Arc-welded joint and arc-welding method

Abstract

This invention provides an arc welding head and an arc welding method. The arc welding head of this invention has a welded portion formed by overlapping and arc welding at least two steel plates. When the weld throat thickness in the welded portion is defined as 'a', and the thickness of the upper plate in the steel plates is defined as 't', the weld throat thickness and the upper plate thickness satisfy the relationship 0.5×t≤a≤1.8×t. Furthermore, the surface area of ​​the weld in the region extending 2.0 mm along the weld metal direction from the weld toe of the welded portion and in the region extending 2.0 mm along the base metal direction from the weld toe is defined as the weld toe surface area S. TOE , the surface area S of the weld toe TOE The area of ​​the region covered by welding slag is denoted as the surface area of ​​the welding slag, S. SLAG At that time, by S RATIO =100×S SLAG / S TOE Calculated slag coverage area ratio S RATIO It is below 50%.

Description

Technical Field

[0001] This invention relates to an arc welded joint with excellent joint strength suitable for automotive parts and the like, and an arc welding method for obtaining such an arc welded joint. Background Technology

[0002] In recent years, there has been a growing demand for automobiles to balance the need for higher strength and rigidity in various components aimed at improving vehicle safety and reliability, with the need for lighter components aimed at improving fuel efficiency. Consequently, the use of high-strength steel sheets to reduce the thickness of steel plates in components is progressing.

[0003] As a manufacturing method for welded joints, lap fillet welding, which involves overlapping two steel plates, is widely used. Since various automotive components operate under repeated loads, ensuring fatigue strength is crucial, and sufficient static strength is also important from a crash safety perspective. Particularly in components used in corrosive environments, the corrosion zone expands over time, and corrosion progresses along the plate thickness, reducing the thickness of the welded portion and its vicinity, making it difficult to ensure component strength.

[0004] For example, Patent Document 1 discloses an arc-welded lap joint structure in which the strength of the weld metal exceeds that of the base material made of a high-strength material, and the base material fractures without the weld metal fracturing under excessive load, thus improving the fracture morphology. In this technology, in a lap joint with a specified weld leg length and theoretical weld throat thickness, the tensile strength (TS) of the steel plate is 640 MPa or higher, and the fracture mode is improved by specifying the Ceq and hardness of the steel plate and the weld metal.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent No. 3905876 Summary of the Invention

[0008] However, the technology disclosed in Patent Document 1 requires the use of steel plates with a tensile strength of 640 MPa or higher. This effect is not demonstrated for steel plates with a tensile strength of less than 640 MPa, which are suitable for chassis components of automobiles. Furthermore, Patent Document 1 focuses on welded joints that have not undergone corrosion, and does not investigate whether the desired joint characteristics can be obtained when the joint strength decreases in a corrosive environment.

[0009] The present invention was made in view of these issues, and aims to provide an arc welded joint that can suppress rusting of the welded part and has excellent joint strength even in a corrosive environment, as well as an arc welding method for obtaining the arc welded joint.

[0010] In order to solve the above-mentioned problems, the inventors have conducted repeated and in-depth research on methods to suppress rusting of welded parts of steel components and to improve the joint strength of welded parts even in corrosive environments.

[0011] The inventors have realized that by specifying the weld throat thickness corresponding to the thickness of the base steel plate, the allowable stress of the weld can be ensured, and sufficient joint strength can be obtained even when tensile loads are applied in a direction perpendicular to the weld line. Furthermore, it is believed that by reducing weld slag adhering to the weld, especially the weld toe, rusting of the weld can be suppressed, thereby preventing a decrease in joint strength caused by corrosion.

[0012] This invention was completed based on the above insights and through further repeated research, and its main points are as follows.

[0013] [1] An arc welding joint is an arc welding joint having a welded portion formed by overlapping and arc welding at least two steel plates.

[0014] When the thickness of the weld throat in the above-mentioned welded part is set as a (mm) and the thickness of the upper plate in the above-mentioned steel plate is set as t (mm), the thickness of the weld throat and the thickness of the upper plate satisfy the relationship 0.5×t≤a≤1.8×t.

[0015] Furthermore, the surface area of ​​the weld from the weld toe in the weld metal direction to 2.0 mm and the surface area of ​​the weld from the weld toe in the base metal direction to 2.0 mm are defined as the weld toe surface area S. TOE (mm 2 ), the surface area S of the toe of the above weld TOE The area of ​​the region covered by welding slag is denoted as the surface area of ​​the welding slag, S. SLAG (mm 2 When ), the slag coverage area ratio S calculated by equation (1) RATIO (%) is below 50%,

[0016] S RATIO =100×S SLAG / S TOE …(1)

[0017] [2] According to the arc welding head described in [1], wherein the maximum value of the weld throat thickness in the weld portion at the end of the weld where the weld seam is removed is set as a. max (mm), minimum value is set to a minWhen the thickness is (mm), the maximum value and the minimum value of the above-mentioned weld throat thickness satisfy a. max / a min A relationship of ≤1.5.

[0018] [3] An arc welding method for obtaining the arc welded joint described in [1] or [2].

[0019] When at least two steel plates are overlapped and arc welded to form a welded section...

[0020] A protective gas consisting of Ar gas and an oxidizing gas, wherein the oxidizing gas satisfies the relationship of equation (2), is used.

[0021] 2×[O2]+[CO2]≤5…(2)

[0022] Where [O2] is the volume percentage of O2 in the protective gas, and [CO2] is the volume percentage of CO2 in the protective gas.

[0023] [4] According to the arc welding method described in [3], wherein, in the above arc welding, the welding speed is set to v. t (cm / min), set the wire feeding speed to v w At (cm / min), the above welding speed and the above wire feeding speed satisfy 5≤v w / v t Relationships ≤35.

[0024] [5] According to the arc welding method described in [3] or [4], wherein, in the above-mentioned arc welding, the steel plate and the welding wire are intermittently short-circuited.

[0025] The average short-circuit frequency F of the above short circuit AVE The frequency (Hz) is 20–300 Hz, and the maximum short-circuit period T of the above short circuit is... CYC (s) is less than 1.5s.

[0026] [6] The arc welding method according to any one of claims [3] to [5], wherein a pulsed current is used as the welding current in the above-mentioned arc welding.

[0027] Let the peak current of the above pulse current be I. PEAK (A) Set the base current to I BASE (A) Set the peak period to t PEAK (ms), set the rise period to t UP (ms), set the descent period to t DOWN When the distance between the steel plate and the conductive nozzle is set to L (mm), the value of X (A·s / m) calculated by equation (3) satisfies 50≤X≤250.

[0028] X = (I PEAK ×t PEAK / L)+(I PEAK +I BASE )×(t UP +t DOWN ) / (2×L)…(3)

[0029] [7] The arc welding method according to any one of [3] to [6], wherein a solid welding wire is used as the welding wire in the above-mentioned arc welding.

[0030] According to the present invention, by specifying a weld throat thickness corresponding to the thickness of the base steel plate, the allowable stress of the welded joint is ensured, and by reducing the amount of weld slag adhering to the welded joint, rusting is suppressed. This results in an arc-welded joint exhibiting stable and excellent joint strength even in corrosive environments. The present invention also provides an arc welding method for obtaining this welded joint. Attached Figure Description

[0031] [ Figure 1 ] Figure 1 This is a perspective view schematically illustrating an example of applying the invention to lap fillet welds.

[0032] [ Figure 2 ] Figure 2 (A) and Figure 2 (B) is to Figure 1 The enlarged cross-sectional view of the welding wire and its vicinity is a schematic diagram representing the state of short-circuit transition.

[0033] [ Figure 3 ] Figure 3 It is a schematic representation of passing through Figure 1 A three-dimensional view of the weld toe and the beginning and end of the weld formed by the lap fillet weld.

[0034] [ Figure 4 ] Figure 4 (A) and Figure 4 (B) is a schematic diagram showing the welded portion in the arc welding joint of the present invention.

[0035] [ Figure 5 ] Figure 5 yes Figure 4 (A) is a cross-sectional view along line A-A of the arc welded joint, and is a schematic representation of the weld toe and its surroundings.

[0036] [ Figure 6 ] Figure 6 This is a diagram showing an example of the waveform of the pulsed current supplied as welding current.

[0037] [ Figure 7 ] Figure 7It is a graph showing the relationship between the weld throat thickness and slag coverage area of ​​the welded part and the ratio of the joint tensile strength to the base metal tensile strength. Detailed Implementation

[0038] Reference Figures 1-7 The arc welding joint and arc welding method of the present invention will be described. Here, as an example, an embodiment of the present invention applied to lap fillet welding will be described. However, the present invention is not limited to lap fillet welding, but can also be applied to various welding techniques (e.g., butt welding).

[0039] First, refer to Figures 1-3 The technical concept of this invention will be explained. Figures 1-3 An example of lap fillet welding of two steel plates using arc welding is shown. It should be noted that, as... Figures 1-3 In the example shown, when two steel plates are overlapped for arc welding, the upper steel plate is called the top plate, and the lower steel plate is called the bottom plate. When three or more steel plates are overlapped, the topmost steel plate is called the top plate.

[0040] In this invention, such as Figure 1 As shown, the welding wire 1, which is continuously fed from the welding torch 2 to the steel plate 3 through the center of the welding torch 2, and the steel plate 3 serve as electrodes, and a welding voltage is applied from a welding power source (not shown). Specifically, "from the welding torch 2 to the steel plate 3" refers to "the welding line formed by the corner joint 4 of the step formed by the overlap of two steel plates 3 as base materials." Part of the shielding gas (not shown) supplied from the welding torch 2 is ionized and plasma-entrained, thereby forming an electric arc 5 between the welding wire 1 and the steel plate 3. Furthermore, the portion of the shielding gas that does not ionize and flows from the welding torch 2 to the steel plate 3 forms a molten pool (e.g., a weld pool formed by melting the electric arc 5 and the steel plate 3). Figure 1 (Not shown in the diagram) This process isolates the welding wire 1 from the outside air. The heat energy of the electric arc 5 melts the tip of the welding wire 1 into a droplet, which is then transported to the molten pool by electromagnetic force, gravity, etc. This phenomenon occurs continuously as the welding torch 2 or the steel plate 3 moves, causing the molten pool to solidify behind the welding line, forming the weld 6. This achieves the joining of the two steel plates.

[0041] In such arc-welded joints, when the ratio of the weld throat thickness to the upper plate thickness (i.e., the ratio of weld throat thickness to the upper plate thickness) is small, the weld wire deposition is insufficient, the weld throat cross-sectional area becomes smaller, and thus the stress in the welded area increases. On the other hand, when this ratio is too large, the weld wire deposition becomes excessive, the weld becomes convex, and thus the stress concentration in the weld toe increases.

[0042] To address this problem, the present invention focuses on specifying the weld throat thickness corresponding to the thickness of the base steel plate used as the upper plate (refer to...). Figure 5Specifically, when the weld throat thickness is set as a (mm) and the thickness of the base steel plate used as the upper plate is set as t (mm), the stress concentration in the welded part can be mitigated by satisfying the relationship 0.5×t≤a≤1.8×t.

[0043] Therefore, in this invention, by specifying the weld throat thickness corresponding to the plate thickness, stress concentration in the weld metal can be mitigated even when a tensile load is applied in a direction perpendicular to the weld line. As a result, it has been found that an arc weld joint with sufficient joint strength can be obtained.

[0044] Furthermore, it is known that to effectively manage weld throat thickness based on plate thickness, it is essential to control the deposition rate per unit length of welding wire during welding. Therefore, in this invention, as described later, the focus is on the relationship between welding speed and wire feed speed.

[0045] As described above, from the viewpoint of improving joint strength even in corrosive environments, the present invention further focuses on suppressing rust in the welded portion, especially the weld toe.

[0046] like Figure 1 As shown, when two steel plates 3 are overlapped and lapped using arc welding, the O2 or CO2 mixed in the shielding gas is heated by the arc 5 to carry out the reaction shown in formula (6) or formula (7).

[0047] O2→2[O]…(6)

[0048] CO2→CO+[O]…(7)

[0049] The oxygen generated in this decomposition reaction dissolves in the molten metal 7 and the molten pool 8 (see reference). Figure 2 (A) and Figure 2 (B) When the weld metal is cooled and solidified, it becomes air bubbles that remain inside the weld metal. In addition, the oxidation reaction between oxygen and iron can sometimes deteriorate the mechanical properties of the weld metal.

[0050] To solve this problem, welding wire 1 and steel plate 3 with added non-ferrous elements such as Si, Mn, and Ti as deoxidizers are used. That is, the reaction between oxygen and iron is suppressed by discharging the oxygen generated by the reaction of formula (6) or formula (7) in the form of welding slag composed of SiO2, MnO, TiO2, etc.

[0051] However, the weld slag discharged onto the surface of the molten pool 8 solidifies during the subsequent cooling process, adhering to the surface of weld 6 and the weld toe 9 (see reference). Figure 3The slag adheres to the weld toe 9 of the arc weld joint, and solidifies. Thus, even with chemical conversion treatment (e.g., zinc phosphate treatment), a chemical conversion layer composed of zinc phosphate crystals will not form in the slag area, which acts as an insulator. Furthermore, in areas not covered by the chemical conversion layer, even with electrodeposition coating, the coating formation becomes insufficient, and the coating adhesion is inadequate, resulting in a significant reduction in corrosion resistance. Consequently, the plate thickness decreases due to the progression of rust corrosion. Therefore, it is necessary to use welding wire 1 and steel plate 3 with added deoxidizers to prevent the deterioration of the mechanical properties of the weld metal and to inhibit slag formation.

[0052] Specifically, without reducing the amount of additives used to ensure the mechanical properties of the weld metal, an oxidizing gas is specified in the protective gas to suppress the slag formation reaction (oxidation reaction). By suppressing the slag formation reaction, poor coating quality in electrodeposition coatings is reduced, thereby improving corrosion resistance and preventing rust and corrosion progression even in corrosive environments.

[0053] That is, in this invention, it has been found that by specifying the oxidizing gas contained in the protective gas as described above, the amount of O2 and CO2 mixed in is reduced, thereby suppressing the formation of weld slag adhering to the welded part, especially the weld toe. This suppresses rusting and inhibits the reduction in joint strength caused by corrosion.

[0054] Here, using Figure 3 The weld toe 9 and the weld termination 10 in weld 6 are described below. Figure 3 As shown, in this invention, "weld start and end points" refers to the regions that respectively include the weld start point and weld end point. "Weld start point" refers to the region extending 15mm along the weld line from the weld start point (welding start position) towards the weld end point (welding end position), and "weld end point" refers to the region extending 15mm along the weld line from the weld end point towards the weld start point. Furthermore, in this invention, "weld toe" refers to the boundary between the weld metal and the unmelted base metal plate in the direction perpendicular to the weld line within the weld. "Weld line" refers to a line parallel to the welding direction of weld 6.

[0055] Next, refer to Figure 4 and Figure 5 The arc welding head of the present invention will be described below.

[0056] Figure 4 (A) shows Figure 1 A three-dimensional view of weld seam 6 of the arc welded joint formed in the lap fillet weld. Figure 4 (B) shows a top view of the arc-welded joint. Figure 5 Showing frontal view Figure 4 (A) is a partial enlarged view of the cross section along line A-A of the arc-welded joint shown in Figure (A).

[0057] The arc welding joint of the present invention is an arc welding joint formed by overlapping at least two steel plates and arc welding as described above. When the weld throat thickness in the weld portion of this arc welding joint is defined as a (mm) and the thickness of the upper plate in the steel plate is defined as t (mm), the weld throat thickness and the upper plate satisfy the relationship 0.5×t≤a≤1.8×t. Furthermore, the surface area of ​​the weld in the region extending 2.0mm along the weld metal direction from the weld toe of the weld portion and in the region extending 2.0mm along the base metal direction from the weld toe is defined as the weld toe surface area S. TOE (mm 2 The surface area S of the weld toe TOE The area of ​​the region covered by welding slag is denoted as the surface area of ​​the welding slag, S. SLAG (mm 2 When ), the slag coverage area ratio S calculated by equation (1) RATIO (%) is below 50%.

[0058] S RATIO =100×S SLAG / S TOE …(1)

[0059] The relationship between the weld throat thickness 'a' in the welded section and the plate thickness 't' of the upper plate is: 0.5 × t ≤ a ≤ 1.8 × t

[0060] Figure 5 A schematic diagram of the weld toe 9 and its surrounding area is shown. Figure 5 The distance a (mm) shown represents the throat thickness, and t (mm) represents the thickness of the upper plate. When the throat thickness a (mm) is less than (0.5 × t) (mm), the welding wire deposition is insufficient, the throat cross-sectional area becomes smaller, and thus the stress in the welded part increases. Therefore, in this invention, the throat thickness a (mm) is (0.5 × t) (mm) or more. The throat thickness a (mm) is preferably (0.6 × t) (mm) or more, more preferably (0.65 × t) (mm) or more, and even more preferably (0.95 × t) (mm) or more. On the other hand, when the throat thickness a (mm) is greater than (1.8 × t) (mm), the welding wire deposition becomes excessive, the weld becomes convex, and thus the stress concentration in the weld toe 9 increases. Therefore, in this invention, the throat thickness a (mm) is (1.8 × t) (mm) or less. The weld throat thickness a (mm) is preferably (1.6×t)(mm) or less, and more preferably (1.5×t)(mm) or less.

[0061] The aforementioned "weld throat thickness a" can be measured as described in the embodiments below. Specifically, the weld throat thickness is measured in a section perpendicular to the weld line in the plate thickness direction at any eight locations along the weld line, within the region excluding the weld seam 6's initial and final ends 10 (each 15 mm in length). Figure 5 As shown, weld 6 was cut at any 8 locations along the plate thickness direction perpendicular to the weld line, and nitric acid ethanol etching was performed. Then, cross-sectional images were taken using an optical microscope (10x magnification) to determine the thickness of each weld throat. Their average value was taken as the "weld throat thickness a (mm)". Figure 5 In the example shown, the shortest distance from the lower surface of the upper plate in steel plate 3 to the boundary between the weld metal 6 and the weld metal surface is taken as the weld throat thickness. Figure 5 The dashed circle shown indicates the range of this shortest distance. The "lower surface" mentioned above refers to the surface where the upper and lower plates of steel plate 3 overlap.

[0062] Slag Coverage Area Ratio RATIO (%): Below 50%

[0063] like Figure 4 As shown, the surface area of ​​a defined region including the weld toe 9 is defined as the weld toe surface area S. TOE (mm 2 ), the surface area S of the weld toe TOE The area covered by the welding slag 11 is defined as the surface area of ​​the welding slag S. SLAG (mm 2 When ), the slag coverage area ratio S calculated by the above formula (1) is... RATIO The percentage (%) is below 50%. If the weld slag 11 generated during welding exceeds 50% of the slag coverage area and adheres to the surface of weld 6, even with chemical conversion treatment of the arc weld joint, a sufficient chemical conversion layer cannot be formed. Even with electrodeposition coating, poor coating formation and reduced coating adhesion will occur. Therefore, rusting and thinning are likely in corrosive environments, resulting in a decrease in joint strength. If the amount of weld slag generated is reduced, the agglomeration of weld slag 11 on the surface of weld 6 is suppressed, thereby improving chemical conversion treatment and electrodeposition coating properties, and suppressing the decrease in joint strength caused by corrosion. Therefore, the slag coverage area S RATIO Preferably, it is 45% or less, more preferably 40% or less.

[0064] The aforementioned "surface area S of the weld toe" TOE” It refers to, for example Figure 4 (A) and Figure 4As shown in (B), the surface area of ​​weld 6 is the region extending 2.0 mm from the weld toe 9 along the weld metal direction perpendicular to the weld line and the region extending 2.0 mm from the weld toe 9 along the base metal direction perpendicular to the weld line. That is, in Figure 4 (A) and Figure 4 In the example shown in (B), the surface area of ​​weld 6 is the 4.0 mm region centered on weld toe 9. Additionally, "slag surface area S" SLAG "refers to such as Figure 4 (A) and Figure 4 As shown in (B), the calculated surface area S at the weld toe TOE Within the area (in) Figure 4 In the example shown, within a 4.0 mm area centered on weld toe 9, the surface area S of the weld toe is... TOE The total area of ​​the region covered by weld slag 11. Surface area S of the weld toe. TOE and the surface area S of welding slag SLAG It can be determined according to the method described in the embodiments described later.

[0065] Because a lower amount of non-conductive welding slag results in better chemical conversion treatment and electrodeposition coating properties, the welding slag coverage area ratio S increases. RATIO Smaller is preferred, but there is no specific lower limit. S slag coverage area ratio RATIO Preferably, it is 0.1% or more, more preferably 0.5% or more, and even more preferably 1.0% or more.

[0066] Thus, by adjusting the weld throat thickness 'a' and the slag coverage area ratio 'S' in the welded section... RATIO Within the aforementioned range, the aforementioned effects can be achieved. Figure 7 The figure illustrates the relationship between weld throat thickness and slag coverage area ratio and the ratio of joint tensile strength to base metal tensile strength (strength ratio). A detailed description follows, such as... Figure 7 As shown, by properly controlling the weld throat thickness and reducing the oxidizing gas contained in the shielding gas, the slag coverage area can be reduced, thereby improving the joint strength.

[0067] When a tensile load is applied in a direction perpendicular to the weld line, in order to further and more effectively alleviate stress concentration, in addition to the above-described configuration, it is preferable to stabilize the shape of the weld 6.

[0068] Therefore, in this invention, as Figure 4 and Figure 5 As shown, the deviation of the weld throat thickness 'a' in the weld portion removed from the area (weld end 10) extending 15 mm from the weld end of weld 6 is preferably controlled within a specified range.

[0069] The ratio of the maximum value to the minimum value of the weld throat thickness 'a' (preferred condition)

[0070] On the cross-section of weld 6 in a direction perpendicular to the line parallel to the welding direction (weld line), the maximum value of the weld throat thickness in the welded part is set as a. max (mm), set the minimum weld throat thickness in the welded section as a. min When the thickness is (mm), the maximum and minimum values ​​of the weld throat thickness preferably satisfy a. max / a min The relationship is ≤1.5. Where, a max / a min The minimum value is 1. By reducing the deviation of the weld throat thickness in the weld (i.e., reducing a) max Relative to a min The proportion of [a specific component] can mitigate stress concentration. As a result, arc-welded joints with excellent joint strength can be obtained. max / a min Preferably, it is 1.01 or higher, more preferably 1.05 or higher. max / a min Preferably, it is 1.4 or less, and more preferably 1.3 or less.

[0071] The above-mentioned "maximum value a of weld throat thickness" max "and "minimum value a of weld throat thickness min "The measurement can be performed as described in the embodiments below. Specifically, in the region of weld 6 where the weld ends 10 (each 15 mm in length) have been removed, the weld throat thickness is measured on a cross-section perpendicular to the weld line at any eight locations on weld 6. Specifically, as..." Figure 5 As shown, weld 6 was cut at any eight locations along the plate thickness direction perpendicular to the weld line, and nitric acid-ethanol etching was performed. Then, cross-sectional images were taken using an optical microscope (10x magnification) to determine the thickness of each weld throat. The maximum value among these values ​​was taken as "the maximum weld throat thickness a". max (mm)”, the minimum of these values ​​is taken as the “minimum weld throat thickness a”. min (mm)

[0072] It should be noted that the steel plate used in the arc welding joint of the present invention is preferably a high-strength steel plate with a tensile strength of 440 MPa or higher.

[0073] There is no specific upper limit to the tensile strength of this steel sheet. From the viewpoint of its suitability for automotive components, a tensile strength of 1200 MPa or less is preferred.

[0074] Next, one embodiment of the arc welding method for manufacturing the arc welded joint of the present invention will be described. It should be noted that using... Figure 1Arc welding has been described, so the explanation is omitted here.

[0075] In this invention, to ensure the relationship between the weld throat thickness 'a' in the arc welding joint and the plate thickness 't' of the upper plate, and the slag coverage area ratio 'S', RATIO (%) Within the above range, it is important to control the welding conditions of arc welding as follows.

[0076] In the arc welding of the present invention, a gas consisting of Ar gas and an oxidizing gas, wherein the oxidizing gas satisfies the relationship of equation (2), is used as the shielding gas.

[0077] 2×[O2]+[CO2]≤5…(2)

[0078] Here, in equation (2), [O2] is the volume percentage of O2 in the protective gas, and [CO2] is the volume percentage of CO2 in the protective gas.

[0079] Arc welding with reverse polarity is used, with welding wire 1 as the anode and steel plate 3 as the cathode (see reference). Figure 1 Then, a welding voltage is applied to the welding wire 1, which is continuously supplied to the steel plate 3 through the center of the welding torch 2, causing a portion of the shielding gas supplied from the welding torch 2 to ionize into plasma. This forms an arc 5 between the welding wire 1 and the steel plate 3. The remaining portion of the shielding gas (i.e., the unionized gas flowing from the welding torch 2 to the steel plate 3) isolates the arc 5, molten metal 7, and weld pool 8 from the external gas (see reference). Figure 2 Therefore, it has the function of preventing the introduction of oxygen (i.e., the formation of welding slag) and nitrogen (i.e., the formation of porosity).

[0080] The tip of the welding wire 1 is melted by the heat energy of the electric arc 5 to become molten metal 7. This molten droplet is transported to the molten pool 8 by electromagnetic force and gravity. At this time, the state of molten metal 7 separating from the molten pool 8 is repeated regularly (refer to...). Figure 2 (A) and the state where molten metal 7 comes into contact with molten pool 8 and is electrically short-circuited (refer to) Figure 2 (B) Then, by continuously generating this phenomenon while moving the welding wire 1 along the welding line direction, the molten pool 8 solidifies behind the welding line, forming the weld 6.

[0081] By specifying the oxidizing gases in the protective gas, the amount of oxygen mixed into the molten metal 7 and the molten pool 8 is reduced, thus preventing the formation of weld slag. As a result, chemical conversion treatment and electrodeposition coating properties are improved, and the weld throat thickness within the specified range can be stably obtained even in corrosive environments.

[0082] From the viewpoint of achieving this effect more effectively, in this invention, the "protective gas" in the above welding conditions is set to a protective gas composed of Ar gas and an oxidizing gas, wherein the oxidizing gas satisfies the relationship of equation (2). When the value on the left side of equation (2) (i.e., the value calculated by (2×[O2]+[CO2])) exceeds 5, the oxygen mixed into the molten metal 7 and the molten pool 8 increases, and the adhesion of weld slag on the weld surface increases. As a result, the chemical conversion treatment and electrodeposition coating properties deteriorate. Therefore, the value on the left side of equation (2) is made to be 5 or less. Preferably, it is 3 or less.

[0083] In this invention, the above-mentioned effects can be obtained even in a protective gas of 100% Ar gas. That is, the value on the left side of equation (2) also includes the case of 0. It should be noted that the condition of "100% Ar gas" refers to an Ar purity of 99.99% or higher.

[0084] In this invention, by controlling the welding conditions of the arc welding in this way, an arc-welded joint having the above-described welded portion can be obtained. It should be noted that, from the viewpoint of more effectively obtaining the effects of this invention, in addition to the welding conditions described above, the following welding conditions can also be specified.

[0085] To manage the weld throat thickness based on the plate thickness, controlling the deposition rate per unit length of welding wire during welding is also effective. As mentioned above, this invention focuses on the relationship between welding speed and wire feed speed.

[0086] Specifically, when the welding speed is set to v t (cm / min), set the wire feeding speed to v w When (cm / min), it is preferable to control it to satisfy 5≤v w / v t A relationship ≤35. In v w / v t When the value is less than 5, the amount of weld wire deposited per unit length relative to the plate thickness is too small because the wire feed speed is lower than the welding speed. As a result, the weld throat thickness is reduced. On the other hand, when v... w / v t When the value exceeds 35, the wire feed rate increases relative to the welding speed, resulting in excessive wire deposition per unit length relative to the plate thickness. Consequently, the weld throat thickness increases. w / v t The value is more preferably 10 or more, and more preferably 30 or less.

[0087] As mentioned above, in arc welding with reduced oxidizing gases in the shielding gas, the amount of weld slag generated can be reduced. On the other hand, due to the drastic changes in the cathode point, the weld seam 6 is sometimes prone to bending or forming an undulating shape.

[0088] To eliminate this drawback, in the arc welding of the present invention, it is preferable that the welding wire 1 and the steel plate 3 are intermittently short-circuited, and the average value of the short-circuit frequency (hereinafter referred to as "short-circuit frequency") and the maximum value of the short-circuit period (hereinafter referred to as "short-circuit period") are controlled as follows. Specifically, it is preferable that the average value of the short-circuit frequency (average short-circuit frequency) F AVE The Hz frequency is 20–300 Hz, and the maximum short-circuit period (maximum short-circuit period) T is maximized. CYC (s) is less than 1.5s.

[0089] The reasons for intermittently short-circuiting the welding wire 1 and the steel plate 3 during arc welding, and for ensuring that the short circuit meets the specified conditions, are as follows.

[0090] The molten droplets generated from the tip of the welding wire 1, whether too large or too small, cause the molten pool 8 to become unstable.

[0091] Specifically, at the average short-circuit frequency F AVE At frequencies below 20 Hz, large droplets move towards the molten pool 8, and droplet transfer mechanisms other than short-circuit transfer (e.g., flow transfer) are irregularly mixed. On the other hand, at the average short-circuit frequency F... AVE At frequencies exceeding 300Hz, although the molten droplets are small, there is excessive re-arcing of the arc accompanying the short circuit. For this reason, disturbances in the molten pool 8 occur under any circumstances, making it difficult to eliminate weld bends and undulations. That is, by increasing the average short-circuit frequency F... AVE With a frequency of 20–300 Hz, the volume of the molten droplet transported to the molten pool 8 through a single short circuit is the same as that of a sphere with the same diameter as the welding wire 1. As a result, not only is the movement of the molten droplet stabilized, but the deposition amount is also uniform, thereby consistently achieving an appropriate weld throat thickness. Therefore, in this invention, the average short-circuit frequency F is... AVE The preferred Hz is 20 to 300 Hz.

[0092] It should be noted that, from the perspective of eliminating the unevenness in the volume of molten droplets transported to the molten pool 8 through a single short circuit and improving the uniformity of the weld, the average short-circuit frequency F AVE More preferably, the Hz frequency is 35Hz or higher, even more preferably 45Hz or higher, and still more preferably 50Hz or higher. Furthermore, if the average short-circuit frequency F... AVE If the frequency is large, even small molten droplets may scatter in large quantities during short circuits and re-arc re-ignition. Therefore, the average short circuit frequency F AVE More preferably, the Hz is below 250Hz, even more preferably below 200Hz, and even more preferably below 190Hz.

[0093] The aforementioned "average short-circuit frequency F" AVEThe average short-circuit frequency refers to the average short-circuit frequency of the weld bead used to obtain the weld joint. Therefore, the change in the arc voltage of the weld bead is measured using a measuring device (such as an oscilloscope), the number of times the arc voltage is zero is measured, and the value obtained by dividing the number of times by the time (s) required for the welding (times / s = Hz) is the "average short-circuit frequency".

[0094] If the maximum short-circuit period T CYC If the time exceeds 1.5 seconds, the droplet transfer becomes unstable, and the weld width and penetration depth become unstable. That is, by maximizing the maximum short-circuit period T... CYC With a short circuit duration of less than 1.5 seconds, a weld seam 6 with a good shape can be obtained. Therefore, in this invention, the maximum short-circuit period T is [not specified]. CYC Preferably, it should be less than 1.5 seconds.

[0095] The aforementioned "maximum short-circuit period T" CYC "" refers to the maximum value of the short-circuit period of the weld bead used to obtain the arc weld joint. That is, it means that each short-circuit period of the weld bead does not exceed 1.5s.

[0096] It should be noted that, in order to achieve the above-mentioned average short-circuit frequency F AVE For frequencies above 20Hz, the maximum short-circuit period T CYC More preferably, it is 1.0s or less; even more preferably, it is 0.2s or less; and still more preferably, it is 0.10s or less. The maximum short-circuit period T is... CYC As long as the average short-circuit frequency F AVE The frequency range below 300Hz is sufficient, therefore the maximum short-circuit period T CYC There is no specific lower limit specified. Maximum short-circuit period T CYC Preferably, the time is 0.004s or more, and more preferably 0.008s or more.

[0097] Thus, by using the average short-circuit frequency F AVE and the maximum short-circuit period T CYC By controlling the use of Ar shielding gas within a specified range, the movement of molten droplets in arc welding is reduced due to the decrease in oxidizing gases. Thus, by balancing the suppression of slag formation and stable arc discharge, the slag coverage ratio S can be obtained. RATIO Weld 6 within the scope described.

[0098] It should be noted that the preferred range of welding conditions includes, for example, an average welding current of 150–300 A, an average arc voltage of 20–35 V, a welding speed of 30–200 cm / min, an Ar gas flow rate of 10–25 Liter / min, and a contact tip to base material distance (hereinafter referred to as “CTWD”) of 5–30 mm.

[0099] In this invention, there are no particular limitations on the method of controlling the average short-circuit frequency and the maximum short-circuit period within the above-mentioned range.

[0100] For example, it is preferable to use such as Figure 6 The pulsed current shown is used to apply current waveform control. Specifically, the peak current of the pulsed current is set to I. PEAK (A) Set the base current to I BASE (A) Set the peak period to t PEAK (ms), set the rise period to t UP (ms), set the descent period to t DOWN When CTWD is set to L (mm), the value of X (A·s / m) calculated by equation (3) is controlled to satisfy 50≤X≤250. This enables stable droplet transfer and allows for more effective determination of the weld throat thickness a and slag coverage area S of the weld metal. RATIO Weld 6 within the aforementioned range.

[0101] X = (I PEAK ×t PEAK / L)+(I PEAK +I BASE )×(t UP +t DOWN ) / (2×L)… (3)

[0103] Equation (3) is expressed as follows: Figure 6 The formula for controlling the current waveform of the pulse current is shown.

[0104] If the value of X (A·s / m) calculated by equation (3) is too small, arc fluctuations and unstable droplet transfer may occur. On the other hand, if the value of X is too large, the welding wire 1 may sometimes get stuck in the molten pool 8, or the grown droplets may scatter during a short circuit, resulting in deterioration of the weld shape and spatter adhesion. Therefore, it is preferable to control the value of X to satisfy 50 ≤ X ≤ 250. The value of X is more preferably 60 or more, and even more preferably 80 or more. The value of X is more preferably 230 or less, and even more preferably 200 or less.

[0105] It should be noted that in the unit of X (A·s / m), "s" stands for second, and t... PEAK t UP t DOWN The unit "ms" stands for millisecond (= 1 / 1000 of a second).

[0106] If the distance L between the steel plate 3 and the contact tip is too small, the welding torch 2 will wear out rapidly, causing unstable welding. If the distance L is too large, the arc 5 will fluctuate. Therefore, in formula (3), the value of L is preferably 5 to 30 mm. The value of L is more preferably 8 mm or more, and more preferably 20 mm or less. The value of L is even more preferably 10 mm or more, and even more preferably 18 mm or less.

[0107] If I PEAK If the value is too small, sufficient heat input cannot be guaranteed, leading to deterioration of the weld shape; if it is too large, it will cause burn-through or increase spatter. Therefore, in equation (3), I PEAK The preferred value is 250–600 A. PEAK More preferably, the A value is 400A or higher, and more preferably, the A value is 500A or lower.

[0108] If I BASE If the value of I is too small, the arc will be unstable; if it is too large, it will cause burn-through. Therefore, in equation (3), I BASE The preferred value is 30–120 A. BASE More preferably, 40A or higher. BASE More preferably, it is 100A or less, and even more preferably 80A or less.

[0109] If t PEAK If the value of t is too small, sufficient heat input cannot be ensured; if it is too large, burn-through will occur. Therefore, in equation (3), t PEAK The preferred value is 0.1–5.0 ms. PEAK More preferably, the response time is 1.0 ms or more, and more preferably 4.0 ms or less. PEAK Further preferably, the time is 1.2ms or more, and even more preferably, 3.5ms or less.

[0110] If t UP and t DOWN If the value is too small, it will induce fluctuations in the electric arc; if it is too large, it will lead to a deterioration of the weld shape. Therefore, in equation (3), t UP and t DOWN The preferred values ​​for t are 0.1–3.0 ms. UP and t DOWN More preferably, the time is 0.5ms or more, more preferably 2.5ms or less. Further preferably, it is 0.8ms or more, and even more preferably 2.0ms or less.

[0111] Although not used in equation (3) for calculating the value of X, the base period of the pulse current is set to t. BASE When (ms), if t BASE If the value is too small, the molten droplet will be too small; if it is too large, the molten droplet will become too large, thus making welding unstable under any circumstances. Therefore, tBASE The preferred time is 0.1–10.0 ms. BASE More preferably, the response time is 1.0 ms or more, and more preferably 8.0 ms or less. BASE Further preferably, the time is 1.5ms or more, and even more preferably, 6.0ms or less.

[0112] It should be noted that in this invention, it is not necessary for a short circuit to occur once in each cycle of the pulse current; it is sufficient for a short circuit to occur once every one to several pulses. Furthermore, if a short circuit can occur once every one to several pulses, the pulse frequency of the pulse current is not particularly limited.

[0113] In this invention, the purpose of specifying the pulsed current is to (i) suppress arc fluctuations and promote stable droplet growth by making it a low current during the base period; and (ii) promote short circuits by pushing the droplets downward into the molten pool through electromagnetic force and the shear force of the Ar shielding gas from the peak period to the fall period, rather than causing the growing droplets to detach from the welding wire.

[0114] In the arc welding method of the present invention, there is no need to supply oxygen or add special elements. Therefore, as a welding wire, a solid welding wire, which is cheaper than a welding wire with added flux, can be used to reduce the cost of the process. In the present invention, there are no particular limitations on the composition of the solid welding wire (the component composition of the welding wire).

[0115] Preferred solid welding wires include, for example, those containing C: 0.020–0.150 wt%, Si: 0.20–1.00 wt%, Mn: 0.50–2.50 wt%, P: less than 0.020 wt%, and S: less than 0.03 wt%. With such a composition, by appropriately adjusting the composition, it can be used for arc welding of a wide range of steel grades, from mild steel to ultra-high strength steel. The diameter of the solid welding wire is preferably 0.4 mm to 2.0 mm.

[0116] The reasons for setting the composition of solid welding wire within the above range will be explained below.

[0117] C: 0.020~0.150% by mass

[0118] Carbon (C) is an element necessary to ensure the strength of weld metal and has the effect of reducing the viscosity of molten metal and improving its fluidity. However, when the C content is less than 0.020% by mass, the strength of the weld metal cannot be guaranteed. On the other hand, if the C content exceeds 0.150% by mass, the toughness of the weld metal decreases. Therefore, the C content is preferably 0.020 to 0.150% by mass. The C content is more preferably 0.050% by mass or more, and more preferably 0.10% by mass or less.

[0119] Si: 0.20–1.00% by mass

[0120] Si is an element that has a deoxidizing effect and, when added in appropriate amounts, improves the hardenability, toughness, and strength of the weld metal. In MIG welding, the use of Ar as a shielding gas can suppress the incorporation of oxygen into the weld metal. Although the deoxidizing effect of Si is not particularly necessary, when the Si content is less than 0.20% by mass, the molten droplets and weld pool oscillate during welding, resulting in a large amount of spatter. On the other hand, if the Si content exceeds 1.00% by mass, the toughness of the weld metal decreases. Therefore, the Si content is preferably 0.20 to 1.00% by mass, more preferably 0.30% by mass or more, and even more preferably 0.90% by mass or less.

[0121] Mn: 0.50–2.50% by mass

[0122] Mn, like Si, is an element that deoxidizes and improves the mechanical properties of weld metal. However, when the Mn content is less than 0.50% by mass, the amount of residual Mn in the weld metal is insufficient, resulting in inadequate strength and toughness. On the other hand, if the Mn content exceeds 2.50% by mass, the toughness of the weld metal decreases. Therefore, the Mn content is preferably 0.50 to 2.50% by mass, more preferably 0.80% by mass or more, and even more preferably 1.80% by mass or less.

[0123] P: less than 0.020% by mass

[0124] Phosphorus (P) is an element that is introduced into steel as an impurity during the steelmaking and casting processes, and it reduces the high-temperature fracture resistance of weld metal; therefore, it is preferable to minimize its content. In particular, if the P content exceeds 0.020% by mass, the high-temperature fracture resistance of the weld metal is significantly reduced. Therefore, the P content is preferably 0.020% by mass or less. More preferably, the P content is 0.010% by mass or less. From the viewpoint of the high-temperature fracture resistance of weld metal, there is no particular lower limit for the P content, and it also includes 0% by mass. The P content is preferably 0.001% by mass or more.

[0125] S: less than 0.03% by mass

[0126] Sulfur (S) is an unavoidable impurity in steel strands and is an element that reduces the high-temperature fracture resistance of the weld metal; therefore, it is preferable to minimize its content. In particular, if the S content exceeds 0.03% by mass, high-temperature fracture of the weld metal is likely to occur. Therefore, the S content is preferably 0.03% by mass or less. More preferably, it is 0.015% by mass or less. From the viewpoint of the high-temperature fracture resistance of the weld metal, there is no particular lower limit for the S content, and it also includes 0% by mass. The S content is preferably 0.001% by mass or more.

[0127] In addition to the above-mentioned welding wire composition, solid welding wire may also contain one or more of the following materials as needed: Ni, Cr, Ti, and Mo.

[0128] Ni is an element that improves the strength and weather resistance of weld metal. However, if the Ni content is less than 0.02% by mass, this effect is not achieved. On the other hand, if the Ni content exceeds 3.50% by mass, the toughness of the weld metal decreases. Therefore, when adding Ni, the Ni content is preferably 0.02% to 3.50% by mass.

[0129] Like Ni, Cr is an element that improves the strength and weather resistance of weld metal. However, if the Cr content is less than 0.01% by mass, this effect is not achieved. On the other hand, if the Cr content exceeds 1.50% by mass, it leads to a decrease in the toughness of the weld metal. Therefore, when Cr is added, the Cr content is preferably 0.01 to 1.50% by mass.

[0130] Ti acts as a deoxidizer and improves the strength and toughness of weld metal. Additionally, Ti stabilizes the arc and reduces spatter. However, if the Ti content exceeds 0.15% by mass, the molten droplets become coarse during welding, resulting in large spatter particles and a significant reduction in the toughness of the weld metal. Therefore, when adding Ti, the Ti content is preferably 0.15% by mass or less.

[0131] Mo is an element that improves the strength of weld metal, but if its content exceeds 0.8% by mass, the toughness of the weld metal decreases. Therefore, when adding Mo, the Mo content is preferably 0.8% by mass or less.

[0132] The remaining portion of the solid welding wire is Fe and unavoidable impurities.

[0133] It should be noted that nitrogen (N) and copper (Cu) are unavoidable impurities in the composition of welding wire. Nitrogen (N) is an impurity that inevitably mixes in during the steel smelting and strand manufacturing stages, negatively impacting the toughness of the weld metal. Therefore, it is preferable to control the N content to 0.01% by mass or less. Cu is an unavoidable impurity in the steel strand and is an element that reduces the toughness of the weld metal. In particular, if the Cu content exceeds 3.0% by mass, the toughness of the weld metal decreases significantly. Therefore, the Cu content is preferably 3.0% by mass or less.

[0134] As described above, according to the present invention, by specifying the weld throat thickness corresponding to the plate thickness in the welded portion of the steel component, stress concentration in the welded portion is mitigated, and rusting is suppressed by reducing the amount of weld slag adhering to the welded portion. This allows for improved joint strength of the welded portion even in corrosive environments. Because the amount of weld slag adhering is reduced, the shape is less prone to change in corrosive environments, thereby maintaining the weld throat thickness. Furthermore, according to the present invention, various components having the above-mentioned characteristics can be manufactured, for example, using high-strength steel plates with a tensile strength of 440 MPa or higher (e.g., 440 MPa, 590 MPa, and 980 MPa grade steel plates). By using such high-strength steel plates, thinner wall thicknesses of the components can also be achieved.

[0135] It should be noted that, since the present invention is applicable to automotive parts, the thickness of the high-strength steel plate is preferably 0.8 to 4 mm.

[0136] Example

[0137] The embodiments of the present invention will be described below.

[0138] First, using the two steel plates shown in Table 1, Figure 1 The lap fillet weld shown is used to create an arc welded joint. The welding conditions are those shown in Table 2. The Ar gas flow rate is 15 liters / min. The welding wire indicated as "welding wire symbol" in Table 2 is a solid welding wire with the welding wire composition shown in Table 4 and a diameter of 1.2 mm. It should be noted that the components other than those shown in "Welding Wire Composition" in Table 4 are Fe and unavoidable impurities. The welding wire symbol "W1" shown in Table 4 contains 0.005% by mass N and 0.27% by mass Cu as unavoidable impurities in the welding wire composition.

[0139] Using the prepared arc welding head, alkaline degreasing, surface conditioning and zinc phosphate chemical conversion treatment were performed. Cationic electrodeposition coating was carried out on the base plate portion other than the welding part with a film thickness of 15 μm. Then, SAE J2334 corrosion test was carried out for 60 cycles.

[0140] The shape of the weld after welding is evaluated as follows.

[0141] [S slag coverage area ratio] RATIO ]

[0142] Weld toe surface area S TOE and the surface area S of welding slag SLAGThe surface of weld 6 is captured by taking a 5x magnification image of the area where the ends 10 of weld 6 (each 15mm long) have been removed, and the area is calculated by measuring the projected area from the upper surface of the weld and slag using the obtained image. It should be noted that if the length of weld 6 is less than 130mm, the entire length of the surface without the ends 10 is captured. If the length of weld 6 is 130mm or more, the surface of weld 6 is captured at any point (100mm long) where the ends 10 have been removed. Furthermore, slag with a total length of 0.5mm or less is excluded from the calculation.

[0143] like Figure 4 and Figure 5 As shown, the surface area of ​​weld 6 in the region extending 2.0 mm from the weld toe 9 along the weld metal direction and in the region extending 2.0 mm from the weld toe 9 along the base metal direction is defined as the weld toe surface area S. TOE (mm 2 The surface area S of the weld toe TOE The total area of ​​the region covered by welding slag 11 is denoted as the welding slag surface area S. SLAG (mm 2 ).

[0144] Using the calculated weld toe surface area S TOE and the surface area S of welding slag SLAG The value of S is used to calculate the slag coverage area ratio S in equation (1) above. RATIO The calculated slag coverage area ratio S RATIO As shown in Table 3.

[0145] [Thickness of the weld throat in the welded section]

[0146] The thickness of the weld throat in the welded section was measured in the area where the end 10 (each 15mm long) of weld seam 6 was removed (refer to...). Figure 3 The weld is performed on a section of the plate along the thickness direction perpendicular to the weld line at any of the eight locations of the internal weld. For example... Figure 5 As shown, weld 6 was cut at any point along the thickness direction perpendicular to the weld line, and nitric acid ethanol etching was performed. Then, cross-sectional images were taken using an optical microscope (10x magnification) to determine the thickness of each weld throat. Here, the average value of these values ​​is taken as "weld throat thickness a (mm)". Furthermore, among the weld throat thickness a measured at any eight locations using the above method, the maximum value is taken as "maximum value a of weld throat thickness a". max (mm)”, the minimum value is taken as the minimum value of “weld throat thickness a”. min (mm)". The calculated thicknesses of each weld throat (a, a) will be... man a min (See Table 3.)

[0147] The evaluation of "joint strength" shown in Table 3 is conducted as follows.

[0148] The tensile strength of the joint was determined according to the following method. First, the arc-welded joint after corrosion testing was immersed in a stripping agent, and the electrodeposited coating was peeled off. Then, corrosion products were removed according to ISO 8407. Next, the tensile test piece described in JIS Z 2241 was obtained by machining. As a tensile test for preparing the tensile test piece, a tensile test was performed at room temperature at a tensile speed of 10 mm / min, and the tensile strength of the joint was recorded. This value was taken as the tensile strength after corrosion.

[0149] Furthermore, the tensile strength of the base material is determined as follows: A base steel sheet that can adequately accommodate the size of a tensile test piece (e.g., 200 mm × 300 mm × plate thickness) is machined to obtain a tensile test piece as described in JIS Z 2241. As a tensile test for preparing the tensile test piece, a tensile test is performed at room temperature at a tensile speed of 10 mm / min, and the tensile strength of the joint is recorded. This value is taken as the tensile strength of the base material.

[0150] Using the obtained values, the joint strength was evaluated according to the following criteria, and ratings A, B, and F were assigned respectively. Table 3 shows the case where "Rating A" is "(Tensile strength of joint after corrosion) / (Tensile strength of base material) ≥ 0.70". "Rating B" is the case where "0.70 > (Tensile strength of joint after corrosion) / (Tensile strength of base material) ≥ 0.60". "Rating F" is the case where "(Tensile strength of joint after corrosion) / (Tensile strength of base material) < 0.60". Rating A is the best, followed by rating B as excellent. Ratings A and B are considered "qualified", and rating F is considered "unqualified". The evaluation results are shown in Table 3. The "Strength Ratio" in Table 3 represents the value of (Tensile strength of joint after corrosion) / (Tensile strength of base material).

[0151] The evaluation of "rust prevention" shown in Table 3 is conducted as follows.

[0152] For the welded joint after the corrosion-promoting test, the surface of weld 6 was photographed from directly above, showing the area where the end 10 (each 15mm long) of weld 6 had been removed (refer to...). Figure 3 ), calculate the average rust area per unit length (mm). 2 / 10mm). The obtained values ​​are shown in Table 3.

[0153] Here, rust prevention is evaluated based on the following criteria.

[0154] The average rust area is greater than 95 (mm) 2 / 10mm) and 100 (mm) 2Cases with an average rust area of ​​less than 10 mm are considered to have excellent rust prevention after corrosion. Additionally, cases with an average rust area greater than 50 mm are considered to have excellent rust prevention. 2 / 10mm) and is 95 (mm) 2 Cases with an average rust area of ​​50 mm or less are considered to have superior rust prevention after corrosion. Furthermore, cases with an average rust area of ​​50 mm are considered to have better rust prevention after corrosion. 2 Cases with a thickness of 10mm or less are evaluated as having an even better rust prevention effect after corrosion.

[0155] [Table 1]

[0156] steel plate Tensile strength (MPa) Plate thickness (mm) a 440 2.6 b 590 2.6 C 980 2.6 d 980 1.0 e 980 3.2

[0157]

[0158]

[0159]

[0160] As shown in Tables 2 and 3, in welding Nos. 1 to 17, which are examples of this invention, 0.5 × t ≤ a ≤ 1.8 × t and S RATIO The percentage is below 50%. This results in an arc-welded joint that prevents rust and exhibits excellent joint strength.

[0161] Because the maximum value a of the weld throat thickness in welds No. 1-3, 9-13, 15, and 17 in these examples of the invention is... max With minimum value a min The ratio (a) max / a min With a value below 1.5, arc welded joints with reduced stress concentration and excellent joint strength can be obtained.

[0162] Furthermore, according to the present invention, it can be confirmed that either the welding wire for ultra-high strength steel (welding wire symbols W1 and W2 in Table 4) or the welding wire for mild steel (welding wire symbol W3 in Table 4) has the above-mentioned effects.

[0163] In contrast, in the comparative example, since a < 0.5 × t or a > 1.8 × t, or S RATIO More than 50% of the joint tensile strength reduction was caused by corrosion.

[0164] It should be noted that, in Figure 7 The figure shows the relationship between the weld throat thickness and slag coverage area of ​​the welded portion in this embodiment and the ratio (strength ratio) of the joint tensile strength to the base metal tensile strength. Figure 7 As shown, joint strength can be improved by appropriately controlling the weld throat thickness and reducing the oxidizing gas content in the shielding gas to decrease the slag coverage area.

[0165] Explanation of reference numerals in the attached figures

[0166] 1 Welding wire

[0167] 2 Welding torch

[0168] 3. Steel plate (base material)

[0169] 4. Corner joints of the steps

[0170] 5. Electric arc

[0171] 6 Welds

[0172] 7. Molten metal (droplets)

[0173] 8. Molten Pool

[0174] 9. Weld toe

[0175] 10. Weld ends

[0176] 11 Welding slag

Claims

1. An arc welding joint, comprising a welded portion formed by overlapping and arc welding at least two steel plates, When the thickness of the weld throat in the welded section is set as a (mm) and the thickness of the upper plate in the steel plate is set as t (mm), the thickness of the weld throat and the thickness of the upper plate satisfy the relationship 0.5×t≤a≤1.8×t. And, the surface area of the weld from the toe of the weld of the weld portion to 2.0 mm in the direction of the weld metal and from the toe of the weld to 2.0 mm in the direction of the base material is set as the toe of the weld surface area S TOE (mm 2 ), the area of the region of the toe of the weld surface area S TOE covered by the slag is set as the slag surface area S SLAG (mm 2 ), when the slag coverage area ratio S RATIO (%) calculated by formula (1) is 50% or less, Let the maximum value of the weld throat thickness in the weld portion at the beginning and end of the weld after removing the weld bead be set as a. max (mm), minimum value is set to a min When the thickness is (mm), the maximum value and the minimum value of the weld throat thickness satisfy a. max / a min A relationship of ≤1.5 S RATIO =100×S SLAG / S TOE …(1)。 2. An arc welding method for obtaining the arc welded joint as described in claim 1. When at least two steel plates are overlapped and arc welded to form a welded section... A protective gas consisting of Ar gas and an oxidizing gas, wherein the oxidizing gas satisfies the relationship of equation (2), is used. In the arc welding, the steel plate and the welding wire are intermittently short-circuited. The average short-circuit frequency F of the short circuit AVE The frequency (Hz) is 20–300 Hz, and the maximum short-circuit period T of the short circuit is... CYC (s) is less than 1.5s, 2×[O2]+[CO2]≤5…(2) in, [O2] represents the volume percentage of O2 in the protective gas, and [CO2] represents the volume percentage of CO2 in the protective gas.

3. The arc welding method according to claim 2, wherein, In the aforementioned arc welding, the welding speed is set to v. t (cm / min), set the wire feeding speed to v w When the welding speed is (cm / min), the welding speed and the wire feeding speed satisfy 5≤v w / v t Relationships ≤35.

4. The arc welding method according to claim 2 or 3, wherein, The arc welding uses pulsed current as the welding current. Set the peak current of the pulse current to I. PEAK (A) Set the base current to I BASE (A) Set the peak period as t PEAK (ms), set the rise period to t UP (ms), set the descent period to t DOWN (ms), and when the distance between the steel plate and the conductive nozzle is set to L (mm), the value of X (A·s / m) calculated by equation (3) satisfies 50≤X≤250, X=(I PEAK ×t PEAK / L)+(I PEAK +I BASE )×(t UP +t DOWN ) / (2×L)…(3)。 5. The arc welding method according to claim 2 or 3, wherein, Solid welding wire is used as the welding wire in the arc welding.

6. The arc welding method according to claim 4, wherein, Solid welding wire is used as the welding wire in the arc welding.

Images