Normal-pressure high-nitrogen steel and efficient nitrogen-increasing production control method thereof

Abstract

The invention relates to the technical field of steel and iron material manufacturing, in particular to normal-pressure high-nitrogen steel and an efficient nitrogen increasing production control method thereof. The method comprises the following steps: electric furnace production, LF refining pretreatment for adjusting the content of other elements except nitrogen and manganese, RH vacuum treatment for adjusting vacuum pressure in the midway to increase the nitrogen content yield, LF treatment for adjusting the content of nitrogen and manganese elements, RH soft blowing and continuous casting for producing the high-nitrogen steel, and has the beneficial effects that the production efficiency is improved, and the use of manganese nitride, vanadium nitride and other alloys is reduced; excessive adding amount and excessive nitrogen content are avoided, the cost is saved, the nitrogen content control hit rate is increased, and the production efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of steel material manufacturing technology, and in particular to a high-nitrogen steel under normal pressure and its efficient nitrogen-enrichment production control method. Background Technology

[0002] In the production control process of a high-nitrogen steel under normal pressure, a significant loss of nitrogen content occurs during the refining process after alloying, resulting in substandard nitrogen content in the finished product. Previously, the production process for common high-nitrogen steels such as 38MnVS6 primarily involved nitrogen enrichment through refining manganese nitride alloys and vanadium nitride alloys, followed by RH bottom-blowing nitrogen enrichment and nitrogen feeding lines. However, in numerous production practices, the nitrogen enrichment yield has been inconsistent. The main reasons for this are: 1. The effects of different alloying elements on nitrogen solubility and yield were not considered; 2. Spectroscopic analysis is fast and convenient, but it has inherent errors such as inaccurate detection of nitrogen in nitrides. Nitrogen-oxygen analyzer analysis is expensive and time-consuming. In this case, excessive nitrogen will lead to excessive composition. If nitrogen is too low and supplementation is continued, on the one hand, other elements will exceed the control target (such as manganese in manganese nitride iron wire), affecting the hardenability control of steel. On the other hand, since the alloy nitrogen addition process is usually accompanied by the generation and overflow of nitrogen gas, the molten steel will churn, thereby destroying its purity and causing inclusions to exceed the standard. 3. The RH extreme vacuum smelting process will cause a large loss of nitrogen content, and the amount of loss is uncertain.

[0003] Chinese invention patent CN116770019A, entitled "A Method and System for Controlling Nitrogen Content in Low-Carbon High-Nitrogen Steel," discloses a method for controlling nitrogen content by monitoring and calculating composition and gas content, and adjusting parameters such as RH vacuum degree and vacuum treatment time. However, this method primarily relies on the results of a gas analyzer for gas content control. This detection method has low applicability, requires significant investment, and has a long detection time, making it difficult to meet the demands of fast-paced production. Furthermore, this method requires frequent adjustments to multiple process parameters, placing certain demands on process stability and adaptability to production rhythm.

[0004] Chinese invention patent CN113416881A, entitled "A Precise Nitrogen Control Method in the Smelting of Nitrogen-Containing Steel," discloses a method for precise nitrogen control by setting a nitrogen-containing alloy wire feeding process. However, the estimation of nitrogen yield is relatively simplistic and does not consider the influence of various alloying elements on nitrogen saturation and yield. Therefore, there is an urgent need for a method to improve the nitrogen content hit rate. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a method for controlling the production of high-nitrogen steel under normal pressure and its efficient nitrogen enrichment process. The method employs electric furnace production + LF refining pretreatment to adjust the content of elements other than nitrogen and manganese + RH vacuum treatment to adjust the vacuum pressure midway to increase the nitrogen content yield + LF treatment to adjust the nitrogen and manganese content + RH soft blowing + continuous casting to produce high-nitrogen steel. This method ensures the nitrogen content hit rate, saves costs, and improves production efficiency.

[0006] To achieve the above objectives, the present invention employs the following technical solution: A high-nitrogen steel under normal pressure, wherein the chemical composition of the high-nitrogen steel under normal pressure is as follows (by weight percentage): C: 0.36–0.48%, Si: 0.60–0.75%, Mn: 1.30–1.50%, P: ≤0.025%, S: 0.02–0.04%, Al: 0.01–0.025%, Ni: ≤0.15%, Cr: 0.1–0.2%, Cu: ≤0.20%, Mo: ≤0.05%, V: 0.1–0.12%, Ti: 0.01–0.03%, N: 0.0150–0.0200%, with the balance being Fe and other unavoidable impurities.

[0007] The rationale for the chemical composition design of this invention is explained in detail below: In steel, carbon (C) often forms carbides with other alloying elements, which strengthens the steel and improves its plasticity and toughness. From the perspective of ensuring the strength of the steel plate, it is desirable to keep the C content at a high level. However, a high C content can cause segregation in the steel, which affects the toughness of the steel plate. Therefore, under the premise of ensuring the strength of the steel plate, the C content is controlled between 0.36% and 0.48%.

[0008] Si has deoxidizing and desulfurizing effects in steel and can improve the strength of steel plates through solid solution strengthening. Adding an appropriate amount of Si to steel can improve the strength and hardness of ferrite in steel, make the ferrite structure more uniform, improve the elastic limit, yield strength and yield ratio, as well as fatigue strength and fatigue ratio of steel, and to a certain extent improve the strength, improve the resistance to local corrosion, and improve the high temperature resistance of steel. The Si content should be controlled at 0.60-0.75%.

[0009] Mn has a desulfurization effect in steel, and Mn easily forms MnS inclusions with S. The combination of Mn and N to form manganese nitride, as well as the high strength and low toughness caused by the segregation of Mn in steel, will increase the tendency for post-weld cracking and have an adverse effect on the toughness of steel. Therefore, the Mn content should not be too high. Taking into account the factors of steel plate strength, toughness and weldability, the Mn content is set at 1.30 to 1.50% in the composition design.

[0010] Phosphorus (P) is a harmful impurity element that increases the brittleness of steel and reduces its plasticity, toughness, and weldability. Lower P content is more beneficial to steel performance. Considering the on-site production process, the P content should be controlled below 0.025%.

[0011] Sulfur is a harmful element. Sulfides are generally distributed in a network at the grain boundaries, which significantly reduces the toughness of steel and easily leads to cracking during processing. Sulfur causes hot cracks in steel during welding. The sulfur content in steel is generally strictly controlled, with the S content controlled between 0.02% and 0.04%.

[0012] Al mainly plays a role in deoxidation and nitrogen fixation in steel, refines grains, improves the toughness of steel at low temperatures, and can also lower the brittle transition temperature of steel and improve the high temperature resistance of materials. Therefore, the Al content in this invention is controlled at 0.01 to 0.025%.

[0013] Ni can improve the strength and toughness of steel, enhance corrosion resistance, improve high-temperature performance, and optimize the material microstructure through austenite stabilization, inhibit grain coarsening at high temperatures, maintain fine grain structure, and help improve the overall performance of the material. Therefore, the Ni content should be controlled within 0.15%.

[0014] Cr improves the strength, hardness, high-temperature mechanical properties and hardenability of steel, as well as its corrosion resistance and oxidation resistance, while reducing its plasticity and toughness. The Cr content should be controlled between 0.1% and 0.2%.

[0015] Cu has stable chemical properties and can improve the thermal conductivity of steel, thereby increasing the cooling rate during alloy solidification and facilitating the formation of a solid solution with a single structure. Cu can also significantly improve the toughness of the alloy. The Cu content should be controlled below 0.20%.

[0016] Mo in steel can improve the steel’s hot strength, corrosion resistance and hardenability. Increasing the Mo content can significantly improve the high-temperature strength of steel at 450-550°C. Mo can extend the service life of steel under high-temperature stress by inhibiting grain boundary slip at high temperature and improve creep resistance. An appropriate amount of Mo can refine the grains. The Mo content should be controlled within 0.05%.

[0017] V can form fine carbonitrides with C and N, effectively preventing austenite grain growth, refining the microstructure, and thus improving the strength and toughness of steel. In high-nitrogen steel, V preferentially combines with free nitrogen atoms to form stable VN, eliminating nitrogen-induced strain-aging brittleness and improving the cold-working properties of the steel. Therefore, the V content is controlled at 0.1–0.12%.

[0018] Ti can capture free nitrogen atoms in steel, thus consolidating nitrogen. Simultaneously, TiN can precipitate during solidification, acting as a grain boundary anchor. Therefore, the Ti content is controlled at 0.01–0.03% in this invention.

[0019] Nitrogen (N) forms nitrides with alloying elements in steel. These nitrides are dispersed in the steel, effectively hindering dislocation movement and playing a role in precipitation strengthening and grain refinement, significantly improving the strength of the steel. However, while increasing the strength and hardness of the steel, it significantly reduces its plasticity and toughness, resulting in age hardening, which seriously affects the safety of the steel in low-temperature environments. Therefore, the N content should be controlled between 0.0150 and 0.0200%.

[0020] A highly efficient nitrogen enrichment production control method for atmospheric pressure high-nitrogen steel, the highly efficient nitrogen enrichment production process includes: electric furnace production - LF refining pretreatment - RH vacuum treatment - LF treatment - RH soft blowing - continuous casting, specifically including the following: S1. Electric furnace production: 400-600 kg of manganese nitride is reserved for the alloy used in electric furnace steelmaking; S2, LF refining pretreatment: After the first full analysis report of LF, adjust the content of elements other than nitrogen and manganese; after the second full analysis report of LF, add 400-600 kg / furnace of manganese nitride to LF; S3, RH vacuum treatment: RH temperature 1653~1666℃, vacuum degree below 67Pa maintained for 5~10min, RH riser gas and bottom blow gas all switched to nitrogen, nitrogen flow rate controlled at 30~50NL / min, riser gas flow rate 25~60NL / min; after RH vacuum treatment at 67pa for 10min, some pumps of B1~B3 are turned off, vacuum degree 4400~4600pa is maintained for 15~20min, then no soft blowing is performed, ladle is hoisted to LF refining; S4, LF treatment-RH soft blowing: Add manganese nitride to LF, return to RH and feed Ca line, soft blow for 15-25 minutes and then feed S line; S5. Continuous casting: The billet is put under light pressure at the end of the casting process. The continuous casting process is protected and cast. A large-capacity tundish with flow field control is used. At the same time, a weak cooling process and uniform electromagnetic stirring are adopted. The hydrogen content of the continuous casting billet meets the requirement of [H] < 2ppm.

[0021] Furthermore, in step S4, manganese nitride is added to the LF, with a manganese content of 1.40% to 1.19% and a nitrogen content of 170 to 200 ppm. 0.76 to 0.81 kg / t of silicon-calcium alloy cored wire is then fed back to the RH. No other component adjustments are made. After the temperature is qualified, the ladle is lifted without further vacuum treatment. The ladle temperature is 1554 to 1559℃.

[0022] A highly efficient nitrogen enrichment production control method for atmospheric pressure high-nitrogen steel, wherein the highly efficient nitrogen enrichment production process includes: electric furnace production - LF refining pretreatment - RH vacuum treatment - continuous casting, specifically including the following: S1. Electric furnace production: 600-1000 kg of manganese nitride is reserved for the alloy in the electric furnace steel tapping process; S2, LF refining pretreatment: After the LF full analysis report is returned, the content of elements other than nitrogen and manganese is adjusted; S3, RH vacuum treatment: RH temperature 1653~1666℃, RH riser gas and bottom blowing gas are all switched to nitrogen, nitrogen flow rate controlled at 30~50NL / min, vacuum pressure below 67Pa, after 5~10min, adjust vacuum pressure to 4400~4600Pa to increase nitrogen content yield; after breaking the vacuum, add 600~1000Kg of manganese nitride and continue to blow nitrogen and stir. After the RH vacuum is completed, feed in the S line, gently blow nitrogen to make the sulfides evenly dispersed and distributed, and perform ladle treatment when the temperature meets 1554~1559℃; S4. Continuous casting: The billet is subjected to light pressure at the end of the casting process. The continuous casting process is protected and cast. A large-capacity tundish with flow field control is used. At the same time, a weak cooling process and uniform electromagnetic stirring are adopted. The hydrogen content of the continuous casting billet meets the requirement of [H] < 2ppm.

[0023] Furthermore, the argon supply tubes before high-nitrogen steel production should have at least 8 vents that are evenly distributed.

[0024] Furthermore, in step S1, the chemical composition of the molten steel tapped from the electric furnace has P ≤ 0.011%, the tapping temperature is 1610~1630℃, the tapping time is 3~5min, 1~2kg / t of aluminum wire is added during pre-deoxidation, and during the alloying process, when 1 / 4 of the steel is tapped, 1.43kg / t~1.8kg / t of carbon raiser, 10.16kg / t~10.90kg / t of silicon-manganese alloy, and 3.67kg / t~4.0kg / t of ferrosilicon are added sequentially.

[0025] Furthermore, in step S2, before refining in the LF furnace, the temperature is first raised to above 1630℃, and the following are added: 3.63-4.54 kg / t of active lime, 3.63-5.45 kg / t of manganese nitride, 2.0-2.2 kg / t of ferrosilicon, 1.7-1.9 kg / t of ferrovanadium, 0.45-0.50 kg / t of high-carbon ferrochrome, 1.9-2.0 kg / t of silicon carbide, 0.42-0.45 kg / t of high-titanium ferrophosphorus, 1.63-1.81 kg / t of alumina balls, 0.54-0.72 kg / t of coke particles, and 0.11-0.16 kg / t of aluminum wire. Argon is blown from the bottom of the ladle for stirring, with an argon pressure of 0.2-0.4 MPa and a static argon blowing time of more than 15 min. The LF furnace temperature at the station is 1660-1670℃.

[0026] Furthermore, the composition of the LF furnace refining slag by weight percentage is as follows: CaO: 49%–54%, Al2O3: 22%–28%, SiO2: 6%–11%, MgO: ≤8%, FeO: ≤0.1%, with the balance being impurities.

[0027] Furthermore, the reduction amount in step S5 of continuous casting is as follows: for large square billets with a product specification ≤ 150mm, the reduction amount is ≥ 25mm; for large square billets with a product specification > 150mm, the reduction amount is ≥ 32mm; and for medium square billets, the reduction amount is ≥ 12mm.

[0028] Furthermore, the mold flux used in the continuous casting process is high-carbon steel mold flux, the superheat of the molten steel is controlled at 20-30°C, the argon flow rate for pouring through the long nozzle of the ladle is 20-40 L / min; the tundish temperature is 1471-1481°C, the casting speed is 0.4-0.43 m / min, and the mold water flow rate is 134-143 m³ / min. 3 / h, the electromagnetic stirring current of the crystallizer is 300~500A, the frequency is 1.5~3.5Hz, the electromagnetic stirring current of the end is 400~450A, the frequency is 7Hz, and the stirring method adopts alternating stirring of 20s~5s~20s; the remaining steel in the ladle is ≥3.5t, and the remaining steel in the tundish is ≥10t in the tail furnace.

[0029] Compared with the prior art, the beneficial effects of the present invention are: 1) By changing the production path, adjusting the vacuum pressure, and increasing the soft blowing time, the problems of difficulty in increasing nitrogen under normal pressure, large loss of vacuum nitrogen content, and difficulty in controlling and grasping nitrogen content are solved. This reduces the use of alloys such as manganese nitride and vanadium nitride, avoids excessive addition and excessive nitrogen content, saves costs, and improves the nitrogen content control hit rate.

[0030] 2) After RH treatment, the method of feeding wire to increase nitrogen is adopted, which results in a higher and more stable yield. Because the LF heating is eliminated, the power consumption is reduced, which saves money and lowers the cost. There is no need to perform LF treatment after RH treatment, which saves time and avoids the risk of secondary oxidation of molten steel. The level of inclusions is also lower.

[0031] 3) It avoids the problem of low accuracy in sample testing and improves production efficiency.

[0032] 4) It overcomes the problem of ensuring the control of H content in high-nitrogen steel while simultaneously increasing nitrogen content and controlling inclusions during the vacuuming process. Detailed Implementation

[0033] The specific embodiments of the present invention will be further described below: The weight percentages of the chemical components in the embodiments of the present invention are shown in Table 1. Table 1 - Chemical composition weight percentage (wt, %) of the embodiments of the present invention: Example 1: A method for controlling the efficient nitrogen enrichment production of high-nitrogen steel under normal pressure. The efficient nitrogen enrichment production process includes: electric furnace production - LF refining pretreatment - RH vacuum treatment - LF treatment - RH soft blowing - continuous casting. Detailed implementation: S1. Electric Furnace Production: In the ECOARC eco-friendly electric furnace smelting process, scrap steel mixed with molten iron is used as the furnace charge, with 60% scrap steel by mass. The slag addition amounts are: 24.54 kg / t of active lime and 18.18 kg / t of dolomite; P: 0.009% by mass. The tapping temperature is 1610℃, and the tapping time is 3 minutes. During pre-deoxidation, 1 kg / t of aluminum wire is added. During alloying, when 1 / 4 of the steel is tapped, 1.43 kg / t of carburizer, 10.16 kg / t of silicon-manganese alloy, and 3.67 kg / t of ferrosilicon are added sequentially. 400 kg of manganese nitride is reserved in the electric furnace tapping alloy. This portion of the alloy is adjusted by LF refining to prevent excessive manganese nitride adjustments later, which could lead to insufficient inclusion floating time and excessively high inclusion levels.

[0034] S2 and LF refining pretreatment: After the molten steel arrives at the refining station, slag formation and deoxidation are performed. After the first full analysis report of the LF furnace, the V content of the molten steel is adjusted by 0.10-0.12%, while Mn is not adjusted, and other components are adjusted normally. After the second full analysis report of the LF furnace, 400 kg / furnace of manganese nitride is added to the LF furnace. During the LF furnace refining process, the temperature is raised to 1630℃ before refining, and 3.63 kg / t of active lime, 3.63 kg / t of manganese nitride, 2.0 kg / t of ferrosilicon, 1.7 kg / t of ferrovanadium, and 0.45 kg / t of high-carbon ferrochrome are added. Silicon carbide 1.9 kg / t, high-titanium ferrophosphate 0.42 kg / t, alumina balls 1.63 kg / t, coke granules 0.54 kg / t, aluminum wire 0.11 kg / t. Argon stirring is applied from the bottom of the ladle at a pressure of 0.2 MPa for 15 minutes. The composition of the LF furnace refining slag, by mass percentage, is: CaO: 49.94%, Al₂O₃: 23.29%, SiO₂: 10.52%, MgO: 7.75%, FeO: 0.09%, with the balance being impurities. The LF furnace's initial temperature at the station is 1660℃, and it is fed into the RH reactor.

[0035] S3, RH Vacuum Treatment: In the RH refining process, the RH inlet temperature is 1658℃, and the vacuum degree is maintained below 67Pa for 10 minutes. All RH booster gas and bottom blower gas are switched to nitrogen, with the nitrogen flow rate controlled at 30NL / min and the booster gas flow rate at 25NL / min. RH vacuum treatment at 67Pa is performed for 10 minutes. After 10 minutes, the three pumps B1-B3 are turned off to maintain a vacuum of 4400Pa, and treatment continues for another 15 minutes. S4, LF treatment - RH soft blowing: Transfer to LF and add 600 kg of manganese nitride as required to meet the standard requirements: manganese content 1.40%, nitrogen content supplemented by 5.45 kg / t to meet the nitrogen content 170 ppm; the total nitrogen added in the two LF treatments is 9.08 kg / t, equivalent to 1000 kg of manganese nitride; return to RH and feed 0.76 kg / t of silicon-calcium alloy cored wire, soft blow for 15 minutes, then feed S wire, supplementing according to the target requirements, without adjusting other components. After the temperature is qualified, lift the ladle; no vacuum treatment is performed during this process. The ladle temperature is 1554℃.

[0036] S5. Continuous Casting: Light reduction is applied at the end of the casting process. For large square billets with a product size ≤150mm, the reduction is 25mm; for large square billets with a product size >150mm, the reduction is 32mm; for medium-sized billets, the reduction is 12mm. The steel production process must ensure the normal operation of the crystallizer and end-of-line electromagnetic stirring equipment. Continuous casting is carried out under full-process protective casting (to prevent nitrogen absorption and secondary oxidation of the molten steel). A large-capacity tundish with flow field control is used to promote inclusion flotation. The tundish capacity is 55t, and the depth is 0.8m. Simultaneously, a weak cooling process is used (to prevent nitrogen precipitation), and uniform electromagnetic stirring is employed to ensure compositional homogeneity. The hydrogen content of the continuously cast billet is strictly controlled, meeting the requirement of 1.5ppm [H] in the tundish; the tundish temperature is 1471℃, the casting speed is 0.4m / min, and the crystallizer water flow rate is 134m³ / min. 3 / h, the electromagnetic stirring current of the crystallizer is 400A, the frequency is 2Hz, the electromagnetic stirring current of the end is 420A, the frequency is 7Hz, the stirring method is alternating stirring from 20s to 5s to 20s, the remaining steel in the ladle is 3.5t, the remaining steel in the tundish is 10t in the tail furnace, the whole process is protected casting, the protective slag of the crystallizer is high carbon steel protective slag, the superheat of the molten steel is controlled at 20℃, and the argon flow rate for protective casting at the long nozzle of the ladle is 20L / min.

[0037] Example 2: A method for controlling the efficient nitrogen enrichment production of the aforementioned atmospheric pressure high-nitrogen steel. The efficient nitrogen enrichment production process includes: electric furnace production - LF refining pretreatment - RH vacuum treatment - continuous casting, specifically including the following: S1. Electric Furnace Production: In the ECOARC eco-friendly electric furnace smelting process, scrap steel mixed with molten iron is used as the furnace charge, with 60% scrap steel by mass. The slag addition amounts are: 24.54 kg / t of active lime and 18.18 kg / t of dolomite; P: 0.009% by mass. The tapping temperature is 1610℃, and the tapping time is 3 minutes. During pre-deoxidation, 1 kg / t of aluminum wire is added. During alloying, when 1 / 4 of the steel is tapped, 1.43 kg / t of carburizer, 10.16 kg / t of silicon-manganese alloy, and 3.67 kg / t of ferrosilicon are added sequentially. 400 kg of manganese nitride is reserved in the electric furnace tapping alloy. This portion of the alloy is adjusted by LF refining to prevent excessive manganese nitride adjustments later, which could lead to insufficient inclusion floating time and excessively high inclusion levels.

[0038] After the initial full analysis report of the S2 and LF refining pretreatment, the content of elements other than nitrogen and manganese was adjusted. During the LF furnace refining process, the temperature was raised to 1630℃ before refining, and 3.63 kg / t of active lime, 3.63 kg / t of manganese nitride, 2.0 kg / t of ferrosilicon, 1.7 kg / t of ferrovanadium, 0.45 kg / t of high-carbon ferrochrome, 1.9 kg / t of silicon carbide, 0.42 kg / t of high-titanium ferrotitanium, 1.63 kg / t of alumina balls, 0.54 kg / t of coke particles, and 0.11 kg / t of aluminum wire were added. Argon was blown from the bottom of the ladle for stirring, with an argon pressure of 0.2 MPa and a static argon blowing time of 15 min. The composition of the LF furnace refining slag by mass percentage was: CaO: 49.94%, Al2O3: 23.29%, SiO2: 10.52%, MgO: 7.75%, FeO: 0.09%, with the remainder being impurities. The LF furnace temperature at the station was 1660℃, and it was fed into RH.

[0039] S3, RH Vacuum Treatment: Initially, vacuum treatment is performed, with the time adjusted to below 67 Pa. After 10 minutes, the vacuum pressure is adjusted to 4400 Pa to increase nitrogen yield. After breaking the vacuum, 800 kg of manganese nitride is added, and argon blowing and stirring are continuously performed to ensure uniform nitrogen dissolution. After the RH vacuum is completed, sulfur wire is fed in, and soft blowing of argon gas continues to ensure uniform dispersion of sulfides. The temperature is maintained at 1554℃ for ladle treatment + continuous casting. No nitrogen addition is performed during LF. The nitrogen content of the LF sample is 90 ppm. Nitrogen addition in RH is estimated at 10 ppm per 100 kg, and nitrogen is added to 170 ppm, along with 800 kg of manganese nitride.

[0040] S4. Continuous Casting: Light reduction is applied at the end of the casting process. For large square billets with a product size ≤150mm, the reduction is 25mm; for large square billets with a product size >150mm, the reduction is 32mm; and for medium-sized billets, the reduction is 12mm. The steel production process must ensure the normal operation of the crystallizer and end-of-line electromagnetic stirring equipment. Continuous casting is carried out under full-process protective casting (to prevent nitrogen absorption and secondary oxidation of the molten steel). A large-capacity tundish with flow field control is used to promote inclusion flotation. The tundish capacity is 55t, and the depth is 0.8m. Simultaneously, a weak cooling process is used (to prevent nitrogen precipitation), and uniform electromagnetic stirring is employed to ensure uniform composition. The hydrogen content of the continuously cast billet is strictly controlled, meeting the requirement of 1.5ppm [H] in the tundish; the tundish temperature is 1471℃, the casting speed is 0.4m / min, and the crystallizer water flow rate is 134m³ / min. 3 / h, the electromagnetic stirring current of the crystallizer is 400A, the frequency is 2Hz, the electromagnetic stirring current of the end is 420A, the frequency is 7Hz, the stirring method is alternating stirring from 20s to 5s to 20s, the remaining steel in the ladle is 3.5t, the remaining steel in the tundish is 10t in the tail furnace, the whole process is protected casting, the protective slag of the crystallizer is high carbon steel protective slag, the superheat of the molten steel is controlled at 20℃, and the argon flow rate for protective casting at the long nozzle of the ladle is 20L / min.

[0041] Comparative example: Under the premise that all other conditions remain unchanged, strictly follow the electric furnace production + LF refining + RH vacuum treatment for 20 minutes, without vacuum adjustment + RH soft blowing + continuous casting. In this method, the nitrogen content is significantly reduced during the RH treatment process, and the amount is immeasurable, resulting in serious waste of alloy. Excessive addition of manganese nitride to increase nitrogen content can easily cause the Mn content of the alloy to exceed the standard.

[0042] The amount of manganese nitride added in the embodiments and comparative examples of the present invention is shown in Table 2; the composition of the refining slag in the embodiments of the present invention is shown in Table 3; the change in nitrogen content during the high-efficiency nitrogen-enhancing production control process in Embodiment 1 of the present invention is shown in Table 4; the change in nitrogen content during the high-efficiency nitrogen-enhancing production control process in Embodiment 2 of the present invention is shown in Table 5; the change in nitrogen content during the conventional production control process in the comparative example of the present invention is shown in Table 6; the comparison of non-metallic inclusions in Embodiments 1 and 2 of the present invention is shown in Table 7.

[0043] Table 2 - Amount of manganese nitride added in the embodiments and comparative examples of the present invention: Table 3 - Composition of refining slag in embodiments of the present invention (wt, %): Table 4 - Changes in nitrogen content during the high-efficiency nitrogen enrichment production control process in Example 1 of the Invention: Table 5 - Changes in nitrogen content during the high-efficiency nitrogen enrichment production control process in Example 2 of the present invention: Table 6 - Changes in nitrogen content during conventional production control in the comparative example of this invention: The above changes in nitrogen content show that the nitrogen content of the composite high-nitrogen steel in Examples 1 and 2 can be increased to 0.015% to 0.02% through efficient nitrogen-increasing production control methods. However, the conventional production methods increase the consumption of manganese nitride, and the final nitrogen content still does not meet the requirements for high-nitrogen steel production.

[0044] Table 7 - Comparison of non-metallic inclusions in Examples 1 and 2 of the present invention: Compared with the non-metallic inclusions in the above embodiments, the efficient nitrogen enrichment production control method can significantly reduce the level of inclusions and reduce the occurrence of inclusion problems.

[0045] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high-nitrogen steel under normal pressure, characterized in that, The chemical composition of the atmospheric pressure high-nitrogen steel, by weight percentage, is as follows: C: 0.36-0.48%, Si: 0.60-0.75%, Mn: 1.30-1.50%, P: ≤0.025%, S: 0.02%-0.04%, Al: 0.01-0.025%, Ni: ≤0.15%, Cr: 0.1-0.2%, Cu: ≤0.20%, Mo: ≤0.05%, V: 0.1-0.12%, Ti: 0.01-0.03%, N: 0.0150%-0.0200%, with the balance being Fe and other unavoidable impurities.

2. A highly efficient nitrogen-enrichment production control method for high-nitrogen steel under normal pressure as described in claim 1, characterized in that, The efficient nitrogen enrichment production process includes: electric furnace production - LF refining pretreatment - RH vacuum treatment - LF treatment - RH soft blowing - continuous casting, specifically including the following: S1. Electric furnace production: 400-600 kg of manganese nitride is reserved for the alloy used in electric furnace steelmaking; S2, LF refining pretreatment: After the first full analysis report of LF, adjust the content of elements other than nitrogen and manganese; after the second full analysis report of LF, add 400-600 kg / furnace of manganese nitride to LF; S3, RH vacuum treatment: RH temperature 1653~1666℃, vacuum degree below 67Pa maintained for 5~10min, RH riser gas and bottom blow gas all switched to nitrogen, nitrogen flow rate controlled at 30~50NL / min, riser gas flow rate 25~60NL / min; after RH vacuum treatment at 67pa for 10min, some pumps of B1~B3 are turned off, vacuum degree 4400~4600pa is maintained for 15~20min, then no soft blowing is performed, ladle is hoisted to LF refining; S4, LF treatment-RH soft blowing: Add manganese nitride to LF, return to RH and feed Ca line, soft blow for 15-25 minutes and then feed S line; S5. Continuous casting: The billet is put under light pressure at the end of the casting process. The continuous casting process is protected and cast. A large-capacity tundish with flow field control is used. At the same time, a weak cooling process and uniform electromagnetic stirring are adopted. The hydrogen content of the continuous casting billet meets the requirement of [H] < 2ppm.

3. The method for efficient nitrogen enrichment production control of high-nitrogen steel under normal pressure according to claim 2, characterized in that, In step S4, manganese nitride is added to the LF at a rate of 600-800 kg to ensure that the nitrogen content of the finished product reaches 170-200 ppm. The silicon-calcium alloy cored wire is then fed back to the RH at a rate of 0.76-0.81 kg / t without any other component adjustments. After the temperature is qualified, the wire is hoisted without further vacuum treatment. The hoisting temperature is 1554-1559℃.

4. A highly efficient nitrogen-enrichment production control method for high-nitrogen steel under normal pressure as described in claim 1, characterized in that, The efficient nitrogen enrichment production process includes: electric furnace production - LF refining pretreatment - RH vacuum treatment - continuous casting, specifically including the following: S1. Electric furnace production: 600-1000 kg of manganese nitride is reserved for the alloy in the electric furnace steel tapping process; S2, LF refining pretreatment: After the LF full analysis report is returned, the content of elements other than nitrogen and manganese is adjusted; S3, RH vacuum treatment: RH temperature 1653~1666℃, RH riser gas and bottom blowing gas are all switched to nitrogen, nitrogen flow rate controlled at 30~50NL / min, vacuum pressure below 67Pa, after 5~10min, adjust vacuum pressure to 4400~4600Pa to increase nitrogen content yield; after breaking the vacuum, add 600~1000Kg of manganese nitride and continue to blow nitrogen and stir. After the RH vacuum is completed, feed in the S line, gently blow nitrogen to make the sulfides evenly dispersed and distributed, and perform ladle treatment when the temperature meets 1554~1559℃; S4. Continuous casting: The billet is subjected to light pressure at the end of the casting process. The continuous casting process is protected and cast. A large-capacity tundish with flow field control is used. At the same time, a weak cooling process and uniform electromagnetic stirring are adopted. The hydrogen content of the continuous casting billet meets the requirement of [H] < 2ppm.

5. The efficient nitrogen enrichment production control method for high-nitrogen steel under normal pressure according to claim 2 or 4, characterized in that, Before producing high-nitrogen steel, there should be at least 8 argon supply tubes with evenly distributed ventilation.

6. The efficient nitrogen enrichment production control method for high-nitrogen steel under normal pressure according to claim 2 or 4, characterized in that, In step S1, the chemical composition of the molten steel tapped from the electric furnace has P ≤ 0.011%, the tapping temperature is 1610~1630℃, the tapping time is 3~5min, and 1~2kg / t of aluminum wire is added during pre-deoxidation. During the alloying process, when 1 / 4 of the steel is tapped, 1.43kg / t~1.8kg / t of carbon raiser, 10.16kg / t~10.90kg / t of silicon-manganese alloy, and 3.67kg / t~4.0kg / t of ferrosilicon are added sequentially.

7. The efficient nitrogen enrichment production control method for high-nitrogen steel under normal pressure according to claim 2 or 4, characterized in that, In step S2, before refining in the LF furnace, the temperature is first raised to above 1630℃, and the following are added: 3.63-4.54 kg / t of active lime, 3.63-5.45 kg / t of manganese nitride, 2.0-2.2 kg / t of ferrosilicon, 1.7-1.9 kg / t of ferrovanadium, 0.45-0.50 kg / t of high-carbon ferrochrome, 1.9-2.0 kg / t of silicon carbide, 0.42-0.45 kg / t of high-titanium ferrophosphorus, 1.63-1.81 kg / t of alumina balls, 0.54-0.72 kg / t of coke particles, and 0.11-0.16 kg / t of aluminum wire. Argon is blown from the bottom of the ladle for stirring, with an argon pressure of 0.2-0.4 MPa and a static argon blowing time of more than 15 min. The LF furnace temperature at the station is 1660-1670℃.

8. The efficient nitrogen enrichment production control method for high-nitrogen steel under normal pressure according to claim 2 or 4, characterized in that, The composition of the LF furnace refining slag by weight percentage is as follows: CaO: 49%–54%, Al2O3: 22%–28%, SiO2: 6%–11%, MgO: ≤8%, FeO: ≤0.1%, with the balance being impurities.

9. The method for efficient nitrogen enrichment production control of high-nitrogen steel under normal pressure according to claim 2 or 4, characterized in that, The reduction amount in step S5 of continuous casting is as follows: for large square billets with a product specification ≤ 150mm, the reduction amount is ≥ 25mm; for large square billets with a product specification > 150mm, the reduction amount is ≥ 32mm; and for medium square billets, the reduction amount is ≥ 12mm.

10. The efficient nitrogen enrichment production control method for high-nitrogen steel under normal pressure according to claim 2 or 4, characterized in that, The continuous casting mold flux uses high-carbon steel flux, the molten steel superheat is controlled at 20-30℃, the argon flow rate for pouring through the ladle long nozzle is 20-40 L / min, the tundish temperature is 1471-1481℃, the casting speed is 0.4-0.43 m / min, and the mold water flow rate is 134-143 m³ / min. 3 / h, the electromagnetic stirring current of the crystallizer is 300~500A, the frequency is 1.5~3.5Hz, the electromagnetic stirring current of the end is 400~450A, the frequency is 7Hz, and the stirring method adopts alternating stirring of 20s~5s~20s; the remaining steel in the ladle is ≥3.5t, and the remaining steel in the tundish is ≥10t in the tail furnace.

Images