LF furnace refining method for A36 steel with less nitrogen addition

Abstract

The present invention relates to the technical field of steelmaking, and discloses a LF furnace refining method for A36 steel with less nitrogen addition, comprising: after molten steel enters the station, it is sent to the slag-forming station for electrification, and the active power is 5500KW-8500KW. The argon flow rate during the slag-forming process is controlled at 50-60m 3 / h, increase the amount of fluorite and lime added; after the slag is added and the slag is completed, power is supplied at an active power of 9000~12000KW, and the argon flow rate is controlled at 35~45m 3 / h, adding 40-60kg / 120 tons of at least one of aluminum-calcium-carbon and silicon carbide to the molten steel to foam the slag to a thickness of 20-25cm. After slagging, aluminum wire is added to control the aluminum content in the molten steel to 0.006-0.015%. Sampling and composition adjustment are then performed. Finally, the molten steel temperature is raised to 1610-1615°C before power supply is stopped. The method provided by the present invention can significantly reduce the amount of nitrogen added compared to existing technologies.

Description

Technical Field

[0001] The present invention relates to the technical field of steelmaking, and in particular to an LF furnace refining method for A36 steel with less nitrogen addition. Background Art

[0002] Currently, A36 adopts converter-LF furnace-RH furnace-continuous casting process. The LF furnace method is as follows:

[0003] 1. Add some aluminum iron, 500 kg of lime, and 300 kg of bauxite to the converter;

[0004] 2. When the LF arrives at the station, add 400-700 kg of lime, 0-100 kg of fluorite, and 70 kg of aluminum slag. At the same time, stir with 100 cubic meters / hour of argon to promote the melting of the slag. After the slag is added, continue stirring for 1-2 minutes.

[0005] It is generally customary to add 400 kg of lime, 60 kg of fluorite, and 70 kg of aluminum slag.

[0006] 3. Use power to slag for 180 seconds at gears 8-11, then switch to power to increase temperature at gears 4-2. After taking sample 1, continue to increase the temperature to the outlet temperature + 20 degrees Celsius, and the outlet temperature is 1610 degrees Celsius. Wait for the sample to come out and mix the ingredients, and stir for 3-5 minutes at the same time. When stirring, feed aluminum wire in an amount equal to the upper limit of aluminum for the steel sample + 0.010%, and the upper limit of aluminum is 0.025%. Then take sample 2, and wait for sample 2 to come out to see if the aluminum is sufficient. If it is not enough, continue to add aluminum wire. If it is sufficient, no need to add. If the temperature is enough, no power is required and it can be directly discharged.

[0007] During the heating process, if the rhythm is tight or the temperature of the molten steel is low when it arrives at the LF furnace, we generally use level 2 to heat up.

[0008] 4. Under the original process, the nitrogen content of molten steel is generally increased by 20-30ppm compared with the sample taken after the steel is discharged from the converter. A36 is a vanadium and niobium-containing steel, and the nitrogen content in the steel is required to be less than 40ppm in the finished product. Although denitrification can be carried out in the RH furnace after refining in the LF furnace, the RH circulation of the molten steel for 15 minutes generally removes 6-11ppm of nitrogen. If the nitrogen content out of the LF furnace is too high, the RH cannot remove it, not to mention that the nitrogen content of the molten steel will increase by 3-7ppm during the continuous casting process.

[0009] Therefore, it is very important to reduce nitrogen in molten steel in LF furnace.

[0010] In view of this, the present invention is proposed. Summary of the Invention

[0011] The object of the present invention is to provide an LF furnace refining method for A36 steel with less nitrogen addition.

[0012] The present invention is achieved in that:

[0013] In a first aspect, the present invention provides an LF furnace refining method for A36 steel with less nitrogen addition, comprising:

[0014] After the molten steel enters the station, it is electrified with active power of 5500KW-8500KW to slag. The argon flow rate during the slag-forming process is controlled at 50~60m 3 / h, first add 130-150kg / 120 tons of fluorite, then add 400-900kg / 120 tons of lime. The lime is added in batches, 70-120kg / 120 tons in each batch. When adding the last two batches of lime, mix 30-40kg of aluminum slag into each batch and add 30-40kg together;

[0015] After the slag is added and slag is formed, power is supplied at an active power of 9000KW to 12000KW, and the argon flow rate is controlled at 35 to 45m 3 / h, adding 40-60kg / 120 tons of at least one of aluminum calcium carbon and silicon carbide to the molten steel to foam the slag to a thickness of 20-25cm;

[0016] After slag melting, aluminum wire is fed in to control the aluminum content in the molten steel to be 0.006-0.015%. Then, the power is continued to be supplied for 5-8 minutes before sampling. After the sample composition is obtained, the chemical composition of the molten steel is adjusted to the target value according to the composition data. During the adjustment process, the argon flow rate is controlled at 95-105m 3 / h argon blowing 2.5~3.5min;

[0017] Then adjust the argon flow rate to 35~45m 3 / h, and stop supplying power until the temperature of the molten steel rises to 1610-1615℃.

[0018] In an optional embodiment, before the molten steel enters the station, when the converter is tapping, when the amount of molten steel in the ladle reaches 30-40 tons, aluminum iron is added first, then slag, and then alloy is added. At the same time, argon is increased from 55-65m3 before tapping. 3 / h is reduced to 20~30m 3 / h.

[0019] In an optional embodiment, before the molten steel enters the station, the carbon content of the molten steel at the converter end point is controlled to be 0.08-0.12%.

[0020] In an optional embodiment, before the molten steel enters the station, the sulfur content of the molten steel at the converter end point is controlled to be 0.020-0.45%.

[0021] In an optional embodiment, the total amount of slag added before and after entering the station is: 900-1400 kg / 120 tons of lime, 130-150 kg / 120 tons of fluorite, 68-72 kg / 120 tons of aluminum slag, and 280-320 kg / 120 tons of bauxite.

[0022] In an optional embodiment, after the molten steel enters the station, electricity is transmitted with an active power of 5500KW to 8500KW.

[0023] In an optional embodiment, after the molten steel enters the station, lime is added in batches, with an interval of 25 to 35 seconds between each batch.

[0024] In an optional embodiment, when the RH furnace cannot be used due to abnormal conditions, calcium wire is fed into the LF furnace at the end of the treatment, and the argon flow rate is adjusted to 5-10m 3 / h soft blowing for 5 to 7 minutes to exit the station.

[0025] In an optional embodiment, the calcium wire is fed 3 minutes after the aluminum wire is fed and 1 minute after the power supply is completed.

[0026] In an optional embodiment, the argon flow rate is controlled to be 10-20 m 3 / h.

[0027] The present invention has the following beneficial effects:

[0028] In the refining method provided by the embodiment of the present invention, after the molten steel arrives at the LF furnace, the amount of slag is adjusted. After the slag addition amount is adjusted, on the one hand, it can ensure that the increase in nitrogen is reduced. On the other hand, the above-mentioned amount of slag addition can also achieve the reduction of molten steel exposure during the desulfurization process. After the slag addition is completed, power is supplied at an active power of 9000 to 11000KW to reduce the arc breakdown of the slag layer and reduce the nitrogen absorption of the molten steel. After the slag is foamed, aluminum wire is fed to make the aluminum content between 0.006 and 0.015%, and argon gas is turned on when the molten steel is prepared for further denitrification. Therefore, the LF furnace refining method for A36 steel with less nitrogen addition provided by the embodiment of the present application has less nitrogen addition during the refining process, and the nitrogen increase after refining is 1-3ppm, which is significantly improved compared to the existing nitrogen increase of 20-30ppm. DETAILED DESCRIPTION

[0029] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0030] The following is a detailed description of an LF furnace refining method for A36 steel with less nitrogen addition provided by an embodiment of the present invention.

[0031] An embodiment of the present invention provides an LF furnace refining method for A36 steel with less nitrogen addition, which comprises:

[0032] After the molten steel enters the station, it is electrified with active power of 5500KW-8500KW to slag. The argon flow rate during the slag-forming process is controlled at 50~60m 3 / h, first add 130-150kg / 120 tons of fluorite, then add 400-900kg / 120 tons of lime. The lime is added in batches, 70-120kg / 120 tons in each batch. When adding the last two batches of lime, mix 30-40kg of aluminum slag into each batch and add 30-40kg together;

[0033] After the slag is added and the slag is melted, the power is supplied at an active power of 9000-12000KW, and the argon flow rate is controlled at 35-45m 3 / h, adding 40-60kg / 120 tons of at least one of aluminum calcium carbon and silicon carbide to the molten steel to foam the slag to a thickness of 20-25cm;

[0034] After slag melting, aluminum wire is fed to make the aluminum content in the molten steel 0.006-0.015%. Then continue to supply power for 5-8 minutes and take samples. After the sample composition comes out, the chemical composition of the molten steel is adjusted to the target value according to the composition data. During the adjustment process, the argon flow rate is controlled at 95-105m 3 / h argon blowing for 2.5 to 3.5 minutes, and then adjust the argon flow rate to 35 to 45m 3 / h;

[0035] Stop power supply after the molten steel temperature rises to 1610-1615℃.

[0036] In the refining method provided by the embodiment of the present invention, the amount of slag is adjusted after the molten steel arrives at the LF furnace. After the amount of slag added is adjusted, it can ensure that the nitrogen increase is reduced on the one hand, and on the other hand, the above-mentioned amount of slag added can also achieve the reduction of molten steel exposure during the desulfurization process. After the slag addition is completed, power is supplied at an active power of 9000~11000K, which can reduce the arc breakdown of the slag layer and reduce the nitrogen absorption of the molten steel. After the slag is foamed, aluminum wire is fed to make the aluminum content between 0.006~0.015%, and argon gas is turned on when the molten steel is prepared, which can further remove nitrogen. Therefore, the LF furnace refining method for A36 steel with less nitrogen increase provided by the embodiment of the present application has less nitrogen increase during the refining process, and the nitrogen increase after refining is 1-3ppm, which is significantly improved compared to the existing nitrogen increase of 20-30ppm.

[0037] Specifically, the refining method is:

[0038] S1. Before the molten steel enters the station and when the converter is tapping, when the amount of molten steel in the ladle reaches 30-40 tons (for example, 30 tons, 35 tons or 40 tons), first add aluminum iron, then add slag, and then add alloy. At the same time, the argon gas is increased from 55-65m3 before tapping.3 / h(e.g. 55m 3 / h、60m 3 / h or 65m 3 / h) is reduced to 20~30m 3 / h (e.g. 20m 3 / h、25m 3 / h or 30m 3 / h).

[0039] Since aluminum, iron, slag and alloys are added during the tapping process of the converter, desulfurization is also carried out while the molten steel is being deoxidized. In order to reduce the desulfurization of the molten steel and reduce the exposure of the molten steel, in a preferred embodiment of the present application, when the converter steel is poured into the ladle to 30-40 tons, aluminum, iron, slag and alloys are added, and at the same time, the argon gas is increased from 55-65m3 before tapping. 3 / h is reduced to 20~30m 3 / h, until the steel tapping is completed.

[0040] 3 minutes before tapping the converter, open the ladle bottom to blow argon at a flow rate of 55-65m 3 / h, the purpose is to drive out the air under the ladle, because argon has a greater specific gravity than air. 1 liter of argon is approximately equal to 1.38 liters of air. When blowing argon at the bottom of the ladle, the argon will sink to the bottom and expel the air upwards, thereby reducing the contact between the molten steel and the air in the ladle during tapping and reducing nitrogen absorption during the tapping process. The design of the argon blowing time is related to the inner diameter of the ladle. For example, if the inner diameter of the bottom of the ladle is about 2.8 meters, then the volume of 0.5 meters at a height of 2.8*1.4*1.4*0.5=3.0772m 3 .

[0041] Preferably, increasing the tapping hole diameter can reduce tapping time, thereby reducing the time the steel stream is exposed to air. Specifically, increasing the original tapping hole inner diameter from 160 cm to 190 cm can reduce the tapping time by 30 seconds, reducing the tapping time from an average of 3.3 minutes to 2.8 minutes.

[0042] S2: After the molten steel enters the station, it is sent to the electrolytic slag. The argon flow rate during the slag process is controlled at 50-60m 3 / h. First add 130-150kg / 120 tons of fluorite, then add 400-900kg / 120 tons of lime. The lime is added in batches of 70-120kg each, with an interval of 25-35 seconds between each batch. When adding the last two batches of lime, mix 30-40kg of aluminum slag into each batch and add them together.

[0043] After the molten steel arrives at the LF furnace, the slag amount is adjusted from the original 400-700kg / 120 tons of lime to 400-900kg / 120 tons (taking a furnace of 120 tons of steel as an example, the amount added is, for example, 400kg, 500kg, 600kg, 700kg or 900kg). The aluminum slag remains unchanged, and the fluorite is increased to 130-150kg / 120 tons (taking a furnace of 120 tons of steel as an example, the amount added is, for example, 130kg, 140kg or 150kg). According to actual test results, when the amount of lime in the LF furnace is 750 kg (plus the amount of slag added after the converter is tapped and before entering the station), the arc is submerged very well during the power transmission process, and the entire refining process can achieve the minimum nitrogen increase; however, if too much lime is added, it will affect the power transmission temperature rise and extend the heating time. The slag addition amount in this application can, after adjustment, ensure that the nitrogen increase is reduced on the one hand, and on the other hand, the above-mentioned slag addition amount can also reduce the risk of molten steel exposure during the desulfurization process. Aluminum slag is chosen to be mixed in with the last two batches of lime. When added, the entire slag will produce a foaming effect. If added in the front, it will also produce a foaming effect, but only part of the slag. The lime added later will not foam, affecting the foaming degree of the slag.

[0044] Preferably, after the molten steel enters the station, power is supplied at a power of 5500KW to 8500KW (e.g., 5500KW, 6500KW, 7500KW, or 8500KW). Taking the Shaoguan Iron and Steel Plant as an example, the above power range corresponds to gears 8-11. Gears 8-11 are used for slag treatment, with gear 11 (corresponding to 5500KW) being the best. This is because the gap is large before the slag is fully treated, and at this gear, the current is minimized, the arc is shortest, and the ionized nitrogen atoms are converted into nitrogen ions. The probability of the nitrogen ions then entering the molten steel from the slag and being absorbed by the molten steel is minimized.

[0045] S3. After the slag is added and slag is formed, power is supplied at an active power of 9000-12000KW (e.g. 9000KW, 10000KW, 11000KW or 12000KW), and the argon flow rate is controlled at 38-42m 3 / h, add 50-60kg / 120 tons of at least one of aluminum calcium carbon and silicon carbide to the molten steel to foam the slag to a thickness of 20-23cm.

[0046] Taking the Shaoguan Iron and Steel Plant as an example, active power of 11,000 to 12,000 kW corresponds to power transmission in gears 4 and 5 of the 2-6 range. Practice has shown that gear 5 (power 11,000 kW) is the best. If gear 6 (active power 9,000 kW) is selected, the temperature rises by approximately 3.5°C per minute, compared to 8°C per minute in gear 2 (active power 15,000 kW) and 6°C per minute in gear 4 (active power 12,000 kW). This significantly increases the heating time. Nitrogen accumulation in LF furnaces is primarily due to nitrogen absorption during power transmission. If power transmission time is too long, nitrogen absorption increases. If gear 2 (active power 15,000 kW) is selected for heating, although the heating time is shortened, the current and voltage are too high, which can break down the slag layer and cause large amounts of nitrogen absorption in the molten steel.

[0047] The size of the argon flow rate is neither the bigger the better nor the smaller the better. If the argon is too large, the molten steel will be exposed during the tumbling process and will easily absorb nitrogen; if the argon is too small, the heat from the electrode heating will be taken away by the slag layer, resulting in slow heating of the molten steel and increased power transmission time, which not only wastes electricity but also increases the nitrogen absorption time. Even if the arc is well submerged, the molten steel will still absorb nitrogen due to the long power transmission time. The inventor found that it is best to use gear 4 or gear 5 (power 11000~12000KW) to transmit power for 15 minutes and control the argon flow rate to 35~45m 3 / h (e.g. 35m 3 / h、40m 3 / h or 45m 3 / h), the molten steel will absorb 4 to 6 ppm of nitrogen, which is significantly reduced compared with the 10 to 23 ppm of nitrogen absorption in the second gear before the improvement.

[0048] The foaming degree of slag is controlled, that is, the less the better, nor the more the better. If the slag does not foam, or foams less, the slag layer will be thinner. 3 / h (e.g. 35m 3 / h、40m 3 / h or 45m 3 / h) of argon flow, the arc will often break through the slag, causing the molten steel to absorb nitrogen. In order to prevent the slag layer from being broken through, the argon gas should be reduced to 25m 3 / h or less is required, but this will extend the power supply time. For example, using gear 4 will reduce the temperature rise by 1°C per minute. However, if the slag foams too much and the electrode is far away from the molten steel surface, the temperature rise rate will also decrease by more than 1°C. In severe cases, the temperature will not rise at all. To allow the molten steel to approach the electrode, the argon gas must be turned on very high. However, if the argon gas is turned on very high, the chance of the molten steel being exposed is also increased. Therefore, controlling the degree of slag foaming is crucial, and it is directly related to the amount of slag added. According to statistics, according to existing technology, for every 100 kg of slag added, the slag layer thickness increases by 0.9 cm. In this application, the amount of slag added before entering the station (the same as the prior art) plus the amount of slag added after entering the station is 1200-1400 kg / 120 tons of lime, 130-150 kg / 120 tons of fluorite, 68-72 kg / 120 tons of aluminum slag, and 280-320 kg / 120 tons of bauxite, with a total amount of 1678-1942 kg / 120 tons, and a thickness of 15.102-17.478 cm. After slag formation, 40-60 kg / 120 tons of aluminum calcium carbon or silicon carbide is added to the slag to foam the slag, and the slag thickness increases to 20-25 cm. In this way, at an argon flow rate of 35-45 m 3 / h, which can ensure good arc submergence and fast heating speed.

[0049] Use 35~45m 3 / h of argon flow rate. When the slag foams, it can not only reduce the nitrogen absorption of the molten steel, but also take away the free nitrogen in the molten steel through the argon bubbles. At the same time, when the slag foams, the reaction interface in the slag will be increased, and the desulfurization speed will be improved. After operating according to the above process, the power transmission process can desulfurize 0.001% on average every 65 seconds. When the molten steel arrives at the LF furnace, if the sulfur content of the molten steel is below 0.040%, the sulfur can be removed to the qualified range (less than or equal to 0.020%) through the power transmission process. There is no need to turn on high-pressure argon stirring to avoid nitrogen absorption by the molten steel.

[0050] When you hear a gurgling sound when power is supplied, it means that the slag is ready, which is similar to the sound of boiling water. After that, power is supplied at an active power of 9000-12000KW, and the argon flow rate is controlled at 38-42m 3 / h, adding silicon carbide or aluminum calcium carbon to the molten steel causes the slag to foam to a thickness of 20-23cm. The principle is similar to mixing flour with water and then adding baking soda (sodium bicarbonate), which causes the flour to foam. The finer the flour and water are mixed, the better the foaming after adding the baking soda. Similarly, when the slag is added to the molten steel, it is also granular or lumpy. After argon stirring and high-temperature melting at the electrode, the slag becomes increasingly fine, like sand. At this time, adding a binder greatly increases the viscosity of the slag, thereby reducing the loss of argon bubbles from the slag and sticking the argon bubbles to the slag. As a result, the slag density decreases, filling it with argon bubbles, forming a foamy slag, and its volume is greatly increased. This function blocks air from contacting the molten steel, reducing the contact between nitrogen ions ionized by the electrode and the molten steel, thereby reducing nitrogen absorption during the power transmission process. Relatively speaking, the thicker the slag, the less nitrogen the molten steel absorbs. However, the thicker the slag, the slower the temperature rises during the power transmission process, the longer the temperature rise time is, and the more time it takes to absorb nitrogen. Therefore, it is necessary to control the slag thickness to ensure good arc submergence during the power transmission process.

[0051] S4. After slag removal, aluminum wire is fed to control the aluminum content in the molten steel to 0.006-0.015% (e.g. 0.006%, 0.01% or 0.015%), and then continue to supply power for 5-8 minutes (e.g. 5 minutes, 7 minutes or 8 minutes) before sampling. After the sample composition is obtained, the chemical composition of the molten steel is adjusted to the target value according to the composition data. During the adjustment process, the argon flow rate is controlled at 95-105m 3 / h (e.g. 95m 3 / h、100m 3 / h or 105m 3 / h) blowing argon for 2.5 to 3.5 min (e.g., 2.5 min, 3 min or 3.5 min).

[0052] It should be noted that the timing of feeding the aluminum wire can be after slagging and before adding aluminum calcium carbon or silicon carbide, or after adding aluminum calcium carbon or silicon carbide.

[0053] Specifically, the power is turned off during sampling. After sampling, the temperature of the molten steel is used to determine whether to continue to supply power. If the temperature is high and the temperature after the composition adjustment is expected to meet the exit temperature, power can be stopped. If the temperature is low, power needs to be continued. After the sample composition is obtained, the chemical composition of the molten steel is adjusted to the target value according to the composition data. During the adjustment process, the argon flow rate is controlled at 95-105m 3 / h argon purge for 3 minutes. Before nitrogen purge and stirring, test the acid-soluble aluminum content in the steel sample. If it is less than 0.006%, continue to add aluminum wire to adjust the content to within 0.006-0.015%. When the acid-soluble aluminum content of the molten steel is greater than 0.006% and the amount of lime is greater than 750kg, each 100kg of lime can remove 0.003%-0.0034% of the molten steel's sulfur. The 400-900kg of lime added after the molten steel arrives at the station not only reduces nitrogen absorption but also serves as a desulfurization agent. The required sulfur content for A36 steel is less than 0.020%, meaning that the sulfur content of the molten steel is less than or equal to 0.039% when it arrives at the LF furnace. Therefore, there is no need to increase the amount of lime. Before stirring, aluminum should be added according to the acid-soluble aluminum content in the molten steel. This is to maintain the slag's good deoxidation ability. Because it is possible that the acid-soluble aluminum added reacts with the residual oxygen in the molten steel before sampling, the acid-soluble aluminum content in the molten steel will be lower than 0.006% after sampling. Adding the acid-soluble aluminum to 0.006%-0.015% can maintain a good deoxidation state. At this time, the acid-soluble aluminum in the molten steel can combine with nitrogen in the molten steel to form aluminum oxide, thereby reducing the nitrogen content in the molten steel. The speed of nitrogen reduction is related to the amount of argon gas. The larger the amount, the faster it is. Stirring for 2.5 to 3.5 minutes not only speeds up denitrification, but also speeds up desulfurization and removes inclusions in the molten steel. If the stirring time is too short, the removal is not thorough, but if the stirring time is too long, the acid-soluble aluminum in the molten steel will burn out more, reaching a non-denitrification condition, and it will be easy to absorb nitrogen.

[0054] By controlling the aluminum content in molten steel to 0.006-0.015%, the increase in nitrogen can be further reduced. The principle is that the aluminum in the molten steel reacts with the nitrogen in the molten steel to synthesize aluminum nitride, thereby reducing the nitrogen in the molten steel. Therefore, it seems that no nitrogen is increased during the power transmission process.

[0055] Select gear 4 or gear 5 (power 11000~12000KW) to supply power for 15 minutes, and control the argon flow rate to 35~45m 3 / h, feeding aluminum wire until the aluminum content in molten steel is 0.006-0.015%, and it can absorb only 1ppm of nitrogen or even no nitrogen for 15 minutes after power supply.

[0056] S5, then adjust the nitrogen flow rate to 35~45m 3 / h (e.g. 35m 3 / h、40m 3 / h or 45m 3 / h) until the molten steel temperature rises to 1610-1615℃ and then power supply is stopped.

[0057] S6. When the RH furnace cannot be sent due to abnormal conditions, the calcium line is fed into the LF furnace at the end of the treatment, and then soft-blown for 5 to 7 minutes (for example, 5 minutes, 6 minutes or 7 minutes) before leaving the station.

[0058] The timing for feeding calcium wire is 3 minutes after feeding aluminum wire (allowing the aluminum wire to form acid-soluble aluminum in the molten steel before feeding calcium wire), and 1 minute after the end of power supply (after the end of power supply, some ionized nitrogen ions are still near the slag surface and need to be removed by dust removal before feeding calcium wire).

[0059] When feeding the calcium wire, the argon flow rate is controlled at 10-20m 3 / h (e.g. 10m 3 / h、15m 3 / h or 20m 3 / h), after feeding the calcium wire, the argon flow rate is controlled to 5-10m 3 / h(e.g. 5m 3 / h、8m 3 / h or 10m 3 / h) Soft blow until exit.

[0060] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0061] Example 1

[0062] This embodiment is a furnace of 120 tons of molten steel.

[0063] 3 minutes before tapping the converter, open the ladle bottom to blow argon at a flow rate of 60m 3 / h, at 60m 3 / h flow rate, blowing argon for 3 minutes, 3m 3 The space at a height of 0.5 meters at the bottom of the ladle is filled, while the space at a height of 0.1 meters can hold nearly 3 tons of molten steel, and 0.5 meters can hold 15 tons. Since the density of argon is greater than that of air, it can basically ensure that during the steel-making process, there is always a layer of argon in the ladle to protect the molten steel from contact with the air.

[0064] When the molten steel in the ladle reaches approximately 35 tons, ferroaluminum is added. Based on the molecular formula for aluminum oxide, the amount of ferroaluminum to be added is calculated as 2*27:3*16=1:1.25. Based on the oxygen value set before tapping, the amount of ferroaluminum to be added is calculated. Oxygen removal is reduced to approximately 30 ppm. Retaining some oxygen can reduce desulfurization in the molten steel, as both oxygen and sulfur can hinder nitrogen absorption in the molten steel. For example, if the endpoint oxygen level in the molten steel is set at 450 ppm before tapping, and ferroaluminum containing 50% is added, assuming a 70% yield and 30 ppm of oxygen remaining, then 1 kg of ferroaluminum can react with 3.27 ppm of oxygen. The calculation is as follows:

[0065] 1*1.125*0.5*0.7*1000000 / 120000=3.28ppm,

[0066] Amount of aluminum and iron added = (450-30) / 3.2 = 128.04 kg;

[0067] After adding aluminum and iron, add 500kg of lime, 300kg of bauxite, and then add 1800kg of silicon manganese, 60kg of ferrovanadium, and 350kg of high manganese. After adding the alloy, the argon gas is increased from 60m3 before steel tapping. 3 / h is reduced to 25m 3 / h until the steel tapping is completed.

[0068] After tapping, a sample of the molten steel will be taken at the argon station and then transferred to the LF furnace.

[0069] After the molten steel enters the LF furnace, it is electrified at level 11 (active power 5500KW) for slag slagging. The argon flow rate during the slag slagging process is controlled at 55m 3 / h. First, add 150kg of fluorite, then 800kg of lime. The lime is added in batches of 100kg each, with 30s between each batch. When adding the last two batches of lime, mix each batch with 35kg of aluminum slag. The total slag volume is 500kg + 300kg + 150kg + 800kg + 70kg = 1820kg. Each 100kg of slag is approximately 0.9cm thick, so the 1820kg slag is 16.38cm thick.

[0070] Add 9 batches of slag, it takes 270 seconds, and it takes 60-100 seconds to complete the slag. After the slag is completed, change to 5th gear (active power 11000KW) to supply power, and control the argon flow rate to 40m 3 / h, 50kg of silicon carbide is added to the molten steel to foam the slag to a thickness of 22cm.

[0071] After slag removal, aluminum wire is fed in. According to the composition of the sample taken at the argon station, the aluminum content in the molten steel is controlled to 0.010%-0.015% by increasing the acid-soluble aluminum by 0.001% every 5 meters. Then the power is turned off after 7 minutes of continuous power supply for sampling. After sampling, the temperature of the molten steel is detected to be low and the power is continued. After the sample composition is obtained, the chemical composition of the molten steel is adjusted to the target value according to the composition data. During the adjustment process, the argon flow rate is controlled at 100m 3 / h argon was blown for 3 minutes with stirring. Before stirring, the chemical composition of the steel sample was tested for acid-soluble aluminum content, and the test results showed that the aluminum content had reached 0.010%-0.015%.

[0072] After the ingredients are prepared and the steel grade composition requirements are met, the argon flow rate is adjusted to 40m 3 / h power supply until the molten steel temperature rises to 1610-1615℃, then power supply is stopped and the steel is shipped out of the station for RH treatment.

[0073] The nitrogen increase before and after LF refining was tested to be 1-3ppm.

[0074] Example 2

[0075] This embodiment is basically the same as the first embodiment, except that:

[0076] Due to abnormal conditions, when the molten steel temperature rises to 1610-1615℃ and is ready to leave the station, a notice is received that the RH furnace cannot be used for processing. At this time, after the LF furnace is powered on, the 40m 3 / h and keep blowing argon softly (5-15m 3 / h), cooling by blowing argon, when it drops to the target temperature of exiting + 20℃, sampling is performed, and then argon is continued to be blown down to the target temperature of exiting + 10℃, aluminum wire is fed. The target temperature of this steel is 1563℃, so when blowing argon to cool it down to 1573℃, it is calculated by adding 0.001% per 5 meters. According to the chemical composition of the sample, the acid-soluble aluminum is adjusted to 0.020-0.025% (the acid-soluble aluminum range of this steel is 0.015%-0.025%), and 60 meters of calcium wire is fed after 3 minutes of aluminum wire feeding. When feeding the calcium wire, the argon flow rate is controlled at 10-15m 3 / h, after feeding the calcium wire, adjust the argon gas to 5-10m 3 / h soft blowing 6 minutes out of the station. If the temperature is not well controlled and the temperature is insufficient, it is necessary to supply power to increase the temperature before feeding calcium money. The calcium wire will be fed 1 minute after the power is supplied. The purpose is to allow the dust removal system to remove the ions generated when the power was just supplied.

[0077] The nitrogen increase before and after refining was tested to be 3-6ppm.

[0078] Comparative Example 1

[0079] This comparative example is basically the same as Example 1, except that after slag melting is completed, power is transmitted at power transmission gear 2 (active power 15000KW) according to the prior art.

[0080] The nitrogen increase before and after refining was tested to be 5-9ppm.

[0081] During the power transmission process, the arc zone ionizes nitrogen in the air into nitrogen atoms, which then enter the molten steel and cause it to absorb nitrogen. The larger the gear, the stronger the arc's penetrating power and the more nitrogen it absorbs.

[0082] Comparative Example 2

[0083] This comparative example is basically the same as Example 1, except that the argon flow rate is controlled to 100m after slag melting is completed. 3 / h.

[0084] The nitrogen increase before and after refining was tested to be 18-25ppm.

[0085] The size of the argon blowing flow rate directly affects the size of the exposed molten steel. The larger the argon blowing flow rate, the larger the argon bubbles produced, the larger the bright circle formed by breaking through the slag surface, the more molten steel is exposed, and the more nitrogen is absorbed.

[0086] Comparative Example 3

[0087] This comparative example is basically the same as Example 1, except that after the slag material is added and the slag is melted, no aluminum wire feeding operation is performed.

[0088] The nitrogen addition before and after refining was 6-10ppm. This method was used before we discovered that aluminum feeding could remove nitrogen.

[0089] Before slag is slag-formed in the LF furnace, it's still lumpy or granular, with large gaps between them. This makes it easy for the molten steel to absorb nitrogen from the arc zone during the power supply process. Consequently, oxygen isn't completely removed during tapping from the converter, leaving some oxygen in the slag. This oxygen and sulfur hinder nitrogen absorption by the molten steel. However, after slag formation through power supply and argon purge, if aluminum wire is not added for deoxidation after slag formation, the slag won't achieve adequate deoxidation. This not only impacts desulfurization but also increases refining and inclusion removal time. Increased refining time inevitably prolongs power supply, further increasing the time it takes for the molten steel to absorb nitrogen during power supply. However, adding aluminum wire not only accelerates deoxidation and desulfurization, reducing refining time, but also allows aluminum to combine with nitrogen in the molten steel, thereby reducing the nitrogen content.

[0090] Comparative Example 4

[0091] This comparative example is basically the same as Example 1, except that the amount of slag added after entering the station is adjusted to 400 kg of lime and 60 kg of fluorite, and the amount of aluminum slag remains unchanged.

[0092] The nitrogen increase before and after refining was tested to be 10-15ppm.

[0093] The technical standard for this steel grade specifies a lime addition rate of 400-900kg for the LF furnace, with fluorite adjusted based on the fluidity of the slag. However, our experiments revealed that nitrogen absorption during the refining process is related to the amount of slag. The amount of lime added ranges from 400-750kg. The greater the amount added, the less nitrogen absorption occurs. However, above 750kg, nitrogen absorption remains essentially stable and does not decrease, so we set the lime addition rate to be greater than 750kg. But why not simply add 1 ton or more? On the one hand, slag consumption will increase costs. On the other hand, the increased thickness of the slag will absorb more heat, increasing power delivery time and the time it takes for the molten steel to absorb nitrogen. Therefore, ensuring that the lime addition rate is greater than 750kg is sufficient. Considering the potential for weighing deviations in practice, we add 800kg. The ratio of lime to fluorite has an impact on the nitrogen absorption of molten steel. The worse the fluidity, the more serious the nitrogen absorption in the arc zone. Therefore, in practice, we have repeatedly explored the optimal ratio. On the basis of adding 70 kg of aluminum slag and feeding aluminum wire after slag melting, lime: fluorite = 800:130-140 will be better. If less fluorite is added, the fluidity of the slag will be poor and the nitrogen absorption will be more, but if too much is added, the slag will be converted into glass slag, and the viscosity of the slag will be reduced, which will affect the foaming property of the slag and the degree of foaming will be greatly reduced.

[0094] Comparison of the nitrogen addition amounts in the above examples and comparative examples shows that the nitrogen addition amounts in the examples of the present application are significantly less than those in the comparative examples. Comparison of Comparative Example 1 with the examples shows that adjusting the power supply to an appropriate range after slagging can reduce the nitrogen addition amount; Comparative Example 2 with the examples shows that adjusting the argon flow rate to an appropriate range is beneficial for reducing nitrogen addition; Comparative Example 3 with the examples shows that feeding aluminum wire after slagging to keep the aluminum content in the molten steel within an appropriate range is beneficial for reducing nitrogen addition; Comparative Example 4 with the examples shows that adjusting the slag addition amount according to the present application solution is beneficial for reducing nitrogen addition.

[0095] In summary, in the refining method provided in the embodiment of the present application, after the molten steel arrives at the LF furnace, the amount of slag is adjusted. After the slag amount is adjusted, on the one hand, it can ensure that the nitrogen increase is reduced while avoiding too slow heating. On the other hand, the above-mentioned slag amount can also achieve the desulfurization process without turning on high-pressure argon stirring, thereby reducing the risk of molten steel exposure. After the slag addition is completed, power is supplied at a power of 9000KW to 12000KW to reduce the current breakdown of the slag layer, and is more conducive to reducing nitrogen absorption by the molten steel. After the slag is foamed, aluminum wire is fed to make the aluminum content between 0.006 and 0.015%, and argon is turned on when the molten steel is prepared, which can further reduce nitrogen increase. Therefore, the LF furnace refining method for A36 steel with less nitrogen increase provided in the embodiment of the present application has less nitrogen increase during the refining process, and the nitrogen increase rate after refining is 1-3ppm, which is significantly improved compared to the existing nitrogen increase of 20-30ppm.

[0096] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A LF furnace refining method for A36 steel with less nitrogen addition, characterized in that: include: After the molten steel enters the station, it is powered by 5500KW-8500KW of active power to slag. The argon flow rate during the slag-forming process is controlled at 50~60 m 3 / h, first add 130~150kg / 120 tons of fluorite, then add 400~900 kg / 120 tons of lime. The lime is added in batches, 70~120kg / 120 tons each batch. When adding the last two batches of lime, mix 30~40kg of aluminum slag into each batch; After the slag is added and the slag is melted, the power is supplied at an active power of 9000KW~12000KW, and the argon flow rate is controlled at 35~45m 3 / h, adding 40-60kg / 120 tons of at least one of aluminum calcium carbon and silicon carbide to the molten steel to foam the slag to a thickness of 20-25cm; After slag melting, aluminum wire is fed in to control the aluminum content in the molten steel to 0.006~0.015%. Then, the power is continued to be supplied for 5~8 minutes before sampling. After the sample composition is obtained, the chemical composition of the molten steel is adjusted to the target value according to the composition data. During the adjustment process, the argon flow rate is controlled at 95~105m 3 / h argon blowing 2.5~3.5min; Then adjust the argon flow rate to 35~45m 3 / h, until the temperature of the molten steel rises to 1610~1615℃ and then the power supply is stopped; Before the molten steel enters the station and when the converter is tapping, when the amount of molten steel in the ladle reaches 30~40 tons, aluminum iron is added first, then slag, and then alloy. At the same time, the argon gas is increased from 55~65 m3 before tapping. 3 / h is reduced to 20~30 m 3 / h.

2. The refining method according to claim 1, characterized in that Before the molten steel enters the station, the carbon content of the final molten steel in the converter is controlled at 0.08~0.12%.

3. The refining method according to claim 1, characterized in that Before the molten steel enters the station, the sulfur content of the final molten steel in the converter is controlled at 0.020~0.45%.

4. The refining method according to claim 1, characterized in that The total amount of slag added before and after entering the station is: lime 900~1400kg / 120 tons, fluorite 130~150kg / 120 tons, aluminum slag 65~80 kg / 120 tons, and bauxite 280~320 kg / 120 tons.

5. The refining method according to claim 1, characterized in that After the molten steel enters the station, lime is added in batches, with an interval of 25 to 35 seconds between each batch.

6. The refining method according to claim 1, characterized in that When the RH furnace cannot be used due to abnormal conditions, calcium wire is fed into the LF furnace at the end of the treatment, and the argon flow rate is adjusted to 5~10 m 3 / h soft blowing for 5~7 minutes to exit the station.

7. The refining method according to claim 6, characterized in that The timing for feeding calcium wire is 3 minutes after feeding aluminum wire and 1 minute after the power supply is completed.

8. The refining method according to claim 6, characterized in that When feeding the calcium wire, the argon flow rate is controlled at 10~20 m 3 / h.