Method for manufacturing lap fillet welded joints, method for setting the overlap width of lap fillet welded joints, and lap fillet welded joints

Abstract

To provide a technique for suppressing the occurrence and the deformation of a lap fillet-welded joint.SOLUTION: A method for welding a lap fillet-welded joint comprises a welding step of lap fillet-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 and second steel materials are welded so as to satisfy "W1≥(0.2s-)(0.45t-1.3T))×V / 2.5", in which W1 denotes the lap width (mm) of the first and second steel materials, T denotes the thickness (mm) of the first steel material, t denotes the thickness (mm) of the second steel material, V (mm / s) denotes a welding speed, 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 method for manufacturing an overlap fillet weld joint, a method for setting an overlap width of an overlap fillet weld joint, and an overlap fillet weld joint.

Background Art

[0002] In the manufacture of automotive exhaust system parts and the like, overlap fillet welding is used, in which parts of two members are overlapped vertically and the end of the upper member is welded to the upper surface of the lower member. In the overlap joint obtained by this overlap fillet welding, cracking may occur in the lower member.

[0003] Therefore, conventionally, techniques for preventing cracking in overlap fillet weld joints have been proposed. For example, Patent Document 1 discloses an overlap fillet welding method in which two steel plates are overlapped, the end of the upper plate and the lower plate are melted, and welding is performed along the end of the upper plate.

[0004] In the overlap fillet welding method disclosed in Patent Document 1, the distance between the melted portion and the end of the lower plate is defined by an equation using the welding speed and the plate thickness of the lower plate as variables. This prevents cracking in the lower plate.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, as a result of the inventors' investigations, it was found that even when the welded joint is manufactured to meet the requirements described in Patent Document 1, cracks may still occur in the lower member. Furthermore, in order to improve the reliability of lap fillet welded joints as components, it is necessary not only to prevent the occurrence of such cracks, but also to suppress the deformation caused by welding.

[0007] Therefore, the present invention aims to provide a technology for appropriately suppressing the occurrence of cracks and deformation in lap fillet welded joints. [Means for solving the problem]

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

[0009] (1) A welding process is performed in which a portion of a first steel material having a predetermined thickness is placed on top of a second steel material having a predetermined thickness, and a fillet weld is performed between the edge of the first steel material and the surface of the second steel material so as to form a weld along the edge of the first steel material. A method for manufacturing a lap fillet welded joint, wherein the welding process involves welding the first steel material and the second steel material such that the following equations (i), (ii), and (iii) are satisfied. W1≧(0.2s-(0.45t-1.3T))×V / 2.5 (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 and second steel materials, T represents the thickness (mm) of the first steel material, t represents the thickness (mm) of the second steel material, V represents the welding speed (mm / s), and s represents the gap (mm) between the first and second steel materials in a cross section perpendicular to the welding line direction of the weld, and is 0 or greater.

[0010] (2) The method for manufacturing an overlap fillet welded joint as described in (1) above, wherein the gap between the first steel material and the second steel material is 0.2 mm or more.

[0011] (3) The method for manufacturing an 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 such that the following equation (iv) is satisfied. (0.2s-(0.45t-1.3T))×V / 2.5≦W1≦5.0+(0.2s-(0.45t-1.3T))×V / 2.5 (iv) In the above formula, W1 represents the overlap width (mm) of the first and second steel materials, T represents the thickness (mm) of the first steel material, t represents the thickness (mm) of the second steel material, V represents the welding speed (mm / s), and s represents the gap (mm) between the first and second steel materials in a cross section perpendicular to the welding line direction of the weld, and is 0 or greater.

[0012] (4) A method for setting the overlap width between the first steel material and the second steel material when manufacturing an overlapped fillet welded joint by overlapping a portion of the 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 the surface of the second steel material so that a welded portion is formed along the edge of the first steel material, A method for setting the overlap width of an overlap fillet weld joint, wherein the overlap width is set such that the following equations (i), (ii), and (iii) are satisfied. W1≧(0.2s-(0.45t-1.3T))×V / 2.5 (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 and second steel materials, T represents the thickness (mm) of the first steel material, t represents the thickness (mm) of the second steel material, V represents the welding speed (mm / s), and s represents the gap (mm) between the first and second steel materials in a cross section perpendicular to the welding line direction of the weld, and is 0 or greater.

[0013] (5) The gap between the first steel material and the second steel material is 0.2 mm or more, a method for setting the overlap width of the overlap fillet welded joint as described in (4) above.

[0014] The method for setting the overlapping width of the overlapping fillet weld joint according to (4) or (5) above, wherein the overlapping width is set so that the following formula (iv) is satisfied. (0.2s - (0.45t - 1.3T)) × V / 2.5 ≤ W1 ≤ 5.0 + (0.2s - (0.45t - 1.3T)) × V / 2.5 ···(iv) In the above formula, W1 represents the overlapping 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, V represents the welding speed (mm / s), s represents the gap (mm) between the first steel material and the second steel material in the cross-section perpendicular to the welding line direction of the welded part, and it is 0 or more.

[0015] (7) An overlapping fillet weld joint in which a part of the first steel material having a predetermined thickness is overlapped on the second steel material having a predetermined thickness so that a gap is formed, and the edge and the surface of the second steel material are fillet welded by a welded part formed along the edge of the first steel material. An overlapping fillet weld joint that satisfies the following formula (v). (D2 - D1) / L ≤ 0.01 ···(v) In the above formula, D1 represents the displacement amount (mm) in the thickness direction before welding of the part corresponding to the welded part on the back surface of the second steel material, D2 represents the displacement amount (mm) in the thickness direction after welding of the part corresponding to the welded part on the back surface of the second steel material, and L represents the length (mm) in the welding line direction of the welded part.

Effect of the Invention

[0016] According to the present invention, the occurrence of cracks and deformation of the overlapping fillet weld joint can be appropriately suppressed.

Brief Description of the Drawings

[0017] [Figure 1] FIG. 1 is a view showing an example of an overlapping fillet weld joint. [Figure 2] FIG. 2 is an enlarged cross-sectional view showing the vicinity of the welded part of the overlapping fillet weld joint of FIG. 1. [Figure 3] FIG. 3 is a view showing the analysis result. [Figure 4] FIG. 4 is a diagram for explaining the deformation mode in the vicinity of the welded part of the welded joint. [Figure 5] FIG. 5 is a diagram for explaining the deformation mode in the vicinity of the welded part of the welded joint. [Figure 6] FIG. 6 is a diagram showing the analysis results. [Figure 7] FIG. 7 is a diagram showing the results of the heat transfer analysis. [Figure 8] FIG. 8 is a diagram showing an example of the deformation mode of the lower steel material. [Figure 9] FIG. 9 is a diagram for explaining the manufacturing method of the fillet lap welded joint. [Figure 10] FIG. 10 is a diagram for explaining the method of measuring the displacement amount on the back surface of the lower steel material. [Figure 11] FIG. 11 is a diagram showing a modified example of the fillet lap welded joint.

MODE FOR CARRYING OUT THE INVENTION

[0018] (Examination by the present inventor) The present inventor has conducted a detailed examination on the technology for preventing cracks and deformation of the fillet lap welded joint. Specifically, in the fillet lap welded joint 100 (hereinafter abbreviated as the welded joint 100) including two steel materials 10 and 12 as shown in FIG. 1, a detailed examination has been conducted on the cracks and deformation occurring in the steel material 12. As a result, the findings described below were obtained. In FIG. 1, (a) is a perspective view showing the welded joint 100, and (b) is a schematic cross-sectional view showing the b-b portion of the welded joint 100 in (a).

[0019] The welded joint 100 shown in FIG. 1 is manufactured by fillet welding the edge portion 10a to the surface 12a of the steel material 12 so that a welded portion (weld metal) 14 is formed along the edge portion 10a of the steel material 10 in a state where a part of the steel material 10 is overlapped on the steel material 12, similar to a conventional general fillet lap welded joint.

[0020] Figure 1 shows the stacking direction X of the steel materials 10 and 12, the welding line direction Y of the welded joint 14, and the direction Z (hereinafter referred to as the width direction Z of the welded joint 14) perpendicular to the stacking direction X and the welding line direction Y. The stacking direction X is parallel to the thickness direction of the steel materials 10 and 12. In this specification, the steel material 10 side is considered the front side of the welded joint 100, and the steel material 12 side is considered the back side of the welded joint 100 in the stacking direction X.

[0021] The inventors investigated the deformation pattern (deformation pattern after cooling) of the welded joint 100 by performing thermal stress analysis using the finite element method. Specifically, a three-dimensional analysis 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. When manufacturing the welded joint 100, a gap s may be provided between the steel material 10 and the steel material 12 in the stacking direction X due to various factors, as shown in Figure 2. In this analysis as well, a gap of 0.5 mm was provided between the steel material 10 and the steel material 12. Figure 3 shows the analysis results.

[0022] Figure 3 shows the analysis results near the weld 14. Figure 3(a) shows the analysis results of an analysis model with an overlap width W1 set to 3 mm, and Figure 3(b) shows the analysis results of an analysis model with an overlap width W1 set to 8 mm. In this analysis, the physical properties of steel materials 10 and 12 were set assuming ferritic stainless steel (17Cr-1.2Mo-0.2Ti-0.09Si-0.02C,N), and the physical properties of the weld 14 were set assuming austenitic stainless steel (WEL MIG 308 manufactured by Nippon Welding Rod Co., Ltd.). The thickness of steel material 10 was set to 1.0 mm, and the length in the width direction Z of steel material 10 was set to 60 mm. The thickness of steel material 12 was set to 1.0 mm, and the length in the width direction Z of steel material 12 was set to 60 mm. Furthermore, in this analysis, it was assumed that during welding (heating and cooling), deformation in the stacking direction X of the welded joint 100 was constrained outside the vicinity of the weld and the overlap (for steel material 10, more than 5 mm outside the end of the overlap 12c of steel material 12 (see Figure 4), and for steel material 12, more than 30 mm outside the end of the overlap 12c). The welding speed was set to 13.3 mm / s.

[0023] As shown in Figure 3(a), when the overlap width W1 is small, tensile strain occurs in the portion of the back surface 12b of the steel material 12 that faces the weld 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 Figure 3(b), when the overlap width W1 is large, compressive strain occurs in the portion of the steel material 12 near the weld 14. It is thought that this compressive strain can prevent cracks from occurring on the back surface 12b of the steel material 12. The reasons why the manner in which strain occurs differs depending on the overlap width W1, as shown in Figures 3(a) and (b), will be explained below.

[0024] Figures 4 and 5 illustrate the deformation of the welded joint 100 near the welded portion 14. (a) shows the welded joint 100 during heating, and (b) shows the welded joint 100 during cooling. Figure 4 shows the deformation when the overlap width between the steel material 10 and the steel material 12 is set to a small value, and Figure 5 shows the deformation when the overlap width between the steel material 10 and the steel material 12 is set to a large value.

[0025] As shown in Figure 4(a), when the overlap width between steel material 10 and steel material 12 is small, when steel material 12 is heated during welding, the surface 12a side of steel material 12 expands thermally in the width direction Z with respect to the weld 14. Along with this thermal expansion, the back surface 12b side of steel material 12 also elongates in the width direction Z, causing tensile strain in the width direction Z. Of steel material 12, the portion on the steel material 10 side of the weld 14 in the width direction Z (hereinafter referred to as the overlap portion 12c) tends to become hot when heated. For this reason, in the portion of steel material 12 near the weld 14, the overlap portion 12c side does not experience a large restraining force and is prone to thermal expansion. On the other hand, of steel material 12, the portion opposite to the overlap portion 12c as viewed from the weld 14 (hereinafter referred to as the non-overlapping portion 12d) is easily cooled by thermal diffusion. Therefore, the deformation of the non-overlapping portion 12d side of the vicinity of the weld 14 is somewhat suppressed because it is constrained by the non-overlapping portion 12d. As a result, in the portion of the steel material 12 near the weld 14, the amount of thermal expansion toward the overlapping portion 12c side tends to be greater than the amount of thermal expansion toward the non-overlapping portion 12d side. Furthermore, during subsequent cooling, as shown in Figure 4(b), the thermal contraction of the weld 14 causes a force to act on the steel material 12 that attempts to deform it into a V-shape with the weld 14 as the bottom when viewed from the direction Y of the weld line of the weld 14. As a result, the overlapping portion 12c curves toward the steel material 10 side, and tensile strain occurs on the back surface 12b of the steel material 12 in the width direction Z. It is presumed that cracks will occur on the back surface 12b side of the steel material 12 due to these tensile strains.

[0026] As shown in Figure 5(a), even when the overlap width between steel material 10 and steel material 12 is large, when steel material 12 is heated during welding, the surface 12a side of steel material 12 undergoes thermal expansion in the width direction Z centered on the weld 14. However, when the overlap width between steel material 10 and steel material 12 is large, the overlap portion 12c is easily cooled by thermal diffusion, and the deformation of the overlap portion 12c is suppressed. Therefore, when the overlap width between steel material 10 and steel material 12 is large, the portion of steel material 12 near the weld 14 is constrained from both the overlap portion 12c side and the non-overlapping portion 12d side. As a result, compressive strain occurs in the portion of steel material 12 on the back surface 12b side near the weld 14. During subsequent cooling, the welded portion 14 undergoes thermal contraction, as shown in Figure 5(b). However, since the portion of the steel material 12 near the welded portion 14 is constrained from both the overlapping portion 12c and the non-overlapping portion 12d, the deformation shown in Figure 4(b) does not occur. This maintains the compressive strain on the back surface 12b of the steel material 12. It is presumed that these compressive strains prevent cracking on the back surface 12b of the steel material 12.

[0027] Furthermore, the inventors also investigated the relationship between welding speed and strain generated near the weld. Specifically, they investigated the relationship between welding speed and the widthwise Z strain generated near the weld 14 of the welded joint 100 after cooling by thermal stress analysis using a three-dimensional analysis model of the welded joint 100. In this analysis as well, a gap of 0.5 mm was provided between the steel material 10 and the steel material 12, similar to the analysis described above. The material, dimensions, and constraint conditions of the steel materials 10 and 12, as well as the material of the weld 14, were set in the same way as in the analysis described above. The overlap width W1 was set to 3 mm so that tensile strain would easily occur on the back surface 12b side of the steel material 12. The welding speeds were set to 13.0 mm / s and 7.0 mm / s. Figure 6 shows the analysis results.

[0028] As shown in Figure 6(a), when the welding speed is high, 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 Figure 6(b), when the welding speed is low, no tensile strain occurs on the back surface 12b of the steel material 12.

[0029] As described above, this analysis revealed that reducing the welding speed can suppress the occurrence of tensile strain on the back surface 12b of the steel material 12. To clarify the cause of this, the inventors created an analytical model simulating the welded joint 100 and investigated the relationship between the welding speed and the temperature distribution generated in the steel material 12 during welding by performing a heat transfer analysis. In this heat transfer analysis, the physical properties of the steel materials 10 and 12 were set assuming ferritic stainless steel, and the physical properties of the welded joint 14 (filler material) were set assuming austenitic stainless steel. The thickness of the steel materials 10 and 12 was set to 1.5 mm each, and a gap of 1.0 mm was provided between the steel materials 10 and 12. In addition, the overlap width W1 between the steel materials 10 and 12 was set to 3 mm.

[0030] Figure 7 shows the results of the heat transfer analysis. Specifically, Figure 7(a) shows the temperature distribution on the back surface 12b of steel material 12 when welding steel materials 10 and 12 at a welding speed of 13.3 mm / s, and Figure 7(b) shows the temperature distribution on the back surface 12b of steel material 12 when welding steel materials 10 and 12 at a welding speed of 5.0 mm / s. From the results shown in Figure 7, it can be seen that the length of the high-temperature region in the welding line direction Y (vertical direction in the plane of the paper in Figure 7) can be reduced by decreasing the welding speed.

[0031] From the above results, the inventors considered that by reducing the welding speed and thereby decreasing the length of the high-temperature region in the welding direction Y of the steel material 12, deformation of the steel material 12 can be suppressed. That is, by reducing the length of the high-temperature region in the welding direction Y of the welding line, the parts before and after the welding portion (hereinafter referred to as the heated portion) in the welding direction Y of the welding line become easier to cool. In this case, the heated portion is constrained by the low-temperature portions before and after the heated portion, so deformation of the heated portion is suppressed. For this reason, as shown in Figure 6(b), it is considered that reducing the welding speed suppresses the occurrence of tensile strain on the back surface 12b side of the steel material 12.

[0032] From the above, it is considered that cracking of the steel material 12 can be prevented by adjusting the overlap width W1 of 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) taking into account the welding speed, and by appropriately restraining the deformation of the steel material 12 with the steel material 10.

[0033] Furthermore, the inventors' investigations revealed that the thickness of the steel material 12 also affects its deformation and cracking. Specifically, they found that the greater the thickness of the steel material 12, the more its deformation and cracking are suppressed. In particular, cracking is suppressed when the thickness of the steel material 12 is greater than that of the steel material 10. In addition, the inventors' investigations revealed that the gap s (see Figure 2) between the steel material 10 and the steel material 12 also significantly affects the occurrence of cracks in the steel material 12. Specifically, the larger the gap s, the weaker the restraint of the steel material 12 by the steel material 10 becomes, making the steel material 12 more susceptible to deformation. As a result, cracks are more likely to occur in the steel material 12.

[0034] To improve the reliability of the welded joint 100 as a component, it is preferable to suppress deformation that occurs during welding. In this regard, as described above, the deformation of the steel material 12 as viewed from the welding line direction Y (V-shaped deformation: see Figure 4) can be suppressed by appropriately adjusting the overlap width of the steel material 10 and the steel material 12, the thickness of the steel material 12, and the size of the gap between the steel material 10 and the steel material 12. On the other hand, in order to further improve the reliability of the welded joint 100, it is also preferable to suppress the deformation of the steel material 12 as viewed from the width direction Z of the welded portion 14.

[0035] As described above, the steel material 12 is subjected to a force that causes it to deform into a V-shape with the weld 14 as the bottom when viewed from the weld line direction Y, due to thermal contraction in the width direction Z of the weld 14. Furthermore, when welding the steel material 10 and the steel material 12, a force due to thermal contraction of the weld 14 in the weld line direction Y also acts on the steel material 12. Thus, due to the thermal contraction of the weld 14 in the width direction Z and the weld line direction Y, a force acts on the steel material 12 that causes it to buckle in a convex shape toward the front side (towards the steel material 10) when viewed from the width direction Z, as shown by arrow A in Figure 8. For this reason, in order to suppress the deformation of the steel material 12 when viewed from the width direction Z, it is necessary to suppress the thermal contraction of the weld 14 in the weld line direction Y.

[0036] In this regard, as explained in Figure 7, when the welding speed is low, the parts before and after the welding area (heated area) in the welding direction Y are more easily cooled. In this case, the heated area is constrained by the low-temperature areas before and after it, so thermal contraction of the welded area 14 in the welding direction Y is suppressed. As a result, it is considered that deformation of the steel material 12 so that it becomes convex toward the front side (steel material 10 side) when viewed from the width direction Z of the welded area 14 is suppressed. Therefore, from the viewpoint of suppressing deformation of the steel material 12 when viewed from the width direction Z, it is preferable to determine the overlap width W1 of the steel material 10 and the steel material 12 while considering the welding speed.

[0037] Based on the above findings, the inventors further investigated the appropriate overlap width between steel material 10 and steel material 12 and found that cracking and deformation of steel material 12 can be suppressed by welding steel material 10 and steel material 12 such that the following equations (i), (ii), and (iii) are satisfied. W1≧(0.2s-(0.45t-1.3T))×V / 2.5 (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, V represents the welding speed (mm / s), and s represents the gap (mm) between steel material 10 and steel material 12 in a cross section perpendicular to the welding line direction Y of the welded joint 14, and is 0 or greater.

[0038] (Embodiments of the present invention) The 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. Figure 9 is a diagram illustrating the method for manufacturing a lap fillet welded joint according to one embodiment of the present invention. In the following, the case of manufacturing the welded joint 100 shown in Figure 1 will be described. 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.

[0039] As shown in Figure 9(a), when manufacturing the welded joint 100, first, a portion of the steel material 10 is overlapped onto the steel material 12. In this specification, overlapping a portion of the steel material 10 onto the steel material 12 means arranging the steel material 10 and the steel material 12 such that a portion of the steel material 10 overlaps the steel material 12 when viewed from the thickness direction of the steel material 12. Therefore, overlapping a portion of the steel material 10 onto the steel material 12 is not limited to the case where a portion of the steel material 10 is placed on the steel material 12 so as to be in contact with the steel material 12, but also includes the case where a portion of the steel material 10 is placed on the steel material 12 so as to form a gap between the steel material 10 and the steel material 12. In the following description, the steel material placed on the upper side will be referred to as the upper steel material, and the steel material placed on the lower side will be referred to as the lower steel material.

[0040] Various steels such as carbon steel or stainless steel can be used as the material for the upper steel member 10 and the lower steel member 12. Furthermore, from the viewpoint of suppressing deformation of the welded joint 100 caused by welding, it is preferable to use materials with low thermal deformation for the upper steel member 10 and the lower steel member 12. Specifically, it is preferable to use materials with high thermal conductivity or low thermal expansion coefficients for the upper steel member 10 and the lower steel member 12. The thermal conductivity of the upper steel member 10 and the lower steel member 12 is preferably, for example, 25.0 W / (m·K) or higher at 800°C. The thermal expansion coefficient of the upper steel member 10 and the lower steel member 12 is preferably, for example, 13.0 × 10⁻⁶ at 800°C. -6 It is preferable that the temperature is below / ℃. When stainless steel is used for the upper steel material 10 and the lower steel material 12, it is preferable to use ferritic stainless steel. 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 steel plates.

[0041] Next, as shown in Figures 1 and 9(b), a fillet weld is performed on the surface 12a of the lower steel member 12 using a welding machine 20 (see Figure 9) and filler material (not shown) so that a weld (weld metal) 14 is formed along the edge 10a of the upper steel member 10 (welding process). This produces a welded joint 100. The penetration depth of the weld 14 into the lower steel member 12 is set, for example, to 1 / 4 or more and 3 / 4 or less of the thickness of the lower steel member 12. In Figure 9(b), the torch of the welding machine 20 is shown. As the filler material, for example, an alloy of the same type as the base material or austenitic stainless steel can be used.

[0042] In this embodiment, the heat input in the welding process is set to, for example, 100 to 710 J / mm, and the welding speed is set to 2.0 to 13.3 mm / s. As the shielding gas, for example, a mixed gas of argon and oxygen is used.

[0043] In the welding process, the upper steel member 10 and the lower steel member 12 are held by a holding member (not shown) and welded together. Referring to Figures 1, 2, and 9, in this embodiment, the upper steel member 10 and the lower steel member 12 are welded together such that equations (i), (ii), and (iii) below are satisfied. W1≧(0.2s-(0.45t-1.3T))×V / 2.5 (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 member 10 and the lower steel member 12, T represents the thickness (mm) of the upper steel member 10, t represents the thickness (mm) of the lower steel member 12, V represents the welding speed (mm / s), and s represents the gap (mm) between the upper steel member 10 and the lower steel member 12 in a cross section perpendicular to the welding line direction Y of the welded joint 14, and is 0 or greater.

[0044] Furthermore, in order to properly weld the upper steel member 10 and the lower steel member 12, it is preferable that the overlap width W1 between the upper steel member 10 and the lower steel member 12 be 2.0 mm or more.

[0045] In this embodiment, the gap s between the upper steel member 10 and the lower steel member 12 is set to 0 mm or more. A gap s is not required. If a gap s exists, the upper limit of the gap s is set to be less than or equal to the smallest value among 1.0 mm, the thickness T (mm) of the upper steel member 10, and the thickness t (mm) of the lower steel member 12. For example, if the thickness T is 0.4 mm and the thickness t is 0.6 mm, the gap s is set to 0.4 mm or less. Also, for example, if the thickness T is 1.2 mm and the thickness t is 1.1 mm, the gap s is set to 1.0 mm or less.

[0046] As mentioned above, the gap s between the upper steel member 10 and the lower steel member 12 greatly affects the occurrence of cracks in the lower steel member 12. When a gap s exists, it is thought that the larger the gap s, the more likely cracks are to occur in the lower steel member 12. In this respect, according to the present invention, cracks can be suppressed even when a gap s exists. From this viewpoint, the present invention is preferably used when a gap s exists, that is, when the gap s is greater than 0 mm, more preferably when it is 0.1 mm or more, and even more preferably when it is 0.2 mm or more.

[0047] Furthermore, it is thought that cracks are more likely to occur in the lower steel member 12 when the gap s is continuous in the welding direction Y. However, according to the present invention, cracks can be suppressed even when the gap s is continuous in the welding direction Y. From this viewpoint, the present invention is preferably used in a welded joint 100 in which a portion of the gap s is larger than 0 mm is continuously present for 50 mm or more along the welding direction Y.

[0048] In addition, in the actually manufactured welded joint 100, the gap s may not be uniform in the welding direction Y. In this case, as shown in Figures 4(b) and 5(b), the maximum distance between the portion of the surface 12a of the lower steel member 12 that is close to the weld 14 (for example, a portion 1.0 mm in the width direction Z from the weld 14) and the upper steel member 10 is taken as the value of the gap s.

[0049] If the overlap width between the upper steel member 10 and the lower steel member 12 becomes too large, the weight of the welded joint 100 will increase. Therefore, in order to reduce the weight of the welded joint 100 while preventing cracking of the lower steel member 12, it is preferable to weld the upper steel member 10 and the lower steel member 12 such that equation (iv) below is satisfied. (0.2s-(0.45t-1.3T))×V / 2.5≦W1≦5.0+(0.2s-(0.45t-1.3T))×V / 2.5 (iv) In the above formula, W1 represents the overlap width (mm) of the upper steel member 10 and the lower steel member 12, T represents the thickness (mm) of the upper steel member 10, t represents the thickness (mm) of the lower steel member 12, V represents the welding speed (mm / s), and s represents the gap (mm) between the upper steel member 10 and the lower steel member 12 in a cross section perpendicular to the welding line direction Y of the welded joint 14, and is 0 or greater.

[0050] Furthermore, since the welded portion 14 melts into the edge portion 10a of the upper steel member 10, the overlap width W2 (see Figure 2) between the upper steel member 10 and the lower steel member 12 in the welded joint 100 becomes about 0.8 to 1.2 mm smaller than the overlap width W1 between the upper steel member 10 and the lower steel member 12 before welding. Therefore, in the cross section perpendicular to the welding line direction Y of the welded portion 14, it is preferable that the welded joint 100 according to this embodiment satisfies equation (vi) below, and more preferably satisfies equation (vii) below. W2≧(0.2s-(0.45t-1.3T))×V / 2.5-1.2 ···(vi) (0.2s-(0.45t-1.3T))×V / 2.5-1.2≦W2≦4.2+(0.2s-(0.45t-1.3T))×V / 2.5 (vii) In the above formula, W2 represents the overlap width (mm) of the upper steel member 10 and the lower steel member 12, T represents the thickness (mm) of the upper steel member 10, t represents the thickness (mm) of the lower steel member 12, V represents the welding speed (mm / s), and s represents the gap (mm) between the upper steel member 10 and the lower steel member 12 in a cross section perpendicular to the welding line direction Y of the welded joint 14, and is 0 or greater.

[0051] In the welded joint 100 according to this embodiment, as shown in Figure 2, the overlap width W2 of the upper steel member 10 and the lower steel member 12 is determined by using the position 14a where the welded portion 14 is most deeply fused towards the upper steel member 10 as the end of the upper steel member 10.

[0052] (Effects of this embodiment)

[0053] According to the manufacturing method of the lap fillet welded joint of this embodiment, it is possible to suppress the occurrence of cracks on the back surface 12b side of the lower steel member 12 in the manufactured welded joint 100. Furthermore, deformation of the steel member 12 as viewed from the width direction Z of the welded portion 14 can also be suppressed. Specifically, a lap fillet welded joint that satisfies the following equation (v) can be obtained. (D2-D1) / L≦0.01 ···(v) As will be explained in detail in Figure 10 below, in the above formula, D1 represents the displacement (mm) in the thickness direction (lamination direction X) of the portion corresponding to the welded portion 14 on the back surface 12b of the lower steel material 12 before welding, D2 represents the displacement (mm) in the thickness direction of the portion corresponding to the welded portion 14 on the back surface 12b of the lower steel material 12 after welding, and L represents the length (mm) in the welding line direction Y of the welded portion 14.

[0054] Figure 10 is a diagram illustrating the displacement in equation (v) above. Specifically, Figure 10(a) is a schematic cross-sectional view of the lower steel member 12 and the weld 14, passing through the center of the weld 14 and perpendicular to the width direction Z, and Figure 10(b) is a conceptual diagram showing the shape of the back surface 12b of the lower steel member 12.

[0055] Referring to Figure 10, the portion of the back surface 12b of the lower steel member 12 corresponding to the weld 14 in the above equation (v) refers to the region 13 (hereinafter referred to as the measurement region 13) located below the weld 14 in a cross section that passes through the center of the weld 14 and is perpendicular to the width direction Z of the back surface 12b.

[0056] Furthermore, the displacement D2 in the thickness direction of the measurement area 13 after welding is calculated by measuring the position of the measurement area 13 in the thickness direction (lamination direction X) along the welding line direction Y of the welded part 14, and taking the difference between the highest and lowest positions in the thickness direction. Note that, as shown in Figure 10(b), if the lower steel material 12 is deformed to be convex toward the front side, the displacement D2 is calculated using the average of the heights of the measurement start point 13a (one end of the measurement area 13 in the welding line direction Y) and the measurement end point 13b (the other end of the measurement area 13 in the welding line direction Y) as the height of the lowest position. Also, although not shown in the figure, if the lower steel material 12 is deformed to be convex toward the bottom, the displacement D2 is calculated using the average of the heights of the measurement start point 13a and the measurement end point 13b as the height of the highest position.

[0057] The displacement D1 in the thickness direction of the measurement area 13 before welding is determined, for example, based on the design drawing of the welded joint 100. Specifically, the design drawing identifies the planned location of the weld 14 on the lower steel member 12. Then, the displacement in the thickness direction (lamination direction X) of the portion of the back surface 12b of the lower steel member 12 corresponding to the planned location of the weld 14 is determined from the design drawing. When welding flat plate-shaped members together, the design drawing is usually an ideal shape without curves, so D1 = 0.

[0058] (modified version) In the embodiments described above, the case in which steel plates (plate-shaped members) are used as the first and second steel materials was explained. However, the shapes of the first and second steel materials are not limited to the examples described above, and steel materials of various shapes can be used as the first and second steel materials. For example, cylindrical steel materials (steel pipes) may be used as the first and / or second steel materials. Also, molded products of various shapes may be used as the first and / or second steel materials. Specifically, for example, the present invention may be applied to a welded joint 100 as shown in Figure 11.

[0059] In the welded joint 100 shown in Figure 11, both the upper steel member 10 (outer steel member) and the lower steel member 12 (inner steel member) have a cylindrical shape. In this embodiment as well, by manufacturing the welded joint 100 to satisfy the above requirements, cracking and deformation of the lower steel member 12 can be suppressed. In the welded joint 100 shown in Figure 11, the upper steel member 10 and the lower steel member 12 have a cylindrical shape, but the upper steel member 10 and the lower steel member 12 may have a rectangular tubular shape. In addition, molded products of various other shapes may be used as the upper steel member 10 and the lower steel member 12.

[0060] The present invention will be described more specifically below with reference to examples, but the present invention is not limited to these examples. [Examples]

[0061] Welded joints having the same configuration as the welded joint 100 shown in Figures 1 and 2 were fabricated by changing the thickness T of the upper steel member 10, the thickness t of the lower steel member 12, the gap s between the upper steel member 10 and the lower steel member 12, the overlap width W1 between the upper steel member 10 and the lower steel member 12, and the welding speed. The presence or absence of cracks occurring on the back surface 12b of the lower steel member 12 was investigated. In addition, the displacement (mm) of the portion corresponding to the welded joint 14 on the back surface 12b of the lower steel member 12 before and after welding was also investigated.

[0062] Specifically, two rectangular steel plates measuring 60 mm x 150 mm were prepared as test plates. One steel plate (upper steel material 10) was positioned so that its back surface and the other steel plate (lower steel material 12) overlapped along their long sides. Arc welding was performed to join one end face of the upper steel plate, extending in the thickness direction, to the surface of the lower steel plate, which was approximately perpendicular to it, thereby obtaining a welded joint. The penetration depth of the weld 14 into the lower steel material 12 was set to half the thickness of the lower steel material 12. The length of the weld 14 was set to 100 mm.

[0063] The upper steel member 10 and the lower steel member 12 were made of ferritic stainless steel (17Cr-1.2Mo-0.2Ti-0.09Si-0.02C,N). The filler material was made of austenitic stainless steel (WEL MIG 308 manufactured by Nippon Welding Rod Co., Ltd.), and the shielding gas was Ar + 2% O2.

[0064] The presence or absence of cracks was confirmed by visual inspection. Specifically, a crack was determined to have occurred if a crack of 2 mm or more in length occurred along the welding line direction Y. In addition, the displacement of the back surface 12b of the lower steel member 12 before and after welding was measured using the method described with reference to Figure 10. The welding conditions and investigation results are shown in Table 1 below. In Table 1, the overlap width W1 represents the overlap width of the upper steel member 10 and the lower steel member 12 during welding, as shown in Figures 2 and 9, and the lower limit W0 of the overlap width W1 is the value obtained by the right side of equation (i) above. Also in Table 1, the deformation amount of the back surface of the lower steel member 12 indicates the difference (D2-D1) in the displacement amount of the back surface 12b of the lower steel member 12 before and after welding. In this embodiment, D1=0. Furthermore, as mentioned above, since the length of the welded part 14 is 100 mm, if the deformation amount of the back surface of the lower steel member 12 is 1 mm or less, the requirements of equation (v) above are satisfied.

[0065] [Table 1]

[0066] As shown in Table 1, in the welded joints of the present invention examples No. 2, 3, 5, 6, 9, 11, 12, 14, 15, and 18, where the overlap width W1 of steel material 10 and steel material 12 during welding was greater than or equal to the lower limit W0, not only did no cracks occur on the back surface 12b of steel material 12, but the amount of deformation of the back surface 12b was also small, less than 1 mm.

[0067] On the other hand, in the welded joints of comparative examples No. 1, 4, 7, 10, 13, 16, and 17, where the overlap width W1 of the upper steel material 10 and the lower steel material 12 during welding was smaller than the lower limit value W0, cracks occurred on the back surface 12b of the steel material 12. In particular, in the welded joints of comparative examples No. 1 and 7, the amount of deformation on the back surface 12b of the lower steel material 12 was also large. Furthermore, in the welded joint of comparative example No. 8, the occurrence of cracks on the back surface 12b of the lower steel material 12 was prevented, but the amount of deformation on the back surface 12b was large.

[0068] From the above results, it can be seen that the method for manufacturing a lap fillet welded joint that satisfies the requirements of the present invention can appropriately suppress the occurrence of cracks and deformation of the welded joint.

[0069] As mentioned above, increasing the thickness of the lower steel member 12 compared to the upper steel member 10 makes it easier to suppress the occurrence of cracks in the lower steel member 12. In other words, if the thickness of the lower steel member 12 cannot be sufficiently increased compared to the upper steel member 10, it becomes difficult to suppress the occurrence of cracks in the lower steel member 12. Even in such cases, as can be seen from the results of the present invention example No. 9, the present invention makes it possible to appropriately suppress the occurrence of cracks and deformation of welded joints. [Industrial applicability]

[0070] According to the present invention, it is possible to suppress the occurrence of cracks and deformation in lap fillet welded joints. [Explanation of symbols]

[0071] 10,12 Steel material 10a Edge 12a surface 12b Reverse side 14. Welded section 100 Welded Joints

Claims

1. The method includes a welding step of fillet welding a portion of a first steel material having a predetermined thickness onto a second steel material having a predetermined thickness, so that a welded portion is formed along the edge of the first steel material and the surface of the second steel material. A method for manufacturing a lap fillet welded joint, wherein the welding process involves welding the first steel material and the second steel material such that the following equations (i), (ii), and (iii) are satisfied. W １ ≧(0.2s-(0.45t-1.3T))×V / 2.5 ・・・(i) 0.5≦T≦3.0...(ii) 0.5≦t≦3.0...(iii) In the above formula, W １ θ represents the overlap width (mm) of the first and second steel materials, T represents the thickness (mm) of the first steel material, t represents the thickness (mm) of the second steel material, V represents the welding speed (mm / s), and s represents the gap (mm) between the first and second steel materials in a cross section perpendicular to the welding line direction of the weld, and is 0 or greater.

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

3. The method for manufacturing an overlap fillet welded joint according to claim 1 or 2, wherein the welding step involves welding the first steel material and the second steel material such that the following equation (iv) is satisfied. (0.2s-(0.45t-1.3T))×V / 2.5≦W １ ≦5.0+(0.2s-(0.45t-1.3T))×V / 2.5 ・・・(iv) In the above formula, W １ θ represents the overlap width (mm) of the first and second steel materials, T represents the thickness (mm) of the first steel material, t represents the thickness (mm) of the second steel material, V represents the welding speed (mm / s), and s represents the gap (mm) between the first and second steel materials in a cross section perpendicular to the welding line direction of the weld, and is 0 or greater.

4. A method for setting the overlap width between a first steel material and a second steel material when manufacturing an overlapped 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 then fillet welding the edge of the first steel material to the surface of the second steel material so that a welded portion is formed along the edge of the first steel material, A method for setting the overlap width of an overlap fillet welded joint, wherein the overlap width is set such that the following equations (i), (ii), and (iii) are satisfied. W １ ≧(0.2s-(0.45t-1.3T))×V / 2.5 ・・・(i) 0.5≦T≦3.0...(ii) 0.5≦t≦3.0...(iii) In the above formula, W １ θ represents the overlap width (mm) of the first and second steel materials, T represents the thickness (mm) of the first steel material, t represents the thickness (mm) of the second steel material, V represents the welding speed (mm / s), and s represents the gap (mm) between the first and second steel materials in a cross section perpendicular to the welding line direction of the weld, and is 0 or greater.

5. The method for setting the overlap width of an overlap fillet welded joint according to claim 4, wherein the gap between the first steel material and the second steel material is 0.2 mm or more.

6. A method for setting the overlap width of an overlap fillet welded joint according to claim 4 or 5, wherein the overlap width is set such that the following equation (iv) is satisfied. (0.2s-(0.45t-1.3T))×V / 2.5≦W １ ≦5.0+(0.2s-(0.45t-1.3T))×V / 2.5 ・・・(iv) In the above formula, W １ θ represents the overlap width (mm) of the first and second steel materials, T represents the thickness (mm) of the first steel material, t represents the thickness (mm) of the second steel material, V represents the welding speed (mm / s), and s represents the gap (mm) between the first and second steel materials in a cross section perpendicular to the welding line direction of the weld, and is 0 or greater.

7. A lap fillet welded joint is formed in which a portion of a first steel material having a predetermined thickness is overlapped on a second steel material having a predetermined thickness such that a gap is formed, and the edge of the first steel material and the surface of the second steel material are fillet welded by a weld formed along the edge of the first steel material, A lap fillet welded joint that satisfies equation (v) below. (D2-D1) / L≦0.01...(v) In the above formula, D1 represents the displacement (mm) in the thickness direction of the portion corresponding to the weld on the back surface of the second steel material before welding, D2 represents the displacement (mm) in the thickness direction of the portion corresponding to the weld on the back surface of the second steel material after welding, and L represents the length (mm) of the weld in the direction of the weld line.

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