Overlap fillet welded joint, and method for manufacturing an overlap fillet welded joint

Abstract

To reduce a porosity defect rate in a weld bead of a lap fillet welded joint.SOLUTION: A lap fillet welded joint of the present disclosure joins a first steel plate and a second steel plate via a weld bead, and satisfies the following requirements (A) to (D): (A) A total adhesion amount of a plated layer existing between the steel plates is 10 g / m2 or more and 120 g / m2 or less. (B) A thickness TA of one of the first steel plate and the second steel plate and a thickness TB of the other of the first steel plate and the second steel plate satisfy the following relationship (1). (C) A gap G between the steel plates is equal to or less than the plate thickness TA. (D) A height H of the weld bead, the plate thickness TA, and the gap G satisfy the following relationship (2). TB≤TA≤2 mm...(1), H≤TA+G+5 mm...(2).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This application discloses a lap fillet welded joint and a method for manufacturing a lap fillet welded joint. [Background technology]

[0002] Arc welding is a well-known technique for joining steel plates together. One challenge with arc welding is that the strength of the weld bead tends to decrease easily. This decrease in weld bead strength is more likely to occur when welding steel plates with a plating layer. Specifically, when welding steel plates together, including the plating layer, plating vapor becomes trapped within the weld bead, creating porosity defects, which is one of the causes of the decrease in strength.

[0003] There are two main methods for reducing porosity defects in weld beads caused by plating vapor: Method 1: A method to reduce the amount of plating vapor itself by reducing the amount of plating layer. Method 2: During welding, a path (gap) is formed between the steel plates to discharge the plating vapor, and the plating vapor is discharged on the opposite side from the weld bead.

[0004] Here, if the amount of plating layer is reduced as in Method 1 above, there is a risk that the desired corrosion resistance and other properties cannot be secured. For this reason, conventionally, when welding steel plates together with the plating layer intact, Method 2 above has been considered effective. For example, Patent Document 1 discloses a technique for providing grooves for discharging plating vapor at the welding location of the steel plate. Patent Document 2 also discloses a technique for securing a path for discharging plating vapor by pre-bending the steel plate before welding. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6965230 [Patent Document 2] Patent No. 6278291 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] As described above, conventionally, it has been considered effective to create grooves or bends in the steel plate to provide pathways (gaps) for the discharge of plating vapor in order to reduce porosity defects in the weld bead. However, according to the inventor's new findings, even if sufficient gaps are provided in the steel plate for the discharge of plating vapor, porosity defects in the weld bead may not be reduced, and in fact, they may even increase. In this respect, a new technology is needed to reduce porosity defects in the weld bead. [Means for solving the problem]

[0007] When the steel plates to be welded are thin, the plates are welded together with low heat input, which can result in a smaller molten pool. In this case, the height (thickness) of the molten pool becomes lower (thinner), and the emission of plating vapor from the surface of the molten pool may become more dominant. From this perspective, the inventors plated thin steel plates with a thickness of 2 mm or less and performed lap fillet welding to investigate the relationship between porosity defects in the weld bead and welding conditions. As a result, it was found that when welding thin steel plates with a thickness of 2 mm or less, bringing the steel plates into close contact (reducing the gap between the steel plates to suppress the emission of plating vapor to the side opposite the weld bead) can reduce porosity defects in the weld bead. Furthermore, it was found that suppressing thermal deformation of the steel plates during welding and maintaining a small gap between the steel plates is effective in bringing the steel plates into close contact. Specifically, it was found that by performing tack welding before the main welding, and by setting the interval of the tack welding to a predetermined or lower interval, it is possible to suppress the widening of the gap between steel plates due to thermal deformation during the main welding, thereby reducing porosity defects in the weld bead.

[0008] Based on the above findings, this application proposes, as one means of solving the above problem, An overlapping fillet weld joint having a first steel plate, a second steel plate, and a weld bead. The first steel plate has a first surface facing the second steel plate side and a second surface facing the side opposite to the first surface. The second steel plate has a third surface facing the first steel plate side and a fourth surface facing the side opposite to the third surface. An end portion of the second steel plate is joined to the first surface via the weld bead. A plating layer is formed on one or both of the first surface and the third surface. The total adhesion amount of the plating layer to the first surface and the third surface is 10 g / m B , or more and 120 g / m 2 or less, where the thickness T of one of the first steel plate and the second steel plate A and the thickness T of the other of the first steel plate and the second steel plate B satisfy the following relationship (1), the gap G between the first surface and the third surface is the plate thickness T A or less, the height H from the first surface to the apex of the weld bead, the plate thickness T A and the gap G satisfy the following relationship (2), the weld bead has a porosity defect rate of 7.0% or less. is disclosed.

[0009] T B ≤ T A ≤ 2 mm …(1) H ≤ T A + G + 5 mm …(2)

[0010] In the overlapping fillet weld joint of the present disclosure, there may be tack weld marks. The interval I between the tack weld marks and the plate thickness T <000001​​​​​​​​​​In the lap fillet welded joint of the present disclosure, the weld bead may have a porosity defect rate of 0.5% or more and 7.0% or less.

[0013] In the lap fillet welded joint of the present disclosure, the plating layer may contain 40% to 100% Zn by mass.

[0014] This application is one means of solving the above problem, A method for manufacturing lap fillet welded joints, The first steel plate and the second steel plate are overlapped, and tack welding is performed on the areas to be welded, and, This includes performing arc welding on the welding location where the tack weld has been applied, thereby joining the first steel plate and the second steel plate via a weld bead. The first steel plate has a first surface facing the second steel plate and a second surface facing the opposite side from the first surface. The second steel plate has a third surface facing the first steel plate and a fourth surface facing the opposite side from the third surface. The end of the second steel plate is joined to the first surface via the weld bead. A plating layer is formed on one or both of the first and third surfaces. The total amount of the plating layer deposited on the first and third surfaces is 10 g / m². 2 More than 120g / m 2 The following: Thickness T of one of the first steel plate and the second steel plate A The thickness T of the other of the first steel plate and the second steel plate. B The following relationship (1) is satisfied, The height H from the first surface to the apex of the weld bead, and the plate thickness T. A The gap G between the first surface and the third surface satisfies the following relationship (2): The spacing I of the tack welds and the plate thickness T B The following relationship (3) is satisfied: Disclose the following.

[0015] TB ≦T A ≤2mm …(1) H≦T A +G+5mm …(2) I ≤ 250 × T B …(3) [Effects of the Invention]

[0016] The welded joint described herein is formed by joining thin steel plates with a thickness of 2 mm or less together with a plating layer by lap fillet welding, wherein the height of the weld bead is below a certain level (i.e., the height of the molten pool during welding is below a certain level), and the gap between the steel plates is below a certain level. In this case, even if plating vapor enters the molten pool during welding, the plating vapor is efficiently discharged from the surface of the molten pool, and as a result, the porosity defect rate in the weld bead is reduced. [Brief explanation of the drawing]

[0017] [Figure 1] This diagram schematically shows the cross-sectional structure of an overlap fillet weld joint. The weld bead extends in the direction from back to front on the page. [Figure 2] This diagram schematically shows the planar configuration of an overlapping fillet weld joint. [Figure 3] This shows a general overview of the condition after tack welding. [Figure 4] This image shows an example of an X-ray radiograph of a weld bead in a plan view. It can be seen that the weld bead extends in the left-right direction, and that porosity defects (relatively dark areas on the inside of the weld bead compared to other parts) are present within the weld bead. [Modes for carrying out the invention]

[0018] 1. Overlap fillet weld joint One embodiment of the lap fillet weld joint described herein will be described below, but the lap fillet weld joint described herein is not limited to this embodiment.

[0019] As shown in Figures 1 and 2, an overlap fillet weld joint 100 according to one embodiment comprises a first steel plate 10, a second steel plate 20, and a weld bead 30. The first steel plate 10 has a first surface 11 facing the second steel plate 20 and a second surface 12 facing the opposite side from the first surface 11. The second steel plate 20 has a third surface 23 facing the first steel plate 10 and a fourth surface 24 facing the opposite side from the third surface 23. The end portion 20x of the second steel plate 20 is joined to the first surface 11 via a weld bead 30. Plating layers 41 and 43 are formed on one or both of the first surface 11 and the third surface 23. The total amount of plating layers 41 and 43 deposited on the first surface 11 and the third surface 23 is 10 g / m². 2 More than 120g / m 2 The following applies: Thickness T of one of the first steel plate 10 and the second steel plate 20 A The thickness T of the other of the first steel plate 10 and the second steel plate 20 B This satisfies the following relationship (1). The gap G between the first surface 11 and the third surface 23 is equal to the plate thickness T mentioned above. A The following applies: The height H from the first surface 24 to the apex P of the weld bead 30, and the plate thickness T mentioned above. A The gap G mentioned above satisfies the following relationship (2). The weld bead 30 has a porosity defect rate of 7.0% or less. T B ≦T A ≤2mm …(1) H≦T A +G+5mm …(2)

[0020] 1.1 First steel plate and second steel plate In the lap fillet welded joint 100, the first steel plate 10 and the second steel plate 20 are welded together to form a lap fillet welded structure. As shown in Figures 1 and 2, in the lap fillet welded structure, a weld bead 30 is formed at the corner between the first surface 11 of the first steel plate 10 and the tip surface of the end 20x of the second steel plate 20. In the lap fillet welded joint 100, if the side of the first steel plate 10 on which the weld bead 30 is formed (the first surface 11 side) is considered the top and the side opposite the weld bead 30 (the second surface 12 side) is considered the bottom, then the second steel plate 20 is the top plate and the first steel plate 10 is the bottom plate.

[0021] 1.1.1 1st to 4th page The first steel plate 10 has a first surface 11 facing the second steel plate 20 and a second surface 12 facing the opposite side of the first surface 11. That is, if the first surface 11 is considered the front surface of the first steel plate 10, then the second surface 12 is the back surface of the first steel plate 10. The second steel plate 20 has a third surface 23 facing the first steel plate 10 and a fourth surface 24 facing the opposite side of the third surface 23. That is, if the fourth surface 24 is considered the front surface of the second steel plate 20, then the third surface 23 is the back surface of the second steel plate 20. If the thickness of the first steel plate 10 is constant, the first surface 11 and the second surface 12 can be parallel to each other. If the thickness of the second steel plate 20 is constant, then the third surface 23 and the fourth surface 24 can be parallel to each other. The planar shapes of the first steel plate 10 and the second steel plate 20 are not particularly limited. The planar shapes of the first steel plate 10 and the second steel plate 20 may be rectangular or other than rectangular.

[0022] 1.1.2 Plate Thickness The first steel plate 10 and the second steel plate 20 each have a thickness of 2 mm or less. Thickness refers to the thickness of the base steel plate excluding the plating layer. The thickness of the first steel plate 10 and the thickness of the second steel plate 20 may be the same or different. The thickness of the first steel plate 10 is the thickness T mentioned above. A Alternatively, the above plate thickness T may be used. B It may also be the case that the thickness of the first steel plate 10 is T A If so, the thickness of the second steel plate 20 is T B Therefore, the thickness of the first steel plate 10 is T BIf so, the thickness of the second steel plate 20 is T A Here, as shown in relation (1) above, plate thickness T A The plate thickness is T B The thickness is as described above. When the thickness of each of the first steel plate 10 and the second steel plate 20 is 2 mm or less, the heat input during arc welding becomes small, which reduces the height of the molten pool, and the height of the weld bead 30, described later, tends to fall below a certain level. The lower limit of the plate thickness is not particularly limited and may be, for example, 0.6 mm or more, 0.8 mm or more, 1.0 mm or more, or 1.2 mm or more.

[0023] 1.1.3 Strength The first steel plate 10 and the second steel plate 20 can have various strengths depending on their application. At least one of the first steel plate 10 and the second steel plate 20 has a plating layer and has excellent corrosion resistance. Furthermore, it is preferable that the lap fillet weld joint 100 has high strength. For example, one or both of the first steel plate 10 and the second steel plate 20 may have a tensile strength of 400 MPa or more, 500 MPa or more, 700 MPa or more, 900 MPa or more, 1000 MPa or more, 1100 MPa or more, 1200 MPa or more, or 1500 MPa or more. That is, the tensile strength of the first steel plate 10 may be 400 MPa or more and the tensile strength of the second steel plate 20 may be less than 400 MPa, or the tensile strength of the first steel plate 10 may be less than 400 MPa and the tensile strength of the second steel plate 20 may be 400 MPa or more, or the tensile strength of both the first steel plate 10 and the second steel plate 20 may be 400 MPa or more. The first steel plate 10 and the second steel plate 20 may have similar tensile strengths, or they may have different tensile strengths. There is no particular upper limit to the tensile strength, but for example, it may be 2500 MPa or less, 2200 MPa or less, or 2000 MPa or less. In this application, the "tensile strength" of the steel plate is in accordance with JIS Z 2241:2011.

[0024] 1.1.4 Chemical composition and microstructure The first steel plate 10 and the second steel plate 20 can be made of various materials with different chemical compositions and metal structures. The first steel plate 10 and the second steel plate 20 may each be ordinary steel plates or steel plates containing additive elements such as chromium, and their chemical composition and metal structure may be adjusted to take into consideration the desired mechanical properties and formability. Regardless of the chemical composition and metal structure of the first steel plate 10 and the second steel plate 20, the effects of the lap fillet weld joint 100 will be achieved. If one or both of the first steel sheet 10 and the second steel sheet 20 are high-strength steel sheets, the chemical composition of the high-strength steel sheet is, for example, in mass%, C: 0.01~0.50%, Si: 0.01~3.50%, Mn: 0.10~5.00%, P: 0.100% or less, S: 0.0300% or less, N: 0.0100% or less, O: 0~0.020%, Al: 0~1.000%, B: 0~0.010%, Nb: 0~0.150%, Ti: 0~0.20%, Mo: It may contain 0-3.00%, Cr:0-2.00%, V:0-1.00%, Ni:0-2.00%, W:0-1.00%, Ta:0-0.10%, Co:0-3.00%, Sn:0-1.00%, Sb:0-0.50%, Cu:0-2.00%, As:0-0.050%, Mg:0-0.100%, Ca:0-0.100%, Zr:0-0.100%, Hf:0-0.100%, and REM:0-0.100%. In the above chemical composition, the lower limit of the content of optional added elements may be 0.0001% or 0.001%.

[0025] 1.2 Plating layer In the lap fillet welded joint 100, a plating layer is formed on one or both of the first surface 11 of the first steel plate 10 and the third surface 23 of the second steel plate 20. According to the inventor's findings, during lap fillet welding, a portion of the plating layer present between the upper and lower plates evaporates and becomes plating vapor, which easily causes porosity defects in the weld bead. More specifically, in the lap fillet welded joint 100 shown in Figure 1, during welding, the plating layers 41 and 43 formed on the first surface 11 facing the second steel plate 20 and the third surface 23 facing the first steel plate 10 evaporate and penetrate into the molten pool, easily causing porosity defects in the weld bead 30. As shown in Figure 1, the plating layer 42 formed on the second surface 12 of the first steel plate 10 does not substantially come into contact with the weld bead 30. Even if the molten pool were to penetrate and reach the second surface 12, the plating vapor from the plating layer 42 would not substantially affect the amount of porosity defects in the weld bead 30. The same applies to the plating layer 44 formed on the fourth surface 24 of the second steel plate; the plating vapor from the plating layer 44 would not substantially affect the amount of porosity defects in the weld bead 30.

[0026] 1.2.1 Amount of plating layer In a lap fillet welded joint 100, the total amount of plating layer 41 applied to the first surface 11 of the first steel plate 10 and the total amount of plating layer 43 applied to the third surface 23 of the second steel plate 20 can significantly affect the porosity defect rate within the weld bead 30. If this total amount is too small, problematic porosity defects within the weld bead 30 will not occur at all. On the other hand, if this total amount is too large, excessive plating vapor will enter the molten pool during welding, and it may become difficult to sufficiently reduce the porosity defect rate within the weld bead 30 even with the technology of this disclosure. In this regard, in the lap fillet welded joint 100 of this disclosure, the total amount of plating layers 41 and 43 applied to the first surface 11 and the third surface 23 is 10 g / m². 2 More than 120g / m 2 The following is important: For example, if no plating layer is formed on the first surface 11, the amount of plating layer 43 formed on the third surface 23 is 10 g / m². 2 More than 120g / m 2The following applies. Alternatively, for example, the amount of plating layer 41 adhering to the first surface 11 is 5 g / m². 2 In that case, the amount of plating layer 43 adhering to the third surface 23 is 5 g / m². 2 More than 115g / m 2 The following applies: Thus, the total amount of plating layers 41 and 43 deposited on the first surface 11 and the third surface 23 is 10 g / m². 2 More than 120g / m 2 The following conditions allow plating vapor to enter the molten pool during welding, while also efficiently discharging it from the surface of the molten pool, thereby reducing the porosity defect rate of the weld bead 30. The total amount of plating layers 41 and 43 adhering to the first surface 11 and the third surface 23 is 20 g / m². 2 More than 25g / m 2 More than 30g / m 2 More than 35g / m 2 Above, or 40g / m² 2 It may be greater than or equal to 115g / m² 2 Below 110g / m 2 Below 105g / m 2 Below 100g / m 2 Below, 95g / m 2 The following, or 90g / m 2 The following is also possible. On the other hand, as shown in Figure 1, a plating layer 42 may be formed on the second surface 12 of the first steel plate 10, and a plating layer 44 may be formed on the fourth surface 24 of the second steel plate. As described above, the plating layer 42 and the plating layer 44 do not substantially affect the porosity defect rate of the weld bead 30, so the amount of plating layer 42 and the plating layer 44 attached is not particularly limited.

[0027] Furthermore, the amount of plating layer adhesion only needs to be determined in an area sufficiently far from the weld bead 30 and unaffected by the heat from welding. The amount of plating layer adhesion can be determined, for example, by dissolving the plating layer in an acid solution containing an inhibitor that suppresses corrosion of the base metal, and measuring the weight change before and after pickling.

[0028] 1.2.2 Plating composition The plating layer may have a chemical composition known to those skilled in the art. When plating layers are formed on both the front and back surfaces of a steel sheet, the plating layers on the front and back surfaces may be of the same type or of different types. Each plating layer (in particular, the plating layer 41 formed on the first surface 11 of the first steel sheet 10 and the plating layer 43 formed on the third surface 23 of the second steel sheet 20) may contain Zn. When the plating layer contains Zn, the amount of plating vapor generated during welding tends to increase, and the problem of porosity defects in the weld bead is likely to occur. For example, each plating layer (in particular, the plating layer 41 formed on the first surface 11 of the first steel sheet 10 and the plating layer 43 formed on the third surface 23 of the second steel sheet 20) may contain 40% to 100% Zn by mass. The Zn content in the plating layer may be 45% by mass or more, 50% by mass or more, 55% by mass or more, or 60% by mass or more. Furthermore, the plating layer may contain additive elements other than Zn, such as Al, and may also contain Fe if an alloying treatment has been applied. For example, the plating layer may be a Zn-Al-Mg alloy plating layer containing at least Zn, Al, and Mg, or it may be a Zn-Al-Mg-Si alloy plating layer further containing Si. The content (concentration) of elements other than Zn in the plating layer may be, in mass%, Al: 0-60%, Mg: 0-10%, Si: 0-2%, Mn: 0-1%, Ni: 0-1%, Sb: 0-1%, Fe: 0-20%. The Zn-containing plating layer may be an alloyed hot-dip galvanized layer, a hot-dip galvanized layer, or an electroplated galvanized layer.

[0029] 1.2.3 Location of the plating layer As described above, in the lap fillet welded joint 100, a plating layer is formed on one or both of the first surface 11 of the first steel plate 10 and the third surface 23 of the second steel plate 20. The plating layer may be formed on one, two, three, or all of the first surface 11 and second surface 12 of the first steel plate 10, and the third surface 23 and fourth surface 24 of the second steel plate 20. Figure 1 shows a configuration in which a plating layer 41 is formed on the first surface of the first steel plate 10 and a plating layer 43 is formed on the third surface 23 of the second steel plate 20, but one or both of the plating layers 41 and 43 may not be present. Also, Figure 1 shows a configuration in which a plating layer 42 is formed on the second surface 12 of the first steel plate 10 and a plating layer 44 is formed on the fourth surface 24 of the second steel plate 20, but one or both of the plating layers 42 and 44 may not be present. Furthermore, the plating layer may be formed only on the front side or only on the back side of the first steel plate 10 and the second steel plate 20. That is, plating layers 41 and 44 may be formed on the first surface 11 of the first steel plate 10 and the fourth surface 24 of the second steel plate 20, respectively, and plating layers 42 and 43 may be formed on the second surface 12 of the first steel plate 10 and the third surface 23 of the second steel plate 20, respectively. Alternatively, the corrosion resistance of the front and back sides of the lap fillet weld joint 100 may be enhanced by forming plating layers 41 to 44 on all of the first surface 11 and the second surface 12 of the first steel plate 10, and the third surface 23 and the fourth surface 24 of the second steel plate 20. The plating layers 41 to 44 may be provided only on a part of the front and / or back surface of the first steel plate 10 and the second steel plate 20, or they may be provided on the entire surface. As shown in Figure 1, the plating layer evaporates and disappears in the weld bead 30 and its surrounding area due to the heat effect during welding. A new plating layer may be provided in the area where the plating layer has disappeared; that is, for example, a new plating layer may be provided on the surface of the weld bead 30 and its surrounding area.

[0030] 1.3 Weld Bead As shown in Figures 1 and 2, the weld bead 30 is formed along the corner between the first surface 11 of the first steel plate 10 and the leading surface of the second steel plate 20, joining the end of the second steel plate 20 to the first surface 11 of the first steel plate 10. The weld bead 30 only needs to have a height H as described later, and can take the same form as a general weld bead formed by lap fillet welding, except for the height H. For example, the weld bead may have a predetermined width and length in a plan view, and may have a starting end (the part where arc welding starts), an ending end (the part where arc welding ends), and a steady end (the part between the starting end and the ending end) in the longitudinal direction. Furthermore, the flank angle of the toe end, which is the widthwise end of the weld bead, is not particularly limited.

[0031] 1.3.1 Bead height In lap fillet welded joints 100, the height H of the weld bead 30 must be below a certain level. A low height H of the weld bead 30 makes it easier to reduce the porosity defect rate of the weld bead 30 through the following mechanism. That is, as described above, during lap fillet welding, the plating layers 41 and 43 provided on the first surface 11 and the third surface 23 evaporate, and plating vapor penetrates from between the steel plates into the molten pool. Here, if the height of the molten pool is low (thin), the distance from the source of the plating vapor to the surface of the molten pool (the surface that can become the apex P of the weld bead 30) is short, and the plating vapor that has penetrated into the molten pool is easily floated up and discharged / removed from the surface of the molten pool. Therefore, pores are less likely to remain inside the weld bead 30, and the porosity defect rate is reduced. According to the inventor's findings, the height H from the first surface 11 of the first steel plate 10 to the apex P of the weld bead 30 and the plate thickness T mentioned above are related. A The gap G, described later, satisfies the above relationship (2), resulting in a significant reduction in the porosity defect rate in the weld bead 30. That is, in the lap fillet weld joint 100, the height H of the weld bead 30 is equal to the thickness T of the thicker of the first steel plate 10 and the second steel plate 20. A (If the first steel plate 10 and the second steel plate 20 have the same thickness, then the same thickness) and the gap G described later are used as references to T A Height up to +G+5mm (H≦T AThe thickness is kept to +G+5mm). The height H of the weld bead 30 is determined by the thickness T of the thinner of the two steel plates, the first steel plate 10 and the second steel plate 20. B (If the first steel plate 10 and the second steel plate 20 have the same thickness, then the same thickness) is used as the basis. B Height up to +G+5mm (H≦T B It may be limited to +G+5mm). Alternatively, the height H of the weld bead 30 is H≦T A +5mm, or H≦T B The relationship +5mm may also be satisfied. The lower limit of the height H of the weld bead 30 is not particularly limited and should be any height that allows the first steel plate 10 and the second steel plate 20 to be properly joined by overlap fillet welding. For example, the height H of the weld bead 30 is the plate thickness T. A It can be larger than T A It can be greater than +G.

[0032] 1.3.2 Bead width As shown in Figure 2, the weld bead 30 may have a width W. The width W of the weld bead 30 does not substantially affect the porosity defect rate in the weld bead 30 and is not particularly limited. The width W may be, for example, 3 mm or more, or 5 mm or more, or 15 mm or less, or 20 mm or less.

[0033] 1.3.3 Bead Length As shown in Figures 1 and 2, the weld bead 30 can be formed continuously along the corner formed by the end face of the second steel plate 20 and the first surface 11 of the first steel plate 10, having a certain length. The length of the weld bead 30 may be, for example, 20 mm or more, or 30 mm or more, and may be 2000 mm or less, or 3000 mm or less. If the length of the weld bead 30 is long, it is advisable to perform tack welding, as described later, at intervals of a certain size or less. This allows the gap G between the steel plates to be controlled to a certain size or less.

[0034] 1.3.4 Components of Weld Bead The weld bead 30 may be composed of a weld metal which is a mixture of the components of the wire used for arc welding, the components of the plating layer, and the components of the steel plate (base material). There are no particular restrictions on the type of wire used to make up the weld metal, and any known solid wire or flux-cored wire can be used. In the weld bead 30, components derived from the plating layer may be present in the form of oxides or the like. For example, at least one oxide selected from the group consisting of zinc-containing oxides, aluminum-containing oxides, magnesium-containing oxides, and silicon-containing oxides may be present in the interior of the weld bead 30, the surface of the weld bead 30, and at least a part of the periphery of the weld bead 30.

[0035] 1.4 Gap between steel plates Conventionally, it has been considered preferable to increase the gap G between steel plates in order to utilize it as a path for discharging plating vapor. For example, it has been considered to create a large gap G between steel plates by forming grooves between the steel plates or by bending the plates. However, according to the present inventor's new findings, when joining thin steel plates with a thickness of 2 mm or less by lap fillet welding, if the gap G between the steel plates (between the first surface 11 of the first steel plate 10 and the third surface 23 of the second steel plate 20) is large, the height of the molten pool increases, and it takes longer for the plating vapor to be discharged, thus increasing the porosity defect rate in the weld bead. When joining steel plates with a thickness of 2 mm or less by lap fillet welding, as described above, it is preferable to lower the height of the molten pool and then deliberately reduce the gap G in order to promote the discharge of plating vapor from the surface of the molten pool. According to the present inventor's findings, in a lap fillet welded joint 100, the gap G between the first surface 11 of the first steel plate 10 and the third surface 23 of the second steel plate 20 is equal to the above plate thickness T A When the following conditions are met, it becomes possible to efficiently discharge plating vapor from the surface of the molten pool, and the porosity defect rate in the weld bead 30 can be significantly reduced. The gap G is the plate thickness T mentioned above. A 75% or less of the above plate thickness T A It may be less than half of that. Alternatively, the gap G may be the plate thickness T mentioned above. B Below, the above plate thickness TB 75% or less of the above plate thickness T B It may be less than half of that.

[0036] Furthermore, the gap G can be defined as the distance I' between the first surface 11 and the third surface 23 of the steel plate 10 and the third surface 23 of the steel plate 20 facing each other in the vicinity of the weld bead 30, in the portion where the first surface 11 and the third surface 23 are parallel to each other, minus the total thickness T' of the plating layer present between the first surface 11 and the third surface 23 (G = I' - T').

[0037] 1.5 Tack weld marks When thin plates with a thickness of 2 mm or less are joined by overlapping fillet welding, the gap G tends to become extremely large due to thermal deformation, regardless of the amount of heat input during welding. In other words, in overlapping fillet welded joint 100, the gap G is equal to the plate thickness T. A To achieve the following, measures must be taken to prevent the gap G from becoming large during welding. For example, by performing tack welding at intervals of a certain size or less before the main welding, the gap G is less likely to become large during the main welding, and a lap fillet welded joint 100 with a small gap G can be obtained. Alternatively, the gap G may be reduced by pressing the steel plate with a vise or the like during the main welding. Tack welding is particularly preferred. Here, if the lap fillet welded joint 100 of this disclosure is manufactured via tack welding, the traces of the tack welding will remain even after the main welding. That is, the lap fillet welded joint 100 of this disclosure may have tack welding traces together with the weld bead 30. Specifically, in the lap fillet welded joint 100 of this disclosure, as shown in Figure 2, tack welding traces 35 may be present, and the interval I of the tack welding traces 35 and the plate thickness T mentioned above are... B The following relationship (3) may also be satisfied. Details of tack welding will be described later.

[0038] I ≤ 250 × T B …(3)

[0039] 1.6 Pore defect rate in weld beads In the lap fillet welded joint 100 of this disclosure, the weld bead 30 has a porosity defect rate of 7.0% or less. Thus, a low porosity defect rate in the weld bead 30 makes it less likely for problems of strength reduction due to porosity defects to occur. However, it can be difficult to completely remove plating vapor that has entered the molten pool during welding, that is, it can be difficult to make the porosity defect rate completely 0%. In this regard, in the lap fillet welded joint 100 of this disclosure, the porosity defect rate in the weld bead 30 may be between 0.5% and 7.0%. The porosity defect rate in the weld bead 30 may be 6.8% or less, 6.4% or less, 6.0% or less, 5.8% or less, 5.4% or less, 5.0% or less, 4.8% or less, 4.4% or less, 4.0% or less, 3.8% or less, 3.4% or less, 3.0% or less, 2.8% or less, 2.4% or less, or 2.0% or less.

[0040] Furthermore, the porosity of a weld bead is determined as the ratio of the area of ​​porosity defects to the projected area of ​​the weld bead in a plan view (Figure 2) (area of ​​porosity defects / projected area of ​​the weld bead). The area of ​​porosity defects in a weld bead can be determined, for example, by X-ray transmission testing. That is, an X-ray transmission test is performed on the weld bead, and an X-ray radiograph is obtained. In the X-ray radiograph, for example, the porosity area appears relatively dark compared to the weld metal portion of the weld bead, making it easy to identify the area of ​​porosity defects.

[0041] 2. Method for manufacturing lap fillet welded joints The following describes an example of a method for manufacturing the lap fillet welded joint described herein. As shown in Figures 2 and 3, the method for manufacturing a lap fillet welded joint 100 according to one embodiment is as follows: The first steel plate 10 and the second steel plate 20 are overlapped, and tack welding Y is performed on the planned welding location X (Figure 3), and, This includes performing arc welding on the welding location X where tack welding Y has been applied, thereby joining the first steel plate 10 and the second steel plate 20 via a weld bead 30 (Figure 2). Here, as mentioned above, The first steel plate 10 has a first surface 11 facing the second steel plate 20 and a second surface 12 facing the opposite side from the first surface 11. The second steel plate 20 has a third surface 23 facing the first steel plate 10 and a fourth surface 24 facing the opposite side from the third surface 23. The end of the second steel plate 20 is joined to the first surface 11 via a weld bead 30. Plating layers 41 and 43 are formed on one or both of the first surface 11 and the third surface 23. The total amount of plating layers 41 and 43 deposited on the first surface 11 and the third surface 23 is 10 g / m². 2 More than 120g / m 2 The following applies: Thickness T of one of the first steel plate 10 and the second steel plate 20 A The thickness T of the other of the first steel plate 10 and the second steel plate 20 B The following relationship (1) is satisfied. The height H from the first surface 11 to the apex P of the weld bead 30, and the plate thickness T. A The gap G between the first surface 11 and the third surface 23 satisfies the following relationship (2). In the manufacturing method disclosed herein, the spacing I of the tack welds and the plate thickness T are B It is important that the following relationship (3) is satisfied.

[0042] T B ≦T A ≤2mm …(1) H≦T A +G+5mm …(2) I ≤ 250 × T B …(3)

[0043] 2.1 Tack welding As shown in FIG. 3, in the manufacturing method of the present disclosure, before performing the main welding, the first steel plate 10 and the second steel plate 20 are overlapped, and temporary welding Y is performed on the planned welding location X. The temporary welding Y may be performed by arc welding or by a welding method other than arc welding. When performing the temporary welding by arc welding, the conditions of arc welding (current value, welding speed, shielding gas, etc.) are not particularly limited. For example, they may be the same as or different from the conditions of arc welding in the main welding. Examples of welding methods other than arc welding include laser welding, resistance spot welding, etc.

[0044] In the manufacturing method of the present disclosure, the interval I of the temporary welding is set according to the plate thickness of the steel plate. Specifically, as shown in the above relationship (3), the interval I of the temporary welding is the thickness T of the thinner one of the first steel plate 10 and the second steel plate 20 B (When the first steel plate 10 and the second steel plate 20 have the same plate thickness, the same plate thickness) is used as a reference, and the interval is set to 250×T B (mm) or less. That is, the thinner the plate thickness, the easier it is for the gap G to increase due to thermal deformation during welding. Therefore, the interval I of the temporary welding is made smaller to make the steel plates adhere to each other as closely as possible before the main welding.

[0045] When performing the temporary welding by arc welding, there are no particular restrictions on the bead height, bead length, and bead width of the temporary welding. Since the bead of the temporary welding is remelted in the main welding, the height of the bead of the temporary welding and pore defects in the bead do not pose a problem in the main welding. The bead length of the temporary welding may be, for example, 3 mm or more, or 5 mm or more, and may also be 10 mm or less, or 20 mm or less. The bead width of the temporary welding may be, for example, 3 mm or more, or 5 mm or more, and may also be 10 mm or less, or 20 mm or less. In addition, even when the length of the planned welding location X is less than 250×T B it is advisable to perform the temporary welding at one or more locations.

[0046] 2.2 Main Welding As shown in Figure 2, in the manufacturing method of the present disclosure, arc welding is performed on the welding location X where tack welding Y has been applied, and the first steel plate 10 and the second steel plate 20 are joined via a weld bead 30. The conditions for arc welding in this welding (current value, welding speed, shielding gas, etc.) are not particularly limited and can be appropriately adjusted to conditions suitable for welding steel plates with a thickness of 2 mm or less, and so that the height H of the weld bead 30 satisfies the above relationship (2). For example, if the penetration depth by arc welding is the thickness of the plate T B Welding conditions such that the ratio is between 5% and 70% may be adopted. Specifically, the arc welding current may be, for example, between 80A and 250A. The welding speed may be, for example, between 30m / min and 150m / min. The shielding gas may be, for example, a mixture of argon and carbon dioxide, in which case the proportion of carbon dioxide in the mixture may be between 5% and 30% by volume. The wire used for arc welding is not particularly limited, and any known solid wire or flux-cored wire can be used. The welding target position may also be a position common in lap fillet welding.

[0047] 2.3 Supplement In this welding process, the plating layer disappears as plating vapor due to the heat effect of the welding. The plating vapor penetrates into the molten pool. At this time, because the gap G between the steel plates is kept small by tack welding, the plating vapor is efficiently discharged from the surface of the molten pool, and the porosity defect rate in the weld bead 30 after the main welding can be reduced. For example, in the lap fillet welded joint 100 obtained by the manufacturing method of this disclosure, as described above, the porosity defect rate in the weld bead 30 can be 7.0% or less.

[0048] 3.Applications The lap fillet welded joint of this disclosure has a plating layer and excellent corrosion resistance. The lap fillet welded joint of this disclosure is suitably used, for example, as a chassis component of an automobile. Alternatively, the lap fillet welded joint of this disclosure is suitably used, for example, as various building material components. [Examples]

[0049] The technology of this disclosure will be described in more detail below with reference to examples, but the technology of this disclosure is not limited to the following examples.

[0050] 1. Preparation of plated steel sheet The steel plates to be welded were prepared with the thickness, plating amount per side, and plating type (Zn content in the plating) shown in Table 1 below. Each steel plate had a strength of 440 MPa or higher. Each steel plate measured 500 mm in width and 3000 mm in length. Among the steel plates shown in Table 1, those with a plating layer had plating on both the front and back sides, and Table 1 shows the plating amount per side.

[0051] 2. Tack welding For the steel plate combinations shown in Table 1 below, tack welding was performed using arc welding to tack weld the edge of the second steel plate (upper plate) to the surface of the first steel plate (lower plate). The spacing I of the tack welds was as shown in Table 1 below. The arc welding conditions for tack welding were the same as those for the main welding.

[0052] 3. Final welding For the steel plate combinations shown in Table 1 below, lap fillet welding was performed using arc welding to join the edge of the second steel plate (upper plate) to the surface of the first steel plate (lower plate) via the weld bead. The welding conditions common to each example are as follows.

[0053] (Arc welding conditions common to each example) Welding current: Conditions under which the penetration depth reaches 20% of the thickness of the lower plate. Welding speed: 0.8 m / min Shielding gas: Ar + 20% CO2 Flow rate: 20L / min Welding wire: YGW16 Welding torch tilt angle: 60° Overlap: 10mm

[0054] 4. Measurement of the gap G and weld bead height H after the final welding. In the lap fillet weld joint after the main welding, the gap G between the steel plates and the height H of the weld bead were measured. The locations of the gap G and height H are shown in Figure 1. The results are shown in Table 1 below.

[0055] 5. Measurement of porosity defect rate in weld beads X-ray radiography was performed on fillet weld joints after arc welding to obtain X-ray radiographs, and the porosity defect rate in the weld bead was measured. The results are shown in Table 1 below.

[0056] Figure 4 shows an example of an X-ray radiograph of a weld bead in plan view. As shown in Figure 4, pores are present in the areas of the weld bead that appear darker than other parts. In this example, the pore defect rate in the weld bead was determined based on the X-ray radiograph as the ratio of the area of ​​pore defects to the projected area of ​​the weld bead (area of ​​pore defects / projected area of ​​the weld bead).

[0057] 6. Evaluation Results Table 1 below shows the evaluation conditions and evaluation results.

[0058] [Table 1]

[0059] The results shown in Table 1 can be summarized as follows:

[0060] Comparative Example 1 is an example where the thickness of the second steel plate, which is the upper plate, exceeds 2.0 mm, resulting in a high weld bead height H. In this case, the porosity defect rate in the weld bead increased. In Comparative Example 1, the height of the weld pool during the actual welding was high, and the distance from which the plating vapor that entered the molten pool was discharged from the surface of the molten pool became long. It is thought that a large amount of plating vapor remained inside the molten pool as bubbles without being discharged from the surface of the molten pool.

[0061] Comparative Example 2 is an example where the gap G between the steel plates was larger than the plate thickness. In this case, the porosity defect rate in the weld bead increased. When joining thin steel plates with a thickness of 2 mm or less by lap fillet welding, if the gap G between the steel plates is large, it becomes difficult for the plating vapor to escape from the surface of the weld pool, which is thought to increase the porosity defect rate in the weld bead.

[0062] Comparative Example 3 is an example where the weld bead height H was increased. In this case, the porosity defect rate in the weld bead increased. In Comparative Example 3, similar to Comparative Example 1, the height of the weld pool during the actual welding was high, and the distance from which the plating vapor that entered the molten pool was discharged from the surface of the molten pool was increased. It is thought that a large amount of plating vapor remained inside the molten pool as bubbles without being discharged from the surface of the molten pool.

[0063] Comparative Example 4 is an example where the gap G between the steel plates was larger than the plate thickness. In this case, the porosity defect rate in the weld bead increased. Similar to Comparative Example 2, it is thought that when the gap G between the steel plates is large, the plating vapor is less able to escape from the surface of the weld pool, which increases the porosity defect rate in the weld bead.

[0064] Comparative Examples 5 and 6 are examples where the amount of plating layer is excessively large. In these cases, the porosity defect rate in the weld bead increased. When the amount of plating layer is excessive, as in Comparative Examples 5 and 6, a large amount of plating vapor enters the molten pool during welding. Therefore, even if the gap G between the steel plates and the height H of the weld bead are controlled, a large amount of plating vapor remains inside the molten pool, which is thought to have increased the porosity defect rate in the weld bead.

[0065] Comparative Example 7 is an example where the gap G between the steel plates was larger than the plate thickness. In this case, the porosity defect rate in the weld bead increased. Similar to Comparative Examples 2 and 4, it is thought that when the gap G between the steel plates is large, the plating vapor is less able to escape from the surface of the weld pool, which increases the porosity defect rate in the weld bead.

[0066] Comparative Example 8 is an example where the deposition amount of the plating layer is excessively small. In this case, there is little plating vapor entering the molten pool during welding, and even without devising the gap G or the height of the weld bead, the porosity defect rate in the weld bead does not increase.

[0067] Comparative Example 9 is an example where the plate thickness of the first steel plate, which is the lower plate, exceeds 2.0 mm and the weld bead height H becomes high. In this case, the porosity defect rate in the weld bead increased. In Comparative Example 9, the height of the welding pool during this welding is high, and the distance from when the plating vapor that has entered the inside of the molten pool until it is discharged from the surface of the molten pool becomes long. It is considered that a large amount of the plating vapor remains as bubbles inside the molten pool without being discharged from the surface of the molten pool.

[0068] On the other hand, it can be seen that in the fillet weld joints that satisfy the following requirements (A) to (D) as in Examples 1 to 15, the porosity defect rate in the weld bead becomes as small as 7.0% or less.

[0069] (A) The total deposition amount of the plating layers existing between the steel plates is 10 g / m 2 or more and 120 g / m 2 or less. (B) One of the plate thicknesses T of the first steel plate and the second steel plate A and the other plate thickness T of the first steel plate and the second steel plate <{ B satisfy the following relationship (1). (C) The gap G between the steel plates is the plate thickness T A or less. (D) The height H of the weld bead, the plate thickness T A and the gap G satisfy the following relationship (2).

[0070] T B ≦ T A ≦ 2 mm …(1) H ≦ T A + G + 5 mm …(2)

[0071] 7. Supplementary Furthermore, the porosity defect rate of the weld bead corresponds to the amount of blowholes present in the weld bead. On the other hand, in addition to blowholes, pits may also be present on the surface of the weld bead. Here, pits have little effect on the strength of the weld bead. Therefore, in this embodiment, the porosity defect rate of the weld bead was used as an indicator of the strength of the weld bead.

[0072] On the other hand, considering appearance and corrosion resistance, it is preferable for the weld bead to be free of pits. As far as the inventors have confirmed, the amount of pits in the weld bead correlates with the porosity defect rate in the weld bead. That is, if the porosity defect rate in the weld bead is small, the amount of pits will also be small. As far as the inventors have confirmed by visual inspection, no pits were present on the surface of the weld bead in any of the above Examples 1 to 15. [Explanation of Symbols]

[0073] 10 First steel plate 11 Page 1 12 Side 2 20 Second steel plate 23 Page 3 24 Page 4 30 Weld beads 35 Temporary welding marks 41, 42, 43, 44 Plating layer 100 overlap fillet weld joint

Claims

1. A lap fillet welded joint comprising a first steel plate, a second steel plate, and a weld bead. The first steel plate has a first surface facing the second steel plate and a second surface facing the opposite side from the first surface. The second steel plate has a third surface facing the first steel plate and a fourth surface facing the opposite side from the third surface. The end of the second steel plate is joined to the first surface via the weld bead. A plating layer is formed on one or both of the first and third surfaces. The total amount of the plating layer deposited on the first and third surfaces is 10 g / m². ２ 120g / m or more ２ The following: The thickness T of one of the first steel plate and the second steel plate Ａ The thickness T of the other of the first steel plate and the second steel plate. Ｂ The following relationship (1) is satisfied, The gap G between the first surface and the third surface is equal to the plate thickness T. Ａ The following: The height H from the first surface to the apex of the weld bead, and the plate thickness T. Ａ The gap G satisfies the following relationship (2): The aforementioned weld bead has a porosity defect rate of 7.0% or less. Overlap fillet weld joint. T Ｂ ≦T Ａ ≦2mm …(1) H≦T Ａ +G+5mm …(2)

2. There are traces of tack welding. The spacing I of the tack weld marks and the plate thickness T Ｂ And satisfy the following relationship (3): The lap fillet welded joint according to claim 1. I≦250×T Ｂ …(3)

3. The aforementioned weld bead has a porosity defect rate of 0.5% or more and 7.0% or less. The lap fillet welded joint according to claim 1 or 2.

4. The aforementioned plating layer contains 40% to 100% Zn by mass. The lap fillet welded joint according to claim 1 or 2.

5. A method for manufacturing lap fillet welded joints, The first steel plate and the second steel plate are overlapped, and tack welding is performed on the areas to be welded, and, This includes performing arc welding on the welding location where the tack weld has been applied, thereby joining the first steel plate and the second steel plate via a weld bead. The first steel plate has a first surface facing the second steel plate and a second surface facing the opposite side from the first surface. The second steel plate has a third surface facing the first steel plate and a fourth surface facing the opposite side from the third surface. The end of the second steel plate is joined to the first surface via the weld bead. A plating layer is formed on one or both of the first and third surfaces. The total amount of the plating layer deposited on the first and third surfaces is 10 g / m². ２ 120g / m or more ２ The following: The thickness T of one of the first steel plate and the second steel plate Ａ The thickness T of the other of the first steel plate and the second steel plate. Ｂ The following relationship (1) is satisfied, The height H from the first surface to the apex of the weld bead, and the plate thickness T. Ａ The gap G between the first surface and the third surface satisfies the following relationship (2): The spacing I of the tack welds and the plate thickness T Ｂ And satisfy the following relationship (3): Manufacturing method. T Ｂ ≦T Ａ ≦2mm …(1) H≦T Ａ +G+5mm …(2) I≦250×T Ｂ …(3)

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