Continuous casting covering slag as well as preparation method and application thereof

Abstract

The invention relates to continuous casting covering slag and a preparation method and application thereof, and belongs to the technical field of ferrous metallurgy continuous casting. The continuous casting covering slag provided by the invention comprises the following components in parts by weight: 27-35 parts of CaO, 23-32 parts of SiO2, 4-10 parts of Al2O3, 0.5-2 parts of Fe2O3, 4-8 parts of MgO, 4-9 parts of Na2O, 0.5-2.5 parts of Li2O, 1-5.5 parts of CaF2 and 3-8 parts of C. The continuous casting covering slag is simple in preparation method, has a stable melting point, moderate viscosity and fluidity, good spreadability and relatively high alkalinity, and is high in slag film stability, good in lubricating property, relatively high in erosion resistance and long in service life. And the continuous casting process requirements of different steel types are met, and the casting blank quality and the continuous casting process stability can be improved in application.

Description

Technical Field

[0001] The invention relates to the technical field of continuous casting in iron and steel metallurgy, and in particular to a continuous casting protection slag and a preparation method and application thereof. Background Art

[0002] Continuous casting is a vital link in steel production, and continuous casting protection slag, as a key auxiliary material required in the continuous casting process, has a very important impact on the quality of the ingot and the smooth operation of the continuous casting process. However, the existing continuous casting protection slag still has some shortcomings in performance. For example, the melting point of some protection slags is unstable, resulting in large fluctuations in slag consumption during the continuous casting process, making it difficult to maintain a stable thickness of the liquid slag layer, thus affecting the surface quality of the ingot; in addition, the slag formation speed of some protection slags is slow, and a complete slag film cannot be formed in time, resulting in poor lubrication between the ingot and the wall of the crystallizer, increasing the resistance to the ingot drawing, and may even cause steel leakage accidents; some protection slags have unreasonable three-layer structures after melting, and the physical and chemical properties of the liquid slag such as viscosity, surface tension and interfacial tension cannot meet the requirements of the continuous casting process, resulting in slag inclusions, cracks and other quality defects on the surface of the ingot.

[0003] In response to the problems existing in the existing continuous casting mold slag, researchers have conducted a lot of research and improvements. For example, by adjusting the chemical composition of the mold slag, such as increasing the content of flux, to reduce the melting point of the mold slag and increase the melting rate; by adding an appropriate amount of flux to further reduce the melting point and improve the lubrication performance of the slag film; by optimizing the particle size distribution of the mold slag to improve the spreadability and uniformity of the mold slag, thereby ensuring the formation of a stable liquid slag layer during the continuous casting process, etc. Although these improvement measures have improved the performance of the continuous casting mold slag to a certain extent, there are still some problems to be solved. Although some improved mold slags have a lower melting point, the slag formation speed is still slow and a complete slag film cannot be formed in time; although some mold slags have a reasonable three-layer structure, the physical and chemical properties of the liquid slag such as viscosity, surface tension and interfacial tension still cannot meet the requirements of the continuous casting process of certain specific steel grades.

[0004] Therefore, in order to solve the problems existing in the existing continuous casting protection slag, it is urgent to develop a continuous casting protection slag with stable melting point, fast slag forming speed, reasonable structure and excellent performance by optimizing the chemical composition and preparation process of the protection slag, so as to meet the requirements of the continuous casting process for different steel grades and improve the quality of the ingot and the stability of the continuous casting process. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a continuous casting mold slag and its preparation method and application. The continuous casting mold slag provided by the present invention has high slag film stability, good lubrication and spreading performance, and strong corrosion resistance, and is suitable for the continuous casting process requirements of different steel grades.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] In a first aspect, the present invention provides a continuous casting protective slag comprising the following components in parts by weight: 27-35 parts of CaO, 23-32 parts of SiO2, 4-10 parts of Al2O3, 0.5-2 parts of Fe2O3, 4-8 parts of MgO, 4-9 parts of Na2O, 0.5-2.5 parts of Li2O, 1-5.5 parts of CaF2, and 3-8 parts of C.

[0008] The continuous casting mold slag provided by the present invention uses SiO2 and CaO as main components, and regulates the melting temperature, viscosity and basicity of the mold slag. Appropriate amounts of SiO2 and CaO can ensure that the mold slag has good solubility and fluidity during the continuous casting process, can form a stable slag film, effectively isolate the molten steel from the copper wall of the crystallizer, and prevent the molten steel from being secondary oxidized and the copper wall from being corroded.

[0009] A specific proportion of Al2O3 can increase the melting point of the mold slag, enhance its corrosion resistance, and help form a dense slag film structure, reduce the permeability of the slag film, and further reduce the risk of secondary oxidation of molten steel. At the same time, a small amount of Fe2O3 is introduced. A lower level of Fe2O3 can reduce the occurrence of slag-steel reaction and avoid the deterioration of the performance of the mold slag.

[0010] The further introduction of Na2O, Li2O and CaF2 can comprehensively regulate the viscosity of the mold slag, improve its fluidity, and help the mold slag to better cover the surface of the molten steel and form a uniform liquid slag layer. The addition of an appropriate amount of MgO can assist in regulating the spreadability and thermal insulation effect of the mold slag, while improving the stability of the slag film and reducing the formation of slag strips.

[0011] The C in the component acts as a reducing agent, which can further reduce the content of FeO in the slag and reduce the occurrence of slag-steel reaction. At the same time, C can also react with oxygen to generate CO gas, which helps to make the mold slag fluffy and spread. In addition to the above main components, the continuous casting mold slag may also include a small amount of inevitable trace elements and impurities introduced during preparation.

[0012] When the components of the above-mentioned continuous casting protective slag are within the weight range specified in the present invention, the melting point of the protective slag can be controlled to be stable at 1050-1100°C, the viscosity at 1300°C is 0.1-0.3Pa·s, and the basicity is 0.9-1.1. It has moderate and stable melting performance, fluidity, basicity, and good spreadability. When the ratio between the components is not suitable, exceeds or is lower than the specified range, it may lead to an increase in melting temperature, unstable melting point, or poor fluidity or excessive thinness due to inappropriate viscosity, or a significant deterioration in spreadability, etc., which may reduce the overall performance of the protective slag.

[0013] The continuous casting protection slag provided by the present invention has excellent performance. In the continuous casting process of steel metallurgy, it can form a stable slag film to isolate the molten steel and the copper wall of the crystallizer, prevent the molten steel from being secondary oxidized and the copper wall from being corroded, and maintain a stable slag consumption and liquid slag layer thickness, thereby improving the surface quality of the ingot. It can meet the requirements of the continuous casting process of different steel grades, improve the quality of the ingot and the stability of the continuous casting process, and has high application value.

[0014] Preferably, the continuous casting protection slag comprises the following components in parts by weight: 30-35 parts of CaO, 25-30 parts of SiO2, 4-6 parts of Al2O3, 0.5-1.5 parts of Fe2O3, 5-6 parts of MgO, 8-9 parts of Na2O, 1.5-2.5 parts of Li2O, 4-5.5 parts of CaF2, and 6-8 parts of C.

[0015] Further preferably, the continuous casting protection slag comprises the following components in parts by weight: 32 parts of CaO, 28 parts of SiO2, 4 parts of Al2O3, 1 part of Fe2O3, 6 parts of MgO, 8 parts of Na2O, 2.5 parts of Li2O, 5 parts of CaF2, and 7 parts of C.

[0016] Under the above-mentioned preferred component ratio, the continuous casting protection slag provided by the present invention has low viscosity and good fluidity, while not being too thin to affect the effect of isolating molten steel and the copper wall of the crystallizer, and has better spreadability.

[0017] Preferably, the melting point of the continuous casting mold slag is 1050-1100°C.

[0018] Preferably, the viscosity of the continuous casting mold slag at 1300° C. is 0.1-0.3 Pa·s.

[0019] Preferably, the basicity of the continuous casting mold slag is 0.9-1.1.

[0020] Preferably, the particle size of the continuous casting protection slag is 1-5 mm.

[0021] Preferably, the spreading diameter of the continuous casting protection slag is ≥100 mm, and the static angle of the continuous casting protection slag is ≤30°.

[0022] Further preferably, the spreading diameter of the continuous casting protection slag is ≥200 mm.

[0023] Both the spreading diameter and the spreading angle reflect the spreadability of the continuous casting protection slag. The spreading diameter is measured by dropping 1L of molten protection slag from a fixed height of 10cm onto the surface of a smooth metal plate or refractory material preheated at high temperature, and the spreading diameter is calculated based on the spreading area formed on the material surface after dropping. The static angle is the angle between the inclined surface and the horizontal plane measured by letting the molten protection slag fall freely from a fixed height to form a conical pile.

[0024] The continuous casting protection slag provided by the present invention has good spreadability and good effect of wetting the mold wall, and can be non-sticky to the mold and automatically fall off at room temperature.

[0025] In a second aspect, the present invention provides a method for preparing the above-mentioned continuous casting mold slag, comprising the following steps:

[0026] The prepared raw materials are ground with water, and then spray granulated, dried and sieved to obtain the continuous casting protection slag.

[0027] Preferably, the pressure of the spray granulation is 0.2-0.4 MPa, and the drying temperature of the spray granulation is 150-250°C.

[0028] The preparation method of the continuous casting mold slag provided by the present invention is relatively simple, easy to industrialize and has low production cost.

[0029] In a third aspect, the present invention provides application of the above-mentioned continuous casting protection slag in continuous casting.

[0030] Preferably, the application is application in a continuous casting crystallizer.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The present invention mainly optimizes the components and proportions in the continuous casting protective slag to give the protective slag a stable melting point, so that it can maintain stable slag consumption and liquid slag layer thickness during the continuous casting process, thereby improving the surface quality of the ingot; at the same time, it has good spreadability, can form a complete slag film in time, and the slag film has high stability, reducing the friction resistance between the ingot and the crystallizer wall, and reducing the difficulty of billet drawing; and the protective slag of the present invention has a reasonable three-layer structure, moderate physical and chemical properties such as liquid slag viscosity, good lubrication performance, and strong corrosion resistance; based on the above advantages, the continuous casting protective slag provided by the present invention can be used in continuous casting crystallizers of different steel metallurgical continuous casting processes, meet the requirements of continuous casting processes of different steel grades, and has high application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the formation of a reasonable three-layer structure when continuous casting protection slag is applied to the crystallizer. DETAILED DESCRIPTION

[0034] In order to better illustrate the purpose, technical scheme and advantages of the present invention, the present invention will be further described below in conjunction with specific examples. The test methods used in the following examples are conventional methods unless otherwise specified; the materials and reagents used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0035] Example 1

[0036] An embodiment of the continuous casting protection slag of the present invention, the continuous casting protection slag described in this embodiment includes the following components in weight parts: 30 parts of SiO2, 30 parts of CaO, 5 parts of Al2O3, 1.5 parts of Fe2O3, 5 parts of MgO, 8 parts of Na2O, 2.5 parts of Li2O, 5.5 parts of CaF2, and 6 parts of C.

[0037] The preparation method of the continuous casting mold slag described in this embodiment is:

[0038] (1) Weighing and mixing: Weigh the raw materials of each component according to the ratio, and all raw materials are accurately weighed to ensure the accuracy of the chemical composition; the raw materials are dried before preparation to ensure that the moisture content is less than 0.5% to avoid affecting the subsequent process and product quality;

[0039] (2) Wet grinding and screening: put the above-prepared raw materials into a mixer, add 30-40% of the total weight of the raw materials into water, wet grind for 2-4 hours, and then screen until all the slurry reaches a uniform and fine state, wherein the sieve aperture is controlled at 0.5 mm;

[0040] (2) Spray granulation: The sieved slurry is fed into a spray granulator to form granular protective slag by spray granulation, wherein the spray granulation pressure is 0.3 MPa and the drying temperature is 200°C;

[0041] (3) Drying and screening: The granular protective slag obtained after spray granulation is sent to a dryer for drying and removal of moisture from the particles, and then the particles that are too large (>5 mm) or too small (<1 mm) are screened to remove the particles to obtain the finished continuous casting protective slag.

[0042] Example 2

[0043] An embodiment of the continuous casting protection slag of the present invention, the continuous casting protection slag described in this embodiment includes the following components in weight parts: 28 parts of SiO2, 32 parts of CaO, 4 parts of Al2O3, 1 part of Fe2O3, 6 parts of MgO, 8 parts of Na2O, 2.5 parts of Li2O, 5 parts of CaF2, and 7 parts of C.

[0044] The preparation method of the continuous casting protection slag described in this embodiment is the same as that in Example 1.

[0045] Example 3

[0046] An embodiment of the continuous casting protection slag of the present invention, the continuous casting protection slag described in this embodiment includes the following components in weight parts: 25 parts of SiO2, 35 parts of CaO, 6 parts of Al2O3, 0.5 parts of Fe2O3, 5 parts of MgO, 9 parts of Na2O, 1.5 parts of Li2O, 4 parts of CaF2, and 8 parts of C.

[0047] The preparation method of the continuous casting protection slag described in this embodiment is the same as that in Example 1.

[0048] Example 4

[0049] An embodiment of the continuous casting mold slag of the present invention, the continuous casting mold slag described in this embodiment is different from that in embodiment 2 only in that the weight portion of CaF2 in the components is reduced and the weight portion of C is increased accordingly;

[0050] The continuous casting protection slag specifically includes the following components in parts by weight: 28 parts of SiO2, 32 parts of CaO, 4 parts of Al2O3, 1 part of Fe2O3, 6 parts of MgO, 8 parts of Na2O, 2.5 parts of Li2O, 3 parts of CaF2, and 8 parts of C.

[0051] The preparation method of the continuous casting protection slag described in this embodiment is the same as that in Example 1.

[0052] Example 5

[0053] An embodiment of the continuous casting mold slag of the present invention, the continuous casting mold slag described in this embodiment is different from that in embodiment 2 only in that the weight portion of CaF2 in the components is reduced and the weight portion of Fe2O3 is increased accordingly;

[0054] The continuous casting protection slag specifically includes the following components in parts by weight: 28 parts of SiO2, 32 parts of CaO, 4 parts of Al2O3, 2 parts of Fe2O3, 6 parts of MgO, 8 parts of Na2O, 2.5 parts of Li2O, 4 parts of CaF2, and 7 parts of C.

[0055] The preparation method of the continuous casting protection slag described in this embodiment is the same as that in Example 1.

[0056] Comparative Example 1

[0057] A continuous casting protective slag comprises the following components in parts by weight: 37 parts of SiO2, 25 parts of CaO, 2 parts of Al2O3, 0.1 parts of Fe2O3, 10 parts of MgO, 10 parts of Na2O, 5 parts of CaF2, and 6 parts of C.

[0058] The preparation method of the continuous casting protection slag is the same as that in Example 1.

[0059] Comparative Example 2

[0060] A continuous casting protective slag comprises the following components in parts by weight: 15 parts of SiO2, 48 parts of CaO, 11 parts of Al2O3, 1 part of Fe2O3, 2 parts of MgO, 2 parts of Na2O, 3 parts of Li2O, 10.3 parts of CaF2, and 6 parts of C.

[0061] The preparation method of the continuous casting protection slag is the same as that in Example 1.

[0062] Comparative Example 3

[0063] The difference between Comparative Example 3 and Example 2 is that the weight portion of CaF2 in the components is reduced and the weight portion of C is increased, specifically including the following components in weight portions: 28 parts of SiO2, 32 parts of CaO, 4 parts of Al2O3, 1 part of Fe2O3, 6 parts of MgO, 8 parts of Na2O, 2.5 parts of Li2O, 0.1 parts of CaF2, and 10 parts of C.

[0064] The preparation method of the continuous casting protection slag is the same as that in Example 1.

[0065] Comparative Example 4

[0066] The only difference between Comparative Example 4 and Example 2 is that the weight portion of Fe2O3 in the components is increased, specifically including the following components in weight portions: 28 parts of SiO2, 32 parts of CaO, 4 parts of Al2O3, 6 parts of Fe2O3, 6 parts of MgO, 8 parts of Na2O, 2.5 parts of Li2O, 5 parts of CaF2, and 7 parts of C.

[0067] The preparation method of the continuous casting protection slag is the same as that in Example 1.

[0068] Effect example

[0069] In order to explore the performance of the continuous casting mold slag provided by the present invention, the melting point, viscosity (1300° C.), spreadability and basicity of the continuous casting mold slag of the examples and comparative examples were measured.

[0070] The detection method of spreadability is:

[0071] 1. Determination of spreading diameter: Prepare a smooth metal plate surface preheated at high temperature, set the preheating temperature to 1200℃, drop 1L of molten continuous casting protection slag on the metal plate from a height of 10cm, and record the spreading area S of the protection slag on the metal plate after dropping. The formula S=0.25πd 2 Calculate the spreading diameter d; a spreading diameter of not less than 100 mm indicates good spreading.

[0072] 2. Determination of static angle: prepare a smooth metal plate surface that has been preheated at high temperature. The preheating temperature is set to 1200°C. Use a funnel to let the molten continuous casting protective slag fall freely from a height of 10 cm to form a conical pile. The static angle is the angle between the inclined surface of the conical pile and the horizontal plane. Measure and evaluate whether the static angle is greater than 30°. If the static angle is not greater than 30°, it means that the spreadability is good.

[0073] The performance test results of the continuous casting protection slag in Examples 1-5 and Comparative Examples 1-4 are shown in Table 1 below.

[0074] From Table 1, we can see that:

[0075] (1) The melting point of the continuous casting protection slag provided by the present invention in Examples 1-5 is between 1050-1100°C and the melting point is stable, which can maintain stable slag consumption and liquid slag layer thickness during the continuous casting process, thereby improving the surface quality of the ingot; and the viscosity and basicity are appropriate, with the viscosity at 1300°C within 0.1-0.3 Pa·s and the basicity within 0.9-1.1, which helps to improve the fluidity of the protection slag after melting, better cover the surface of the molten steel, form a uniform liquid slag layer, and prevent the molten steel from being oxidized again and the copper wall from being corroded; at the same time, the spreading diameter of the continuous casting protection slag in the examples is greater than 200 mm and the spreading angle is less than 30°, which has excellent spreading property and mold wall wetting effect, and can be non-sticky to the mold and automatically fall off at room temperature. In Example 2, by adjusting the ratio of SiO2 and CaO and adding MgO in an appropriate amount, the melting property and fluidity of the mold slag are further improved, and the stability of the slag film is enhanced; in Example 3, by increasing the content of CaO and reducing the content of SiO2 in an appropriate amount, the basicity and melting point of the mold slag can be increased, thereby enhancing its corrosion resistance. At the same time, by increasing the content of C and reducing the content of CaF2, the reducibility and lubricity of the mold slag can be improved, the corrosion resistance can be improved, and the surface quality of the ingot can be improved.

[0076] (2) Comparison of the embodiments and comparative examples 1 and 2: In comparative example 1, the weight parts of the components of the protective slag other than CaF2 and C are outside the scope defined by the present invention, the amount of SiO2 is too high, and the amount of CaO is reduced, resulting in the melting temperature of the protective slag rising to above 1100°C, the viscosity significantly increasing, the basicity decreasing, and the spreadability significantly deteriorating, affecting various performances of the protective slag in the continuous casting process; In comparative example 2, the weight parts of the components of the protective slag other than C are outside the scope defined by the present invention, and the amount of CaF2 is increased to 10 parts by weight on the basis of comparative example 1, which significantly affects the viscosity of the protective slag, reducing it to only 0.09 Pa·s. Although the fluidity of the protective slag is improved, the slag film will become too thin, which is not conducive to isolating the molten steel and the copper wall of the crystallizer and affects its performance in continuous casting.

[0077] (3) Comparison of the embodiments and comparative examples 3 and 4: The continuous casting protective slag in comparative example 3 reduces the weight portion of CaF2 in the components on the basis of embodiment 2 and increases the weight portion of C to outside the specified range, resulting in a significant increase in the viscosity of the protective slag and a decrease in fluidity, making it difficult to form a good liquid slag layer during the continuous casting process; at the same time, due to the excessively high C content, although the reducibility of the protective slag is enhanced, excessive C leads to an intensified slag-steel reaction, which in turn affects the overall performance of the protective slag; the continuous casting protective slag in comparative example 4 increases the amount of Fe2O3 to outside the specified range on the basis of embodiment 2, resulting in an increase in the melting point of the protective slag to above 1100°C and a deterioration in solubility, making it difficult to melt and cover the surface of the molten steel in time during the continuous casting process. At the same time, excessive Fe2O3 will also intensify the slag-steel reaction, resulting in deterioration of the performance of the protective slag.

[0078] The schematic diagram of the continuous casting mold slag of the present invention being applied to a crystallizer to form a three-layer structure is shown in FIG. Figure 1 . The present invention provides a continuous casting protective slag with suitable and stable melting temperature, viscosity, basicity, and good spreadability. The continuous casting protective slag has good solubility and fluidity. When applied to the continuous casting crystallizer in the continuous casting process, it can form a stable slag film, effectively isolate the molten steel from the copper wall of the crystallizer, and prevent the molten steel from being secondary oxidized and the copper wall from being corroded. At the same time, the appropriate ratio can reduce the slag-steel reaction and avoid the deterioration of the protective slag performance. The continuous casting protective slag provided by the present invention has excellent comprehensive properties, can maintain a stable slag consumption and liquid slag layer thickness, thereby improving the surface quality of the ingot, and is adapted to meet the requirements of the continuous casting process of different steel grades. It has high application value in the continuous casting process of steel metallurgy.

[0079] Table 1 Continuous casting mold slag performance test results of the embodiment and comparative example

[0080]

[0081]

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A continuous casting mold slag, characterized in that: It includes the following components in parts by weight: 27-35 parts of CaO, 23-32 parts of SiO2, 4-10 parts of Al2O3, 0.5-2 parts of Fe2O3, 4-8 parts of MgO, 4-9 parts of Na2O, 0.5-2.5 parts of Li2O, 1-5.5 parts of CaF2, and 3-8 parts of C.

2. The continuous casting mold slag according to claim 1, characterized in that: It includes the following components in parts by weight: 30-35 parts of CaO, 25-30 parts of SiO2, 4-6 parts of Al2O3, 0.5-1.5 parts of Fe2O3, 5-6 parts of MgO, 8-9 parts of Na2O, 1.5-2.5 parts of Li2O, 4-5.5 parts of CaF2, and 6-8 parts of C.

3. The continuous casting mold slag according to claim 2, characterized in that: It includes the following components in parts by weight: 32 parts of CaO, 28 parts of SiO2, 4 parts of Al2O3, 1 part of Fe2O3, 6 parts of MgO, 8 parts of Na2O, 2.5 parts of Li2O, 5 parts of CaF2, and 7 parts of C.

4. The continuous casting mold slag according to claim 1, characterized in that: The melting point of the continuous casting protection slag is 1050-1100°C.

5. The continuous casting mold slag according to claim 1, characterized in that: The viscosity of the continuous casting mold slag at 1300° C. is 0.1-0.3 Pa·s.

6. The continuous casting mold slag according to claim 1, characterized in that: The basicity of the continuous casting mold slag is 0.9-1.

1.

7. The continuous casting mold slag according to claim 1, characterized in that: The spreading diameter of the continuous casting protection slag is ≥100 mm, and the static angle of the continuous casting protection slag is ≤30°.

8. The method for preparing continuous casting mold slag according to any one of claims 1 to 7, characterized in that: The following steps are involved: The prepared raw materials are ground with water, and then spray granulated, dried and sieved to obtain the continuous casting protection slag.

9. The method for preparing continuous casting mold slag according to claim 8, characterized in that: The pressure of the spray granulation is 0.2-0.4 MPa, and the drying temperature of the spray granulation is 150-250°C.

10. Use of the continuous casting protection slag according to any one of claims 1 to 7 in continuous casting.

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