Corrosion fatigue resistant high-strength bolt steel for offshore wind power and preparation method of corrosion fatigue resistant high-strength bolt steel

Abstract

The invention discloses corrosion-fatigue-resistant high-strength bolt steel for offshore wind power and a preparation method, and belongs to the technical field of metal materials, and the corrosion-fatigue-resistant high-strength bolt steel comprises the following components in percentage by mass: 0.38-0.45% of C, 0.17-0.37% of Si, 0.50-0.80% of Mn, 0.9-1.2% of Cr, 0.15-0.25% of Mo, less than or equal to 0.03% of P, less than or equal to 0.03% of S, and at least one element selected from Nb and Ce; wherein when Nb is contained, the mass fraction of the Nb is 0.04%-0.20%; when the catalyst contains Ce, the mass fraction of the catalyst is 0.001%-0.1%; and the balance of Fe and inevitable impurities. According to the high-strength bolt steel for offshore wind power and the preparation method, generation and expansion of corrosion fatigue cracks are inhibited by adding trace Nb and Ce, so that excellent corrosion fatigue resistance is obtained.

Description

Technical Field

[0001] This invention relates to the field of metallic materials technology, and in particular to a high-strength bolt steel for offshore wind power that is resistant to corrosion fatigue and its preparation method. Background Technology

[0002] Driven by global energy shortages and China's "dual-carbon" strategy, wind power, as a clean and renewable energy source, has developed rapidly. Offshore wind power, in particular, has attracted significant attention due to its advantages such as high energy density and lack of land occupation. However, the marine environment, characterized by high humidity, high salinity, and high radiation, presents wind turbines with a severe corrosion threat. Simultaneously, external loads such as wind and waves, combined with fatigue vibration loads from blade rotation, cause wind turbine bolts to endure complex alternating stresses. The synergistic coupling of corrosion and fatigue further exacerbates the material degradation process, resulting in offshore wind turbine bolts commonly facing the risk of corrosion fatigue failure during their service life.

[0003] High-strength bolts are the most critical load-bearing and connecting components in offshore wind power equipment, and their corrosion resistance and reliability directly affect the service safety of the entire wind turbine. Components such as wind turbine tower flange bolts and blade bolts have gap structures. In the marine environment, crevice fluid easily forms within these bolt gaps, leading to crevice corrosion of the bolt steel. Hydrolysis products can cause acidification of the liquid film within the crevice and promote the migration of chloride ions into the crevice, leaving the bolts in a long-term acidic, high-chlorine corrosive environment. Under external fatigue loads, this can easily induce corrosion fatigue fracture accidents in the bolts, becoming one of the common failure modes of wind turbine bolts both domestically and internationally. Therefore, improving the corrosion fatigue resistance of bolt steel is a crucial measure to enhance the durability of wind power equipment.

[0004] Currently, the mainstream bolt steel used in my country for wind power is 42CrMo. Although it has good strength, toughness and corrosion resistance, it still suffers from a large number of stress corrosion and corrosion fatigue fracture failures in harsh marine environments, which seriously threatens the service safety of offshore wind power equipment. Therefore, the development of high-strength bolt steel with excellent corrosion fatigue resistance has important engineering practical value. Summary of the Invention

[0005] The purpose of this invention is to provide a corrosion-resistant high-strength bolt steel for offshore wind power and its preparation method, so as to solve the problem that the bolt steel used in existing offshore wind power is prone to corrosion fatigue failure.

[0006] To achieve the above objectives, the present invention provides a high-strength bolt steel for offshore wind power that is resistant to corrosion fatigue, comprising, by mass fraction (100%), 0.38%-0.45% C, 0.17%-0.37% Si, 0.50%-0.80% Mn, 0.9%-1.2% Cr, 0.15%-0.25% Mo, P≤0.03%, S≤0.03%, and at least one element selected from Nb and Ce; Specifically, when Nb is present, its mass fraction is 0.04%-0.20%; when Ce is present, its mass fraction is 0.001%-0.1%. The balance is Fe and unavoidable impurities.

[0007] In an embodiment of the present invention, a corrosion-resistant and fatigue-resistant high-strength bolt steel for offshore wind power, based on a mass fraction of 100%, comprises 0.44% C, 0.25% Si, 0.61% Mn, 1.01% Cr, 0.20% Mo, 0.0052% P, 0.0029% S, 0.059% Nb, with the balance being Fe and unavoidable impurities.

[0008] In an embodiment of the present invention, a corrosion-resistant and fatigue-resistant high-strength bolt steel for offshore wind power, based on a mass fraction of 100%, comprises 0.44% C, 0.28% Si, 0.62% Mn, 1.01% Cr, 0.20% Mo, 0.0052% P, 0.0015% S, 0.043% Ce, with the balance being Fe and unavoidable impurities.

[0009] This invention also provides a method for preparing high-strength bolt steel for offshore wind power that is resistant to corrosion fatigue, comprising the following steps: S1. Mix C, Si, Mn, Cr, Mo, Nb, Ce, and Fe, melt, and cast to obtain bolt steel ingots; S2. Forging, heat preservation, and rolling of bolt steel ingots to obtain bolt steel round bars; S3. Quench and temper the round bolt steel to obtain high-strength bolt steel for offshore wind power that is resistant to corrosion fatigue.

[0010] Preferably, in S1, the melting temperature is 1600-1700℃.

[0011] Preferably, in S2, the forging temperature is 1100-1200℃.

[0012] Preferably, in S2, the heat preservation temperature is 1150-1250℃, and the heat preservation time is 1-2 hours.

[0013] Preferably, in S2, the initial rolling temperature is 1000-1200℃, and the final rolling temperature is 850-900℃.

[0014] Preferably, in S3, the holding temperature before quenching is 850-900℃, and the holding time before quenching is 0.5-1h.

[0015] Preferably, in S3, the tempering temperature is 500-600℃ and the tempering holding time is 0.5-1h.

[0016] In the composition design of the corrosion-resistant and fatigue-resistant high-strength bolt steel for offshore wind power as described in this invention: Carbon (C), as an additive element in this application, can improve the strength, hardness, and hardenability of the material. If the C content is less than 0.38 wt%, the strength is insufficient, making it difficult to meet the performance grade of offshore wind turbine bolts of not less than 10.9; if the C content is greater than 0.45 wt%, the toughness and plasticity of the material are greatly reduced, making it prone to brittle fracture. Therefore, the C content should be controlled between 0.38 wt% and 0.45 wt%.

[0017] Silicon (Si) is a good deoxidizer for materials. Adding Si to bolt steel can improve the solid solution strength of the bolt steel and is beneficial to increasing the tempering stability of the material. If the silicon content is too high, it will reduce the plasticity of the material; if the content is too low, the deoxidation and solid solution strengthening effects will be weak. Therefore, the silicon content should be controlled between 0.17wt% and 0.37wt%.

[0018] Manganese (Mn) improves the hardenability, strength, and toughness of materials, and refines the microstructure. It combines with sulfur (S) to form MnS, reducing the hot embrittlement caused by sulfur. However, excessively high Mn content can lead to component segregation (Mn-rich zones), becoming preferential initiation areas for corrosion fatigue cracks and reducing the corrosion resistance of steel. If the manganese content is below 0.5% wt%, hardenability is insufficient, and the strength cannot be guaranteed to reach the target value; if the manganese content is above 0.8 wt%, component segregation and temper embrittlement risks are likely to occur. Therefore, the manganese content should be controlled between 0.5 wt% and 0.8 wt%.

[0019] Chromium (Cr) can significantly improve hardenability, inhibit the coarsening of tempered cementite, enhance high-temperature tempering stability, and improve the corrosion resistance of bolt steel. Below 0.9 wt%, hardenability is insufficient, making it unsuitable for large-size wind turbine bolts; above 1.2 wt%, it increases cost and may form intergranular chromium carbide, leading to intergranular corrosion and inducing corrosion fatigue crack initiation. Therefore, the chromium content should ideally be controlled between 0.9 wt% and 1.2 wt%.

[0020] The addition of molybdenum (Mo) can refine grain size, increase hardenability, significantly suppress temper brittleness, improve high-temperature strength, and form nano-precipitates such as Mo2C with carbon, thereby enhancing resistance to temper softening and corrosion resistance. Below 0.15%, hardenability and resistance to temper softening are insufficient, and the required strength and toughness are difficult to meet; above 0.25%, the cost increases significantly, hindering engineering application. Therefore, the molybdenum content should be controlled between 0.15wt% and 0.25wt%.

[0021] Niobium (Nb) precipitates as finely dispersed Nb(C,N) particles during high-temperature forging and hot rolling, pinning grain boundaries and hindering grain growth. After the phase transformation, the ferrite grain size inherits the original austenite grain size, resulting in a finer and more uniform microstructure. This improves the steel's strength, toughness, and corrosion resistance. Furthermore, it enhances the steel's corrosion fatigue resistance by refining grains and inhibiting the diffusion of free hydrogen. If the Nb content is below 0.04 wt%, the grain refinement and precipitation effects are not significant, and the improvement in corrosion fatigue performance is not substantial. If the Nb content is above 0.20 wt%, not only does the cost increase significantly, but the steel's hot plasticity also deteriorates. Therefore, the Nb content should ideally be controlled between 0.04 wt% and 0.20 wt%.

[0022] Cerium (Ce) possesses extremely strong deoxidizing and desulfurizing capabilities. Its addition can react with O and S in molten steel to form stable Ce–O, Ce–S, or complex rare earth oxysulfide inclusions. It can also purify grain boundaries and enhance grain boundary bonding, thereby reducing the tendency for intergranular corrosion and intergranular crack initiation / propagation, thus improving corrosion fatigue resistance. When the Ce content is below 0.001 wt%, its purifying and modifying inclusion effects are not fully realized; when the Ce content exceeds 0.1 wt%, supersaturated rare earth oxysulfides easily grow into coarse inclusions, becoming new crack initiation points, which is detrimental to corrosion fatigue performance. Therefore, controlling the Ce content between 0.001 wt% and 0.1 wt% is the optimal range to balance inclusion modification, grain boundary purification, and improved strength, toughness, and corrosion fatigue performance.

[0023] Therefore, the present invention, employing the above-mentioned corrosion-resistant fatigue-resistant high-strength bolt steel for offshore wind power and its preparation method, has the following beneficial effects: (1) In this invention, the beneficial effects of each alloying element are fully utilized, so that the bolt steel can meet the requirements of high tensile strength and toughness, and the corrosion fatigue performance is also significantly improved. This provides stable support, fixation and connection for large-scale engineering equipment / facilities, effectively improves the service life of high-strength bolts, and provides a strong guarantee for the long-term stable operation of major engineering equipment.

[0024] (2) The trace amount of Nb in this invention mainly serves to refine grains and increase grain boundary density, particularly increasing the proportion of small-angle grain boundaries. Simultaneously, Nb inhibits the intergranular precipitation and coarsening of cementite, reduces the tendency for crack initiation, and hinders crack propagation, thereby increasing the resistance to the initiation and propagation of corrosion fatigue cracks in bolt steel. Furthermore, Nb may precipitate nanoscale NbC precipitates, which can act as deep hydrogen traps, capturing free hydrogen atoms that enter the steel during corrosion, reducing hydrogen segregation at microscopic defects such as grain boundaries and crack tips, and inhibiting the initiation of hydrogen-induced cracks. Overall, the addition of Nb can play a beneficial role in many ways, significantly improving the corrosion fatigue resistance of high-strength bolt steel.

[0025] (3) In this invention, the rare earth element Ce mainly improves the corrosion fatigue resistance of bolt steel in marine environments through inclusion modification and grain boundary purification. Ce has extremely strong deoxidation and desulfurization capabilities, and can form stable Ce–O, Ce–S or composite rare earth oxysulfides with O and S in steel, causing the originally sharp, brittle, and highly corrosion-sensitive Al2O3 and banded MnS inclusions to become spheroidized, refined, and softened, thereby inhibiting local corrosion of the steel. More importantly, rare earth Ce can purify grain boundaries, reduce S and P segregation at grain boundaries, improve the bonding strength between grain boundaries and the matrix, mitigate the adverse effects of hydrogen on grain boundary weakening, and hinder the initiation and propagation of hydrogen-induced intergranular fatigue cracks, thereby improving the corrosion fatigue resistance of high-strength bolt steel.

[0026] (4) The alloying element Nb added in this invention is not easily burned during smelting, and its composition is easy to control. Rare earth Ce has abundant reserves and production in my country, and its price is low. Moreover, the amount of Nb and Ce added is relatively small, which is lower in cost compared with precious alloying elements such as Ni, Cr, and Mo. Significant corrosion resistance and anti-corrosion fatigue effects can be obtained by adding a small amount, which has a high cost performance. At the same time, the preparation process of the material is simple and easy to promote and apply on a large scale.

[0027] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0028] Figure 1 These are SEM images of the high-strength bolt steel for offshore wind power prepared in Examples 1-2 and Comparative Example 1 of this invention; Figure 2 These are TEM images of the high-strength bolt steel for offshore wind power prepared in Examples 1-2 and Comparative Example 1 of this invention; Figure 3 These are EBSD grain boundary feature maps of the high-strength bolt steel for offshore wind power prepared in Examples 1-2 and Comparative Example 1; Figure 4 This is a grain boundary density diagram of the high-strength bolt steel for offshore wind power prepared in Examples 1-2 and Comparative Example 1; Figure 5 These are stress-strain curves of the high-strength bolt steel for offshore wind power prepared in Examples 1-2 and Comparative Example 1. Figure 6 This is a corrosion stress-life curve of the high-strength bolt steel for offshore wind power prepared in Examples 1-2 and Comparative Example 1 in a simulated marine crevice environment; Figure 7 These are SEM images of the corrosion fatigue fracture surfaces of the high-strength bolt steel for offshore wind power prepared in Examples 1-2 and Comparative Example 1 in a simulated marine crevice environment. Detailed Implementation

[0029] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0030] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0031] In this invention, unless otherwise specified, the test materials and instruments are all conventional test materials in the field and can be purchased through commercial channels.

[0032] Example 1 A corrosion-fatigue resistant high-strength bolt steel for offshore wind power, comprising, by mass fraction 100%, 0.44% C, 0.25% Si, 0.61% Mn, 1.01% Cr, 0.20% Mo, 0.0052% P, 0.0029% S, 0.059% Nb, with the balance being Fe and unavoidable impurities.

[0033] The above-mentioned method for preparing high-strength bolt steel for offshore wind power with corrosion fatigue resistance includes the following steps: S1. C, Si, Mn, Cr, Mo, Nb and Fe are mixed according to the above mass fractions, melted in a vacuum induction furnace at 1650°C, and cast to obtain bolt steel ingots; S2. The bolt steel ingot is forged at 1150℃ to eliminate the structural defects generated during the casting process. The forged bolt steel ingot is heated to 1200℃ and held at this temperature for 2 hours to fully austenitize it. Then it is rolled at an initial rolling temperature of 1100℃ and a final rolling temperature of 875℃ to obtain bolt steel round bars. S3. After holding the bolt steel round bar at 850℃ for 1 hour, it is quenched and then tempered at 560℃ for 1 hour. After tempering, it is water-cooled to room temperature to obtain high-strength bolt steel for offshore wind power.

[0034] Example 2 A corrosion-fatigue resistant high-strength bolt steel for offshore wind power, comprising, by mass fraction 100%, 0.44% C, 0.28% Si, 0.62% Mn, 1.01% Cr, 0.20% Mo, 0.0052% P, 0.0015% S, 0.043% Ce, with the balance being Fe and unavoidable impurities.

[0035] The above-mentioned method for preparing high-strength bolt steel for offshore wind power with corrosion fatigue resistance includes the following steps: S1. C, Si, Mn, Cr, Mo, Ce and Fe are mixed according to the above mass fractions, melted in a vacuum induction furnace at 1650°C, and cast to obtain bolt steel ingots; S2. The bolt steel ingot is forged at 1150℃ to eliminate the structural defects generated during the casting process. The forged bolt steel ingot is heated to 1200℃ and held at this temperature for 2 hours to fully austenitize it. Then it is rolled at an initial rolling temperature of 1100℃ and a final rolling temperature of 875℃ to obtain bolt steel round bars. S3. After holding the bolt steel round bar at 850℃ for 1 hour, it is quenched and then tempered at 560℃ for 1 hour. After tempering, it is water-cooled to room temperature to obtain high-strength bolt steel for offshore wind power.

[0036] Comparative Example 1 A corrosion-fatigue resistant high-strength bolt steel for offshore wind power, comprising, by mass fraction 100%, 0.44% C, 0.22% Si, 0.60% Mn, 1.00% Cr, 0.20% Mo, 0.0051% P, 0.0029% S, with the balance being Fe and unavoidable impurities.

[0037] The above-mentioned method for preparing high-strength bolt steel for offshore wind power with corrosion fatigue resistance includes the following steps: S1. C, Si, Mn, Cr, Mo and Fe are mixed according to the above mass fractions and smelted in a vacuum induction furnace at 1650°C to obtain bolt steel ingots; S2. The bolt steel ingot is forged at 1150℃ to eliminate the structural defects generated during the casting process. The forged bolt steel ingot is heated to 1200℃ and held at this temperature for 2 hours to fully austenitize it. Then it is rolled at an initial rolling temperature of 1100℃ and a final rolling temperature of 875℃ to obtain bolt steel round bars. S3. After holding the bolt steel round bar at 850℃ for 1 hour, it is quenched and then tempered at 560℃ for 1 hour. After tempering, it is water-cooled to room temperature to obtain high-strength bolt steel for offshore wind power.

[0038] The morphology of the high-strength bolt steel for offshore wind power prepared in Examples 1-2 and Comparative Example 1 was characterized using scanning electron microscopy (SEM). The results are as follows: Figure 1 As shown, where Figure 1 Image (a) in the figure is a SEM image of the high-strength bolt steel used in offshore wind power in Comparative Example 1. Figure 1 Image (b) is a SEM image of the high-strength bolt steel for offshore wind power in Example 1. Figure 1 Image (c) in Example 2 is a SEM image of the high-strength bolt steel for offshore wind power. From... Figure 1 As can be seen from the data, the high-strength bolt steel for offshore wind power in Comparative Example 1 and Examples 1-2 are both tempered martensite structures. The addition of Nb and Ce can significantly refine the tempered cementite / carbides, which is beneficial to improving the strength, toughness and corrosion resistance of the steel.

[0039] The morphology of the high-strength bolt steel for offshore wind power prepared in Examples 1-2 and Comparative Example 1 was characterized by transmission electron microscopy (TEM). The results are as follows: Figure 2 As shown, where Figure 2 (a) in the figure is a TEM image of the high-strength bolt steel for offshore wind power in Comparative Example 1. Figure 2 Image (b) is a TEM image of the high-strength bolt steel for offshore wind power in Example 1. Figure 2 Image (c) is a TEM image of the high-strength bolt steel for offshore wind power in Example 2. From... Figure 2 As can be seen, in Comparative Example 1, the high-strength bolt steel for offshore wind power forms continuous or chain-like coarse cementite along the original austenite grain boundaries, which can capture more free hydrogen and generate greater stress and strain concentration at the phase interface. At the same time, the coarse cementite can induce obvious microgalvanic corrosion effect, thus easily inducing the initiation of corrosion fatigue cracks. In Examples 1 and 2, the high-strength bolt steel for offshore wind power forms dispersed fine needle-like or ellipsoidal cementite within the grains and at the grain boundaries. In particular, the cementite in Nb-containing steel is significantly refined, making it less likely to induce the initiation of corrosion fatigue cracks.

[0040] The microstructure of the high-strength bolt steel for offshore wind power prepared in Examples 1-2 and Comparative Example 1 was characterized using scanning electron microscopy (SEM) equipped with an electron backscatter diffraction (EBSD) detector. The results are as follows: Figure 3 As shown, where Figure 3 (a) in the figure is the EBSD grain boundary characteristic diagram of the high-strength bolt steel for offshore wind power in Comparative Example 1. Figure 3 (b) in the figure is the EBSD grain boundary characteristic diagram of the high-strength bolt steel for offshore wind power in Example 1. Figure 3 (c) in the figure is the EBSD grain boundary characteristic map of the high-strength bolt steel for offshore wind power in Example 2. The large-angle grain boundary density and total grain boundary density were obtained through EBSD data analysis, and the results are as follows: Figure 4 As shown.

[0041] from Figure 3 and Figure 4As can be seen, the addition of Ce has little effect on the density of large and small angle grain boundaries, while the addition of Nb can increase the grain boundary density, especially the density of small angle grain boundaries. Numerous studies have shown that small angle grain boundaries have an inhibitory effect on crack initiation and propagation, thus improving the corrosion fatigue resistance of steel.

[0042] The high-strength bolt steel for offshore wind power prepared in Comparative Example 1 and Examples 1-2 were subjected to mechanical property tests according to the national standard GB / T 228-09. The results are as follows. Figure 5 As shown in Table 1, where Figure 5 Table 1 shows the stress-strain curves of the high-strength bolt steel for offshore wind power prepared in Comparative Example 1 and Examples 1-2, and the mechanical properties of the high-strength bolt steel for offshore wind power prepared in Comparative Example 1 and Examples 1-2. Figure 5 As can be seen from Table 1, the high-strength bolt steel obtained by this invention has a yield strength of over 1000 MPa, a tensile strength of over 1100 MPa, and an elongation of over 10%, exhibiting excellent strength and toughness.

[0043] Table 1 Mechanical properties of bolt steel in Comparative Example 1 and Examples 1-2

[0044] The corrosion fatigue resistance of high-strength bolt steel for offshore wind power prepared in Comparative Example 1 and Examples 1-2 was tested using an axial stress-controlled corrosion fatigue test method. The test conditions were a simulated marine crevice environment solution (3.5% NaCl solution, pH=4), with peak stresses of 800 MPa, 700 MPa, 600 MPa, and 500 MPa, a stress ratio of 0.1, and a frequency of 1 Hz. The results are as follows: Figure 6 As shown, from Figure 6 As can be seen, there are significant differences in the stress-life (SN) curves of the high-strength bolt steel for offshore wind power in corrosive environments of Comparative Example 1, Example 1, and Example 2. The SN curve of Comparative Example 1 is generally on the far left, and its fatigue life is the shortest under the same stress level. The fatigue life decreases rapidly with increasing stress, and its corrosion fatigue performance is the worst. The SN curve of Example 1 of the present invention is generally shifted to the right, and it shows a high fatigue life in the entire stress range. The SN curve of Example 2 of the present invention is also significantly shifted to the right compared to Comparative Example 1, especially in the high stress region, indicating that the high-strength bolt steel with rare earth Ce microalloying has a more obvious advantage in the high stress region.

[0045] The improvement rate of fatigue life of Examples 1 and 2 under different stress levels relative to Comparative Example 1 was calculated, and the results are shown in Table 2. Table 2 shows that, compared to Comparative Example 1, Examples 1-2 achieved a fatigue life improvement rate of 30%-160% under different stress levels, indicating that the present invention significantly improved the corrosion fatigue life of bolt steel in marine environments through the microalloying of Nb and Ce, achieving good results.

[0046] Table 2. Fatigue life improvement rate of Examples 1-2 compared to Comparative Example 1 under different stress levels.

[0047] Scanning electron microscopy (SEM) was used to characterize the corrosion fatigue fracture morphology of the high-strength bolt steel for offshore wind power obtained in Comparative Example 1 and Examples 1-2 in a simulated marine environment. The results are as follows: Figure 7 As shown, where Figure 7 Image (a) in the figure is a SEM image of the port side under a 1 mm scale in Comparative Example 1. Figure 7 (b) in the figure is a SEM image of the port side at a scale of 50 μm in Comparative Example 1. Figure 7 Image (c) in the figure is a SEM image of the port side under a 1mm scale in Example 1. Figure 7 Image (d) in the figure is a SEM image of the port side of Example 1 on a 50 μm scale. Figure 7 Image (e) in Example 2 is a side view of the port under a 1mm scale. Figure 7 (f) is a port side SEM image of Example 2 on a 50μm scale.

[0048] from Figure 7 As can be seen, there are significant differences in the side surface morphology after corrosion fatigue fracture between Comparative Example 1 and Examples 1-2 of the present invention. Comparative Example 1 exhibits numerous intergranular corrosion morphologies and intergranular microcracks near the fracture surface, indicating that Comparative Example 1 is prone to intergranular corrosion under acidic marine environments and fatigue loads. This is due to the interactive coupling effect of micro-galvanic corrosion and stress concentration between the intergranular cementite and the matrix, thereby inducing the initiation and propagation of intergranular corrosion and intergranular cracks. Examples 1 and 2 show significantly improved surface corrosion morphology; no intergranular corrosion or intergranular cracks were observed on the surface, and the overall corrosion morphology is uniform, with only a few shallow corrosion pits. This indicates that intergranular corrosion in Examples 1-2 is effectively suppressed, avoiding the initiation of intergranular corrosion fatigue cracks. This is attributed to the fact that Nb and Ce inhibit the precipitation and coarsening of intergranular cementite, reducing micro-galvanic corrosion between the coarse intergranular cementite and the matrix, and suppressing the initiation of intergranular corrosion and cracks.

[0049] Therefore, the present invention adopts the above-mentioned corrosion fatigue resistant high-strength bolt steel for offshore wind power and its preparation method. By adding trace amounts of Nb and Ce elements to the high-strength bolt steel, the grains can be significantly refined, the grain boundary distribution characteristics can be changed, the precipitation of coarse cementite at the grain boundaries can be reduced, and the dispersion precipitation of nanoscale fine cementite within the grains and at the grain boundaries can be promoted. This reduces the segregation of hydrogen at large-angle grain boundaries, alleviates the microgalvanic corrosion effect, and inhibits the initiation and propagation of corrosion fatigue cracks, thereby obtaining excellent corrosion fatigue resistance.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A high-strength bolt steel for offshore wind power that is resistant to corrosion fatigue, characterized in that: Based on a mass fraction of 100%, it includes 0.38%-0.45% C, 0.17%-0.37% Si, 0.50%-0.80% Mn, 0.9%-1.2% Cr, 0.15%-0.25% Mo, P≤0.03%, S≤0.03%, and at least one element selected from Nb and Ce; Specifically, when Nb is present, its mass fraction is 0.04%-0.20%; when Ce is present, its mass fraction is 0.001%-0.1%. The balance is Fe and unavoidable impurities.

2. The method of producing a high-strength bolt steel for offshore wind power with corrosion fatigue resistance according to claim 1, characterized in that: Includes the following steps: S1. Mix C, Si, Mn, Cr, Mo, Nb, Ce, and Fe, melt, and cast to obtain bolt steel ingots; S2. Forging, heat preservation, and rolling of bolt steel ingots to obtain bolt steel round bars; S3. Quench and temper the round bolt steel to obtain high-strength bolt steel for offshore wind power that is resistant to corrosion fatigue.

3. The method of claim 2, wherein the method comprises: In S1, the melting temperature is 1600-1700℃. ​ 4. The method of claim 2, wherein the method is characterized by: In S2, the forging temperature is 1100-1200℃.

5. The method of claim 2, wherein the method is characterized by: In S2, the heat preservation temperature is 1150-1250℃, and the heat preservation time is 1-2 hours.

6. The method of claim 2, wherein the method is characterized by: In S2, the initial rolling temperature is 1000-1200℃, and the final rolling temperature is 850-900℃.

7. The method of claim 2, wherein the method is characterized by: In S3, the holding temperature before quenching is 850-900℃, and the holding time before quenching is 0.5-1h.

8. The method of claim 2, wherein the method is characterized by: In S3, the tempering temperature is 500-600℃, and the tempering holding time is 0.5-1h.

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