Low-nitrogen smelting method in low-iron-steel-ratio mode

Abstract

The invention discloses a low-nitrogen smelting method in a low-iron-steel ratio mode, which comprises the following steps: (1) before converter blowing, an oxygen lance adopts an oxygen-argon combined blowing mode in the middle stage, so as to ensure that scrap steel is thoroughly dissolved and cleared within 9 minutes of converter blowing; (2) when the converter starts blowing, if the content of Si in molten iron is less than or equal to 0.50%, adding a silicon-aluminum composite exothermic agent into the converter to ensure that the temperature of a molten pool of the converter is more than or equal to 1420 DEG C when blowing is carried out for 4-4 minutes and 30 seconds, so that the C-O reaction condition is met; (3) when the end point P or the temperature is unqualified, reblowing is needed at the end point of the converter, argon bottom blowing of the converter is adjusted for 30-40 s before reblowing, the argon flow of an oxygen lance during reblowing is 35000-40000 m / h, nitrogen suction during reblowing is avoided, and S after converter argon blowing is smaller than or equal to 0.010%; (4) the bottom blowing argon flow is 50-150 L / min in the whole process of the refining power transmission period of the LF furnace, the diameter of the bright surface of the molten steel is smaller than 25 cm, high-power-supply-gear long-arc power transmission is adopted for primary power transmission of the LF furnace, argon is blown to the electrode circle area of the molten steel surface for 20-50 s, and 10-15 Kg of calcium carbide is added to the electrode circle area every 2 min in the whole power transmission process; lF desulfurization is completed during power failure, the power failure stirring time is less than or equal to 40s / time, and the nitrogen content of tapping of a refining station is less than or equal to 44ppm.

Description

Technical Field

[0001] The present invention relates to the technical field of steelmaking, in particular to a low-nitrogen smelting method in a low iron-to-steel ratio mode. Background Art

[0002] The converter itself has excellent denitrification capabilities under normal iron-to-steel ratio conditions. The converter's denitrification capacity is characterized by excellent denitrification in the early and middle stages of smelting, but poorer performance in the final stages due to the weakening of CO reaction. To reduce carbon emissions from steelmaking, many steelmakers are reducing the amount of hot metal used in their converters and increasing scrap steel usage (i.e., adopting a low iron-to-steel ratio model). To control carbon emissions and achieve dual carbon goals, some companies have increased their converter scrap ratio to nearly 30-40%. Some companies, pursuing extremely low iron consumption, even use scrap levels exceeding 40%. However, adopting a low iron-to-steel ratio significantly increases nitrogen levels at the converter end point. According to statistics, when the converter iron-to-steel ratio drops below 750 kg / t, nitrogen levels at the converter end point are 20-30 ppm higher in the low iron-to-steel ratio model compared to the high iron-to-steel model.

[0003] Therefore, studying low-nitrogen smelting methods under a low iron-steel ratio mode has become an urgent problem to be solved in the industry. Summary of the Invention

[0004] The purpose of the present invention is to provide a low-nitrogen smelting method with a low iron-steel ratio mode to address the problem that when a low iron-steel ratio is used in current converter smelting, the nitrogen content in the converter terminal increases significantly, making it impossible to achieve the normal smelting and steelmaking goal of the converter.

[0005] A low-nitrogen smelting method in a low iron-to-steel ratio mode of the present invention comprises the following steps: (1) In the converter blowing period of 0-9 minutes, that is, in the early and middle stages of converter smelting, the oxygen lance adopts the oxygen-argon composite blowing mode, adopting oxygen as the main blowing, the oxygen flow rate of the oxygen lance within 0-3 minutes of converter blowing is 35000-38000 m³ / h, and the oxygen flow rate of the oxygen lance within 3-9 minutes of blowing is 35000-40000 m³ / h, and the oxygen lance is opened for argon auxiliary blowing at 2-3 minutes and 4-6 minutes of blowing respectively, with the argon auxiliary blowing flow rate of 10000-20000 m³ / h, so as to increase the stirring and melting of the scrap steel, and ensure that the scrap steel is completely dissolved within 9 minutes of converter blowing; (2) When the converter is started, if the Si content of the molten iron is ≤0.50%, 1000-1500 kg / furnace of silicon-aluminum composite heating agent is added to the converter to ensure that the converter bath temperature is ≥1420°C during the blowing period of 4 min-4 min 30 s. If the Si content of the molten iron is >0.50%, there is no need to add silicon-aluminum composite heating agent; (3) Control of converter end-point re-blowing: If the end-point P component and temperature are qualified, no re-blowing is required; if the end-point P or temperature is unqualified, the converter end-point needs to be re-blown. Before re-blowing, adjust the converter bottom blowing argon for 30-40s, and the bottom blowing argon flow rate is 800-1000L / min. During re-blowing, the oxygen lance argon flow rate is 35000-40000m³ / h, so as to discharge the air above the molten pool before and during re-blowing to avoid nitrogen absorption. After re-blowing, S of the converter is ≤0.010%; (4) During the entire LF furnace refining power supply period, the bottom blowing argon flow rate is 50-150L / min, and the diameter of the bright surface of the molten steel is controlled to be less than 25cm. During the initial power supply process of the LF furnace, the slag material is burned using a high power supply gear and long arc power supply, and the arc voltage is controlled to be 275-285V. Argon is sprayed in the electrode circle area on the molten steel surface for 20-50s, and the flow rate of the sprayed argon is 150-250L / min. After the arc flow is stable, 10-15Kg of calcium carbide is added to the electrode circle area every 2min during the entire power supply process; LF desulfurization is completed during power outages, and the power outage strong stirring desulfurization time is ≤40s / time, and the strong stirring argon flow rate is 250-350L / min. Desulfurization is completed when the S content is ≤0.005%, and the nitrogen content of the steel discharged from the refining station is ≤44ppm.

[0006] The low iron-steel ratio refers to an iron-steel ratio of 693-747 kg / t (the iron-steel ratio calculation formula is: molten iron volume × 1000 / molten steel volume), and the proportion of scrap steel entering the furnace is required to be 30%-35%, that is, scrap steel volume / (molten iron + scrap steel volume).

[0007] The converter described in the present invention is a 130t top and bottom blown converter.

[0008] The silicon-aluminum composite heating agent of the present invention contains the following substances in percentage by mass: Si: 40-55%, Ti: 5-7%, Al: 5-7%, SiO2: 10-20%, Al2O3: 10-15%, and the remainder is impurity elements.

[0009] The mass fraction of CaC2 in the calcium carbide of the present invention is ≥95%.

[0010] The present invention conducts in-depth research on the reasons for the increase in nitrogen content in the smelting process under the low iron-steel ratio mode, which mainly include the following two aspects: first, the nitrogen content of the scrap steel itself is relatively high, and after the amount of scrap steel added increases, the time for the scrap steel to be completely dissolved is delayed, and the original nitrogen content of the scrap steel increases; second, the amount of scrap steel increases, the surplus heat of the converter decreases, and the CO reaction time is reduced due to the temperature reduction during the entire blowing process, which in turn affects the denitrification efficiency of the converter.

[0011] Therefore, the present invention divides the nitrogen control tasks of the smelting process into the converter and the LF furnace. The converter mainly solves how to improve the denitrification capacity of the converter body and control the nitrogen increase capacity under the low iron-steel ratio mode. The LF furnace needs to optimize the refining process and reduce the nitrogen increase in LF refining compared with the conventional iron-steel ratio mode to achieve the goal of reducing nitrogen increase in the smelting process. Therefore, the main research and development ideas of the present invention are as follows: First, the present invention aims to improve the denitrification efficiency of the converter and control the increase in nitrogen at the end of the blowing process. When the amount of scrap steel is increased under low iron-steel conditions, the converter's CO reaction and molten pool stirring are weakened due to the influence of heat balance and temperature, significantly reducing the denitrification capacity in the early and middle stages of the converter smelting process. Furthermore, as the amount of scrap steel increases, the time it takes for the scrap steel to completely melt (dissolve) in the molten steel is extended. Tracking the scrap steel melting data during the actual blowing process under low iron-steel ratio conditions shows that some scrap steel is still melting at the end of the smelting process when the CO reaction is weak, and even at the end of the smelting process, some scrap steel is still melting. Because the scrap steel itself has a high nitrogen content, the scrap steel melting process at the end of the converter smelting process (converter) is actually a process of increasing nitrogen in the molten steel. The melting of scrap steel at this stage will directly cause nitrogen increase. Furthermore, from the perspective of nitrogen control, converter end point control is very important. Both converter end carbon and end blowdown will cause nitrogen increase, and the converter end point should also be reasonably controlled.

[0012] Secondly, the present invention should control the nitrogen addition in the LF furnace. The control of nitrogen addition in the LF furnace mainly controls the absorption of nitrogen ions ionized by the arc and the nitrogen absorption by the strong stirring desulfurization of the molten steel. The optimization can be carried out from the aspects of power supply system, strong stirring time, desulfurization amount, etc.

[0013] To achieve the above-mentioned purpose, the smelting principle of the smelting method of the present invention is as follows: (1) In the 0-9 minutes of converter blowing, that is, in the early and middle stages of converter smelting, the oxygen lance adopts an oxygen-argon composite blowing mode, with oxygen as the main blowing and argon as the auxiliary blowing mode, to increase the stirring and melting of the scrap steel, ensuring that the scrap steel is completely dissolved within 9 minutes of converter blowing; (2) When the converter is started, if the Si content of the molten iron is ≤0.50%, 1000-1500 kg / furnace of silicon-aluminum composite heating agent is added to the converter to ensure that the converter bath temperature is ≥1420°C during the blowing period of 4 min-4 min 30 s. This will ensure sufficient CO reaction time and the denitrification efficiency of the smelting process. If the Si content of the molten iron is >0.50%, there is no need to add silicon-aluminum composite heating agent. (3) Control of re-blowing at the converter end point: if the P component and temperature at the end point are qualified, no re-blowing is required; if the P component or temperature at the end point is unqualified, re-blowing is required at the converter end point. Before re-blowing, adjust the converter bottom blowing argon for 30-40s, and the argon flow rate is 800-1000L / min. During re-blowing, the argon flow rate of the oxygen lance is 35000-40000m³ / h, so as to discharge the air above the molten pool before and during re-blowing to avoid nitrogen absorption during re-blowing. After the converter argon is added, S is ≤0.010% (the desulfurization task is moved forward to control the refining desulfurization amount, ensuring that the desulfurization amount in the LF smelting process is ≤0.005%, reducing the increase in nitrogen in the refining process; (4) During the LF furnace refining power supply period, the argon flow rate is low at 50-150L / min, and the diameter of the bright surface of the molten steel is controlled to be less than 25cm. Avoid blowing a large amount of argon from the bottom of the ladle during power supply, which will expose the molten steel surface and cause nitrogen increase. During the initial power supply process of the LF furnace, the slag material is burned using a high power supply gear and long arc power supply. The arc voltage is controlled to be 275-285V, and argon is sprayed in the electrode circle area on the molten steel surface for 20-50s. The argon flow rate is 150-250L / min. Nitrogen increase is most likely to occur during this period. When the power is initially supplied, argon is sprayed in the electrode circle area for 20s. The LF desulfurization process is completed during power outages. The desulfurization cycle is ≤40 seconds per cycle with strong agitation, with an argon flow rate of 250-350 L / min. Desulfurization is performed to a sulfur content of ≤0.005%, avoiding nitrogen absorption caused by prolonged strong agitation of the molten steel. This completes refining, with the nitrogen content of the tapped steel at ≤44 ppm.

[0014] The beneficial effects of the present invention are as follows: 1) The present invention systematically optimizes the converter and LF processes, improving converter denitrification efficiency and reducing nitrogen addition in the converter tail stage and LF furnace at low iron-steel ratios, thereby reducing steelmaking costs. 2) This invention realizes low-nitrogen smelting under low-iron and low-steel conditions, which conforms to the concept of green and low-consumption steelmaking; 3) The process flow of the present invention is simple and clear, highly operable and easy to control.

[0015] The present invention aims at the increase of nitrogen content in the smelting process under the low iron-steel ratio mode. The method of the present invention addresses the high nitrogen problem caused by the low iron-steel ratio by targetedly improving the smelting operation method, and correspondingly optimizes the nitrogen increase in the LF refining link, thereby making up for the shortcomings of other steelmaking methods. The operation is simple and safe, and low-nitrogen smelting in the whole process under low iron-steel ratio conditions is achieved, which has high promotion value. DETAILED DESCRIPTION

[0016] In order to better explain the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with specific embodiments. The following embodiments are merely exemplary of the technical solution of the present invention and do not limit the present invention in any form. The serial numbers of the following embodiments are for description only and do not represent the advantages or disadvantages of the embodiments.

[0017] Example 1 In this embodiment, the converter has 112 tons of molten iron, 48 tons of scrap steel, an iron-steel ratio of 747 kg / t, and a silicon content of 0.35%.

[0018] A low-nitrogen smelting method in a low iron-to-steel ratio mode of this embodiment includes the following methods: (1) In the converter blowing period of 0-9 minutes, that is, in the early and middle stages of converter smelting, the oxygen lance adopts the oxygen-argon composite blowing mode, adopting oxygen as the main blowing, the oxygen flow rate of the oxygen lance is 35,000 m³ / h within 0-3 minutes of converter blowing, and the oxygen flow rate of the oxygen lance is 35,000 m³ / h within 3-9 minutes of blowing, and the oxygen flow rate of the oxygen lance is 35,000 m³ / h at the same time, and the oxygen lance is opened for 2-3 minutes and 4-6 minutes of blowing respectively. The argon auxiliary blowing flow rate is 10,000 m³ / h to increase the stirring and melting of the scrap steel. The scrap steel has been completely dissolved in the converter blowing period of 9 minutes; (2) When the converter is started, because the Si content of the molten iron is 0.32%, which is less than 0.50%, 1500 kg / furnace of silicon-aluminum composite heating agent is added to the converter. When the blowing reaches 4 minutes, the temperature of the auxiliary lance model converter bath is 1420 ° C, which can ensure the CO reaction intensity and improve the denitrification efficiency in the early and middle stages of the converter; (3) Control of converter end-point re-blowing: The end-point P content is 0.026% and the temperature is 1610℃. The end-point P is unqualified and needs to be re-blown. Before re-blowing, adjust the converter bottom blowing argon for 30s. The bottom blowing argon flow rate is 800L / min. The oxygen lance argon flow rate during re-blowing is 35000m³ / h, which is convenient for discharging the air above the molten pool before and during re-blowing to avoid nitrogen absorption after re-blowing. S after converter argon: 0.010%; (4) During the entire LF furnace refining power supply period, the bottom blowing argon flow rate is 50L / min, and the diameter of the bright surface of the molten steel is controlled to be less than 25cm. During the initial power supply process of the LF furnace, the slag material is burned using a high power supply gear and long arc power supply, and the arc voltage is controlled to be 275V. Argon is sprayed in the electrode circle area of ​​the molten steel surface for 20s, and the argon flow rate is 150L / min. After the arc flow is stable, 10Kg of calcium carbide is added to the electrode circle area every 2min during the entire power supply process; LF desulfurization is completed during power outages, and the power outage strong stirring desulfurization time is 36-38s / time, and the strong stirring argon flow rate is 250L / min. Desulfurization is completed when the S content is ≤0.005%, and the nitrogen content of the steel discharged from the refining station is 44ppm.

[0019] During the smelting process of this embodiment, the nitrogen at the converter outlet is 37ppm, the nitrogen added during refining is 7ppm, and the nitrogen at the refined outlet is 44ppm, thus achieving the goal of low-nitrogen smelting.

[0020] Example 2 In this embodiment, the converter has 110 tons of molten iron, 50 tons of scrap steel, an iron-steel ratio of 733 kg / t, and a Si content of 0.40%; A low-nitrogen smelting method in a low iron-to-steel ratio mode of this embodiment includes the following methods: (1) In the converter blowing period of 0-9 minutes, that is, in the early and middle stages of converter smelting, the oxygen lance adopts the oxygen-argon composite blowing mode, adopting oxygen as the main blowing, the oxygen flow rate of the oxygen lance is 37,000 m³ / h within 0-3 minutes of converter blowing, and the oxygen flow rate of the oxygen lance is 38,000 m³ / h within 3-9 minutes of blowing. At the same time, the oxygen lance is opened for argon auxiliary blowing at 2-3 minutes and 4-6 minutes of blowing, respectively, to increase the stirring and melting of the scrap steel. The scrap steel has been completely dissolved in the converter blowing period of 8 minutes; (2) When the converter is started, since the Si content of the molten iron is 0.40%, which is less than 0.50%, 1200 kg / furnace of silicon-aluminum composite heating agent is added to the converter. When the blowing reaches 4 min 10 s, the temperature of the converter bath of the auxiliary lance model converter is 1430 ° C, which can ensure the CO reaction intensity and improve the denitrification efficiency in the early and middle stages of the converter; (3) Control of converter end-point re-blowing: The end-point P content is 0.027% and the temperature is 1612℃. The end-point P is unqualified and needs to be re-blown. Before re-blowing, adjust the converter bottom blowing argon for 35s and the bottom blowing argon flow rate is 900L / min. During re-blowing, the oxygen lance argon flow rate is 38000m³ / h, which is convenient for discharging the air above the molten pool before and during re-blowing to avoid nitrogen absorption. The S of the converter after argon is 0.009%; (4) During the entire LF furnace refining power supply period, the bottom blowing argon flow rate is 100L / min, and the diameter of the bright surface of the molten steel is controlled to be less than 25cm. During the initial power supply process of the LF furnace, the slag material is burned using a high power supply gear and long arc power supply, and the arc voltage is controlled to be 280V. Argon is sprayed in the electrode circle area on the molten steel surface for 30s, and the flow rate of the argon spraying is 200L / min. After the arc flow is stable, 12Kg of calcium carbide is added to the electrode circle area every 2min during the entire power supply process; LF desulfurization is completed during power outages, and the power outage strong stirring desulfurization time is 30-32s / time, and the strong stirring argon flow rate is 300L / min. Desulfurization is completed when the S content is ≤0.005%, and the nitrogen content of the steel discharged from the refining station is 44ppm.

[0021] During the smelting process of this embodiment, the nitrogen at the converter outlet is 35ppm, the nitrogen added during refining is 6ppm, and the nitrogen at the refined outlet is 41ppm, thus achieving the goal of low-nitrogen smelting.

[0022] Example 3 In this embodiment, the converter has 104 tons of molten iron, 51 tons of scrap steel, an iron-steel ratio of 693 kg / t, and a Si content of 0.50%; A low-nitrogen smelting method in a low iron-to-steel ratio mode of this embodiment includes the following methods: (1) In the converter blowing period of 0-9 minutes, that is, in the early and middle stages of converter smelting, the oxygen lance adopts the oxygen-argon composite blowing mode, adopting oxygen as the main blowing, the oxygen flow rate of the oxygen lance is 38,000 m³ / h within 0-3 minutes of converter blowing, and the oxygen flow rate of the oxygen lance is 40,000 m³ / h within 3-9 minutes of blowing. At the same time, the oxygen lance is opened for argon auxiliary blowing at 20,000 m³ / h at 2-3 minutes and 4-6 minutes of blowing, respectively, to increase stirring and melting of scrap steel. The scrap steel is completely dissolved after 7 minutes of converter blowing; (2) When the converter is started, since the Si content of the molten iron is 0.50%, 1000 kg / furnace of silicon-aluminum composite heating agent is added to the converter. When the blowing reaches 4 min 10 s, the temperature of the auxiliary lance model converter molten pool is 1450 ° C, which can ensure the CO reaction intensity and improve the denitrification efficiency of the converter in the early and middle stages; (3) Control of converter end-point re-blowing: The end-point P content is 0.019% and the temperature is 1598℃. The end-point temperature is unqualified and re-blowing is required. Before re-blowing, adjust the converter bottom blowing argon for 40s. The bottom blowing argon flow rate is 1000L / min. The oxygen lance argon flow rate during re-blowing is 40000m³ / h. It is convenient to discharge the air above the molten pool before and during re-blowing to avoid nitrogen absorption after re-blowing. After the converter argon, S: 0.008%, N: 34ppm; (4) During the entire LF furnace refining power supply period, the bottom blowing argon flow rate is 150L / min, and the diameter of the bright surface of the molten steel is controlled to be less than 25cm. During the initial power supply process of the LF furnace, the slag material is burned using a high power supply gear and long arc power supply, and the arc voltage is controlled to be 285V. Argon is sprayed in the electrode circle area on the molten steel surface for 50s, and the argon flow rate is 250L / min. After the arc flow is stable, 15Kg of calcium carbide is added to the electrode circle area every 2min during the entire power supply process; LF desulfurization is completed during power outages, and the power outage strong stirring desulfurization time is 38-40s / time, and the strong stirring argon flow rate is 350L / min. Desulfurization is completed when the S content is ≤0.005%, and the nitrogen content of the steel discharged from the refining station is 39.5ppm.

[0023] During the smelting process of this embodiment, the nitrogen at the converter outlet is 34ppm, the nitrogen added during refining is 5.5ppm, and the nitrogen at the refined outlet is 39.5ppm, thus achieving the goal of low-nitrogen smelting.

[0024] Comparative Example 1 In this embodiment, the converter has 108 tons of molten iron, 52 tons of scrap steel, an iron-steel ratio of 720 kg / t, and a Si content of 0.42%; This embodiment adopts conventional smelting mode, including the following steps: (1) After the converter is started, the oxygen lance only blows oxygen without composite blowing. The oxygen flow rate of the oxygen lance is 35,000 m³ / h within 0-3 minutes of the converter start-up, and the oxygen flow rate of the oxygen lance is 38,000 m³ / h within 3-9 minutes of blowing. Because there is no auxiliary argon blowing to increase stirring and melt the scrap steel, the scrap steel is still not completely dissolved after 9 minutes of blowing; (2) When the Si content in molten iron is ≤0.50%, no exothermic agent is added to compensate for the heat source when the converter is started. The converter steel liquid temperature is 1408℃ at 4min-4min30s, which does not meet the CO reaction temperature condition and cannot provide conditions for CO stage denitrification; (3) The converter endpoint P was 0.028% and the temperature was 1596℃, both of which were unqualified. The oxygen lance was directly lowered for supplementary blowing. During the supplementary blowing, the top oxygen lance was not switched to argon to exhaust the air in the furnace first. The top oxygen lance was directly opened to blow oxygen, with an oxygen flow rate of 39,000 m³ / h. The bottom blowing gas flow rate was not adjusted, and the bottom blowing flow rate was only 200-300 L / min. The bottom blowing flow rate was too low to remove the air in the furnace. The conventional mode did not use top and bottom combined blowing of inert gas to remove the air in the furnace. It was extremely easy to increase nitrogen in the high-temperature open environment at the end point. The converter endpoint S: 0.025%, N: 65ppm; (4) During the power supply process of the LF furnace, the argon flow rate is 200L / min, the diameter of the bright surface of the molten steel is less than 50cm, and the LF desulfurization is carried out during power supply and power outage. The strong stirring desulfurization time is 50-70s / time, and the strong stirring argon flow rate is 300L / min. Desulfurization is carried out to a S content of ≤0.005%. The molten steel is exposed for a long time. At the end of smelting, the N content of the molten steel is 78ppm.

[0025] During the smelting process of this embodiment, the nitrogen at the converter outlet was 65ppm, the nitrogen added during refining was 13ppm, and the nitrogen at the refined outlet was 78ppm, which failed to achieve the goal of low-nitrogen smelting.

[0026] The effects of the smelting processes of Examples 1-3 and Comparative Example 1 are compared, and the results are shown in Table 1 below.

[0027] Table 1 Comparison of smelting process effects of Examples 1-3 and Comparative Example 1

[0028] The technical means of the smelting process of Examples 1-3 and Comparative Example 1 are compared. The results are shown in Table 2 below.

[0029] A comparison of Tables 1 and 2 shows that the low-nitrogen smelting method of the present invention, operating in a low iron-to-steel ratio mode, achieves the desired low-nitrogen smelting goal, whereas conventional smelting fails to achieve this goal. The present method achieves low-nitrogen smelting by controlling each step in the smelting process where nitrogen may be added, optimizing the corresponding process parameters and operating mode. The entire process is simple to operate and suitable for widespread adoption.

Claims

1. A low-nitrogen smelting method with a low iron-steel ratio mode, characterized in that The steps include: (1) In the converter blowing period of 0-9 minutes, that is, in the early and middle stages of converter smelting, the oxygen lance adopts the oxygen-argon composite blowing mode, adopting oxygen as the main blowing, the oxygen flow rate of the oxygen lance within 0-3 minutes of converter blowing is 35000-38000 m³ / h, and the oxygen flow rate of the oxygen lance within 3-9 minutes of blowing is 35000-40000 m³ / h, and the oxygen lance is opened for argon auxiliary blowing at 2-3 minutes and 4-6 minutes of blowing respectively, with the argon auxiliary blowing flow rate of 10000-20000 m³ / h, so as to increase the stirring and melting of the scrap steel, and ensure that the scrap steel is completely dissolved within 9 minutes of converter blowing; (2) When the converter is started, if the Si content of the molten iron is ≤0.50%, 1000-1500 kg / furnace of silicon-aluminum composite heating agent is added to the converter to ensure that the converter bath temperature is ≥1420°C during the blowing period of 4 min-4 min 30 s. If the Si content of the molten iron is >0.50%, there is no need to add silicon-aluminum composite heating agent; (3) Control of converter end-point re-blowing: If the end-point P component and temperature are qualified, no re-blowing is required; if the end-point P or temperature is unqualified, the converter end-point needs to be re-blown. Before re-blowing, adjust the converter bottom blowing argon for 30-40s, and the bottom blowing argon flow rate is 800-1000L / min. During re-blowing, the oxygen lance argon flow rate is 35000-40000m³ / h, so as to discharge the air above the molten pool before and during re-blowing to avoid nitrogen absorption. After re-blowing, S of the converter is ≤0.010%; (4) During the entire LF furnace refining power supply period, the bottom blowing argon flow rate is 50-150L / min, and the diameter of the bright surface of the molten steel is controlled to be less than 25cm. During the initial power supply process of the LF furnace, the slag material is burned using a high power supply gear and long arc power supply, and the arc voltage is controlled to be 275-285V. Argon is sprayed in the electrode circle area on the molten steel surface for 20-50s, and the flow rate of the sprayed argon is 150-250L / min. After the arc flow is stable, 10-15Kg of calcium carbide is added to the electrode circle area every 2min during the entire power supply process; LF desulfurization is completed during power outages, and the power outage strong stirring desulfurization time is ≤40s / time, and the strong stirring argon flow rate is 250-350L / min. Desulfurization is completed when the S content is ≤0.005%, and the nitrogen content of the steel discharged from the refining station is ≤44ppm.

2. The low-nitrogen smelting method in a low iron-to-steel ratio mode according to claim 1, characterized in that: The low iron-steel ratio refers to an iron-steel ratio of 693-747 kg / t, requiring the mass percentage of scrap steel entering the furnace to be 30%-35%.

3. The low-nitrogen smelting method in a low iron-to-steel ratio mode according to claim 1, characterized in that: The converter is a 130t top and bottom blown converter.

4. The low-nitrogen smelting method in a low iron-to-steel ratio mode according to claim 1, characterized in that: The silicon-aluminum composite heating agent contains the following substances in percentage by mass: Si: 40-55%, Ti: 5-7%, Al: 5-7%, SiO2: 10-20%, Al2O3: 10-15%, and the remainder is impurity elements.

5. The low-nitrogen smelting method in a low iron-to-steel ratio mode according to claim 1, characterized in that: The mass fraction of CaC2 in the calcium carbide is ≥95%.

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