JP2749968B2 - High current density welding method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a gas shielded arc welding method, and more particularly, to high welding at high current density welding, excellent welding workability, and good performance. The present invention relates to a high-efficiency and high-quality welding method capable of obtaining a suitable penetration shape.

[Related Art] In recent years, in the construction of various welded structures, the application of the gas shielded arc welding method has been rapidly increasing in various fields since the welding efficiency can be improved. Above all, the biggest issues at present are how to increase the welding and efficiency of thick plate welding in the steel frame, bridge and shipbuilding fields, as well as the total cost reduction including downward long leg welding and welding work.

As a means for increasing the efficiency, it is generally employed to increase the current density to increase the welding speed of the wire. However, in high current density welding, spatter frequently occurs, porosity resistance,
Many problems such as crack resistance and poor fusion occur.

First, in gas shielded arc welding in which a small diameter solid wire is welded with carbon dioxide gas, in the so-called short-circuit transition area where the welding current is about 250 A (current density is about 180 A / mm ² ), droplet transfer of particles smaller than the wire diameter As a result, stable short arc welding with small spatter particles can be performed. When the welding current is sequentially increased, the arc does not short-circuit at 200 to 400 A (current density of about 180 to about 350 A / mm ² ), droplets slightly larger than the wire diameter migrate to the base metal, and large spatter particles are generated. The amount also increased,
The welding workability also deteriorates. Furthermore, in the large current range where the welding current exceeds 400 A (current density is about 350 A / mm ² ), the arc becomes extremely unstable, spatters of large grains larger than the wire diameter occur frequently, and the workability is extremely poor. Misalignment of bead appearance and toe occurs. Therefore, if a gas mixture containing Ar and CO ₂ or O ₂ is used as the shielding gas, welding with good bead appearance with less spatter can be performed, but excessive penetration with a narrow width at the center of the bead due to pinch force. So-called "finger-shaped" penetration. In addition, in lamination welding and butt joint welding, since the penetration width is small, there has been a problem that shape defects such as poor fusion often occur.

As a means for improving this finger-shaped penetration shape into a circular penetration, He is added to a shielding gas, for example, by using a mixed gas of four kinds of Ar-He-CO ₂ -O ₂ disclosed in JP-A-59-45084. Welding methods have been proposed. However, in this method, a small droplet scatters and adheres to both ends of the bead due to the rotation of the tip of the wire in a molten state, which is difficult to remove, and a special shielding gas is used, so the gas cost increases. This leaves a practical challenge.

Therefore, high current density welding using a shielding gas of carbon dioxide gas and a flux cored wire is disclosed in
91041, JP-A-55-68184 and JP-A-56-160878-56-
It is proposed in Japanese Patent Publication No. 160880. However, these methods are related to the electrogas welding method, and the total cross-sectional area of flux + iron powder with respect to the total cross-sectional area of the wire is 30 to 35%.
In order to improve arc stability and droplet transferability by using such a thin-walled flux-cored wire, and to obtain a high melting rate, the length of the projecting wire is usually set by welding. 35-70 beyond 20-30nm used
This is a method of setting a very long length of mm and welding. For this reason, spatter is generated very frequently, and the flux cored wire is very thin in terms of wire production, so that there remains a problem that it is extremely difficult to draw a thinner wire.

[Problems to be Solved by the Invention] The present invention focuses on such circumstances, and solves various problems of high current density welding. A high welding amount can be obtained, and the arc is soft even in a large current range. The purpose of the present invention is to provide a high current density welding method in which droplets show small and stable transferability, spatter is small, the amount of generation is small, good bead appearance, circular penetration, and excellent welding workability. It is.

Means for Solving the Problems The gist of the present invention is to provide a flux-cored wire in which the cross-sectional area occupied by a flux containing iron powder using carbon dioxide gas as a shielding gas is less than 5 to 30% of the total cross-sectional area of the wire. It is a high current density gas shielded arc welding method characterized in that welding is performed at a high current density of 300 (A / mm ² ) or more.

[Operation] The present inventors have conducted various experiments on bead formation of high current density gas shielded arc welding using a flux-cored wire, and as a result, obtained the following knowledge and completed the present invention.

As shown in FIG. 1, the relationship between the bead shape and the shielding gas composition when welding was performed at a high current density of 300 (A / mm ₂ ) or more was that the shielding gas was pure Ar (FIG. 1 (a)), Ar-CO
₂ (the (b)), Ar-O ₂ (the (c)) Ar-CO ₂ -O ₂ (same (e)), Ar-He-CO 2 -O 2 ( same (d)) and various mixtures The penetration shape is finger-like even when any of the gases is used, and in some cases, poor fusion occurs in the weld metal. However, only when the CO ₂ gas shown in FIG. Is obtained.

In welding with carbon dioxide gas, it is most preferable to use a flux-cored wire from the viewpoints of arc conditions, droplet transferability, bead appearance, shape, and spatter generation.

Furthermore, the cross-sectional area of the flux containing the iron powder of the flux-cored wire limits the ratio to the total cross-sectional area of the wire, so that the droplet transferability at high current is stable, and the amount of welding can be increased without increasing the wire protrusion length Is obtained.

The present invention has been completed based on the above findings, and the reasons for the constitution of the present invention will be described in detail below.

Carbon dioxide gas is used as the shielding gas. However, if the wire used is a solid wire, stable droplet transferability cannot be obtained, spatter is generated frequently, and a good bead appearance and shape cannot be obtained. Therefore, if a flux-cored wire is used, since a small amount of an arc stabilizer and a slag agent are also contained, a bead appearance, a shape and a stable arc state can be obtained, and excellent welding workability can be obtained.

Regarding the current density, if the current density is less than 300 (A / mm ² ), a predetermined effect, particularly a wide circular penetration and a high welding amount cannot be obtained, and the welding efficiency cannot be improved. ² ) Limited to the above.

 The current density is calculated by the following equation.

Current ÷ cross-sectional area of steel sheath of wire = current density By the way, wire cross-sectional area of solid wire is simply ｛π
× (wire diameter) It can be calculated as ² ｝ / 4. However, in the case of flux-cored wire, since it is distinguished into a steel sheath portion that carries current and a flux portion that does not seem to carry current, even if the wire diameter is the same, The thickness of the steel sheath through which the current flows varies depending on the filling rate of the flux and the specific gravity of the filling flux, so that the area also changes based on the thickness. Therefore, the cross-sectional area of the flux-cored wire is substantially smaller than that of the solid wire, and the current density is higher. Therefore, as the wire cross-sectional area for calculating the current density specified by the welding method of the present invention, the cross-sectional area of the steel sheath shown in FIG. 2 is used.

High current density gas shielded arc welding method ensures stable droplet transferability, good bead shape and wire protrusion length of 35
Even if it is less than mm, it is necessary to limit the ratio of the cross-sectional area occupied by the flux containing the iron powder of the flux-cored wire to the total cross-sectional area of the wire in order to obtain a high welding amount.

That is, the reason why the cross-sectional area occupied by the flux containing iron powder is limited to less than 5 to 30% of the total cross-sectional area of the wire is that if it is less than 5%, the wire component that the flux-cored wire should have originally, for example, the arc stabilizer constituting the flux Cannot contain a predetermined amount of slag forming agent, alloying agent, and deoxidizing agent, which slows down the melting rate of the wire and reduces the current density, not only does not provide a high welding amount, but also causes arcing and spattering. Is very similar when a solid wire is used. At 30% or more, the arc state and droplet transferability are improved, but in the case of high current density welding, as shown in FIG. 3, the steel outer shell 2 rapidly melts first and transfers to the base material. As a result, the unmelted flux L becomes longer, penetrates into the molten pool, spatters are generated more frequently, and it becomes difficult to draw a thinner diameter which is usually used in wire production. Therefore, the ratio of the cross-sectional area occupied by the flux containing iron powder to the total cross-sectional area of the wire is limited to less than 5 to 30%.

The sectional shape of the wire is not particularly limited, and any of the shapes shown in FIGS. 2 (a) to 2 (d) can be adopted (2 indicates a steel sheath, 3 indicates a flux), but arc stability is shown. The seamless type (FIG. 2 (d)), which is excellent in wire feedability and straightness, is most suitable for high current density welding. The material of the steel shell of the present invention is not particularly limited, but mild steel and alloy steel can be used.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples.

(Example 1) with various changing the flux cored wire the ratio of the cross-sectional area and the total wire cross-sectional area occupied by the flux containing solid wire and iron _{powder, Ar-He-CO 2 -O} 2 gas mixture shield gas (hereinafter 4), Ar-CO ₂ mixed gas (hereinafter abbreviated as 2 types) and carbon dioxide (hereinafter abbreviated as CO ₂ )
Bead-on-plate welding was performed under the welding conditions shown in Table 1 using the types. The flow rate of the shielding gas is 25 / m
In, the steel plate used was implemented with SM-50B (plate thickness 25 mm).
Table 2 shows the welding results.

Here, the arc stability is very good when the arc is sharp and stable droplets are transferred without being disturbed during welding. ◎ The arc stability is good when the arc is not disturbed but the droplets are transferred in a slightly larger form. ○, and those in which even a slight arc also caused the flapping droplets to move irregularly by that amount were regarded as defective, and were evaluated as ×.

In addition, as shown in FIG. 4, the penetration width (W ₁ ) at a half position (P / 2) of the maximum penetration depth (P) is 60% or more of the maximum bead width (W), as shown in FIG. Was determined to be good. That is, if it is smaller than 60%, so-called finger-shaped penetration is obtained, and as the value becomes larger, a circular penetration becomes wider.

Wire numbers 14 to 18 are the results when solid wires were used, and among them, numbers 14 to 16 had a wire feed speed of 30 m / mi
n is a welding result at a high current density which is fast, and Nos. 17 to 18 are welding results at a wire feeding speed of about 10 m / min which has been conventionally used.

By the way, wire numbers 15 to 16 use two or four kinds of mixed gas as shielding gas, and although the arc stability and bead formation are good, the gas cost is high,
Although spatter generation itself is small, minute droplets adhere to both ends of the bead, and it is difficult to remove the droplet.

In the case of wire number 14, the arc state deteriorates, spatter occurs frequently, and the bead appearance becomes uneven. Similarly, the wire No. 17 also suffers from deterioration of the arc state, frequent spattering and poor bead appearance, and cannot have high welding because the current density is lower than the range of the present invention.

Wire No. 18 has a wire feeding speed of 1/3 slower than wire Nos. 15 to 16, and the current density is lower than the range of the present invention, and the welding current is as low as 300 A, so that fine droplets adhere to both ends of the bead. However, high welding cannot be obtained, and the gas cost increases because a mixed gas is used.

Next, the wire numbers 9 to 13 and 19 and 20 are the results when the flux-cored wires were used.

Wire number 13 is within the scope of the present invention except for the composition of the shielding gas. However, when a mixed gas of four types is used as the shielding gas, the arc stability, the occurrence of spatter is small, and the welding workability is good, but the bead appearance is uneven. In this case, both ends of the bead are not uniform, the penetration shape is a finger shape, the gas cost is high, and there is a problem in everything.

Wire No. 9 is a thin-walled flux-cored wire in which the ratio of the cross-sectional area occupied by the flux containing iron powder to the total cross-sectional area of the wire exceeds the scope of the present invention, and the result is that the protruding length of the wire is 50 mm. In addition, the arc stability is poor, the length of the unmelted flux column (FIG. 3L) is long, the amount of spatter is large, and the penetration shape and bead appearance are poor.

Wire No. 10 is a very thick flux-cored wire in which the ratio of the cross-sectional area occupied by the flux containing iron powder to the total cross-sectional area of the wire is 2% or less, which is below the range of the present invention. As in the case of the solid wire, the arc spray is strong and unstable as in the case of the solid wire, and the spatter generation and the bead appearance are poor. Further, wire number 11 is a case where the flux-cored wire of wire number 10 is used at a high current density within the range of the present invention. Similar to wire number 10, in addition to defects such as arc state, spatter generation, bead appearance, etc. Is similar to a finger-shaped penetration shape as in the case of a solid wire and is defective.

Wire No. 12, using a good portion of the wire that has been broken several times in the wire production because the ratio of the cross-sectional area occupied by the flux containing iron powder and the total cross-sectional area of the wire is 33%, which exceeds the range of the present invention. As a result of welding, although the stability and penetration shape of the arc are good, the unmelted flux column is long and the unmelted flux column penetrates into the molten pool, spatters are generated and the bead appearance is poor.

The wire number 19 is the same as the wire number 11 and has a thick wire diameter of 1.4 mm, but all of the arc stability, spatter generation, bead appearance, and penetration shape are poor.

Wire No. 20 is within the scope of the present invention in terms of the ratio of the cross-sectional area occupied by the flux containing iron powder and the total cross-sectional area of the wire containing iron powder at a wire diameter of 1.2 mm, but the current density is as low as the present invention or lower. It becomes a slightly convex bead, the penetration is shallow, and the penetration shape becomes poor. If the current density is below the range of the present invention, a high welding amount cannot be obtained, and in multi-pass welding, lamination cannot be performed unless there are many welding passes, so that the welding time is long and the cost is disadvantageous.

On the other hand, according to the present invention examples with various wire diameters shown in the wire numbers 1 to 8, arc stability, droplet transferability, arc spraying and bead shape are good, and gas cost is low,
In any of the items, gas shielded arc welding can be performed with good, remarkably high stability and high current density.

(Example 2) Among the wires in Table 1, wires Nos. 1, 6, 9, and 11 were used, and a steel plate (steel type SM-50B, t = 25 mm, D
= 100mm, H = 100mm, length 500mm) as shown in Table 1 with welding current, arc voltage and tip base metal distance of 45cm / m.
In, the large leg-length horizontal fillet welding was performed with the torch angle 45 degrees from the lower plate side and the torch angle 0 degrees with respect to the welding direction.
Note that a steel plate (thickness: 30 μm) coated with an inorganic zinc primer was used for the surface of the steel plate.

The arc stability and penetration shape were evaluated in the same manner as in Example 1. Table 3 shows the test results.

Wire No. 9 in which the ratio of the cross-sectional area occupied by the flux containing iron powder to the total cross-sectional area of the wire exceeds the range of the present invention, and wire No. 11 in which this ratio is lower than the range of the present invention have unstable arcs. The undercut on the board side and the deterioration of the bead appearance are caused and cannot be adopted at all. On the other hand, it is clear that the wire numbers 1 and 6 of the present invention are excellent wires that have good arc state, spatter generation state, bead appearance, penetration shape, particularly good conformity with steel plates and no welding defects such as pits. Became.

[Effects of the Invention] As described above, according to the high current density welding method of the present invention, a high welding amount can be obtained using inexpensive carbon dioxide gas, the arc is stable, soft, droplets are small, and spatter is small. Welding with a small amount of generation and excellent welding workability can be performed, and a weld having a better bead appearance and a circular penetration can be obtained.
This welding method greatly contributes to high efficiency and labor saving.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a bead shape by various shield gas compositions, FIG. 2 is a cross-sectional view of a flux-cored wire, and FIG.
The figure is a schematic diagram showing the wire melting state, FIG. 4 is a diagram showing the penetration shape, and FIG. 5 is a cross-sectional view of the test piece. 1 ... defective fusion part, 2 ... steel sheath, 3 ... flux, 4 ... droplet, 5 ... arc, 6 ... torch, 7 ...
Steel plate surface, 8 Wire

Continuation of the front page (72) Inventor Kozo Yamashita 5-10-1 Fuchinobe, Sagamihara-shi, Kanagawa Prefecture Nippon Steel Corporation 2nd Technical Research Institute (56) References JP-A-56-160880 (JP, A) JP-A-56-160878 (JP, A) JP-A-3-35881 (JP, A) JP-A-3-169485 (JP, A)

Claims (1)

(57) [Claims] A flux-cored wire having a cross-sectional area occupied by a flux containing iron powder of less than 5 to 30% of the total cross-sectional area of the wire using carbon dioxide gas as a shielding gas.
A high current density gas shielded arc welding method characterized by welding at a high current density of (A / mm ² ) or more.