420 MPa-grade wind power steel welded joint with fatigue grade of DC112 and preparation method of 420 MPa-grade wind power steel welded joint

Abstract

The invention belongs to the technical field of metallurgy, and particularly relates to a 420 MPa-grade wind power steel welded joint with the fatigue grade of DC112 and a preparation method. According to the 420 MPa grade wind power steel welded joint, under the tension-tension fatigue test condition that the stress ratio R is equal to 0.5, after 2 * 106 times of cyclic loading, the fatigue strength of the 420 MPa grade wind power steel welded joint reaches 112 MPa, and the strict requirement for the DC112 grade fatigue grade in the international standard DNV-ST-0126 is completely met. The performance index is obviously superior to the prior art level, and key technical support is provided for high-reliability design and light-weight manufacturing of a wind power tower tube structure.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a 420 MPa grade wind power steel welded joint with fatigue level DC112 and its preparation method. Background Technology

[0002] In recent years, as wind turbine generators have developed towards larger sizes, taller towers, and offshore applications, more stringent requirements have been placed on the strength, weldability, and fatigue life of key metallic materials used in wind turbine structures. Currently, domestic wind turbine tower manufacturing still widely uses traditional low-strength steel of the 355 MPa grade. Under the same ultimate load conditions, this type of low-strength steel material leads to a significant increase in structural wall thickness and cross-sectional dimensions, resulting in a surge in steel consumption. This severely restricts the lightweight and economical design of tower structures, making it difficult to meet the manufacturing needs of modern high-power wind turbines.

[0003] Current wind turbine steel structures generally adopt the DC90 grade from international standards (such as DNV) as the fatigue design benchmark for welded joints. This relatively conservative design principle has become a technical bottleneck restricting the further development of wind turbines towards larger size, lighter weight, and offshore applications. Although higher-strength 420 MPa grade steel can solve the problem of insufficient static strength of materials, industry research shows that about 20% of design types cannot achieve large-scale upgrades due to insufficient fatigue strength of welded joints. Currently, several studies have been dedicated to optimizing the performance of wind turbine steel welded joints, but none have been able to meet the requirements of the ultra-high fatigue level of DC112. Summary of the Invention

[0004] The purpose of this invention is to provide a 420 MPa grade wind turbine steel welded joint with a fatigue level of DC112 and a preparation method thereof. The 420 MPa grade wind turbine steel welded joint provided by this invention can meet the requirements of the DC112 grade ultra-high fatigue level.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a wind turbine steel welded joint, comprising a steel plate and a weld. The steel plate, by mass percentage, comprises: C≤0.10%, Si: 0.20~0.45%, Mn: 1.20~1.50%, Ni≤0.20%, Cr≥0.20%, Nb, V and Ti: 0.060~0.095%, Mo≤0.05%, B≤0.0005%, Al≤0.035%, P≤0.015%, S≤0.015%; the remainder being iron and unavoidable impurities. The composition of the weld includes: C≥0.060%, Si: 0.20~0.60%, Mn: 1.40~1.80%, P≤0.020%, S≤0.015%, Ni: 0.05~0.35%, Cr≥0.05%, Mo: 0.20~0.40%, Cu≥0.05%, Nb, V and Ti: 0.040~0.080%, with the remainder being iron and unavoidable impurities.

[0006] Preferably, the thickness of the steel plate is 5~50 mm; the yield strength of the steel plate is ≥400 MPa, the tensile strength is 520~680 MPa, the elongation is ≥19%, the yield strength ratio is ≥0.81, and the Charpy V-notch impact energy at -20℃ is ≥290 J.

[0007] This invention also provides a method for preparing the wind turbine steel welded joint described in the above technical solution, comprising the following steps: After machining double "V" shaped bevels on both sides of the steel plate, welding is performed to obtain the wind power steel welded joint. The welding process involves a root pass using gas metal arc welding (GMAW) followed by double-sided welding using submerged arc welding (SAW).

[0008] Preferably, the welding conditions for the root pass include: the welding wire is CHW-55C1R with a diameter of Φ1.2mm, the shielding gas is CO2, the current is 200~250A, the voltage is 24~30V, the welding speed is 28~35cm / min, and the number of welding passes is one.

[0009] Preferably, the submerged arc welding is carried out using single-wire submerged arc welding, and the welding heat input of the submerged arc welding is 20~40kJ / cm.

[0010] Preferably, the weld reinforcement height on both sides of the wind turbine steel welded joint is ≤1 mm, and the joint transition angle is ≥150°.

[0011] Preferably, the submerged arc welding conditions include: the welding process uses welding wire and submerged arc flux; the welding wire is of grade CHW-S9 and has a diameter of Φ4mm; the submerged arc flux is of grade CHF101.

[0012] Preferably, the submerged arc welding uses a welding current of 400~600A, a voltage of 25~35V, a welding speed of 30~45cm / min, and an interpass temperature of 80~150℃; three passes are welded on each side.

[0013] Preferably, the welding process further includes preheating the steel plate at a temperature of 100~180℃.

[0014] Preferably, the submerged arc welding flux is dried before use; the drying temperature is 350°C and the holding time is 2 hours.

[0015] In this invention, carbon (C) is an essential alloying element in steel, effectively improving the strength of the steel plate. However, excessive C content can impair low-temperature toughness and weldability. Therefore, this invention controls C content to ≤0.10%. Si is an important alloying element in steel, effectively enhancing the strength and hardenability of the steel plate through its solid solution strengthening effect and its ability to inhibit cementite precipitation. However, excessive Si content can reduce the toughness of the weld heat-affected zone and increase the risk of surface oxidation. Therefore, in this invention, the Si content is controlled at 0.20~0.45%. Mn is a key alloying element in steel, effectively improving the strength and hardenability of the steel plate through its solid solution strengthening and austenite stabilization effects. However, excessive Mn content can easily lead to segregation in the center of the steel plate, reducing low-temperature toughness and increasing the embrittlement tendency of the weld heat-affected zone. Therefore, in this invention, the Mn content is controlled at 1.20~1.50%. Ni, through its solid solution strengthening and ability to lower the ductile-brittle transition temperature, effectively improves the low-temperature toughness of the steel plate. However, excessive Ni content significantly increases production costs and has limited contribution to strength. Therefore, this invention controls Ni ≤ 0.20%; Cr is an important strengthening element that can improve the strength and corrosion resistance of steel plates, but excessive Cr content will impair weldability and toughness. Therefore, this invention controls Cr ≥ 0.20%. Nb, V, Ti: Nb, V, and Ti are key microalloying elements that can significantly improve the strength and toughness of steel plates, but excessive content will reduce material properties. Therefore, in this invention, the total content of Nb, V, and Ti is controlled at 0.060~0.095%. Mo is a significant hardenability element that can refine bainite laths and inhibit tempering softening, but excessive content can easily promote the formation of hard and brittle MA islands and increase crack sensitivity. Therefore, this invention controls Mo at ≤ 0.05%; B is a strong grain boundary segregating element, and even trace amounts can significantly improve hardenability, but excessive content can easily form brittle phases at grain boundaries and deteriorate the toughness of the weld heat-affected zone. Therefore, this invention controls B at ≤0.0005%; Al is used as a deoxidizer and grain refiner, which can improve the purity of molten steel and inhibit grain growth, but excessive content can easily generate coarse Al2O3 inclusions, reduce impact toughness, and clog the nozzle. Therefore, this invention controls Al at ≤0.035%; P is a grain boundary segregation embrittlement element, and even trace amounts can significantly reduce low-temperature impact toughness and weld heat-affected zone toughness, and excessive content can also exacerbate cold cracking sensitivity. Therefore, this invention controls P at ≤0.015%; S easily combines with Mn to form MnS inclusions, and segregates at grain boundaries, leading to hot embrittlement. Excessive content will significantly reduce the steel's transverse toughness, impact energy absorption, and weldability. Therefore, this invention controls S at ≤0.015%. This invention strictly limits the content of each component in the steel plate based on the properties of each element. The 420 MPa grade wind turbine steel welded joint provided by this invention, under room temperature and tensile fatigue test conditions with a stress ratio R=0.5, passed 2×10 6After several cycles of loading, its fatigue strength reached 112 MPa, meeting the requirements of the international standard DNV-ST-0126 for the DC112 fatigue level. This performance index is significantly better than the existing technology level, providing key technical support for the high reliability design and lightweight manufacturing of wind turbine tower structures.

[0016] This invention also provides a method for preparing the wind turbine steel welded joint described above. The invention uses 420 MPa grade wind turbine steel plates with a specific composition system, combined with specialized submerged arc welding materials, and employs optimized welding process parameters. The resulting welded joint exhibits excellent forming quality, a smooth and flat weld surface, and stable internal metallurgical quality. Non-destructive testing shows that the weld area has a dense and uniform microstructure, free from defects such as cracks, porosity, slag inclusions, lack of fusion, and incomplete penetration, and all performance indicators meet high standards.

[0017] The welded joints obtained using the material combination and process scheme provided by this invention exhibit excellent geometric characteristics: the joint reinforcement is strictly controlled within 1 mm, the joint transition angle is not less than 150°, the weld toe area achieves a smooth transition with the base material, and there are no undercuts or other surface defects. The weld has a uniform and aesthetically pleasing appearance, regular geometry, and significantly reduces the stress concentration factor. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is the double V-shaped bevel form of Embodiment 1 of the present invention; Figure 2 This is the single V-groove form of Comparative Example 2 of the present invention; Figure 3 This is a macroscopic cross-sectional view of the welded joint in Embodiment 1 of the present invention; Figure 4 This is a macroscopic cross-sectional view of the welded joint in Comparative Example 2 of the present invention; Figure 5 The fatigue life fitting curves are for Examples 1-4 and Comparative Examples 1-3. Detailed Implementation

[0020] This invention provides a wind turbine steel welded joint, comprising a steel plate and a weld. The chemical composition of the steel plate, by mass percentage, includes: C≤0.10%, Si: 0.20~0.45%, Mn: 1.20~1.50%, Ni≤0.20%, Cr≥0.20%, Nb, V and Ti: 0.060~0.095%, Mo≤0.05%, B≤0.0005%, Al≤0.035%, P≤0.015%, S≤0.015%; the remainder being iron and unavoidable impurities. By mass percentage, the weld composition includes: C≥0.060%, Si: 0.20~0.60%, Mn: 1.40~1.80%, P≤0.020%, S≤0.015%, Ni: 0.05~0.35%, Cr≥0.05%, Mo: 0.20~0.40%, Cu≥0.05%, Nb, V and Ti: 0.040~0.080%, with the remainder being iron and unavoidable impurities.

[0021] In this invention, carbon (C) is an essential alloying element in steel, effectively improving the strength of the steel plate. However, excessive C content can impair low-temperature toughness and weldability. Therefore, this invention controls C content to ≤0.10%. Si is an important alloying element in steel, effectively enhancing the strength and hardenability of the steel plate through its solid solution strengthening effect and its ability to inhibit cementite precipitation. However, excessive Si content can reduce the toughness of the weld heat-affected zone and increase the risk of surface oxidation. Therefore, in this invention, the Si content is controlled at 0.20~0.45%. Mn is a key alloying element in steel, effectively improving the strength and hardenability of the steel plate through its solid solution strengthening and austenite stabilization effects. However, excessive Mn content can easily lead to segregation in the center of the steel plate, reducing low-temperature toughness and increasing the embrittlement tendency of the weld heat-affected zone. Therefore, in this invention, the Mn content is controlled at 1.20~1.50%. Ni, through its solid solution strengthening and ability to lower the ductile-brittle transition temperature, can effectively improve the low-temperature toughness of the steel plate. However, excessive Ni content can significantly increase production costs and has limited contribution to strength. Therefore, this invention controls Ni ≤ 0.20%; Cr is an important strengthening element that can improve the strength and corrosion resistance of steel plates, but excessive Cr content will impair weldability and toughness, therefore, this invention controls Cr ≥ 0.20%. Nb, V, Ti: Nb, V, and Ti are key microalloying elements that can significantly improve the strength and toughness of steel plates, but excessive content will reduce material properties, therefore, the total content of Nb, V, and Ti in this invention is controlled at 0.060~0.095%. Mo is a significant hardenability element that can refine bainite laths and inhibit tempering softening, but excessive content can easily promote the formation of hard and brittle MA islands and increase crack sensitivity. Therefore, this invention controls Mo ≤ 0.05%; B is a strong grain boundary segregating element, and even trace amounts can significantly improve hardenability, but excessive content can easily form brittle phases at grain boundaries and deteriorate the toughness of the weld heat-affected zone. Therefore, this invention controls B to ≤0.0005%; Al is used as a deoxidizer and grain refiner, which can improve the purity of molten steel and inhibit grain growth, but excessive content can easily generate coarse Al2O3 inclusions, reducing impact toughness and clogging the nozzle. Therefore, this invention controls Al to ≤0.035%; P is a grain boundary segregation embrittlement element, and even trace amounts can significantly reduce low-temperature impact toughness and weld heat-affected zone toughness, and excessive content can also exacerbate cold cracking sensitivity. Therefore, this invention controls P to ≤0.015%; S easily combines with Mn to form MnS inclusions, and segregates at grain boundaries, leading to hot embrittlement. Excessive content will significantly reduce the transverse toughness, impact energy absorption, and weldability of steel. Therefore, this invention controls S to ≤0.015%.

[0022] As one embodiment of the present invention, the chemical composition of the steel plate, by mass percentage, is specifically C: 0.07~0.09%, Si: 0.30~0.35%, Mn: 1.25~1.49%, Ni: 0.02~0.08%, Cr: 0.25~0.40%, Nb: 0.032~0.040%, V: 0.010~0.015%, Ti: 0.020~0.025%, Mo: 0.01~0.03%, B: 0.0002~0.0003%, Al: 0.023~0.035%, P: 0.007~0.008%, S: 0.001~0.002%, with the remainder being iron and unavoidable impurities.

[0023] As one embodiment of the present invention, the chemical composition of the weld, by mass percentage, is specifically C: 0.060~0.070%, Si: 0.35~0.40%, Mn: 1.46~1.50%, P: 0.007~0.009%, S: 0.002~0.005%, Ni: 0.15~0.30%, Cr: 0.05~0.07%, Nb: 0.032~0.036%, V: 0.005~0.007%, Ti: 0.008~0.010%, Mo: 0.25~0.35%, Cu: 0.1~0.15%, with the remainder being iron and unavoidable impurities.

[0024] In one embodiment of the present invention, the thickness of the steel plate can be 5~50 mm, specifically 5 mm, 10 mm, 20 mm, 25 mm, 30 mm, 40 mm or 50 mm; the yield strength of the steel plate is ≥400 MPa, the tensile strength is 520~680 MPa, the elongation is ≥19%, the yield strength ratio is ≥0.81, and the Charpy V-notch impact energy at -20℃ is ≥290 J.

[0025] The present invention also provides a method for preparing the above-described wind turbine steel welded joint, comprising the following steps: After machining double "V" shaped bevels on both sides of the steel plate, welding is performed to obtain the wind power steel welded joint. The welding process involves a root pass using gas metal arc welding (GMAW) followed by a double-sided pass using submerged arc welding (SAW).

[0026] The present invention involves machining double "V" shaped bevels on both sides of the steel plate and then welding them to obtain a welded steel plate. In one embodiment of the present invention, the bevel angle of the "V" shaped bevel can be 50~70°.

[0027] As one embodiment of the present invention, the steel plate is preheated before welding; the preheating temperature can be 100~180℃, specifically 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃ or 180℃.

[0028] As one embodiment of the present invention, the welding conditions for the root pass may include: the welding wire grade is CHW-55C1R, the diameter is Φ1.2mm, the shielding gas is CO2, the current is 200~250A, specifically 200A, 210A, 220A, 230A, 240 or 250A, the voltage is 24~30V, specifically 24V, 25V, 26V, 27V, 28V, 29V or 30V; the welding speed is 28~35cm / min, specifically 28cm / min, 29cm / min, 30cm / min, 31cm / min, 32cm / min, 33cm / min, 34cm / min or 35cm / min; and the welding pass is one.

[0029] As one embodiment of the present invention, the submerged arc welding can be carried out by single-wire submerged arc welding, and the welding heat input of the submerged arc welding is 20~40 kJ / cm, specifically 20 kJ / cm, 30 kJ / cm or 40 kJ / cm; As one embodiment of the present invention, the welding reinforcement height on both sides of the wind turbine steel welded joint is ≤1 mm, and the joint transition angle is ≥150°.

[0030] As one embodiment of the present invention, the conditions for submerged arc welding may include: the welding process uses welding wire and submerged arc flux; the welding wire is CHW-S9 with a diameter of Φ4mm; the submerged arc flux is CHF101; the welding current is 400~600A, specifically 400A, 500A, or 600A; the voltage is 25~35V, specifically 25V, 26V, 27V, 28V, 29V, 30V, 31V, 32V, 33V, 34V, or 35V; and the welding speed... The speed is 30~45cm / min, specifically 30cm / min, 31cm / min, 32cm / min, 33cm / min, 34cm / min, 35cm / min, 40cm / min, 41cm / min, 42cm / min, 43cm / min, 44cm / min or 45cm / min; the interpass temperature is 80~150℃, specifically 80℃, 90℃, 100℃, 120℃ or 150℃; three passes are welded on each side.

[0031] As one embodiment of the present invention, the submerged arc welding flux is further dried before use; the drying temperature can be 350°C and the holding time can be 2 hours.

[0032] As one embodiment of the present invention, before the reverse welding, carbon gouging and grinding are performed; the reverse welding also includes covering with asbestos for insulation and slow cooling to room temperature.

[0033] To further illustrate the present invention, the following detailed description of the invention's solutions, in conjunction with the accompanying drawings and embodiments, is provided, but should not be construed as limiting the scope of protection of the present invention.

[0034] The chemical composition of the 420MPa grade steel plates in the examples and comparative examples is shown in Table 1, with the balance being iron and unavoidable impurities; the chemical composition of the welds in the examples and comparative examples is shown in Table 2, with the balance being iron and unavoidable impurities; the process parameters in the examples and comparative examples are shown in Table 3; the flux was dried in an oven at 350°C for 2 hours in advance to remove moisture.

[0035] Example 1 The chemical composition of the 420MPa grade steel plate used in the examples and comparative examples is shown in Table 1. The steel plate thickness is 25mm. Pre-treatment of the steel plate before welding includes beveling and cleaning to ensure the welding area is free of oil, moisture, and oxides. Double "V" shaped bevels (bevel angles of 52° and 65°, see [reference to table]) are machined on both sides of the steel plate. Figure 1 The steel plate was preheated to 140℃. First, GMAW welding was used for the root pass, employing CHW-55C1R welding wire with a diameter of Φ1.2mm, 100% CO2 shielding gas, 225A current, 25V voltage, and a welding speed of 32cm / min, with one pass. Then, SAW welding was used for double-sided welding on both sides, using CHW-S9 welding wire with a diameter of Φ4mm and CHF101 flux. Three passes were applied to each side, with a welding current of 500A, a voltage of 30V, a welding speed of 38cm / min, and a welding heat input of 24kJ / cm. The interpass temperature was 115℃. Before welding the reverse side, carbon gouging and grinding were performed. After welding, asbestos was used for insulation and slow cooling to room temperature. The weld reinforcement on both sides of the joint was 0.9mm, and the joint transition angle was 158°. Figure 3 This is a macroscopic cross-sectional view of the welded joint in Embodiment 1 of the present invention. Non-destructive testing was performed on the weld and heat-affected zone 48 hours after welding to meet the following quality requirements: ultrasonic testing was performed on the weld, and the internal quality of the weld met the relevant requirements of ISO 17635.

[0036] Examples 2-4 The parameters that differentiate Examples 2-4 from Example 1 are shown in Table 3.

[0037] Comparative Examples 1-3 The parameters that differentiate Comparative Examples 1-3 from Example 1 are shown in Table 3. Figure 2 This is the single V-groove form of Comparative Example 2 of the present invention. Figure 4 This is a macroscopic cross-sectional view of the welded joint in Comparative Example 2 of the present invention.

[0038] Table 1. Chemical composition (wt.%) of steel plates from the examples and comparative examples

[0039] Table 2 Chemical composition (wt.%) of welds in the examples and comparative examples

[0040] Table 3 Welding process parameters (all welding processes use GMAW+SAW)

[0041] The welded joints obtained by this invention underwent comprehensive testing and demonstrated excellent metallurgical quality, with no internal welding defects such as porosity, slag inclusions, lack of fusion, or cracks. The basic mechanical properties (including tensile strength, bending performance, and -20℃ low-temperature impact energy) of Examples 1-5 and Comparative Examples 1 and 3 all met the standard requirements, and the impact energy of their welds and heat-affected zones was also all qualified. However, Comparative Example 2's failure to meet the tensile strength standard resulted in poor fatigue performance. The next step focused on fatigue performance testing, using an MTS high-frequency fatigue testing machine. Fatigue tests were conducted under a series of peak stresses, a stress ratio of 0.5, and a frequency of 10Hz. Ten sets of effective samples were taken from each example and comparative example. The fatigue results of the wind power steel in Examples 1-4 and Comparative Examples 1-3 are shown in Table 4.

[0042] Table 4. Fatigue performance of welded joints in the examples and comparative examples

[0043] Figure 5 The figures show the fatigue life fitting curves for Examples 1-4 and Comparative Examples 1-3, and their fatigue life (N) f ) and stress amplitude (σ a The relationship is as follows: Example 1: logσ a =4.077-0.333*log N f Example 2: logσ a =4.073-0.333*log N f Example 3: logσ a =4.071-0.333*log N f Example 4: logσ a =4.066-0.333*log N f Comparative Example 1: logσ a =3.983-0.333*log N f Comparative Example 2: logσ a =3.947 - 0.333 * log N f Comparative Example 3: logσ a =4.000-0.333*log N f .

[0044] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A wind turbine steel welded joint, comprising a steel plate and a weld, characterized in that, The steel plate comprises, by mass percentage: C ≤ 0.10%, Si: 0.20~0.45%, Mn: 1.20~1.50%, Ni ≤ 0.20%, Cr ≥ 0.20%, Nb, V and Ti: 0.060~0.095%, Mo ≤ 0.05%, B ≤ 0.0005%, Al ≤ 0.035%, P ≤ 0.015%, S ≤ 0.015%; the remainder being iron and unavoidable impurities. The composition of the weld includes: C≥0.060%, Si: 0.20~0.60%, Mn: 1.40~1.80%, P≤0.020%, S≤0.015%, Ni: 0.05~0.35%, Cr≥0.05%, Mo: 0.20~0.40%, Cu≥0.05%, Nb, V and Ti: 0.040~0.080%, with the remainder being iron and unavoidable impurities.

2. The wind turbine steel welded joint as described in claim 1, characterized in that, The thickness of the steel plate is 5~50 mm; the yield strength of the steel plate is ≥400 MPa, the tensile strength is 520~680 MPa, the elongation is ≥19%, the yield strength ratio is ≥0.81, and the Charpy V-notch impact energy at -20℃ is ≥290 J.

3. The method for preparing the wind turbine steel welded joint according to claim 1 or 2, comprising the following steps: After machining double "V" shaped bevels on both sides of the steel plate, welding is performed to obtain the wind power steel welded joint; The welding process involves a root pass using gas metal arc welding (GMAW) followed by double-sided welding using submerged arc welding (SAW).

4. The preparation method according to claim 3, characterized in that, The welding conditions for the root pass include: the welding wire is CHW-55C1R, the diameter is Φ1.2mm, the shielding gas is CO2, the current is 200~250A, the voltage is 24~30V, the welding speed is 28~35cm / min, and the welding pass is one.

5. The preparation method according to claim 3, characterized in that, The submerged arc welding adopts a single-wire submerged arc welding method, and the welding heat input of the submerged arc welding is 20~40 kJ / cm.

6. The preparation method according to claim 3, characterized in that, The weld reinforcement height on both sides of the wind turbine steel welded joint is ≤1 mm, and the joint transition angle is ≥150°.

7. The preparation method according to claim 3, characterized in that, The conditions for submerged arc welding include: the welding process uses welding wire and submerged arc flux; the welding wire is of grade CHW-S9 and has a diameter of Φ4mm; the submerged arc flux is of grade CHF101.

8. The preparation method according to any one of claims 5 to 7, characterized in that, The submerged arc welding uses a welding current of 400~600A, a voltage of 25~35V, a welding speed of 30~45cm / min, and an interpass temperature of 80~150℃; three passes are welded on each side.

9. The preparation method according to claim 3, characterized in that, The process before welding also includes preheating the steel plate at a temperature of 100-180°C.

10. The preparation method according to claim 3, characterized in that, Before using the submerged arc welding flux, it is also dried; the drying temperature is 350℃ and the holding time is 2 hours.

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