Gas shielded arc welding method and method for manufacturing welded joint

Abstract

The purpose of the present invention is to provide a gas-shielded arc welding method and a method for manufacturing a welded joint, with which it is possible to stably obtain a welded joint having a satisfactory bead shape while preventing the mixing of oxygen into a welded metal and suppressing the generation of slag even without using a special device. The gas-shielded arc welding method is a pulse welding in which a pulse peak current (Ip) and a pulse base current (Ib) are periodically repeated, the pulse peak current (Ip) of the pulse welding being 300 A to 600 A inclusive, the welding speed (V) being 80 cm / min to 200 cm / min inclusive, and the pulse base current (Ib) being 50 A to 60 A inclusive. The pulse peak current (Ip), the pulse base current (Ib), the distance (L) between the base material and the contact tip, and the welding speed (V) satisfy a predetermined formula, and 98 vol% or more of Ar gas is used as a shielding gas.

Description

Technical Field

[0001] The present invention relates to a gas shielded arc welding method and a method for manufacturing a welded joint for obtaining a stable welded joint shape while suppressing slag. Background Art

[0002] In recent years, for automobiles, there has been an increasing demand for both high strength and high rigidity of components used in the vehicle body for the purpose of improving the safety and reliability of the vehicle body and light weight of components for the purpose of improving fuel consumption. As a result, the thinning of component steel plates due to the application of high strength steel plates has been promoted. On the other hand, among various components used in automobiles, particularly running components (such as lower arms, etc.), steel plates with a thicker wall than the vehicle body are used from the viewpoints of component strength and rigidity. Therefore, if the high strength of the steel plates used in running components is pursued and the thinning of the steel plates is further achieved, the further light weight of the vehicle body can be realized. Thereby, the improvement of fuel consumption can be achieved while ensuring component strength and rigidity.

[0003] Generally, components used in a corrosive environment are subjected to rust prevention treatments such as chemical conversion treatment and electrodeposition coating after welding for the purpose of ensuring corrosion resistance. However, over time, rust and corrosion are sometimes confirmed in the welded part and its vicinity. As described above, corrosion occurring in components subjected to electrodeposition coating easily starts from the welded part, and over time, it expands over a large area in the welded part and its periphery along with film swelling, and also intensifies in the plate thickness direction. If the corrosion intensifies in this way, the plate thickness in the welded part and its vicinity decreases, and as a result, the strength of the welded part decreases, and further the strength of the component decreases. That is, if corrosion occurs and progresses in a component where a load acts on the welded part (such as a running component of an automobile), sometimes the component is damaged.

[0004] When performing electrodeposition coating, in order to improve the adhesion of the base metal steel plate and the weld metal to the electrodeposition coating film, chemical conversion treatment (such as zinc phosphate treatment, etc.) is performed on the base metal steel plate and the weld metal as a pretreatment, and then electrodeposition coating is performed. Zinc phosphate treatment, which is widely popular as an example of chemical conversion treatment, is a technique for growing zinc phosphate crystals on the surfaces of the base metal steel plate and the weld metal to improve the adhesion of the coating film in electrodeposition coating. However, in the prior art, in components subjected to chemical conversion treatment before electrodeposition coating, film swelling frequently occurs over a large area in the welded part and its periphery over time. That is, in the technique of performing electrodeposition coating after performing the above chemical conversion treatment as a pretreatment, it is difficult to completely suppress the occurrence of corrosion starting from the welded part.

[0005] In addition, when arc welding is performed on a component using a steel sheet with a coating, in the welded portion exposed to high heat due to the arc plasma (hereinafter referred to as the arc) as the heat source, the coating evaporates and the non-coated portion is locally exposed. Therefore, a significant improvement in corrosion resistance commensurate with the use of the expensive steel sheet with a coating cannot be expected.

[0006] As described above, although various techniques have been developed in the manufacturing technology for improving the corrosion resistance of components, they all have both advantages and disadvantages. Moreover, from the viewpoint of suppressing the increase in manufacturing cost and achieving an improvement in corrosion resistance, techniques for more effectively preventing the generation and development of corrosion starting from the welded portion are being studied.

[0007] As the starting point of corrosion from the welded portion, the following have been conventionally known:

[0008] (a) Slag adhering to the welded portion (mainly the surface of the welding bead),

[0009] (b) Welding fume adhering to the welded portion,

[0010] (c) Oxides formed on the surface of the steel sheet exposed to high temperature due to welding.

[0011] Even if a component in which the attachments of (a) and (b) and the oxides of (c) exist in the welded portion is subjected to chemical conversion treatment, regions not covered by the chemical conversion treatment layer composed of zinc phosphate crystals will remain locally starting from these attachments and products. Even if electrodeposition coating is applied to such regions, the formation of the coating film is insufficient and the adhesion of the coating film becomes insufficient. Therefore, the corrosion resistance is significantly reduced, leading to a reduction in the plate thickness due to the generation and development of corrosion. As techniques for preventing the generation of the attachments of (a) and (b) and the oxides of (c), the following have been studied.

[0012] For example, Patent Document 1 discloses the following technique: after arc welding, spray treatment or immersion treatment is performed on the welded portion and its vicinity before electrodeposition coating using a non-oxidizing acidic solution with a pH of 2 or less and a liquid temperature of 30 to 90°C. This technique removes the slag of (a), the welding fume of (b), and the oxides of (c) by dissolving the welding bead and the steel sheet with the non-oxidizing solution.

[0013] However, in the technology disclosed in Patent Document 1, it is necessary to rinse the acidic solution before electrodeposition coating, so the manufacturing process of the component becomes complicated. In addition, the component formed into the desired shape is made by overlapping and joining steel plates of various shapes, so the acidic solution remaining in the gaps formed by overlapping causes severe corrosion. Also, since a large amount of acidic solution is used, the manufacturing equipment is exposed to a corrosive environment and is prone to corrosion and failure. In addition, it is necessary to prevent the scattering of soot to ensure the safety of the operator.

[0014] Patent Document 2 discloses the following technology: by reducing the total Si content of the welding wire and the base material used in arc welding and increasing the total Mn content of the welding wire and the base material, the corrosion resistance after coating of the welded part and its vicinity is improved.

[0015] However, from the viewpoint of suppressing the generation of slag, if the Si content is reduced, the strength of the steel plate will inevitably decrease. That is, in the technology disclosed in Patent Document 2, in order to ensure the strength of the component, it is necessary to use thick-walled steel plates, and it is difficult to achieve the light weight of the vehicle body.

[0016] Patent Document 3 discloses the following technology: Even for a welded bead with slag, welding fume, and oxides, by adjusting the composition of the treatment liquid used in the chemical conversion treatment, a chemical conversion treatment layer can be sufficiently formed. Specifically, a surface adjustment liquid containing zinc phosphate colloid is used for surface treatment, whereby a chemical conversion treatment layer is easily formed. And a zinc phosphate treatment liquid with an F content of 100 mass ppm or more is used for chemical conversion treatment, so as to dissolve and remove slag, welding fume, and oxides to improve the adhesion of the coating film based on electrodeposition coating.

[0017] However, in the technology disclosed in Patent Document 3, a zinc phosphate treatment liquid containing fluorine designated as a poison is used. Therefore, when discharging its waste liquid outside the factory, it is necessary to reduce the fluorine to a level that meets the environmental standards. Therefore, in addition to the manufacturing equipment of the component, large-scale waste liquid treatment equipment is also required.

[0018] Patent Document 1: Japanese Patent Laid-Open No. 9-20994

[0019] Patent Document 2: Japanese Patent Laid-Open No. 8-33997

[0020] Patent Document 3: Japanese Patent No. 5549615 Summary of the Invention

[0021] The present invention has been accomplished in view of these problems, and an object thereof is to provide a gas shielded arc welding method and a method for manufacturing a welded joint, which can prevent oxygen from being mixed into the welded metal without using a special device, suppress the generation of slag, and can stably obtain a welded joint with a good bead shape.

[0022] The inventors of the present invention have found that, in order to improve the corrosion resistance of the welded portion and stably obtain a welded joint with a good bead shape, it is most effective to reduce the slag adhering to the welded portion and then use pulsed welding to achieve periodic short-circuit transfer.

[0023] In order to suppress the amount of slag generated in the welded portion, it is important to suppress the oxidation of Si, Mn, Ti, etc. contained in the steel plate and the welding wire. By using a shielding gas with a reduced content of oxidizing gas, the oxidation of these elements can be suppressed, and the amount of slag generated can be reduced. However, in gas shielded arc welding with an increased Ar gas ratio in the shielding gas, when the welding speed is set to 80 to 200 cm / min, after the oxide film on the steel plate surface is removed by the cleaning action, the cathode spot crawls everywhere on the steel plate surface, so the arc becomes unstable. As a result, new problems such as oxygen mixing into the molten pool caused by the entrainment of the atmosphere or deterioration of the shape of the welding bead occur. Therefore, the inventors believe that by using pulsed welding, the crawling of the cathode spot is reduced, and periodic short-circuit transfer that is not easily affected by the swaying of the arc is achieved. In the pulsed current waveform, it is found that the factor obtained by dividing the difference between the pulsed peak current (Ip) and the pulsed base current (Ib) by the distance (L) between the base material and the contact tip has a high correlation with the ease of short circuit. Furthermore, by satisfying the welding speed (V) and a specified relational expression, a welded joint with a good bead shape can be stably obtained. That is, in the present invention, the factor obtained by dividing the difference between the pulsed peak current (Ip) and the pulsed base current (Ib) by the distance (L) between the base material and the contact tip is found as an index of the ease of short circuit, and the following technique is found: the above factor satisfies a specified relational expression with the welding speed (V) according to the welding speed, so that a welded joint with a good bead shape can be stably obtained.

[0024] Based on the above insights, the gist of the present invention is as follows.

[0025] [1] A gas shielded arc welding method for joining by short-circuiting a welding wire supplied from a contact tip in a welding torch to a base material, wherein,

[0026] The gas shielded arc welding method is pulsed welding that periodically repeats a pulsed peak current (Ip) and a pulsed base current (Ib), and the pulsed peak current (Ip) of the pulsed welding is 300 A or more and 600 A or less.

[0027] The welding speed (V) is 80 cm / min or more and 200 cm / min or less,

[0028] and when the welding speed (V) is 80 cm / min or more and less than 120 cm / min, the pulse peak current (Ip), the pulse base current (Ib), the distance (L) between the base material and the welding tip, and the welding speed (V) satisfy the following formula (1),

[0029] when the welding speed (V) is 120 cm / min or more and 200 cm / min or less, the pulse peak current (Ip), the pulse base current (Ib), the distance (L) between the base material and the welding tip, and the welding speed (V) satisfy the following formula (2),

[0030] and an Ar gas of 98 vol% or more is used as the shielding gas.

[0031] 0.15V - 3 ≤ (Ip - Ib) / L ≤ 0.1V + 38…(1)

[0032] 0.18V - 5 ≤ (Ip - Ib) / L ≤ 0.12V + 35…(2)

[0033] Here, in formula (1) and formula (2), Ip (A) refers to the pulse peak current, Ib (A) refers to the pulse base current, L (mm) refers to the distance between the base material and the welding tip, and V (cm / min) refers to the welding speed.

[0034] [2] According to the gas shielded arc welding method described in [1], wherein,

[0035] the pulse base current (Ib) of the pulse welding is 30 A or more and 120 A or less.

[0036] [3] A method for manufacturing a welded joint, wherein,

[0037] the gas shielded arc welding method described in [1] or [2] is used.

[0038] According to the present invention, a welded joint with a good bead shape can be stably obtained under a wide range of welding speed conditions. Moreover, even without changing the welding device used in existing CO₂ gas welding, MAG welding using a mixed gas of an inert gas and an active gas, or MIG welding using a gas mainly composed of an inert gas to a special specification, it is possible to suppress the mixing of oxygen into the welding metal and the generation of slag. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a schematic diagram showing an example of a welded joint produced by arc welding.

[0040] Figure 2 (a) and Figure 2 (b) of are schematic diagrams showing the droplet transfer based on existing arc welding.

[0041] Figure 3 (a) and Figure 3 (b) of are schematic diagrams showing the short-circuit transfer based on the present invention.

[0042] Figure 4 is a schematic diagram showing the pulsed current waveform of the arc welding of the present invention.

[0043] Figure 5 is a schematic diagram showing the bead area and the slag covering area of the weld bead.

[0044] Figure 6 is a schematic diagram showing the minimum and maximum values of the weld bead width. Detailed Description of the Invention

[0045] Hereinafter, the details of the present invention will be described with reference to the accompanying drawings. Figure 1 is a schematic diagram showing an example of an embodiment of the present invention and an example of a welded joint produced by arc welding. In this example, a fillet weld of an overlapping joint is shown as a representative, but in the present invention, the shape of the welded joint and the welding posture are not limited.

[0046] In the present invention, for example, as Figure 1 shown, the welding wire 1 that passes through the central part of the welding torch 2 and continuously feeds from the welding torch 2 to the base material 3 (specifically, for example, the welding line formed by the corner part of the step formed by overlapping two base materials 3) is used as the anode, and the base material 3 is used as the cathode, and a welding voltage is applied from a welding power source (not shown). A contact tip 11 is installed in the welding torch 2, and the contact tip 11 serves to supply power to the welding wire 1 and guide the feeding. An arc 5 is formed between the welding wire 1 and the base material 3 by the ionization and plasma formation of a part of the Ar shielding gas (not shown) supplied from inside the welding torch 2. In addition, the part of the above-mentioned Ar shielding gas that does not generate ionization and flows from the welding torch 2 to the base material 3 has the function of separating the molten pool (not shown in Figure 1 ) formed by melting the arc 5 and the base material 3 from the external air. Due to the heat input from the arc 5, the front end of the welding wire 1 melts to become a molten droplet, and this molten droplet is transported to the molten pool by electromagnetic force, gravity, etc. This phenomenon continuously occurs along with the movement of the welding torch 2 or the base material 3, so that the molten pool solidifies behind the welding line, forming a weld bead 6. Thereby, the joining of at least two steel plates is achieved.

[0047] On the other hand, when performing existing MIG welding on carbon steel targeted by the present invention, there is a problem that welding is extremely unstable. In MAG welding or MIG welding, it is reverse polarity welding with the electrode (metal wire) as the anode. Therefore, on the surface of the base metal steel plate, a cathode spot is formed starting from an area with a low work function and easy electron emission like an oxide. For example, in aluminum alloy with a firm oxide film on the surface of the base metal, a cathode spot is stably formed starting from the oxide film on the welding line, so good welding can be performed. However, in steel that is not likely to have an oxide film, in MIG welding where oxides from O 2 or CO 2 are not generated, the cathode spot is uncertain, and the cathode spot moves violently everywhere on the surface of the base metal while searching for a part with a low work function. Therefore, welding is unstable, and a welded joint with a meandering shape or a wavy shape of the welding bead 6 is obtained.

[0048] Regarding this phenomenon, the inventors of the present invention observed the arc behavior based on welding experiments and considered that the main cause of the meandering and undulating shapes of the welding bead 6 cited above as problems in MIG welding with carbon steel as the target is unstable droplet transfer.

[0049] In Figure 2 (a) of Figure 2 and Figure 2 (b) of

[0050] show schematic diagrams for explaining the case of droplet transfer based on existing MIG welding. In the droplet transfer of existing MIG welding, as shown in Figure 3 (a) of Figure 3 , the welding wire 1 melts, and a form of continuously supplying to the molten pool 8 from a slender liquid column coexists. In order to suppress this unstable droplet transfer, it is considered effective to regularly separate the droplet 7 from the tip of the welding wire 1. However, in the case of an Ar shielding gas, the electromagnetic constriction force acting on the welding wire 1 is small, and the separation of the droplet 7 becomes difficult.

[0050] Therefore, in the present invention, as a means to stabilize droplet transfer, it was found that it is effective to complete the joining by periodically short-circuiting transition, which regularly repeats the non-short-circuit state of Figure 3 (a) and the short-circuit state of Figure 3 (b) between the tip of the welding wire 1 and the base metal 3 and transferring the droplet 7 to the base metal 3 during the short-circuit state. Furthermore, as a result of further repeating welding experiments, it was found that the factor ((Ip - Ib) / L) obtained by dividing the difference between the pulse peak current (Ip) and the pulse base current (Ib) by the distance (L) between the contact tip and the base metal 3 is the ease of short-circuit transition. It is preferably set in the range of 20 to 43 for (Ip - Ib) / L. Furthermore, it was found that the meandering of the welding bead 6 can be suppressed when a specified relationship is satisfied for various welding speeds.

[0051] Ar gas of 98% by volume or more

[0052] In order to improve the corrosion resistance of the welded part, it is necessary to suppress the amount of slag formed on the welded part. Therefore, it is important to suppress the oxidation of Si, Mn, Ti, etc. contained in the steel plate and the welding wire. Therefore, as the shielding gas, a gas with Ar of 98% by volume or more is required. It is preferred that Ar is 99% by volume or more. The upper limit is not limited, and Ar can be 100% by volume.

[0053] The pulsed peak current (Ip) is 300 A or more and 600 A or less

[0054] Figure 4 The figure shows a simplified diagram of the pulsed current waveform of the arc welding of the present invention. Pulsed welding is a method of welding by periodically repeating the pulsed peak current (Ip) and the pulsed base current (Ib). If the pulsed peak current (Ip) is too small, sometimes the effect of pressing the molten droplet 7 formed at the tip of the welding wire 1 downward into the molten pool 8 cannot be obtained, the short circuit becomes unstable, and in addition, sufficient heat input cannot be ensured, resulting in deterioration of the bead shape. Therefore, the pulsed peak current (Ip) is 300 A or more. The pulsed peak current (Ip) is preferably 350 A or more, more preferably 380 A or more, and further preferably 400 A or more. On the other hand, if it is too large, burn-through will occur, or an increase in the amount of slag formation due to poor shielding or an increase in spatter will result. Therefore, the pulsed peak current (Ip) is 600 A or less. It is preferably 590 A or less, more preferably 580 A or less, and further preferably 570 A or less. In order to cause a short circuit at the pulsed peak current, the pulsed peak current time (tp) per cycle is preferably 0.5 ms or more. The pulsed peak current time (tp) per cycle is more preferably 0.7 ms or more, and further preferably 0.8 ms or more. If the pulsed peak current time (tp) per cycle is too large, the disturbance of the arc 5 and the molten pool 8 during the short circuit becomes large, and sometimes poor welding bead shape occurs. Therefore, the pulsed peak current time (tp) per cycle is preferably 3.5 ms or less. The pulsed peak current time (tp) per cycle is more preferably 3.3 ms or less, and further preferably 3.2 ms or less.

[0055] The pulsed base current (Ib) is 30 A or more and 120 A or less (preferred condition)

[0056] If the pulse base current (Ib) is too small, the arc discharge during the pulse base period sometimes becomes unstable, resulting in deterioration of the bead shape and insufficient penetration. Therefore, the pulse base current (Ib) is preferably 30 A or more. More preferably, the pulse base current (Ib) is 35 A or more. Further preferably, it is 40 A or more, and most preferably, it is 45 A or more. On the other hand, if it is too large, burn-through may sometimes occur, and in addition, the difference between the pulse peak current (Ip) and the pulse base current (Ib) cannot be sufficiently ensured, and the effect of pressing the molten droplet 7 formed at the tip of the welding wire 1 downward into the molten pool 8 to cause short-circuiting cannot be obtained sufficiently, and the welding is unstable. Therefore, the pulse base current (Ib) is preferably 120 A or less. More preferably, the pulse base current (Ib) is 110 A or less. Further preferably, it is 100 A or less, and most preferably, it is 90 A or less.

[0057] In addition, if the pulse base current time (tb) is too short, the molten droplet 7 sometimes cannot grow to an ideal size, and periodic short-circuiting cannot be achieved. Therefore, the pulse base current time (tb) for each cycle (one pulse cycle) is preferably 1.0 ms or more. More preferably, the pulse base current time (tb) for each cycle (one pulse cycle) is 1.5 ms or more, and further preferably, it is 2.0 ms or more. If the pulse base current time (tb) is too long, the target short-circuit sometimes cannot be controlled at the pulse peak, or the disturbance of the arc 5 and the molten pool 8 during short-circuiting becomes large. Therefore, the pulse base current time (tb) for each cycle is preferably 10.0 ms or less. More preferably, the pulse base current time (tb) for each cycle is 9.0 ms or less, and further preferably, it is 8.0 ms or less.

[0058] In addition, if the rise time (tup) and the fall time (tdown) are too short, the arc 5 is induced to shake, and if they are too long, the bead shape deteriorates. Therefore, the rise time (tup) is preferably 0.1 ms or more. More preferably, it is 0.3 ms or more, and further preferably, it is 0.5 ms or more. The rise time (tup) is preferably 3.0 ms or less. More preferably, it is 2.8 ms or less, and further preferably, it is 2.5 ms or less. In addition, the fall time (tdown) is preferably 0.1 ms or more. More preferably, it is 0.3 ms or more, and further preferably, it is 0.5 ms or more. The fall time (tdown) is preferably 3.0 ms or less. More preferably, it is 2.8 ms or less, and further preferably, it is 2.5 ms or less.

[0059] The welding speed (V) is 80 cm / min or more and 200 cm / min or less

[0060] If the welding speed (V) increases, the stability of the arc 5 decreases, making it difficult to control the periodic short-circuit transfer. In particular, the above phenomenon becomes obvious under welding conditions of 80 cm / min or more, and it is necessary to limit it to the content described below. On the other hand, under welding conditions where the welding speed (V) exceeds 200 cm / min, it is sometimes difficult to obtain the desired weld bead shape and penetration shape, or air entrainment occurs due to the disturbance of the arc 5, causing slag formation. Therefore, in the present invention, the welding speed (V) as the object is 80 cm / min or more and 200 cm / min or less.

[0061] The factor (Ip - Ib) / L obtained by dividing the difference between the pulsed peak current (Ip) and the pulsed base current (Ib) by the distance (L) between the base material 3 and the contact tip 11 is not particularly limited, but it has been found in the present invention as an index of the ease of short-circuit transfer and is an important feature in the present invention. If (Ip - Ib) / L is too small, it is difficult to cause short-circuit transfer, and even if it occurs, it is difficult to perform stable short-circuit transfer, and the bead shape becomes poor. Therefore, (Ip - Ib) / L is preferably 20 A / mm or more. More preferably, it is 22 A / ms or more, and still more preferably, it is 25 A / ms or more. On the other hand, if (Ip - Ib) / L is too large, although the molten droplet 7 is small, the reignition of the arc 5 accompanying the short circuit becomes excessive, and the arc 5 becomes unstable. Therefore, (Ip - Ib) / L is preferably 43 A / mm or less. More preferably, it is 41 A / ms or less, and still more preferably, it is 40 A / ms or less.

[0062] The above pulsed peak current (Ip), the above pulsed base current (Ib), the distance (L) between the base material and the contact tip, and the above welding speed (V) satisfy the expressions defined in the following (1) and (2).

[0063] 0.15V - 3 ≤ (Ip - Ib) / L ≤ 0.1V + 38 (when the welding speed V is 80 cm / min or more and less than 120 cm / min)... (1)

[0064] 0.18V - 5 ≤ (Ip - Ib) / L ≤ 0.12V + 35 (when the welding speed V is 120 cm / min or more and 200 cm / min or less)... (2)

[0065] Here, in equations (1) and (2), Ip (A) refers to the pulsed peak current, Ib (A) refers to the pulsed base current, L (mm) refers to the distance between the base material and the contact tip, and V (cm / min) refers to the welding speed.

[0066] In order to achieve periodic short-circuit transfer in a gas shielded arc welding method with an increased Ar ratio, it is necessary to keep the difference between the pulsed peak current (Ip) and the pulsed base current (Ib) and the distance (L) between the base material 3 and the contact tip 11 within the ranges of formulas (1) and (2). When the welding speed V is 80 cm / min or more and less than 120 cm / min, if (Ip - Ib) / L is less than 0.15V - 3, it is difficult to achieve short-circuit transfer that is not affected by the swaying of the arc 5, so it needs to be 0.15V - 3 or more. It is preferably 0.15V - 2 or more, and more preferably 0.15V - 1 or more. On the other hand, if it exceeds 0.1V + 38, the disturbances of the arc 5 and the molten pool 8 during short circuit sometimes become larger, resulting in poor welding bead shape, so it needs to be 0.1V + 38 or less. It is preferably 0.1V + 36 or less, and more preferably 0.1V + 34 or less. In addition, when the welding speed V is 120 cm / min or more and 200 cm / min or less, if (Ip - Ib) / L is less than 0.18V - 5, it is difficult to achieve short-circuit transfer that is not affected by the swaying of the arc 5, so it needs to be 0.18V - 5 or more. It is preferably 0.18V - 4 or more, and more preferably 0.18V - 3 or more. On the other hand, if it exceeds 0.12V + 35, the disturbances of the arc 5 and the molten pool 8 during short circuit sometimes become larger, resulting in poor welding bead shape, so it needs to be 0.12V + 35 or less. It is preferably 0.12V + 33 or less, and more preferably 0.12V + 31 or less.

[0067] In addition, under the condition that the welding speed V is higher, 120 cm / min or more and 200 cm / min or less, the arc 5 is more likely to become unstable, so it is effective to make the slope of (Ip - Ib) / L with respect to V larger than the case where the welding speed is 80 cm / min or more and less than 120 cm / min.

[0068] In addition, the average frequency (short-circuit frequency) F (Hz) of short-circuit transfer affects the volume of the molten droplet 7 at the wire end. Although not particularly limited, it is preferably 20 Hz or more, more preferably 30 Hz or more, and still more preferably 40 Hz or more. As the upper limit, it is preferably 200 Hz or less, more preferably 180 Hz or less, and still more preferably 150 Hz or less. The average frequency (short-circuit frequency) F (Hz) of short-circuit transfer can be measured, for example, by monitoring the change in the arc voltage during welding with an oscilloscope, counting the number of times it becomes zero, and dividing the count by the monitoring time to obtain the count per second. If the above-mentioned monitoring time is too short, the deviation of the above-mentioned count becomes large, so it is preferably 0.5 s or more, more preferably 0.8 s or more, and still more preferably 1.0 s or more. On the other hand, the upper limit is not particularly limited, but if the capacity of the measurement data becomes large, statistical processing requires a lot of time and the workability deteriorates, so it is preferably 3.0 s or less. For example, for the above reasons, it can be cited that when measuring the short-circuit frequency in-process and implementing feedback control of the welding conditions, if the above-mentioned monitoring time is too long, instantaneous feedback control corresponding to the welding condition becomes difficult.

[0069] In addition, as the preferred range of welding conditions, for example, it can be cited that: the welding current is 150 A to 300 A, the arc voltage is 20 V to 35 V, the distance between the base material 3 and the contact tip 11 is 5 mm to 30 mm, and the Ar shielding gas flow rate is 10 L / min to 25 L / min. That is, the welding current is preferably 150 A or more, more preferably 170 A or more, and still more preferably 180 A or more. Regarding the upper limit, the welding current is preferably 300 A or less, more preferably 280 A or less, and still more preferably 270 A or less. The arc voltage is preferably 20 V or more, more preferably 21 V or more, and still more preferably 22 V or more. Regarding the upper limit, the arc voltage is preferably 35 V or less, more preferably 32 V or less, and still more preferably 30 V or less. The distance between the base material 3 and the contact tip 11 is preferably 5 mm or more, more preferably 8 mm or more, and still more preferably 10 mm or more. The distance between the base material 3 and the contact tip 11 is preferably 30 mm or less, more preferably 25 mm or less, and still more preferably 20 mm or less. The Ar shielding gas flow rate is preferably 10 L / min or more, more preferably 12 L / min or more, and still more preferably 15 L / min or more. The Ar shielding gas flow rate is preferably 25 L / min or less, more preferably 24 L / min or less, and still more preferably 22 L / min or less. In addition, the welding current and the arc voltage are the averages within each welding pass. More specifically, the welding current is the average of the pulse peak current and the pulse base current. By managing this, the total heat input during welding can be grasped.

[0070] The welding wire 1 used in the present invention is not particularly limited. For example, solid wires such as YGW12 and YGW16 described in JIS Z 3312 can be used.

[0071] In addition, the base material 3 of the present invention targets steel plates and plated steel plates. The composition of the steel plate is not limited, but for example, a steel plate containing C: 0.02% by mass to 0.3% by mass, Si: 0.01% by mass or more, Mn: 0.5% by mass or more, P: 0.05% by mass or less, and S: 0.05% by mass or less is preferably used. In addition to these, alloy elements such as Cu, Ni, Cr, and Ti can also be contained. In the above steel plate, Si is preferably 3.0% by mass or less, and Mn is preferably 5.0% by mass or less. In addition, the lower limit of P is not particularly limited, but is preferably 0.0005% by mass or more, and the lower limit of S is not particularly limited, but is preferably 0.0005% by mass or more. In addition, the plating composition of the plated steel plate is not particularly limited, and for example, Zn can be cited.

[0072] Furthermore, by limiting as described above, the generation of slag at the welded part can be suppressed, and a welded joint with a good bead shape can be manufactured, and the above-mentioned welded joint can be obtained. The amount of slag generation was evaluated by the method described in the examples. And in the control of the bead shape, it was found that the factor obtained by dividing the difference between the pulse peak current (Ip) and the pulse base current (Ib) by the distance (L) between the base material 3 and the contact tip 11 becomes an index of the ease of short-circuiting, and it is extremely effective to control the bead shape by combining it with the welding speed, which is a new technical idea of the present invention.

[0073] In addition, for the present invention, in addition to the above, high robustness is also a useful feature. Furthermore, high robustness means that it is not easily affected by disturbances such as the environment and plate shape, and the appropriate welding conditions are wide.

[0074] Examples

[0075] Hereinafter, examples of the present invention will be described. Two steel plates (both with a thickness of 2.6 mm) having the compositions shown in Table 1 were overlapped and fillet welded, for example, by the Figure 1 shown method. In addition, as components other than those shown in Table 1, alloy elements such as Fe, Cu, Ni, Cr, and Ti are included. Welding was carried out under the welding conditions shown in Table 2. As the welding wire 1, YGW16 described in JIS Z3312 was used.

[0076] For the welded steel plates obtained as above, the blank coating area ratio and the bead width ratio were evaluated according to the following test methods.

[0077] (Slag coating area ratio)

[0078] Figure 5 It is a schematic diagram showing the bead area of a welded bead and the slag covering area. Figure 5 The bead surface area S shown BEAD and the slag covering surface area S SLAG are calculated by photographing the surface of the area of the welded bead 6 except for the end portions 10 (each with a length of 15 mm) of the bead from directly above and measuring the projected area from the upper surfaces of the welded bead 6 and the slag. When the length of the welded bead 6 is less than 130 mm, the surface of the entire length except for the end portions 10 of the bead is photographed. When the length of the welded bead 6 is 130 mm or more, the surface of any part (with a length of 100 mm) except for the end portions 10 of the bead is photographed. By dividing the value of the calculated slag surface area S SLAG by the bead surface area S BEAD the slag covering area ratio S RATIO is obtained. Setting S RATIO to 30% or less is considered qualified.

[0079] (Bead width ratio)

[0080] Figure 6 It is a schematic diagram showing the minimum and maximum values of the bead width. Similarly, Figure 6 the maximum value W of the bead width shown MAX and the minimum value W MIN are measured by photographing the surface of the area of the welded bead 6 except for the end portions 10 (each with a length of 15 mm) of the bead and analyzing the obtained photograph. When the length of the welded bead 6 is less than 130 mm, the surface of the entire length except for the end portions 10 of the bead is photographed. When the length of the welded bead 6 is 130 mm or more, the surface of any part (with a length of 100 mm) except for the end portions 10 of the bead is photographed. By dividing the calculated minimum value W of the bead width min by the maximum value W max the bead width ratio W RATIO is obtained. Setting W RATIO to 60% or more is considered qualified.

[0081] According to Table 2, the welding conditions No.1 to 7, 15, 16 as inventive examples satisfy that S RATIO is 30% or less and W RATIO is 60% or more, and a stable welded joint shape is obtained while suppressing slag.

[0082] For the welding conditions No.1 to 5 in the above inventive examples, W RATIO is 80% or more, and a more stable welded joint shape is obtained.

[0083] In contrast, the welding conditions No. 8 to 14 as comparative examples do not satisfy S RATIO being 30% or less, W RATIO being 60% or more, and slag formation cannot be suppressed, and a good weld bead is not obtained.

[0084] In addition, in Table 2, when “S RATIO is 30% or less and W RATIO is 80% or more”, it is rated as Evaluation A (particularly excellent), and when “S RATIO is 30% or less and W RATIO is 60% or more and less than 80%”, it is rated as Evaluation B (excellent), and when “S RATIO is greater than 30% or W RATIO is less than 60%”, it is rated as Evaluation F (unqualified).

[0085] [Table 1]

[0086]

[0087] [Table 2]

[0088]

[0089] Explanation of Reference Numerals

[0090] 1... welding wire; 2... welding torch; 3... base material; 5... arc; 6... weld bead; 7... molten droplet; 8... molten pool; 10... end of weld bead; 11... contact tip; tup... rise time; tp... pulse peak current time; tdown... fall time; tb... pulse base current time; tup + tp + tdown + tb... one pulse cycle; S BEAD ... weld bead surface area; S SLAG ... slag-covered surface area; W MAX ... maximum value of weld bead width; W min ... minimum value of weld bead width.

Claims

1. A gas shielded arc welding method for joining by short-circuiting a welding wire supplied with power from a contact tip in a welding torch to a base material, characterized in that, the gas shielded arc welding method is pulsed welding that periodically repeats a pulsed peak current (Ip) and a pulsed base current (Ib), and the pulsed peak current (Ip) of the pulsed welding is 300 A or more and 600 A or less, the welding speed (V) is 80 cm / min or more and 200 cm / min or less, and when the welding speed (V) is 80 cm / min or more and less than 120 cm / min, the pulsed peak current (Ip), the pulsed base current (Ib), the distance (L) between the base material and the contact tip, and the welding speed (V) satisfy the following formula (1), when the welding speed (V) is 120 cm / min or more and 200 cm / min or less, the pulsed peak current (Ip), the pulsed base current (Ib), the distance (L) between the base material and the contact tip, and the welding speed (V) satisfy the following formula (2), and an Ar gas of 98 vol% or more is used as a shielding gas, 0.15V - 3 ≤ (Ip - Ib) / L ≤ 0.1V + 38…(1) 0.18V - 5 ≤ (Ip - Ib) / L ≤ 0.12V + 35…(2) Here, in formula (1) and formula (2), Ip (A) refers to the pulsed peak current, Ib (A) refers to the pulsed base current, L (mm) refers to the distance between the base material and the contact tip, and V (cm / min) refers to the welding speed.

2. The gas shielded arc welding method according to claim 1, characterized in that, the pulsed base current (Ib) of the pulsed welding is 30 A or more and 120 A or less.

3. A method for manufacturing a welded joint, characterized in that, the gas shielded arc welding method according to claim 1 or 2 is used.

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