Method for manufacturing welded structure

Abstract

This method is for manufacturing a welded structure having a welded metal portion extending along a first direction, and a first portion and second portion which sandwich the welded metal portion therebetween in a second direction intersecting the first direction. This method for manufacturing a welded structure is provided with: a step for forming the welded metal portion by moving a welding torch along the first direction, from one side in the first direction to the other side in the first direction; and a step for moving one or more auxiliary torches along the first direction, from one side in the first direction to the other side in the first direction, and thereby heating but not melting the first portion and / or the second portion, during at least a portion of the time that the welding torch is moving. Each of the positions of the one or more auxiliary torches in the first direction is offset from the position of the welding torch in the first direction.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a welded structure. [Background technology]

[0002] Patent Document 1 (JP 2015-199111 A) describes a method for manufacturing a welded structure. The welded structure described in Patent Document 1 has a first member and a second member superimposed on the first member. The weld metal portion where the first member and the second member are welded extends along the weld line direction. The portions sandwiching the weld metal portion in a direction intersecting the weld line direction are referred to as the first portion and the second portion.

[0003] When manufacturing the welded structure described in Patent Document 1, a welded metal part is formed by irradiating a first laser while moving it along the weld line direction. While irradiating the first laser while moving it, a second laser is irradiated onto the first part. The first part is not melted by the irradiation of the second laser. The irradiation position of the first laser in the weld line direction and the irradiation position of the second laser in the weld line direction are aligned with each other. The manufacturing method of the welded structure described in Patent Document 1 is said to be able to suppress the occurrence of hot cracking (solidification cracking) in the welded metal part. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-199111 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the method for manufacturing a welded structure described in Patent Document 1 leaves room for improvement in terms of the occurrence of hot cracks in the welded metal portion.

[0006] The present invention has been made in view of the above-mentioned problems of the conventional art. More specifically, the present invention provides a method for manufacturing a welded structure that can suppress the occurrence of hot cracking. [Means for solving the problem]

[0007] A method for manufacturing a welded structure according to one aspect of the present invention is a method for manufacturing a welded structure having a weld metal portion extending along a first direction and a first portion and a second portion sandwiching the weld metal portion in a second direction intersecting the first direction. The method for manufacturing the welded structure includes the steps of: forming a weld metal portion by moving a welding torch along the first direction from one side in the first direction to the other side in the first direction; and heating at least one of the first portion and the second portion so as not to melt them by moving at least one auxiliary torch along the first direction from one side in the first direction to the other side in the first direction during at least a portion of the time the welding torch is moving. Each of the positions of the at least one auxiliary torch in the first direction is offset from the position of the welding torch in the first direction.

[0008] In the above-described method for manufacturing a welded structure, the at least one auxiliary torch may include a first auxiliary torch that heats the first portion and a second auxiliary torch that heats the second portion. The first auxiliary torch and the second auxiliary torch may face each other in the second direction. The first auxiliary torch and the second auxiliary torch may be located on one side of the welding torch in the first direction.

[0009] In the method for manufacturing a welded structure, a solidification brittle temperature zone, in which a liquid phase and a solid phase coexist, may be formed adjacent to one side of the molten pool formed by the welding torch in a first direction, and the first auxiliary torch and the second auxiliary torch may face the solidification brittle temperature zone in a second direction.

[0010] In the above-described method for manufacturing a welded structure, the at least one auxiliary torch may include a third auxiliary torch that heats the first portion and a fourth auxiliary torch that heats the second portion. The third auxiliary torch and the fourth auxiliary torch may be located on the other side of the welding torch in the first direction. The third auxiliary torch and the fourth auxiliary torch may face each other in the second direction. [Effects of the Invention]

[0011] According to a welded structure and a method for manufacturing a welded structure according to one aspect of the present invention, it is possible to suppress the occurrence of hot cracking in a weld metal part. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a plan view of a welded structure according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] 1A to 1C are process diagrams illustrating a method for manufacturing a welded structure according to a first embodiment. [Figure 4] 3 is a schematic diagram for explaining a preparation step S1 in the method for manufacturing a welded structure according to the first embodiment. FIG. [Figure 5] 5 is a schematic view for explaining a welding step S2 in the method for manufacturing a welded structure according to the first embodiment. FIG. [Figure 6] 1 is a schematic high-temperature ductility curve of a solidification brittle temperature region 52 between the liquidus temperature and the solidus temperature. [Figure 7] 10 is a schematic view for explaining a welding step S2 in the method for manufacturing a welded structure according to the second embodiment. FIG. [Figure 8] 10 is a schematic diagram showing in-plane rotational deformation of a first member 1 and a second member 2 that occurs during a weld metal formation step S21. FIG. [Figure 9] FIG. 10 is a plan view of a welded structure according to a third embodiment. [Figure 10] FIG. 10 is a cross-sectional view taken along line XX in FIG. 9. [Figure 11]10 is a schematic diagram for explaining a preparation step S1 in a method for manufacturing a welded structure according to a third embodiment. FIG. [Figure 12] FIG. 10 is a schematic view illustrating a welding step S2 in the method for manufacturing a welded structure according to the third embodiment. [Figure 13] FIG. 10 is a cross-sectional view of a welded structure according to a fourth embodiment. [Figure 14] FIG. 10 is a cross-sectional view illustrating a preparation step S1 in a method for manufacturing a welded structure according to a fourth embodiment. [Figure 15] FIG. 10 is a perspective view of a welded structure according to a fifth embodiment before a weld metal portion 3 is formed. [Figure 16] FIG. 10 is a cross-sectional view of a welded structure according to a fifth embodiment. [Figure 17] FIG. 13 is a schematic view illustrating a welding step S2 in the method for manufacturing a welded structure according to the fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the accompanying drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and redundant description will not be repeated.

[0014] (Configuration of the welded structure according to the first embodiment) The configuration of the welded structure according to the first embodiment will be described below.

[0015] Fig. 1 is a plan view of a welded structure according to a first embodiment. Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1. As shown in Figs. 1 and 2, the welded structure according to the first embodiment has a first member 1, a second member 2, and a welded metal portion 3. A first portion 7 and a second portion 8 in the welded structure according to the first embodiment are portions that sandwich the welded metal portion 3 in a second direction DR2 described below.

[0016] <First member 1 and second member 2> The first member 1 and the second member 2 are, for example, flat plate-shaped members. The first member 1 and the second member 2 are made of, for example, steel. The first member 1 and the second member 2 are, for example, rolled steel plate for welded structures (SM material) specified in the JIS standard (JIS G 3106:2008). The first member 1 and the second member 2 are formed of, for example, the same material. The first member 1 and the second member 2 may be formed of different materials. The first member 1 and the second member 2 do not have to be made of steel. The first member 1 and the second member 2 may be, for example, a non-ferrous alloy such as an aluminum (Al) alloy.

[0017] <Welded metal part 3> The weld metal portion 3 extends along a first direction DR1. The first direction DR1 is the direction of the weld line. The weld metal portion 3 is a portion formed of a weld metal obtained by mixing the molten first member 1 and the second member 2 (or by further mixing the molten welding material, if a welding material is used) and solidifying. The weld metal portion 3 is sandwiched between the first member 1 and the second member 2 in a second direction DR2. That is, the first member 1 forms a first portion 7, and the second member 2 forms a second portion 8. The second direction DR2 intersects with the first direction DR1. The second direction DR2 is preferably perpendicular to the first direction DR1.

[0018] <Heat-affected zone 4> A heat-affected zone 4 is formed around the weld metal portion 3. In FIG. 2, the heat-affected zone 4 is indicated by a dotted line. The heat-affected zone 4 is a portion that is not melted by the heat input during welding, but whose metal structure and mechanical properties are changed from those of the base material by the heat input during welding. The heat-affected zone 4 has a width W. The width W is the width of the heat-affected zone 4 in the second direction DR2. The width W is wider than when the auxiliary heating step S22 is not performed in the welding step S2 (when only the weld metal formation step S21 is performed in the welding step S2). Therefore, by measuring the width W, it is possible to determine whether both the weld metal formation step S21 and the auxiliary heating step S22 have been performed.

[0019] (Method for manufacturing a welded structure according to the first embodiment) A method for manufacturing a welded structure according to the first embodiment will be described below.

[0020] Fig. 3 is a process diagram showing a method for manufacturing a welded structure according to the first embodiment. As shown in Fig. 3, the method for manufacturing a welded structure according to the first embodiment includes a preparation step S1 and a welding step S2. The welding step S2 is performed after the preparation step S1. The welding step S2 includes a weld metal formation step S21 and an auxiliary heating step S22.

[0021] <Preparation process S1> 4 is a schematic diagram illustrating a preparation step S1 in the method for manufacturing a welded structure according to the first embodiment. As shown in FIG. 4, in the preparation step S1, a first member 1 and a second member 2 are prepared. The first member 1 has a first end face 1a. The first end face 1a is the end face of the first member 1 in the second direction DR2. The second member 2 has a second end face 2a. The second end face 2a is the end face of the second member 2 in the second direction DR2.

[0022] The first member 1 and the second member 2 are butted against each other so that the first end surface 1a and the second end surface 2a face each other in the second direction DR2. Although not shown, the first member 1 and the second member 2 are temporarily fixed together. This temporary attachment is performed at multiple points along the first direction DR1.

[0023] <Weld metal formation process S21> FIG. 5 is a schematic diagram illustrating the welding step S2 in the method for manufacturing a welded structure according to the first embodiment. In FIG. 5, the welding torch 5, the first auxiliary torch 6a, and the second auxiliary torch 6b are indicated by dotted lines. As shown in FIG. 5, in the weld metal formation step S21, the weld metal portion 3 is formed by moving the welding torch 5 along the first direction DR1. The welding torch 5 is moved from one side (starting end side) in the first direction DR1 to the other side (terminating end side) in the first direction DR1. The welding torch 5 is positioned so as to straddle the first member 1 and the second member 2. As a result, the first member 1 on the first end face 1a side and the second member 2 on the second end face 2a side melt and solidify, forming the weld metal portion 3.

[0024] The welding torch 5 is, for example, a welding torch for an arc welding machine. However, the welding torch 5 is not limited to this, and may be, for example, a welding torch for a laser welding machine.

[0025] As the welding torch 5 moves from the starting end to the terminal end along the first direction DR1, a molten pool 51 is formed near the welding torch 5. The molten pool 51 is composed of the molten first member 1 and the second member 2 (if a welding material is used, the molten pool 51 also contains the molten welding material). A solidification brittle temperature region 52 is formed adjacent to the starting end of the molten pool 51 in the first direction DR1. The solidification brittle temperature region 52 is a region where a solid phase and a liquid phase coexist. From another perspective, the solidification brittle temperature region 52 is a region where the temperature exceeds the solidus temperature of the base material (the first member 1 and the second member 2) and is below the liquidus temperature of the base material.

[0026] <Auxiliary heating process S22> The auxiliary heating step S22 is performed at least partly while the welding torch 5 is moving from the starting end to the terminal end along the first direction DR1. In the auxiliary heating step S22, the first auxiliary torch 6a and the second auxiliary torch 6b are moving from the starting end to the terminal end along the first direction DR1. The moving speed of the first auxiliary torch 6a and the second auxiliary torch 6b in the first direction DR1 is, for example, equal to the moving speed of the welding torch 5 in the first direction DR1.

[0027] The first auxiliary torch 6a heats the first member 1. The second auxiliary torch 6b heats the second member 2. From another perspective, the position of the first auxiliary torch 6a in the second direction DR2 and the position of the second auxiliary torch 6b in the second direction DR2 are shifted from the position of the welding torch 5 in the second direction DR2. The distance between the first auxiliary torch 6a and the welding torch 5 in the second direction DR2 is equal to the distance between the second auxiliary torch 6b and the welding torch 5 in the second direction DR2, for example.

[0028] The output of the first auxiliary torch 6a and the second auxiliary torch 6b is smaller than the output of the welding torch 5. As a result, the first member 1 is not melted by heating from the first auxiliary torch 6a, and the second member 2 is not melted by heating from the second auxiliary torch 6b.

[0029] The position of the first auxiliary torch 6a in the first direction DR1 and the position of the second auxiliary torch 6b in the first direction DR1 are shifted from the position of the welding torch 5 in the first direction DR1. More specifically, the first auxiliary torch 6a and the second auxiliary torch 6b are located closer to the starting end than the welding torch 5 in the first direction DR1.

[0030] The position of the first auxiliary torch 6a in the first direction DR1 and the position of the second auxiliary torch 6b in the first direction DR1, for example, are aligned with each other. That is, the first auxiliary torch 6a and the second auxiliary torch 6b are opposed to each other in the second direction DR2, for example. The first auxiliary torch 6a and the second auxiliary torch 6b are preferably opposed to the solidification brittle temperature region 52 in the second direction DR2.

[0031] The first auxiliary torch 6a and the second auxiliary torch 6b are, for example, welding torches of an arc welding machine. However, the first auxiliary torch 6a and the second auxiliary torch 6b are not limited to this and may be, for example, welding torches of a laser welding machine.

[0032] (Effects of the manufacturing method of the welded structure according to the first embodiment) The effects of the method for manufacturing a welded structure according to the first embodiment will be described below.

[0033] First, the mechanism of hot cracking during welding will be explained. Figure 6 is a schematic high-temperature ductility curve of the solidification brittle temperature region 52 between the liquidus temperature and the solidus temperature. In Figure 6, the horizontal axis represents the temperature in the solidification brittle temperature region 52, and the vertical axis represents the strain applied to the solidification brittle temperature region 52. The high-temperature ductility curve (solid line) in Figure 6 indicates the limit strain at which hot cracking occurs at a specified temperature. Also, T in Figure 6 L and T S indicate the liquidus temperature and the solidus temperature, respectively.

[0034] As shown in Fig. 6, in the solidification brittle temperature region 52, tensile strain increases as the molten metal solidifies (i.e., as the temperature decreases) (see the dotted line in Fig. 6). If this dotted line passes through the region above the high-temperature ductility curve (see the hatched region in Fig. 6), hot cracking will occur in the solidification brittle temperature region 52.

[0035] In the method for manufacturing a welded structure according to the first embodiment, auxiliary heating is performed by the first auxiliary torch 6 a and the second auxiliary torch 6 b. The portion of the first member 1 heated by the first auxiliary torch 6 a and the portion of the second member 2 heated by the second auxiliary torch 6 b thermally expand, and compressive stress is applied from these portions to the solidification brittle temperature region 52.

[0036] This compressive stress reduces the tensile strain applied to the solidification brittle temperature region 52 (or applies compressive strain to the solidification brittle temperature region 52) (see the dashed-dotted line in FIG. 6). As a result, it becomes difficult for this dashed-dotted line to pass through the region above the high-temperature ductility curve, and hot cracking becomes less likely to occur in the solidification brittle temperature region 52.

[0037] (Variation) In the above, an example has been described in which the auxiliary heating step S22 is performed using the first auxiliary torch 6a and the second auxiliary torch 6b. However, either the first auxiliary torch 6a or the second auxiliary torch 6b may be used in the auxiliary heating step S22 (Modification 1). When either the first auxiliary torch 6a or the second auxiliary torch 6b is used, hot cracking may not be sufficiently suppressed depending on the arrangement of the weld metal portion 3 (for example, when the weld metal portion 3 is located near the end of the welded structure). On the other hand, when both the first auxiliary torch 6a and the second auxiliary torch 6b are used, it is possible to stably suppress the occurrence of hot cracking regardless of the arrangement of the weld metal portion 3.

[0038] In the above, an example has been described in which the position of the first auxiliary torch 6a in the second direction DR2 (the position of the second auxiliary torch 6b in the second direction DR2) is shifted from the position of the welding torch 5 in the second direction DR2. However, in Modification 1, the position of the first auxiliary torch 6a (second auxiliary torch 6b) in the second direction DR2 may coincide with the position of the welding torch 5 in the second direction DR2 (Modification 2). In both Modifications 1 and 2, hot cracking is less likely to occur in the solidification brittle temperature region 52, as in the method for manufacturing a welded structure according to the first embodiment.

[0039] (Configuration of welded structure according to the second embodiment) The configuration of the welded structure according to the second embodiment is similar to the configuration of the welded structure according to the first embodiment, so a description of the configuration of the welded structure according to the second embodiment will be omitted here.

[0040] (Method for manufacturing a welded structure according to the second embodiment) The method for manufacturing a welded structure according to the second embodiment will be described below. Here, differences from the method for manufacturing a welded structure according to the first embodiment will be mainly described, and overlapping descriptions will not be repeated.

[0041] The method for manufacturing a welded structure according to the second embodiment includes a preparation step S1 and a welding step S2. The welding step S2 includes a weld metal formation step S21 and an auxiliary heating step S22. In these respects, the method for manufacturing a welded structure according to the second embodiment is common to the method for manufacturing a welded structure according to the first embodiment.

[0042] However, the method for manufacturing a welded structure according to the second embodiment differs from the method for manufacturing a welded structure according to the first embodiment in terms of the details of the auxiliary heating step S22.

[0043] Fig. 7 is a schematic diagram for explaining the welding step S2 in the method for manufacturing a welded structure according to the second embodiment. In Fig. 7, the welding torch 5, the third auxiliary torch 6c, and the fourth auxiliary torch 6d are indicated by dotted lines. As shown in Fig. 7, in the auxiliary heating step S22 in the method for manufacturing a welded structure according to the second embodiment, the third auxiliary torch 6c and the fourth auxiliary torch 6d are used instead of the first auxiliary torch 6a and the second auxiliary torch 6b.

[0044] The third auxiliary torch 6c and the fourth auxiliary torch 6d move from the starting end to the terminal end along the first direction DR1. The moving speed of the third auxiliary torch 6c and the fourth auxiliary torch 6d in the first direction DR1 is equal to the moving speed of the welding torch 5 in the first direction DR1, for example.

[0045] The third auxiliary torch 6c heats the first member 1. The fourth auxiliary torch 6d heats the second member 2. From another perspective, the position of the third auxiliary torch 6c in the second direction DR2 and the position of the fourth auxiliary torch 6d in the second direction DR2 are shifted from the position of the welding torch 5 in the second direction DR2. The distance between the third auxiliary torch 6c and the welding torch 5 in the second direction DR2 is equal to the distance between the fourth auxiliary torch 6d and the welding torch 5 in the second direction DR2, for example.

[0046] The output of the third auxiliary torch 6c and the fourth auxiliary torch 6d is smaller than the output of the welding torch 5. As a result, the first member 1 is not melted by heating from the third auxiliary torch 6c, and the second member 2 is not melted by heating from the fourth auxiliary torch 6d.

[0047] The position of the third auxiliary torch 6c in the first direction DR1 and the position of the fourth auxiliary torch 6d in the first direction DR1 are shifted from the position of the welding torch 5 in the first direction DR1. More specifically, the third auxiliary torch 6c and the fourth auxiliary torch 6d are located closer to the terminal end than the welding torch 5 in the first direction DR1.

[0048] The position of the third auxiliary torch 6c in the first direction DR1 and the position of the fourth auxiliary torch 6d in the first direction DR1, for example, coincide with each other. That is, the third auxiliary torch 6c and the fourth auxiliary torch 6d face each other in the second direction DR2, for example.

[0049] The first auxiliary torch 6a and the second auxiliary torch 6b are, for example, welding torches of an arc welding machine. However, the first auxiliary torch 6a and the second auxiliary torch 6b are not limited to this and may be, for example, welding torches of a laser welding machine.

[0050] (Effects of the manufacturing method of the welded structure according to the second embodiment) The effects of the method for manufacturing a welded structure according to the second embodiment will be described below.

[0051] 8 is a schematic diagram showing the in-plane rotational deformation of the first member 1 and the second member 2 that occurs during the weld metal formation step S21. As shown in Fig. 8, during the weld metal formation step S21, the temperatures of the first member 1 and the second member 2 increase significantly in the vicinity of the welding torch 5, whereas the temperatures of the first member 1 and the second member 2 do not increase significantly in positions away from the welding torch 5.

[0052] As a result, a difference in the amount of thermal expansion occurs between the vicinity of the welding torch 5 and a position farther from the welding torch 5, and an in-plane rotational deformation (see dotted line in FIG. 8) occurs in which the distance between the first member 1 and the second member 2 increases as the distance approaches the terminal end. This in-plane rotational deformation applies tensile strain to the solidification brittle temperature region 52, and this tensile strain is one of the causes of hot cracking in the solidification brittle temperature region 52.

[0053] In the method for manufacturing a welded structure according to the second embodiment, the third auxiliary torch 6c and the fourth auxiliary torch 6d heat the first member 1 and the second member 2, respectively, at positions closer to the terminal end than the welding torch 5, thereby reducing the difference in the amount of thermal expansion between the vicinity of the welding torch 5 and a position farther from the welding torch 5. As a result, the amount of in-plane deformation of the first member 1 and the second member 2 is reduced, and the tensile strain applied to the solidification brittle temperature region 52 is also reduced. In this way, according to the method for manufacturing a welded structure according to the second embodiment, hot cracking is less likely to occur in the solidification brittle temperature region 52.

[0054] When a temporary joint is formed between the first member 1 and the second member 2, the temporary joint suppresses in-plane rotational deformation of the first member 1 and the second member 2, even if there is a difference in the amount of thermal expansion between a position near the welding torch 5 and a position away from the welding torch 5. However, if the welding torch 5 approaches the temporary joint and the temporary joint melts, the in-plane rotational deformation that was suppressed by the temporary joint is suddenly released, and as a result, a large tensile strain acts on the solidification brittle temperature region 52.

[0055] In the method for manufacturing a welded structure according to the second embodiment, the third auxiliary torch 6c and the fourth auxiliary torch 6d heat the first member 1 and the second member 2, respectively, on the terminal end side of the welding torch 5, and therefore the temporary joint on the terminal end side of the welding torch 5 is preheated. That is, in the method for manufacturing a welded structure according to the second embodiment, the constraint on in-plane rotational deformation caused by the temporary joint is weakened in advance.

[0056] As a result, even if the welding torch 5 approaches the tack and melts the tack, the in-plane rotational deformation is not suddenly released, and the tensile strain applied to the solidification brittle temperature region 52 is reduced. In this way, according to the method for manufacturing a welded structure according to the second embodiment, hot cracking is less likely to occur in the solidification brittle temperature region 52 even when the first member 1 and the second member 2 are tacked together.

[0057] (Variation) In the above, an example has been described in which the third auxiliary torch 6c and the fourth auxiliary torch 6d are used instead of the first auxiliary torch 6a and the second auxiliary torch 6b, but the first auxiliary torch 6a and the second auxiliary torch 6b may be used in combination with the third auxiliary torch 6c and the fourth auxiliary torch 6d (Modification 1). The method for manufacturing a welded structure according to the first embodiment and the method for manufacturing a welded structure according to the second embodiment have different mechanisms for suppressing the occurrence of hot cracking in the solidification brittle temperature region 52. Therefore, by using the first auxiliary torch 6a and the second auxiliary torch 6b in combination with the third auxiliary torch 6c and the fourth auxiliary torch 6d, the occurrence of hot cracking in the solidification brittle temperature region 52 can be further suppressed.

[0058] In the above, an example has been described in which the auxiliary heating step S22 is performed using the third auxiliary torch 6c and the fourth auxiliary torch 6d. However, either the third auxiliary torch 6c or the fourth auxiliary torch 6d may be used in the auxiliary heating step S22 (Modification 2). When either the third auxiliary torch 6c or the fourth auxiliary torch 6d is used, hot cracking may not be sufficiently suppressed depending on the arrangement of the weld metal portion 3 (for example, when the weld metal portion 3 is located near the end of the welded structure). On the other hand, when both the third auxiliary torch 6c and the fourth auxiliary torch 6d are used, hot cracking can be stably suppressed regardless of the arrangement of the weld metal portion 3.

[0059] In the above, an example has been described in which the position of the third auxiliary torch 6c in the second direction DR2 (the position of the fourth auxiliary torch 6d in the second direction DR2) is shifted from the position of the welding torch 5 in the second direction DR2. However, in Modification 2, the position of the third auxiliary torch 6c (fourth auxiliary torch 6d) in the second direction DR2 may coincide with the position of the welding torch 5 in the second direction DR2 (Modification 3). In both Modifications 2 and 3, hot cracking is less likely to occur in the solidification brittle temperature region 52, as in the method for manufacturing a welded structure according to the second embodiment.

[0060] (Configuration of welded structure according to the third embodiment) The configuration of the welded structure according to the third embodiment will be described below. Here, differences from the configuration of the welded structure according to the first embodiment will be mainly described, and overlapping descriptions will not be repeated.

[0061] Fig. 9 is a plan view of a welded structure according to a third embodiment. Fig. 10 is a cross-sectional view taken along line XX in Fig. 9. As shown in Figs. 9 and 10, the welded structure according to the third embodiment has a first member 1, a second member 2, and a welded metal part 3. In this respect, the configuration of the welded structure according to the third embodiment is common to the configuration of the welded structure according to the first embodiment.

[0062] However, in the welded structure according to the third embodiment, the second member 2 is overlapped on the first member 1. The weld metal portion 3 is formed so as to penetrate the first member 1 and the second member 2. That is, in the welded structure according to the third embodiment, the portions of the first member 1 and the second member 2 adjacent to the weld metal portion 3 from one side in the second direction DR2 are the first portion 7, and the portions of the first member 1 and the second member 2 adjacent to the weld metal portion 3 from the other side in the second direction DR2 are the second portion 8. In these respects, the configuration of the welded structure according to the third embodiment differs from the configuration of the welded structure according to the first embodiment.

[0063] In the welded structure according to the third embodiment, the width of the first portion 7 in the second direction DR2 and the width of the second portion 8 in the second direction DR2 may be different from each other.

[0064] (Method for manufacturing a welded structure according to the third embodiment) The method for manufacturing a welded structure according to the third embodiment will be described below. Here, differences from the method for manufacturing a welded structure according to the first embodiment will be mainly described, and overlapping descriptions will not be repeated.

[0065] The method for manufacturing a welded structure according to the third embodiment includes a preparation step S1 and a welding step S2. The welding step S2 includes a weld metal formation step S21 and an auxiliary heating step S22. In these respects, the method for manufacturing a welded structure according to the third embodiment is common to the method for manufacturing a welded structure according to the first embodiment.

[0066] However, the method for manufacturing a welded structure according to the third embodiment differs from the method for manufacturing a welded structure according to the first embodiment in terms of the details of the preparation step S1, the details of the weld metal forming step S21, and the details of the auxiliary heating step S22.

[0067] 11 is a schematic diagram for explaining a preparation step S1 in a method for manufacturing a welded structure according to the third embodiment. In the preparation step S1 in the method for manufacturing a welded structure according to the third embodiment, a second member 2 is placed on a first member 1.

[0068] Fig. 12 is a schematic diagram for explaining the welding step S2 in the method for manufacturing a welded structure according to the third embodiment. In Fig. 12, the welding torch 5, the first auxiliary torch 6a, and the second auxiliary torch 6b are indicated by dotted lines. As shown in Fig. 12, in the weld metal formation step S21 in the method for manufacturing a welded structure according to the third embodiment, the welding torch 5 is moved from the starting end to the terminal end along the first direction DR1 to form the weld metal portion 3 so as to penetrate the first member 1 and the second member 2.

[0069] In the auxiliary heating step S22 in the method for manufacturing a welded structure according to the third embodiment, the first portion 7 (portion of the first member 1 and the second member 2 adjacent to the weld metal portion 3 from one side in the second direction DR2) is heated by the first auxiliary torch 6a, and the second portion 8 (portion of the first member 1 and the second member 2 adjacent to the weld metal portion 3 from the other side in the second direction DR2) is heated by the second auxiliary torch 6b. Note that the first portion 7 does not melt when heated by the first auxiliary torch 6a, and the second portion 8 does not melt when heated by the second auxiliary torch 6b.

[0070] (Effects of the manufacturing method of the welded structure according to the third embodiment) In the manufacturing method of the welded structure according to the third embodiment, the heating of the first auxiliary torch 6a and the second auxiliary torch 6b reduces the tensile strain applied to the solidification brittle temperature region 52 (or applies compressive strain to the solidification brittle temperature region 52), making it less likely that hot cracking will occur in the solidification brittle temperature region 52.

[0071] In this way, the method of suppressing the occurrence of hot cracking in the solidification brittle temperature region 52 by using the first auxiliary torch 6a and the second auxiliary torch 6b to heat the first portion 7 and the second portion 8 without melting them, while using the welding torch 5 to form the weld metal portion 3, can be applied regardless of the type of welding (butt welding or lap welding).

[0072] (Configuration of welded structure according to the fourth embodiment) The configuration of the welded structure according to the fourth embodiment will be described below. Here, differences from the configuration of the welded structure according to the first embodiment will be mainly described, and overlapping descriptions will not be repeated.

[0073] Fig. 13 is a cross-sectional view of a welded structure according to a fourth embodiment. Fig. 13 shows a cross-sectional view perpendicular to the extension direction (first direction DR1) of the weld metal portion 3. As shown in Fig. 13, the first member 1 has a thickness T1, and the second member 2 has a thickness T2. The thicknesses T1 and T2 are 16 mm or more and 40 mm or more. That is, the welded structure according to the fourth embodiment is similar to the welded structure according to the first embodiment in that it is a butt-welded joint, but differs from the welded structure according to the first embodiment in that thick plates are used as the first member 1 and the second member 2.

[0074] (Method for manufacturing a welded structure according to the fourth embodiment) A method for manufacturing a welded structure according to the fourth embodiment will be described below. Here, differences from the method for manufacturing a welded structure according to the first embodiment will be mainly described, and overlapping descriptions will not be repeated.

[0075] The method for manufacturing a welded structure according to the fourth embodiment includes a preparation step S1 and a welding step S2. The welding step S2 includes a weld metal forming step S21 and an auxiliary heating step S22. In these respects, the method for manufacturing a welded structure according to the fourth embodiment differs from the method for manufacturing a welded structure according to the first embodiment. However, the method for manufacturing a welded structure according to the fourth embodiment differs from the method for manufacturing a welded structure according to the first embodiment in terms of the details of the preparation step S1 and the welding step S2.

[0076] 14 is a cross-sectional view illustrating a preparation step S1 in a manufacturing method for a welded structure according to a fourth embodiment. As shown in FIG. 14, in the preparation step S1 in the manufacturing method for a welded structure according to the fourth embodiment, the end face (first end face 1a) of the first member 1 facing the second member 2 and the end face (second end face 2a) of the second member 2 facing the first member 1 form a Y-shaped groove. However, the groove formed by the first end face 1a and the second end face 2a is not limited to a Y-shaped groove. The groove formed by the first end face 1a and the second end face 2a may be a V-shaped groove, an X-shaped groove, a K-shaped groove, or the like.

[0077] The welding step S2 (weld metal forming step S21 and auxiliary heating step S22) in the method for manufacturing a welded structure according to the fourth embodiment may be repeated multiple times. That is, the welded metal portion 3 of the welded structure according to the fourth embodiment may be formed by multi-layer welding. Note that the welding step S2 in the method for manufacturing a welded structure according to the fourth embodiment may be replaced by the welding step S2 in the method for manufacturing a welded structure according to the second embodiment.

[0078] (Effects of the manufacturing method of the welded structure according to the fourth embodiment) According to the manufacturing method of the welded structure of the fourth embodiment, it is possible to suppress the occurrence of hot cracking even when butt welding thick plates that are particularly susceptible to hot cracking.

[0079] (Configuration of welded structure according to the fifth embodiment) The configuration of the welded structure according to the fifth embodiment will be described below. Here, differences from the configuration of the welded structure according to the first embodiment will be mainly described, and overlapping descriptions will not be repeated.

[0080] Fig. 15 is a perspective view of a welded structure according to a fifth embodiment. Fig. 15 shows a cross-sectional view perpendicular to the extension direction of a welded metal portion 3. Fig. 16 is a cross-sectional view of the welded structure according to the fifth embodiment. As shown in Figs. 15 and 16, the welded structure according to the fifth embodiment has a first member 1, a second member 2, and a welded metal portion 3.

[0081] The first member 1 has a first end surface 1a and a first main surface 1b. The second member 2 has a second end surface 2a and a second main surface 2b. The second member 2 is disposed on the first member 1 (on the first main surface 1b) so that the second end surface 2a faces the first main surface 1b. The weld metal portion 3 extends along the first direction DR1 and joins the first main surface 1b side of the first member 1 and the second end surface 2a side of the second member 2. In other words, while the welded structure according to the first embodiment is a butt joint, the welded structure according to the fifth embodiment is a T-joint.

[0082] (Method for manufacturing a welded structure according to the fifth embodiment) The method for manufacturing a welded structure according to the fifth embodiment will be described below. Here, differences from the method for manufacturing a welded structure according to the first embodiment will be mainly described, and overlapping descriptions will not be repeated.

[0083] The method for manufacturing a welded structure according to the fifth embodiment includes a preparation step S1 and a welding step S2. The welding step S2 includes a weld metal forming step S21 and an auxiliary heating step S22. In these respects, the method for manufacturing a welded structure according to the fifth embodiment differs from the method for manufacturing a welded structure according to the first embodiment. However, the method for manufacturing a welded structure according to the fifth embodiment differs from the method for manufacturing a welded structure according to the first embodiment in terms of the details of the preparation step S1 and the welding step S2.

[0084] In the preparation step S1 in the method for manufacturing a welded structure according to the fifth embodiment, the second member 2 is placed on the first member 1 (on the first main surface 1b) so that the second end surface 2a faces the first main surface 1b.

[0085] Fig. 17 is a schematic diagram for explaining a welding step S2 in a manufacturing method of a welded structure according to embodiment 5. As shown in Fig. 17, in a weld metal formation step S21 in the manufacturing method of a welded structure according to embodiment 5, a welding torch 5 is moved from one side in a first direction DR1 to the other side in the first direction DR1 to melt the first main surface 1b side of the first member 1 and the second end surface 2a side of the second member 2 to form a weld metal portion 3.

[0086] In the auxiliary heating step S22 in the method for manufacturing a welded structure according to the fifth embodiment, the first auxiliary torch 6a and the second auxiliary torch 6b are moved from one side in the first direction DR1 to the other side in the first direction DR1 together with the welding torch 5. At this time, the first auxiliary torch 6a heats the first main surface 1b without melting it, and the second auxiliary torch 6b heats the second main surface 2b without melting it.

[0087] The first auxiliary torch 6a and the second auxiliary torch 6b are located on one side in the first direction DR1 of the welding torch 5. Preferably, the positions of the first auxiliary torch 6a and the second auxiliary torch 6b in the first direction DR1 overlap with the position in the first direction DR1 of the solidification brittle temperature region 52 formed by the welding torch 5.

[0088] Although not shown, in the method for manufacturing a welded structure according to the fifth embodiment, a third auxiliary torch 6c and a fourth auxiliary torch 6d may be used instead of the first auxiliary torch 6a and the second auxiliary torch 6b, or the third auxiliary torch 6c and the fourth auxiliary torch 6d may be used together with the first auxiliary torch 6a and the second auxiliary torch 6b. When the third auxiliary torch 6c and the fourth auxiliary torch 6d are used, the third auxiliary torch 6c and the fourth auxiliary torch 6d heat the first main surface 1b and the second main surface 2b, respectively, on the other side of the welding torch 5 in the first direction DR1 so as not to melt them.

[0089] (Effects of the manufacturing method of the welded structure according to the fifth embodiment) According to the method for manufacturing a welded structure in accordance with the fifth embodiment, even when a T-joint is formed by welding, the occurrence of hot cracking can be suppressed.

[0090] (Other embodiments) The fifth embodiment describes the case where a T-joint is formed by welding, the first, second and fourth embodiments describe the case where a butt joint is formed by welding, and the third embodiment describes the case where a lap joint is formed by welding, but the present invention is also applicable to the case where other joints (for example, corner joints) are formed by welding.

[0091] Although the embodiments of the present invention have been described above, the above-described embodiments can be modified in various ways. Furthermore, the scope of the present invention is not limited to the above-described embodiments. The scope of the present invention is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0092] 1 first member, 1a first end surface, 2 second member, 2a second end surface, 3 weld metal portion, 4 heat-affected zone, 5 welding torch, 6a first auxiliary torch, 6b second auxiliary torch, 6c third auxiliary torch, 6d fourth auxiliary torch, 7 first portion, 8 second portion, 51 molten pool, 52 solidification brittle temperature region, 1b first main surface, 2b second main surface, DR1 first direction, DR2 second direction, S1 preparation process, S2 welding process, S21 weld metal forming process, S22 auxiliary heating process, W width, T1, T2 thickness.

Claims

1. A method for manufacturing a welded structure having a weld metal portion extending along a first direction and a first portion and a second portion sandwiching the weld metal portion in a second direction intersecting the first direction, forming the weld metal part by moving a welding torch along the first direction from one side in the first direction to the other side in the first direction; and heating at least one of the first portion and the second portion so as not to melt by moving at least one auxiliary torch along the first direction from one side in the first direction to the other side in the first direction during at least a portion of the time the welding torch is moving, each of the positions of the at least one auxiliary torch in the first direction is offset from the position of the welding torch in the first direction; the at least one auxiliary torch includes a first auxiliary torch that heats the first portion and a second auxiliary torch that heats the second portion; the first auxiliary torch and the second auxiliary torch face each other in the second direction, the first auxiliary torch and the second auxiliary torch are located on one side of the welding torch in the first direction, a solidification brittle temperature region in which a liquid phase and a solid phase coexist is formed adjacent to one side of the molten pool formed by the welding torch in the first direction, The first auxiliary torch and the second auxiliary torch face the solidification brittle temperature region in the second direction.

2. the at least one auxiliary torch includes a third auxiliary torch that heats the first portion and a fourth auxiliary torch that heats the second portion; the third auxiliary torch and the fourth auxiliary torch are located on the other side of the welding torch in the first direction, The method for manufacturing a welded structure according to claim 1 , wherein the third auxiliary torch and the fourth auxiliary torch face each other in the second direction.

3. the first portion is a first member; The method for manufacturing a welded structure according to claim 1 or 2, wherein the second portion is a second member.

4. a thickness of the first member and a thickness of the second member are equal to or greater than 16 mm and equal to or less than 40 mm; The method for manufacturing a welded structure according to claim 3 , wherein an end face of the first member facing the second member and an end face of the second member facing the first member form a groove.

5. A method for manufacturing a welded structure including: a first member including a first main surface and a first end surface; a second member including a second main surface and a second end surface, the second member being disposed on the first member such that the second end surface faces the first main surface; and a weld metal portion extending along a first direction and joining the first member and the second member, forming the weld metal part by moving a welding torch along the first direction from one side in the first direction to the other side in the first direction; and heating at least one of the first main surface and the second main surface so as not to melt the first main surface by moving at least one auxiliary torch along the first direction from one side in the first direction to the other side in the first direction during at least a portion of the time while the welding torch is moving, each of the positions of the at least one auxiliary torch in the first direction is offset from the position of the welding torch in the first direction; the at least one auxiliary torch includes a first auxiliary torch that heats the first main surface and a second auxiliary torch that heats the second main surface; the first auxiliary torch and the second auxiliary torch are aligned in the first direction; the first auxiliary torch and the second auxiliary torch are located on one side of the welding torch in the first direction, a solidification brittle temperature region in which a liquid phase and a solid phase coexist is formed adjacent to one side of the molten pool formed by the welding torch in the first direction, The first auxiliary torch and the second auxiliary torch face the solidification brittle temperature region.

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