Synthetic refining slag for removing titanium-containing and aluminum-containing inclusions in molten steel and method for removing titanium-containing and aluminum-containing inclusions in molten steel

Abstract

The invention belongs to the technical field of slagging in cold heading steel production, and particularly discloses synthetic refining slag for removing titanium and aluminum type inclusions in molten steel and a method thereof, the synthetic refining slag comprises 25-29% of Al2O3, 8-11% of SiO2, 55-65% of CaO, 1-4% of FeO, less than 2% of CaF, less than or equal to 0.5% of S, less than or equal to 0.05% of N and less than or equal to 0.5% of H20, the granularity of the synthetic refining slag is 1-50 mm, the granularity of 1-5 mm is less than or equal to 5%, the granularity of 5-40 mm is more than or equal to 90%, and the granularity of 40-50 mm is less than or equal to 5%; by accurately controlling the components of the synthesized refining slag, the refining slag can react with sulfur and phosphorus in molten steel, so that the content of sulfur and phosphorus in steel is reduced, the purity of the molten steel is improved, the melting point and viscosity of the refining slag can be adjusted, the moderate fluidity of the slag in the smelting process can be ensured, titanium and aluminum type inclusions cannot be hindered due to too large viscosity, and the slag can be recycled. And the impurity removal effect cannot be influenced due to too low viscosity, so that the problems that the existing refining slag has too high viscosity and can hinder scum separation, and the impurity adsorption effect of the refining slag can be reduced due to too low viscosity are solved.

Description

Technical Field

[0001] The invention relates to the technical field of slag making in cold heading steel production, and in particular to a synthetic refined slag for removing titanium and aluminum type inclusions in molten steel and a method thereof. Background Art

[0002] Titanium easily reacts with nitrogen in molten steel to produce high-hardness inclusions, which will greatly affect the mechanical properties of steel, such as toughness, plasticity and strength. Aluminum may lead to the formation of aluminum deoxidation product Al2O3 in steel. These oxide inclusions will affect the toughness and processing performance of steel. By precisely controlling the element content in molten steel and removing unnecessary titanium, aluminum and their compounds, the purity of steel can be improved, the performance of steel can be optimized and potential adverse effects can be avoided. The methods for removing titanium, aluminum and their compounds from molten steel mainly include chemical precipitation, vacuum melting, electrolysis and the interaction between slag and molten steel. The principle of the interaction between slag and molten steel is: by adjusting the composition and temperature of the slag, the slag reacts with the oxides in the molten steel to remove impurities such as titanium and aluminum oxides in the molten steel.

[0003] The process of molten steel smelting is: molten iron pretreatment, converter steelmaking, refining treatment, continuous casting (mold casting) and subsequent processing. When the molten steel is treated in the refining furnace, the inclusions in the molten steel, such as rich titanium, Al2O3, TiO2, etc., are removed through refining operations such as blowing, temperature control and composition control, as well as possible degassing, dehydrogenation and decarburization. During the refining process, the composition of the molten steel is assisted by refining slag. When the basicity of the existing refining slag is low, there are more acidic compounds such as SiO2 and Al2O3, which will increase the viscosity and thus hinder the separation of slag. When the basicity of the refining slag is high, there are more alkaline compounds such as CaO and MgO, which will reduce the viscosity and cause the adsorption effect of the refining slag on impurities to be reduced. Too high or too low viscosity will reduce the effect of impurity removal. Therefore, a refining slag that can effectively remove titanium-rich, Al2O3, TiO2 and other inclusions in molten steel is needed. Summary of the invention

[0004] The purpose of the present invention is to provide a synthetic refining slag for removing titanium and aluminum type inclusions in molten steel, so as to solve the problem that the viscosity of the existing refining slag is too high, which will hinder the separation of slag, and the viscosity is too low, which will reduce the adsorption effect of the refining slag on impurities.

[0005] To achieve the above-mentioned purpose, the basic scheme provided by the present invention is: a synthetic refined slag for removing titanium and aluminum type inclusions in molten steel, the composition of the synthetic refined slag is 25-29% Al2O3, 8-11% SiO2, 55-65% CaO, 1-4% FeO, CaF<2%, S≤0.5%, N≤0.05%, H20≤0.5%, and the particle size of the synthetic refined slag is 1-50mm, among which 1-5mm≤5%, 5-40mm≥90%, and 40-50mm≤5%.

[0006] The principle and beneficial effect of the present invention are as follows: by precisely controlling the composition of the synthetic refined slag, the sulphur and phosphorus in the molten steel are reacted to form a stable compound, thereby reducing the sulphur and phosphorus content in the steel and improving the purity of the molten steel; SiO2 is a surfactant, and its increase is beneficial to improving the elasticity and strength of the adsorption film, and reducing the density of the refined slag, increasing the viscosity, reducing the surface tension, promoting the foaming of the refined slag, and being beneficial to reducing the point-like inclusions in the steel; increasing the CaF2 content can reduce the surface tension of the slag, which is beneficial to the foaming of the slag; components such as alumina (Al2O3) can adjust the melting point and viscosity of the refined slag, and can ensure that the fluidity of the slag is moderate during the smelting process, and neither the removal of titanium and aluminium type inclusions is hindered due to excessive viscosity, nor the removal effect is affected due to too low viscosity; by precisely controlling the composition of the slag, the contact between air and molten steel can be more effectively isolated, the occurrence of oxidation reaction can be reduced, and the quality of the molten steel can be protected; by precisely controlling the composition of the synthetic refined slag, high-quality pre-melting type refined slag can be prepared, thereby improving smelting efficiency and reducing production costs.

[0007] Option 2 is the preferred basic option. The physical and chemical indicators of the synthetic refined slag are: binary basicity of 5-10, liquid viscosity of 0.75-0.85P, and liquid rate of 90-95%. Inclusions in the steel float to the surface of the molten steel, and will be adsorbed and quickly dissolved by the synthetic refined slag. If the slag has insufficient adsorption capacity for inclusions, the inclusions may be brought back into the molten steel by the steel flow, causing failure in removing inclusions. Accurate control of the physical and chemical indicators of the synthetic refined slag, such as basicity and viscosity, can ensure that the fluidity of the refined slag during the refining process is moderate, and the refining operation will not be hindered due to excessive viscosity, nor will the refining effect be affected due to too low viscosity. It is helpful to improve refining efficiency and shorten refining time. Accurate control of the physical and chemical indicators can also ensure that the refined slag meets environmental protection requirements and reduces adverse effects on the environment.

[0008] Scheme 3, which is a basic scheme: a method for removing titanium and aluminum type inclusions in molten steel using the synthetic refined slag in Scheme 2, comprising the following steps:

[0009] S1. The molten steel after argon blowing is sealed and enters the LF refining furnace, the temperature of the molten steel is raised to 1600℃, and argon is continuously blown into the molten steel;

[0010] S2. After the molten steel reaches the specified temperature for 5 minutes, a certain amount of synthetic refined slag is added;

[0011] S3. After adding the refined slag for 10 minutes, the oxygen content in the molten steel was detected, and calcium carbide was added according to the oxygen content in the molten steel;

[0012] S4. After adding calcium carbide for 5 minutes, the aluminum content in the molten steel is detected, and aluminum-iron alloy is added according to the aluminum content in the molten steel;

[0013] S5. After maintaining the fluidity of the white slag for at least 15 minutes, control the final refining temperature at 1600-1630℃, and the refined molten steel can enter the subsequent continuous casting stage.

[0014] During production, the temperature is fixed at 1600℃ and argon is kept flowing to prevent oxidation of molten steel. Argon can also be used to stir the molten steel, accelerate chemical reactions in the molten steel, and shorten refining time. By adding a certain amount of synthetic refining slag, impurities such as titanium and aluminum oxides in the molten steel can be removed. The refining slag can remove impurities, deoxidize, and desulfurize, and can also form foam slag to improve thermal efficiency and prevent secondary oxidation and air absorption of molten steel, thereby protecting the quality of molten steel. The function of controlling calcium carbide and aluminum-iron alloy is to deoxidize and adjust the composition of molten steel to meet the purity and composition requirements of steel. By precisely controlling the temperature, the scrap rate caused by improper temperature can be reduced and the qualified rate and output of steel can be improved.

[0015] Scheme 4: This is the preferred option of Scheme 3. In step S1, the argon flow rate is 20-25m 3 / h; Controlling the argon flow rate can achieve effective stirring of the molten steel, making the chemical composition and temperature in the molten steel more uniform. The stirring effect of argon can accelerate the chemical reaction in the molten steel, shorten the refining time, and thus improve production efficiency. It can also effectively remove harmful gases (such as hydrogen, nitrogen, etc.) and non-metallic inclusions in the molten steel, purify the molten steel, improve the purity of the steel, and improve the stability of the refining process. As an inert gas, argon can effectively isolate the air, prevent the molten steel from being oxidized during the refining process, and ensure the quality of the molten steel.

[0016] Option 5 is a preferred option of Option 3. In step S2, the amount of refined slag added is 4-5 kg / t. By precisely controlling the amount added, it can be ensured that the slag fully reacts with impurities such as oxygen and sulfur in the molten steel to form stable compounds and are effectively removed. Adding too much or too little refined slag may affect the refining effect. Precise control can achieve the best refining effect, thereby improving the purity of the molten steel.

[0017] Option six is ​​a preferred option of option three. In step S3, if the oxygen content in the molten steel is ≥15ppm, 0.6kg / t of calcium carbide is added. If the oxygen content in the molten steel is <15ppm, no calcium carbide is added. Adding calcium carbide can carry out deoxidation and reduce the oxygen content in the molten steel. At the same time, the calcium oxide formed during the deoxidation process of calcium carbide helps to form foamy slag. The foamy slag can not only reduce noise, but also shield the thermal radiation of the molten steel and reduce the heating time. Using calcium carbide for deoxidation is not only simple to operate and low in cost, but also can significantly improve the quality of the molten steel and production efficiency.

[0018] Option 7 is a preferred option of Option 3. In step S4, if the aluminum content in the molten steel is ≥0.04%, 1 kg / t of aluminum-iron alloy is added. If the aluminum content in the molten steel is <0.04%, no aluminum-iron alloy is added. The main function of adding aluminum-iron alloy is to further deoxidize and control the grain size of steel. Aluminum can also refine the intrinsic grains of steel and increase the grain coarsening temperature of steel, thereby improving the quality and performance of steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention is a flow chart of a method for removing titanium and aluminum type inclusions in molten steel. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below through specific embodiments:

[0021] Example 1

[0022] A synthetic refining slag for removing titanium and aluminum type inclusions in molten steel. The composition of the synthetic refining slag is 25-29% Al2O3, 8-11% SiO2, 55-65% CaO, 1-4% FeO, CaF<2%, S≤0.5%, N≤0.05%, H20≤0.5%, the particle size of the synthetic refining slag is 1-50mm, wherein 1-5mm≤5%, 5-40mm≥90%, 40-50mm≤5%, and the physical and chemical indicators of the synthetic refining slag are: binary basicity is 5-10, liquid viscosity is 0.75-0.85P, and liquid rate is 90-95%.

[0023] Example 2

[0024] Compared with Example 1, the composition of the synthetic refined slag is different in that 16-21% Al2O3, 10-18% SiO2, 45-60% CaO, and 3-8% FeO.

[0025] Example 3

[0026] Compared with Example 1, the composition of the synthetic refined slag is different in that 6-10% SiO2, 45-55% CaO, and 0.1-1% FeO.

[0027] Comparative Example 1

[0028] Compared with Example 1, the composition of the synthetic refined slag is different in that 15-19% Al2O3, 9-15% SiO2, 55-60% CaO, 3-8% FeO, and 3-10% MgO.

[0029] Comparative Example 2

[0030] Compared with Example 1, the composition of the synthetic refined slag is different in that 7-12% SiO2, 50-60% CaO, 0.1-1% FeO, and 3-10% MgO.

[0031] In order to verify the effectiveness of the refined slag composition in Example 1, the composition of the refined slag was compared with the composition of the above four refined slags in different proportions, and five synthetic refined slags were added to the same weight of molten steel for experiments. The experiments were tested and analyzed using an X-ray diffraction method, a viscometer, a liquid rate meter, and an inclusion analyzer. By comparing the binary basicity, liquid viscosity, liquid rate, and inclusion content in the molten steel before and after the addition of the synthetic refined slag, the comparison results are shown in Table 1:

[0032] Table 1 Comparison results of refined slags with different compositions

[0033]

[0034]

[0035] By comparing the liquid viscosities of the synthetic refined slags of Example 2 and Comparative Example 1, and Example 3 and Comparative Example 2, it can be seen that MgO has little effect on the liquid viscosity of the synthetic refined slag.

[0036] The inclusions in the molten steel before and after the experiment using synthetic refined slags of different compositions were compared to evaluate the ability of synthetic refined slags of different compositions to remove inclusions. The total amount of inclusions removed in Example 1 was 21 / mm 2 The removal efficiency is 79%. The total amount of inclusions removed in Example 2 is 2.7 / mm 2 , the removal efficiency is 20%, and the total amount of inclusions removed in Example 3 is 11.6 / mm 2 The removal efficiency is 68%, and the total amount of inclusions removed in Comparative Example 1 is 12.4 / mm 2 The removal efficiency is 59%, and the total amount of inclusions removed in Comparative Example 2 is 23.2 / mm 2 The removal efficiency is 81%. However, the presence of MgO promotes the formation of new inclusions and affects the removal process of inclusions from the refined slag. By comparing the ability of synthetic refined slags with different compositions to remove inclusions, it can be seen that the efficiency of removing inclusions from the refined slag in Example 1 is higher, and titanium-rich, solid alumina, and aluminum-titanium type inclusions are effectively removed, and no new inclusions are generated.

[0037] Example 4

[0038] like Figure 1 As shown: A method for removing titanium and aluminum inclusions in molten steel using synthetic refined slag, comprising the following steps:

[0039] S1. After argon blowing, the molten steel is sealed and enters the LF refining furnace. The temperature of the molten steel is raised to 1600℃, and argon is continuously blown into the molten steel. The argon flow rate is 20-25m 3 / h;

[0040] S2. After the molten steel reaches the specified temperature for 5 minutes, the amount of refined slag added is 4-5 kg / t;

[0041] S3. After adding the refined slag for 10 minutes, the oxygen content in the molten steel is detected, and calcium carbide is added according to the oxygen content in the molten steel. If the oxygen content in the molten steel is ≥15ppm, calcium carbide 0.6kg / t is added. If the oxygen content in the molten steel is <15ppm, no calcium carbide is added;

[0042] S4. After adding calcium carbide for 5 minutes, the aluminum content in the molten steel is detected, and aluminum-iron alloy is added according to the aluminum content in the molten steel. If the aluminum content in the molten steel is ≥0.04%, 1kg / t of aluminum-iron alloy is added. If the aluminum content in the molten steel is <0.04%, no aluminum-iron alloy is added;

[0043] S5. After maintaining the fluidity of the white slag for at least 15 minutes, control the final refining temperature at 1600-1630℃, and the refined molten steel can enter the subsequent continuous casting stage.

[0044] The implementation method of this embodiment is as follows: during production, the molten steel after argon blowing treatment is sealed and enters the LF refining furnace, the molten steel temperature is raised to 1600°C, and the argon flow rate blown into the molten steel is controlled to be 20-25m 3 / h, argon can stir the molten steel, accelerate the chemical reaction in the molten steel, and shorten the refining time. After the molten steel temperature reaches 1600℃ for 5min, the amount of refining slag added is 4-5kg / t. In addition to removing inclusions, the refining slag can also form foam slag to improve thermal efficiency and prevent secondary oxidation and air absorption of the molten steel. After 10min of adding the refining slag, if the oxygen content in the molten steel is ≥15ppm, add 0.6kg / t of calcium carbide. If the oxygen content in the molten steel is <15ppm, no calcium carbide is needed. If the aluminum content in the molten steel is ≥0.04%, add 1kg / t of aluminum-iron alloy. If the aluminum content in the molten steel is <0.04%, no aluminum-iron alloy is needed. The function of controlling calcium carbide and aluminum-iron alloy is to deoxidize and adjust the composition of the molten steel to meet the requirements of steel for purity and composition. Finally, after maintaining the fluidity of the white slag for not less than 15min, the refining end temperature is controlled to 1600-1630℃, and the refined molten steel can enter the subsequent continuous casting stage.

[0045] The above is only an embodiment of the present invention, and the common knowledge such as the known specific structure and characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A synthetic refined slag for removing titanium and aluminum type inclusions in molten steel, characterized in that: The composition of the synthetic refined slag is 25-29% Al2O3, 8-11% SiO2, 55-65% CaO, 1-4% FeO, CaF<2%, S≤0.5%, N≤0.05%, H20≤0.5%, and the particle size of the synthetic refined slag is 1-50mm, of which 1-5mm≤5%, 5-40mm≥90%, and 40-50mm≤5%.

2. The synthetic refined slag for removing titanium and aluminum type inclusions in molten steel according to claim 1, characterized in that ,The physical and chemical indicators of synthetic refined slag are: binary basicity is 5-10, liquid viscosity is 0.75-0.85P, and liquid rate is 90-95%.

3. A method for removing titanium and aluminum type inclusions in molten steel using the synthetic refined slag described in claim 2, characterized in that: The following steps are involved: S1. The molten steel after argon blowing is sealed and enters the LF refining furnace, the temperature of the molten steel is raised to 1600℃, and argon is continuously blown into the molten steel; S2. After the molten steel reaches the specified temperature for 5 minutes, a certain amount of synthetic refined slag is added; S3. After adding the refined slag for 10 minutes, the oxygen content in the molten steel was detected, and calcium carbide was added according to the oxygen content in the molten steel; S4. After adding calcium carbide for 5 minutes, the aluminum content in the molten steel is detected, and aluminum-iron alloy is added according to the aluminum content in the molten steel; S5. After maintaining the fluidity of the white slag for at least 15 minutes, control the final refining temperature at 1600-1630℃, and the refined molten steel can enter the subsequent continuous casting stage.

4. The method for removing titanium and aluminum inclusions in molten steel according to claim 3, characterized in that: In step S1, the argon gas flow rate is 20-25m 3 / h.

5. The method for removing titanium and aluminum inclusions in molten steel according to claim 3, characterized in that: In step S2, the amount of refined slag added is 4-5 kg / t.

6. The method for removing titanium and aluminum inclusions in molten steel according to claim 3, characterized in that: In step S3, if the oxygen content in the molten steel is ≥15ppm, 0.6kg / t of calcium carbide is added; if the oxygen content in the molten steel is <15ppm, no calcium carbide is added.

7. The method for removing titanium and aluminum inclusions in molten steel according to claim 3, characterized in that In step S4, if the aluminum content in the molten steel is ≥0.04%, 1 kg / t of aluminum-iron alloy is added; if the aluminum content in the molten steel is <0.04%, no aluminum-iron alloy is added.

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