500MPa-grade wind power steel with high strength and toughness and high crack arrest toughness and production method of 500MPa-grade wind power steel

Abstract

The invention discloses 500MPa-grade wind power steel with high strength and toughness and high crack arrest toughness. The 500MPa-grade wind power steel comprises the following alloy components in percentage by mass: 0.06-0.09% of C; 0.20% to 0.60% of Si; mn: 1.48% to 1.80%; 0.15% to 0.30% of Ni; 0.02 to 0.04 percent of Al; 0.02 to 0.08% of Nb, V and Ti; cr: 0.2 to 0.4%; 0.01 to 0.02 percent of Cu; 0.01 to 0.03 percent of Zr; p < = 0.008%; s < = 0.003%; and the balance of Fe and other inevitable impurity elements. On the basis of low-carbon equivalent component design, the structure of the obtained steel plate is a heterogeneous structure composed of coarse quasi-polygonal ferrite and fine acicular ferrite, the thickness of the steel plate is 20-60 mm, the yield strength of the steel plate is larger than or equal to 500 MPa, the tensile strength is larger than or equal to 660 MPa, the percentage elongation after fracture is larger than or equal to 20%, the impact energy at the temperature of-40 DEG C is larger than or equal to 250 J, the CTOD value at the temperature of-20 DEG C is larger than or equal to 0.8 mm, and the fatigue strength gt of the steel plate under the conditions that the stress ratio is 0.5 and circulation is 107 is achieved; the critical crack length gt of the steel plate when fatigue failure occurs under the pressure of 640 MPa; and therefore, the development requirements of steel for wind power can be met.

Description

Technical Field

[0001] The present invention relates to the technical field of steel production, and more specifically, to a 500MPa-grade wind power steel with high strength, toughness and high crack arrest toughness and a production method thereof. Background Art

[0002] Under the strategic goal of "dual carbon", new energy industries including wind power generation, hydrogen energy and photovoltaic power generation have become key development areas and have played a significant role in supporting the adjustment of energy structure. In 2023, the newly installed capacity of wind power generation and photovoltaic power generation will reach 75.9GW and 216.3GW respectively, and the installed capacity will once again rank first in the world. With the advent of the era of wind power parity, the pressure to reduce the cost of wind power has increased. The large-scale wind turbines have attracted attention as the main cost-reduction measures, and the single-unit capacity of new units has risen rapidly. At present, the single-unit capacity of onshore wind power has exceeded 10MW, and the single-unit capacity of offshore wind power has developed towards 18MW and 20MW. In addition, many places have also issued relevant policies to promote the "large-scale replacement of small" projects and encourage the upgrading of units with a single capacity of <1.5MW that have been in operation for more than 15 years. The large-scale wind turbines and their harsh service environment have put forward higher requirements on the performance of wind power steel. At present, the strength levels of wind power steel are mainly 355MPa and 420MPa, and there is a lack of development and application of higher-strength steel grades.

[0003] Patent CN115537681A discloses a 500MPa grade steel plate with high toughness, low yield ratio and low longitudinal and transverse strength anisotropy and a manufacturing method thereof, wherein 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. 05~0.30%,Alt:0.020~0.040%;Adopt controlled rolling and controlled cooling process, strictly control the rolling pass reduction rate and cooling rate, when the thickness of the steel plate is ≥50mm during cooling, the steel plate is slowly cooled, the slow cooling temperature is not less than 250℃, and the temperature is kept for more than 24 hours, and then the steel plate is naturally air-cooled to room temperature; the yield strength of the obtained extra-thick corrosion-resistant steel plate with a thickness of 16~100mm is 389~423MPa, the tensile strength is 401~445MPa, and the impact energy at -40℃ is 271~344J. However, the strength of the extra-thick corrosion-resistant steel plate protected by this patent is relatively low, resulting in higher product costs.

[0004] Patent CN118147412A discloses a method for preparing a Q500ME high-strength and high-toughness steel plate for wind power, wherein 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%, Als: 0.020~0.035%, the balance is Fe and unavoidable impurities; controlled rolling and controlled cooling are used, the finishing rolling temperature is ≤900℃, the final rolling temperature is ≤800℃, and laminar cooling is performed after rolling, and the final cooling temperature is 600~630℃; the steel plate has a yield strength of ≥500MPa, a tensile strength of 610~770MPa, an elongation after fracture of ≥17%, and an impact energy of ≥150J at -40℃, and is easy to form, easy to weld, and has good fatigue resistance. However, its impact energy is low at -40℃, which limits its practical application.

[0005] The above-mentioned prior arts all relate to a 500MPa grade steel plate and its production method, but the production methods all involve precise control of the content of microalloying elements and production process parameters, and the production difficulty is relatively high. In addition, the prior arts have not paid attention to the fatigue performance and crack arrest performance of the steel plate, and the strength and low-temperature impact toughness are relatively low. Therefore, in view of the current demand for upgrading steel for wind power towers, the alloy composition and production process of 500MPa grade wind power steel plates are redesigned. On the basis of meeting the standards, while ensuring the strength and toughness of the steel plates, the fatigue performance and crack arrest performance of the steel plates are improved, which has become a technical problem that needs to be solved urgently by technical personnel in this field. Summary of the invention

[0006] In view of this, the object of the present invention is to provide a 500MPa grade wind power steel with high strength and high crack arrest toughness and a production method thereof to meet the development needs of wind power steel.

[0007] The present invention provides a 500MPa grade wind power steel with high strength and high crack arrest toughness, comprising the following alloy components in percentage by mass:

[0008] C: 0.06~0.09%;

[0009] Si: 0.20~0.60%;

[0010] Mn: 1.48-1.80%;

[0011] Ni: 0.15-0.30%;

[0012] Al: 0.02~0.04%;

[0013] Nb+V+Ti: 0.02~0.08%;

[0014] Cr: 0.2~0.4%;

[0015] Cu: 0.01~0.02%;

[0016] Zr: 0.01~0.03%;

[0017] P≤0.008%;

[0018] S≤0.003%;

[0019] The rest is Fe and other inevitable impurity elements.

[0020] Preferably, the Ceq of the steel is < 0.42%.

[0021] Preferably, the microstructure of the steel is quasi-polygonal ferrite, acicular ferrite and a small amount of granular bainite, and the average grain size is less than 5 μm.

[0022] Preferably, the thickness of the steel is 25 mm to 60 mm, the yield strength is ≥500 MPa, the tensile strength is ≥680 MPa, and the elongation after fracture is ≥20%.

[0023] Preferably, the steel has an impact energy of ≥250 J at -40°C and a CTOD characteristic value of >0.8 mm at -20°C.

[0024] Preferably, the steel is subjected to a stress ratio of 0.5 and a cycle of 10 7 The fatigue strength under the conditions is >640MPa, and the critical crack length of the organization when fatigue failure occurs is >25mm.

[0025] The present invention also provides a method for producing the 500MPa grade wind power steel with high strength, toughness and high crack arrest toughness as described in the above technical solution, comprising the following steps:

[0026] The alloy components are smelted, continuously cast, heated, rolled and cooled in sequence to obtain the product.

[0027] Preferably, the heated ingot has a thickness of 100 mm to 300 mm, a holding temperature of 1150° C. to 1210° C., and a furnace time of 240 min to 260 min.

[0028] Preferably, the thickness of the rolled intermediate billet is 50 mm to 100 mm, the start temperature of the finishing rolling is 880° C. to 960° C., the final rolling temperature is 850° C. to 890° C., and the total number of finishing rolling passes is 6 to 10.

[0029] Preferably, the thickness of the cooled finished product is 25 mm to 60 mm, the start cooling temperature is 770°C to 870°C, and the final cooling temperature is 450°C to 550°C.

[0030] The invention provides a 500MPa-level wind power steel with high strength and high crack arrest toughness and a production method thereof; the steel comprises the following alloy components in percentage by mass: 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 rest are Fe and other inevitable impurity elements. Compared with the prior art, the present invention is based on the design of low carbon equivalent components, strictly controls the hot rolling and cooling process parameters, and the obtained steel plate structure is a heterogeneous structure composed of coarse quasi-polygonal ferrite and fine acicular ferrite. The thickness of the steel plate is 20-60 mm, the yield strength of the steel plate is ≥500 MPa, the tensile strength is ≥660 MPa, the elongation after fracture is ≥20%, the impact energy at -40°C is ≥250 J, the CTOD value at -20°C is ≥0.8 mm, and the stress ratio is 0.5, the cycle is 10 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 steel for wind power. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The microstructure morphology of the 25 mm thick 500 MPa grade wind power steel of Example 1;

[0032] Figure 2 The fracture morphology of the 25 mm thick 500 MPa grade wind power steel -40°C impact specimen of Example 1;

[0033] Figure 3 The fracture morphology of the CTOD sample of 25 mm thick 500 MPa grade wind power steel at -20°C in Example 1;

[0034] Figure 4 The microstructure morphology of the 40 mm thick 500 MPa grade wind power steel of Example 2;

[0035] Figure 5 This is the fracture morphology of the 40mm thick 500MPa grade wind power steel -40℃ impact specimen of Example 2;

[0036] Figure 6 This is the fracture morphology of the CTOD sample of 40 mm thick 500 MPa grade wind power steel at -20°C in Example 2. DETAILED DESCRIPTION

[0037] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The present invention provides a 500MPa grade wind power steel with high strength and high crack arrest toughness, comprising the following alloy components in percentage by mass:

[0039] C: 0.06~0.09%;

[0040] Si: 0.20~0.60%;

[0041] Mn: 1.48-1.80%;

[0042] Ni: 0.15-0.30%;

[0043] Al: 0.02~0.04%;

[0044] Nb+V+Ti: 0.02~0.08%;

[0045] Cr: 0.2~0.4%;

[0046] Cu: 0.01~0.02%;

[0047] Zr: 0.01~0.03%;

[0048] P≤0.008%;

[0049] S≤0.003%;

[0050] The rest is Fe and other unavoidable impurity elements;

[0051] Preferably:

[0052] C: 0.09%;

[0053] Si: 0.22-0.23%;

[0054] Mn: 1.48-1.50%;

[0055] Ni: 0.18-0.20%;

[0056] Al: 0.02;

[0057] Nb+V+Ti: 0.06~0.07%;

[0058] Cr: 0.35%;

[0059] Cu: 0.01%;

[0060] Zr: 0.02~0.03%;

[0061] P: 0.008%;

[0062] S: 0.002%;

[0063] The rest is Fe and other inevitable impurity elements.

[0064] In the present invention, the role of the alloying components (alloying elements) of the steel is as follows:

[0065] C: C is the main alloying element of low alloy steel, which has a great influence on the strength, low temperature toughness, crack arrest performance and welding performance of the steel plate. From the perspective of improving the mechanical properties of the steel plate, a higher C content should be guaranteed. However, a higher C content will deteriorate the welding performance of the steel plate. At the same time, from the perspective of the production cost of high-strength and tough steel plates, the C content should not be controlled too low. Too low a C content will cause the grain boundary mobility to be too high, resulting in coarse structure of the steel plate and the heat affected zone of welding, thereby reducing the low temperature toughness of the mother plate and the heat affected zone. Therefore, in the present invention, the reasonable range of the C content is 0.06-0.09%.

[0066] Si: Si can promote the deoxidation of molten steel and improve the strength of steel plates. However, during the welding process of steel plates, Si elements will promote the formation of MA islands at the welded joints. The MA islands formed are large in size and unevenly distributed, which seriously deteriorates the low-temperature toughness and crack arrest properties of the weld heat affected zone. Therefore, the Si content in the steel of the present invention should be controlled within a reasonable range as much as possible. Considering the smelting level and manufacturing cost, the Si content should be 0.20-0.60%.

[0067] Mn: The main function of Mn is to expand the austenite phase area, reduce the Ar3 phase transformation point, and refine the steel plate structure to improve its low-temperature toughness and crack arrest characteristics. However, when the Mn content is too high, it will cause conjugate segregation with C, P and S during the solidification of molten steel, forming a serious western band in the core of the ingot, and forming abnormal structure in the subsequent rolling, cooling and welding processes, resulting in fluctuations in the impact energy of the core of the steel plate and unstable performance. Therefore, the appropriate Mn content in the present invention should be 1.48-1.80%.

[0068] Ni: Ni is a key element for low alloy steel to obtain good low temperature toughness. Ni and Fe can be infinitely dissolved, which can expand the austenite phase region and reduce the phase transition temperature from austenite to ferrite, thereby refining the grains and improving the low temperature toughness of the steel plate. Moreover, the Ni element has little effect on the welding performance of the steel plate. Theoretically, the higher the Ni content within an appropriate range, the better, but considering the production cost, the reasonable Ni content in the present invention should be 0.15-0.30%.

[0069] Nb+V+Ti: The main functions of Nb, V and Ti elements are similar. At high temperatures, they form Nb(C, N), VC and TiN particles with C and N atoms, inhibit the growth of austenite grains during TMCP, and refine the ferrite grain size in the steel plate, thereby improving the mechanical properties of the steel plate. However, when the Nb content is less than 0.01% and the Ti content is less than 0.008%, the refinement 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%, it is easy to induce performance granular bainite or form Nb(C, N) secondary precipitation embrittlement at the weld joint during welding. When the Ti content is too high, it combines with N to form TiN particles, which leads to a reduction in the number of BN particles, and the low-temperature toughness of the heat-affected zone after welding cannot be guaranteed. Considering the production cost and actual performance requirements, the sum of the Nb+V+Ti content in the present invention should be in the range of 0.02-0.08%.

[0070] Cr: The addition of appropriate Cr can improve the hardenability of the steel plate without damaging the low-temperature toughness of the steel plate, thereby improving the strength and weather resistance of the steel plate. When the Cr content is low (<0.05%), the contribution to the strength and toughness of the steel plate is insufficient, and it cannot completely make up for the strength reduction caused by the reduction of carbon equivalent. When the Cr content is too high (>0.40%), coarse bainite or widmanstattenite structure is easily formed in the heat-affected zone of the steel plate after welding, resulting in a significant decrease in the low-temperature toughness and plasticity of the welding heat-affected zone. Therefore, the Cr content in the present invention should be controlled within the range of 0.2-0.4%.

[0071] Cu: The addition of a small amount of Cu can reduce the Ar3 phase transition point, and react with other alloy elements to enhance the strength of the steel plate, improve the low-temperature toughness and surface corrosion resistance. If the added Cu content is too low, the improvement effect on the performance is limited. However, when the Cu content is too high, it not only increases the production cost of the steel plate, but also forms a Cu GP zone during the heating and rolling process, thereby deteriorating the low-temperature toughness of the steel plate, and in severe cases, it can also cause copper embrittlement. Taking all factors into consideration, the Cu content in the present invention should be controlled at 0.01-0.02%.

[0072] Zr: As an element in the same family and adjacent to Ti, it has a strong chemical affinity for elements such as O, N, S and C, and can refine and modify the inclusions of low-alloy Ti-containing steels. An appropriate amount of Zr with strong deoxidation ability and high yield can effectively inhibit the coarsening of grains in the heat-affected zone and promote the nucleation of acicular ferrite, thereby improving the welding performance of low-alloy high-strength steel plates. However, the Zr content has little effect on the strength and plasticity of low-alloy steels, but when the Zr content is 0.01-0.03%, the low-temperature toughness of the steel plate is the best. Therefore, the reasonable range of the Zr content in the present invention should be 0.01-0.03%.

[0073] P, S: P and S are harmful elements to steel and have a great damaging effect on the low-temperature toughness, welding performance and fatigue performance of steel. In theory, the content of the two should be as low as possible. However, considering the actual operation and cost of the steelmaking process, the P content in the present invention needs to be controlled at ≤0.008%, and the S content should be controlled at ≤0.003%.

[0074] In the present invention, the Ceq (carbon equivalent) of the high-strength and high-crack-arrest toughness 500MPa grade wind power steel is preferably <0.42%, Ceq=C+Mn / 6+Si / 24+Ni / 40+Mo / 4+V / 14.

[0075] In the present invention, the microstructure of the high-strength and high-crack-arrest-toughness 500MPa-grade wind power steel in the full-thickness direction is preferably mainly quasi-polygonal ferrite, acicular ferrite and a small amount of granular bainite, and the average grain size is preferably <5μm.

[0076] In the present invention, the thickness of the high-strength and high-crack-arrest-toughness 500MPa-grade wind power steel is preferably 25mm to 60mm, specifically 25mm and 40mm.

[0077] In the present invention, the yield strength of the high-strength and high-crack-arrest-toughness 500MPa-grade wind power steel is preferably ≥500MPa, the tensile strength is preferably ≥680MPa, the elongation after fracture is preferably ≥20%, the impact energy at -40°C is preferably ≥250J, and the -20°C CTOD characteristic value is preferably >0.8mm.

[0078] In the present invention, the 500MPa grade wind power steel with high strength and high crack arrest toughness is subjected to stress ratio of 0.5 and cycle 10 7 The fatigue strength under certain conditions is preferably >640MPa, and the critical crack length of the tissue when fatigue failure occurs is preferably >25mm.

[0079] The present invention also provides a method for producing the 500MPa grade wind power steel with high strength, toughness and high crack arrest toughness as described in the above technical solution, comprising the following steps:

[0080] The alloy components are smelted, continuously cast, heated, rolled and cooled in sequence to obtain 500MPa grade wind power steel with high strength, toughness and high crack arrest toughness.

[0081] The present invention adopts a controlled rolling and controlled cooling process to shorten the production process flow; the present invention has no special restrictions on the smelting and continuous casting process, and the technical means of making the alloy composition into a casting billet well known to those skilled in the art can be used. In a preferred embodiment of the present invention, smelting and casting are preferably carried out according to the above alloy composition, continuous casting is used to form a slab, and dynamic light pressure and heavy pressure coordinated control technology is used to reduce the center segregation of the continuous casting billet above 200 mm, and the light pressure reduction is controlled between 2% and 5%.

[0082] The main processes for producing steel plates of the present invention include: a heating process (i.e., heating of the ingot), a controlled rolling process and a controlled cooling process (i.e., controlled rolling and controlled cooling), wherein the controlled rolling process is divided into two stages of rolling, namely, a rough rolling process and a finishing rolling process, wherein the single-pass reduction amount in the rough rolling stage is >15%, and the cumulative reduction rate is >50%, so as to fully refine the original austenite grains in the ingot.

[0083] In the present invention, the thickness of the heated ingot is preferably 100 mm to 300 mm, more preferably 200 mm. During the heating treatment of the ingot, in order to ensure that microalloying elements such as Nb, V and Ti are completely dissolved, the holding temperature is preferably 1150°C to 1210°C, more preferably 1194°C to 1202°C, and the time in the furnace is preferably 240 min to 260 min, more preferably 245 min to 256 min.

[0084] In the present invention, the thickness of the rolled intermediate billet is preferably 50 mm to 100 mm, more preferably 80 mm, in the finishing rolling process, the finishing rolling start temperature is preferably 880°C to 960°C, more preferably 882°C to 937°C, the final rolling temperature is preferably 850°C to 890°C, more preferably 864°C to 881°C, and the total number of finishing passes is preferably 6 to 10, more preferably 7. The present invention fully rolls in the austenite non-recrystallization zone to refine the original austenite grains, thereby obtaining uniform and fine ferrite grains and improving the comprehensive performance of the steel plate.

[0085] In the present invention, the thickness of the cooled finished product is preferably 25 mm to 60 mm, more preferably 25 mm to 40 mm, and the controlled cooling process after rolling is preferably water cooling; the start cooling temperature is preferably 770°C to 870°C, more preferably 824°C to 855°C, and the final cooling temperature is preferably 450°C to 550°C, more preferably 505°C to 530°C, and then the steel plate is air-cooled to room temperature. A higher start cooling temperature can slow down the enrichment of carbon elements inside the original austenite grains, reduce the proportion of bainite in the final microstructure, and avoid the occurrence of local mixed crystals.

[0086] The invention provides a 500MPa-level wind power steel with high strength and high crack arrest toughness and a production method thereof; the steel comprises the following alloy components in percentage by mass: 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 rest are Fe and other inevitable impurity elements. Compared with the prior art, the present invention is based on the design of low carbon equivalent components, strictly controls the hot rolling and cooling process parameters, and the obtained steel plate structure is a heterogeneous structure composed of coarse quasi-polygonal ferrite and fine acicular ferrite. The thickness of the steel plate is 20-60 mm, the yield strength of the steel plate is ≥500 MPa, the tensile strength is ≥660 MPa, the elongation after fracture is ≥20%, the impact energy at -40°C is ≥250 J, the CTOD value at -20°C is ≥0.8 mm, and the stress ratio is 0.5, the cycle is 10 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 steel for wind power.

[0087] In order to further illustrate the present invention, the following examples are provided for detailed description.

[0088] Example 1

[0089] 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.

[0090] 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, wherein the specific parameters of the heating, rolling and cooling processes are as follows:

[0091] (1) Heating process: ingot thickness 200 mm, holding temperature 1202°C, furnace time 245 min;

[0092] (2) Rolling process: intermediate billet thickness 80 mm, finishing rolling start temperature 937 °C, final rolling temperature 881 °C, total finishing rolling passes 7 times;

[0093] (3) Cooling process: finished product thickness 25 mm, initial cooling temperature 855 ° C, final cooling temperature 505 ° C.

[0094] The microstructure of the high-strength and tough 500MPa grade wind power steel plate prepared in this embodiment is as follows: Figure 1As shown in the figure, it can be seen that the microstructure is mainly composed of quasi-polygonal and acicular ferrite. The mechanical properties of the steel plate are shown in Table 2. The fracture morphologies of the standard V-shaped impact specimens of the steel plate at -40°C are as follows: Figure 2 The fracture morphology of the steel plate CTOD specimen at -20℃ is shown in Figure 3 shown.

[0095] Example 2

[0096] The thickness of the 500MPa grade wind power steel plate with high strength and high crack arrest toughness in this embodiment is 40mm, and its chemical composition and percentage are shown in Table 1.

[0097] 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, wherein the specific parameters of the heating, rolling and cooling processes are as follows:

[0098] (1) Heating process: ingot thickness 200 mm, holding temperature 1194 °C, furnace time 256 min;

[0099] (2) Rolling process: intermediate billet thickness 80 mm, finishing rolling start temperature 882 °C, final rolling temperature 864 °C, total finishing rolling passes 7 times;

[0100] (3) Cooling process: finished product thickness 40 mm, initial cooling temperature 824 °C, final cooling temperature 530 °C.

[0101] The microstructure of the high-strength and tough 500MPa grade wind power steel plate prepared in this embodiment is as follows: Figure 4 As shown in the figure, it can be seen that the microstructure is mainly composed of quasi-polygonal and acicular ferrite. The mechanical properties of the steel plate are shown in Table 2. The fracture morphologies of the standard V-shaped impact specimens of the steel plate at -40°C are as follows: Figure 5 The fracture morphology of the steel plate CTOD specimen at -20℃ is shown in Figure 6 shown.

[0102] Table 1 Chemical composition and percentage (wt%) of 500MPa grade wind power steel plates with high strength and high crack arrest toughness provided by Examples 1 to 2

[0103] C Si Mn Cr Al Nb+V+Ti P S Ni Cu Zr Example 1 0.09 0.22 1.50 0.35 0.02 0.06 0.008 0.002 0.20 0.01 0.02 Example 2 0.09 0.23 1.48 0.35 0.02 0.07 0.008 0.002 0.18 0.01 0.03

[0104] Table 2 Mechanical properties of 500MPa grade wind power steel plates with high strength and high crack arrest toughness provided by Examples 1 to 2

[0105]

[0106] The experimental results show that:

[0107] The high-strength and high-crack-arrest-toughness 500MPa-grade wind power steel plate provided by the present invention has a thickness of 25 to 60mm, a yield strength of ≥500MPa, a tensile strength of ≥680MPa, an elongation after fracture of ≥20%, and an impact energy of ≥250J at -40°C. Based on a three-point bending specimen, the characteristic value of crack tip propagation displacement (CTOD) is measured using GB / T 21143-2014 "Uniform Test Method for Quasi-static Fracture Toughness of Metallic Materials", and the CTOD characteristic value of the -20°C steel plate is ≥0.8mm; the steel plate has a stress ratio of 0.5 and a cycle of 10 7 The fatigue strength under the condition is >640MPa. The compliance method is used to determine the critical crack length of the steel plate when fatigue occurs. The specific formula is:

[0108]

[0109] Where P i is the load size, B is the specimen thickness, and B N is the thickness of the specimen after processing, B is taken, W is the width of the specimen, a i is the crack length; when fatigue failure occurs in the steel plate structure, the critical crack length of the steel plate is >25mm.

[0110] In summary, compared with steel plates of the same strength level, the product provided by the present invention has the following beneficial effects:

[0111] The chemical composition design of the present invention reduces the carbon content to 0.06-0.09%, increases the uniformity of the structure of the 500MPa-grade high-strength and high-crack-arrest-toughness wind power steel plate, and expands the phase change range; adds 0.01-0.03% of the Zr element to reduce the central segregation and improve the quality of the ingot; controls the water cooling temperature and regulates the steel plate structure to obtain a steel plate structure dominated by quasi-polygonal ferrite and acicular ferrite, which has high strength, high and low temperature toughness, and also has excellent fatigue performance and anti-crack-arrest performance.

[0112] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be 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 present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A 500MPa grade wind power steel with high strength and high crack arrest toughness, comprising the following alloy components in percentage by mass: 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 rest is Fe and other inevitable impurity elements.

2. The 500MPa grade wind power steel with high strength, toughness and high crack arrest toughness according to claim 1 is characterized in that: The Ceq of steel is <0.42%.

3. The 500MPa grade wind power steel with high strength, toughness and high crack arrest toughness according to claim 1 is characterized in that: The microstructure of the steel is quasi-polygonal ferrite, acicular ferrite and a small amount of granular bainite, and the average grain size is less than 5μm.

4. The 500MPa grade wind power steel with high strength, toughness and high crack arrest toughness according to claim 1 is characterized in that: The thickness of the steel is 25mm to 60mm, the yield strength is ≥500MPa, the tensile strength is ≥680MPa, and the elongation after fracture is ≥20%.

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

6. The 500MPa grade wind power steel with high strength, toughness and high crack arrest toughness according to claim 1 is characterized in that: Steel at stress ratio 0.5, cycle 10 7 The fatigue strength under the conditions is >640MPa, and the critical crack length of the organization when fatigue failure occurs is >25mm.

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

8. The production method according to claim 7, characterized in that: The thickness of the heated ingot is 100 mm to 300 mm, the insulation temperature is 1150° C. to 1210° C., and the time in the furnace is 240 min to 260 min.

9. The production method according to claim 7, characterized in that: The thickness of the rolled intermediate billet is 50 mm to 100 mm, the start temperature of the finishing rolling is 880° C. to 960° C., the final rolling temperature is 850° C. to 890° C., and the total number of finishing rolling passes is 6 to 10 times.

10. The production method according to claim 7, characterized in that: The thickness of the cooled finished product is 25 mm to 60 mm, the start cooling temperature is 770° C. to 870° C., and the final cooling temperature is 450° C. to 550° C.

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