LF furnace dephosphorization method

Abstract

The invention discloses a method for efficiently dephosphorizing by using an LF (Ladle Furnace), which comprises the following steps of: firstly, keeping the oxidability of molten steel and steel slag without deoxidizing and alloying in the tapping process of a converter; and the molten steel is heated to 1620 DEG C by utilizing the characteristic that the LF refining furnace can be used for heating. Lime and a slagging agent are added for slagging in the heating process according to the sticky and thin condition of the steel slag, so that the alkalinity of the steel slag is improved; and after the target temperature is reached, argon is blown from the bottom of a steel ladle to stir the molten steel, and dephosphorization is performed through a steel slag reaction, so that the production of steel with the phosphorus element content of less than or equal to 0.003% in the molten steel is realized. The invention aims to provide a novel method capable of efficiently dephosphorizing after converter tapping so as to ensure the realization of batch production of special steel with high additional value, such as phosphorus content less than or equal to 0.003%, and the method can be applied to ultra-low phosphorus steel, such as industrial pure iron, ultra-deep drawing automobile outer plates and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to a dephosphorization method for an LF furnace. Background Art

[0002] In order to meet the current market demand and smelt special steel with high added value, all steel mills are working hard to reduce the P element in molten steel during the smelting process. The dephosphorization capacity of the converter itself is limited, and in some areas of the steel mills, due to the limitation of ore raw material conditions, the phosphorus content of the molten iron entering the furnace cannot meet the requirements for smelting ultra-low phosphorus steel. Under the above background, the production of steel with a phosphorus content of ≤0.003% in molten steel cannot be achieved by using the converter alone, and this technical problem has become increasingly prominent.

[0003] Phosphorus is a harmful element in molten steel. Steel with excessive phosphorus content is prone to "cold brittleness". Reducing the phosphorus content in molten steel is a necessary condition for smelting high value-added steel. With the development of converter technology, the main processes used at home and abroad at this stage are "double slag method" and "double connection method". Through these two methods, in production practice, by optimizing the dephosphorization process parameters, the purpose of deep dephosphorization is achieved, and the dephosphorization rate can be effectively achieved as high as 95%, and the stable batch production of extremely low-phosphorus steel is also achieved.

[0004] However, the above methods have very strict requirements on the raw materials of molten iron. In the existing process, the dephosphorization task of molten iron is mainly completed in the converter link, and the dephosphorization capacity of the converter is about 90%, which requires that the phosphorus content of the molten iron entering the furnace should be relatively low, usually the phosphorus content of the molten iron entering the furnace cannot exceed 0.08%. It is difficult to smelt ultra-low phosphorus molten steel with a phosphorus content below 0.003% under poor molten steel conditions.

[0005] In summary, there is a need for a new method that can efficiently dephosphorize steel after the converter is tapped to ensure the mass production of high value-added special steels with a phosphorus content of ≤0.003%. Summary of the invention

[0006] The purpose of the present invention is to provide a new method for efficient dephosphorization after steel is tapped from a converter, so as to ensure the mass production of high value-added special steels with a phosphorus content of ≤0.003%.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for dephosphorizing an LF furnace, comprising the following steps:

[0009] The converter does not carry out deoxidation and alloying during the steel-making process, so as to maintain the oxidizability of the molten steel and slag;

[0010] During the steel-making process, the converter does not add deoxidizer for deoxidation, but only adds lime for slag making;

[0011] The oxygen content of the steel out of the converter is controlled at 600ppm-900ppm to ensure the oxidizability of the slag and create an oxidizability basis for refining and dephosphorization;

[0012] Taking advantage of the heating feature of the LF refining furnace, the molten steel is heated to 1620°C, the most effective temperature for dephosphorization, which can greatly improve the dephosphorization efficiency;

[0013] During the heating process of the LF furnace refining furnace, slag is added to make slag;

[0014] During the LF refining and heating process, lime and slag-removing agent are added to obtain the high-basicity slag required for dephosphorization, so as to achieve efficient dephosphorization; then, the amount of lime added is increased by adjusting the slag composition, thereby increasing the phosphorus capacity of the slag, thereby increasing the distribution ratio of phosphorus in the slag and the molten steel, providing favorable conditions for dephosphorization, so that the LF refining furnace has the dephosphorization ability, and finally achieving the purpose of reducing the phosphorus content in the molten steel during the LF refining process;

[0015] During the arc heating process of the LF furnace, good foam slag is produced to increase the slag-steel interface area and enhance the kinetic conditions of the dephosphorization reaction, thereby enabling better removal of phosphorus;

[0016] By blowing argon from the bottom of the ladle, the molten steel is stirred to obtain good kinetic conditions, allowing the slag to fully react and dephosphorize; the phosphorus content in the molten steel is removed to within the required composition range through stirring; during the arc heating process of the LF furnace, good foamy slag is produced to increase the slag-steel interface area and enhance the kinetic conditions of the dephosphorization reaction, thereby allowing phosphorus to be better removed.

[0017] Further, the specific steps include:

[0018] 1) After the LF furnace is in place, add 600kg of lime at one time;

[0019] 2) After heating for 5 minutes using double-line argon gas at 600L / min, add the second batch of slag and 500kg of lime, and then continue to increase the temperature to 1610℃;

[0020] 3) Adjust the argon flow rate to 800L / min. When the argon is weak, turn on the emergency argon for stirring and dephosphorization, and add lime according to the slag situation. After stirring with large argon for 5 minutes, turn off the argon and take a sample, recorded as G1. After sampling, heat the temperature to 1610℃.

[0021] 4) If G1 meets the standard, the argon flow rate is set to 400L / min and heated to the required temperature for reform; if G1 phosphorus does not meet the standard, add 500kg lime and 200kg slag-removing agent, adjust the argon to double-line 800L / min and stir for 5 minutes, then turn off the argon to measure the temperature and take samples, which is recorded as G2;

[0022] 5) After the ingredients are qualified, add the temperature to the required temperature for reforming according to the current temperature;

[0023] 6) After heating to the target temperature, turn off the argon gas and add aluminum particles in 3 batches for reforming. Each batch of aluminum particles is added 1 minute apart, and the amount added in each batch is 50 kg;

[0024] 7) After the top slag is reformed, the molten steel is transported to the RH furnace for subsequent production.

[0025] Furthermore, in the step 1), the amount of lime added is adjusted according to the conditions of the steel slag.

[0026] Furthermore, taking molten iron with a phosphorus content of 0.122% as raw material, the converter has a steel-tapping temperature of 1623°C, a steel-tapping oxygen content of 811ppm, and a steel-tapping phosphorus content of 0.011% under normal process smelting conditions; the LF refining furnace is at a temperature of 1533°C, 2404kg of lime and 212kg of slag-removing agent are added during the LF furnace refining process, heating for 32 minutes, and dephosphorization argon stirring time of 13 minutes. When the LF refining furnace is off-site, the phosphorus content is 0.0027%; the dephosphorization rate of the LF refining furnace is 75.45%.

[0027] Furthermore, taking molten iron with a phosphorus content of 0.116% as raw material, the converter has a steel-tapping temperature of 1626°C, a steel-tapping oxygen content of 842ppm, and a steel-tapping phosphorus content of 0.0113% under normal smelting process conditions; the LF refining furnace is at a temperature of 1535°C, 2104kg of lime and 236kg of slag-removing agent are added during the LF furnace refining process, heated for 26min, and the dephosphorization argon stirring time is 14min. When the LF refining furnace is off-site, the phosphorus content is 0.0025%; the dephosphorization rate of the LF refining furnace is 77.88%.

[0028] Furthermore, taking molten iron with a phosphorus content of 0.116% as raw material, the converter has a steel-tapping temperature of 1625°C, a steel-tapping oxygen content of 733ppm, and a steel-tapping phosphorus content of 0.0133% under normal process smelting conditions; the LF refining furnace is at a temperature of 1530°C, 2705kg of lime and 172kg of slag-removing agent are added during the LF furnace refining process, heated for 30min, and the dephosphorization argon stirring time is 16min. When the LF refining furnace is off-site, the phosphorus content is 0.0025%; the dephosphorization rate of the LF refining furnace is 81.20%.

[0029] Compared with the prior art, the beneficial technical effects of the present invention are:

[0030] The present invention provides a method for efficient dephosphorization using an LF refining furnace to solve the problem that ultra-low phosphorus steel cannot be smelted solely by a converter process under existing steelmaking conditions. By inventing a LF refining furnace dephosphorization process, the process successfully breaks through this technical bottleneck and realizes mass production of steel with a phosphorus content of ≤0.003%.

[0031] In the traditional process, the effect of converter dephosphorization can reach 85%-95%. Under the condition that the molten iron entering the furnace is high-phosphorus molten iron with a phosphorus content higher than 0.120%, the phosphorus content in the molten steel can only be stably controlled below 0.012%. The present invention greatly reduces the pressure of converter dephosphorization by developing the LF refining furnace dephosphorization process, so that ultra-low phosphorus steel can be mass-produced. DETAILED DESCRIPTION

[0032] A method for smelting ultra-low phosphorus steel from high-phosphorus molten iron specifically comprises the following steps:

[0033] 1. After the LF furnace is in place, add 600kg of lime at one time (it can be adjusted according to the situation of steel slag).

[0034] 2. Use double-line argon gas at 600L / min for heating for 5 minutes, then add the second batch of slag, 500kg of lime, and continue to increase the temperature to about 1610℃.

[0035] 3. Adjust the argon flow rate to 800L / min. When the argon is weak, turn on the emergency argon to stir and dephosphorize, and add lime according to the slag situation. After stirring with large argon for 5 minutes, turn off the argon and take a sample, recorded as G1. After sampling, heat the temperature to 1610℃.

[0036] 4. If G1 meets the standard, the argon flow rate is set to 400L / min and heated to the temperature required for the reform; if G1 phosphorus does not meet the standard, add 500kg of lime and 200kg of slagging agent, adjust the argon to double-line 800L / min and stir for 5 minutes, then turn off the argon to measure the temperature and take samples, which is recorded as G2.

[0037] 5. After the ingredients are qualified, heat the current temperature to the required temperature for reforming.

[0038] 6. After heating to the target temperature, turn off the argon gas and add aluminum particles in three batches for modification. The interval between each batch of aluminum particles is 1 minute, and the amount added in each batch is 50 kg;

[0039] 7. After the top slag is reformed, the molten steel is transported to the RH furnace for subsequent production.

[0040] Example 1

[0041] Using molten iron with a phosphorus content of 0.122% as raw material, the tapping temperature of the converter under normal process smelting conditions is 1623℃, the oxygen content of the tapping steel is 811ppm, and the phosphorus content of the tapping steel is 0.011%. The LF refining furnace is at a temperature of 1533℃. During the LF furnace refining process, 2404kg of lime and 212kg of slag-removing agent are added, and the heating time is 32 minutes. The dephosphorization argon stirring time is 13 minutes. The phosphorus content of the LF refining furnace is 0.0027% when it is off-site. The dephosphorization rate of the LF refining furnace is 75.45%.

[0042] Example 2

[0043] Using molten iron with a phosphorus content of 0.116% as raw material, the tapping temperature of the converter under normal process smelting conditions is 1626℃, the oxygen content of the tapping steel is 842ppm, and the phosphorus content of the tapping steel is 0.0113%. The LF refining furnace is at a temperature of 1535℃. During the LF furnace refining process, 2104kg of lime and 236kg of slag-removing agent are added, and the heating time is 26min. The dephosphorization argon stirring time is 14min. The phosphorus content of the LF refining furnace is 0.0025% when it is off-site. The dephosphorization rate of the LF refining furnace is 77.88%.

[0044] Example 3

[0045] Using molten iron with a phosphorus content of 0.116% as raw material, the tapping temperature of the converter under normal process smelting conditions is 1625℃, the oxygen content of the tapping steel is 733ppm, and the phosphorus content of the tapping steel is 0.0133%. The LF refining furnace is in place at a temperature of 1530℃. During the LF furnace refining process, 2705kg of white ash and 172kg of slag-removing agent are added, heated for 30 minutes, and the dephosphorization argon stirring time is 16 minutes. The phosphorus content is 0.0025% when the LF refining furnace is off-site. The dephosphorization rate of the LF refining furnace is 81.20%.

[0046] In the above three actual production cases, the phosphorus content of the hot metal entering the furnace exceeded 0.110%, and the phosphorus content after dephosphorization in the converter was 0.011%, 0.0113%, and 0.0133%. After further dephosphorization in the LF refining furnace, the phosphorus content of the molten steel further decreased, and finally met the composition control requirements. The average dephosphorization rate of the LF furnace was 78.18%.

[0047] Table 1 below shows the in-situ and out-of-situ temperatures and the proportions of additives added for the three cases.

[0048] Table 1

[0049]

[0050] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for dephosphorization in a LF furnace, characterized in that: The steps include: The converter does not carry out deoxidation and alloying during the steel-making process, so as to maintain the oxidizability of the molten steel and slag; During the steel-making process, the converter does not add deoxidizer for deoxidation, but only adds lime for slag making; The oxygen content of the steel out of the converter is controlled at 600ppm-900ppm to ensure the oxidizability of the slag and create an oxidizability basis for refining and dephosphorization; Taking advantage of the heating feature of the LF refining furnace, the molten steel is heated to 1620°C, the most effective temperature for dephosphorization, which can greatly improve the dephosphorization efficiency; During the heating process of the LF furnace refining furnace, slag is added to make slag; During the LF refining and heating process, lime and slag-reducing agent are added to obtain the high-basicity slag required for dephosphorization, so as to achieve efficient dephosphorization; Then, by adjusting the slag composition and increasing the amount of lime added, the phosphorus capacity of the slag is increased, thereby increasing the distribution ratio of phosphorus in the slag and molten steel, providing favorable conditions for dephosphorization, so that the LF refining furnace has the dephosphorization ability, and finally achieving the purpose of reducing the phosphorus content in molten steel during the LF refining process; During the arc heating process of the LF furnace, good foam slag is produced to increase the slag-steel interface area and enhance the kinetic conditions of the dephosphorization reaction, thereby enabling better removal of phosphorus; By blowing argon from the bottom of the ladle, the molten steel is stirred to obtain good kinetic conditions, allowing the slag to fully react and dephosphorize; the phosphorus content in the molten steel is removed to within the required composition range through stirring; during the arc heating process of the LF furnace, good foamy slag is produced to increase the slag-steel interface area and enhance the kinetic conditions of the dephosphorization reaction, thereby allowing phosphorus to be better removed.

2. The method for dephosphorization in a LF furnace according to claim 1, wherein: The specific steps include: 1) After the LF furnace is in place, add 600kg of lime at one time; 2) After heating for 5 minutes using double-line argon gas at 600L / min, add the second batch of slag and 500kg of lime, and then continue to increase the temperature to 1610℃; 3) Adjust the argon flow rate to 800L / min. When the argon is weak, turn on the emergency argon for stirring and dephosphorization, and add lime according to the slag situation. After stirring with large argon for 5 minutes, turn off the argon and take a sample, recorded as G1. After sampling, heat the temperature to 1610℃. 4) If G1 meets the standard, the argon flow rate is set to 400L / min and heated to the required temperature for reform; if G1 phosphorus does not meet the standard, add 500kg lime and 200kg slag-removing agent, adjust the argon to double-line 800L / min and stir for 5 minutes, then turn off the argon to measure the temperature and take samples, which is recorded as G2; 5) After the ingredients are qualified, add the temperature to the required temperature for reforming according to the current temperature; 6) After heating to the target temperature, turn off the argon gas and add aluminum particles in 3 batches for reforming. Each batch of aluminum particles is added 1 minute apart, and the amount added in each batch is 50 kg; 7) After the top slag is reformed, the molten steel is transported to the RH furnace for subsequent production.

3. The method for dephosphorization in a LF furnace according to claim 1, wherein: In the step 1), the amount of lime added is adjusted according to the condition of the steel slag.

4. The method for dephosphorization in a LF furnace according to claim 1, wherein: Using molten iron with a phosphorus content of 0.122% as raw material, the converter has a steel-tapping temperature of 1623°C, a steel-tapping oxygen content of 811ppm, and a steel-tapping phosphorus content of 0.011% under normal smelting process conditions; the LF refining furnace is at a temperature of 1533°C, 2404kg of lime and 212kg of slag-removing agent are added during the LF furnace refining process, heating for 32 minutes, and dephosphorization argon stirring time of 13 minutes. The phosphorus content is 0.0027% when the LF refining furnace is off-site; the dephosphorization rate of the LF refining furnace is 75.45%.

5. The method for dephosphorization in a LF furnace according to claim 1, characterized in that: Using molten iron with a phosphorus content of 0.116% as raw material, under normal smelting conditions, the steel-tapping temperature of the converter is 1626°C, the steel-tapping oxygen content is 842ppm, and the steel-tapping phosphorus content is 0.0113%; the LF refining furnace is at a temperature of 1535°C, 2104kg of lime and 236kg of slag-removing agent are added during the LF furnace refining process, heating for 26min, dephosphorization argon stirring time for 14min, and the phosphorus content of the LF refining furnace is 0.0025% when the LF refining furnace is off-site; the dephosphorization rate of the LF refining furnace is 77.88%.

6. The method for dephosphorization in a LF furnace according to claim 1, characterized in that: Using molten iron with a phosphorus content of 0.116% as raw material, the converter has a steel-tapping temperature of 1625°C, a steel-tapping oxygen content of 733ppm, and a steel-tapping phosphorus content of 0.0133% under normal smelting process conditions; the LF refining furnace is at a temperature of 1530°C, 2705kg of lime and 172kg of slag-removing agent are added during the LF furnace refining process, heating for 30min, and dephosphorization argon stirring time of 16min. The phosphorus content is 0.0025% when the LF refining furnace is off-site; the dephosphorization rate of the LF refining furnace is 81.20%.

Images