500 mpa-grade wind power steel having high strength, toughness and high crack arrest toughness, and production method therefor

Abstract

Disclosed is a 500 MPa-grade wind power steel having high strength, toughness and high crack arrest toughness, comprising the following alloy components in percentage by mass: 0.06-0.09% of C, 0.20-0.60% of Si, 1.48-1.80% of Mn, 0.15-0.30% of Ni, 0.02-0.04% of Al, 0.02-0.08R of Nb+V+Ti, 0.2-0.4% of Cr, 0.01-0.02% of Cu, 0.01-0.03% of Zr, P≤0.008%,,S≤0.003%, and the balance being Fe and other inevitable impurity elements. The present invention is based on a low-carbon equivalent composition design. The microstructure of the resulting steel plate is a heterogeneous structure composed of coarse quasi-polygonal ferrite and fine acicular ferrite. The steel plate has a thickness of 20-60 mm, a yield strength ≥ 500 MPa, a tensile strength ≥ 660MPa, a percentage elongation after fracture ≥ 20%, an impact energy at -40ºC ≥ 250 J, a CTOD value at -20ºC ≥ 0.8 mm, a fatigue strength > 640 MPa under the conditions of a stress ratio of 0.5 and 107 cycles, and a critical crack length > 25 mm when fatigue failure occurs. The present invention can meet the development requirements of wind power steel.

Description

A high-strength, high-toughness, and high-cracking-toughness 500MPa grade wind power steel and its production method

[0001] This application claims priority to Chinese Patent Application No. 202510202642.8, filed on February 24, 2025, entitled "A 500MPa Grade Wind Power Steel with High Strength, Toughness and High Crack Arrest Toughness and Its Production Method", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to the field of steel production technology, and more specifically, to a 500MPa grade wind power steel with high strength, toughness, and crack arrest toughness, and its production method. Background Technology

[0003] Under the "dual-carbon" strategic goal, new energy industries, including wind power, hydrogen energy, and photovoltaic power, have become key development areas, playing a significant role in supporting energy structure adjustment. In 2023, newly installed capacity of wind power and photovoltaic power reached 75.9GW and 216.3GW respectively, once again ranking first in the world in terms of installed capacity. With the arrival of the era of grid parity for wind power, the pressure to reduce costs has increased, and the trend towards larger wind turbines as a major cost-reduction measure has attracted attention, leading to a rapid increase in the single-unit capacity of newly added units. Currently, the single-unit capacity of onshore wind power has exceeded 10MW, while the single-unit capacity of offshore wind power is developing towards 18MW and 20MW. Furthermore, many regions have also issued relevant policies to promote "replacing small with large" projects, encouraging the upgrading and replacement of units that have been in operation for over 15 years and have a single-unit capacity of <1.5MW. The increasing size of wind turbines and their harsh service environment have placed higher demands on the performance of steel used in wind power. Currently, the strength levels of steel used in wind power are mainly 355MPa and 420MPa, with a lack of development and application of higher-strength steel grades.

[0004] Patent CN115537681A discloses a 500MPa grade steel plate with high toughness, low yield strength ratio, and low longitudinal and transverse strength anisotropy, and its manufacturing method. The alloy composition is designed as follows: C: 0.10–0.12%, Si: 0.20–0.30%, Mn: 1.15–1.65%, P≤0.013%, S≤0.030%, Ti: 0.008–0.016%, Nb: 0.008–0.030%, V: 0.050–0.065%, Cr: 0. 0.05~0.30%, Alt: 0.020~0.040%; A controlled rolling and cooling process is adopted, strictly controlling the reduction rate and cooling rate of each rolling pass. During the cooling process, when the steel plate thickness is ≥50mm, the steel plate is slowly cooled at a temperature not lower than 250℃ and held for more than 24 hours, after which the steel plate is naturally air-cooled to room temperature; the resulting extra-thick corrosion-resistant steel plate with a thickness of 16~100mm has a yield strength of 389~423MPa, a tensile strength of 401~445MPa, and an impact energy of 271~344J at -40℃. However, the strength of the extra-thick corrosion-resistant steel plate protected by this patent is relatively low, resulting in higher product costs.

[0005] Patent CN118147412A discloses a method for preparing Q500ME high-strength and high-toughness wind power steel plates. The alloy composition is designed as follows: C: 0.10–0.12%, Si: 0.20–0.30%, Mn: 1.55–1.70%, P≤0.015%, S≤0.005%, Nb: 0.040–0.050%, V: 0.035–0.045%, Ti: 0.012–0.022%, Cr: 0.20–0.3%. 0%, Al: 0.020~0.035%, balance being Fe and unavoidable impurities; processed using controlled rolling and cooling methods, with a finishing rolling initial rolling temperature ≤900℃ and a final rolling temperature ≤800℃, followed by laminar flow cooling at a final cooling temperature of 600~630℃; yielding steel plates with a yield strength ≥500MPa, tensile strength 610~770MPa, elongation after fracture ≥17%, and impact energy ≥150J at -40℃, while also possessing easy formability, easy welding, and good fatigue resistance. However, its impact energy at -40℃ is relatively low, limiting its practical applications.

[0006] The aforementioned existing technologies all involve a 500MPa grade steel plate and its production method. However, these methods all require precise control of microalloying element content and production process parameters, making production quite challenging. Furthermore, none of the existing technologies address the fatigue and crack arrest properties of the steel plate, and their strength and low-temperature impact toughness are relatively low. Therefore, to meet the current demand for upgrading and replacing steel used in wind turbine towers, redesigning the alloy composition and production process of 500MPa grade wind turbine steel plates, while ensuring compliance with standards and maintaining the steel plate's strength and toughness, while simultaneously improving its fatigue and crack arrest properties, has become a pressing technical challenge for those skilled in the art. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a 500MPa grade wind power steel with high strength, high toughness and high crack arrest toughness and its production method, so as to meet the development needs of wind power steel.

[0008] This invention provides a 500MPa grade wind power steel with high strength, toughness, and high crack arrest toughness, comprising the following alloy composition by mass percentage:

[0009] C: 0.06–0.09%;

[0010] Si: 0.20–0.60%;

[0011] Mn: 1.48–1.80%;

[0012] Ni: 0.15–0.30%;

[0013] Al: 0.02–0.04%;

[0014] Nb+V+Ti: 0.02~0.08%;

[0015] Cr: 0.2–0.4%;

[0016] Cu: 0.01–0.02%;

[0017] Zr: 0.01~0.03%;

[0018] P≤0.008%;

[0019] S≤0.003%;

[0020] The remainder consists of Fe and other unavoidable impurity elements.

[0021] Preferably, the steel has a Ceq of <0.42%.

[0022] Preferably, the microstructure of the steel is quasi-polygonal ferrite, acicular ferrite and a small amount of granular bainite, with an average grain size of <5μm.

[0023] Preferably, the steel has a thickness of 25mm to 60mm, a yield strength ≥500MPa, a tensile strength ≥680MPa, and an elongation after fracture ≥20%.

[0024] Preferably, the steel has an impact energy of ≥250J at -40℃ and a CTOD characteristic value of >0.8mm at -20℃.

[0025] Preferably, the steel is subjected to a stress ratio of 0.5 and 10 cycles. 7 The fatigue strength under the given conditions is >640MPa, and the critical crack length of the microstructure at the time of fatigue failure is >25mm.

[0026] This invention also provides a method for producing the high-strength, high-toughness, and high-cracking-toughness 500MPa grade wind power steel described in the above technical solution, comprising the following steps:

[0027] The alloy components are sequentially smelted, continuously cast, heated, rolled and cooled to obtain the product.

[0028] Preferably, the thickness of the heated billet is 100mm to 300mm, the holding temperature is 1150℃ to 1210℃, and the furnace time is 240min to 260min.

[0029] Preferably, the thickness of the rolled intermediate billet is 50mm to 100mm, the initial rolling temperature is 880℃ to 960℃, the final rolling temperature is 850℃ to 890℃, and the total number of finishing rolling passes is 6 to 10.

[0030] Preferably, the thickness of the cooled finished product is 25mm to 60mm, the initial cooling temperature is 770℃ to 870℃, and the final cooling temperature is 450℃ to 550℃.

[0031] This invention provides a high-strength, high-toughness, and high-crack-arresting-toughness 500MPa grade wind power steel and its production method; the steel comprises the following alloy composition by mass percentage: C: 0.06-0.09%; Si: 0.20-0.60%; Mn: 1.48-1.80%; Ni: 0.15-0.30%; Al: 0.02-0.04%; Nb+V+Ti: 0.02-0.08%; Cr: 0.2-0.4%; Cu: 0.01-0.02%; Zr: 0.01-0.03%; P≤0.008%; S≤0.003%; the remainder being Fe and other unavoidable impurity elements. Compared with existing technologies, this invention is based on a low-carbon equivalent composition design and strictly controls the hot rolling and cooling process parameters. The resulting steel plate has a heterogeneous structure composed of coarse quasi-polygonal ferrite and fine acicular ferrite. The steel plate thickness is 20-60 mm, and the yield strength is ≥500 MPa, tensile strength is ≥660 MPa, elongation after fracture is ≥20%, impact energy at -40℃ is ≥250 J, and CTOD value at -20℃ is ≥0.8 mm. Under a stress ratio of 0.5 and 10 cycles... 7 Under these conditions, the fatigue strength of the steel plate is >640MPa, and the critical crack length of the steel plate when fatigue failure occurs is >25mm, which can meet the development needs of wind power steel. Attached Figure Description

[0032] Figure 1 shows the microstructure of the 25mm thick 500MPa grade wind power steel of Example 1;

[0033] Figure 2 shows the fracture morphology of the 25mm thick 500MPa grade wind power steel impact specimen at -40℃ in Example 1.

[0034] Figure 3 shows the fracture morphology of the CTOD sample of 25mm thick 500MPa grade wind power steel in Example 1 at -20℃.

[0035] Figure 4 shows the microstructure of the 40mm thick 500MPa grade wind power steel of Example 2;

[0036] Figure 5 shows the fracture morphology of a 40mm thick 500MPa grade wind power steel impact specimen at -40℃ from Example 2.

[0037] Figure 6 shows the fracture morphology of the CTOD sample of 40mm thick 500MPa grade wind power steel in Example 2 at -20℃. Detailed Implementation

[0038] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0039] This invention provides a 500MPa grade wind power steel with high strength, toughness, and high crack arrest toughness, comprising the following alloy composition by mass percentage:

[0040] C: 0.06–0.09%;

[0041] Si: 0.20–0.60%;

[0042] Mn: 1.48–1.80%;

[0043] Ni: 0.15–0.30%;

[0044] Al: 0.02–0.04%;

[0045] Nb+V+Ti: 0.02~0.08%;

[0046] Cr: 0.2–0.4%;

[0047] Cu: 0.01–0.02%;

[0048] Zr: 0.01~0.03%;

[0049] P≤0.008%;

[0050] S≤0.003%;

[0051] The remainder consists of Fe and other unavoidable impurity elements;

[0052] Preferred options are:

[0053] C: 0.09%;

[0054] Si: 0.22–0.23%;

[0055] Mn: 1.48–1.50%;

[0056] Ni: 0.18–0.20%;

[0057] Al: 0.02%;

[0058] Nb+V+Ti: 0.06~0.07%;

[0059] Cr: 0.35%;

[0060] Cu: 0.01%;

[0061] Zr: 0.02–0.03%;

[0062] P: 0.008%;

[0063] S: 0.002%;

[0064] The remainder consists of Fe and other unavoidable impurity elements.

[0065] In this invention, the role of the alloy composition (alloying elements) of the steel is as follows:

[0066] C: Carbon (C) is the main alloying element in low-alloy steel, significantly affecting the strength, low-temperature toughness, crack arrest performance, and weldability of the steel plate. From the perspective of improving the mechanical properties of the steel plate, a relatively high C content should be maintained. However, a high C content will deteriorate the weldability of the steel plate. Simultaneously, from the perspective of the production cost of high-strength and high-toughness steel plates, the C content should not be controlled too low. An excessively low C content will cause excessively high grain boundary mobility, leading to coarse microstructure in the steel plate and the weld heat-affected zone, thereby reducing the low-temperature toughness of the base plate and the heat-affected zone. Therefore, in this invention, the reasonable range for C content is 0.06%–0.09%.

[0067] Si: While Si can promote deoxidation of molten steel and increase the strength of steel plates, during welding, Si promotes the formation of macromolecular islands (MA islands) at the weld joint. These MA islands are large and unevenly distributed, severely deteriorating the low-temperature toughness and crack arrest characteristics of the weld heat-affected zone. Therefore, the Si content in the steel of this invention should be controlled within a reasonable range. Considering smelting level and manufacturing cost, the Si content should be 0.20–0.60%.

[0068] Mn: The main function of Mn is to expand the austenite phase region, lower the Ar3 phase transformation point, and refine the microstructure of the steel plate to improve its low-temperature toughness and crack arrest properties. However, when the Mn content is too high, it will undergo conjugate segregation with C, P, and S during the solidification process of molten steel, forming a severe segregated zone in the core of the billet. This leads to abnormal microstructures during subsequent rolling, cooling, and welding, causing fluctuations in the impact energy of the steel plate core and resulting in unstable performance. Therefore, the appropriate Mn content in this invention should be 1.48–1.80%.

[0069] Ni: Ni is a key element for achieving good low-temperature toughness in low-alloy steel. Ni and Fe are infinitely soluble in each other, which can expand the austenite phase region, lower the austenite-to-ferrite phase transformation temperature, thereby refining the grains and improving the low-temperature toughness of the steel plate. Moreover, Ni has little effect on the weldability of the steel plate. Theoretically, the higher the Ni content within an appropriate range, the better. However, considering production costs, the reasonable Ni content in this invention should be 0.15%–0.30%.

[0070] Nb+V+Ti: The main functions of Nb, V, and Ti are similar. At high temperatures, they combine with C and N atoms to form Nb(C,N), VC, and TiN particles, inhibiting austenite grain growth during TMCP and refining the ferrite grain size in the steel plate, thereby improving the mechanical properties of the steel plate. However, when the Nb content is below 0.01% and the Ti content is below 0.008%, the refining effect on the original austenite grains is not significant, and the improvement in mechanical properties is not obvious. However, when the Nb content exceeds 0.03%, granular bainite or Nb(C,N) secondary precipitation embrittlement is easily induced at the weld joint during welding. When the Ti content is too high, it combines with N to form TiN particles, resulting in a reduction in the number of BN particles, which cannot guarantee the low-temperature toughness of the heat-affected zone after welding. Considering both production costs and actual performance requirements, the total Nb+V+Ti content in this invention should be in the range of 0.02% to 0.08%.

[0071] Cr: Appropriate Cr addition can improve the hardenability of the steel plate without compromising its low-temperature toughness, thereby improving its strength and weather resistance. When the Cr content is too low (<0.05%), its contribution to the strength and toughness of the steel plate is insufficient, and it cannot fully compensate for the strength reduction caused by the decrease in carbon equivalent. When the Cr content is too high (>0.40%), coarse bainite or Widmanstätten structure easily forms in the heat-affected zone after welding, leading to a significant reduction in the low-temperature toughness and plasticity of the weld heat-affected zone. Therefore, the Cr content in this invention should be controlled within the range of 0.2% to 0.4%.

[0072] Cu: The addition of a small amount of Cu can lower the Ar3 phase transformation point and, through combined action with other alloying elements, improve the strength of the steel plate, low-temperature toughness, and surface corrosion resistance. Too low a Cu content has limited effect on performance improvement. However, too high a Cu content not only increases the production cost of the steel plate but also forms Cu GP zones during heating and rolling, thus deteriorating the low-temperature toughness of the steel plate and, in severe cases, causing copper embrittlement. Considering all factors, the Cu content in this invention should be controlled between 0.01% and 0.02%.

[0073] Zr, as an element in the same group as and adjacent to Ti, has a strong chemical affinity for elements such as O, N, S, and C. It can refine and modify inclusions in low-alloy Ti-containing steels. A suitable amount of Zr, with its strong deoxidizing ability and high yield, can effectively inhibit grain coarsening in the heat-affected zone and promote acicular ferrite nucleation, thereby improving the weldability of low-alloy high-strength steel plates. However, the Zr content has little effect on the strength and plasticity of low-alloy steel, but the low-temperature toughness of the steel plate is best when the Zr content is between 0.01% and 0.03%. Therefore, the reasonable range for Zr content in this invention should be 0.01% to 0.03%.

[0074] P and S: P and S are harmful elements in steel, which have a great detrimental effect on the low-temperature toughness, weldability and fatigue performance of steel. Theoretically, the lower the content of the two, the better. However, considering the actual operation and cost of steelmaking process, the P content in this invention needs to be controlled at ≤0.008% and the S content should be controlled at ≤0.003%.

[0075] In this invention, the Ceq (carbon equivalent) of the high-strength, high-toughness, and high-cracking-toughness 500MPa grade wind power steel is preferably <0.42%, and Ceq=C+Mn / 6+Si / 24+Ni / 40+Mo / 4+V / 14.

[0076] In this invention, the microstructure of the 500MPa grade wind power steel with high strength, high toughness and high crack arrest toughness is preferably mainly quasi-polygonal ferrite, acicular ferrite and a small amount of granular bainite in the full thickness direction, and the average grain size is preferably <5μm.

[0077] In this invention, the thickness of the high-strength, high-toughness, and high-crack-arresting-toughness 500MPa grade wind power steel is preferably 25mm to 60mm, specifically 25mm or 40mm.

[0078] In this invention, the high-strength, high-toughness, and high-crack-arresting-toughness 500MPa grade wind power steel preferably has a yield strength ≥500MPa, a tensile strength ≥680MPa, an elongation after fracture ≥20%, an impact energy at -40℃ ≥250J, and a CTOD characteristic value at -20℃ >0.8mm.

[0079] In this invention, the high-strength, high-toughness, and high-cracking-toughness 500MPa grade wind power steel is subjected to a stress ratio of 0.5 and 10 cycles. 7 The fatigue strength under the conditions is preferably >640MPa, and the critical crack length of the microstructure at the time of fatigue failure is preferably >25mm.

[0080] This invention also provides a method for producing the high-strength, high-toughness, and high-cracking-toughness 500MPa grade wind power steel described in the above technical solution, comprising the following steps:

[0081] The alloy components are sequentially smelted, continuously cast, heated, rolled and cooled to obtain 500MPa grade wind power steel with high strength, toughness and high crack arrest toughness.

[0082] This invention employs a controlled rolling and cooling process, shortening the production process. This invention does not impose special limitations on the smelting and continuous casting processes; any techniques familiar to those skilled in the art for preparing alloy components into billets can be used. In a preferred embodiment of this invention, smelting and casting are preferably carried out according to the aforementioned alloy composition, and continuous casting is used to form slabs. A dynamic light reduction and heavy reduction synergistic control technology is employed to reduce center segregation in continuously cast billets larger than 200mm, with the light reduction controlled between 2% and 5%.

[0083] The main processes for producing steel plates according to this invention include: heating process (i.e. heating of the billet), controlled rolling process and controlled cooling process (i.e. controlled rolling and controlled cooling). The controlled rolling process is divided into two stages: rough rolling and finish rolling. In the rough rolling stage, the single-pass reduction is >15% and the cumulative reduction rate is >50% to fully refine the original austenite grains in the billet.

[0084] In this invention, the thickness of the heated billet is preferably 100mm to 300mm, more preferably 200mm. During the heat treatment of the billet, in order to ensure the complete solid solution of microalloying elements such as Nb, V and Ti, the holding temperature is preferably 1150℃ to 1210℃, more preferably 1194℃ to 1202℃, and the furnace time is preferably 240min to 260min, more preferably 245min to 256min.

[0085] In this invention, the thickness of the intermediate slab is preferably 50mm to 100mm, more preferably 80mm. In the finishing rolling process, the initial rolling temperature is preferably 880℃ to 960℃, more preferably 882℃ to 937℃, and the final rolling temperature is preferably 850℃ to 890℃, more preferably 864℃ to 881℃. The total number of finishing rolling passes is preferably 6 to 10, more preferably 7. This invention performs thorough rolling in the non-recrystallized austenite region, refining the original austenite grains, thereby obtaining uniform and fine ferrite grains and improving the overall performance of the steel plate.

[0086] In this invention, the thickness of the cooled finished product is preferably 25mm to 60mm, more preferably 25mm to 40mm. The post-rolling controlled cooling process preferably uses water cooling. The initial cooling temperature is preferably 770℃ to 870℃, more preferably 824℃ to 855℃, and the final cooling temperature is preferably 450℃ to 550℃, more preferably 505℃ to 530℃. The steel plate is then air-cooled to room temperature. A higher initial cooling temperature can slow down the enrichment of carbon elements within the original austenite grains, reduce the proportion of bainite in the final microstructure, and avoid localized mixed crystal phenomena.

[0087] This invention provides a high-strength, high-toughness, and high-crack-arresting-toughness 500MPa grade wind power steel and its production method; the steel comprises the following alloy composition by mass percentage: C: 0.06-0.09%; Si: 0.20-0.60%; Mn: 1.48-1.80%; Ni: 0.15-0.30%; Al: 0.02-0.04%; Nb+V+Ti: 0.02-0.08%; Cr: 0.2-0.4%; Cu: 0.01-0.02%; Zr: 0.01-0.03%; P≤0.008%; S≤0.003%; the remainder being Fe and other unavoidable impurity elements. Compared with existing technologies, this invention is based on a low-carbon equivalent composition design and strictly controls the hot rolling and cooling process parameters. The resulting steel plate has a heterogeneous structure composed of coarse quasi-polygonal ferrite and fine acicular ferrite. The steel plate thickness is 20-60 mm, and the yield strength is ≥500 MPa, tensile strength is ≥660 MPa, elongation after fracture is ≥20%, impact energy at -40℃ is ≥250 J, and CTOD value at -20℃ is ≥0.8 mm. Under a stress ratio of 0.5 and 10 cycles... 7 Under these conditions, the fatigue strength of the steel plate is >640MPa, and the critical crack length of the steel plate when fatigue failure occurs is >25mm, which can meet the development needs of wind power steel.

[0088] To further illustrate the present invention, the following embodiments will be described in detail.

[0089] Example 1

[0090] The thickness of the 500MPa grade wind power steel plate with high strength and high crack arrest toughness in this embodiment is 25mm, and its chemical composition and percentage are shown in Table 1.

[0091] The production method of the 500MPa grade wind power steel plate with excellent low-temperature toughness in this embodiment includes smelting, continuous casting, heating, rolling and cooling processes. The specific parameters of the heating, rolling and cooling processes are as follows:

[0092] (1) Heating process: billet thickness 200mm, holding temperature 1202℃, furnace time 245min;

[0093] (2) Rolling process: intermediate billet thickness 80mm, finishing rolling start temperature 937℃, finishing rolling temperature 881℃, finishing rolling total 7 passes;

[0094] (3) Cooling process: The finished product thickness is 25mm, the initial cooling temperature is 855℃, and the final cooling temperature is 505℃.

[0095] The microstructure of the high-strength and high-toughness 500MPa grade wind power steel plate prepared in this embodiment is shown in Figure 1. It can be seen that the microstructure is mainly composed of quasi-polygonal and acicular ferrite. The various mechanical properties of the steel plate are shown in Table 2. The fracture morphology of the standard V-shaped impact specimen of the steel plate at -40℃ is shown in Figure 2. The fracture morphology of the CTOD specimen of the steel plate at -20℃ is shown in Figure 3.

[0096] Example 2

[0097] The 500MPa grade wind power steel plate of this embodiment has a thickness of 40mm and its chemical composition and percentage are shown in Table 1.

[0098] The production method of the 500MPa grade wind power steel plate with excellent low-temperature toughness in this embodiment includes smelting, continuous casting, heating, rolling and cooling processes. The specific parameters of the heating, rolling and cooling processes are as follows:

[0099] (1) Heating process: billet thickness 200mm, holding temperature 1194℃, furnace time 256min;

[0100] (2) Rolling process: intermediate billet thickness 80mm, finishing rolling start temperature 882℃, finishing rolling temperature 864℃, finishing rolling total 7 passes;

[0101] (3) Cooling process: The finished product thickness is 40mm, the initial cooling temperature is 824℃, and the final cooling temperature is 530℃.

[0102] The microstructure of the high-strength and high-toughness 500MPa grade wind power steel plate prepared in this embodiment is shown in Figure 4. It can be seen that the microstructure is mainly composed of quasi-polygonal and acicular ferrite. The various mechanical properties of the steel plate are shown in Table 2. The fracture morphology of the standard V-shaped impact specimen of the steel plate at -40℃ is shown in Figure 5. The fracture morphology of the CTOD specimen of the steel plate at -20℃ is shown in Figure 6.

[0103] Table 1. Chemical composition and percentage (wt%) of the high-strength, high-crack-arresting-toughness 500MPa grade wind power steel plates provided in Examples 1-2

[0104] Table 2 shows the mechanical properties of the high-strength, high-crack-arresting-toughness 500MPa grade wind power steel plates provided in Examples 1 and 2.

[0105] Experimental results show that:

[0106] The present invention provides a high-strength, high-crack-arresting toughness 500MPa grade wind power steel plate with a thickness of 25-60mm, yield strength ≥500MPa, tensile strength ≥680MPa, elongation after fracture ≥20%, and impact energy ≥250J at -40℃. Based on a three-point bending specimen, the crack tip extension displacement (CTOD) characteristic value is measured using GB / T 21143-2014 "Unified Test Method for Quasi-Static Fracture Toughness of Metallic Materials". The CTOD characteristic value of the steel plate at -20℃ is ≥0.8mm. The steel plate is subjected to a stress ratio of 0.5 and 10 cycles. 7 The fatigue strength under the given conditions is >640 MPa. The critical crack length at which fatigue occurs in the steel plate is determined using the compliance method; the specific formula is as follows:

[0107] In the formula P i B is the load magnitude, and B is the sample thickness. N To determine the thickness of the specimen after processing, B is taken as the thickness, W is the width of the specimen, and a is the thickness of the specimen after processing. i The critical crack length is >25 mm when the steel plate fails due to fatigue.

[0108] In summary, compared with steel plates of the same strength grade, the product provided by this invention has the following beneficial effects:

[0109] The chemical composition design of this invention reduces the carbon content to 0.06-0.09%, increasing the uniformity of the microstructure of the 500MPa grade high-strength, high-crack-arresting toughness wind power steel plate and expanding the phase transformation range; the addition of 0.01-0.03% Zr element reduces central segregation and improves the quality of the billet; by controlling the water cooling temperature, the microstructure of the steel plate is regulated, thereby obtaining a steel plate microstructure mainly composed of quasi-polygonal ferrite and acicular ferrite, which, while possessing high strength and high and low temperature toughness, also exhibits excellent fatigue performance and crack arrest resistance.

[0110] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. 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 the invention. Therefore, the invention 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 disclosed herein.

Claims

1. A high-strength, high-toughness, and high-crack-arresting-toughness 500MPa grade wind power steel, comprising the following alloy composition by weight percentage: C：0.06～0.09％； Si: 0.20–0.60%; Mn: 1.48–1.80%; Ni: 0.15–0.30%; Al：0.02～0.04％； Nb+V+Ti: 0.02~0.08%; Cr：0.2～0.4％； Cu: 0.01–0.02%; Zr：0.01～0.03％； P≤0.008％； S≤0.003％； The remainder consists of Fe and other unavoidable impurity elements.

2. The high strength high crack tough 500 MPa grade steel for wind turbine according to claim 1, characterized in that, The Ceq of steel is less than 0.42%.

3. The high strength high crack tough 500 MPa grade steel for wind mill as claimed in claim 1, wherein, The microstructure of the steel consists of quasi-polygonal ferrite, acicular ferrite, and a small amount of granular bainite, with an average grain size of <5μm.

4. The high strength high crack tough 500 MPa grade steel for wind mill as claimed in claim 1, wherein, The steel has a thickness of 25mm to 60mm, a yield strength ≥500MPa, a tensile strength ≥680MPa, and an elongation after fracture ≥20%.

5. The high tough high crack tough 500 MPa grade steel for wind power application according to claim 1 characterized in that, The impact energy of steel at -40℃ is ≥250J, and the CTOD characteristic value at -20℃ is >0.8mm.

6. The high strength high crack tough 500 MPa grade steel for wind mill as claimed in claim 1, wherein, The fatigue strength of the steel is > 640 MPa at a stress ratio of 0.5, 10 7 cycles and the critical crack length of the microstructure at the time of fatigue failure is > 25 mm.

7. A method for producing 500MPa grade wind power steel with high strength, toughness, and high crack arrest toughness as described in any one of claims 1 to 6, comprising the following steps: The alloy components are sequentially smelted, continuously cast, heated, rolled and cooled to obtain the product.

8. The production method according to claim 7, characterized by, The thickness of the heated billet is 100mm to 300mm, the holding temperature is 1150℃ to 1210℃, and the furnace time is 240min to 260min.

9. The production method according to claim 7, characterized by, The thickness of the intermediate billet is 50mm to 100mm, the initial rolling temperature is 880℃ to 960℃, the final rolling temperature is 850℃ to 890℃, and the total number of finishing rolling passes is 6 to 10.

10. The production method according to claim 7, characterized by, The thickness of the cooled finished product is 25mm to 60mm, the initial cooling temperature is 770℃ to 870℃, and the final cooling temperature is 450℃ to 550℃.

Images