JPH079148A - Gas shielded arc welding method for galvanized steel sheet and galvanized steel sheet product welded by the welding method - Google Patents

Abstract

PURPOSE:To provide the welding method to suppress a large quantity of spatters generated when the galvanized steel sheet is subjected to gas shielded arc welding and the occurrence of pores such as pits and blowholes which are weld defects and undercuts and the satisfactory galvanized steel sheet product. CONSTITUTION:The generation of spatters, pores, such as pits and blowholes and undercuts is suppressed by performing pulse MAG welding 1 superimposed with a pulse current in advance and then performing short circuiting transfer welding 2 continuously.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas shielded arc welding method suitable for welding galvanized steel sheets and a galvanized steel sheet product welded by the welding method.

[0002]

2. Description of the Related Art In recent years, steel sheets coated with zinc or a zinc alloy (hereinafter referred to as galvanized steel sheets) have corrosion resistance,
Due to its excellent weather resistance, it is used for automobile parts, steel members for construction, etc., and its demand is increasing year by year.

Short-circuit transfer welding (carbon dioxide welding, MAG welding) and pulse MAG welding are generally widely used for welding galvanized steel sheets. When performing these arc welding, the zinc plated on the surface of the steel sheet has a lower melting point than iron, the zinc is vaporized, and this vapor zinc tries to diffuse to the outside through the molten pool and the molten metal. When the solidification speed of the molten metal is high, the vapor zinc cannot be fully diffused to the outside and remains as bubbles in the weld metal and on the surface of the weld metal. This steam zinc has been a cause of welding defects such as blowholes and pits (hereinafter referred to as pores). In addition, the generation of zinc vapor also disturbed the arc and caused a large amount of spatter.

As described above, the galvanized steel sheet is short-circuited and transition-welded. The characteristics of spattering and porosity are remarkable as described above. However, when pulse MAG welding is used, spattering is reduced as compared with short-circuiting and transitional welding. It Further, since the amount of heat input is large, the diffusion of zinc vapor is promoted and the generation of pores is suppressed. However, since the amount of heat input is large, the occurrence of welding defects such as undercut is promoted and it is difficult to cope with the welding of thin plate materials.

The generation of such pores, undercuts, and spatters not only deteriorates the welding quality, but if the frequency of occurrence of these pores, undercuts, and spatters is not allowed, it is necessary to rework the welded portion. If it cannot be repaired, the member may be discarded, resulting in a reduction in work efficiency and a significant uneconomical result.

As described above, the pulse MAG is also used for short-circuit transfer welding.
Welding also had its drawbacks. Therefore, at present, with respect to the generation of pores and spatter, low-speed welding having a relatively slow speed, welding with a gap between steel plates, etc. is performed, and with respect to the occurrence of undercut, the welding voltage is lowered, etc. This was mainly done by devising the construction aspect based on experience.

[0007]

As described above, in arc welding of galvanized steel sheet by the conventional method, the efficiency is low due to the low speed welding, and defects such as burn-through and undercut are likely to occur due to the gap between the steel sheets. . Moreover, when the welding voltage was lowered, the amount of spatter increased.

The present invention solves the above-mentioned problems, and in arc welding of galvanized steel sheet, a gas that has a higher welding speed than before and can suppress the generation of pores, spatters, and undercuts. It is intended to provide a shield arc welding method and a galvanized steel sheet product welded by the welding method.

[0009]

In order to solve the above problems, the invention according to claim 1 provides a gas shielded arc welding method comprising a pulse MAG welding process in which a pulse current is superposed and a short-circuit transfer welding process. It was done.

The invention according to claim 2 is the welding method according to claim 1, wherein the shielding gas is 2 to
The gas shielded arc welding method is characterized in that 7% by volume of oxygen gas is mixed.

Further, the invention according to claim 3 is a galvanized steel product which is welded by pulse MAG welding on which a pulse current is superposed and subsequently welded by short-circuit transfer welding.

[0012]

In the gas shielded arc welding method for galvanized steel sheet of the present invention, pulse MAG welding is performed in a relatively low welding current region to promote diffusion of zinc vapor and remove zinc from the surface layer of the galvanized steel sheet. . Subsequently, the surface of the steel sheet from which zinc has been removed is further subjected to short-circuit transfer welding to obtain a bead with less spatter and no welding defects such as pores and undercuts.

Further, when oxygen gas is mixed in the shield gas, the viscosity of the molten metal decreases, facilitating droplet transfer,
Suppress the disturbance of the arc. Therefore, the generation of spatter is suppressed, the diffusion of steam zinc from the molten portion to the outside is promoted, and the generation of pores is suppressed.

[0014]

【Example】

(Embodiment 1) FIG. 1 shows a schematic explanatory view of a welding method according to an embodiment of the present invention. In the figure, 1 indicates the state of pulse MAG welding which is performed in advance, and 2 is followed by the state of short circuit transfer welding
Indicate.

In the pulse MAG welding of No. 1, the welding current region is set to be relatively low to promote the diffusion of zinc vapor generated in the surface layer of the galvanized steel sheet, and to cause a large amount of spatter and the generation of porosity. To remove. This allows
In the subsequent short-circuit transfer welding shown by 2, the generation of these spatters and pores is suppressed and welding is performed. Further, since the heat input to the base material is reduced, the occurrence of undercut is suppressed. The shield gas was mainly composed of a mixed gas of argon gas and carbon dioxide gas.

(Example 2) 2 to 7 volume% of oxygen gas was mixed in the shielding gas used in the welding method of Example 1 described above.

When this oxygen gas is mixed, the viscosity of the molten metal is lowered, the droplet transfer is facilitated, and the turbulence of the arc is suppressed. Therefore, generation of spatter is suppressed, diffusion of steam zinc from the molten portion to the outside is promoted, and generation of pores is suppressed. If the amount of oxygen gas is too large, the viscosity of the molten portion will be lowered too much, which will conversely disturb the molten pool and promote the generation of spatter and pores. Therefore, good results were obtained when the mixing ratio of oxygen gas was 2 to 7% by volume.

[0018]

As is apparent from the above description, the present invention has the following effects.

(1) It is possible to suppress the generation of spatter, pores and undercuts, thus improving welding quality.
It is possible to realize a welding method for galvanized steel sheets that suppresses deterioration of bead appearance, eliminates work efficiency such as spatter removal work and weld rework, and maintains good welding workability.

(2) By reducing the heat input to the base metal, the range of application for welding thin plate materials can be widened.

(3) A welded galvanized steel sheet product having few pores and undercuts can be realized.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating a welding method according to an embodiment of the present invention.

[Explanation of symbols]

 1 Pulse MAG welding 2 Short-circuit transfer welding

Claims (3)

[Claims] 1. A consumable electrode type welding method in which a gas containing argon gas or carbon dioxide gas is used as a shield gas for welding, in a galvanized steel sheet having a short-circuit transfer welding step following a pulse MAG welding step in which a pulse current is superimposed. Gas shield arc welding method. 2. The gas shield arc welding method for galvanized steel sheet according to claim 1, wherein 2 to 7% by volume of oxygen gas is mixed with the shield gas and the mixture is welded. 3. A galvanized steel sheet product which is welded by short-circuit transfer welding following welding by pulse MAG welding on which pulse current is superimposed.