A copper-containing fe-cr-mn-mo high strength and toughness steel for wind turbine main shaft

Abstract

The application relates to a copper-containing Fe-Cr-Mn-Mo high-strength and high-toughness wind power main shaft steel, and belongs to the technical field of material modification; the application comprises the following steps: step 1, mixing iron powder with Cr, Mn, Mo and Cu powder, wherein the content of Cr is 1.0-1.2 wt%, the content of Mn is 0.8-0.9 wt%, the content of Mo is 0.2-0.4 wt%, the content of Cu is 1-3 wt%, and the balance is Fe; step 2, vacuum smelting; step 3, pouring the molten liquid into a mold to obtain a steel ingot after cooling; step 4, after preliminary flaw detection, heating for free forging; step 5, heating and heat preservation of the steel in a gas furnace, and then normalizing; step 6, heating and heat preservation again for quenching, and then tempering treatment, and air cooling to room temperature; the copper-alloyed Fe-Cr-Mn-Mo steel is particularly suitable for application scenarios such as wind power main shafts which bear high alternating loads for a long time, not only effectively improves the strength, plasticity and impact resistance of the material, but also improves the stability and reliability of the material in a complex environment, and meets the high requirements of large-megawatt wind power main shafts on material performance.

Description

Technical Field

[0001] This invention relates to a copper-containing Fe-Cr-Mn-Mo high-strength and high-toughness steel for wind turbine main shafts, which belongs to the field of material modification technology. Background Technology

[0002] Fe-Cr-Mn-Mo steel is a typical medium-carbon low-alloy structural steel. Due to its excellent mechanical properties and good machinability, it is widely used in the manufacture of high-strength and high-toughness critical components, especially suitable for large-section load-bearing components such as wind turbine main shafts, large gears for locomotive traction, and connecting rods under high loads. However, with increasingly complex application environments and diversified load conditions, the performance limitations of traditional Fe-Cr-Mn-Mo steel have gradually become apparent. In actual operation, especially in large components such as wind turbine main shafts, Fe-Cr-Mn-Mo steel often bears irregular alternating loads. The unpredictability of these loads can easily lead to fatigue damage or premature failure of the material. Because the maintenance of critical components such as wind turbine main shafts is difficult and the production losses due to downtime for maintenance are high, the requirements for the safety, reliability, and long-term stability of this type of material are extremely stringent.

[0003] Improving the service life and reliability of materials under harsh working conditions has become a key focus of current industrial development. Especially in the field of wind turbine main shafts, the conventional mechanical properties of Fe-Cr-Mn-Mo steel, such as yield strength, tensile strength, and low-temperature impact toughness, are difficult to fully meet the increasingly stringent usage requirements under extreme environments or long-term alternating loads. Summary of the Invention

[0004] To address the shortcomings of the prior art, this invention provides a copper-containing Fe-Cr-Mn-Mo high-strength and high-toughness steel for wind turbine main shafts. The technical solution of the present invention to solve the above-mentioned technical problems is as follows: A copper-containing Fe-Cr-Mn-Mo high-strength and high-toughness steel for wind turbine main shafts includes the following steps: Step 1: Mix iron powder with Cr, Mn, Mo and Cu powders with an average particle size of about 100 micrometers in a certain proportion, wherein the Cr content is controlled at 1.0-1.2 wt%, the Mn content is controlled at 0.8-0.9 wt%, the Mo content is about 0.2-0.4 wt%, the Cu content is controlled at 1-3 wt%, and the balance is Fe; Step 2: The mixed powder is placed in a vacuum induction melting furnace, and after step-by-step vacuuming, argon gas is purged, followed by vacuum melting. Step 3: After melting, the alloy melt is poured into a water-cooled copper mold or a gray cast iron mold coated with a refractory coating. Ultrasonic treatment is performed in the early stage of solidification, and then the steel ingot is obtained after cooling. Step 4: After preliminary flaw detection, the steel ingot is heated in a gas furnace, then taken out for free forging, and then air-cooled to room temperature; Step 5: Put the free-forged steel back into the gas furnace for heating and holding, then air-cool it to room temperature before normalizing. Step 6: After normalizing, heat and hold the steel at that temperature, then place it in PAG water-soluble quenching medium for rapid cooling, followed by tempering, and finally air-cool to room temperature.

[0005] Furthermore, the specific process of step-by-step vacuuming in step 2 is as follows: first, a mechanical pump is used to pump to a lower vacuum level (i.e., <10 Pa), and then low-temperature preheating is performed to allow low-boiling-point contaminants such as moisture or oil on the surface of the raw material to fully evaporate and be removed, avoiding sudden high temperature causing them to decompose and dissolve into the molten steel. Subsequently, a molecular pump is used to pump to a high vacuum level (i.e., <0.001 Pa) to deeply remove hydrogen or nitrogen gas.

[0006] Furthermore, in step 2, the temperature is controlled at 1600℃-1650℃ during the vacuum melting process.

[0007] Furthermore, in step 2, after a uniform melt is formed by high-frequency electromagnetic stirring during the vacuum melting process, the content of each element is detected.

[0008] Furthermore, the detection of the content of each element is specifically achieved through online monitoring using LIBS laser-induced breakdown spectroscopy.

[0009] Furthermore, in step 2, the high-purity argon gas being filled is precisely measured using a mass flow meter.

[0010] Furthermore, in step 3, the steel ingot is removed when it is cooled to a surface temperature of 600℃-650℃.

[0011] Furthermore, in step 4, the steel ingot is placed in a gas furnace and heated to 1200℃-1250℃, and then taken out and free forged at above 900℃, with a forging ratio greater than 2.

[0012] Furthermore, in step 5, the free-forged steel is placed in a gas furnace and heated to 880℃-900℃ and held at that temperature for 2 hours, and then air-cooled to room temperature.

[0013] Furthermore, in step 6, the normalized steel is heated to 860℃-880℃ and held for 40 minutes before quenching. Then, the steel is heated to 500℃-650℃ and held for 1 hour before tempering.

[0014] The beneficial effects of this invention are as follows: This invention proposes a copper alloying scheme for Fe-Cr-Mn-Mo steel used in wind turbine main shafts. By adding an appropriate amount of Cu element and combining optimized heat treatment and free forging processes, the comprehensive mechanical properties of the material are significantly improved. In terms of process design, based on the alloying effect of Cu, an optimized heat treatment path is proposed, such as high-temperature quenching and medium-temperature tempering processes, to ensure that the material maintains good toughness and impact resistance while possessing high strength. Based on traditional vacuum induction melting, high-frequency electromagnetic stirring and ultrasonic waves are introduced to eliminate component segregation and refine the as-cast microstructure. In addition, by rationally designing the free forging parameters, namely the free forging temperature and forging ratio, the uniform microstructure and grain refinement of the material are ensured, further improving the material's lifespan. The Fe-Cr-Mn-Mo steel prepared by the method of this application... n-Mo steel has highly uniform and dispersed nano-Cu particles. After high-temperature free forging, it can eliminate microscopic defects such as segregation, porosity, and shrinkage cavities inside the cast alloy. It also has uniform and fine precipitates, which have a good strengthening effect on the entire Fe-Cr-Mn-Mo steel. The steel prepared by the method of this application has a tensile strength greater than 807MPa-1100MPa and an elongation greater than 16%-19%, which is superior to similar products and meets the performance requirements of steel for wind turbine main shafts. This copper alloyed Fe-Cr-Mn-Mo steel is particularly suitable for applications such as wind turbine main shafts that are subjected to high alternating loads for a long time. It not only effectively improves the strength, plasticity, and impact resistance of the material, but also enhances its stability and reliability in complex environments, meeting the high performance requirements of large-megawatt wind turbine main shafts. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments 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 these drawings without creative effort.

[0016] Figure 1 Metallographic images of copper-containing Fe-Cr-Mn-Mo high-strength and tough steels obtained in Examples 1, 2, 3 and 4 of this invention; Figure 2 The mechanical tensile curves of the copper-containing Fe-Cr-Mn-Mo high-strength and tough steels obtained in Examples 1, 2, 3 and 4 of this invention are shown. Figure 3 The XRD diffraction patterns of the copper-containing Fe-Cr-Mn-Mo high-strength and high-toughness steels obtained in Examples 1, 2, 3 and 4 of this invention are shown. Figure 4 The diagrams are the reverse pole figure and GND diagram of the copper-containing Fe-Cr-Mn-Mo high-strength and tough steel obtained in Example 1 of this invention. Detailed Implementation

[0017] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0018] A copper-containing Fe-Cr-Mn-Mo high-strength and high-toughness steel for wind turbine main shafts includes the following steps: Step 1: Mix iron powder with Cr, Mn, Mo and Cu powders with an average particle size of about 100 micrometers in a certain proportion, wherein the Cr content is controlled at 1.0-1.2 wt%, the Mn content is controlled at 0.8-0.9 wt%, the Mo content is about 0.2-0.4 wt%, the Cu content is controlled at 1-3 wt%, and the balance is Fe; Step 2: Place the mixed powder in a vacuum induction melting furnace, perform vacuum melting by step-by-step vacuuming and argon purging; during the vacuum melting process, the temperature is controlled at 1600℃-1650℃. This temperature range ensures that the metal powder is completely melted. High-frequency electromagnetic stirring is used during the melting process to form a uniform melt, and the content of various elements is detected to ensure that the elemental composition is controlled within the range. Step 3: After melting, pour the alloy molten liquid into a water-cooled copper mold or a gray cast iron mold coated with a refractory coating. In the early stage of solidification, perform ultrasonic treatment and remove the steel ingot when the steel surface temperature is 600℃-650℃. Step 4: Obtain a steel ingot with a surface temperature of 600℃-650℃. After preliminary flaw detection, place it in a gas furnace and heat it to about 1200℃-1250℃. Then, take it out and perform free forging at a temperature above 900℃, with a forging ratio greater than 2. Finally, air cool it to room temperature. The product after free forging is air cooled to avoid generating large thermal stress and control deformation. Step 5: Put the free-forged steel back into the gas furnace and heat it to 880℃-900℃. Hold it at that temperature for 2 hours to ensure full austenitization of the microstructure. Then air cool it to room temperature and normalize it to further refine the grain structure of the steel ingot. Step 6: Heat the normalized steel to 860℃-880℃ and hold for 40 minutes to ensure full austenitization of the microstructure. Then, rapidly cool the steel in PAG water-soluble quenching medium to transform the microstructure from austenite to martensite. Next, heat the steel to about 500℃-650℃ and hold for 1 hour for tempering to eliminate residual stress generated during quenching and transform the material into tempered martensite with better toughness. After tempering, air cool the workpiece to room temperature. This tempering process effectively improves the toughness and ductility of the material, enabling it to maintain good impact resistance even at high strength.

[0019] After the smelting process is started, the system is not directly evacuated to a high vacuum. Instead, a "stepped" procedure is adopted. First, a mechanical pump is used to evacuate to a lower vacuum (<10 Pa). Then, low-temperature preheating is carried out to allow low-boiling-point contaminants such as moisture and oil on the surface of the raw materials to fully evaporate and be removed, avoiding sudden high temperature that could cause them to decompose and dissolve into the molten steel. Subsequently, a molecular pump is used to evacuate to a high vacuum (<0.001 Pa) to deeply remove gases such as hydrogen and nitrogen.

[0020] In step 2, high-purity argon gas can be precisely backfilled using a mass flow meter as needed. The argon gas is used for stirring to promote degassing and the floating of inclusions.

[0021] The detection of the content of various elements described in step 2 is achieved through online monitoring using LIBS laser-induced breakdown spectroscopy. During the vacuum melting process, a high-energy laser beam continuously strikes the surface of the molten pool, generating plasma. The concentration of all key elements in the molten pool is monitored in real time by a spectrometer. For elements that burn out, the LIBS system issues a command to trigger an automatic feeding system, precisely feeding a trace amount of alloy wire into the feeding area above the molten pool. This achieves "closed-loop control of composition," keeping composition fluctuations within an extremely narrow range and ensuring stable control of the material composition during the melting process, thereby guaranteeing the stability and optimization of the melting production process.

[0022] Based on traditional vacuum induction melting, an induction coil is introduced to generate an electromagnetic field whose direction and intensity can be programmed, thereby achieving "non-contact vigorous stirring" of the melt, completely eliminating component segregation, and using the powerful Lorentz force to "drive" fine inclusions to the surface of the molten pool, where they are absorbed by the slag layer.

[0023] In the early stage of solidification, a high-energy ultrasonic radiation rod is inserted into the surface of the molten pool; dendrites are broken up before solidification, which greatly increases the nucleation core and significantly refines the as-cast structure; degassing is promoted, and the collapse of cavitation bubbles provides nuclei for the precipitation of hydrogen and nitrogen, accelerating their removal; inclusions are dispersed to prevent the agglomeration of nano-reinforced phases.

[0024] Example 1 Fe, Cr, Mn, Mo, and Cu powders were mixed in a specific ratio and added to a crucible in a vacuum induction melting furnace. The furnace was then evacuated in stages to below 0.001 Pa, and vacuum melting was performed under high-frequency electromagnetic stirring and argon protection to form a metallic liquid. The content of each element was monitored in real time to ensure that the elemental composition was controlled within the specified range. The liquid was then cast into a gray cast iron mold at 1600℃, ultrasonically treated, and cooled to a surface temperature of 600℃-650℃ to obtain a steel ingot. The obtained alloy steel ingot was heated to 1250℃ and subjected to free forging with a forging ratio of 2. The free-forged steel ingot was then air-cooled to room temperature. The free-forged steel ingot was then placed back into a gas furnace, heated to 900℃ and held for 2 hours. After air-cooling to room temperature, it was normalized. The normalized steel was heated to 860℃ and held for 40 minutes. It was then immersed in a PAG water-soluble quenching medium solution and cooled to room temperature. The quenched steel ingot was then reheated to 650℃, held for 1 hour, and air-cooled to room temperature.

[0025] Example 2: Fe, Cr, Mn, Mo and Cu powders are mixed in proportion and put into the crucible of a vacuum induction melting furnace. After being evacuated to below 0.001 Pa in a stepwise manner, vacuum melting is carried out under the protection of high-frequency electromagnetic stirring and argon gas to melt into a metal mixture. The content of each element is monitored in real time to ensure that the element composition is controlled within the range. Then, it is cast into a gray cast iron mold at 1600℃, ultrasonically treated, and cooled to a surface temperature of 600℃-650℃ to obtain a steel ingot. The obtained alloy steel ingot is heated to 1250℃ and subjected to free forging with a forging ratio of 2. The free-forged steel ingot is then air-cooled to room temperature. The free-forged steel ingot is then placed back into a gas furnace, heated to 900℃ and held for 2 hours, and air-cooled to room temperature before normalizing. The normalized steel is heated to 860℃ and held for 40 minutes, then immersed in a PAG water-soluble quenching medium solution and cooled to room temperature. The quenched steel ingot is then reheated to 600℃, held for 1 hour, and air-cooled to room temperature.

[0026] Example 3: Fe, Cr, Mn, Mo and Cu powders are mixed in proportion and put into the crucible of a vacuum induction melting furnace. After being evacuated to below 0.001 Pa in a stepwise manner, vacuum melting is carried out under the protection of high-frequency electromagnetic stirring and argon gas to melt into a metal mixture. The content of each element is monitored in real time to ensure that the element composition is controlled within the range. Then, it is cast into a gray cast iron mold at 1600℃, ultrasonically treated, and cooled to a surface temperature of 600℃-650℃ to obtain a steel ingot. The obtained alloy steel ingot is heated to 1250℃ and subjected to free forging with a forging ratio of 2. The free-forged steel ingot is then air-cooled to room temperature. The free-forged steel is then placed back into a gas furnace, heated to 900℃ and held for 2 hours, and air-cooled to room temperature before normalizing. The normalized steel is heated to 860℃ and held for 40 minutes, then immersed in a PAG water-soluble quenching medium solution and cooled to room temperature. The quenched steel ingot is then reheated to 550℃, held for 1 hour, and air-cooled to room temperature.

[0027] Example 4: Fe, Cr, Mn, Mo, and Cu powders were mixed in a specific ratio and added to a crucible in a vacuum induction melting furnace. The furnace was then evacuated in stages to below 0.001 Pa, and vacuum melting was performed under high-frequency electromagnetic stirring and argon protection to form a metallic liquid. The content of each element was monitored in real time to ensure that the elemental composition was controlled within the specified range. The liquid was then cast into a gray cast iron mold at 1600℃, ultrasonically treated, and cooled to a surface temperature of 600℃-650℃ to obtain a steel ingot. The obtained alloy steel ingot was heated to 1250℃ and subjected to free forging with a forging ratio of 2. The free-forged steel ingot was then air-cooled to room temperature. The free-forged steel was then placed back into a gas furnace, heated to 900℃ and held for 2 hours. After air-cooling to room temperature, it was normalized. The normalized steel was heated to 860℃ and held for 40 minutes. It was then immersed in a PAG water-soluble quenching medium solution and cooled to room temperature. The quenched steel ingot was then reheated to 500℃, held for 1 hour, and air-cooled to room temperature.

[0028] Further analysis of the copper-containing Fe-Cr-Mn-Mo high-strength and high-toughness steels prepared in Examples 1-4 revealed... Figure 1 These are metallographic images of the high-strength and high-toughness steels obtained in Examples 1, 2, 3, and 4. Figure 2 The mechanical tensile curves of the high-strength and high-toughness steels obtained in Examples 1, 2, 3, and 4 are shown. Figure 3 The XRD diffraction patterns are those of the high-strength and high-toughness steels obtained in Examples 1, 2, 3, and 4. Figure 4 The diagrams are the reverse pole figure and GND diagram of the high-strength and high-toughness steel obtained in Example 1.

[0029] The high-strength and high-toughness copper-containing Fe-Cr-Mn-Mo steels prepared in Examples 1-4 were subjected to mechanical property tests, and the results are shown in Table 1.

[0030] Table 1 Results of Mechanical Property Tests As can be seen from Table 1, the copper-containing Fe-Cr-Mn-Mo high-strength and tough steels prepared in Examples 1-4 have stable properties. Among them, the tensile strength reaches more than 800 MPa, the elongation reaches 16% or more, and the impact absorption energy reaches more than 20 J, all of which meet the standards of commonly used Fe-Cr-Mn-Mo materials. This shows that the copper-containing Fe-Cr-Mn-Mo high-strength and tough steels prepared by this method have excellent and stable performance.

[0031] This invention proposes a copper alloying scheme for Fe-Cr-Mn-Mo steel used in wind turbine main shafts. By adding an appropriate amount of Cu and combining it with optimized heat treatment and free forging processes, the comprehensive mechanical properties of the material are significantly improved. In terms of process design, based on the alloying effect of Cu, an optimized heat treatment path is proposed, such as high-temperature quenching and medium-temperature tempering, to ensure that the material maintains good toughness and impact resistance while possessing high strength. High-frequency electromagnetic stirring and ultrasonic waves are introduced on the basis of traditional vacuum induction melting to eliminate component segregation and refine the as-cast microstructure. In addition, by rationally designing the free forging parameters, namely the free forging temperature and forging ratio, the uniform microstructure and grain refinement of the material are ensured, further improving the material's lifespan. The Fe-Cr-Mn-Mo steel prepared by the method of this application... The steel contains highly uniform and dispersed nano-Cu particles. After high-temperature free forging, microscopic defects such as segregation, porosity, and shrinkage cavities inside the cast alloy can be eliminated. It also has uniform and fine precipitates, which have a good strengthening effect on the entire Fe-Cr-Mn-Mo steel. The steel prepared by the method of this application has a tensile strength greater than 807-1100MPa and an elongation greater than 16%-19%, which is superior to similar products and meets the performance requirements of steel for wind turbine main shafts. This copper alloyed Fe-Cr-Mn-Mo steel is particularly suitable for applications such as wind turbine main shafts that are subjected to high alternating loads for a long time. It not only effectively improves the strength, plasticity, and impact resistance of the material, but also enhances its stability and reliability in complex environments, meeting the high performance requirements of large-megawatt wind turbine main shafts.

[0032] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A copper-containing Fe-Cr-Mn-Mo high-strength and high-toughness steel for wind turbine main shafts, characterized in that, Includes the following steps: Step 1: Mix iron powder with Cr, Mn, Mo and Cu powders with an average particle size of about 100 micrometers in a certain proportion, wherein the Cr content is controlled at 1.0-1.2 wt%, the Mn content is controlled at 0.8-0.9 wt%, the Mo content is 0.2-0.4 wt%, the Cu content is controlled at 1-3 wt%, and the balance is Fe; Step 2: The mixed powder is placed in a vacuum induction melting furnace, and after step-by-step vacuuming, argon gas is purged, followed by vacuum melting. Step 3: After melting, the alloy melt is poured into a water-cooled copper mold or a gray cast iron mold coated with a refractory coating. Ultrasonic treatment is performed in the early stage of solidification, and then the mixture is cooled to obtain a steel ingot. Step 4: After preliminary flaw detection, the steel ingot is placed in a gas furnace and heated to 1200℃-1250℃. Then it is taken out and free forged at above 900℃ with a forging ratio greater than 2. Then it is air-cooled to room temperature. Step 5: Put the free-forged steel back into the gas furnace for heating and holding, then air-cool it to room temperature before normalizing. Step 6: After normalizing, heat the steel to 860℃-880℃ and hold for 40 minutes. Then, place it in PAG water-soluble quenching medium for rapid cooling. Subsequently, heat the steel to 500℃-650℃ and hold for 1 hour, and then perform tempering treatment. Finally, air cool to room temperature.

2. The high-strength and high-toughness wind turbine main shaft steel containing copper Fe-Cr-Mn-Mo according to claim 1, characterized in that, The specific process of step-by-step vacuuming in step 2 is as follows: first, a mechanical pump is used to pump to a low vacuum of <10 Pa, and then low-temperature preheating is performed to allow low-boiling-point contaminants such as moisture or oil on the surface of the raw material to fully evaporate and be removed, avoiding sudden high temperature that could cause them to decompose and dissolve into the molten steel. Then, a molecular pump is used to pump to a high vacuum of <0.001 Pa to deeply remove hydrogen or nitrogen gas.

3. The high-strength and high-toughness steel for wind turbine main shafts containing copper Fe-Cr-Mn-Mo according to claim 1, characterized in that, In step 2, the temperature is controlled at 1600℃-1650℃ during the vacuum melting process.

4. The high-strength and high-toughness wind turbine main shaft steel containing copper Fe-Cr-Mn-Mo according to claim 3, characterized in that, In step 2, after a uniform melt is formed by high-frequency electromagnetic stirring during the vacuum melting process, the content of each element is detected.

5. The high-strength and high-toughness steel for wind turbine main shafts containing copper (Fe-Cr-Mn-Mo) according to claim 4, characterized in that, The detection of the content of each element is specifically achieved through online monitoring using LIBS laser-induced breakdown spectroscopy.

6. The high-strength and high-toughness steel for wind turbine main shafts containing copper Fe-Cr-Mn-Mo according to claim 1, characterized in that, In step 2, the high-purity argon gas being filled is precisely measured using a mass flow meter.

7. The high-strength and high-toughness wind turbine main shaft steel containing copper Fe-Cr-Mn-Mo according to claim 1, characterized in that, In step 3, the steel ingot is taken out when it is cooled to a surface temperature of 600℃-650℃.

8. The high-strength and high-toughness steel for wind turbine main shafts containing copper Fe-Cr-Mn-Mo according to claim 1, characterized in that, In step 5, the free-forged steel is placed in a gas furnace and heated to 880℃-900℃ and held for 2 hours, and then air-cooled to room temperature.

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