Arc-welded joint and arc-welding method

Abstract

This invention provides an arc welding joint and an arc welding method. In the arc welding joint of this invention, the side angle θ in the welded portion formed by overlapping and arc welding at least two steel plates is θ≥100°. ° Furthermore, the surface area of ​​the weld toe, extending 2.0 mm along the weld metal direction from the weld toe of the welded part and extending 2.0 mm along the base metal direction from the weld toe of the welded part, is defined as S. TOE Set the surface area of ​​the welding slag to 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 weld joint with excellent fatigue characteristics suitable for automotive parts and the like, and an arc welding method for obtaining such an arc weld 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, there is a growing trend towards thinner-walled steel plates for components, driven by the application of high-strength steel sheets.

[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, sufficient fatigue strength is required in addition to static tensile strength. This is especially true for components used in corrosive environments, where the corrosion zone expands over time and progresses along the plate thickness, reducing the thickness of the welded portion and its vicinity, making it difficult to ensure component strength.

[0004] As a technique for improving the fatigue strength of components, Patent Document 1 can be cited as an example. Patent Document 1 discloses a technique in which welding wire with a specific composition is used during welding to smooth the shape of the weld toe of the weld metal, thereby improving the wettability of the molten metal to the base steel plate.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent No. 3860438 Summary of the Invention

[0008] However, in the technology disclosed in Patent Document 1, since the composition of the welding wire needs to be adjusted, it is difficult to say that the technology can be applied to all kinds of steel plates.

[0009] Furthermore, when the welding wire composition contains a large amount of alloying elements that serve as slag components, the adhesion of the slag hinders electrodeposition coating and makes it difficult to suppress rusting. As a result, corrosion can be considered to lead to a significant reduction in plate thickness, deterioration of the weld toe shape, and a substantial decrease in fatigue strength.

[0010] The present invention was made in view of these issues, and aims to provide an arc welded joint that can suppress rust and has excellent fatigue characteristics even in corrosive environments, as well as an arc welding method for obtaining the arc welded joint.

[0011] In order to solve the above-mentioned problems, the inventors have repeatedly and thoroughly studied methods for suppressing rusting of welded parts of steel components and improving the fatigue characteristics of welded parts in corrosive environments.

[0012] The inventors have obtained the following insights: by specifying the side angle of the weld toe in the welded part, stress concentration in the welded part can be reduced, thereby improving fatigue characteristics (fatigue strength). Furthermore, it is believed that by reducing the welding slag (hereinafter sometimes referred to as "slag") adhering to the welded part, especially the weld toe, rusting can be suppressed, and the decrease in fatigue strength caused by corrosion can be suppressed.

[0013] This invention was completed based on the above insights and through further repeated research, and its main points are as follows.

[0014] [1] An arc welding head, wherein the side angle θ ( ) in the welded part formed by overlapping and arc welding at least two steel plates ° ) for θ≥100 ° ,

[0015] Furthermore, the surface area of ​​the weld from the weld toe in the weld metal direction to 2.0 mm and the area from the weld toe in the base metal direction to 2.0 mm is 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], the maximum value of the side angle of the weld portion in which a 15mm area is removed from the weld end of the weld is set as θmax. ° The minimum value is set as θmin. ° When the maximum and minimum values ​​of the above-mentioned lateral angles satisfy θmax-θmin≤30°, ° The relationship.

[0018] [3] An arc welding method, which is the arc welding method for 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 part, a protective gas composed of Ar gas and an oxidizing gas, wherein the oxidizing gas satisfies the relationship of equation (2), is used.

[0020] When the average welding current is set as I (A), the average arc voltage as V (V), the welding speed as s (cm / min), and the value of (2×[O2]+[CO2]) in the above-mentioned shielding gas equation (2) is set as Y, these I, V, s, and Y satisfy the relationship of equation (3).

[0021] 2×[O2]+[CO2]≤16…(2)

[0022] 50≤(I×V) / s×(24+Y) / 24≤200…(3)

[0023] Where [O2] is the volume percentage of O2 in the protective gas, and [CO2] is the volume percentage of CO2 in the protective gas.

[0024] [4] According to the arc welding method described in [3], the shielding gas satisfies the relationship of equation (4).

[0025] In the above-mentioned arc welding, the steel plate and the welding wire intermittently short-circuit.

[0026] 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.

[0027] 2×[O2]+[CO2]≤5…(4)

[0028] Where [O2] is the volume percentage of O2 in the protective gas, and [CO2] is the volume percentage of CO2 in the protective gas.

[0029] [5] According to the arc welding method described in [3] or [4], wherein a pulsed current is used as the welding current in the above-mentioned arc welding.

[0030] Set the peak current of the pulse current 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 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 (5) satisfies 50≤X≤250.

[0031] X = (I PEAK×t PEAK / L)+(I PEAK +I BASE )×(t UP +t DOWN ) / (2×L)…(5)

[0032] [6] The arc welding method according to any one of [3] to [5], wherein solid welding wire is used as the welding wire in the above-mentioned arc welding.

[0033] According to the present invention, stress concentration in the weld joint is reduced by specifying the side angle in the weld toe, and rusting is suppressed by reducing the amount of weld slag adhering to the weld joint. Thus, an arc-welded joint with stable and excellent fatigue characteristics can be obtained even in corrosive environments. The present invention also provides an arc welding method for obtaining this welded joint. Attached Figure Description

[0034] [ Figure 1 ] Figure 1 This is a perspective view schematically illustrating an example of applying the invention to lap fillet welds.

[0035] [ Figure 2 ] Figure 2 (A) and Figure 2 (B) is to Figure 1 The image shows an enlarged cross-sectional view of the welding wire and its vicinity, and is a schematic diagram representing the state of short-circuit transition.

[0036] [ 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.

[0037] [ 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.

[0038] [ 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.

[0039] [ Figure 6 ] Figure 6 This is a diagram showing an example of the waveform of the pulsed current supplied as welding current.

[0040] [ Figure 7 ] Figure 7 This is a graph showing the relationship between the side angle and the fatigue strength after corrosion. Detailed Implementation

[0041] 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).

[0042] 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.

[0043] 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." The shielding gas (not shown) supplied from the welding torch 2 is partially ionized and plasma-induced, 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 that melts 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.

[0044] In such an arc welded joint, at the side angle of the weld (refer to...) Figure 5 In cases where the weld is small, the weld becomes convex, leading to increased stress concentration at the weld toe. To address this issue, this invention specifies that the side angle of the weld toe in the weld portion must reach a predetermined range. Specifically, it is understood that setting the side angle to 100°... ° The above measures can reduce stress concentration in the welded areas.

[0045] Furthermore, when the deviation of the side angle of the weld is large, a problem arises where a large local stress concentration occurs at the position where the side angle is smallest. To solve this problem, the present invention removes the weld end 10 (refer to) of weld 6. Figure 3 The region satisfies the above requirements, and the difference between the maximum and minimum values ​​of the lateral angle is 30°. ° Therefore, it can be seen that stress concentration in the width direction of the weld can be further reduced.

[0046] That is, it has been found in this invention that by specifying the side angle of the weld toe in this way, stress concentration in the weld can be reduced, and as a result, the fatigue characteristics (fatigue strength) of the weld can be improved.

[0047] In addition, as mentioned above, from the viewpoint of improving fatigue characteristics even in corrosive environments, the present invention also focuses on suppressing rust in welded parts.

[0048] 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).

[0049] O2→2[O]…(6)

[0050] CO2→CO+[O]…(7)

[0051] 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.

[0052] 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.

[0053] 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 3 The 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 does 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 is insufficient, and the coating adhesion is inadequate, resulting in a significant reduction in corrosion resistance. Consequently, the plate thickness is reduced 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.

[0054] 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 aforementioned 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.

[0055] That is, in this invention, it was discovered that by specifying the oxidizing gas contained in the protective gas to reduce the amount of O2 and CO2 mixed in, the formation of weld slag adhering to the welded part, especially the weld toe, is suppressed. Thus, rusting can be suppressed, and fatigue strength reduction caused by corrosion can be prevented.

[0056] 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. Additionally, "weld width" refers to the length of the straight line connecting the intersection point (two intersection points) of the surface perpendicular to the weld line of weld 6 and the weld toe.

[0057] Next, refer to Figure 4 (A)~ Figure 5 The arc welding head of the present invention will be described below.

[0058] Figure 4 (A) shows Figure 1 A three-dimensional view of weld seam 6 of the arc weld 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 partially enlarged view of the cross section along line A-A of the arc-welded joint shown in Figure 1.

[0059] 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. The side angle θ in the weld portion of this arc welding joint... ° ) for θ≥100 °Furthermore, the surface area of ​​the weld in the region extending 2.0 mm from the weld toe along the weld metal direction and the region extending 2.0 mm from the weld toe 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 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%.

[0060] S RATIO =100×S SLAG / S TOE · · · (1)

[0061] The side angle θ in the welded part ° ): θ≥100 °

[0062] Figure 5 This is a schematic diagram showing the weld toe 9 and its surrounding area. Figure 5 The angle θ in ° ) is the side angle of weld toe 9. At the side angle θ( ° Less than 100 ° In this case, since weld 6 is convex, there is a problem of increased stress concentration at the weld toe 9. Therefore, in this invention, the side angle θ ( ° ) is 100 ° That's all. If the side angle θ increases, the weld toe 9 becomes smoother, which reduces stress concentration in the weld, therefore 110 is preferred. ° The above is further optimized to 120. ° That's all. From the viewpoint of preventing excessive expansion of the weld width, the side angle θ is preferably 160°. ° The following is more preferably 150 ° Hereinafter, 140 is further preferred. ° the following.

[0063] It should be noted that the lateral angle θ can be measured according to the method described in the embodiments described later.

[0064] Slag Coverage Area Ratio RATIO (%): Below 50%

[0065] like Figure 4 (A) Figure 4 (B) and Figure 5 As shown, the surface area of ​​a defined region including the weld toe 9 is defined as the weld toe surface area S. TOE (mm2 ), the surface area S of the weld toe TOE The area of ​​the region covered by 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 equation (1) RATIO The percentage (%) is less than 50%. If the weld slag 11 generated during welding exceeds 50% of the slag coverage area and adheres to the surface of weld 6, a chemical conversion layer cannot be sufficiently formed even after chemical conversion treatment of the arc weld joint. If the amount of weld slag generated is reduced, the agglomeration of weld slag on the surface of weld 6 is suppressed. Therefore, the slag coverage area S is reduced. RATIO Preferably, it is 45% or less, more preferably 40% or less.

[0066] The aforementioned "surface area S of the weld toe" TOE "refers to such as Figure 4 (A) and Figure 4 As 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 within a 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 The total area of ​​the region covered by weld slag 11 within the area. Weld toe surface area S TOE and the surface area S of welding slag SLAG It can be determined according to the method described in the embodiments described later.

[0067] It should be noted that, as the amount of non-conductive welding slag generated decreases, the chemical conversion treatment and electrodeposition coating properties improve, thus increasing the welding slag coverage area ratio S. RATIO The smaller the value, the better; there is no specific lower limit. S (Soil 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.

[0068] Thus, by adjusting the side angle θ and the slag coverage area S in the welded part... RATIO Within the aforementioned range, the aforementioned effects can be achieved. Figure 7 A graph showing the relationship between the side angle and the fatigue strength after corrosion is presented. This will be described in detail later, as... Figure 7 As shown, by considering the side corners and the slag coverage area S RATIOProper control can improve fatigue intensity.

[0069] As described above, when the deviation of the side angle of the weld is large, there is a problem of localized large stress concentration at the position where the side angle is smallest. Therefore, in addition to the above-described configuration, it is preferable to make the shape of the weld 6 stable. Therefore, in the present invention, as Figure 4 (A) and Figure 4 As shown in (B), it is preferable to reduce the deviation of the side angle θ of the weld portion where a region of 15 mm has been removed from the beginning and end of the weld (the beginning and end of the weld 10).

[0070] The difference between the maximum and minimum values ​​of the lateral angle θ (preferred condition)

[0071] The maximum value of the lateral angle within the area of ​​the welded portion where the weld end 10 has been removed, perpendicular to the line (weld line) parallel to the welding direction of weld 6, is set as θmax. ° ), set the minimum value of the lateral angle as θmin ( ° When θmax - θmin ≤ 30°, the maximum and minimum values ​​of the lateral angle preferably satisfy θmax - θmin ≤ 30°. ° The relationship is as follows. By reducing the deviation of the side angle of the weld (i.e., reducing the difference between θmax and θmin), the shape of weld 6 is stabilized. As a result, local stress concentration is alleviated. Therefore, the difference between the maximum and minimum side angles (θmax - θmin) is preferably 25°. ° The following is more preferably 20 ° the following.

[0072] The lower limit of the difference between the maximum and minimum values ​​of the aforementioned lateral angles is not specifically specified. (θmax - θmin) is preferably 0.1. ° The above is more preferably 0.2. ° The above is further preferred to be 0.5. ° above.

[0073] 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 more. More preferably, it is 500 MPa or more. More preferably, it is 900 MPa or more.

[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 1 Arc welding has been described, so the explanation is omitted here.

[0075] In this invention, to make the side angle θ in the arc welding joint ( ° ) and slag coverage area S RATIO(%) Within the above range, it is important to control the welding conditions for arc welding as follows.

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

[0077] 2×[O2]+[CO2]≤16…(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] In addition to this condition, when the average welding current of the arc welding is set to I (A), the average arc voltage is set to V (V), the welding speed is set to s (cm / min), and the value of (2×[O2]+[CO2]) in the shielding gas is set to Y, these I, V, s and Y are controlled to satisfy the relationship of equation (3).

[0080] 50≤(I×V) / s×(24+Y) / 24≤200…(3)

[0081] Here, in the protective gas Y in equation (3), [O2] is the volume percentage of O2 in the protective gas, and [CO2] is the volume percentage of CO2 in the protective gas.

[0082] When the center value of equation (3) (i.e., the value calculated from ((I×V) / s×(24+Y) / 24)) is less than 50, the cooling rate of the welded part increases due to the small heat input. As a result, the weld width becomes narrower and becomes convex. Therefore, the center value of equation (3) is set to 50 or more. From the viewpoint of ensuring heat input, the center value of equation (3) is preferably 60 or more, and more preferably 75 or more.

[0083] On the other hand, when the center value of Equation (3) exceeds 200, the heat input becomes excessive. As a result, burn-through may occur or the weld may become convex due to the increase in the amount of fusion deposited. Therefore, the center value of Equation (3) is set to 200 or less. The center value of Equation (3) is preferably 190 or less, more preferably 180 or less, and even more preferably 170 or less.

[0084] The "average welding current I" and "average arc voltage V" mentioned above refer to the average value of the welding current and the average value of the arc voltage in each weld pass.

[0085] It should be noted that preferred ranges for welding conditions include, for example, an average welding current I of 100–300 A, an average arc voltage V of 10–30 V, and a welding speed s of 30–150 cm / min. Within these ranges, a distance (hereinafter referred to as "CTWD") between the contact tip and the base material is more preferably 5–30 mm.

[0086] Further preferably, the average welding current I is set to 150A or more, or 260A or less. Further preferably, the average arc voltage V is set to 15V or more, or 28V or less. Further preferably, the welding speed s is set to 35cm / min or more, or 130cm / min or less. Further preferably, the total tangential weld depth (CTWD) is set to 8mm or more, or 20mm or less.

[0087] 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 electric 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 electric arc 5, molten metal 7, and weld pool 8 from the external gas (see reference). Figure 2 (A) and Figure 2 (B)). Therefore, it has the function of preventing the mixing of oxygen (i.e., the formation of welding slag) and nitrogen (i.e., the formation of porosity).

[0088] 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.

[0089] By specifying the oxidizing gases contained in the protective gas, the amount of oxygen mixed into the molten metal 7 and the molten pool 8 can be reduced, thereby preventing the formation of welding slag.

[0090] From the viewpoint of achieving this effect more effectively, in this invention, the "shielding gas" in the above welding conditions is set to a shielding 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 16, the weld tends to become convex due to arc compression, and the side angle of the weld toe may sometimes become larger. Therefore, the value on the left side of Equation (2) is set to 16 or less. The value on the left side of Equation (2) is preferably 10 or less, more preferably 5 or less. In addition, the value on the left side of Equation (2) is preferably 0.005 or more.

[0091] In this invention, the protective gas consisting of 100% Ar gas can also achieve the above-mentioned effects. The condition for "100% Ar gas" is that the Ar purity is 99.99% or higher, and it contains less than 0.01% of unavoidable oxidizing gases.

[0092] 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.

[0093] 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 is prone to bending or forming an undulating shape.

[0094] To eliminate this drawback, in this invention, it is preferable to further define equation (2) as the shielding gas condition, using a shielding gas that satisfies the relationship of equation (4), and further, in addition to this condition, the welding wire 1 and the steel plate 3 are intermittently short-circuited in the arc welding, and the maximum value of the short-circuit period (hereinafter referred to as "short-circuit period") and the average value of the short-circuit frequency (hereinafter referred to as "short-circuit frequency") are controlled as follows. Specifically, it is preferable to set the maximum value of the short-circuit period (maximum short-circuit period) T. CYC (s) is set to less than 1.5s, and the average short-circuit frequency (average short-circuit frequency) F is set. AVE (Hz) is set to 20-300Hz.

[0095] 2×[O2]+[CO2]≤5…(4)

[0096] Here, in equation (4), [O2] is the volume percentage of O2 in the protective gas, and [CO2] is the volume percentage of CO2 in the protective gas.

[0097] When the value on the left side of equation (4) (i.e., the value calculated from (2×[O2]+[CO2])) exceeds 5, the oxygen mixed into the molten metal 7 and the molten pool 8 increases, and the slag adhesion on the weld surface increases. As a result, the chemical conversion treatment and electrodeposition coating properties sometimes deteriorate compared to the conditions satisfying equation (4). Therefore, the value on the left side of equation (4) is 5 or less. The value on the left side of equation (4) is preferably 3 or less. The value on the left side of equation (4) is preferably 0.005 or more.

[0098] Under the condition that the shielding gas satisfies equation (4), the welding wire 1 and the steel plate 3 in the arc welding are intermittently short-circuited, and the short circuit satisfies the above conditions. The reason is as follows.

[0099] 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.

[0100] 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 obtaining an appropriate side angle. Therefore, in this invention, the average short-circuit frequency F is... AVE The preferred Hz is 20 to 300 Hz.

[0101] 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, and even more preferably, it is 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.

[0102] 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".

[0103] 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.

[0104] 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.

[0105] 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 0.5s or less; even more preferably, it is 0.2s or less; and still more preferably, it is 0.1s 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.

[0106] Thus, by using the average short-circuit frequency F AVE and the maximum short-circuit period T CYC Controlling the flow of molten droplets in arc welding within a specified range, and using Ar as the shielding gas, can reduce the oxidizing gas content and flow more steadily. In the absence of a short circuit, large arc fluctuations lead to unstable droplet transfer, sometimes resulting in larger deviations in the side angles of the same weld. However, as mentioned above, by controlling the average short-circuit frequency F... AVE and the maximum short-circuit period T CYC By controlling the flow within a specified range, a regular and stable droplet transfer is achieved, thereby balancing the suppression of slag formation and stable arc discharge. Therefore, the side angle and slag coverage area S can be obtained. RATIO Weld 6 within the aforementioned range.

[0107] It should be noted that, as preferred ranges of welding conditions, examples include average welding current I: 150–300 A, average arc voltage V: 20–35 V, Ar gas flow rate: 10–25 Liter / min, and CTWD: 5–30 mm.

[0108] 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.

[0109] 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 (5) is controlled to satisfy 50≤X≤250. This enables stable droplet transfer and more effectively obtains the side angle and slag coverage area S. RATIO Weld 6 within the aforementioned range.

[0110] X = (I PEAK ×t PEAK / L))+(I PEAK +I BASE )×(t UP +t DOWN ) / (2×L)…(5)

[0111] Equation (5) is expressed as follows: Figure 6 The formula for controlling the current waveform of the pulse current is shown.

[0112] If the value of X (A·s / m) calculated by equation (5) 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 weld shape deterioration, spatter adhesion, etc. 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, further preferably 80 or more, and even more preferably 100 or more. The value of X is more preferably 230 or less, further preferably 200 or less, and even more preferably 180 or less.

[0113] It should be noted that in the unit of X (A·s / m), "s" stands for second, and t... PEAK t UP t DOWNThe unit "ms" stands for millisecond (= 1 / 1000 of a second).

[0114] 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 it is too large, the arc 5 will fluctuate. Therefore, in formula (5), the value of L is preferably 5 to 30 mm. The value of L is more preferably 8 mm or more. The value of L is more preferably 20 mm or less.

[0115] If I PEAK If the value of I is too small, sufficient heat input cannot be guaranteed, resulting in deterioration of the weld shape; if it is too large, it will cause burn-through or increase spatter. Therefore, in equation (5), I PEAK The preferred value is 250–600 A. PEAK More preferably, 400A or higher. PEAK More preferably, it is 500A or less.

[0116] 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 (5), I BASE The preferred value is 30–120 A. BASE More preferably, 40A or higher. BASE More preferably, it is 100A or less.

[0117] 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 (5), t PEAK The preferred value is 0.1–5.0 ms. PEAK More preferably, it should be 1.0ms or longer. PEAK More preferably, it is below 4.0ms.

[0118] 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 (5), t UP and t DOWN The preferred values ​​for t are 0.1–3.0 ms. UP and t DOWN More preferably, the response time is 0.5ms or more. UP and t DOWN More preferably, the response time is less than 2.5ms.

[0119] Although not used in equation (5) 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, it is 1.0ms or more, and even more preferably 1.5ms or more. Additionally, t BASE More preferably, the ms is 8.0ms or less, and even more preferably, it is 6.0ms or less.

[0120] 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.

[0121] In this invention, the purpose of specifying the pulse current is to (1) suppress arc fluctuations and promote stable droplet growth by making the current low during the base period; and (2) push the growing droplets downward into the molten pool by electromagnetic force and the shear force of Ar shielding gas from the peak period to the fall period, rather than causing the growing droplets to detach from the welding wire, thereby promoting a short circuit.

[0122] 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).

[0123] 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.

[0124] The reasons for setting the composition of solid welding wire within the above range will be explained below.

[0125] C: 0.020~0.150% by mass

[0126] Carbon (C) is an element necessary to ensure the strength of weld metal, and it 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.

[0127] Si: 0.20–1.00% by mass

[0128] 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 oxygen ingress 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.

[0129] Mn: 0.50–2.50% by mass

[0130] 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 preferred Mn content is 0.50 to 2.50% by mass.

[0131] P: less than 0.020% by mass

[0132] Phosphorus (P) is an element that is introduced into steel as an impurity during the steelmaking and casting processes, and it is also an element that reduces the high-temperature crack 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 crack resistance of the weld metal is significantly reduced. Therefore, the P content is preferably 0.020% by mass or less.

[0133] S: less than 0.03% by mass

[0134] Sulfur (S) is an unavoidable impurity in steel strands and reduces the high-temperature crack resistance of weld metal; therefore, it is preferable to minimize its content. Specifically, if the S content exceeds 0.03% by mass, high-temperature cracking of the weld metal is more likely to occur. Therefore, the S content is preferably 0.03% by mass or less.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] The remaining portion of the solid welding wire consists of Fe and unavoidable impurities.

[0141] It should be noted that nitrogen (N) and copper (Cu) are unavoidable impurities in the composition of welding wire. N is an impurity that inevitably mixes in during the steel smelting stage and the manufacturing stage of the steel strand, adversely affecting 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 is significantly reduced. Therefore, the Cu content is preferably 3.0% by mass or less.

[0142] As described above, according to the present invention, rust in the welded portions of steel components can be suppressed, and the fatigue characteristics of the welded portions can be improved even in corrosive environments. In particular, since rust can be suppressed, the shape of the welded portions is less likely to change in corrosive environments, thereby maintaining the side angles. 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, it is also possible to achieve thinner wall thicknesses in the components.

[0143] 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.

[0144] Example

[0145] The embodiments of the present invention will be described below.

[0146] 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 adjusted appropriately within the range of 10–25 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 the remainder (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.

[0147] 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.

[0148] The shape of the weld after welding is evaluated as follows.

[0149] [S slag coverage area ratio] RATIO ]

[0150] Weld toe surface area S TOE With the surface area S of the welding slag SLAG The surface of weld 6 was photographed from directly above, within the area where the ends 10 (each 15mm long) of weld 6 were removed (magnification: 5x). The projected area from the upper surface of the weld and slag was calculated using the obtained image. Figure 4 (A) Figure 4 (B) 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 at the toe of the weld. TOE In this context, the total area of ​​the region covered by the welding slag 11 is defined as the surface area of ​​the welding slag, S. SLAG (mm 2 ).

[0151] It should be noted that when the length of weld 6 is less than 130 mm, the entire length of the surface excluding the ends 10 of the weld is photographed. When the length of weld 6 is 130 mm or more, the surface of weld 6 is photographed with any portion (100 mm in length) of the ends 10 removed. Furthermore, weld slag with a total length of 0.5 mm or less is excluded from the calculation.

[0152] 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.

[0153] [lateral angle θ]

[0154] The side angle θ was measured on a plate thickness section perpendicular to the weld line at eight arbitrary locations within the area where the ends 10 (each 15mm long) of weld 6 were removed. These eight locations were spaced at least 5mm apart. The side angle was calculated by cutting along the plate thickness direction perpendicular to the weld line at any arbitrary location of the weld, and the average value of these values ​​was defined as "side angle θ". ° )".

[0155] [Maximum and minimum values ​​of the lateral angle θ]

[0156] The maximum value of the side angle θ at any of the eight positions measured by the method described above for measuring the side angle θ is defined as "the maximum value of the side angle θ, θmax". ° The minimum value is set as "the minimum value of the lateral angle θmin". ° The maximum and minimum values ​​of the lateral angles, θmax and θmin, are shown in Table 3.

[0157] The evaluation of “fatigue strength” shown in Table 3 is conducted as follows.

[0158] 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, fatigue strength test pieces with a parallel section width of 22 mm were obtained by machining, centered on the weld toe (weld toe 9) along the length direction. The fatigue tests on the prepared fatigue strength test pieces were conducted using a pendulum bending fatigue test. The load applied to the fatigue strength test pieces was 100–500 MPa, the repetition frequency was 20 Hz, and the number of repetitions was 1,000,000. The strengths (post-corrosion fatigue strength) (MPa) obtained through this bending fatigue test are shown in Table 3.

[0159] It should be noted that the evaluation of post-corrosion fatigue strength is based on the following criteria, assigned the symbols A, B, and F respectively. In Table 3, "Symbol A" represents the case where "post-corrosion fatigue strength is 320 MPa or higher." "Symbol B" represents the case where "post-corrosion fatigue strength is 190 MPa or higher but less than 320 MPa." "Symbol F" represents the case where "post-corrosion fatigue strength is less than 190 MPa." Symbol A is the best, followed by B as excellent. Symbols A and B are evaluated as "acceptable," and symbol F is evaluated as "unacceptable." The evaluation results are shown in Table 3.

[0160] The evaluation of "rust prevention" shown in Table 3 is conducted as follows.

[0161] For the welded joint after the accelerated corrosion test, the surface of weld 6 was photographed from directly above, showing the area where the ends 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.

[0162] Here, the following criteria will be used as the basis for evaluating rust prevention.

[0163] The average rust area is greater than 95 (mm) 2 / 10mm) and 100 (mm) 2 Cases 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.

[0164] [Table 1]

[0165] 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

[0166]

[0167]

[0168]

[0169] As shown in Tables 2 and 3, the side angle θ of welds No. 1 to 17, which are examples of this invention, is 100°. ° The above, and S RATIO The content is below 50%. Thus, an arc-welded joint that can prevent rust and exhibits excellent fatigue characteristics after corrosion was obtained.

[0170] In these examples of the invention, welding No. 1 to 16, the difference (θmax - θmin) between the maximum value of the side angle θ and the minimum value of the side angle θ is 30°. ° Therefore, an arc welded joint with reduced stress concentration and excellent fatigue characteristics was obtained.

[0171] 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.

[0172] In contrast, the side angle θ of welds No. 18-21 in comparative examples is less than 100°. ° Or S RATIO The rate exceeds 50%, therefore the reduction in fatigue strength caused by corrosion is significant.

[0173] It should be noted that, in Figure 7 The figure shows the relationship between the side angle and the fatigue strength after corrosion in this embodiment. Figure 7 The symbols “〇 (example of the invention)” and “△ (comparative example)” satisfy the above formula (2). Figure 7 As shown, fatigue strength increases with increasing side angle. Besides the side angle, the slag coverage area S... RATIO When the coverage area of ​​weld slag is less than 50%, it is related to the weld slag coverage area S. RATIO Compared to 50%, higher fatigue strength can be obtained. Attached Figure Description

[0175] 1 Welding wire

[0176] 2 Welding torch

[0177] 3. Steel plate (base material)

[0178] 4. Corner joints of the steps

[0179] 5. Electric arc

[0180] 6 Welds

[0181] 7. Molten metal (droplets)

[0182] 8 Molten Pool

[0183] 9. Weld toe

[0184] 10. Weld ends

[0185] 11 Welding slag

Claims

1. An arc-welded joint, wherein the side angle θ (°) of the welded portion formed by overlapping and arc-welding at least two steel plates is θ ≥ 100°. Furthermore, the surface area of ​​the weld from the weld toe along the weld metal direction to 2.0 mm and the area from the weld toe towards 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 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%, S RATIO =100×S SLAG / S TOE ···(1)。 2. The arc welding joint according to claim 1, wherein, When the maximum value of the side angle in the welded part, which is a region of 15mm removed from the weld end of the weld, is set as θmax (°) and the minimum value is set as θmin (°), the maximum and minimum values ​​of the side angle satisfy the relationship θmax-θmin≤30°.

3. An arc welding method, which is the arc welding method for the arc welded joint as described in claim 1 or 2. When at least two steel plates are overlapped and arc welded to form a welded part, a shielding gas consisting of Ar gas and an oxidizing gas, wherein the oxidizing gas satisfies the relationship of equation (4), is used. When the average welding current is set as I (A), the average arc voltage as V (V), the welding speed as s (cm / min), and the value of the shielding gas according to equation (4), i.e., 2×[O2]+[CO2], is set as Y, these I, V, s, and Y satisfy the relationship of equation (3). 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···(4) 50≤(I×V) / s×(24+Y) / 24≤200···(3) in, [O2] represents the volume percentage of O2 in the protective gas, and [CO2] represents the volume percentage of CO2 in the protective gas.

4. The arc welding method according to claim 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 (5) satisfies 50≤X≤250, X=(I PEAK ×t PEAK / L)+(I PEAK +I BASE )×(t UP +t DOWN ) / (2×L)···(5)。 5. An arc welding method, which is the arc welding method for the arc welded joint as described in claim 1 or 2. When at least two steel plates are overlapped and arc welded to form a welded part, a shielding gas consisting of Ar gas and an oxidizing gas, wherein the oxidizing gas satisfies the relationship of equation (2), is used. When the average welding current is set as I (A), the average arc voltage as V (V), the welding speed as s (cm / min), and the value of the shielding gas according to equation (2), i.e., 2×[O2]+[CO2], is set as Y, these I, V, s, and Y satisfy the relationship of equation (3). 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 (5) satisfies 50≤X≤250, 2×[O2]+[CO2]≤16···(2) 50≤(I×V) / s×(24+Y) / 24≤200···(3) X=(I PEAK ×t PEAK / L)+(I PEAK +I BASE )×(t UP +t DOWN ) / (2×L)···(5) in, [O2] represents the volume percentage of O2 in the protective gas, and [CO2] represents the volume percentage of CO2 in the protective gas.

6. The arc welding method according to any one of claims 3 to 5, wherein, Solid welding wire is used as the welding wire in the arc welding.

Images