7Ni steel back-gouging-free welding method

Abstract

The invention discloses a 7Ni steel back-gouging-free welding method which comprises the following steps: carrying out spot welding assembly on a 7Ni steel workpiece to be welded, carrying out backing welding on the inner root part of a front groove by adopting argon tungsten-arc welding, then carrying out shielded metal arc welding filling, then carrying out shielded metal arc welding or submerged-arc welding for capping, and not carrying out back gouging in a back groove, shielded metal arc welding is directly adopted for filling, and then shielded metal arc welding or submerged arc welding is adopted for capping. According to the 7Ni steel back-gouging-free welding method, the groove form and size are designed according to different thicknesses, argon tungsten-arc welding is adopted for backing welding, single-face welding and double-face forming are carried out, a full-penetration-welding root welding seam is formed, carbon arc gouging back gouging is replaced, the front and back grooves are filled with shielded metal arc welding, shielded metal arc welding or submerged-arc welding is adopted for capping, and the 7Ni steel back-gouging-free welding method is achieved. And the influence of carbon arc gouging on the performance of 7Ni steel can be effectively avoided, the working environment can be improved, the production efficiency can be improved, and the welding quality can be guaranteed.

Description

Technical Field

[0001] The present invention belongs to the technical field of welding, and particularly relates to a root-free welding method for 7Ni steel. Background Art

[0002] 7Ni steel is a new type of nickel-saving low-temperature performance steel for LNG storage tanks. Its chemical composition by mass percentage is: C≤0.13%, Mn≤0.98%, P≤0.010%, S≤0.010%, Si: 0.05% - 0.30%, Ni: 6.5% - 7.5%, Mo: 0.10% - 0.30%, Nb≤0.03%.

[0003] During the manufacturing process of LNG storage tanks, for the welding of 7Ni steel, shielded metal arc welding or submerged arc welding is usually used for double-sided welding on both sides. Before the reverse welding, it is necessary to use carbon arc air gouging for root cleaning. However, carbon arc air gouging has the following disadvantages: a. Carbon arc air gouging generates a large amount of smoke and dust, the working environment is poor, and it has high requirements for the skills of operators. If the operation is improper, it will cause carbon increase phenomenon, and the parts after carbon arc air gouging also need to be polished and cleaned, increasing the workload; b. Carbon arc air gouging has a large current and a high heat input, which is likely to have an adverse impact on the weld performance. For the root cleaning of thin plates, it will also bring deformation problems; c. 7Ni steel is easy to be magnetized. When carbon arc air gouging uses a DC power supply, the magnetic field in the groove will increase after root cleaning, and magnetic blowout is likely to occur during welding. When carbon arc air gouging uses an AC power supply, the gouging depth of the groove is shallow during root cleaning, the arc is difficult to control, the operation difficulty is high, it is easy to damage the base metal, and multiple root cleaning operations are required, increasing the workload and making the temperature of the root weld too high, affecting the performance; d. The operation of carbon arc air gouging is actually to remove the root of the weld that has been welded on one side. This removal operation not only removes the root of the original weld, but also partially removes the base metal on the other side along the groove edge, resulting in material waste and violating the principle of cost reduction by using 7Ni steel.

[0004] Based on this, the present invention discloses a root-free welding method for 7Ni steel. Summary of the Invention

[0005] In order to solve the technical problems existing in the prior art, the purpose of the present invention is to provide a root-free welding method for 7Ni steel.

[0006] To achieve the above purpose and reach the above technical effects, the technical solution adopted by the present invention is as follows: A root-free welding method for 7Ni steel, comprising the following steps: Spot weld and assemble the 7Ni steel workpiece to be welded. First, perform root welding at the root inside the front groove, then perform filling and capping. For the reverse groove, there is no need to remove the root, directly perform filling, and then perform capping.

[0007] Further, the method includes the following steps: Spot weld and assemble the 7Ni steel workpiece to be welded. For root welding at the root inside the front groove, use tungsten inert gas welding. Then perform filling with shielded metal arc welding, and perform capping with shielded metal arc welding or submerged arc welding. For the reverse groove, there is no need to remove the root, directly perform filling with shielded metal arc welding, and then perform capping with shielded metal arc welding or submerged arc welding.

[0008] Even further, the method includes the following steps: (1) Assemble the 7Ni steel workpiece to be welded, use tungsten inert gas welding for spot welding, and design the groove form and size according to different thicknesses; (2) At the root inside the front groove of the workpiece, use tungsten inert gas welding for root welding to form a fully penetrated root weld; (3) Inside the front groove of the workpiece, use shielded metal arc welding for filling, and then use shielded metal arc welding or submerged arc welding for capping; (4) For the reverse groove of the workpiece, there is no need to remove the root, directly use shielded metal arc welding for filling, and then use shielded metal arc welding or submerged arc welding for capping.

[0009] Even further, in step (1), the designed groove form and size according to different thicknesses satisfy: When the thickness of the 7Ni steel workpiece to be welded is 5 - 15 mm, the workpiece is opened with a single-sided V-groove, the groove angle is 50 - 60°, the groove gap is 2.5 - 3.5 mm, and the groove root face is 0 - 1 mm; When the thickness of the 7Ni steel workpiece to be welded is 16 - 30 mm, the workpiece is opened with an X-groove, the front groove angle is 50 - 60°, the groove gap is 3 - 3.5 mm, the groove root face is 0 - 1 mm, the depth of the front groove is 2 / 3 of the plate thickness, and the reverse groove angle is 60 - 70°; When the thickness of the 7Ni steel workpiece to be welded is more than 30 mm, the workpiece is opened with a U-V groove, the front is a U-groove, the groove angle is 20 - 30°, the root arc radius is 6 - 8 mm, the groove gap is 3.5 - 4.0 mm, the groove root face is 0 - 1 mm, the depth of the front groove is 2 / 3 of the plate thickness, and the reverse is a V-groove, the groove angle is 50 - 60°.

[0010] Even further, in step (2), the parameters for root welding are: When the thickness of the workpiece to be welded of 7Ni steel is 5 - 15 mm, the welding current is 100 - 140 A, the welding speed is 10 - 15 cm / min, 99.99% argon is used for protection on the front side with a flow rate of 10 - 15 L / min, and 99.99% argon is used for protection on the back side with a flow rate of 8 - 12 L / min; When the thickness of the workpiece to be welded of 7Ni steel is 16 - 30 mm, the welding current is 120 - 160 A, the welding speed is 10 - 15 cm / min, 99.99% argon is used for protection on the front side with a flow rate of 10 - 15 L / min, and 99.99% argon is used for protection on the back side with a flow rate of 10 - 12 L / min; When the thickness of the workpiece to be welded of 7Ni steel is over 30 mm, the welding current is 140 - 180 A, the welding speed is 12 - 18 cm / min, 99.99% argon is used for protection on the front side with a flow rate of 10 - 15 L / min, and 99.99% argon is used for protection on the back side with a flow rate of 10 - 15 L / min.

[0011] Furthermore, the welding wire used for backing welding is ERNiCrMo - 4 with a diameter of φ2.4 mm.

[0012] Furthermore, in step (3), the parameters for filling with shielded metal arc welding in the front - side groove of the workpiece are as follows: When the thickness of the workpiece to be welded of 7Ni steel is 5 - 15 mm, fill 1 - 2 layers, use a welding electrode with a diameter of φ3.2 mm, the welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 15 - 20 cm / min, and the electrode does not oscillate during welding. For filling the 3rd and the remaining layers, use a welding electrode with a diameter of φ4.0 mm, the welding current is 150 - 170 A, the arc voltage is 24 - 27 V, the welding speed is 15 - 20 cm / min, and the electrode does not oscillate during welding; When the thickness of the workpiece to be welded of 7Ni steel is 16 - 30 mm, fill 1 - 3 layers, use a welding electrode with a diameter of φ3.2 mm, the welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 15 - 20 cm / min, and the electrode does not oscillate during welding. For filling the 4th and the remaining layers, use a welding electrode with a diameter of φ4.0 mm, the welding current is 150 - 170 A, the arc voltage is 24 - 27 V, the welding speed is 10 - 15 cm / min, and the oscillation width of the electrode during welding is no more than 15 mm; When the thickness of the workpiece to be welded of 7Ni steel is more than 30 mm, 1 - 4 layers are filled. A welding rod with a diameter of φ3.2 mm is used, the welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 15 - 20 cm / min, and the welding rod does not swing during welding. For the 5th layer and the remaining layers, a welding rod with a diameter of φ4.0 mm is used, the welding current is 150 - 170 A, the arc voltage is 24 - 27 V, the welding speed is 10 - 15 cm / min, and the width of the swing of the welding rod during welding is not more than 15 mm.

[0013] Furthermore, in step (4), the parameters for filling with shielded metal arc welding are as follows: When the thickness of the workpiece to be welded of 7Ni steel is 5 - 15 mm, there is no groove on the reverse side, and the shielded metal arc welding is directly used for surfacing. A welding rod with a diameter of φ3.2 mm is used, the welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 12 - 18 cm / min, and the width of the swing of the welding rod during welding is not more than 12 mm. When the thickness of the workpiece to be welded of 7Ni steel is 16 - 30 mm, the root is not cleared on the reverse side, and the shielded metal arc welding is used for filling in the groove. 1 layer is filled. A welding rod with a diameter of φ3.2 mm is used, the welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 15 - 20 cm / min, and the welding rod does not swing during welding. For the 2nd layer and the remaining layers, a welding rod with a diameter of φ4.0 mm is used, the welding current is 150 - 170 A, the arc voltage is 24 - 27 V, the welding speed is 10 - 15 cm / min, and the width of the swing of the welding rod during welding is not more than 15 mm. When the thickness of the workpiece to be welded of 7Ni steel is more than 30 mm, the root is not cleared on the reverse side, and the shielded metal arc welding is used for filling in the groove. 1 - 2 layers are filled. A welding rod with a diameter of φ3.2 mm is used, the welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 15 - 20 cm / min, and the welding rod does not swing during welding. For the 3rd layer and the remaining layers, a welding rod with a diameter of φ4.0 mm is used, the welding current is 150 - 170 A, the arc voltage is 24 - 27 V, the welding speed is 10 - 15 cm / min, and the width of the swing of the welding rod during welding is not more than 15 mm.

[0014] Furthermore, the welding rod used for shielded metal arc welding is ENiCrMo - 6, with a diameter of φ3.2 mm or φ4.0 mm.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention discloses a root - cleaning - free welding method for 7Ni steel. According to different thicknesses, the groove form and size are designed. Tungsten inert gas arc welding is used for backing welding, with one - side welding and double - side forming to form a full - penetration root weld, replacing carbon arc air gouging for root cleaning. In the positive and negative grooves, shielded metal arc welding is used for filling and shielded metal arc welding or submerged arc welding is used for surfacing. This can effectively avoid the influence of carbon arc air gouging on the performance of 7Ni steel, improve the working environment, increase production efficiency, and ensure welding quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is the groove design drawing of the 7Ni steel workpiece to be welded with a plate thickness T = 5 - 15mm according to the present invention; Figure 2 It is the groove design drawing of the 7Ni steel workpiece to be welded with a plate thickness T = 16 - 30mm according to the present invention; Figure 3 It is the groove design drawing of the 7Ni steel workpiece to be welded with a plate thickness T > 30mm according to the present invention; Figure 4 It is the welding flow chart of the 7Ni steel workpiece to be welded with a plate thickness T = 5 - 15mm according to the present invention; Figure 5 It is the welding flow chart of the 7Ni steel workpiece to be welded with a plate thickness T = 16 - 30mm according to the present invention; Figure 6 It is the welding flow chart of the 7Ni steel workpiece to be welded with a plate thickness T > 30mm according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The following elaborates on the present invention in detail so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making the protection scope of the present invention more clearly defined.

[0018] The following gives a brief overview of one or more aspects to provide a basic understanding of these aspects. This overview is not an exhaustive survey of all contemplated aspects, and is neither intended to identify key or decisive elements of all aspects nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that follows.

[0019] As Figure 1-6 shown, a root - cleaning - free welding method for 7Ni steel includes the following steps: Spot - weld and assemble the 7Ni steel workpiece to be welded. For the root in the positive groove, tungsten inert gas arc welding is used for backing welding, then shielded metal arc welding is used for filling, and finally shielded metal arc welding or submerged arc welding is used for surfacing. For the negative side, no root cleaning is performed, then shielded metal arc welding is used for filling, and shielded metal arc welding or submerged arc welding is used for surfacing.

[0020] A method for root - free welding of 7Ni steel disclosed by the present invention specifically includes the following steps: (1) Assemble the 7Ni steel workpieces to be welded. Use tungsten inert gas arc welding for spot welding, and design the groove form and size according to different thicknesses; (2) Use tungsten inert gas arc welding to carry out backing welding at the root inside the groove on the front side of the workpiece to form a full - penetration backing weld; (3) Use shielded metal arc welding for filling inside the groove on the front side of the workpiece, and then use shielded metal arc welding or submerged arc welding for surfacing; (4) Without root - cleaning inside the groove on the reverse side of the workpiece, directly use shielded metal arc welding for filling, and then use shielded metal arc welding or submerged arc welding for surfacing.

[0021] In step (1), the groove form and size designed according to different thicknesses meet the following requirements: When the thickness of the 7Ni steel workpiece to be welded is 5 - 15 mm, the workpiece is opened with a single - side V - shaped groove, the groove angle is 50 - 60°, the groove gap is 2.5 - 3.5 mm, and the groove root face is 0 - 1 mm; When the thickness of the 7Ni steel workpiece to be welded is 16 - 30 mm, the workpiece is opened with an X - shaped groove, the front - side groove angle is 50 - 60°, the groove gap is 3 - 3.5 mm, the groove root face is 0 - 1 mm, the depth of the front - side groove is 2 / 3 of the plate thickness, and the reverse - side groove angle is 60 - 70°; When the thickness of the 7Ni steel workpiece to be welded is more than 30 mm, the workpiece is opened with a U - V - shaped groove. The front side is a U - shaped groove, the groove angle is 20 - 30°, the root arc radius is 6 - 8 mm, the groove gap is 3.5 - 4.0 mm, the groove root face is 0 - 1 mm, the depth of the front - side groove is 2 / 3 of the plate thickness, and the reverse side is a V - shaped groove, the groove angle is 50 - 60°.

[0022] In step (2), the parameters of the backing welding are as follows: When the thickness of the 7Ni steel workpiece to be welded is 5 - 15 mm, the welding current is 100 - 140 A, the welding speed is 10 - 15 cm / min, 99.99% argon is used for protection on the front side, and the flow rate is 10 - 15 L / min. 99.99% argon is used for protection on the reverse side, and the flow rate is 8 - 12 L / min; When the thickness of the 7Ni steel workpiece to be welded is 16 - 30 mm, the welding current is 120 - 160 A, the welding speed is 10 - 15 cm / min, 99.99% argon is used for protection on the front side, and the flow rate is 10 - 15 L / min. 99.99% argon is used for protection on the reverse side, and the flow rate is 10 - 12 L / min; When the thickness of the 7Ni steel workpiece to be welded is more than 30 mm, the welding current is 140 - 180 A, the welding speed is 12 - 18 cm / min, 99.99% argon is used for protection on the front side with a flow rate of 10 - 15 L / min, and 99.99% argon is used for protection on the back side with a flow rate of 10 - 15 L / min.

[0023] In step (3), the parameters for filling in the groove on the front side of the workpiece using shielded metal arc welding are as follows: When the thickness of the 7Ni steel workpiece to be welded is 5 - 15 mm, 1 - 2 layers are filled. A welding electrode with a diameter of φ3.2 mm is used, the welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 15 - 20 cm / min, and the electrode is not oscillated during welding. For the 3 - remaining layers, a welding electrode with a diameter of φ4.0 mm is used, the welding current is 150 - 170 A, the arc voltage is 24 - 27 V, the welding speed is 15 - 20 cm / min, and the electrode is not oscillated during welding; When the thickness of the 7Ni steel workpiece to be welded is 16 - 30 mm, 1 - 3 layers are filled. A welding electrode with a diameter of φ3.2 mm is used, the welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 15 - 20 cm / min, and the electrode is not oscillated during welding. For the 4 - remaining layers, a welding electrode with a diameter of φ4.0 mm is used, the welding current is 150 - 170 A, the arc voltage is 24 - 27 V, the welding speed is 10 - 15 cm / min, and the oscillation width of the electrode during welding is not more than 15 mm; When the thickness of the 7Ni steel workpiece to be welded is more than 30 mm, 1 - 4 layers are filled. A welding electrode with a diameter of φ3.2 mm is used, the welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 15 - 20 cm / min, and the electrode is not oscillated during welding. For the 5 - remaining layers, a welding electrode with a diameter of φ4.0 mm is used, the welding current is 150 - 170 A, the arc voltage is 24 - 27 V, the welding speed is 10 - 15 cm / min, and the oscillation width of the electrode during welding is not more than 15 mm.

[0024] In step (4), no root cleaning is required in the groove on the back side of the workpiece, and the parameters for directly filling using shielded metal arc welding are as follows: When the thickness of the 7Ni steel workpiece to be welded is 5 - 15 mm, there is no groove on the back side, and the surface layer is directly welded using shielded metal arc welding. A welding electrode with a diameter of φ3.2 mm is used, the welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 12 - 18 cm / min, and the oscillation width of the electrode during welding is not more than 12 mm; When the thickness of the workpiece to be welded of 7Ni steel is 16 - 30 mm, the root face on the reverse side is not gouged. The groove is filled by shielded metal arc welding, with 1 layer filled. A welding electrode with a diameter of φ3.2 mm is used, the welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 15 - 20 cm / min, and the electrode is not oscillated during welding. For the 2nd layer and the remaining layers, a welding electrode with a diameter of φ4.0 mm is used, the welding current is 150 - 170 A, the arc voltage is 24 - 27 V, the welding speed is 10 - 15 cm / min, and the width of electrode oscillation during welding is not more than 15 mm. When the thickness of the workpiece to be welded of 7Ni steel is more than 30 mm, the root face on the reverse side is not gouged. The groove is filled by shielded metal arc welding, with 1 - 2 layers filled. A welding electrode with a diameter of φ3.2 mm is used, the welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 15 - 20 cm / min, and the electrode is not oscillated during welding. For the 3rd layer and the remaining layers, a welding electrode with a diameter of φ4.0 mm is used, the welding current is 150 - 170 A, the arc voltage is 24 - 27 V, the welding speed is 10 - 15 cm / min, and the width of electrode oscillation during welding is not more than 15 mm.

[0025] In the present invention, the welding wire used for the backing weld by tungsten inert gas welding is ERNiCrMo - 4, with a diameter of φ2.4 mm.

[0026] The welding electrode used for the filler shielded metal arc welding is ENiCrMo - 6, with a diameter of φ3.2 mm or φ4.0 mm.

[0027] Aiming at the problems caused by carbon arc air gouging for root face cleaning on the reverse side of 7Ni steel welding, the present invention proposes to use tungsten inert gas welding for backing instead of carbon arc air gouging for root face cleaning. By using the single - side welding with both - side forming operation of tungsten inert gas welding, a fully penetrated backing weld seam is formed. The root face on the reverse side does not need to be gouged, and shielded metal arc welding is directly used for filling, and shielded metal arc welding or submerged arc welding is used for surfacing. This can effectively avoid various problems caused by carbon arc air gouging for root face cleaning, is beneficial to improving production efficiency, improving the working environment, ensuring welding quality, and saving the consumption of welding materials.

[0028] Example 1

[0029] In this example, for the workpiece to be welded of 7Ni steel with a thickness T = 5 - 15 mm, the groove design is as Figure 1 shown. The workpiece is opened with a single - side V - shaped groove, the groove angle is 50 - 60°, the groove gap is 2.5 - 3.5 mm, the groove root face is 0 - 1 mm, and the groove depth on the reverse side is 2 mm. As Figure 4 shown, the root - face - cleaning - free welding method for 7Ni steel specifically includes the following steps: (1)The 7Ni steel workpiece to be welded is assembled according to the groove design dimensions. Tungsten inert gas (TIG) welding is used for tack welding in the front groove. When tack welding, 99.99% argon is passed for protection on the front side, with a flow rate of 10 - 15 L / min, and 99.99% argon should be passed for protection on the back side, with a flow rate of 8 - 10 L / min; (2)TIG welding is used for root welding in the root of the front groove of the workpiece. The welding current is 100 - 140 A, the welding speed is 10 - 15 cm / min, 99.99% argon is passed for protection on the front side, with a flow rate of 10 - 15 L / min, and 99.99% argon is passed for protection on the back side, with a flow rate of 8 - 12 L / min; (3)Shielded metal arc welding (SMAW) is used for welding 1 - 2 layers of the filler layer in the front groove of the workpiece. A welding electrode with a diameter of φ3.2 mm is used. The welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 15 - 20 cm / min, and the electrode is not oscillated during welding; (4)SMAW is used for welding 3 - the remaining layers of the filler layer in the front groove of the workpiece. SMAW is used, and a welding electrode with a diameter of φ4.0 mm is used. The welding current is 150 - 170 A, the arc voltage is 24 - 27 V, the welding speed is 15 - 20 cm / min, and the electrode is not oscillated during welding; (5)SMAW or submerged arc welding (SAW) is used for welding the cover layer in the front groove of the workpiece; (6)No root cleaning is required on the back side. SMAW is directly used for covering the surface. A welding electrode with a diameter of φ3.2 mm is used. The welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 12 - 18 cm / min, and the width of the electrode oscillation during welding is not more than 12 mm.

[0030] Example 2

[0031] In this example, for the 7Ni steel workpiece to be welded with a plate thickness T = 16 - 30 mm, the groove design is as Figure 2 shown. A double-sided X-shaped groove is opened for the workpiece to be welded. The groove angle is 50 - 60°, the groove gap is 3 - 3.5 mm, the groove root face is 0 - 1 mm, the depth of the front groove is 2 / 3 of the plate thickness, the angle of the back groove is 60 - 70°, and the depth of the back groove is 8 mm. As Figure 5 shown, the root cleaning-free welding method for 7Ni steel specifically includes the following steps: (1)The 7Ni steel workpiece to be welded is assembled according to the groove design dimensions. TIG welding is used for tack welding in the front groove. When tack welding, 99.99% argon is passed for protection on the front side, with a flow rate of 10 - 15 L / min, and 99.99% argon should be passed for protection on the back side, with a flow rate of 8 - 10 L / min; (2)The root of the groove on the front side of the workpiece is welded by tungsten inert gas welding. The welding current is 120 - 160 A, the welding speed is 10 - 15 cm / min, 99.99% argon is used for protection on the front side with a flow rate of 10 - 15 L / min, and 99.99% argon is used for protection on the back side with a flow rate of 10 - 12 L / min; (3)For the filling layer welding of 1 - 3 layers in the groove on the front side of the workpiece, shielded metal arc welding is used. A welding rod with a diameter of φ3.2 mm is adopted, the welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 15 - 20 cm / min, and the welding rod is not swung during welding; (4)For the filling layer welding of the 4th layer and the remaining layers in the groove on the front side of the workpiece, shielded metal arc welding is used. A welding rod with a diameter of φ4.0 mm is adopted, the welding current is 150 - 170 A, the arc voltage is 24 - 27 V, the welding speed is 15 - 20 cm / min, and the swinging width of the welding rod during welding is not more than 15 mm; (5)For the cover layer welding in the groove on the front side of the workpiece, shielded metal arc welding or submerged arc welding is used; (6)Root cleaning is not required on the back side. For the filling layer welding of 1 layer in the groove, shielded metal arc welding is used. A welding rod with a diameter of φ3.2 mm is adopted, the welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 15 - 20 cm / min, and the welding rod is not swung during welding; (7)For the filling layer welding of the 2nd layer and the remaining layers in the groove on the back side, shielded metal arc welding is used. A welding rod with a diameter of φ4.0 mm is adopted, the welding current is 150 - 170 A, the arc voltage is 24 - 27 V, the welding speed is 15 - 20 cm / min, and the swinging width of the welding rod during welding is not more than 15 mm; (8)For the cover layer welding in the groove on the back side, shielded metal arc welding or submerged arc welding is used.

[0032] Example 3

[0033] In this example, for the 7Ni steel workpiece to be welded with a plate thickness T > 30 mm, the groove design is as Figure 3 shown. The workpiece to be welded has a U - V groove. The front side is a U - shaped groove with a groove angle of 30 - 40°, a root arc radius of 8 - 10 mm, a groove gap of 3.5 - 4.0 mm, a groove root face of 0 - 1 mm, and the depth of the front - side groove is 2 / 3 of the plate thickness. The back side is a V - shaped groove with a groove angle of 50 - 60° and the depth of the back - side groove is 10 mm. As Figure 6 shown, the root - cleaning - free welding method for 7Ni steel specifically includes the following steps: (1)For the 7Ni steel workpiece to be welded, assemble it according to the groove design dimensions. Use tungsten inert gas welding for tack welding inside the front groove. When tack welding, pass 99.99% argon for protection on the front side, with a flow rate of 10 - 15 L / min, and pass 99.99% argon for protection on the back side, with a flow rate of 8 - 10 L / min; (2)Use tungsten inert gas welding for root welding inside the front groove of the workpiece. The welding current is 140 - 180 A, the welding speed is 12 - 18 cm / min, pass 99.99% argon for protection on the front side, with a flow rate of 10 - 15 L / min, and pass 99.99% argon for protection on the back side, with a flow rate of 10 - 15 L / min; (3)Use shielded metal arc welding to carry out the filling layer welding of 1 - 4 layers inside the front groove of the workpiece. Use a φ3.2 mm electrode. The welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 15 - 20 cm / min, and the electrode movement does not swing during welding; (4)Use shielded metal arc welding to carry out the filling layer welding of 5 - remaining layers inside the front groove of the workpiece. Use a φ4.0 mm electrode. The welding current is 150 - 170 A, the arc voltage is 24 - 27 V, the welding speed is 15 - 20 cm / min, and the width of the electrode movement swing during welding is not more than 15 mm; (5)Use shielded metal arc welding or submerged arc welding to carry out the cover layer welding inside the front groove of the workpiece; (6)No root cleaning is required on the back side. Use shielded metal arc welding to carry out the filling layer welding of 1 - 2 layers inside the groove. Use a φ3.2 mm electrode. The welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 15 - 20 cm / min, and the electrode movement does not swing during welding; (7)Use shielded metal arc welding to carry out the filling layer welding of 3 - remaining layers inside the back groove. Use a φ4.0 mm electrode. The welding current is 150 - 170 A, the arc voltage is 24 - 27 V, the welding speed is 10 - 15 cm / min, and the width of the electrode movement swing during welding is not more than 15 mm; (8)Use shielded metal arc welding or submerged arc welding to carry out the cover layer welding inside the back groove.

[0034] For the parts or structures not specifically described in the present invention, existing technologies or existing products can be used, and no further elaboration will be made here.

[0035] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made using the content of the specification of the present invention, or directly or indirectly applied in other related technical fields, shall be included in the patent protection scope of the present invention by the same token.

Claims

1. A root-free welding method for 7Ni steel, characterized in that, It includes the following steps: Spot weld and assemble the 7Ni steel workpiece to be welded. First, carry out backing welding at the root inside the front groove, then carry out filling and capping. There is no need to root cleaning inside the reverse groove, directly carry out filling, and then carry out capping.

2. The method for root-free welding of 7Ni steel according to claim 1, characterized in that, It includes the following steps: Spot weld and assemble the 7Ni steel workpiece to be welded. At the root inside the front groove, carry out backing welding using tungsten inert gas welding, then carry out filling using shielded metal arc welding, and then carry out capping using shielded metal arc welding or submerged arc welding. There is no need to root cleaning inside the reverse groove, directly carry out filling using shielded metal arc welding, and then carry out capping using shielded metal arc welding or submerged arc welding.

3. A root-free welding method for 7Ni steel according to claim 2, characterized in that, It includes the following steps: (1) Carry out assembly of the 7Ni steel workpiece to be welded, use tungsten inert gas welding for spot welding, and design the groove form and size according to different thicknesses; (2) At the root inside the front groove of the workpiece, carry out backing welding using tungsten inert gas welding to form a full penetration backing weld; (3) Inside the front groove of the workpiece, carry out filling using shielded metal arc welding, and then carry out capping using shielded metal arc welding or submerged arc welding; (4) There is no need to root cleaning inside the reverse groove of the workpiece, directly carry out filling using shielded metal arc welding, and then carry out capping using shielded metal arc welding or submerged arc welding.

4. A root-free welding method for 7Ni steel according to claim 3, characterized in that, In step (1), the groove form and size designed according to different thicknesses satisfy: When the plate thickness of the 7Ni steel workpiece to be welded is 5 - 15 mm, the workpiece is opened with a single-sided V-groove, the groove angle is 50 - 60°, the groove gap is 2.5 - 3.5 mm, and the groove root face is 0 - 1 mm; When the plate thickness of the 7Ni steel workpiece to be welded is 16 - 30 mm, the workpiece is opened with an X-groove, the front groove angle is 50 - 60°, the groove gap is 3 - 3.5 mm, the groove root face is 0 - 1 mm, the depth of the front groove is 2 / 3 of the plate thickness, and the reverse groove angle is 60 - 70°; When the plate thickness of the 7Ni steel workpiece to be welded is more than 30 mm, the workpiece is opened with a U-V groove, the front is a U-groove, the groove angle is 20 - 30°, the root arc radius is 6 - 8 mm, the groove gap is 3.5 - 4.0 mm, the groove root face is 0 - 1 mm, the depth of the front groove is 2 / 3 of the plate thickness, and the reverse is a V-groove, the groove angle is 50 - 60°.

5. A root-free welding method for 7Ni steel according to claim 3, characterized in that, In step (2), the parameters of the backing welding are: When the plate thickness of the 7Ni steel workpiece to be welded is 5 - 15 mm, the welding current is 100 - 140 A, the welding speed is 10 - 15 cm / min, 99.99% argon is passed for protection on the front, the flow rate is 10 - 15 L / min, 99.99% argon is passed for protection on the reverse, and the flow rate is 8 - 12 L / min; When the plate thickness of the 7Ni steel workpiece to be welded is 16 - 30 mm, the welding current is 120 - 160 A, the welding speed is 10 - 15 cm / min, 99.99% argon is passed for protection on the front, the flow rate is 10 - 15 L / min, 99.99% argon is passed for protection on the reverse, and the flow rate is 10 - 12 L / min; When the thickness of the 7Ni steel workpiece to be welded is more than 30 mm, the welding current is 140 - 180 A, the welding speed is 12 - 18 cm / min, 99.99% argon is used for shielding on the front side with a flow rate of 10 - 15 L / min, and 99.99% argon is used for shielding on the back side with a flow rate of 10 - 15 L / min.

6. A root-free welding method for 7Ni steel according to claim 3, characterized in that The welding wire used for backing welding is ERNiCrMo-4 with a diameter of φ2.4 mm.

7. A root-free welding method for 7Ni steel according to claim 3, characterized in that In step (3), the parameters for filling by shielded metal arc welding in the front groove of the workpiece are: When the thickness of the 7Ni steel workpiece to be welded is 5 - 15 mm, 1 - 2 layers are filled. A φ3.2 mm electrode is used, the welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 15 - 20 cm / min, and the electrode is not waved during welding. For the 3rd - remaining layers, a φ4.0 mm electrode is used, the welding current is 150 - 170 A, the arc voltage is 24 - 27 V, the welding speed is 15 - 20 cm / min, and the electrode is not waved during welding; When the thickness of the 7Ni steel workpiece to be welded is 16 - 30 mm, 1 - 3 layers are filled. A φ3.2 mm electrode is used, the welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 15 - 20 cm / min, and the electrode is not waved during welding. For the 4th - remaining layers, a φ4.0 mm electrode is used, the welding current is 150 - 170 A, the arc voltage is 24 - 27 V, the welding speed is 10 - 15 cm / min, and the width of the electrode wave during welding is not more than 15 mm; When the thickness of the 7Ni steel workpiece to be welded is more than 30 mm, 1 - 4 layers are filled. A φ3.2 mm electrode is used, the welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 15 - 20 cm / min, and the electrode is not waved during welding. For the 5th - remaining layers, a φ4.0 mm electrode is used, the welding current is 150 - 170 A, the arc voltage is 24 - 27 V, the welding speed is 10 - 15 cm / min, and the width of the electrode wave during welding is not more than 15 mm.

8. A method for root-free welding of 7Ni steel according to claim 3, characterized in that In step (4), the parameters for filling by shielded metal arc welding are: When the thickness of the 7Ni steel workpiece to be welded is 5 - 15 mm, there is no groove on the back side, and the surface is directly covered by shielded metal arc welding. A φ3.2 mm electrode is used, the welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 12 - 18 cm / min, and the width of the electrode wave during welding is not more than 12 mm; When the thickness of the 7Ni steel workpiece to be welded is 16 - 30 mm, the root of the reverse side is not gouged. The groove is filled by shielded metal arc welding with 1 layer. The electrode with a diameter of φ3.2 mm is used, the welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 15 - 20 cm / min, and the electrode is not oscillated during welding. For the 2nd layer and the remaining layers, the electrode with a diameter of φ4.0 mm is used, the welding current is 150 - 170 A, the arc voltage is 24 - 27 V, the welding speed is 10 - 15 cm / min, and the oscillation width of the electrode is not more than 15 mm during welding. When the thickness of the 7Ni steel workpiece to be welded is more than 30 mm, the root of the reverse side is not gouged. The groove is filled by shielded metal arc welding with 1 - 2 layers. The electrode with a diameter of φ3.2 mm is used, the welding current is 100 - 130 A, the arc voltage is 22 - 25 V, the welding speed is 15 - 20 cm / min, and the electrode is not oscillated during welding. For the 3rd layer and the remaining layers, the electrode with a diameter of φ4.0 mm is used, the welding current is 150 - 170 A, the arc voltage is 24 - 27 V, the welding speed is 10 - 15 cm / min, and the oscillation width of the electrode is not more than 15 mm during welding.

9. A root-free welding method for 7Ni steel according to claim 3, characterized in that The electrodes used for shielded metal arc welding are ENiCrMo - 6 with a diameter of φ3.2 mm or φ4.0 mm.

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