Anti-fatigue load bearing steel for wind turbine main shaft, preparation method therefor, and use thereof

Abstract

The present invention relates to the technical field of metallurgical steels, in particular to an anti-fatigue load bearing steel for a wind turbine main shaft, a preparation method therefor, and a use thereof. The present invention herein provides the following solution, comprising: S1. smelting: refining a raw material steel into molten iron, carrying out impurity removal and deoxidization, and adjusting the content of each component to obtain molten steel for casting; S2. continuous casting: carrying out electroplusing crystallization and solidification on the molten steel for casting to obtain a continuous casting billet; S3. rolling: carrying out rough rolling on the continuous casting billet and then carrying out finish rolling to obtain a finish-rolled billet; and S4. post-rolling treatment: first slowly cooling the finish-rolled billet and then air cooling same to obtain an anti-fatigue load bearing steel. In the present invention, by component and process control, a specific microstructure can be formed; the surface of a grain has a corrugated grain boundary; the corrugated grain boundary reduces the orientation difference between adjacent grains, lowers the grain boundary energy, and can effectively impede dislocation propagation and grain boundary sliding; and high-density dislocations formed within grains, interactions between dislocations, and the development of Cottrell atmosphere have a deformation strengthening effect on a material, thus achieving an excellent anti-fatigue effect.

Description

A kind of anti-fatigue load-bearing steel for wind turbine main shaft and its preparation method and application Technical Field

[0001] The present invention relates to the technical field of metallurgical steel materials, and in particular to fatigue-resistant load-bearing steel for a wind turbine main shaft, and a preparation method and application thereof. Background Art

[0002] Wind turbine load-bearing components are a crucial component of wind turbines, primarily responsible for supporting and securing the turbine. These components, including the tower, nacelle, hub, and blades, must meet specific manufacturing and design requirements to ensure safe and stable operation. Generally speaking, wind turbine load-bearing components must possess high strength, corrosion resistance, and fatigue resistance, while also possessing excellent machinability and weldability. During the manufacturing process, these components undergo rigorous process flow and quality control to ensure their quality and reliability.

[0003] In recent years, as wind turbine power continues to increase, the dimensions of structures such as towers have also grown, increasing the difficulty of manufacturing and designing wind turbine load-bearing components. Furthermore, the complex and ever-changing operating environment of wind turbines places complex loads and stresses on load-bearing components. This, in order to ensure the safety and stability of wind turbines, places higher demands on the steel used in wind turbine main shafts.

[0004] However, the wind turbine load-bearing parts are subjected to the periodic action of wind force during the operation of the wind turbine generator set, which causes the load-bearing parts to suffer fatigue due to vibration, which has a great impact on the stability and service life of the wind turbine generator set. At present, the causes of wind-induced fatigue of wind power mainly include two aspects: First, the structural characteristics and design problems of the wind turbine generator set itself, such as unreasonable load-bearing structure, insufficient rigidity, loose connection parts, etc., which cause the unit to vibrate and fatigue during operation due to the action of wind force; second, due to the complex and changeable operating environment of the wind turbine generator set, changes in parameters such as wind direction, wind speed, and wind force will have an impact on the unit, causing the unit to be continuously subjected to impact loads during operation, thereby accelerating the fatigue of the load-bearing parts and seriously affecting the life and safety of the wind turbine generator set. For this reason, the present invention proposes a fatigue-resistant load-bearing steel for a wind turbine main shaft, a preparation method, and an application thereof.

[0005] Summary of the Invention

[0006] In order to solve the problem in the prior art that the steel used for load-bearing parts is prone to fatigue under the action of external forces in the use environment, the present invention proposes a fatigue-resistant load-bearing steel for a wind turbine main shaft, a preparation method and an application thereof.

[0007] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0008] The first aspect of the present invention provides a method for preparing fatigue-resistant load-bearing steel for a wind turbine main shaft, comprising the following steps:

[0009] S1. Smelting: The raw steel is smelted into molten iron, and impurities are removed, deoxidized and the content of each component is adjusted to obtain casting molten steel;

[0010] S2, continuous casting: the molten steel is crystallized and solidified by electric pulses to obtain continuous casting billets;

[0011] S3, rolling: the continuous casting billet is first subjected to rough rolling, and then to finish rolling to obtain a finished rolled billet;

[0012] S4. Post-rolling treatment: The finished rolled billet is first slowly cooled and then air-cooled to obtain fatigue-resistant load-bearing steel.

[0013] In some embodiments, the components and contents of the cast steel in S1 include Al content 0.12-0.15%, Si content 0.35-0.60%, Cr content 1.62-2.35%, V content 0.15-0.21%, Ti content 0.78-1.21% and Nb content 0.27-0.32%.

[0014] The steel composition of the present invention is designed to contain 0.15-0.21% V, 0.78-1.21% Ti, 0.27-0.32% Nb and 1.62-2.35% Cr by mass. V, Ti, Nb and Cr are all environmental embedding energy-sensitive alloying elements. From a thermodynamic perspective, they are easily segregated at defects such as dislocation lines and interfaces, and are very likely to form Kovarig gas clusters, which have a dragging effect on grain boundary movement.

[0015] In some embodiments, the components and contents of the molten steel in S1 include 0.15-0.20% C, 0.39-0.48% Ni, 0.18-0.23% Mn, and the remainder Fe.

[0016] In some embodiments, the impurity removal, deoxidation and adjustment of the content of each component of S1 include the following steps:

[0017] S1.1: Pre-desulfurize the raw steel using the KR stirring method at 1575-1605°C, with the stirrer positioned 1660-1680 mm below the molten iron surface, at a speed of 115-130 rpm, for 15-25 minutes; to obtain molten iron with a sulfur content ≤ 0.02%, a phosphorus content ≤ 0.10%, and a silicon content ≤ 0.60%.

[0018] The preferred raw material steel comprises the following components: C: 0.19-0.32%, Cr: 1.95-2.30%, Ti: 0.92-1.20%, Mn: 0.19-0.22%, Ni: 0.40-0.45%, Al: 0.07-0.11%, Nb: 0.28-0.31%, P: 0.008-0.030%, V: 0.17-0.20%, S: 0.01-0.03%, Si: 0.37-0.58%, and the balance is Fe.

[0019] S1.2: The molten iron is fed into a converter and kept at 1650-1690°C for 80-130 minutes to produce molten steel with a phosphorus content of ≤0.03%;

[0020] S1.3: The molten steel is transferred to an LF refining furnace and subjected to argon blowing and refining at 1610-1630°C, deoxidation and impurity removal, and alloys containing various components are added to achieve the desired content of each component, thereby obtaining a refined molten steel with a sulfur content of ≤0.01%.

[0021] Preferably, the predetermined values ​​include Si content 0.35-0.60%, Cr content 1.62-2.35%, V content 0.15-0.21%, Nb content 0.27-0.32%, Ti content 0.78-1.21%, C content 0.15-0.20%, Ni content 0.39-0.48%, Mn content 0.18-0.23%, and the balance is Fe.

[0022] Preferably, the alloy of each component is an alloy of each component and iron.

[0023] S1.4: Place the refined molten steel in a vacuum refining furnace and treat the molten steel in a vacuum furnace at 1615-1630℃ with a vacuum degree of 50-100Pa for 35-55min, with a circulation pipe flow rate of 100-118NM 3 / h, vacuum stirring treatment, add Al as a deoxidizer for deoxidation, the added amount is calculated based on the Al content in the molten steel at 0.12-0.15%, and soft stirring is carried out for 30-60 minutes to obtain casting molten steel.

[0024] In some embodiments, the S2 continuous casting process includes transferring the cast steel liquid to a continuous casting machine, setting the pulling speed to 0.52-0.64 m / min, the casting start temperature to 1520-1535°C, and turning on the electric pulse transmitter after the molten steel flows into the crystallizer. The setting parameters of the electric pulse transmitter are: voltage 2500-2600 V, frequency 0.80-0.88 Hz, capacitance 180-200 μF. After solidification, the ingot is pulled out to obtain a continuously cast ingot.

[0025] In the continuous casting method of the present invention, electric pulse crystallization under the process of voltage 2500-2600V, frequency 0.80-0.88Hz, and capacitance 180-200μF causes the grain growth orientation and distribution and the segregation of alloy elements to change periodically, thereby ensuring the formation of corrugated grain boundaries from a dynamic perspective, and then forming obvious corrugated grain boundaries under the reduction rate and temperature control processing of the following 4 stages of rough rolling and 3 stages of finishing rolling.

[0026] In some embodiments, the rolling process in step S3 includes:

[0027] S3.1: The continuous casting slab is introduced into a roughing mill for rolling: two cross-rolling passes with reduction ratios of 25-28% and 20-22% at a rolling temperature of 1200-1275°C; two longitudinal rolling passes with reduction ratios of 16-19% and 13-15% at a rolling temperature of 1100-1200°C to obtain a rough-rolled slab;

[0028] S3.2: The rough rolled billet is introduced into the finishing mill for finishing rolling, with three rolling passes, reduction ratios of 12-14%, 10-12%, and 8-10%, respectively, and a rolling temperature of 850-1050°C to obtain a finished rolled billet.

[0029] The present invention's electric pulse treatment, along with the reduction ratio and temperature control during the four-stage rough rolling and three-stage finishing rolling, enhances cross-slip dislocations, produces a wavy dislocation morphology, and strengthens twinning deformation, resulting in a high dislocation density within the grains. The grain surfaces exhibit wavy grain boundaries, which, when subjected to wind vibration, inhibit the nucleation and expansion of pores during the material's periodic vibrations, reducing stress concentration within the material and reducing pore size, resulting in excellent fatigue resistance. Furthermore, the wavy grain boundaries minimize the orientation difference between adjacent grains, lowering grain boundary energy and effectively preventing dislocation expansion and grain boundary slip, further enhancing the material's fatigue resistance.

[0030] In some embodiments, the S4, post-rolling treatment process includes quickly placing the finished rolled billet in a slow cooling pit in the range of 800-850°C and sealing it with a cover, with a cooling rate of 8-9°C / h and a sealed cooling time of 7-8h; then opening the sealed cover halfway, with a cooling rate of 15-20°C / h and a cooling time of 7-8h; finally, opening the sealed cover completely, ventilating, with a cooling rate of 40-50°C / h, and waiting for the billet temperature to be lower than 280°C, taking it out of the pit and air-cooling it to room temperature to obtain fatigue-resistant load-bearing steel.

[0031] A second aspect of the present invention provides a fatigue-resistant load-bearing steel prepared according to the above preparation method.

[0032] In some embodiments, the components and contents of the fatigue-resistant load-bearing steel include: C content 0.15-0.20%, Cr content 1.62-2.35%, Ti content 0.78-1.21%, Mn content 0.18-0.23%, Ni content 0.39-0.48%, Al content 0.12-0.15%, V content 0.15-0.21%, Nb content 0.27-0.32%, Si content 0.35-0.60%, S content ≤0.01%, P content ≤0.03%, and the balance is Fe.

[0033] The third aspect of the present invention proposes the use of the above-mentioned fatigue-resistant load-bearing steel in wind power generation load-bearing components or wind turbine main shafts.

[0034] Beneficial effects of the present invention:

[0035] 1. The present invention is capable of forming a specific microstructure through composition and process control. First, the steel composition of the present invention is designed to include 0.15-0.21% V, 0.78-1.21% Ti, 0.27-0.32% Nb, and 1.62-2.35% Cr by mass. V, Ti, Nb, and Cr are all environmentally sensitive alloying elements. From a thermodynamic perspective, they tend to segregate at defects such as dislocation lines and interfaces, easily forming Koch gas clusters, which have a dragging effect on grain boundary movement. Second, electric pulse crystallization under a voltage of 2500-2600V, a frequency of 0.80-0.88Hz, and a capacitance of 180-200μF causes periodic changes in the grain growth orientation and distribution, as well as the segregation of alloying elements, thereby ensuring the formation of wavy grain boundaries from a dynamic perspective. Consequently, distinct wavy grain boundaries are formed under the reduction rate and temperature control of four rough rolling stages and three finishing stages. In addition, electric pulse treatment and reduction rate and temperature control during 4-stage rough rolling and 3-stage finishing rolling enhance cross-slip of dislocations, produce wavy dislocation morphology, and strengthen twinning deformation, resulting in high dislocation density inside the grains.

[0036] 2. The fatigue-resistant, load-bearing steel produced by the method of the present invention has corrugated grain boundaries on its grain surface. This inhibits the nucleation and expansion of pores during periodic vibrations in the material during wind vibration, reducing stress concentration and pore size within the material, resulting in excellent fatigue resistance. Furthermore, the corrugated grain boundaries minimize the orientation difference between adjacent grains, lowering grain boundary energy and effectively preventing dislocation expansion and grain boundary slip, further enhancing the material's fatigue resistance.

[0037] 3. The grains of the fatigue-resistant load-bearing steel of the present invention have a 14 -5.5×10 14 m -2High-density dislocations, during wind vibration, the interaction between dislocations and the formed Coriolis air masses have a significant deformation strengthening effect on the material and have a good anti-fatigue effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG1 is a metallographic diagram of the material microstructure of the fatigue-resistant load-bearing steel prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0040] Unless otherwise specified, the experimental materials and reagents used in the following examples are all currently available and commercially available. Where specific techniques or conditions are not specified in the examples, they can be carried out according to conventional techniques or conditions disclosed in the art.

[0041] In the following embodiments and comparative examples, the components and contents of the steel raw materials are as follows: C: 0.19-0.32%, Cr: 1.95-2.30%, Ti: 0.92-1.20%, Mn: 0.19-0.22%, Ni: 0.40-0.45%, Al: 0.07-0.11%, Nb: 0.28-0.31%, V: 0.17-0.20%, Si: 0.37-0.58%, impurity P: 0.008-0.030%, impurity S: 0.01-0.03%, and the balance is Fe.

[0042] Example 1

[0043] S1. Smelting:

[0044] S1.1: Pre-desulfurize the raw steel using the KR stirring method at 1575°C. The stirrer is located 1660mm below the molten iron surface, the speed is 115 rpm, and the stirring time is 15 minutes. The final molten iron has a sulfur content of ≤0.02%, a phosphorus content of ≤0.10%, and a silicon content of ≤0.60%.

[0045] S1.2: The molten iron is fed into a converter and kept at 1650°C for 80 minutes to produce molten steel, with the phosphorus content in the molten steel being controlled to ≤0.03%;

[0046] S1.3: The molten steel is transferred to an LF refining furnace and subjected to argon blowing refining, deoxidation, desulfurization, and impurity removal at 1610°C. During the refining process, the content of each component in the molten steel is tested. Based on the test results, an alloy containing each component in the form of a ferroalloy of each component element is added to achieve the predetermined content of each component: Si content 0.35%, Cr content 1.62%, V content 0.15%, Nb content 0.27%, Ti content 0.78%, C content 0.15%, Ni content 0.39%, Mn content 0.18%, and the balance Fe, to obtain a refined molten steel with a S content ≤ 0.01%;

[0047] S1.4: Place the refined molten steel in a vacuum refining furnace and treat the molten steel in a vacuum furnace at 1615°C with a vacuum degree of 50Pa for 35 minutes, with a circulation pipe flow rate of 100NM 3 / h, vacuum stirring treatment, add Al as a deoxidizer for deoxidation, the added amount is calculated based on the Al content in the molten steel at 0.12%, and soft stirring is carried out for 30 minutes to obtain casting molten steel.

[0048] S2. Continuous casting: The molten steel is transferred to the continuous casting machine, the pulling speed is set to 0.52 m / min, the casting start temperature is set to 1520°C, and after the molten steel flows into the crystallizer, the electric pulse transmitter is turned on. The setting parameters of the electric pulse transmitter are: voltage 2500 V, frequency 0.80 Hz, capacitance 180 μF. After solidification, the ingot is pulled out to obtain a continuously cast ingot.

[0049] S3, rolling:

[0050] S3.1: The continuous casting slab is introduced into a roughing mill for rolling: two cross-rolling passes with reduction ratios of 25% and 20% at a rolling temperature of 1200°C; two longitudinal rolling passes with reduction ratios of 16% and 13% at a rolling temperature of 1100°C to obtain a rough-rolled slab;

[0051] S3.2: The rough-rolled billet is introduced into the finishing mill for finishing rolling. The rolling passes are 3 times with reduction ratios of 12%, 10%, and 8% respectively. The rolling temperature is 850°C to obtain the finished billet.

[0052] S4. Post-rolling treatment: quickly place the finished rolled billet into a slow cooling pit within the range of 800℃ and seal it with a cover. The cooling rate is 8℃ / h and the sealed cooling time is 7h. Then open the sealed cover halfway, the cooling rate is 15℃ / h and the cooling time is 7h. Finally, open the sealed cover completely, ventilate, and cool at a cooling rate of 40℃ / h. When the billet temperature is lower than 280℃, take it out of the pit and air-cool it to room temperature to obtain fatigue-resistant load-bearing steel.

[0053] Example 2

[0054] S1. Smelting:

[0055] S1.1: Pre-desulfurize the raw steel using the KR stirring method at 1580°C. The stirrer is located 1670mm below the molten iron surface, the speed is 120 rpm, and the stirring time is 20 minutes. The final molten iron has a sulfur content of ≤0.02%, a phosphorus content of ≤0.10%, and a silicon content of ≤0.60%.

[0056] S1.2: The molten iron is fed into a converter and kept at 1680°C for 90 minutes to produce molten steel, with the phosphorus content in the molten steel being controlled to ≤0.03%;

[0057] S1.3: The molten steel is transferred to an LF refining furnace and subjected to argon blowing refining, deoxidation, desulfurization, and impurity removal at 1620°C. During the refining process, the content of each component in the molten steel is tested. Based on the test results, an alloy containing each component in the form of an iron alloy of each component element is added to achieve the predetermined content of each component: Si content 0.40%, Cr content 2.0%, V content 0.19%, Nb content 0.3%, Ti content 1.0%, C content 0.18%, Ni content 0.4%, Mn content 0.2%, and the balance Fe, to obtain a refined molten steel with a S content ≤ 0.01%;

[0058] S1.4: Place the refined molten steel in a vacuum refining furnace at 1620°C with a vacuum degree of 80Pa for 40 minutes, with a circulation pipe flow rate of 115NM 3 / h, vacuum stirring treatment, add Al as a deoxidizer for deoxidation, the added amount is calculated based on the Al content in the molten steel at 0.13%, and soft stirring is carried out for 40 minutes to obtain casting molten steel.

[0059] S2. Continuous casting: The molten steel was transferred to a continuous casting machine, and the pulling speed was set to 0.60 m / min and the casting start temperature was set to 1530°C. After the molten steel flowed into the crystallizer, the electric pulse transmitter was turned on. The setting parameters of the electric pulse transmitter were: voltage 2550 V, frequency 0.85 Hz, and capacitance 190 μF. After solidification, the ingot was pulled out to obtain a continuously cast ingot.

[0060] S3, rolling:

[0061] S3.1: The continuous casting slab is introduced into a roughing mill for rolling: two cross-rolling passes with reduction ratios of 27% and 21% at a rolling temperature of 1260°C; two longitudinal rolling passes with reduction ratios of 17% and 14% at a rolling temperature of 1150°C to obtain a rough-rolled slab;

[0062] S3.2: The rough-rolled billet is introduced into the finishing mill for finishing rolling. The rolling passes are 3 times with reduction ratios of 13%, 11%, and 9% respectively. The rolling temperature is 900°C to obtain the finished billet.

[0063] S4. Post-rolling treatment: quickly place the finished rolled billet in a slow cooling pit at 830℃ and seal it with a cooling rate of 8℃ / h and a sealed cooling time of 7.5h; then open the sealed cover halfway, cool it at a cooling rate of 18℃ / h and a cooling time of 7.58h; finally, open the sealed cover completely, ventilate it, and cool it at a cooling rate of 45℃ / h. When the billet temperature is lower than 280℃, take it out of the pit and air-cool it to room temperature to obtain fatigue-resistant load-bearing steel.

[0064] Example 3

[0065] S1. Smelting:

[0066] S1.1: Pre-desulfurize the raw steel using the KR stirring method at 1605°C. The stirrer is located 1680mm below the molten iron surface, the speed is 130rpm, and the stirring time is 25min. The final molten iron has a sulfur content of ≤0.02%, a phosphorus content of ≤0.10%, and a silicon content of ≤0.60%.

[0067] S1.2: The molten iron is fed into a converter and kept at 1690°C for 130 minutes to produce molten steel, with the phosphorus content in the molten steel being controlled to ≤0.03%;

[0068] S1.3: The molten steel is transferred to an LF refining furnace and subjected to argon blowing refining, deoxidation, desulfurization, and impurity removal at 1630°C. During the refining process, the content of each component in the molten steel is tested. Based on the test results, an alloy containing each component in the form of a ferroalloy of each component element is added to achieve the predetermined content of each component: Si content 0.60%, Cr content 2.35%, V content 0.21%, Nb content 0.32%, Ti content 1.21%, C content 0.20%, Ni content 0.48%, Mn content 0.23%, and the balance Fe, to obtain a refined molten steel with a S content ≤ 0.01%;

[0069] S1.4: Place the refined molten steel in a vacuum refining furnace at 1630°C with a vacuum degree of 100 Pa for 55 minutes, with a circulation pipe flow rate of 118 NM 3 / h, vacuum stirring treatment, add Al as a deoxidizer for deoxidation, the added amount is calculated based on the Al content in the molten steel at 0.15%, and soft stirring is carried out for 60 minutes to obtain casting molten steel.

[0070] S2. Continuous casting: The molten steel was transferred to the continuous casting machine, the pulling speed was set to 0.64 m / min, the casting start temperature was set to 1535°C, and after the molten steel flowed into the crystallizer, the electric pulse transmitter was turned on. The setting parameters of the electric pulse transmitter were: voltage 2600 V, frequency 0.88 Hz, capacitance 200 μF. After solidification, the ingot was pulled out to obtain a continuously cast ingot.

[0071] S3, rolling:

[0072] S3.1: The continuous casting slab is introduced into a roughing mill for rolling: two cross-rolling passes with reduction ratios of 28% and 22% respectively, and a rolling temperature of 1275°C; two longitudinal rolling passes with reduction ratios of 19% and 15% respectively, and a rolling temperature of 1200°C, to obtain a rough-rolled slab;

[0073] S3.2: The rough-rolled billet is introduced into the finishing mill for finishing rolling. The rolling passes are 3 times with reduction ratios of 14%, 12%, and 10% respectively. The rolling temperature is 1050°C to obtain the finished billet.

[0074] S4. Post-rolling treatment: quickly place the finished rolled billet into a slow cooling pit at 850℃ and seal it with a cooling rate of 9℃ / h and a sealed cooling time of 8h; then open the sealed cover halfway, cool it at a cooling rate of 20℃ / h and a cooling time of 8h; finally open the sealed cover completely, ventilate it, and cool it at a cooling rate of 50℃ / h. When the billet temperature is lower than 280℃, take it out of the pit and air-cool it to room temperature to obtain fatigue-resistant load-bearing steel.

[0075] Example 4

[0076] S1. Smelting:

[0077] S1.1: Pre-desulfurize the raw steel using the KR stirring method at 1575°C. The stirrer is located 1680 mm below the molten iron surface, the speed is 130 rpm, and the stirring time is 25 minutes. The final molten iron has a sulfur content of ≤0.02%, a phosphorus content of ≤0.10%, and a silicon content of ≤0.60%.

[0078] S1.2: The molten iron is fed into a converter and kept at 1650°C for 130 minutes to produce molten steel, with the phosphorus content in the molten steel being controlled to ≤0.03%;

[0079] S1.3: The molten steel is transferred to an LF refining furnace and subjected to argon blowing refining, deoxidation, desulfurization, and impurity removal at 1630°C. During the refining process, the content of each component in the molten steel is tested. Based on the test results, an alloy containing each component in the form of a ferroalloy of each component element is added to achieve the predetermined content of each component: Si content 0.60%, Cr content 1.62%, V content 0.15%, Nb content 0.32%, Ti content 0.78%, C content 0.20%, Ni content 0.39%, Mn content 0.23%, and the balance Fe, to obtain a refined molten steel with a S content ≤ 0.01%;

[0080] S1.4: Place the refined molten steel in a vacuum refining furnace at 1630°C with a vacuum degree of 100 Pa for 55 minutes, with a circulation pipe flow rate of 100 NM 3 / h, vacuum stirring treatment, add Al as a deoxidizer for deoxidation, the added amount is calculated based on the Al content in the molten steel at 0.12%, and soft stirring is carried out for 50 minutes to obtain casting molten steel.

[0081] S2. Continuous casting: The molten steel was transferred to the continuous casting machine, and the pulling speed was set to 0.64 m / min and the casting start temperature was set to 1535°C. After the molten steel flowed into the crystallizer, the electric pulse transmitter was turned on. The setting parameters of the electric pulse transmitter were: voltage 2500 V, frequency 0.88 Hz, capacitance 200 μF. After solidification, the ingot was pulled out to obtain a continuously cast ingot.

[0082] S3, rolling:

[0083] S3.1: The continuous casting slab is introduced into a roughing mill for rolling: two cross-rolling passes with reduction ratios of 28% and 20% at a rolling temperature of 1275°C; two longitudinal rolling passes with reduction ratios of 19% and 14% at a rolling temperature of 1200°C to obtain a rough-rolled slab;

[0084] S3.2: The rough-rolled billet is introduced into the finishing mill for finishing rolling. The rolling passes are 3 times with reduction rates of 12%, 12%, and 10% respectively. The rolling temperature is 1050°C to obtain the finished billet.

[0085] S4. Post-rolling treatment: quickly place the finished rolled billet into a slow cooling pit at 850℃ and seal it with a cover. The cooling rate is 8℃ / h and the sealed cooling time is 7h. Then open the sealed cover halfway, cool it at a rate of 20℃ / h and the cooling time is 7h. Finally, open the sealed cover completely, ventilate it, and cool it at a rate of 50℃ / h. When the billet temperature is lower than 280℃, take it out of the pit and air-cool it to room temperature to obtain fatigue-resistant load-bearing steel.

[0086] Example 5

[0087] S1. Smelting:

[0088] S1.1: Pre-desulfurize the raw steel using the KR stirring method at 1600°C. The stirrer is located 1675mm below the molten iron surface, the speed is 125rpm, and the stirring time is 23min. The final molten iron has a sulfur content of ≤0.02%, a phosphorus content of ≤0.10%, and a silicon content of ≤0.60%.

[0089] S1.2: The molten iron is fed into a converter and kept at 1685°C for 110 minutes to produce molten steel, with the phosphorus content in the molten steel being controlled to ≤0.03%;

[0090] S1.3: The molten steel is transferred to an LF refining furnace and subjected to argon blowing refining, deoxidation, desulfurization, and impurity removal at 1625°C. During the refining process, the content of each component in the molten steel is tested. Based on the test results, an alloy containing each component in the form of a ferroalloy of each component element is added to achieve the predetermined content of each component: Si content 0.55%, Cr content 2.1%, V content 0.19%, Nb content 0.3%, Ti content 1.1%, C content 0.18%, Ni content 0.47%, Mn content 0.21%, and the balance Fe, to obtain a refined molten steel with a S content ≤ 0.01%;

[0091] S1.4: Place the refined molten steel in a vacuum refining furnace at 1628°C with a vacuum degree of 70Pa for 45 minutes, with a circulation pipe flow rate of 110NM 3 / h, vacuum stirring treatment, add Al as a deoxidizer for deoxidation, the added amount is calculated based on the Al content in the molten steel at 0.13%, and soft stirring is carried out for 50 minutes to obtain casting molten steel.

[0092] S2. Continuous casting: The molten steel was transferred to a continuous casting machine, and the pulling speed was set to 0.62 m / min and the casting start temperature was set to 1532°C. After the molten steel flowed into the crystallizer, the electric pulse transmitter was turned on. The setting parameters of the electric pulse transmitter were: voltage 2580 V, frequency 0.87 Hz, and capacitance 195 μF. After solidification, the ingot was pulled out to obtain a continuously cast ingot.

[0093] S3, rolling:

[0094] S3.1: The continuous casting slab is introduced into a roughing mill for rolling: two cross-rolling passes with reduction ratios of 27% and 21% at a rolling temperature of 1270°C; two longitudinal rolling passes with reduction ratios of 18% and 14% at a rolling temperature of 1160°C to obtain a rough-rolled slab;

[0095] S3.2: The rough rolled billet is introduced into the finishing mill for finishing rolling. The rolling passes are 3 times with reduction ratios of 13%, 12%, and 9% respectively. The rolling temperature is 1000°C to obtain the finished rolled billet.

[0096] S4. Post-rolling treatment: quickly place the finished rolled billet in a slow cooling pit at 830℃ and seal it with a cooling rate of 9℃ / h and a sealed cooling time of 8h; then open the sealed cover halfway, cool it at a cooling rate of 20℃ / h and a cooling time of 8h; finally open the sealed cover completely, ventilate it, and cool it at a cooling rate of 50℃ / h. When the billet temperature is lower than 280℃, take it out of the pit and air-cool it to room temperature to obtain fatigue-resistant load-bearing steel.

[0097] Comparative Example 1

[0098] Purchase commercial steel Q460 for wind turbine load-bearing parts (component content: C content 0.18%, Si content 0.55%, Mn content 1.5%, Nb content 0.05%, V content 0.13%, Cr content 0.3%, Ti content 0.05%, Ni content 0.8%, Cu content 0.38%, Mo content ≤0.15%, N content 0.015%, S content 0.03%, P content 0.03%, and the rest is Fe.) and take samples.

[0099] Comparative Example 2 (Compared with Example 1, the electric pulse parameters during the S2 continuous casting process were changed so that their parameter range was outside the parameter range of the claims of the present invention)

[0100] S1. Smelting is the same as step S1 of Example 1;

[0101] S2. Continuous casting: The molten steel is transferred to the continuous casting machine, the pulling speed is set to 0.52 m / min, the casting start temperature is set to 1520°C, and after the molten steel flows into the crystallizer, the electric pulse transmitter is turned on. The setting parameters of the electric pulse transmitter are: voltage 1000 V, frequency 2 Hz, capacitance 150 μF. After solidification, the ingot is pulled out to obtain a continuously cast ingot.

[0102] S3, rolling, and S4, post-rolling treatment are the same as steps S3 and S4 of Example 1.

[0103] Comparative Example 3 (Compared with Example 1, the content ranges of V, Ti, Nb and Cr components in the S1 smelting process were changed to be outside the content range of the claims of the present invention)

[0104] S1.1 and S1.2 are the same as S1.1 and S1.2 in Example 1;

[0105] S1.3: The molten steel is transferred to an LF refining furnace and subjected to argon blowing refining, deoxidation, desulfurization, and impurity removal at 1610°C. During the refining process, the content of each component in the molten steel is tested. Based on the test results, an alloy containing each component in the form of a ferroalloy of each component element is added to achieve the predetermined content of each component: Si content 0.35%, Cr content 0.5%, V content 0.5%, Nb content 0.7%, Ti content 0.3%, C content 0.15%, Ni content 0.39%, Mn content 0.18%, and the balance Fe, to obtain a refined molten steel with a S content ≤ 0.01%;

[0106] S1.4: Place the refined molten steel in a vacuum refining furnace and treat the molten steel in a vacuum furnace at 1615°C with a vacuum degree of 50Pa for 35 minutes, with a circulation pipe flow rate of 100NM 3 / h, vacuum stirring treatment, add Al as a deoxidizer for deoxidation, the added amount is calculated based on the Al content in the molten steel at 0.12%, and soft stirring is carried out for 30 minutes to obtain casting molten steel.

[0107] S2, continuous casting; S3, rolling; and S4, post-rolling treatment are the same as steps S2, S3, and S4 of Example 1.

[0108] Comparative Example 4 (Compared with Example 1, the S3 rolling process was changed so that the rolling method is outside the method claimed in the present invention)

[0109] S1, smelting and S2, continuous casting are the same as S1 and S2 of Example 1;

[0110] S3, rolling:

[0111] S3.1: The continuous casting slab is introduced into a roughing mill for rolling: three cross-rolling passes with reduction ratios of 10%, 15%, and 25% at a rolling temperature of 1150°C; three longitudinal rolling passes with reduction ratios of 25%, 8%, and 8% at a rolling temperature of 1250°C to obtain a rough-rolled slab;

[0112] S3.2: The rough-rolled billet is introduced into the finishing mill for finishing rolling. The rolling passes are 3 times with reduction ratios of 18%, 8%, and 5% respectively. The rolling temperature is 1100°C to obtain the finished billet.

[0113] S4. Post-rolling treatment: quickly place the finished rolled billet into a slow cooling pit at 800℃ and seal it with a cover. The cooling rate is 8℃ / h and the sealed cooling time is 7h. Then half of the sealed cover is opened, the cooling rate is 15℃ / h and the cooling time is 7h. Finally, the sealed cover is fully opened, ventilated, and the cooling rate is 40℃ / h. When the billet temperature is lower than 280℃, it is taken out of the pit and air-cooled to room temperature to obtain load-bearing steel.

[0114] Test example

[0115] The steel materials of Examples 1-3 and Comparative Examples 1-4 were tested according to the following test methods:

[0116] 1. Measurement of intracrystalline dislocation density: Measured according to the method of "Microbeam analysis electron microscopy - Determination of dislocation density in thin metal crystal specimens (GB / T 43088-2023)";

[0117] 2. Mechanical properties measurement: Measure tensile strength + elongation in accordance with the method of "Tensile tests on metallic materials - Part 1: Room temperature test method (GB / T228.1-2021)";

[0118] 3. Fatigue resistance: Fatigue test shall be carried out in accordance with the method of "Axial force control method for fatigue test of metallic materials (GB / T 3075-2021)".

[0119] The test data of the above steel materials are shown in Table 1 below:

[0120] Table 1 Test data of steel materials of Examples 1-3 and Comparative Examples 1-4

[0121] From the data in Table 1, it can be seen that the grain surface of the fatigue-resistant load-bearing steel prepared by the method of the present invention has a corrugated grain boundary. The corrugated grain boundary reduces the orientation difference between adjacent grains, reduces the grain boundary energy, and can effectively prevent the expansion of dislocations and grain boundary sliding, further improving the fatigue resistance of the material. The intragranular dislocation density is 4.8×10 14 -5.5×10 14 m -2 High-density dislocations, tensile strength of about 860 MPa, elongation of about 23%, and fatigue strength of about 345 MPa. These performance values ​​are much higher than those of the commercial steel Q460 for wind turbine load-bearing parts in the prior art of Comparative Example 1. The interaction between the high-density dislocations within the crystal and the resulting Coriolis air masses during wind vibration significantly strengthen the material through deformation, resulting in good fatigue resistance.

[0122] In Comparative Example 2, the electric pulse parameters during the S2 continuous casting process were changed so that their parameter range was outside the parameter range of the method of the present invention. No wavy interface was formed, the intragranular dislocation density was much lower than that of Example 1, and the mechanical properties were also lower than those of Example 1. This is because the electric pulse crystallization under the process of the electric pulse parameters of the method of the present invention caused the grain growth orientation and distribution and the segregation of alloy elements to change periodically, thereby ensuring the formation of wavy grain boundaries from a kinetic perspective. Consequently, obvious wavy grain boundaries were formed under the reduction rate and temperature control processing of 4-stage rough rolling and 3-stage finishing rolling.

[0123] The V, Ti, Nb, and Cr content ranges during the smelting process of S1 in Comparative Example 3 are outside the content range required by the method of the present invention, and no wavy interface is formed. The intragranular dislocation density is much lower than that of Example 1, and its mechanical properties are also lower than those of Example 1, but higher than those of Comparative Example 1. This is because the specific V, Ti, Nb, and Cr content ratios of the present invention, coupled with the fact that V, Ti, Nb, and Cr are all alloying elements sensitive to environmental embedding energy, tend to segregate at defects such as dislocation lines and boundaries from a thermodynamic perspective, and are very likely to form Koch gas clusters, which drag grain boundary movement, thereby enhancing the mechanical properties and fatigue resistance of the steel.

[0124] Comparative Example 4 changes the S3 rolling process so that its rolling method is outside the required method of the present invention. It does not form a corrugated interface, and the dislocation density within the grain is much lower than the value of Example 1. Its mechanical properties are also lower than the mechanical properties of Example 1, but are all higher than the values ​​of Comparative Example 1. The reason is that the electric pulse treatment method and the reduction rate and temperature control of the 4-stage rough rolling and 3-stage finishing rolling enhance the cross-slip of dislocations, produce a wavy dislocation morphology, and enhance the twin deformation, so that a high dislocation density is formed inside the grain. During the wind vibration process, the interaction between dislocations and the formed Coriolis gas clusters have a significant deformation strengthening effect on the material, and have a good anti-fatigue effect.

[0125] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A preparation method of anti-fatigue load-bearing steel for a wind power spindle, characterized in that: It includes the following steps: S1. Smelting: Smelt the raw material steel into molten iron, remove impurities, deoxidize and adjust the content of each component to obtain casting molten steel. The components and their contents of the casting molten steel include Al content of 0.12 - 0.15%, Si content of 0.35 - 0.60%, Cr content of 1.62 - 2.35%, V content of 0.15 - 0.21%, Ti content of 0.78 - 1.21%, Nb content of 0.27 - 0.32%, C content of 0.15 - 0.20%, Ni content of 0.39 - 0.48%, Mn content of 0.18 - 0.23%, and the remaining amount is Fe; S2. Continuous casting: Use electro - pulse crystallization and solidification for the casting molten steel to obtain continuous casting billets; The process of S2, continuous casting includes transferring the casting molten steel into a continuous caster, setting the drawing speed at 0.52 - 0.64 m / min, the starting casting temperature at 1520 - 1535 °C, and the set parameters of the electro - pulse emission device are: voltage 2500 - 2600 V, frequency 0.80 - 0.88 Hz, capacitance 180 - 200 μF, and continuous casting billets are obtained after solidification; S3. Rolling: First rough - roll the continuous casting billets and then finish - roll them to obtain finish - rolled billets; The process of S3, rolling includes: S3.1: Introduce the continuous casting billets into a roughing mill for rolling: 2 transverse rolling passes with reduction ratios of 25 - 28% and 20 - 22% respectively, and the rolling temperature is 1200 - 1275 °C; 2 longitudinal rolling passes with reduction ratios of 16 - 19% and 13 - 15% respectively, and the rolling temperature is 1100 - 1200 °C, to obtain rough - rolled billets; S3.2: Introduce the rough - rolled billets into a finishing mill for finish - rolling. There are 3 rolling passes with reduction ratios of 12 - 14%, 10 - 12%, and 8 - 10% respectively, and the rolling temperature is 850 - 1050 °C, to obtain finish - rolled billets; S4. Post - rolling treatment: First slow - cool the finish - rolled billets and then air - cool them to obtain anti - fatigue load - bearing steel.

2. The preparation method of an anti-fatigue load-bearing steel for a wind power main shaft according to claim 1, characterized in that, The impurity removal, deoxidation and adjustment of the content of each component in S1 include the following steps: S1.1: Use the KR stirring method to pre - desulfurize the raw material steel at 1575 - 1605 °C, and smelt to obtain molten iron with S content ≤ 0.02%, P content ≤ 0.10%, and Si content ≤ 0.60%; S1.2: Feed the molten iron into a converter and smelt it into molten steel at 1650 - 1690 °C, and the P content of the molten steel ≤ 0.03%; S1.3: Transfer the molten steel to an LF refining furnace, blow argon for refining, deoxidize and remove impurities at 1610 - 1630 °C, and add alloys containing each component to make the content of each component reach the predetermined value, to obtain refined molten steel with S content ≤ 0.01%; S1.4: Place the refined molten steel in a vacuum refining furnace, conduct vacuum stirring treatment at 1615 - 1630 °C, and add Al for deoxidation to obtain casting molten steel.

3. The preparation method of an anti-fatigue load-bearing steel for a wind power main shaft according to claim 1, characterized in that, The process of S4, post - rolling treatment includes: S4.1: Quickly put the finish - rolled billets into a slow - cooling pit within the range of 800 - 850 °C, cover and seal it for slow - cooling; S4.2: Then open the sealing cover halfway, with a cooling rate of 15 - 20 °C / h and a cooling time of 7 - 8 h; S4.3: Finally, fully open the sealing cover for ventilation. The cooling rate is 40 - 50 °C / h. Wait until the temperature of the blank is lower than 280 °C, then take it out of the pit and air-cool it to room temperature to obtain the anti-fatigue load-bearing steel.

4. The preparation method of an anti-fatigue load-bearing steel for a wind power main shaft according to claim 3, characterized in that, The cooling rate in S4.1 is 8 - 9 °C / h, and the sealing and cooling time is 7 - 8 h.

5. An anti-fatigue load-bearing steel prepared by the preparation method of an anti-fatigue load-bearing steel for a wind power spindle according to any one of claims 1 - 4.

6. The anti-fatigue load-bearing steel according to claim 5, characterized in that, Each component and its content include: The C content is 0.15 - 0.20%, the Cr content is 1.62 - 2.35%, the Ti content is 0.78 - 1.21%, the Mn content is 0.18 - 0.23%, the Ni content is 0.39 - 0.48%, the Al content is 0.12 - 0.15%, the V content is 0.15 - 0.21%, the Nb content is 0.27 - 0.32%, the Si content is 0.35 - 0.60%, the S content is ≤0.01%, the P content is ≤0.03%, and the remaining amount is Fe.

7. The anti-fatigue load-bearing steel according to claim 6, characterized in that, Its grain boundary has a typical corrugated interface.

8. The anti-fatigue load-bearing steel according to claim 7, characterized in that, The intracrystalline dislocation density ≥ 4.8×10 14 m -2 .

9. The application of the anti-fatigue load-bearing steel according to claim 5 or any one of claims 6 - 8 in a wind power generation load-bearing component or a wind power spindle.

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