Welding method for 690mpa grade high-strength steel plate

Abstract

The application discloses a welding method for a 690MPa high-strength steel plate, which comprises the following steps: bevel processing; cleaning and polishing; preheating to 50-80 DEG C; submerged arc welding, welding current is 375-550A, welding voltage is 26-30V, welding speed is 40-48cm / min, welding heat input is 12-25kJ / cm, and the welding wire comprises the following components: C 0.04-0.08%, Si 0.22-0.32%, Mn 1.3-1.5%, Ni 2.7-3.3%, S≤0.008%, P≤0.0015%, Cu 0.043-0.062%, Cr 0.2-0.28%, Mo 0.44-0.56%, Ti 0.015-0.025%, and the rest is Fe and impurities. The CTOD of the weld metal and the coarse grain zone of the welding heat affected zone at-35 DEG C is greater than or equal to 0.25mm.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of welding, and particularly relates to a welding method suitable for 690MPa high-strength steel plate. BACKGROUND

[0002] In recent years, steel structure engineering such as bridges, offshore platforms, the construction industry, engineering machinery, LPG storage tanks and the like are developing in the direction of large-scale, and the strength grade of steel is required to be higher and higher. However, large-scale steel structure engineering often needs to weld steel, and as the design requirements of steel structure engineering are higher and higher, the steel field not only puts forward higher requirements on the strength and toughness of steel, but also needs to have excellent welding performance, such as excellent fracture toughness of the welding heat-affected zone, to improve the service safety.

[0003] At present, most of the large steel structure parts such as bridges, offshore platforms, engineering machinery and LPG storage tanks adopt high-strength medium-thick steel plates with a yield strength of 690MPa. However, such steel plates have problems such as great cold crack sensitivity, softening of the welding heat-affected zone, insufficient toughness reserve and the like in the welding process. Brittle fracture easily occurs in the coarse grain zone of the welding heat-affected zone, and such brittle fracture is difficult to be detected by ultrasonic or radiographic inspection methods, which has great safety hazards. SUMMARY

[0004] In order to solve the above technical problems, the purpose of the present application is to provide a welding method suitable for 690MPa high-strength steel plate, so as to improve the welding performance of 690MPa high-strength steel plate and improve the low-temperature fracture toughness of the welded joint.

[0005] In order to achieve the above-mentioned purpose of the application, an embodiment of the present application provides a welding method suitable for 690MPa high-strength steel plate, which is used for welding 690MPa high-strength steel plate. In the steel plate, the content of C is 0.06-0.09wt%, the carbon equivalent Ceq is <0.58%, and the cold crack sensitivity index Pcm is ≤0.235%.

[0006] The welding method comprises the following steps:

[0007] Beveling processing is performed on the to-be-welded end of the steel plate;

[0008] The bevel surface of the steel plate is cleaned and polished;

[0009] The steel plate is preheated to a steel plate temperature of 50-80℃;

[0010] The same thickness steel plates are welded by submerged arc welding to form welded joints between the steel plates, the welding current is controlled to be 375-550A, the welding voltage is controlled to be 26-30V, the welding speed is controlled to be 40-48cm / min, the welding heat input is controlled to be 12-25kJ / cm, and the chemical composition of the submerged arc welding wire used includes, by mass percent: C 0.04-0.08%, Si 0.22-0.32%, Mn 1.3-1.5%, Ni 2.7-3.3%, S≤0.008%, P≤0.0015%, Cu 0.043-0.062%, Cr 0.20-0.28%, Mo 0.44-0.56%, Ti 0.015-0.025%, and the rest is Fe and inevitable impurities.

[0011] Preferably, in the steel plate, the content of Ni is 1.7-1.9wt%, the content of P is≤0.008wt%, the content of S is≤0.005wt%, and the content of N is≤0.005wt%.

[0012] Preferably, the submerged arc welding uses high-alkaline non-alloyed sintered flux.

[0013] Preferably, the flux used for the submerged arc welding is OK Flux 10.62 flux.

[0014] Preferably, the thickness of the steel plate is 20-55mm, and the diameter of the welding wire is 3.2mm.

[0015] Preferably, in the beveling process of the to-be-welded end of the steel plate, V-shaped bevels with a bevel angle of θ / 2 are respectively formed on the upper and lower surfaces of the to-be-welded end of each of the two steel plates to-be-welded, so that V-shaped bevels with a bevel angle of θ are formed between the two steel plates, and θ is 65°-70°.

[0016] Preferably, in the beveling process of the to-be-welded end of the steel plate, V-shaped bevels with a bevel angle of θ / 2 and a bevel depth of d / 2 are respectively formed on the upper and lower surfaces of the to-be-welded end of each of the two steel plates to-be-welded, and X-shaped bevels with a bevel angle of θ are formed on the to-be-welded ends of the two steel plates after abutting, θ is 65°-70°, and d is the thickness of the steel plate.

[0017] Preferably, in the beveling process of the to-be-welded end of the steel plate, the to-be-welded end of one of the two steel plates to-be-welded is not beveled, V-shaped bevels with a bevel angle of θ and a bevel depth of d / 2 are respectively formed on the upper and lower surfaces of the to-be-welded end of the other steel plate, and K-shaped bevels with a bevel angle of θ are formed on the to-be-welded ends of the two steel plates after abutting, θ is 50°-55°, and d is the thickness of the steel plate.

[0018] Preferably, the weld seam structure of the welded joint cooled to room temperature is a composite phase structure of acicular ferrite and bainite.

[0019] Preferably, the tensile strength Rm of the welded joint is >770 MPa, the impact energy KV2 of the welded heat-affected zone at -60 DEG C is ≥150 J, the crack tip opening displacement CTOD characteristic value of the weld metal and the coarse-grained zone of the welded heat-affected zone at -35 DEG C is all ≥0.25 mm, and the welded joint is free of cracks after 180 DEG cold bending at room temperature, wherein the bending core diameter D=40 mm.

[0020] Compared with the prior art, the welding method for the 690 MPa grade high-strength steel plate has the following beneficial effects: after the 690 MPa grade high-strength steel plate is welded and cooled to room temperature, the weld structure of the obtained welded joint is a composite phase structure of acicular ferrite + bainite, thereby dividing the original austenite grains of the weld metal into multiple small regions, forming fine grains in the austenite grains of the composite phase division structure, so that the welded joint has excellent strength and toughness to match the 690 MPa grade high-strength steel plate, the tensile strength Rm of the welded joint is >770 MPa, the impact energy KV2 of the welded heat-affected zone at -60 DEG C is ≥150 J, the crack tip opening displacement CTOD characteristic value of the weld metal and the coarse-grained zone of the welded heat-affected zone at -35 DEG C is all ≥0.25 mm, and the welded joint is free of cracks after 180 DEG cold bending at room temperature, wherein the bending core diameter D=40 mm. The welded joint has excellent low-temperature fracture toughness, high toughness reserve and safety margin, the strength and toughness of the welded joint match the strength and toughness of the steel plate, have high matching, the heat treatment process after welding is cancelled, the production process is simplified, the production cost is reduced, and the production efficiency is improved. DETAILED DESCRIPTION

[0021] The technical solutions of the present application will be further described below in combination with specific embodiments, but the scope of protection is not limited to the description.

[0022] An embodiment of the present application provides a welding method for a 690 MPa grade high-strength steel plate, which is suitable for welding the 690 MPa grade high-strength steel plate.

[0023] The 690 MPa grade high-strength steel plate refers to a steel plate with a yield strength ≥690 MPa, and the content of C in the steel plate is 0.06-0.09 wt%, the carbon equivalent Ceq is <0.58%, and the cold crack sensitivity index Pcm is ≤0.235%.

[0024] Specifically, the carbon equivalent of the steel plate is

[0025] Ceq=[C]+[Mn] / 6+([Cr]+[Mo]+[V]) / 5+([Ni]+[Cu]) / 15;

[0026] cold crack sensitivity index

[0027] Pcm = [C] + [Si] / 30 + ([Mn] + [Cu] + [Cr]) / 20 + [Ni] / 60 + [Mo] / 15 + [V] / 10 + 5[B];

[0028] wherein [C], [Mn], [Cr], [Mo], [V], [Ni], [Cu], [Si], [B] represent the mass percentage of the corresponding element in the steel plate.

[0029] Preferably, in the steel plate, the content of Ni is 1.7-1.9wt%, P≤0.008wt%, S≤0.005wt%, N≤0.005wt%.

[0030] The welding method suitable for the aforementioned 690MPa grade high-strength steel plate specifically comprises the groove processing procedure, the pretreatment procedure, the preheating procedure and the welding procedure in sequence. Each procedure is described in detail as follows.

[0031] (1) Groove processing procedure

[0032] Two pieces of the aforementioned 690MPa grade high-strength steel plate with the same thickness are taken for welding, the thickness d of the steel plate is 20-55mm, and groove processing is performed on the welding end of the steel plate.

[0033] Wherein, the groove can be V-type, X-type or K-type. Specifically as follows:

[0034] a. V-type groove is processed on the welding end of the steel plate, the groove angle θ is 65°-70°

[0035] The groove processing mode of the two steel plates is the same, V-type groove with groove angle θ / 2 is processed on the welding end of each steel plate to be welded, and the welding ends of the two steel plates are butted together towards each other, so that V-type groove with groove angle θ is formed between the two steel plates.

[0036] b. X-type groove is processed on the welding end of the steel plate, the groove angle θ is 65°-70°

[0037] The groove processing mode of the two steel plates is the same, V-type groove with groove angle θ / 2 and groove depth d / 2 is processed on the upper and lower surfaces of the welding end of each steel plate to be welded, and the welding ends of the two steel plates are butted together towards each other, so that after butting, the welding ends of the two steel plates together form X-type groove with groove angle 65°-70°.

[0038] c. K-type groove is processed on the welding end of the steel plate, the groove angle θ is 50°-55°

[0039] The groove processing mode of the two steel plates to be welded is different, one of the steel plates is not processed, and a V-shaped groove with a groove angle of θ and a groove depth of d / 2 is processed on the upper and lower surfaces of the other steel plate, and the welding ends of the two steel plates are butted together towards each other, so that the welding ends of the two steel plates form a K-shaped groove with a groove angle of 50°-55°.

[0040] Through the design of the groove type and the groove angle, the fusion ratio can be reduced, and the dilution rate of the steel plate base metal to the weld metal can be reduced.

[0041] (2) Pretreatment process

[0042] The groove surface of the steel plate is cleaned and polished, and the so-called groove surface includes the outer peripheral surface of the welding end of the steel plate. In this way, the oxide scale, rust, oil stains and moisture on the groove surface are removed by cleaning and polishing, so that the final obtained welded joint is avoided to have micro-cracks and affect the welding performance, and the welding safety is improved.

[0043] (3) Preheating process

[0044] The steel plate is preheated to a steel plate temperature of 50-80℃, so that the welding heat affected zone can be avoided to be weakened, and cold cracks can be prevented.

[0045] (4) Welding process

[0046] After preheating, the same thickness steel plates are welded by submerged arc welding to form a welded joint between the steel plates, the welding current is controlled to be 375-550A, the welding voltage is controlled to be 26-30V, the welding speed is controlled to be 40-48cm / min, and the welding heat input is controlled to be 12-25kJ / cm.

[0047] The chemical composition of the used submerged arc welding wire includes, by mass percent: C 0.04-0.08%, Si 0.22-0.32%, Mn 1.3-1.5%, Ni 2.7-3.3%, S≤0.008%, P≤0.0015%, Cu 0.043-0.062%, Cr 0.20-0.28%, Mo 0.44-0.56%, Ti 0.015-0.025%, and the rest is Fe and inevitable impurities. Through the multi-element alloy components of the welding wire and the control of the welding process, the microstructure of the weld formed after welding can be refined, and the strength and fracture toughness of the weld are improved.

[0048] Preferably, the diameter of the welding wire is 3.2mm, and the number of layers and the number of passes of submerged arc welding are selected according to the thickness of the steel plate, the groove form and the welding heat input, and the inter-pass temperature is controlled to be 50-170℃.

[0049] Preferably, the flux used for submerged arc welding is high alkaline non-alloyed sintered flux, and the flux is preferably OK Flux 10.62 flux.

[0050] Compared with the prior art, the welding method suitable for the 690MPa high-strength steel plate of the present application, through the comprehensive design of the steel plate base material, welding wire material and welding process, after the 690MPa high-strength steel plate is welded and cooled to room temperature, the weld joint obtained has a complex phase structure of acicular ferrite + bainite, thereby dividing the original austenite grains of the weld metal into multiple small regions, forming fine grains in the austenite grains with complex phase division structure, so that the weld joint has excellent strength and toughness to match the 690MPa high-strength steel plate, the tensile strength Rm of the weld joint is >770MPa, the impact energy KV2 of the weld heat affected zone at-60℃ is ≥150J, the CTOD characteristic value of the weld metal and the coarse grain zone of the weld heat affected zone at-35℃ is all ≥0.25mm, and the weld joint has no cracks at room temperature under 180° cold bending, wherein the bending core diameter D=40mm. The weld joint has excellent low-temperature fracture toughness, high toughness reserve and safety margin, the strength and toughness of the weld joint match the strength and toughness of the steel plate, has high matching, and the heat treatment process after welding is cancelled, the production process is simplified, the production cost is reduced, and the production efficiency is improved.

[0051] The detailed description listed above is only a specific description of the feasible embodiments of the present application, and is not used to limit the protection scope of the present application. Equivalent embodiments or changes made without departing from the spirit of the present application should be included in the protection scope of the present application.

[0052] The following provides several embodiments of the present application to further illustrate the technical solutions of the present application. Of course, these embodiments are only a part of the preferred embodiments of the numerous change embodiments contained in the present application, but not all.

[0053] Embodiment 1

[0054] The steel plate to be welded is a high-strength steel plate with a yield strength ≥690MPa, and in the steel plate, the C content is 0.06-0.09wt%, the Ni content is 1.7-1.9wt%, P≤0.008wt%, S≤0.005wt%, N≤0.005wt%, the carbon equivalent Ceq<0.58%, and the cold crack sensitivity index Pcm≤0.235%.

[0055] The welding method has the following procedures:

[0056] (1) Groove machining process

[0057] The aforementioned high-strength steel plate samples were taken. The thickness of the steel plate samples was 20 mm, and the cross-sectional dimensions of the steel plate samples were 1000 mm × 400 mm.

[0058] Take two steel plate samples and machine a V-shaped bevel with a bevel angle of 25° on the welding end of each steel plate sample. Then, align the welding ends of the two steel plate samples together and join them together. In this way, a V-shaped bevel with a bevel angle of 50° will be formed at the joint of the two steel plates after joining.

[0059] (2) Pretreatment process

[0060] The bevel surface of the steel plate sample is cleaned and polished until all oxide scale, loose rust, oil and moisture are removed.

[0061] (3) Preheating process

[0062] The two steel plate samples were preheated to a temperature of 50°C.

[0063] (4) Welding process

[0064] After preheating, the two steel plate samples were welded together by submerged arc welding to form a welded joint between the steel plates. The welding current was controlled at 375A, the welding voltage at 26V, the welding speed at 48cm / min, and the welding heat input at 12kJ / cm.

[0065] The submerged arc welding wire used has a diameter of 3.2 mm and its chemical composition by mass percentage includes: C 0.05-0.09%, Si 0.22-0.32%, Mn 1.3-1.5%, Ni 2.7-3.3%, S≤0.008%, P≤0.0015%, Cu 0.043-0.062%, Cr 0.20-0.28%, Mo 0.44-0.56%, Ti 0.015-0.025%, with the remainder being Fe and unavoidable impurities.

[0066] The matching flux is a high-alkaline non-alloy sintered flux, specifically OK Flux 10.62 flux.

[0067] After cooling to room temperature, samples were taken from the weld joint in a direction parallel to the weld seam, and the microstructure of the weld joint was examined using a metallographic microscope. In this embodiment, the weld seam microstructure of the weld joint is a composite phase microstructure of acicular ferrite and bainite, and the grain size is fine.

[0068] According to GB / T2653, a side bend test specimen of the welded joint is taken, and the welded joint is subjected to bending test at room temperature with a bending mandrel diameter D =

[0069] A 40mm bend at 180° results in no cracks on the surface of the welded joint, indicating excellent cold bending performance.

[0070] Example 2

[0071] The steel plate to be welded is a high-strength steel plate with a yield strength of ≥690 MPa, and in the steel plate, the C content is 0.06-0.09wt%, the Ni content is 1.7-1.9wt%, P≤0.008wt%, S≤0.005wt%, N≤0.005wt%, the carbon equivalent Ceq<0.58%, and the cold crack sensitivity index Pcm≤0.235%.

[0072] The welding method is as follows:

[0073] (1) Groove machining process

[0074] The aforementioned high-strength steel plate samples were taken, and the thickness of the steel plate samples was 55 mm, and the cross-sectional size of the steel plate samples was 1000 mm x 460 mm.

[0075] Two steel plate samples were taken, and the welding end of one of the steel plate samples was not subjected to groove machining. A V-shaped groove with a groove angle of 55° and a groove depth of 27.5 mm was machined on the upper and lower surfaces of the welding end of the other steel plate sample, and the V-shaped groove was butted towards the welding end of the steel plate sample that was not subjected to groove machining. Thus, a K-shaped groove with a groove angle of 55° was formed at the joint of the two butted steel plate samples.

[0076] (2) Pretreatment process

[0077] The groove surface of the steel plate sample was cleaned and polished until all the oxide scale, rust, oil stains and moisture on the groove surface were removed.

[0078] (3) Preheating process

[0079] The two steel plate samples were preheated to a temperature of 80°C.

[0080] (4) Welding process

[0081] After preheating, the two steel plate samples were welded using submerged arc welding to form a welded joint between the steel plates. The welding current was controlled at 550 A, the welding voltage was 30 V, the welding speed was 40 cm / min, and the welding heat input was 25 kJ / cm.

[0082] The diameter of the submerged arc welding wire used is 3.2 mm, and the chemical composition of the welding wire includes, in mass percentage: C 0.05-0.09%, Si 0.22-0.32%, Mn 1.3-1.5%, Ni 2.7-3.3%, S≤0.008%, P≤0.0015%, Cu 0.043-0.062%, Cr 0.20-0.28%, Mo 0.44-0.56%, Ti 0.015-0.025%, and the rest is Fe and inevitable impurities.

[0083] The matching flux uses high-alkaline non-alloy sintered flux, and OK Flux 10.62 flux is specifically selected.

[0084] After cooling to room temperature, the welded joint is sampled in the direction parallel to the weld, and the microstructure of the welded joint is detected by a metallographic microscope. The weld microstructure of the welded joint of the embodiment is a composite phase microstructure of acicular ferrite + bainite, and the grain size is small.

[0085] According to GB / T2653, a joint side bend sample is taken, and the welded joint is bent at room temperature with a bend core diameter D=40mm by 180°. The surface of the welded joint is free of cracks, that is, the cold bending performance of the welded joint is excellent.

[0086]

[0087] (1) In terms of tensile properties, the tensile properties of the welded joint cooled to room temperature are tested according to GB / T2651, and the tensile strength Rm of the welded joint is shown in Table 1. In the tensile test, the welded joint is sampled and stretched, and the stretching direction is parallel to the welding direction.

[0088] (2) In terms of impact properties, the impact properties of the welded joint cooled to room temperature are tested according to GB / T2650, and the-60℃ low temperature impact property test results of each region of the welded joint are shown in Table 1. The-60℃ low temperature impact energy Ak2 of the impact notch position at the weld metal, the fusion line FL, 1mm outside the fusion line (i.e. FL+1), 3mm outside the fusion line (i.e. FL+3), and 5mm outside the fusion line (i.e. FL+5) are detected, and three sampling test results are shown for each detection position.

[0089] (3) According to the standard BS7448, the-35℃ crack tip opening displacement CTOD characteristic value of the welded joint is measured by three-point bending test, and the notch position is located at the weld metal and the coarse grain zone of the heat affected zone (i.e. CGHAZ), and three sampling test results are shown for each detection position, and the test results are shown in Table 2.

[0090] Table 1

[0091] ​

[0092] Table 2

[0093]

[0094] In summary, the welding method of the present application is used to weld the 690MPa high-strength steel plate, and the weld joint after cooling to room temperature has a complex phase structure of acicular ferrite + bainite, and the grain size is small; the tensile strength Rm of the welded joint is >770MPa, the impact energy KV2 of the welded heat-affected zone at-60℃ is ≥150J, the CTOD characteristic value of the weld metal and the coarse-grained zone of the welded heat-affected zone at-35℃ is ≥0.25mm, and the welded joint has no cracks at room temperature under 180° cold bending, wherein the bending core diameter D=40mm. The welded joint has excellent low-temperature fracture toughness, high toughness reserve and safety margin, and the strength and toughness of the welded joint are matched with the strength and toughness of the steel plate, and have high matching.

[0095] As can be seen from the above examples, the welding method of the present application is used to weld the 690MPa high-strength steel plate, and the welded joint not only has excellent low-temperature fracture toughness, high toughness reserve and safety margin, but also has high matching of the strength and toughness of the welded joint with the strength and toughness of the steel plate, and in addition, the heat treatment process after welding is cancelled, the production process is simplified, the production cost is reduced, and the production efficiency is improved.

[0096] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can make equivalent replacements or changes within the technical range disclosed by the present application according to the technical solution and inventive concept of the present application, which should be covered within the protection scope of the present application.

Claims

1. A welding method suitable for a 690 MPa grade high-strength steel sheet, characterized by, The application relates to a welding method for a 690MPa high-strength steel plate, wherein the content of C is 0.06-0.09wt%, the carbon equivalent Ceq is less than 0.58%, and the cold crack sensitivity index Pcm is less than or equal to 0.235%. The welding method comprises the following steps: bevel processing is performed on the welding end of the steel plate; the bevel surface of the steel plate is cleaned and polished; the steel plate is preheated to a steel plate temperature of 50-80 DEG C; the same thickness steel plates are welded by adopting submerged arc welding to form a welding joint between the steel plates, the welding current is controlled to be 375-550 A, the welding voltage is controlled to be 26-30 V, the welding speed is controlled to be 40-48 cm / min, the welding heat input is controlled to be 12-25 kJ / cm, and the chemical components of the submerged arc welding wire used are as follows in percentage by mass: C 0.04-0.08%, Si 0.22-0.32%, Mn 1.3-1.5%, Ni 2.7-3.3%, S less than or equal to 0.008%, P less than or equal to 0.0015%, Cu 0.043-0.062%, Cr 0.20-0.28%, Mo 0.44-0.56%, Ti 0.015-0.025%, and the rest is Fe and inevitable impurities; the welding method cancels the heat treatment process after welding, and the crack tip opening displacement CTOD characteristic value of the welding seam metal and the welding heat affected zone coarse grain zone at-35 DEG C is greater than or equal to 0.25 mm.

2. The welding method suitable for a 690 MPa grade high-strength steel sheet according to claim 1, characterized by, In the steel plate, the content of Ni is 1.7-1.9wt%, the content of P is less than or equal to 0.008wt%, the content of S is less than or equal to 0.005wt%, and the content of N is less than or equal to 0.005wt%.

3. The welding method suitable for a 690 MPa grade high-strength steel sheet according to claim 1, characterized by, The submerged arc welding adopts high-alkaline non-alloy sintered flux.

4. The welding method suitable for a 690 MPa grade high-strength steel sheet according to claim 1, characterized by, The flux for the submerged arc welding is OK Flux 10.62 flux.

5. The welding method suitable for a 690 MPa grade high-strength steel sheet according to claim 1, characterized by, The thickness of the steel plate is 20-55 mm, and the diameter of the welding wire is 3.2 mm.

6. The welding method suitable for a 690 MPa grade high-strength steel sheet according to claim 1, characterized by, In the bevel processing step, V-shaped bevels with a bevel angle of theta / 2 are respectively processed on the welding ends of the two steel plates to be welded, so that V-shaped bevels with a bevel angle of theta are formed between the two steel plates, and theta is 65 DEG -70 DEG.

7. The welding method suitable for 690 MPa grade high-strength steel sheet according to claim 1, characterized by, In the bevel processing step, V-shaped bevels with a bevel angle of theta / 2 and a bevel depth of d / 2 are respectively processed on the upper and lower surfaces of the welding ends of the two steel plates to be welded, and X-shaped bevels with a bevel angle of theta are formed on the welding ends of the two steel plates after abutting, theta is 65 DEG -70 DEG, and d is the thickness of the steel plate.

8. The welding method suitable for 690 MPa grade high-strength steel sheet according to claim 1, characterized by, In the bevel processing step, the welding end of one of the two steel plates to be welded is not processed, V-shaped bevels with a bevel angle of theta and a bevel depth of d / 2 are respectively processed on the upper and lower surfaces of the welding end of the other steel plate, K-shaped bevels with a bevel angle of theta are formed on the welding ends of the two steel plates after abutting, theta is 50 DEG -55 DEG, and d is the thickness of the steel plate.

9. The welding method suitable for 690 MPa grade high-strength steel sheet according to claim 1, characterized by, The welding seam structure of the welding joint after cooling to room temperature is a composite phase structure of acicular ferrite and bainite.

10. The welding method suitable for 690 MPa grade high-strength steel sheet according to claim 1, characterized by, The tensile strength Rm of the welded joint is > 770 MPa, the impact energy KV2 of the welded heat-affected zone at -60°C is ≥ 150 J, and the welded joint is free of cracks at 180° cold bending at room temperature, wherein the bending core diameter D = 40 mm.

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