Acidic flux-cored welding wire for X80 automatic welding, preparation method and girth welding joint

Abstract

The invention relates to the technical field of welding materials, in particular to an acidic flux-cored welding wire for X80 automatic welding, a preparation method and a girth welding joint. The invention comprises a flux core and a steel strip, wherein, by mass percentage, the flux core comprises 4% to 4.5% of SiO2, ≤7% of MgO, 15% to 20% of MnO, 45% to 55% of TiO2, 14% to 20% of NiO, ≤3% of Na2O, ≤2% of Al2O3 and ≤3% of ZrO2; and the steel strip comprises 0.02% to 0.04% of C, 0.15% to 0.35% of Mn, ≤0.03% of Si, ≤0.0015% of S, ≤0.015% of P, ≤0.05% of Al, ≤0.005% of N and ≤0.001% of B, with the balance being Fe. By controlling the composition of the steel strip and flux core, the optimal ratio of C, Mn, Si, and Ni in the welding wire is selected, improving the tensile strength, elongation at break, and impact absorption of the deposited metal. Controlling the P and S contents influences the CTOD value, ensuring that the CTOD value meets the standard requirement of ≥ 0.254 mm. This addresses the existing problem of weld joint performance requirements in which the CTOD value does not meet the standard value of 0.254 mm.

Description

Technical Field

[0001] The present invention relates to the technical field of welding materials, in particular to an acid flux-cored welding wire for X80 automatic welding, a preparation method and a girth welding joint. Background Art

[0002] The development of welding materials has evolved alongside industrial progress. Long-distance oil and gas pipelines utilize thick-walled, large-diameter steel pipes, whose strength is ensured through the use of various alloying elements, microstructure types, and grain refinement. Solid-wire gas-shielded automatic welding and gas-shielded flux-cored automatic welding are the development trends for welding large-diameter, thick-walled oil and gas pipelines. However, limited research has examined the suitability of newly developed welding materials for these processes for welding thick-walled, high-grade pipeline steel pipes of varying chemical compositions, hindering the large-scale application of these high-grade girth weld materials.

[0003] Currently, many welding construction standards are required for external piping systems. However, regardless of the welding construction standard, the requirements and acceptance criteria for tensile, impact, bending, and notch hammer fracture tests vary significantly. The number of tensile and bending tests varies depending on the pipe diameter. The tensile acceptance index must be greater than or equal to the nominal minimum tensile strength of the pipe. When fractured in the parent material, the strength must be no less than 95% of the nominal minimum tensile strength of the pipe to be considered acceptable. For example, the impact toughness acceptance index, for example, of X80-grade pipeline steel, must meet the design requirements or have a minimum average of 40 J and a minimum individual value of 30 J. Regarding the acceptance value of crack tip opening displacement (CTOD), only AS2885.2 and DNV F101 have relevant requirements. AS2885.2 requires CTOD test results to meet an average of 0.15 mm and a minimum of 0.10 mm, while DNV F101 requires them to meet the design requirements, generally 0.15 mm.

[0004] At present, the most stringent international acceptance standard is the CTOD acceptance value of 0.254mm stipulated in DEC-NGP-G-WD-002-2020-1 "Technical Regulations for Welding of Oil and Gas Pipeline Engineering Lines". The distribution trend of the CTOD value of the weld joint inspection of the currently used gas shielded flux-cored welding wire is shown in Figure 1 As can be seen, the CTOD values ​​of welds undergoing welding procedure qualification generally ranged from 0.10 to 0.213 mm. Only one specimen achieved a value of 0.261 mm, meeting the requirement. All weld CTOD tests failed to meet the standard requirement of 0.254 mm. This demonstrates that existing welding technology still fails to meet the standard value of 0.254 mm in terms of weld performance requirements. Summary of the Invention

[0005] Aiming at the problem that the welding technology in the prior art cannot meet the standard value of 0.254mm in terms of weld performance requirements, the present invention provides an X80 acid flux-cored welding wire for automatic welding.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention provides an acidic flux-cored welding wire for X80 automatic welding, comprising a flux core and a steel strip, wherein the flux core is filled in the steel strip;

[0008] The core comprises the following components by mass percentage: 4% to 4.5% SiO2, ≤7% MgO, 15% to 20% MnO, 45% to 55% TiO2, 14% to 20% NiO, ≤3% Na2O, ≤2% Al2O3 and ≤3% ZrO2; the rest are CaO, K2O, CeO2, P2O5, Bi2O3, La2O3 and Nb2O5, and the sum of CaO, K2O, CeO2, P2O5, Bi2O3, La2O3 and Nb2O5 is ≤0.7%;

[0009] The steel strip comprises the following components by mass percentage:

[0010] 0.02% to 0.04% C, 0.15% to 0.35% Mn, ≤0.03% Si, ≤0.0015% S, ≤0.015% P, ≤0.05% Al, ≤0.005% N and ≤0.001% B, with the balance being Fe.

[0011] Preferably, the deposited metal composition of the welding wire includes, by mass percentage, 0.03% to 0.06% C, 1% to 1.7% Mn, 0.15 to 0.5% Si, S≤0.01%, and P≤0.012%.

[0012] Preferably, the deposited metal has a tensile strength of ≥674 MPa, a yield strength of ≥615 MPa, an elongation after fracture of ≥22%, an impact energy of 122 to 123 J at -20°C, and an impact energy of 81 to 109 J at -40°C.

[0013] Preferably, the steel strip has a tensile strength of 280-360 MPa, a yield strength of ≥140 MPa, an elongation of ≥38%, and a hardness HRB of ≥40.

[0014] Preferably, the steel belt is a U-shaped steel belt.

[0015] Preferably, the steel strip oil content is 0.2-0.5 g / 10 kg.

[0016] The method for preparing the above-mentioned X80 acid flux-cored welding wire for automatic welding comprises the following steps:

[0017] Mixing the raw material powders of the core components uniformly according to the percentage of the raw material components to obtain a core mixed powder;

[0018] Prepare the steel strip and treat the surface of the steel strip;

[0019] Filling the flux core mixed powder into the steel strip to prepare a prefabricated welding wire;

[0020] The prefabricated welding wire is drawn and reduced in diameter to reach a target diameter, thereby obtaining an acid flux-cored welding wire.

[0021] Preferably, the prefabricated welding wire is drawn at a speed of 100±50 m / min.

[0022] A girth weld joint is formed by welding with the above-mentioned X80 automatic welding acid flux-cored wire.

[0023] Preferably, the tensile strength of the girth weld joint should be ≥625MPa; the fracture toughness test value CTOD of the weld and heat-affected zone should be ≥0.254mm; the hardness value of the girth weld joint weld metal and heat-affected zone root weld should be ≤300HV 10 , other locations ≤325HV 10 ; The Charpy impact toughness of the girth weld joint at -20℃ has a single value of ≥38J and an average value of ≥50J.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention discloses an acidic flux-cored welding wire for X80 automatic welding, comprising a flux core and a steel strip, wherein the flux core is filled in the steel strip;

[0026] The core comprises the following components by mass percentage: 4% to 4.5% SiO2, ≤7% MgO, 15% to 20% MnO, 45% to 55% TiO2, 14% to 20% NiO, ≤3% Na2O, ≤2% Al2O3 and ≤3% ZrO2;

[0027] The steel strip comprises the following components by mass percentage:

[0028] 0.02% to 0.04% C, 0.15% to 0.35% Mn, ≤0.03% Si, ≤0.0015% S, ≤0.015% P, ≤0.05% Al, ≤0.005% N and ≤0.001% B, with the balance being Fe.

[0029] The flux system of this welding wire is TiO2-MnO-NiO-Fe2O3-MgO-SiO2. By controlling the composition of the steel strip and flux core, the optimal ratio of C, Mn, Si, and Ni is selected throughout the wire, thereby improving the tensile strength, elongation at break, and impact absorption of the deposited metal. Further control of the P and S contents influences the CTOD value, ensuring that the CTOD value meets the standard requirement of ≥0.254mm. Testing has shown that the deposited metal, weld seam, and other joint properties of this welding wire meet the highest international standards.

[0030] The C content in the deposited metal is set between 0.030% and 0.060%. A C content less than 0.030% cannot meet the strength requirements of the deposit and process joint. A C content greater than 0.060% will easily cause the tensile strength of the deposited metal to exceed 690MPa, affecting the elongation, impact absorption capacity and CTOD value of the deposited metal and process joint. The Mn content is set between 1.00% and 1.70%, the Si content is set between 0.15% and 0.50%, and the Ni content is designed to be between 1.5% and 2.0%. This combination can achieve good impact performance, elongation and CTOD value. P ≤ 0.012%, S ≤ 0.010%. High P and S contents will reduce the low-temperature impact value and increase the brittle temperature, thereby affecting the CTOD value.

[0031] The present invention also provides a method for preparing an acidic flux-cored welding wire for automatic welding, such as X80. The method comprises the following steps: uniformly mixing the raw material powders of the flux-cored components according to the raw material component percentages to obtain a flux-cored mixed powder; preparing a steel strip and treating the surface of the steel strip; filling the steel strip with the flux-cored mixed powder to prepare a prefabricated welding wire; and drawing and reducing the prefabricated welding wire to a target diameter to obtain the acidic flux-cored welding wire. The preparation method is simple and easily industrialized.

[0032] The present invention also provides a girth weld joint, which is welded using the above-mentioned X80 automatic welding acid flux-cored wire. The tensile strength of the girth weld joint should be ≥625MPa; the fracture toughness test value CTOD of the weld and heat-affected zone should be ≥0.254mm; the hardness value of the weld metal and heat-affected zone of the girth weld joint should be ≤300HV 10 , other locations ≤325HV 10 The Charpy impact toughness of girth welded joints at -20℃ is ≥38J in single value and ≥50J in average value, meeting the highest international standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a distribution trend diagram of the CTOD value of the weld detection of the gas shielded flux-cored welding wire used in the prior art of the present invention.

[0034] Figure 2 The present invention is a flow chart of a method for preparing an acidic flux-cored welding wire for X80 automatic welding.

[0035] Figure 3 This is a macroscopic view of the girth weld after welding using the acid flux-cored wire for X80 automatic welding according to the present invention.

[0036] Figure 4 This is a sampling diagram for testing the mechanical properties of the girth weld after welding using the acidic flux-cored wire for X80 automatic welding according to the present invention.

[0037] Figure 5 This is a tensile stress-strain curve diagram of the girth weld after welding using the acid flux-cored wire for X80 automatic welding of the present invention, wherein a is the tensile stress-strain curve diagram of the entire weld numbered T0-WM, and b is the tensile stress-strain curve diagram of the entire weld numbered T6-WM.

[0038] Figure 6 This is a diagram of the indentation positions of the girth weld sample taken after welding with the acidic flux-cored wire for X80 automatic welding according to the present invention.

[0039] Figure 7 These are macroscopic morphologies of the girth weld sampled after welding using the acid flux-cored wire for X80 automatic welding according to the present invention, wherein a is the macroscopic morphology of the weld in the M0 flat welding position, b is the macroscopic morphology of the weld in the M3 vertical welding position, and c is the macroscopic morphology of the weld in the M6 ​​overhead welding position.

[0040] Figure 8 This is the flat weld after welding using the acid flux-cored wire for X80 automatic welding of the present invention, where a is the stress loading and crack tip angular displacement diagram of the CTOD test of D0-WM, and b is the weld fracture morphology after the CTOD test.

[0041] Figure 9 This is the heat-affected zone of the flat weld after welding with the acid flux-cored wire for X80 automatic welding according to the present invention, where a is the stress loading and crack tip angular displacement diagram of the CTOD test of the D0-HAZ, and b is the fracture morphology of the weld heat-affected zone after the CTOD test.

[0042] Figure 10 This is a vertical weld obtained by welding with the acidic flux-cored wire for X80 automatic welding according to the present invention, wherein a is a stress loading and crack tip angular displacement diagram of the CTOD test of D3-WM, and b is a weld fracture morphology diagram after the CTOD test.

[0043] Figure 11 This is the heat-affected zone of the vertical girth weld after welding with the acidic flux-cored wire for X80 automatic welding according to the present invention, wherein a is the stress loading and crack tip angular displacement diagram of the CTOD test of D3-HAZ, and b is the fracture morphology of the weld heat-affected zone after the CTOD test.

[0044] Figure 12This is a weld welded in the backward position using the acid flux-cored wire for X80 automatic welding according to the present invention. a is the stress loading and crack tip angular displacement diagram of the CTOD test of D6-WM, and b is the weld fracture morphology after the CTOD test.

[0045] Figure 13 This is the heat-affected zone of the weld in the backward tilt position welded with the acid flux-cored wire for X80 automatic welding according to the present invention, wherein a is the stress loading and crack tip angular displacement diagram of the CTOD test of D6-HAZ, and b is the fracture morphology of the weld heat-affected zone after the CTOD test. DETAILED DESCRIPTION

[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of 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. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0047] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0048] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0049] In the description of the embodiments of the present invention, it should be noted that if the terms "upper," "lower," "horizontal," "inner," etc. appear, the orientation or positional relationship indicated is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the inventive product is typically placed when in use. These terms are merely for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first," "second," etc. are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0050] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0051] In the description of the embodiments of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0052] The present invention will be further described in detail below with reference to specific embodiments, which are intended to explain the present invention rather than to limit it.

[0053] The present invention provides an acidic flux-cored welding wire for X80 automatic welding, comprising a flux core and a steel strip, wherein the flux core is filled in the steel strip;

[0054] The core comprises the following components by mass percentage: 4% to 4.5% SiO2, ≤7% MgO, 15% to 20% MnO, 45% to 55% TiO2, 14% to 20% NiO, ≤3% Na2O, ≤2% Al2O3 and ≤3% ZrO2;

[0055] The steel strip comprises the following components by mass percentage:

[0056] 0.02% to 0.04% C, 0.15% to 0.35% Mn, ≤0.03% Si, ≤0.0015% S, ≤0.015% P, ≤0.05% Al, ≤0.005% N and ≤0.001% B, with the balance being Fe.

[0057] Calculated by mass percentage, the deposited metal composition of the welding wire is: 0.03% to 0.06% C, 1% to 1.7% Mn, 0.15% to 0.5% Si, S < 0.01%, and P < 0.012%.

[0058] The deposited metal has a tensile strength greater than 674 MPa, a yield strength greater than 615 MPa, an elongation after fracture greater than 22%, an impact energy at -20°C of 122 to 123 J, and an impact energy at -40°C of 81 to 109 J.

[0059] The composition system TiO2-MnO-NiO-MgO-Al2O3-SiO2 powder and steel strip components are key factors to ensure the performance of girth welds and excellent welding processability. The total amount of TiO2-MnO-NiO-MgO-Al2O3-SiO2 in the composition system does not exceed 95%; MgO+Na2O≤8.3%; trace oxides are residual in minerals, with a total amount of ≤0.7%;

[0060] Preferably, the steel belt is a U-shaped steel belt, and the oil content of the steel belt is 0.2-0.5 g / 10 kg.

[0061] See also Figure 2 The present invention also provides a method for preparing the above-mentioned X80 acid flux-cored welding wire for automatic welding, comprising the following steps:

[0062] S1: Mix the raw material powders of the core components uniformly according to the percentage of the raw material components to obtain the core mixed powder; according to the mechanical properties and diffusible hydrogen content requirements of the deposited metal of the welding wire, the requirements of GB / T 36233-2018 "High-strength Steel Flux-cored Welding Wire", the mechanical properties of the girth weld joint welded with this welding wire meet the requirements of DEC-NGP-G-WD-002-2020-1 "Technical Regulations for Welding of Oil and Gas Pipeline Engineering Lines", to determine the design and optimization of the composition system of the flux powder in the flux-cored welding wire. Furthermore, the influence of the welding process parameters on the process performance of the welding wire during on-site combined automatic welding is analyzed, such as welding spatter, molten iron fluidity and spreadability, droplet transfer form, slag removal, etc., and the alloy composition of the flux core is slightly adjusted so that the flux core includes 4% to 4.5% SiO2, ≤7% MgO, 15% to 20% MnO, 45% to 55% TiO2, 14% to 20% NiO, ≤3% Na2O, ≤2% Al2O3 and ≤3% ZrO2 by mass percentage;.

[0063] S2: Prepare the steel strip and treat its surface. According to the provisions of GB / T 36233-2018, "High-Strength Steel Flux-Cored Welding Wire," the requirements for diffusible hydrogen content in the deposited metal and wire feeding stability are ensured. The steel strip process required for producing acidic flux-cored welding wire is specified, and process control of the steel strip surface treatment and oil content is performed. This application uses SPCC cold-rolled bright steel strip for production. The protective oil content and cleaning conditions on the steel strip surface are also specified. After the flux stirring and steel strip rewinding processes, the welding wire is formed. The steel strip is a U-shaped steel strip, and the oil content of the steel strip is 0.2 to 0.5 g / 10 kg.

[0064] S3: Filling the steel strip with the flux core powder mixture to prepare the prefabricated welding wire; removing the crystal water from the welding wire core and then mixing it evenly to achieve the target flux core powder particle size. The flux core powder mixture is added to the U-shaped groove of the steel strip via a powder feeder. The filling ratio of the flux core powder mixture in the steel strip is controlled to a standard value of 13%-15%, with a filling ratio deviation within ±0.6% of the standard value. The target filling ratio is 14%, with a deviation of ±0.6%.

[0065] S4: The preformed welding wire is drawn and reduced to the target diameter, producing acidic flux-cored welding wire. The drawing process is strictly controlled to maintain stable wire specifications, with the wire diameter deviation from the standard wire diameter required to be within a range of -0.03mm to -0.01mm. The preformed wire is drawn at a speed of 100±50m / min. The drawing process continues with a high-strength, straight-line wire drawing machine. Fine drawing of the flux-cored wire is achieved using the drawing die on the production line. Each cross-sectional diameter deformation is drawn through a die hole of a specific shape and size, ultimately achieving the required diameter of the finished product. The wire diameter is strictly controlled, and online real-time wire diameter monitoring equipment is installed to ensure consistent quality. The fine drawing line speed is ≤1500m / min, and the oil content is specified within a range of 0.2-1.0g / 10kg. Specifically, the preformed welding wire is wound onto wire reels according to a specific weight. The winding process relies primarily on linear adjustment of the wire to improve wire feedability. During the coiling process, wire pressing wheels acting in different directions eliminate internal stress in the wire while adjusting the relaxation diameter and pitch. Appropriate relaxation diameter and pitch reduce resistance to wire passing through the wire feed tube, ensuring consistent wire feeding and enabling on-site welding testing. Welding is performed according to the on-site combined automatic welding procedure specifications. After on-site welding process tests and weld joint mechanical property tests meet the requirements, the X80 fully automatic acid-cored welding wire for stress-based design is obtained, achieving both the required welding process and weld joint performance.

[0066] During operation, test welds are conducted according to established on-site welding procedure specifications, and the welding parameters of the on-site combined automatic welding equipment are adjusted. Continuous joint welding is then performed, with precise adjustments made to welding process parameters such as welding current, welding voltage, wire feed speed, dwell time, gas flow rate, and welding heat input. During automatic welding, the welding wire's welding processability is evaluated, including arc stability, droplet transfer, weld pool fluidity, spatter, and slag removal. After the girth weld is welded and passes nondestructive testing, transverse and longitudinal tensile testing, lateral bending, hardness, metallography, notch hammer fracture, impact toughness testing at different locations, and CTOD specimen cutting and machining are performed on the girth weld. Transverse plate specimens of the girth weld are subjected to tensile testing. The fracture location is recorded. If the fracture occurs in the parent material and the tensile strength is greater than or equal to 95% of the nominal strength of the pipe, it is considered acceptable. If the fracture occurs in the weld, the tensile strength is greater than or equal to the nominal strength of the pipe, which is considered acceptable.

[0067] After the combined automatic welding is performed, the welding procedure is evaluated and the performance indicators of the weld are as follows: the tensile strength of the girth weld joint shall not be less than 625MPa, and the tensile strength of the weld round bar specimen shall be equivalent to the strength of the pipe; the fracture toughness test value of the weld and heat-affected zone, i.e. the crack tip displacement (CTOD), shall meet the requirement of ≥0.254mm. The CTOD specimens shall be prepared and tested in accordance with GB / T 21143, and the test results shall be calculated in accordance with GB / T 28896; the hardness value of the weld metal and heat-affected zone of the girth weld joint shall not exceed 300HV for root welding. 10 , the rest of the parts are not more than 325HV 10 ; The single value of Charpy impact toughness of girth weld joint at -20℃ should not be less than 38J, and the average value should not be less than 50J.

[0068] The present invention provides a girth weld joint, which is welded using the above-mentioned X80 automatic welding acid flux-cored wire. The tensile strength of the girth weld joint should be ≥625MPa; the fracture toughness test value CTOD of the weld and heat-affected zone should be ≥0.254mm; the hardness value of the weld metal and heat-affected zone of the girth weld joint should be ≤300HV 10 , the rest of the parts are not more than 325HV 10 ; The Charpy impact toughness of the girth weld joint at -20℃ has a single value of ≥38J and an average value of ≥50J.

[0069] Example

[0070] An analysis is conducted using the stress-based design of the X80 domestically produced acidic flux-cored wire for automatic welding in an X80 pipeline project. The composition and properties of the deposited metal, the on-site welding process performance, and the mechanical properties of the completed weld joint are evaluated.

[0071] First, the powder is mixed according to the ingredient ratio of the core to obtain the core mixed powder. The core ingredients are shown in the following table:

[0072]

[0073] The steel strip is then re-cut and rewound according to the requirements. A powder feeder then feeds the flux-cored mixed powder into the steel strip, which has been rolled into a U-shaped groove by a forming machine. The strip is then drawn, resulting in the X80 fully automatic acid-cored welding wire for stress-based design that meets the requirements.

[0074] The deposited metal performance test of the prepared welding wire is carried out. The test results and standards are shown in the following table:

[0075]

[0076] It can be seen that the deposited metal composition of the X80 acid flux-cored welding wire for automatic welding prepared in this application is better than the current standard values.

[0077] The yield strength, tensile strength and -40°C Charpy impact performance tests were performed on the deposited metal of the X80 acidic flux-cored wire for automatic welding prepared in this application. The test results and standard values ​​are shown in the following table:

[0078]

[0079] It can be seen that the mechanical properties of the deposited metal are also better than the standard values.

[0080] See also Figure 3 The circumferential welds welded with the welding wire produced by this invention patent have beautiful weld surface, small welding spatter, no large particles of molten metal spatter, and the weld height is evenly distributed throughout the weld, indicating that the process parameters of the welding wire are stable, the wire feeding speed is stable, and it has excellent welding processability.

[0081] After the deposited metal passed the test, an on-site automatic welding test was conducted. The macroscopic image of the girth weld after welding showed that the pipes butt-welded in all positions using the X80 automatic welding acid flux-cored wire had uniform weld morphology, beautiful weld surface, good slag removal, and low spatter during the welding process, indicating that the product has good welding process performance. The appearance process evaluation indicators are shown in the table below:

[0082]

[0083] It can be seen that the appearance after welding is good and meets the appearance requirements of welding.

[0084] After welding, the weld joint is subjected to non-destructive testing, and after non-destructive testing, mechanical properties testing is performed. Figure 4 , the sampling diagram of the mechanical test is used for sampling, and the tensile, impact, bending, notch hammer fracture, hardness, metallographic and CTOD tests are carried out at different welding positions of the weld to test the mechanical properties of the weld and check its welding processability. The tensile test is based on the standard GB / T228.1-2021. The tensile strength test results are shown in the table below:

[0085]

[0086] In the table, T0-WM and T6-WM are full weld specimens, and T1, T2, T3 and T4 are welded joint specimens. Figure 5The stress-strain curves of the full-weld longitudinal tensile specimens show that the weld metal has a yield strength of 620MPa-650MPa, a tensile strength of 641MPa-677MPa, and a uniform elongation of 26.5%-28.0%, all meeting the requirements of DEC-NGP-G-WD-002-2020-1, "Technical Specifications for Welding of Oil and Gas Pipeline Engineering Lines," and exhibiting excellent tensile properties. The transverse tensile strength of the girth weld reaches 662MPa-688MPa, achieving an equal strength match with X80-grade pipeline steel and meeting the DEC standard for tensile strength of X80-grade girth welds.

[0087] Charpy impact test: welding was performed using the welding wire prepared in this application, and samples were taken from the weld after welding. The sampling number was based on the standard GB / T 229-2020. The test results are shown in the table below:

[0088]

[0089]

[0090] The weld joints were sampled and numbered after welding, and the notch hammer fracture test was carried out according to the standard GB / T 31032-2014. The test results are shown in the following table:

[0091]

[0092] The samples were numbered and subjected to guided bending tests according to the standard GB / T2653-2008. The test results are shown in the table below:

[0093]

[0094]

[0095] See also Figure 6 According to the indentation position, the Vickers hardness test is carried out and the hardness value is 211HV 10 ~245HV 10 The hardness distribution of the overall girth weld is stable, with no prominent high-value hardness points, indicating that the heat input temperature during the welding process is high and the structure of the girth weld joint is uniform. The test results are shown in the table below:

[0096]

[0097] The samples were numbered and radial analysis was performed on samples with different numbers. The analysis results are shown in Figure 7 It can be seen that the number of welding layers at different positions of the weld is consistent, the weld layer is clear, and there are no welding defects, indicating that the welding wire has good welding processability.

[0098] The results of the weld low-magnification inspection are shown in the following table:

[0099]

[0100] From the above mechanical property test results, it can be seen that the mechanical properties of the welding wire prepared by the present application after welding are better than the standard value. It can be seen that the welds welded by the welding wire prepared by the present application have excellent strengthening and toughening properties.

[0101] Yield strength R of the sample material at the test temperature p0.2 =744MPa; tensile strength R m =807MPa, Poisson's ratio is taken as 0.3 during the calculation process, and elastic modulus E = 210GPa.

[0102] One specimen was taken from each of the weld seam and heat-affected zone (HAZ) at the flat, vertical, and overhead positions of the weld. The specimens were numbered D0-WM, D0-HAZ, D3-WM, D3-HAZ, D6-WM, and D6-HAZ. The specimens were three-point bend specimens with nominal dimensions of W = 36 mm and B = 18 mm. A solid knife-edge specimen (Z = 0) was used. Prefabricated fatigue crack data is shown in the table below:

[0103]

[0104] The test was conducted in accordance with the standard GB / T21143-2014, with a loading speed of 1 mm / min. The COD gauge model used to monitor the crack mouth opening displacement was 3541-005M-100M-ST. The crack length was measured using a fracture analyzer with a measurement accuracy of 0.001 mm. The crack size test results are shown in the table below:

[0105]

[0106] The results of the CTOD test are shown in the table below:

[0107]

[0108]

[0109] The results of the validation of the CTOD test results are shown in the following table:

[0110] Serial number Judgment content Is it satisfied 1 The specimen shall meet the requirements of 5.4.1 for dimensions and tolerances; satisfy 2 The test device shall meet the requirements of 5.7 for error and coaxiality; satisfy 3 The testing machine and extensometer shall meet the accuracy requirements of 5.6; satisfy 4 <![CDATA[The average initial crack length a0 should be between 0.45W and 0.7W;]]> satisfy 5 The length of the prefabricated fatigue crack should be no less than 1.3 mm or 2.5% W, whichever is greater; satisfy 6 The fatigue pre-cracks on both surfaces of the specimen should be within the envelope; satisfy 7 The stress intensity factor of prefabricated fatigue cracks shall meet the requirements of 5.4.2.4; satisfy 8 <![CDATA[The difference between the initial crack length at the middle seven points and the average value of the initial cracks at the nine points should not exceed 0.10a0;]]> satisfy 9 The initial slope of the force-displacement recording should be between 0.85 and 1.5; satisfy

[0111] Combine Figures 8 to 13, the stress loading and crack tip angular displacement diagram (Figure a) of the weld and heat-affected zone in the CTOD test at different welding positions (0-point flat welding, 3-point vertical welding and 6-point overhead welding) and the fracture morphology after the CTOD test show that the CTOD values ​​of the weld and heat-affected zone calculated according to GB / T 28896 are both >0.254mm, showing good fracture toughness and crack propagation resistance. The above description is only a preferred embodiment of the present invention and is not intended to limit the technical solution of the present invention in any way. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can also be subjected to several simple modifications and replacements, and these modifications and replacements are also within the scope of protection covered by the claims.

Claims

1. An acid flux-cored wire for X80 automatic welding, characterized in that: It comprises a core and a steel strip, wherein the core is filled in the steel strip; The core comprises the following components by mass percentage: 4% to 4.5% SiO2, greater than 0 and less than or equal to 7% MgO, 15% to 20% MnO, 45% to 55% TiO2, 14% to 20% NiO, ≤3% Na2O, greater than 0 and less than or equal to 2% Al2O3 and ≤3% ZrO2; the rest are CaO, K2O, CeO2, P2O5, Bi2O3, La2O3 and Nb2O5, and the sum of CaO, K2O, CeO2, P2O5, Bi2O3, La2O3 and Nb2O5 is ≤0.7%; MgO+Na2O≤8.3%; The steel strip comprises the following components by mass percentage: 0.02% to 0.04% C, 0.15% to 0.35% Mn, ≤0.03% Si, ≤0.0015% S, ≤0.015% P, ≤0.05% Al, ≤0.005% N and ≤0.001% B, with the balance being Fe; Calculated by mass percentage, the deposited metal composition of the welding wire includes: 0.03% to 0.06% C, 1% to 1.7% Mn, 0.15% to 0.5% Si, S≤0.01%, P≤0.012% and 1.5% to 2.0% Ni.

2. The X80 acid flux-cored welding wire for automatic welding according to claim 1, characterized in that: The deposited metal has a tensile strength of ≥674 MPa, a yield strength of ≥615 MPa, an elongation after fracture of ≥22%, an impact energy of 122 to 123 J at -20°C, and an impact energy of 81 to 109 J at -40°C.

3. The X80 acid flux-cored welding wire for automatic welding according to claim 1, characterized in that: The steel strip has a tensile strength of 280-360 MPa, a yield strength of ≥140 MPa, an elongation of ≥38%, and a hardness HRB of ≥40.

4. The X80 acid flux-cored welding wire for automatic welding according to claim 1, characterized in that: The steel belt is a U-shaped steel belt.

5. The X80 acid flux-cored welding wire for automatic welding according to any one of claims 1 to 4, characterized in that: The steel strip oil content is 0.2-0.5 g / 10 kg.

6. The method for preparing the X80 acid flux-cored welding wire for automatic welding according to any one of claims 1 to 5, characterized in that: The following steps are involved: Mixing the raw material powders of the core components uniformly according to the percentage of the raw material components to obtain a core mixed powder; Prepare the steel strip and treat the surface of the steel strip; Filling the flux core mixed powder into the steel strip to prepare a prefabricated welding wire; The prefabricated welding wire is drawn and reduced in diameter to reach a target diameter, thereby obtaining an acid flux-cored welding wire.

7. The method for preparing the X80 acid flux-cored welding wire for automatic welding according to claim 6, characterized in that: The prefabricated welding wire is drawn at a speed of 100±50m / min.

8. A girth weld joint, characterized in that: The welding method is achieved by welding the X80 acid flux-cored wire for automatic welding according to any one of claims 1 to 5.

9. The girth weld joint according to claim 8, characterized in that: The tensile strength of the girth weld joint should be ≥625MPa; the fracture toughness test value CTOD of the weld and heat-affected zone should be ≥0.254mm; the hardness value of the girth weld weld metal and heat-affected zone root weld should be ≤300HV 10 , other locations ≤325HV 10 ; The Charpy impact toughness of the girth weld joint at -20℃ has a single value of ≥38J and an average value of ≥50J.

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