A slag conditioning agent and its preparation method and application

Abstract

The present invention discloses a slag conditioner and its preparation method and application, belonging to the technical field of iron and steel smelting. The weight percentages of the chemical components of the slag conditioner are as follows: CaO: 37.0% - 39.0%, SiC: 32.0% - 34.0%, C: 15% - 16%, CaMg(CO3)2: 6% - 7%, binder 6%, S ≤ 0.15%, P ≤ 0.08%, H2O ≤ 1.5%. Among them, SiC and carbon powder have certain reducibility, and at the same time, the SiO2 and CO generated by the reaction can make the steel slag foam, increasing the spreadability of the steel slag and improving the covering effect of the steel slag. After the addition of this slag conditioner, it can quickly react with the steel slag surface and make the steel slag spread rapidly to achieve the effect of diffusion and heat generation, effectively improving the state of the steel slag, solving the problem of poor covering effect caused by easy crusting and agglomeration of the ladle top slag, and reducing the oxidability of the steel slag to a certain extent, providing good reaction conditions for the subsequent addition of steel slag deoxidizer.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron and steel metallurgy and steelmaking, and more specifically, relates to a slag regulator and a preparation method and application thereof. Background Art

[0002] Slag is a melt floating on the surface of molten steel generated during the steelmaking process. It is mainly composed of oxides and often contains sulfides and a small amount of metal. When the molten steel is discharged into the ladle (steel ladle) after the converter smelting is completed, slag is often used to tap the steel, but some slag will inevitably enter the ladle. This part of the final slag is called ladle top slag. The final slag of converter smelting has the characteristics of high oxidizing property, high alkalinity and high melting point. The mass fraction of total iron (TFe) in the slag can reach 13-15%. If the subsequent process is not handled properly, the oxidizing ladle top slag will continue to transfer oxygen to the molten steel and react with aluminum in the molten steel to produce alumina inclusions. This is one of the main reasons for the secondary oxidation of molten steel, which seriously affects the cleanliness of high-quality steel.

[0003] To improve the oxidizability of the ladle top slag, the method of adding an aluminum-based composite modifier to reduce the oxidizability of the ladle top slag is currently commonly used, such as patent CN114350880A. However, after the aluminum-based composite modifier is added, it reacts with the steel slag to produce a large amount of explosive mushroom cloud of smoke. This is because the modifier fails to fully react with the top slag during the smelting process and continues to react, resulting in a long period of smoke and dust, polluting the environment, and being detrimental to human health and environmental protection. The insufficient reaction of the modifier will ultimately lead to a large dispersion in the control of the TFe mass fraction in the ladle top slag, affecting the quality of the molten steel. Patent CN101545017A discloses a ladle slag modifier, whose chemical components are: CaO: 61-70%; Al2O3: 15-28%; Al: 3.5-7%; CaF2: 6-10%; MgO: 1.5-5%; SiO2: <3%; C ≤ 0.01%; controlled moisture ≤ 0.3%; its main purpose is to reduce the ∑(FeO+MnO)% in the ladle top slag. For example, patent CN108018398A discloses a ladle top slag deoxidation modifier for ultra-low carbon steel and a method for using the same. The weight percentages of the components are: Al: 18-28%, CaCO3: 20-30%, CaO: 3-7%, Al2O3: 5-10%, CaF2: 5-9%, MgO: 5-8%, Na2CO3≤6%, and the rest are unavoidable impurities. The particle size of each component of the ladle top slag deoxidation modifier is ≤1mm; although the addition of CaF2 can improve the problem of poor fluidity of molten steel, fluoride is not environmentally friendly; and if too much CaF2 is added, it will corrode the refractory material on the surface of the ladle and accelerate the dissolution rate of the refractory material.

[0004] In the above patents, the deoxidizer aluminum is mixed in the modifier. When added to the molten steel, the temperature cannot reach the melting point of the aluminum-based composite modifier. The modifier is in an accumulated state, the reaction is slow and insufficient, and the quality of the molten iron is poor.

[0005] Therefore, it is very necessary to develop a new type of slag conditioner that has little impact on the environment, has a good effect on adjusting the ladle top slag, and provides a good slag state for the use of subsequent deoxidizers. The ladle top slag adjustment technology is also one of the key technologies for smelting ultra-low carbon steel. Summary of the Invention

[0006] 1. Problem to be solved

[0007] Aiming at the problem that the existing aluminum-based composite modifier is not fully melted in molten steel, resulting in poor molten steel quality, the present invention provides a slag regulator and a preparation method thereof. The prepared slag regulator is conducive to the full melting of the deoxidizer.

[0008] The slag regulator is used in steel smelting to effectively improve the quality of molten steel and control the total iron content of ladle slag to be within 7%.

[0009] 2. Technical solution

[0010] Prior art methods reduce the oxidizing properties of ladle top slag by adding aluminum-based composite modifiers. Al is added to the modifier, which also acts as a deoxidizer. However, aluminum-based composite modifiers have a high melting point. The melting point of the commonly added Al2O3 is 2054°C, requiring a certain temperature to fully melt. However, the slag surface temperature rapidly drops to approximately 700°C-800°C after tapping. Furthermore, the addition of aluminum-based composites is an endothermic reaction. Consequently, the temperature of the ladle top slag does not reach the melting point of the aluminum-based composites, leading to accumulation and crusting. Without fully melting, the aluminum-based composites react with the CaO in the slag, resulting in a slow reaction, continuous smoke generation, and incomplete melting. This results in significant variability in the control of the TFe mass fraction in the ladle top slag and poor molten steel quality.

[0011] In order to solve the above problems, the technical solutions adopted by the present invention are as follows:

[0012] A slag adjuster, the chemical components of which include CaO: 37.0%-39.0%, SiC: 32.0%-34.0%, C: 15%-16%, CaMg(CO3)2: 6%-7%, binder: 6%, and the rest are inevitable impurities, wherein: S≤0.15%, P≤0.08%, and H2O≤1.5%.

[0013] CaO: The deoxidizer aluminum reacts with FeO in the ladle top slag to generate Al2O3. Al2O3 combines with CaO in the slag to generate 12CaO·7Al2O3 with a lower melting point, which reduces the oxidizing property of the ladle top slag and enables the ladle top slag to have a certain ability to absorb Al2O3 inclusions in molten steel. The chemical reaction formula is:

[0014] 3FeO+2Al→Al2O3+3Fe

[0015] 12CaO+7Al2O3→12CaO·7Al2O3

[0016] By reducing the activity of Al2O3, the slag melting point is lowered, and the mass transfer coefficient of Al2O3 is increased. The present invention controls the CaO content to 37.0%-39.0%. The reason is that CaO added to molten steel undergoes an endothermic decomposition reaction. If the content is less than 37%, the Al2O3 activity is too high. If the content is greater than 39%, the excessive CaO addition reduces the reactivity of the slag surface, preventing the spreading effect, resulting in the generation of smoke and dust during the subsequent addition of metallic aluminum.

[0017] Among them, SiC and carbon powder have certain reducing properties, and their reaction formula with steel slag is as follows: SiC+3(FeO)=3Fe+SiO2+CO(g), C+FeO=Fe+CO(g).

[0018] SiC and carbon powder can quickly react with FeO in the steel slag to produce CO, causing the steel slag to foam and spread out quickly within 1 minute. The generated SiO2 and CO can cause the steel slag to foam, increasing the spreadability of the steel slag and improving the slag covering effect. In addition, SiC can play a role in diffusion deoxidation, and the reaction heat generated has a high thermal conductivity coefficient, which not only causes foaming but also increases the temperature, which is conducive to the rapid reaction of metal aluminum with the steel slag surface after addition, causing the steel slag to spread out quickly to achieve a diffuse heating effect. The SiC content is controlled at 32.0%-34.0%. If SiC is lower than 32.0%, the steel slag surface reacts too slowly and the diffuse heating effect is not ideal. If SiC is higher than 34.0%, the steel slag surface reacts too quickly and foams quickly, which can easily cause the top slag to overflow the ladle, which is a safety hazard.

[0019] Controlling the carbon powder content to 15%-16% effectively maintains foaming time. Adding carbon powder prolongs the time the slag maintains optimal thermal efficiency, preventing slag agglomeration and maintaining a visually molten slag surface. This allows for secondary slag adjustments after the addition of a strong aluminum deoxidizer. If the carbon powder content is less than 15%, the foaming and molten state duration is short, hindering the reduction of TFe content in the slag. If the carbon powder content is greater than 16%, the molten state duration is prolonged, causing temperature loss in the molten steel and increasing carbon content in the molten steel.

[0020] During the reaction, SiC is first used to stimulate the heat source, and then carbon powder is used to foam and insulate the heat, extending the high-temperature period. Furthermore, the addition of aluminum also generates heat. Therefore, the present invention further controls the mass ratio of SiC to carbon powder to (2.0-2.2):1, achieving both heat source stimulation and a long insulation period.

[0021] CaMg(CO3)2 is dolomite, which contains free CaO, which can purify molten steel, increase slag viscosity, and absorb inclusions in the molten steel. Later, when aluminum is added for deoxidation, it helps improve slag separation and removes oxygen from the slag. If the CaMg(CO3)2 content is less than 6%, the slag viscosity is too low, resulting in poor slag separation. Above 7%, the slag viscosity is too thick, easily causing accumulation after the addition of aluminum, reducing the reaction rate.

[0022] To improve the reaction speed, spreadability, and solubility of the slag conditioner, the particle size of the slag conditioner should be as small as possible. However, if the particle size is too small, the slag conditioner will easily disperse during addition and be extracted by the dust removal system. Therefore, the particle size of the slag conditioner of the present invention is set to 10-40 mm. To achieve a particle size of 10-40 mm, the present invention adds a certain proportion of binder. Although it is desirable to use as little or no binder as possible during manufacturing, the slag conditioner of the present invention is a composite product and the particle size must be set to 10-40 mm. Without a binder, it is difficult to press into balls. After repeated testing, it was found that the binder must reach 6% for compression molding. Too little or no binder will cause the slag to become loose. If the particles are too small during addition, they are easily extracted by the dust removal system. Too much binder will slow the material dissolution reaction rate, which is not conducive to the fluidity of the slag. Ultimately, the particle size of the slag conditioner of the present invention is set to 10-40 mm.

[0023] The present invention discloses a method for preparing the above-mentioned slag conditioning agent, which specifically comprises the following steps:

[0024] (1) Crushing: The raw materials are crushed and selected by the crusher, and then screened and stirred. The particle size is controlled at 0-5mm. The particle size ratio is reasonable and the distribution is uniform after stirring. It is easy to decompose under high temperature and the product efficacy is fully exerted.

[0025] (2) Ball pressing: Use a super dry ball pressing machine to perform high-pressure ball forming to form pressed balls;

[0026] (3) Screening: Use a screening machine to screen the pellets to select pellets with a particle size of 10-40 mm;

[0027] (4) Drying: The sieved pellets are heated and dried for more than 48 hours. After drying, they are packaged in moisture-proof, metered packaging. Experiments have shown that the adhesive has both bonding and drying functions. During the ball rolling process, the adhesive heats up instantly under high pressure, and the surface temperature of the ball is around 150°C. As long as the storage and packaging are appropriate, the H2O content in the product can be controlled below 1.5%. If affected by climate, storage and other conditions, electric furnace drying can be used if necessary. The furnace temperature should be controlled between 200-300°C and the drying time should be ≥3 hours.

[0028] The produced pelletized products are sent for inspection and analysis to ensure that the specifications and quality of the products meet the requirements.

[0029] The present invention provides a slag conditioning agent with a particle size of 10-40 mm and chemical components including CaO, SiC, C, and CaMg(CO3)2. A certain amount of CaO added to the slag increases the slag basicity. The presence of CaO, as a high-melting-point particle, in the slag increases the surface viscosity of the base slag and the reaction rate between the slag and steel, supporting the adjustment of the slag thermal efficiency and steadily reducing TFe in the slag. SiC and carbon powder possess a certain degree of reducing power and can rapidly react with FeO in the slag to produce CO, causing the slag to foam. SiC can directly react with oxygen, providing diffusion deoxidation and allowing the conditioning agent to spread rapidly across the ladle slag surface within 1 minute. The agent exhibits excellent spreadability and solubility, effectively improving the thermal state of the slag.

[0030] The present invention adopts a two-step method. First, a slag regulator is used to stimulate the heat source on the slag surface. The addition of the slag regulator is an exothermic reaction, which quickly turns the reaction slag system into a molten state, making the slag temperature higher than the melting point of aluminum. Then, the deoxidizer aluminum is added, and the aluminum melts on the surface and spreads quickly and evenly on the surface. The reaction is rapid and sufficient, reducing the generation of smoke and dust and lowering the oxidizability of the ladle top slag.

[0031] The present invention is particularly suitable for the production of ultra-low carbon steel, which requires oxygen to be retained in the molten steel for decarburization. Excessive oxygen in the slag can lead to poor steel quality, forming oxide inclusions, exacerbating the tendency of cast steel to hot crack, and reducing its performance. The slag conditioner and deoxidizer aluminum of the present invention remove oxygen from the ladle top slag while retaining oxygen in the molten steel, achieving spatial separation between the slag and steel and reducing the total iron content on the ladle surface.

[0032] After the slag regulator is added to the surface of the ladle slag, it can quickly melt and spread out without accumulating crust. The ladle slag is in good condition, providing good reaction conditions for reducing the oxidizability of the ladle top slag. The results of the total iron analysis of the ladle slag tracked by large production data are all within 7%. At the same time, less smoke and dust are generated at the production site when the slag regulator is added, and basically no smoke and dust are generated during the subsequent ladle lifting and smelting process.

[0033] 3. Beneficial effects

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The present invention adopts a two-step process. First, a slag regulator is used to stimulate the heat source on the slag surface, quickly turning the reaction slag system into a molten state. Then, a deoxidizer, aluminum, is added. The aluminum melts on the surface and spreads quickly and evenly on the surface. The reaction is rapid and sufficient, reducing the generation of smoke and dust. The total iron content analysis results of the ladle slag are all within 7%, meeting the supply demand.

[0036] (2) A low-dust slag conditioning agent of the present invention comprises a certain amount of SiC and carbon powder. SiC excites the heat source, and carbon powder is used for foaming and heat preservation, thereby extending the high-temperature time and allowing the slag to spread out quickly. The agent has good spreadability and solubility, effectively improves the state of the slag, and reduces the oxidizability of the slag to a certain extent.

[0037] (3) The preparation method and application of a low-dust slag adjusting agent of the present invention are relatively simple in preparation method and application operation, suitable for industrial production and use, and improve the production environment and reduce pollution to the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that these drawings are designed for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, unless otherwise specified, these drawings are intended only to conceptually illustrate the structures described herein and are not necessarily drawn to scale.

[0039] Figure 1 This is a diagram showing the state of the ladle slag after adding the slag conditioning agent of Example 1;

[0040] Figure 2 This is a diagram showing the state of the ladle slag after adding the slag conditioning agent of Example 2;

[0041] Figure 3 This is a diagram showing the state of the ladle slag after adding the slag conditioning agent of Example 3;

[0042] Figure 4 This is a diagram showing the state of the ladle slag after adding the slag conditioning agent of Example 4;

[0043] Figure 5 This is a diagram showing the state of the ladle slag after adding the slag conditioning agent of Example 5;

[0044] Figure 6 This is a flow chart for the production of the slag conditioning agent in Example 1;

[0045] Figure 7 This is a flow chart of the application of the slag conditioning agent in Example 1;

[0046] Figure 8 The ladle slag state diagram after adding the slag conditioning agent of Comparative Example 1, (a) agglomeration and caking state; (b) smoke and dust state;

[0047] Figure 9 This is a comparison chart of the ladle slag status before and after adding slag regulator. DETAILED DESCRIPTION

[0048] The following detailed description of exemplary embodiments of the present invention refers to the accompanying drawings, which form a part of the description, and in which exemplary embodiments of the present invention that can be implemented are shown as examples. Although these exemplary embodiments are described in sufficient detail to enable those skilled in the art to implement the present invention, it should be understood that other embodiments can be implemented and various changes can be made to the present invention without departing from the spirit and scope of the present invention. The following more detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but is merely for illustration and does not limit the description of the features and characteristics of the present invention, so as to propose the best way to perform the present invention and be sufficient to enable those skilled in the art to implement the present invention. Therefore, the scope of the present invention is limited only by the appended claims.

[0049] According to the technical requirements of the slag regulator for improving the state of the ladle top slag of the present invention, this patent is specifically explained through examples.

[0050] A slag conditioner for improving the ladle top slag condition, comprising 37.0%-39.0% CaO, 32.0%-34.0% SiC, 15%-16% C, 6%-7% CaMg(CO3)2, 6% binder, 0.15% S≤0.15%, 0.08% P≤0.08%, and 1.5% H2O. The slag conditioner has a particle size of 10-40 mm.

[0051] The binder in the embodiment comprises hexasodium phosphate, iron, and industrial white sugar. The binder comprises greater than 68% phosphate, less than 7.5% inactive phosphate, less than 0.2% iron, and ≥99% industrial white sugar. Hexasodium phosphate provides strong bonding strength, preventing cracking and powdering of the pelletized product, and allowing for storage for more than 180 days. Industrial white sugar also offers excellent bonding properties, a high calorific value, and strong water-wicking properties.

[0052] A slag conditioner for improving the ladle top slag state, the chemical composition of which is shown in Table 1:

[0053] Table 1 Composition of slag conditioning agent (wt%)

[0054]

[0055]

[0056] This embodiment also provides a method for producing the slag conditioning agents for improving the ladle top slag state in Table 1. The process is as follows: Figure 6 As shown, the specific steps include:

[0057] (1) Crushing: Weigh the raw materials according to their components, crush and select them in a crusher, and then screen and stir them;

[0058] (2) Ball pressing: Use a super-strong dry ball pressing machine to perform high-pressure ball forming to form slag adjusting agent ball pressing;

[0059] (3) Screening: Use a screening machine to screen the slag conditioning agent pellets to select pellets with a particle size of 10-40 mm;

[0060] (4) Drying: The pelletized particles after screening are heated and dried for more than 48 hours. After drying, they are packaged in a metered, moisture-proof manner.

[0061] Example 6

[0062] This embodiment provides the application of slag regulator, which is added to adjust the ladle top slag after steel tapping, and is applied to the KR→300tBOF→RH→CC steel smelting process path, such as Figure 7 shown.

[0063] The slag regulator provided by the present invention is added immediately through the alloy chute at 1.0-1.6 kg / t of steel per ton of steel when the steel is finished and the furnace is lifted. After the slag regulator is added, 0.4-0.8 kg / t of deoxidizer aluminum particles per ton of steel is added immediately. After the addition, the slag regulator is added to the surface of the ladle slag and can be quickly melted and spread without accumulating crust. The ladle slag is in a good state, providing good reaction conditions for reducing the oxidizability of the ladle top slag. In the embodiment, the slag surface state after addition is shown as follows: Figure 1-5 The addition of the slag conditioner improves the oxidizing properties of the slag system, preventing slag agglomeration on the slag surface after converter tapping. This reduces oxygenation and cooling of the molten steel, achieving the process conditions where the slag surface is molten. This facilitates secondary adjustment of the slag's oxidizing properties, reduces the chemical reaction between the deoxidizing material and the slag, and reduces the high volume of dense smoke and dust emitted continuously. This reduces the TFe content in the slag, meeting our steel quality requirements. Follow-up analysis of the total iron content in the ladle slag has consistently been within 7%. Furthermore, minimal smoke and dust is generated on the production site during the addition of the slag conditioner, and virtually no smoke and dust is generated during subsequent ladle handling and smelting.

[0064] Comparative Example 1

[0065] Comparative Example 1 is to add aluminum-based composite modifier to the ladle. The components of the aluminum-based composite modifier are as shown in Example 1 of Patent CN108018398A. The slag regulator of the present invention is not added first. The smelting process is as follows: Figure 8 and Figure 9 shown.

[0066] like Figure 8 As shown in the figure, after the aluminum-based composite modifier is added, it accumulates on the surface of the ladle top slag, but the temperature of the ladle top slag is low, the thermal effect is poor, and the ladle top slag forms agglomerates and lumps.

[0067] like Figure 9 As shown in the figure, after the aluminum-based composite modifier is added, a large amount of thick smoke and dust is continuously emitted due to the chemical reaction between the modifier and the slag. Even when the molten steel is hoisted to the RH treatment process, a large amount of smoke and dust continues to be emitted, seriously polluting the on-site working environment and safe operation, which is not conducive to environmentally friendly smelting.

Claims

1. An application of a slag conditioning agent, characterized in that: The slag regulator is applied to the KR→300tBOF→RH→CC steel smelting process, which specifically includes the following steps: S1. Add lime when the converter is 1 / 3-2 / 3 of the way through. The amount of lime added is 1.5-2.5 kg per ton of steel. S2. When the furnace is lifted after steel tapping, a slag regulator is added immediately, and the amount of the slag regulator added is 1.0-1.6 kg per ton of steel; the slag regulator is composed of the following chemical components by mass percentage: CaO: 37.0%-39.0%, SiC: 32.0%-34.0%, C: 15%-16%, CaMg(CO3)2: 6%-7%, binder 6%, and the rest are unavoidable impurities; S3. Add deoxidizer aluminum particles immediately after adding the slag adjuster. The amount of deoxidizer aluminum particles added is 0.4-0.8kg per ton of steel. S4. The ladle car is taken out and covered and lifted for RH processing.

2. The use of the slag conditioning agent according to claim 1, characterized in that: The mass ratio of SiC to C in the slag adjuster is (2.0-2.2):

1.

3. The use of the slag conditioning agent according to claim 2, characterized in that: The particle size of the slag conditioning agent is 10-40 mm.

4. The use of the slag conditioning agent according to any one of claims 1 to 3, characterized in that: The method for preparing a slag conditioning agent comprises the following steps: S1. Crushing: The raw materials are crushed and selected by the crusher, and then screened and stirred; S2, briquetting, using super strong dry briquetting machine for high pressure briquetting; S3. Screening: Use a screening machine to screen the slag conditioning agent pellets to select pellets with a particle size of 10-40 mm.

5. The use of the slag conditioning agent according to claim 4, characterized in that: The method also includes a drying step, in which the pressed balls are heated and dried after screening, and the drying time is greater than 48 hours.

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