Method for reducing boron content of axle steel during LF refining

Abstract

The invention belongs to the technical field of axle steel smelting, and discloses a method for reducing the boron content of axle steel during LF refining. Comprising the following steps: receiving molten electric furnace axle steel by using a steel ladle made of a magnesia-carbon refractory material, adding an aluminum deoxidizer in the tapping process, transferring the steel ladle to an LF refining station, adding LF refining slag to carry out the LF refining process of the axle steel, and carrying out the LF refining process of the axle steel through the coupling effect of the LF refining slag, the aluminum deoxidizer and the magnesia-carbon refractory material. And the content of the boron element in the axle steel is reduced to 10 ppm or below. According to the method for reducing the boron content of the axle steel in the LF refining process, the qualified rate of the axle steel can be effectively increased.

Description

Technical Field

[0001] The present invention relates to the technical field of axle steel smelting, and particularly relates to a method for reducing the boron content in axle steel during LF refining. Background Art

[0002] Axle steel is widely used in axles of railway locomotives and vehicles. During use, it is subjected to multiple complex stresses, and its main failure form is fatigue cracking. When boron enters the molten steel of axle steel, it will not only form inclusions, but also form bainite structures other than ferrite and pearlite during heat treatment, seriously affecting the performance of axle steel and bringing huge potential safety hazards. Therefore, it is necessary to strictly control the boron content in the steel.

[0003] In the prior art, the smelting route of axle steel is: electric furnace + LF + VD - casting / continuous casting. During this process, aluminum deoxidizer is added for deoxidation. The B content of all steel-related raw and auxiliary materials is less than 0.01% after detection. However, during the smelting of axle steel, it is found that the boron content often increases by 1 - 2 ppm, resulting in a low product qualification rate and huge economic losses. Therefore, it is difficult to reduce the B content in axle steel starting from the raw materials. During the electric furnace smelting process, although some boron elements can be removed through methods such as oxidation and refining slag, its boron removal efficiency is relatively low, and it is difficult to reduce the boron element content to the ppm level. Moreover, compared with the converter, the ability of the electric furnace to remove boron is also weaker. The VD furnace (vacuum degassing furnace) also has corresponding defects, and it is difficult to remove boron elements through slag adjustment and oxidation. In addition, the continuous casting powder and ingot casting slag in the prior art do not have the effect of boron removal.

[0004] It can be seen that in the prior art, the boron element content during the smelting process of axle steel cannot be effectively controlled. In view of this, those skilled in the art are urgently hoping to seek a method for reducing the boron content in axle steel during LF refining to improve the product qualification rate. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention proposes a method for reducing the boron content in axle steel during LF refining.

[0006] According to the method for reducing the boron content in axle steel during LF refining of the present invention, it includes: using a ladle made of magnesia-carbon refractory material to receive the molten steel of axle steel from the electric furnace, adding aluminum deoxidizer during the tapping process, then transporting the ladle to the LF refining station, adding LF refining slag for the LF refining process of axle steel, and reducing the boron element content in axle steel to below 10 ppm through the coupling effect of LF refining slag, aluminum deoxidizer, and magnesia-carbon refractory material.

[0007] Furthermore, the method for reducing the boron content in axle steel during LF refining includes the following steps: Step 1: Do not use a new ladle to receive the axle steel liquid, and control the number of times the ladle is used to be not less than 5 times; the ladle uses magnesia-carbon refractory material, and before receiving the molten steel, the temperature of the ladle is controlled at 1540 - 1590 °C; Step 2: During the tapping process after the electric furnace smelting is completed, add 10 - 30 kg of aluminum deoxidizer to the ladle, and the control time for the ladle to be transferred to the LF refining station is 5 - 12 min; Step 3: After the ladle arrives at the LF refining station, add 15 - 25 kg of LF refining slag per ton of steel, insert the electrode to heat up to 1650 - 1680 °C, turn on the electromagnetic stirring and bottom blowing Ar system, and keep it for 25 - 30 min until the slag cross-section is white and the color is uniform, then tap the steel.

[0008] Furthermore, the method for reducing the boron content in axle steel during LF refining also includes: Step 4: Control the boron content of all metallurgical auxiliary materials involved in the LF refining of axle steel ≤ 0.01%.

[0009] Furthermore, the aluminum deoxidizer is composed of 90 - 95% aluminum powder and 5 - 10% of a substance containing Na2O.

[0010] Furthermore, the total nitrogen content of the aluminum deoxidizer ≤ 0.0051%, the Al content is 90 - 93%, the Na2O content is 5 - 8%, the particle size is 20 - 30 mm, and the moisture content ≤ 0.1%.

[0011] Furthermore, the magnesia-carbon refractory material includes 80 - 85% fused magnesia and sintered magnesia, 8 - 15% graphite (the particle size is preferably 0.1 - 2 mm), 3 - 6% liquid phenolic resin binder, and 0.9 - 1.2% aluminum powder additive. The MgO content of the magnesia-carbon refractory material is 75 - 84%, the C content is 7 - 15%, the apparent porosity is 5 - 7%, the bulk density is 2.96 - 3.24 g / cm3, and the compressive strength is 35.3 - 87.9 MPa.

[0012] Furthermore, the content composition of the LF refining slag is: CaO: 45 - 55%, SiO2: 10 - 20%, Al2O3: 15 - 25%, MgO: 8 - 10%, FeO + MnO ≤ 2%, P2O5 < 0.3%, S < 0.1%, the basicity is 2.5 - 3.5, and the moisture content ≤ 2%.

[0013] Furthermore, in Step 3, the diameter of the electrode is φ350 ± 10 mm, the electrode consumption per ton of steel is 0.25 - 0.50 kg; the electromagnetic stirring intensity is 0.7 - 1.2%, the frequency is 1 - 8 Hz; the bottom blowing Ar pressure is 0.2 - 0.3 MPa, the Ar purity ≥ 99.9%, and the Ar flow rate is preferably 10 - 30 Nm 3 / h.

[0014] Furthermore, the metallurgical auxiliary materials include alloys, refractory materials for electric furnaces, refractory materials for tundishes, submerged nozzles, long nozzles, stopper rods, ladle covering agents, tundish covering agents, mold powder, LF refining slag, lime, fluorite, and slag melting agents.

[0015] Furthermore, the rated capacity of the ladle is 70 - 90 tons, and the rated capacity of the electric furnace is 70 - 90 tons.

[0016] Compared with the prior art, the method for reducing the boron content in axle steel during LF refining of the present invention has the following advantages:

[0017] 1) Through the coupling effect of LF refining slag, aluminum deoxidizer, and magnesia - carbon refractory materials, a multi - dimensional boron removal mechanism is formed, changing the limitation of relying solely on a certain step or substance for boron removal in the past, achieving deep removal of boron elements in axle steel, and accurately controlling the boron content below 10 ppm, far exceeding the control accuracy of the prior art. Among them, the LF refining slag is a high - alkalinity slag that can efficiently adsorb B2O3; the aluminum deoxidizer with a high Na2O content can optimize the slag structure and inhibit boron redissolution; the high - aluminum - powder magnesia - carbon refractory material can block the oxygen supply of the refractory material, reduce the generation of B2O3, and at the same time prevent the oxidation of graphite;

[0018] 2) Ensure that the B content of the auxiliary materials ≤ 0.01%, and the auxiliary materials cover all auxiliary materials such as alloys, refractory materials, and three major continuous casting parts (submerged nozzles, long nozzles, stopper rods), controlling the boron content of metallurgical auxiliary materials from the source, avoiding the complex operations of repeatedly removing boron elements, reducing energy consumption and waste of raw materials; at the same time, improving the product qualification rate and reducing the scrap loss caused by excessive boron;

[0019] 3) Fine - tune the key process parameters of LF refining, such as ladle temperature, transfer time, etc., to make the entire refining process more stable and efficient, creating ideal conditions for the full removal of boron elements, and avoiding boron content exceeding the standard due to process fluctuations;

[0020] 4) Fine - design the indicators such as the composition, particle size, and moisture content of the aluminum deoxidizer to make it have high - efficiency deoxidation and auxiliary boron - removal capabilities, while maintaining good stability to ensure the stability of the refining process, customize the magnesia - carbon refractory material formula to endow it with excellent erosion resistance and boron - adsorption ability, extend the service life of the ladle, reduce the replacement frequency of refractory materials, and reduce production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a flowchart of the method for reducing the boron content in axle steel during LF refining according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] In order to better understand the purpose, structure, and function of the present invention, the present invention will be further described in detail below with reference to the drawings.

[0023] A method for reducing the boron content in axle steel during LF refining according to an embodiment of the present invention may include: using a ladle made of magnesia-carbon refractory to receive the molten steel of axle steel from an electric furnace, adding an aluminum deoxidizer during the tapping process, then transporting the ladle to the LF refining station, adding LF refining slag to carry out the LF refining process of the axle steel, and reducing the boron element content in the axle steel to below 10 ppm through the coupling effect of the LF refining slag, the aluminum deoxidizer, and the magnesia-carbon refractory. The method for reducing the boron content in axle steel during LF refining according to the embodiment of the present invention forms a multi-dimensional boron removal mechanism through the coupling effect of the LF refining slag, the aluminum deoxidizer, and the magnesia-carbon refractory, changes the limitation of relying solely on a certain step or substance for boron removal in the past, realizes the deep removal of boron elements in the axle steel, can accurately control the boron content below 10 ppm, far exceeding the control accuracy of the prior art. Among them, the LF refining slag is a high-alkalinity slag, which can efficiently adsorb B2O3; the aluminum deoxidizer with a high Na2O content can optimize the slag structure and inhibit the reverse dissolution of boron; the high-aluminum powder magnesia-carbon refractory can block the oxygen supply of the refractory and reduce the generation of B2O3.

[0024] In a preferred embodiment as shown in Figure 1 the method for reducing the boron content in axle steel during LF refining may include the following steps: Step S1: Do not use a new ladle to receive the molten steel of axle steel, and control the number of uses of the ladle to be not less than 5 times to reduce the initial pollution of the molten steel by the refractory of the new ladle; the ladle is made of magnesia-carbon refractory, and before receiving the molten steel, the temperature of the ladle is controlled at 1540 - 1590 °C to ensure the fluidity of the molten steel; Step S2: During the tapping process after the electric furnace smelting is completed, add 10 - 30 kg of aluminum deoxidizer to the ladle to achieve precise deoxidation, optimize the slag-steel interface reaction, and the control time for transporting the ladle to the LF refining station is 5 - 12 min to prevent the temperature drop of the molten steel; Step S3: After the ladle arrives at the LF refining station, add 15 - 25 kg of LF refining slag per ton of steel, insert the electrode to heat up to 1650 - 1680 °C to make the high-alkalinity slag fully adsorb B2O3, turn on the electromagnetic stirring and bottom blowing Ar system to strengthen the stirring, and keep it for 25 - 30 min until the slag cross-section is white and the color is uniform, and then tap the steel.

[0025] Furthermore, the method for reducing the boron content in axle steel during LF refining may further include Step S4: Control the boron content of all metallurgical auxiliary materials involved in the LF refining of axle steel ≤ 0.01% to control the boron content of metallurgical auxiliary materials at the source, avoid the complex operation of repeatedly removing boron elements, reduce energy consumption and waste of raw materials; at the same time, improve the product qualification rate and reduce the loss of defective products caused by boron exceeding the standard.

[0026] Preferably, the metallurgical auxiliary materials may include alloys, refractory materials for electric furnaces, refractory materials for tundishes, three major continuous casting components (submerged nozzles, long nozzles, stopper rods), ladle covering agents, tundish covering agents, mold fluxes, LF refining slags, lime, fluorite, and slag melting agents.

[0027] According to the present invention, the aluminum deoxidizer may be composed of 90 - 95% aluminum powder and 5 - 10% of a substance containing Na2O. Adding the aluminum deoxidizer during the tapping process can make full contact with the axle steel liquid, which is beneficial for diffusion aluminum deoxidation and reducing the content of O in the molten steel. The aluminum deoxidizer contains a certain amount of Na2O, which will react with Al2O3 during the deoxidation process to form Na2O·11Al2O3. When it enters the LF refining slag, it will convert the aluminum oxygen hexahedron in the slag into an aluminum oxygen tetrahedron, increasing the viscosity of the refining slag; since the radius of Al 3+ is larger than that of Si 4 + , the Al - O vacancy is larger. Therefore, B is easily captured by the slag and enters the refining slag to form a boron oxygen triangle to reduce the viscosity of the refining slag and maintain the overall viscosity balance. The presence of Na2O also maintains the stability of the boron oxygen triangle, preventing the formation of boron oxygen tetrahedrons and the return of boron from the refining slag to the molten steel.

[0028] Furthermore, the total nitrogen content of the aluminum deoxidizer is ≤0.0051%, the Al content is 90 - 93%, the Na2O content is 5 - 8%, the particle size is 20 - 30mm, and the moisture content is ≤0.1%. Low nitrogen (≤0.0051%) can reduce the nitrogen increase in the molten steel and avoid the damage to toughness caused by nitride inclusions; the particle size (20 - 30mm) and moisture content (≤0.1%) can ensure the uniform dissolution of the deoxidizer and avoid local oxidation or caking; the ratio of Al (90 - 93%) to Na2O (5 - 8%) can balance the deoxidation ability and the slag structure regulation effect.

[0029] According to the present invention, by weight percentage, the magnesia - carbon refractory material may include 80 - 85% of fused magnesia and sintered magnesia, 8 - 15% of graphite (preferably with a particle size of 0.1 - 2mm), 3 - 6% of liquid phenolic resin binder, and 0.9 - 1.2% of aluminum powder additive. The MgO content of the magnesia - carbon refractory material can be 75 - 84%, the C content can be 7 - 15%, the apparent porosity can be 5 - 7%, and the bulk density can be 2.96 - 3.24g / cm 3, the compressive strength can be 35.3 - 87.9 MPa. The main role of aluminum powder in magnesia-carbon refractories is as an antioxidant to prevent the oxidation of graphite and increase the erosion resistance of magnesia-carbon refractories. Since most of the steelmaking process is in an oxidizing atmosphere and various magnesia in magnesia-carbon refractories also have a strong ability to supply [O], aluminum powder will oxidize to form Al2O3 during use, protecting graphite from oxidation. Due to the presence of a large amount of liquid phase between the grains of various magnesia in refractories, there is also a strong ability to supply [O]. When [B] contacts [O] to form B2O3, due to the presence of a large amount of Al2O3 in the refractory, the two react to form 9Al2O3·2B2O3 with a high melting point (1965 °C), which can not only reduce the [B] content in steel but also adsorb on the surface of graphite to prevent the oxidation of graphite.

[0030] Among them, high MgO (75 - 84%) and C (7 - 15%) can enhance erosion resistance and oxidation resistance; aluminum powder additive (0.9 - 1.2%) can inhibit graphite oxidation and protect the structural integrity of refractories; apparent porosity (5 - 7%) and compressive strength (35.3 - 87.9 MPa) help to ensure the service life of the ladle, ensure the safety of the smelting process, and reduce maintenance costs.

[0031] According to the present invention, the content (weight percentage) composition of the LF refining slag can be: CaO: 45 - 55%, SiO2: 10 - 20%, Al2O3: 15 - 25%, MgO: 8 - 10%, FeO + MnO ≤ 2%, P2O5 < 0.3%, S < 0.1%, basicity 2.5 - 3.5, moisture ≤ 2%. The LF refining slag is a high basicity slag, which is easy to adsorb boron elements in the axle steel water. At the same time, the presence of Al2O3 in the LF refining slag can reduce the melting point and viscosity of the slag, form aluminates, increase the sulfur capacity of the slag, and improve the desulfurization efficiency. At the same time, Al2O3 helps to adsorb Al2O3-type inclusions. MgO can protect magnesia-carbon refractories and reduce the erosion of the refining slag on the ladle slag line refractories; the solubility of MgO increases with the increase of temperature, maintaining the balance between the refining slag and the refractories, which is beneficial to better adsorb boron elements in steel. FeO + MnO further increases the oxygen supply capacity, which is beneficial to the combination of B and O and strengthens the adsorption of boron.

[0032] Among them, high CaO (45 - 55%) and low SiO2 (10 - 20%) can increase the basicity (2.5 - 3.5) and enhance the adsorption ability of B2O3; Al2O3 (15 - 25%) and MgO (8 - 10%) can reduce the melting point of the slag, improve the fluidity, and promote the slag-steel interface reaction; low FeO + MnO (≤ 2%) and S (< 0.1%) can reduce the oxidation of molten steel and improve the desulfurization efficiency.

[0033] In a preferred embodiment, in step S3, the diameter of the electrode can be φ350 ± 10 mm, the electrode consumption per ton of steel can be 0.25 - 0.50 kg, so as to accurately control the temperature and avoid local overheating or energy waste; the electromagnetic stirring intensity can be 0.7 - 1.2%, and the frequency can be 1 - 8 Hz, so as to enhance the molten pool flow, eliminate the "dead zone", and promote slag-steel contact; the bottom blowing Ar pressure can be 0.2 - 0.3 MPa, the Ar purity ≥ 99.9%, and the Ar flow rate is preferably 10 - 30 Nm 3 / h, so as to stabilize the bubble distribution, strengthen degassing and inclusion floating up.

[0034] Furthermore, the rated capacity of the ladle is 70 - 90 tons, and the rated capacity of the electric furnace is 70 - 90 tons, so as to ensure the standardization of process parameters (such as slag amount, temperature, stirring intensity) in large-scale production.

[0035] The following gives specific embodiments of smelting axle steel by the method for reducing the boron content of axle steel during LF refining of the present invention. The detailed steelmaking data of each specific embodiment are shown in Table 1, and the specific embodiments of smelting axle steel without implementing the present invention are shown in Table 2.

[0036] Table 1

[0037]

[0038]

[0039]

[0040] Table 2

[0041]

[0042] As can be seen from Table 1 and Table 2, after implementing the method for reducing the boron content of axle steel during LF refining of the present invention, the proportion of axle steel meeting the internal control standard B ≤ 10 ppm is 100%, which is 76.47 percentage points higher than 23.53% before implementation.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered by the scope of the claims and the description of the present invention. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any way. The present invention is not limited to the specific embodiments disclosed in the text, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for reducing the boron content in axle steel during LF refining, characterized in that, Including: Using a ladle made of magnesia-carbon refractory material to receive the molten steel of electric furnace axle steel, adding an aluminum deoxidizer during the tapping process, and then transporting the ladle to the LF refining station, adding LF refining slag to carry out the LF refining process of the axle steel. Through the coupling effect of the LF refining slag, the aluminum deoxidizer and the magnesia-carbon refractory material, the boron content in the axle steel is reduced to less than 10 ppm.

2. The method for reducing the boron content in axle steel during LF refining according to claim 1, characterized in that, Including the following steps: Step 1: Do not use a new ladle to receive the axle steel molten steel, and control the use times of the ladle to be not less than 5 times; the ladle uses the magnesia-carbon refractory material, and before receiving the molten steel, the temperature of the ladle is controlled at 1540 - 1590 °C; Step 2: During the tapping process after the electric furnace smelting is completed, add 10 - 30 kg of the aluminum deoxidizer to the ladle, and the control time for transporting the ladle to the LF refining station is 5 - 12 min; Step 3: After the ladle arrives at the LF refining station, add 15 - 25 kg of the LF refining slag per ton of steel, insert the electrode to heat up to 1650 - 1680 °C, turn on the electromagnetic stirring and bottom blowing Ar system, and keep it for 25 - 30 min until the slag section is white and the color is uniform, then tap the steel.

3. The method for reducing the boron content in axle steel during LF refining according to claim 2, characterized in that The method for reducing the boron content of the axle steel during LF refining further includes: Step 4: Control the boron content of all metallurgical auxiliary materials involved in the LF refining of the axle steel ≤ 0.01%.

4. The method for reducing the boron content in axle steel during LF refining according to claim 2 or 3, characterized in that, The aluminum deoxidizer includes 90 - 95% aluminum powder and 5 - 10% of the substance containing Na2O.

5. The method for reducing the boron content in axle steel during LF refining according to claim 4, characterized in that, The total nitrogen content of the aluminum deoxidizer ≤ 0.0051%, the Al content is 90 - 93%, the Na2O content is 5 - 8%, the particle size is 20 - 30 mm, and the moisture content ≤ 0.1%.

6. The method for reducing the boron content in axle steel during LF refining according to claim 2 or 3, characterized in that, The magnesia-carbon refractory material comprises 80-85% of fused magnesia and sintered magnesia, 8-15% of graphite, 3-6% of liquid phenolic resin binder, and 0.9-1.2% of aluminum powder additive. The MgO content of the magnesia-carbon refractory material is 75-84%, the C content is 7-15%, the apparent porosity is 5-7%, and the bulk density is 2.96-3.24 g / cm 3 , and the compressive strength is 35.3-87.9 MPa.

7. The method for reducing the boron content in axle steel during LF refining according to claim 2 or 3, characterized in that, The content composition of the LF refining slag is: CaO: 45 - 55%, SiO2: 10 - 20%, Al2O3: 15 - 25%, MgO: 8 - 10%, FeO + MnO ≤ 2%, P2O5 < 0.3%, S < 0.1%, the basicity is 2.5 - 3.5, and the moisture content ≤ 2%.

8. The method for reducing the boron content in axle steel during LF refining according to claim 2 or 3, characterized in that, In the third step, the diameter of the electrode is φ350±10mm, and the electrode consumption per ton of steel is 0.25 - 0.50kg; the electromagnetic stirring intensity is 0.7 - 1.2%, and the frequency is 1 - 8Hz; the bottom blowing Ar pressure is 0.2 - 0.3MPa, the Ar purity ≥99.9%, and the Ar flow rate is preferably 10 - 30Nm 3 / h.

9. The method for reducing the boron content in axle steel during LF refining according to claim 3, characterized in that, The metallurgical auxiliary materials include alloys, refractory materials for electric furnaces, refractory materials for tundishes, submerged nozzles, long nozzles, stopper rods, ladle covering agents, tundish covering agents, mold fluxes, LF refining slag, lime, fluorite, and slag melting agents.

10. The method for reducing the boron content in axle steel during LF refining according to claim 2 or 3, characterized in that, The rated capacity of the ladle is 70 - 90 tons, and the rated capacity of the electric furnace is 70 - 90 tons.

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