JPS597545B2 - Consumable electrode arc welding method for steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a gas-shield consumable electrode arc welding method for steel that is highly efficient and has significantly fewer defects than similar conventional gas-shield arc welding methods. It is something that can be done.

Conventionally, a submerged arc welding method has been generally used as a high-efficiency arc welding method in a downward position.

In particular, this welding method can achieve high speed and high efficiency by using multiple electrodes, and has fewer welding defects, making it excellent for general use. However, when low-temperature toughness is required, for example, when attempting to use it in the manufacturing and welding process of cryogenic line pipes, the heat input is large and embrittlement of the heat-affected zone becomes a problem. If an attempt is made to perform multilayer welding by limiting the amount of heat input in the submerged arc welding method, the problem of slag peeling between the buses will occur, resulting in a significant drop in efficiency. Moreover, the original advantage of the supmerged arc welding method, which is that it causes fewer defects, is largely lost, and welding defects such as slag entrainment increase. For the above reasons, in recent years, attention has been paid to the MIG welding method, which performs high-speed welding with a large current, that is, the consumable electrode type arc welding method using an inert gas.

For example, Japanese Patent Publication No. 53-9571 proposes to suppress the current density and optimize the arc electrode pressure by using a large diameter electrode wire. In general, in the MIG welding method, the arc electromagnetic pressure is strong, so the tip of bead 1 tends to bite deeply into so-called finger-shaped welding, as shown in the cross-sectional view of the bead in Figure 1, resulting in poor fusion in this area. Defect 2 often occurs. This defect is conceptually different from the general defect of fusion failure. In other words, in the case of normal fusion failure, the base metal is not melted due to insufficient heat of the molten metal, and the welded metal remains in a state of being cast into a mold. However, the poor fusion observed in this MIG welding method is caused by the weld metal not filling well into the space created when the base metal is dug down by the arc, resulting in a defect. Therefore, a countermeasure for general fusion defects is to increase the retained heat of the molten metal so as to promote melting of the base metal, but this countermeasure is ineffective for this defect. It is thought that complex factors such as the convection situation of molten metal in the molten pool are intertwined,
Although research reports investigating the cause of this have been published, the essence has not yet been elucidated.It is true that if the weld into ι becomes finger-like, the rate of defect occurrence will increase significantly. However, even if the welding condition is improved, defects may occur if the movement of the molten pool due to the arc force changes, so it cannot be said that it corresponds completely to the welding condition alone. In the technique described in Japanese Patent Publication No. 53-9571 mentioned above, it can be said that by employing a wire having a large diameter, the concentration of the arc force is avoided and the melting of the fingers is prevented.

However, according to the findings of the present inventors, the effect of preventing the occurrence of defects by using a large diameter wire is not necessarily effective, and when the welding current exceeds about 700 A, the occurrence of defects increases. One of the reasons for this is thought to be that even if a wire with a large diameter is used, the current distribution within the arc does not decrease evenly, and the current density at the center is still high due to the pinch of the arc itself. It will be done. In the end, with this welding method, the most effective measure that can be taken is to increase the carbon dioxide content in the inert gas, and if the carbon dioxide content in the shielding gas is less than 15%, defects often occur, but it is around 20%. If the increase is more than that, it will decrease significantly.However, Figure 2 shows the relationship between the carbon dioxide content ((f/)) in the shielding gas (remaining argon) and the oxygen content ((:f)) in the weld metal. As shown in the example above, the oxygen content in the weld metal increases as the carbon dioxide content increases.As a result, Figure 3 shows the relationship between the test temperature and the Shalpy test impact value for the shielding gas component. As shown in the figure corresponding to the difference, toughness deteriorates as carbon dioxide gas in the shielding gas increases.In addition, this example shows 2%Ni-0.8%Cr-0.6%M.
This is a welding wire of low alloy steel containing O. In this way, shielding gas with a large amount of carbon dioxide gas greatly reduces the toughness of the weld metal, and the characteristic that MIG welding generally has superior weld metal toughness compared to submerged arc welding is also lost. As a countermeasure to the problem of uniform welding, it is conceivable to change the polarity of the electrode in the DC arc. Of course, MIG welding uses a DC power source, but most of them use reverse polarity, with the electrode being positive and the base metal being negative. Even in the welding method described in Japanese Patent Publication No. 53-9571 mentioned above, there is no description regarding the polarity of the power source, but it is natural that the polarity is reversed. When the electrode is negative or positive, the electron current flows from the wire toward the base metal, and electrons are also emitted from the wire surface where there is an oxide film, so the arc spreads and the positive airflow weakens, causing the central part of the bead to emit electrons. Since the holes are not dug deeply, the fingers are less likely to become one. However, on the other hand, it is difficult for the electromagnetic pincher to act on the droplet at the tip of the wire, and the droplet migrates into a droplet, causing many respatter, and the arc tends to wander and become unstable. Especially carbon dioxide gas in shielding gas,
If the content of oxidizing gases such as oxygen is low, the droplets at the tip of the wire will not be oxidized, resulting in a decrease in electron emitting ability, and the arc may creep up the electrode in pursuit of the oxide that should emit electrons, potentially causing parts packs. . Due to such unresolved problems, the MIG welding method using direct current positive polarity has hardly been put into practical use, although test results and the like have been published. In particular, if the amount of carbon dioxide and oxygen in the shielding gas is not increased, the arc will become unstable, which is disadvantageous in terms of the toughness of the weld metal, as mentioned above. It must be said that this is incompatible with obtaining a tough welded joint. The present invention solves the problems of the conventional method b as described above, and its gist is that the electrode protrusion length d x 4 is ~d×15TWL
The welding current is 600 to 20 A/Md using an AC power source equipped with a restriking means within the current density range of 40 to 150 A/Md.
A consumable electrode type arc welding method for steel, characterized by welding in a shielding gas containing at least one of carbon dioxide gas of 15% or less or oxygen of 5% or less, and the remainder consisting of an inert gas while supplying 0.0A. It is in.

The details will be explained below.

The first feature of the present invention is that alternating current is used as the welding power source.
AC power sources are very commonly used in arc welding using flux, such as non-gas welding.

In an AC arc, the arc current drops to zero every half cycle and the arc is extinguished, and it must be re-ignited, but in welding using flux, when the current drops to zero due to ions generated by the flux. However, plasma with good electrical conductivity remains and the arc can be easily regenerated. However, in arc welding that does not use flux, ie, MIG welding or TIG welding that uses solid wire, it is difficult to re-ignite the weld simply by connecting it to an AC power source, and the arc cannot be sustained. In TIG welding, an AC power source is used for limited purposes, namely aluminum welding, because it is effective in removing oxides. In this case, in order to sustain the arc, high voltage and high frequency waves are superimposed to create a spark discharge between the electrode and the base metal! It is occurring. If such measures are taken, MI
It is also possible to use an AC power source for G welding. However, the aluminum T that has not been put into practical use until now is
Since no particular advantage over IG welding was found, it is thought that there was no point in taking special measures to perform AC welding. However, the inventors of the present invention have discovered that when an AC power source is applied to high-current MIG welding under certain conditions such as the diameter of the electrode wire and its current density, a very remarkable effect can be obtained. FIG. 4 shows a particularly preferred restriking means when applied to the welding method of the present invention.

An alternating current is supplied by a welding power source transformer 7 between the base material 3 and the welding torch 4 through which the electrode wire 5 is passed. On the other hand, from the primary power source 6, alternating current is supplied to the pulse generator 8 in synchronization with that supplied to the welding power source transformer 7. The welding current is detected by the current transformer 9, and a pulse voltage is generated from the pulse generator 8 when the welding current is near zero. This pulse voltage is supplied between the welding torch 4 and the base material 3 through the resistor 10. FIG. 5 is a diagram illustrating the operation of this device, in which the welding current flows in a sinusoidal waveform, whereas the welding voltage has a square waveform. The voltage rises to a high level at the rising edge of the positive/negative polarity change, and the peak value of this is the restriking voltage. On the other hand, the pulse voltage indicates the voltage at the output terminal of the pulse generator, and a voltage is generated only when the welding current is near zero. This voltage must be higher than the maximum value of the restriking voltage, for example, with a peak value of 300 V, so that the arc can be sustained without being extinguished. If the welding conditions are within the range of the welding conditions of the welding method of the present invention, the re-ignition voltage on the negative side of the electrode will be relatively low, and if the no-load voltage of the welding power source transformer 7 is sufficiently high, the supply of pulses may be omitted. It can be done. However, on the positive side of the electrode, re-ignition is impossible, at least within the safe no-load voltage range, and pulse supply is essential. Such a restriking means using a pulse generator has several advantages over the above-mentioned restriking means using a high frequency generator. In other words, unlike high-frequency welding, there is almost no risk of radio interference, and in the case of high-frequency welding, as in the case of the present invention, the coils used to carry the current are large and there is no risk of high-frequency waves flowing into the welding power transformer. It is difficult to prevent this, and if this is omitted, there is a risk of insulation breakdown due to the high voltage of 3000V.
There is no fear of this at all with a pulse voltage of about 100 mL. A further feature of the present invention is that, in addition to employing an AC power source equipped with the above-mentioned restriking means, the present invention has a diameter of 3.
A solid wire with a large diameter of 2 to 6.4 mm is used, and a current density of 600 to 2
000A of welding current is applied. In order to perform high-efficiency and high-speed welding, a large welding current of 600A or more must be used, but for such a large current, the current density of the welding wire must be in the range of 40 to 150A/〒. be. Normal MIG welding using a DC power source uses a current density of about 200 A/MJ, but in the welding method of the present invention using an AC power source, if the voltage drop at the part of the wire protruding from the current-carrying tip is too large, arcing may occur. Since it becomes unstable, it is necessary to keep it below 150A/〒. On the other hand, if the current density is less than 40 A/〒, the penetration becomes shallow, which is not only disadvantageous for the purpose of high-speed welding, but also makes the arc unstable. In the welding method of the present invention, there is no need to lower the current density in order to avoid finger-like welding. In the high-current MIG welding method using a DC power source mentioned above, welding conditions with a current density much lower than that of the welding method of the present invention are adopted to prevent finger-like penetration as much as possible. The welding method of the present invention does not result in finger-like welding at all due to the adoption of an AC power source, etc.
Unnecessarily lowering the current density may lead to instability of the arc and is useless. A larger welding current is advantageous for high-efficiency, high-speed welding, but if it exceeds 2000 A, so-called puckering, which causes bead disturbance, tends to occur. A solid wire is used as the electrode wire, and the appropriate diameter is 3.2 to 6.6 WrfL from the relationship with the current density mentioned above; if it is thinner than this, the fluctuation of the arc length will increase and the stability of the arc will be impaired. If the welding process becomes thicker, it will only make the work more difficult, and there will be no benefit in the welding method of the present invention, which does not require any particular reduction in current density. In addition, in the welding method of the present invention, the length of the electrode protruding from the current-carrying tip is
d×4 to d×15 for the electrode wire diameter DTvn
It is necessary to keep it within the range of Tm.

As mentioned earlier, by setting the electrode protrusion length as above within the current density range of 40 to 150 A/MJ, the wire tip is moderately heated due to electrical resistance, and the droplet transfer state is improved. The arc becomes stable. If the wire protrusion length is longer than d×157 m, the shape of the bead becomes convex with a narrow width and a raised center, which is not preferable. Further, fluctuations in arc length tend to occur, making the arc unstable. Moreover, if the DX is smaller than 4 mm, the melting rate of the electrode will decrease, resulting in a disadvantage in terms of efficiency. Furthermore, the welding method of the present invention is characterized by the shielding gas component.

Generally, in TIG welding, pure inert gas such as argon or helium is used, whereas in MIG welding, inert gas to which carbon dioxide, oxygen, etc. are added is used. There is a reason for this, such as the ability to adjust the potential gradient of the arc by adding these gases, but the essential reason is that these oxidizing gases cause oxides that easily emit electrons to be generated in the molten pool, and the cathode The purpose is to distribute the dots widely and prevent the fingers from melting into one shape. As is well known, in TIG welding, the electrode is negative, and thorium is added to the tungsten electrode to help emit electrons. Since the arc column has a widening on the anode side, T
In IG welding or MIG welding with a negative electrode, that is, positive polarity, the penetration is rarely in the form of a single finger. By the way, even in the welding method of the present invention, a shielding gas containing an inert gas as a main component is used, but the addition of oxidizing gases such as carbon dioxide and oxygen may be carried out in small amounts. As mentioned earlier, in the DC high current MIG welding method, unless the carbon dioxide content in the argon is about 20 (f) or more, defects similar to poor fusion occur frequently and it is not practical. However, in the welding method of the present invention, if the amount of oxidizing gas added is small, the penetration will be slightly shallower if other conditions are the same, but the fingers will not be in the same shape at all, and the number of defects will not increase. Even in pure inert gas, the arc will come out not only from the tip of the welding wire but also from quite a bit above, but the welding work can be performed normally and no defects will occur. In the case of positive polarity welding where the electrode is negative, if the amount of oxidizing gas added is small, the arc will creep up the wire surface and normal welding will not be possible. Even if the arc creeps up, it will return to the tip again if the polarity reverses at the next moment, so it is thought that eventually it will reach a certain equilibrium state and the arc will not creep up enough to cause a disturbance. . Also, if you add even 1% carbon dioxide gas, the creeping up of the arc will be greatly reduced.
It is not much different from when carbon dioxide gas is added in an amount of 5%. By reducing the amount of oxidizing gas added to the inert gas in this way, the oxygen content in the weld metal can be reduced, and a weld metal with high toughness can be obtained. In addition, in the case of carbon dioxide gas, the amount added is 15% or less, preferably 1
0% or less is appropriate. When it exceeds 15%, the restriking voltage becomes extremely high, and even if an AC power supply equipped with a restriking means is used, there is a high risk of arc breakage due to restriking failure.
Also, the occurrence of spatter increases.

Not only for high-current MIG welding, but also for DC MIG welding, the most common shielding gas is argon with 20% carbon dioxide added, and with this level of carbon dioxide content, there are not particularly many spatters. Such shielding gases are inappropriate for the inventive welding process. In the case of oxygen, from the viewpoint of oxidation of the weld metal, it is appropriate to use 50 t) or less, and this amount is slightly lower than the limit value for increasing the restriking voltage and generating spatter. Therefore, as long as the carbon dioxide content is 15% and the ζ oxygen content is 5Cf or less, there is no problem in adding both gases. Naturally, helium can be used in addition to argon for the inert glass. 7. In the welding method of the present invention, the welding speed can be varied within a wide range depending on the situation.

Since welding is carried out with a large current and low heat input, it is naturally desired that the speed be high, but in the case of a single electrode, if the speed exceeds about 150 cm/min, undercuts will occur in the bead, which is a limitation. On the other hand, in the welding method of the present invention, the lower limit of the welding current is 600 A, so if the welding speed is less than 30 cm/min, there is a risk of the molten metal leading and the occurrence of defects due to bead overlap, and the heat input will also increase. Undesirable. Furthermore, when using tandem welding, in which two or more electrodes are lined up and run simultaneously, the occurrence of undercuts can be suppressed even at high speeds due to the preheating effect of the preceding electrode, and the
Welding speeds of up to 1/min are also possible.

Tandem welding, in which multiple electrodes are arranged at a certain distance, is particularly effective in improving the toughness of joints. This can be prevented by the tempering effect. Therefore, it is possible to perform welding at higher speeds and with higher efficiency than with a single electrode without reducing toughness. The welding method of the present invention is extremely advantageous in such tandem welding. In the conventional high-current DC MIG welding method described above, in the case of tandem welding, the arcs interfere with each other due to magnetic induction and become unstable. According to experiments conducted by the inventors, when welding two electrodes, the distance between the electrodes is 3.
Even if the distance is 0 cm, the arcs strongly interfere with each other. When welding with two electrodes, when welding starts, an arc is generated only on the leading electrode, and after welding has progressed by the distance between the electrodes, an arc is generated from the trailing torch, but as soon as this happens, the leading arc is disturbed. It often disappeared.

Even if arcs are generated on both electrodes, if one arc is disturbed for some reason, it will spread to the other, and this will disturb the arc that was about to recover again, like a seesaw. There was even a phenomenon where the arcs were disturbed alternately.

In the welding method of the present invention using an AC power source, arc interference can be prevented by performing a spot connection in which the phase of the power source is shifted by 90 degrees, and this problem does not occur. The problem of arc disturbance due to magnetism, that is, magnetic blowing, is a big problem not only in tandem welding as described above, but the welding method of the present invention is different from conventional MIG welding methods such as high current MIG welding method using a DC power source. It is essentially superior to . In particular, when welding vertical seams on the inner surface of a pipe, the pipe itself forms a magnetic path with the groove as the magnetic pole for the power supply cable to the torch, and the conventional MIG welding method cannot be applied due to the strong magnetic blow. The welding method of the present invention is also applicable to such uses. Examples of the present invention will be shown below. Example
1. The welding method of the present invention and DC high current MIG welding were compared in terms of defect occurrence in bead-on-plate steel sheets.

The welding method of the present invention utilized an AC power source equipped with a pulsed restriking device. Further, the DC power source had a drooping characteristic and was used with the same reverse polarity (electrode positive) as in the normal MIG welding method.
Other welding conditions are as follows. Welding wire lithography wire diameter 4.07m2%Ni-1.2%Mn-
0.3% MO low alloy steel Welding voltage: 30V Welding current: 8
00A (current density 63A/M7l) electrode protrusion length: 3
0wm shield gas carbon dioxide in realgon 2f),
I changed it to 5%, 10%, and 20%.

The flow rate is 50υ on the inside and 25υ on the outside for the concentric double nozzle.
t/min, total 75t/min.

Welding speed: changed to 50 cm/min, 70 cm/min, and 90 cm/min.

Table 1 summarizes the occurrence of poor fusion defects by examining about 10 cross-sections of beads placed under these welding conditions for each welding condition.

The numbers in this column indicate (number of defective sections/number of inspected sections). However, in this table, for simplicity, the size of the fusion defect is shown regardless of the size of the defect. As described above, the welding method of the present invention is completely free of defects and can be said to be revolutionary.

On the other hand, in the DC high current MIG welding method, the amount of carbon dioxide added is 2
001), the occurrence of defects is significant. The occurrence of defects roughly corresponds to the shape of the welding, and when welding using DC high current MIG welding (2001), welding speed was 1/10 even with carbon dioxide at a welding speed of 50cm/min, but the reason defects appeared was because the penetration was deep. This is because they are in one state, and on the other hand, 10
% carbon dioxide gas, there are fewer defects at 90 cm/min because the melt itself becomes shallower and the finger uniformity is not so pronounced. In addition, in the welding method of the present invention, carbon dioxide gas is 15
% or less, but in this example it is 20%
Although welding is possible, it is not recommended because there are many spatters and restriking failures are likely to occur. Example 2 Welding was performed using the welding method of the present invention on a plate thickness of 20wn (7) KT5OQ steel with a groove angle of 45 root face 4Tm0V groove.

The joint was fabricated by two-pass welding with a single electrode. The welding power source was the same as in Example 1, and the welding conditions for each pass were as follows. Welding wire Resolid wire diameter 3.2wm 1.6%
Mn-0.2%MO-0.1%Ti-0.008(Ff
) has an alloy component of B. Welding voltage: 32 Welding current: 850 A (current density: 105 A/MJ) Electrode protrusion length: 25 Trm Shielding gas: Oxygen 1% in Realgon Flow rate: Inside 50 L/min, outside 25 t/min Total 75 t/min Welding speed 80 cm/min Under these welding conditions The chemical composition of the obtained weld metal is as shown in Table 2, and since there is little oxidizing gas in the shielding gas, the oxygen content is as low as 0.016 (f).

In the case of DC high-current MIG welding using Ar-20% CO2 shielding gas or submerged arc welding using TiO2-based molten flux, the oxygen amount is approximately 0.03 (f) under similar welding conditions. In this example, -6
The impact value at 0°C is 11.2 kf-m for the weld metal and 10.6 kf-m for the base metal heat-affected zone, indicating good toughness. Example 3 A 257 m<7>X65 steel plate with a groove angle of 50 and a root face of 5wIn<7)X groove was welded by two-electrode tandem welding with one pass on each of the front and back surfaces.

The welding current was the same as in the previous example, and the welding conditions were as follows. Welding wire Resolid wire 4.8
- 3.5%Ni-201:f) Mn-0.3%MO as an alloy component.

Welding voltage: Leading 32V, Trailing 31V Welding current: Leading 1200A (current density 66A/m Small trailing 1000A (current density 55A/71J) Electrode protrusion length: Both leading and trailing 35ff1FF! Distance between electrodes: 50c
5% carbon dioxide gas in shield gas Rialgon Flow rate: 50 t/min inside for each torch, 25 t/min outside,
Total 75 t/min Welding speed: 1 m/min The chemical composition of the weld metal obtained by this welding is as shown in Table 3, and the oxygen content is as low as 0.012 (f).

The impact value is also excellent, with a weld metal of 8.5 kg-M at -60°C and a base metal thermal effect of 12.3 k1-m. As described above, the consumable electrode arc welding method of the present invention has a higher welding rate than the conventional submerged arc welding method when welding materials that require high toughness and have a limited heat input. A joint with excellent efficiency and toughness can be obtained. Not only that, but also proposed as an alternative to submerged arc welding? This method does not have the disadvantage of a high incidence of poor fusion defects, which is a problem with the conventional high-current MIG welding method, and also provides a higher toughness of the weld metal than any of the above welding methods due to the low oxygen content of the weld metal. Furthermore, the welding method of the present invention does not essentially have the drawbacks of being easily affected by magnetic blowing, which is a problem with the high-current MIG welding method, and therefore making tandem welding difficult. is easy and excellent. Furthermore, the ability to perform good welding even with a small content of oxidizing gas in the shielding gas is extremely suitable for welding high alloy steels such as stainless steel, where oxidation of components is particularly problematic. In addition, the tandem welding method, in which the welding method of the present invention is used in advance and the submerged arc welding method is used in the subsequent welding process, can be easily performed because there is no need to remove slag from the leading bead, and the surface of the finished bead is said to be beautiful. It has characteristics.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a weld bead showing poor fusion, Figure 2 is a graph showing the relationship between the amount of carbon dioxide in the shielding gas (the remainder is argon) and the oxygen content in the weld metal, and Figure 3 is a welding bead. A graph showing the difference in the impact value of metal depending on the shielding gas component, FIG. 4 is a diagram showing an example of the restriking means used in the welding method of the present invention, and FIG. 5 is a diagram explaining the operation of this. . DESCRIPTION OF SYMBOLS 1... Bead, 2... Poor fusion defect, 3... Base metal, 4... Welding, torch, 5... Electrode wire, 6-,
...Primary power source, 7... Welding power source transformer, 8... Pulse generator, 9... Current transformer, 10... Resistor.

Claims (1)

[Claims] 1. Equipped with restriking means within the range of electrode protrusion length d x 4 to d x 15 mm and current density 40 to 150 A/mm^2 for a solid wire with a diameter d of 3.2 to 6.4 mm. The steel is characterized in that it is welded in a shielding gas containing at least one of 15% or less carbon dioxide and 5% or less oxygen, the remainder being an inert gas while supplying a welding current of 600 to 2000A using an AC power supply. consumable electrode arc welding method.