. Calcite or lime is very easy to hydrate and pulverize, which will seriously affect the self-casting rate of the drainage sand, and calcite will decompose and discharge CO during high-temperature use. 2, causing the C content of molten steel to increase, creating a new source of pollution.

[0047] The magnesia sand and magnesia-calcium sand used in the drainage sand of the present invention are conventional refractory raw materials with abundant sources and low prices. The recycled materials of waste magnesia-carbon bricks are even cheaper and more abundant. The waste resources are reused and endowed with high value and high performance. The overall cost is low, and it has high economic and social value, meeting the all-round needs of the drainage sand manufacturing end and the steel plant use end. DETAILED DESCRIPTION

[0048] The present invention is further described below in conjunction with specific embodiments.

[0049] The composition of the drainage sand in the embodiment of the present invention is shown in Table 1.

[0050] The drainage sand obtained in the embodiment of the present invention was subjected to oxide content determination and self-casting rate detection, and the drainage sand of the comparative example was subjected to comparative detection. The specific results are shown in Table 2 below.

[0051] It can be seen from Table 2 that the total amount of MgO and CaO in the drainage sand obtained according to the formula of the present invention exceeds 90wt%, which can cause the Cr 2 O 3 、SiO 2 、Al 2 O 3 , Fe 2 O 3 The oxide content is low; the self-casting rate is high, and the self-casting rate is ≥99.3%.

[0052] The traditional chromium drainage sand (Comparative Examples 1-3) contains Cr 2 O 3 、SiO 2 、Al 2 O 3 , Fe 2 O 3 Mainly oxides, these oxides will cause oxygenation in molten steel and affect the quality of steel.

[0053] Comparative Example 4 is a drainage sand prepared with alkaline forsterite as the main raw material. Although the total content of MgO and CaO is increased, the SiO 2 High content, SiO 2 It has a great influence on the oxygenation of molten steel and is not suitable for high-quality steel grades with long smelting time. The self-casting rate of drainage sand obtained is also low.

[0054] Comparative Example 5 is a conventional method of preparing drainage sand using passivated lime and forsterite as main raw materials. Although the total MgO and CaO have been further improved, the drainage sand still contains a large amount of SiO which will cause the molten steel to increase oxygen. 2 、Al2 O 3 , Fe 2 O 3 Oxide, but lime is easily hydrated and powdered, and is difficult to store and use, which will seriously affect the self-casting rate of the finished drainage sand, so the self-casting rate of the drainage sand obtained is low.

[0055] Table 1 Unit: Weight percentage

[0056]

[0057]

[0058] Table 2

[0059]

[0060]

Claims

1. A basic ladle drainage sand for clean molten steel, the weight percentage of its components include: Magnesia sand 40-60%, magnesium calcium sand 35-55%, waste magnesium carbon brick recycled material 2-6%.

2. The basic ladle drainage sand for clean molten steel according to claim 1, It is characterized in that The magnesia is sintered magnesia or fused magnesia.

3. The basic ladle drainage sand for clean molten steel according to claim 1 or 2, It is characterized in that The MgO content in the magnesia is ≥97wt%, Al 2 O 3 Content ≤0.8wt%Fe 2 O 3 Content ≤0.8wt%, SiO 2 Content ≤1.0wt%.

4. The basic ladle drainage sand for clean molten steel according to claim 1, 2 or 3, It is characterized in that The magnesia sand has a particle size of 1.0 to 0.1 mm and a bulk density of ≥3.3 g / cm 3 .

5. The basic ladle drainage sand for clean molten steel according to claim 1, It is characterized in that The magnesium calcium sand has a MgO content of ≥70wt%, a CaO content of ≥20wt%, and an Al 2 O 3 Content ≤0.3wt%, Fe 2 O 3 Content ≤1.0wt%, SiO 2 Content ≤0.8wt%.

6. The basic ladle drainage sand for clean molten steel according to claim 1 or 5, It is characterized in that The magnesium calcium sand has a particle size of 1.5 to 0.5 mm and a bulk density of ≥3.4 g / cm 3 .

7. The basic ladle drainage sand for clean molten steel according to claim 1, It is characterized in that The recycled waste magnesia carbon bricks contain MgO content ≥50wt%, C content ≤32wt%, Al 2 O 3 Content ≤8wt%, SiO 2 Content ≤4wt%.

8. The basic ladle drainage sand for clean molten steel according to claim 1 or 7, It is characterized in that The particle size of the recycled waste magnesia carbon bricks is ≤0.088mm.

9. The basic ladle drainage sand for clean molten steel according to any one of claims 1 to 8, It is characterized in that The content of MgO+CaO in the basic ladle drainage sand is ≥90wt%, and the self-casting rate is ≥99.3%.

10. A method for preparing basic ladle drainage sand for clean molten steel according to any one of claims 1 to 9, Its characteristics are: The magnesia sand and the magnesia-calcium sand are mixed evenly, and then the waste magnesia-carbon brick recycled material is added, stirred and mixed, so that the surfaces of the magnesia-calcium sand and the magnesia sand are evenly coated with the waste magnesia-carbon brick recycled material to obtain alkaline ladle drainage sand.

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