JP2614892B2 - Gas shielded arc welding method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to gas shielded arc welding of thin plates, and more particularly to a welding power source and a flux-cored wire (FCW).
The present invention relates to a welding method in which the penetration depth and the bead shape are controlled by a combination of the methods, whereby the condition range is wider and the efficiency is higher than in the conventional method.

(Prior Art and Problems to be Solved) In gas shielded arc welding of a thin steel sheet, a gap between the sheets is likely to be generated due to processing distortion, thermal distortion, or the like because the thickness is thin.

For this reason, in the conventional gas shielded arc welding method, that is, a method using a solid wire having the opposite polarity, when high-speed welding is performed at a high current, so-called "burn-through" is likely to occur due to the effect of the penetration depth. Therefore, the upper limits of the welding current and the welding speed are suppressed by “burn through”.

Therefore, in the gas shielded arc welding method using a solid wire, which is widely used in the welding of thin plates, in order to prevent such “burn through”, welding conditions are set to a low current, a low speed, a torch angle or a torch angle. This is dealt with by adjusting the aiming position of the wire and further studying the composition of the shielding gas. For this reason, a welding speed of about 30 to 100 cm / min is generally used, and there is a problem that construction efficiency is low.

Moreover, because of this situation, the plate thickness is 1 mm
In addition to the welding of the following ultra-thin steel sheets, it was difficult to weld a thin steel sheet having a particularly wide gap or a thin steel sheet subjected to a surface treatment such as galvanization.

The present invention has been made in order to solve the above-described problems of the prior art relating to gas shielded arc welding of thin steel sheets. It is an object of the present invention to provide a novel gas shielded arc welding method that can prevent and improve the soundness and construction efficiency of a joint and has a wide application range.

(Means for Solving the Problems) In order to achieve the above aim, the present inventors have considered that there is a limit to the welding of a thin plate by the conventional gas shielded arc welding method using a solid wire. In order to find out various problems in gas shielded arc welding using a flux-cored wire as a wire, and to find a solution that can effectively solve the problems, intensive studies have been made.

As a result, not only the flux cored wire is used as the welding wire, but also the use of the flux cored wire under specific conditions and the penetration depth and bead shape are controlled by the combination with the penetration control welding power source, thereby improving the soundness of the joint. It has been found that performance and high construction efficiency can be achieved, and the applicable range can be significantly expanded.

That is, according to the present invention, in gas shielded arc welding of a steel sheet having a thickness of 3.2 mm or less, an arbitrary ratio alternates between the positive electrode and the reverse electrode with respect to the polarity of the electrode and the base material in the range of 20 to 85% of the positive electrode. The flux containing the following components, metal powder: ≧ 70 wt% Total Mn + Total Si: 9-25 wt% Total Mn / Total Si: 1.7-5.0 is filled into the steel sheath at a rate of 8-20%. A gas shielded arc welding method characterized by performing welding using a flux-cored wire comprising:

 Hereinafter, the present invention will be described in more detail.

(Operation) In general, regarding the penetration depth, the flux-cored wire is shallower than the solid wire. Therefore, it is desirable to use the flux-cored wire to suppress “burn through” which is a problem in thin plate welding.

However, in the conventional titania-based flux-cored wire, a large amount of slag is generated after welding, so that various problems occur when used in place of a solid wire. Therefore, a so-called metal-based flux-cored wire containing a large amount of metal powder having a slag generation amount similar to that of a solid wire is more desirable.

Also, in the welding of surface-treated steel sheets such as galvanized steel sheets,
The smaller the amount of slag generated, the easier gas is released from the molten metal, so that pore defects such as pits or blow holes are less likely to occur. Therefore, a metal-based flux-cored wire that generates less slag than a conventional titania-based flux-cored wire is more suitable for such welding.

For these reasons, in the present invention, first, as the flux-cored wire, a metal-based flux-cored wire having a regulated flux composition and flux filling rate is used. The reasons for the limitation are as follows.

Flux filling ratio: 8 to 20% When encapsulating a flux mainly composed of metal powder, it is difficult to industrially wire to 1.2 mmφ if the flux filling ratio exceeds 20% even if the particle size is adjusted. Become. On the other hand, if it is less than 8%, the penetration depth and the arc stability are not much different from those of the solid wire. Therefore, the flux filling rate is set to 8 to 20%. In this case, it is desirable to control the bulk density of the flux in the range of 1.2 to 4.5 g / cm ³ .

Flux composition (wt%) (a) Metal powder ≧ 70% If the metal powder is less than 70%, the slag is affected by the raw materials (arc stabilizer, slag forming agent, etc.) such as metal or non-metal oxides. The amount generated increases. As a result, the time and labor required for the slag removal step and the like are increased, and pore defects are easily generated in welding of a galvanized steel sheet or the like. When short arc welding is performed, the arc stability at low current may be impaired. Therefore, the metal powder needs to be 70% or more.

The metal powders defined here are Total Mn, To
Of course, tal Si may include those contained as metal powder.

(B) Total Mn + Total Si: 9 to 25% When the total amount of Total Mn + Total Si in the flux is less than 9%, pore defects tend to occur due to insufficient deoxidation. On the other hand, if it exceeds 25%, the yield of Mn and Si in the deposited metal increases, and the local area rises. As a result, the strength exceeds the strength range of a thin plate having a plate thickness of about 3.2 mm or less (50 kgf / mm ² class HT or less). Further, in some cases, the strength becomes too high, and the toughness of the welded joint portion may be reduced. Also
If it exceeds 25%, the amount of oxygen in the molten metal decreases and the viscosity of the molten metal increases. For this reason, when welding at a speed of about 1 m / min or more, the ability of the molten metal to follow the movement of the arc point is reduced, and the arc directly hits the steel sheet, and "burn-through" tends to occur. Therefore, Total Mn + Total Si
Must be in the range of 9-25%.

When the Mn source and the Si source contain an oxide of Mn and an oxide of Si, these oxides are converted to Mn and Si to obtain a total M
Calculate n, Total Si. This is based on Total Mn /
The same applies to the calculation of Total Si.

(C) Total Mn / Total Si: 1.7 to 5.0 If the ratio of Total Mn to Total Si (Total / Total Si) is less than 1.7, blow holes are likely to occur. This is presumed to be due to the formation of a solid composite oxide by the deoxidation reaction in the molten metal, which serves as a nucleus to mainly generate and grow CO gas. On the other hand, if it exceeds 5.0, the shape of the arc becomes unclear, the amount of spatter generated increases, and the workability decreases. Therefore, Total Mn / Total Si needs to be in the range of 1.7 to 5.0.

Mild steel is generally used as the metal sheath (skin), but it is desirable to control the C content to 0.08% or less.

(D) C ≦ 0.08 in the metal shell If the amount of C in the metal shell increases, particularly when welding with a high current, CO gas is generated in the droplet formed at the tip of the skin, and the droplet explodes accordingly. As a result, spatter occurs.
Therefore, it is desirable that the C content in the metal shell is small,
It is better to be 0.08% or less.

There is no particular limitation on components other than C. The alloy component is generally contained in the flux, but may be contained in the metal sheath if necessary.

As described above, the flux-cored wire used in the present invention is a metal-based flux-cored wire that satisfies the above-mentioned conditions, and is used in combination with a penetration control welding power source under specific conditions as described later. As a result, a bead having a shallow penetration can be obtained while having a good bead shape, so that "burn through" in thin plate welding can be suppressed.

According to the present invention, it is possible to expand the applicable range of the gas shielded arc welding method, particularly when welding ultra-thin sheets, welding thin sheets of surface-treated steel sheets, etc., as follows:
If the above conditions are satisfied and special consideration is given to the flux-cored wire, welding can be performed more effectively.

 The reason is as follows.

Welding current of about 50 to 8 when welding ultra-thin sheets with a thickness of 1 mm or less
In the case of a surface-treated steel sheet having a low coating rate of 0 A and a large amount of zinc or the like applied thereto, the amount of generated gas is also large, so that “better arc stability” is required.

In such a case, the stability of the arc is further improved by setting the amount of carbon (C) and the amount of alkali metals in the flux as follows.

(E) Alkali metal: 0.1 to 5% When the alkali metal is less than 0.1%, arc stability becomes insufficient in short arc welding in a low current range, and burnout or other welding defects are likely to occur. In addition, in high-speed welding (about 1-2 m / min) in the high current range, the arc voltage is set lower than in the case of normal speed (about 30-50 cm / min) in order to ensure high speed. Insufficient relaxation of the increasing concentration of the arc becomes insufficient, and burnout tends to occur.

Furthermore, in welding of a galvanized steel sheet or the like, the transfer of droplets becomes unstable due to the effect of gas (eg, steam of zinc) generated by the heat of the arc, but it is difficult to suppress the transfer.

On the other hand, if the content exceeds 5%, not only the arc stability cannot be further improved, but also the arc concentration is excessively reduced, and welding defects are liable to occur. Further, the bead appearance is impaired because the melting point of the slag decreases. Therefore, the addition amount of the alkali metal is 0.1 to
It is preferred to be in the range of 5%.

When alkali metal compounds (oxides, fluorides, carbonates, etc.) are contained as the alkali metal source, these compounds are converted into alkali metals and the amount of alkali metal added is calculated.

(F) Na / K: 1 to 50 When the ratio of the Na amount to the K amount (Na / K) is less than 1, the arc stability becomes insufficient, and burnout or other welding defects are liable to occur. On the other hand, if Na / K exceeds 50, the shape of the arc becomes unclear, the arc force decreases, and defects such as poor fusion are likely to occur. Therefore, Na / K is preferably in the range of 1 to 50.

When Na and K are contained as their compounds (oxides, fluorides, carbonates, etc.), these compounds may be used as Na, K
Then, calculate the ratio of Na / K.

(G) Li / (Na + K): 0.1 to 2.4 When Li / (Na + K) is less than 0.1, arc stability particularly in welding of a galvanized steel sheet or the like is insufficient, and burnout tends to occur. Further, a large amount of spatter is generated, and the workability is reduced. On the other hand, if it exceeds 2.4, the shape of the arc becomes unclear, the arc force is reduced, and defects such as poor fusion are likely to occur. Therefore, particularly in welding of a galvanized steel sheet or the like, it is preferable that Li / (Na + K) be in the range of 0.1 to 2.4.

When Li, Na, and K are contained as compounds (oxides, fluorides, carbonates, etc.), these compounds may be used as L
After conversion into i, Na, and K, the ratio of Li / (Na + K) is calculated.

(H) C: 0.3 to 2.5% C also becomes an arc stabilizer depending on the amount of addition and the range of current used. However, if the C content is less than 0.3%, arc stability is insufficient, and burn-through and other welding defects are likely to occur. Also 2.
If it exceeds 5%, CO or CO ₂ is generated in the droplet formed at the tip of the wire, and the explosion causes the droplet to be scattered as small spatter. Therefore, the amount of C is 0.3-2.5%
It is preferable to be within the range.

As described above, in the present invention, since a metal-based flux-cored wire containing a flux satisfying these conditions is used, the penetration depth is shallower than that of the solid wire, and the amount of slag generated is the same as that of the solid wire. About. Further, the effect of the arc stabilizer has the effect of increasing the arc stability as compared with the solid wire and reducing the amount of spatter generated.

The present invention relates to a conventional solid wire and a DC reverse polarity power supply by combining such a metal flux cored wire with a power supply capable of controlling the penetration depth by arbitrarily changing the ratio between the positive electrode and the reverse pole. This enabled welding that was difficult with the combination.

In other words, in general, not only welding of a steel sheet having a thickness of 3.2 mm or less can be performed, but also welding of an extremely thin sheet having a thickness of about 0.6 to 0.8 mm or welding of a thin sheet having a wide gap (about 2 to 3 mm). Alternatively, high-speed welding of a thin plate using a high welding current (about 1 to 2 m / min), and welding of a galvanized steel plate or the like are facilitated, and the quality and work efficiency of a welded joint are improved.

At this time, the ratio of the positive polarity to the polarity of the welding power source needs to be within the range of 20 to 85% for the following reason.

Positive electrode ratio: 20-85% When the positive electrode ratio is less than 20%, the penetration depth of the deposited metal is not much different from the conventional DC reverse polarity power supply. The effect of suppressing burn through is not significant. On the other hand, if it exceeds 85%, the penetration depth becomes shallow. However, although it is eased as compared with the case of the solid wire and the titania-based flux-cored wire, it is not suitable for practical use because the bead becomes convex due to the influence of the positive polarity and the amount of spatters increases. Therefore, the ratio of the positive polarity must be in the range of 20 to 85%, and must be alternately repeated at an arbitrary ratio within this range.

In addition, as shown in FIG. 1, the ratio of the polarity is represented by the area ratio or the time ratio in the current fluctuation during welding, and is defined as follows.

Here, i: current value _{t 1, t 2, t 3} , t 4: shows an embodiment of the present invention will now Time (Example).

Example 1 Metal-based flux-cored wires having various flux compositions and flux rates shown in Tables 2 to 4 (wire diameter 1.
2mm) using the following welding method and conditions, and a steel base material (JIS G3141 SPCC, thickness 3.2mm) with the chemical composition shown in Table 1.
Was subjected to gas shielded arc welding.

The results of evaluation of penetration depth, arc stability, high speed, spatter, blowhole, slag, etc. are also shown in the same table.

(Welding method) As shown in FIG. 8, the welding method is bead-on-plate welding by an automatic machine.

(Welding conditions) Shielding gas: 100% CO ₂ , 20 / min 80% Ar−20% O ₂ , 20 / min Current, voltage, speed, etc .: 150A− (17, 18) V−30cpm−Ext.15mm 300A− (17, 26) V-200cpm-Ext. 15mm (Voltage was adjusted by the shielding gas composition. Ext: wire protrusion length) Positive electrode ratio: 40% Example 2 A metal-based flux-cored wire (No. 3 in Table 2) and a solid wire (both with a wire diameter of 1.2 mm) were used, and the positive electrode ratio of the power supply was changed as shown in FIG. Under the same conditions, gas shield arc welding was performed on the same base material as in Example 1, and the relationship with the bead cross-sectional shape was examined.
The result is shown in FIG.

(Welding method) Same as in Example 1.

(Welding conditions) Shielding gas: 100% CO ₂ , 20 / min Current, voltage, speed, etc .: 150A-18V-30cpm-Ext. 15mm Example 3 Metal flux cored wire (No. 3 in Table 2) and solid Using a wire and changing the positive electrode ratio of the power source as shown in FIG. 3, gas shield arc welding was performed on the same base material as in Example 1 under the following welding method and conditions, and the gap resistance (in butt welding) (Tolerable limit of the gap). FIG. 3 shows the results.

(Welding method) As shown in FIG. 9, the welding method is butt welding by an automatic machine.

(Welding conditions) Shielding gas: 100% CO ₂ , 20 / min Current, voltage, speed, etc .: 150A-18V-30cpm-Ext. 15mm Example 4 Metallic flux cored wire (No. 3 in Table 2) and solid Using a wire, the positive electrode ratio of the power source was changed as shown in FIG. 4, and gas shielded arc welding was performed on the same base material as in Example 1 using the following welding method and conditions, and high-speed weldability (the welding speed And the upper limit). The result is shown in FIG.

(Welding method) As shown in FIG. 8, the welding method is bead-on-plate welding by an automatic machine.

(Welding conditions) Shielding gas: 100% CO ₂ , 20 / min Current, voltage, speed, etc .: 150 to 300 A-18 to 26 V-30 to 500 cpm
-Ext.15mm Example 5 Using a metal-based flux-cored wire (No. 3 in Table 2), a commercially available solid wire and a titania-based flux-cored wire (both with a wire diameter of 1.2 mm), the following welding methods and Under the same conditions, gas shield arc welding was performed on the same base material as in Example 1, and the gap resistance was examined. The results are shown in FIG.

(Welding method) As shown in FIG. 9, the welding method is butt welding by an automatic machine.

(Welding conditions) Shielding gas: 100% CO ₂ , 20 / min Current, voltage, speed, etc .: 150 A-18 V-30 cpm-Ext. 15 mm Power supply: See FIG. 5 Example 6 The same welding wire as in Example 5 was used. Using the same welding method and conditions as described below, the same base metal as in Example 1 was subjected to gas shielded arc welding, and high-speed weldability was examined. The results are shown in FIG.

(Welding method) As shown in Fig. 10, the welding method is lap fillet welding (with a gap).

(Welding conditions) Shielding gas: 100% CO ₂ , 20 / min Current, voltage, speed, etc .: 250 to 350 A-22 to 26 V-Ext. 15 mm Power supply: See FIG. 6 Example 7 For welding similar to Example 5 Using a wire, under the following welding method and conditions, with a base material of the same material as in Example 1,
Gas shielded arc welding was performed on a galvanized steel sheet having a Zn basis weight of 90 g / m ^{2 on} one side, and the porosity was examined. The results are shown in FIG.

(Welding method) As shown in Fig. 11, the welding method is lap fillet (no gap).

(Welding conditions) Shielding gas: 100% CO ₂ , 20 / min Current, voltage, speed, etc .: 120 A-16 V-60 cpm-Ext. 15 mm Power supply: See FIG. 7 The following is the result of the above Examples 1-7. I understand.

From the results of Example 1, as shown in Table 2, No. 1 to No. 5 of the present invention are examples in which the amount of C in the flux was changed, and all of them had good penetration depth and bead shape. It is. In addition, No. 1 has an unstable arc, and No. 5 has a relatively large amount of spatter, and it is desirable to appropriately mix the C amount.

No. 6 to No. 11 are examples in which Total Mn + Total Si in the flux was changed, and Nos. 8 to No. 10 of the present invention were all excellent in both the penetration depth and the bead shape.

No. 12 to No. 16 are examples in which Total Mn / Total Si in the flux was changed, and No. 13 to No. 15 of the present invention all have good penetration depth and good bead shape.

In addition, as shown in Tables 3 and 4, No. 17 to No. 38
Are examples of the present invention, No. 17 to No. 22 are examples in which Na / K in the flux was changed, and No. 23 to No. 28 were Li in the flux.
No. 29 to No. 32 are examples in which the amount of alkali metal in the flux was changed, No. 33 to No. 38 were examples in which the amount of the metal powder in the flux was changed, Both have good penetration depth and bead shape.

Furthermore, as shown in Table 4, No. 39 to No. 44 are examples in which the flux ratio was changed, but Nos. 40 to No. 43 of the present invention were all good in both the penetration depth and the bead shape. And
There are no manufacturing problems.

Next, the results of Examples 2 to 4 indicate the following.

As the positive electrode ratio increases, (a) the penetration depth decreases (Fig. 2, upper right) (b) the bead width decreases (Fig. 2, upper right) (c) the extra height increases (Fig. 2, lower right).

When the positive electrode ratio is the same, (a) the metal flux cored wire has a smaller penetration depth (FIG. 1, d _M <ds). (B) The metal flux cored wire has a wider bead width ( (FIG. 2, W _M > Ws) c) The metal-based flux-cored wire has a lower margin height (FIG. 2, h _M <hs).

Since the penetration depth decreases as the positive electrode ratio increases, (a) the tolerance of the gap increases (Fig. 3, upper right) (b) The upper limit of the welding speed increases (Fig. 4, upper right) When the positive electrode ratio is the same, due to the difference in the penetration shape, (a) the metal-based flux-cored wire has a larger allowable gap limit (FIG. 3, G _M > Gs). (Fig. 4, Vh> Vs) In addition, as is clear from the results of Examples 5 and 6,
As shown in FIG. 6 and FIG. 6, although the titania-based flux-cored wire has improved gap resistance and high-speed weldability compared to the solid wire, the metal-based flux-cored wire has more gap resistance and high-speed welding. Both sexes are improved.

Further, as is clear from the results of Example 7, the solid wire or the titania-based flux-cored wire does not improve the porosity resistance, but the metal-based flux-cored wire significantly improves the porosity resistance.

In each of the above Examples 1 to 7, CO ₂ was used as a shielding gas, but an Ar—CO ₂ mixed gas (Ar: 0 to 95%) was used.
%), Or Ar-O ₂ mixed gas (Ar: 95-98%) even in the case of using a similar phenomenon was observed.

(Effects of the Invention) As described in detail above, according to the present invention, in gas shielded arc welding of a thin steel plate, a metal-based flux-cored wire under specific conditions is used, and the positive electrode ratio is controlled using a penetration control power supply. Since welding is performed while being adjusted, the penetration depth and the bead shape can be controlled, and there is no "burn through" as in conventional welding, and high working efficiency can be achieved. In particular, it can be used for welding ultra-thin plates, surface-treated thin plates, and the like, so that the applicable range of the present welding method can be further expanded, and the effect is remarkable.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a polarity ratio, FIG. 2 is a diagram showing a relationship between a bead cross-sectional shape and a positive electrode ratio, and FIG. 3 is a diagram showing a relationship between gap resistance and a positive electrode ratio. 4 is a diagram showing the relationship between the maximum welding speed and the positive electrode ratio, FIG. 5 is a diagram showing the gap resistance, FIG. 6 is a diagram showing the high-speed weldability, and FIG. FIG. 8 to FIG. 11 are explanatory views showing a welding method performed in the embodiment.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-180696 (JP, A) JP-A-62-282800 (JP, A) JP-A-56-131080 (JP, A) JP-A 52-182 78731 (JP, A) JP-A-62-248593 (JP, A)

Claims (2)

(57) [Claims] 1. In gas shielded arc welding of a steel sheet having a thickness of 3.2 mm or less, a positive electrode and a reverse electrode are alternately switched at an arbitrary ratio in a range of 20 to 85% with respect to the polarity of an electrode and a base material. A gas shielded arc welding method, wherein welding is performed using a flux-cored wire in which a steel sheath is filled with a flux containing the following components at a rate of 8 to 20% while repeating. Note Metal powder: ≧ 70 wt% Total Mn + Total Si: 9 to 25 wt% Total Mn / Total Si: 1.7 to 5.0 2. The method according to claim 1, wherein the steel sheet has a zinc-plated surface.