Control method for nitrogen content in steel, alloy steel and production method of alloy steel

Abstract

The invention relates to the technical field of metal material preparation, and discloses a control method for the nitrogen content in steel, alloy steel and a production method of the alloy steel. According to the method, firstly, Thermo-Calc software is utilized, and the nitrogen solubility of each phase of steel in the cooling phase change process is accurately determined in an iterative calculation mode, specifically, under the conditions of fixed steel components and pressure, the nitrogen content of an initial system is gradually increased for multiple times of calculation until the nitrogen distribution of each phase output by two adjacent times of calculation is the same, and the nitrogen solubility of each phase is determined; at the moment, the nitrogen is judged to be saturated in each phase, and the obtained nitrogen content is the actual solubility. On the basis, the nitrogen content in the molten steel is accurately regulated and controlled according to the compression ratio range of the casting blank on the basis of the austenite nitrogen solubility, the nitrogen precipitation strengthening effect can be fully played, the bubble defect caused by nitrogen supersaturation can be effectively avoided, and the technical problem that the strengthening effect and defect control are difficult to consider in alloy steel production is solved.

Description

Technical Field

[0001] This invention belongs to the field of alloy steel production technology, specifically relating to a method for controlling nitrogen content in steel, alloy steel and its production method. Background Technology

[0002] In the course of the continuous and vigorous development of the steel industry, production technology is constantly innovating and advancing, and the requirements for steel performance are becoming increasingly stringent and diversified. To meet the urgent needs of industries such as aerospace, automotive manufacturing, and high-end construction for steel with comprehensive properties such as high strength, high toughness, good weldability, and corrosion resistance, steel companies are constantly exploring and applying new alloying technologies. Among these, nitrogen microalloying technology, with its significant advantages, has gradually become one of the key methods for improving steel performance and conserving precious alloy resources.

[0003] Nitrogen, as an effective alloying element, plays a unique role in precipitation strengthening in steel. It can form fine, dispersed nitride precipitates with microalloying elements such as titanium, niobium, and vanadium in steel. These precipitates effectively hinder dislocation movement during steel deformation, thereby increasing the yield strength and tensile strength of the steel. Simultaneously, nitrogen microalloying can refine the grain structure of steel to a certain extent, further improving its toughness and weldability. Compared with traditional alloying elements, nitrogen is abundant and inexpensive. The use of nitrogen microalloying technology can significantly improve the performance of steel without significantly increasing production costs, thus attracting widespread attention and in-depth research in the steel industry.

[0004] However, with the widespread application of nitrogen microalloying technology in steel production, a series of new problems have emerged. As the nitrogen content in steel continuously increases, various defects easily occur during the production process, severely affecting the quality and performance of the steel. Among these, cracks, rotten steel, and porosity are particularly prominent. Cracks reduce the strength and toughness of the steel, making it prone to fracture during use and seriously affecting structural safety; rotten steel leads to deterioration of the steel's surface quality, increasing the difficulty and cost of subsequent processing; and the presence of porosity reduces the steel's density, affecting its corrosion resistance and mechanical properties. Therefore, it is necessary to provide a method for controlling the nitrogen content in steel, alloy steel, and its production method to alleviate or solve the above problems. Summary of the Invention

[0005] To address the technical problem of simultaneously achieving precipitation strengthening and defect avoidance capabilities in the preparation of alloy steel using commonly used techniques, this invention provides a method for controlling nitrogen content in steel, comprising the following steps: S1. Obtain the nitrogen solubility of each phase during the cooling phase transformation of steel: The thermo-calc software is used to calculate the nitrogen solubility of each phase during the cooling phase transformation of steel. After inputting the steel composition, pressure and initial system nitrogen content, the nitrogen distribution of the first phase is output. S2. While keeping the steel composition, pressure and other calculation conditions unchanged, increase the nitrogen content of the initial system, repeat step S1, and output the nitrogen distribution of the second phase; S3. If the nitrogen distribution in the second phase is the same as that in the first phase, it is determined that the nitrogen in each phase has reached saturation. At this time, the nitrogen content in each phase is the actual solubility of nitrogen in each phase. If the nitrogen distribution of the second phase is different from that of the first phase, repeat step S2; set the number of input-output operations to N times (N≥2), and continue to perform iterative calculations until the nitrogen distribution of the Nth phase is the same as that of the (N-1)th phase. At this time, the nitrogen content in each phase is the nitrogen solubility in each phase. S4. Obtain the nitrogen solubility in austenite based on the nitrogen solubility in each phase. When the billet compression ratio is 60~120, adjust the nitrogen content in the molten steel within the range of the lower limit of nitrogen solubility in austenite +0.004% to the lower limit of nitrogen solubility in austenite +0.006%. When the billet compression ratio is >7 to <60, adjust the nitrogen content in the molten steel within the range of the lower limit of nitrogen solubility in austenite +0.002% to the lower limit of nitrogen solubility in austenite +0.003%.

[0006] Furthermore, the initial nitrogen content of the system is set to be much greater than the sum of nitrogen solubility in each phase as estimated empirically.

[0007] Furthermore, the nitrogen content of the initial system is not less than 0.1%.

[0008] Furthermore, by mass fraction, the steel composition includes: C 0.22%~0.25%, Si 0.5%~0.6%, Mn 1.2%~1.4%, P≤0.03%, S≤0.03%, V 0.06%~0.09%; when the billet compression ratio is >7 to <60, Nb 0.003%~0.006%, and when the billet compression ratio is 60~120, Nb 0.006%~0.01%.

[0009] This invention provides a method for producing alloy steel using the method for controlling nitrogen content in steel as described in any one of the above claims, comprising the following steps: The raw materials are mixed according to the preset proportions and smelted into molten steel. The molten steel is refined to obtain refined molten steel, the refining process including but not limited to deoxidation and nitrogen microalloying; during the nitrogen microalloying process, the nitrogen content in the molten steel is adjusted by any of the above methods for controlling the nitrogen content in the steel. The refined molten steel is then subjected to continuous casting, rolling, and cooling treatment to obtain alloy steel.

[0010] Furthermore, the continuous casting and rolling process includes continuous casting, heat treatment, and rolling. The heating temperature during the heat treatment process is the (Nb,V)(C,N) precipitation temperature +30℃. The (Nb,V)(C,N) precipitation temperature is calculated using thermo-calc software, and the heating time is 100~120 min.

[0011] Furthermore, the casting speed during the continuous casting process is controlled to be 3.1~3.5 m / min.

[0012] Furthermore, the cooling process includes air cooling.

[0013] This invention provides an alloy steel prepared by any of the alloy steel production methods described above.

[0014] Furthermore, the average size of (Nb, V) and (C, N) in the alloy steel is 20-80 nm, and the grain size level is 10-11, that is, the number of grains per square inch is 2. 9 ~2 10 The yield strength of the alloy steel is increased to 50~120 MPa, and the tensile strength is increased to 60~150 MPa.

[0015] Compared with the prior art, the present invention has at least the following advantages: This invention provides a method for controlling nitrogen content in steel. Using thermo-calc software, scientific calculations are performed to first obtain the nitrogen distribution of each phase during the cooling phase transformation of steel under initial conditions. Then, by gradually increasing the initial nitrogen content and performing iterative calculations, the nitrogen distribution of each phase is the same in two consecutive outputs. At this point, the actual solubility of nitrogen in each phase is determined. This precise determination of nitrogen solubility provides a reliable basis for subsequent nitrogen content control, effectively avoiding defects caused by nitrogen escaping in the form of bubbles due to excessive nitrogen content. Simultaneously, it rationally guides nitrogen into the precipitated phase, fully utilizing the precipitation strengthening ability of nitrogen microalloying. This successfully solves the long-standing technical challenge of simultaneously improving precipitation strengthening ability and avoiding defects in alloy steel preparation.

[0016] This invention uses austenite nitrogen solubility as a control target, significantly improving the stability and consistency of steel quality, and providing a strong guarantee for the production of high-performance, high-quality alloy steel. Austenite is an important microstructure of steel at high temperatures, and its nitrogen solubility has a key impact on the distribution of nitrogen in the steel and its final properties. This invention obtains the nitrogen solubility in austenite and controls the nitrogen content in molten steel (when the billet compression ratio is 60~120, the nitrogen content in the molten steel is controlled within the range of nitrogen solubility in austenite + 0.006%; when the billet compression ratio is >7 to <60, the nitrogen content in the molten steel is controlled within the range of nitrogen solubility in austenite + 0.003%). This control strategy ensures that nitrogen has sufficient driving force to form fine and dispersed nitride precipitates during the cooling phase transformation process, enhancing the steel properties; and it also prevents nitrogen content from exceeding the solubility capacity of austenite, thus preventing defects such as nitrogen bubbles. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram showing the solubility of nitrogen in different phases during the cooling phase transition process in Example 1 of the present invention, with an initial nitrogen content of 0.5%.

[0019] Figure 2 This is a schematic diagram showing the solubility of nitrogen in different phases during the cooling phase transition process in Example 1 of the present invention, with an initial nitrogen content of 1%.

[0020] Figure 3 This is a schematic diagram of the nitrogen solubility in molten steel measured in Example 3 of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. 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.

[0022] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0023] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of the invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to the methods, devices, and materials in the embodiments of the present invention.

[0024] This invention provides a method for controlling the nitrogen content in steel, comprising the following steps: S1. Obtain the nitrogen solubility of each phase during the cooling phase transformation of steel: The thermo-calc software is used to calculate the nitrogen solubility of each phase during the cooling phase transformation of steel. After inputting the steel composition, pressure and initial system nitrogen content, the nitrogen distribution of the first phase is output.

[0025] In this invention, the Thermo-Calc thermodynamic software calls the TCFE9: Steels / Fe-Alloys v9.0 database.

[0026] In this invention, the initial nitrogen content of the system is set to be much greater than the sum of nitrogen solubility in each phase as estimated empirically.

[0027] In some embodiments of the present invention, the nitrogen content of the initial system is not less than 0.5.

[0028] In this invention, the steel composition, by mass fraction, may include: C 0.22%~0.25%, Si 0.5%~0.6%, Mn 1.2%~1.4%, P≤0.03%, S≤0.03%, V 0.06%~0.09%; when the compression ratio is >7 to <60, Nb 0.003%~0.006%, and when the compression ratio is 60~120, Nb 0.006%~0.01%.

[0029] In this invention, the pressure can be 1~1.5 atm.

[0030] S2. While keeping the steel composition, pressure and other calculation conditions unchanged, increase the nitrogen content of the initial system, repeat step S1, and output the nitrogen distribution of the second phase.

[0031] S3. If the nitrogen distribution in the second phase is the same as that in the first phase, it is determined that the nitrogen in each phase has reached saturation. At this time, the nitrogen content in each phase is the actual solubility of nitrogen in each phase. If the nitrogen distribution of the second phase is different from that of the first phase, repeat step S2; set the number of input-output operations to N times (N≥2), and continue to perform iterative calculations until the nitrogen distribution of the Nth phase is the same as that of the (N-1)th phase. At this time, the nitrogen content in each phase is the nitrogen solubility in each phase.

[0032] The iterative calculation method employed in this invention is both efficient and reliable. By setting the number of input-output operations to N (N≥2), and repeatedly increasing the initial nitrogen content of the system while calculating the nitrogen distribution in each phase, the actual solubility of nitrogen in each phase is gradually approximated. Compared to traditional experimental trial-and-error methods, this method eliminates the need for numerous tedious experiments, significantly shortening the development cycle and reducing production costs. Furthermore, due to its scientific software calculations and rigorous iterative logic, the results are accurate and reliable, directly guiding nitrogen content control in actual production, improving production efficiency, and bringing significant economic benefits to enterprises.

[0033] S4. Obtain the nitrogen solubility in austenite based on the nitrogen solubility in each phase. When the billet compression ratio is 60~120, adjust the nitrogen content in the molten steel within the range of the lower limit of nitrogen solubility in austenite +0.004% to the lower limit of nitrogen solubility in austenite +0.006%. When the billet compression ratio is >7 to <60, adjust the nitrogen content in the molten steel within the range of the lower limit of nitrogen solubility in austenite +0.002% to the lower limit of nitrogen solubility in austenite +0.003%.

[0034] It should be emphasized that the lower limit of nitrogen solubility in austenite mentioned in all embodiments of the present invention is the mass fraction of nitrogen in the system in the initial stage, and the upper limit is the maximum mass fraction of nitrogen in the system in austenite.

[0035] For example, refer to Figure 1 In one embodiment of the present invention, under the condition that the initial nitrogen content is 0.5%, a schematic diagram of the solubility of nitrogen in different phases during the cooling phase transformation is shown. The lower limit of nitrogen solubility in austenite is 0.0222%, and the upper limit is 0.0331%.

[0036] Nitrogen solubility in austenite refers to the maximum mass percentage (wt%) of nitrogen (N) atoms that can dissolve into a face-centered cubic (FCC) austenite (γ-Fe) lattice and form a stable solid solution without precipitating nitrides or other second phases under certain thermodynamic equilibrium conditions (specific temperature, nitrogen partial pressure, and alloy composition).

[0037] This invention provides a method for producing alloy steel using the method for controlling nitrogen content in steel as described in any one of the above claims, comprising the following steps: A1. Prepare the raw materials according to the preset proportions and melt them into molten steel.

[0038] In this invention, the weighed raw materials can be added to the mixing equipment in a certain order, such as adding scrap steel and pig iron first, and then adding ferroalloys, and mixing them thoroughly and evenly to ensure that the various raw materials are evenly distributed, so as to provide raw materials with stable composition for subsequent smelting.

[0039] In this invention, the mixed raw materials can be added to a melting furnace, such as an electric arc furnace or a converter. Taking an electric arc furnace as an example, an arc ignition operation is first performed to generate an electric arc between the electrode and the furnace charge. The high temperature of the electric arc (up to 3000-6000℃) is used to rapidly melt the furnace charge.

[0040] During the smelting process, the furnace temperature and steel composition are continuously monitored. Once the furnace charge has completely melted and the composition is uniform, a slag removal operation is performed to remove the slag from the surface of the molten steel, reducing the impact of the slag on the quality of the molten steel.

[0041] A2. The molten steel is refined to obtain refined molten steel, wherein the refining process includes, but is not limited to, deoxidation treatment and nitrogen microalloying; during the nitrogen microalloying process, the nitrogen content in the molten steel is adjusted using the nitrogen content control method in steel as described above.

[0042] In this invention, the deoxidation treatment can be silicon deoxidation.

[0043] In this invention, the molten steel can be poured into a refining furnace (such as an LF furnace) to carry out refining operations.

[0044] In this invention, the refined steel is preferably low-alloy steel, in which vanadium and / or niobium may be added as alloying elements. Specifically, the vanadium content in the steel is controlled within the range of 0.06% to 0.09% by mass fraction; the niobium content is closely related to the billet compression ratio: when the compression ratio is >7 to <60, the Nb content is 0.003% to 0.006%; when the compression ratio is increased to 60 to 120, the Nb content is adjusted accordingly to 0.006% to 0.01%. By controlling the niobium content in relation to the compression ratio, the precipitation behavior under different deformation conditions can be better adapted.

[0045] Under the process control of this invention, the cooling phase transformation process provides nitrogen atoms with sufficient time and a suitable migration path, enabling them to effectively diffuse into the vanadium and / or niobium precipitates. Because the alloy element content is controlled at a low level, the formation and growth process of the precipitates is more orderly, avoiding excessive aggregation and coarsening of the precipitates caused by excessive alloy elements. Simultaneously, by matching the niobium content with the billet compression ratio, the quantity, size, and distribution of the precipitates are further optimized, thereby achieving precipitation strengthening while effectively preventing problems such as uneven steel properties caused by abnormal precipitate growth.

[0046] In this invention, the dual objectives of precipitation strengthening and defect avoidance are achieved under low alloy content conditions. The key lies in accurately controlling the synergistic mechanism between nitrogen content and alloying elements, as detailed below: When the nitrogen in molten steel is controlled to approach or reach the solubility of nitrogen in austenite, austenite is in a state of relative nitrogen saturation. At this point, during subsequent cooling phase transformations, the stability of austenite is affected by factors such as temperature reduction, and nitrogen atoms possess the driving force to transfer from austenite to the precipitated phase. Vanadium and / or niobium have a very high affinity for nitrogen, preferentially combining with nitrogen atoms to form stable nitride precipitates, such as vanadium nitride (VN) and niobium nitride (NbN). These precipitates are finely and dispersedly distributed in the steel, effectively hindering dislocation movement, thereby achieving precipitation strengthening and significantly improving the strength and hardness of the steel.

[0047] Furthermore, the precise control of nitrogen content to near or at the austenite solubility level plays a crucial role in this invention. If the nitrogen content is too high, nitrogen exceeding the austenite solubility will escape in gaseous form during solidification, forming nitrogen bubbles and pores, leading to defects such as rotten steel and cracks. This invention, by controlling the nitrogen content to near or at the austenite solubility level, allows most of the nitrogen to participate in the formation of precipitated phases with vanadium and / or niobium, reducing the content of free nitrogen and effectively preventing nitrogen gas from escaping and forming defects. Simultaneously, the low alloy content also reduces the risk of other defects arising from the interaction between alloying elements and impurity elements.

[0048] In summary, this invention achieves a perfect balance between precipitation strengthening and defect avoidance capabilities in the case of low alloy content by precisely controlling the solubility of nitrogen in molten steel to be close to or reach that of nitrogen in austenite and making full use of the interaction between vanadium and / or niobium and nitrogen.

[0049] A3. The refined molten steel is successively subjected to continuous casting, rolling and cooling treatment to obtain alloy steel.

[0050] In this invention, the continuous casting and rolling process includes continuous casting, heat treatment, and rolling. The heating temperature during the heat treatment process is the (Nb,V)(C,N) precipitation temperature +30℃. The (Nb,V)(C,N) precipitation temperature is calculated using thermo-calc software, and the heating time is 100~120 min.

[0051] In this invention, the casting speed during the continuous casting process can be controlled to be 3.1~3.5 m / min.

[0052] In this invention, the cooling process includes air cooling.

[0053] This invention provides an alloy steel prepared by any of the alloy steel production methods described above.

[0054] In this invention, the average size of (Nb, V) and (C, N) in the alloy steel is 20-80 nm, and the grain size level is 10-11, i.e., the number of grains per square inch is 2. 9 ~2 10 The yield strength of the alloy steel is increased to 50~120 MPa, and the tensile strength is increased to 60~150 MPa.

[0055] To facilitate a further understanding of the present invention by those skilled in the art, the following examples are provided: Example 1 This invention provides a method for controlling the nitrogen content in steel.

[0056] S1. Obtaining the nitrogen solubility of each phase during the steel cooling phase transformation: Thermo-calc software is used to calculate the nitrogen solubility of each phase during the steel cooling phase transformation. After inputting the steel composition, pressure, and initial nitrogen content of the system, the nitrogen distribution of the first phase is output. The nitrogen distribution of the first phase is as follows: Figure 1 As shown in Table 1, the steel composition is as follows: pressure is 1 atm, initial nitrogen content is 0.5%, and billet compression ratio is >7 to <60.

[0057] Table 1. Steel composition, % S2. While keeping the steel composition, pressure, and other calculation conditions unchanged, adjust the nitrogen content of the initial system to 1%, repeat step S1, and output the nitrogen distribution of the second phase. The nitrogen distribution of the second phase is as follows: Figure 2 As shown (for better illustration of the calculation results, nitrogen entering the gas phase is not included in the diagram), Figure 1 , Figure 2 (as shown in the image).

[0058] S3. By Figure 1 as well as Figure 2 It can be seen that when the initial nitrogen content of the system is 0.5% and 1%, the mass percentage of nitrogen in each phase is equal, indicating that as the nitrogen content in the system increases, the nitrogen content in each phase no longer increases, and the nitrogen in each phase has reached saturation, i.e., reached its solubility limit. Figure 1 It can be seen that the solubility of nitrogen in austenite gradually increases from 0.0222% in the initial stage to a maximum of 0.0331%, and then disappears as austenite disappears.

[0059] Example 2 To verify the accuracy of the nitrogen solubility calculation results and the ability of steel to dissolve nitrogen under actual production conditions, the solubility of nitrogen in steel was measured using a self-designed nitrogen solubility measuring device. The composition of the experimental steel is shown in Table 2.

[0060] Table 2. Composition of the experimental steel The molten steel was heated to 1600℃, and nitrogen gas was directly blown into it through an air blowing pipe at a flow rate of 70 ml / min and a pressure of 0.1 MPa. The molten steel was covered with a slag layer to prevent direct contact between the steel and air. Samples were taken every 10 minutes to analyze the nitrogen content in the molten steel. The nitrogen content determination results are as follows: Figure 3 As shown.

[0061] Depend on Figure 3 It can be seen that as nitrogen is continuously blown in, the mass fraction of nitrogen in the molten steel gradually increases. After 30 minutes, the mass fraction of nitrogen in the molten steel no longer increases, indicating that the nitrogen in the molten steel has reached saturation.

[0062] Combination Figure 3 As shown in Table 2, the nitrogen solubility in molten steel increases with increasing alloy content. Under the current experimental conditions, the nitrogen solubility in molten steels a, b, and c are 0.025%, 0.027%, and 0.031%, respectively. The composition of steel b is the same as that used in Thermo-Calc calculations. Under the experimental conditions, the nitrogen content in the molten steel is close to the solubility of nitrogen in austenite, ranging from 0.0222% to 0.0331%. Considering that nitrogen escapes from the steel sample during cooling, the calculated results can be considered close to the experimental results.

[0063] Example 3 This invention provides an alloy steel production method for controlling nitrogen content in steel. (It should be noted that some process parameters and their corresponding results in this embodiment are expressed as data ranges. This is based on the actual situation of multiple heat tests and aims to reflect the stability and reproducibility of this invention under different production conditions. Therefore, a single fixed value is not used.) A1. Prepare the raw materials according to the preset proportions and melt them into molten steel; the composition of the molten steel is shown in Table 1.

[0064] A2. The molten steel is refined to obtain refined molten steel. The refining process includes, but is not limited to, deoxidation and nitrogen microalloying. During the nitrogen microalloying process, the nitrogen content in the molten steel is controlled to be within the range of 0.0222% + 0.002% to 0.0222% + 0.003%, i.e., 0.0242% - 0.0252%, using the nitrogen content control method described in Example 1. A3. The refined molten steel is then subjected to continuous casting, rolling, and cooling treatment to obtain alloy steel; The heating temperature during the heat treatment process is the (Nb,V)(C,N) precipitation temperature +30℃. The (Nb,V)(C,N) precipitation temperature is calculated using thermo-calc software to be 1150~1210℃, and the heating time is 100~120min.

[0065] Testing revealed that the average size of (Nb, V) and (C, N) in the alloy steel was 20–80 nm, with a grain size grade of 10–11, meaning there were 2 grains per square inch. 9 ~2 10 The yield strength of the alloy steel is increased by 60-100 MPa and the tensile strength is increased by 70-120 MPa. Specifically, the yield strength of the alloy steel is 590-640 MPa and the tensile strength is 733-795 MPa.

[0066] Comparative Example 1 This invention provides an alloy steel production method that controls the nitrogen content in steel. Compared with Example 3, this comparative example keeps other conditions unchanged, only adjusting the amount of nitrogen content control.

[0067] A1. Prepare the raw materials according to the preset proportions and melt them into molten steel; the composition of the molten steel is shown in Table 1.

[0068] A2. The molten steel is refined to obtain refined molten steel, wherein the refining process includes, but is not limited to, deoxidation treatment and nitrogen microalloying; during the nitrogen microalloying process, the nitrogen content in the molten steel is adjusted to 0.01%~0.016%; A3. The refined molten steel is sequentially subjected to continuous casting, rolling, and cooling treatment to obtain alloy steel; upon inspection, the average size of (Nb, V) and (C, N) in the alloy steel is 10~60nm, and the grain size level is 9~10, that is, the number of grains per square inch is 2. 8 ~2 9 The alloy steel has a yield strength of 530~540 MPa and a tensile strength of 663~675 MPa.

[0069] Comparative Example 2 This invention provides an alloy steel production method that controls the nitrogen content in steel. Compared with Example 3, this comparative example keeps other conditions unchanged, only adjusting the amount of nitrogen content control.

[0070] A1. Prepare the raw materials according to the preset proportions and melt them into molten steel; the composition of the molten steel is shown in Table 1.

[0071] A2. The molten steel is refined to obtain refined molten steel, wherein the refining process includes, but is not limited to, deoxidation treatment and nitrogen microalloying; during the nitrogen microalloying process, the nitrogen content in the molten steel is adjusted to 0.03%~0.035%; A3. The refined molten steel is sequentially subjected to continuous casting, rolling, and cooling treatment to obtain alloy steel; upon inspection, the average size of (Nb, V) and (C, N) in the alloy steel is 30~100nm, and the grain size level is 10~11, that is, the number of grains per square inch is 2. 9 ~2 10 The alloy steel was defective, indicating a failed rolling process.

[0072] Comparative Example 3 This invention provides an alloy steel production method that controls the nitrogen content in steel. Compared with Example 3, this comparative example keeps other conditions unchanged, only adjusting the niobium content.

[0073] A1. Prepare the raw materials according to the preset proportions and melt them into molten steel; the composition of the molten steel is shown in Table 1.

[0074] A2. The molten steel is refined to obtain refined molten steel, wherein the refining process includes, but is not limited to, deoxidation and nitrogen microalloying; during the nitrogen microalloying process, the niobium content in the molten steel is adjusted to 0.02%~0.025%; A3. The refined molten steel is sequentially subjected to continuous casting, rolling, and cooling treatment to obtain alloy steel; upon inspection, the average size of (Nb, V) and (C, N) in the alloy steel is 40~120nm, and the grain size level is 10~11, that is, the number of grains per square inch is 2. 9 ~2 10 One, the alloy steel developed transverse rib longitudinal cracks.

[0075] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for controlling nitrogen content in steel, characterized in that, Including the following steps: S1. Obtain the nitrogen solubility of each phase during the cooling phase transformation of steel: The thermo-calc software is used to calculate the nitrogen solubility of each phase during the cooling phase transformation of steel. After inputting the steel composition, pressure and initial system nitrogen content, the nitrogen distribution of the first phase is output. S2. While keeping the steel composition, pressure and other calculation conditions unchanged, increase the nitrogen content of the initial system, repeat step S1, and output the nitrogen distribution of the second phase; S3. If the nitrogen distribution in the second phase is the same as that in the first phase, it is determined that the nitrogen in each phase has reached saturation. At this time, the nitrogen content in each phase is the actual solubility of nitrogen in each phase. If the nitrogen distribution of the second phase is different from that of the first phase, repeat step S2; set the number of input-output operations to N times (N≥2), and continue to perform iterative calculations until the nitrogen distribution of the Nth phase is the same as that of the (N-1)th phase. At this time, the nitrogen content in each phase is the nitrogen solubility in each phase. S4. Obtain the nitrogen solubility in austenite based on the nitrogen solubility in each phase. When the billet compression ratio is 60~120, adjust the nitrogen content in the molten steel within the range of the lower limit of nitrogen solubility in austenite +0.004% to the lower limit of nitrogen solubility in austenite +0.006%. When the billet compression ratio is >7 to <60, adjust the nitrogen content in the molten steel within the range of the lower limit of nitrogen solubility in austenite +0.002% to the lower limit of nitrogen solubility in austenite +0.003%.

2. The method for controlling nitrogen content in steel according to claim 1, characterized in that, The initial nitrogen content of the system is set to be much greater than the sum of nitrogen solubility in each phase as estimated empirically.

3. The method for controlling nitrogen content in steel according to claim 2, characterized in that, The initial system has a nitrogen content of not less than 0.1%.

4. The method for controlling nitrogen content in steel according to claim 1, characterized in that, The steel composition, by mass fraction, includes: C 0.22%~0.25%, Si 0.5%~0.6%, Mn 1.2%~1.4%, P≤0.03%, S≤0.03%, V 0.06%~0.09%; when the billet compression ratio is >7 to <60, Nb 0.003%~0.006%, and when the billet compression ratio is 60~120, Nb 0.006%~0.01%.

5. A method for producing alloy steel using the method for controlling nitrogen content in steel according to any one of claims 1 to 4, characterized in that, Including the following steps: The raw materials are mixed according to the preset proportions and smelted into molten steel. The molten steel is refined to obtain refined molten steel, the refining process including but not limited to deoxidation and nitrogen microalloying; during the nitrogen microalloying process, the nitrogen content in the molten steel is adjusted by the nitrogen content control method in any one of claims 1 to 4; The refined molten steel is then subjected to continuous casting, rolling, and cooling treatment to obtain alloy steel.

6. The method for producing alloy steel according to claim 5, characterized in that, The continuous casting and rolling process includes continuous casting, heat treatment, and rolling. The heating temperature during the heat treatment process is the (Nb,V)(C,N) precipitation temperature +30℃. The (Nb,V)(C,N) precipitation temperature is calculated using thermo-calc software, and the heating time is 100~120 min.

7. The method for producing alloy steel according to claim 6, characterized in that, The casting speed during the continuous casting process is controlled to be 3.1~3.5 m / min.

8. The method for producing alloy steel according to claim 5, characterized in that, The cooling method includes air cooling.

9. An alloy steel, prepared by the alloy steel production method according to any one of claims 5 to 8.

10. The alloy steel according to claim 9, characterized in that, The alloy steel has an average (Nb, V) and (C, N) grain size of 20-80 nm and a grain size level of 10-11, meaning there are 2 grains per square inch. 9 ~2 10 The yield strength of the alloy steel is increased by 50-120 MPa, and the tensile strength is increased by 60-150 MPa.

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