A low-fluorine small round billet protection slag and its preparation method and application

Abstract

The present invention belongs to the technical field of metallurgical auxiliary materials, and specifically discloses a low-fluorine small round billet protective slag and a preparation method thereof. The low-fluorine small round billet protective slag includes the following raw materials in percentage by mass: phosphorus slag 15%-25%, blast furnace slag 25%-35%, diopside 15%-20%, medium carbon graphite 5%-8%, earthy graphite 6%-10%, basic salt 5%-10%, fluorite 0.5%-2%, limestone 8%-10%, carbon black 0.5%-2% and binder 1%-3%. The low-fluorine small round billet protective slag replaces traditional wollastonite with phosphorus slag, blast furnace slag and diopside, which greatly reduces the addition of two fluxes, fluorite and sodium carbonate, while reducing the melting point viscosity of the product, and reduces the corrosion of the protective slag to the refractory. The present invention effectively solves the problem in the prior art that a large amount of flux needs to be added to the protective slag base material to adjust the melting point viscosity of the product, but these fluxes will corrode the refractory.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgical auxiliary materials, and specifically discloses a low-fluorine small round billet protection slag and a preparation method and application thereof. Background Art

[0002] In response to market demand, in order to improve production efficiency and reduce production costs, steel companies have begun to gradually pay attention to and pursue reducing refractory erosion and reducing the cost per ton of steel. Among them, protective slag is an important auxiliary production material in the continuous casting production process. It has the functions of preventing molten steel oxidation, absorbing inclusions, heat insulation, lubrication and heat transfer. However, since the melting point viscosity of protective slag plays a vital role in the absorption of molten steel inclusions, the viscosity directly affects the speed of protective slag absorbing oxide inclusions and the effect of lubricating the ingot. If the melting point viscosity of protective slag is too low, a large amount of liquid slag will flow into the gap, resulting in uneven slag film, slow local solidification, deformation of the solidified ingot shell, and longitudinal cracks and leakage accidents; if the melting point viscosity of protective slag is too high, it will make the surface of the ingot rough. Therefore, the optimization of the melting point viscosity characteristics of protective slag is one of the important topics in the field of metallurgical auxiliary materials.

[0003] In general ternary slag system, the method of controlling or adjusting the melting point viscosity of the mold slag is mainly through Na + and F - , and the base material is basically wollastonite. The advantage of wollastonite is good stability, especially in the melting process, it shows high chemical stability and is not easy to react chemically with other substances. The basic chemical indicators are SiO2: 53% ± 3%, CaO: 42% ± 3%, Al2O3: ≤ 5%, ignition loss ≤ 3.5%, and does not contain fluorine and sodium. Wollastonite belongs to silicate minerals, and its melting point is usually high. During the heating process, it may first undergo a phase change and then melt. After melting, it forms a highly viscous liquid, which is easy to form a glassy substance when cooled. Therefore, when wollastonite is generally used as the protective slag of the base material, it is inevitable to add a large amount of flux such as fluorite or soda ash to adjust the melting point viscosity of the product, and a large amount of flux will inevitably corrode the refractory and reduce the life of the refractory.

[0004] Based on this, developing a protective slag material with low viscosity, good fluidity and no corrosion to refractory materials is of great significance for the development of metallurgical auxiliary materials. Summary of the invention

[0005] In view of the problem that a large amount of flux needs to be added to the protective slag base material in the prior art to adjust the melting point viscosity of the product, but these fluxes will corrode the refractory, the present invention provides a low-fluorine protective slag for small round billets. The low-fluorine protective slag for small round billets replaces the traditional wollastonite with phosphorus slag, blast furnace slag and diopside, which greatly reduces the addition amount of fluorite and soda ash, two fluxes, while reducing the melting point viscosity of the product, and further improves the corrosion resistance of the refractory to molten steel, and reduces the corrosion of the protective slag to the refractory.

[0006] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0007] The first aspect of the present invention provides a low-fluorine small round billet protection slag, which includes the following raw materials in percentage by weight: 15%-25% phosphorus slag, 25%-35% blast furnace slag, 15%-20% diopside, 5%-8% medium carbon graphite, 6%-10% earthy graphite, 5%-10% sodium carbonate, 0.5%-2% fluorite, 8%-10% limestone, 0.5%-2% carbon black and 1%-3% binder.

[0008] Compared with the prior art, the present invention selects phosphorus slag, blast furnace slag and diopside instead of wollastonite as the base material, wherein the phosphorus slag exhibits relatively low viscosity and low melting point during the melting process, and the chemical composition of the phosphorus slag is mainly composed of silicon and calcium. In addition to the glass content as high as 85% to 90%, there are also potential mineral phases such as wollastonite and lanceolite in the phosphorus slag, as well as some crystalline phases such as quartz, pseudowollastonite, calcite and calcium fluoride. These crystalline phases and mineral phases can give the protective slag good stability, and will not form high-melting-point crystalline phases during high temperature and cooling processes, thereby meeting the application requirements of the protective slag.

[0009] After melting at high temperature, blast furnace slag forms a uniform liquid with good stability and homogeneity, showing relatively high viscosity and low melting point. The chemical composition of blast furnace slag is mostly calcium oxide, silicon dioxide and aluminum oxide. Affected by factors such as cooling rate and basicity of slag, its mineral phase composition mainly includes glass, perovskite, calcite and magnesia calcite. These mineral phases can adjust the melting temperature of the protective slag, prevent the protective slag from melting prematurely on the crystallizer, and ensure a reasonable thickness of the liquid slag layer. In addition, these mineral phases can also adjust the viscosity of the protective slag to ensure that the protective slag forms a stable slag film between the crystallizer wall and the billet, reducing the resistance of billet drawing. The melting point viscosity of phosphorus slag and blast furnace slag is lower than that of wollastonite, and after melting and solidification, the billet shell is mainly glass, which can provide excellent lubrication and meet the design characteristics of small round billet protective slag.

[0010] From the perspective of elements, the present invention uses phosphorus slag and blast furnace slag to replace wollastonite, but the melting points of phosphorus slag and blast furnace slag are lower than that of wollastonite, and it is still inevitable to add a small amount of flux (fluorite and sodium carbonate) to make the protective slag meet the use requirements. Based on this, in order to further avoid the corrosion of the flux on the refractory material, the present invention also adds magnesium-containing ore (diopside). The magnesium element in diopside exists in the form of magnesium oxide, which has a low ignition loss and a stable melting state. At the same time, it contains some silicon and calcium elements, and can also be used as a substitute for wollastonite. More importantly, magnesium oxide can effectively improve the corrosion resistance of refractory materials to molten steel, extend the service life of continuous casting nozzles, enhance the oxidation resistance of refractory materials, improve their thermomechanical strength, optimize the chemical stability of refractory materials, especially in acidic and alkaline environments, and improve the stability of the product's melting state. In addition to the above direct protective effect on refractory materials, magnesium oxide, when added in a certain proportion, also plays a role in reducing the melting point and viscosity, thereby further reducing the amount of flux added.

[0011] Preferably, the basicity of the low-fluorine small round billet protection slag is 1.05-1.15.

[0012] Preferably, the viscosity of the low-fluorine small round billet protection slag at 1189° C.-1193° C. is 0.85 Pa·S-0.95 Pa·S.

[0013] After a large number of creative experiments, the inventors determined that it is more appropriate to control the basicity of the protective slag to 1.05-1.15 and the viscosity at 1189℃-1193℃ to be controlled between 0.85Pa·S-0.95Pa·S. Under this basicity condition, the protective slag can promote the absorption and dissolution of inclusions on the surface of the molten steel, avoiding the formation of inclusions on the surface of the cast steel billet and affecting the performance of the steel billet. In addition, the viscosity of the protective slag at 1189℃-1193℃ can ensure that the protective slag has excellent lubrication, flow and heat transfer properties, can reduce the friction between the inner wall of the crystallizer and the surface of the billet shell, and the liquid slag obtained by the present invention can evenly flow into the gap between the crystallizer wall and the new billet shell, and can form a uniform solid slag film, thereby controlling the heat transfer between the two and improving the surface quality of the cast billet.

[0014] Preferably, the phosphorus slag comprises the following chemical components in percentage by mass: SiO2: 36%-40%, CaO: 42%-48%, Al2O3: 3%-7%, Na2O: ≤1.0%; F - : ≤3.0% and the balance is inevitable impurities.

[0015] Preferably, the blast furnace slag comprises the following chemical components in percentage by mass: SiO2: 34%-40%, CaO: 35%-41%, Al2O3: 12%-16%, Na2O: ≤1.0%; F -: ≤1.0% and the balance is inevitable impurities.

[0016] Preferably, the binder is any one of dextrin, pregelatinized starch or sodium carboxymethyl cellulose.

[0017] Preferably, the low-fluorine small round billet protection slag is a hollow granular ball with a particle size of 0.1mm-1.5mm.

[0018] Hollow ball protection slag has the advantages of good thermal insulation performance and good spreadability on the molten steel surface.

[0019] The second aspect of the present invention provides a method for preparing low-fluorine small round billet protection slag, comprising the following steps:

[0020] Step 1: weigh all raw material components except the binder according to the designed ratio, crush and sieve them respectively, and then mix them evenly to obtain a mixed material;

[0021] Step 2: adding a binder and water to the mixed material, mixing evenly, and obtaining a mixed slurry with a mass concentration of 55wt%-65wt%;

[0022] Step three, granulating the mixed slurry by spraying, sieving, and obtaining low-fluorine small round billet protective slag.

[0023] Preferably, in step 1, the mesh size of the sieve used for screening is 300 meshes, and the mass percentage of the material under the sieve is ≥96%.

[0024] Preferably, in step three, the pressure of the spray granulation is 14MPa-18MPa.

[0025] Preferably, in step three, the spray granulation is carried out in a high-temperature spray tower, the temperature in the high-temperature spray tower is 720°C-780°C, and the air outlet temperature of the high-temperature spray tower is 140°C-160°C.

[0026] Preferably, in step three, the sieves used for sieving have mesh sizes of 10 and 60.

[0027] The third aspect of the present invention provides an application of the low-fluorine small round billet protection slag or the low-fluorine small round billet protection slag prepared by the low-fluorine small round billet protection slag preparation method in the field of steel smelting.

[0028] Compared with the prior art, the present invention provides a low-fluorine small round billet protective slag and its preparation method and application, using phosphorus slag, blast furnace slag and diopside to replace the wollastonite in the traditional protective slag, greatly reducing the addition of two fluxes, fluorite and soda ash, further improving the corrosion resistance of the refractory to molten steel, and reducing the corrosion degree of the protective slag to the refractory. The technical solution of the present invention effectively solves the problem that a large amount of flux needs to be added to the protective slag base material in the prior art to adjust the melting point viscosity of the product, but these fluxes will corrode the refractory. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1

[0031] This embodiment provides a low-fluorine small round billet protection slag, the specific content is as follows:

[0032] The low-fluorine small round billet protection slag is prepared from the following raw materials in percentage by weight: 20% phosphorus slag, 30% blast furnace slag, 17% diopside, 6% medium carbon graphite, 8% earthy graphite, 6% sodium carbonate, 1% fluorite, 9% limestone, 1% carbon black and 2% dextrin;

[0033] The specific preparation process of the low-fluorine small round billet protection slag is as follows:

[0034] Step 1: weigh all raw material components except the binder according to the designed ratio, crush them, pass through a 300-mesh sieve, control the mass ratio of the material under the sieve to be 97.5%, put them into a vertical mixing tank in ascending order of specific gravity, mix them evenly, and obtain a mixed material;

[0035] Step 2: Add a binder to the mixed material, add water and stir for 75 minutes, and control the mass concentration of the slurry to 60wt% to obtain a mixed slurry;

[0036] Step three, pressurize the mixed slurry to 16MPa through a plunger pump, and pump it into a high-temperature spray tower for granulation. Set the temperature in the spray tower to 760°C and the air outlet temperature of the spray tower to 150°C. Sieve the protective slag after spray granulation through 10-mesh and 60-mesh sieves to obtain low-fluorine small round billet protective slag.

[0037] The analysis shows that the basicity of the obtained low-fluorine small round billet protection slag is 1.07, the morphology is hollow granular balls, and the particle size is 0.1mm-1.0mm.

[0038] Example 2

[0039] This embodiment provides a low-fluorine small round billet protection slag, the specific content is as follows:

[0040] The low-fluorine small round billet protection slag is prepared from the following raw materials in percentage by weight: 25% phosphorus slag, 26% blast furnace slag, 15% diopside, 6% medium carbon graphite, 8% earthy graphite, 6% sodium carbonate, 1% fluorite, 10% limestone, 1% carbon black and 2% dextrin;

[0041] The specific preparation process of the low-fluorine small round billet protection slag is as follows:

[0042] Step 1: weigh all raw material components except the binder according to the designed ratio, crush them, pass through a 300-mesh sieve, control the mass ratio of the material under the sieve to be 96.8%, put them into a vertical mixing tank in ascending order of specific gravity, mix them evenly, and obtain a mixed material;

[0043] Step 2: Add a binder to the mixed material, add water and stir for 80 minutes, and control the mass concentration of the slurry to 65wt% to obtain a mixed slurry;

[0044] Step three, pressurize the mixed slurry to 18MPa through a plunger pump, and pump it into a high-temperature spray tower for granulation. Set the temperature in the spray tower to 780°C and the air outlet temperature of the spray tower to 140°C. Sieve the protective slag after spray granulation through 10-mesh and 60-mesh sieves to obtain low-fluorine small round billet protective slag.

[0045] The analysis shows that the basicity of the obtained low-fluorine small round billet protection slag is 1.12, the morphology is hollow granular balls, and the particle size is 0.2mm-0.9mm.

[0046] Example 3

[0047] This embodiment provides a low-fluorine small round billet protection slag, the specific content is as follows:

[0048] The low-fluorine small round billet protection slag is prepared from the following raw materials in percentage by weight: phosphorus slag 22%, blast furnace slag 26%, diopside 17%, medium carbon graphite 6%, earthy graphite 8%, sodium carbonate 7%, fluorite 1%, limestone 10%, carbon black 1% and dextrin 2%;

[0049] The specific preparation process of the low-fluorine small round billet protection slag is as follows:

[0050] Step 1: weigh all raw material components except the binder according to the designed ratio, crush them, pass through a 300-mesh sieve, control the mass ratio of the material under the sieve to be 98.1%, put them into a vertical mixing tank in ascending order of specific gravity, mix them evenly, and obtain a mixed material;

[0051] Step 2: Add a binder to the mixed material, add water and stir for 70 minutes, and control the mass concentration of the slurry to 55wt% to obtain a mixed slurry;

[0052] Step three, pressurize the mixed slurry to 14MPa through a plunger pump, and pump it into a high-temperature spray tower for granulation. Set the temperature in the spray tower to 720°C and the air outlet temperature of the spray tower to 160°C. Sieve the protective slag after spray granulation through 10-mesh and 60-mesh sieves to obtain low-fluorine small round billet protective slag.

[0053] The analysis shows that the basicity of the obtained low-fluorine small round billet protection slag is 1.1, the morphology is hollow granular balls, and the particle size is 0.1mm-1.2mm.

[0054] Comparative Example 1

[0055] This comparative example provides a low-fluorine small round billet protection slag, the specific contents are as follows:

[0056] The low-fluorine small round billet protection slag is prepared from the following raw materials in percentage by weight: 54% wollastonite, 3% bentonite, 5% bauxite, 6% medium carbon graphite, 8% earthy graphite, 10% sodium carbonate, 6% fluorite, 5% limestone, 1% carbon black and 2% dextrin;

[0057] The specific preparation process of the low-fluorine small round billet protection slag is as follows:

[0058] Step 1: weigh all raw material components except the binder according to the designed ratio, crush them, pass through a 300-mesh sieve, control the mass ratio of the material under the sieve to be 97.2%, put them into a vertical mixing tank in ascending order of specific gravity, mix them evenly, and obtain a mixed material;

[0059] Step 2: Add a binder to the mixed material, add water and stir for 75 minutes, and control the mass concentration of the slurry to 60wt% to obtain a mixed slurry;

[0060] Step three, pressurize the mixed slurry to 16MPa through a plunger pump, and pump it into a high-temperature spray tower for granulation. Set the temperature in the spray tower to 760°C and the air outlet temperature of the spray tower to 150°C. Sieve the protective slag after spray granulation through 10-mesh and 60-mesh sieves to obtain low-fluorine small round billet protective slag.

[0061] The analysis shows that the basicity of the obtained low-fluorine small round billet protection slag is 0.97, the morphology is hollow granular balls, and the particle size is 0.1mm-1.0mm.

[0062] Comparative Example 2

[0063] This comparative example provides a low-fluorine small round billet protection slag, the specific contents are as follows:

[0064] The low-fluorine small round billet protection slag is prepared from the following raw materials in percentage by weight: 30% phosphorus slag, 38% blast furnace slag, 6% medium carbon graphite, 8% earthy graphite, 8% sodium carbonate, 2% cryolite, 5% limestone, 2% bauxite, 1% carbon black and 2% dextrin;

[0065] The specific preparation process of the low-fluorine small round billet protection slag is as follows:

[0066] Step 1: weigh all raw material components except the binder according to the designed ratio, crush them, pass through a 300-mesh sieve, and then put them into a vertical mixing tank in increasing order of specific gravity, mix them evenly, and obtain a mixed material;

[0067] Step 2: Add a binder to the mixed material, add water and stir for 75 minutes, and control the mass concentration of the slurry to 60wt% to obtain a mixed slurry;

[0068] Step three, pressurize the mixed slurry to 16MPa through a plunger pump, and pump it into a high-temperature spray tower for granulation. Set the temperature in the spray tower to 760°C and the air outlet temperature of the spray tower to 150°C. Sieve the protective slag after spray granulation through 10-mesh and 60-mesh sieves to obtain low-fluorine small round billet protective slag.

[0069] The analysis shows that the basicity of the obtained low-fluorine small round billet protection slag is 1.17, the morphology is hollow granular balls, and the particle size is 0.1mm-1.0mm.

[0070] Comparative Example 3

[0071] This comparative example provides a low-fluorine small round billet protection slag, the specific contents are as follows:

[0072] The low-fluorine small round billet protection slag is made of the following raw materials in percentage by weight: 45% phosphorus slag, 20% diopside, 6% medium carbon graphite, 8% earthy graphite, 6% sodium carbonate, 3% bauxite, 7% limestone, 2% fluorite, 1% carbon black and 2% dextrin;

[0073] The specific preparation process of the low-fluorine small round billet protection slag is as follows:

[0074] Step 1: weigh all raw material components except the binder according to the designed ratio, crush them, pass through a 300-mesh sieve, and then put them into a vertical mixing tank in increasing order of specific gravity, mix them evenly, and obtain a mixed material;

[0075] Step 2: Add a binder to the mixed material, add water and stir for 75 minutes, and control the mass concentration of the slurry to 60wt% to obtain a mixed slurry;

[0076] Step three, pressurize the mixed slurry to 16MPa through a plunger pump, and pump it into a high-temperature spray tower for granulation. Set the temperature in the spray tower to 780°C and the air outlet temperature of the spray tower to 150°C. Sieve the protective slag after spray granulation through 10-mesh and 60-mesh sieves to obtain low-fluorine small round billet protective slag.

[0077] The analysis shows that the basicity of the obtained low-fluorine small round billet protection slag is 1.05, the morphology is hollow granular balls, and the particle size is 0.1mm-1.0mm.

[0078] Test example

[0079] The samples obtained from each embodiment and comparative example were respectively added into a single-strand round billet continuous casting crystallizer with a cross-section of Φ200mm and a pulling speed of 0.9m / min. After the liquid level pulling speed was stabilized for 10 minutes, the stability of use and the resistant material erosion were observed. The results are shown in Table 1.

[0080] Table 1 Test results of the protective slag obtained in each embodiment and comparative example

[0081]

[0082] It can be seen from Table 1 that the protective slag obtained in Examples 1-3 has more excellent and stable performance, stable performance during use, and good effect on erosion of the refractory material at the water outlet, while the protective slag obtained in Comparative Examples 1-3 has poor stability and high viscosity, and causes more serious erosion of the refractory material at the water outlet, especially in Comparative Example 1, which requires frequent replacement of the water outlet.

[0083] In order to further demonstrate the performance of the protective slag provided by the present invention, the present invention carried out an expanded test on the protective slag obtained in Examples 1-3 in a single-stream round billet continuous casting crystallizer with a cross-section of Φ200mm and a pulling speed of 0.9m / min. In the first expanded test, the protective slag obtained in Examples 1-3 was used in four streams at the same time, and in the second expanded test, the protective slag obtained in Examples 1-3 was used in all streams. The results are shown in Table 2.

[0084] Table 2 Expanded test results of mold slag obtained in each embodiment

[0085]

[0086] It can be seen from Table 2 that the protective slag obtained in Examples 1-3 provided by the present invention still has stable performance during use, and the qualified rate of the cast steel billets after two expanded tests (judgment criteria: the surface quality of the steel billets is intact, there are no irregular slag blocks inside the crystallizer, and the erosion resistance of the material is normal) is as high as more than 99%.

[0087] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A low-fluorine small round billet protection slag, characterized in that: The low-fluorine small round billet protection slag comprises the following raw materials in percentage by weight: phosphorus slag 15%-25%, blast furnace slag 25%-35%, diopside 15%-20%, medium carbon graphite 5%-8%, earthy graphite 6%-10%, sodium carbonate 5%-10%, fluorite 0.5%-2%, limestone 8%-10%, carbon black 0.5%-2% and binder 1%-3%; The phosphorus slag includes the following chemical components in percentage by mass: SiO2: 36%-40%, CaO: 42%-48%, Al2O3: 3%-7%, Na2O: ≤1.0%; F - : ≤3.0% and the balance is unavoidable impurities; The blast furnace slag includes the following chemical components in percentage by mass: SiO2: 34%-40%, CaO: 35%-41%, Al2O3: 12%-16%, Na2O: ≤1.0%; F - : ≤1.0% and the balance is inevitable impurities.

2. The low-fluorine small round billet protection slag according to claim 1, characterized in that: The basicity of the low-fluorine small round billet protection slag is 1.05-1.

15.

3. The low-fluorine small round billet protection slag according to claim 1, characterized in that: The viscosity of the low-fluorine small round billet protection slag at 1189° C.-1193° C. is 0.85 Pa·S-0.95 Pa·S.

4. The low-fluorine small round billet protection slag according to claim 1, characterized in that: The binder is any one of dextrin, pregelatinized starch or sodium carboxymethyl cellulose.

5. The low-fluorine small round billet protection slag according to claim 1, characterized in that: The low-fluorine small round billet protection slag is a hollow particle ball with a particle size of 0.1mm-1.5mm.

6. A method for preparing low-fluorine small round billet protection slag according to any one of claims 1 to 5, characterized in that: The steps include: Step 1: weigh all raw material components except the binder according to the designed ratio, crush and sieve them respectively, and then mix them evenly to obtain a mixed material; Step 2: adding a binder and water to the mixed material, mixing evenly, and obtaining a mixed slurry with a mass concentration of 55wt%-65wt%; Step three, granulating the mixed slurry by spraying, sieving, and obtaining low-fluorine small round billet protective slag.

7. The method for preparing low-fluorine small round billet protection slag according to claim 6, characterized in that: In step 1, the mesh size of the sieve used for sieving is 300 mesh, and the mass percentage of the material under the sieve is ≥ 96%; and / or In step 3, the granulation pressure is 14MPa-18MPa.

8. The method for preparing low-fluorine small round billet protection slag according to claim 6, characterized in that: In step 3, the granulation is carried out in a high-temperature spray tower, the temperature in the high-temperature spray tower is 720°C-780°C, and the outlet temperature of the high-temperature spray tower is 140°C-160°C; and / or In step 3, the sieves used for screening are 10 mesh and 60 mesh.

9. Use of the low-fluorine small round billet protection slag as described in any one of claims 1 to 5 or the low-fluorine small round billet protection slag prepared by the preparation method of the low-fluorine small round billet protection slag as described in any one of claims 6 to 8 in the field of steel smelting.

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