Efficient desulfurization smelting method of LF refining process

Abstract

The invention relates to an efficient desulfurization smelting method of an LF (ladle furnace) refining process, which comprises the following steps of: 1, preparing casting residues, normally pouring LF deeply desulfurized steel, closing a sliding plate after a roughing slag detection system gives an alarm, transferring a steel ladle with the casting residues to a corresponding station, and waiting for tapping, 2, adjusting the components of the casting residues, transporting the steel ladle with the casting residues to a tapping station before converter tapping, (3) adding a deoxidizing agent, namely adding a certain amount of aluminum alloy according to oxygen at the end point of molten steel of the converter before tapping of the converter so as to quickly remove oxygen elements in the molten steel, (4) controlling stirring, controlling the flow of low argon blowing of a steel ladle to be 400-500Nm < 3 > / h in the tapping process of the converter, and stirring the molten steel with argon to be mixed with top slag of the steel ladle, and (5) carrying out residual desulfurization on the molten steel, and 6, top slag of the steel ladle is adjusted, the steel ladle is conveyed to an LF refining process work station, lime and a top slag deoxidizing agent are added, and the top slag of the steel ladle is further treated so as to further remove the sulfur element in the steel.

Description

Technical Field

[0001] The invention relates to a smelting method, in particular to an LF refining process high-efficiency desulfurization smelting method, belonging to the technical field of steelmaking and refining processes. Background Art

[0002] Desulfurization of molten steel is one of the most important functions of the LF refining process. The principle of desulfurization in the LF refining process is that CaO in the ladle top slag reacts chemically with S in the molten steel to produce CaS. In order to remove sulfur from steel, the chemical activity of CaO in the ladle top slag is the key. However, during the converter tapping process, the lime added to the ladle has not been completely melted. In addition, the oxidizing property of the ladle slag is high due to the converter slag. This leads to the weak desulfurization capacity of the ladle top slag at this time. After the ladle enters the LF refining process working position, a large amount of deoxidizer is added to remove oxygen from the ladle top slag; in addition, a large amount of lime is added and the lime is melted by electrode heating to increase the chemical activity of CaO in the top slag. At this point, the LF refining process ladle top slag has the desulfurization capacity. However, especially when smelting low-sulfur steel, the amount of lime added is extremely large, even exceeding 2t, and the lime melting time of the LF refining process is long. At present, with the advancement of efficient continuous casting, the long cycle of the LF refining process has become a limiting link of this work. If the ladle top slag is modified at the beginning of the converter tapping process to make it have a stronger desulfurization capacity, part of the sulfur in the steel will be removed from the converter tapping to the ladle reaching the LF refining station. This will inevitably reduce the desulfurization burden of the LF refining process, thereby effectively shortening the refining cycle of the LF refining process, solving the furnace-machine matching problem, and realizing an efficient continuous casting process. Therefore, an efficient desulfurization smelting method for the LF refining process that quickly removes sulfur from steel and shortens the smelting cycle is very necessary.

[0003] After searching, the Chinese patent "CN 100564548 C" discloses a high-basicity refined slag for washing converter steelmaking slag, and the method provides a high-basicity refined slag with active lime, fluorite and industrial soda as raw materials and a preparation method. The Chinese patent "CN 101235431A" discloses a method for rapid desulfurization of converter steelmaking slag washing and refining furnace, which is to add pre-melted slag and lime for ladle slag washing and pre-desulfurization, and add pre-melted slag and slag-making agent to LF refining for desulfurization to produce low-sulfur steel. The Chinese patent "CN 102277472 A" discloses a method for rapid deep desulfurization of LF refining and a deep desulfurizer, which provides a desulfurizer that is more suitable for the rapid deep desulfurization process of LF refining. The Chinese patent "CN 102719588 A" discloses a method for slag washing and desulfurization of molten iron using hot slag from casting, which uses continuous casting slag to pour into an empty molten iron tank, and slag washing and desulfurization of the molten iron during the iron mixing process. Chinese patent "CN 104313245 A" discloses a method for rapid desulfurization of heavy rail steel refining, which adopts lime added during the converter steel-tapping process to perform slag washing and desulfurization on molten steel. Chinese patent "CN105714022 A" discloses a method for pre-treating molten steel in a LF furnace to improve the desulfurization rate at low cost, which adopts lime used in making top slag in the LF furnace and adds it all during the converter steel-tapping process to make LF desulfurization slag in advance. Chinese patent "CN 108977623 A" discloses a method for desulfurizing high-sulfur molten steel using a ladle refining furnace, which adopts a large amount of lime added during the converter steel-tapping process to perform ladle slag washing and desulfurization. Chinese patent "CN 110804685 A" discloses a converter steel-tapping slag washing and refining process, which adopts the converter steel-tapping process to add slag washing material and small white ash slag to the ladle to realize the slag washing and desulfurization process. Chinese patent "CN110923404 A" discloses a process for low-cost desulfurization of molten steel outside the furnace. The method adopts the process of adding desulfurizer and deoxidizing alloy to the ladle during the converter steel-making process to realize the slag washing and desulfurization function. Chinese patent "CN 115927792 A" discloses a slag washing desulfurizer and desulfurization process for the converter steel-making ladle. The method provides a slag washing desulfurizer. The slag washing desulfurizer is added during the converter steel-making process to achieve a slag washing molten steel desulfurization rate of ≥25%. Chinese patent "CN 101798612 A" discloses a converter steel-making slag washing pre-desulfurization refining process. The method provides a slag washing desulfurizer. The slag washing desulfurizer is added during the converter steel-making process to achieve a slag washing molten steel desulfurization rate of ≥25%.

[0004] By searching for efficient refining desulfurization, the above 11 patents were found. From the above patents, it can be seen that at present, the desulfurization of converter ladle slag washing is mainly done by adding prefabricated desulfurizer or a large amount of lime during the steelmaking process to produce ladle top slag with desulfurization ability. However, this method has the problem of desulfurizer or lime melting, resulting in unstable desulfurization effect. Therefore, a new solution is urgently needed to solve the above technical problems. Summary of the invention

[0005] The present invention is aimed at the problems existing in the prior art, and provides an efficient desulfurization smelting method for LF refining process, which has a strong desulfurization capacity. The method has two functions: first, the ladle top slag has pre-desulfurization capacity during the transportation stage from the converter tapping to the ladle reaching the LF refining process working position, which reduces the desulfurization burden of the LF refining process; second, the ladle top slag is pre-treated to reduce the modification degree of the LF refining process top slag. The method can significantly shorten the LF refining process processing cycle.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows: the key to solving the long LF refining cycle is to quickly modify the ladle top slag during the steel tapping process so that it has desulfurization ability. It can be seen that the modification direction of the ladle top slag during the steel tapping process is the fundamental point to solve the problem. To this end, the present invention analyzes the desulfurization reaction process of the ladle top slag, and the sulfur content in the steel during the CaO desulfurization process in the ladle top slag can be expressed as formula (1).

[0007]

[0008] Where, [S] is the sulfur content in steel; [S]0 is the initial sulfur content in steel; (S)0 is the sulfur content in slag; L S is the sulfur distribution ratio, which is the ratio of sulfur content in slag to sulfur content in steel; K is the apparent desulfurization rate constant; F is the steel-slag contact area; V is the volume of molten steel in the LF furnace; w is the ratio of the mass of molten steel to the mass of top slag. S The sulfur distribution ratio can be expressed as formula (2).

[0009]

[0010] In the formula, C S is the sulfur content of the top slag; T is the temperature of the molten steel; f S is the sulfur activity coefficient in steel; a [O] is the oxygen activity in steel. S The sulfur capacity of top slag can be expressed as formula (3).

[0011]

[0012] In the formula, x CaO is the molar mass fraction of calcium oxide in the slag; x MgO is the molar mass fraction of magnesium oxide in the slag; x Al2O3 is the molar mass fraction of alumina in the slag; x SiO2is the molar mass fraction of silicon oxide in the slag. According to formula (1), to reduce the sulfur content in steel, it is necessary to increase the sulfur distribution ratio and increase the steel-slag contact area. According to formula (2), to increase the sulfur distribution ratio, it is necessary to increase the top slag sulfur capacity and reduce the oxygen activity in the steel. According to formula (3), to increase the top slag sulfur capacity, it is necessary to increase the CaO content in the slag and reduce the Al2O3 and SiO2 contents in the slag. According to the above analysis, in order for the ladle top slag to have the ability to remove sulfur from the steel during the converter steelmaking process, it is necessary to reduce the oxygen activity in the slag, increase the CaO content in the slag, reduce the Al2O3 and SiO2 contents in the slag, and increase the steel-slag contact area.

[0013] The main sources of Al2O3 and SiO2 in the slag are deoxidation products and ladle slag, respectively, which are difficult to control. At present, the main source of CaO in the slag is the melting of lime in the steel-making process. The oxygen activity in the slag can be removed by adding a deoxidizer. Increasing the steel-slag contact area can be controlled by stirring. At the same time, after the desulfurization of the LF refining process is completed, there is still a large amount of CaO and extremely low oxidizability in the ladle top slag, so it still has a strong desulfurization ability. If the LF refining process casting slag is used to replace part of the lime-modified ladle top slag in the steel-making process, there is no melting process and rapid slag making. In other words, the casting slag after the desulfurization of the LF refining process has the ability to quickly modify the ladle top slag in the steel-making process. This not only solves the problem of resource utilization of high-temperature slag, but also solves the problem of long refining cycle of the LF furnace process. Therefore, the idea of ​​the present invention is to use the previous furnace LF casting slag to modify the ladle top slag in the converter steel-making process, so as to achieve a strong desulfurization ability of the ladle top slag in the converter steel-making process. In order to achieve the purpose of efficient desulfurization in LF refining process, a specific technical scheme of efficient desulfurization smelting method in LF refining process is as follows:

[0014] Step 1: Prepare the casting slag. LF deep desulfurized steel is poured normally. After the slag detection system alarms, the slide plate is closed. The ladle with casting slag is transferred to the corresponding station and waits for steel tapping.

[0015] Step 2: Adjust the composition of the casting slag. Before the converter taps out steel, the casting slag ladle is transported to the tapping position. According to the converter end oxygen, a certain amount of lime is added to control the composition of the casting slag.

[0016] Step 3: Add deoxidizer. Before tapping the converter, add a certain amount of aluminum alloy according to the final oxygen of the molten steel in the converter to quickly remove oxygen from the molten steel.

[0017] Step 4: Control stirring. During the converter tapping process, the ladle low-pressure argon gas flow rate is controlled at 400-500Nm 3 / h, argon is used to stir the molten steel and mix it with the ladle top slag. In addition, the molten steel mixed flushing strengthens the ladle stirring.

[0018] Step 5: Desulfurization of molten steel. The ladle is transported from the converter tapping position to the argon station transfer position with argon blowing throughout the process. The argon flow rate is controlled at 200-300Nm 3 / h. Use argon as stirring gas to stir the steel slag and increase the contact area of ​​the steel slag.

[0019] Step 6: Adjust the ladle top slag. The ladle is transported to the LF refining process workstation, lime and top slag deoxidizer are added, and the ladle top slag is further treated to further remove sulfur from the steel.

[0020] The above steps 1 to 3 are the key to obtain ladle top slag with high CaO content and low oxidizability, so that the ladle top slag has desulfurization ability.

[0021] The above steps 4 and 5 are to increase the reaction area between CaO in the slag and S in the steel, and remove sulfur in the steel as much as possible. The method recycles high-basicity and low-oxidizing casting slag to adjust the composition of the ladle top slag in the converter steel-tapping process, and forms a ladle top slag with desulfurization ability. When the ladle is transported from the converter steel-tapping position to the argon station transfer position, the top slag in the ladle is stirred and mixed with molten steel to preliminarily remove sulfur in the steel, thereby reducing the LF desulfurization burden.

[0022] Compared with the prior art, the present invention has the following advantages: (1) It realizes the direct recycling of hot casting slag, replacing part of the lime with casting slag; (2) The casting slag can quickly form ladle top slag with desulfurization ability; (3) It makes full use of the impact of the converter steel-making process and the stirring effect of the low-level argon blowing of the ladle to pre-desulfurize the molten steel from the converter working position to the argon station transfer position; (4) The LF furnace processing time is shortened by 10-20 minutes, matching the furnace machine rhythm, and realizing efficient continuous casting; (5) It reduces the lime consumption and saves production costs. DETAILED DESCRIPTION

[0023] In order to deepen the understanding of the present invention, a detailed description is given below in conjunction with embodiments.

[0024] Example 1: A highly efficient desulfurization smelting method for LF refining process

[0025] Step 1: Prepare the casting slag. The molten steel is poured normally in the LF refining process. After the slag detection system alarms, the slide plate is closed. The ladle with casting slag is transferred to the corresponding station and waits for steel tapping.

[0026] Step 2: Adjust the composition of the casting slag. Before the converter is tapped, the casting slag ladle is transported to the tapping position, and 200 kg of lime is added to adjust the composition of the ladle casting slag.

[0027] Step 3: Add deoxidizer. Before tapping the converter, add 800kg of aluminum alloy according to the final oxygen of 421ppm of the converter molten steel to quickly remove oxygen from the molten steel.

[0028] Step 4: Control stirring. During the converter tapping process, the ladle low-pressure argon gas flow rate is controlled at 400-500Nm 3 / h, argon is used to stir the molten steel and mix it with the ladle top slag. In addition, the molten steel mixed flushing strengthens the ladle stirring.

[0029] Step 5: Desulfurization of molten steel. The ladle is transported from the converter tapping position to the argon station transfer position with argon blowing throughout the process. The argon flow rate is controlled at 200-300Nm 3 / h. Use argon as stirring gas to stir the slag and increase the contact area of ​​the slag. The sulfur content of the molten steel at the converter end is 0.0231%, and the sulfur content of the molten steel entering the LF station is 0.014%.

[0030] Step 6: Adjust the top slag of the ladle. The ladle is transported to the LF refining process workstation, and 700kg of lime and 100kg of top slag deoxidizer are added. The electrode heating time is 10.6min, the LF refining cycle is 34.33min, and the sulfur content in the steel is reduced to 0.003%.

[0031] Comparative Example

[0032] Step 1: No slag preparation.

[0033] Step 2: The molten steel from the converter covers the bottom of the ladle, and 600 kg of lime is added into the ladle;

[0034] Step 3: When the molten steel in the converter reaches 1 / 3 of the height of the ladle, add 800kg of aluminum alloy into the ladle.

[0035] Step 4: During the converter steel tapping process, the ladle low blowing argon flow rate is controlled at 400-500Nm 3 / h.

[0036] Step 5: The ladle is transported from the converter tapping position to the argon station transfer position, and argon is blown from the bottom throughout the process. The argon flow rate is controlled at 10-20Nm 3 / h, to prevent the molten steel from being exposed. The sulfur content of the molten steel discharged from the converter is 0.0246%, and the sulfur content of the molten steel entering the LF station is 0.0216%.

[0037] Step 6: The ladle is transported to the LF refining process workstation, 1500kg of lime and 300kg of top slag deoxidizer are added, the electrode heating time is 21.2min, the LF refining cycle is as long as 53.5min, and the sulfur content in the steel is reduced to 0.0031%.

[0038] By comparing the embodiment with the comparative example, it can be seen that the smelting method of the present invention shortens the heating time of the LF furnace from 21.2 min to 10.6 min. From the stage of steel tapping from the converter to the stage of steel ladle transportation to the LF working station, the sulfur content in the steel is reduced from 0.0231% to 0.014, and the LF treatment cycle is shortened from 53.5 min to 34.33 min. The amount of desulfurized lime in the LF furnace is reduced from 1500 kg to 700 kg, and the deoxidizer in the LF furnace is reduced from 300 kg to 100 kg.

[0039] It should be noted that the above embodiments are not intended to limit the protection scope of the present invention, and equivalent changes or substitutions made on the basis of the above technical solutions all fall within the protection scope of the claims of the present invention.

Claims

1. An LF refining process efficient desulfurization smelting method, characterized in that: The method comprises the following steps: Step 1: Prepare the casting slag, and pour the LF deep desulfurized steel normally. After the slag detection system alarms, close the slide plate, transfer the ladle with casting slag to the corresponding station, and wait for steel tapping. Step 2: Adjust the composition of the casting slag. Before the converter taps out steel, the casting slag ladle is transported to the tapping position. According to the final oxygen of the converter, a certain amount of lime is added to control the composition of the casting slag. Step 3: Add deoxidizer. Before tapping the converter, add a certain amount of aluminum alloy according to the final oxygen of the molten steel in the converter to quickly remove oxygen from the molten steel. Step 4: Control stirring, converter tapping process, ladle low blowing argon flow rate is controlled at 400-500Nm 3 / h, using argon to stir the molten steel and the ladle top slag, Step 5: The molten steel is desulfurized, and the ladle is transported from the converter tapping position to the argon station transfer position. Argon is blown from the bottom of the ladle throughout the process, and the argon flow rate is controlled at 200-300Nm 3 / h, using argon as stirring gas to stir the steel slag mixture to increase the contact area of ​​the steel slag. Step 6: Adjust the ladle top slag, transport the ladle to the LF refining process work station, add lime and top slag deoxidizer, and further treat the ladle top slag to further remove sulfur from the steel.

2. The LF refining process efficient desulfurization smelting method according to claim 1 is characterized in that: The method analyzes the desulfurization reaction process of ladle top slag. The sulfur content in the steel during the desulfurization process of CaO in the ladle top slag can be expressed as formula (1): Where, [S] is the sulfur content in steel; [S]0 is the initial sulfur content in steel; (S)0 is the sulfur content in slag; L S is the sulfur distribution ratio, which is the ratio of sulfur content in slag to sulfur content in steel; K is the apparent desulfurization rate constant; F is the steel-slag contact area; V is the volume of molten steel in the LF furnace; w is the ratio of the mass of molten steel to the mass of top slag, where L S The sulfur distribution ratio can be expressed as formula (2): In the formula, C S is the sulfur content of the top slag; T is the temperature of the molten steel; f S is the sulfur activity coefficient in steel; a [O] is the oxygen activity in steel, where C S The sulfur capacity of top slag can be expressed as formula (3): In the formula, x CaO is the molar mass fraction of calcium oxide in the slag; x MgO is the molar mass fraction of magnesium oxide in the slag; is the molar mass fraction of alumina in the slag; is the molar mass fraction of silicon oxide in the slag. According to formula (1), to reduce the sulfur content in steel, it is necessary to increase the sulfur distribution ratio and increase the steel-slag contact area. According to formula (2), to increase the sulfur distribution ratio, it is necessary to increase the top slag sulfur capacity and reduce the oxygen activity in steel. According to formula (3), to increase the top slag sulfur capacity, it is necessary to increase the CaO content in the slag and reduce the Al2O3 and SiO2 contents in the slag. According to the above analysis, in order for the ladle top slag to have the ability to remove sulfur from steel during the converter steelmaking process, it is necessary to reduce the oxygen activity in the slag, increase the CaO content in the slag, reduce the Al2O3 and SiO2 contents in the slag, and increase the steel-slag contact area.

3. The LF refining process efficient desulfurization smelting method according to claim 1 is characterized in that: The method recycles high-basicity and low-oxidizing casting slag to adjust the composition of ladle top slag in the converter tapping process to form ladle top slag with desulfurization ability; in the stage of transporting the ladle from the converter tapping position to the argon station transfer position, the top slag in the ladle is stirred and mixed with molten steel to preliminarily remove sulfur elements in the steel, thereby reducing the LF desulfurization burden.

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