Manufacturing method of lap fillet welded joint, method of setting overlap width of lap fillet welded joint, and lap fillet welded joint

Abstract

To provide a technique for suppressing generation of cracks in a lap fillet-welded joint.SOLUTION: A method for welding a lap fillet-welded joint comprises a welding step of lap-welding the edge of a first steel material and the surface of a second steel material so as to form a welded part along the edge of the first steel material. In the welding step, the first steel material and the second welding material are welded so as to satisfy (W1≥6.0+2s-(t-T)) in a section orthogonal to a welding line of the welded part, in which W1 denotes the lap width (mm) of the first and second steel materials, T denotes the thickness of the first steel material, t denotes the thickness (mm) of the second steel material, and s denotes a gap (mm) between the first and second steel materials.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a manufacturing method of a lap fillet welded joint, a method for setting the overlap width of a lap fillet welded joint, and a lap fillet welded joint. [Background technology]

[0002] In the manufacture of automobile exhaust system parts and the like, lap fillet welding is used, in which parts of two members are overlapped one on the other and the edge of the upper member is welded to the top surface of the lower member. In fillet weld joints obtained by this lap fillet welding, cracks can sometimes occur in the lower member.

[0003] Therefore, techniques have been proposed to prevent cracks from occurring in fillet welded joints. For example, Patent Document 1 discloses a lap fillet welding method in which two steel plates are overlapped, the edge of the upper plate and the lower plate are melted, and welding is performed along the edge of the upper plate.

[0004] In the lap fillet welding method disclosed in Patent Document 1, the distance between the fusion zone and the edge of the lower plate is determined by a formula that uses the welding speed and the thickness of the lower plate as variables, thereby preventing cracks from occurring in the lower plate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-285722 Summary of the Invention [Problem to be solved by the invention]

[0006] However, as a result of investigations by the present inventors, it has been found that even when a welded joint is manufactured so as to satisfy the requirements set forth in Patent Document 1, cracks may occur in the lower member.

[0007] Therefore, an object of the present invention is to provide a technique for appropriately suppressing the occurrence of cracks in lap fillet welded joints. [Means for solving the problem]

[0008] The present invention relates to the following method for manufacturing a lap fillet welded joint, a method for setting the overlap width of a lap fillet welded joint, and a lap fillet welded joint.

[0009] (1) A welding process is provided in which a part of a first steel material having a predetermined thickness is overlapped on a second steel material having a predetermined thickness, and the edge portion of the first steel material and a surface of the second steel material are fillet welded together by fillet welding so as to form a weld along the edge portion of the first steel material; In the welding step, the first steel material and the second steel material are welded together so that the following formulas (i), (ii), and (iii) are satisfied in a cross section of the weld portion perpendicular to the weld line direction. W1≧6.0+2s-(tT) (i) 0.5≦T≦3.0 (ii) 0.5≦t≦3.0 (iii) In the above formula, W1 represents the overlap width (mm) of the first steel material and the second steel material, T represents the thickness (mm) of the first steel material, t represents the thickness (mm) of the second steel material, and s represents the gap (mm) between the first steel material and the second steel material, and is 0 or more.

[0010] (2) The method for manufacturing a lap fillet welded joint according to (1) above, wherein the gap between the first steel material and the second steel material is 0.2 mm or more.

[0011] (3) A method for manufacturing a lap fillet welded joint according to (1) or (2) above, wherein in the welding step, the first steel material and the second steel material are welded together so that the following formula (iv) is satisfied in the cross section perpendicular to the weld line direction of the weld portion: 6.0+2s-(tT)≦W1≦8.0+2s-(tT) ···(iv) In the above formula, W1 represents the overlap width (mm) of the first steel material and the second steel material, T represents the thickness (mm) of the first steel material, t represents the thickness (mm) of the second steel material, and s represents the gap (mm) between the first steel material and the second steel material, and is 0 or more.

[0012] (4) A method for setting an overlap width between a first steel material and a second steel material when manufacturing a fillet welded joint by overlapping a portion of a first steel material having a predetermined thickness on a second steel material having a predetermined thickness and fillet welding the edge of the first steel material and a surface of the second steel material so as to form a weld along the edge of the first steel material, A method for setting an overlap width of a lap fillet welded joint, wherein the overlap width is set so that the following equations (i), (ii), and (iii) are satisfied in a cross section of the weld perpendicular to the weld line direction: W1≧6.0+2s-(tT) (i) 0.5≦T≦3.0 (ii) 0.5≦t≦3.0 ···(iii) In the above formula, W1 represents the overlap width (mm) of the first steel material and the second steel material, T represents the thickness (mm) of the first steel material, t represents the thickness (mm) of the second steel material, and s represents the gap (mm) between the first steel material and the second steel material, and is 0 or more.

[0013] (5) A method for setting the overlap width of a lap fillet welded joint according to (4) above, wherein the gap between the first steel material and the second steel material is 0.2 mm or more.

[0014] (6) A method for setting an overlap width of a lap fillet welded joint according to (4) or (5) above, wherein the overlap width is set so that the following formula (iv) is satisfied in the cross section of the weld perpendicular to the weld line direction: 6.0+2s-(tT)≦W1≦8.0+2s-(tT) ···(iv) In the above formula, W1 represents the overlap width (mm) of the first steel material and the second steel material, T represents the thickness (mm) of the first steel material, t represents the thickness (mm) of the second steel material, and s represents the gap (mm) between the first steel material and the second steel material, and is 0 or more.

[0015] (7) A lap fillet welded joint in which a portion of a first steel material having a predetermined thickness is overlapped on a second steel material having a predetermined thickness, and the edge portion and the surface of the second steel material are fillet welded by a weld formed along the edge portion of the first steel material, A lap fillet welded joint, wherein the following formulas (v), (ii), and (iii) are satisfied in a cross section of the welded portion perpendicular to the weld line direction: W2≧4.8+2s-(tT) (v) 0.5≦T≦3.0 (ii) 0.5≦t≦3.0 (iii) In the above formula, W2 represents the overlap width (mm) of the first steel material and the second steel material, T represents the thickness (mm) of the first steel material, t represents the thickness (mm) of the second steel material, and s represents the gap (mm) between the first steel material and the second steel material, and is 0 or more.

[0016] (8) The lap fillet welded joint according to (7) above, wherein the gap between the first steel material and the second steel material is 0.2 mm or more.

[0017] (9) The lap fillet welded joint according to (7) or (8) above, wherein the following formula (vi) is satisfied in a cross section of the welded portion perpendicular to the weld line direction: 4.8+2s-(tT)≦W2≦7.2+2s-(tT) ···(vi) In the above formula, W2 represents the overlap width (mm) of the first steel material and the second steel material, T represents the thickness (mm) of the first steel material, t represents the thickness (mm) of the second steel material, and s represents the gap (mm) between the first steel material and the second steel material, and is 0 or more. [Effects of the Invention]

[0018] According to the present invention, it is possible to appropriately suppress the occurrence of cracks in lap fillet welded joints. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram showing an example of a lap fillet weld joint. [Figure 2]FIG. 2 is an enlarged cross-sectional view showing the vicinity of the welded portion of the lap fillet welded joint of FIG. [Figure 3] FIG. 3 is a diagram showing the analysis results. [Figure 4] FIG. 4 is a diagram for explaining deformation in the vicinity of the welded portion of the welded joint. [Figure 5] FIG. 5 is a diagram for explaining deformation in the vicinity of the welded portion of the welded joint. [Figure 6] FIG. 6 is a diagram for explaining a method for manufacturing a lap fillet welded joint. [Figure 7] FIG. 7 is a diagram showing a modified example of a lap fillet welded joint. DETAILED DESCRIPTION OF THE INVENTION

[0020] (Study by the inventor) The present inventors have conducted detailed studies on techniques for preventing cracks in lap fillet welded joints. Specifically, they conducted detailed studies on cracks that occur in the steel material 12 in a fillet lap welded joint 100 (hereinafter abbreviated as welded joint 100) that includes two steel materials 10, 12, as shown in Fig. 1. As a result, they have obtained the findings described below. In Fig. 1, (a) is a perspective view showing the welded joint 100, and (b) is a schematic cross-sectional view showing the bb portion of the welded joint 100 in (a).

[0021] The welded joint 100 shown in FIG. 1 is manufactured in the same manner as a conventional fillet lap welded joint by overlapping a portion of steel material 10 on steel material 12 and fillet welding edge portion 10a of steel material 10 to surface 12a of steel material 12 so that a weld (weld metal) 14 is formed along edge portion 10a of steel material 10.

[0022] 1 shows a stacking direction X of the steel materials 10 and 12, a weld line direction Y of the welded portion 14, and a direction Z (hereinafter referred to as the width direction Z of the welded portion 14) perpendicular to the stacking direction X and the weld line direction Y. The stacking direction X is a direction parallel to the thickness directions of the steel materials 10 and 12. In this specification, the steel material 10 side in the stacking direction X is referred to as the front side of the welded joint 100, and the steel material 12 side is referred to as the back side of the welded joint 100.

[0023] As a result of detailed studies by the present inventors on cracks that occur in the steel material 12 of the welded joint 100, it has been found that the deformation of the steel material 12 during welding has a significant effect on the occurrence of cracks in the steel material 12. Furthermore, as a result of studies by the present inventors, it has been found that the overlap width W1 between the steel material 10 and the steel material 12 (the length in the width direction Z of the portion where the steel material 10 and the steel material 12 overlap each other) has an effect on the deformation of the steel material 12. This will be explained in detail below.

[0024] The present inventors investigated the deformation of the welded joint 100 (deformation after cooling) by conducting thermal stress analysis using the finite element method. Specifically, a two-dimensional analytical model simulating the welded joint 100 was created, and the relationship between the overlap width W1 and the strain in the width direction Z that occurs near the welded portion 14 of the welded joint 100 after cooling was investigated. Note that, when manufacturing the welded joint 100, as shown in FIG. 2, a gap s may be provided between the steel material 10 and the steel material 12 in the lamination direction X due to various factors. In this analysis, a gap of 0.5 mm was also provided between the steel material 10 and the steel material 12. The analysis results are shown in FIG. 3.

[0025] Note that Figure 3 shows the analysis results for the vicinity of the weld 14. Figure 3(a) shows the analysis results for an analytical model in which the overlap width W1 was set to 3 mm, and Figure 3(b) shows the analysis results for an analytical model in which the overlap width W1 was set to 13 mm. In this analysis, the physical properties of the steel materials 10 and 12 were set to ferritic stainless steel (17Cr-1.2Mo-0.2Ti-0.09Si-0.02C,N), and the physical properties of the weld 14 were set to austenitic stainless steel (WEL MIG 308 manufactured by Nippon Welding Rod Co., Ltd.). The thickness of the steel material 10 was 1.0 mm, and the length of the steel material 10 in the width direction Z was 60 mm. The thickness of the steel material 12 was 1.0 mm, and the length of the steel material 12 in the width direction Z was 60 mm. In addition, in this analysis, it was assumed that during welding (heating and cooling), deformation in the plate thickness direction X was constrained outside the vicinity of the welded portion and the vicinity of the overlapping portion of the welded joint 100 (for the steel material 10, outside 5 mm from the end of the overlapping portion 12c of the steel material 12 (see Figure 4), and for the steel material 12, outside 30 mm from the end of the overlapping portion 12c).

[0026] As shown in FIG. 3(a), when the overlap W1 is small, tensile strain occurs in the portion of the back surface 12b of the steel material 12 that faces the welded portion 14 in the thickness direction of the steel material 12. In this case, it is thought that cracks are more likely to occur in the portion where tensile strain occurs. On the other hand, as shown in FIG. 3(b), when the overlap W1 is large, compressive strain occurs in the portion of the steel material 12 near the welded portion 14. It is thought that this compressive strain can prevent cracks from occurring on the back surface 12b of the steel material 12. Below, we will explain why the manner in which strain occurs differs depending on the overlap W1, as shown in FIGS. 3(a) and 3(b).

[0027] 4 and 5 are diagrams for explaining deformation modes in the vicinity of the welded portion 14 of the welded joint 100, where (a) is a diagram showing the welded joint 100 during heating, and (b) is a diagram showing the welded joint 100 during cooling. Note that Fig. 4 is a diagram showing deformation modes when the overlap width between the steel materials 10 and 12 is set small, and Fig. 5 is a diagram showing deformation modes when the overlap width between the steel materials 10 and 12 is set large.

[0028] As shown in FIG. 4( a), when the overlap width between the steel material 10 and the steel material 12 is small, when the steel material 12 is heated during welding, the front surface 12a side of the steel material 12 thermally expands in the width direction Z around the welded portion 14. This thermal expansion also causes the back surface 12b side of the steel material 12 to elongate in the width direction Z, resulting in tensile strain in the width direction Z. Note that the portion of the steel material 12 closer to the steel material 10 than the welded portion 14 in the width direction Z (hereinafter referred to as the overlapping portion 12c) is likely to reach a high temperature during heating. Therefore, of the portion of the steel material 12 near the welded portion 14, the overlapping portion 12c side is not subject to a large restraining force and is therefore likely to thermally expand. Meanwhile, the portion of the steel material 12 opposite the overlapping portion 12c from the welded portion 14 (hereinafter referred to as the non-overlapping portion 12d) is likely to cool by thermal diffusion. Therefore, the non-overlapping portion 12d side of the portion near the welded portion 14 is restrained by the non-overlapping portion 12d, and deformation is somewhat suppressed. Therefore, in the portion of the steel material 12 near the welded portion 14, the amount of thermal expansion toward the overlapping portion 12c is likely to be greater than the amount of thermal expansion toward the non-overlapping portion 12d. Furthermore, during subsequent cooling, as shown in FIG. 4(b), the welded portion 14 thermally contracts, and a force acts on the steel material 12 to deform it into a V-shape with the welded portion 14 as the bottom when viewed from the weld line direction Y of the welded portion 14. This causes the overlapping portion 12c to bend toward the steel material 10, and tensile strain is generated in the back surface 12b of the steel material 12 in the width direction Z. It is estimated that these tensile strains cause cracks on the back surface 12b side of the steel material 12.

[0029] As shown in FIG. 5( a), when the overlap width between the steel material 10 and the steel material 12 is large, when the steel material 12 is heated during welding, the front surface 12a side of the steel material 12 thermally expands in the width direction Z around the welded portion 14. However, when the overlap width between the steel material 10 and the steel material 12 is large, the overlapped portion 12c is easily cooled by thermal diffusion, and deformation of the overlapped portion 12c is suppressed. Therefore, when the overlap width between the steel material 10 and the steel material 12 is large, the portion of the steel material 12 near the welded portion 14 is restrained from the overlapped portion 12c side and the non-overlapped portion 12d side. As a result, compressive strain occurs in the portion on the back surface 12b side of the steel material 12 near the welded portion 14. During the subsequent cooling, as shown in Fig. 5(b), the welded portion 14 thermally contracts, but the portion of the steel material 12 near the welded portion 14 is constrained from the overlapping portion 12c side and the non-overlapping portion 12d side, so the deformation shown in Fig. 4(b) does not occur. This maintains the compressive strain occurring on the back surface 12b side of the steel material 12. It is presumed that these compressive strains can prevent cracks from occurring on the back surface 12b side of the steel material 12.

[0030] From the above, it is considered that cracking of steel material 12 can be prevented by adjusting the overlap width W1 of steel material 10 and steel material 12 (the length in the width direction Z of the part where steel material 10 and steel material 12 overlap each other) and by appropriately restraining the deformation of steel material 12 by steel material 10.

[0031] As a result of the inventor's investigation, it has been found that deformation of the steel material 12 can also be suppressed by increasing the thickness of the steel material 12. In particular, by making the steel material 12 thicker than the steel material 10, cracking can be more easily suppressed. Furthermore, as a result of the inventor's investigation, it has been found that the gap s (see FIG. 2 ) between the steel material 10 and the steel material 12 also has a significant effect on the occurrence of cracks in the steel material 12. Specifically, the larger the gap s, the weaker the constraint on the steel material 12 by the steel material 10, making the steel material 12 more likely to deform. As a result, cracks are more likely to occur in the steel material 12.

[0032] Based on the above findings, the inventors further investigated the appropriate overlap width of steel material 10 and steel material 12, and found that the occurrence of cracks in steel material 12 can be suppressed by welding steel material 10 and steel material 12 together so that the following equations (i), (ii), and (iii) are satisfied in a cross section perpendicular to the weld line direction Y of weld portion 14. W1≧6.0+2s-(tT) (i) 0.5≦T≦3.0 (ii) 0.5≦t≦3.0 (iii) In the above formula, W1 represents the overlap width (mm) of steel material 10 and steel material 12, T represents the thickness (mm) of steel material 10, t represents the thickness (mm) of steel material 12, and s represents the gap (mm) between steel material 10 and steel material 12, and is 0 or more.

[0033] (Embodiments of the present invention) A method for manufacturing a lap fillet welded joint according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 6 is a diagram for explaining a method for manufacturing a lap fillet welded joint according to one embodiment of the present invention. The following describes the case of manufacturing the welded joint 100 shown in FIG. 1. The method for manufacturing a lap fillet welded joint according to this embodiment includes a method for setting the overlap width of the lap fillet welded joint. In this embodiment, steel material 10 corresponds to the first steel material, and steel material 12 corresponds to the second steel material.

[0034] As shown in FIG. 6( a), when manufacturing a welded joint 100, first, a portion of the steel material 10 is overlapped on the steel material 12. In this specification, overlapping a portion of the steel material 10 on the steel material 12 means arranging the steel material 10 and the steel material 12 so that a portion of the steel material 10 overlaps the steel material 12 when viewed in the thickness direction of the steel material 12. Therefore, overlapping a portion of the steel material 10 on the steel material 12 is not limited to placing a portion of the steel material 10 on the steel material 12 so that it contacts the steel material 12, but also includes placing a portion of the steel material 10 on the steel material 12 so that a gap is formed between the steel material 10 and the steel material 12. In the following description, the steel material arranged on the upper side will be referred to as the upper steel material, and the steel material arranged on the lower side will be referred to as the lower steel material.

[0035] As the material for the upper steel material 10 and the lower steel material 12, various steels such as carbon steel or stainless steel (ferritic stainless steel, austenitic stainless steel, duplex stainless steel, etc.) can be used. In this embodiment, for example, stainless steel containing Ti and / or Nb is used. In this embodiment, the overlapping portions of the upper steel material 10 and the lower steel material 12 have a flat plate shape. In this embodiment, the upper steel material 10 and the lower steel material 12 are each a steel plate.

[0036] The thicknesses of the upper steel material 10 and the lower steel material 12 are each set to 0.5 mm or more and 3.0 mm or less. As described above, by making the lower steel material 12 thicker than the upper steel material 10, it becomes easier to suppress the occurrence of cracks in the lower steel material 12. In other words, if the thickness of the lower steel material 12 cannot be made sufficiently thicker than the upper steel material 10, it becomes difficult to suppress the occurrence of cracks in the lower steel material 12. Even in such cases, according to the present invention, the occurrence of cracks in the lower steel material 12 can be appropriately suppressed. The relationship between the thickness of the upper steel material 10 and the thickness of the lower steel material 12 will be described later.

[0037] Next, as shown in FIGS. 1 and 6(b), a welding machine 20 (see FIG. 6) and a filler metal (not shown) are used to fillet weld the edge 10a of the upper steel material 10 to the surface 12a of the lower steel material 12 so as to form a weld (weld metal) 14 along the edge 10a of the upper steel material 10 (welding process). This produces a welded joint 100. The penetration depth of the weld 14 into the lower steel material 12 is set to, for example, between ¼ and ¾ of the thickness of the lower steel material 12. Note that a torch of the welding machine 20 is shown in FIG. 6(b). As the filler metal, for example, austenitic stainless steel or duplex stainless steel can be used.

[0038] In this embodiment, the heat input in the welding process is set to, for example, 150 to 300 J / mm, and the welding speed is set to 10 to 20 mm / s. As the shielding gas, for example, a mixed gas of argon and oxygen is used.

[0039] In the welding process, the upper steel material 10 and the lower steel material 12 are welded together while being held by a holding member (not shown). With reference to Figures 1, 2 and 6, in this embodiment, the upper steel material 10 and the lower steel material 12 are welded together so that the following formulas (i), (ii) and (iii) are satisfied in a cross section of the welded portion 14 that is perpendicular to the weld line direction Y. W1≧6.0+2s-(tT) (i) 0.5≦T≦3.0 (ii) 0.5≦t≦3.0 (iii) In the above formula, W1 represents the overlap width (mm) of the upper steel material 10 and the lower steel material 12, T represents the thickness (mm) of the upper steel material 10, t represents the thickness (mm) of the lower steel material 12, and s represents the gap (mm) between the upper steel material 10 and the lower steel material 12.

[0040] In this embodiment, the gap s between the upper steel material 10 and the lower steel material 12 is set to 0 mm or more. Gap s does not have to be provided. Furthermore, when gap s exists, the upper limit of gap s is set to 1.0 mm or less, whichever is smaller among the thickness T (mm) of the upper steel material 10 and the thickness t (mm) of the lower steel material 12. For example, when thickness T is 0.4 mm and thickness t is 0.6 mm, gap s is set to 0.4 mm or less. Furthermore, when thickness T is 1.2 mm and thickness t is 1.1 mm, gap s is set to 1.0 mm or less.

[0041] As mentioned above, when gap s exists, the larger gap s becomes, the more likely cracks are to occur in the lower steel material 12. For this reason, the present invention is preferably used when gap s exists, i.e., when gap s is larger than 0 mm, more preferably when gap s is 0.1 mm or more, and even more preferably when gap s is 0.2 mm or more.

[0042] Furthermore, when the gap s exists continuously in the weld line direction Y, cracks are more likely to occur in the lower steel material 12. For this reason, the effects of the present invention are preferably used in a welded joint 100 in which a portion where the gap s is larger than 0 mm exists continuously for 50 mm or more along the weld line direction Y.

[0043] If the overlap width between the upper steel material 10 and the lower steel material 12 becomes too large, the weight of the welded joint 100 increases. Therefore, in order to prevent cracking of the lower steel material 12 while realizing a reduction in the weight of the welded joint 100, it is preferable to weld the upper steel material 10 and the lower steel material 12 so that the following formula (iv) is satisfied in a cross section of the welded portion 14 perpendicular to the weld line direction Y. 6.0+2s-(tT)≦W1≦8.0+2s-(tT) ···(iv) In the above formula, W1 represents the overlap width (mm) of the upper steel material 10 and the lower steel material 12, T represents the thickness (mm) of the upper steel material 10, t represents the thickness (mm) of the lower steel material 12, and s represents the gap (mm) between the upper steel material 10 and the lower steel material 12, and is 0 or more.

[0044] Since the welded portion 14 melts into the edge portion 10a of the upper steel material 10, the overlap width W2 between the upper steel material 10 and the lower steel material 12 in the welded joint 100 is approximately 0.8 to 1.2 mm smaller than the overlap width W1 between the upper steel material 10 and the lower steel material 12 before welding. Therefore, it is preferable that the welded joint 100 according to this embodiment satisfies the following formula (v) in a cross section of the welded portion 14 perpendicular to the weld line direction Y. W2≧4.8+2s-(tT) (v) In the above formula, W2 represents the overlap width (mm) of the upper steel material 10 and the lower steel material 12, T represents the thickness (mm) of the upper steel material 10, t represents the thickness (mm) of the lower steel material 12, and s represents the gap (mm) between the upper steel material and the lower steel material, and is 0 or more.

[0045] In the lap fillet welded joint according to this embodiment, as shown in Figure 2, the overlap width W2 of the upper steel material 10 and the lower steel material 12 in the welded joint 100 is determined by defining the position 14a of the weld 14 that is most deeply penetrated into the upper steel material 10 as the end of the upper steel material 10.

[0046] Furthermore, in order to prevent cracking of the lower steel material 12 while realizing a reduction in the weight of the welded joint 100, it is preferable that the welded joint 100 satisfies the following formula (vi) in a cross section perpendicular to the weld line direction Y of the welded portion 14. 4.8+2s-(tT)≦W2≦7.2+2s-(tT) ···(vi) In the above formula, W2 represents the overlap width (mm) of the upper steel material 10 and the lower steel material 12, T represents the thickness (mm) of the upper steel material 10, t represents the thickness (mm) of the lower steel material 12, and s represents the gap (mm) between the upper steel material 10 and the lower steel material 12, and is 0 or more.

[0047] (Variation) In the above-described embodiment, the case where steel plates (plate-shaped members) are used as the first steel material and the second steel material has been described. However, the shapes of the first steel material and the second steel material are not limited to the above-described example, and steel materials of various shapes can be used as the first steel material and the second steel material. For example, a cylindrical steel material (steel pipe) may be used as the first steel material and / or the second steel material. Furthermore, formed products of various shapes may be used as the first steel material and / or the second steel material. Specifically, for example, the present invention may be applied to a welded joint 100 as shown in FIG. 7.

[0048] In the welded joint 100 shown in FIG. 7, both the upper steel material 10 (outer steel material) and the lower steel material 12 (inner steel material) have a cylindrical shape. In this embodiment, too, by manufacturing the welded joint 100 so as to satisfy the above-mentioned requirements, it is possible to suppress the occurrence of cracks in the lower steel material 12. Note that in the welded joint 100 shown in FIG. 7, the upper steel material 10 and the lower steel material 12 have a cylindrical shape, but the upper steel material 10 and the lower steel material 12 may also have a rectangular cylindrical shape. Furthermore, formed products of various other shapes may be used as the upper steel material 10 and the lower steel material 12.

[0049] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples. [Example]

[0050] Welded joints having a configuration similar to that of the welded joint 100 shown in Figures 1 and 2 were fabricated by varying the thickness T of the upper steel material 10, the thickness t of the lower steel material 12, the gap s between the upper steel material 10 and the lower steel material 12, and the overlap width W1 between the upper steel material 10 and the lower steel material 12. The presence or absence of cracks on the back surface 12b of the lower steel material 12 was investigated. Specifically, two rectangular steel plates measuring 60 mm x 150 mm were prepared as test plates. The back surface of one steel plate (the upper steel material 10) and the front surface of the other steel plate (the lower steel material 12) were arranged so that their long sides overlapped. Arc welding was performed to join one end face extending in the thickness direction of the upper steel plate to the surface of the lower steel plate, which was approximately perpendicular to the end face, to obtain a welded joint. The penetration depth of the weld 14 into the lower steel material 12 was set to 1 / 2 the thickness of the lower steel material 12. The length of the weld 14 was set to 100 mm. The occurrence of cracks was confirmed visually. Specifically, cracks were judged to have occurred when a crack of 2 mm or more in length occurred along the weld line direction Y. The welding conditions and investigation results are shown in Table 1 below. The upper steel material 10 and the lower steel material 12 were made of ferritic stainless steel (NSSC436S: 17Cr-1.2Mo-0.2Ti-0.09Si-0.02C,N manufactured by Nippon Steel Stainless Steel Corporation) and austenitic stainless steel (SUS316L). The filler metal was austenitic stainless steel (WEL MIG 308 manufactured by Nippon Welding Rod Co., Ltd.), and the shielding gas was Ar + 2% O2.

[0051] In Table 1, overlap width W1 represents the overlap width of the upper steel material 10 and the lower steel material 12 during welding, as shown in Figures 2 and 6, the lower limit value W0 of overlap width W1 is the value calculated from the right side of equation (i) above, and overlap width W2 represents the overlap width of the upper steel material 10 and the lower steel material 12 in the welded joint 100, as shown in Figure 2. In addition, the lower limit value of overlap width W2 is the value calculated from the right side of equation (v) above.

[0052] [Table 1]

[0053] As shown in Table 1, in the welded joints of the present invention examples Nos. 2, 3, 5, 6, 8, 9, 11, 12, 14, 15, 19, and 20, in which the overlap width W1 of the steel material 10 and the steel material 12 during welding was greater than the lower limit W0, no cracks occurred on the back surface 12b of the steel material 12.

[0054] On the other hand, in the welded joints of comparative examples Nos. 1, 4, 7, 10, 13, and 16 to 18 in which the overlap width W1 of the steel material 10 and the steel material 12 during welding was smaller than the lower limit W0, cracks occurred on the back surface 12b of the steel material 12.

[0055] From the above results, it can be seen that the manufacturing method of a lap fillet welded joint that satisfies the requirements of the present invention can suppress the occurrence of cracks in the welded joint. [Industrial Applicability]

[0056] According to the present invention, by appropriately setting the overlap width between the first steel material and the second steel material, it is possible to suppress the occurrence of cracks in the lap fillet welded joint. [Explanation of symbols]

[0057] 10,12 Steel material 10a Edge 12a surface 12b Back 14 Welded parts 100 Welded joints

Claims

1. A method for setting an overlap width between a first steel material and a second steel material when manufacturing a lap fillet welded joint by overlapping a portion of a first steel material having a predetermined thickness on a second steel material having a predetermined thickness and fillet welding the edge portion of the first steel material and a surface of the second steel material so as to form a weld along the edge portion of the first steel material, a method for setting an overlap width of a lap fillet welded joint, the method comprising: setting the overlap width so that the following formulas (i), (ii), and (iii) are satisfied in a cross section of the weld perpendicular to the weld line direction: W １ ≧6.0+2s-(t-T) ・・・(i) 0.5≦T≦3.0...(ii) 0.5≦t≦3.0...(iii) In the above formula, W １ represents the overlap width (mm) of the first steel material and the second steel material, T represents the thickness (mm) of the first steel material, t represents the thickness (mm) of the second steel material, and s represents the gap (mm) between the first steel material and the second steel material, and is 0 or more.

2. 2. The method for setting an overlap width of a lap fillet welded joint according to claim 1, wherein a gap between the first steel material and the second steel material is 0.2 mm or more.

3. 3. The method for setting an overlap width of a lap fillet welded joint according to claim 1, wherein the overlap width is set so that the following formula (iv) is satisfied in the cross section perpendicular to the weld line direction of the weld. 6.0+2s-(t-T)≦W １ ≦8.0+2s-(t-T) ・・・(iv) In the above formula, W １ represents the overlap width (mm) of the first steel material and the second steel material, T represents the thickness (mm) of the first steel material, t represents the thickness (mm) of the second steel material, and s represents the gap (mm) between the first steel material and the second steel material, and is 0 or more.

4. A lap fillet welded joint in which a portion of a first steel material having a predetermined thickness is overlapped on a second steel material having a predetermined thickness, and the edge portion and a surface of the second steel material are fillet welded by a weld formed along the edge portion of the first steel material, A lap fillet welded joint, wherein the following formulas (v), (ii), and (iii) are satisfied in a cross section of the weld portion perpendicular to the weld line direction: W ２ ≧4.8+2s-(t-T) ・・・(v) 0.5≦T≦3.0...(ii) 0.5≦t≦3.0...(iii) In the above formula, W ２ represents the overlap width (mm) of the first steel material and the second steel material, T represents the thickness (mm) of the first steel material, t represents the thickness (mm) of the second steel material, s represents the gap (mm) between the first steel material and the second steel material and is 0 or more, and W2 is determined by taking the position of the weld that is most deeply penetrated into the first steel material as the end of the first steel material.

5. 5. The lap fillet welded joint according to claim 4, wherein a gap between the first steel material and the second steel material is 0.2 mm or more.

6. The lap fillet welded joint according to claim 4 or 5, wherein the following formula (vi) is satisfied in a cross section of the weld portion perpendicular to the weld line direction: 4.8+2s-(t-T)≦W ２ ≦7.2+2s-(t-T) ・・・(vi) In the above formula, W ２ represents the overlap width (mm) of the first steel material and the second steel material, T represents the thickness (mm) of the first steel material, t represents the thickness (mm) of the second steel material, s represents the gap (mm) between the first steel material and the second steel material and is 0 or more, and W2 is determined by taking the position of the weld that is most deeply penetrated into the first steel material as the end of the first steel material.

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