Method for controlling nitrogen content in S460NL steel

Abstract

The invention belongs to the technical field of steel and iron smelting, and particularly relates to a method for controlling the nitrogen content in S460NL steel, which comprises the following steps: primary smelting in an electric furnace or a converter, refining in an LF furnace, refining in a VD furnace and casting, after VD vacuumizing is finished, nitrogen is blown into a steel ladle through two air bricks at the bottom of the steel ladle, so that the nitrogen content in the steel reaches the target content, and after nitrogen blowing is finished, argon is switched for soft stirring. According to the method, after VD vacuumizing refining is finished, nitrogen is blown through the two air bricks at the bottom of the steel ladle at the same time to increase nitrogen of the S460NL steel for the high-strength wind power flange, and compared with a mode of increasing nitrogen by adding nitrided ferromanganese alloy, the method has the advantages of being lower in cost, higher in molten steel purity, high in component hit rate, simpler to operate and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and in particular relates to a method for controlling the nitrogen content in S460NL steel. Background Art

[0002] With the rapid increase in wind turbine power and the need to reduce the weight of wind turbine towers, higher-strength wind turbine flanges are urgently needed to replace low-strength wind turbine flanges. At present, the strength of wind turbine flanges at home and abroad is mostly 355MPa and a small amount of 420MPa. In order to promote the high-quality and rapid development of my country's wind power industry, the 460MPa high-strength S460NL steel for wind turbine flanges was developed first. In order to improve the strength without affecting the welding performance and corrosion resistance of wind turbine flanges, the carbon content of S460NL steel should not be too high, and the mass fraction of carbon needs to be controlled at ≤0.2%, so a certain amount of nitrogen content needs to be added to increase the strength. The production process of S460NL steel is: electric furnace or converter primary refining → LF furnace refining → VD vacuum refining → casting (continuous casting or mold casting), and the N content is required to be ≤0.025%.

[0003] At present, S460NL steel is nitrogen-added by adding manganese nitride alloy in the LF furnace. The nitrogen recovery rate of this method is low. 7.5kg of manganese nitride needs to be added to smelt 1t of steel, and the cost per ton of steel increases by about 60 yuan / ton. In addition, the nitrogen content in the molten steel fluctuates greatly during the subsequent VD vacuum smelting process, making it difficult to accurately control the final nitrogen content of the molten steel (the current nitrogen content control range is 35-180ppm). The mechanical properties of the product, especially the low-temperature impact toughness, fluctuate greatly. Through the data collation of the relationship between nitrogen content and mechanical properties, the nitrogen content is stably controlled at 120±10ppm, and the mechanical properties are optimized. In order to obtain stable nitrogen content and excellent mechanical properties, this field urgently needs to develop a method that can stably control the nitrogen content in S460NL steel. Summary of the invention

[0004] In view of the defects of the prior art, the present invention provides a method for controlling the nitrogen content in S460NL steel.

[0005] Specifically, the present invention is achieved through the following technical solutions:

[0006] A method for controlling nitrogen content in S460NL steel comprises: primary smelting in an electric furnace or a converter → refining in an LF furnace → refining in a VD furnace → casting. After the VD vacuuming is completed, nitrogen is blown into the ladle through two air-permeable bricks at the bottom of the ladle to make the nitrogen content in the steel reach a target content. After the nitrogen blowing is completed, argon is switched for soft stirring.

[0007] In the above method for controlling the nitrogen content in S460NL steel, the nitrogen flow rate of each of the air-permeable bricks is 3.8-4.2NL / min / t.

[0008] In the above method for controlling the nitrogen content in S460NL steel, the blowing time of the nitrogen is controlled at 13-17 minutes.

[0009] In the above method for controlling the nitrogen content in S460NL steel, when the nitrogen content in the steel is 35<[N]≤45ppm, the nitrogen blowing time is controlled within 15-17min; when the nitrogen content in the steel is 45<[N]≤55ppm, the nitrogen blowing time is controlled within 13-15min.

[0010] In the above method for controlling nitrogen content in S460NL steel, the duration of soft stirring is 2-2.5 minutes.

[0011] In the above method for controlling the nitrogen content in S460NL steel, argon is blown for stirring without blowing nitrogen during the LF furnace refining process, and the steel is discharged from the station after alloying treatment and the nitrogen content is initially measured.

[0012] In the above method for controlling the nitrogen content in S460NL steel, after the VD furnace refining is completed, the ladle is vacuumed and degassed in the VD furnace, and only argon gas is blown for stirring during the vacuuming process, and the vacuum is broken after being maintained at a vacuum degree of ≤67 Pa for ≥15 minutes.

[0013] In the above method for controlling nitrogen content in S460NL steel, the casting is continuous casting or die casting.

[0014] On the other hand, the present invention further provides an S460NL steel, which is prepared by the above method.

[0015] In yet another aspect, the present invention further provides the use of the above-mentioned S460NL steel in the preparation of high-strength wind power flanges.

[0016] The technical solution of the present invention has the following beneficial effects:

[0017] After the VD vacuum refining is completed, the present invention adds nitrogen to the S460NL steel for high-strength wind power flange by blowing nitrogen through two air-permeable bricks at the bottom of the ladle at the same time. Compared with adding nitrogen by adding nitrided manganese iron alloy, the present invention has the advantages of lower cost, higher purity of molten steel, high component hit rate and simpler operation.

[0018] Cost advantage: Compared with adding nitrided manganese iron alloy to increase nitrogen, the method of adding nitrogen by blowing nitrogen can significantly reduce costs. For example, a steel plant produces S460NL steel for high-strength wind power flanges. When adding nitrided manganese iron alloy to increase nitrogen, about 7.5 kg / t of nitrided manganese iron alloy needs to be added. The unit price of nitrided manganese iron alloy is 13,550 yuan / ton, and the cost is 13,550 / 1000×7.5=101.6 yuan / t steel; when adding nitrogen by blowing nitrogen, about 7.5 kg / t of ordinary manganese iron alloy can meet the corresponding Mn content requirements. The unit price of ordinary Mn iron alloy is 5,500 yuan / ton, and the cost is 5,500 / 1000×7.5=41.3 yuan / ton steel; Therefore, compared with adding nitrogen by nitrided manganese iron alloy, adding nitrogen by blowing nitrogen can save costs of 101.6-41.3=60.3 yuan / ton;

[0019] Higher purity: Purity directly affects the mechanical properties of the finished wind turbine flange. The use of alloy nitrogen addition is to add nitrided manganese iron alloy after VD breaks the air. The next step will be directly cast. The purity of the added alloy material is difficult to guarantee, which will inevitably increase the non-metallic inclusions and P, S, O, N gas content in the steel, polluting the molten steel. The method of nitrogen addition by blowing nitrogen through double holes at the bottom of the ladle does not have the problem of polluting the molten steel. At the same time, it can also make the inclusions float more fully, making the molten steel purer.

[0020] High component hit rate and simpler operation: In order to save costs, the addition of nitrided manganese iron alloy to increase nitrogen requires adding high carbon ferromanganese and nitrided manganese iron twice or even multiple times to ensure the Mn content and N content in the molten steel. Therefore, there is interference between the Mn and N components, and the operation is complicated and affects the production rhythm. While the use of nitrogen blowing to increase nitrogen directly adds high carbon / medium carbon ferromanganese to control the manganese content and nitrogen content respectively, without interfering with each other, the operation is simple and the manganese and nitrogen contents can be accurately controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the following detailed description of the preferred embodiment.The drawings are only for the purpose of illustrating the preferred embodiments and are not to be construed as limiting the invention.

[0022] Figure 1 This is a schematic diagram of the arrangement of double-hole nitrogen-blowing permeable bricks at the bottom of the ladle;

[0023] Among them, 1 is the first diameter, 2 is the second diameter, 3 is the first air permeable brick, 4 is the second air permeable brick, and 5 is the ear axis. DETAILED DESCRIPTION

[0024] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments. Except for the following contents, the process method of the present invention adopts conventional methods or devices in the art. Unless otherwise specified, the following terms have the meanings commonly understood by those skilled in the art.

[0025] When a numerical range is disclosed herein, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0026] In order to accurately control the nitrogen content in S460NL steel for high-strength wind power flanges (target requirement 120±10ppm), the present invention provides a method for increasing nitrogen by blowing nitrogen through double holes at the bottom of the ladle, which can not only accurately control the nitrogen content in the steel, but also effectively reduce costs and is simple to operate.

[0027] Specifically, the method for controlling the nitrogen content in S460NL steel of the present invention comprises: primary smelting in an electric furnace or a converter → refining in an LF furnace → refining in a VD furnace → casting, wherein, after the VD vacuuming is completed, nitrogen is blown into the ladle through two air-permeable bricks at the bottom of the ladle to make the nitrogen content in the steel reach the target content, and after the nitrogen blowing is completed, argon is switched for soft stirring.

[0028] In some preferred embodiments, Figure 1 As shown, the first air brick 3 and the second air brick 4 are respectively located at the bottom of the ladle and on the same side of the first diameter 1 of the bottom of the ladle where the ear axis 5 is located, and the distances between the first air brick 3 and the second air brick 4 and the first diameter 1 and the second diameter 2 of the bottom of the ladle perpendicular to the first diameter 1 are respectively half of the radius R of the bottom of the ladle.

[0029] Through practice, breathable bricks are used Figure 1 The arrangement can effectively improve the nitrogen absorption rate. At the same time, when the nitrogen flow fluctuates, the top slag will not be discharged to expose the molten steel, reducing the risk of secondary oxidation of the molten steel.

[0030] In some other embodiments, the number of air bricks is not limited to two.

[0031] Among them, the main chemical composition of the air brick is Al2O3 (≥87%) and MgO+Al2O 3+ Cr2O3 content ≥92%, volume density ≥3.05g / cm 3, apparent porosity ≤18%, compressive strength ≥100MPa.

[0032] In some preferred embodiments, the nitrogen flow rates of the two air bricks are both 3.8-4.2NL / min / t. When the nitrogen content in the steel is 35<[N]≤45ppm, the nitrogen blowing time is controlled at 15-17min; when the nitrogen content in the steel is 45<[N]≤55ppm, the nitrogen blowing time is controlled at 13-15min.

[0033] The present invention controls the nitrogen flow rate to 3.8-4.2NL / min / t, thereby ensuring the nitrogen addition effect and duration, and avoiding secondary oxidation of molten steel.

[0034] When the nitrogen flow rate is less than 3.8NL / min / t, the nitrogen addition efficiency is too low and the temperature drop of the molten steel is too large, affecting the subsequent production rhythm; when the nitrogen flow rate is greater than 4.2NL / min / t, the nitrogen absorption rate is reduced, and there may be a risk of secondary oxidation of the molten steel due to large flow fluctuations and the discharge of top slag.

[0035] In some preferred embodiments, after nitrogen blowing and nitrogen increase are completed, argon gas is switched to perform soft stirring for 2-2.5 minutes, and the nitrogen content in the steel is analyzed. According to the gap between the actual value of the nitrogen content and the target value, the nitrogen blowing time is determined according to the nitrogen blowing flow rate (3.8-4.2NL / min / t steel) and the nitrogen increase rate. After the nitrogen blowing is completed, argon gas is switched to perform soft stirring. When the specified molten steel temperature requirement is met, the steel is tapped for casting.

[0036] The electric furnace or converter primary smelting is carried out by conventional methods in the prior art, and the present invention does not make any specific limitation on this.

[0037] In some preferred embodiments, argon is blown for stirring during the LF refining process without blowing in nitrogen, ferromanganese, ferrosilicon, ferroniobium and ferrovanadium are added for alloying treatment, the content of alloy elements is controlled to be within the target range, and the temperature is exited after reaching the target, and the N content is initially measured.

[0038] In some preferred embodiments, after the VD furnace refining is completed, the ladle is vacuumed and degassed in the VD furnace, and only argon is blown for stirring during the vacuuming process, and the vacuum is broken after being maintained at a vacuum degree of ≤67 Pa for ≥15 minutes. Ensuring the vacuuming time of the VD furnace can effectively degas and remove inclusions, and at the same time can ensure the range of N content between heats, and nitrogen addition after breaking the vacuum is more conducive to nitrogen absorption.

[0039] The casting of the present invention is continuous casting or mold casting, which is not specifically limited in the present invention.

[0040] The method of controlling the nitrogen content in the high-strength wind power flange steel S460NL of the present invention increases the nitrogen content in the steel by blowing nitrogen into the steel through two air-permeable bricks at the bottom of the ladle after the VD vacuum is completed. The method can stably control the nitrogen content at 120±10ppm, ensuring the mechanical properties and stability of the finished flange. Compared with the existing method of adding nitrided manganese iron alloy to increase nitrogen, it has the advantages of lower cost, higher purity of molten steel, high component hit rate and simpler operation.

[0041] Example

[0042] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods without specific conditions in the following examples are based on conventional methods and conditions.

[0043] Example 1

[0044] The high-strength wind power flange steel S460NL is produced by the process of "electric furnace smelting → LF furnace refining → VD vacuum smelting → φ800mm continuous casting large round billet". The production process is as follows:

[0045] Electric furnace smelting: smelting is carried out according to the smelting process requirements, the end point C is 0.071%, the end point P is 0.005%, the end point temperature of the electric furnace is 1650℃, the auxiliary materials added for steel production are lime and synthetic slag, the alloys added with the steel flow are aluminum shot, ferromanganese, silicon-manganese alloy, and the steel output is 82.7 tons.

[0046] LF refining: Argon is blown throughout the LF refining process. Medium carbon ferromanganese, high carbon ferromanganese, ferrosilicon, ferroniobium, ferrovanadium, aluminum shots and aluminum wires are used to adjust the elements such as C, Mn, Si, Al, P, S, Nb and V to the target requirements. The weight percentage of the chemical composition at the LF endpoint is (%): C: 0.167, Si: 0.31, Mn: 1.567, P: 0.008, S: 0.001, Nb: 0.03, V: 0.06, Ti: 0.0028, Cr: 0.05, Ni: 0.02, Cu: 0.01, Mo: 0.0036: Al: 0.064; the balance is Fe, the LF endpoint temperature is 1672°C, and the endpoint [N] is 85ppm.

[0047] VD vacuum treatment: VD vacuum treatment is carried out after LF refining. After the bag is hoisted into the VD station, argon blowing is turned on. The temperature is measured at 1660℃. After the vacuum reaches 67Pa and is maintained for 15 minutes, the temperature is measured at 1605℃. The composition and gas content mass percentage (%) are measured: C: 0.168, Si: 0.34, Mn: 1.576, P: 0.007, S: 0.002, Nb: 0.03, V: 0.06, Ti: 0.0025, Cr: 0.05, Ni: 0.02, Cu: 0.01, Mo: 0.0033: Al: 0.036. At this time, the N content in the steel is 36ppm. Stop blowing argon and switch to blowing nitrogen. The nitrogen blowing flow rates of 1# breathable brick and 2# breathable brick are 340NL / min (about 4.11NL / min / t steel) and 335NL / min (about 4.05NL / min / t steel), respectively. The total flow rate of the two breathable bricks is 675NL / min. After blowing nitrogen for 17 minutes, switch to blowing argon for 2 minutes. Take gas samples for analysis, and the [N] content is 124ppm, which meets the target requirements.

[0048] Example 2

[0049] A company uses the process of "electric furnace smelting → LF furnace refining → VD vacuum smelting → φ800mm continuous casting large round billet" to produce high-strength wind power flange steel S460NL. The production process is as follows:

[0050] Electric furnace smelting: smelting is carried out according to the smelting process requirements, the end point C is 0.074%, the end point P is 0.004%, the end point temperature is 1642℃, the auxiliary materials added for steel production are lime and synthetic slag, the alloys added with the steel flow are aluminum shot, ferromanganese, silicon-manganese alloy, and the steel output is 82.5 tons.

[0051] LF refining: Argon is blown throughout the LF refining process. Medium carbon ferromanganese, high carbon ferromanganese, ferrosilicon, ferroniobium, ferrovanadium, aluminum shots and aluminum wires are used to adjust elements such as C, Mn, Si, Al, P, S, Nb and V to the target requirements. The weight percentage of the chemical composition at the LF endpoint is (%): C: 0.165, Si: 0.40, Mn: 1.614, P: 0.006, S: 0.001, Nb: 0.03, V: 0.06, Ti: 0.0034, Cr: 0.05, Ni: 0.02, Cu: 0.01, Mo: 0.0037: Al: 0.062; the balance is Fe, the LF endpoint temperature is 1668°C, and the endpoint [N] is 90ppm.

[0052] VD treatment: After LF refining, VD vacuum treatment is carried out. After the bag is placed in the VD station, argon gas is blown and the temperature is measured at 1653℃. After the vacuum reaches 67Pa and is maintained for 15 minutes, the temperature is measured at 1604℃. The composition and gas content are measured. The weight percentage of the composition is (%): C: 0.176, Si: 0.38, Mn: 1.608, P: 0.007, S: 0.002, Nb: 0.03, V: 0.06, Ti: 0.0027, Cr: 0.05, Ni: 0.02, Cu: 0. 01. Mo: 0.0035: Al: 0.033; at this time, the N content in the steel is 44ppm. Stop blowing argon and switch to blowing nitrogen. The nitrogen blowing flow rates of 1# breathable brick and 2# breathable brick are 323NL / min (about 3.92NL / min / t steel) and 340NL / min (about 4.12NL / min / t steel), respectively. The total flow rate of the two breathable bricks is 663NL / min. After blowing nitrogen for 15 minutes, switch to blowing argon for 2 minutes. Take gas samples for analysis, and the [N] content is 123ppm, which meets the target requirements.

[0053] Example 3

[0054] A company uses the process of "electric furnace smelting → LF furnace refining → VD vacuum smelting → φ800mm continuous casting large round billet" to produce high-strength wind power flange steel S460NL. The production process is as follows:

[0055] Electric furnace smelting: smelting is carried out according to the smelting process requirements, the end point C is 0.056%, the end point P is 0.005%, the end point temperature is 1642℃, the auxiliary materials added for steel production are lime and synthetic slag, the alloys added with the steel flow are aluminum shot, ferromanganese, silicon-manganese alloy, and the steel output is 82.2 tons.

[0056] LF refining: Argon is blown throughout the LF refining process. Medium carbon ferromanganese, high carbon ferromanganese, ferrosilicon, ferroniobium, ferrovanadium, aluminum shots and aluminum wires are used to adjust elements such as C, Mn, Si, Al, P, S, Nb and V to the target requirements. The weight percentage of the chemical composition at the LF endpoint is (%): C: 0.167, Si: 0.41, Mn: 1.623, P: 0.006, S: 0.001, Nb: 0.03, V: 0.06, Ti: 0.0038, Cr: 0.05, Ni: 0.02, Cu: 0.01, Mo: 0.0033: Al: 0.061; the balance is Fe, the LF endpoint temperature is 1675°C, and the endpoint [N] is 96ppm.

[0057] VD treatment: After LF refining, VD vacuum treatment is carried out. After the bag is hoisted into the VD station, argon blowing is turned on. The temperature is measured at 1654℃. After the vacuum reaches 67Pa and is maintained for 15 minutes, the air is broken and the temperature is measured at 1605℃. The composition and gas content are measured. The weight percentage of the components is (%): C: 0.0.175, Si: 0.39, Mn: 1.603, P: 0.0071, S: 0.001, Nb: 0.03, V: 0.06, Ti: 0.0028, Cr: 0.05, Ni: 0.03, Cu: 0.01, Mo: 0.0034: Al: 0.032. At this time, the N content in the steel is 47ppm. Stop blowing argon and switch to blowing nitrogen. The nitrogen blowing flow rates of 1# breathable brick and 2# breathable brick are 342NL / min (about 4.16NL / min / t steel) and 339NL / min (about 4.12NL / min / t steel), respectively. The total flow rate of the two breathable bricks is 681NL / min. After blowing nitrogen for 14 minutes, switch to blowing argon for 2.5 minutes. Take gas samples for analysis, and the [N] content is 121ppm, which meets the target requirements.

[0058] Example 4

[0059] A company uses the process of "electric furnace smelting → LF furnace refining → VD vacuum smelting → φ800mm continuous casting large round billet" to produce high-strength wind power flange steel S460NL. The production process is as follows:

[0060] Electric furnace smelting: smelting is carried out according to the smelting process requirements, the end point C is 0.055%, P is 0.005%, the end point temperature is 1643℃, the auxiliary materials added for steelmaking are lime and synthetic slag, the alloys added with the steel flow are aluminum shot, ferromanganese, silicon-manganese alloy, and the steel output is 82.9 tons.

[0061] LF refining: Argon is blown throughout the LF refining process. Medium carbon ferromanganese, high carbon ferromanganese, ferrosilicon, ferroniobium, ferrovanadium, aluminum shots and aluminum wires are used to adjust elements such as C, Mn, Si, Al, P, S, Nb and V to the target requirements. The weight percentage of the chemical composition at the LF endpoint is (%): C: 0.163, Si: 0.43, Mn: 1.618, P: 0.007, S: 0.001, Nb: 0.03, V: 0.06, Ti: 0.0038, Cr: 0.05, Ni: 0.02, Cu: 0.01, Mo: 0.0040: Al: 0.060; the balance is Fe, the LF endpoint temperature is 1677°C, and the endpoint [N] is 103ppm.

[0062] VD treatment: After LF refining, VD vacuum treatment is carried out. After the bag is hoisted into the VD station, argon blowing is turned on. The temperature is measured at 1655℃. After the vacuum reaches 67Pa and is maintained for 15 minutes, the air is broken and the temperature is measured at 1606℃. The composition and gas content are measured. The weight percentage of the components is (%): C: 0.172, Si: 0.40, Mn: 1.61, P: 0.007, S: 0.001, Nb: 0.03, V: 0.06, Ti: 0.0030, Cr: 0.05, Ni: 0.02, Cu: 0.01, Mo: 0.0039: Al: 0.032. At this time, the N content in the steel is 54ppm. Stop blowing argon and switch to blowing nitrogen. The nitrogen blowing flow rates of 1# breathable brick and 2# breathable brick are 320NL / min (about 3.86NL / min / t steel) and 340NL / min (about 4.1NL / min / t steel), respectively. The total flow rate of the two breathable bricks is 660NL / min. After blowing nitrogen for 13 minutes, switch to blowing argon for 2.5 minutes. Take gas samples for analysis, and the [N] content is 118ppm, which meets the target requirements.

[0063] The present invention has been disclosed above with preferred embodiments, but those skilled in the art should understand that these embodiments are only used to describe the present invention and should not be understood as limiting the scope of the present invention. It should be noted that all changes and substitutions equivalent to these embodiments should be deemed to be included in the scope of the claims of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined in the claims.

Claims

1. A method for controlling nitrogen content in S460NL steel, comprising: Primary refining in electric furnace or converter → refining in LF furnace → refining in VD furnace → casting, which is characterized in that after the VD vacuum is completed, nitrogen is blown into the ladle through the two air-permeable bricks at the bottom of the ladle to make the nitrogen content in the steel reach the target content, and after the nitrogen blowing is completed, argon is switched for soft stirring.

2. The method according to claim 1, characterized in that The nitrogen flow rate of each of the air-permeable bricks is 3.8-4.2NL / min / t.

3. The method according to claim 1, characterized in that The blowing time of the nitrogen is controlled at 13-17 minutes.

4. The method according to claim 1, characterized in that: When the nitrogen content in the steel is 35<[N]≤45ppm, the nitrogen blowing time is controlled at 15-17min; when the nitrogen content in the steel is 45<[N]≤55ppm, the nitrogen blowing time is controlled at 13-15min.

5. The method according to claim 1, characterized in that The duration of the soft stirring is 2-2.5 min.

6. The method according to claim 1, characterized in that During the LF furnace refining process, argon gas is blown for stirring without blowing nitrogen, and the furnace is discharged from the furnace after alloying treatment and the N content is initially measured.

7. The method according to claim 1, characterized in that After the VD furnace refining is completed, the ladle is vacuumed and degassed in the VD furnace. During the vacuuming process, only argon gas is blown for stirring. The vacuum is broken after being maintained at a vacuum degree of ≤67 Pa for ≥15 minutes.

8. The method according to claim 1, characterized in that The casting is continuous casting or mold casting.

9. A S460NL steel, characterized in that: The method is prepared by any one of claims 1 to 8.

10. Use of the S460NL steel according to claim 9 in the preparation of high-strength wind power flanges.

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