Clad steel welding method

Abstract

To weld clad steel while suppressing a corrosion-resistant metal welding material from diluting after welding a base material.SOLUTION: A method for welding clad steel 10, which uses stainless steel or nickel alloy as laminating materials 14 and carbon steel or low-alloy steel as base materials 12, comprises: a step of applying edge-preparation for forming exposed surfaces 12A of the base materials 12 by performing cut-back of the laminating materials 14; a step of butting the clad steel 10 subjected to the edge preparation to each other so that a route interval G between the base materials 12 becomes to be equal to or greater than 3 mm or more; a lining material arranging step of arranging lining materials 26 on the exposed surfaces 12A of the base materials 12 after the butting step; a base material welding step of performing butting-groove welding of the base materials 12 from the base material 12 sides after the lining material arranging step; a lining material detaching step of detaching the lining materials 26 after the base material welding step; and a laminating material welding step of performing butting-groove welding of the laminating materials 14 from the laminating material 14 side, after the lining material detaching step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a clad steel welding method, and more particularly to a clad steel welding method that suppresses the dilution of the welding material, which is a corrosion-resistant metal, after base metal welding. [Background technology]

[0002] Clad steel is a composite steel material in which a cladding material (such as stainless steel) with excellent corrosion resistance and other functional properties is metallurgically bonded to the surface of a base material (carbon steel or low-alloy steel). It possesses the strength necessary for structural members, while also having functional properties such as corrosion resistance, and is less expensive than when the base material and cladding material are made of the same material. These are its excellent characteristics, and it is widely used in structures and components placed in corrosive environments.

[0003] However, because clad steel is a composite material, welding it requires more ingenuity compared to welding carbon steel to carbon steel. Conventional clad steel welding methods involve downward welding from the base metal side, but the first layer is prone to welding defects such as incomplete melting, blowholes, and slag inclusion. Therefore, after welding the base metal, the piece is inverted and the back side is gouged or ground down to remove the welding defects, and then TIG (Tungsten Inert Gas) welding or arc welding using flux-cored wire is performed downward welding from the clad material side.

[0004] In contrast, Patent Document 1 proposes a butt welding method for clad steel that allows welding in all positions from the inside of the pipe without having to chip away the back bead after base metal welding, and enables welding with a welding material that has strength equal to or greater than that of the non-corrosion-resistant steel on the non-corrosion-resistant steel side, thereby achieving both corrosion resistance and high strength in the clad steel pipe.

[0005] In the technology described in Patent Document 1, the end of the clad steel 100 to be butt-welded is processed into a groove 120 of the shape shown in Figure 11 (the shape of the base material side groove 122 is not particularly limited), and then the first layer welding is performed on the base material side groove 122 on the non-corrosion-resistant steel (base material 102) side, resulting in a predetermined shape (H) as shown in Figure 12. bx / W bx <1, Here H bx : Back bead height [mm], W bx After forming a back bead 132 with a back bead width [mm] within the cladding groove 124 on the high-corrosion-resistant (cladding material 104) side, the cladding groove 124 on the high-corrosion-resistant (cladding material 104) side is welded using a welding material with corrosion resistance equal to or greater than that of the high-corrosion-resistant (cladding material 104) of the clad steel 100, without chipping away at the back bead 132. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2021-137860 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the technology described in Patent Document 1 involves forming a back bead 132 made of non-corrosion-resistant steel within the groove 124 on the high-corrosion-resistant side (clamping material 104), and then welding the groove 124 on the high-corrosion-resistant side (clamping material 104) without chipping away the back bead 132, but the width W of the back bead 132 formed within the groove 124 is different. bx Height H bx Ratio (H bx / W bx The inventors considered that because no measures have been taken to reduce the size of the back bead 132, there is a risk that the welding material, which is highly corrosion-resistant, may be diluted in the vicinity of the back bead 132. Therefore, the inventors considered that the following problems, specifically (1) and (2), may occur.

[0008] (1) When a nickel alloy welding material is used when welding the groove 124 on the mating material side, the corrosion resistance decreases locally as the dilution increases.

[0009] (2) When welding the groove 124 on the joint side using 309 series welding material, if the dilution is large, the corrosion resistance will decrease locally and the weld metal will become martensitic. A martensitic structure is extremely hard and has poor ductility, which can cause cracking. In addition, when a martensitic structure is formed, delayed cracking may occur due to diffusible hydrogen.

[0010] The present invention has been made in view of the above, and aims to provide a clad steel welding method that suppresses the dilution of the welding material, which is a corrosion-resistant metal, after base metal welding. [Means for solving the problem]

[0011] The present invention solves the aforementioned problems and is a clad steel welding method as described below.

[0012] That is, the first aspect of the clad steel welding method according to the present invention is a method for welding clad steel in which stainless steel or nickel alloy is used as the cladding material and carbon steel or low-alloy steel is used as the base material, and is characterized by comprising: a beveling step of performing a beveling process in which a cutback is performed to remove the cladding material at the part of the clad steel to be welded to form an exposed surface of the base material; a butt joint step of butting the beveled clad steels together so that the root gap between the base materials is 3 mm or more; a backing material placement step of placing a backing material on the exposed surface of the base material after the butt joint step; a base material welding step of performing a butt joint bevel welding from the base material side to the base material side after the backing material placement step; a backing material removal step of removing the backing material after the base material welding step; and a cladding material welding step of performing a butt joint bevel welding of the cladding material from the cladding material side after the backing material removal step.

[0013] Here, in the present application, carbon steel is a type of steel that is an alloy of iron and carbon, and is steel with a carbon content usually in the range of 0.02 to about 2%, and contains a small amount of silicon, manganese, phosphorus, sulfur, etc. Low alloy steel refers to steel in which the total amount of predetermined alloying elements is 5% by mass or less.

[0014] Also, in the present application, cutback means removing the filler material substantially parallel to the direction in which the filler material spreads to expose the base material.

[0015] A second aspect of the clad steel welding method according to the present invention is an aspect configured such that in the first aspect of the clad steel welding method, the backing material is made of ceramic.

[0016] A third aspect of the clad steel welding method according to the present invention is an aspect configured such that in the first or second aspect of the clad steel welding method, in the butting step, the parallel portion length of the groove bottom on the filler material side including the exposed surface is 15 mm or more, and the clad steels subjected to the beveling are butted together.

[0017] A fourth aspect of the clad steel welding method according to the present invention is an aspect configured such that in any one of the first to third aspects of the clad steel welding method, in the filler material welding step, arc welding is performed from the filler material side using a flux cored wire having a welding material of a corrosion-resistant metal.

[0018] A fifth aspect of the clad steel welding method according to the present invention is an aspect configured such that in any one of the first to fourth aspects of the clad steel welding method, the backing material is a backing material without a recess for forming a back bead.

[0019] The sixth aspect of the clad steel welding method according to the present invention is an aspect configured such that, in any one of the first to fifth aspects of the clad steel welding method, in the beveling process, a cutback for removing the backing material is performed to form a groove wall having an angle of 130° or more with the exposed surface.

[0020] The seventh aspect of the clad steel welding method according to the present invention is an aspect configured such that, in any one of the first to sixth aspects of the clad steel welding method, after performing the base metal welding process, the backing material welding process is performed without inverting the clad steel.

[0021] The eighth aspect of the clad steel welding method according to the present invention is an aspect configured such that, in any one of the first to seventh aspects of the clad steel welding method, in the backing material welding process, a mixed gas of CO2 and argon is used as a shielding gas, the content ratio of CO2 in the mixed gas is 0 mol% or more and 95 mol% or less, and the heat input amount during the arc welding is 5 kJ / cm or more and 40 kJ / cm or less.

[0022] The ninth aspect of the clad steel welding method according to the present invention is an aspect configured such that, in any one of the first to eighth aspects of the clad steel welding method, after the backing material welding process, at least one of mechanical polishing, electrolytic polishing, or passivation treatment using an abrasive material that does not contain iron and is at least one of aluminum oxide, silicon carbide, boron nitride, diamond, corundum, garnet and has a particle size equivalent to or finer than the F80 particle size defined in JIS R6001 (1998) is performed to treat the surface of the welded portion in the backing material welding process.

[0023] The tenth aspect of the clad steel welding method according to the present invention is an aspect configured such that, in the ninth aspect of the clad steel welding method, after performing the mechanical polishing on the surface of the welded portion in the backing material welding process, either electrolytic polishing or passivation treatment is further performed on the surface.

[0024] An eleventh aspect of the clad steel welding method according to the present invention is an aspect in which, in any of the first to tenth aspects of the clad steel welding method, the clad steel is configured to be a clad steel plate or a clad steel pipe. [Effects of the Invention]

[0025] According to the present invention, it is possible to provide a clad steel welding method that suppresses the dilution of the welding material, which is a corrosion-resistant metal, after base metal welding. [Brief explanation of the drawing]

[0026] [Figure 1] This diagram schematically shows the main parts of the clad steel 10 when a groove preparation process and a butt joint process are performed, relating to a clad steel welding method according to an embodiment of the present invention. [Figure 2] This diagram schematically shows the main parts of the clad steel 10 when the backing material placement step is performed, relating to a clad steel welding method according to an embodiment of the present invention. [Figure 3] This invention relates to a clad steel welding method according to an embodiment of the present invention, and schematically shows the main parts of the clad steel 10 when the base metal welding process is performed. [Figure 4] This diagram schematically shows the main parts of the clad steel 10 when the backing material removal step is performed, relating to a clad steel welding method according to an embodiment of the present invention. [Figure 5] This invention relates to a clad steel welding method according to an embodiment of the present invention, and provides a schematic diagram showing the main parts of the clad steel 10 when the cladding welding process is performed. [Figure 6] Cross-sectional view of a specific example of a backing material usable in the clad steel welding method according to an embodiment of the present invention ((A) has a recess, (B) does not). [Figure 7] (Figure (A) schematically shows the shape of a back bead 32 formed with a backing material, and (B) schematically shows the shape of a back bead 33 formed without a backing material.) [Figure 8]A schematic diagram showing the first modified example of the jointed material side groove 24, namely the jointed material side groove 24A. [Figure 9] A schematic diagram showing a second modified example of the jointed material side groove 24, namely the jointed material side groove 24B. [Figure 10] This figure schematically shows another specific example of a backing material (backing material 29) that can be used in the clad steel welding method according to an embodiment of the present invention ((A) is a cross-sectional view of the backing material 29, and (B) is a schematic diagram showing the backing material 29 attached to the groove 24 on the mating material side). [Figure 11] A diagram illustrating the technology described in Patent Document 1 (a cross-sectional view showing the groove shape of clad steel 100 used for butt welding). [Figure 12] A diagram illustrating the technology described in Patent Document 1 (cross-sectional view of the shape of the back bead 132 formed by the first layer welding on the non-corrosion-resistant steel (base material 102) side). [Modes for carrying out the invention]

[0027] Embodiments of the present invention will be described in detail below with reference to the drawings.

[0028] Figures 1 to 5 are schematic cross-sectional views illustrating typical process scenes of a clad steel welding method according to an embodiment of the present invention. Figure 1 is a schematic diagram illustrating the main parts of the clad steel 10 when the groove processing process and butt joint process are performed in a clad steel welding method according to an embodiment of the present invention. Figure 2 is a schematic diagram illustrating the main parts of the clad steel 10 when the backing material placement process is performed in a clad steel welding method according to an embodiment of the present invention. Figure 3 is a schematic diagram illustrating the main parts of the clad steel 10 when the base metal welding process is performed in a clad steel welding method according to an embodiment of the present invention. Figure 4 is a schematic diagram illustrating the main parts of the clad steel 10 when the backing material removal process is performed in a clad steel welding method according to an embodiment of the present invention. Figure 5 is a schematic diagram illustrating the main parts of the clad steel 10 when the cladding material welding process is performed in a clad steel welding method according to an embodiment of the present invention. Figure 6 is a cross-sectional view of a specific example of a backing material that can be used in the clad steel welding method according to an embodiment of the present invention ((A) shows a recessed area, (B) shows a non-recessed area). Figure 7 is a diagram for explaining the shape of the back bead ((A) schematically shows the shape of the back bead 32 formed with a backing material, and (B) schematically shows the shape of the back bead 33 formed without a backing material). Figure 8 is a schematic diagram showing a cladding material side groove 24A, which is a first modified example of the cladding material side groove 24. Figure 9 is a schematic diagram showing a cladding material side groove 24B, which is a second modified example of the cladding material side groove 24. Figure 10 is a schematic diagram showing another specific example of a backing material (backing material 29) that can be used in the clad steel welding method according to an embodiment of the present invention ((A) is a cross-sectional view of the backing material 29, and (B) is a schematic diagram showing the state in which the backing material 29 is attached to the cladding material side groove 24).

[0029] In the following description of the embodiments, the clad steel 10 to which the clad steel welding method according to this embodiment is applied is described as being plate-shaped. However, the shape of the clad steel to which the present invention can be applied is not limited to plate shape; any shape that allows the clad steel welding method according to the present invention to be implemented is acceptable. The clad steel welding method according to the present invention is widely applicable to clad steel of various shapes, such as plate-shaped or tubular clad steel, and other clad steel shapes. Furthermore, in the following description of the embodiments, various materials are specifically described, but these are merely examples, and the present invention is not limited to the described examples.

[0030] The clad steel 10 to which the clad steel welding method according to this embodiment is applied comprises a base material 12 and a cladding material 14, as shown in Figure 1. The base material 12 is carbon steel or low-alloy steel, and the cladding material 14 is stainless steel or nickel alloy, and the cladding material 14 is a corrosion-resistant metal. As mentioned above, in this application, low-alloy steel refers to steel in which the total amount of a predetermined alloying element is 5% by mass or less.

[0031] As described above, the cladding material 14 of the clad steel 10 to which the clad steel welding method according to this embodiment is applied is stainless steel or a nickel alloy. Specifically, for example, as stainless steel, austenitic stainless steels such as SUS304, SUS304L, SUS316, SUS316L, SUS316LN, SUS317, SUS317L, SUS312L, SUS836L, JSL310Mo, UNS S31254, UNS S32053, UNS S32050, UNS S08354, UNS N08904, etc. can be used, and as nickel alloys, nickel alloys containing chromium and molybdenum such as NCF825, NCF625, NW6022, NW0276, UNS N08825, UNS N06625, UNS N06022, UNS N10276, etc. can be used.

[0032] In the clad steel welding method according to this embodiment, the clad steel 10 is welded in the following steps (steps 1 to 6).

[0033] <Step 1 (Beveling and Butt Joining Process)> A predetermined bevel is made at the end of the clad steel 10 that will be welded, and the ends of the clad steel 10 with the predetermined bevel are butted together to create a groove 20, a base material side groove 22, and a cladding material side groove 24, as shown in Figure 1. Here, the base material side groove 22 is a groove provided on the base material 12 side, and the cladding material side groove 24 is a groove provided on the cladding material 14 side, and the base material side groove 22 and the cladding material side groove 24 together are referred to as groove 20.

[0034] The base metal side groove 22, which is used for welding the base metal 12, is formed by butting the ends of the base metal 12 together so that it is V-shaped as shown in Figure 1, and the root gap G of the base metal side groove 22 is formed by butting the ends together so that it is 3 mm or more and 10 mm or less. Providing an appropriate root gap makes it easier to integrate the weld metal and the base metal 12 together (complete penetration). In the clad steel welding method according to this embodiment, in order to provide a predetermined root gap, a backing material 26 (see Figure 2) is installed to prevent leakage of the weld metal, and an appropriate overlap is provided between the base metal 12 and the backing material 26 to prevent leakage of the weld metal. If the root gap G of the base metal side groove 22 is less than 3 mm, it becomes difficult for the weld metal to enter the root gap G, making it difficult to perform complete penetration welding. Furthermore, if the root gap G of the base metal groove 22 is less than 3 mm, welding defects such as poor fusion, blowholes, and slag inclusion are likely to occur, even when using a backing material 26. On the other hand, if the root gap G exceeds 10 mm, the number of welding passes increases, reducing the efficiency of the welding operation. It also leads to an increase in the amount of deposited metal, resulting in higher material costs.

[0035] Furthermore, the groove 24 on the cladding material side, where the cladding material 14 is welded, is formed by cutting back the cladding material 14 at the end of the clad steel 10 that is to be welded, thereby exposing the base material 12. This groove processing creates a base material exposed surface 12A in which the base material 12 is exposed over a certain range. In the clad steel welding method according to this embodiment, the base material exposed surface 12A is provided as a plane that extends in substantially the same direction as the direction in which the surface of the cladding material 14 expands. The groove 24 on the cladding material side is a rectangular groove (see Figure 1) with the base material exposed surface 12A as the groove bottom and the cladding material end face 14A of the cladding material 14 as the groove wall, and the cladding material end face (groove wall) 14A is substantially perpendicular to the base material exposed surface (groove bottom) 12A.

[0036] In the groove 20, the base material side groove 22 is set so that the root spacing G is 3 mm or more and 10 mm or less, as described above, while the length W of the parallel section at the bottom of the groove on the mating material side of the mating material side groove 24 is set to be 15 mm or more.

[0037] The reason for setting the length W of the parallel section at the bottom of the groove on the mating material side of the mating material side groove 24 to 15 mm or more is to ensure that in the next step 2 (backing material placement step), the backing material 26 is in close contact with the exposed surface 12A of the base material by a sufficient distance, thereby preventing the weld metal from leaking between the backing material 26 and the exposed surface 12A of the base material. In order to prevent the weld metal from leaking between the backing material 26 and the exposed surface 12A of the base material, it is necessary to ensure a contact distance d (see Figure 2) of 6 mm or more on one side between the backing material 26 and the exposed surface 12A of the base material, and it is preferable to ensure a distance of 7 mm or more. For example, if the root spacing G of the base material side groove 22 is 3 mm, and the contact distance d is set to 6 mm on each side, the length W of the parallel section at the bottom of the groove on the mating material side of the mating material side groove 24 will be 3 mm + 6 mm + 6 mm = 15 mm. If the contact distance d is set to 7 mm on each side, the length W of the parallel section at the bottom of the groove on the mating material side of the mating material side groove 24 will be 3 mm + 7 mm + 7 mm = 17 mm. Therefore, it is necessary to ensure that the length W of the parallel section at the bottom of the groove on the mating material side of the mating material side groove 24 is 15 mm or more, and it is preferable to ensure that it is 17 mm or more.

[0038] Furthermore, if the length W of the parallel section at the bottom of the groove on the mating material side of the mating material side groove 24 becomes too long, the number of welding passes for the corrosion-resistant metal welding material used for welding the mating material side groove 24 will increase, reducing the efficiency of the welding work. In addition, the amount of weld metal of the corrosion-resistant metal will increase, leading to increased material costs. Therefore, the groove spacing is preferably 40 mm or less, and more preferably 32 mm or less.

[0039] Therefore, the length W of the parallel portion at the bottom of the groove on the mating material side of the mating material side groove 24 is preferably 15 mm or more and 40 mm or less, and more preferably 17 mm or more and 32 mm or less.

[0040] <Step 2 (Backing material placement process)> After forming the groove 20 shown in Figure 1 in Step 1 (grooving and butt joint process), in Step 2 (backing material placement process), as shown in Figure 2, the backing material 26 is placed in close contact with the exposed surface 12A of the base material. When placing the backing material 26 in close contact with the exposed surface 12A of the base material, aluminum tape can be used, for example. The length of the backing material 26 can be set to an appropriate length depending on the welding situation, and when using a short backing material, it is placed in a row. Short backing materials are easy to place along the shape of the object to be welded.

[0041] In the clad steel welding method according to this embodiment, the backing material 26 is removed in the later step 4 (backing material removal step), so the backing material 26 must be a backing material that can be removed after welding the base metal groove 22 with the base metal weld metal 30 in step 3 (base metal welding step). For example, a ceramic backing material can be removed after step 3 (base metal welding step), so it can be used as the backing material 26 in the clad steel welding method according to this embodiment. Furthermore, since ceramics have a high melting point and hardly melt even when in contact with molten metal, and have little effect on the weld metal, it is preferable to use a ceramic backing material as the backing material 26. Specifically, a ceramic backing material can be manufactured by molding a mixture of at least one of SiO2, Al2O3, MgO, kaolin, and talc into a predetermined shape.

[0042] In addition, since a copper backing material, a flux backing material, etc. can also be removed after Step 3 (base material welding step), it can be used as the backing material 26 used in the clad steel welding method according to the present embodiment.

[0043] In the clad steel welding method according to the present embodiment, in this Step 2 (backing material placement step), since the backing material 26 is placed in close contact with the base material exposed surface 12A, it is not necessary to perform the sagging operation of the back bead after the next Step 3 (base material welding step).

[0044] When placing the backing material 26, as described above, it is necessary to ensure a close contact distance d of 6 mm or more on one side between the backing material 26 and the base material exposed surface 12A, and it is preferable to ensure 7 mm or more. Further, when bringing the backing material 26 into close contact with the base material exposed surface 12A, for example, it can be performed using an aluminum tape, but attention is paid to ensuring the flatness of the base material exposed surface 12A in order to more reliably prevent the welding metal from leaking between the backing material 26 and the base material exposed surface 12A. Also, a pressing material or jig that strongly presses the backing material 26 against the base material exposed surface 12A may be used.

[0045] Generally, for full penetration butt welding, a backing material provided with a recess for forming a back bead is used. In the clad steel welding method according to the present embodiment as well, as shown in FIG. 2, a backing material 26 (see FIG. 6(A)) provided with a recess 26A for forming a back bead is used. The width of the recess 26A is made equal to or greater than the root interval G.

[0046] In the clad steel welding method according to the present embodiment, when welding the base materials 12 together, even when using the backing material 26 with the recess 26A, the height of the back bead is limited to the height of the recess 26A, and by using the backing material 26, the root interval G can be widened to 3 mm or more. Therefore, as shown in FIG. 7(A), the height H of the back bead 32 b1 is the width W b1As a result, the relative value is lower, and dilution of the welding material, which is a corrosion-resistant metal, is less likely to occur during welding of the masonry materials 14 together in step 5 (masonry material welding process). On the other hand, when welding of the base materials 12 together without using a backing material, as in the technology described in Patent Document 1, it is necessary to narrow the root gap G to prevent leakage of weld metal, and the height of the back bead is not limited by the backing material, so as shown in Figure 7(B), the height H of the back bead 33 that occurs in the groove 25 on the masonry material side b2 is width W b2 This becomes relatively higher, and in step 5 (joint welding process), during the welding of the joint members 14 together (welding of the joint member side groove 24), dilution of the welding material, which is a corrosion-resistant metal, is more likely to occur locally near the back bead 33.

[0047] In addition, in the clad steel welding method according to this embodiment, a backing material 28 (see Figure 6(B)) can be used in which the surface that comes into contact with the welding area is formed only of a flat surface 28A and has no recesses. Generally, in full penetration butt welding, it is confirmed that full penetration has been achieved by confirming the formation of a back bead, so in full penetration butt welding from one side, it is necessary to form a back bead on the surface opposite to the welding side. However, in the clad steel welding method according to this embodiment, as will be described later, after welding the base materials 12 together in step 3 (base material welding process), welding the cladding materials 14 together on the cladding material 14 side opposite to the base material 12 is performed in step 5 (cladding material welding process). Therefore, in the clad steel welding method according to this embodiment, it is not necessarily required to confirm the formation of a back bead in step 3 (base material welding process), and a backing material 28 without recesses can be used.

[0048] In the clad steel welding method according to this embodiment, when a backing material 28 without a recess is used, a back bead is not formed in the groove 24 on the cladding material side. Therefore, in the welding of the cladding materials 14 together in step 5 (cladding material welding process), dilution of the welding material, which is a corrosion-resistant metal, is less likely to occur.

[0049] <Step 3 (Base Metal Welding Process)> In step 2 (backing material placement step), as shown in Figure 2, the backing material 26 is placed in close contact with the exposed surface 12A of the base material. Then, in step 3 (base material welding step), a butt groove welding of the base material 12 is performed from the base material 12 side using a welding material suitable for the base material 12, and as shown in Figure 3, the base material side groove 22 is filled with base material weld metal 30 and the base material side groove 22 is welded.

[0050] As for the welding method of the base metal 12 (carbon steel or low-alloy steel) in the groove 22 on the base metal side, for example, gas shielded arc welding (gas metal arc welding), submerged arc welding, shielded metal arc welding, self-shielded arc welding, and TIG welding can be used. Among these, gas shielded arc welding and submerged arc welding are often used in terms of cost and ease of construction.

[0051] The welding material used for welding the base metals 12 together in the groove 22 on the base metal side should, in principle, be a welding material with a composition similar to that of the base metal. However, the composition of the welding material should be selected taking into account component losses such as evaporation and transfer to slag during welding. Furthermore, it is preferable to use a welding material with strength equal to or greater than that of the base metal, i.e., equivalent to or overmatching.

[0052] <Step 4 (Removal of backing material)> In step 3 (base metal welding process), as shown in Figure 3, the base metal groove 22 is welded with the base metal weld metal 30. Then, in step 4 (backing material removal process), as shown in Figure 4, the backing material 26 is removed. As shown in Figure 4, a back bead 32 with a shape similar to the recess 26A of the backing material 26 is formed in the mating material groove 24. However, in the clad steel welding method according to this embodiment, the backing material 26 is placed in step 2 (backing material placement process) before step 3 (base metal welding process), so as mentioned above, the height H of the back bead 32 b1 is width W b1 The ratio is relatively low (see Figure 7(A)), and dilution of the welding material, which is a corrosion-resistant metal, is unlikely to occur during the groove welding of the butt joint of the masonry material 14 in step 5 (masonry material welding process).

[0053] Furthermore, in the clad steel welding method according to this embodiment, the backing material 26 is placed in close contact with the exposed surface 12A of the base material before the base material welding process in step 3 is performed. Therefore, welding defects in the first layer are less likely to occur, and there is no need to perform chipping work on the back bead after step 4 (backing material removal process).

[0054] <Step 5 (Welding Process for Joints)> In step 4 (backing material removal step), as shown in Figure 4, the backing material 26 is removed to expose the joint groove 24 on the joint material side, making it possible to weld from the joint material 14 side. Then, in step 5 (joint material welding step), a butt groove weld of the joint material 14 is performed from the joint material 14 side using a corrosion-resistant welding material used for welding the joint groove 24, and as shown in Figure 5, the joint groove 24 on the joint material side is filled with the joint material weld metal 34, which is a corrosion-resistant weld metal, and the joint groove 24 is welded.

[0055] Before step 5 (cladding welding process), a back bead 32 is formed in the groove 24 on the cladding side. However, in the clad steel welding method according to this embodiment, the backing material 26 is placed in step 2 (backing material placement process) before step 3 (base metal welding process). Therefore, as mentioned above, the height H of the back bead 32 b1 is width W b1 It is relatively low (see Figure 7(A)), and in the groove welding of the butt joint of the masonry material 14 in this step 5 (masonry material welding process), dilution of the welding material, which is a corrosion-resistant metal, is unlikely to occur. If the backing material 26 is not placed before step 3 (base metal welding process), the height H of the back bead 33 b2 Width W b2 This area becomes relatively larger (see Figure 7(B)), and in this step 5 (joint welding process), it may be immediately melted, potentially leading to localized dilution of the welding material.

[0056] Furthermore, in the clad steel welding method according to this embodiment, in step 2 (backing material placement step), the backing material 26 is placed in close contact with the exposed surface 12A of the base material, so welding defects in the first layer of the base material groove 22 are less likely to occur, there is no need to chip away the back bead after step 3 (base material welding step), gouging is unnecessary, and deep grooves are not created. For this reason, in principle, welding with corrosion-resistant welding material in step 5 (cladding material welding step) only needs to be done in one layer.

[0057] As mentioned above, the composite material 14 is stainless steel or a nickel alloy, and is a corrosion-resistant metal.

[0058] In this embodiment, when austenitic stainless steel with a pitting index of less than 31 is used as the cladding material 14 for the clad steel 10 to which this embodiment applies, the metal component of the flux-cored wire (FCW) used as the welding material can be stainless steel of the 309 series, 309L series, 309J series, 309Mo series, 309LMo series, or 309LNb series. Specifically, for example, TS309-FB0, TS309-FB1, TS309-FC0, TS309-FC1, TS309-FM0, TS309-FM1, TS309-MI0, TS309-MI1, TS309L-FB0, TS309L-FB1, TS309L-FC0, Flux-cored wires such as TS309L-FC1, TS309L-FM0, TS309L-FM1, TS309L-MI0, TS309L-MI1, TS309J-FB0, TS309J-FB1, TS309Mo-FB0, TS309Mo-FB1, TS309Mo-FC0, TS309Mo-FC1, TS309Mo-FM0, TS309Mo-FM1, TS309Mo-MI0, TS309Mo-MI1, TS309LMo-FB0, TS309LMo-FB1, TS309LMo-FC0, TS309LMo-FC1, TS309LMo-FM0, TS309LMo-FM1, TS309LMo-MI0, TS309LMo-MI1, and TS309LNb-FB0 (metal component is 309 series stainless steel) can be used. When 309 series stainless steel is used as the welding material, the weld metal near the boundary between the carbon steel and the weld metal is less likely to form a martensitic structure, thus suppressing the occurrence of cracks. In this application, the pitting index is an index calculated using the content (mass%) of Cr, Mo, and N contained in the stainless steel, and is a value (expressed as mass%) calculated by the formula Pitting Index = Cr + 3.3Mo + 16N (where each element symbol in the formula represents the content of that element).

[0059] As the laminated material 14, if austenitic stainless steel with a pitting index of 31 or higher is used, such as SUS312L, SUS836L, JSL310Mo, UNS S31254, UNS S32053, UNS S32050, UNS S08354, UNS N08904, or NCF825, NCF625, NW6022, NW0276, UNS N08825, UNS N06625, UNS N06022, UNS When using a nickel alloy containing chromium and molybdenum, such as N10276, the metal components of the flux-cored wire (FCW) used as the welding material can be Ni6625 series, Ni6276 series, Ni6022 series, Ni6059 series, Ni6275 series, Ni6455 series, Ni6456 series, Ni6686 series, and Ni1013 series nickel alloys. Specifically, for example, TNi6625-PB0, TNi6625-PB1, TNi6625-BM0, TNi6625-BM1, TNi6625-PM0, TNi6625-PM1, TNi6276-PB0, TNi6276-PB1, TNi6276-BM0, TNi6276-BM1, TNi6276-PM0, TNi6276-PM1, TNi 6022-PB0, TNi6022-PB1, TNi6022-BM0, TNi6022-BM1, TNi6022-PM0, TNi6022-PM1, TNi6059-P B0, TNi6059-PB1, TNi6059-BM0, TNi6059-PM1, TNi6059-PB1, TNi6275-PB1, TNi6275-BM0, TNi Flux-cored wires such as 6275-PM1, TNi6455-PB1, TNi6455-BM0, TNi6455-PM1, TNi6456-PB1, TNi6456-BM0, TNi6456-PM1, TNi6686-PB1, TNi6686-BM0, TNi6686-PM1, TNi1013-PB1, TNi1013-BM0, TNi1013-PM1, and AWS A5.34 ENiMo13T1-1 / 4 (metal components are nickel alloys) can be used. When using nickel alloy welding materials containing Cr and Mo, the corrosion resistance of the welded part of the corrosion-resistant metal is less likely to decrease even if dilution occurs.

[0060] In Step 5 (cladding welding process), the welding method can be TIG welding, stick welding, or MAG welding using flux-cored wire (FCW) (arc welding using a mixture of inert gas and carbon dioxide as shielding gas). MAG welding using flux-cored wire (FCW) has a higher welding efficiency compared to other welding methods (TIG welding, stick welding, etc.), and even in overhead or vertical welding, the welding efficiency does not deteriorate as much as other welding methods (TIG welding, stick welding, etc.). Therefore, from the viewpoint of workability and constructability, it is preferable to use MAG welding using flux-cored wire (FCW) as the welding method in Step 5 (cladding welding process). In Step 5 (cladding welding process), by using MAG welding using flux-cored wire (FCW), even if the clad steel 10 is not inverted or its orientation is not changed, overhead or vertical welding is performed to weld the cladding material 14 side, and a decrease in welding efficiency can be suppressed. Therefore, by using MAG welding with flux-cored wire (FCW) in step 5 (cladding welding process), the clad steel welding method according to this embodiment can be suitably used for welding clad steel to fixed structures such as bridges.

[0061] In Step 5 (composite welding process), when performing MAG welding using flux-cored wire (FCW), a mixed gas of CO2 and argon is used as the shielding gas. Increasing the proportion of argon improves the finish of the weld bead and reduces spatter, but since argon is more expensive than CO2, it is preferable to keep the CO2 content of the shielding gas between 0 mol% and 95 mol%.

[0062] Furthermore, in step 5 (clamping welding process), it is preferable that the heat input when performing arc welding in MAG welding using flux-cored wire (FCW) be between 5 kJ / cm and 40 kJ / cm. If the welding heat input is less than 5 kJ / cm, it may not reach a sufficient amount of heat to adequately melt the toe and groove ends of the back bead formed on the clamping side during the clamping welding process, potentially leading to poor fusion. If the welding heat input exceeds 40 kJ / cm, the base metal 12 may melt excessively during the clamping welding process, leading to a greater dilution of the corrosion-resistant metal welding material and potentially reducing the corrosion resistance of the weld.

[0063] In step 5 (joint welding process), it is not always necessary to cover the surface of the joint material 14 with a sheet for protection, but it is preferable to apply a spatter inhibitor to the surface of the joint material 14 by spraying or brushing in order to prevent spatter from adhering to it during welding.

[0064] <Step 6 (Polishing Process)> In step 5 (joint welding process), a groove weld is performed on the joint of the joint material 14 from the joint material 14 side using corrosion-resistant weld metal, and as shown in Figure 5, the joint material side groove 24 is filled with joint material weld metal 34, and the end of the joint material 14 is welded. Then, in step 6 (polishing process), the surface of the welded part of the joint material 14 is polished to finish it.

[0065] Although the corrosion resistance of the welded areas is reduced, polishing the surface of the welded joint of the composite material 14 removes the corrosion-reduced areas, preventing them from becoming the starting point of corrosion. Furthermore, polishing the surface of the welded joint of the composite material 14 reduces surface irregularities, making it more difficult for iron powder and rust to adhere, thus preventing galvanic corrosion. Polishing the surface of the welded joint of the composite material 14 also improves its aesthetic appearance.

[0066] The surface of the welded joint of the composite material 14 can be polished using, for example, a grinder or a belt sander. In the first half of the polishing process, to improve the efficiency of the polishing work, abrasives with a coarser grit size than F80 specified in JIS R6001 (1998) may be used. However, in the final finishing stage, polishing should be done using abrasives with a grit size equivalent to or finer than F80 specified in JIS R6001 (1998). By polishing with fine-grained abrasives in the final finishing stage, surface irregularities are reduced, resulting in a better appearance and making it less likely for iron filings to adhere. If the surface is very rough, iron filings are more likely to adhere, and rust is more likely to occur.

[0067] The abrasive material is preferably at least one of the following, which does not contain iron: aluminum oxide, silicon carbide, boron nitride, diamond, corundum, or garnet. If the abrasive material contains iron, rust from the abrasive material itself may adhere to the polished area.

[0068] Furthermore, the surface of the welded joint of the cladding material 14 may be polished by electrolytic polishing. Portable electrolytic polishing equipment is also available, making it possible to perform electrolytic polishing on the welded joint of the cladding material 14 even on fixed structures such as bridges.

[0069] Alternatively, instead of electrolytic polishing, a solution containing at least one of sulfuric acid, hydrochloric acid, hydrofluoric acid, nitric acid, phosphoric acid, and hydrogen peroxide may be applied to the surface of the weld of the composite material 14 to remove welding discoloration and perform passivation treatment. It is preferable to perform at least one of mechanical polishing using an abrasive, electrolytic polishing, or passivation treatment on the surface of the weld of the composite material 14.

[0070] Furthermore, electrolytic polishing and passivation treatments can improve corrosion resistance because they preferentially dissolve the iron in the passivation film on the surface of the composite material, such as stainless steel or nickel alloy, thereby concentrating chromium.

[0071] Therefore, it is preferable to perform both mechanical polishing using abrasives and electrolytic polishing or passivation treatment. However, in this case, due to the difference in the range of polishing that can be performed (polishing is on the order of millimeters, while electrolytic polishing and passivation treatment are on the order of tens of nanometers), it is preferable to perform mechanical polishing using abrasives first, followed by electrolytic polishing or passivation treatment.

[0072] Furthermore, the surface of the welded joint on the base material 12 is blast-treated and then painted. This treatment is the same as the usual surface treatment for steel structures.

[0073] <Supplement> As mentioned above, in step 1 (grooving and butt jointing), a cutback process is performed on the cladding material 14 to form the base metal exposed surface 12A. Figure 1 shows the state after the cutback process is performed to remove the cladding material 14 by the same thickness as the cladding material 14. In this cutback process, as shown in Figure 8, the cladding material side groove 24A (first modified example of the cladding material side groove 24) may be cut back to a thickness greater than the cladding material 14, so that not only the cladding material 14 but also a small amount of the base metal 12 is cut off to form the base metal exposed surface 12B. If the cladding material 14 remains in the cladding material side groove 24, the cladding material 14 may melt into the welding material during welding on the base metal 12 side, potentially adversely affecting the base metal weld metal 30, so the cladding material 14 is reliably removed from the cladding material side groove 24.

[0074] Furthermore, in the cutback process for the cladding material 14, as shown in Figure 1, the cladding material side groove 24 is processed to be rectangular in shape, with the base material exposed surface 12A as the groove bottom and the cladding material end face 14A of the cladding material 14 as the groove wall, and the cladding material end face (groove wall) 14A is approximately perpendicular to the base material exposed surface (groove bottom) 12A. However, nickel alloys have a higher viscosity when melted than carbon steel and tend to become spherical due to surface tension, so nickel alloy welding material does not easily penetrate into fine gaps, and welding defects due to poor fusion may occur at the approximately 90° inside corner of the rectangular cladding material side groove 24 as shown in Figure 1. For this reason, when using nickel alloy welding material, it is preferable to have an isosceles trapezoidal cladding material side groove 24B as shown in Figure 9 rather than a rectangular cladding material side groove 24 as shown in Figure 1. Specifically, it is preferable to perform a cutback process in the mating material side groove 24B (a second modified example of the mating material side groove 24) such that the angle θ between the exposed base material surface (groove bottom) 12A and the mating material end face (groove wall) 14B is 130° or more.

[0075] Furthermore, while Figure 6 shows specific examples of backing materials (backing materials 26, 28) that can be used in the clad steel welding method according to this embodiment, the cross-sectional shapes of the backing materials that can be used in the clad steel welding method according to this embodiment are not limited to these. Any backing material that can ensure a predetermined contact length (6 mm or more is required, and 7 mm or more is preferable) on the exposed surface (groove bottom) 12A of the base material is acceptable, and it is also possible to use backing materials with a square or isosceles triangular cross-section. Figure 10(A) shows the cross-sectional shape of backing material 29 with an isosceles triangular cross-section, and Figure 10(B) shows the backing material 29 with an isosceles triangular cross-section attached to the groove 24 on the clad material side. [Explanation of symbols]

[0076] 10, 100... Clad steel 12, 102...Base material 12A, 12B...Base metal exposed surface (groove bottom) 14, 104... composite material 14A, 14B... End face of laminated material (groove wall) 20, 120…bevel 22, 122...Base metal side groove 24, 24A, 24B, 25, 124... Bevel on the laminate side 26, 28, 29... backing material 26A...dent 28A…Flat surface 30... Base metal weld 32, 33, 132... Reverse bead 34... Welded metal G... Root interval W... Length of the parallel section at the bottom of the groove on the joint side. d... Contact distance between the backing material 26 and the exposed surface 12A of the base material H b1 H b2 H bx ...bead height W b1 , W b2 , W bx ...back bead width θ...Angle between the exposed surface 12A of the base material and the groove wall 14B

Claims

1. A welding method for clad steel, in which stainless steel or nickel alloy is used as the cladding material and carbon steel or low-alloy steel is used as the base material, A beveling process is performed in which a cutback is made at the part of the clad steel to be welded to remove the cladding material and to form a beveled surface of the base material, A butt joint step in which the beveled clad steels are butted together such that the root gap between the base materials is 3 mm or more, After the butt joint step, a backing material placement step is performed in which the backing material is placed on the exposed surface of the base material, After the backing material placement step, a base material welding step is performed in which a butt joint groove welding is carried out from the base material side to the base material side, After the base material welding process, a backing material removal process is performed to remove the backing material, After the backing material removal step, a joint welding step is performed in which a groove welding of the joint is performed from the joint material side, A clad steel welding method characterized by having the following features.

2. The clad steel welding method according to claim 1, characterized in that the backing material is made of ceramic.

3. The clad steel welding method according to claim 1, characterized in that, in the butt joint step, the beveled clad steels are butted together such that the parallel length of the groove bottom on the clad material side, which includes the exposed surface, is 15 mm or more.

4. The clad steel welding method according to claim 1, characterized in that, in the cladding welding step, arc welding is performed from the cladding side using a flux-cored wire having a welding material of corrosion-resistant metal.

5. The clad steel welding method according to any one of claims 1 to 4, characterized in that the backing material is a backing material without a recess for forming a back bead.

6. The clad steel welding method according to any one of claims 1 to 4, characterized in that the groove preparation step involves performing a cutback to remove the cladding material and forming a groove wall with an angle of 130° or more with respect to the exposed surface.

7. The clad steel welding method according to any one of claims 1 to 4, characterized in that, after performing the base material welding step, the clad steel is welded without inverting it.

8. In the aforementioned welding process for the composite material, CO 2 A mixed gas of CO and argon is used as a shielding gas, and the CO of the mixed gas 2 The clad steel welding method according to claim 4, characterized in that the content ratio of is 0 mol% or more and 95 mol% or less, and the heat input when performing the arc welding is 5 kJ / cm or more and 40 kJ / cm or less.

9. A clad steel welding method according to any one of claims 1 to 4, characterized in that, after the aforementioned cladding welding step, at least one of mechanical polishing, electrolytic polishing, or passivation treatment is performed using an abrasive material that does not contain iron and has a particle size equivalent to or finer than F80 as defined in JIS R6001 (1998), to treat the surface of the area welded in the cladding welding step.

10. The clad steel welding method according to claim 9, characterized in that after performing the mechanical polishing on the surface of the welded portion in the aforementioned cladding welding process, either electropolishing or passivation treatment is further performed on the said surface.

11. The clad steel welding method according to any one of claims 1 to 4, characterized in that the clad steel is a clad steel plate or a clad steel pipe.

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