A stranded submerged arc welding wire for wind power, a core-shell gradient fluorine-alkali type sintered flux and a preparation method and application thereof

Abstract

This invention discloses a stranded submerged arc welding wire for wind power, a core-shell gradient fluorine-alkali sintered flux, its preparation method, and its application, belonging to the technical field of welding materials and their preparation. This invention uses two different diameter welding wires stranded together with a variable pitch to obtain a different diameter variable pitch stranded submerged arc welding wire. By adjusting the diameter ratio, axial variable pitch, and circumferential phase distribution of the two welding wires, the spatial position of Mo element in the stranded welding wire changes according to a set pattern, enabling Mo element to enter the molten pool periodically. This approach balances alloy design and wire feed section adjustment, effectively improving weld strength, promoting microstructure refinement, and enhancing low-temperature impact toughness. Simultaneously, the flux consists of purified core particles and a forming layer covering the purified core particles. The purified components, forming and arc-stabilizing components are partitioned within the particles, facilitating adjustments in low hydrogen, oxygen control, particle strength, arc stabilization, and slag removal. The aforementioned welding wire and flux are suitable for automatic submerged arc welding of long welds on thick plates of wind turbine towers.

Description

Technical Field

[0001] This invention relates to a stranded submerged arc welding wire for wind power, a core-shell gradient fluorine-alkali sintering flux, its preparation method and application, belonging to the technical field of welding materials and their preparation. Background Technology

[0002] As wind power equipment develops towards larger sizes, taller towers, and offshore applications, the plate thickness and service requirements for wind turbine towers, transition sections, and large connecting steel structures are continuously increasing. Q420 and Q460 grade low-alloy high-strength steels, due to their high yield strength and good overall performance, are used in wind turbine towers and related load-bearing components. These structures typically employ long welds, thick plates, and multi-layer, multi-pass submerged arc welding. The welding materials must not only meet strength matching requirements but also consider low-temperature impact toughness, resistance to hydrogen-induced cracking, weld formation, slag removal performance, and continuous wire feeding stability. The alloy design of a single welding wire is limited by both composition and process performance. Ordinary multi-strand welding wires often use fixed diameters and fixed strand pitches, making it difficult to adjust the spatial position, melting rhythm, and wire feeding torque of different alloy welding wires.

[0003] On the other hand, in homogeneous sintered fluxes, the purification components, arc-stabilizing components, and forming components are randomly distributed within the same particle, making it difficult to simultaneously achieve a stable balance between particle strength, low hydrogen content, oxygen control, arc stabilization, and slag removal. Therefore, it is necessary to design the diameter ratio, strand pitch, phase, and surface structure of the welding wire and to use it in conjunction with a sintered flux that has a layered component distribution. Summary of the Invention

[0004] In view of the above-mentioned deficiencies and problems of the prior art, the present invention provides a stranded submerged arc welding wire for wind power, a core-shell gradient fluorine-alkali sintering flux, its preparation method and application.

[0005] The technical solution of this invention: One objective of this invention is to provide a stranded submerged arc welding wire for the wind power industry. This stranded submerged arc welding wire is formed by stranding 2 to 7 strands of Class A welding wire and / or Class B welding wire. The total equivalent diameter after stranding is 3.2 to 5.5 mm. The strand pitch P varies periodically along the axial direction according to the length with alternating pitches P1 and P2, respectively; P1 is 8 to 18 mm, and P2 is 18 to 40 mm.

[0006] Further specified, the axial length of each pitch P1 segment and each pitch P2 segment is 50-250mm, and adjacent segments can be switched in steps, or the pitch can be continuously changed through a transition segment of 20-80mm.

[0007] Further specified, the single wire diameter dA of Class A welding wire is 1.0 to 2.5 mm, and by mass percentage includes: C 0.03 to 0.14%, Si ≤ 0.35%, Mn 1.35 to 2.05%, S ≤ 0.030%, P ≤ 0.030%, with the balance being Fe and unavoidable impurities.

[0008] Further specified, the single wire diameter of Class B welding wire is 1.0 to 2.5 mm, and by mass percentage includes: C 0.04 to 0.13%, Si ≤ 0.45%, Mn 1.40 to 2.15%, Mo 0.35 to 0.85%, S ≤ 0.030%, P ≤ 0.030%, with the balance being Fe and unavoidable impurities.

[0009] Further specified, dB / dA is 0.85–0.98 or 1.02–1.25.

[0010] Further specified, the stranded submerged arc welding wire is formed by twisting Class A welding wire and Class B welding wire together, and the ratio of the total cross-sectional area of ​​Class A welding wire to the total cross-sectional area of ​​Class B welding wire is (35~70):(65~30).

[0011] Further specifying, when the stranded submerged arc welding wire has a 3-strand structure, it includes 2 strands of Class A welding wire and 1 strand of Class B welding wire.

[0012] Further specifying, when the stranded submerged arc welding wire has a 4-strand structure, it includes 2 strands of Class A welding wire and 2 strands of Class B welding wire.

[0013] Further specifying, when the stranded submerged arc welding wire has a 5-strand structure, the B welding wire shall have at least 2 strands, and the B-type welding wire shall be the center strand, or the B-type welding wire shall be the center strand, and the A-type welding wire and the B-type welding wire shall be alternately arranged in the outer layer along the circumferential direction.

[0014] Furthermore, the stranded submerged arc welding wire also has a reverse twist structure. The reverse twist structure is formed by applying a slight retwisting in the opposite direction to the basic stranding after the basic stranding is completed. The reverse twist angle α within each basic strand length is 3° to 12°.

[0015] Furthermore, the reverse rotation angle α is specified to be 5° to 8°.

[0016] Furthermore, during the retwisting process, the axial tension of the stranded welding wire is maintained so that each strand of welding wire remains in contact or in a stable relative position.

[0017] Furthermore, retwisting can be accomplished either by setting an independent retwisting head at the output end of the stranding equipment or by the speed difference between the take-up reel and the stranding head.

[0018] Further specified, the surface of Class A welding wire and / or Class B welding wire is provided with at least one continuous or discontinuous spiral microgroove, wherein the depth h of the spiral microgroove is 0.5 to 5% of the diameter of the single wire, the width w is 3 to 20% of the diameter of the single wire, and the pitch L is 2 to 20 mm.

[0019] Furthermore, the helical microgrooves can be single-start helices, multi-start helices, continuous helices, or helices intermittently arranged along the axial direction.

[0020] Furthermore, the cross-section of the spiral microgroove can be arc-shaped, V-shaped, or trapezoidal, with arc-shaped or rounded trapezoidal without sharp notches being preferred.

[0021] Furthermore, the depth h of the spiral microgroove is 0.01–0.08 mm, and the width w is 0.05–0.30 mm.

[0022] Furthermore, the spiral microgrooves are formed by laser grooving or micro-rolling.

[0023] Furthermore, when using laser grooving, the single filament rotates around its own axis and is fed axially. The groove size is controlled by the laser pulse energy, scanning speed, and rotation feed ratio. After processing, the surface slag is removed and the area is cleaned.

[0024] Furthermore, when using micro-rolling, the embossing wheel with spiral ridges contacts the monofilament, and the groove depth is controlled by the amount of pressing and the feed speed, while the groove edges are rounded.

[0025] The second objective of this invention is to provide a method for preparing the above-mentioned stranded submerged arc welding wire for the wind power industry. The method is as follows: basic stranding is performed under the conditions that the tension of Class A welding wire is 40-140N and the tension of Class B welding wire is 50-160N. The stranding pitch P is changed periodically by alternating pitch P1 and pitch P2 by a servo stranding head. Finally, the wire is kept at 180℃-320℃ for 0.5-2h.

[0026] Further specifying, when a reverse twist structure is set, a reverse angle is applied along the opposite twist direction after the basic strand of each basic twist pitch is completed.

[0027] The third objective of this invention is to provide a core-shell gradient fluorine-alkali sintered flux for use with the aforementioned stranded submerged arc welding wire in the wind power industry. This core-shell gradient fluorine-alkali sintered flux has a particle size of 10-60 mesh and a moisture content of no more than 0.08%. It consists of purified core particles and a forming layer covering the purified core particles. The purified core particles account for 35-70% of the total mass of the flux particles, and the forming layer accounts for 30-65% of the total mass of the flux particles.

[0028] Further specifying, the core-shell gradient fluorine-alkali type sintering flux is 14-50 mesh.

[0029] Further specified, the core-shell gradient fluorine-alkali sintering flux comprises, by mass percentage: CaF2 18-35%, CaO 10-24%, MgO 4-12%, Al2O3 10-24%, SiO2 3-14%, MnO 2-10%, TiO2 1-8%, ZrO 20-3.0%, B2O 30-1.2%, CeO2 and / or La2O 30-1.5%, Na2O and K2O combined amount of 0.8%-5.0%, Li2O 0-1.0%, Fe-Mn or metallic manganese powder 0.5%-5%, sintering binder 1%-7%, and the balance being unavoidable impurities.

[0030] Further specifying, the IIW basicity index of the core-shell gradient fluorine-alkali sintered flux is 1.9 to 3.3.

[0031] Furthermore, the IIW basicity index of the core-shell gradient fluorine-alkali sintered flux is specified as 2.2–2.9.

[0032] Further specifying, the sintering binder is sodium silicate, potassium silicate, and / or sodium-potassium composite silicate.

[0033] Furthermore, the content of ZrO2 is 0.2-3.0%, the content of B2O3 is 0.05-1.2%, and the content of CeO2 and / or La2O3 is 0.05-1.5%.

[0034] Further specify that the core-shell gradient fluorine-alkali type sintered flux should be dried at 300℃~450℃ for 1~3h before use, until the flux moisture content is no more than 0.08%.

[0035] The fourth objective of this invention is to provide a method for preparing the above-mentioned core-shell gradient fluorine-alkali sintered flux. The method involves: using disc granulation, drum granulation, extrusion granulation, drum coating, or fluidized bed coating to mix and granulate the purified core particles with a portion of the sintering binder to form purified core particles. These particles are then pre-dried at 100–180°C for 1–3 hours. The pre-dried core particles are then placed in a rolling or suspended state. The remaining sintering binder and outer shell material are sprayed in, allowing the outer shell material to coat the surface of the core particles. The particles are then dried at 120–200°C and sintered at 650–850°C for 0.5–2.5 hours. After cooling and sieving, the core-shell gradient fluorine-alkali sintered flux is obtained.

[0036] Further specified, the sintering temperature is 750℃~800℃, and the sintering time is 1~1.5h.

[0037] The fifth objective of this invention is to provide a welding material for the wind power industry, specifically including the above-mentioned stranded submerged arc welding wire for the wind power industry and the above-mentioned core-shell gradient fluorine-alkali sintered flux. This welding material is applied to automatic submerged arc welding of longitudinal seams, circumferential seams, flange connection areas, transition sections, or door frame reinforcement areas of Q420 or Q460 grade wind turbine towers.

[0038] Beneficial effects: This invention uses a variable pitch stranding method to obtain a variable pitch stranded submerged arc welding wire with two different diameter welding wires. By adjusting the diameter ratio, axial pitch, and circumferential phase distribution of the A-type and B-type welding wires, the spatial position of the Mo-containing B-type welding wire in the stranded wire changes according to a set pattern. This allows Mo to enter the molten pool periodically, taking into account both alloy design and wire feed section adjustment, effectively improving weld strength, promoting microstructure refinement, and enhancing low-temperature impact toughness. Simultaneously, the stranded structure with different diameters, variable pitch, and phase variations enhances micro-stirring of the molten pool, reducing alloy segregation and impact toughness dispersion. Furthermore, a reverse twisting structure is used to reduce the residual torsional tendency after stranding, or spiral microgrooves are set on the surface of the single wire to further change the local surface morphology and inter-strand contact state of the welding wire without significantly weakening the single wire cross-section. At the same time, the reverse twisting structure can partially offset the residual torsional tendency generated by the basic strand, reducing the possibility of the strand rotating or loosening during the wire feeding process.

[0039] The core-shell gradient fluorine-alkali sintering flux provided by the present invention consists of purified core particles and a forming layer covering the purified core particles. The purification components and forming and arc-stabilizing components are partitioned within the particles, which is beneficial for adjusting between low hydrogen, oxygen control, particle strength, arc stabilization and slag removal.

[0040] This invention utilizes variable diameter, variable pitch stranded submerged arc welding wire and core-shell gradient fluorine-alkali sintered flux for automatic submerged arc welding of long welds on thick plates of wind turbine towers. The resulting welds are full, evenly spread, and have good slag removal properties, making them suitable for continuous automatic welding production of long welds and thick plates in the wind power industry. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the structure of a stranded submerged arc welding wire when two strands of welding wire are twisted together. Figure 2 This is a schematic diagram of the structure of a stranded submerged arc welding wire when three strands of welding wire are twisted together. Figure 3 This is a schematic diagram of the structure of a stranded submerged arc welding wire when four strands of welding wire are twisted together. Figure 4 This is a schematic diagram of the structure of a stranded submerged arc welding wire when 5 strands of welding wire are twisted together. Figure 5 This is a schematic diagram of a variable pitch and reverse twist structure; Figure 6This is a schematic diagram of the spiral microgroove structure on the surface of a single filament; Figure 7 This is a schematic diagram of the cross-sectional dimensions of the spiral microgroove; In the figure, 1-Type A welding wire, 2-Type B welding wire, 4-Axial direction, 5-Helical microgroove structure, 6-Circular bottom groove, 9-Reverse retwisting direction. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0043] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0044] The terms and parameters defined in this invention are as follows: The cross-sectional area ratio of Class A welding wire to Class B welding wire refers to the ratio of the total cross-sectional area of ​​Class A welding wire to the total cross-sectional area of ​​Class B welding wire in stranded submerged arc welding wire. When each individual wire has a circular cross-section, the ratio can be calculated by the square of the diameter of each individual wire.

[0045] Total equivalent diameter Deq: is the diameter of a circular solid welding wire that is equal to the sum of the cross-sectional areas of all the individual welding wire strands, satisfying Deq=√Σdi 2 , where di is the diameter of the i-th welding wire.

[0046] Pitch P: is the axial distance corresponding to one revolution of any outer strand around the axis of the stranded welding wire. Short pitch P1 and long pitch P2 alternate periodically along the axial direction. The axial length of a short pitch segment or a long pitch segment is the length of the section in which the pitch remains at a set value or smoothly transitions around that set value.

[0047] Reverse twist angle α: refers to the relative twist angle applied to the strand in the opposite direction to the basic twist direction after the basic strand is completed, while maintaining the axial tension of the strand welding wire. The axial length of one basic strand pitch is used as the unit of measurement. Reverse twist is a slight retwisting that does not reverse the final twist direction of the outer strands.

[0048] The depth h of the spiral microgroove is the normal distance from the baseline of the unprocessed surface to the lowest point of the groove.

[0049] The width w of the spiral microgroove is the distance between the intersection lines of the two sides of the groove and the unprocessed surface.

[0050] The pitch L of the spiral microgroove is the axial distance corresponding to one revolution of the same groove around the axis of a single filament.

[0051] The depth, width, and pitch of the spiral microgrooves can be measured using a three-dimensional optical profilometer, laser confocal microscope, or metallographic section. At least five positions along the axial direction should be selected for each sample and the average value should be taken.

[0052] Flux basicity: expressed as the IIW Basicity Index (BI), calculated using the following formula: BI=[CaO+MgO+CaF2+Na2O+K2O+Li2O+0.5(MnO+FeO)] / [SiO2+0.5(Al2O3+TiO2+ZrO2)] In the formula, each component represents a mass percentage.

[0053] Example 1 The stranded submerged arc welding wire prepared in this embodiment is formed by twisting three single wires together, such as... Figure 2 As shown, it includes two strands of Class A welding wire and one strand of Class B welding wire. The diameter of the Class A welding wire is 2.10 mm, and the diameter of the Class B welding wire is 2.40 mm. The cross-sectional area ratio of the Class A welding wire to the Class B welding wire is approximately 60.5:39.5, and the total equivalent diameter is approximately 3.82 mm. The pitch P varies periodically along the axial direction with alternating pitches P1 and P2, where P1 is 14 mm and P2 is 22 mm. The axial length of each P1 segment and each P2 segment is 120 mm.

[0054] Class A welding wire, by mass percentage, comprises: C 0.09%, Si 0.25%, Mn 1.85%, S 0.010%, P 0.015%, with the balance being Fe and unavoidable impurities.

[0055] Class B welding wire, by weight percentage, comprises: C 0.08%, Si 0.22%, Mn 1.90%, Mo 0.52%, S 0.009%, P 0.012%, with the balance being Fe and unavoidable impurities.

[0056] When twisting the wires, the tension of welding wire A should be controlled at 100N, and the tension of welding wire B should be controlled at 100N.

[0057] The core-shell gradient fluorine-alkali sintering flux prepared in this embodiment comprises, by mass percentage: 24% CaF2, 17% CaO, 10% MgO, 18% Al2O3, 11% SiO2, 7% MnO, 5% TiO2, 3% Na2O and K2O combined, 2% metallic manganese powder, and 3% sintering binder, with the balance being unavoidable impurities. The sintering binder is sodium silicate and potassium silicate in a 1:1 mass ratio.

[0058] The purified core particles include CaF2, CaO, MgO, and some sintering binder. The forming layer includes Al2O3, SiO2, MnO, TiO2, Na2O and K2O, metallic manganese powder, and the remaining sintering binder. The mass ratio of purified core particles to forming layer is 55:45, and the flux particle size is 14-50 mesh.

[0059] The preparation method of the core-shell gradient fluorine-alkali sintered flux provided in this embodiment is as follows: using disc granulation, the purified core particle raw material is mixed with a portion of the sintering binder and granulated to form purified core particles, which are pre-dried at 150°C for 2 hours. Then, the pre-dried purified core particles are placed in a disc coating device in a rolling or suspended state, the remaining sintering binder is sprayed in and the outer shell layer raw material is added, so that the outer shell layer raw material coats the surface of the core particles. The particles are dried at 180°C for 2 hours and sintered at 780°C for 1.2 hours. After cooling and sieving, a core-shell gradient fluorine-alkali sintered flux with a particle size of 14-50 mesh is obtained.

[0060] The core-shell gradient fluorine-alkali sintering flux prepared in this embodiment was dried at 350°C for 2 hours before use to ensure that its moisture content was no more than 0.08%.

[0061] Welding tests were conducted using the aforementioned stranded submerged arc welding wire and core-shell gradient fluorine-alkali sintered flux. The base material was Q420D, with a plate thickness of 28 mm, and a butt joint. The welding current was 640 A, the arc voltage was 32 V, the welding speed was 36 m / h, the heat input was approximately 34 kJ / cm, the preheating temperature was 80 °C, and the interpass temperature was 120 °C–160 °C. The test results are shown in the table below.

[0062] Example 2 The difference between this embodiment and Embodiment 1 is that the stranded submerged arc welding wire is formed by twisting together four single wires, such as... Figure 3 As shown, the welding includes two strands of Type A welding wire and two strands of Type B welding wire. The diameter of the Type A welding wire is 2.50 mm, and the diameter of the Type B welding wire is 2.30 mm. The cross-sectional area ratio of the Type A welding wire to the Type B welding wire is approximately 54.2:45.8, and the total equivalent diameter is approximately 4.80 mm. The two strands of Type B welding wire are arranged at intervals relative to each other in the circumferential direction. The strand pitch P changes periodically along the axial direction with alternating pitches P1 and P2, where P1 is 15 mm and P2 is 25 mm. The axial length of each P1 segment and each P2 segment is 150 mm. The remaining process steps and parameter settings are the same as in Example 1.

[0063] Welding tests were conducted using the aforementioned stranded submerged arc welding wire and core-shell gradient fluorine-alkali sintered flux. The base material was Q460D, with a thickness of 36mm. Double-sided, multi-layer, multi-pass butt welding was employed. The welding current was 720A, the arc voltage was 34V, the welding speed was 34m / h, the heat input was approximately 43kJ / cm, the preheating temperature was 100℃, and the interpass temperature was 140℃~180℃. The test results are shown in the table below.

[0064] Example 3 The difference between this embodiment and Embodiment 1 is that the stranded submerged arc welding wire is formed by twisting two single wires together, such as... Figure 1 As shown, it includes one strand of Class A welding wire and one strand of Class B welding wire. The diameter of Class A welding wire is 2.15 mm, and the diameter of Class B welding wire is 2.38 mm. The cross-sectional area ratio of Class A welding wire to Class B welding wire is approximately 44.9:55.1, and the total equivalent diameter is approximately 3.21 mm. The pitch P varies periodically along the axial direction with alternating pitches P1 and P2, P1 being 15 mm and P2 being 20 mm. The axial length of each P1 segment and each P2 segment is 200 mm. The core-shell gradient fluorine-alkali sintering flux IIW has an alkalinity index of 2.6 and a particle size of 10-60 mesh. By mass percentage, it includes: CaF2 24%, CaO 17%, MgO 10%, Al2O3 17%, SiO2 8%, MnO 7%, TiO2 5%, ZrO2 1.0%, B2O3 0.3%, CeO2 and La2O3 combined 0.4%, Na2O and K2O combined 3%, metallic manganese powder 2%, sintering binder 5.3%, and the balance being unavoidable impurities. The remaining process steps and parameter settings are the same as in Example 1.

[0065] Welding tests were conducted using the aforementioned stranded submerged arc welding wire and core-shell gradient fluorine-alkali sintered flux. The base material was Q420D, with a plate thickness of 28 mm, and a butt joint. The welding current was 640 A, the arc voltage was 32 V, the welding speed was 36 m / h, the heat input was approximately 34 kJ / cm, the preheating temperature was 80 °C, and the interpass temperature was 120 °C–160 °C. The test results are shown in the table below.

[0066] Example 4 The difference between this embodiment and Embodiment 1 is that: after the basic strand of the stranded submerged arc welding wire is prepared in Embodiment 1, an axial tension of 80N is maintained at the lead-out end, and retwisting is applied in the opposite direction of the basic stranding through an independent retwisting head. The reverse retwisting direction is as follows: Figure 5 As shown, the retwisting angle is set at 6° for each corresponding basic strand pitch. After retwisting, the wire is held at 240℃ for 1 hour for stress relief. After cooling, it is straightened and wound up. The final strand direction of the resulting stranded welding wire is still the basic strand direction, and each strand of welding wire maintains its original phase relationship, as shown. Figure 5 As shown, the retwisting angle can be set by the ratio of the retwisting head rotation speed to the traction speed, and verified by the surface marking method of stranded wire. During verification, reference marks are set at both ends of a basic strand pitch, and the relative circumferential angle change of the two marks before and after retwisting is measured.

[0067] Example 5 The difference between this embodiment and Embodiment 1 is that, in Embodiment 1, a spiral microgroove structure 5 is prepared on the surface of the Type B welding wire before the stranded submerged arc welding wire is prepared. Specifically, pulsed laser processing is used. The Type B welding wire rotates around its own axis and is continuously fed along the axial direction to form... Figure 6 and Figure 7 The circular arc bottom groove 6 is shown. The groove design depth h is 0.03mm (1.25% of the single wire diameter), the width w is 0.12mm (5% of the single wire diameter), and the pitch L is 6mm.

[0068] After laser processing, non-destructive mechanical brushing and solvent cleaning are used to remove adhering substances. Then, a three-dimensional optical profilometer is used to detect the depth and width of the groove at five positions along the axial direction. After surface inspection confirms the absence of continuous cracks, sharp edges, and obvious burrs, the B welding wire is twisted with two strands of A welding wire with a diameter of 2.10 mm according to the tension and variable pitch parameters of Example 1.

[0069] When using micro-roll forming, an embossing wheel with arc-shaped spiral ridges can be used instead of laser processing. The mounting angle between the embossing wheel and the welding wire axis, as well as the welding wire feed speed, jointly determine the groove pitch, while the reduction amount is used to control the groove depth.

[0070] Comparative Example 1 The difference between this comparative example and Example 1 is that: the stranded submerged arc welding wire is replaced with a single Class A welding wire, and the core-shell gradient fluorine-alkali sintering flux is replaced with a fluorine-alkali sintering flux. The specific fluorine-alkali sintering flux includes, by mass percentage: 30% CaF2, 10% CaO, 20% MgO, 20% Al2O3, 8% SiO2, 4% MnO, 2% metallic manganese powder, 1% 75# ferrosilicon powder, and 5% sintering binder. The remaining process steps and parameter settings are the same as in Example 1.

[0071] Comparative Example 2 The difference between this comparative example and Example 1 is that: the stranded submerged arc welding wire is replaced with a single type B welding wire, and the core-shell gradient fluorine-alkali sintering flux is replaced with a fluorine-alkali sintering flux. Specifically, the fluorine-alkali sintering flux includes, by mass percentage: 35% CaF2, 8% CaO, 25% MgO, 15% Al2O3, 25% SiO, 4% MnO, 1% metallic manganese powder, 1% 75# ferrosilicon powder, and 6% sintering binder; the remaining process steps and parameter settings are the same as in Example 1.

[0072] Comparative Example 3 The difference between this comparative example and Example 1 is that: the stranded submerged arc welding wire is replaced with ordinary stranded welding wire, which is an integrated solid welding wire made of multiple thin solid welding wires of the same material twisted into a rope shape; the core-shell gradient fluorine-alkali sintering flux is replaced with ordinary low-alkalinity sintering flux, which specifically includes the following by mass percentage: CaF2 20%, CaO 3%, MgO 15%, Al2O3 22%, SiO2 25%, MnO 4%, metallic manganese powder 2%, 75# ferrosilicon powder 1%, and sintering binder 8%; the remaining process steps and parameter settings are the same as in Example 1.

[0073] Welding tests were conducted on the welding wire and flux combinations provided in Comparative Examples 1-3. The base material was Q420D, with a plate thickness of 28mm, and it was a butt joint. The welding current was 640A, the arc voltage was 32V, the welding speed was 36m / h, the heat input was approximately 34kJ / cm, the preheating temperature was 80℃, and the interpass temperature was 120℃~160℃. The test results are shown in the table below.

[0074] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A stranded submerged arc welding wire for the wind power industry, characterized in that, The stranded submerged arc welding wire is formed by stranding 2 to 7 strands of Class A welding wire and / or Class B welding wire. The total equivalent diameter after stranding is 3.2 to 5.5 mm. The strand pitch P varies periodically along the axial direction with alternating pitches P1 and P2. P1 is 8 to 18 mm and P2 is 18 to 40 mm. The axial length of each P1 segment and each P2 segment is 50 to 250 mm.

2. The stranded submerged arc welding wire for the wind power industry according to claim 1, characterized in that, The single wire diameter dA of Class A welding wire is 1.0–2.5 mm, and by mass percentage includes: C 0.03–0.14%, Si≤0.35%, Mn 1.35–2.05%, S≤0.030%, P≤0.030%, with the balance being Fe and unavoidable impurities; the single wire diameter dB of Class B welding wire is 1.0–2.5 mm, and by mass percentage includes: C 0.04–0.13%, Si≤0.45%, Mn 1.40–2.15%, Mo 0.35–0.85%, S≤0.030%, P≤0.030%, with the balance being Fe and unavoidable impurities. And dB / dA is 0.85–0.98 or 1.02–1.

25.

3. The stranded submerged arc welding wire for the wind power industry according to claim 1, characterized in that, The stranded submerged arc welding wire is formed by twisting Class A welding wire and Class B welding wire together. The ratio of the total cross-sectional area of ​​Class A welding wire to the total cross-sectional area of ​​Class B welding wire is (35~70):(65~30). When the stranded submerged arc welding wire has a 3-strand structure, it includes 2 Class A welding wires and 1 Class B welding wire. When the stranded submerged arc welding wire has a 4-strand structure, it includes 2 Class A welding wires and 2 Class B welding wires. When the stranded submerged arc welding wire has a 5-strand structure, there are at least 2 Class B welding wires, and the Class B welding wire is the center strand, or the Class B welding wire is the center strand, and the Class A welding wires and Class B welding wires are alternately arranged in the outer layer along the circumferential direction.

4. The stranded submerged arc welding wire for the wind power industry according to claim 1, characterized in that, The stranded submerged arc welding wire also has a reverse twist structure, which is formed by applying a slight retwisting in the opposite direction to the basic stranding after the basic stranding is completed. The reverse twist angle α within each basic strand length is 3° to 12°.

5. The stranded submerged arc welding wire for the wind power industry according to claim 1, characterized in that, The surface of Class A welding wire and / or Class B welding wire is provided with at least one continuous or discontinuous spiral microgroove, wherein the depth h of the spiral microgroove is 0.5 to 5% of the diameter of the single wire, the width w is 3 to 20% of the diameter of the single wire, and the pitch L is 2 to 20 mm.

6. A method for preparing stranded submerged arc welding wire for the wind power industry according to any one of claims 1 to 5, characterized in that, Basic stranding was performed under the conditions of 40-140N tension for Class A welding wire and 50-160N tension for Class B welding wire. The stranding pitch P was changed periodically with alternating pitches P1 and P2 by a servo stranding head. Finally, the stranding was kept at 180℃-320℃ for 0.5-2 hours. When a reverse twist structure is set, a reverse twist angle of 3° to 12° is applied along the opposite twist direction after the basic strand of each basic twist pitch is completed.

7. A core-shell gradient fluorine-alkali type sintered flux for use with the stranded submerged arc welding wire for the wind power industry as described in any one of claims 1 to 5, characterized in that, The core-shell gradient fluorine-alkali sintered flux has a particle size of 10-60 mesh and a moisture content of no more than 0.08%. It consists of purified core particles and a forming layer covering the purified core particles. The purified core particles account for 35-70% of the total mass of the flux particles, and the forming layer accounts for 30-65% of the total mass of the flux particles. The core-shell gradient fluorine-alkali sintering flux comprises, by mass percentage: CaF2 18-35%, CaO 10-24%, MgO 4-12%, Al2O3 10-24%, SiO2 3-14%, MnO 2-10%, TiO2 1-8%, ZrO 20-3.0%, B2O 30-1.2%, CeO2 and / or La2O 30-1.5%, Na2O and K2O combined amount of 0.8%-5.0%, Li2O 0-1.0%, Fe-Mn or metallic manganese powder 0.5%-5%, sintering binder 1%-7%, and the balance being unavoidable impurities.

8. A method for preparing a core-shell gradient fluorine-alkali type sintering flux according to claim 7, characterized in that, The purified core particles are mixed with a portion of the sintering binder and granulated using disc granulation, drum granulation, extrusion granulation, drum coating, or fluidized bed coating to form purified core particles. These particles are then pre-dried at 100–180°C for 1–3 hours. The pre-dried core particles are then placed in a rolling or suspended state, and the remaining sintering binder and outer shell material are sprayed in to coat the surface of the core particles. The particles are then dried at 120–200°C and sintered at 650–850°C for 0.5–2.5 hours. After cooling and sieving, a core-shell gradient fluorine-alkali type sintered flux is obtained.

9. The preparation method according to claim 8, characterized in that, The sintering temperature is 750℃~800℃, and the sintering time is 1~1.5h.

10. A welding material for the wind power industry, characterized in that, The welding material includes the stranded submerged arc welding wire for the wind power industry as described in any one of claims 1 to 5 and the core-shell gradient fluorine-alkali sintered flux as described in claim 7. This welding material is used for automatic submerged arc welding of longitudinal seams, circumferential seams, flange connection areas, transition sections, or door frame reinforcement areas of Q420 or Q460 grade wind turbine towers.

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