JP6285062B1 - Arc welding method of hot-dip Zn-based plated steel sheet and method of manufacturing welded member - Google Patents

Abstract

The present invention provides an arc welding method of a hot-dip Zn-based plated steel sheet and a method of manufacturing a welded member, which are excellent in weld appearance and weld strength. An arc welding method for welding molten Zn-based plated steel sheets to each other by a pulsed arc welding method in which an arc is generated by alternately supplying a peak current and a base current, and an Ar + CO2 mixed gas is ejected as a shielding gas. And a step of generating a pulse arc at a period set according to the CO2 concentration in the shielding gas. [Selection] Figure 4

Description

  The present invention relates to an arc welding method for a hot-dip Zn-based plated steel sheet and a method for manufacturing a welded member.

  Hot dip galvanized steel sheets (hot galvanized steel sheets) have good corrosion resistance and are used in a wide range of applications including building members and automobile members. Among them, a hot-dip Zn—Al—Mg plated steel sheet containing 1% by mass or more of Al maintains excellent corrosion resistance over a long period of time, and therefore, the demand is increasing as a material to replace the conventional hot-dip Zn plated steel sheet. In addition, the Al concentration in the plating layer in the conventional hot-dip Zn-plated steel sheet is usually 0.3% by mass or less (see JIS G3302).

  When a hot-dip Zn-based plated steel sheet is used for a building member, an automobile member, etc., it is often assembled using an arc welding method. However, when arc welding is performed on a hot-dip Zn-based plated steel sheet, usually spatter, pits, and blow holes (hereinafter, blow holes include pits unless otherwise specified) are remarkably inferior in arc weldability. This is because the boiling point of Zn (about 906 ° C.) is lower than the melting point of Fe (about 1538 ° C.), so that Zn vapor is generated during arc welding, the arc becomes unstable, and spatter and blow holes are likely to occur. Because. In addition, a sputter | spatter is welding debris, such as a slag and a metal particle which disperse | distributes at the time of welding, and a blowhole is a pore included by the weld bead. This weld bead is a portion where the metal melted at the time of welding (the part where the base metal and the weld metal are melted) is cooled and solidified, and is a weld metal that joins the materials to be welded metallurgically. That is. The pit means a recess formed by pores appearing on the surface of the weld bead.

  When spatter adheres to the plated surface of the hot-dip Zn-based plated steel sheet, not only the appearance of the welded portion is impaired, but also the portion where the spatter adheres becomes the starting point of corrosion. Therefore, if a large amount of spatter adheres, the corrosion resistance is remarkably lowered, which causes a problem. Further, a process of removing the spatter with a wire brush or the like is required, which increases the cost. On the other hand, if blowholes are significantly generated, the welding strength may be reduced, which may be a problem.

In particular, for members that require long-term durability, a hot-dip Zn-plated steel sheet having a thickness of 90 g / m ² or more per side is used, but arc welding increases as the amount of plating per side increases. Since the amount of Zn vapor at the time increases, the generation of spatter and blow holes becomes even more remarkable.

  In addition, in this specification, as for the amount of plating adhesion per one surface of a hot-dip Zn-based plated steel sheet, a material with a small amount of plating may be referred to as thin, and a material with a large amount of plating may be referred to as thick.

  A pulse arc welding method using a welding wire as an electrode has been proposed as a method for suppressing the occurrence of spatter and blowholes during welding of a hot-dip Zn-based plated steel sheet. According to this pulse arc welding method, the droplet transfer from the welding wire used as the electrode to the base material becomes spray transfer, and the droplet is small and spatter is suppressed. In addition, the molten pool (the weld bead portion before solidification) is agitated by the pulse arc, and the molten pool is pushed down to make the molten pool thinner, and the discharge of Zn vapor is promoted to suppress the generation of blowholes. .

  For example, Patent Documents 1 and 2 disclose a pulse arc welding method that suppresses sputtering by controlling the welding wire composition and pulse current waveforms such as peak current, peak period, and frequency within an appropriate range.

Japanese Patent Laid-Open No. 9-206984 (published on August 12, 1997) JP 2013-184216 A (published September 19, 2013)

However, Patent Documents 1 and ² only disclose an example of a thin-walled hot-dip Zn-plated steel sheet having a coating adhesion amount per side of 45 g / m ^2. There is no description on the method of suppressing spatter and blowholes in

  As described above, the hot-dip Zn-plated steel sheet is more excellent in corrosion resistance as the coating amount increases. However, spatter and blow holes are remarkably generated during arc welding, and the weld appearance and weld strength are reduced. In view of the present situation, the present invention can suppress the occurrence of spatter and blowholes in arc welding even when the hot-dip Zn-based plated steel sheet is thick, and has a welded portion appearance and weld strength that is excellent. An object of the present invention is to provide an arc welding method for a plated steel sheet and a manufacturing method for a welded member.

As a result of detailed studies by the present inventors, the following knowledge was obtained in performing arc welding using pulsed arc welding in arc welding of hot-dip Zn-based plated steel sheets. That is, by appropriately setting the pulse period according to the CO ₂ concentration in the shield gas, it is possible to suppress the arc from becoming unstable (difficult to transfer to spray) and to connect the tip of the welding wire and the molten pool. Has been found that it is possible to prevent the occurrence of short-circuiting and to suppress the occurrence of spatter and blow holes from thin to thick coatings on the hot-dip Zn-based plated steel sheet. The present invention has been completed based on this finding.

In other words, the arc welding method for hot-dip Zn-plated steel sheets in one aspect of the present invention welds hot-dip Zn-plated steel sheets by pulsed arc welding that generates an arc by alternately supplying peak current and base current. An arc welding method, which includes a step of ejecting an Ar + CO ₂ mixed gas as a shielding gas, and a step of generating a pulse arc at a period set according to the CO ₂ concentration in the shielding gas.

  Moreover, the arc welding method of the hot-dip Zn-based plated steel sheet according to one aspect of the present invention is the welding distance from the tip of the welding wire to the weld target part in the contact portion between the hot-dip Zn-plated steel sheets that are the weld targets. It is preferable that the molten Zn-based plated steel sheets are welded to each other so that the wire and the molten pool generated in the contact portion do not short-circuit each other and the arc does not extinguish.

Further, in the arc welding method for a hot-dip Zn-based plated steel sheet according to one aspect of the present invention, the CO ₂ concentration is 5% by volume or more and 30% by volume or less, and the period of the pulse is represented by the following formula (1). It is preferable to adjust within the range.

1 ≦ f ≦ −0.4C _{CO 2} +22 (1)
(here,
f: Pulse period (ms)
C _CO2 : CO ₂ concentration in shield gas (volume%))
Moreover, it is preferable that the distance from the front-end | tip of the said welding wire to the said welding object part is 2 mm or more and 20 mm or less as for the arc welding method of the hot dip Zn type plated steel plate in 1 aspect of this invention.

  Moreover, it is preferable that the said peak current is 350 A or more and 650 A or less in the arc welding method of the hot dip Zn type plated steel plate in 1 aspect of this invention.

  In the arc welding method of a hot-dip Zn-plated steel sheet according to an aspect of the present invention, the plating layer of the hot-dip Zn-plated steel sheet contains Zn as a main component and contains 1.0 mass% or more and 22.0 mass% or less of Al. May be.

  Furthermore, in the arc welding method for a hot-dip Zn-plated steel sheet according to one embodiment of the present invention, the plated layer of the hot-dip Zn-plated steel sheet may contain 0.05% by mass or more and 10.0% by mass or less of Mg.

  Furthermore, in the arc welding method for a hot-dip Zn-based plated steel sheet according to an aspect of the present invention, the composition of the plating layer of the hot-dip Zn-plated steel sheet is Ti: 0.002 to 0.1 mass%, B: 0.001 to 0 One or more conditions selected from the group consisting of 0.05 mass%, Si: 0 to 2.0 mass%, and Fe: 0 to 2.5 mass% may be satisfied.

  Further, in the arc welding method of the hot-dip Zn-based plated steel sheet according to one aspect of the present invention, the blow hole occupancy Br represented by the following formula (2) is 30% or less, and the length is 100 mm and the width is 100 mm centering on the weld bead. Arc welding can be performed so that the number of sputters deposited in this region is 20 or less.

Br = (Σdi / L) × 100 (2)
(here,
di: length of the i-th blow hole observed in the weld bead L: length of the weld bead).

The method for manufacturing a welded member according to one aspect of the present invention is a method for manufacturing a welded member in which molten Zn-based plated steel plates are welded to each other by a pulse arc welding method, and the amount of plating adhered per one side of the molten Zn-based plated steel plate Is 15 g / m ² or more and 250 g / m ² or less, a step of jetting an Ar + CO ₂ mixed gas as a shielding gas, and a step of generating a pulse arc at a period set according to the CO ₂ concentration in the shielding gas The distance from the tip of the welding wire to the welding target part at the contact part of the hot-dip Zn-based plated steel sheets to be welded is 2 mm or more and 20 mm or less, and the peak current of the welding current that generates a pulse arc but no more than than 350A 650A, and the CO ₂ concentration of the shielding gas is below 5 vol% to 30 vol%, and the pulse The cycle method of welding members, characterized in that it is adjusted to within the range of the following equation (1).

1 ≦ f ≦ −0.4C _{CO 2} +22 (1)
(here,
f: Pulse period (ms)
C _CO2 : CO ₂ concentration in shield gas (volume%))

  According to one aspect of the present invention, even if the hot-dip Zn-based plated steel sheet is thick, it is possible to suppress the occurrence of spatter and blowholes in arc welding, and the hot-melt Zn-base is excellent in weld appearance and weld strength. An arc welding method for a plated steel sheet and a manufacturing method for a welded member can be provided.

It is a figure which shows typically the pulse current waveform in the pulse arc welding method. It is sectional drawing which shows a pulse arc welding phenomenon typically. (A) is a schematic diagram showing a positional relationship between a welding wire and a contact portion between hot-dip Zn-based plated steel sheets in the case of fillet welding by a lap joint in the method for arc welding of hot-dip Zn-plated steel sheets in the embodiment of the present invention. It is sectional drawing shown typically, (b) is sectional drawing which shows typically the said positional relationship in the case of fillet welding by a T-shaped joint. And conditions of the shield CO ₂ concentration (vol%) in the gas and periodically f (ms) is a diagram showing the relationship between blowhole occupancy and sputter deposition number. It is a top view explaining the measuring method of the blowhole occupation rate in the welding member formed by welding hot-dip Zn system plated steel plates. It is a top view explaining the measuring method of the sputter | spatter adhesion number in the welding member formed by welding hot-dip Zn series plated steel plates.

  Embodiments of the present invention will be described below. The following description is for better understanding of the gist of the invention and does not limit the present invention unless otherwise specified. Moreover, in this specification, "A-B" has shown that it is A or more and B or less.

  In the following description, in order to facilitate understanding of the arc welding method of the hot-dip Zn-based plated steel sheet in the embodiment of the present invention, first, an outline of a general pulse arc welding method is based on FIG. 1 and FIG. I will explain. The principle of pulse arc welding in the embodiment of the present invention is the same as that of a general pulse arc welding method.

  FIG. 1 is a diagram schematically showing a pulse current waveform in the pulse arc welding method. As shown in FIG. 1, the pulse arc welding method is an arc welding method in which a peak current IP and a base current IB are alternately and repeatedly supplied, and the peak current IP is set to be equal to or higher than a critical current at which the droplets are sprayed. Is done. A time during which the peak current IP is flowing is defined as a peak period PP, and a pulse period of a pulse current composed of the peak current IP and the base current IB is defined as a period f. When the peak current IP is set to be equal to or higher than the critical current, an effect of drawing the droplet at the wire tip due to electromagnetic force (electromagnetic pinch effect) occurs, and this electromagnetic pinch effect causes a constriction on the droplet at the tip of the welding wire. The droplets are atomized and regular droplet transfer (spray transfer) is performed for each pulse period. Thereby, a droplet transfers to a molten pool smoothly and generation | occurrence | production of a sputter | spatter is suppressed.

  FIG. 2 is a cross-sectional view schematically showing the pulse arc welding phenomenon. Here, fillet welding using a lap joint will be described as an example. As shown in FIG. 2, in the pulse arc welding method in which the peak current value is appropriately set, short droplets are unlikely to occur because the small droplets 5 are transferred from the welding wire 2 to the molten pool 3. Further, the molten pool 3 immediately below the arc is pushed down by the pulse arc 4 and the depth of the molten pool is reduced and stirred, and the discharge of Zn vapor is promoted to suppress generation of spatter and blowholes. A portion where the molten pool 3 is cooled and solidified becomes a weld bead 6.

  More specifically, in such a pulse arc welding method, as the distance between the tip of the welding wire 2 and the molten pool 3, that is, the arc length becomes shorter, the effect of pushing down the molten pool 3 by the pulse arc 4 becomes larger. Steam discharge is promoted. However, if the arc length becomes too short, the tip of the welding wire 2 and the molten pool 3 are short-circuited and sparked, and the molten pool 3 is blown away and a large amount of spatter is generated. In particular, when the molten Zn-based plated steel sheet is thick, the amount of Zn vapor generated increases, so that Zn vapor does not escape from the molten pool 3 even if the pulse arc welding method is used. The molten pool 3 undulates at a stretch, the tip of the welding wire 2 and the molten pool 3 are short-circuited, and the generation of spatter becomes significant.

  Accordingly, in the present invention, the short-circuit between the tip of the welding wire 2 and the molten pool 3 and the arc are prevented from becoming unstable, and the influence of Zn vapor is suppressed even when the molten Zn-based plated steel sheet is thick. This stabilizes droplet transfer and suppresses spatter and blowholes.

In the pulse arc welding method, Ar—CO ₂ gas is used as a shielding gas in order to transfer the droplets to the spray. CO ₂ is dissociated into CO, O _{2 and the} like in the arc plasma. Since this dissociation reaction is an endothermic reaction, the pulse arc 4 is cooled and contracted by the dissociation of CO ₂ . If the pulse arc 4 is too tight, the melting suit will not easily transfer to the spray, and spatter will easily occur. Further, if the pulse arc 4 becomes too tight, the arc force becomes small and the stirring effect due to the depression of the molten pool 3 becomes weak, and Zn vapor is hardly discharged from the molten pool 3 and blow holes are generated. For this reason, in pulse welding, the CO ₂ concentration in the shielding gas is usually 20% by volume or less.

On the other hand, when the CO ₂ concentration in the shielding gas is lowered, the arc force is weakened due to the spread of the pulse arc 4, the penetration becomes shallower and the bonding strength is lowered, and the ratio of expensive Ar gas is large. Therefore, there is a problem that the welding cost becomes high. Thus, although the CO ₂ concentration of the shielding gas from the viewpoint of bonding strength and weld costs higher is preferred, the higher the CO ₂ concentration of the shielding gas above as sputtering, blowholes increased.

As a result of intensive studies, the present inventors have set the pulse period f appropriately according to the CO ₂ concentration in the shield gas, thereby suppressing the difficulty of spray transfer, and the welding wire 2. The present invention has been completed with the knowledge that the tip and the molten pool 3 can be prevented from being short-circuited, and the occurrence of spatter and blowholes can be suppressed.

That is, the arc welding method according to an aspect of the present invention is an arc welding method in which hot-dip Zn-based plated steel sheets are welded to each other by a pulsed arc welding method in which an arc is generated by alternately supplying a peak current and a base current. And a step of jetting an Ar + CO ₂ mixed gas as a shielding gas, and a step of generating a pulse arc at a cycle set according to the CO ₂ concentration in the shielding gas.

In the step of ejecting the Ar + CO ₂ mixed gas, it is sufficient so that it can control the CO ₂ concentration in the Ar + CO ₂ mixed gas may be a known device. The CO ₂ concentration in the Ar + CO ₂ mixed gas may be, for example, the CO ₂ concentration in a gas cylinder filled with the mixed gas. Also, Ar gas and CO ₂ gas supplied from separate gas cylinders can be mixed and used. In this case, the CO ₂ concentration in the Ar + CO ₂ mixed gas may be obtained based on the flow rate ratio, and the CO ₂ concentration can be easily adjusted by changing the flow rate ratio. The Ar + CO ₂ mixed gas is jetted around the weld using a welding torch generally used in pulse mag welding.

In the step of generating a pulse arc with the period f set according to the CO ₂ concentration in the shield gas, the period f is set as follows, as will be described in detail later. That is, the present inventors have a range of the period f and the concentration of CO ₂ in the shielding gas that can suppress the generation of spatter and blowholes under conditions in which various welding conditions other than the CO ₂ concentration and the period f are fixed. And obtained new knowledge that the period f can be set using the obtained range (refer to FIG. 4 for a specific example). Under the conditions of the CO ₂ concentration and the period f outside the obtained range, the arc is likely to be unstable, and the tip of the welding wire 2 and the molten pool 3 are likely to be short-circuited.

Then, by setting the period f and the CO ₂ concentration in the shielding gas within the obtained range, the following effects can be obtained. As described above, it is preferable that the CO ₂ concentration in the shield gas is high from the viewpoint of joint strength and welding cost. However, when the CO ₂ concentration is increased, the pulse arc 4 is contracted, the arc force is weakened, and the stirring effect due to the depression of the molten pool 3 is reduced. According to the arc welding method of the present embodiment, the number of times the molten pool 3 is pushed down by the pulse arc 4 is increased by setting the pulse cycle short as the CO ₂ concentration is increased. The discharge of Zn vapor can be promoted. Therefore, even when the hot-dip Zn-based plated steel sheet is thick, the generation of spatter and blow holes can be effectively suppressed. Further, the CO ₂ concentration in the shielding gas can be increased, and according to the arc welding method of the present embodiment, it is possible to reduce the manufacturing cost of a welding member having excellent joint strength.

  This embodiment will be described in detail below.

Here, when appropriately setting the pulse period according to the CO ₂ concentration in the shield gas, in the present embodiment, the positional relationship between the welding wire and the contact portion between the hot-dip Zn-based plated steel sheets before welding is determined. It is defined as follows. In addition, the arc welding method in one aspect of the present invention is not limited to a specific aspect described below, and may be, for example, as follows. That is, based on various welding conditions, a suitable positional relationship (numerical range of distance) between the welding wire and the contact portion between the hot-dip Zn-based plated steel sheets before welding is defined. And the range of the CO ₂ concentration in the shielding gas are determined. Based on the obtained range, the pulse period can be appropriately set according to the CO ₂ concentration in the shield gas.

[Positional relationship between the welding wire and the contact portion between the hot-dip Zn-plated steel sheets before welding]
The positional relationship between the welding wire and the contact portion between the hot-dip Zn-plated steel sheets before welding in the arc welding method for hot-dip Zn-plated steel sheets in the present embodiment will be described with reference to FIG.

  FIG. 3 (a) shows the contact between the welding wire 2 and the molten Zn-based plated steel sheet 1 · 1 ′ in the case of fillet welding by a lap joint in the arc welding method of the molten Zn-based plated steel sheet in the present embodiment. 7 is a cross-sectional view schematically showing a positional relationship with a part 7. FIG. FIG. 3B is a cross-sectional view schematically showing the positional relationship between the welding wire 2 and the contact portion 7 between the hot-dip Zn-based plated steel plates 1 and 1 ′ in the case of fillet welding with a T-shaped joint. . 3 (a) and 3 (b) both show a cross section in a direction perpendicular to the welding direction and a state before welding.

  As shown in (a) and (b) of FIG. 3, before welding, the hot-dip Zn-based plated steel plate 1 and the hot-zinc-plated steel plate 1 ′ to be welded can be arranged in various joint shapes. In (a) of FIG. 3, it arrange | positions at a lap joint, and is arrange | positioned at the T-shaped joint in (b) of FIG. Between the arranged hot-dip Zn-based plated steel plate 1 and hot-dip Zn-plated steel plate 1 ′, a contact portion 7 is formed as a contact surface with which they contact each other. Here, the end portion closest to the tip of the welding wire 2 in the contact portion 7 is referred to as a corner portion 7a. The corner portion 7a is a portion where a weld bead 6 (see FIG. 5) is formed at a portion where the molten Zn-based plated steel plate 1 and the molten Zn-based plated steel plate 1 'are adjacent to each other. More specifically, in the case of a lap joint, the corner 7a intersects a plane including the side surface at the end of the molten Zn-based plated steel sheet 1 ′ disposed on the upper surface of the molten Zn-based plated steel sheet 1 with the upper surface. Part. In the case of the T-shaped joint, the corner portion 7a includes a plane including a wide surface substantially perpendicular to the upper surface of the molten Zn-based plated steel plate 1 'erected on the upper surface of the molten Zn-based plated steel plate 1; This is the part where the upper surface intersects.

  In other words, the corner portion 7a is formed with the molten Zn-based plated steel plate 1 and the molten Zn-based plated steel plate 1 ′ in a state where the molten Zn-based plated steel plate 1 and the molten Zn-based plated steel plate 1 ′ are arranged in an arbitrary joint shape. This is a portion irradiated with an arc for welding, and can also be referred to as a welding target portion. In the case where the joint shape is a butt joint, the weld target portion is on the side of the welding wire 2 on the surface where the end portion of the molten Zn-based plated steel plate 1 and the end portion of the molten Zn-based plated steel plate 1 ′ face each other. An edge (ridgeline) is meant.

  As described above, in order to suppress the occurrence of spatter due to a short circuit between the tip of the welding wire 2 and the molten pool 3, it is important to manage the arc length within an appropriate range. However, referring again to FIG. 2, the weld pool 3 moves up and down within a very short time in synchronism with the waveform of the pulse arc 4 due to the depressing effect of the pulse arc 4. It is difficult to measure and manage itself. Therefore, in this specification, as shown in FIGS. 3A and 3B, from the wire tip portion 2a which is the tip of the welding wire 2, the contact portion 7 between the hot-dip Zn-based plated steel sheets before welding is used. The distance to the corner 7a on the welding wire 2 side is defined as a distance D. In the arc welding method of the present embodiment, the distance D is a length that does not cause the welding wire 2 and the molten pool 3 to short-circuit each other, and that the pulse arc 4 is not extinguished.

  Here, for example, when pulse arc welding is performed on the joint shapes shown in FIGS. 3A and 3B, the welding wire 2 moves in a direction perpendicular to the paper surface, and sequentially welds the welding target portions. Will go. Therefore, the distance D indicates the length of the perpendicular drawn from the wire tip 2a as a point to the welding object (the corner 7a or the edge on the welding wire 2 side) as a line. Yes. In addition, the straight line passing through the central axis of the welding wire 2 does not necessarily pass through the corner portion 7a, and the straight line only needs to pass through the vicinity of the corner portion 7a. Therefore, in a broad sense, the distance D is defined as a point where the straight line passing through the central axis of the welding wire 2 intersects the molten Zn-based plated steel sheet 1 or the molten Zn-based plated steel sheet 1 ′ (welding target part) and the wire tip 2a. Is the distance between.

  Thus, in the arc welding method for the hot-dip Zn-based plated steel sheet of the present embodiment, the distance D from the wire tip 2a to the corner 7a is such that the welding wire 2 and the molten pool 3 do not short-circuit each other. Weld and maintain the length so that the arc does not turn off. This method does not measure the arc length itself, but welds while maintaining the distance D.

  Thereby, even if the hot-dip Zn-based plated steel sheet is thick, the occurrence of spatter and blowholes in arc welding can be more effectively suppressed.

  In the arc welding method of the hot-dip Zn-plated steel sheet of the present embodiment, the distance D from the wire tip 2a to the corner 7a is preferably in the range of 2 to 20 mm. When the distance D is less than 2 mm, the welding wire 2 and the molten pool 3 are short-circuited and spatter occurs. When spatter is generated, stirring by depressing the molten pool 3 is not performed, so that Zn vapor is not discharged and blow holes are generated. On the other hand, when the distance D exceeds 20 mm, the arc is extinguished, so-called arc breakage occurs. When the arc break occurs, when the welding wire 2 is short-circuited to the molten pool 3 and the pulse arc 4 is re-ignited, the spark is blown off and the molten pool 3 is blown off to generate spatter. Further, while the pulse arc 4 is extinguished, stirring by pushing down the molten pool 3 is not performed, so that Zn vapor is not discharged and blow holes are generated. In addition, when the distance D exceeds 20 mm, the arc spreads and the pinch effect due to the electromagnetic force is weakened, so that the droplet 5 is difficult to break. End up.

Setting the distance D from the wire tip 2a to the corner 7a to be in the range of 2 to 20 mm appropriately sets the pulse period according to the CO ₂ concentration in the shield gas as will be described later. By doing so, it can be easily realized. By setting the distance D in the range of 2 to 20 mm, it is possible to effectively suppress the generation of spatter and blow holes even if the hot-dip Zn-based plated steel sheet is thick.

  In addition, the arc welding method in one aspect of the present invention is the length that the welding wire 2 and the molten pool 3 do not short-circuit each other before the welding of the molten Zn-based plated steel sheets is started, and You may include the position setting process set to the length which does not turn off an arc. And in the welding process of welding the hot-dip Zn-based plated steel sheets, the distance D is maintained and welding is performed. Means for grasping the positional relationship between the wire tip 2a and the corner 7a and controlling the distance D is not particularly limited, and a known device can be used.

[Period and the CO ₂ concentration of the shielding gas]
In the pulse mag welding method, an Ar—CO ₂ mixed gas is used as a shielding gas in order to cause the droplets to be sprayed. An arc welding method according to an aspect of the present invention includes a step of ejecting an Ar + CO ₂ mixed gas as a shielding gas, and a step of generating a pulse arc at a period set according to the CO ₂ concentration in the shielding gas. .

FIG. 4 shows the relationship between the conditions of the CO ₂ concentration (volume%) and the period f (milliseconds) in the shielding gas, the blow hole occupation ratio, and the number of sputter deposits. In the figure, a circle indicates a case where the blow hole occupancy described later satisfies both of 30% or less and the number of sputter adhesion is 20 or less. In the figure, the x mark indicates the case where the blowhole occupancy exceeds 30%, the number of sputtered deposits exceeds 20, or both. The ● mark in the figure indicates the case where a humping bead has occurred.

In the range surrounded by the solid line in FIG. 4, that is, the CO ₂ concentration C _CO2 in the shield gas is 5 to 30% by volume, and the period f is within a predetermined range (within the range of the expression (1) described later). The occurrence of blow holes and spatter is suppressed, and the bead shape is also good. However, if the CO ₂ concentration C _CO2 in the shielding gas is less than 5% by volume, the pulse arc 4 becomes unstable, the beads meander due to the humping phenomenon, and the bead appearance is significantly lowered. In addition, blowholes and spatter are also significantly generated. When the CO ₂ concentration C _CO2 exceeds 30% by volume, the droplets do not transfer to the spray, but transfer to the short circuit, so that the generation of blow holes and spatters becomes significant.

  Here, when the pulse period f is shortened, the number of times the molten pool 3 is pushed down by the pulse arc 4 increases, so that the discharge of Zn vapor is promoted. However, if the period f is too short as less than 1 ms, the welding wire 2 is excessively melted when the supply speed of the welding wire 2 is 3 m / min or less, and the distance from the tip of the welding wire 2 to the molten pool 3 is increased. As a result, the arc breaks and the droplet 5 becomes coarse. As a result, droplet transfer becomes unstable and spatter occurs. Further, since the molten pool 3 is not pushed down by the pulse arc 4 during the arc break, blow holes are also generated.

  On the other hand, if the period f is too long, the welding wire 2 is insufficiently melted, the distance from the tip of the welding wire 2 to the molten pool becomes too short, the tip of the welding wire 2 and the molten pool 3 are short-circuited, and sputtering occurs. Occur. Further, since the number of times the molten pool 3 is pushed down by the pulse arc 4 is reduced, Zn vapor is not discharged, and spatter and blow holes are generated.

Further, even if the CO ₂ concentration C _CO2 in the shielding gas is in the range of 5 to 30% by volume, as described above, when the CO ₂ concentration C _CO2 increases, the pulse arc contracts and the arc force becomes weak, and the molten pool The stirring effect by pushing down 3 is reduced.

As described above, the arc welding method according to an aspect of the present invention jets the mixed gas by setting the CO ₂ concentration C _CO2 in the Ar + CO ₂ mixed gas as the shielding gas to 5 vol% or more and 30 vol% or less, and It is preferable to generate a pulse arc by adjusting the pulse period f within the range of the following equation (1) according to the CO ₂ concentration C _CO2 .

1 ≦ f ≦ −0.4C _CO2 +22 (1)
(here,
f: Pulse period (ms)
C _CO2 : CO ₂ concentration in shield gas (volume%))
In the arc welding method according to one aspect of the present invention, when the CO ₂ concentration C _CO2 increases as shown in the above equation (1), the upper limit of the period f is shortened to increase the number of times the molten pool 3 is pushed down by the pulse arc 4. Accelerate the discharge of Zn vapor from the molten pool 3. Then, short-circuit between the tip of the welding wire 2 and the molten pool 3 and arc extinction are prevented, and even if the molten Zn-based plated steel sheet is thick, the influence of Zn vapor is suppressed and the droplet transfer is stabilized. And the generation of spatter and blowholes can be suppressed.

  Therefore, even if the hot-dip Zn-based plated steel sheet is thick, it is possible to suppress the occurrence of spatter and blowholes in arc welding, and the arc-welding method of the hot-dip Zn-based plated steel sheet excellent in weld appearance and weld strength and A method for manufacturing a welding member can be provided.

  Next, preferable specific examples of various conditions used in the arc welding method of the hot-dip Zn-based plated steel sheet according to the present embodiment will be described.

[Peak current]
The peak current IP for generating the pulse arc is preferably in the range of 350 to 650A. When the supply speed of the welding wire 2 is 15 m / min, if the peak current IP falls below 350 A, the welding wire 2 becomes insufficiently melted, the supply of the welding wire 2 becomes excessive, and the wire tip 2a and the molten pool 3 are connected. Can be short-circuited. Moreover, arc force becomes weak and the stirring effect by pushing down of the molten pool 3 becomes weak. On the contrary, when the peak current IP exceeds 650 A, the welding wire 2 is excessively melted, the distance D exceeds 20 mm, and arc breakage or coarsening of the droplet 5 occurs.

(Fitting shape)
In addition to fillet welding with the lap joint shown in (a) of FIG. 3 and fillet welding with the T-shaped joint shown in (b) of FIG. 3, a corner joint, a cross joint, a metal fitting, a flare joint, etc. The present invention can be applied to any joint shape. The present invention can also be applied to butt welding using a butt joint, a corner joint, a cross joint, and a T-shaped joint.

[Hot Zn-plated steel sheet]
In the present embodiment, the hot-dip Zn-plated steel sheet to be welded has a plated layer such as a hot-dip Zn-plated steel sheet, an alloyed hot-dip Zn-plated steel sheet, a hot-dip Zn-Al-plated steel sheet, and a hot-dip Zn-Al-Mg-plated steel sheet. A hot-dip galvanized steel sheet mainly composed of Zn is preferred.

Among the hot-dip Zn-based plated steel sheets, the hot-dip Zn-Al-Mg plated steel sheets contain Al: 1.0 to 22.0 mass%, Mg: 0.05 to 10.0 mass%, and are excellent in corrosion resistance. It is. The plating layer of the hot-dip Zn—Al—Mg plated steel sheet is Ti: 0.002 to 0.1% by mass in order to suppress the formation and growth of a Zn ₁₁ Mg ₂ phase that causes the appearance and corrosion resistance of the plating layer to deteriorate. , B: You may add 0.001-0.05 mass%. In addition, Si is added up to 2.0% by mass in order to suppress excessive growth of the Fe-Al alloy layer formed at the interface between the plating plate surface and the plating layer and improve the adhesion of the plating layer during processing. May be.

[Amount of plating]
When the coating amount of the hot-dip Zn-based plated steel sheet is small, it is disadvantageous for maintaining the corrosion resistance and sacrificial anticorrosive action of the plated surface over a long period of time. As a result of various studies, it is more effective to set the amount of plating deposited on one surface to 15 g / m ² or more. On the other hand, if the coating adhesion amount per side exceeds 250 g / m ² , the amount of Zn vapor generated becomes too large, and spatter and blow holes are generated even when the arc welding method of the hot-dip Zn-based plated steel sheet of this embodiment is used. Therefore, it is preferable that the plating adhesion amount per side is 250 g / m ² or less.

(Welding wire)
The welding wire 2 is preferably JIS Z3312 YGW15 or JIS Z3312 YGW16. In addition to these, various solid wires defined in JIS Z3312 may be used, and other types may be used. For example, a platingless wire, a flux-cored wire, a slag wire, or the like may be used.

The wire diameter of the welding wire 2 can use the diameter of 1.2 mm, for example, and may be the diameter of 0.8-1.6 mm.

[Wire supply speed]
The wire supply speed is preferably 3 m / min or more in order to prevent the welding wire 2 from being excessively melted and the distance from the tip of the welding wire 2 to the molten pool 3 to be longer, and arc breakage or droplet 5 enlargement. It is. When the wire supply speed exceeds 15 m / min, the supply of the welding wire 2 becomes excessive and a short circuit between the wire tip 2a and the molten pool 3 occurs. Therefore, the upper limit is preferably 15 m / min. What is necessary is just to select a wire supply speed suitably according to welding conditions, such as a wire diameter, the period f, and peak current IP.

[Base current]
The base current IB is preferably 10 to 200A. If it is less than 10A, the arc is easily extinguished, and if it exceeds 200 A, the droplets are difficult to break.

[Arc voltage]
The arc voltage is preferably 10 to 100V. If it is less than 10 V, the distance from the tip of the welding wire 2 to the molten pool 3 will be short, and if it exceeds 100 V, the distance from the tip of the welding wire 2 to the molten pool 3 will be too long.

[Torch holding angle]
Among the torch holding angles, the torch angle is preferably 30 to 60 °. Further, the advancing angle or the receding angle is preferably 0 to 30 °. The torch angle, advancing angle or receding angle is appropriately selected within the above range depending on the welding conditions such as the joint shape and the welding posture.

[Target position]
The target position is preferably the corner 7a on the welding wire 2 side in the abutting portion 7 between the molten Zn-based plated steel sheets before welding, but is not limited to the corner 7a as long as the desired bead shape and joint strength can be obtained. .

(Welding posture, traveling direction)
The welding posture and the traveling direction are not particularly limited. The horizontal orientation, vertical orientation, upward movement, and downward movement may be appropriately selected depending on the shape of the welding member.

(Welding power supply method)
The welding power source is not limited. Either DC arc method or AC arc method can be used. What is necessary is just to select suitably according to the plate | board thickness of a welding member, a shape, and penetration.

[Welding speed]
The welding speed can be set to 0.4 m / min, for example, and may be set in the range of 0.1 to 2 m / min according to various welding conditions.

In the arc welding method of the present embodiment, various welding conditions are set within the above-described preferable range, and the welding wire and the hot-dip Zn-based plated steel sheet before welding as described above are used. A preferable positional relationship with the abutting portion is defined. Under such conditions, in the arc welding method of the present embodiment, a suitable range of CO ₂ concentration and period f (range surrounded by a solid line in FIG. 4) is required.

Here, in the arc welding method according to another aspect of the present invention, when various welding conditions and the above positional relationship are changed, preferred ranges of the CO ₂ concentration and the period f are different from the ranges shown in FIG. Can be a range. That is, it is difficult to specify universally the range for appropriately setting the period f according to the CO ₂ concentration in the shield gas.

According to one aspect of the present invention, the following arc welding method can be provided. That is, in the arc welding method of a hot dip Zn-based plated steel sheet, there are cases where various welding conditions are adjusted ad hoc (empirically) in the presence of various adjustable welding conditions. Instead, according to one aspect of the present invention, welding conditions other than the CO ₂ concentration and the period f are fixed, and a suitable range of the CO ₂ concentration and the period f is obtained. It is possible to provide a useful method in which a suitable welding condition that can effectively suppress generation can be obtained.

[Blow hole occupancy, number of spatters attached]
According to the arc welding method of the hot-dip Zn-plated steel sheet of the present embodiment, welding of hot-dip Zn-plated steel sheets can be performed while suppressing the occurrence of spatter and blowholes. Can be provided. The evaluation of the welded member (blow hole occupancy, number of spatter deposits) will be described with reference to FIGS.

  FIG. 5 is a plan view for explaining a method for measuring the blowhole occupancy rate in the welded member 10 formed by welding the molten Zn-based plated steel sheets. As shown in FIG. 5, a weld bead 6 is formed on a welded member 10 formed by welding a hot-dip Zn-based plated steel plate 1 and a hot-dip Zn-based plated steel plate 1 ′, and the weld bead 6 has a blow hole 6a. Many have. Further, the length in the longitudinal direction (weld line direction) of the weld bead 6 is defined as a length L, and the length of the i-th blow hole from one end of the weld bead 6 is defined as di. Here, for example, when the joint shape is a T-shaped joint, the molten Zn-based plated steel sheet 1 and the molten Zn-based plated steel sheet 1 ′ shown in FIG. 5 are welded vertically three-dimensionally.

  According to the architectural thin plate welded joint design / construction manual (architecture thin plate welded joint design / construction manual editing committee), the integrated value of the length di of each blowhole 6a schematically shown in FIG. If the blowhole occupancy Br calculated by the following equation (2) from the measured value of the integrated value Σdi (mm) obtained by measuring and integrating the lengths of all the blowholes 6a formed in the bead 6 is 30% or less It is said that there is no problem in welding strength. The welded member 10 in the present invention has a blowhole occupation ratio Br of 30% or less, and is excellent in welding strength.

Br = (Σdi / L) × 100 (2)
here,
di: length of the i-th blow hole observed in the weld bead L: length of the weld bead.

  FIG. 6 is a plan view for explaining a method of measuring the number of spatter deposits in the welded member 10 formed by welding the molten Zn-based plated steel plates. If the number of sputter deposits in the region 8 having a length of 100 mm and a width of 100 mm centered on the weld bead 6 indicated by the dotted line in FIG. 6 is 20 or less, spatter is not noticeable and the influence on the corrosion resistance is small. Here, the center of the region 8 may be the center of the weld bead 6, and the length of 100 mm is 50 mm from the weld bead 6 to one (hot Zn-plated steel sheet 1) and the other (hot Zn-plated steel sheet 1). ') Means 50mm on the side. At this time, for example, when the joint shape of the welding member 10 is a T-shaped joint, the length 100 mm of the region 8 may be 50 mm in the perpendicular direction with the weld bead 6 as the center. Further, the width of 100 mm means the width of the region 8 in the same direction as the longitudinal direction of the weld bead 6.

  The welding member 10 according to the present invention has 20 or less spatter deposits in the region 8 and is excellent in weld appearance and corrosion resistance.

  Using four types of hot-dip Zn-based plated steel sheets shown in Table 1, lap fillet welded joints were constructed and pulse arc welding was performed. The welding wire 2 used was JIS Z3312 YGW12 having a diameter of 1.2 mm, a welding speed of 0.4 m / min, a bead length of 180 mm, and an overlap margin of 30 mm.

Further, during welding, the welding state of the portion including the tip of the welding wire 2 and the corner 7a on the welding wire 2 side in the contact portion 7 between the hot-dip Zn-based plated steel sheets before welding is high under the conditions shown below. The distance D from the tip of the welding wire 2 to the corner 7a was measured by taking a picture with a speed camera. After pulsed arc welding, the number of sputtered deposits and blowhole occupancy Br were measured by the methods described above.

[High-speed camera shooting conditions]
High-speed camera: M310 manufactured by Novitec Corporation
Laser light source for visualization: CAVLUX HF manufactured by Cavitra
Pulse wavelength: 810 nm
Number of frames: 4000 frames / second.

Tables 2 and 3 show the types of hot-dip Zn-based plated steel sheets, pulse arc welding conditions, distance D from the tip of welding wire 2 to corner 7a, the number of sputter deposits, and the measurement results of blowhole occupancy Br. .

  Table 2 uses a molten Zn-6% Al-3% Mg plated steel sheet as the molten Zn-based plated steel sheet, the type of shield gas, the peak current IP, the period f, and the distance D from the tip of the welding wire 2 to the corner 7a. This is the result of investigating the number of sputtered deposits and the blow hole occupation ratio Br by changing.

No. When the pulse period f is appropriately set according to the CO ₂ concentration C _CO2 in the shield gas, and the CO ₂ concentration C _CO2 and the period f are within the scope of the present invention, as in the embodiments 1 to 22, With an appropriate distance D from the tip of the welding wire 2 to the corner 7a, the number of sputtered deposits can be less than 20 and the blowhole occupancy can be less than 30%. Therefore, it can be seen that an arc welding member excellent in weld appearance and weld strength can be obtained by suppressing the occurrence of spatter and blow holes.

On the other hand, the pulse period f is not appropriately set according to the CO ₂ concentration C _CO2 in the shield gas, and either the CO ₂ concentration C _CO2 or the period f is out of the condition range of the present invention. No. In the comparative examples of Nos. 23, 24, 26, and 29, spatters and blowholes are remarkably generated, and an arc welded member having excellent weld appearance and weld strength cannot be obtained.

  In addition, the distance D from the tip of the welding wire 2 to the corner 7a is too far or too close. Also in the comparative examples of 25, 27, and 28, spatter and blowhole are remarkably generated, and an arc welded member excellent in weld appearance and weld strength cannot be obtained.

  Table 3 shows the results of investigating the number of sputter deposits and the blow hole occupancy Br by performing welding under various pulse arc welding conditions and distance D using hot-dip Zn-based plated steel sheets having various plating compositions and adhesion amounts. is there.

No. As shown in 30 to 42, CO ₂ concentration _{C CO2,} the distance D, the peak current IP, the period f, the embodiment within the scope amount plating adhesion of the present invention, even in the welding member according to any of the molten Zn-plated steel sheet Sputtering and blowholes are suppressed. In particular, no. In 38 to 42, spatter and blowholes are suppressed from being thin with a coating weight of 15 g / m ² to 250 g / m ² , and the hot-dip Zn-based plated steel has excellent weld appearance and weld strength. It can be seen that an arc welding member is obtained.

On the other hand, no. In Comparative Examples 43 to 51, the plating adhesion amount exceeds the upper limit of 250 g / m ² of the present invention, and the CO ₂ concentration C _CO2 , distance D, peak current IP, and period f are within the scope of the present invention. However, since the generation of Zn vapor is remarkable, the generation of spatter and blowholes cannot be suppressed, and a hot-dip Zn-based plated steel-iron-welded member excellent in weld appearance and weld strength has not been obtained.

1.1 'Hot-dip Zn-based plated steel plate 2 Welding wire 2a Wire tip (tip of welding wire)
3 weld pool 4 pulse arc 5 droplet 6 weld bead 7 abutting part 7a corner (weld part)
8 areas (area where the number of spatters is counted)
10 Welded parts

Claims (9)

An arc welding method for welding molten Zn-based plated steel sheets by a pulsed arc welding method in which an arc is generated by alternately supplying a peak current and a base current,
A step of jetting an Ar + CO ₂ mixed gas as a shielding gas;
In set period in accordance with the CO ₂ concentration of the shielding gas, I saw including a step of generating a pulsed arc,
The arc of the hot-dip Zn-based plated steel sheet, wherein the CO ₂ concentration is 5% by volume or more and 30% by volume or less, and the cycle of the pulse is adjusted within a range represented by the following formula (1): Welding method.
1 ≦ f ≦ −0.4C _{CO 2} +22 (1)
(here,
f: Pulse period (ms)
C _CO2 : CO ₂ concentration in shield gas (volume%))   The distance from the tip of the welding wire to the welding target part at the contact part between the hot-dip Zn-based plated steel sheets that are the welding objects is such that the welding wire and the molten pool generated at the contact part do not short-circuit each other. 2. The arc welding method for hot-dip Zn-based plated steel sheets according to claim 1, wherein the hot-dip Zn-based plated steel sheets are welded to each other as long as the arc does not extinguish. The distance from the front-end | tip of the said welding wire to the said welding object part is 2 mm or more and 20 mm or less, The arc welding method of the hot-dip Zn type plated steel plate of Claim 2 characterized by the above-mentioned. The arc welding method for hot-dip Zn-based plated steel sheets according to any one of claims 1 to 3 , wherein the peak current is 350 A or more and 650 A or less. Plating layer of the molten Zn-plated steel sheet is mainly composed of Zn, in any one of claims 1 to 4, characterized in that it contains 1.0 wt% or more 22.0 wt% Al An arc welding method for the hot-dip Zn-based plated steel sheet. 6. The arc welding method for a hot-dip Zn-plated steel sheet according to claim 5 , wherein the plated layer of the hot-dip Zn-plated steel sheet contains 0.05% by mass or more and 10.0% by mass or less of Mg. The composition of the plated layer of the hot-dip Zn-based plated steel sheet is Ti: 0.002 to 0.1 mass%, B: 0.001 to 0.05 mass%, Si: 0 to 2.0 mass%, and Fe: The arc welding method for a hot-dip Zn-based plated steel sheet according to claim 5 or 6 , wherein one or more conditions selected from the group consisting of 0 to 2.5 mass% are satisfied. Arc welding is performed so that the blow hole occupancy Br represented by the following formula (2) is 30% or less, and the number of sputter deposits in the region of 100 mm length and 100 mm width centering on the weld bead is 20 or less. The arc welding method for hot-dip Zn-based plated steel sheets according to any one of claims 1 to 7 , characterized in that
Br = (Σdi / L) × 100 (2)
(here,
di: length of the i-th blow hole observed in the weld bead L: length of the weld bead) A method for producing a welded member in which hot-dip Zn-based plated steel sheets are welded together by a pulse arc welding method,
The plating adhesion amount per side of the hot-dip Zn-based plated steel sheet is 15 g / m ² or more and 250 g / m ² or less,
A step of jetting an Ar + CO ₂ mixed gas as a shielding gas;
Generating a pulse arc at a period set according to the CO ₂ concentration in the shielding gas,
The distance from the tip of the welding wire to the welding target part in the contact part between the hot-dip Zn-based plated steel sheets to be welded is 2 mm or more and 20 mm or less,
The peak current of the welding current that generates the pulse arc is 350 A or more and 650 A or less,
The CO ₂ concentration of the shielding gas is 30 vol% or more 5% by volume, and the period of the pulses, the production of the welding member, characterized in that it is adjusted within the following ranges (1) Method.
1 ≦ f ≦ −0.4C _{CO 2} +22 (1)
(here,
f: Pulse period (ms)
C _CO2 : CO ₂ concentration in shield gas (volume%))

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