A wind power fastener steel and a preparation method thereof, and a wind power fastener

Abstract

The application provides a wind power fastener steel and a preparation method thereof and a wind power fastener, and belongs to the field of steel preparation.The chemical components of the wind power fastener steel include C, Si, Mn, Cr, Ni, Mo, Al, P, S, Nb, V, Ti and Fe; the content of C is 0.32-0.36% by mass fraction, the content of Si is 0.30-0.50% by mass fraction, the content of Mn is 0.40-0.60% by mass fraction, the content of Cr is 0.50-0.70% by mass fraction, the content of Ni is 1.65-1.90% by mass fraction, the content of Mo is 0.10-0.15% by mass fraction, the content of Al is 0.015-0.035% by mass fraction, the content of P is less than or equal to 0.010% by mass fraction, the content of S is less than or equal to 0.010% by mass fraction, and the sum of the contents of Nb, V and Ti is less than or equal to 0.010% by mass fraction; the wind power fastener steel can meet the use requirements of the wind power generator set on the basis of being applicable to the induction heating and other rapid heating modes.

Description

Technical Field

[0001] This application relates to the field of steel preparation technology, and in particular to a wind power fastener steel and its preparation method, and wind power fasteners. Background Technology

[0002] Compared to fasteners in other industries, wind power fasteners have the following characteristics: First, they have high strength grades. Wind power fasteners simultaneously withstand axial tensile loads, shear loads, and impact loads, with most locations on wind turbines requiring a strength grade of 10.9 or higher. Second, they have large dimensions. As wind turbines become larger, the load-bearing capacity requirements for fasteners are increasing. Commonly used wind power fasteners are generally M36mm or larger, while requiring a cross-sectional hardness difference of ≤3HRC. Third, they require high low-temperature impact toughness. Wind farms are mostly located in northern regions such as Inner Mongolia and Xinjiang, and an impact energy of ≥27J at -40℃ has become a basic requirement for wind power fasteners. Therefore, the manufacturing of wind power fasteners places high demands on steel raw materials.

[0003] Meanwhile, the deep processing industry of wind power fasteners has also undergone new changes, with heat treatment methods gradually shifting from traditional mesh belt furnaces to green and low-energy induction heat treatment. Induction heat treatment has advantages such as fast heating rate, short heating time, low heat loss, and ease of automation. Furthermore, its quenching medium often uses water, resulting in significant energy savings and environmental benefits. However, these very advantages often become disadvantages when dealing with large-size, high-alloy steel. Firstly, due to the skin effect of induction heating, the cross-sectional microstructure of large-size bars is less uniform. Secondly, the significantly increased heating rate, coupled with a short holding time, is insufficient to completely dissolve carbides or precipitates in high-alloy steel. These carbides easily become nucleation sites for newly formed carbides or precipitates during subsequent tempering, leading to coarse carbides and reduced performance. Currently, the heat treatment of wind turbine fasteners mainly refers to the heat treatment processes recommended by national standards. When using a mesh belt heating furnace, the process can be fine-tuned according to the characteristics of the steel grade. Due to the slow heating rate and long heating time, the carbides in the steel can be fully dissolved back into austenite, and the performance can meet the requirements of wind turbine units. However, when using rapid heating methods such as induction heat treatment, the heat treatment processes recommended by national standards are no longer applicable, and the performance is difficult to meet the requirements of wind turbine units. How to solve the problem of carbide dissolution and precipitation under rapid heating conditions is the key to achieving green, stable, and efficient production of high-strength wind turbine fasteners. In existing technologies, the published patents for wind turbine fastener steel mainly focus on cleanliness, high strength, uniform microstructure, and low cost. No wind turbine fastener steel suitable for downstream induction heat treatment has yet been found. In summary, how to ensure that wind turbine fastener steel is suitable for rapid heating methods such as induction heating while meeting the requirements of wind turbine units is a technical problem that urgently needs to be solved. Summary of the Invention

[0004] This application provides a wind power fastener steel and its preparation method, as well as a wind power fastener, to solve the technical problem in the prior art that it is difficult to meet the usage requirements of wind turbine units while ensuring that the wind power fastener steel is suitable for rapid heating methods such as induction heating.

[0005] In a first aspect, this application provides a wind power fastener steel, the chemical composition of which includes: C, Si, Mn, Cr, Ni, Mo, Al, P, S, Nb, V, Ti, and Fe; by mass fraction,

[0006] The content of C is 0.32%–0.36%, the content of Si is 0.30%–0.50%, the content of Mn is 0.40%–0.60%, the content of Cr is 0.50%–0.70%, the content of Ni is 1.65%–1.90%, the content of Mo is 0.10%–0.15%, the content of Al is 0.015%–0.035%, the content of P is ≤0.010%, the content of S is ≤0.010%, and the sum of the contents of Nb, V and Ti is ≤0.010%.

[0007] Optionally, the microstructure of the wind power fastener steel is spheroidized pearlite; the microstructure contains Fe3C, and the particle diameter of the Fe3C is <200nm.

[0008] Secondly, this application provides a method for preparing wind power fastener steel as described in the embodiments of the first aspect, the method comprising:

[0009] A cast billet having the aforementioned chemical composition is obtained;

[0010] The billet is subjected to staged heating, rolling, staged cooling, and continuous spheroidizing annealing to obtain wind power fastener steel.

[0011] Optionally, the continuous spheroidizing annealing includes: a first annealing section, a second annealing section, a third annealing section, and a fourth annealing section.

[0012] Optionally, the first annealing stage includes: heating from room temperature to 740°C to 760°C and holding at that temperature for 6 to 8 hours;

[0013] The second annealing stage includes: cooling from 740℃~760℃ in the first annealing stage to 680℃~700℃, and holding at that temperature for 2h~3h;

[0014] The third annealing stage includes: cooling from 680℃~700℃ in the second annealing stage to 500℃~680℃ at a rate of ≤0.1℃ / s;

[0015] The fourth annealing stage includes air cooling from 500℃ to 680℃ in the third annealing stage to room temperature.

[0016] Optionally, the staged heating includes: a preheating section, a first heating section, a second heating section, and a soaking section; wherein,

[0017] The preheating section includes heating the billet to 700℃~750℃;

[0018] The first heating section includes: heating from 700°C to 750°C in the preheating section to 850°C to 900°C;

[0019] The second heating section includes: heating from 850°C to 900°C in the first heating section to 1150°C to 1200°C;

[0020] The heat spreader section includes: maintaining the temperature of the second heating section at 1150℃~1200℃ and keeping it at that temperature for ≥0.5h.

[0021] Optionally, the initial rolling temperature is 1050℃~1100℃, and the final rolling temperature is 800℃~850℃.

[0022] Optionally, the staged cooling includes: a first cooling section, a second cooling section, and a third cooling section; wherein,

[0023] The first cooling section includes: rapidly cooling from the final rolling temperature of 800℃~850℃ to 500℃~600℃ at a rate of ≥7℃ / s;

[0024] The second cooling section includes: slowly cooling from 500℃~600℃ in the first cooling section to 300℃~400℃ at a rate of ≤3℃ / s;

[0025] The third cooling section includes air cooling from 300℃ to 400℃ in the second cooling section to room temperature.

[0026] Thirdly, this application provides a wind power fastener, which is prepared from the wind power fastener steel described in the first aspect embodiment after induction heat treatment, and the microstructure of the wind power fastener is tempered martensite.

[0027] Optionally, the wind power fastener satisfies at least one of the following properties: tensile strength R m ≥1040MPa, yield strength R p0.2 ≥940MPa, cross-sectional hardness difference ≤2HRC, reduction of area ≥50%, impact energy at -40℃ (A) kv2 ≥35J.

[0028] The technical solutions provided in this application have the following advantages compared with the prior art:

[0029] This application provides a wind power fastener steel. By optimizing the chemical composition of the steel, the formation of insoluble carbides or precipitates is reduced, resulting in fine and dispersed carbides or precipitates in the finished steel. During downstream processing, this steel meets the requirements for cross-sectional uniformity and low-temperature impact toughness under rapid heating conditions, thus satisfying the requirements for use in wind turbine units. The mechanical properties of the 10.9 grade wind power fastener obtained through this application are: tensile strength Rm ≥ 1040 MPa, yield strength Rp0.2 ≥ 940 MPa, cross-sectional hardness difference ≤ 2 HRC, reduction of area ≥ 50%, and impact energy A at -40℃. kv2 ≥35J. Attached Figure Description

[0030] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0031] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 A schematic flowchart illustrating a method for preparing wind power fastener steel provided in this application embodiment;

[0033] Figure 2 This is a microstructure diagram of the wind power fastener provided in Embodiment 1 of this application;

[0034] Figure 3 This is a microstructure diagram of the wind power fastener provided in Embodiment 2 of this application;

[0035] Figure 4 This is a microstructure diagram of the wind power fastener provided in Embodiment 3 of this application;

[0036] Figure 5 This is a microstructure diagram of the wind power fastener provided in Comparative Example 1 of this application;

[0037] Figure 6 This is a microstructure diagram of the wind power fastener provided in Comparative Example 2 of this application;

[0038] Figure 7 This is a microstructure diagram of the wind power fastener provided in Comparative Example 3 of this application;

[0039] Figure 8 This is a microstructure diagram of the wind power fastener provided in Comparative Example 4 of this application;

[0040] Figure 9This is a microstructure diagram of the wind power fastener provided in Comparative Example 5 of this application. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0042] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0043] Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0044] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0045] This application provides a wind power fastener steel, the chemical composition of which includes: C, Si, Mn, Cr, Ni, Mo, Al, P, S, Nb, V, Ti, and Fe; by mass fraction,

[0046] The content of C is 0.32%–0.36%, the content of Si is 0.30%–0.50%, the content of Mn is 0.40%–0.60%, the content of Cr is 0.50%–0.70%, the content of Ni is 1.65%–1.90%, the content of Mo is 0.10%–0.15%, the content of Al is 0.015%–0.035%, the content of P is ≤0.010%, the content of S is ≤0.010%, and the sum of the contents of Nb, V and Ti is ≤0.010%.

[0047] The main functions and design basis of each chemical element in the steel of this invention are as follows:

[0048] Carbon (C) is the most commonly used strengthening element in steel, and the strength of steel gradually increases with increasing carbon content. Since induction hardening, an induction heat treatment method, uses water as the quenching medium, the steel produced is stronger than that produced by traditional oil-based heat treatment. Therefore, compared to conventional wind power fastener steels 42CrMo and 40CrNiMo, the carbon content of this invention is slightly lower, ranging from 0.32% to 0.36%. For example, the C content can be 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, etc.

[0049] As a carbide suppressor, silicon (Si) can inhibit the precipitation of carbon atoms from supersaturated austenite, thereby reducing cementite precipitation. Furthermore, during martensitic tempering, silicon can significantly delay the precipitation of ε-Fe. x C transforms into Fe3C, inhibiting the aggregation and growth of carbides. Since silicon increases the cold work hardening rate of steel, the silicon content is optimized to 0.30%–0.50%. Examples of Si content include 0.30%, 0.32%, 0.35%, 0.37%, 0.39%, 0.41%, 0.43%, 0.45%, 0.47%, and 0.50%.

[0050] Mn, as one of the elements that improve hardenability, can significantly increase the strength of steel after quenching and tempering. In induction hardening, water is used as the quenching medium, which reduces the hardenability requirements of the steel, allowing for an appropriate reduction in hardenability-enhancing elements in the steel. Manganese, as an element prone to segregation, reduces the uniformity of cross-sectional elements, resulting in a higher hardness difference across the cross-section. Simultaneously, as a weak carbide-forming element, manganese carbides can dissolve into cementite, increasing carbide stability. Therefore, to adapt to induction heat treatment, the manganese content can be appropriately reduced to 0.40%–0.60%. Examples of Mn contents include 0.40%, 0.42%, 0.45%, 0.48%, 0.50%, 0.52%, 0.55%, 0.58%, and 0.60%.

[0051] The main role of chromium in steel is to improve hardenability, resulting in good comprehensive mechanical properties after quenching and tempering. However, as a medium-strength carbide-forming element, chromium can form various carbides with carbon, and its affinity for carbon is much greater than that for iron. Examples include Cr7C3 and Cr... 23 The dissolution temperature of C6 is ≥950℃. Therefore, to adapt to induction heat treatment, the chromium content can be appropriately reduced to 0.50%–0.70%. For example, the Cr content can be 0.50%, 0.52%, 0.54%, 0.56%, 0.58%, 0.60%, 0.62%, 0.65%, 0.68%, 0.70%, etc.

[0052] As a non-carbide-forming element, Ni not only improves hardenability but also significantly enhances the impact toughness and symmetrical tensile and compressive fatigue strength of steel. Its content can be appropriately increased to 1.65%–1.90%. Examples of Ni content include 1.65%, 1.68%, 1.70%, 1.75%, 1.78%, 1.80%, 1.82%, 1.85%, 1.88%, and 1.90%.

[0053] Mo, as a strong carbide-forming element, forms stable carbides with carbon in steel, significantly reducing the steel's tendency for hot brittleness. However, it also decreases the spheroidization rate of pearlite. The Fe2Mo3C carbide formed by Mo with iron has a dissolution temperature of 1150–1300°C, making it extremely difficult to dissolve at normal temperatures. Therefore, the molybdenum content is set at 0.10%–0.15%. For example, the Mo content is 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, etc.

[0054] Al, as a deoxidizing element in steel, not only reduces the oxygen content and improves the cleanliness of the steel, but also plays an important role in refining grains by forming AlN, thereby improving the matrix strength and symmetrical compressive fatigue strength. Therefore, the aluminum content is set to 0.015% to 0.035%. For example, the Al content is 0.015%, 0.017%, 0.019%, 0.022%, 0.025%, 0.028%, 0.030%, 0.032%, 0.035%, etc.

[0055] Phosphorus (P) is a grain boundary element that easily segregates, which is particularly detrimental to the low-temperature impact resistance of steel. Therefore, the wind power fastener steel of this invention minimizes its content as much as possible, preferably P ≤ 0.010%. For example, the content of P can be 0.005%, 0.006%, 0.007%, 0.008%, 0.009%, 0.010%, etc.

[0056] As a free-machining element, sulfur (S) significantly increases the hot brittleness of steel and deteriorates its hot working properties. This invention aims to minimize its content, preferably S ≤ 0.010%. For example, the S content can be 0.005%, 0.006%, 0.007%, 0.008%, 0.009%, 0.010%, etc.

[0057] While Nb, V, and Ti, as strong carbide-forming elements, can refine grains and their carbides can act as hydrogen traps, improving the steel's resistance to hydrogen-induced delayed fracture, their carbides, nitrides, and carbonitrides are extremely stable. NbC and TiC are almost insoluble in the general heating process of steel, and the dissolution temperature of VC exceeds 1100℃. Therefore, this invention aims to minimize the presence of these three alloying elements, preferably with Nb+V+Ti ≤ 0.010%. For example, the sum of the contents of Nb, V, and Ti can be 0.005%, 0.006%, 0.007%, 0.008%, 0.009%, 0.010%, etc.

[0058] The strength loss caused by the reduction of the aforementioned alloying elements is precisely controlled by subsequent induction heat treatment (rapid heating, short-time holding, and rapid water cooling) to ultimately obtain a fine, uniform, and diffusely distributed microstructure, achieving a good balance between strength and plasticity.

[0059] In some embodiments, the microstructure of the wind power fastener steel is spheroidized pearlite.

[0060] In some embodiments, the microstructure contains Fe3C particles with a diameter of <200 nm.

[0061] The wind power fastener steel obtained according to the chemical composition and preparation method designed in this invention does not contain Nb, V, Ti stable carbides and precipitates. The main carbide type in the steel is Fe3C, with a particle diameter of less than 200 nm, which can be completely dissolved during induction heating. For example, the particle diameter of the Fe3C can be 140 nm, 145 nm, 150 nm, 155 nm, 160 nm, 165 nm, 170 nm, 175 nm, 180 nm, 190 nm, etc.

[0062] Figure 1 This is a schematic flowchart illustrating a method for preparing wind power fastener steel according to an embodiment of this application.

[0063] Please see Figure 1 This application provides a method for preparing wind power fastener steel, the method comprising:

[0064] S1. Obtain a cast billet having the stated chemical composition.

[0065] In some embodiments, before step S1, the process further includes: sequentially passing the steel through a converter or electric furnace for steelmaking, refining it in an LF furnace, and vacuum degassing it using VD or RH to obtain molten steel with the stated chemical composition; and continuously casting the molten steel to obtain a billet.

[0066] S2. The billet is subjected to staged heating, rolling, staged cooling and continuous spheroidizing annealing to obtain wind power fastener steel.

[0067] In some embodiments, the staged heating includes: a preheating section, a first heating section, a second heating section, and a soaking section; wherein,

[0068] The preheating section includes heating the billet to 700℃~750℃;

[0069] The first heating section includes: heating from 700°C to 750°C in the preheating section to 850°C to 900°C;

[0070] The second heating section includes: heating from 850°C to 900°C in the first heating section to 1150°C to 1200°C;

[0071] The heat spreader section includes: maintaining the temperature of the second heating section at 1150℃~1200℃ and keeping it at that temperature for ≥0.5h.

[0072] The positive effects of controlling the temperature of the preheating section to 700℃~750℃: This stage mainly heats the steel billet by heating the waste heat of the flue gas. The heating rate is lower than that of the heating section. The temperature range of this stage is exactly at the α-Fe to γ-Fe transformation stage of the steel grade of this invention. If the heating rate is too fast, the internal and external temperature difference will be too large, the phase transformation will be asynchronous, and cracks will easily be generated. For example, the temperature of this preheating section is 700℃, 705℃, 710℃, 715℃, 720℃, 730℃, 735℃, 740℃, 745℃, 750℃, etc.

[0073] The positive effects of controlling the temperature of the first heating section to be between 850℃ and 900℃ are as follows: At this stage, the structure has completely transformed into austenite, allowing the temperature to be rapidly increased to the required austenite recrystallization temperature. Rapid heating also reduces oxidation loss. For example, the temperature of this first heating section can be 850℃, 860℃, 870℃, 880℃, 885℃, 890℃, 895℃, 900℃, etc.

[0074] The positive effects of controlling the temperature of the second heating section to 1150℃~1200℃ are as follows: To prevent heating inertia, the heating rate is appropriately reduced during this stage, preparing for heat homogenization. For example, the temperature of the second heating section can be 1150℃, 1155℃, 1160℃, 1170℃, 1175℃, 1180℃, 1190℃, 1200℃, etc.

[0075] The positive effects of controlling the soaking time to ≥0.5h are: ensuring consistent internal and external temperature differences, as well as consistent temperature differences at the beginning and end, and ensuring the uniformity of the steel rolling structure. For example, the soaking time can be 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1.0h, 1.5h, 2.0h, etc.

[0076] In some embodiments, the initial rolling temperature is 1050°C to 1100°C, and the final rolling temperature is 800°C to 850°C.

[0077] The positive effects of controlling the initial rolling temperature to 1050℃~1100℃ and the final rolling temperature to 800℃~850℃ are as follows: Initial rolling ensures rolling within the dynamic recrystallization zone of austenite, resulting in finer austenite grains; final rolling ensures rolling within the non-recrystallization zone of austenite, increasing deformation bands and the number of phase deformation nucleation sites within the austenite grains. For example, the initial rolling temperature can be 1050℃, 1060℃, 1070℃, 1075℃, 1080℃, 1090℃, 1100℃, etc.; and the final rolling temperature can be 800℃, 810℃, 820℃, 825℃, 830℃, 835℃, 840℃, 845℃, 850℃, etc.

[0078] In some embodiments, the staged cooling includes: a first cooling stage, a second cooling stage, and a third cooling stage; wherein,

[0079] The first cooling section includes: rapidly cooling from the final rolling temperature of 800℃~850℃ to 500℃~600℃ at a rate of ≥7℃ / s;

[0080] The second cooling section includes: slowly cooling from 500℃~600℃ in the first cooling section to 300℃~400℃ at a rate of ≤3℃ / s;

[0081] The third cooling section includes air cooling from 300℃ to 400℃ in the second cooling section to room temperature.

[0082] The first cooling stage is a rapid cooling process, with a cooling rate controlled at ≥7℃ / s and a final cooling temperature of 500℃~600℃. The positive effects of this rapid cooling stage are: it increases the undercooling of austenite and enhances the phase transformation activation energy. For example, the cooling rate of the first cooling stage can be 7℃ / s, 7.5℃ / s, 8℃ / s, 8.5℃ / s, 9℃ / s, 9.5℃ / s, 10℃ / s, etc.; and the final cooling temperature can be 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, 600℃, etc.

[0083] The second cooling stage, characterized by slow cooling with a controlled cooling rate ≤3℃ / s and a final cooling temperature of 300℃~400℃, has the following positive effects: This stage is the γ-Fe to α-Fe transformation stage, and slow cooling prolongs the phase transformation time and increases the phase transformation ratio. For example, the cooling rate of the second cooling stage can be 0.5℃ / s, 1.0℃ / s, 1.5℃ / s, 2.0℃ / s, 2.5℃ / s, 3℃ / s, etc.; and the final cooling temperature can be 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃, or 400℃.

[0084] The third annealing stage involves air cooling to room temperature.

[0085] In some embodiments, the continuous spheroidizing annealing includes: a first annealing section, a second annealing section, a third annealing section, and a fourth annealing section.

[0086] In some embodiments, the first annealing stage includes: heating from room temperature to 740°C to 760°C and holding at that temperature for 6 to 8 hours;

[0087] The second annealing stage includes: cooling from 740℃~760℃ in the first annealing stage to 680℃~700℃, and holding at that temperature for 2h~3h;

[0088] The third annealing stage includes: cooling from 680℃~700℃ in the second annealing stage to 500℃~680℃ at a rate of ≤0.1℃ / s;

[0089] The fourth annealing stage includes air cooling from 500℃ to 680℃ in the third annealing stage to room temperature.

[0090] The positive effects of controlling the temperature range of the first annealing stage to 740℃~760℃ and the holding time to 6h~8h are as follows: This stage is the pearlite lamellar melting process, and 6h~8h is exactly the melting time for most of the pearlite lamellars in the steel of the present invention. For example, the temperature range of the first annealing stage can be 740℃, 745℃, 748℃, 750℃, 755℃, 758℃, 760℃, etc.; and the holding time can be 6h, 6.3h, 6.5h, 6.8h, 7.0h, 7.5h, 7.8h, 8h, etc.

[0091] The positive effects of controlling the temperature range of the second annealing stage to 680℃~700℃ and the holding time to 2h~3h are as follows: This stage is when spherical carbides begin to grow, promoting the transformation of carbides into spherical shapes, and 2h~3h ensures a smaller carbide sphere size. For example, the temperature range of the second annealing stage can be 680℃, 682℃, 685℃, 687℃, 690℃, 695℃, 700℃, etc.; the holding time can be 2h, 2.2h, 2.4h, 2.6h, 2.8h, 3h, etc.

[0092] The third annealing stage involves slow cooling within the furnace. Controlling the temperature range in this stage to 500℃~680℃ and the cooling rate to ≤0.1℃ / s has the positive effect of homogenizing the spherical carbides. For example, the temperature range of the third annealing stage can be 500℃, 520℃, 540℃, 560℃, 580℃, 600℃, 630℃, 650℃, 660℃, 680℃, etc.; and the cooling rate can be 0.05℃ / s, 0.06℃ / s, 0.07℃ / s, 0.08℃ / s, 0.09℃ / s, 0.1℃ / s, etc.

[0093] The fourth annealing stage involves air cooling after the furnace is removed from the furnace.

[0094] The product prepared by the preparation method of wind power fastener steel is the aforementioned wind power fastener steel. The chemical composition and microstructure of the wind power fastener steel prepared by the preparation method can be referred to the above embodiments. Since the preparation method of wind power fastener steel adopts some or all of the technical solutions of the wind power fastener steel embodiments, it has at least all the beneficial effects brought about by the technical solutions of the wind power fastener steel embodiments, which will not be elaborated here.

[0095] This application provides a wind power fastener, which is prepared from the wind power fastener steel described in the first aspect embodiment after induction heat treatment, and the microstructure of the wind power fastener is tempered martensite.

[0096] The raw material for this wind power fastener is the aforementioned wind power fastener steel, which is prepared based on the aforementioned wind power fastener steel preparation method. Since the raw material for this wind power fastener, the wind power fastener steel, adopts some or all of the technical solutions of the aforementioned embodiments, it has at least all the beneficial effects brought about by the technical solutions of the wind power fastener steel embodiments, which will not be elaborated here.

[0097] In some embodiments, the wind power fastener simultaneously meets the following properties: tensile strength R m ≥1040MPa, yield strength R p0.2 ≥940MPa, cross-sectional hardness difference ≤2HRC, reduction of area ≥50%, impact energy at -40℃ (A) kv2 ≥35J.

[0098] The wind turbine fastener steel obtained according to the chemical composition and preparation method designed in this invention can meet the requirements of cross-sectional microstructure uniformity and low-temperature impact toughness of wind turbine fasteners under rapid heating conditions during downstream deep processing, thus meeting the requirements for use in wind turbine units. For example, the tensile strength R... m The yield strength R can be 1040MPa, 1045MPa, 1050MPa, 1055MPa, 1060MPa, 1070MPa, 1080MPa, 1090MPa, etc. p0.2 The pressure ratings can be 940MPa, 950MPa, 960MPa, 970MPa, 980MPa, 990MPa, 1000MPa, 1010MPa, etc.; the cross-sectional hardness difference can be 1.1HRC, 1.2HRC, 1.4HRC, 1.5HRC, 1.6HRC, 1.7HRC, 1.8HRC, 1.9HRC, 2HRC, etc.; the reduction of area can be 50%, 50.5%, 51%, 51.5%, 52%, 52.5%, 53%, 54%, 55%, etc.; the -40℃ impact energy A kv2 It can be 35J, 36J, 37J, 38J, 39J, 40J, 41J, 42J, etc.

[0099] In some embodiments, the induction heat treatment includes: induction hardening, first water cooling, induction tempering, and second water cooling; wherein the heating temperature of the induction hardening is 850℃~950℃, and the heating temperature of the induction tempering is 450℃~550℃.

[0100] Induction heat treatment has advantages such as fast heating rate, low heat loss, and ease of automation. Furthermore, it uses water as the quenching medium, resulting in significant energy savings and environmental benefits. For example, the heating temperature for induction quenching can be 850℃, 860℃, 880℃, 900℃, 910℃, 930℃, 950℃, etc.; the heating temperature for induction tempering can be 450℃, 460℃, 480℃, 500℃, 510℃, 530℃, 540℃, 550℃, etc.

[0101] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then common international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0102] Example 1

[0103] This embodiment provides a wind power fastener steel, the chemical composition of which is shown in Table 1 by mass percentage.

[0104] The preparation method of wind power fastener steel in this embodiment includes: obtaining molten steel with the above-mentioned chemical composition through converter steelmaking, LF furnace refining, and VD vacuum degassing; continuously casting the molten steel to obtain a billet; subjecting the billet to staged heating, wherein the preheating section is 750°C, the first heating section is 900°C, the second heating section is 1175°C, the temperature of the soaking section is 1200°C, and the soaking time is 30 minutes; rolling the heated billet, with an initial rolling temperature of 1050°C and a final rolling temperature of 800°C; and performing staged cooling after rolling, with the first cooling... The first cooling stage involves a cooling rate of 10℃ / s and a final cooling temperature of 550℃. The second cooling stage is a slow cooling process with a cooling rate of 3℃ / s and a final cooling temperature of 300℃, followed by air cooling to room temperature. The rolled material cooled to room temperature is then subjected to a staged continuous annealing process. The temperature of the first annealing stage is 740℃, and the holding time is 6 hours. The temperature of the second annealing stage is 680℃, and the holding time is 2 hours. The third annealing stage is a slow cooling process in the furnace with a cooling rate of 0.1℃ / s and a final cooling temperature of 500℃. The fourth annealing stage is an air cooling process after exiting the furnace, resulting in wind power fastener steel.

[0105] Wind power fastener steel is induction hardened at 900℃ and water-cooled; then induction tempered at 500℃ and water-cooled to obtain the wind power fastener. The microstructure of the wind power fastener is as follows: Figure 2 As shown.

[0106] Example 2

[0107] This embodiment provides a wind power fastener steel, the chemical composition of which is shown in Table 1 by mass percentage.

[0108] The preparation method of wind power fastener steel in this embodiment includes: obtaining molten steel with the above-mentioned chemical composition through electric arc furnace steelmaking + LF furnace refining + RH vacuum degassing; continuously casting the molten steel to obtain a billet; subjecting the billet to staged heating, wherein the preheating section is 750°C, the first heating section is 900°C, the second heating section is 1175°C, the temperature of the soaking section is 1175°C, and the soaking time is 35 minutes; rolling the billet, with an initial rolling temperature of 1100°C and a final rolling temperature of 850°C; and performing staged cooling after rolling, with the cooling rate of the first cooling section being... The cooling rate is controlled at 7℃ / s, and the final cooling temperature is 500℃. The second cooling stage is slow cooling with a cooling rate controlled at 2℃ / s and a final cooling temperature of 350℃, followed by air cooling to room temperature. The rolled material cooled to room temperature is then subjected to staged continuous annealing treatment. The temperature of the first annealing stage is 750℃, and the holding time is 7h. The temperature of the second annealing stage is 690℃, and the holding time is 3h. The third annealing stage is slow cooling in the furnace with a cooling rate of 0.1℃ / s and a final cooling temperature of 500℃. The fourth annealing stage is air cooling after exiting the furnace, resulting in wind power fastener steel that meets the requirements for induction heat treatment.

[0109] Wind turbine fastener steel is induction hardened at 900℃ and water-cooled; then induction tempered at 500℃ and water-cooled to obtain the wind turbine fastener. Microstructure of the wind turbine fastener Figure 3 As shown.

[0110] Example 3

[0111] This embodiment provides a wind power fastener steel, the chemical composition of which is shown in Table 1 by mass percentage.

[0112] The preparation method of wind power fastener steel in this embodiment includes: obtaining molten steel with the above-mentioned chemical composition through converter steelmaking + LF furnace refining + RH vacuum degassing; continuously casting the molten steel to obtain a billet; subjecting the billet to staged heating, wherein the preheating section is 750°C, the first heating section is 900°C, the second heating section is 1150°C, the temperature of the soaking section is 1150°C, and the soaking time is 40 minutes; rolling the billet, with an initial rolling temperature of 1100°C and a final rolling temperature of 850°C; and performing staged cooling after rolling, with the cooling rate of the first cooling section being [missing information]. The cooling rate is controlled at 7℃ / s, and the final cooling temperature is 500℃. The second cooling stage is slow cooling with a cooling rate controlled at 2℃ / s and a final cooling temperature of 400℃, followed by air cooling to room temperature. The rolled material cooled to room temperature is then subjected to staged continuous annealing treatment. The temperature of the first annealing stage is 750℃, and the holding time is 7h. The temperature of the second annealing stage is 690℃, and the holding time is 3h. The third annealing stage is slow cooling in the furnace with a cooling rate of 0.1℃ / s and a final cooling temperature of 500℃. The fourth annealing stage is air cooling after exiting the furnace, resulting in wind power fastener steel that meets the requirements for induction heat treatment.

[0113] Wind turbine fastener steel is induction hardened at 900℃ and water-cooled; then induction tempered at 500℃ and water-cooled to obtain the wind turbine fastener. Microstructure of the wind turbine fastener Figure 4 As shown.

[0114] Comparative Example 1

[0115] This comparative example uses conventional 10.9 grade wind turbine fastener steel 42CrMo, whose chemical composition by mass percentage is shown in Table 1. The wind turbine fastener steel is induction hardened at 900℃, water-cooled, induction tempered at 500℃, and water-cooled to obtain the wind turbine fasteners. The microstructure of the wind turbine fasteners is shown in Table 1. Figure 5 As shown.

[0116] Comparative Example 2

[0117] This comparative example uses conventional 10.9 grade wind turbine fastener steel 40CrNiMo, whose chemical composition by mass percentage is shown in Table 1. The wind turbine fastener steel is induction hardened at 900℃, water-cooled, induction tempered at 500℃, and water-cooled to obtain the wind turbine fasteners. The microstructure of the wind turbine fasteners is shown in Table 1. Figure 6 As shown.

[0118] Comparative Example 3

[0119] This comparative example uses Ti-containing grade 10.9 wind turbine fastener steel, and its chemical composition by mass percentage is shown in Table 1. The wind turbine fastener steel was induction hardened at 900℃, water-cooled, induction tempered at 500℃, and water-cooled to obtain the wind turbine fasteners. The microstructure of the wind turbine fasteners is shown in Table 1. Figure 7 As shown.

[0120] Comparative Example 4

[0121] This comparative example uses Nb-containing grade 10.9 wind turbine fastener steel, the chemical composition by mass percentage of which is shown in Table 1. The wind turbine fastener steel is induction hardened at 900℃, water-cooled, induction tempered at 500℃, and water-cooled to obtain the wind turbine fasteners. The microstructure of the wind turbine fasteners is shown in Table 1. Figure 8 As shown.

[0122] Comparative Example 5

[0123] This comparative example uses a 10.9 grade wind turbine fastener steel with Nb and V composite composition. The chemical composition by mass percentage is shown in Table 1. The wind turbine fastener steel was induction hardened at 900℃, water-cooled, induction tempered at 500℃, and water-cooled to obtain the wind turbine fasteners. The microstructure of the wind turbine fasteners is shown in Table 1. Figure 9 As shown.

[0124] Table 1. Chemical composition (mass fraction, %) of wind power fastener steel in the examples and comparative examples.

[0125]

[0126]

[0127] The wind power fasteners obtained in Examples 1-3 and Comparative Examples 1-5 were sampled and tested for mechanical properties in accordance with GB / T 2975-2018 "Sampling Location and Sample Preparation for Mechanical Property Testing of Steel and Steel Products". The performance results are shown in Table 2.

[0128] Table 2 Performance of wind power fasteners in the embodiments and comparative examples

[0129]

[0130] As shown in Table 2, the mechanical properties of the grade 10.9 wind power fasteners obtained in the embodiments of this application satisfy the following: tensile strength R m ≥1040MPa, yield strength R p0.2 ≥940MPa, cross-sectional hardness difference ≤2HRC, reduction of area ≥50%, impact energy at -40℃ (A) kv2 ≥35J. The comparative example shows differences in areas such as reduction of area and impact energy at -40℃.

[0131] Appendix Figures 2-9 Detailed explanation:

[0132] Figures 2-9 The images show the microstructure of the wind power fasteners in Examples 1-3 and Comparative Examples 1-5. The wind power fastener steel was processed by the user and then subjected to induction quenching and tempering to obtain the wind power fasteners. All the wind power fasteners have a tempered martensitic structure. The induction tempered carbide particles have different sizes, as shown in Table 2. It is these differences in carbide size that cause the differences in the above-mentioned mechanical properties.

[0133] In summary, this invention reduces the generation of insoluble carbides or precipitates in steel by designing the chemical composition and optimizing the steel rolling and annealing processes. This results in steel products with fine and dispersed carbides or precipitates, which can meet the requirements of cross-sectional uniformity and low-temperature impact toughness of wind power fasteners under rapid heating conditions during downstream deep processing, thus satisfying the requirements for use in wind turbine units.

[0134] Furthermore, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0135] In this embodiment of the invention, the wind power fastener steel does not contain Nb, V, Ti stable carbides and precipitates. The main carbide type in the steel is Fe3C, with a particle diameter of less than 200 nm, which can be completely dissolved during induction heating. The quenched and tempered wind power fastener has a cross-sectional hardness difference ≤2HRC, a section reduction rate ≥50%, and an impact energy A at -40℃. kv2 ≥35J.

[0136] In this embodiment of the invention, rapid heating methods such as induction heat treatment are used, which greatly improves the heating rate, shortens the holding time, increases the production rate, and can significantly save production costs.

[0137] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A wind turbine fastener steel characterized in that, The wind power fastener steel has a chemical composition including C, Si, Mn, Cr, Ni, Mo, Al, P, S, Nb, V, Ti, and the balance being Fe, and the mass fraction of each component is as follows: The content of C is 0.32% to 0.36%, the content of Si is 0.30% to 0.50%, the content of Mn is 0.40% to 0.60%, the content of Cr is 0.50% to 0.70%, the content of Ni is 1.65% to 1.90%, the content of Mo is 0.10% to 0.15%, the content of Al is 0.015% to 0.035%, the content of P is ≤0.010%, the content of S is ≤0.010%, and the sum of the contents of Nb, V and Ti is ≤0.010%. The preparation method of the wind power fastener steel includes obtaining a casting blank with the chemical composition, and performing stage-by-stage heating, rolling, stage-by-stage cooling and continuous spheroidizing annealing on the casting blank to obtain the wind power fastener steel. The continuous spheroidizing annealing includes a first annealing section, a second annealing section, a third annealing section and a fourth annealing section. The first annealing section includes heating from room temperature to 740°C to 760°C and maintaining for 6h to 8h. The second annealing section includes cooling from 740°C to 760°C in the first annealing section to 680°C to 700°C and maintaining for 2h to 3h. The third annealing section includes cooling from 680°C to 700°C in the second annealing section to 500°C to 680°C at a rate of ≤0.1°C / s. The fourth annealing section includes air cooling from 500°C to 680°C in the third annealing section to room temperature. The stage-by-stage cooling includes a first cooling section, a second cooling section and a third cooling section. The first cooling section includes fast cooling from the finish rolling temperature of 800°C to 850°C at a rate of ≥7°C / s to 500°C to 600°C. The second cooling section includes slow cooling from 500°C to 600°C in the first cooling section to 300°C to 400°C at a rate of ≤3°C / s. The third cooling section includes air cooling from 300°C to 400°C in the second cooling section to room temperature.

2. The wind turbine fastener steel of claim 1, wherein, The microstructure of the wind power fastener steel is spheroidized pearlite, and the microstructure contains Fe3C with a particle diameter size of <200nm.

3. A method of producing a wind turbine fastener steel as claimed in claim 1 or 2, characterized in that The method includes: obtaining a casting blank with the chemical composition; performing stage-by-stage heating, rolling, stage-by-stage cooling and continuous spheroidizing annealing on the casting blank to obtain the wind power fastener steel.

4. The method of claim 3, wherein, The stage-by-stage heating includes a preheating section, a first heating section, a second heating section and a soaking section. The preheating section includes heating the casting blank to 700°C to 750°C. The first heating section includes heating from 700°C to 750°C in the preheating section to 850°C to 900°C. The second heating section includes heating from 850°C to 900°C in the first heating section to 1150°C to 1200°C. The soaking section includes maintaining 1150°C to 1200°C in the second heating section for ≥0.5h.

5. The method of claim 3, wherein, The rolling has a opening rolling temperature of 1050°C to 1100°C and a finish rolling temperature of 800°C to 850°C.

6. A wind power fastener, characterized in that The wind power fastener is prepared from the wind power fastener steel according to claim 1 or 2, or the wind power fastener steel prepared by the method according to any one of claims 3-5 after induction heat treatment, and the microstructure of the wind power fastener is tempered martensite.

7. The wind power fastener of claim 6, wherein, The wind power fastener satisfies at least one of the following properties: tensile strength R m ≥ 1040 MPa, yield strength R p0.2 ≥ 940 MPa, cross-sectional hardness difference ≤ 2 HRC, reduction of area ≥ 50%, -40 °C impact energy A kv2 ≥ 35 J.

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