A method for increasing nitrogen in high-nitrogen steel

Abstract

This invention discloses a method for producing high-nitrogen steel with nitrogen enhancement, comprising: Step 1, converter smelting: using bottom blowing mode with nitrogen blowing throughout the process; Step 2, refining LF furnace: the LF furnace is bottom-blown with nitrogen before the third power supply and bottom-blown with argon after the third power supply. Slag formation, deoxidation, and alloying are performed during the refining LF furnace process, and the composition of the molten steel is controlled and tested; Step 3, refining RH furnace: nitrogen is used as the vacuum treatment driving gas, and the nitrogen content is controlled by adjusting the high and low vacuum times. After RH furnace vacuum breaking, calcium treatment is performed, carbonized rice husks are added to cover the molten steel surface, and argon flow is adjusted for soft blowing. Samples are taken to confirm the nitrogen content; Step 4, continuous casting: continuous casting is performed using a continuous casting machine. This application achieves precise control and stable maintenance of the nitrogen content in high-nitrogen steel by using nitrogen blowing throughout the converter process, nitrogen enhancement in the refining LF furnace before the third power supply, and nitrogen enhancement in the refining RH furnace, thus meeting the quality requirements of high-nitrogen steel. The production process is simple, which is beneficial for improving production efficiency and reducing production costs.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, and in particular relates to a method for producing and smelting high-nitrogen steel with nitrogen enrichment. Background Technology

[0002] With the rapid development of industry and the continuous improvement of the performance requirements of steel in various industries, high-nitrogen steel has broad application prospects in aerospace, automobile manufacturing, energy equipment and other fields due to its high strength, good impact toughness and excellent corrosion resistance.

[0003] Nitrogen, as a key alloying element in high-nitrogen steel, plays a crucial role in its performance. Therefore, effectively improving and stabilizing nitrogen composition control in high-nitrogen steel has become a key research focus and critical technological requirement in this field.

[0004] Existing technologies primarily involve adding nitrogen-enhancing alloys and bottom-blown nitrogen during converter tapping or refining processes to increase nitrogen content. However, the nitrogen content of the steel can fluctuate by tens of ppm, which not only severely affects the consistency and stability of the properties of high-nitrogen steel but also makes it difficult to meet the high-precision material performance requirements of high-end applications. This results in a large number of products failing quality inspections, increasing production costs and wasting resources. Therefore, the technical problem this invention aims to solve is how to design a smelting technology that can effectively improve and stabilize the nitrogen composition of high-nitrogen steel while maintaining a simple process and controllable cost. Summary of the Invention

[0005] The purpose of this invention is to provide a method for producing high-nitrogen steel with nitrogen enhancement, achieving a smelting technology that can effectively improve and stabilize the nitrogen content of high-nitrogen steel, with simple procedures and controllable costs.

[0006] To solve the above-mentioned technical problems, the present invention is mainly achieved through the following technical solutions: In the first aspect, the present invention provides a method for producing and smelting high-nitrogen steel with nitrogen enhancement, specifically including the following steps: Step 1, converter smelting: Nitrogen gas is blown throughout the smelting process using bottom blowing mode; Step 2, refining the LF furnace: The refining process in the LF furnace includes four power supply cycles. Before the third power supply, the LF furnace is bottom-blown with nitrogen, and after the third power supply, the LF furnace is bottom-blown with argon. During the refining process in the LF furnace, slag formation, deoxidation, and alloying are carried out, and the composition of the molten steel leaving the station is controlled and tested. Step 3, Refining RH Furnace: Nitrogen is used as the driving gas for vacuum treatment. The nitrogen content is controlled by adjusting the high and low vacuum time. After the RH furnace is broken, calcium treatment is performed. Carbonized rice husks are added to cover the surface of the molten steel. After adding the carbonized rice husks, the argon flow rate is adjusted for soft blowing. Samples are taken to confirm the nitrogen content. Step 4, continuous casting: Continuous casting is carried out using a continuous casting machine.

[0007] In some embodiments of this application, in step one, the converter smelting includes a converter blowing period, which includes an early blowing period, a middle blowing period, and a late blowing period; the early blowing period accounts for 30% of the total process, and the bottom blowing flow rate in the early blowing period is 320 NL / min; the middle blowing period accounts for 50% of the total process, and the bottom blowing flow rate in the middle blowing period is 240 NL / min; the late blowing period accounts for 20% of the total process, and the bottom blowing flow rate in the middle blowing period is 480 NL / min.

[0008] In some embodiments of this application, in step one, after the converter smelting is completed, the final carbon content is controlled at 0.05%~0.12%; the final phosphorus content is controlled at ≤0.015%; and the final temperature is controlled at ≥1600℃.

[0009] In some embodiments of this application, in step one, the bottom blowing of the ladle during the converter tapping process is driven by nitrogen. The nitrogen flow rate is 800~1000NL / min in the early stage of tapping; 300~600NL / min in the middle stage of tapping; and 50~200NL / min in the later stage of tapping.

[0010] In some embodiments of this application, in step two, the time for bottom blowing nitrogen is 10-20 min; the time for bottom blowing argon is 10-20 min.

[0011] In some embodiments of this application, during the LF furnace refining process, the first nitrogen flow rate is 200~500 NL / min, controlling the exposed diameter of the molten steel to be >400 mm; the second nitrogen flow rate is 150~250 NL / min, controlling the exposed diameter of the molten steel to be 250~350 mm; the third argon flow rate is 70~130 NL / min, controlling the exposed diameter of the molten steel to be 150~250 mm; and the fourth argon flow rate is 30~70 NL / min, controlling the exposed diameter of the molten steel to be 50~150 mm.

[0012] In some embodiments of this application, in step two, the steel composition detection includes the content of C, Si, Mn, Cr, N, S, and P; when the content of C, Si, Mn, and Cr is lower than the target lower limit, the corresponding carbon powder and alloy are added, and the mixture is stirred for 3 to 5 minutes.

[0013] In some embodiments of this application, in step three, during the vacuum treatment process of the refining RH furnace, the high vacuum degree is controlled at ≤67Pa and the high vacuum time is 5~15min; the low vacuum degree is controlled at ≤4000Pa and the low vacuum time is 10~20min.

[0014] In some embodiments of this application, in step three, after the RH is broken, calcium treatment is performed by feeding calcium wire. The calcium wire feeding speed is 1~3m / s, and the calcium wire feeding amount is 0.2~0.5kg / t steel.

[0015] In some embodiments of this application, in step three, the amount of carbonized rice husk added is 0.3~0.8 kg / t steel, the soft blowing time after adding the carbonized rice husk is 15~25 min, and the argon flow rate is <50 NL / min. Compared with the prior art, the advantages and positive effects of this invention are as follows: The production and smelting method for increasing nitrogen content in high-nitrogen steel includes converter smelting, refining LF furnace, refining RH furnace, and continuous casting. During converter smelting, nitrogen is blown continuously from the bottom in a bottom-blowing mode. Through sufficient contact between nitrogen and molten steel, a basic nitrogen content is imparted to the steel, while simultaneously promoting the homogenization of the steel composition. Continuous bottom-blowing of nitrogen in the refining LF furnace before the third power-on further replenishes the nitrogen content in the molten steel. After the third power-on, bottom-blowing of argon in the LF furnace prevents excessive nitrogen escape in subsequent processes and also stirs the molten steel and promotes the flotation of inclusions. The refining RH furnace uses nitrogen as the driving gas for vacuum treatment, achieving precise control of nitrogen content by adjusting the high and low vacuum times. This application achieves precise control and stable maintenance of nitrogen content in high-nitrogen steel through full-process nitrogen blowing in the converter, nitrogen addition in the refining LF furnace before the third power-on, and nitrogen addition in the refining RH furnace, meeting the quality requirements of high-nitrogen steel. The production process is simple, which is beneficial for improving production efficiency and reducing production costs. After the RH is broken, calcium treatment is performed to improve the purity of the molten steel by reacting calcium with inclusions in the molten steel. Adding carbonized rice husks to cover the surface of the molten steel reduces secondary oxidation of the molten steel. Adjusting the argon flow rate for soft blowing ensures that the molten steel is in a micro-peristaltic state in the ladle, avoiding fluctuations in nitrogen content. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] It should be noted that in the description of this invention, the terms "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," which indicate directional or positional relationships, are merely for ease of description and do not indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0018] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0019] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0020] The following disclosure provides many different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0021] In the first aspect, embodiments of this disclosure provide a method for producing high-nitrogen steel with nitrogen enrichment, specifically including the following steps: converter smelting → refining LF furnace → refining RH furnace → continuous casting.

[0022] Step 1, converter smelting: During the converter smelting process, nitrogen is blown throughout the process in a bottom-blowing mode to initially increase the nitrogen content of the molten steel. Through the full contact between nitrogen and molten steel, the steel is given a basic nitrogen content, which also helps to promote the homogenization of the steel composition.

[0023] Specifically, the bottom blowing flow rate of the converter ranges from 200 to 480 NL / min.

[0024] In some embodiments of this application, in step one, the bottom blowing of the ladle during the converter tapping process is driven by nitrogen to stir and homogenize the composition of the molten steel. The nitrogen flow rate is 800~1000NL / min in the early stage of tapping; 300~600NL / min in the middle stage of tapping; and 50~200NL / min in the later stage of tapping.

[0025] In some embodiments of this application, step one, the converter smelting includes a material preparation stage (i.e., adding molten iron and scrap steel into the converter), a converter blowing period, and a tapping stage. The bottom blowing flow rate during the material preparation and tapping stages is 200 NL / min. The converter blowing period includes an early blowing stage, a middle blowing stage, and a late blowing stage. The early blowing stage accounts for 30% of the total process, with a bottom blowing flow rate of 320 NL / min. At this stage, the steel reaction is in its initial phase, and this flow rate effectively promotes the contact between the steel and nitrogen. The middle blowing stage accounts for 50% of the total process, with a bottom blowing flow rate of 240 NL / min to accommodate changes in the steel reaction. The late blowing stage accounts for 20% of the total process, with a bottom blowing flow rate of 480 NL / min to provide sufficient stirring speed for the final smelting of the steel, ensuring uniform steel composition and temperature.

[0026] In some embodiments of this application, the pressure of the bottom-blown nitrogen gas is ≥1.3 MPa. For example, the pressure of the bottom-blown nitrogen is 1.4 MPa.

[0027] In some embodiments of this application, in step one, after the converter smelting is completed, the final composition and temperature of the molten steel are controlled to meet the requirements for tapping. Specifically, the final carbon content is controlled at 0.05%~0.12%; the final phosphorus content is controlled at ≤0.015%; and the final temperature is controlled at ≥1600℃ to ensure that the composition and temperature of the molten steel meet the requirements for tapping the steel grade and to meet the requirements for charging into the furnace in the subsequent refining process.

[0028] Specifically, top slag lime is added during the deoxidation and alloying process of converter steelmaking, and the excess heat of the converter steel is used to pre-melt the top slag lime.

[0029] Step 2, refining the LF furnace: The refining process in the LF furnace includes four power supply cycles: the first power supply, the second power supply, the third power supply, and the fourth power supply. The third power supply is the dividing point for the LF furnace. Before the third power supply, the LF furnace is bottom-blown with nitrogen to add nitrogen to the molten steel. After the third power supply, the LF furnace is bottom-blown with argon to improve the stability of the molten steel composition and make the composition and temperature of the molten steel more uniform.

[0030] During the refining process in the LF furnace, normal slag formation, deoxidation, and alloying (non-nitrogen alloys, such as aluminum, silicon, manganese, carbon, and chromium alloys) are carried out. Slag formation is performed normally during refining, and the slag composition is adjusted to ensure the fluidity of the steel slag. Deoxidation is performed simultaneously to reduce the impact of oxygen content in the molten steel on nitrogen stability. After alloying, the contents of C, Si, Mn, Cr, N, S, and P in the molten steel are detected using a spectrometer. If the contents of C, Si, Mn, and Cr are below the target lower limit, corresponding carbon powder and alloys are added, followed by stirring for 3-5 minutes to homogenize the molten steel composition. Ultimately, the composition of the molten steel leaving the station is controlled within the required range for the steel grade.

[0031] In some embodiments of this application, during the LF furnace refining process, the first nitrogen supply flow rate is 200~500 NL / min, controlling the exposed diameter of the molten steel to >400 mm, ensuring that the nitrogen is fully integrated into the molten steel; the second nitrogen supply flow rate is 150~250 NL / min, controlling the exposed diameter of the molten steel to 250~350 mm, balancing the nitrogen addition efficiency and the stability of the molten steel; the third argon supply flow rate is 70~130 NL / min, controlling the exposed diameter of the molten steel to 150~250 mm, reducing nitrogen loss while promoting uniform reaction; the fourth argon supply flow rate is 30~70 NL / min, controlling the exposed diameter of the molten steel to 50~150 mm, creating conditions for the stability of the molten steel composition before leaving the furnace.

[0032] Specifically, in the refining LF process, the diameter of the exposed molten steel is used as the basis for controlling the gas flow rate.

[0033] In some embodiments of this application, in step two, the time for bottom blowing nitrogen is 10-20 minutes, which can further replenish the nitrogen content in the molten steel; the time for bottom blowing argon is 10-20 minutes, which can prevent excessive nitrogen escape in subsequent processes, and at the same time play a role in stirring the molten steel and promoting the floating of inclusions.

[0034] Step 3, Refining RH Furnace: Nitrogen is used as the driving gas for vacuum treatment. The nitrogen content is precisely controlled by adjusting the high and low vacuum times. After RH vacuum is broken, calcium treatment is performed. The reaction between calcium and inclusions in the molten steel improves the purity of the steel. Adding carbonized rice husks to cover the surface of the molten steel can achieve the functions of heat preservation and air isolation, reducing secondary oxidation of the molten steel and preventing the molten steel surface from being completely exposed. After adding carbonized rice husks, the argon flow rate is adjusted for soft blowing to prevent nitrogen from escaping, improve the impurity removal effect, and facilitate a micro-peristaltic state of the molten steel in the ladle, avoiding nitrogen content fluctuations and making the temperature and composition of the molten steel more uniform. A vacuum sample is used to confirm whether the nitrogen content meets the standard. If the nitrogen content does not meet the standard, the high and low vacuum times are adjusted to control the nitrogen content until the nitrogen content meets the standard.

[0035] In some embodiments of this application, in step three, during the vacuum treatment of the refining RH furnace, the high vacuum degree is controlled at ≤67Pa and the high vacuum time is 5~15min; the low vacuum degree is controlled at ≤4000Pa and the low vacuum time is 10~20min. The nitrogen content of the molten steel is adjusted to the target range by utilizing the principle of gas dissolution balance under vacuum.

[0036] In some embodiments of this application, in step three, the amount of carbonized rice husk added is 0.3~0.8 kg / t steel, the soft blowing time after adding the carbonized rice husk is 15~25 min, and the argon flow rate is <50 NL / min.

[0037] In some embodiments of this application, the calcium treatment after RH void breaking adopts the method of feeding calcium wire. The calcium wire feeding speed is 1~3 m / s, and the calcium wire feeding amount is 0.2~0.5 kg / t steel. The purity of the molten steel is improved by the reaction of calcium element with inclusions in the molten steel.

[0038] In some embodiments of this application, in step three, after the RH is broken, calcium treatment is performed by feeding calcium wire. The calcium wire feeding speed is 1~3m / s, and the calcium wire feeding amount is 0.2~0.5kg / t steel.

[0039] Step 4, Continuous casting: Continuous casting is carried out using a continuous casting machine. During the continuous casting process, protective casting is strictly implemented to avoid secondary oxidation of the molten steel and fluctuations in nitrogen composition caused by nitrogen absorption.

[0040] In some embodiments of this application, in step four, the protective casting for continuous casting steel pulling adopts a combination of long nozzle + submerged nozzle + protective slag to prevent contact between molten steel and air. The argon sealing flow rate of the long nozzle and the ladle bottom nozzle is 90~140NL / min, and air is prevented from entering the steel flow by argon gas sealing.

[0041] Specifically, the immersion nozzle is inserted into the liquid level of the crystallizer to a depth of 180~220mm. Combined with the covering effect of the protective slag, it avoids secondary oxidation or abnormal nitrogen absorption of molten steel during the casting process, ensuring the stability of the nitrogen composition of the final billet.

[0042] In some embodiments of this application, in step four, 4-8 bags (10 kg each) of tundish covering agent are added to each baking hole during the continuous casting opening, and 4-8 bags of tundish covering agent are added to the impact zone, with a total amount of tundish covering agent added of 300-600 kg.

[0043] Specifically, the principle for adding protective slag is to ensure that the surface does not "turn red". Add it frequently and in small amounts, and it is strictly forbidden to add it intermittently or in large quantities.

[0044] Example 1: A350-LF6 steel grade was selected and produced in a 100-ton converter, LF furnace, and RH furnace. The chemical composition of this steel grade is as follows: By mass percentage, C 0.12%~0.17%, Si 0.2%~0.3%, Mn 1.25%~1.35%, P≤0.015%, S≤0.010%, V 0.04%~0.08%, Al 0.025%~0.040%, Ti 0.006%~0.050%, N 0.010%~0.030%, Nb 0.01%~0.02%, with the balance being Fe and unavoidable impurities.

[0045] (1) Converter smelting process ① The converter is charged with 90 tons of molten iron and 17 tons of scrap steel (total charge 107 tons). The temperature of the molten iron entering the furnace is 1382℃. The composition of the molten iron is: Si content 0.45%, Mn content 0.43%, P content 0.128%, and S content 0.015%.

[0046] ② The converter bottom blowing process is nitrogen blowing throughout, with a bottom blowing flow rate range of 200~480NL / min.

[0047] ③ Oxygen lance blowing under the converter, with the ignition lance position at 1500~1700mm and the ignition oxygen flow rate at 14000~18000 Nm. 3 / h, after normal ignition, the lance position during the blowing process is 1400~1800mm, and the oxygen flow rate during the blowing process is 28000~36000 Nm 3 / h, the final drop of the lance is 1400mm, and the composition and temperature of the molten steel are uniform.

[0048] ④ Initial charging: After normal ignition, add the first batch of lime, which is 1 / 3 to 1 / 2 of the total amount. The first batch of cold material should also be 1 / 3 to 1 / 2 of the total amount. The principle of charging during the process is to add frequently but in small amounts, with each batch consisting of 200 to 500 kg. Ten minutes before smelting, prepare enough lime according to the alkalinity target requirements; twelve minutes before smelting, prepare enough cold material according to the requirements and furnace temperature.

[0049] ⑤ Based on the oxygen blowing progress, furnace mouth flame and audio slag formation, carry out the next process auxiliary lance and the final auxiliary lance. The final carbon content is controlled at 0.05~0.09%, the final phosphorus content is controlled at ≤0.010%, and the final temperature is controlled at ≥1600℃ to ensure that the molten steel with the composition and temperature meet the requirements of the steel grade for tapping and meets the requirements of subsequent refining processes for entering the furnace.

[0050] ⑥ When the steel is tapped from the converter, silicon-manganese alloy and aluminum-iron are added for deoxidation and alloying; 400~600 kg of top slag lime is added to pre-melt the top slag using the heat of the molten steel from the converter.

[0051] ⑦ During the converter tapping process, the bottom blowing of the ladle is driven by nitrogen to stir and homogenize the composition of the molten steel. The nitrogen flow rate is 800~1000 NL / min in the early stage of tapping; 300~600 NL / min in the middle stage of tapping; 50~200 NL / min in the later stage of tapping; and 30~70 NL / min at the end of tapping. The diameter of the molten steel turbulence at the nitrogen point is ≤200mm.

[0052] (2) Refining LF furnace process ① The ladle car enters the refining station, the ladle position is adjusted, alignment is confirmed, the furnace cover is lowered, the temperature is measured, and then slag is added. Based on the temperature measurement results, the final power supply current and power supply time are determined.

[0053] ② Bottom-blown gas control: Dynamic control of bottom blowing flow: Based on the dual control criteria of "gas flow rate + exposed diameter of molten steel", the flow rate is precisely adjusted in stages. First power supply: Nitrogen flow rate 200~500NL / min, control the exposed diameter of molten steel >400 mm, and ensure that nitrogen is fully integrated into the molten steel; Second power supply: nitrogen flow rate 150~250NL / min, exposed diameter of molten steel 250~350mm, balancing nitrogen increase efficiency and molten steel stability; Third power supply: Argon flow rate 100±50 NL / min, exposed diameter of molten steel 150~250mm, to reduce nitrogen loss and promote uniform reaction; The fourth power supply: argon gas flow rate 30~70NL / min, exposed steel diameter 50~150mm, to create conditions for stabilizing the steel composition before leaving the station.

[0054] ③ Adding materials: Add 200~600kg of lime and 0~300kg of slag-forming agent, control the total slag amount to 1000~1500kg (including the amount of slag added from the converter tapping), adjust the appropriate slag fluidity, and control the alkalinity range to 4~8.

[0055] ④ Power supply and temperature control: Use setting 10-13 for the first power supply. After the three-phase electrodes start to saturate the arc and the current stabilizes after 30 seconds, use setting 5-10 according to the temperature. Take the first temperature measurement 10-25 minutes after power supply. Take a sample if the temperature is 50°C above the liquidus line. Take intermittent temperature measurements during the refining process to ensure that the LF tapping temperature = liquidus line + (110-120)°C.

[0056] ⑤ Deoxidation: During the LF power transmission process, deoxidizers such as silicon carbide, aluminum granules, carbon powder, and calcium carbide are used to deoxidize the molten steel according to its composition.

[0057] ⑥ Alloying: The composition is finely adjusted using alloys such as ferrosilicon, ferromanganese, ferroniobium, and ferrovanadium according to the target composition of the steel grade, to ensure that the composition is within the required range for the steel grade.

[0058] ⑦ Composition confirmation: For the first sampling, the temperature is measured 10-25 minutes after power is supplied. Sampling is performed when the temperature is 50°C above the liquidus line to ensure that the slag has good fluidity.

[0059] For the second sampling, after adding the alloy and powering on for 3-5 minutes, take another sample to ensure the uniformity of the composition.

[0060] LF endpoint sample: Samples are taken for component testing before LF tapping, and nitrogen components are also taken for testing.

[0061] (3) Vacuum treatment process of refining RH furnace ① The ladle car enters the steel loading station, the ladle position is adjusted, the alignment is confirmed, and it is driven to the refining station.

[0062] ② Vacuum treatment: 1) Confirm the slag layer thickness, and after clearing the space, lift the ladle to 150 mm below the insertion pipe using the jacking device, and take temperature measurements and sample analysis of the composition.

[0063] 2) Continue to lift the ladle until the lower edge of the insertion tube contacts the molten steel. Then, reset the lifting height value to zero and continue lifting for about 350-400mm. Confirm that the driving gas is nitrogen and open the vacuum main valve to start the vacuum process.

[0064] 3) During the early stage of refining, the flow rate of nitrogen driving gas is controlled at 25~35m³ / h. After the vacuum degree in the vacuum chamber stabilizes at the working state (vacuum degree below 133Pa), high vacuum (below 67Pa) treatment is started for 5~15min according to the nitrogen composition of molten steel, followed by low vacuum (below 4000Pa) treatment for 10~20min. The vacuum treatment is then completed.

[0065] ③ Temperature measurement: First temperature measurement: After confirming the slag layer thickness and clearing the space, lift the ladle to 150mm below the insertion pipe using the lifting device, and then measure the temperature.

[0066] Second temperature measurement: Temperature measurement ends after high vacuum maintenance; Third temperature measurement: Temperature measurement after vacuum treatment ends; Fourth temperature measurement: Measure the temperature after 5-10 minutes of soft blowing; Fifth temperature measurement: Temperature measurement before steel is applied.

[0067] ④ Sampling: First sampling: After confirming the slag layer thickness and clearing the space, the ladle is lifted to 150mm below the insertion pipe using a jacking device, and a sample is taken for testing of the composition.

[0068] Second sampling: High vacuum treatment for 5-10 minutes.

[0069] Melting composition: 5 minutes before steel loading.

[0070] ⑤ Calcium treatment: After vacuum treatment is completed, the lifting device is lowered and moved to the wire feeding position for calcium treatment. The wire feeding speed is 1~3m / s and the wire feeding amount is 0.2~0.5kg / ton of steel.

[0071] ⑥ Soft blow Optimize the addition of carbonized rice husks and the soft blowing parameters: The amount of carbonized rice husks added is 0.3~0.8 kg / t of steel, which serves to keep the steel warm and isolate it from the air; finally, set the soft blowing parameters. Argon gas is used in the soft blowing stage (to avoid nitrogen escape and improve the impurity removal effect), with a flow rate of <50 NL / min and a soft blowing time of 15~25 min, to ensure that the exposed part of the molten steel is in a creeping state. It is strictly forbidden for the molten steel surface to be completely exposed to avoid fluctuations in nitrogen content.

[0072] (4) Continuous casting steel pulling process ① The continuous casting process adopts a combination of "long nozzle + submerged nozzle + protective slag" to protect the casting process, thereby blocking the contact between molten steel and air, avoiding secondary oxidation and nitrogen absorption of molten steel, and preventing fluctuations in nitrogen composition.

[0073] ② The argon sealing flow rate of the long water inlet and the ladle water outlet is controlled at 90~140NL / min, and air is prevented from entering the steel flow by argon sealing.

[0074] ③ The immersion nozzle is inserted into the liquid level of the crystallizer to a depth of 180~220mm. Combined with the covering effect of the protective slag, it avoids secondary oxidation or abnormal nitrogen absorption of molten steel during the casting process, and ensures the stability of nitrogen composition in the final billet.

[0075] ④ Adding protective slag: The principle of adding protective slag is to ensure that the surface does not "leak red". Add it frequently and in small amounts. It is strictly forbidden to add it intermittently or in large quantities.

[0076] ⑤ Addition of tundish covering agent: Add 4-8 bags (10 kg each) to each baking hole during the first casting of continuous casting, and add 4-8 bags to the impact zone, with a total addition of 300-600 kg.

[0077] ⑥ Take nitrogen samples from the continuous casting tundish to confirm the nitrogen composition of the molten metal.

[0078] (5) Using the above method, high-nitrogen steel was produced in different batches. The composition of each process in different batches is shown in Table 1 below: Table 1 shows the nitrogen composition of different batches of high-nitrogen steel produced in each process of Example 1.

[0079] As shown in Table 1 above, in the first batch, the nitrogen content detected at the converter endpoint was 30 ppm, the nitrogen content detected at the argon blowing station after the furnace was 30 ppm, the nitrogen content detected at LF-1 (after the first power supply to the refining LF furnace) was 80 ppm, the nitrogen content detected at LF-1 (after the fourth power supply to the refining LF furnace) was 110 ppm, and the nitrogen content detected at RH (after tapping) was 125 ppm. It can be seen that the nitrogen content gradually increases throughout the process. The nitrogen content detected in the continuous casting tundish was 123 ppm, which is very close to the nitrogen content detected at RH. This shows that the nitrogen content of high-nitrogen steel is relatively stable, and the total amount of oxide inclusions in high-nitrogen steel is controlled, which is beneficial to ensuring the mechanical properties of high-nitrogen steel.

[0080] Comparative Example 1: Select the same steel grade A350-LF6 and produce it in a 100-ton converter, LF furnace, and RH furnace.

[0081] The converter smelting process is the same as in Example 1 above, but the bottom blowing of the ladle during the converter tapping process is driven by argon gas.

[0082] Example 1 illustrates the refining process of the LF furnace, but argon is used throughout the bottom blowing gas operation. Nitrogen is increased to the target requirements of the finished steel by adding a nitrogen-containing alloy (nitrogen-manganese wire). The main components of the nitrogen-manganese wire are: nitrogen content 5.45%, manganese content 75.9%, 0.48 kg / meter, nitrogen recovery rate 50%, manganese recovery rate 90%. Based on the target nitrogen content (120 ppm) of the finished product, 950 meters of nitrogen-manganese wire need to be added (theoretical calculation reference), while simultaneously increasing manganese by 0.30%.

[0083] The refining RH furnace process is operated in the same way as in Example 1.

[0084] The operation of the continuous casting steel pulling process is the same as in Example 1.

[0085] Table 2 shows the nitrogen composition of different batches of high-nitrogen steel in different processes in Comparative Example 1.

[0086] As can be seen from Table 2, the nitrogen content of the first and second batches of Comparative Example 1 at the end of RH basically met the target requirements of Example 1. However, Comparative Example 1 required the addition of nitrogen-containing alloy (nitrogen-manganese wire) to increase the nitrogen content to the target. Example 1 only needed to control the bottom blowing of nitrogen in the ladle to increase the nitrogen content to the target. Therefore, Example 1 made full use of the cheap nitrogen resources in the steel plant to meet the production process of each process. There was no need to add additional nitrogen-containing raw materials, which could reduce costs and effectively improve and stabilize the control effect of nitrogen content in high-nitrogen steel, meet the quality requirements of subsequent processes, and the refining furnace did not need to feed nitrogen-manganese wire, which would not cause agitation of the molten steel surface, reduce the introduction of foreign inclusions, and greatly improve the purity of molten steel.

[0087] This invention employs a bottom-blowing nitrogen blowing mode throughout the converter smelting process, with nitrogen blowing into the ladle during tapping to ensure uniform steel composition. In the LF refining process, nitrogen is blown into the bottom initially, followed by argon, while slag formation, deoxidation, and alloying occur normally, precisely controlling the composition of the molten steel leaving the station. In the RH vacuum refining process, nitrogen is used as the driving gas, and precise control of nitrogen content is achieved by adjusting the high and low vacuum times. Strict protective casting is implemented during the continuous casting process. This method controls the nitrogen content of the molten steel to 0.010%~0.030%, achieving a finished product nitrogen content qualification rate (target value ±15ppm) of over 96%, thus achieving stable nitrogen enhancement.

[0088] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing and smelting high-nitrogen steel with nitrogen enhancement, characterized in that, Specifically, it includes the following steps: Step 1, converter smelting: Nitrogen gas is blown throughout the smelting process using bottom blowing mode; Step 2, refining the LF furnace: The refining process in the LF furnace includes four power supply cycles. Before the third power supply, the LF furnace is bottom-blown with nitrogen, and after the third power supply, the LF furnace is bottom-blown with argon. During the refining process in the LF furnace, slag formation, deoxidation, and alloying are carried out, and the composition of the molten steel leaving the station is controlled and tested. Step 3, Refining RH Furnace: Nitrogen is used as the driving gas for vacuum treatment. The nitrogen content is controlled by adjusting the high and low vacuum time. After the RH furnace is broken, calcium treatment is performed. Carbonized rice husks are added to cover the surface of the molten steel. After adding the carbonized rice husks, the argon flow rate is adjusted for soft blowing. Samples are taken to confirm the nitrogen content. Step 4, Continuous casting: Continuous casting is carried out using a continuous casting machine.

2. The method for producing and smelting high-nitrogen steel with nitrogen enrichment according to claim 1, characterized in that, In step one, the converter smelting includes a converter blowing period, which includes an early blowing period, a middle blowing period, and a late blowing period. The early blowing period accounts for 30% of the total process, and the bottom blowing flow rate during the early blowing period is 320 NL / min. The middle blowing period accounts for 50% of the total process, and the bottom blowing flow rate during the middle blowing period is 240 NL / min. The late blowing period accounts for 20% of the total process, and the bottom blowing flow rate during the middle blowing period is 480 NL / min.

3. The method for producing and smelting high-nitrogen steel with nitrogen enrichment according to claim 1, characterized in that, In step one, the converter smelting is completed, and the final carbon content is controlled at 0.05%~0.12%; the final phosphorus content is controlled at ≤0.015%; and the final temperature is controlled at ≥1600℃.

4. The method for producing and smelting high-nitrogen steel with nitrogen enrichment according to claim 1, characterized in that, In step one, nitrogen is used to drive the bottom blowing of the ladle during the converter tapping process. The nitrogen flow rate is 800~1000NL / min in the early stage of tapping; 300~600NL / min in the middle stage of tapping; and 50~200NL / min in the later stage of tapping.

5. The method for producing and smelting high-nitrogen steel with nitrogen enrichment according to claim 1, characterized in that, In step two, the bottom blowing time for nitrogen is 10-20 minutes; the bottom blowing time for argon is 10-20 minutes.

6. The method for producing and smelting high-nitrogen steel with nitrogen enrichment according to claim 1, characterized in that, During the refining process in the LF furnace, the first nitrogen supply flow rate is 200~500 NL / min, controlling the exposed diameter of the molten steel to be >400 mm; the second nitrogen supply flow rate is 150~250 NL / min, controlling the exposed diameter of the molten steel to be 250~350 mm; the third argon supply flow rate is 70~130 NL / min, controlling the exposed diameter of the molten steel to be 150~250 mm; and the fourth argon supply flow rate is 30~70 NL / min, controlling the exposed diameter of the molten steel to be 50~150 mm.

7. The method for producing and smelting high-nitrogen steel with nitrogen enrichment according to claim 1, characterized in that, In step two, the steel composition is tested, including the content of C, Si, Mn, Cr, N, S, and P. If the content of C, Si, Mn, and Cr is lower than the target lower limit, the corresponding carbon powder and alloy are added, and the mixture is stirred for 3 to 5 minutes.

8. The method for producing and smelting high-nitrogen steel with nitrogen enrichment according to claim 1, characterized in that, In step three, during the vacuum treatment process of the refining RH furnace, the high vacuum degree is controlled at ≤67Pa and the high vacuum time is 5~15min; the low vacuum degree is controlled at ≤4000Pa and the low vacuum time is 10~20min.

9. The method for producing and smelting high-nitrogen steel with nitrogen enrichment according to claim 1, characterized in that, In step three, after the RH is broken, calcium treatment is carried out by feeding calcium wire. The calcium wire feeding speed is 1~3m / s, and the calcium wire feeding amount is 0.2~0.5kg / t steel.

10. The method for producing and smelting high-nitrogen steel with nitrogen enrichment according to claim 1, characterized in that, In step three, the amount of carbonized rice husk added is 0.3~0.8 kg / t steel, the soft blowing time after adding the carbonized rice husk is 15~25 min, and the argon flow rate is <50 NL / min.

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