JP2008178894A - Both-side welding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a both-side welding method which is effective for obtaining a sound welded joint part with deep penetration and no blow hole or insufficient melting by melt-sealing before application of a penetration accelerator and front and rear both-side welding after the application, while being a roughly I-joint or a roughly T-joint with no groove applied, and requiring no penetration welding for forming a back bead. <P>SOLUTION: The both-side welding method comprises steps of applying the penetration accelerator on front and rear sides of the roughly I-joint or the roughly T-joint comprising a stainless steel material or a low carbon steel material, and executing a non-consumable electrode arc welding. In the method, the front or the both front and rear sides of the joint is melt-sealed with a tacking condition of small energy before applying the penetration accelerator, fusion welding is conducted to the penetration depth within a specific range by the execution of the arc welding after applying the penetration accelerator on the front side of the joint after melt-sealing, thereafter fusion welding is conducted to the penetration depth within a specific range by the execution of the arc welding after applying the penetration accelerator on the rear side of the remaining joint on the opposite side. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a double-sided welding method in which a welding accelerator is applied to the front and back surfaces of a joint portion made of a stainless steel material or a low carbon steel material and arc welding is performed.

  There have been proposed a penetration accelerator (or a fluxing agent) capable of deep welding and a welding method and welded joint using the same.

  For example, in the welding method and welded joint described in Patent Document 1, it has been proposed to perform TIG welding after applying a penetration accelerator formed by mixing a metal oxide powder and a solvent to the surface of a stainless steel base material. .

Further, the deep penetration arc welding flux described in Patent Document 2 and the welding method using the same are metal oxides not containing Cr ₂ O ₃ , and the mixing ratio of TiO ₂ and SiO ₂ is 1: 1. It has been proposed to use a mixed oxide flux.

  In the TIG welding method described in Patent Document 3, a flux-cored wire including a flux containing 6% by mass or more of a metal oxide is used as a filler material, and 0.05 to 3 g of the metal oxide is contained in a molten metal. It has been proposed to perform TIG welding while supplying at a minute / minute.

  Further, in the TIG welding apparatus and method described in Patent Document 4, the first shield gas made of an inert gas is caused to flow toward the work piece so as to surround the electrode, and the first shield gas is moved to the peripheral side of the first shield gas. It has been proposed to flow a second shield gas containing an oxidizing gas toward the workpiece. Further, Patent Document 5 proposes the use of an accelerator (flux agent) for submerged arc welding.

  On the other hand, Patent Document 6 is a welding method and its welded structure filed by the present inventors, and is insufficiently bonded due to the double-sided deep penetration welding from the front side and the back side of the joint applied with the penetration accelerator. It was proposed that a sound weld with a deep penetration shape can be obtained.

  In the methods described in Patent Document 1 and Patent Document 2, welding is performed so that a back bead is formed on the back surface side by arc welding from the surface side of the joint member to which the penetration accelerator is applied. For this reason, in particular, if there is a gap in the butt joint or if the gap changes, the width of the back bead on the back side formed by arc welding will change greatly, or it will come out too much, and the quality of the weld will be reduced. May be exacerbated. Also, in welding of I-type joints with a plate thickness exceeding 6 mm, the molten pool cannot be retained (for example, surface tension acting on the molten pool <gravity), so it easily melts down on the back side, and the back bead without a backing material It is difficult to form. During welding of the second layer in the groove joint, a part of the penetration accelerator (metal oxide flux agent) that was heated during the welding of the previous layer (first layer) is fixed to the surface of the weld bead (slab fixing). Therefore, the molten pool directly under the arc welding is difficult to spread in the groove width direction, and there is a possibility of poor fusion without melting the both wall surfaces of the groove to be melted. Furthermore, it is single-sided penetration welding only from the front surface side, and is different from double-sided penetration welding in which arc welding is alternately performed from the front surface side and the back surface side. This double-sided penetration welding is not described at all in the examples.

In the case of Patent Document 2, arc welding is performed after a mixed oxide (penetration accelerator) of TiO ₂ and SiO ₂ not containing Cr ₂ O ₃ is applied to the joint surface. However, there is a problem in welding as described above, and unlike double-sided penetration welding in which welding is alternately performed from the front surface side and the back surface side, the example thereof is not described.

  And the back bead is formed by TIG welding from the front surface or back surface (surface on the non-groove side) of the groove joint portion on which the metal oxide film (5 μm or more) is formed. In the I-type butt joint, a back bead is formed on the back surface side by TIG welding from the front surface side. For this reason, if there is a gap in the butt joint or if the gap has changed, the width of the back bead on the back side formed by arc welding will change greatly, or it will come out too much and the quality of the weld will deteriorate. there is a possibility. In addition, in the welding of an I-type joint having a plate thickness exceeding 6 mm, the molten pool cannot be held, so that it easily melts down to the back side, and it is difficult to form a back bead without a backing material. Moreover, when the coating thickness of the metal oxide is thin, the metal oxide is not melted to a desired depth and is likely to become shallow. During welding of the second layer in the groove joint, part of the penetration accelerator that has been heated and reacted during the welding of the previous layer adheres to the surface of the weld bead, so that the molten pool directly under arc welding does not easily spread in the groove width direction. There is a possibility that poor fusion occurs without melting up to both wall surfaces of the groove to be melted. In the case of reverse V groove, reverse Y groove and X groove, double side penetration welding is used, but a back bead is formed on the back side. In the case of I groove, the back side is formed by single side penetration welding. A back bead is formed on the side.

  In the case of Patent Document 3, a deep penetration portion is obtained by TIG welding while supplying a predetermined amount of flux-cored wire containing 6% or more of a metal oxide. In particular, a measurement result of a penetration depth is shown by performing a welding test on an I-type butt joint having a thickness of 9 mm. However, flux-cored wires are vulnerable to moisture, which is a major factor in the occurrence of weld defects such as porosity, and therefore must be stored in a special drying room or the like for quality control at all times. Moreover, not only does the penetration depth change greatly due to the increase or decrease in the feed amount of the flux-cored wire, but at the same time, the bead width and bead surplus height are also likely to change greatly. Although the test result of one-side penetration welding from the front side is shown, unlike the double-side penetration welding in which welding is alternately performed from the front side and the back side, the example is not described.

In the case of Patent Document 4, a mixed gas of an oxidizing gas (O ₂ gas or CO ₂ gas) and an inert gas (Ar gas) is caused to flow through the arc welding portion to increase the penetration depth. The penetration accelerator is not used. Moreover, although the relationship between a penetration depth, oxygen concentration, and a carbon dioxide concentration is disclosed, it is a penetration result on a flat plate different from the joint member. The double-sided penetration welding of the joint member is not performed at all.

  In the case of submerged arc welding described in Patent Document 5, a large amount of flux agent is supplied and used, an arc is generated in the welding wire in this flux agent, and arc welding is performed by burying it. This is a welding method completely different from the electrode type arc welding.

  On the other hand, Patent Document 6 is a welding method and a welded structure that the inventors have applied for an invention, and microporosity (blowhole) may be generated in the welded bottom portion after application of the penetration accelerator, In some cases, the melted shape was insufficiently melted due to bending or misalignment. As a result of investigating the cause of this occurrence, it was found that a part of the penetration accelerator penetrates into the gap of the joint part during application, and cannot be lifted from the molten pool during welding and is trapped and fixed in the molten low part or in the vicinity thereof. . Further, it has been found that when the coating thickness of the penetration accelerator changes greatly in the left-right direction of the welding, the weld pool is widened and the penetration becomes shallower at the time of welding, and at the same time, the weld pool bends toward the thinner side.

  For this reason, various effective preventive measures were examined. As a result, the most effective measure to prevent the occurrence of porosity is to melt and seal the surface or back or both sides of the joint part under low energy temporary conditions before applying the penetration accelerator, It was confirmed that no porosity was generated by the inclusion of the penetration accelerator during welding of the coated portion by the melt sealing applied before coating. Further, the most effective measure for preventing the melting shortage is to form the film thickness of 20 μm or more in the left and right direction of the weld line by applying the penetration accelerator once or more times in the weld line direction of the joint part. It was confirmed that a deep penetration of almost symmetrical shape with no deviation or bending was formed.

JP 2000-102890 A Japanese Patent Laid-Open No. 2002-120088 JP 2001-219274 A JP 2004-298963 A JP 2001-239394 A JP 2006-231359 A

  In the present invention, it is not necessary to carry out reverse wave welding for forming a back bead while maintaining a substantially I-shaped joint or a substantially T-shaped joint that is not subjected to groove processing, and melt sealing before application of a penetration accelerator and front and back after application. An object of the present invention is to provide a double-sided welding method effective for obtaining a sound fusion joint having a deep penetration without blowholes or lack of melting by double-sided welding.

  In order to achieve the above-mentioned object, the present invention applies a non-consumable electrode method by applying a melting accelerator to the front side and the back side of a substantially I-type joint part or a substantially T-type joint part made of stainless steel material or low-carbon steel material. In the double-sided welding method for performing arc welding, before applying the penetration accelerator, both surfaces of the joint part are melt-sealed under low energy temporary attachment conditions on the front surface, back surface, or both front and back surfaces. We propose a welding method.

  In order to achieve the above object, the present invention is a non-consumable electrode by applying a penetration accelerator to the front side and the back side of a substantially I-type joint part or a substantially T-type joint part made of stainless steel or low carbon steel material. In the double-sided welding method in which arc welding is performed, the surface of the joint part or both front and back surfaces are melt-sealed under a low energy temporary condition before applying the penetration accelerator, and the joint after the melt-sealing After applying the penetration accelerator to the surface side of the part, after melting and joining to the penetration depth of a specific range by the construction of the arc welding, then after applying the penetration accelerator to the back side of the remaining joint part on the opposite side A double-sided welding method is proposed, characterized by performing melt welding to a specific range of penetration depth by the arc welding.

  In order to achieve the above object, the present invention is a non-consumable electrode by applying a penetration accelerator to the front side and the back side of a substantially I-type joint part or a substantially T-type joint part made of stainless steel or low carbon steel material. In a double-sided welding method for performing arc welding of a method, a sealing step of melt-sealing the surface of the joint part or both front and back surfaces with a low energy temporary condition before applying the penetration accelerator, and the melt-sealing A first welding step in which the welding accelerator is applied to the surface side of the subsequent joint part and then melt-bonded to a specific range of penetration depth by the arc welding, and the back side of the remaining joint part on the opposite side The present invention proposes a double-sided welding method comprising: a second welding step in which a melt accelerator is applied and then melt-bonded to a specific range of penetration depth by arc welding.

  In particular, the joint portion has gaps or steps, or both of the gaps and steps are irregularly formed, and the fusion sealing is performed at least in the gap forming portion and in the vicinity thereof, or a length portion of a specific portion or welding. It is good to apply to the entire length of the line.

  The penetration accelerator may be applied at least once in the weld line direction of the joint portion to form a film thickness of 20 μm or more in the left-right direction of the weld line.

  That is, in the double-sided welding method of the present invention, before applying the penetration accelerator, by melting and sealing the front surface or back surface or both front and back surfaces of the joint part under low energy temporary attachment conditions, The accelerator does not enter the gap, and the cause of blowhole (porosity) generation during welding can be eliminated. In addition, after applying the penetration accelerator to the surface side of the joint after the melt sealing, the porosity is not melted to the back side of the joint by melting and joining to a specific range of penetration depth by the arc welding. It is possible to form a sound penetration portion with no specific depth. After that, by applying the penetration accelerator on the back side of the remaining joint portion on the opposite side and then melt-bonding to a specific range of penetration depth by the arc welding construction, the tip portions melt-bonded from both the front and back sides, respectively. Can be overlapped upside down. Moreover, even if it is a substantially I-type butt joint or a substantially T-shaped joint that does not require time-consuming groove processing, there is no need to perform back wave welding for forming a back bead, and it can be reliably melt-bonded by the double-sided welding. It is possible to obtain a welded section with a sound deep penetration without porosity. Furthermore, deep double-sided penetration welding, which was impossible with conventional TIG welding with shallow penetration, is possible, and thermal deformation can be reduced and the number of welding passes can be reduced.

The arc welding is performed in a downward posture, a vertical posture, or a horizontal posture, so that the heat reaction of the metal oxide contained in the penetration accelerator (for example, oxygen dissociates from the metal oxide and the dissociation thereof). As a result of the convection of the molten metal (molten pool) immediately below the arc changing in the depth direction and promoting the melting by a chemical reaction in which part of the oxygen dissolved in the molten metal), the penetration depth increases. This penetration depth can be adjusted depending on the welding heat input conditions such as welding current and welding speed, and it is possible to adjust the penetration depth appropriately so that the penetration depth is within a predetermined range corresponding to the plate thickness and welding position of the joint member. What is necessary is just to determine a thermal condition in advance. The penetration accelerator is a flux solvent obtained by mixing a metal oxide powder such as TiO ₂ , SiO ₂ , Cr ₂ O ₃ and a solvent, and a commercially available product that is already known may be used.

  Before applying the penetration accelerator, as described above, the penetration accelerator does not enter the gap at the time of application by the sealing process of melting and sealing the surface or both sides of the joint part under low energy temporary attachment conditions. The cause of porosity generation during welding can be eliminated. In addition, as described above, by the first welding step of melting and joining to a specific range of penetration depth by applying the arc welding after applying the penetration accelerator on the surface side of the joint after the fusion sealing, Without melting to the back side of the joint, a sound penetration portion without porosity can be formed to a specific depth. Furthermore, after applying the penetration accelerator to the back side of the remaining joint portion on the opposite side, after the second welding process of melting and joining to the penetration depth in a specific range by the arc welding, as described above, from both the front and back sides The respective melt bonded end portions can be overlapped in the upside down direction. Moreover, even if it is a substantially I-type butt joint or a substantially T-shaped joint that does not require time-consuming groove processing, there is no need to perform back wave welding for forming a back bead, and it can be reliably melt-bonded by the double-sided welding. It is possible to obtain a welded section with a sound deep penetration without porosity.

  The joint portion has gaps or steps, or both of the gaps and steps are irregularly formed, and the fusion sealing is performed at least in the gap forming portion and in the vicinity thereof, or a length portion of a specific portion or a weld line. By applying to the full length portion, as described above, the penetration accelerator does not enter the gap at the time of application, and the porosity generation factor at the time of welding can be eliminated.

  The penetration accelerator is reciprocally applied at least once in the weld line direction of the joint portion to form a film thickness of 20 μm or more in the left-right direction of the weld line. It is possible to obtain a penetration section having almost no symmetrical shape.

  As described above, according to the double-sided welding method of the present invention, the back bead forming back wave welding can be performed even when the substantially I-type butt joint or the substantially T-shaped joint is not subjected to laborious groove processing. It is not necessary to carry out, and a sound fusion joint with deep penetration without porosity and lack of melting can be obtained by fusion sealing before application of the penetration accelerator and front and back double-side welding after application. Further, the assembly work of the welded member joint is facilitated, and thermal deformation can be reduced and the number of welding passes can be reduced as compared with the conventional welding construction, so that the man-hour and cost can be greatly reduced.

  Hereinafter, the contents of the present invention will be specifically described with reference to the embodiments shown in FIGS.

  FIG. 1 is an explanatory view showing an example of a welding procedure outline and penetration shape of an I-type joint according to the double-sided welding method of the present invention. As shown in FIG. 1 (1), the joint members 1a, 1b, 2a, 2b are stainless steel or low carbon steel having a plate thickness T of 4 mm or more and 16 mm or less. For example, in order to manufacture a long cylindrical tube One flat plate is bent into a cylindrical tube and the flat plate end surfaces are butted together to form the I-shaped joint portion 3. Alternatively, the I-type joint portion 3 can be formed by abutting the end faces of two flat plates. The I-shaped joint 3 is irregularly formed with gaps G and steps b (also referred to as misinterpretations). By relieving the butt accuracy, the joint matching operation becomes easy, and the assembly time can be greatly shortened. If the plate thickness is too thin, it is not preferable because the depth of penetration is difficult to stop at a predetermined depth and the back side may melt. On the other hand, if the plate thickness is more than 16 mm, a large current exceeding 350 A and a large heat input exceeding 35 kJ / cm are required.

  As shown in FIG. 1 (2), before applying the penetration accelerator 4a (a metal solvent-containing flack solvent), the gap G and the joint surface in the vicinity thereof are melt-sealed under low energy tacking conditions (melting). Sealing part 17a). The penetration depth d of the melt-sealed portion 17a may be 1 mm or less or about 1 mm. The melt-sealing construction 20 prevents the penetration accelerator 4a from entering the gap G at the time of application, and eliminates the cause of blow hole (porosity) generation during welding. The fusion sealing operation 20 may be performed at least in the gap G forming portion and in the vicinity thereof, or in the length portion of the specific portion or the entire length portion of the weld line. When the weld line (welding position) is difficult to understand due to the fusion sealing, a visual line (scribing line) parallel to the weld line may be scratched in advance at a position slightly away from the weld line to be welded. Using this marking line as a mark, it is possible to easily perform positioning of the torch during welding and copying adjustment of the position of the welding line.

As shown in FIG. 1 (3), after the melt sealing 20 is completed, a melt accelerator 4 a is applied 21 to the surface of the melt sealing portion 17 a and the surface side of the I-type joint portion 3. The penetration accelerator 4a is a flux solvent obtained by mixing a metal oxide powder such as TiO ₂ , SiO ₂ , Cr ₂ O ₃ and a solvent, and may be applied using a commercially available product already known in the art. In particular, when the penetration accelerator 4a is applied with a brush or the like, the coating thickness in the weld line direction is preferably 20 μm or more by reciprocating at least once in the weld line direction of the I-type joint portion 3. The penetration accelerator 4a does not enter the gap G of the I-type joint portion 3 by prior melt sealing. For this reason, the porosity by the penetration of a penetration accelerator during welding does not occur.

  After the penetration accelerator 4a applied in this manner is dried, as shown in FIG. 1 (4), the melt bonding 22 (first welding process) is applied to the penetration depth H2 in a specific range by arc welding. This is arc welding using non-consumable tungsten for the electrode 5, and is melt-bonded to a specific range of penetration depth H1. By this fusion bonding 22, a heating reaction of the metal oxide contained in the penetration accelerator 4a (for example, a chemical reaction in which oxygen is dissociated from the metal oxide and a part of the dissociated oxygen is dissolved in the molten metal). As a result, the convection of the molten pool 8a directly under the arc changes in the inward direction and the depth direction to promote melting. As a result, compared to the conventional TIG welding result, it is possible to obtain a melt-bonded portion 8b having a penetration depth that is about two to three times deeper and a narrow bead width. In addition, it is possible to obtain a sound quality with no deep porosity and no porosity in the melt pool 8a having a substantially bilaterally symmetric shape without any deviation or bending.

  The penetration depth H1 of the melt-bonded portion 8b is preferably formed in the range of 1/2 or more and 9/10 or less of the plate thickness T. Without melting up to the back surfaces 1b and 2b of the joint member, it is possible to reliably obtain the welded surface having the melted joint portion 8b and the surplus bead melted to the penetration depth H1. If the penetration depth H1 is too smaller than ½ of the plate thickness T, it has not melted to the center of the plate thickness, and when the remaining joint portion 3b on the opposite side (back side) is melt-bonded, the bonding is insufficient ( This is not preferable because there is a possibility that melting will be insufficient. On the other hand, if the penetration depth H1 is too larger than 9/10 of the plate thickness T, there is a possibility of melting to the back side, which is not preferable. If there is a large gap (gap G) in the I-type joint 3, it melts to the back side, which may deteriorate the bead shape on the front side. The penetration depth H1 can be adjusted according to the welding heat input conditions such as welding current and welding speed, and the penetration depth (0.5 × T) within a predetermined range corresponding to the thickness T and welding posture of the joint member. It is advisable to determine the appropriate welding conditions in advance so that ≦ H1 ≦ 0.9 × T), and to perform the melt bonding 22 by arc welding.

  In addition, when an undercut or a dent has occurred on a part of the surface of the weld bead formed by the melt bonding 22, the welding failure portion and the vicinity thereof are remelted by a wire feed arc and the superposition of shallow penetration is obtained. By forming the bead, the undercut and the dent are repaired, and the quality can be improved to be similar to a sound welded portion.

  The back side after welding tends to be in a state where there is no initial gap G due to thermal shrinkage during welding. If there is no gap G in the joint portion on the back side, the step of melting and sealing can be omitted, and it is preferable to proceed to step 25 of applying a penetration accelerator to the back surface of the joint. If there is a gap G in the joint portion on the back side, the gap G portion and the joint surface in the vicinity thereof may be melt-sealed as shown in FIG. Moreover, what is necessary is just to invert and reverse joint member 1a, 1b, 2a, 2b beforehand, when changing to a downward attitude | position.

  As shown in FIG. 1 (5), a melt accelerator 4b is applied 25 to the back side of the remaining joint. When applying the penetration accelerator 4b with a brush or the like, as described above, it is preferable that the coating thickness in the weld line direction is 20 μm or more by reciprocating at least once in the weld line direction of the I-type joint portion 3. After the penetration accelerator 4b applied in this manner is dried, as shown in FIG. 1 (6), the melted joint 26 (second welding process) is applied to the penetration depth H2 in a specific range by arc welding. As shown in FIGS. 1 (6) and (7), the melt joint 26 is formed on the tip side of the melt joint portion 9b formed on the back surface side of the remaining joint portion 3b and on the joint surface side on the opposite side. The tip portion of the portion 8b can be overlapped in the upside down direction. A melt-bonded portion 9b having no defects such as insufficient melting and porosity can be obtained.

  The penetration depth H2 of the melt-bonding portion 9b on the back surface side is approximately the same as the penetration depth H1 on the front side, and is preferably formed in a range of 1/2 or more and 9/10 or less of the plate thickness T. The welding depth can be adjusted according to the welding heat input conditions such as welding current and welding speed, and the penetration depth (0.5 × T ≦ H2 ≦ 0.9 ×) corresponding to the plate thickness T and welding position of the joint member. It is preferable to determine the appropriate welding conditions in advance so as to satisfy T) and to perform the melt bonding 26 by wire-feed arc welding. Moreover, arc welding without wire feeding can also be performed.

  FIG. 2 is an explanatory view showing the penetration of the penetration accelerator into the joint gap part and the generation of the porosity in the molten joint part. As shown in FIG. 2 (1), gaps G and steps b are irregularly formed in the I-type joint 3. When a penetration accelerator (a flux solvent containing a metal oxide) is applied as shown in FIG. 2 (2) while the joint surface of the gap G is not melt-sealed in advance, a part of the penetration accelerator is removed. Enter the gap G. When melt joining by arc welding is performed 22 in this state, as shown in FIG. 2 (3), the penetration accelerator remaining in the gap C lower part cannot be lifted from the molten pool and is confined in the molten lower part or its vicinity. Then, the defects (porosity 34) due to the penetration of the penetration accelerator are generated inside the weld. When such a welding defect occurs, if the size and number of porosity defined by the quality inspection of the welded part are exceeded, it will be rejected and the defect part and its vicinity must be repaired and welded. In order to prevent the occurrence of the porosity 34, the generation factor is eliminated. As described with reference to FIG. 1, the joint gap G portion and its vicinity may be melt-sealed before applying the penetration accelerator. By this fusion sealing, the penetration accelerator does not enter the gap during application, and generation of porosity 34 due to the penetration of the penetration accelerator during welding can be prevented.

FIG. 3 is an explanatory diagram showing changes in the coating thickness of the penetration accelerator and changes in the shape of the penetration. As a result of the experiment, it was found that the penetration shape (depth, bead width, bending) changes when the film thickness of the penetration accelerator 4a applied in the direction of the weld line 35 changes greatly. The film thickness change on the left and right of the weld line 35 can be made by thinly scraping off one application portion along the weld line 35 after application and drying of the penetration accelerator. When the coating film thickness on the left side of the weld line is thin, as shown in FIG. 3 (1), the melt pool 8a is wide and the penetration H _L becomes shallow (H _L <H1) at the same time as arc welding. Bend away. On the other hand, when the coating film thickness on the right side of the weld line is thin, as shown in FIG. 3 (3), at the time of arc welding, the molten pool 8a is wide and the penetration H _R becomes shallow (H _R <H1). Gently lean to the right side of the. For this reason, if the coating film thickness in the weld line direction changes significantly, convection in the weld width direction (outward direction) occurs, disturbing convection in the depth direction (inward direction), and the molten pool It is considered that the left and right unbalanced state is reached, spreads to the thin film side, is offset, and melts into a shallow shape due to distortion. The penetration depths H _L and H _{R of the} bent shape are shallow and tend to be less than half of the plate thickness T. If the above-mentioned shallow penetration and bending occur even in the welding on the back side of the joint, there is a high possibility that a defect insufficiently melted in the central portion of the plate thickness will lead to a failure.

  On the other hand, when the coating film thickness is substantially equal to the left and right, as shown in FIG. 3B, a deep penetration having a substantially bilaterally symmetric shape with no deviation or bending can be obtained at the melt bonded portion. Further, deep welding can be obtained even by welding on the back side of the joint, and a sound double-sided melt-bonded portion without lack of melting can be secured.

  FIG. 4 is an example showing the relationship between the coating thickness of the penetration accelerator, the penetration depth, and the bead width. In the welding test, a plurality of test pieces (plate thickness: 10.6 to 12 mm) having different coating thicknesses were prepared, and the welding current was 280 A and the welding speed was constant at 70 mm / min. The horizontal axis represents the coating film thickness α (average film thickness) in the left-right direction of the weld line, which is a value measured with a minute thickness measuring device. The vertical axis represents the penetration depth H1 and the bead width w of the weld, which are values measured from an enlarged photograph of the weld cross section. As the coating film thickness α increases, the penetration depth H1 increases and the bead width w decreases. In particular, in the thin region where the coating film thickness α is 20 μm or less, the changes in the penetration depth H1 and the bead w are large. In the region of 20 μm or more, the change in the penetration depth H1 and the bead w is small, and is almost the same as the value of the thick region of 70 μm or more. The penetration depth H1 and the bead w vary depending on the welding current, welding speed, and plate thickness, but the effect of the penetration accelerator on the coating thickness is similar to the characteristics of the embodiment shown in FIG. It is thought that it becomes the characteristic to do.

  By forming the coating film thickness α of the penetration accelerator to be 20 μm or more, deep penetration can be obtained during welding, and at the same time, a substantially symmetric penetration cross section without deviation or bending can be obtained. If it is applied once or more in the weld line direction at the time of application of the penetration accelerator, the film thickness in the left-right direction of the weld line can be reliably formed to 20 μm or more. Moreover, if the frequency | count of application | coating is increased, a film thickness can be made still thicker and the penetration depth at the time of welding can be obtained more stably.

  FIG. 5 shows an example of the results of studying the relationship between the thickness of the double-sided welding, the welding current, and the penetration depth on the back side. In the figure, according to the thickness (6, 9, 12) , 16 mm) and a cross-sectional photograph of a 9 mm plate welded on both sides without a penetration accelerator. When conventional TIG welding (welding without penetration accelerator) is performed on both sides of the I-type butted portion of a 9 mm plate, the penetration depth is shallow (eg, about 2 mm) as shown in the cross-sectional photograph shown in FIG. As a result, insufficient bonding occurs in the central portion of the plate thickness. On the other hand, in the case of the double-sided welding method of the present invention using a penetration accelerator, an appropriate welding current I corresponding to the plate thickness T (4 to 16 mm) is output as shown in FIG. Even if it is a butt joint without groove processing or a joint member with or without a gap or a step in the joint by melting and joining each to a specific range of penetration depth, It is possible to surely overlap and bond at the central portion or in the vicinity thereof, and to obtain a welded section having good quality without melting, porosity and undercut. In addition, although the cross-sectional photograph to plate thickness 16mm was shown in FIG. 5, if double-sided welding is performed using the welding power source which can output welding current to about 500A higher than 350A, plate thickness will be about 20mm. Double-sided melt bonding is possible.

FIG. 6 is an explanatory view showing another embodiment of the welding procedure of the I-type joint and the penetration shape according to the double-sided welding method of the present invention. As shown in FIG. 6 (1), before applying the penetration accelerator 4a 21, the gap G portion and the joint surface in the vicinity thereof or the length portion of a specific portion are melt-sealed under a low energy tacking condition (melting) Sealing part 17a). The penetration depth d of the melt-sealed portion 17a may be 1 mm or less or about 1 mm. The melt sealing construction 20 prevents the penetration accelerator 4a from entering the gap G at the time of application, and eliminates the cause of porosity generation during welding.

  As shown in FIG. 6 (2), after the fusion sealing 20 is completed, the melt accelerator 4a is applied 21 to the surfaces of the fusion sealing portions 17a and 17b and the joint surface. The coating film thickness in the weld line direction is preferably formed to 20 μm or more at the time of application, and does not enter the penetration accelerator 4a into the gap G of the I-type joint portion 3 by prior melt sealing. For this reason, the porosity by the entrainment of the penetration accelerator 4a does not occur during welding.

After the penetration accelerator 4a is dried, as shown in FIG. 6 (3), a melt bonding 22 (first welding process) is performed by wire-feed arc welding, and the fusion bonding is performed to a specific depth of penetration H1. . The penetration depth H1 of the melt-bonding portion 8b on the surface side is not less than 1/2 of the plate thickness T and 9 /
It is good to form in the range of 10 or less. It can be adjusted according to the welding heat input conditions such as welding current and welding speed, and the penetration depth within a specific range corresponding to the plate thickness (4 ≦ T ≦ 16) and welding position of the joint members 1a, 1b, 2a, 2b An appropriate welding condition is set so as to satisfy (0.5 × T ≦ H1 ≦ 0.9 × T), and the fusion bonding 22 by wire feed arc welding may be performed.

  By this fusion joining 22, it is possible to reliably weld to a penetration depth H1 within a specific range without melting up to the back surfaces 1b and 2b of the joint member, and a healthy fusion joining in which no porosity is generated due to the penetration of a penetration accelerator inside the weld. Part 8b can be obtained. In particular, even in the case of arc welding that outputs a wide range of welding current (for example, 100 A to 350 A) by feeding the welding wire 7 to the arc welding portion from the rear in the welding direction, the inside of the molten pool 8a of the arc welding portion. Thus, the welding wire 7 smoothly enters and can be stably melted without forming large droplets. Moreover, even if it is a joint member in which the gap G and the level | step difference b do not exist in the I-type joint part 3, the fusion | melting junction part 8b with an undercut and a dent and a surplus bead can be obtained on a welding surface.

  After the end of the melt bonding 22, the joint members 1a, 1b, 2a, 2b are turned upside down 24 as shown in FIG. 6 (4). After the reversal, as shown in FIG. 6 (5), the gap G portion of the remaining joint portion 3b and the back surface of the joint in the vicinity thereof or the length portion of the specific portion are melt-sealed 24 (melt-sealed) under the low energy temporary attachment condition. Stop part 17b). The melt-sealing construction 24 prevents the penetration accelerator 4b from entering the gap G at the time of application, thereby eliminating the cause of porosity generation during welding. As shown in FIG. 6 (6), after the fusion sealing 24 is completed, the melting accelerator 4 b is applied 25 to the surface of the fusion sealing portion 17 b and the back side of the joint.

Then, after the penetration accelerator 4b is dried, as shown in FIG. 6 (7), a melted joint 26 (second welding process) is performed by wire-feed arc welding to melt to a penetration depth H2 in a specific range. Join. The penetration depth H2 of the melt-bonded portion 9b on the back surface side is preferably formed in the range of 1/2 or more and 9/10 or less of the plate thickness T. As shown in FIGS. 6 (7) and 8 (8), by this melt bonding 26, the front end portion of the melt joint portion 9 b formed on the joint back surface side and the front end of the melt joint portion 8 b formed on the opposite joint surface side. 89 can be overlapped with each other upside down. It is possible to obtain melt-bonded portions 8b and 9b having no excess cut or dent on the weld surface and having a surplus bead without generating porosity due to the penetration of a penetration accelerator in the weld. In addition, since the front end portion of the melt-bonded portion 8b formed on the front surface side is remelted by the melt-bonding 26 on the back surface side, even when a minute porosity remains at the front-end portion of the melt-bonded portion 8b. It can melt and disappear. Deep double-sided penetration welding, which was impossible with conventional TIG welding with shallow penetration, is possible, and thermal deformation can be reduced and the number of welding passes can be reduced. In particular, when applied to welding of a small structure in which the joint member can be easily turned over, it is possible to significantly reduce man-hours and costs.

The arc welding arc 6 is generated between the tip of the non-consumable electrode 5 (a tungsten alloy electrode containing tungsten as a main component) and the joint member in a shield gas atmosphere, What is necessary is just to supply the welding current suitable for 26. For the shielding gas (not shown), an inert Ar gas may be flowed from a gas nozzle provided on the outer periphery of the non-consumable electrode 5. It is also possible to use a mixed gas of Ar + He or Ar + H ₂ mainly containing Ar gas. Further, if a welding torch having a double shield structure is used, for example, an inert gas such as Ar gas or He gas is flowed around the non-consumable electrode 5 and the mixed gas or O ₂ is flowed around the outer periphery thereof. The first stage arc welding may be performed while flowing a mixed gas of gas or CO ₂ oxidizing gas and Ar gas.

FIG. 7 is an explanatory diagram of an embodiment showing an outline of a welding procedure and a penetration shape of an I-shaped joint in a standing posture. The main difference from FIG. 6 is that the joint member 1a has a vertical posture different from the downward posture.
1b, 2a, and 2b, and after melt-sealing the joint surface and the joint back surface, the penetration accelerators 4a and 4b are applied, and the melt joints 22 and 26 by wire-feed arc welding are applied respectively. . A joint member in a lateral orientation may be used. That is, as shown in FIG. 7 (1), the surfaces 1a and 2a of the substantially I-shaped joint portion 3 installed in the standing posture or the lateral posture are melt-sealed under a low energy tacking condition. This melt-sealing construction 20 prevents the penetration accelerator from entering the gap during application and eliminates the cause of porosity generation during welding.

As shown in FIG. 7 (2), after the fusion sealing is completed, the penetration accelerator 4a is reciprocally applied 21 at least once in the welding line direction to form a film thickness in the horizontal direction of the welding line of 20 μm or more. The joint members 1a, 1b, 2a, 2b are stainless steel or low carbon steel having a plate thickness T of 4 mm or more and 16 mm or less. The substantially I-shaped joint portion 3 may have a small chamfering process (for example, 1 mm or less) on the end surface. Then, after the applied penetration accelerator 4a is dried, as shown in FIG. 7 (3), melting by wire welding arc welding from the surface side (left side surface) of the I-type joint portion 3 in a standing posture or a lateral posture. The joining 22 (first welding step) is performed, and the melt joining 22 is performed up to a specific range of penetration depth (0.5 × T ≦ H1 ≦ 0.9 × T).

  By this fusion joining 22, it is possible to reliably weld to a penetration depth H1 within a specific range without melting up to the back surfaces 1b and 2b of the joint member, and a healthy fusion joining in which no porosity is generated due to the penetration of a penetration accelerator inside the weld. Part 8b can be obtained. Moreover, even if it is the joint members 1a, 1b, 2a, 2b where the I-type joint part 3 has or does not have a gap G or a step, as described above, the welding wire 7 is connected to the arc welding part from the rear in the welding progress direction. , The welded surface 8b can be obtained without any undercuts or dents on the welding surface. In addition, when an undercut or a dent has occurred in a part of the surface of the weld bead formed by the melt-bonding 22, re-melting the poorly welded portion and its vicinity to form a shallow weld bead. Thus, the undercut and the dent are repaired, and the quality can be improved to be similar to a sound welded portion.

  Next, with the joint member in a fixed state where it is not reversed, as shown in FIG. 7 (4), before applying the penetration accelerator 4b, the gap G on the opposite side of the joint back surface and its vicinity are melt sealed 24. (Melt sealing portion 17b). As described above, the melt-sealing construction 24 prevents the penetration accelerator from entering the gap at the time of application, thereby eliminating the cause of porosity generation at the time of welding.

  As shown in FIG. 7 (5), after the fusion sealing 24 is completed, the melt accelerator 4b is applied 25 to the surface of the fusion sealing portion 17b and the back side of the joint. Then, after the penetration accelerator 4b is dried, as shown in FIG. 7 (6), the wire feed arc welding is performed from the back surface side (right side surface) of the I-type joint portion 3 in the standing posture or the lateral posture. The fusion bonding 26 (second welding process) is performed, and the fusion bonding 26 is performed up to a penetration depth H2 in a specific range. The penetration depth H2 on the back side is approximately the same as the penetration depth H1 on the front side, and is preferably formed within a range of 1/2 to 9/10 of the plate thickness T. It can be adjusted according to the welding heat input conditions such as welding current and welding speed, and the penetration depth within a specific range corresponding to the plate thickness (4 ≦ T ≦ 16) and welding position of the joint members 1a, 1b, 2a, 2b It is preferable to set an appropriate welding condition so as to satisfy (0.5 × T ≦ H2 ≦ 0.9 × T) and to perform the fusion bonding 26 by wire feed arc welding.

  As shown in FIGS. 7 (6) and 7 (7), by this melt bonding 26, the tip end portion of the melt joint portion 9 b formed on the joint back surface side and the tip end of the melt joint portion 8 b formed on the opposite joint surface side. 89 can be overlapped with each other. Further, as described above, the melt seals 20 and 24 in the gap G portion and the melt joints 22 and 26 by the arc welding of the welding wire 7 feed, there is no generation of porosity due to the penetration of the penetration accelerator inside the weld, and the welding surface Therefore, it is possible to obtain the melt-bonded portions 8b and 9b having no overcuts or dents and having a surplus bead. It should be noted that the rear surface side (right side surface) fusion bonding 26 may be performed first, and then the front surface side (left side surface) fusion bonding 22 may be performed. In particular, when applied to welding of large structures where it is difficult to turn the joint member upside down, it is possible to significantly reduce man-hours and costs.

  Further, in the double-sided welding method of the present invention, before applying the penetration accelerator 4a, a sealing step of melting and sealing the surface or both sides of the I-type joint part 3 under low energy temporary attachment conditions, Contrary to the first welding process in which the welding accelerator 4a is applied to the surface side of the I-type joint 3 after the melt sealing 20 and then melt-bonded 22 to a specific depth of penetration H1 by arc welding. It is also possible to include a second welding step in which the melt accelerator 26 is applied to the back surface side of the remaining joint portion on the side and then melt-bonded 26 to the penetration depth H2 in a specific range by the arc welding.

  By constructing and carrying out in this way, it is not necessary to perform back wave welding for back bead formation, even if it is a substantially I-type butt joint or a substantially T joint that does not require laborious groove processing, Even in the joint members 1a, 1b, 2a, and 2b where the joint portions 3 and 3b have the gap G and the step b, as described above, the gap G portion and the melt seals 20 and 24 in the vicinity thereof, Melting joints 22 and 26 by arc welding with 7-wire welding wire eliminate the occurrence of porosity due to the penetration of a penetration accelerator inside the weld, and weld joints 8b and 9b have no undercuts or dents on the weld surface and have extra bead. Can be obtained. Furthermore, deep double-sided penetration welding, which was impossible with conventional TIG welding with shallow penetration, is possible, and thermal deformation can be reduced and the number of welding passes can be reduced.

  FIG. 8 is an explanatory view of an embodiment showing an outline of a welding procedure and a penetration shape of a substantially T-shaped joint by the double-side welding method of the present invention. The main difference from FIGS. 1 and 5 to 7 is the shape of a substantially T-shaped joint whose joint shape is different from a substantially I-shaped joint. About the attitude | position of welding, it is a downward attitude | position or an upright attitude | position similarly to the above. As shown in FIG. 8 (1), before applying the penetration accelerator 4 a 21, the joint surface of the gap G portion and the vicinity thereof or a length portion of a specific portion is melt sealed 20 ( Melting and sealing part 17a). As described above, the melt sealing construction 20 does not allow the penetration accelerator to enter the gap at the time of application, thereby eliminating the cause of porosity generation at the time of welding.

  As shown in FIG. 8 (2), after completion of the melt sealing 20, the melt accelerator 4 a is applied 21 to the surface of the melt sealing 17 a and the standing plate surface 30 a of the T-shaped joint portion 32. The substantially T-shaped joint portion is made of stainless steel or carbon steel having a plate thickness T of 4 mm to 16 mm. Further, the substantially T-shaped joint portion 32 may have a small chamfering process on the end face of the standing plate.

Then, after the applied penetration accelerator 4a is dried, as shown in FIG. 8 (3), in the downward posture or the standing posture, the fusion bonding 22 (first first) by wire feed arc welding from the surface side (left side surface). Welding process) is performed, and melt bonding 22 is performed to a specific range of penetration depth (0.5 × T ≦ H1 ≦ 0.9 × T). Without melting up to the standing plate back surface 30b, it is possible to reliably weld up to the penetration depth H1 in a specific range, and it is possible to obtain a sound fusion bonded portion 18b in which no porosity is generated due to the penetration of the penetration accelerator inside the weld. Further, even when welding a T-shaped joint with or without a gap G in the T-shaped joint portion 32, as described above, welding is performed by fusion sealing of the gap G portion and arc welding of the welding wire 7 feed. There is no generation of porosity due to the inclusion of a penetration accelerator inside, and it is possible to obtain a melt-bonded portion 18b having no overcut or dent on the weld surface and having a surplus bead.

  Next, with the joint member remaining in a state where it is not inverted 24, as shown in FIGS. 8 (4) and (5), the back surface portion of the remaining joint opposite to the front surface side is melt-sealed 24, and then the penetration accelerator is used. 4b is applied 25. Then, after the penetration accelerator 4b is dried, as shown in FIG. 8 (6), a melt bonding 26 (second welding process) is performed by wire-feed arc welding from the back surface side (right side surface). The melt bonding 26 is performed up to the penetration depth (0.5 × T ≦ H2 ≦ 0.9 × T).

  As shown in FIGS. 8 (6) and 7 (7), by this melt bonding 26, the tip end portion of the melt joint portion 19 b formed on the joint back surface side and the tip end of the melt joint portion 18 b formed on the opposite joint surface side. 89 can be overlapped with each other. Further, no porosity is generated due to the penetration of the penetration accelerator in the inside of the weld, and it is possible to obtain the melt-joined portions 18b and 19b having an undercut or a dent and a surplus bead on the weld surface. Deep double-sided penetration welding, which was impossible with conventional TIG welding with shallow penetration, is possible, and thermal deformation can be reduced and the number of welding passes can be reduced. In particular, when applied to welding of large structures that do not require the work of turning the joint member upside down, it is possible to significantly reduce man-hours and costs.

  Thermal deformation (warp deformation) due to welding causes warp deformation on the welding side due to heating and cooling (melting and solidification), and increases when the welding heat input is large and the number of welding paths increases. In particular, warpage deformation increases in the case of multi-pass welding on one side having a groove. In order to reduce the thermal deformation (warp deformation) due to this welding, (1) to reduce the welding path and heat input, (2) to change from single-sided welding to double-sided welding, and (3) groove joint I This can be achieved by forming a mold joint or a T-shaped joint.

  The embodiment shown in FIGS. 1 to 8 satisfies the above conditions (1) to (3), and the thermal deformation of each of the joints is substantially uniform by forming the molten joints from both the front and back surfaces of the joint member. Reduction can be achieved. In addition, the number of welding passes can be reduced by a total of two passes, one pass welding on the front side of the joint member and one pass welding on the back side. It can be surely reduced.

  For reference, FIG. 9 is a cross-sectional view showing an example of a shallow penetration shape of a conventional I-type joint by TIG welding. FIG. 10 is a cross-sectional view of a multi-pass weld shape of a U-shaped groove joint by conventional TIG welding. As shown in FIGS. 9 (1) and (2), when the conventional TIG welding is performed on the I-type joint 3 from both the front and back surfaces, the penetration depth H3 of the melt-bonded portions 10a and 10b is shallow (for example, about 2 mm). For this reason, insufficient bonding occurs in the central portion of the plate thickness, and for example, it cannot be applied to a joint member having a plate thickness exceeding 4 mm. For this reason, it is common to perform multi-pass welding on a grooved joint. For example, as shown in FIGS. 10 (1) and 10 (2), a U-shaped groove joint portion 33 is provided, and the first layer back wave welding 11 for forming a back bead at the bottom is applied, and thereafter, to the top of the groove. Multi-pass welding with multiple layers 12 is performed.

  Thus, not only multi-pass welding is required, but thermal deformation tends to increase. Although not shown, in the case of the V groove joint, it is difficult to form a uniform back bead as compared with the U groove joint. After stacking 12 by multi-pass welding, and further gouging the back bead portion and the unmelted portion on the back side, a few passes of welding may be applied from the back side.

FIG. 11 is a cross-sectional view of a multi-pass weld shape of a T-shaped groove joint by conventional TIG welding. Further, FIG. 12 is a cross-sectional view of a multi-pass weld shape of a conventional groove joint by TIG welding. As shown in FIG. 11 and FIG. 12, after performing the first layer back wave welding 11 for forming the back bead on the bottom of the groove 15, multi-pass welding in which a plurality of layers 13 a and 13 b are stacked up to the top of the double-sided groove or Multi-pass welding is performed in which a plurality of layers 14 are laminated up to the upper part of the single-sided groove. For this reason, many man-hours and time are required for the welding operation, and thermal deformation is likely to increase.

In contrast, in the double-sided welding method of the present invention, as described above, deep double-sided penetration welding, which was impossible with conventional TIG welding with shallow penetration, is possible. Even if it is a substantially T-shaped joint, it is possible to obtain a weld metal part with good quality without melting or porosity. Further, the assembly work of the welded member joint is facilitated, and thermal deformation can be reduced and the number of welding passes can be reduced as compared with the conventional welding construction, so that the man-hour and cost can be greatly reduced.

It is explanatory drawing which shows one Example of the welding procedure outline | summary of the I-type joint concerning the double-sided welding method of this invention, and a penetration shape. It is explanatory drawing which shows the penetration | invasion to the joint gap part of a penetration accelerator, and generation | occurrence | production to the fusion-bonding part of a porosity. It is explanatory drawing which shows the coating film thickness change of a penetration accelerator, and the shape change of a penetration. It is one Example which shows the relationship between the coating film thickness of a penetration accelerator, a penetration depth, and a bead width. It is one example of the result of examining the relationship between the plate thickness of double-sided welding, the welding current, and the penetration depth on the back side. In the figure, cross-sectional photographs (6, 9, 12, 16 mm) according to the thickness of the double-sided welds are shown. 2 shows a cross-sectional photograph of a 9 mm plate welded on both sides without a penetration accelerator. It is explanatory drawing which shows another Example of the welding procedure outline | summary of the I-type joint concerning the double-sided welding method of this invention, and a penetration shape. It is explanatory drawing of one Example which shows the welding procedure outline | summary and penetration shape of an I-shaped joint in a standing posture. It is explanatory drawing of one Example which shows the welding procedure outline | summary and penetration shape of the T-shaped joint by the double-sided welding method of this invention. It is sectional drawing which shows an example of the shallow penetration shape of the I-type coupling by the conventional TIG welding. It is sectional drawing of the multipass welding shape of the U-shaped groove joint by the conventional TIG welding. It is sectional drawing of the multipass welding shape of the T type groove joint by the conventional TIG welding. It is sectional drawing of the multipass welding shape of the ladle type groove joint by the conventional TIG welding.

Explanation of symbols

1a, 2a Joint member surfaces 1b, 2b Joint member back surface 3 I-type joint part 3b Remaining joint parts 4a, 4b Penetration accelerator 5 Non-consumable electrode 6 Arc 7 Welding wires 8a, 9a, 18a, 19a Molten pool 8b, 9b, 18b, 19b Melt joints 10a, 10b Melt joint 11 of conventional welding 11 First layer back wave welding 12-14 Lamination 15 Leve 16 Welding direction 17a, 17b Melting seal 30a Standing plate surface of T-type joint 30b Standing plate back surface 31a of T type joint, 31b Horizontal plate 32 of T type joint 32 T type joint part 33 U type groove joint part 34 Porosity 35 Welding line H1 to H3 Penetration depth G Gap T Thickness

Claims (5)

In a double-sided welding method in which a welding accelerator is applied to the front side and the back side of a substantially I-type joint part or a substantially T-type joint part made of stainless steel material or low-carbon steel material, and arc welding of a non-consumable electrode method is performed,
A double-sided welding method characterized by melting and sealing the front surface, the back surface, or both front and back surfaces of the joint before applying the penetration accelerator. In a double-sided welding method in which a welding accelerator is applied to the front side and the back side of a substantially I-type joint part or a substantially T-type joint part made of stainless steel material or low-carbon steel material, and arc welding of a non-consumable electrode method is performed,
Before applying the penetration accelerator, melt and seal the surface or both sides of the joint,
Applying the penetration accelerator to the surface side of the joint after the melt sealing,
After application of the accelerator, it is melt-bonded by the arc welding construction,
A double-sided welding method characterized in that after the penetration accelerator is applied to the back side of the remaining joint portion on the opposite side, fusion bonding is performed by the arc welding. In a double-sided welding method in which a welding accelerator is applied to the front side and the back side of a substantially I-type joint part or a substantially T-type joint part made of stainless steel material or low-carbon steel material, and arc welding of a non-consumable electrode method is performed,
Before applying the penetration accelerator, a sealing step of melting and sealing the surface or both sides of the joint part, and after applying the penetration accelerator to the surface side of the joint part after the fusion sealing A first welding step in which the fusion welding is performed by arc welding, and a second welding step in which the melting accelerator is applied to the back side of the remaining joint portion on the opposite side and then melt-bonded by the arc welding. A double-sided welding method characterized by that.   4. The double-sided welding method according to claim 1, wherein the joint portion is formed with a gap or a step or both of the gap and the step irregularly, and the fusion seal is at least the gap forming portion or the weld. A double-sided welding method characterized by being applied to a wire.   The double-sided welding method according to any one of claims 1 to 3, wherein the penetration accelerator is reciprocally applied at least once in the weld line direction of the joint part to form a film thickness of 20 μm or more in the left-right direction of the weld line. Double-side welding method.

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