Welded joint and welding method of 400MPa-grade high heat input welding ship steel

Abstract

The invention relates to the technical field of steel new material connection, in particular to a welding joint and a welding method of 400MPa-grade high heat input welding ship steel, and the welding method specifically comprises the following steps: assembling a steel plate to be welded by adopting a butt joint form, setting an assembly gap to be 8-12mm, forming a single V-shaped groove, welding by adopting a double-wire electro-gas welding process when t is more than or equal to 60mm and less than or equal to 80mm, and welding by adopting a double-wire electro-gas welding process when t is more than or equal to 60mm and less than or equal to 80mm; a water-cooling copper sliding block is arranged on the front face of the groove, and a ceramic gasket is arranged on the back face of the groove. The electro-gas welding mode is adopted, single-face welding and double-face forming are achieved, the situation that the toughness of a welding joint and a heat affected zone is greatly deteriorated can be avoided, the impact energy KV2 at the low temperature of-40 DEG C of the welding seam of the welding joint and the 1 / 4 position and the 1 / 2 position of the heat affected zone is larger than or equal to 80 J, the tensile strength of the welding joint is larger than or equal to 390 MPa, the tensile strength Rm is larger than or equal to 530 MPa, the lateral bending d of the welding joint is 4a or 180 degrees, cracks are avoided, and the performance of the welding joint is excellent.

Description

Technical Field

[0001] The present invention relates to the technical field of steel new material connection, and particularly to a welding joint and a welding method for a 400MPa grade steel for shipbuilding with high heat input welding. Background Art

[0002] With the rapid development of China's steel industry, the hull structural steel used in high-tech ships and offshore engineering equipment and other fields is developing towards high strength grade, high quality grade, efficient welding, lightweight and other directions. The market demand for large structures such as ships and offshore platforms is developing towards lightweight, low cost, efficient and high quality welding and other directions. The 400MPa grade steel for shipbuilding with high heat input welding has many advantages such as effectively improving welding efficiency, reducing cost, and reducing welding labor intensity. At the same time, it well solves the shortcomings such as the reduction of low temperature toughness of the welding joint caused by high heat input welding of ordinary steel. The demand for the construction of large structures such as ships and offshore platforms is becoming increasingly clear and urgent. Summary of the Invention

[0003] In view of the above technical problems, the present invention overcomes the shortcomings of the prior art and provides a welding joint and a welding method for a 400MPa grade steel for shipbuilding with high heat input welding, solves the welding problem of the anti-torsion box steel with a thickness specification of 60-80mm for large ships, obtains a welding joint with excellent mechanical properties, ensures safety during use, and fills the current technical gap.

[0004] In a first aspect, the welding method for a 400MPa grade steel for shipbuilding with high heat input welding provided by the present invention includes the following steps:

[0005] Assemble the steel plates to be welded in a butt joint form, set the assembly gap to 8-12mm, and open a single V-groove;

[0006] When 60mm≤t≤80mm, the double-wire electro-gas vertical welding process is used for welding, where t is the thickness of the steel plate to be welded. A water-cooled copper slider is arranged on the front of the groove, and a ceramic backing is arranged on the back.

[0007] Further, during the welding process, the wire diameter used is 1.6mm, and the wire has the following components by weight percentage: C: 0.04%-0.06%, Mn: 0.7%-0.8%, Si: 0.07%-0.08%, S: ≤0.01%, P: ≤0.02%, Ni: 1.0%-1.8%, and the balance is Fe and unavoidable impurities.

[0008] Further, during the welding process, the shielding gas is CO2 gas, and the CO2 gas flow rate is 15L / min-25L / min.

[0009] Furthermore, the process parameters of twin-wire electro-gas vertical welding include: no preheating before welding, root side welding current of 340 - 360 A, welding voltage of 30 - 36 V, welding speed of 2.5 cm / min; face side welding current of 430 - 450 A, welding voltage of 40 - 44 V, welding speed of 2.5 cm / min, and welding heat input of 600 - 750 kJ / cm.

[0010] Furthermore, the chemical composition and percentage of the steel plate to be welded are: C: 0.05 - 0.08, Mn: 1.30 - 1.70, Si: 0.10 - 0.20, P: ≤0.012, S: ≤0.020, Ni: 0.10 - 0.30, Cr: 0.10 - 0.40, V: 0.030 - 0.050, Al: 0.025 - 0.050, Ti: 0.005 - 0.020, and the balance is Fe and incidental impurities.

[0011] In a second aspect, the present invention also provides a welded joint of a 400 MPa grade high heat input welding steel for ships, which is specifically obtained by welding using the welding method described in any one of the first aspect.

[0012] Furthermore, at the 1 / 4 position and 1 / 2 position of the weld seam and heat affected zone of the welded joint, the low-temperature impact energy KV2 at -40°C ≥ 80 J, the tensile strength of the welded joint ≥ 390 MPa, the tensile strength Rm ≥ 530 MPa, the side bend of the welded joint d = 4a, 180°, without cracks, and the performance of the welded joint is excellent.

[0013] The beneficial effects of the present invention are:

[0014] The present invention adopts a high-efficiency welding process, performs twin-wire electro-gas vertical welding on 400 MPa grade high heat input welding steel for ships with a thickness of 60 - 80 mm. The steel plate does not need to be preheated before welding, only one welding is required, and double-sided forming is achieved. The performance of the welded joint meets the relevant technical standard requirements of current mainstream classification societies, and is applicable to the welding of thick ship plates, large ship torsion boxes, etc., filling the gap in the existing high heat input welding technology methods.

[0015] The present invention designs a V-shaped groove for 400 MPa grade high heat input welding steel for ships with a specification of 60 - 80 mm, and realizes one-time welding forming by controlling parameters such as the welding current, welding voltage, and welding speed of the twin wires; secondly, at the 1 / 4 position and 1 / 2 position of the weld seam and heat affected zone of the welded joint, the low-temperature impact energy KV2 at -40°C ≥ 80 J, the tensile strength of the welded joint ≥ 390 MPa, the tensile strength Rm ≥ 530 MPa, the side bend of the welded joint d = 4a, 180°, without cracks, and the performance of the welded joint is excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1Schematic diagram of the welding groove for electro-gas vertical welding in the specific embodiment of the present invention;

[0017] Figure 2 Schematic diagram of the post-welding formation in the specific embodiment of the present invention. Specific embodiment

[0018] The present invention provides a welding method for shipbuilding steel with a large heat input of 400 MPa grade. The chemical composition percentage of the shipbuilding steel with a large heat input is as follows: C: 0.05 - 0.08, Mn: 1.30 - 1.70, Si: 0.10 - 0.20, P: ≤0.012, S: ≤0.020, Ni: 0.10 - 0.30, Cr: 0.10 - 0.40, V: 0.030 - 0.050, Al: 0.025 - 0.050, Ti: 0.005 - 0.020, and the balance is Fe and incidental impurities.

[0019] As Figure 1 shown, the welding joint method is butt joint, with a V-shaped groove, and the welding method is electro-gas vertical welding, where T is the thickness of the steel plate; α is the groove angle; A is the groove gap, R is the root side wire, F is the face side wire; a welding process method is formulated for a plate thickness of 60 - 80 mm. Figure 2 Then it is the schematic diagram of the post-welding formation in the specific embodiment of the present invention.

[0020] Among them, the wire used is 1.6 mm, and the chemical composition and mass percentage are: C: 0.04% - 0.06%, Mn: 0.7% - 0.8%, Si: 0.07% - 0.08%, S: ≤0.01%, P: ≤0.02%, Ni: 1.0% - 1.8%, and the balance is Fe and unavoidable impurities. The shielding gas is CO2 gas (purity 99.9%).

[0021] Before welding in the present invention, the integrity of the groove should be checked, including groove grinding to prevent groove corrosion. Preheating is not required before welding. A water-cooled copper slider should be installed on the front of the groove, and a ceramic backing (KL-4) should be pasted on the back.

[0022] The present invention is for butt welding of plates. Before welding the butt weld, a fixture and a corresponding welding witness plate should be installed. For shipbuilding steel with a large heat input, there are corresponding welding processes according to different plate thickness ranges, which will be described through the following specific examples.

[0023] Example 1

[0024] The electro-gas vertical welding method for large heat input welded ship steel in this embodiment uses twin-wire gas shielded welding, with a V-groove opened. The plate thickness is 60mm + 60mm, the size is 800mm × 250mm × 60mm, and the properties of the steel plate are: yield strength ReH ≥ 390MPa, ReH ≤ 510MPa, elongation ≥ 22%, and -40°C low-temperature impact energy ≥ 50J.

[0025] The wire diameter is Φ1.6mm, and the chemical composition and mass percentage are: C: 0.04% - 0.06%, Mn: 0.7% - 0.8%, Si: 0.07% - 0.08%, S: ≤0.01%, P: ≤0.02%, Ni: 1.0% - 1.8%, and the balance is Fe and unavoidable impurities.

[0026] The groove type is V-groove, the groove angle is 20 - 25°, and the groove assembly has an 8 - 12mm gap.

[0027] Preheating is not required before welding, and the welding is formed in one pass. The shielding gas composition is CO2 (99.9%), and the gas flow rate is 15L / min; its process parameters include: root side wire welding current 320A, welding voltage 32V, welding speed 3cm / min; face side wire welding current 420A, welding voltage 40V, welding speed 3cm / min.

[0028] Example 2

[0029] The electro-gas vertical welding method for large heat input welded ship steel in this embodiment uses twin-wire gas shielded welding, with a V-groove opened. The plate thickness is 70mm + 70mm, the size is 800mm × 250mm × 70mm, and the properties of the steel plate are: yield strength ReH ≥ 390MPa, ReH ≤ 510MPa, elongation ≥ 22%, and -40°C low-temperature impact energy ≥ 50J.

[0030] The wire diameter is Φ1.6mm, and the chemical composition and mass percentage are: C: 0.04% - 0.06%, Mn: 0.7% - 0.8%, Si: 0.07% - 0.08%, S: ≤0.01%, P: ≤0.02%, Ni: 1.0% - 1.8%, and the balance is Fe and unavoidable impurities.

[0031] The groove type is V-groove, the groove angle is 20 - 25°, and the groove assembly has an 8 - 12mm gap.

[0032] Preheating is not required before welding, and the welding is formed in one pass. The shielding gas composition is CO2 (99.9%), and the gas flow rate is 20L / min; its process parameters include: root side wire welding current 360A, welding voltage 34V, welding speed 3cm / min; face side wire welding current 460A, welding voltage 42V, welding speed 3cm / min.

[0033] Example 3

[0034] For the electro - gas vertical welding method of large heat - input welding ship steel in this example, double - wire gas shielded welding is adopted, with a V - shaped groove opened. The plate thickness is 80mm + 80mm, and the size is 800mm×250mm×80mm. The properties of the steel plate are: yield strength ReH≥390MPa, ReH≤510MPa, elongation ≥22%, and low - temperature impact energy at - 40°C ≥50J.

[0035] The wire diameter is Φ1.6mm, and the chemical composition and mass percentage are: C: 0.04% - 0.06%, Mn: 0.7% - 0.8%, Si: 0.07% - 0.08%, S: ≤0.01%, P: ≤0.02%, Ni: 1.0% - 1.8%, and the balance is Fe and unavoidable impurities.

[0036] The groove type is a V - shaped groove, the groove angle is 20 - 25°, and an 8 - 12mm gap is left for groove assembly.

[0037] Pre - heating is not required before welding, and the welding is formed in one pass. The composition of the shielding gas is CO2(99.9%), and the gas flow rate is 25L / min. Its process parameters include: the welding current of the root - side wire is 400A, the welding voltage is 36V, and the welding speed is 3cm / min; the welding current of the face - side wire is 500A, the welding voltage is 44V, and the welding speed is 3cm / min.

[0038] Performance Test

[0039] The mechanical properties of the welded joints of Examples 1 - 3 were tested by using the conventional welding procedure qualification method, and the test results are shown in Table 1.

[0040] Table 1 Properties of the welded joints

[0041]

[0042] The effects of the examples of the present invention are as follows:

[0043] In the 3 examples, the fracture position is in the base metal. After ultrasonic non - destructive testing, no internal defects were found. At the 1 / 4 position and 1 / 2 position of the weld seam and heat - affected zone of the welded joint, the low - temperature impact energy KV2 at - 40°C ≥80J, the tensile strength of the welded joint ≥390MPa, the tensile strength Rm≥530MPa, and the side - bend of the welded joint d = 4a, 180°, without cracks. From the test data in Table 1, it can be seen that the welded joints obtained in Examples 1 - 3 have excellent performance.

[0044] In the three embodiments of the present invention, according to the actual welding process evaluation, the mechanical properties are good, and it can cover the welding of shipbuilding steel with a heat input in the range of 60-80 mm. This welding method does not require preheating before welding. With one pass of welding, double-sided forming can be achieved, and the welding efficiency can be increased by more than 90%.

[0045] In addition to the above embodiments, the present invention may have other implementation manners. Any technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope required by the present invention.

Claims

1. A welding method for a 400MPa grade steel for shipbuilding with large heat input welding, characterized in that, It includes the following steps: Assemble the steel plates to be welded in the form of butt joints, set the assembly gap to 8 - 12 mm, and make a single V-groove; When 60 mm ≤ t ≤ 80 mm, use the twin-wire electro-gas vertical welding process for welding, where t is the thickness of the steel plate to be welded. Set a water-cooled copper slider on the front of the groove and a ceramic backing on the back.

2. The welding method according to claim 1, wherein, During the welding process, the wire diameter used is 1.6 mm, and the wire has the following components by weight percentage: C: 0.04% - 0.06%, Mn: 0.7% - 0.8%, Si: 0.07% - 0.08%, S: ≤0.01%, P: ≤0.02%, Ni: 1.0% - 1.8%, and the balance is Fe and inevitable impurities.

3. The welding method according to claim 1, characterized in that, During the welding process, the shielding gas is CO2 gas, and the CO2 gas flow rate is 15 L / min - 25 L / min.

4. The welding method according to claim 1, characterized in that, The twin-wire electro-gas vertical welding process parameters include: no preheating before welding, root side welding current 340 - 360 A, welding voltage 30 - 36 V, welding speed 2.5 cm / min; face side welding current 430 - 450 A, welding voltage 40 - 44 V, welding speed 2.5 cm / min, and the heat input during welding is 600 - 750 kJ / cm.

5. The welding method according to claim 1, characterized in that, The chemical composition and percentage of the steel plate to be welded are: C: 0.05 - 0.08, Mn: 1.30 - 1.70, Si: 0.10 - 0.20, P: ≤0.012, S: ≤0.020, Ni: 0.10 - 0.30, Cr: 0.10 - 0.40, V: 0.030 - 0.050, Al: 0.025 - 0.050, Ti: 0.005 - 0.020, and the balance is Fe and incidental impurities.

6. A welded joint of a 400 MPa grade steel for shipbuilding with high heat input welding, characterized in that, Obtained by welding using the welding method described in any one of claims 1 - 5.

7. The welded joint according to claim 6, wherein At the 1 / 4 position and 1 / 2 position of the weld seam and heat affected zone of the welded joint, the low-temperature impact energy KV2 ≥ 80 J at -40°C, the tensile strength of the welded joint ≥ 390 MPa, the tensile strength Rm ≥ 530 MPa, the side bend of the welded joint d = 4a, 180°, without cracks.

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