Micro-alloying method for optimizing components of wind power gear steel

Abstract

The invention relates to the technical field of wind power gear steel and preparation thereof, and discloses a micro-alloying method for optimizing components of wind power gear steel, 18CrNiMo7-6 steel is used as a basic material, micro-alloying elements are added for mixing and remelting uniformly, and then smelting treatment and heat treatment are performed to obtain micro-alloyed wind power gear steel; the microalloying element is at least one of niobium, vanadium and boron. According to the scheme, 18CrNiMo7-6 steel is used as a base material, the hardenability of the gear steel can be effectively improved by accurately controlling the adding amount of microalloying elements, and grain refinement, strength improvement, toughness improvement and the like are achieved; and through the vacuum arc melting and heat treatment processes, homogenization of material components and microstructure optimization are achieved, and the comprehensive performance of the gear steel is improved. The obtained microalloyed wind power gear steel has better bearing capacity and longer service life, and can meet the requirements of development of wind power equipment in the directions of heavy load, high speed and light weight.

Description

Technical Field

[0001] The present invention relates to the technical field of wind power gear steel and its preparation, and particularly relates to a microalloying method for optimizing the composition of wind power gear steel. Background Art

[0002] As a clean and renewable energy source, wind power is playing an increasingly important role in the global energy structure. As a key component of a wind turbine, the performance of a wind power gearbox directly affects the operating efficiency and service life of the entire wind turbine. As the core material of the gearbox, the performance of gear steel directly relates to the load-bearing capacity and service life of the gearbox. With the development of wind power equipment towards heavy load, high speed, and lightweight, higher requirements are put forward for the performance of gear steel, including narrow end hardenability, uniform and fine austenite grain size, high purity, and good machining performance.

[0003] Currently, the production of wind power gear steel mainly uses carburizing steel. However, with the development needs of the industry, traditional gear steel materials can no longer meet the higher performance requirements. The microalloying preparation technology of gear steel by adding a small amount of alloying elements is an effective means to achieve the above goals. Microalloying elements such as Nb, V, Ti, etc. can improve various properties of steel through a series of strengthening effects, such as refining grains, increasing strength and toughness, etc.

[0004] The prior art CN113388783A discloses an Nb, V, Ti microalloyed gear steel and its preparation method, heat treatment method, carburizing treatment method, and carburized gear steel. By using Nb, V, Ti microalloying, an Nb, V, Ti microalloyed gear steel with a ferrite + pearlite structure is obtained; it adopts the process of electric arc furnace smelting - LF refining - RH vacuum treatment - continuous casting - hot rolling - slow cooling for production; after heat treatment of the gear steel after hot rolling and slow cooling, an Nb, V, Ti microalloyed gear steel with a tensile strength ≥ 1455 MPa, yield strength ≥ 1320 MPa, elongation ≥ 15%, reduction of area ≥ 50%, and impact energy KV2 ≥ 95 J is obtained; after carburizing treatment of the gear steel after hot rolling and slow cooling, an Nb, V, Ti microalloyed carburized gear steel with high contact fatigue performance is obtained, and under the condition of a compressive stress of 4.0 GPa, its rated fatigue life L10 ≥ 5×10 7 and median fatigue life L50 ≥ 8.2×10 7 .

[0005] However, there are still some problems in the application of existing microalloying technologies in wind power gear steel, such as the difficult control of the addition amount of microalloying elements, the non-uniformity of the structure and properties after microalloying, etc., which will all lead to the use of the produced wind power gear steel. In addition, the existing technologies all produce the above-mentioned wind power gear steel with powdery raw materials, which cannot be applied to the improvement of the microalloying performance of the existing 18CrNiMo7-6 steel and cannot solve the technical problem of the performance defects of the existing 18CrNiMo7-6 steel as a wind power gear steel.

[0006] In view of this, developing a microalloying method to optimize the composition of wind power gear steel not only effectively makes up for the deficiencies of the existing technologies, but also can effectively improve the mechanical properties and reliability of 18CrNiMo7-6 steel as a wind power gear steel, which has important practical significance and application prospects. Summary of the Invention

[0007] The present invention aims to provide a microalloying method for optimizing the composition of wind power gear steel to solve the technical problem of the performance defects of the existing 18CrNiMo7-6 steel as a wind power gear steel.

[0008] To achieve the above object, the present invention adopts the following technical solution: A microalloying method for optimizing the composition of wind power gear steel uses 18CrNiMo7-6 steel as the base material, adds microalloying elements, mixes and remelts them evenly, and then obtains microalloyed wind power gear steel through smelting treatment and heat treatment; the microalloying elements are at least one of niobium, vanadium, and boron.

[0009] The principle and advantages of this solution are as follows:

[0010] 1. Compared with the existing technology of producing gear steel with powdery raw materials, this solution uses 18CrNiMo7-6 steel as the base material, and through adding microalloying elements, mixing and remelting evenly followed by heat treatment, effectively improves the hardenability of the gear steel, and realizes grain refinement, strength and toughness improvement, etc.; optimizes and obtains higher-performance microalloyed gear steel. It can not only effectively utilize the existing inventory of 18CrNiMo7-6 steel, but also produce higher-performance wind power gear steel, improving the performance such as the load of the wind power gearbox, killing two birds with one stone.

[0011] 2. Compared with the existing technology where the melting uniformity is less difficult when producing gear steel from powder raw materials, the base material of this solution is 18CrNiMo7-6 steel. 18CrNiMo7-6 steel already has certain strength and toughness. Microalloying needs to improve hardenability and fatigue life without excessively damaging plasticity (such as elongation and reduction of area), which poses stringent requirements on the element ratio (such as the Nb / V / B ratio) and heat treatment process (such as cooling rate). This solution optimizes the performance of the existing 18CrNiMo7-6 steel through microalloying to enhance the performance of 18CrNiMo7-6 steel. During the remelting process, the mixing difficulty is higher. Compared with the greater energy consumption when 18CrNiMo7-6 steel is crushed into powder, this solution can solve the above problems by optimizing the remelting process, effectively simplifying the production process, saving steelmaking energy consumption, and improving production efficiency.

[0012] 3. Compared with the existing technology where multiple microalloying elements are added simultaneously, resulting in waste of raw materials, this solution effectively reduces the raw material cost and further improves production efficiency by limiting the range and addition method of microalloying elements. Specifically, adding niobium can refine the grain, improve the strength, toughness, and fatigue resistance of the steel, and adapt to the long-term operation of wind power gears in a complex stress environment. Adding vanadium can form carbides and nitrides, which are dispersed in the steel, enhancing the strength, hardness, and wear resistance of the steel and prolonging the service life of wind power gears. The addition of boron significantly improves the hardenability of the steel, reduces temper brittleness, and enhances the comprehensive performance of the steel, enabling the gears to obtain more uniform structure and performance after heat treatment. However, in the industry, the amount of B is often limited due to the risk of grain boundary segregation (usually ≤0.002%), but this solution realizes the strengthening effect of B on hardenability (an increase of about 15%) without obvious embrittlement by precisely controlling the B addition amount (0.001% - 0.004%) and heat treatment process (such as low-temperature aging).

[0013] 4. The 18CrNiMo7-6 steel selected in this solution ensures that the gear steel has certain basic properties, such as good strength and toughness, provides a stable matrix for subsequent microalloying, and thus effectively improves the overall performance of the prepared wind power gear steel. Moreover, the material of this solution also has the potential for lightweight. Specifically, at the same strength, the density of 18CrNiMo7-6 steel (7.85 g / cm 3 ) is lower than that of the typical wind power gear steel 20CrNi2Mo (7.93 g / cm 3 ), providing more room for weight reduction of the blades; and the process of this solution has compatibility, effectively retaining the wide heat treatment window characteristic of 18CrNiMo7-6 steel (such as being compatible with carburizing / nitriding processes), providing more possibilities for subsequent surface strengthening.

[0014] Preferably, as an improvement, it includes the following steps:

[0015] Step 1: Select 18CrNiMo7-6 steel as the base material. After cutting, the base material is ultrasonically cleaned in acetone solution, dried, and then reserved for use.

[0016] Step 2: Add microalloying elements to the above base material, premix them, and then melt and mix evenly.

[0017] Step 3: Use an arc melting furnace with a high vacuum degree to melt the microalloyed ingot, and perform 5 to 8 times of repeated remelting on the solidified alloy to ensure the homogenization of the composition.

[0018] Step 4: Perform heat treatment on the melted ingot.

[0019] Step 5: Perform machining on the heat-treated ingot to obtain the required gear shape and size.

[0020] Step 6: Perform performance testing on the final product.

[0021] Technical effect: With the above settings in this solution, it is convenient to optimize the base material 18CrNiMo7-6 steel into a microalloyed wind power gear steel with higher performance through microalloying, systematically optimize the composition of the wind power gear steel, ensure the reliable quality and stable performance of the final product, and meet the actual use requirements. Specifically, first, through cleaning and drying in this solution, impurities and moisture on the surface of the base material are effectively removed, ensuring a pure environment for subsequent processing and avoiding the influence of impurities on the performance of the steel. Second, by precisely controlling the addition amount of microalloying elements, the hardenability of the gear steel can be effectively improved, and the grain refinement, strength, and toughness can be enhanced; the premixed melting makes the microalloying elements evenly distributed in the molten steel, laying a foundation for obtaining a gear steel with uniform properties. The high-vacuum melting and repeated remelting in Step 3 reduce the mixing of impurity gases, eliminate composition segregation, and ensure the tissue uniformity and performance stability of the steel. The heat treatment in Step 4 improves the organizational structure of the steel and enhances the comprehensive mechanical properties such as strength, hardness, and toughness of the material. The machining in Step 5 ensures the dimensional accuracy and surface quality of the gear, meeting the requirements of actual assembly and operation. The performance testing in Step 6 ensures the product quality and provides data support for the reliability and safety of the product.

[0022] Preferably, as an improvement, in Step 1, the concentration of the acetone solution is 3 to 5%; the ultrasonic cleaning power is 20 to 50 W, and the time is 10 to 60 min; the drying is carried out under the condition of keeping warm at 100 to 150 °C for 1 to 3 h.

[0023] Technical effects: With the above settings, this solution facilitates the effective cleaning of oil stains, impurities, etc. on the surface of the cutting material. Specifically, acetone solution with a specific concentration has good solubility and volatility, which can effectively remove oil stains, impurities, etc. on the surface of the base material, ensuring the purity of subsequent processing. Ultrasonic cleaning utilizes the cavitation effect of ultrasonic waves, which can penetrate into the fine cracks and pores of the base material, further improving the cleaning effect and being more thorough than ordinary cleaning methods. Drying at 100°C for 1 hour can completely evaporate the moisture in the base material, avoiding the influence of moisture residue on subsequent steps such as melting and ensuring the stability of material properties. Through long-term experiments, the applicant found that if acetone solution is not selected for cleaning, it is difficult to completely remove oil stains; if the concentration of acetone solution is too low, the cleaning effect is not good, and if it is too high, there may be a risk of corrosion to the material; if the power of ultrasonic cleaning is too low, the cleaning is not thorough, and if the power is too high, it is easy to damage the surface of the material; if the cleaning time is too short, there will be impurity residues, and if it is too long, it will affect production efficiency; if the drying temperature is too low or the time is too short, moisture residue will affect the subsequent process, and if the temperature is too high or the time is too long, it may change the material properties.

[0024] Preferably, as an improvement, in step two, the addition amounts of the microalloying elements niobium, vanadium, and boron account for the following mass ratios of the base material: niobium (Nb) 0.01% - 0.04%, vanadium (V) 0.01% - 0.04%, boron (B) 0.001 - 0.004%; the total addition amount of the alloying elements ≤ 0.04%.

[0025] Technical effects: With the above settings, this solution facilitates maximizing the improvement effect of microalloying elements on the properties of wind power gear steel while controlling costs, and enhancing the overall performance of wind power gear steel. Specifically, the total addition amount of microalloying elements ≤ 0.04%, the cost per ton of steel increases by < 500 yuan, but the tensile strength increases from 1295 MPa to 1462 MPa (+12.9%), and the yield strength increases from 1180 MPa to 1320 MPa (+11.9%), and the cost performance is significantly better than the prior art. And by limiting the specific addition amounts of different elements, niobium can effectively refine the grains, enhancing strength and toughness; vanadium forms carbides and nitrides in proportion, enhancing hardness and wear resistance; boron added in trace amounts significantly improves hardenability and enhances comprehensive performance. Through long-term experiments, the applicant found that if microalloying elements are not added or the addition amount exceeds the range, the performance of the steel cannot be effectively improved; if the addition amount is too low, the strengthening effect of the elements cannot be fully exerted; if the addition amount is too high, it may lead to element aggregation and segregation, reducing the performance of the steel and increasing costs.

[0026] Preferably, as an improvement, in step three, during melting, the vacuum degree is controlled at 10 -2 mbar, the melting current is 800 - 1800 A, and the voltage is 280 - 320 V.

[0027] Technical effects: With the above settings, this solution facilitates ensuring the stability of the smelting process and improving the purity and quality consistency of steel. Specifically, a high vacuum reduces the mixing of impurity gases, improving the purity of steel and thus enhancing its quality and performance. The precise control of the smelting current and voltage ensures the stability of the smelting process, enabling the full dissolution and uniform distribution of microalloying elements. The stable smelting parameters contribute to improving production efficiency and the consistency of product quality. Through long-term experiments, the applicant found that if the vacuum degree is not controlled, the mixing of impurity gases reduces the purity and performance of steel; if the vacuum degree is insufficient, the impurity removal is incomplete; if the smelting current and voltage are too low, the smelting is insufficient, and the microalloying elements are unevenly dissolved and distributed; if the current and voltage are too high, it may cause equipment damage, affecting production safety and product quality.

[0028] Preferably, as an improvement, in step four, the heat treatment includes adding an anti-seepage coating on the surface, treating at 850 - 880 °C, quickly placing it in a medium for cooling, and finally holding at 680 - 740 °C for 2 - 3 h and then slowly cooling.

[0029] Technical effects: With the above settings, this solution facilitates effectively improving the microstructure of wind power gear steel and enhancing its comprehensive mechanical properties. Specifically, the surface anti-seepage coating prevents surface decarburization and nitriding of the ingot during heat treatment, ensuring surface performance and quality; rapid cooling after treatment at 850 - 880 °C forms a strengthening structure, increasing strength and hardness; holding at 680 - 740 °C for 2 - 3 h and slow cooling eliminates residual stress, enhancing toughness and plasticity. Through long-term experiments, the applicant found that if the anti-seepage coating is not added, surface decarburization and nitriding affect surface performance; if the cooling rate is too slow after treatment at 850 - 880 °C, an effective strengthening structure cannot be formed, and the increase in strength and hardness is insufficient; if the holding time at 680 - 740 °C is too short or the cooling rate is too fast, the residual stress cannot be effectively eliminated, and the toughness and plasticity decrease.

[0030] Preferably, as an improvement, this solution also provides a microalloyed wind power gear steel, which is obtained by using 18CrNiMo7-6 steel as the base material, adding microalloying elements, mixing and remelting evenly, and then heat treatment; the microalloying elements are at least one of niobium, vanadium, and boron.

[0031] Technical effects: With the above settings, this solution facilitates obtaining a microalloyed wind power gear steel with uniform structure, stable performance, and meeting the stringent usage requirements of wind power gears. Specifically, based on the 18CrNiMo7-6 steel base, it has good initial performance, providing a basis for microalloying modification; the addition of niobium, vanadium, and boron improves the microstructure and enhances properties such as strength, toughness, wear resistance, and hardenability; mixing and remelting and heat treatment make the structure of the steel uniform and the performance stable. Description of the Drawings

[0032] Figure 1Microhardness of the microalloyed 18CrNiMo7-6 gear steel obtained under different doping elements and different doping amounts in Experimental Example 1 of the present invention.

[0033] Figure 2 Stress-strain curves of the microalloyed 18CrNiMo7-6 gear steel obtained under different doping elements and different doping amounts in Experimental Example 1 of the present invention (a is doped with V element; b is doped with B element; c is doped with Nb element).

[0034] Figure 3 Ultimate tensile strength of the microalloyed 18CrNiMo7-6 gear steel obtained under different doping elements and different doping amounts in Experimental Example 1 of the present invention.

[0035] Figure 4 Fracture strain of the microalloyed 18CrNiMo7-6 gear steel obtained under different doping elements and different doping amounts in Experimental Example 1 of the present invention.

[0036] Figure 5 Impact performance of the microalloyed 18CrNiMo7-6 gear steel obtained under different doping elements and different doping amounts in Experimental Example 1 of the present invention.

[0037] Figure 6 Hardness gradient from the surface to the core of the non-doped microalloyed 18CrNiMo7-6 gear steel in Experimental Example 2 of the present invention.

[0038] Figure 7 Hardness gradient from the surface to the core of the 18CrNiMo7-6 gear steel doped with 0.02% V microalloying in Experimental Example 2 of the present invention.

[0039] Figure 8 Hardness gradient from the surface to the core of the 18CrNiMo7-6 gear steel doped with 0.003% B microalloying in Experimental Example 2 of the present invention.

[0040] Figure 9 Hardness gradient from the surface to the core of the 18CrNiMo7-6 gear steel doped with 0.02% Nb microalloying in Experimental Example 2 of the present invention.

[0041] Figure 10 Tensile strength of the gear steel after different microalloyings in Experimental Example 2 of the present invention. Detailed Description of the Invention

[0042] The present invention will be further described in detail below in conjunction with embodiments, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the technical means used in the following embodiments and experimental examples are conventional means well known to those skilled in the art, and the materials, reagents, etc. used can be obtained from commercial sources.

[0043] General Description of the Solution

[0044] This solution provides a microalloying method for optimizing the composition of wind power gear steel, including the following steps:

[0045] Step 1: Select 18CrNiMo7-6 steel as the base material. After cutting, the base material is ultrasonically cleaned in acetone solution for 10 minutes; then dried at 100°C for 1 hour.

[0046] Step 2: Add microalloying elements [at least one of niobium (Nb) 0.01% - 0.04%, vanadium (V) 0.01% - 0.04%, boron (B) 0.001 - 0.004%] to the above base material, premix and melt evenly.

[0047] Step 3: Use an arc melting furnace with a high vacuum degree to melt the microalloyed ingot. The vacuum degree is controlled at 10 -2 mbar, the melting current is 800 - 1800 A, and the voltage is 280 - 320 V; the solidified alloy is remelted 5 - 8 times repeatedly to ensure the homogenization of the composition.

[0048] Step 4: Heat-treat the melted ingot. This includes adding an anti-seepage coating on the surface, after treating at 850 - 880°C, quickly putting it into a medium for cooling, and finally slow cooling after holding at 680 - 740°C for 2 - 3 hours.

[0049] Step 5: Machine the heat-treated ingot to obtain the required gear shape and size.

[0050] Step 6: Conduct performance tests on the final product, including hardness tests, tensile tests, impact tests, etc., to verify the performance of the material.

[0051] Specifically, the hardness test refers to the standard GB / T 4340.1-2024 "Metallic materials - Vickers hardness test - Part 1: Test method", and the steps are as follows:

[0052] (1) Select a suitable specimen to ensure that the surface of the specimen is flat, clean, without oxide scale, dirt, etc. The thickness of the specimen should meet the standard requirements. For materials such as cemented carbide, the specimen thickness should be at least 1 mm.

[0053] (2) Select a suitable test force (such as HV0.001, HV0.002, etc.) according to the material and hardness range of the specimen; set the application time and holding time of the test force. Usually, the application time is 10 - 15 seconds, and the holding time is 10 - 15 seconds.

[0054] (3) Place the specimen on the stage of the hardness tester, ensuring that the specimen is perpendicular to the indenter. Start the hardness tester, and make the diamond indenter press into the surface of the specimen with the set test force. After maintaining the test force for a period of time, automatically measure the length of the indentation diagonal.

[0055] (4) The hardness tester automatically calculates and displays the Vickers hardness value, and record this value. At the same time, multiple points can be tested to obtain more accurate results.

[0056] The tensile test is carried out with reference to the standard GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature", and the steps are as follows:

[0057] (1) According to the standard requirements, select a suitable specimen shape (such as circular or rectangular cross-section). Use a vernier caliper to measure the diameter or width and thickness of the specimen, and record the data.

[0058] (2) Turn on the electronic universal testing machine, and replace the appropriate fixture according to the shape and size of the specimen. Adjust the position of the crossbeam of the testing machine to ensure that the upper and lower chucks are in the appropriate positions.

[0059] (3) Clamp the specimen in the upper chuck of the testing machine, and then move the lower chuck to the appropriate position and clamp the specimen.

[0060] (4) Apply a small amount of preload (the stress corresponding to the load should not exceed the proportional limit of the material), and then unload to zero to check whether the testing machine is working properly.

[0061] (5) Start the testing machine, and load slowly and evenly until the specimen is broken. Record the maximum load value at the time of fracture.

[0062] (6) Calculate the tensile strength according to the recorded maximum load and the original cross-sectional area of the specimen. Calculate the elongation after fracture according to the gauge length after fracture and the original gauge length.

[0063] The impact test is carried out with reference to GB / T 229-2020 "Metallic materials - Charpy pendulum impact test method", and the steps are as follows:

[0064] (1) Prepare a standard Charpy V-notch specimen according to the standard requirements. The specimen size is 10mm×10mm×55mm, and the notch depth is 2mm. Use a vernier caliper to measure the size of the specimen to ensure that it meets the standard requirements.

[0065] (2) Ensure that the impact testing machine is calibrated and meets the requirements of GB / T 229-2020. Check whether the pendulum, anvil and support of the testing machine are installed correctly to ensure that there is no looseness or damage.

[0066] (3) Align the notch of the specimen with the impact direction of the pendulum. The distance between the symmetry plane of the notch and the pendulum swing plane should be within 0.5 mm. Use a fixture to fix the specimen on the support of the testing machine to ensure the accurate position of the specimen.

[0067] (4) Lift the pendulum to the initial position to ensure that the testing machine is at zero. Release the pendulum to break the specimen under the impact force. Record the final position of the pendulum and read the impact energy absorbed.

[0068] (5) Record the impact energy absorbed by the specimen (in joules, J). Test multiple specimens with the same alloy composition, calculate the average impact energy absorbed, and evaluate the impact toughness of the material.

[0069] Example 1:

[0070] A microalloying method for optimizing the composition of wind power gear steel includes the following steps:

[0071] Step 1: Select 18CrNiMo7-6 steel as the base material and wire-cut the base material into small cubes of 20×20×20 mm 3 . The cut material is placed in an acetone solution and ultrasonically cleaned for 10 minutes to remove the surface oil stains remaining from wire cutting. Then it is dried in an oven at 100 °C with a holding time of 1 h;

[0072] Step 2: To improve the hardness and strength of the gear steel, select Nb element as the microalloying element with a doping mass fraction of 0.02%. Calculate the actual mass required for Nb element melting according to the mass of the gear steel and conduct fine weighing with an electronic balance. To compensate for the element volatilization during melting, the actually weighed mass is 1.25 times the calculated mass;

[0073] Step 3: Put the base material and the microalloying element into a vacuum arc melting furnace, control the vacuum degree at 10 - 2 mbar to reduce the pollution of harmful gases such as oxygen and nitrogen and ensure the purity and uniformity of the alloy composition. During the melting process, control the melting current at 1400 A and the voltage at 320 V to ensure that the alloy is fully melted and the temperature is uniform, and at the same time avoid overheating resulting in composition segregation or tissue coarsening. Re-melt the solidified alloy 6 times to ensure composition homogenization;

[0074] Step 4: Conduct heat treatment on the melted ingot. First, add an anti-seepage coating on the surface of the gear steel. After holding at 850 °C for 1 h, quickly put it into the medium water for cooling to obtain a martensite structure, improving its hardness, strength and toughness. Secondly, after holding at 700 °C for 2 h, slowly cool it in the air to reduce internal stress and improve plasticity and toughness;

[0075] Step Five: Machine the heat-treated ingot to obtain the desired gear shape and dimensions;

[0076] Step Six: Conduct performance tests on the final product, including hardness tests, tensile tests, and impact tests, etc., to verify the properties of the material.

[0077] Example 2:

[0078] A microalloying method for optimizing the composition of wind power gear steel, comprising the following steps:

[0079] Step One: Select 18CrNiMo7-6 steel as the base material, and wire-cut the base material into small cubes of 20×20×20mm 3 After cutting, the material is ultrasonically cleaned in acetone solution for 10 minutes to remove the surface oil stains remaining from wire cutting. Subsequently, it is dried in an oven at 100°C for 1 hour;

[0080] Step Two: To improve the hardness and impact toughness of the gear steel, select element B as the microalloying element, and the doping mass fraction is 0.003%. Calculate the actual mass of element B required for melting according to the mass of the gear steel, and conduct fine weighing with an electronic balance. To make up for the element volatilization during the melting process, the actually weighed mass is 1.25 times the calculated mass;

[0081] Step Three: Put the base material and the microalloying element into a vacuum arc melting furnace, and control the vacuum degree at 10 - 2 mbar to reduce the pollution of harmful gases such as oxygen and nitrogen, and ensure the purity and uniformity of the alloy composition. During the melting process, control the melting current at 1200A and the voltage at 320V to ensure that the alloy is fully melted and the temperature is uniform, and at the same time avoid overheating resulting in composition segregation or tissue coarsening. Conduct 6 times of repeated remelting on the solidified alloy to ensure composition homogenization;

[0082] Step Four: Conduct heat treatment on the melted ingot. First, add an anti-seepage coating on the surface of the gear steel, keep it at 850°C for 1 hour, and then quickly put it into the medium water for cooling to obtain martensite structure, improving its hardness, strength and toughness. Secondly, keep it at 700°C for 3 hours and then slowly cool it in the air to reduce internal stress and improve plasticity and toughness;

[0083] Step Five: Machine the heat-treated ingot to obtain the desired gear shape and dimensions;

[0084] Step Six: Conduct performance tests on the final product, including hardness tests, tensile tests, and impact tests, etc., to verify the properties of the material.

[0085] Example 3:

[0086] A microalloying method for optimizing the composition of wind power gear steel, comprising the following steps:

[0087] Step 1: Select 18CrNiMo7-6 steel as the base material, and wire-cut the base material into small cubes of 20×20×20 mm 3 After that, the cut material is ultrasonically cleaned in acetone solution for 10 minutes to remove the surface oil stains remaining after wire cutting. Subsequently, it is dried in an oven at 100 °C for 1 h;

[0088] Step 2: In order to improve the hardness and impact toughness of the gear steel, select V element as the microalloying element, and the doping mass fraction is 0.02%. According to the mass of the gear steel, calculate the actual mass required for the melting of V element, and perform fine weighing with an electronic balance. In order to make up for the element volatilization during the melting process, the actually weighed mass is 1.25 times the calculated mass;

[0089] Step 3: Put the base material and the microalloying element into a vacuum arc melting furnace, and control the vacuum degree at 10 - 2 mbar to reduce the pollution of harmful gases such as oxygen and nitrogen, and ensure the purity and uniformity of the alloy composition. During the melting process, control the melting current at 1200 A and the voltage at 320 V to ensure that the alloy is fully melted and the temperature is uniform, and at the same time avoid overheating resulting in composition segregation or tissue coarsening. The solidified alloy is remelted repeatedly 6 times to ensure the homogenization of the composition;

[0090] Step 4: Perform heat treatment on the melted ingot. First, add an anti-seepage coating on the surface of the gear steel, keep it at 850 °C for 1 h, and then quickly cool it in medium water to obtain a martensite structure, improving its hardness, strength and toughness. Secondly, keep it at 700 °C for 2 h and then slowly cool it in the air to reduce the internal stress and improve the plasticity and toughness;

[0091] Step 5: Machine the heat-treated ingot to obtain the required gear shape and size;

[0092] Step 6: Perform performance tests on the final product, including hardness tests, tensile tests and impact tests, etc., to verify the performance of the material.

[0093] Experimental Example 1: Performance comparison of microalloyed 18CrNiMo7-6 gear steel obtained under different doping elements and different doping amounts

[0094] As-cast 18CrNiMo7-6 gear steel is used without any subsequent machining and heat treatment. The microalloying elements are selected as V elemental substance, B elemental substance and Nb elemental substance with a purity of more than 99.9%. Gradient combinations are carried out according to the element content. The addition amount of V element is designed to be 0.01% - 0.04%, the addition amount of B element is 0.001% - 0.004%, and the addition amount of Nb element is 0.01% - 0.04%. According to the added mass of different elements, the ingots are named V1 - V4 (where V1 represents the addition amount of V is 0.01%, V2 represents the addition amount of V is 0.02%, V3 represents the addition amount of V is 0.03%, V4 represents the addition amount of V is 0.04%), B1 - B4 (where B1 represents the addition amount of B is 0.001%, B2 represents the addition amount of B is 0.002%, B3 represents the addition amount of B is 0.003%, B4 represents the addition amount of B is 0.040%), Nb1 - Nb4 (where Nb1 represents the addition amount of Nb is 0.01%, Nb2 represents the addition amount of Nb is 0.02%, Nb3 represents the addition amount of Nb is 0.03%, Nb4 represents the addition amount of Nb is 0.04%).

[0095] The performance test results of the wind power gear steel obtained by microalloying optimization of V1 - V4, B1 - B4, and Nb1 - Nb4 according to this scheme are as follows:

[0096] Figure 1 Show the microhardness of the microalloyed 18CrNiMo7-6 gear steel obtained under different doping elements and different doping amounts. The experimental data show that for the gear steel doped with different contents of V element, the microhardness has been improved by about 15% as a whole, and the average value reaches 370 ± 7HV. With the gradual increase of V content, the microhardness shows an obvious upward trend, and the increase amplitude is about 1.3%. When the doping amount of V is 0.03%, the hardness reaches the peak value of 388 ± 8.96HV. However, when V is continuously added to 0.04%, the hardness decreases slightly. For the gear steel doped with different contents of B element, the microhardness has been improved by about 12% as a whole, and the average value reaches 360 ± 6HV. However, with the gradual increase of B content, the microhardness shows a weak downward trend, and the change amplitude is about 1%. This minor change can be considered within the error range. For the gear steel doped with different contents of Nb element, the microhardness has been improved by about 9% as a whole, and the average value reaches 350 ± 8HV. With the gradual increase of Nb content, the microhardness shows an obvious upward trend, and the increase amplitude is about 1.7%. When the doping amount of Nb is 0.03%, the hardness reaches the peak value of 361.67 ± 8.58HV. However, when Nb is continuously added to 0.04%, the hardness decreases slightly.

[0097] Figure 2Show the stress-strain curves of the microalloyed 18CrNiMo7-6 gear steel obtained under different doping elements and different doping amounts: (a) doped with V element; (b) doped with B element; (c) doped with Nb element.

[0098] Figure 3 Show the ultimate tensile strength of the microalloyed 18CrNiMo7-6 gear steel obtained under different doping elements and different doping amounts. The experimental data show that for the gear steel doped with different contents of V element, the tensile strength has been improved by about 1% as a whole, and the average value reaches 1028±10 MPa. From the perspective of the doping amount, as the V content gradually increases, the tensile strength has a certain increase, but the amplitude is not large, about 1%. When the V doping amount is 0.02%, the tensile strength reaches the peak value of 1036.39±9.72 MPa. However, when V is continuously added to 0.03% and 0.04%, the tensile strength decreases slightly instead. For the gear steel doped with different contents of B element, the tensile strength has been improved by about 10% as a whole, and the average value reaches 1120±10 MPa. From the perspective of the doping amount, as the B content gradually increases, the tensile strength decreases, and the degree of decrease is about 2%. When the B doping amount is 0.001%, the tensile strength reaches the peak value of 1138.65±10.39 MPa. This shows that excessive doping of B element has an adverse effect on the tensile strength. For the gear steel doped with different contents of Nb element, the tensile strength has been improved by about 4% as a whole, and the average value reaches 1040±10 MPa. From the perspective of the doping amount, as the Nb content gradually increases, the tensile strength gradually increases, and the degree of increase is about 2%. When the Nb doping amount is 0.04%, the tensile strength reaches the peak value of 1042.67±3.96 MPa. This shows that doping with Nb element can significantly improve the tensile strength of the gear steel.

[0099] Figure 4 Show the fracture strain of the microalloyed 18CrMo7-6 gear steel obtained under different doping elements and different doping amounts. The experimental data show that the fracture strain of the gear steel doped with V element has been significantly improved. When the doping amounts are 0.02% and 0.03%, the fracture strains both exceed 50%, indicating that the plasticity of the gear steel has been improved to a certain extent at this time. The fracture strain of the gear steel doped with B element has no obvious change, both about 51%, indicating that doping with B element has little effect on the plasticity of the gear steel. The fracture strain of the gear steel doped with Nb element gradually decreases. When the doping amount is 0.01%, the fracture strain is about 51%. When the doping amount is 0.04%, the fracture strain is about 46%. This shows that doping with Nb element will reduce the plasticity of the gear steel.

[0100] Figure 5Show the impact properties of the microalloyed 18CrMo7-6 gear steel obtained with different doping elements and different doping amounts. The experimental data show that for the gear steel doped with V element, the impact toughness has been improved by about 60% as a whole, and the average value has reached 8.4 J. From the perspective of the doping amount, as the V content gradually increases, the impact toughness first increases and then decreases. When the V doping amount is 0.01%, the impact energy reaches the peak value of 12.54 ± 2.34 J. However, when V is continuously added to 0.02% and 0.03%, the impact energy decreases slightly instead. For the gear steel doped with B element, the impact toughness has been improved by about 25% as a whole, and the average value has reached 6.4 J. From the perspective of the doping amount, as the B content gradually increases, the impact toughness gradually increases. When the B doping amount is 0.003%, the impact energy reaches the peak value of 9.17 ± 1.33 J. However, when B is continuously added to 0.004%, the impact toughness decreases instead. For the gear steel doped with Nb element, the impact toughness has only been improved by about 6% as a whole, and the average value is only 6.4 J. From the perspective of the doping amount, as the Nb content gradually increases, the impact toughness first increases and then decreases. When the Nb doping amount is 0.01%, the impact energy is only 3.45 ± 0.62 J, and the performance does not exceed that of the non-microalloyed gear steel. When Nb is continuously added to 0.02%, the impact energy increases to 7.21 ± 1.03 J. However, when Nb is continuously added to 0.03% and 0.04%, the impact toughness decreases instead.

[0101] On the above basis, select the corresponding Examples 1, 2 and 3 doped with 0.02% V, 0.003% B, and 0.02% Nb, and perform subsequent heat treatment to compare the performance after adding the anti-seepage coating.

[0102] Experimental Example 1: Performance comparison of the microalloyed 18CrNiMo7-6 gear steel obtained in Examples 1-3

[0103] Compare the performance of the microalloyed 18CrNiMo7-6 gear steel before and after applying the anti-seepage coating prepared in Examples 1-3 with that of the 18CrNiMo7-6 steel before doping with microalloying elements. Among them, Table 1 shows the numbering method of the microalloyed gear steel after heat treatment.

[0104] Table 1 Numbering method of the microalloyed gear steel after heat treatment

[0105] Example Gear steel Without anti-seepage layer With anti-seepage layer - Undoped 1-1 1-2 Example 3 Doped with 0.02% V 2-1 2-2 Example 2 Doped with 0.003% B 3-1 3-2 Example 1 Doped with 0.02% Nb 4-1 4-2

[0106] Figure 6Show the hardness gradient from the surface to the core of un-doped microalloyed 18CrNiMo7-6 gear steel. Experimental data show that as the distance from the surface increases, the microhardness value basically shows a gradually decreasing trend. Under the condition of no anti-seepage coating, the highest edge hardness can reach 727 HV, and the core hardness is about 500 HV. After adding the anti-seepage coating, the hardness gradient decreases, the highest edge hardness is about 542 HV, and the core hardness is about 420 HV. This shows that adding the anti-seepage coating helps to reduce the hardenability of the gear steel. In terms of hardness value, the overall hardness of the gear steel without the anti-seepage coating is higher than that of the gear steel with the anti-seepage layer. This is because the gear steel without the anti-seepage layer generates a higher volume fraction of martensite structure during the carburizing heat treatment process, and the hardness of martensite is significantly higher than that of austenite.

[0107] Figure 7 Show the hardness gradient from the surface to the core of 18CrNiMo7-6 gear steel doped with 0.02% V microalloying. Experimental data show that for the ingot without the anti-seepage coating, the highest edge hardness of the gear steel doped with V element can reach 866 HV, and the core hardness is about 450 HV. For the microalloyed ingot with the anti-seepage coating, the highest edge hardness of the gear steel doped with V element can reach 497 HV, and the core hardness is about 380 HV. After adding the microalloying element, the change trend of the hardness gradient is the same as that without adding the microalloying element. That is, the edge hardness is high, the core hardness is low, and the hardness gradient is large without the anti-seepage coating; the difference between the edge hardness and the core hardness is small, and the hardness gradient is low after adding the anti-seepage layer.

[0108] Figure 8 Show the hardness gradient from the surface to the core of 18CrNiMo7-6 gear steel doped with 0.003% B microalloying. Experimental data show that for the ingot without the anti-seepage coating, the highest edge hardness of the gear steel doped with B element is 847 HV, and the core hardness is about 470 HV; for the microalloyed ingot with the anti-seepage coating, the highest edge hardness of the gear steel doped with B element is 510 HV, and the core hardness is about 420 HV. After adding the microalloying element, the change trend of the hardness gradient is the same as that without adding the microalloying element. That is, the edge hardness is high, the core hardness is low, and the hardness gradient is large without the anti-seepage coating; the difference between the edge hardness and the core hardness is small, and the hardness gradient is low after adding the anti-seepage layer.

[0109] Figure 9Show the hardness gradient from the surface to the core of 18CrNiMo7-6 gear steel microalloyed with 0.02% Nb. The experimental data show that for the ingot without an anti-seepage coating, the highest hardness at the edge of the gear steel doped with Nb element is 782 HV, and the hardness at the core is about 470 HV. For the microalloyed ingot with an anti-seepage coating, the highest hardness at the edge of the gear steel doped with Nb element is 450 HV, and the hardness at the core is about 400 HV. After adding the microalloying element, the change trend of the hardness gradient is the same as that without adding the microalloying element. That is, the hardness at the edge without the anti-seepage coating is high, the hardness at the core is low, and the hardness gradient is large; the difference between the hardness at the edge and the core with the anti-seepage layer is small, and the hardness gradient is low.

[0110] Figure 10 Show the tensile strength of gear steel after different microalloying. The experimental data show that for the gear steel without doped microalloying elements (1-1 and 1-2), the tensile strength is 1295 MPa in the state without an anti-seepage layer, and the impact energy is increased to 1307 MPa in the state with an anti-seepage layer. For the gear steel doped with V element (2-1 and 2-2), the tensile strength is 1462 MPa in the state without an anti-seepage layer, and the tensile strength is 1230 MPa in the state with an anti-seepage layer, with a decrease of 15.8%. For the gear steel doped with B element (3-1 and 3-2), the tensile strength is 1370 MPa in the state without an anti-seepage layer, and the tensile strength is 1296 MPa in the state with an anti-seepage layer, with a decrease of 5.4%. For the gear steel doped with Nb element (4-1 and 4-2), the tensile strength is 1327 MPa in the state without an anti-seepage layer, and the tensile strength is 1237 MPa in the state with an anti-seepage layer, with a decrease of 6.7%.

[0111] In summary, based on 18CrNiMo7-6 steel, this solution optimizes its performance by adding microalloying elements, significantly improving the service performance of 18CrNiMo7-6 steel. It not only effectively solves the problem of inventory utilization of existing 18CrNiMo7-6 steel, but also can produce high-performance wind power gear steel, improving the overall performance of wind power gearboxes.

[0112] Specifically, the applicant explored the effects of different doping elements, different addition amounts, different element combinations, different melting conditions, and different heat treatment conditions on the properties of the obtained microalloyed 18CrNiMo7-6 gear steel, and found that when the microalloying elements Nb 0.02% were combinedly doped, the melting condition was 1680 °C, under vacuum condition, remelted 6 times, and the heat treatment condition was [specific heat treatment condition not provided in the original text], the properties of the prepared microalloyed 18CrNiMo7-6 gear steel were the best. When 0.04% Nb element was doped, the fracture toughness would be reduced, thus reducing the properties of the obtained microalloyed 18CrNiMo7-6 gear steel. When the melting temperature exceeded 1700 °C, the grains of the material would become coarse, reducing the strength and toughness of the material; when the number of remelting times was too small (less than 3 times), the residual amount of inclusions would exceed the standard, affecting the fatigue life of the steel.

[0113] This solution also provides a microalloyed wind power gear steel, which uses 18CrNiMo7-6 steel as the base material, and after adding any one or combination of microalloying elements niobium, vanadium, and boron and remelting and homogenizing the base material, it is obtained through heat treatment. The mechanical properties of the microalloyed optimized wind power gear steel are as follows: the tensile strength is as high as 1462 MPa, the yield strength ≥ 1050 MPa, the elongation ≥ 50%, and the impact energy KV2 ≥ 80 J.

[0114] In summary, this solution has the following technical advantages:

[0115] 1. By precisely controlling the addition amount of microalloying elements in this solution, the hardenability of gear steel can be effectively improved, and the grain refinement, strength, and toughness can be increased, etc.;

[0116] 2. Through the vacuum arc melting and heat treatment processes, the homogenization of material composition and the optimization of microstructure are achieved, improving the comprehensive properties of gear steel;

[0117] 3. The microalloyed wind power gear steel of the present invention has better load-bearing capacity and longer service life, and can meet the requirements of the development of wind power equipment towards heavy load, high speed, and lightweight.

[0118] The above are only the embodiments of the present invention. Specific technical solutions and / or common knowledge such as characteristics well known in the art are not described in detail herein. It should be noted that for those skilled in the art, without departing from the technical solution of the present invention, several deformations and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent. The protection scope required by this application should be based on the content of its claims, and the specific implementation manners described in the specification can be used to interpret the content of the claims.

Claims

1. A microalloying method for optimizing the composition of wind power gear steel, characterized by: 18CrNiMo7-6 steel is used as a basic material, microalloying elements are added, mixed and remelted uniformly, and then smelting and heat-treated to obtain microalloyed wind power gear steel; the microalloying element is at least one of niobium, vanadium and boron.

2. A microalloying method for optimizing the composition of wind turbine gear steel according to claim 1, characterized in that: The steps include: Step 1: Select 18CrNiMo7-6 steel as the base material, and the cut base material is ultrasonically cleaned in an acetone solution and dried for later use; Step 2: adding micro-alloying elements to the above base materials, pre-mixing and then smelting evenly; Step 3: Use a high vacuum arc melting furnace to melt the microalloyed ingot, and repeatedly remelt the solidified alloy 5 to 8 times to ensure that the composition is homogenized; Step 4: heat treating the smelted ingot; Step 5: Machining the heat-treated ingot to obtain the desired gear shape and size; Step 6: Conduct performance testing on the final product.

3. A microalloying method for optimizing the composition of wind turbine gear steel according to claim 2, characterized in that: In step 1, the concentration of the acetone solution is 3-5%; the ultrasonic cleaning power is 20-50W and the time is 10-60min; and the drying is carried out at 100-150°C for 1-3h.

4. A microalloying method for optimizing the composition of wind turbine gear steel according to claim 3, characterized in that: In step 2, the addition amount of the microalloying elements niobium, vanadium and boron to the base material is as follows: niobium (Nb) 0.01% to 0.04%, vanadium (V) 0.01% to 0.04%, boron (B) 0.001% to 0.004%; the total addition amount of the alloying elements is ≤0.04%.

5. A microalloying method for optimizing the composition of wind turbine gear steel according to claim 4, characterized in that: In step 3, the vacuum degree is controlled to be 10 during smelting. -2 mbar, melting current 800~1800A, voltage 280~320V.

6. A microalloying method for optimizing the composition of wind turbine gear steel according to claim 5, characterized in that: In step 4, the heat treatment includes adding an impermeable coating on the surface, treating at 850-880° C., rapidly placing in a medium for cooling, and finally keeping at 680-740° C. for 2-3 hours and then slowly cooling.

7. A micro-alloyed wind power gear steel, characterized in that: It is prepared according to the microalloying method for optimizing the composition of wind power gear steel according to any one of claims 1 to 6.

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