Graphite electrode recarburization method and application

Abstract

The invention discloses a graphite electrode recarburization method and application, and relates to the technical field of steel smelting. The recarburization method comprises the step of obtaining the required recarburization time according to the required recarburization amount, the actual insertion length of the graphite electrode into the molten steel, the flow of argon introduced into the molten steel and the loss of the graphite electrode. The graphite electrode recarburization method is used for fine adjustment of the carbon content at the refining end point of the LF furnace. The effect of accurate recarburization through the graphite electrode is achieved, and it is ensured that the graphite electrode recarburization achieves the optimal use effect in different scenes in the production process.

Description

Technical Field

[0001] This invention relates to the field of iron and steel smelting technology, specifically to a method for carbonizing graphite electrodes and its application. Background Technology

[0002] Carburization is a common and crucial process step in steelmaking, where scrap steel is the main raw material. CN118147394A discloses a method for carburizing molten steel using a bubbling electrode technique. However, it only considers the relationship between electrode insertion depth and carburization rate, neglecting the significant impact of argon flow rate and electrode erosion on the carburization effect. This leads to unsatisfactory carburization results in actual production, especially under conditions such as low ladle clearance, low argon flow rate, or thick slag. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art or related art.

[0004] Therefore, in a first aspect, the present invention provides a method for carbonizing a graphite electrode, comprising: determining the required carbonization time based on the required carbonization amount, the actual length of the graphite electrode inserted into molten steel, the flow rate of argon gas introduced into the molten steel, and the wear of the graphite electrode.

[0005] Furthermore, the required carbon increase is the difference between the target carbon content and the carbon content of the second sample.

[0006] Furthermore, the actual insertion length of the graphite electrode = the length from the lower end of the graphite electrode holder to the bottom end of the graphite electrode - the distance from the lower end of the holder to the slag surface when the graphite electrode is inserted - the thickness of the slag.

[0007] Furthermore, when three graphite electrodes are inserted into molten steel to a depth of 0.9 meters for carbonization, the mathematical relationship between the amount of carbonization and the flow rate of argon gas introduced into the molten steel and the argon blowing time is: W[%C]=(0.0005%×Q) Ar +0.005%)×t1; where W[%C] is the carbon increase amount at different argon flow rates, by mass percentage; Q Ar t1 is the argon flow rate in L / min; t1 is the argon blowing time in min.

[0008] Furthermore, the argon flow rate is controlled at 0 L / min < Q. Ar ≤50L / min.

[0009] Furthermore, the loss of the graphite electrode affects the carbonization effect of the graphite electrode. The mathematical relationship between the carbonization effect coefficient En of the graphite electrode and the number of carbonization cycles of the graphite electrode is: En = 1 - 0.013% × (n-1), where n represents the number of carbonization cycles.

[0010] Furthermore, the number of carbon additions n∈{1,2,3,4,5}.

[0011] Furthermore, the formula for calculating the required carbon addition time is as follows: in,

[0012] t2 is the required carbonization time, in minutes;

[0013] △W[%C] represents the required carbon increase, as a percentage by mass.

[0014] H represents the actual insertion length of the graphite electrode, in meters;

[0015] W[%C] represents the carbon gain per unit mass for different argon flow rates; W[%C] = (0.0005% × Q) Ar +0.005%)×t1;Q Ar t1 is the argon gas flow rate, in L / min; t1 is the argon blowing time, in min.

[0016] En is the electrode carbonization efficiency coefficient, En = 1 - 0.013% × (n-1), where n represents the number of carbonization cycles, n∈{1,2,3,4,5}.

[0017] In a second aspect, the present invention provides an application of a graphite electrode carbonization method, wherein the graphite electrode carbonization method is used for fine-tuning of carbon content in LF furnace refining.

[0018] Furthermore, the fine-tuning of carbon content in the LF furnace refining process includes the following steps:

[0019] S1. Before refining molten steel, adjust the bottom of the graphite electrode to the alignment position;

[0020] S2. Temperature check upon entry;

[0021] S3. Introduce argon gas at 580L / min to 750L / min to perform slag melting and heating operations. Then, introduce argon gas at 1330L / min to 1670L / min and stir to homogenize the composition and temperature of the molten steel and promote the flotation of inclusions.

[0022] S4. Introduce argon gas at 130L / min~200L / min, take the first sample and measure the temperature, then continue to supply power;

[0023] S5. First addition of components, then argon gas is introduced at 1330L / min~1670L / min and stirred. Second sampling and temperature measurement are performed.

[0024] S6. Continue power supply and heat up to the required temperature before leaving the station or before soft blowing;

[0025] S7. Power outage, second component addition; during this process, the carbon content at the endpoint is fine-tuned using a graphite electrode carbonization method.

[0026] S8: Measure the slag thickness, measure the length from the lower end of the graphite electrode holder to the bottom of the graphite electrode, and measure the distance from the lower end of the holder to the slag surface.

[0027] S9: Electrode carbonization complete, lift the graphite electrode;

[0028] S10: Molten steel is soft-blown or leaves the station to proceed to the next process.

[0029] Compared with the prior art, the present invention has at least the following beneficial effects:

[0030] The graphite electrode carbonization method provided by this invention determines the required carbonization time based on the required carbonization amount, the actual length of the graphite electrode inserted into the molten steel, the flow rate of argon gas introduced into the molten steel, and the wear (corrosion degree) of the graphite electrode. This achieves the effect of precise carbonization through the graphite electrode, ensuring that the graphite electrode carbonization achieves the best performance in different scenarios during the production process. Detailed Implementation

[0031] To better understand the above technical solutions, the technical solutions of the embodiments of this application will be described in detail below through specific embodiments. It should be understood that the embodiments of this application and the specific features in the embodiments are detailed descriptions of the technical solutions of the embodiments of this application, rather than limitations on the technical solutions of this application. In the absence of conflict, the embodiments of this application and the technical features in the embodiments can be combined with each other.

[0032] A first aspect of the present invention provides a method for increasing the carbon content of a graphite electrode, comprising: determining the required carbon increase time based on the required amount of carbon increase, the actual length of the graphite electrode inserted into molten steel, the flow rate of argon gas introduced into the molten steel, and the wear of the graphite electrode.

[0033] The graphite electrode carbonization method provided in this invention determines the required carbonization time based on the required carbonization amount, the actual length of the graphite electrode inserted into the molten steel, the flow rate of argon gas introduced into the molten steel, and the wear (corrosion degree) of the graphite electrode. This achieves the effect of precise carbonization through the graphite electrode, ensuring that the graphite electrode carbonization achieves the best performance in different scenarios during the production process.

[0034] In some embodiments, the required carbon addition is the difference between the target carbon content and the secondary sampling carbon content. The target carbon content is the final carbon content (mass percentage, %) required for steel smelting, and the secondary sampling carbon content is the actual carbon content (mass percentage, %) measured by secondary sampling analysis of the steel after the first addition of components.

[0035] In some embodiments, the actual insertion length of the graphite electrode = the length from the lower end of the graphite electrode holder to the bottom end of the graphite electrode - the distance from the lower end of the holder to the slag surface when the graphite electrode is inserted - the thickness of the slag.

[0036] In some embodiments, when three graphite electrodes are inserted into molten steel to a depth of 0.9 meters for carbonization, the mathematical relationship between the amount of carbonization and the flow rate of argon gas introduced into the molten steel and the argon blowing time is: W[%C]=(0.0005%×Q) Ar +0.005%)×t1; where W[%C] is the carbon increase amount at different argon flow rates, by mass percentage; Q Ar t1 is the argon gas flow rate, in L / min; t1 is the argon blowing time, in min. Optionally, the argon gas flow rate is controlled at 0 L / min < Q. Ar ≤50L / min.

[0037] Specifically, in production practice, it was found that when the argon gas flow rate was 0 L / min, inserting three electrodes into molten steel for 0.9 meters for 1 minute increased the carbon content of the molten steel by 0.005%; when the argon gas flow rate was 10 L / min, it increased the carbon content by 0.01%; when the argon gas flow rate was 20 L / min, it increased the carbon content by 0.015%; when the argon gas flow rate was 30 L / min, it increased the carbon content by 0.02%; when the argon gas flow rate was 40 L / min, it increased the carbon content by 0.025%; and when the argon gas flow rate was 50 L / min, it increased the carbon content by 0.03%. Therefore, the mathematical relationship between different argon flow rates, the carbon increase from inserting three electrodes 0.9 meters into molten steel, and the argon blowing time is further derived as: W[%C]=(0.0005%×Q Ar +0.005%)×t1.

[0038] In some embodiments, the loss of the graphite electrode affects the carbonization effect of the graphite electrode. The mathematical relationship between the carbonization effect coefficient En of the graphite electrode and the number of carbonization cycles of the graphite electrode is: En = 1 - 0.013% × (n-1), where n represents the number of carbonization cycles, and the number of carbonization cycles n∈{1,2,3,4,5}.

[0039] Specifically, in production practice, it was found that when three electrodes are inserted into molten steel to a depth of 0.9 meters and the argon flow rate (Ar) is 10 L / min, the carbon content of the molten steel increases by 0.01% (mass fraction). Continuing, one electrode weighs 500 kg and is 1.8 m long; a 0.9 m electrode weighs 250 kg; and three 0.9 m electrodes weigh 750 kg. 0.10101 kg of electrode weight per ton of steel can increase the carbon content of the molten steel by 0.01% (assuming a carbon content of 99% for the graphite electrode). Each time the molten steel increases carbon by 0.01%, the electrode consumed is: 0.10101 ÷ 750 = 0.00013 = 0.013%, meaning that each time the molten steel increases carbon by 0.01%, 0.013% of the used electrode is consumed. As the number of times the graphite electrode is used for carbon increase increases, the graphite electrode burn-out will increase, the erosion will become greater, and the carbon increase effect will become worse.

[0040] Furthermore, for every 0.01% increase in carbon in the molten steel, the wear on the three electrodes decreases by 0.013%. The effect of the first carbon increase is 100%, the effect of the second carbon increase is 100% - 0.013%, and the effect of the third carbon increase is 100% - 0.013% - 0.013%. Therefore, the formula for the effect of the nth carbon increase is derived as follows:

[0041] E(n) electrode carbon enhancement effect coefficient = 1 - 0.013% × (n-1);

[0042] Where E(n): the carbon enhancement effect of the nth time; 0.013%: the fixed amount of reduction each time; n: the number of carbon enhancements, n∈{1,2,3,4,5}. When the number of n is greater than 5, the electrode burn-out and corrosion are greater, the carbon enhancement effect is poor, and it is not recommended to continue using it.

[0043] In addition, the main chemical components of graphite electrodes are as follows: Carbon content: typically ≥98%–99.5%. Ash content: ≤0.1%–0.5% (ash is mainly composed of metal oxides, such as SiO2, Al2O3, Fe2O3, etc.). Sulfur (S): ≤0.02%–0.05% (low sulfur content reduces steel contamination). Nitrogen (N): ≤0.01%–0.03% (affects electrode oxidation resistance). Volatile matter: ≤0.1% (residual organic matter after high-temperature treatment). Other trace element metal impurities (such as Fe, Ca, Na, K, etc.) are present in extremely low amounts, usually controlled at the ppm level, to avoid oxidation or corrosion of the electrode at high temperatures.

[0044] In a second aspect, the present invention provides the application of the above-described graphite electrode carbonization method for fine-tuning the carbon content in LF furnace refining.

[0045] In some embodiments, the smelting steps for any steel grade requiring LF furnace refining and carbon enrichment include:

[0046] S1: The final composition of the converter is controlled according to the normal process manufacturing standards.

[0047] S2: The tapping temperature of the converter is controlled according to the normal process manufacturing standards.

[0048] S3: Alloying of converter steel and slag washing (or recovery of liquid slag) shall be carried out in accordance with normal process manufacturing standards.

[0049] It should be noted that S1 to S3 are the initial conditions provided for the previous process of LF (i.e., the converter).

[0050] S4: After tapping the steel, reduce the argon gas flow rate to a soft-blowing state of 83L / min~133L / min to prevent the molten steel from being exposed. Take a sample from the argon station to obtain the W[%C] argon station.

[0051] S5: Perform LF refining:

[0052] S51: Before refining molten steel, adjust the bottom ends of the three graphite electrodes to the aligned position.

[0053] S52: Temperature measurement upon entry, TLF entry result obtained.

[0054] S53: Introduce argon gas at 580L / min to 750L / min, and use power setting 11 for slag melting. During the power supply process, add the corresponding slag material according to the normal manufacturing process standards. After slag melting at power setting 11 for 3 to 5 minutes, switch to power setting 4 to rapidly heat the steel to above the liquidus temperature of the grade by 30°C. Then, introduce argon gas at 1670L / min and stir for 2 minutes to homogenize the composition and temperature of the molten steel and promote the flotation of inclusions.

[0055] S54: Introduce argon gas at 167 L / min, take sample 1, and obtain the elemental contents of W1[%C], W1[%Si], W1[%Mn], W1[%P], W1[%S], and W1[%Als]; measure the temperature and obtain T1. Continue power supply at level 4.

[0056] S55: Obtain the element contents of W1[%C], W1[%Si], W1[%Mn], W1[%P], W1[%S], and W1[%Als] from step S54; add the components according to the conventional method. The required added components are W process target[%C]﹣W1[%C], W process target[%Si]﹣W1[%Si], W process target[%Mn]﹣W1[%Mn], W process target[%P]﹣W1[%P], W process target[%S]﹣W1[%S], and W process target[%Als]﹣W1[%Als].

[0057] Argon gas was introduced at a rate of 1670 L / min and the mixture was stirred under the bottom for 2 minutes. Two samples were taken to obtain the contents of elements such as W2[%C], W2[%Si], W2[%Mn], W2[%P], W2[%S], and W2[%Als]. The temperature was measured to obtain T2.

[0058] S56: Continue power supply at level 4, and heat up to the temperature required before leaving the station or before soft blowing.

[0059] S57: Power outage. From step S55, the following elemental contents are obtained: W2[%C], W2[%Si], W2[%Mn], W2[%P], W2[%S], and W2[%Als]. W2[%C] is affected by various objective factors, including: deviations in component detection, or ① low ladle clearance, failing to meet the conditions for strong stirring and carbonization; low-pressure stirring, insufficient power, and poor carbonization effect; ② insufficient argon gas for strong stirring and poor carbonization effect; ③ excessively thick recycled liquid slag and furnace slag, resulting in poor strong stirring and carbonization effect; leading to failure to reach the process target value W[%C], requiring precise addition using the graphite electrode carbonization method. Required carbonization amount ΔW[%C] = W_process_target[%C] - W2[%C].

[0060] The content of elements such as W2[%Si], W2[%Mn], W2[%P], W2[%S], and W2[%Als] will continue to be added according to the conventional method. The required added components are W process target[%Si]﹣W2[%Si], W process target[%Mn]﹣W2[%Mn], W process target[%P]﹣W2[%P], W process target[%S]﹣W2[%S], and W process target[%Als]﹣W2[%Als].

[0061] S58: Measure the slag thickness using an iron pipe;

[0062] S59: Length from the lower end of the graphite electrode holder to the bottom end of the graphite electrode;

[0063] S60: Insert all three electrodes into the molten steel at the same time (in step S51, the bottom ends of the three electrodes have been aligned), and measure the distance from the lower end of the clamp to the slag surface using an iron pipe.

[0064] The actual insertion length H of the graphite electrode = the length from the lower end of the graphite electrode holder to the bottom end of the graphite electrode - the distance from the lower end of the holder to the slag surface when the graphite electrode is inserted - the thickness of the slag.

[0065] The formula for calculating the required carbon addition time is: in,

[0066] t2 is the required carbonization time, in minutes;

[0067] △W[%C] represents the required carbon increase, as a percentage by mass.

[0068] H represents the actual electrode insertion length in meters; W[%C] represents the carbon increase at different argon flow rates, expressed as a percentage by mass.

[0069] W[%C]=(0.0005%×Q) Ar+0.005%)×t1;

[0070] Q Ar t1 is the argon gas flow rate, in L / min; t1 is the argon blowing time, in min.

[0071] En is the electrode carbonization efficiency coefficient, En = 1 - 0.013% × (n-1), where n represents the number of carbonization cycles, n∈{1,2,3,4,5}.

[0072] S61: Electrode carbonization complete. Raise the electrode to the upper limit. Introduce argon gas at 1670 L / min and stir for 1 min to homogenize the molten steel composition. Introduce argon gas at 167 L / min and perform temperature measurement and sampling. Determine the contents of T3 and W3[%C], W3[%Si], W3[%Mn], W3[%P], W3[%S], and W3[%Als].

[0073] S62: Molten steel is soft-blown or leaves the station to proceed to the next process.

[0074] Example 1: A method for carbonizing a graphite electrode

[0075] 130 tons of molten steel, with recovered liquid slag, 0.4 meters thick. The target process values ​​for the steel grade are W[%C] 0.15% and W2[%C] 0.12%.

[0076] Required carbon increase ΔW[%C] = W_process target value[%C] - W2[%C] = 0.15% - 0.12% = 0.03%.

[0077] H=0.8 (meter), n=1 (times), En=1-0.013%×(n-1)=1, Q Ar =20 (L / min), t1=2

[0078] (min).

[0079] W[%C]=(0.0005%×Q) Ar +0.005%)×t1=(0.0005%×20+0.005%)×2=(0.01%+0.00)

[0080] 5% × 2 = 0.015% × 2 = 0.03%.

[0081] Required carbonization time:

[0082] Sample 3 yielded W3[%C] = 0.152%. W3[%C] - W process target value[%C] = 0.002%.

[0083] Comparative Example 1: A Traditional Argon Stirring Method for Carburization

[0084] 130 tons of molten steel, with recovered liquid slag, 0.4 meters thick. The target process values ​​for the steel grade are W[%C] 0.15% and W2[%C] 0.12%.

[0085] Required carbon increase ΔW[%C] = W_process target value[%C] - W2[%C] = 0.15% - 0.12% = 0.03%.

[0086] Q Ar = At 60 L / min, the carbon increase is 0.005% in 1 min, and the time required for carbon increase by argon stirring is 0.03% ÷ 0.005% = 6 (min).

[0087] Sample 3 yielded W3[%C] = 0.145%. W3[%C] - W process target value[%C] = -0.005%.

[0088] Results and Discussion: A comparison of Example 1 and Comparative Example 1 shows that, in the case of recovering liquid slag (with a thick slag layer), the graphite electrode carbonization method is significantly more effective than the traditional argon gas stirring carbonization method, with higher composition accuracy and less time consumption.

[0089] Example 2: A method for carbonizing a graphite electrode

[0090] 125 tons of molten steel, with unrecovered liquid slag, slag thickness 0.2 meters. The target process values ​​for the steel grade are W[%C] 0.16% and W2[%C] 0.11%.

[0091] Required carbon increase ΔW[%C] = W_process target value[%C] - W2[%C] = 0.16% - 0.11% = 0.05%.

[0092] H=1.2 (meter), n=2 (times), En=1-0.013% × (n-1)=1-0.013%, Q Ar =30 (L / min), t1 = 2 (min).

[0093] W[%C]=(0.0005%×Q) Ar +0.005%)×t1=(0.0005%×30+0.005%)×2=(0.015%+0.005%)×2=0.02%×2=0.04%.

[0094] Required carbonization time:

[0095]

[0096] Sample 3 yielded W3[%C] = 0.161%. W3[%C] - W process target value[%C] = 0.001%.

[0097] Comparative Example 2: A Traditional Argon Stirring and Carburizing Method

[0098] 125 tons of molten steel, with unrecovered liquid slag, slag thickness 0.2 meters. The target process values ​​for the steel grade are W[%C] 0.16% and W2[%C] 0.11%.

[0099] Required carbon increase ΔW[%C] = W_process target value[%C] - W2[%C] = 0.16% - 0.11% = 0.05%.

[0100] Q Ar When the flow rate is 60 L / min, the carbon increase is 0.01% in 1 min. The time required for carbon increase by argon stirring is 0.05% ÷ 0.01% = 5 (min).

[0101] Sample 3 yielded W3[%C] = 0.158%. W3[%C] - W process target value[%C] = -0.002%.

[0102] Results and Discussion: A comparison between Example 2 and Comparative Example 2 shows that, without recovering liquid slag (normal slag thickness), the graphite electrode carbonization method is significantly more effective than the traditional argon gas stirring carbonization method, with higher composition accuracy and less time consumption.

[0103] It will be readily understood by those skilled in the art that the above-described advantageous methods can be freely combined and superimposed without conflict. The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application. The above are merely preferred embodiments of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of this application, and these improvements and modifications should also be considered within the protection scope of this application.

Claims

1. A method for carbonizing a graphite electrode, characterized in that, include: The required carbonization time can be determined based on the required carbonization amount, the actual length of the graphite electrode inserted into the molten steel, the flow rate of argon gas introduced into the molten steel, and the wear of the graphite electrode.

2. The method for carbonizing a graphite electrode according to claim 1, characterized in that, The required carbon increase is the difference between the target carbon content and the carbon content of the second sample.

3. The method for carbonizing a graphite electrode according to claim 1, characterized in that, The actual insertion length of the graphite electrode = the length from the lower end of the graphite electrode holder to the bottom end of the graphite electrode - the distance from the lower end of the holder to the slag surface when the graphite electrode is inserted - the thickness of the slag.

4. The method for carbonizing a graphite electrode according to claim 1, characterized in that, When three graphite electrodes are inserted into molten steel to a depth of 0.9 meters for carbonization, the mathematical relationship between the amount of carbonization and the flow rate of argon gas introduced into the molten steel and the argon blowing time is: W[%C]=(0.0005%×Q) Ar +0.005%)×t1; where W[%C] is the carbon increase amount at different argon flow rates, by mass percentage; Q Ar t1 is the argon flow rate in L / min; t1 is the argon blowing time in min.

5. The method for carbonizing a graphite electrode according to claim 4, characterized in that, The argon gas flow rate is controlled at 0 L / min < Q. Ar ≤50L / min.

6. The method for carbonizing a graphite electrode according to claim 1, characterized in that, The loss of the graphite electrode affects the carbonization effect of the graphite electrode. The mathematical relationship between the carbonization effect coefficient En of the graphite electrode and the number of carbonization times of the graphite electrode is: En = 1 - 0.013% × (n-1), where n represents the number of carbonization times.

7. The method for carbonizing a graphite electrode according to claim 6, characterized in that, The number of carbon additions n∈{1,2,3,4,5}.

8. The method for carbonizing a graphite electrode according to any one of claims 1-7, characterized in that, The formula for calculating the required carbon addition time is: in, t2 is the required carbonization time, in minutes; △W[%C] represents the required carbon increase, as a percentage by mass. H represents the actual insertion length of the graphite electrode, in meters; W[%C] represents the carbon gain per unit mass for different argon flow rates; W[%C] = (0.0005% × Q) Ar +0.005%)×t1;Q Ar t1 is the argon gas flow rate, in L / min; t1 is the argon blowing time, in min. En is the electrode carbonization efficiency coefficient, En = 1 - 0.013% × (n-1), where n represents the number of carbonization cycles, n∈{1,2,3,4,5}.

9. An application of a method for carbonizing graphite electrodes, characterized in that, The graphite electrode carbonization method according to any one of claims 1-8 is used for fine-tuning the carbon content at the end point of LF furnace refining.

10. The application of the graphite electrode carbonization method according to claim 9, characterized in that, The fine-tuning of carbon content in the LF furnace refining process includes the following steps: S1. Before refining molten steel, adjust the bottom of the graphite electrode to the alignment position; S2. Temperature check upon entry; S3. Introduce argon gas at 580L / min to 750L / min to perform slag melting and heating operations. Then, introduce argon gas at 1330L / min to 1670L / min and stir to homogenize the composition and temperature of the molten steel and promote the flotation of inclusions. S4. Introduce argon gas at 130L / min~200L / min, take the first sample and measure the temperature, then continue to supply power; S5. First addition of components, then argon gas is introduced at 1330L / min~1670L / min and stirred. Second sampling and temperature measurement are performed. S6. Continue power supply and heat up to the required temperature before leaving the station or before soft blowing; S7. Power outage, second component addition; during this process, the carbon content at the endpoint is fine-tuned using a graphite electrode carbonization method. S8: Measure the slag thickness, measure the length from the lower end of the graphite electrode holder to the bottom of the graphite electrode, and measure the distance from the lower end of the holder to the slag surface. S9: Electrode carbonization complete, lift the graphite electrode; S10: Molten steel is soft-blown or leaves the station to proceed to the next process.

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