A method for rapid desulfurization of low-sulfur steel at low iron-to-steel ratio at low temperature

Abstract

The present invention discloses a method for low-temperature rapid desulfurization of low-sulfur steel at a low iron-to-steel ratio, and belongs to the technical field of steel smelting. The desulfurization method mainly includes an early deoxidation treatment and two consecutive desulfurization treatments in the later stage. During the early deoxidation treatment, slag washing and deep deoxidation treatment are carried out by adding aluminum iron, lime and bauxite, so as to facilitate the later refining and desulfurization. In addition, the slag making operation of continuous foaming is added. During the two consecutive desulfurization treatments in the later stage, the power transmission gear and time are controlled to cooperate with argon gas, and the desulfurization temperature is not lower than 1540°C for precise desulfurization. Using the desulfurization method provided by the present invention, as long as the temperature of the molten steel at the station is not lower than 1515°C, the general desulfurization time can be controlled within 12-16 minutes, and the desulfurization rate of the molten steel can reach 75%-81%, which greatly reduces the desulfurization temperature and cost and shortens the desulfurization time.

Description

Technical Field

[0001] The invention relates to the technical field of steel smelting, and in particular to a method for low-temperature rapid desulfurization of low-sulfur steel with a low iron-to-steel ratio. Background Art

[0002] Q345T slab steel is a low-sulfur steel, and the steel grade range requires sulfur to be less than 0.007%. Originally, this steel grade was aluminum-containing steel, and the aluminum requirement range was 0.015-0.03%. Now it has been changed to titanium instead of aluminum, and there is no requirement for aluminum, that is, it can be present or not.

[0003] Due to the cancellation of the requirement for aluminum, the LF furnace refining method has also changed. In the past, aluminum wire would be punched before taking the first and second samples to control the aluminum at 0.03-0.04%. Now, aluminum wire is seldom punched during the process unless there are abnormal situations such as slag unloading from the converter or going to the RH washing tank.

[0004] Due to the lack of aluminum wire, the desulfurization speed of the LF furnace is relatively slow. In the past, it took 26-28 minutes to remove sulfur below 0.007%. Later, after technical breakthroughs, it was reduced to 18-22 minutes. Now, under the requirement of reducing the iron-steel ratio, a faster desulfurization speed is needed to add more steel bar heads during the refining process. Because steel bar heads contain sulfur and oxygen, adding steel bar heads before removing sulfur below 0.007% will oxidize the refining slag, reduce the desulfurization capacity, and make desulfurization slower. However, after removing sulfur below 0.007%, adding steel bar heads again, although desulfurization cannot be achieved or very little desulfurization is achieved, after adding steel bar heads into the molten steel, although the slag will be worse, it will basically not increase sulfur. It is only necessary to add some deoxidizer after adding the last batch of steel bar heads to ensure the stability of sulfur in the molten steel. For example, when taking the first sample, the sulfur content of molten steel drops to 0.006%. After taking the first sample, 3-5 tons of steel bar heads are added, and the sulfur content is still 0.006% or 0.007%. After adding 20 kg of aluminum slag, the sulfur content can be reduced to and stabilized at 0.006%.

[0005] Therefore, the earlier the sulfur is removed, the longer the time for adding the steel bar head will be, and the lower the iron-steel ratio will be.

[0006] In view of this, it is necessary to provide a method for low-temperature rapid desulfurization of low-sulfur steel with low iron-to-steel ratio. Summary of the invention

[0007] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to propose a method for low-temperature rapid desulfurization of low-sulfur steel with a low iron-to-steel ratio.

[0008] The present invention is achieved in that:

[0009] The present invention provides a method for low-sulfur steel rapid desulfurization at low temperature. When the initial sulfur content of the low-sulfur steel is ≤0.035%, the desulfurization method comprises the following steps:

[0010] Converter tapping: During the converter tapping process, ferroaluminum, lime and bauxite are added for slag washing and deep deoxidation treatment;

[0011] Primary desulfurization: After the molten steel arrives at the LF furnace, argon gas is blown at a rate of 100 m3 / h for 60-90 seconds. After observing on-site that the slag surface is completely broken by the molten steel, the argon gas flow rate is adjusted to 50-60 m3 / h. A small gear potential is selected for power transmission. After arcing, slag is added. After the slag is melted, the electrode is lifted and the aluminum wire is fed. Then, a large gear is used for power transmission to raise the temperature of the molten steel to not less than 1540°C.

[0012] Secondary desulfurization: After the molten steel temperature reaches 1540℃, adjust the power supply gear to a small gear potential and stir while blowing argon.

[0013] The present invention has the following beneficial effects:

[0014] The present invention provides a method for low-temperature rapid desulfurization of low-sulfur steel at a low iron-steel ratio. The desulfurization method mainly includes early slag making and deep deoxidation treatment and subsequent primary desulfurization and secondary desulfurization. Early slag making and deep deoxidation improve the subsequent process of refining, so that the refining slag forming speed is fast. By controlling the power transmission gear and time during the primary desulfurization process, the desulfurization amount of the primary desulfurization is obtained, and at the end of the primary desulfurization, the temperature of the molten steel is controlled to be not less than 1540°C, and the secondary desulfurization is carried out under this low temperature condition. The desulfurization method provided by the present invention can greatly reduce the desulfurization cost and shorten the desulfurization time. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0016] The low-sulfur steel produced by Shaoguan Iron and Steel Plant includes grades of steel such as Q460C, Q420C, Q345T, Q345C and HQ435T. The purpose of the present invention is to provide a method for low-temperature rapid desulfurization of low-sulfur steel with a low iron-to-steel ratio.

[0017] In order to achieve the above-mentioned purpose of the present invention, the following technical scheme is specially adopted.

[0018] The embodiment of the present invention provides a method for low-temperature rapid desulfurization of low-sulfur steel at a low iron-to-steel ratio. When the initial sulfur content of the low-sulfur steel is ≤0.035%, the desulfurization method comprises the following steps:

[0019] Converter tapping: During the converter tapping process, ferroaluminum, lime and bauxite are added for slag washing and deep deoxidation treatment;

[0020] Primary desulfurization: After the molten steel arrives at the LF furnace, argon gas is blown at a rate of 100 m3 / h for 60-90 seconds. After observing on-site that the slag surface is completely broken by the molten steel, the argon gas flow rate is adjusted to 50-60 m3 / h. A small gear potential is selected for power transmission. After arcing, slag is added. After the slag is completely melted, the electrode is lifted, aluminum wire is fed, and then a large gear is switched to power transmission to heat the molten steel to a temperature not lower than 1540°C.

[0021] Secondary desulfurization: After the molten steel temperature reaches 1540℃, adjust the power supply gear to a low gear and stir while blowing argon.

[0022] The iron-steel ratio refers to the ratio of the amount of molten iron put into the steelmaking process to the steel output. Reducing the iron-steel ratio helps to maximize the steel output under the condition of limited molten iron resources, thereby maximizing the benefits. In order to pursue the maximization of benefits, the relevant technology adopts various means to reduce the iron-steel ratio and increase the amount of scrap steel added. However, 3 tons of scrap steel are added to each furnace, and the temperature is reduced by 45°C, so it is difficult to have the opportunity to desulfurize under normal high temperature conditions. In order to achieve low-temperature rapid desulfurization of low-sulfur steel under low iron-steel ratio, the inventor has carried out research and development, and provided a method for low-temperature rapid desulfurization of low-sulfur steel under low iron-steel ratio. The method is suitable for low-sulfur steel with an initial sulfur content of ≤0.035%. The desulfurization method mainly includes early slag making and deep deoxidation treatment and subsequent primary desulfurization and secondary desulfurization. Early slag making and deep deoxidation improve the subsequent process of refining, so that the refining slag speed is fast. By controlling the power transmission gear and time in the primary desulfurization process, the desulfurization amount of the primary desulfurization is obtained, and at the end of the primary desulfurization, the temperature of the molten steel is controlled to be not less than 1540°C, and secondary desulfurization is carried out under this low temperature condition. The current desulfurization temperature of slab steel is generally around 1600°C. Compared with the commonly used desulfurization methods, the desulfurization method provided in the embodiment of the present invention performs desulfurization at a lower desulfurization temperature, which can not only achieve the purpose of precise desulfurization, but also shorten the desulfurization time.

[0023] In an optional implementation, the small-gear power transmission gear is 8-11 gears, and the large-gear power transmission gear is 2-4 gears.

[0024] In an optional embodiment, 90-110 kg of ferroaluminum / 120t of molten steel is added during the steelmaking process of the converter, and then 490-510 kg of lime / 120t of molten steel and 290-310 kg of bauxite / 120t of molten steel are added for slag making and deep deoxidation treatment. The carbon content of the finished low-sulfur steel produced by our factory is controlled to be 0.14%-0.18%, so the carbon content of the converter terminal is generally controlled to be 0.06%-0.11% for steelmaking. When the carbon is greater than 0.06%, the oxygen content in the molten steel will be relatively low, calculated based on the carbon-oxygen product, that is, carbon multiplied by oxygen is a constant, and the average value of the factory is 0.3. Then, when the carbon is 0.06%, the oxygen in the molten steel is 0.3 / 0.0006=500ppm, and 100 kg of ferroaluminum (containing 90% aluminum) is melted in 120 tons of molten steel, and the aluminum content = 100*1000 000 / 120000*90%=833ppm*90%=749.7ppm, in the chemical formula Al2O3, aluminum: oxygen=2*27:3*16=54:48=9:8=1.125, so it can be explained that even if the carbon is 0.06%, the oxygen in the steel is 500ppm, and the required aluminum is 500*1.125=562.5ppm. Adding 100 kg of aluminum can completely react with the oxygen in the molten steel, and there is a surplus. Even if the aluminum recovery rate is only 80%, it can still react completely with the oxygen in the steel. Therefore, the design of this aluminum addition amount is to take into account the removal of all oxygen in the molten steel during the precipitation and deoxidation process of the molten steel, and considering that slag may be discharged when the converter is tapped, so it is necessary to reserve more surplus aluminum to react with the oxygen in the slag. If less aluminum is added, the desulfurization coefficient in the molten steel will be reduced. The higher the aluminum content in the steel, the higher the desulfurization coefficient will be, and the faster the desulfurization speed will be. However, if more is added regardless of the cost, the aluminum oxide content in the steel will also increase, the inclusions in the molten steel will increase, and the quality of the molten steel will be reduced. After adding aluminum, lime and bauxite are added to help the refining furnace slag in advance, which can speed up the slag formation time and desulfurization time. But why not add more slag? It is because the ability to melt slag is limited during the steelmaking process. If too much is added, the slag will not be melted and the slag will agglomerate. The more it is added, the larger the agglomeration will be. This will not only fail to form slag, but also reduce the slag formation speed and the desulfurization speed. Therefore, determining this slag amount and ratio is a more reasonable value explored in practical work.

[0025] In an optional embodiment, during the primary desulfurization process, fluorite is first added after arcing, and then lime and aluminum slag are added;

[0026] Preferably, the amount of lime added is calculated as follows: (initial sulfur content of molten steel entering the station - target sulfur content)*1000 / 0.0003, and the mass ratio of lime to fluorite is 580-610:90-110, more preferably 600:105;

[0027] Preferably, after arcing, when adding slag in each batch, first add 100-150 kg fluorite / 120 t molten steel, then add 95-105 kg lime / 120 t molten steel and 18-20 kg aluminum slag / 120 t molten steel at the same time;

[0028] More preferably, the interval between adding each batch of slag is 32-35s;

[0029] More preferably, during a desulfurization process, a small gear potential is selected for power transmission, slag is added after arcing, and after 180-300 seconds when the slag is completely vaporized, the electrode is lifted and 60-80 meters of aluminum wire is fed to increase the acid-soluble aluminum in the steel by 0.012%-0.016%, and then a large gear potential is used for power transmission.

[0030] When adding slag at arc starting, the amount of slag added must be accurately calculated based on the desulfurization requirements. For example, the initial sulfur content of molten steel is 0.024%, and it needs to be desulfurized to 0.007%. The desulfurization amount = 0.024% - 0.007 = 0.017%, and the amount of lime added = 0.017% * 1000 / 0.0003 = 566 kg. If the amount of lime is too much, fluorite must also keep up, otherwise the slag will be thick, with poor fluidity, and desulfurization will slow down. If too little lime is added, the slag will become glassy and the desulfurization will also be slow.

[0031] The speed of adding lime and aluminum slag is the moment when each batch of molten steel is added, that is, when you see aluminum slag added to the molten steel, you start adding the next batch until the slag is added. The slag adding speed here is 25 seconds, that is, the time for the slag to go from the vibrator to the belt and then to the molten steel is 25 seconds, so the slag adding speed for each batch is 35 seconds, and it takes 10 seconds to shake 100 kg of lime from the slag bin.

[0032] During the process of power transmission and slag material addition, at 180-300s, lift the electrode and feed 60-80 meters of aluminum wire. Every 5 meters of aluminum wire increases the acid-soluble aluminum in the steel by 0.001%, and 60-80 meters increases the acid-soluble aluminum by 0.012%-0.016%, and then change to a larger gear to transmit power. Among them, the aluminum wire is used to speed up the desulfurization speed. If the aluminum wire is not fed enough, when the acid-soluble aluminum content in the molten steel is lower than 0.06%, the molten steel will not be deoxidized enough and the desulfurization will be slow. That is, the original 100 kg of lime can remove 0.003% of sulfur, but now it can only remove 0.0025%. If it is fed too much, the aluminum oxide in the slag will be high, making the slag glassy, ​​and the calcium oxide content in the lime will be reduced, and the desulfurization capacity will decrease, so more lime needs to be added. Without considering the cost, feeding more aluminum wire and adding more lime will definitely be beneficial to speeding up desulfurization. When producing ultra-low sulfur steel, that is, steel with a sulfur requirement of less than 0.002%, it is indeed necessary to feed more aluminum wire and add more lime, which is another control method. This case considers the production of low-sulfur steel, and the sulfur content can be less than 0.007%, so there is no need to do so to meet the requirements, which is also based on cost considerations.

[0033] From the power transmission process to the electrode lifting process, the slag adding speed remains unchanged, because if the slag is added too quickly, the slag will not be fine enough and the desulfurization will slow down. If it is added too slowly, the slag foaming time will be shortened and the desulfurization will also slow down. Therefore, it is necessary to accurately control the slag adding speed in order to keep the slag in a foaming state.

[0034] In an optional implementation manner, the desulfurization amount of one desulfurization operation = (small-gear power transmission time + large-gear power transmission time) × desulfurization efficiency.

[0035] In an optional embodiment, the calculation method of the high-speed power transmission time is (molten steel target temperature - station entry temperature + slag cooling temperature - low-speed power transmission heating temperature) / high-speed power transmission heating temperature per minute, where the molten steel target temperature is not lower than 1540°C.

[0036] In an optional embodiment, the desulfurization time of the secondary desulfurization is calculated as (initial sulfur content of the molten steel entering the station - target sulfur content - desulfurization amount of the primary desulfurization) / desulfurization efficiency.

[0037] In an optional embodiment, during the power transmission process, the desulfurization efficiency under argon blowing conditions is: argon flow rate is 50-60 cubic meters / hour, desulfurization rate is 0.001% per minute, and argon flow rate is 100 cubic meters / hour, desulfurization rate is 0.003% per minute.

[0038] In an optional embodiment, the method further includes: after power is supplied, lifting the electrode, adjusting the argon gas flow rate to 10-30 cubic meters per hour, and performing temperature measurement and sampling.

[0039] In an optional embodiment, when the temperature of the molten steel entering the station is not lower than 1515°C, the sulfur content of the low-sulfur steel is 0.003%-0.007% after desulfurization using a desulfurization method.

[0040] In an optional embodiment, the desulfurization time of the low-sulfur steel using the desulfurization method is 12-16 minutes.

[0041] As described above, the embodiment of the present invention provides a method for low-temperature rapid desulfurization of low-sulfur steel. By adopting the diffusion deoxidation + precipitation deoxidation method, combined with the continuous foaming slag making operation, and controlling the power supply gear and time in coordination with argon gas, as long as the temperature of the molten steel arriving at the station is not lower than 1515°C, the general desulfurization time can be controlled within 12-16 minutes, and the molten steel desulfurization rate can reach 75%-81%.

[0042] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0043] Example 1

[0044] A method for low-sulfur steel rapid desulfurization at low temperature, comprising the following steps:

[0045] Using Q345T slab steel, the converter end point carbon is 0.067%, the initial sulfur content of the molten steel entering the station is 0.029%, the target sulfur content is 0.007%, the molten steel entering the station temperature is 1515℃, and the molten steel temperature at the end point of the primary desulfurization is 1540℃, the desulfurization method includes the following steps:

[0046] 1. During the steelmaking process of the converter, 101 kg of aluminum iron / 120 t of molten steel is added, followed by 502 kg of lime / 120 t of molten steel and 301 kg of bauxite / 120 t of molten steel.

[0047] 2. After the molten steel arrives at the LF furnace, start blowing argon at a rate of 100 cubic meters per hour for 67 seconds. After observing on-site that the slag surface is completely broken by the molten steel, adjust the rate to 50-60 cubic meters per hour, select the power supply gear at gear 8, supply power, and start adding slag after arcing.

[0048] 3. Calculate the amount of slag added: lime added = (0.029% - 0.007%) * 1000 / 0.0003 = 733 kg. According to lime: fluorite = 600: 105, the amount of fluorite added is calculated to be 128 kg. When adding slag, first add 128 kg of fluorite, and then add lime + aluminum slag in 7 batches, adding 90-105 kg of lime and 18-20 kg of aluminum slag to each batch.

[0049] 4. During the process of supplying power and adding slag, at 180 seconds, lift the electrode and feed 70 meters of aluminum wire.

[0050] 5. After the molten steel arrives at the LF furnace, the temperature is measured. While executing the previous operation, according to the temperature calculation, the 2nd gear is switched to power transmission. It is estimated that the temperature of the molten steel rises to above 1540°C (for example, the temperature is 1515°C when entering the station, and the temperature is reduced by about 2.8°C for every 100 kg of slag, then 733 kg of lime + 132 kg of aluminum slag + 128 kg of fluorite = 993 kg, and the temperature is reduced by 993 / 100*2.8 = 27.8°C. The 8th gear power transmission can increase the temperature by 3.3°C per minute, and the temperature rises by 10°C in 180 seconds. The 2nd gear power transmission can increase the temperature by 8°C per minute, so the time required for the 2nd gear power transmission to increase the temperature to 1540°C = (1540-1515+27.8-10) / 8 = 321 seconds). With a desulfurization rate of 0.001% per minute, the desulfurization amount is calculated to be 321 / 60*0.001% = 0.00535%.

[0051] When the expected temperature is greater than 1540℃, switch to 8th gear for power supply and change the argon gas to 100 cubic meters / hour. The time for blowing argon while supplying power = (initial sulfur content of molten steel entering the station - target sulfur content - desulfurization amount of one desulfurization) / desulfurization efficiency = (0.029% - 0.007% - 0.00535%) / 0.003% = 0.01665% / 0.003% = 5.55 minutes, i.e. 5.55*60 = 333 seconds.

[0052] Total desulfurization time = 67 + 180 + 321 + 333 = 901 seconds = 15 minutes.

[0053] 6. After power supply is completed, lift the electrode, adjust the argon gas to 10-30 cubic meters per hour, and measure the temperature and take samples. The sulfur content of the molten steel is 0.0069%, which meets the target.

[0054] Example 2: For Example 1, other operations remain unchanged, only the power transmission time of the second gear is changed

[0055] Slag is added from the first second of power supply, 25-35 seconds for each batch, and 35 seconds is taken as 8 batches (the first batch of fluorite, followed by 7 batches of lime + aluminum slag). It takes 8*35=280 seconds. After adding the slag, it is necessary to use gear 2 to supply power for 250 seconds or more. Even if the temperature of the molten steel arriving at the station is high, it takes this long. If the temperature of the molten steel arriving at the station is very low, the power supply time must be increased to ensure that the power reaches above 1540 degrees Celsius before switching to gear 8.

[0056] In the early stage, the power supply time of 8th gear is 180 seconds, and the power supply time of 2th gear is reduced. For example, after only 100 seconds, it is immediately changed to 8th gear and 100 cubic meters / hour of argon is used to supply power and stir at the same time. At this time, not only the slag is not melted well, but also the foaming degree is not enough. The added lime is still in block form and is converted into granular form. It does not have enough time to be turned into powder. The slag will not foam, which will affect the desulfurization. Even if the power supply and stirring time of 8th gear is extended, such a good effect cannot be achieved. After such operation, the final sulfur content will be 0.009%, because the argon is turned on when the lime is not melted, or the argon is turned on when the temperature is not enough to 1540, a high-melting-point dicalcium aluminate will form on the surface of the lime block, which will hinder the melting of the lime or prolong the melting time of the lime.

[0057] Example 3, with respect to Example 1, other operations remain unchanged, only the time of turning on argon gas at the station is changed. If it is too short, the slag shell is not completely broken, the surface of the molten steel is not wetted by the molten steel, and there is still a crust. Then, when power is supplied, firstly, the electrode is easy to break, because the electrode is very brittle, and it will break if it hits hard, and secondly, the slag is not wetted by the molten steel, and the electrode will directly arc on the slag shell, and the arc light will easily burn through the furnace cover, and thirdly, the slag added during power supply is not easy to enter the molten steel, and it is easy to form on the slag shell, reducing the slagging speed.

[0058] If the argon gas is not turned on to break the slag shell when entering the station, then after other similar operations, the final sulfur content will be 0.010%.

[0059] Example 4, with respect to Example 1, other operations remain unchanged, only the order and quantity of adding materials are changed.

[0060] If aluminum slag is added first, then lime, and finally fluorite, a large amount of aluminum slag will be burned and the slag will not be deoxidized enough. If lime is added first and fluorite or aluminum slag is added later, the lime added in the early stage will easily generate calcium aluminate with a high melting point, which will reduce the slagging rate. Therefore, fluorite needs to be added first to promote the melting of the slag added to the converter. The role of fluorite is to lower the melting point of lime and speed up the melting of lime. Lime and aluminum slag are added only after the slag added to the converter is melted. The difference between adding lime and aluminum slag together and separately is the foaming time and degree. If they are added separately, the foaming time is the time when the aluminum slag is added, and it will be gone after a few tens of seconds. If they are added separately, the foaming time can be maintained all the time. The foaming of slag is directly related to desulfurization, because when the slag is not foaming, the reaction volume or interface of the steel slag is assumed to be 1, then after the slag foams, the volume increases, and the reaction interface must be greater than 1. The melting rate of lime + aluminum slag in steel is relatively fast, because once it is added, the slag will foam, which naturally increases the contact area of ​​the electrode to the molten slag, generally more than 20 seconds is enough.

[0061] Therefore, if the order of adding materials is changed, or if the materials are not added in batches for multiple times, the slagging speed and foaming time will be reduced, and the final sulfur content will be 0.012%.

[0062] Comparative Example 1

[0063] The steps are similar to those in Example 1, except that the terminal temperature of the first desulfurization is 1590°C, so the power transmission time = (1590-1515+27.8-10) / 8 = 11.6 minutes = 696 seconds, the desulfurization amount is 11.6*0.001% = 0.0116%, and the secondary desulfurization time is (0.029%-0.0116%-0.007%) / 0.003% = 0.0104% / 0.003% = 3.46 minutes = 208 seconds.

[0064] The total time = 67 + 180 + 696 + 208 = 1151 seconds = 19.1 minutes.

[0065] Comparative Example 2

[0066] The steps are similar to those in Example 1, except that the terminal temperature of the first desulfurization is 1580°C, so the power transmission time = (1580-1515+27.8-10) / 8 = 10.35 minutes = 621 seconds, the desulfurization amount is 10.35*0.001% = 0.01035%, and the secondary desulfurization time is (0.029%-0.01035%-0.007%) / 0.003% = 0.01165% / 0.003% = 3.88 minutes = 233 seconds.

[0067] The total time = 67 + 180 + 621 + 233 = 1101 seconds = 18.35 minutes.

[0068] Comparative Example 3

[0069] The steps are similar to those in Example 1, except that: the terminal temperature of the first desulfurization is 1560°C, then the power transmission time = (1560-1515+27.8-10) / 8 = 7.85 minutes = 471 seconds, the desulfurization amount is 7.85*0.001% = 0.00785%, and the secondary desulfurization time is (0.029%-0.00785%-0.007%) / 0.003% = 0.01415% / 0.003% = 4.71 minutes = 283 seconds.

[0070] The total time = 67 + 180 + 471 + 283 = 1001 seconds = 16.68 minutes.

[0071] Comparative Example 4

[0072] The steps are similar to those in Example 1, except that during the steel-making process of the converter, the deoxidizer is 50 kg of aluminum iron added, which will result in incomplete deoxygenation in the molten steel. After the molten steel reaches the refining furnace, the oxygen in the steel will limit the desulfurization reaction. The aluminum slag added during the refining process will preferentially react with the oxygen in the steel and consume a portion of it. Therefore, the amount used to improve the desulfurization distribution coefficient is less, and the desulfurization amount per 100 kg of lime will not reach 0.003%, and the final sulfur content is 0.017%.

[0073] In summary, the embodiment of the present invention provides a method for low-temperature rapid desulfurization of low-sulfur steel at a low iron-steel ratio. The desulfurization method mainly includes early slag making and deep deoxidation treatment and subsequent primary desulfurization and secondary desulfurization. Early slag making and deep deoxidation improve the subsequent process of refining, making the refining slag speed fast. By controlling the power transmission gear and time during the primary desulfurization process, the desulfurization amount of the primary desulfurization is obtained, and at the end of the primary desulfurization, the temperature of the molten steel is not lower than 1540°C, and secondary desulfurization is carried out under this low temperature condition. This method of diffusion deoxidation + precipitation deoxidation is adopted, coupled with the continuous foaming slag making operation, and the control of the power transmission gear and time and the coordination with argon gas, as long as the temperature of the molten steel at the station is not lower than 1515°C, the general desulfurization time can be controlled within 12-16 minutes, and the desulfurization rate of the molten steel can reach 75%-81%.

[0074] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for rapid desulfurization of low sulfur steel at low temperature with low iron to steel ratio, characterized in that: When the initial sulfur content of the low-sulfur steel is ≤0.035%, the desulfurization method comprises the following steps: Converter tapping: During the converter tapping process, ferroaluminum, lime and bauxite are added for slag washing and deep deoxidation treatment; Primary desulfurization: After the molten steel arrives at the LF furnace, the temperature of the molten steel entering the station is 1515℃. Start blowing argon at a rate of 100 cubic meters per hour for 60-90 seconds. After observing on-site that the slag surface is completely broken by the molten steel, adjust the argon flow rate to 50-60 cubic meters per hour. Select a small gear potential for power transmission. Start adding slag after arcing. After the slag is melted, lift the electrode, feed the aluminum wire, and then switch to a large gear for power transmission to heat the molten steel to a temperature not lower than 1540℃. Secondary desulfurization: After the molten steel temperature reaches 1540℃, adjust the power transmission gear to a small gear, and stir while blowing argon; Among them: During the steelmaking process of the converter, 90-110 kg of aluminum iron / 120 t of molten steel is added, followed by 490-510 kg of lime / 120 t of molten steel and 290-310 kg of bauxite / 120 t of molten steel for deep deoxidation treatment; In the primary desulfurization process, fluorite is added first after arcing, and then lime and aluminum slag are added. The calculation method of the amount of lime added is: (initial sulfur content of molten steel entering the station - target sulfur content) * 1000 / 0.0003, and the mass ratio of the lime to the fluorite is 580-610:90-110; Total desulfurization amount = desulfurization amount of primary desulfurization + desulfurization amount of secondary desulfurization, desulfurization amount of primary desulfurization = (power transmission time of small gear + power transmission time of large gear) × desulfurization efficiency, desulfurization amount of secondary desulfurization = desulfurization time of secondary desulfurization × desulfurization efficiency; The calculation method of the high-speed power transmission time is (molten steel target temperature - station entry temperature + slag cooling temperature - low-speed power transmission heating temperature) / high-speed power transmission heating temperature per minute, where the molten steel target temperature is not less than 1540°C; The calculation method of the desulfurization time of secondary desulfurization is (initial sulfur content of molten steel entering the station - target sulfur content - desulfurization amount of primary desulfurization) / desulfurization efficiency.

2. The method according to claim 1, characterized in that: After arcing, when adding slag in each batch, first add 100-150 kg fluorite / 120t molten steel, and then add 95-105 kg lime / 120t molten steel and 18-20 kg aluminum slag / 120t molten steel at the same time.

3. The method according to claim 1, characterized in that The interval time for adding each batch of slag is 32-35s.

4. The method according to claim 1, characterized in that: During the primary desulfurization process, a small gear potential is selected for power transmission. Slag is added after arcing. After 180-300 seconds when the slag is completely dissolved, the electrode is lifted and 60-80 meters of aluminum wire is fed to increase the acid-soluble aluminum in the steel by 0.012%-0.016%, and then the power is transmitted at a large gear.

5. The method according to claim 1, characterized in that The low-speed power transmission gears are 8-11, and the high-speed power transmission gears are 2-4.

6. The method according to claim 1, characterized in that During the power transmission process, the desulfurization efficiency under argon blowing conditions is: argon flow rate is 50-60 cubic meters / hour, desulfurization rate is 0.001% per minute, argon flow rate is 100 cubic meters / hour, desulfurization rate is 0.003% per minute.

7. The method according to claim 1, characterized in that Also includes: After power is supplied, lift the electrode, adjust the argon flow rate to 10-30 cubic meters per hour, and take temperature measurements and samples.

8. The method according to claim 1, characterized in that When the inlet temperature of the molten steel is 1515° C., after desulfurization by the desulfurization method, the sulfur content of the low-sulfur steel is 0.003%-0.007%.

9. The method according to claim 1, characterized in that: The desulfurization time using the desulfurization method is 12-16 minutes.