JPH05329682A - Welding wire and welding method for galvanized steel sheet - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce pits, blowholes, and spatter in gas shielded arc welding of zinc-based plated steel sheets. [Structure] C: 0.15% or less by weight, Si: 0.1 to 0.1.
4%, Mn: 1.2 to 1.7%, P: 0.03% or less, S: 0.0.
Includes up to 03% and one or two of Ti and Nb
A steel wire containing 0.04 to 0.10% in total of the seeds and the balance being Fe and inevitable impurities is used. A ternary shield gas of O ₂ + Ar + CO ₂ containing 1% or more and 7% or less by volume of O ₂ gas is used. Perform pulse MAG welding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding wire used for gas shielded arc welding of zinc-based plated steel sheet and a gas shielded arc welding method using the same, and more particularly to suppressing generation of pits, blow holes and spatters. A welding wire and a welding method.

[0002]

2. Description of the Related Art Zinc-based plated steel sheets are hot-dipped or electroplated with zinc or a zinc alloy on the surface of rolled steel sheets for the purpose of improving corrosion resistance, and are widely used in the fields of automobiles, electrical appliances, building materials, etc. Has been done. However, this zinc-based plated steel sheet is inferior in weldability to the bare steel sheet due to the fact that the surface of the steel sheet is plated with zinc.

That is, zinc in the vicinity of the weld is heated to a temperature higher than its boiling point by the heat of welding and is evaporated, and the weldability is deteriorated. More specifically, evaporated zinc mixes into the arc column, causing instability of the arc and causing an increase in spatter. In addition, in the case of welded joints where zinc vapor is likely to penetrate into the weld metal such as lap fillet welding, the zinc vapor remains in the weld metal as it is, and welding defects due to pores such as pits and blowholes frequently occur. ..

In order to solve such a problem, for example, a welding wire containing Bi and a welding method using the same are disclosed in Japanese Patent Application Laid-Open No. 1-309796. The typical welding method disclosed here performs MAG or pulse MAG welding using a _binary wire containing steel wire containing Bi and Ar containing CO ₂ . It is described that Bi reduces the viscosity of the wire metal, facilitates the escape of zinc vapor from the molten metal, and atomizes the droplets in pulse MAG welding to reduce spatter.

Further, a ternary shield gas in which a trace amount of O ₂ is added to a _binary shield gas in which Ar ₂ is mixed with CO ₂ is also used in the above welding method, and its effect is disclosed in JP-A-2-
It is described in more detail in Japanese Patent No. 37975.

[0006]

However, Bi is expensive and causes an increase in welding cost. Further, in order to increase the concentration of the arc, there is a great risk that the protrusion of the bead becomes large and the steel plate burns down. Many methods have been proposed to reduce the number of pits and the like by adjusting the composition of the welding wire other than the addition of Bi, but satisfactory results have not been obtained only by adjusting the wire composition.

Regarding the ternary shield gas in which CO ₂ and O ₂ are mixed with Ar, it is described in JP-A-2-37975 that this is effective in reducing spatter and fume. However, there is no description of the relationship with the occurrence of pits, which is a major problem when welding zinc-based plated steel sheets.

An object of the present invention is to provide a welding wire and a welding method for a zinc-based plated steel sheet which suppresses not only spatters but also pits and blow holes and is economical.

[0009]

[Means for Solving the Problems] To reduce the occurrence of blowholes in arc welding of zinc-based plated steel sheets,
It is effective to release zinc vapor positively from the molten metal, and therefore keeping the viscosity and surface tension of the molten metal low is an effective means. In addition, the turbulence of the molten pool due to the instability of the arc hinders the release of zinc vapor,
It may cause a blow hole by involving the shield gas. Therefore, increasing the stability of the arc is also an effective means for reducing blowholes.

Blow holes in the molten pool appear on the surface of the pit, so basically a means for reducing blow holes is an effective measure. However, even if the amount of blowholes is the same, the amount of pits generated may change greatly depending on the stability of the molten pool. That is, even if blowholes occur in the molten pool, pits are unlikely to occur if the molten pool maintains a stable and constant shape. On the other hand, blowholes appear on the surface of the molten pool when the molten pool is irregularly disturbed significantly, and become pits when the molten pool solidifies as it is. Therefore, in order to prevent the formation of pits, arc stability is required more than blowholes.

The reason why there are many spatters in galvanized steel sheets is that
Basically, zinc vapor enters the arc, hinders the smooth transfer of droplets, and tends to cause a short circuit for a long time. Therefore, in order to prevent the generation of spatter, it is an effective measure to improve the stability of the arc and realize smooth droplet transfer, as in the case of the pit.

As described above, the stabilization of the arc greatly contributes to the reduction of blowholes, pits and spatters.

The inventors of the present invention have studied a method for reducing blowholes, pits and spatters mainly from the viewpoint of arc stabilization, and as a result, added Ti and / or Nb to the steel wire, and further added shield gas to the steel. Adding a small amount of O ₂ gas is particularly effective in stabilizing the arc,
It was found that this can economically reduce blowholes, pits, and spatter.

The present invention has been made on the basis of such findings, and is a steel wire used for gas shielded arc welding of zinc-based plated steel sheet, wherein C: 0.15% or less by weight and S
i: 0.1 to 0.4%, Mn: 1.2 to 1.7%, P: 0.03%
Hereinafter, S: 0.03% or less, and one or two kinds of Ti and Nb in a total amount of 0.04 to 0.10%, and the balance being Fe and inevitable impurities. The first gist is a welding wire of a plated steel sheet.

The second gist is the weight ratio of C: 0.15% or less, Si: 0.1 to 0.4%, Mn: 1.2 to 1.7%, P: 0.1%.
03% or less, S: 0.03% or less, and 1 or 2 kinds of Ti and Nb in total of 0.04 to 0.10%,
Pulse MAG welding is performed using a steel wire with the balance being Fe and unavoidable impurities and a ternary mixed gas of O ₂ + Ar + CO ₂ containing 1% to 7% by volume of O ₂ gas as a shielding gas. It is a method of welding a zinc-based plated steel sheet, which is characterized in that it is performed.

Here, the volume of CO ₂ in the ternary mixed gas is preferably 5% or more and 15% or less.

[0017]

In the present invention, the wire component and the shield gas function as follows.

The wire component C adversely affects the stabilization of the arc and causes spatter and pits. Further, it is necessary to reduce the amount in order to maintain the toughness of the molten metal. Therefore, C is set to 0.15% or less.

Si and Mn are deoxidizing agents, but when they are contained in large amounts, they tend to increase the viscosity of the molten metal,
The amount of blowholes is increased without the steam being released as it is. Therefore, Si has a deoxidizing effect of 0.1 to 0.4% and M
n was set to 1.2 to 1.7%.

P and S are impurity elements, and a large amount of P
And S cause cracking due to segregation.
In addition, a large amount of P makes the arc unstable and causes frequent spattering. Therefore, P and S are both set to 0.03% or less.

Ti and Nb are elements that increase the viscosity of the molten metal, and from this point of view, they cannot be said to be effective elements for reducing blowholes and pits. However, on the other hand, it significantly contributes to the improvement of arc stability, and stabilizes the molten pool to reduce blowholes and pits, and also reduces spatter. In particular, when a small amount of O ₂ gas is mixed with the shield gas, these effects largely overcome the adverse effects such as the obstruction of vapor emission due to the increase in viscosity, and remarkably reduce blowholes, pits and spatter.

Both Ti and Nb can be added alone, but preferably Nb is added alone or in combination. This is because Nb makes it easier to secure the strength of the weld metal. Addition amount is 0.04 to 0.10 when added alone
%, Even in the case of composite addition, the total amount is 0.04 to 0.10%. If it is less than 0.04%, the effect of arc stabilization cannot be sufficiently obtained, and if it exceeds 0.10%, the release of zinc vapor is hindered or the entrainment of the shield gas becomes remarkable. 0.04 to 0.
At 10%, the mechanical properties (elongation, strength, etc.) of the weld metal do not deteriorate. Desirably, it is more than 0.06% and 0.10% or less.

Shield Gas The shield gas has a great influence on the stability of the arc (the transition form and the concentration of the arc). In ordinary MAG welding, a binary mixed gas in which CO ₂ is mixed with Ar is used. However, in the case of a binary shield gas, the arc becomes unstable in the case of welding zinc-plated steel sheet, which causes frequent occurrence of pits and spatter. to solve this problem,
A ternary mixed gas in which a small amount of O ₂ gas is mixed is used.

This ternary shield gas improves the concentration of the arc and also makes the droplets smaller so that the droplets can be smoothly transferred. Therefore, pits and spatters are reduced. Further, by reacting with zinc vapor, it is converted into zinc oxide having a high boiling point, and zinc vapor is prevented from becoming blowholes. This will be explained below.

Generally, spatter is mainly caused by a short circuit between a droplet at a wire tip and a molten pool. Specifically, since a large short-circuit current flows during a short circuit, a large amount of spatter is generated when the short circuit is released, that is, when the arc is regenerated. When welding a galvanized steel sheet, the droplets at the tip of the wire tend to grow larger than when welding a bare steel sheet, and the grown droplets move around irregularly with the arc. Such droplets cause a short circuit for a relatively long time. In a momentary short-circuit for a short time, the short-circuit current is not so large that spatter is small. However, since a large short-circuit current flows when a short-circuit occurs for a long time, spatter during arc regeneration occurs violently. Therefore, a large amount of spatter is generated during welding of the galvanized steel sheet.

On the other hand, during welding of a galvanized steel sheet, a pit formed especially in a lap fillet weld portion is a blow hole formed by the zinc in the lap portion being evaporated by the heat effect of welding and released into the molten metal. Is an opening on the bead surface. However, whether or not a blowhole similarly grown becomes a pit greatly depends on the stability of the molten pool. That is, when the molten pool is largely rocked, blowholes are likely to appear on the surface, and pits are easily formed. In this way, the molten pool oscillates largely when the short circuit is released after the relatively short circuit has occurred.

The inventors of the present invention have found that in order to reduce pits and spatters based on the above phenomenon, the droplet transfer should be in a smooth and regular transfer mode with no short circuit. And as this method, Ar
It was found that a ternary shield gas in which O ₂ and CO ₂ are added to is effective.

The addition of O ₂ reduces the adverse effect of zinc vapor by reacting vaporized zinc, which has an adverse effect on droplet transfer morphology and arc stability, with oxygen to form zinc oxide having a high boiling point. Further, the arc becomes stable because the cathode spot is fixed in the molten pool. Further, although the reason is not clear, it also has the effect of making droplets finer. However, addition of a large amount of O ₂ results in insufficient deoxidation, and defects tend to occur conversely. In addition, since the arc is excessively concentrated, it becomes a bumpy bead, which is not preferable. Further, since the arc length is shortened, a short circuit easily occurs, which causes spatter, which is not preferable. Since the addition of O ₂ has both the effect of improving the weldability and the effect of decreasing the weldability as described above, Ar and O
There is no optimum composition for the ₂ gas mixture.

On the other hand, the addition of CO ₂ stabilizes the arc, but when a large amount is added, the arc contracts at the anode point, that is, at the droplet at the tip of the wire, so that there is a force to prevent the droplet from detaching from the wire. The working droplets grow to a large extent, and a short circuit is likely to occur for a long time when a short circuit occurs, and spatter and pits easily occur.

As described above, appropriate amounts of O ₂ and CO ₂ are
Improves the weldability of galvanized steel sheets. However, the effect is limited when each is added alone. Therefore, by adding O ₂ and CO ₂ in combination to Ar, the weldability improving factors of the respective gases are exhibited.
That is, by the synergistic effect of the stabilization of the arc by the addition of O _{2 and} the atomization of the droplets, and the stabilizing effect of the arc by the addition of CO ₂ , a smooth and smooth droplet transfer under the stable arc. Is done.

The specific composition is obtained as a result of detailed experiments, and it is desirable that the volume ratio of CO ₂ is 5% or more and 15% or less, and that of O ₂ is 1% or more and 7% or less,
It is preferably 2% or more and 6% or less.

Such a ternary shield gas contains Ti,
It is also effective in suppressing the adverse effects caused by the addition of Nb, and is premised on the combination with a welding wire to which Ti and / or Nb is added, but it is also true that the effect is recognized regardless of the welding wire component, for example, , C: 0.04 to 0.10%,
Si: 0.1 to 0.6%, Mn: 1.2 to 1.7%, P, S: 0.
Reduces spatter and pits for steel wires whose basic constituent is less than 03%.

As the power source, a DC power source and a pulse power source are known, but in the case of the DC power source, a short circuit cannot be avoided with a small current, and spatter occurs. Further, since the molten pool is disturbed by the short circuit, pits are easily generated. Therefore, the power supply is a pulse power supply, and the droplets are forcibly transferred to enable smooth melting transfer with few short circuits. This reduces the amount of spatter and maintains a stable molten pool, which reduces pits.

In the present invention, the zinc-based plated steel sheet includes not only pure zinc-plated steel sheet but also zinc alloy-plated steel sheet, and its manufacturing method may be electroplating or hot dipping.

[0035]

EXAMPLES Examples of the present invention will be described below.

Example 1 Using a steel wire having a composition shown in Table 1 and a diameter of 1.2 mm,
Overlap fillet welding was performed by MAG welding. FIG. 1 shows a welding mode. Reference numeral 1 is a material to be welded, 2 is a steel wire, and 3 is a torch. The material to be welded 1 is a double-sided alloyed hot-dip galvanized steel sheet having a plate thickness of 2.3 mm and a basis weight of 45 g / m ² , and the gap between the overlapping portions was 0.05 mm. Other welding conditions are as follows.

Power supply: Pulse power supply Average current: 230A Peak current: 420A Base current: 50A Pulse width: 1.2msec Welding speed: 120cm / min Voltage: 24V Welding length: 30cm Shielding gas: Ar + 15% CO ₂ + 3% O ₂

Table 1 shows the results of investigation of weldability in the following manner.

Pit: Measure the number in the welding length of 30 cm Blow hole: Measure the ratio (%) of the total of the blow hole lengths in the welding line direction to the total welding line length by X-ray transmission inspection Spatter: Generated spatter Measure the total weight and convert it to the amount generated per unit time (g / min)

As is clear from Table 1, pits, blowholes and spatters are reduced by the limitation of C, Si and Mn and addition of Ti and Nb in the steel wire.

Example 2 Using the steel wire indicated by No. 1 in Table 1, the effects of the shield gas composition and the power source on the weldability were investigated. The conditions other than the shield gas composition were the same as in Example 1. The survey results are shown in Table 2. The DC current was 230 A, which corresponds to the average current of the pulse power supply. The combination of a ternary shield gas containing a trace amount of O ₂ and a pulse power source is effective in reducing pits, blow holes and spatters.

Example 3 Table 3 and Table 4 show the results of a more detailed investigation of the effect of the shield gas composition on the weldability using the steel wire shown in No. 1 of Table 2. The welding conditions were set to be more severe with respect to the generation of pits and spatters than in Examples 1 and 2. That is, the clearance of the overlap portion was set to 0 mm to facilitate the generation of pits, and the arc voltage was set to 21 V to increase the generation of spatter. The O ₂ amount in the shield gas is appropriately 1 to 7%, and particularly preferably 2 to 6%. Then, if the amount of CO ₂ is 5 to 15%, pits and spatters are further reduced.

[0043]

[Table 1]

[0044]

[Table 2]

[0045]

[Table 3]

[0046]

[Table 4]

[0047]

As is apparent from the above description, the welding wire of the zinc-based plated steel sheet according to the present invention has a T
With the addition of i and Nb, the welding method can be performed with a trace amount of O ₂
By using a ternary shield gas containing, pits, blow holes and spatters can be economically reduced.

[Brief description of drawings]

FIG. 1 is a schematic view showing a form of overlap fillet welding used in an example of the present invention.

[Explanation of symbols]

 1 Welded material 2 Steel wire 3 Torch

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location C22C 38/14 (72) Inventor Masashi Takaso 4-53-3 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industry Co., Ltd. (72) Inventor Takao Taka, 4-53-3 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Sumitomo Metal Industries Co., Ltd. (72) Inventor Hiroyasu Tsumura 1-17 Fuso-cho, Amagasaki City, Hyogo Sumikin Welding Kogyo Co., Ltd. (72) Inventor Takashi Kurimoto 1-17 Fuso-cho, Amagasaki-shi, Hyogo Sumikin Welding Co., Ltd. (72) Inventor Kaoru Yokoyama 1-1-17 Fuso-cho, Amagasaki-shi, Hyogo Sumikin Welding Co., Ltd. Incorporated (72) Inventor Hisahiko Miyazaki 1850 Minato Minato, Wakayama, Wakayama Joint oxygen stock company

Claims (3)

[Claims] 1. A steel wire used for gas shielded arc welding of a zinc-based plated steel sheet, which has a weight ratio of C: 0.15.
%, Si: 0.1 to 0.4%, Mn: 1.2 to 1.7%,
P: 0.03% or less, S: 0.03% or less, and Ti
And one or two of Nb in total of 0.04 to 0.10%
A welding wire for a zinc-based plated steel sheet, which comprises Fe and the unavoidable impurities as the balance. 2. C: 0.15% or less by weight, Si: 0.1
~ 0.4%, Mn: 1.2 to 1.7%, P: 0.03% or less,
S: 0.03% or less, and a total of 0.04 to 0.10% of one or two of Ti and Nb, with the balance being Fe and inevitable impurities. A steel wire is used as a shielding gas. Using a ternary mixed gas of O ₂ + Ar + CO ₂ containing 1% or more and 7% or less by volume of O ₂ gas,
A method for welding a zinc-based plated steel sheet, which comprises performing pulse MAG welding. 3. The method for welding zinc-based plated steel sheet according to claim _{2, wherein the} amount of CO ₂ in the ternary mixed gas is 5% or more and 15% or less by volume ratio.