Manufacturing method for overlap fillet welded joints

Abstract

To provide a method for manufacturing an overlapping fillet-welded joint in which pore defects in a weld bead are reduced.SOLUTION: A method for manufacturing an overlapping fillet-welded joint includes performing tack welding on a first steel plate and a second steel plate while overlapping the steel plates, and performing final welding on a final welding schedule part after the tack welding, wherein a plated layer exists in the final welding schedule part, and at least one of the following conditions 1 to 3 is satisfied. Condition 1: A start end side of the final welding schedule part is subjected to tack welding, and then final welding is performed from the start end side to the final end side without performing tack welding on the final end side. Condition 2: A terminal end of the final welding schedule part is subjected to tack welding, then the start end side is subjected to tack welding, and then final welding is performed from the start end side to the final end side. Condition 3: both of the start end side and the final end side of the final welding schedule part are subjected to tack welding, and final welding is performed from the start end side toward the terminal end side, after elapse of 60 seconds or more.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] This application discloses a method for manufacturing lap fillet welded joints. [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. This decrease in weld bead strength is particularly likely to occur when welding steel plates with a plating layer. Specifically, when steel plates are welded together with the plating layer intact, plating vapor becomes trapped within the weld bead, resulting in porosity defects (pits, blowholes, wormholes), which is one of the causes of reduced strength. Furthermore, porosity defects can impair the appearance of the joint. These problems occur regardless of the welding method, such as lap fillet welding or T-fillet welding. As a method to reduce porosity defects in the weld bead, for example, a method is known in which a gap is formed between steel plates when welding them together, and plating vapor is discharged from the molten pool into this gap (Patent Documents 1 and 2). Specifically, when welding steel plates together, protrusions are created on the upper and lower plates by press working so that a gap is formed on the overlapping surface of the steel plates. Alternatively, methods such as coining to create numerous grooves can be used to ensure that the steel plates are tightly bonded together while also providing a path for the plating vapor to be discharged. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2016-153129 [Patent Document 2] Japanese Patent Publication No. 2016-198796 [Overview of the project] [Problems that the invention aims to solve]

[0004] When performing lap fillet welding, if the upper and lower plates are positioned and fixed to a jig or similar fixture, it is difficult to form protrusions or grooves on the upper and lower plates. Therefore, it is necessary to form protrusions or grooves on the surface of the steel plates before lap fillet welding, which requires additional processing and increases costs. Also, when performing lap fillet welding, if the gap between the upper and lower plates is too large, there is a risk of excessive perforation, burn-through, and back-side penetration during welding, making it difficult to form a sound weld bead. In this regard, in order to keep the gap between the upper and lower plates small, it is necessary to make the protrusions or grooves on the surface of the steel plates small, but it is difficult to stably form such small protrusions or gaps. Furthermore, sufficient overlap is required to form protrusions or grooves, which leads to increased weight and material costs. [Means for solving the problem]

[0005] This application discloses several embodiments as one means of solving the above-mentioned problems. <Aspect 1> A method for manufacturing lap fillet welded joints, The first steel plate and the second steel plate are overlapped and then tack-welded, and This includes performing the main welding on the area to be welded after the aforementioned tack welding, A plating layer exists at the location where the welding is to be performed. A manufacturing method that satisfies at least one of the following conditions 1 to 3. Condition 1: After applying the tack weld to the starting end of the area to be welded, the main weld is performed from the starting end to the ending end without applying the tack weld to the ending end. Condition 2: After applying the tack weld to the end of the area where the main welding is to be performed, the tack weld is then applied to the start end, and then the main welding is performed from the start end towards the end. Condition 3: Apply the tack weld to both the starting and ending ends of the area to be welded, and after 60 seconds or more have elapsed, perform the main weld from the starting end towards the ending end. <Aspect 2> The thickness of the first steel plate and the second steel plate is 3.2 mm or less. Manufacturing method of embodiment 1. <Aspect 3> The ratio W1 / W2 of the bead width W1 of the tack welding to the bead width W2 of the main welding is 1.2 or more and 2.0 or less. The manufacturing method according to Aspect 1 or 2. <Aspect 4> The tack welding is performed at a position within 50 mm from the planned main welding location. The manufacturing method according to any one of Aspects 1 to 3. <Aspect 5> When a plurality of tack weldings are performed, the interval between the tack weldings is 30 mm or more. The manufacturing method according to any one of Aspects 1 to 4. <Aspect 6> The plating layer is a zinc-based plating layer. The manufacturing method according to any one of Aspects 1 to 5. <Aspect 7> 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. The end portion of the second steel plate is joined to the first surface via a weld bead. The 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 2 or more and 500 g / m 2 or less. The manufacturing method according to any one of Aspects 1 to 6.

Advantages of the Invention

[0006] According to the method of the present disclosure, it is possible to manufacture an overlap fillet weld joint with reduced pore defects in the weld bead. In the method of the present disclosure, since there is no need to provide protrusions or grooves on the steel plate surface, an increase in cost and an increase in weight can be easily suppressed.

Brief Description of the Drawings

[0007] [Figure 1]An example of the process of manufacturing an overlapping fillet weld joint that satisfies Condition 1 is schematically shown. [Figure 2] An example of the process of manufacturing an overlapping fillet weld joint that satisfies Condition 2 is schematically shown. [Figure 3] An example of the process of manufacturing an overlapping fillet weld joint that satisfies Condition 3 is schematically shown. [Figure 4A] It schematically shows the form of the cross-section taken along the IVA-IVA arrow direction in FIGS. 1 to 3 (the form near the corner before the main welding). [Figure 4B] It schematically shows the form of the cross-section taken along the IVB-IVB arrow direction in FIGS. 1 to 3 (the form near the corner after the main welding). [Figure 5] An example of an X-ray transmission photograph observing the pore defect in the weld bead of the overlapping fillet weld joint is shown.

Mode for Carrying Out the Invention

[0008] Hereinafter, a method for manufacturing an overlapping fillet weld joint according to an embodiment will be described while referring to the drawings. However, the manufacturing method of the present disclosure is not limited to the illustrated form. As shown in FIGS. 1 to 3, the manufacturing method of the present disclosure includes overlapping the first steel plate 10 and the second steel plate 20 and performing tack welding X1, and after the tack welding, performing main welding X2 on the main welding planned location 30. Here, as shown in FIG. 4A, plating layers 41 and 43 exist at the main welding planned location 30. Also, as shown in FIGS. 1 to 3, in the manufacturing method of the present disclosure, at least one of the following Conditions 1 to 3 is satisfied.

[0009] Condition 1: After performing the tack welding X1 on the start end 31 side of the main welding planned location 30, without performing the tack welding X1 on the end 32 side, perform the main welding X2 from the start end 31 side toward the end 32 side (FIG. 1).

[0010] Condition 2: After applying the tack weld X1 to the end 32 side of the planned welding location 30, the tack weld X1 is applied again to the starting end 31 side, and then the main weld X2 is applied from the starting end 31 side toward the end 32 side (Figure 2).

[0011] Condition 3: Apply the tack weld X1 to both the starting end 31 and the ending end 32 of the planned welding location 30, and after 60 seconds or more have elapsed, apply the main weld X2 from the starting end 31 towards the ending end 32 (Figure 3).

[0012] 1. Tack welding Tack welding is also called temporary welding. Conventional tack welding is used to prevent displacement of the steel plate due to welding deformation during main welding. Specifically, conventional tack welding is performed on the terminal side of the area to be welded in order to prevent displacement of the steel plate during main welding. In contrast, in the manufacturing method of the present disclosure, tack welding X1 is performed to reduce porosity defects in the weld bead 50. In the manufacturing method of the present disclosure, the welding method and weld shape of the tack welding X1 may be the same as conventional tack welding, but the position and order of the tack welding X1 are different. Specifically, in the manufacturing method of the present disclosure, tack welding X1 is performed such that at least one of the following conditions 1 to 3 is satisfied.

[0013] 1.1 Condition 1 As shown in Figure 1, under condition 1, a tack weld X1 is performed on the starting end 31 side of the planned welding location 30, and then the main weld X2 is performed from the starting end 31 side toward the ending end 32 side without performing a tack weld X1 on the ending end 32 side. Under condition 1, there is no particular limit on the time from the completion of the tack weld X1 on the starting end 31 side to the start of the main weld X2. For example, the main weld X2 may be started before the molten pool of the tack weld X1 cools and solidifies, or it may be started after it has cooled and solidified. Preferably, the main weld X2 may be started after the molten pool of the tack weld X1 has cooled and solidified, and more preferably after the molten pool of the tack weld X1 has cooled and solidified to a temperature below which the red-hot state substantially disappears (for example, below 500°C). According to the inventor's new findings, the tack weld X1 on the starting end 31 side has a small effect in suppressing displacement of the steel plate, but it has a significant effect in reducing porosity defects in the weld bead 50. Although the detailed mechanism is unknown, it is thought that by applying a tack weld X1 to the starting end 31, an appropriate gap G is created between the first steel plate 10 and the second steel plate 20 during the main weld X2. Through this gap G, plating vapor is efficiently discharged from the molten pool, resulting in a weld bead 50 with fewer porosity defects.

[0014] 1.2 Condition 2 As shown in Figure 2, under condition 2, a tack weld X1 is performed on the terminal side 32 of the planned welding location 30, then another tack weld X1 is performed on the starting side 31, and finally, the main weld X2 is performed from the starting side 31 toward the terminal side 32. Under condition 2, there are no particular restrictions on the time from the completion of the tack weld X1 on the terminal side 32 to the start of the tack weld X1 on the starting side 31, or from the completion of the tack weld X1 on the starting side 31 to the start of the main weld X2. For example, the next tack weld X1 or main weld X2 may be started before the molten pool of the tack weld X1 cools and solidifies, or it may be started after it has cooled and solidified. Preferably, the main weld X2 may be started after the molten pool of the tack weld X1 has cooled and solidified, and more preferably after the molten pool of the tack weld X1 has cooled and solidified to a temperature below which the red-hot state substantially disappears (for example, below 500°C). In this case as well, the tack welding X1 on the starting end 31 side has the effect of significantly reducing porosity defects in the weld bead 50. Although the detailed mechanism is unknown, it is thought that, similar to condition 1, the application of tack welding X1 on the starting end 31 side creates an appropriate gap G between the first steel plate 10 and the second steel plate 20 in the main weld X2, allowing plating vapor to be efficiently discharged from the molten pool through this gap G, resulting in a weld bead 50 with fewer porosity defects.

[0015] 1.3 Condition 3 As shown in Figure 3, under condition 3, tack welding X1 is performed on both the starting end 31 and the ending end 32 of the planned welding location 30, and after 60 seconds or more, the main welding X2 is performed from the starting end 31 towards the ending end 32. Under condition 3, tack welding X1 may be performed on the starting end 31 first and then on the ending end 32, or tack welding X1 may be performed on the ending end 32 first and then on the starting end 31. After 60 seconds or more have elapsed since the tack welding X1, the molten pool of the tack weld cools and solidifies, and the first steel plate 10 and the second steel plate 20 are constrained in the planar direction (a direction substantially perpendicular to the plate thickness direction), making it difficult for positional displacement in the planar direction to occur. Although the detailed mechanism is unknown, it is believed that by performing the main welding X2 while constraining the first steel plate 10 and the second steel plate 20 in the planar direction by tack welding X1 on the starting end 31 and the ending end 32, the first steel plate 10 and the second steel plate 20 deform in the thickness direction during the main welding, creating an appropriate gap G between the first steel plate 10 and the second steel plate 20. Through this gap G, plating vapor is efficiently discharged from the molten pool, resulting in a weld bead 50 with fewer porosity defects.

[0016] 1.4 Size and shape of tack welds The bead width of the tack weld X1 is not particularly limited; it may be smaller than, larger than, or the same as, the bead width of the main weld X2. However, a larger bead width for the tack weld X1 is thought to enhance the restraining effect of the tack weld X1, thereby increasing the effectiveness of reducing the aforementioned porosity defects. On the other hand, if the bead width of the tack weld X1 is too large, there is a risk of perforation and see-through, and the thermal impact on the steel plate and plating layer may become excessive. Also, the tack weld may become conspicuous, impairing the appearance quality. In this regard, the ratio W1 / W2 of the tack weld bead width W1 to the main weld bead width W2 may be between 1.2 and 2.0. The shape of the tack weld X1 is not particularly limited; it may be point-shaped, linear, or any other shape. The bead length of the tack weld X1 may be, for example, 1 mm or more, 3 mm or more, or 5 mm or more, or 10 mm or less, or 20 mm or less. The bead width of the tack weld X1 may be, for example, 1 mm or more, 3 mm or more, or 5 mm or more, or 10 mm or less, or 20 mm or less.

[0017] 1.5 Tack welding location In conditions 1 to 3, "tack welding on the starting end side of the planned welding location" refers to welding performed on the starting end side 31 of the planned welding location 30, with the center in the longitudinal direction (weld line direction) of the planned welding location 30 as the boundary. "Tack welding on the starting end side of the planned welding location" may be performed at a position on the terminal end 32 side of the starting end 31 of the planned welding location 30 (i.e., inside the planned welding location 30), or at a position away from the planned welding location 30. Figures 1 to 3 illustrate an example where tack welding X1 on the starting end side 31 is performed at a position away from the planned welding location 30, but the main welding X2 may be performed so as to overlap with the part where tack welding X1 has been performed, or so as to go over that part.

[0018] In conditions 1 to 3, "tack welding on the terminal side of the planned welding location" refers to welding performed on the terminal side 32 of the planned welding location 30, with the center in the longitudinal direction (weld line direction) as the boundary. "Tack welding on the terminal side of the planned welding location" may be performed at a position closer to the start end 31 than the end end 32 of the planned welding location 30 (i.e., inside the planned welding location 30), or at a position away from the planned welding location 30. Figures 1 to 3 illustrate an example where tack welding X1 on the terminal side 32 is performed at a position away from the planned welding location 30, but the main weld X2 may be performed so as to overlap with the part where tack welding X1 has been performed, or so as to go over that part.

[0019] The tack weld X1 should be placed as close as possible to the planned welding location 30. This is because the influence (e.g., restraining force) exerted from the tack weld X1 to the planned welding location 30 is expected to be greater, thereby increasing the effectiveness of reducing the aforementioned porosity defects. In this regard, the tack weld X1 may be placed within 50 mm, 30 mm, or 20 mm of the planned welding location 30.

[0020] 1.6 Tack welding spacing For example, as in conditions 2 and 3 above, multiple tack welds X1 may be applied. In this case, it is thought that the longer the interval between the tack welds X1, the larger the gap G between the first steel plate 10 and the second steel plate 20 in the main weld X2, and the greater the effect of reducing the aforementioned porosity defects. In this regard, when multiple tack welds X1 are applied, the interval between the tack welds X1 (assuming that the first tack weld and the second tack weld exist sequentially from the starting end 31 to the ending end 32, the distance from the ending end of the first tack weld to the starting end of the second tack weld) may be 30 mm or more. The upper limit of the interval when multiple tack welds X1 are applied is not particularly limited and depends on the length of the main weld X2. Furthermore, if the main weld X2 is an intermittent weld (tap weld), tack welds X1 may be applied to the interrupted portion of the main weld X2.

[0021] 1.7 Others The tack weld X1 may be performed by arc welding or by a welding method other than arc welding. When tack welding is performed by arc welding, the arc welding conditions (current value, welding speed, shielding gas, etc.) are not particularly limited and may be the same as or different from the arc welding conditions in the main weld. In this case, the shape and size of the tack weld X1 can be adjusted as appropriate by adjusting the welding current value, time, or both. Examples of tack welding methods other than arc welding include resistance spot welding.

[0022] 2. Main welding In the manufacturing method of this disclosure, the main weld X2 is performed after the tack weld X1 so as to satisfy the above conditions 1 to 3. The main weld X2 may be performed under the same conditions as conventionally known main welds.

[0023] 2.1 Conditions for the final welding In the manufacturing method disclosed herein, arc welding is employed as the main weld X2. The conditions for arc welding related to the main weld X2 (current value, welding speed, shielding gas, etc.) are not particularly limited and can be appropriately adjusted according to the plate thickness, etc. For example, welding conditions may be adopted such that the penetration depth by arc welding is 5% to 70% of the plate thickness of the steel plate. The current value for arc welding may be, for example, 60A to 300A. The welding speed may be, for example, 200mm / min to 1000mm / min. The shielding gas may be, for example, carbon dioxide or a mixture of argon and carbon dioxide, in which case the proportion of carbon dioxide in the mixture gas may be 5% to 30% by volume. The wire used for arc welding is also 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.

[0024] 2.2 Weld Bead As shown in Figure 4B, a weld bead 50 is formed by this weld X2. As shown in Figures 1 to 3, the weld bead 50 may have a predetermined width and length in a plan view, and may have a starting end (the part where arc welding begins), a ending end (the part where arc welding ends), and a steady-state section (the part between the starting and ending ends) 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.

[0025] 2.2.1 Weld Bead Width As described above, the weld bead 50 formed by this weld X2 may have a width W2. The width W2 of the weld bead 50 does not substantially affect the porosity defect rate in the weld bead 50 and is not particularly limited. The width W2 may be, for example, 1 mm or more, 3 mm or more, or 5 mm or more, or 10 mm or less, or 15 mm or less.

[0026] 2.2.2 Weld bead length The weld bead 50 formed by this weld X2 may be formed continuously along the corner formed by the first steel plate 10 and the second steel plate 20, having a certain length. The length of the weld bead 50 may be, for example, 10 mm or more, 20 mm or more, or 30 mm or more, and may be 500 mm or less, or 2000 mm or less.

[0027] 2.2.3 Weld bead height The height of the weld bead 50 (H shown in Figure 4B) formed by this weld X2 is not particularly limited and can be adjusted as appropriate according to the thickness of the steel plate, etc. The height H of the weld bead 50 may be up to T + G + 5 mm (H ≤ T + G + 5 mm), including the thickness T of the upper plate and the gap G between the steel plates. The lower limit of the height H of the weld bead 50 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 50 may be greater than the plate thickness T and may be greater than T + G. Note that the thickness of the plating layer is negligibly thin and is therefore not particularly considered in this application.

[0028] 2.2.4 Components of the weld bead The weld bead 50 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; known solid wires and flux-cored wires can both be used. In the weld bead 50, 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 50, the surface of the weld bead 50, and at least a part of the periphery of the weld bead 50. The same applies to the weld bead when arc welding is performed as tack welding X1.

[0029] 2.2.5 Pore defect rate of weld beads The lap fillet welded joints manufactured by the method of this disclosure have fewer porosity defects in the weld bead 50. The porosity defect rate in the weld bead 50 of the lap fillet welded joints manufactured by the method of this disclosure may be, for example, 40% or less, 35% or less, 30% or less, or 25% or less. Thus, the low porosity defect rate in the weld bead 50 makes it less likely for problems of strength reduction due to porosity defects to occur. However, it may be difficult to completely remove the plating vapor that has entered the molten pool during welding, that is, it is considered difficult to make the porosity defect rate completely 0%. In this regard, the lap fillet welded joints manufactured by the method of this disclosure may have a porosity defect rate in the weld bead 50 that is greater than 0%, 0.5% or more, 1.0% or more, 5.0% or more, or 10.0% or more.

[0030] Furthermore, the porosity of a weld bead is determined as the ratio of the total length of porosity defects to the length of the weld bead in a plan view (Figures 1-3, 5) (sum of the lengths of each porosity defect in the direction of the weld line / length of the weld bead). The length 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 determine the length of the porosity defects.

[0031] 3. Other matters In the manufacturing method of this disclosure, tack welding X1 and main welding X2 are performed so as to satisfy the above conditions 1 to 3, and the first steel plate 10 and the second steel plate 20 are joined to obtain an overlap fillet welded joint. The first steel plate 10 and the second steel plate 20 may be any known steel plates. Furthermore, the manufacturing method of this disclosure aims to reduce porosity defects in the weld bead that are caused by plating vapor, in other words, it is assumed that a plating layer is formed on one or both of the first steel plate 10 and the second steel plate 20. An example of the first steel plate 10, the second steel plate 20 and the plating layer will be described below.

[0032] 3.1 First steel plate and second steel plate As described above, in the manufacturing method of the present disclosure, the first steel plate 10 and the second steel plate 20 are welded together to form an overlap fillet weld structure. As shown in Figure 4B, in the overlap fillet weld structure, for example, a weld bead 50 is formed at the corner between the first surface 11 of the first steel plate 10 and the tip surface of the end portion 20x of the second steel plate 20. If the side of the first steel plate 10 on which the weld bead 50 is formed (the first surface 11 side) is considered the top and the side opposite to the weld bead 50 (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.

[0033] As shown in Figures 4A and 4B, 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.

[0034] The thickness of the first steel sheet 10 and the second steel sheet 20 is not particularly limited. "Thickness" refers to the thickness of the base steel sheet excluding the plating layer. The thickness of the first steel sheet 10 and the thickness of the second steel sheet 20 may be the same or different. According to the inventor's new findings, the effects of the manufacturing method of the present disclosure are particularly pronounced when the thickness of the first steel sheet 10 and the second steel sheet 20 are thin. For example, the thickness of the first steel sheet 10 and the second steel sheet 20 may be less than 4.0 mm, 3.8 mm or less, 3.6 mm or less, 3.4 mm or less, 3.2 mm or less, 3.0 mm or less, 2.8 mm or less, 2.6 mm or less, 2.4 mm or less, 2.2 mm or less, 2.0 mm or less, 1.8 mm or less, or 1.6 mm or less. Furthermore, the plate thickness may be 0.6 mm or more, 0.8 mm or more, 1.0 mm or more, or 1.2 mm or more.

[0035] The first steel plate 10 and the second steel plate 20 may have various strengths depending on their application. For example, one or both of the first steel plate 10 and the second steel plate 20 may have a tensile strength of 270 MPa or more and 980 MPa or less. The first steel plate 10 and the second steel plate 20 may have similar tensile strengths, or they may have different tensile strengths. In this application, "tensile strength" of the steel plate refers to the standard defined in JIS Z 2241:2011.

[0036] The first steel sheet 10 and the second steel sheet 20 may have various chemical compositions and metal structures. The first steel sheet 10 and the second steel sheet 20 may each be ordinary steel sheets or steel sheets containing additive elements such as chromium, and their chemical composition and metal structure may be adjusted considering the desired mechanical properties and formability. Regardless of the chemical composition and metal structure of the first steel sheet 10 and the second steel sheet 20, the effects of the manufacturing method of this disclosure will be achieved.

[0037] 3.2 Plating layer As described above, a plating layer is provided on the surface of one or both of the first steel plate 10 and the second steel plate 20, thereby ensuring excellent corrosion resistance. However, during lap fillet welding, a portion of the plating layer between the upper and lower plates evaporates and becomes plating vapor, which is likely to cause porosity defects in the weld bead 50. More specifically, in a lap fillet welded joint as shown in Figure 4B, 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 50. However, 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 50, and even if the molten pool penetrates to the second surface 12, the plating vapor from the plating layer 42 is unlikely to substantially affect the amount of porosity defects in the weld bead 50. The same applies to the plating layer 44 formed on the fourth surface 24 of the second steel plate; the plating vapor of the plating layer 44 has little substantial effect on the amount of porosity defects in the weld bead 50.

[0038] When manufacturing an overlapping fillet weld joint as shown in Fig. 4B, the total deposition amount of the plating layer 41 formed on the first surface 11 of the first steel plate 10 and the plating layer 43 formed on the third surface 23 of the second steel plate 20 can have a significant impact on the porosity defect rate in the weld bead 50. If this total deposition amount is small, the porosity defects in the weld bead 50 will also be reduced. On the other hand, if the deposition amount is too large, the effect of improving corrosion resistance will saturate and the cost will increase. In this regard, in the manufacturing method of the present disclosure, the first steel plate 10 has a first surface 11 facing the second steel plate 20 side and a second surface 12 facing the side opposite to the first surface 11, and the second steel plate 20 has a third surface 23 facing the first steel plate 10 side and a fourth surface 24 facing the side opposite to the third surface 23. The end of the second steel plate 20 is joined to the first surface 11 via the weld bead 50, and when the plating layers 41 and 43 are formed on one or both of the first surface 11 and the third surface 23 (as shown in Fig. 4B), the total deposition amount of the plating layers 41 and 43 on the first surface 11 and the third surface 23 is 10 g / m 2 or more and 500 g / m 2 or less may be acceptable. For example, when no plating layer is formed on the first surface 11, the deposition amount of the plating layer 43 formed on the third surface 23 may be 10 g / m 2 or more and 500 g / m 2 or less. Alternatively, for example, when the deposition amount of the plating layer 41 on the first surface 11 is 5 g / m 2 the deposition amount of the plating layer 43 on the third surface 23 may be 5 g / m 2 or more and 495 g / m 2 or less. Thus, by setting the total deposition amount of the plating layers 41 and 43 on the first surface 11 and the third surface 23 to be 10 g / m 2 or more and 500 g / m 2 or less, it is considered that although plating vapor enters the molten pool during this welding, the plating vapor is efficiently discharged through the gap G between the steel plates, and the porosity defect rate of the weld bead 50 can be reduced. The total deposition amount of the plating layers 41 and 43 on the first surface 11 and the third surface 23 is 20 g / m 2 or more, 25 g / m 2 or more, 30 g / m 2 or more, 35 g / m 2 or more, or 40 g / m2 It may be greater than or equal to 450g / m². 2 Below 400g / m 2 The following, or 350g / m² 2 The following is also possible. On the other hand, as shown in Figure 4A, 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 50, so the amount of plating layer 42 and the plating layer 44 attached is not particularly limited.

[0039] Furthermore, the amount of plating layer adhesion only needs to be determined in an area sufficiently far from the weld bead 50 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. Alternatively, it can be determined by measuring the thickness of the plating layer using a cross-sectional microscope or an electromagnetic film thickness gauge, and calculating the amount from the density of the plating layer.

[0040] 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 (zinc-based plating layer), for example. 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 Zn in mass% of 40% or more and 100% or less. The Zn content in the plating layer may be 45% or more by mass, 50% or more by mass, 55% or more by mass, or 60% or more by mass. 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 performed. For example, the plating layer may be a Zn-Al alloy plating layer containing at least Zn and Al, a Zn-Al-Mg alloy plating layer containing Mg, or a Zn-Al-Si alloy plating layer or a Zn-Al-Mg-Si alloy plating layer 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%. Specific examples of the chemical composition of the zinc-based plating layer include, but are not limited to, Zn-19%Al-6%Mg-0.2%Si, Zn-11%Al-3%Mg-0.2%Si, Zn-6%Al-3%Mg, Zn-55%Al-1.6%Si, and Zn-5%Al-0.1%Mg. The zinc-based plating layer may be an alloyed hot-dip galvanized layer, a hot-dip galvanized layer, or an electroplated galvanized layer.

[0041] As described above, in the manufacturing method of the present disclosure, a plating layer is formed on one or both of the first surface 11 of the first steel sheet 10 and the third surface 23 of the second steel sheet 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 sheet 10, and the third surface 23 and fourth surface 24 of the second steel sheet 20. Figure 4A shows a configuration in which a plating layer 41 is formed on the first surface of the first steel sheet 10 and a plating layer 43 is formed on the third surface 23 of the second steel sheet 20, but one or both of the plating layers 41 and 43 may not be present. Also, Figure 4A shows a configuration in which a plating layer 42 is formed on the second surface 12 of the first steel sheet 10 and a plating layer 44 is formed on the fourth surface 24 of the second steel sheet 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 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 each 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 4B, the area surrounding the weld bead 50 after welding may become a heat-affected zone 45 due to the heat effects during welding. More specifically, in the heat-affected zone 45, all or part of the plating layer may evaporate due to the heat effects during welding, and the plating layer may be altered or degraded. Furthermore, this state may vary depending on the composition and structure of the plating and the degree of heat effects due to 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 50 and its surrounding area. Alternatively, post-treatment such as applying touch-up paint may be performed.

[0042] 3.3 Gap As explained with respect to conditions 1 to 3, in the manufacturing method of this disclosure, it is assumed that a gap G will be created between the first steel plate 10 and the second steel plate 20 when the welding X2 is performed. However, the gap G before the molten pool cools and solidifies and the gap G after the molten pool cools and solidifies as a weld bead 50 are not necessarily the same. As stated above, the effect of reducing porosity defects is thought to be due to the gap G before the molten pool cools and solidifies, and the size of the gap G after cooling and solidification is not particularly limited. As stated above, in the manufacturing method of this disclosure, it is assumed that the gap G before the molten pool cools and solidifies is appropriately controlled when conditions 1 to 3 are met. For example, the gap G before the molten pool cools and solidifies may be 0.05 mm or more and 0.3 mm or less. On the other hand, the gap G after the molten pool cools and solidifies may be 0 mm or greater than 0 mm. [Examples]

[0043] 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.

[0044] 1. Preparation of plated steel sheet The plated steel sheets to be welded were prepared with the "plating composition," "total plating adhesion amount" on both sides, and "sheet thickness" shown in Table 1 below. The tensile strength of each steel sheet was 400 MPa. The dimensions of the steel sheets were 50 mm wide x 170 mm long for steel sheet 1 and 50 mm wide x 150 mm long for steel sheet 2. The steel sheets shown in Table 1 have plating layers on both the front and back sides, and the amount of plating adhesion on the front side and the back side are substantially the same.

[0045] [Table 1]

[0046] 2. Tack welding and main welding Tack welding and main welding were performed on each of the "steel plate 1" and "steel plate 2" sections as follows.

[0047] 2.1 Welding conditions for steel plates 1 Two of the above steel plates 1 were overlapped, and tack welding was performed under one of the conditions shown in patterns A to F below, followed by main welding to obtain an overlap fillet welded joint. The welding conditions for the main welding were as follows. In addition, during both tack welding and main welding, the entire upper plate and only one point in the longitudinal center of the lower plate were fixed with a jig at a distance of 10 mm from the overlap portion on the upper plate side and 40 mm from the overlap portion on the lower plate side. Joint type: Overlap fillet joint Overlap: 5mm Welding machine: Daihen Welbee P350L II Welding mode: DC-CO2 Gas flow rate: 20 L / min Welding wire type: YM-28 (φ1.2mm) manufactured by Nippon Steel Welding Industries Co., Ltd. Protrusion length: 15mm Welding position: Downward horizontal Torch angle: Upright angle 45 degrees, forward / backward angle 0 degrees Targeting the wire: corner Welding speed: 400 mm / min Welding current: 140A

[0048] 2.2 Welding conditions for steel plate 2 Two of the above steel plates 2 were overlapped, and tack welding was performed under one of the conditions shown in patterns A to F below, followed by main welding to obtain an overlap fillet welded joint. The welding conditions for the main welding were as follows. In addition, during both tack welding and main welding, the entire upper plate and only one point in the longitudinal center of the lower plate were fixed with a jig at a distance of 10 mm from the overlap portion on the upper plate side and 40 mm from the overlap portion on the lower plate side. Joint type: Overlap fillet joint Overlap: 5mm Welding machine: Daihen Welbee P350L II Welding mode: DC-CO2 Gas flow rate: 20 L / min Welding wire type: YM-28 (φ1.2mm) manufactured by Nippon Steel Welding Industries Co., Ltd. Protrusion length: 15mm Welding position: Downward horizontal Torch angle: Upright angle 60 degrees, forward / backward angle 0 degrees Targeting the wire: corner Welding speed: 400 mm / min Welding current: 200A

[0049] 2.3 Welding Patterns Patterns A through F are as follows: Pattern A: Main welding was performed without tack welding. Pattern B: After applying a tack weld to the end of the area to be welded, the main weld was performed from the start end to the end end without applying a tack weld to the start end. Pattern C: After applying a tack weld to the starting end of the area to be welded, another tack weld was applied to the ending end, and then the main weld was performed from the starting end to the ending end. Pattern D: After applying a tack weld to the starting end of the area to be welded, the main weld was performed from the starting end to the ending end without applying a tack weld to the ending end. Pattern E: After applying a tack weld to the end of the area to be welded, another tack weld was applied to the start end, and then the main weld was performed from the start end towards the end. Pattern F: Tack welding was performed on both the start and end ends of the area to be welded, and after 60 seconds, the main weld was performed from the start end to the end end.

[0050] 3. Evaluation of stomatal defect rate For each lap fillet welded joint obtained as described above, the porosity defect rate in the weld bead was measured. Specifically, the porosity defect rate was calculated as the ratio of the sum of the lengths of the porosity defects to the length of the weld bead in a plan view (sum of the lengths of each porosity defect in the direction of the weld line / length of the weld bead). The length of the weld bead and the length of the porosity defects in the weld bead were determined based on X-ray radiographs obtained by X-ray transmission testing. The results are shown in Table 2 below. For reference, Figure 5 shows an X-ray radiograph of a lap fillet welded joint between two steel plates 1.

[0051] [Table 2]

[0052] The results shown in Table 2 above indicate the following: (1) Regardless of the thickness of the steel plate, the rate of porosity defects in the weld bead is reduced when tack welding is performed before main welding (Pattern B~F) compared to when main welding is performed without tack welding (Pattern A). (2) Regardless of the thickness of the steel plate, patterns D to F can reduce the porosity defect rate more effectively than pattern B. Here, pattern B involves applying tack welding only to the end of the area to be welded, and is similar to conventional tack welding used to suppress displacement of the steel plate during main welding. In contrast, patterns D to F differ from conventional tack welding in the position, sequence, or waiting time of the tack welding. That is, by applying tack welding in a different position, sequence, or waiting time than conventional tack welding, as in patterns D to F, and then performing main welding, it can be said that porosity defects in the weld bead can be reduced more significantly. (3) In addition, although pattern C differs from conventional tack welding in terms of position and order, in this case the effect is not as good as patterns D to F, and the rate of porosity defects in the weld bead may be higher than in pattern B. (4) The effect of reducing the porosity defect rate by tack welding is more pronounced when the steel plate is thinner than when it is thicker.

[0053] As described above, when manufacturing lap fillet welded joints by welding steel plates with a plating layer, tack welding and main welding can be performed in such a way that at least one of the following conditions 1 to 3 is satisfied, thereby significantly reducing porosity defects in the weld bead. Condition 1 corresponds to pattern D above, condition 2 corresponds to pattern E above, and condition 3 corresponds to pattern F above.

[0054] Condition 1: After applying a tack weld to the starting end of the area to be welded, perform the main weld from the starting end to the ending end without applying a tack weld to the ending end. Condition 2: After applying a tack weld to the end of the area to be welded, apply another tack weld to the start end, and then perform the main weld from the start end towards the end. Condition 3: Tack welds are applied to both the start and end ends of the area to be welded, and after 60 seconds or more have elapsed, the main weld is performed from the start end towards the end end. [Explanation of Symbols]

[0055] X1 Tack Welding X2 welded 10 First steel plate 11 Page 1 12 Side 2 20 Second steel plate 20x ends 23 Page 3 24 Page 4 30 welding locations 31 Starting point 32 Termination 41-44 Plating layer 50 weld beads

Claims

1. A method for manufacturing lap fillet welded joints, The first steel plate and the second steel plate are overlapped and then tack-welded, and This includes performing the main welding on the area to be welded after the aforementioned tack welding, A plating layer exists at the location where the welding is to be performed. A manufacturing method that satisfies at least one of the following conditions 1 to 3. Condition 1: After applying the tack weld to the starting end of the area to be welded, the main weld is performed from the starting end to the ending end without applying the tack weld to the ending end. Condition 2: After applying the tack weld to the end of the area where the main welding is to be performed, the tack weld is then applied to the start end, and then the main welding is performed from the start end towards the end. Condition 3: Apply the tack weld to both the starting and ending ends of the area to be welded, and after 60 seconds or more have elapsed, perform the main weld from the starting end towards the ending end.

2. The thickness of the first steel plate and the second steel plate is 3.2 mm or less. The manufacturing method according to claim 1.

3. The bead width W of the aforementioned tack weld １ and the bead width W of the main weld ２ W １ / W ２ The value is between 1.2 and 2.

0. The manufacturing method according to claim 1 or 2.

4. The aforementioned tack weld is performed within 50 mm of the location where the main weld is to be made. The manufacturing method according to claim 1 or 2.

5. When multiple tack welds are performed, the interval between the tack welds is 30 mm or more. The manufacturing method according to claim 1 or 2.

6. The aforementioned plating layer is a zinc-based plating layer. The manufacturing method according to claim 1 or 2.

7. 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 a weld bead. The 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 500g / m ２ The following is: The manufacturing method according to claim 1 or 2.

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