A method for reducing the refining cost of low-carbon cold heading steel

Abstract

This invention discloses a method for reducing the refining cost of low-carbon cold heading steel, belonging to the field of iron and steel metallurgical technology. The method includes: recovering molten slag before tapping from the converter; reducing carbon content to below 0.06% in the later stages of smelting; bottom blowing argon after oxygen blowing and measuring oxygen content, dynamically calculating the addition amounts of ferroaluminum and lime; adding ferroaluminum and lime during tapping; adjusting aluminum to 0.050%-0.055% after tapping by feeding aluminum wire; slag breaking and power supply after the molten steel reaches the LF furnace, adding lime at 1.3 times the amount of aluminum added after tapping; raising the temperature to 1600-1605℃ after a second sampling, adding ferromanganese, calculating aluminum loss based on power supply time, and controlling aluminum at 0.035%-0.040%; finally, calcium treatment and soft blowing are performed. This invention achieves low-cost and high-efficiency refining of low-carbon cold heading steel through optimizations such as recovering molten slag, dynamically calculating material addition amounts, moving deoxidation and slag formation forward, reducing material consumption, and replacing large-scale argon agitation for impurity removal.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, and specifically to a method for reducing the refining cost of low-carbon cold heading steel. Background Technology

[0002] Currently, the production of low-carbon cold heading steel typically employs a process flow of "converter smelting + LF ladle refining". In existing technologies, a fixed amount of aluminum iron and lime is often added during converter tapping. After tapping, the aluminum content of the molten steel is usually only 0.016%-0.022%, requiring secondary adjustments in the LF furnace by supplementing aluminum wire, adding lime and aluminum slag, etc., which is complex and consumes a lot of materials.

[0003] Furthermore, existing processes in LF furnace refining commonly employ large-scale argon agitation (90-120 m³ / h, lasting 3-5 minutes) to promote the flotation and removal of inclusions, and utilize large amounts of fluorite, synthetic slag, and other auxiliary materials to improve slag fluidity. These methods not only result in high refining costs but also prolonged refining times, and the use of fluorite increases the environmental burden.

[0004] Therefore, how to reduce material consumption, shorten refining time, simplify operations and reduce auxiliary material usage while ensuring the quality of molten steel has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the existing technology, the present invention proposes a method to reduce the refining cost of low carbon cold heading steel. The method aims to reduce slag consumption, shorten processing time and simplify operation by optimizing the refining process, so as to achieve the purpose of cost reduction and efficiency improvement.

[0006] Therefore, the present invention provides a method for reducing the refining cost of low-carbon cold heading steel, comprising the following steps: Converter charging: Select scrap steel and molten iron according to the trace element composition of low carbon cold heading steel; Recovery of molten slag from casting: Before tapping from the converter, recover one batch of molten slag from casting into the ladle; Converter smelting control: In the later stage of oxygen blowing in the converter, after measuring the carbon content of the molten steel, the oxygen pressure is increased and the oxygen lance position is lowered to bring the carbon content of the molten steel down to below 0.06%, while ensuring that the temperature is not lower than 1640℃. Converter bottom blowing argon and oxygen control: After oxygen blowing is completed, adjust the converter bottom blowing argon flow rate to 240-270 m³ / h. 3 / h, purge with argon for 2.5-3 minutes, then measure the oxygen content of the molten steel; Converter tapping: The amount of aluminum iron and lime to be added is calculated based on the measured oxygen content of the molten steel and added during the tapping process; after tapping, the molten steel is purged with argon, and then the aluminum content is tested for the first time. Based on the test results, an aluminum wire is fed into the molten steel to adjust the aluminum content in the molten steel to 0.050%-0.055%, and then the molten steel is transferred to the LF furnace. LF furnace slag removal and power supply: After the molten steel arrives at the LF furnace, use 30-50m 3 Bottom-blown argon gas is used to break the slag at a rate of / h, and then power is supplied at a power of 12000-12500kw. Lime is added at 1.3 times the amount of aluminum added after steel tapping. After powering on for 4-5 minutes, samples are taken, the temperature is measured, and the slag is observed. Adjustments are made according to the state of the slag. LF furnace refining adjustment: For the second sampling, raise the temperature to 1600-1605℃ based on the temperature at the time of the second sampling. Simultaneously, adjust the composition based on the results of the second sampling. First, add ferromanganese alloy, and calculate the aluminum loss based on the power supply time. Subtract the aluminum loss during the heating process from the aluminum content of the second sampling composition. If the aluminum content is less than 0.035%, add aluminum wire; if the aluminum content is greater than 0.040%, continue argon blowing to reduce the aluminum content, adjusting it to 0.035%-0.040%. Calcium treatment and soft blowing: After the composition, temperature and slag meet the standards, calcium treatment and soft blowing are carried out, and then the product leaves the station.

[0007] Furthermore, in the step of recovering the residual liquid slag, the residual liquid slag is derived from low alloy steel with a carbon content ≤0.50%, a silicon content ≤0.40%, and a manganese content ≤1.45%, and the residual vanadium, chromium, and copper content in the residual liquid slag does not exceed the control limit of the low carbon cold heading steel.

[0008] Furthermore, in the converter smelting control step, the oxygen pressure is increased to 0.90-0.92 MPa, and the oxygen lance position is lowered to 1.3-1.4 meters.

[0009] Furthermore, in the converter tapping step, the calculation of the amount of aluminum ferroalloy and lime added based on the measured oxygen content of the molten steel is as follows: The formula for calculating the amount of aluminum-iron added, m1, is: m1 = (oxygen content in molten steel × 1.125 ÷ 2.717) + (350 ÷ 2.717), where m1 is in kg and the oxygen content in molten steel is in ppm. The formula for calculating the amount of lime added, m2, is: m2 = k × m1, where k takes a value of 1.3-1.6.

[0010] Furthermore, when the oxygen content is 800-900 ppm, k is taken as 1.3; when the oxygen content is 901-1000 ppm, k is taken as 1.4; when the oxygen content is 1001-1100 ppm, k is taken as 1.5; and when the oxygen content is 1101-1200 ppm, k is taken as 1.6. If the oxygen content is below 800 ppm, the amount of lime added is fixed at 600 kg. If the oxygen content is above 1200 ppm, the converter will not produce steel and will continue to blow argon for deoxidation. The oxygen content value is accurate to the unit.

[0011] Furthermore, in the converter tapping step, aluminum wire is fed in at a ratio of 0.001% increase in aluminum per 5-meter aluminum wire to adjust the acid-soluble aluminum content in the molten steel to 0.050%-0.055%; in the LF furnace refining adjustment step, aluminum wire is fed in at a ratio of 0.001% increase in aluminum per 5-meter aluminum wire to adjust the acid-soluble aluminum content to 0.035%-0.040%.

[0012] Furthermore, in the LF furnace slag breaking and power supply steps, the corresponding adjustments based on the slag state include: if the slag is yellow and opaque, no treatment is required; if the slag is green and opaque, add 0.18-0.25 kg / ton of aluminum slag; if the slag is transparent green glass, add 0.60-0.85 kg / ton of lime; if the slag is transparent black glass, add 0.36-0.50 kg / ton of aluminum slag and 1.20-1.70 kg / ton of lime.

[0013] Furthermore, in the LF furnace refining adjustment step, if the slag condition is abnormal after the second sampling, aluminum slag and / or lime are added according to the slag condition for adjustment; after the second sampling component is obtained, the component is mixed, and after the mixing is completed, a third sampling is performed to check the effect of the adjustment; if the white slag effect is achieved, the power supply is turned on to 1600-1605℃ and then the power supply is stopped, and aluminum mixing control is performed; if the white slag effect is not achieved, the operation of adding aluminum slag and / or lime is repeated.

[0014] Furthermore, in the calcium treatment and soft blowing step, the calcium treatment and soft blowing are as follows: feed in 160-190m of calcium wire for calcium treatment, followed by using 3-8m of... 3 Blow argon gas at a rate of 1 / h for 10-15 minutes, then exit the station.

[0015] Furthermore, the total processing time for refining in the LF furnace is 25-35 minutes.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: The method for reducing the refining cost of low-carbon cold heading steel provided by this invention achieves comprehensive benefits of cost reduction, efficiency improvement, quality enhancement, and consumption reduction while ensuring the quality of molten steel. Specifically, it is reflected in: (1) Significantly reduce material costs: By recovering the residual liquid slag before the converter tapping and dynamically calculating the amount of aluminum, iron and lime to be added based on the oxygen content of the molten steel, excessive material addition is avoided.

[0017] (2) Shorten the refining time of the LF furnace: The deoxidation and slag-making operations are moved to the converter tapping stage. When the molten steel arrives at the LF furnace, it already has good white slag conditions. The overall refining cycle is shortened to 25-35 minutes, which improves the production rhythm.

[0018] (3) Improved steel cleanliness: The formation time of white slag is advanced, which enhances the ability to adsorb inclusions and replaces the 90-120m process in the traditional process. 3 The impurity removal operation of stirring with argon gas for 3-5 minutes per hour reduces secondary oxidation of molten steel and nitrogen absorption.

[0019] (4) Reduce abnormal adjustment operations: By accurately adjusting the aluminum content to 0.050%-0.055% after tapping the steel, the frequency of adjustments required for the LF furnace due to insufficient or excessive aluminum, such as additional wire feeding and argon blowing to burn aluminum, is reduced, and the process stability is enhanced.

[0020] (5) Improved environmental friendliness: The absence of fluorite and synthetic slag reduces the difficulty of slag treatment and the environmental burden. Detailed Implementation

[0021] To better understand the above technical solutions, the technical solutions of the embodiments of this application are described in detail below through specific examples. 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. Unless otherwise specified, the embodiments of this application and the technical features in the embodiments can be combined with each other. It should be noted that, unless otherwise specified, the percentage symbol % in this document represents a mass percentage.

[0022] This invention provides a method for reducing the refining cost of low-carbon cold heading steel, comprising the following steps: Step 1, Converter charging: Select scrap steel and molten iron according to the trace element composition of low carbon cold heading steel.

[0023] Specifically, the converter selects scrap steel and molten iron based on the trace element composition of low-carbon cold heading steel (carbon 0.04%-0.07%, silicon ≤0.10%, manganese ≤0.60%, phosphorus ≤0.025%, sulfur ≤0.015%, Als 0.020%-0.040%), requiring chromium ≤0.05%, nickel ≤0.05%, copper ≤0.05%, arsenic ≤0.04%, and tin ≤0.028%.

[0024] Step 2, recovering residual molten slag: Before tapping from the converter, recover one batch of residual molten slag into the ladle.

[0025] Specifically, before tapping steel from the converter, the molten slag is recovered. Low-alloy steel is used for the recovered molten slag to avoid exceeding trace element limits. Based on a charge of 140 tons, the weight of the recovered slag is 1-1.2 tons. If the weight of the recovered slag is too low, it will affect the submerged arc furnace (LF) heating and inclusion adsorption (less slag results in a weaker LF arc, slower heating, and the slag provides less protection, allowing the molten steel to absorb nitrogen, thus reducing its ability to adsorb inclusions). If the weight of the recovered slag is too high, it will increase LF slag consumption and reduce the heating rate (the slag is oxidized during recovery; more recovered slag requires more deoxidation in the LF furnace, more lime needs to be added to achieve the same inclusion adsorption effect, and more heat is absorbed by the slag during electrode heating, reducing the heat available for heating the molten steel).

[0026] Step 3, Converter Smelting Control: After the converter oxygen blowing reaches the later stage, measure the carbon content of the molten steel, increase the oxygen pressure and lower the oxygen lance position to bring the carbon content of the molten steel down to below 0.06%, while ensuring that the temperature is not lower than 1640℃.

[0027] Specifically, in the later stage of converter smelting (approximately 700 seconds after oxygen blowing), the carbon content of the molten steel is measured using a TSC (Total Stress Test). The oxygen pressure is then adjusted to 0.90-0.92 MPa, and the oxygen lance position (distance from the bottom of the lance head to the surface of the molten iron) is lowered to 1.3-1.4 m, reducing the carbon content of the molten steel to below 0.06% while ensuring the temperature does not fall below 1640℃. Oxygen blowing must end under two conditions: first, the carbon content must be reduced to the target range; second, the temperature must meet the process requirements. If either condition is not met, oxygen blowing must continue until both conditions are met simultaneously.

[0028] Step 4, Bottom blowing of argon and oxygen: After oxygen blowing is completed, adjust the bottom blowing argon flow rate to 240-270 m³ / h. 3 / h, purge with argon for 2.5-3 minutes, then measure the oxygen content of the molten steel.

[0029] Specifically, after oxygen blowing is completed, adjust the argon flow rate at the bottom of the converter to 240-270 m³ / h. 3 Argon is purged for 2.5-3 minutes per hour. Since the oxygen content of the molten steel is high at the end of the converter smelting process, atmospheric balance is used to reduce the oxygen content. Subsequently, TSO is used to determine the oxygen content of the molten steel. Based on the final oxygen content of the molten steel, the amounts of aluminum ferroalloy and lime added during steelmaking are calculated.

[0030] (1) The increase in aluminum content in molten steel after 1 kg of aluminum-iron is melted into the molten steel can be calculated using the following formula: ; In the formula: the aluminum content of the aluminum-iron alloy is 50%, and the yield is 70%; The amount of molten steel (molten iron + scrap steel) charged is 140 tons; The steel recovery rate was 92%, meaning that about 8% of the material was lost during the smelting process.

[0031] (2) The amount of aluminum and iron added shall be calculated according to the following formula: ; In the formula: the coefficient 1.125 is the ratio of the atomic weights of aluminum and oxygen in Al2O3 (54 / 48=1.125), which represents the amount of aluminum (ppm) required to be added for every 1 ppm of oxygen consumed.

[0032] For example: The TSO test shows the oxygen content of molten steel to be 900 ppm, and the volume of molten steel is 140 × 92% × 1000 = 128800 kg. The amount of aluminum added by 1 kg of ferroaluminum in this volume of molten steel is 2.717 ppm. Therefore, the amount of ferroaluminum added is: .

[0033] (3) Aluminum and iron required for aluminum production If the aluminum content in the molten steel is to be adjusted to 350 ppm, the required amount of aluminum and iron is: .

[0034] Therefore, the total amount of aluminum and iron added when the converter produces steel is 372.6 + 128.8 = 501.4 kg.

[0035] (4) Amount of lime added The amount of lime added should be controlled at 1.3 to 1.6 times the amount of aluminum and iron added, with the specific ratio determined based on the final oxygen content of the molten steel. The recommended formula is as follows: Lime addition amount = Total aluminum and iron content × 1.3 to 1.6.

[0036] Calculation example (based on 1.3 times the total amount of aluminum and iron): Deoxidized aluminum iron content: 372.6 kg; The amount of aluminum and iron required to bring the aluminum concentration to 650 ppm is: 650 / 2.717 = 239.9 kg. Total aluminum and iron content: 372.6 + 239.9 = 612.5 kg; Amount of lime added: 612.5 × 1.3 = 796.2 kg.

[0037] Specifically, after the addition of aluminum and iron, the deoxidation reaction produces Al2O3. If the amount of lime added is insufficient, the slag, after cooling, tends to become glassy and brittle, easily detaching from the slag stick and failing to effectively adsorb inclusions in the molten steel. When the amount of lime added is controlled at approximately 1.3 times the amount of aluminum and iron, the slag, after cooling, becomes jade-like, dense, and not easily detached, which is beneficial for adsorbing inclusions. If the amount of lime added exceeds 1.6 times the amount of aluminum and iron, the slag becomes too viscous, its fluidity decreases, and it negatively affects the adsorption effect of inclusions. Since the final oxygen content of each furnace of molten steel varies (mostly within the range of 800-1200 ppm), the higher the oxygen content, the greater the amount of lime required. Therefore, in actual production, the amount of lime added needs to be dynamically adjusted according to the oxygen content, as shown in Table 1.

[0038] Table 1

[0039] In addition, if the oxygen content is below 800 ppm, the amount of lime added is fixed at 600 kg. If it is above 1200 ppm, the converter will not produce steel and will continue to blow argon to deoxidize using the atmospheric balance method, calculated based on the empirical value of 150 ppm deoxidation per minute.

[0040] Step 5, Converter tapping: Calculate the amount of aluminum iron and lime to be added based on the measured oxygen content of the molten steel, and add them during the tapping process; after tapping, blow argon into the molten steel, then take a sample for the first time to test the aluminum content, and feed an aluminum wire according to the test results to adjust the aluminum content in the molten steel to 0.050%-0.055%, and then leave the station and transfer the molten steel to the LF furnace.

[0041] Specifically, aluminum ferroalloy and lime are added during converter tapping. After tapping, the molten steel is argon-purged for 3 minutes, and then sample 1 is taken for analysis. Based on the aluminum content of sample 1, the aluminum content of the molten steel is adjusted to the target range (0.050%–0.055%) by feeding aluminum wire. The aluminum wire is calculated to increase the aluminum content by 0.001% for every 5 meters.

[0042] For example, if the aluminum content measured in sample 1 is 0.026% (260ppm), and the target value is 0.055% (550ppm), then: the required increase in aluminum = 0.055% - 0.026% = 0.029% (i.e., 290ppm); the required aluminum wire length = (0.029% / 0.001%) × 5 = 145m.

[0043] After aluminum is added, the molten steel leaves the station and is transferred to the LF furnace for further processing.

[0044] Step 6, LF Furnace Slag Removal and Power Supply: After the molten steel arrives at the LF furnace, use 30-50m... 3Bottom-blown argon gas is used to break the slag at a rate of / h, and then power is supplied at a power of 12000-12500kw. Lime is added at 1.3 times the amount of aluminum added after steel tapping. After 4-5 minutes of power supply, samples are taken, the temperature is measured, and the slag is observed. Adjustments are made according to the state of the slag.

[0045] Specifically, after the molten steel reaches the LF furnace, it first undergoes a 30-50m... 3 Bottom-blown argon gas is used for slag removal at a rate of / h. Subsequently, the electrodes are heated by electricity at a power of 12000-12500 kW, and lime is added. The amount of lime added is calculated as 1.3 times the amount of aluminum added after steel tapping, i.e.: The amount of lime added = the amount of aluminum added after steelmaking × 1.3 = 290 × 1.3 = 377 kg; Four to five minutes after power is supplied, sample taking, temperature measurement, and residue removal are performed.

[0046] Ideally, if there is no slag accumulation during the converter tapping process, the oxygen value is accurate, and the composition of the sample taken after tapping is reliable, the LF furnace slag should be white and opaque, indicating good deoxidation. However, in actual production, various uncertainties often affect the slag, leading to poor deoxidation after the molten steel reaches the LF furnace. This can result in abnormal slag colors, such as yellow or green opaque slag, or transparent green or black glassy slag. The corresponding measures to address these abnormalities are shown in Table 2.

[0047] Table 2

[0048] Step 7, LF furnace refining and adjustment: Take a second sample, raise the temperature to 1600-1605℃ based on the temperature of the second sample, and prepare the composition according to the composition results of the second sample. First, add ferromanganese alloy, and calculate the aluminum loss according to the power supply time. After subtracting the aluminum loss during the heating process from the aluminum content of the second sample composition, if the aluminum content is less than 0.035%, add aluminum wire. If the aluminum content is greater than 0.040%, continue blowing argon to reduce the aluminum content, and adjust the aluminum content to 0.035%-0.040%.

[0049] Specifically, based on the temperature at sampling point 2, the temperature is raised to 1600-1605℃, and alloys are added according to the composition. This steel grade does not require carbon or silicon, only manganese and aluminum. Therefore, after adding low-carbon ferromanganese, the aluminum content is adjusted to 0.035%-0.040% by feeding in aluminum wire. The calculation method remains the same: increase aluminum by 0.001% for every 5 meters of aluminum wire, while also considering aluminum loss during power transmission, calculated at 0.001% per minute.

[0050] For example, if the temperature of sample 2 is 1550℃, and the temperature rises by 5℃ per minute, the time required to reach 1605℃ is (1605-1550) / 5 = 11 minutes. The aluminum loss is 0.001% × 11 = 0.011%, and the length of aluminum wire to be replenished is 0.011% / 0.001% × 5 = 55 meters. Based on the aluminum content of sample 2, if the aluminum content after deducting the aluminum loss due to temperature rise is less than 0.035%, then aluminum wire needs to be replenished; if it is greater than 0.040%, then no replenishment is needed, and argon blowing should continue to burn off the aluminum.

[0051] Unlike previous methods, this one eliminates the need for large-scale argon agitation to remove inclusions. Traditional processes require 90-120m... 3 / h bottom blowing argon gas stirring for 3-5 minutes, while the present invention moves the lime and aluminum deoxidation forward when the steel is tapped from the converter, which can form white slag in advance. The extended time of white slag formation replaces the impurity removal effect of large argon gas stirring.

[0052] In actual production, abnormal situations often arise, and measures may need to be taken for the slag after sampling 2, affecting the control of aluminum in the molten steel. Therefore, after the composition of sampling 2 is obtained, the composition is adjusted, and sampling 3 is taken after adjustment to verify the effect of the measures. If the slag condition reaches the white slag level at sampling 2, the power is supplied to 1600-1605℃ and then stopped, during which aluminum blending control is performed according to step 7; if the white slag level is not reached, the operation is carried out according to the measures in Table 2 of step 6.

[0053] Step 8, Calcium Treatment and Soft Blowing: After the composition, temperature and slag meet the standards, calcium treatment and soft blowing are carried out, and then the slag is discharged from the station.

[0054] Specifically, after the LF furnace meets the requirements for composition, temperature, and slag control, the calcium feed line is 160-190m, and then 3-8m is used. 3 Bottom blowing, argon blowing, and soft blowing for 10-15 minutes per hour before exiting the station.

[0055] Example 1 A method for reducing the refining cost of low-carbon cold heading steel includes the following steps: (1) Converter charging: 112 tons of molten iron and 28 tons of high-quality scrap steel were charged, totaling 140 tons. The expected output of steel was 128.8 tons.

[0056] (2) Recovery of casting residue liquid slag: During converter smelting, 1.1 tons of low alloy steel slag were recovered from the empty ladle.

[0057] (3) Converter smelting control: When oxygen blowing lasts for 720 seconds, the TSC measured the carbon content of the molten steel to be 0.15% and the temperature to be 1611℃. The oxygen pressure was increased from 0.86MPa to 0.92MPa, the oxygen lance position was reduced from 1.6 meters to 1.4 meters, and the carbon content was reduced to 0.035%.

[0058] (4) Bottom blowing of argon and oxygen determination in converter: After the oxygen blowing is completed, the bottom blowing argon flow rate is adjusted to 250 m³ / h and argon is blown for 3 minutes. The oxygen content of the molten steel is measured to be 900 ppm by TSO.

[0059] (5) Steel tapping from the converter: Calculate the oxygen content and add 501.4 kg of aluminum iron (372.6 kg for deoxidation and 128.8 kg for aluminum to be adjusted to 0.035%) and 796.2 kg of lime. After tapping, take a sample 1 and find that the aluminum content is 0.026%. Feed 145 m of aluminum wire at a rate of 0.001% per 5 m of aluminum wire to adjust the aluminum content to 0.055% before leaving the station.

[0060] (6) Slag breaking and power supply in LF furnace: After the molten steel arrives at the LF furnace, 40 m³ / h of bottom-blown argon gas is used to break the slag, and power is supplied at 12500 kW. 377 kg of lime is added at 1.3 times the amount of aluminum (290 ppm) after steel tapping. Sample 2 is taken 5 minutes after power supply, and the temperature is measured at 1550 ℃. The slag is observed to be white.

[0061] (7) LF furnace refining adjustment: Sample 2 components: carbon 0.052%, silicon 0.033%, manganese 0.12%, aluminum 0.048%, and add 150 kg of low carbon ferromanganese; calculated at a temperature increase of 5°C per minute, it will take 11 minutes to reach 1605°C, with an aluminum loss of 0.011%, and the expected final aluminum content is 0.037%, so no additional aluminum wire is needed.

[0062] (8) Calcium treatment and soft blowing: After the composition, temperature and slag meet the standards, feed in 160m of calcium line, and then use 3m 3 / h bottom blowing argon blowing soft blowing 10min out of station.

[0063] The above amounts are: lime added = 796.2 + 377 = 1173.2 kg, aluminum and iron added = 501.4 kg, and aluminum wire fed = 145 meters.

[0064] Example 2 A method for reducing the refining cost of low-carbon cold heading steel includes the following steps: (1) Converter charging: 112 tons of molten iron and 28 tons of high-quality scrap steel were charged, totaling 140 tons. The expected output of steel was 128.8 tons.

[0065] (2) Recovery of casting residue liquid slag: During converter smelting, 1.1 tons of low alloy steel slag were recovered from the empty ladle.

[0066] (3) Converter smelting control: When oxygen blowing lasts for 720 seconds, the TSC measured the carbon content of the molten steel to be 0.07% and the temperature to be 1611℃. The oxygen pressure was adjusted to 0.92MPa, the oxygen lance position was lowered to 1.4 meters, and the carbon content was reduced to 0.022%.

[0067] (4) Bottom blowing of argon and oxygen determination in converter: 250 m³ / h of argon is blown at the bottom for 3 minutes, and the oxygen content is determined to be 1080 ppm by TSO.

[0068] (5) Steel tapping from the converter: Calculate the addition of 575.92 kg of aluminum iron (447.1 kg for deoxidation, and 128.8 kg for aluminum to be adjusted to 0.035%) and 863.8 kg of lime; after tapping, take a sample of 0.021% aluminum and feed 170 m of aluminum wire to adjust the aluminum to 0.055%.

[0069] (6) LF furnace slag breaking and power supply: bottom blowing argon 40m³ / h slag breaking, 12500kW power supply, add 442kg of lime; 5 minutes after power supply, take 2 samples, the temperature is 1560℃, the slag is green and opaque, add 30kg of aluminum slag.

[0070] (7) LF furnace refining adjustment: Sample 2 has carbon 0.052%, silicon 0.033%, manganese 0.12%, and aluminum 0.040%. Add 150 kg of low-carbon ferromanganese. It takes 9 minutes to heat from 1560℃ to 1605℃. The aluminum loss is 0.009%. The expected aluminum is 0.031%. Add 25 m of aluminum wire to pre-mix to 0.038%. Because measures were taken after sample 2, after adding the alloy and aluminum wire, sample 3 was taken. The slag was white slag. Continue to supply power to 1605℃.

[0071] (8) Calcium treatment and soft blowing: After the composition, temperature and slag meet the standards, feed in 170m of calcium line, and then use 3m 3 / h bottom blowing argon blowing soft blowing 11min out of station.

[0072] The above amounts are: lime added = 863.8 + 442 = 1305 kg, aluminum and iron added = 575.92 kg, aluminum wire fed = 195 m, and aluminum slag = 30 kg.

[0073] Comparative Example 1 The difference from Example 1 is that the slag collection time was changed to after all steel was tapped. As a result, the nitrogen content in the molten steel was higher than that in Example 1, while the aluminum content in the molten steel was lower than that in Example 1.

[0074] The principle is to collect the slag before tapping the steel. After the molten steel penetrates the slag layer, the slag layer can play a certain protective role, reducing the absorption of nitrogen and the replenishment of oxidation by the molten steel.

[0075] Comparative Example 2 The difference from Example 1 is that, in the later stage of converter blowing, the oxygen pressure is reduced or the lance position is raised in order to reduce the oxidation of molten steel.

[0076] This can easily lead to decarburization or unstable temperature rise. The principle is that in the later stages of smelting, as the temperature of the molten steel rises, using a low lance position and high oxygen pressure can melt the scrap steel that was stuck to the bottom of the furnace and not completely melted in the early stages. At the same time, maintaining sufficient oxygen penetration is necessary to effectively ensure strong decarburization of the molten steel. If the oxygen pressure is too low or the lance position is too high, it will lead to poor decarburization or slow temperature rise.

[0077] Comparative Example 3 The difference from Example 1 is that the amount of aluminum iron and lime added during the tapping of steel in the converter is fixed, which is convenient for operation, and the aluminum iron and lime are added in the LF furnace later.

[0078] This results in increased refining time and costs. The principle is that, under the same conditions of adding aluminum, ferroalloy, and lime, there is a significant difference between adding them first and later. Adding deoxidizers and slag first promotes the formation of white slag, thereby shortening refining time and reducing costs. While adding later can also produce white slag, the refining time and adsorption time for white slag are shorter, requiring increased argon blowing flow or refining time to achieve the same steel purity as the first-addition method.

[0079] Comparative Example 4 The difference from Example 1 is that after the steel is tapped, the sample is taken and aluminum is not added to 0.050-0.055%, or higher or lower.

[0080] The result is that if the aluminum content is low, the LF furnace process often requires additional aluminum wire feeding due to insufficient aluminum in the molten steel. The larger the amount of aluminum wire fed, the more inclusions are generated, and the longer the adsorption time is required. If the aluminum content is high, the aluminum content in the LF furnace process is likely to exceed the upper limit, requiring an increase in argon blowing flow or refining time to burn off the aluminum.

[0081] Comparative Example 5 One existing technology for slag-free processing involves reducing the carbon content in the converter to below 0.05% before tapping. During tapping, a fixed amount of 550 kg of ferroaluminum and 500 kg of lime is added. After tapping, sample 1 is taken (0.022% aluminum). Based on sample 1, the aluminum content is adjusted to 0.040%, and 90 m of aluminum wire is fed. The molten steel is then transferred to the LF furnace for further processing. The LF furnace is equipped with a fixed amount of 500 kg of lime, 300 kg of synthetic slag, 200 kg of aluminum slag, and 60 kg of fluorite. Five minutes after power is supplied, sample 2 is taken (coated slag, which is green and transparent glassy slag). 100 kg of lime is added. Based on the composition of sample 2 (0.019% aluminum), the aluminum content is adjusted to 0.055%, and 180 m of aluminum wire is fed, while 250 kg of lime is added simultaneously. A 100 m long aluminum wire is then used. 3 / h bottom blowing argon gas stirring for 3 minutes, then take 3 samples; after the composition and slag meet the standards, then send the power to 1605℃ to blow calcium wire soft blowing.

[0082] The above amounts are: lime (500 + 500 + 250 = 1250 kg), aluminum and iron (550 kg), aluminum wire (270 meters), aluminum slag (200 kg), fluorite (60 kg), and synthetic slag (300 kg).

[0083] Comparative Example 6 The second existing technology involves slag collection in the converter, where the final carbon content is reduced to below 0.05% before tapping. During tapping, a fixed amount of 550 kg of ferroaluminum and 500 kg of lime is added. After tapping, slag is collected, and sample 1 is taken. The aluminum content is 0.016%. Based on sample 1, the aluminum content is adjusted to 0.040%, and 120 m of aluminum wire is fed. The molten steel is then transferred to the LF furnace for further processing. The LF furnace is equipped with a fixed amount of 200 kg of lime and 100 kg of aluminum slag. Five minutes after power is supplied, sample 2 is taken. The slag is sticky and white. Based on the composition of sample 2, the aluminum content is 0.027%. The aluminum content is adjusted to 0.055%, and 140 m of aluminum wire is fed, while 200 kg of lime is added simultaneously. A 100 m long aluminum wire is then used. 3 / h bottom blowing argon gas stirring for 3 minutes, then take 3 samples; after the composition and slag meet the standards, then send the power to 1605℃ to blow calcium wire soft blowing.

[0084] The above amounts are: lime added = 500 + 200 + 200 = 900 kg, aluminum and iron added = 550 kg, aluminum wire fed = 260 meters, and aluminum slag added = 100 kg.

[0085] Table 3. Refining costs of low-carbon cold heading steel in Examples 1-2 and Comparative Examples 5-6

[0086] As can be seen from Table 3, the total costs of Examples 1 and 2 are approximately RMB 7,776 and RMB 9,291, respectively, which are significantly lower than those of Comparative Example 5 (approximately RMB 16,008) and Comparative Example 6 (approximately RMB 14,301). There are significant savings in aluminum wire and aluminum slag, and fluorite and synthetic slag are not used.

[0087] 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 reducing the refining cost of low-carbon cold heading steel, characterized in that, Includes the following steps: Converter charging: Select scrap steel and molten iron according to the trace element composition of low carbon cold heading steel; Recovery of molten slag from casting: Before tapping from the converter, recover one batch of molten slag from casting into the ladle; Converter smelting control: In the later stage of oxygen blowing in the converter, after measuring the carbon content of the molten steel, the oxygen pressure is increased and the oxygen lance position is lowered to bring the carbon content of the molten steel down to below 0.06%, while ensuring that the temperature is not lower than 1640℃. Converter bottom argon blowing and oxygen fixing: After the oxygen blowing is finished, adjust the converter bottom argon flow to 240-270 m 3 / h, blow argon for 2.5-3 minutes, and then measure the oxygen content of the molten steel; Converter tapping: The amount of aluminum iron and lime to be added is calculated based on the measured oxygen content of the molten steel and added during the tapping process; after tapping, the molten steel is purged with argon, and then the aluminum content is tested for the first time. Based on the test results, an aluminum wire is fed into the molten steel to adjust the aluminum content in the molten steel to 0.050%-0.055%, and then the molten steel is transferred to the LF furnace. LF furnace slag removal and power supply: After the molten steel arrives at the LF furnace, use 30-50m 3 Bottom-blown argon gas is used to break the slag at a rate of / h, and then power is supplied at a power of 12000-12500kw. Lime is added at 1.3 times the amount of aluminum added after steel tapping. After powering on for 4-5 minutes, samples are taken, the temperature is measured, and the slag is observed. Adjustments are made according to the state of the slag. LF furnace refining adjustment: For the second sampling, raise the temperature to 1600-1605℃ based on the temperature at the time of the second sampling. Simultaneously, adjust the composition based on the results of the second sampling. First, add ferromanganese alloy, and calculate the aluminum loss based on the power supply time. Subtract the aluminum loss during the heating process from the aluminum content of the second sampling composition. If the aluminum content is less than 0.035%, add aluminum wire; if the aluminum content is greater than 0.040%, continue argon blowing to reduce the aluminum content, adjusting it to 0.035%-0.040%. Calcium treatment and soft blowing: After the composition, temperature and slag meet the standards, calcium treatment and soft blowing are carried out, and then the product leaves the station.

2. The method for reducing the refining cost of low-carbon cold heading steel according to claim 1, characterized in that, In the step of recovering the residual liquid slag, the residual liquid slag is derived from low alloy steel with a carbon content ≤0.50%, a silicon content ≤0.40%, and a manganese content ≤1.45%, and the residual vanadium, chromium, and copper content in the residual liquid slag does not exceed the control limit of the low carbon cold heading steel.

3. The method for reducing the refining cost of low-carbon cold heading steel according to claim 1, characterized in that, In the converter smelting control steps, the oxygen pressure is increased to 0.90-0.92 MPa, and the oxygen lance position is lowered to 1.3-1.4 meters.

4. The method for reducing the refining cost of low-carbon cold heading steel according to claim 1, characterized in that, In the converter tapping step, the amount of aluminum ferrophosphate and lime added is calculated based on the measured oxygen content of the molten steel: wherein, The formula for calculating the amount of aluminum-iron added, m1, is: m1 = (oxygen content in molten steel × 1.125 ÷ 2.717) + (350 ÷ 2.717), where m1 is in kg and the oxygen content in molten steel is in ppm. The formula for calculating the amount of lime added, m2, is: m2 = k × m1, where k takes a value of 1.3-1.

6.

5. The method for reducing the refining cost of low-carbon cold heading steel according to claim 4, characterized in that, When the oxygen content is 800-900ppm, k is 1.3; when the oxygen content is 901-1000ppm, k is 1.4; when the oxygen content is 1001-1100ppm, k is 1.5; when the oxygen content is 1101-1200ppm, k is 1.

6. If the oxygen content is below 800ppm, the amount of lime added is fixed at 600kg. If the oxygen content is above 1200ppm, the converter will not produce steel and will continue to blow argon for deoxidation. The oxygen content value is accurate to the unit.

6. The method for reducing the refining cost of low-carbon cold heading steel according to claim 1, characterized in that, In the converter tapping step, aluminum wire is fed in at a ratio of 0.001% increase in aluminum per 5-meter aluminum wire to adjust the acid-soluble aluminum content in the molten steel to 0.050%-0.055%; in the LF furnace refining adjustment step, aluminum wire is fed in at a ratio of 0.001% increase in aluminum per 5-meter aluminum wire to adjust the acid-soluble aluminum content to 0.035%-0.040%.

7. The method for reducing the refining cost of low-carbon cold heading steel according to claim 1, characterized in that, In the LF furnace slag breaking and power supply steps, the corresponding adjustments based on the slag state include: if the slag is yellow and opaque, no treatment is required; if the slag is green and opaque, add 0.18-0.25 kg of aluminum slag per ton of molten steel; if the slag is transparent green glass, add 0.60-0.85 kg of lime per ton of molten steel; if the slag is transparent black glass, add 0.36-0.50 kg of aluminum slag per ton of molten steel and 1.20-1.70 kg of lime per ton of molten steel.

8. The method for reducing the refining cost of low-carbon cold heading steel according to claim 1, characterized in that, In the LF furnace refining adjustment step, if the slag condition is abnormal after the second sampling, aluminum slag and / or lime are added according to the slag condition for adjustment; after the second sampling component is obtained, the component is mixed, and after the mixing is completed, a third sampling is performed to check the effect of the adjustment; if the white slag effect is achieved, the power supply is turned on to 1600-1605℃ and then the power supply is stopped, and aluminum mixing control is performed; if the white slag effect is not achieved, the operation of adding aluminum slag and / or lime is repeated.

9. The method for reducing the refining cost of low-carbon cold heading steel according to claim 1, characterized in that, In the calcium treatment and soft blowing steps, the calcium treatment and soft blowing are as follows: feed in 160-190m of calcium wire for calcium treatment, and then use 3-8m of... 3 Blow argon gas at a rate of 1 / h for 10-15 minutes, then exit the station.

10. The method for reducing the refining cost of low-carbon cold heading steel according to any one of claims 1-9, characterized in that, The total processing time for refining in the LF furnace is 25-35 minutes.

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