Production method of high-quality low-nitrogen hard wire steel

Abstract

The invention belongs to the technical field of steelmaking, and particularly discloses a production method of high-quality low-nitrogen hard wire steel, which comprises the following steps: S1, pure scrap steel and molten iron are sequentially added into a converter, and the molten iron comprises the following components: 0.30-0.50% of Si, less than or equal to 0.080% of P and less than or equal to 0.040% of S; s2, a converter is started for bottom argon blowing, the argon flow is controlled to be 0.10-0.20 m < 3 > / h, the oxygen flow is controlled to be 30000-40000 m < 3 > / h, and 600-1000 kg of pellets are added into the converter; s3, continuous smelting is conducted for 6-7 min, and when the oxygen content of the converter reaches 70%-90%, the pellets are added again; s4, the oxygen flow is set to be 25000-40000 m < 3 > / h, the lance position of an oxygen lance is raised to 1.4 m, and the temperature in the furnace is controlled to be 1560-1570 DEG C; s5, opening bottom argon blowing of the steel ladle, and adding 100kg of carburant into the steel ladle; s6, in the early stage of tapping, 1.5 kg / t of molten steel deoxidizer and 200-300 kg of lime are added in sequence, and alloy is added in sequence when 1 / 3 of steel is tapped; s7, after complete tapping, LF refining is started, and the nitrogen increasing amount is controlled to be smaller than or equal to 10 ppm; s8, RH refining is conducted again after LF refining, and the nitrogen content in the molten steel is further reduced to 20 ppm or below; and S9, entering a continuous casting procedure after RH refining.

Description

Technical Field

[0001] The present invention relates to the technical field of steelmaking, and in particular to a method for producing high-quality low-nitrogen hard wire steel. Background Art

[0002] In steelmaking production, the nitrogen content in hard wire steel is one of the key factors affecting its performance and quality. The introduction of nitrogen may come from raw materials, smelting processes or air pollution, and its content needs to be strictly controlled. In existing production technologies, due to the fluctuation of nitrogen content in raw material scrap steel, the initial nitrogen exceeds the standard, and high-temperature ionized nitrogen causes the molten steel to absorb nitrogen, which will cause high-nitrogen steel to be prone to surface cracks or wire breakage during drawing and cold heading. In particular, ultra-fine wires with a diameter of <0.2mm are more sensitive to nitrogen content. When the nitrogen content increases from 60ppm to 80ppm, the wire breakage rate during drawing may increase by more than 3 times. Therefore, there is an urgent need for an efficient, economical and stable full-process nitrogen control method that can achieve coordinated optimization from raw material pretreatment, smelting nitrogen control, refining and denitrification to continuous casting protection to solve the problem of wire breakage caused by nitrogen embrittlement. Summary of the Invention

[0003] The object of the present invention is to provide a method for producing high-quality low-nitrogen hard wire steel to solve the problem of wire breakage caused by embrittlement due to nitrogen.

[0004] To achieve the above object, the present invention provides a basic solution: a method for producing high-quality low-nitrogen hard wire steel, comprising the following steps:

[0005] S1: Add pure scrap steel and molten iron into the converter in sequence. The scrap steel composition mainly consists of internal recycled billet heads and tails, laths, and steel bar cuts. The molten iron composition is Si: 0.30-0.50%, P: ≤0.080%, S: ≤0.040%. The furnace temperature is controlled within 1280℃.

[0006] S2: After the molten iron is added, start blowing argon from the bottom of the converter and control the argon flow rate at 0.10-0.20m3 through the central control panel. 3 / h, the converter enters the oxygen blowing smelting stage, and the oxygen flow rate is controlled at 30000-40000m 3 / h, after smelting in the converter for 7-9 minutes, add 600-1000kg of pellets into the converter according to the slag situation in the furnace;

[0007] S3: After the pellets are added for the first time, smelting is continued for 6-7 minutes. When the oxygen content in the converter reaches 70%-90%, the pellets are added again in batches;

[0008] S4: After adding pellets for the second time, set the oxygen flow rate to 25000-40000m3 through the central control panel. 3 / h, at this time the oxygen lance is at 1.3m, when the carbon fire is burning in a stable state, the oxygen lance is raised to 1.4m, and the oxygen is continuously sprayed to control the temperature in the furnace at 1560℃-1570℃;

[0009] S5: Real-time monitoring is performed during the combustion process. When the molten steel content reaches the target value, argon is blown from the bottom of the ladle, 100 kg of recarburizer is added to the ladle, and the steel can be tapped after waiting for 2 minutes.

[0010] S6: In the early stage of tapping, 1.5kg / t steel deoxidizer and 200-300kg lime are added to the molten steel in sequence. When the steel is 1 / 3 tapped, silicon manganese alloy, ferrosilicon, carburizer and high carbon ferrochrome are added in sequence. The amount of alloy added is set according to the ladle composition requirements of each steel grade. All the addition is completed when 3 / 4 of the steel is tapped until the steel is fully tapped.

[0011] S7: After the steel is completely tapped, the ladle is hoisted to the LF furnace to start refining, and the nitrogen addition is controlled to ≤10ppm;

[0012] S8: The molten steel after LF refining is subjected to RH refining again to further reduce the nitrogen content in the molten steel to below 20 ppm;

[0013] S9: The molten steel after RH refining enters the continuous casting process.

[0014] The working principle of the present invention is as follows: the converter steelmaking process uses scrap steel and molten iron with specific composition as raw materials, first controls the furnace temperature to initially melt the raw materials, and stirs the molten pool by blowing argon from the bottom; in the oxygen blowing smelting stage, oxygen reacts with impurities to raise the temperature and remove impurities, and pellets are added in time to supplement iron elements and adjust the slag; the oxygen flow rate and oxygen lance position are precisely controlled to ensure that the reaction rate and temperature meet the standards; real-time monitoring is carried out during smelting, and the molten steel composition is adjusted after meeting the standards, and deoxidizer, lime and alloy are added before tapping, and then LF refining and RH refining are carried out to reduce the impurity content, and finally enter the continuous casting process to cast into steel billets.

[0015] The beneficial effects of the present invention are as follows: this process effectively removes impurities by precisely controlling parameters such as bottom blowing argon flow rate and oxygen flow rate, thereby improving the quality of molten steel; optimizing process steps and parameter settings, shortening smelting time, reducing energy consumption, and improving production efficiency; using recycled scrap steel raw materials and reasonably controlling alloy dosage can reduce production costs; real-time monitoring and precise control make production stable and reduce the occurrence of accidents; flexible adjustment of alloys and process parameters can produce a variety of steel grades, thereby enhancing the company's market competitiveness.

[0016] Option 2 is the preferred option of the basic option. In step S1, the total amount of scrap steel and molten iron added is 187±2t, of which the molten iron accounts for >85%.

[0017] Option 3 is the preferred option of the basic option. In step S3, the requirement for adding pellets in batches is: adding pellets in 2-4 batches, with the weight of each batch of pellets being 500 kg, and controlling the converter slag basicity R=3.5-4.0.

[0018] Option 4 is the preferred option of the basic option. In step S5, the target value of the molten iron content is: C: 0.08-0.12%, P≤0.012%, S≤0.010%.

[0019] Option 5 is the preferred option of the basic option. In step S6, the steel tapping time is controlled within 3-6 minutes.

[0020] Scheme 6, which is the preferred basic scheme, in step S7, the specific steps of LF furnace refining are as follows:

[0021] 1) Use micro-positive pressure operation to control the pressure at 50-80kPa, turn on the pressure sensor for real-time monitoring, and set interlock protection: automatically replenish air when the pressure is lower than 50kPa, and activate the pressure relief valve when the pressure is higher than 80kPa;

[0022] 2) Then, high basicity refined slag is added in batches, with 60%-70% added in the first batch, to initially form a high basicity slag layer;

[0023] 3) After stirring with argon for 3-5 minutes, add the remaining refined slag and control the final basicity at R = 3.5-4.0;

[0024] 4) Add deoxidizer and observe the color change of slag. When the slag surface is silvery white and fluffy, and the sampled slag turns white after cooling in the air, it is judged to be qualified reduced white slag;

[0025] 5) Maintain the bottom argon soft blowing state to avoid violent stirring and slag rolling, and ensure that the white slag state lasts for ≥10 minutes;

[0026] 6) 1 minute before the end of refining, take a steel sample to test the nitrogen content. If it exceeds the standard, add ferrotitanium to control the nitrogen addition amount to ≤10ppm.

[0027] Scheme 7, which is the preferred basic scheme, in step S8, the specific steps of RH refining are as follows:

[0028] 1) After the ladle arrives at the RH refining station, a staged vacuuming is adopted. First, a Roots pump is used for rough pumping for 5 minutes to control the vacuum chamber pressure at 10±2kPa. Then, a steam jet pump is used for fine pumping for 8 minutes to reduce the vacuum chamber pressure to ≤133Pa.

[0029] 2) Blow argon into the riser, and control the argon flow rate at 60-125Nm 3 / h, driving the molten steel to form an upward flow rate of 4-6m / s;

[0030] 3) During the argon blowing process, the top oxygen gun is at 2000-3000Nm 3 / h flow rate of continuous oxygen blowing;

[0031] 4) Real-time monitoring of gas content. When the hydrogen content is ≤3ppm, the nitrogen content is ≤30ppm, and the carbon content is ≤10ppm, alloy material is added to the molten steel to control the composition accuracy deviation to: C ≤±0.003%;

[0032] 5) Use natural gas injection to increase temperature and control the natural gas flow rate at 1500-2000Nm 3 / h, the temperature is maintained at 1600-1620℃;

[0033] 6) Start the vacuum breaking operation. When the vacuum chamber pressure is increased, move the ladle to the argon blowing station and perform bottom argon blowing for 5-10 minutes. The argon flow rate is controlled at 5-8NL / min. DETAILED DESCRIPTION

[0034] The present invention will be further described in detail below through specific embodiments:

[0035] Example

[0036] A method for producing high-quality low-nitrogen hard wire steel comprises the following steps:

[0037] S1: Add pure scrap steel and molten iron to the converter in sequence. The scrap steel composition is mainly composed of internal recycled billet heads and tails, laths, and steel bar strips. The molten iron composition is Si: 0.30-0.50%, P: ≤0.080%, S: ≤0.040%. The furnace temperature is controlled within 1280℃. The total amount of scrap steel and molten iron added is 187±2t, of which the molten iron accounts for >85%;

[0038] S2: After the molten iron is added, start blowing argon from the bottom of the converter and control the argon flow rate at 0.10-0.20m3 through the central control panel. 3 / h, the converter enters the oxygen blowing smelting stage, and the oxygen flow rate is controlled at 30000-40000m 3 / h, after smelting in the converter for 7-9 minutes, add 600-1000kg of pellets into the converter according to the combustion conditions in the furnace;

[0039] S3: After the first addition of pellets, continue smelting for 6-7 minutes. When the oxygen content in the converter reaches 70%-90%, add pellets again in 2-4 batches. The weight of each batch of pellets is 500 kg. The converter slag basicity R is controlled at 3.5-4.0.

[0040] S4: After adding pellets for the second time, set the oxygen flow rate to 25000-40000m3 through the central control panel. 3 / h, at this time the oxygen lance is at 1.3m, when the carbon fire is burning in a stable state, the oxygen lance is raised to 1.4m, and the oxygen is continuously sprayed to control the temperature in the furnace at 1560℃-1570℃;

[0041] S5: Real-time monitoring during the combustion process. When the molten steel content reaches C: 0.08-0.12%, P≤0.012%, and S≤0.010%, argon is blown from the bottom of the ladle, 100kg of recarburizer is added to the ladle, and the steel can be tapped after waiting for 2 minutes.

[0042] S6: In the early stage of tapping, 1.5kg / t steel deoxidizer and 200-300kg lime are added to the molten steel in sequence. When the steel is 1 / 3 tapped, silicon manganese alloy, ferrosilicon, carburizer and high carbon ferrochrome are added in sequence. The amount of alloy added is set according to the ladle composition requirements of each steel grade. All the addition is completed when 3 / 4 of the steel is tapped, until the steel is completely tapped, and the tapping time is controlled within 3-6 minutes.

[0043] S7: After the steel is completely tapped, the ladle is hoisted to the LF furnace for refining. The nitrogen addition is controlled to be ≤10ppm. The specific steps of LF furnace refining are as follows:

[0044] 1) Use micro-positive pressure operation to control the pressure at 50-80kPa, turn on the pressure sensor for real-time monitoring, and set interlock protection: automatically replenish air when the pressure is lower than 50kPa, and activate the pressure relief valve when the pressure is higher than 80kPa;

[0045] 2) Then, high basicity refined slag is added in batches, with 60%-70% added in the first batch, to initially form a high basicity slag layer;

[0046] 3) After stirring with argon for 3-5 minutes, add the remaining refined slag and control the final basicity at R = 3.5-4.0;

[0047] 4) Add deoxidizer and observe the color change of slag. When the slag surface is silvery white and fluffy, and the sampled slag turns white after cooling in the air, it is judged to be qualified reduced white slag;

[0048] 5) Maintain the bottom argon soft blowing state to avoid violent stirring and slag rolling, and ensure that the white slag state lasts for ≥10 minutes;

[0049] 6) 1 minute before the end of refining, take a steel sample to test the nitrogen content. If it exceeds the standard, add ferrotitanium to control the nitrogen addition amount to ≤10ppm;

[0050] S8: The molten steel after LF refining is subjected to RH refining again to further reduce the nitrogen content in the molten steel to below 20ppm. The specific steps of RH refining are as follows:

[0051] 1) After the ladle arrives at the RH refining station, a staged vacuuming is adopted. First, a Roots pump is used for rough pumping for 5 minutes to control the vacuum chamber pressure at 10±2kPa. Then, a steam jet pump is used for fine pumping for 8 minutes to reduce the vacuum chamber pressure to ≤133Pa.

[0052] 2) Blow argon into the riser, and control the argon flow rate at 60-125Nm 3 / h, driving the molten steel to form an upward flow rate of 4-6m / s;

[0053] 3) During the argon blowing process, the top oxygen gun is at 2000-3000Nm 3 / h flow rate of continuous oxygen blowing;

[0054] 4) Real-time monitoring of gas content. When the hydrogen content is ≤3ppm, the nitrogen content is ≤30ppm, and the carbon content is ≤10ppm, alloy material is added to the molten steel to control the composition accuracy deviation to: C ≤±0.003%;

[0055] 5) Use natural gas injection to increase temperature and control the natural gas flow rate at 1500-2000Nm 3 / h, the temperature is maintained at 1600-1620℃;

[0056] 6) Start the vacuum breaking operation. When the vacuum chamber pressure is increased, move the ladle to the argon blowing station and perform bottom argon blowing for 5-10 minutes. The argon flow rate is controlled at 5-8NL / min.

[0057] S9: The molten steel after RH refining enters the continuous casting process.

[0058] The implementation method of this embodiment is as follows:

[0059] When smelting YL82HQ steel, first prepare pure scrap steel and molten iron. The amount of pure scrap steel added is 27t, including 12t of billet heads and tails, 10t of plates, and 5t of steel bar strips. The amount of molten iron added is 160t, and the molten iron composition is Si: 0.40%, P: 0.075%, S: 0.035%. The prepared scrap steel and molten iron are added to the converter in turn. During the addition process, the temperature in the furnace is monitored in real time to ensure that the temperature is controlled within 1280℃. After the molten iron is added, the argon blowing at the bottom of the converter is immediately turned on, and the argon blowing flow rate is set to 0.15m 3 / (t·min), then the converter enters the oxygen blowing smelting stage, and the oxygen flow rate is controlled at 35500m 3 / h, after 7 minutes of smelting in the converter, add 800kg of pellets into the converter and continue smelting for 8 minutes. When the oxygen content in the converter reaches 80%, start adding pellets in three batches, adding 500kg each batch. During the addition process, monitor the converter slag basicity in real time and control the converter slag basicity at R=3.8. Maintain the oxygen flow rate at 35500m3 / h, at this time the oxygen lance position is maintained at 1.3m, when it is observed that the carbon fire is burning in a stable state, the oxygen lance position is raised to 1.4m, and the blowing is continued. The temperature in the furnace is 1565℃. During the combustion process, the molten steel composition is continuously monitored in real time. When the molten steel composition reaches C: 0.10%, P: 0.010%, and S: 0.008%, the ladle bottom argon is opened, 100kg of recarburizer is added to the ladle, and steel is prepared after waiting for 2 minutes. In the early stage of steel tapping, deoxidizer is added to the molten steel according to the standard of 1.5kg / t steel, and 250kg of lime is added at the same time. When the steel is tapped to 1 / 3, 800kg of silicon-manganese alloy, 300kg of ferrosilicon, 150kg of recarburizer, and 1200kg of high-carbon ferrochrome are added in the amount set according to the target steel grade composition requirements. All of them are added when 3 / 4 of the steel is tapped. The entire steel tapping process is controlled within 4.5min.

[0060] The ladle after complete tapping is lifted to the LF furnace for refining. Micro-positive pressure operation is adopted, and the pressure is controlled at 65KPa by a pressure sensor. Real-time monitoring is started, and an interlock protection mechanism is set. Argon is automatically added when the pressure is less than 50kPa, and the pressure is automatically released when the pressure is greater than 80kPa. Then high-basicity refined slag is added in batches. The first batch of refined slag is 700kg to initially form a high-basicity slag layer. Then argon blowing and stirring are started. After stirring for 4 minutes, the remaining 300kg of refined slag is added to control the final basicity at R=3.8. Deoxidizer is added and the color change of the slag is observed. When the slag surface is silvery white and fluffy, and the sampled slag turns white after cooling in the air, it is judged to be qualified reduced white slag. The bottom argon soft blowing state is maintained to ensure that the white slag state lasts for 12 minutes. 1 minute before the end of refining, a steel sample is taken to test the nitrogen content. The nitrogen content is 28ppm. 50kg of titanium iron is added to increase the nitrogen amount by +8ppm, and finally maintain N≤36ppm.

[0061] The molten steel after LF refining is hoisted to the RH refining station, and the sectional exhaust is adopted. The roots pump is used for rough pumping for 5 minutes to control the vacuum chamber pressure at 9kPa. Then the steam jet pump is used for fine pumping for 8 minutes to reduce the vacuum chamber pressure to 120Pa. Then the riser is opened to blow argon and the argon flow rate is controlled at 90Nm 3 / h, the rising velocity of molten steel reaches 5m / s, and during the argon blowing process, the top oxygen gun is operated at 2500Nm 3 Oxygen is continuously blown at a flow rate of / h to assist decarburization. The gas content is monitored in real time during the process. When the hydrogen content is ≤3ppm, the nitrogen content is ≤30ppm, and the carbon content is ≤10ppm, 200kg of FeMo alloy is added to the molten steel to ensure that the component accuracy deviation is controlled at C≤±0.003%. Then, natural gas injection is turned on to increase the temperature and the natural gas flow rate is controlled at 1800Nm 3 / h, so that the temperature is maintained at 1610 ° C. After completing various indicators, the vacuum breaking operation begins. When the vacuum chamber pressure is increased, the ladle is moved to the argon blowing station for 8 minutes of bottom argon blowing. The argon flow rate is controlled at 6NL / min.

[0062] The final composition of the molten steel after RH refining is C: 0.22%, Mn: 1.35%, Cr: 0.85%, Mo: 0.25%, and the purity is [N] ≤ 21ppm, [S] ≤ 0.005%, [P] ≤ 0.010%. It is transported to the continuous casting process for subsequent casting and molding operations. The final steel billet meets the YL82HQ requirements, with a yield strength of 735MPa after rolling, a tensile strength of 865MPa, and an impact energy of 52J at -40℃.

[0063] In addition, the implementation results for different steel grades are shown in the following table.

[0064] Table 182B Summary of nitrogen content control levels for multiple batches of steel grades

[0065]

[0066]

[0067] The above is only an embodiment of the present invention, and the common knowledge such as the specific structure and characteristics of the scheme is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for producing high-quality low-nitrogen hard wire steel, characterized in that: The following steps are involved: S1: Add pure scrap steel and molten iron into the converter in sequence. The scrap steel composition mainly consists of internal recycled billet heads and tails, laths, and steel bar cuts. The molten iron composition is Si: 0.30-0.50%, P: ≤0.080%, S: ≤0.040%. The furnace temperature is controlled within 1280℃. S2: After the molten iron is added, start blowing argon from the bottom of the converter and control the argon flow rate at 0.10-0.20m3 through the central control panel. 3 / h, the converter enters the oxygen blowing smelting stage, and the oxygen flow rate is controlled at 30000-40000m 3 / h, after smelting in the converter for 7-9 minutes, add 600-1000kg of pellets into the converter according to the slag situation in the furnace; S3: After the pellets are added for the first time, smelting is continued for 6-7 minutes. When the oxygen content in the converter reaches 70%-90%, the pellets are added again in batches; S4: After adding pellets for the second time, set the oxygen flow rate to 25000-40000m3 through the central control panel. 3 / h, at this time the oxygen lance is at 1.3m, when the carbon fire is burning in a stable state, the oxygen lance is raised to 1.4m, and the oxygen is continuously sprayed to control the temperature in the furnace at 1560℃-1570℃; S5: Real-time monitoring is performed during the combustion process. When the molten steel content reaches the target value, argon is blown from the bottom of the ladle, 100 kg of recarburizer is added to the ladle, and the steel can be tapped after waiting for 2 minutes. S6: In the early stage of tapping, 1.5kg / t steel deoxidizer and 200-300kg lime are added to the molten steel in sequence. When the steel is 1 / 3 tapped, silicon manganese alloy, ferrosilicon, carburizer and high carbon ferrochrome are added in sequence. The amount of alloy added is set according to the ladle composition requirements of each steel grade. All the addition is completed when 3 / 4 of the steel is tapped until the steel is fully tapped. S7: After the steel is completely tapped, the ladle is hoisted to the LF furnace to start refining, and the nitrogen addition is controlled to ≤10ppm; S8: The molten steel after LF refining is subjected to RH refining again to further reduce the nitrogen content in the molten steel to below 20 ppm; S9: The molten steel after RH refining enters the continuous casting process.

2. The method for producing high-quality low-nitrogen hard wire steel according to claim 1, characterized in that: In step S1, the total amount of scrap steel and molten iron added is 187±2t, of which the molten iron accounts for >85%.

3. The method for producing high-quality low-nitrogen hard wire steel according to claim 1, characterized in that: In step S3, the requirements for adding pellets in batches are: adding pellets in 2-4 batches, the weight of each batch of pellets is 500 kg, and controlling the converter slag basicity R=3.5-4.

0.

4. The method for producing high-quality low-nitrogen hard wire steel according to claim 1, characterized in that: In step S5, the target value of the molten iron content is: C: 0.08-0.12%, P≤0.012%, S≤0.010%.

5. The method for producing high-quality low-nitrogen hard wire steel according to claim 1, characterized in that: In step S6, the tapping time is controlled within 3-6 minutes.

6. The method for producing high-quality low-nitrogen hard wire steel according to claim 1, characterized in that: In step S7, the specific steps of LF furnace refining are as follows: 1) Use micro-positive pressure operation to control the pressure at 50-80kPa, turn on the pressure sensor for real-time monitoring, and set interlock protection: automatically replenish air when the pressure is lower than 50kPa, and activate the pressure relief valve when the pressure is higher than 80kPa; 2) Then, high basicity refined slag is added in batches, with 60%-70% added in the first batch, to initially form a high basicity slag layer; 3) After stirring with argon for 3-5 minutes, add the remaining refined slag and control the final basicity at R = 3.5-4.0; 4) Add deoxidizer and observe the color change of slag. When the slag surface is silvery white and fluffy, and the sampled slag turns white after cooling in the air, it is judged to be qualified reduced white slag; 5) Maintain the bottom argon soft blowing state to avoid violent stirring and slag rolling, and ensure that the white slag state lasts for ≥10 minutes; 6) 1 minute before the end of refining, take a steel sample to test the nitrogen content. If it exceeds the standard, add ferrotitanium to control the nitrogen addition amount to ≤10ppm.

7. The method for producing high-quality low-nitrogen hard wire steel according to claim 1, characterized in that: In step S8, the specific steps of RH refining are as follows: 1) After the ladle arrives at the RH refining station, a staged vacuuming is adopted. First, a Roots pump is used for rough pumping for 5 minutes to control the vacuum chamber pressure at 10±2kPa. Then, a steam jet pump is used for fine pumping for 8 minutes to reduce the vacuum chamber pressure to ≤133Pa. 2) Blow argon into the riser, and control the argon flow rate at 60-125Nm 3 / h, driving the molten steel to form an upward flow rate of 4-6m / s; 3) During the argon blowing process, the top oxygen gun is at 2000-3000Nm 3 / h flow rate of continuous oxygen blowing; 4) Real-time monitoring of gas content. When the hydrogen content is ≤3ppm, the nitrogen content is ≤30ppm, and the carbon content is ≤10ppm, alloy material is added to the molten steel to control the composition accuracy deviation to: C ≤±0.003%; 5) Use natural gas injection to increase temperature and control the natural gas flow rate at 1500-2000Nm 3 / h, the temperature is maintained at 1600-1620℃; 6) Start the vacuum breaking operation. When the vacuum chamber pressure is increased, move the ladle to the argon blowing station and perform bottom argon blowing for 5-10 minutes. The argon flow rate is controlled at 5-8NL / min.

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