JP2016168612A - ARC WELDING METHOD AND WELDING MEMBER FOR MOLTEN Zn BASED PLATED STEEL PLATE EXCELLENT IN WELDING APPEARANCE AND WELDING STRENGTH - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an arc welding method and a welding member for a molten Zn-Al-Mg based plated steel plate excellent in weld zone appearance and welding strength.SOLUTION: An arc welding method for a molten Zn based plated steel enables arc welding so that a solid wire diameter Wd and the maximum diameter Dd of a droplet before transit to a molten pool may satisfy the relation of the following (1) expression, the solid wire diameter Wd being 0.8-1.6 mm, and the count of sputter pieces in a region with a length of 100 mm and a width of 100 mm centered around a welding bead may be 20 or less with a blow hole occupancy Br of 30% or less. 0.8Wd≤Dd≤3Wd...(1), where Dd is the maximum diameter (mmm) of a droplet before transit to a molten pool, and Wd is the diameter (mm) of a solid wire.SELECTED DRAWING: None

Description

  The present invention relates to an arc welding method and a welded member for a hot-dip Zn-based plated steel sheet that generates less spatter and blowholes and has an excellent weld appearance and weld strength.

  Since the hot-dip Zn-based plated steel sheet has good corrosion resistance, it is used in a wide range of applications including building members and automobile members. Among them, the hot-dip Zn—Al—Mg-based steel sheet maintains excellent corrosion resistance for a long period of time, and therefore, the demand is increasing as a material to replace the conventional hot-dip Zn-plated steel sheet.

  When a hot-dip Zn-based plated steel sheet is used for a building member, an automobile member, etc., it is often assembled by an arc welding method. However, when arc welding is performed on a hot-dip Zn-based plated steel sheet, spatter, pits, and blow holes (hereinafter, blow holes include pits unless otherwise specified) are remarkably generated, resulting in poor arc weldability. This is because the boiling point of Zn is as low as about 906 ° C. compared with the melting point of Fe of about 1538 ° C., so that Zn vapor is generated during arc welding, the arc becomes unstable due to this Zn vapor, and spatter is generated. When spatter adheres to the plated surface, not only the appearance of the welded portion is deteriorated, but also that portion becomes a starting point of corrosion, so that the corrosion resistance is lowered. In addition, blowholes are generated when the molten pool solidifies before the Zn vapor can escape. If blowholes are noticeably generated, the welding strength decreases, which causes a problem.

For example, in Patent Document 1 and Patent Document 2, when lap fillet welding is performed on a zinc-based plated steel sheet by gas shield welding, welding defects such as pits and blow holes may occur due to zinc vapor. It is disclosed. As a solution to this problem, Patent Document 1 discloses that the zinc content of the plating film is 93% by weight or more, so that the boiling point is lowered and the zinc is easily evaporated, so that the zinc vapor entering the molten pool is reduced and defects are generated. There are going to be fewer. In Patent Document 2, it is effective to positively release zinc vapor from the molten metal in order to suppress the occurrence of blowholes. For that purpose, Ti and / or Nb is added to the steel wire, and further The above discloses that a small amount of O ₂ gas is added to the shielding gas.

JP-A-5-305445 JP-A-5-329682

As described above, the hot-dip Zn-based plated steel sheet is excellent in corrosion resistance, but spatter and blow holes are generated during arc welding, and the weld appearance and weld strength are reduced. In view of such a current situation, an object of the present invention is to provide an arc welding method and a welded member for a hot-dip Zn-based plated steel sheet that are excellent in appearance and weld strength of a welded part.

  As a result of detailed research by the inventors, the solid wire diameter in arc welding of hot-dip Zn-based plated steel sheet, the diameter of the droplet before transfer of the droplet to the solid wire diameter, the blow hole occupation rate and the number of sputter deposits are within the appropriate range. The present invention has been completed by obtaining the knowledge that by controlling it, spatter and blowholes can be suppressed without impairing the appearance of the weld.

That is, the above problem is that when arc welding a hot-dip Zn-based plated steel sheet, the solid wire diameter Wd is 0.8 to 1.6 mm, and the maximum diameter Dd of the droplet before moving to the molten pool is expressed by the following equation (1). Arc welding 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. Is achieved.
0.8 Wd ≦ Dd ≦ 3 Wd (1)
here,
Dd: Maximum diameter of droplet before moving to molten pool (mm)
Wd: Solid wire diameter (mm)
Also,
Br = (Σdi / L) × 100 (2)
Σdi: Integrated value of blowhole length (mm)
L: Weld bead length (mm)

In the present invention, the gap between the plates is preferably 2 mm or less, the welding voltage is 15 to 35 V, and the welding current is preferably 80 to 350 A.

  In the hot-dip Zn-based plated steel sheet according to the present invention, the composition of the plating layer is mainly composed of Zn, and contains Al: 1.0 to 22.0% and Mg: 0.05 to 10.0% by mass.

  The above-mentioned coating layer of the hot-dip Zn—Al—Mg-based steel sheet is further in mass%, Ti: 0.002 to 0.10%, B: 0.001 to 0.05%, Si: 0 to 2.0%, Fe: 1 or 2 or more selected from the group consisting of 0 to 2.5% can be contained.

The welded member of the present invention is excellent in welding strength when the blowhole occupation ratio Br shown by the following formula (2) is 30% or less.
Br = (Σdi / L) × 100 (2)
Where Σdi: integrated value of blowhole length (mm)
L: Weld bead length (mm)

In addition, the welded member of the present invention is excellent in the appearance and corrosion resistance of the welded portion when the number of sputtered deposits in the region of 100 mm length and 100 mm width centering on the weld bead is 20 or less.

  ADVANTAGE OF THE INVENTION According to this invention, the sputter | spatter and blowhole in arc welding of a hot dip Zn system plating steel plate can be suppressed, and the welding member which is excellent in a welded part external appearance, weld strength, and corrosion resistance can be provided.

Schematic diagram of pits and blowholes in a lap fillet welded joint The figure which showed the droplet transfer phenomenon of the present invention typically Schematic illustration of spattering and blowhole generation phenomena during droplet transfer when droplets become coarse Diagram showing the effect of additive elements on the viscosity of Fe Diagram explaining the number of spatter deposits and the definition of blowhole occupancy

  FIG. 1 schematically illustrates a cross-sectional structure of a welded portion of a lap fillet weld joint. This type of welded joint by arc welding is frequently used for automobile chassis. A molten Zn-based plated steel sheet 1, 1 ′ having a molten Zn-based plated layer 2 is disposed on the surface, and a weld bead 3 is disposed on the surface of the molten Zn-based plated steel sheet 1 ′ and the end surface of the molten Zn-based plated steel sheet 1. Is formed, and both members are joined.

  FIG. 1A is a cross section of a welded portion in which pits 4 are generated without allowing Zn vapor to escape from the weld metal. FIG. 1B is a cross-sectional view of a welded portion where a blow hole 5 is generated by confining Zn vapor in the weld metal. FIG. 1A and FIG. 1B are cross sections of a welded portion when no inter-plate gap is provided. If there is no gap between the plates, there is no route for the Zn vapor to escape only from the front side of the weld metal 3, so that pits and blow holes are likely to occur. Further, when Zn vapor staying in the weld metal is ejected all at once, the arc becomes unstable and spatter is generated. FIG. 1C is a cross-sectional view of the welded portion when the inter-plate gap 6 is provided. When the inter-plate gap is provided, Zn vapor is also discharged to the inter-plate gap 6 side, so that the effect of suppressing spatter and blow holes is great.

  However, depending on the shape of the arc welded structural member, the gap between the plates may not be provided or may not be increased. Therefore, in the present invention, by appropriately managing the solid wire diameter and the maximum diameter of the droplet before the droplet transfer, the droplet is smoothly transferred to the molten pool to suppress spatter and blowholes.

The inventors of the present invention observed the droplet transfer phenomenon in the lap fillet welding in detail using a high speed camera, and completed the present invention. The high-speed camera shooting conditions are shown below.
[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 taken: 4000 frames / second Test material: Molten Zn-6 mass%-3 mass% Mg-plated steel sheet

  FIG. 2 schematically shows the droplet transfer phenomenon when arc welding is performed within the condition range of the present invention. FIG. 2A shows a state where an arc 8 is ignited between the solid wire 7 and the molten pool 9. The tip of the solid wire 7 is melted by the arc 8, and a droplet 10 is formed as shown in FIG. As shown in FIG. 2 (c), the droplet 10 is short-circuited with the molten pool 9, and moves to the molten pool 9 as shown in FIG. 2 (d). Next, as shown in FIG. 2 (e), the droplet 10 is separated from the solid wire 7 by the pinch effect of the arc 8 that has been ignited. And as shown in FIG.2 (f), the molten pool 9 just under the solid wire 7 is pushed down by the arc 8, and discharge | emission of Zn vapor | steam is accelerated | stimulated. 2A to 2F are repeated to form a weld bead.

  As shown in FIG. 2, when arc welding is performed within the condition range of the present invention, the droplet formed on the tip of the solid wire smoothly moves to the molten pool, and further, the Zn vapor from the molten pool is caused by the effect of pushing down the molten pool by the arc. Discharge is promoted to suppress spatter and blow holes.

FIG. 3 schematically shows the droplet transfer phenomenon when the droplets are coarsened by arc welding outside the condition range of the present invention. 3A shows a state in which the arc 8 has been ignited, and FIG. 3B shows a state in which the droplet 10 has been formed. As shown in FIG. 3 (c), the droplet 10 moves short-circuited with the molten pool 9, but if the droplet becomes too large, it does not move to the molten pool 9 as shown in FIG. 3 (e) and 3 (f), the droplet 10 is blown off by the arc 8 that has been ignited, and the sputter 11 is generated. Further, when sputtering occurs, the arc 8 is extinguished and the molten pool 9 cannot be pushed down as shown in FIG. 3 (f), so that Zn vapor is not discharged and a blow hole 12 is generated.

  The arc welding conditions of the present invention are described in detail below.

[Solid wire diameter and maximum diameter of droplets]
In the present invention, the solid wire diameter Wd is 0.8 to 1.6 mm, and the maximum diameter Dd of the droplet before moving to the molten pool is within the range of the following formula (1).
0.8 Wd ≦ Dd ≦ 3 Wd (1)
here,
Dd: Maximum diameter of droplet before moving to molten pool (mm)
Wd: Solid wire diameter (mm)

In the present invention, the maximum diameter Dd of the droplets is the largest diameter of the droplets regardless of the horizontal direction or the vertical direction, and the droplets in any part except the part from the welding start end part to 10 mm and the welding end part to 10 mm. The transition phenomenon is defined as the average value of the maximum diameter of the droplets measured by photographing with a high speed camera 10 times.

  When the solid wire diameter Wd is less than 0.8 mm and the maximum diameter Dd of the droplet with respect to the solid wire diameter Wd is less than the range of the above formula (1), the arc force becomes weak and the effect of pushing down the molten pool cannot be obtained. In addition, the amount of droplets transferred per unit time decreases because the droplets become too small, and the viscosity of the molten pool decreases and the viscosity increases, so that it is difficult for Zn vapor to be discharged, and Zn vapor remains in the molten pool. Spatter and blow holes are generated.

When the solid wire diameter Wd exceeds 1.6 mm, or the maximum diameter Dd of the droplet is larger than the range of the above formula (1), the droplet is coarsened and sputtering is likely to occur. In addition, when the maximum diameter Dd of the droplet becomes too large with respect to the solid wire diameter Wd, the droplet becomes unstable, and the droplet drops from the solid wire before moving to the molten pool, resulting in a large spatter. When spatter occurs, the arc is extinguished, so the effect of pushing down the molten pool by the arc becomes small, and Zn vapor is difficult to be discharged from the molten pool, so that blow holes are generated.
In order to perform droplet transfer stably and smoothly and suppress spatter and blowholes, it is necessary to manage the solid wire diameter Wd and the maximum droplet diameter Dd within the above ranges. In the present invention, the composition of the solid wire is not particularly limited. JIS Z3312 YGW12 for steel materials may be used.

[Gap between plates, welding current, welding voltage]
In the present invention, the gap between the plates is preferably 2 mm or less, the welding voltage is 15 to 35 V, and the welding current is preferably 80 to 350 A.

When the gap between the plates is provided, the discharge of Zn vapor from the molten pool is promoted as described above, and stable droplet transfer is achieved, thereby suppressing spatter and blowholes. However, when the gap between the plates exceeds 2 mm, the throat thickness becomes thin and the welding strength is lowered, so 2 mm or less is preferable.

If the welding voltage is less than 15 V, the heat of the molten pool decreases due to insufficient heat input, the viscosity increases, Zn vapor is difficult to be discharged, Zn vapor remains in the molten pool, and spatter and blow holes are generated. On the other hand, when the welding voltage exceeds 35V, the arc length becomes long, and the distance between the solid wire tip and the molten pool becomes long. As a result, it takes time to transfer the droplets, and during that time the droplets become coarse and spatter and blowholes are likely to be generated.

If the welding current is less than 80 A, heat input is insufficient, the temperature of the molten pool decreases, the viscosity increases, Zn vapor is difficult to be discharged, Zn vapor remains in the molten pool, and spatter and blow holes are generated. The welding current is linked to the feed amount of the solid wire, and if the welding current is increased more than necessary, the droplets become coarse, so 350 A or less is preferable.

[Welding speed]
In the present invention, the welding speed is not particularly limited. It selects suitably by the plate | board thickness of a hot-dip Zn type plated steel plate.

〔Shielding gas〕
In the present invention, the type of the shielding gas is not particularly limited, but inexpensive carbon dioxide gas, Ar-20 volume% CO2 gas having a large sputtering suppression effect, or Ar-5 volume% CO2 gas with a further reduced CO2 concentration, etc. are suitable. is there.

[Hot Zn-plated steel sheet]
In the hot-dip Zn-based plated steel sheet according to the present invention, the composition of the plating layer is mainly composed of Zn, and contains Al: 1.0 to 22.0%, Mg: 0.05 to 10.0% by mass, Corrosion resistance is enhanced by Al and Mg.

  The above-mentioned coating layer of the hot-dip Zn—Al—Mg-based steel sheet is further in mass%, Ti: 0.002 to 0.10%, B: 0.001 to 0.05%, Si: 0 to 2.0%, Fe: 1 or 2 or more selected from the group consisting of 0 to 2.5% can be contained.

Although the method of hot dipping is not particularly limited, it is generally advantageous in terms of cost to use an in-line annealing type hot dipping equipment. The plating layer composition substantially reflects the hot-dip plating bath composition. Hereinafter, the component elements of the plating layer will be described. “%” Of the plating layer component element means “mass%” unless otherwise specified.

  Al is effective in improving the corrosion resistance of the plated steel sheet, and suppresses the generation of Mg oxide dross in the plating bath. Furthermore, as shown in FIG. 4, Al has the effect of lowering the viscosity of Fe by adding a small amount, and during arc welding, Al in the plating layer is taken into the molten pool to lower the viscosity of the molten pool and promote the discharge of Zn vapor. Thus, spatter and blowholes are suppressed. In order to fully exhibit these actions, it is necessary to secure an Al content of 1.0% or more, and it is more preferable to secure an Al content of 4.0% or more. On the other hand, when the Al content increases, a brittle Fe—Al alloy layer easily grows on the base of the plating layer, and excessive growth of the Fe—Al alloy layer causes a decrease in plating adhesion. As a result of various studies, the Al content is more preferably 22.0% or less, and may be controlled to 15.0% or less, or even 10.0% or less.

Mg exhibits the effect | action which produces | generates a uniform corrosion product on the surface of a plating layer, and raises the corrosion resistance of a plated steel plate remarkably. The Mg content is more preferably 0.05% or more, and more preferably 1.0% or more. On the other hand, if the Mg content in the plating bath increases, Mg oxide-based dross is likely to occur, which causes a deterioration in the quality of the plating layer, so the Mg content is set to a range of 10.0% or less. Mg has a boiling point of about 1091 ° C., which is lower than the melting point of Fe,
Like Zn, it is considered that it evaporates during arc welding and causes spatter and blowholes, so the Mg content is preferably 10.0% or less.

When Ti is contained in the hot dipping bath, it is preferable because generation and growth of a Zn11Mg2 phase that causes deterioration of the plating layer appearance and corrosion resistance are suppressed. If the Ti addition amount is less than 0.002%, the suppression effect is insufficient, and if it exceeds 0.1%, the appearance of the plating layer surface due to the formation and growth of Ti-Al-based precipitates at the time of plating is caused. Become. For this reason, in this invention, Ti addition amount is limited to 0.002-0.1%.

  B also has the effect of suppressing the formation and growth of a Zn11Mg2-based phase like Ti. In the case of B, it is more effective to make the addition amount 0.001% or more. However, excessive addition of B causes a poor appearance of the plating layer surface due to Ti-B or Al-B-based precipitates, so B is preferably set to a range of 0.05% or less.

When Si is contained in the hot dipping bath, excessive growth of the Fe—Al alloy layer formed at the interface between the plating original plate surface and the plating layer is suppressed, and the workability of the hot-dip Zn—Al—Mg plated steel sheet is improved. This is advantageous. Therefore, Si can be contained as necessary. In that case, it is more effective to set the Si content to 0.005% or more. However, since excessive Si content causes an increase in the dross amount in the hot dipping bath, the Si content is preferably 2.0% or less.

In the hot dipping bath, Fe is likely to be mixed because the steel sheet is immersed and passed. Zn-
When Fe is mixed in the Al—Mg-based plating layer, the corrosion resistance is lowered, so the Fe content is preferably 2.5% or less.

  If the coating amount of the molten Zn—Al—Mg based steel sheet is small, it is disadvantageous for maintaining the corrosion resistance and sacrificial anticorrosive action of the plated surface for a long period of time. As a result of various studies, it is more effective that the amount of plating deposited per side is 20 g / m 2 or more. On the other hand, when the amount of plating adhesion increases, the amount of evaporated Zn during welding increases, and sputtering and blowholes are likely to occur. For this reason, it is desirable that the plating adhesion amount per one side is 250 g / m 2 or less.

[Blow hole occupancy, number of spatters attached]
According to the Architectural Thin Plate Welded Joint Design and Construction Manual (Architecture Thin Plate Welded Joint Design and Construction Manual Editorial Committee), the measurement of the integrated value Σdi (mm) of the blowhole length schematically shown in FIG. If the blow hole occupancy Br calculated by the following equation (2) from the value is 30% or less, there is no problem in the welding strength. The welded member of the present invention is excellent in weld strength when the blowhole occupation ratio Br is 30% or less.
Br = (Σdi / L) × 100 (2)
here,
Σdi: Integrated value of blowhole length (mm)
L: Weld bead length (mm)

If the number of sputter deposits in the region of 100 mm wide and 100 mm long centered on the weld bead 3 indicated by the dotted line in FIG. The welded member of the present invention has a sputter adhesion number of 20 or less, and is excellent in welded portion appearance and corrosion resistance.

  A hot rolled steel strip having a thickness of 3.2 mm and a plate width of 1000 mm having the composition shown in Table 1 was used as a plating base plate, and this was passed through a hot dipping line to produce a hot-dip Zn—Al—Mg plated steel plate.

A sample having a width of 100 mm and a length of 200 mm was cut out from the plated steel sheet and arc welded with a lap fillet welded joint. JIS Z3312 YGW12 was used for the solid wire, and the bead length was 180 mm. Other welding conditions are shown in Table 2. Under the conditions shown below, the droplet transfer phenomenon during arc welding of the 90 mm portion from the welding start end is photographed 10 times with a high-speed camera, and the maximum diameter Dd (average value of 10 times) of the droplet before transfer is measured. did. After arc welding, an X-ray transmission photograph was taken, and blow hole occupancy Br was measured by the method described above. Moreover, the number of spatter adhesion was measured visually. Table 2 shows the composition of the plating layer, the amount of plating, arc welding conditions, the maximum diameter of the droplets before transfer of the droplets, the blow hole occupation ratio, and the number of sputter deposits.
[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

No. in Table 2 As shown in 1 to 20, in the examples in which the arc welding conditions and the maximum diameter Dd of the droplet before the droplet transfer are within the scope of the present invention, the blow hole occupation ratio is 30% or less, and the number of sputters is 20 or less. there were. From this example, it can be seen that the present invention can provide a welded Zn-Al-Mg-based plated steel sheet arc welded member having excellent weld appearance and corrosion resistance and weld strength.

  On the other hand, the welding current, welding voltage, solid wire diameter Wd, and the maximum diameter of the droplet before droplet transfer are less than the range of the present invention. Nos. 31 to 33, and No. 31 in which the welding current, the welding voltage, the maximum diameter Dd of the droplet before droplet transfer, and the diameter of the solid wire exceed the range of the present invention. In the comparative examples 34 to 39, blowholes and spatter were remarkably generated.

No. of the gap between the plates exceeds the preferred range in the present invention. In No. 20, blowholes and spatter were suppressed, but the throat thickness was reduced, and the weld was broken in a tensile test, resulting in insufficient weld strength.

1, 1 ′ Molten Zn—Al—Mg plated steel sheet 2 Plating layer 3 Weld bead 4 Pit 5 Blow hole 6 Inter-plate gap

Claims (6)

When arc welding a hot-dip Zn-based plated steel sheet,
Solid wire diameter Wd is 0.8-1.6mm,
The solid wire diameter Wd and the maximum diameter Dd of the droplet before moving to the molten pool satisfy the relationship of the following formula (1):
Blow hole occupancy Br is 30% or less,
An arc welding method for a hot-dip Zn-based plated steel sheet, in which arc welding is performed so that the number of sputter deposits in a region of 100 mm length and 100 mm width centering on a weld bead is 20 or less.
0.8 Wd ≦ Dd ≦ 3 Wd (1)
here,
Dd: Maximum diameter of droplet before moving to molten pool (mm)
Wd: Solid wire diameter (mm) The arc welding method for hot-dip Zn-based plated steel sheets according to claim 1, wherein the gap between the plates is 2 mm or less, the welding voltage is 15 to 35 V, and the welding current is 80 to 350 A.   The composition of the plating layer of the hot-dip Zn-plated steel sheet contains Zn as a main component and contains Al: 1.0 to 22.0% and Mg: 0.05 to 10.0% by mass%. An arc welding method for the hot-dip Zn-based plated steel sheet.   The plating layer of the hot-dip Zn-based plated steel sheet is further mass% in Ti: 0.002-0.10%, B: 0.001-0.05%, Si: 0-2.0%, Fe: 0-2. The arc welding method for hot-dip Zn-based plated steel sheets according to any one of claims 1 to 3, comprising 1 or 2 or more selected from the group consisting of 0.5%. The welding member which carried out the arc welding by the arc welding method of the hot-dip Zn type plated steel plate of Claims 1-4. 6. The arc-welded welded member according to claim 5, wherein the number of sputter deposits in a region of 100 mm in length and 100 mm in width centering on the weld bead is 20 or less.

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