JPH0692032B2 - Solid wire for pulse mag welding - Google Patents

Description

TECHNICAL FIELD The present invention relates to a gas shielded arc welding wire that uses a mixed gas mainly containing an inert gas such as Ar as a shield gas, and has a small amount of spatter generation. In particular, the present invention relates to a welding wire suitable for a gas shield arc welding method (pulse mag welding) using a pulse power source.

(Attempts to prior art and solve problems) Ar, used alone or mixed gases, such as CO _2, O _2, He as the shielding gas, a relatively small diameter electrodes (welding wire) was continuously fed The welding method to be performed (that is, the gas shield arc welding method) is often used for welding using a robot because it enables highly efficient welding and is a welding method that can be easily automated.

Further, among the gas shielded arc welding methods, the welding method using a mixed gas mainly containing an inert gas such as Ar and He as the gas shield gas has good arc stability as compared with the case where only CO ₂ is used. Although there is little spatter, there is a limit to the welding current range for low spatter,
At low welding current, spatter is generated as in the case of using CO ₂ gas.

Further, a pulsed mag welding method has been proposed for the purpose of improving spatter in the low current region, but the following problems remain.

That is, the pulsed mag welding method alternately flows a high current and a low current to form a droplet on the tip of the welding wire during the high current period, and separates the droplet from the tip of the welding wire during the low current period (hereinafter (Referred to as “base material”) and welded (see FIG. 1).

At this time, the droplet formed by one pulse current (high current period) shifts to the subsequent low current period (this is 1 pulse 1
If the phenomenon of droplet transfer) continues, spatter does not occur. However, since the formation and separation of droplets are greatly affected by the physical properties of the droplets, which are determined by the main components and impurities of the welding wire, in addition to the welding current / voltage pulse conditions, one pulse / one droplet transfer is not always continuous. It doesn't happen to me. If the detachment in the low current period fails, the detachment occurs in the next high current period, or the droplets grow largely due to a plurality of pulse currents (high current) and short-circuit with the molten pool of the base material. When it leaves during a high current period, the strong arc causes the droplets to be blown off as spatter, and even if a short circuit occurs, the short circuit is broken and the arc repulsion force when the arc occurs again causes the droplets and molten pool to scatter. It becomes spatter.

For these problems, for example, attention has been paid to the short-circuit phenomenon at the time of pulse mag welding, and a technique has been proposed in which the amount of spatter generated at the time of short-circuit is adjusted by adjusting the welding wire component (for example, JP-A-62-296993). ), The occurrence of spatter is basically unsolved as long as the short circuit phenomenon occurs.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a welding wire which solves the above-mentioned problems in pulse mag welding and has a characteristic that pulse 1 droplet transfer is continuously performed and a short circuit phenomenon does not occur. .

(Means for Solving the Problems) In order to solve the above problems, the present inventors have recognized that the occurrence of spatter is an unavoidable phenomenon as long as a droplet and a molten pool are short-circuited, The present invention has been completed here by conducting extensive research on a welding wire having a characteristic of continuously performing one pulse / one droplet transfer and not causing a short circuit phenomenon.

That is, the present invention, C: 0.07 ~ 0.12%, Si: 0.20 ~ 0.50
%, Mn: 1.0 to 1.5% and Ti: 0.01 to 0.06%, the balance consisting of Fe and inevitable impurities, and O (oxygen) and N (nitrogen) in the inevitable impurities are 80 ppm or less, respectively. ,
Potassium compound in K equivalent 0.5 to 7pp per weight before welding wire
The gist of the solid wire for pulsed mag welding is that m is attached to the surface of the welding wire.

The present invention will be described in more detail below.

(Operation) Considering the characteristics of the construction method, the point to solve the problem in the pulse mag welding method is to prevent the short circuit between the droplet and the molten pool even under the welding condition of the short arc length.
That is, since the distance between the tip of the wire and the molten pool is physically long in the condition where the arc is long, the short-circuit phenomenon itself does not easily occur, but in the condition where the arc length is short, the formation and separation phenomena of droplets are less likely to occur. This is because a short circuit may occur even in such an unstable state.

The arc length is macroscopically dependent on the distance between the welding wire tip and the molten pool after the droplet has separated, so the smaller the welding, the shorter the arc length can be set. . Forming small droplets means
It is sufficient that one pulse / one droplet transfer can be obtained in a state where the high current period for formation is shortened and the pulse frequency of the current is increased.

The inventors of the present invention focused on the above points, conducted welding experiments using welding wires of various component systems, found the droplet transfer characteristics by direct observation with a high-speed camera, and found that even with a short arc length Examination of the influence of each major component of C, Si, Mn, and Ti in the steel wire for pulse-mag welding, inevitable impurity components such as O and N, and components applied to the surface of the welding wire, in which drops do not short-circuit with the molten pool did.

The aim is to reduce the spatter by adjusting the short-circuit state with the components of the welding wire in the conventional technique, whereas the present invention does not cause the short-circuit phenomenon as much as possible. Thus, the generation of spatter is prevented.

In pulse mag welding, as shown in Fig. 1, it is a condition for stable droplet transfer that droplets are formed at the tip of the welding wire during the pulse current supply period and leave during the low current period. It was mentioned above that it is necessary for prevention.

Here, when the C content of the welding wire and the transfer characteristics of the droplets were examined, the following results were obtained.

FIG. 3 shows from the start of holding the peak current value of the pulse current supply period to the detachment of the droplet when pulse mag welding was performed under the welding conditions shown in Table 1 for the welding wire in which only the C content in the welding wire was changed. Time of high speed camera (2000
This is the result of observation and measurement in frames / second).

As shown in FIG. 3, the smaller the C content in the wire, the longer the droplet detachment time. This phenomenon also appears in images taken by high-speed cameras. That is, it was confirmed that the constricted portion formed between the droplet and the unmelted wire when the droplet was detached was less likely to be broken as the C content was smaller, and extended without being detached (see FIG. 4). . Since C combines with oxygen (O) in the droplet and also acts as a deoxidizing element, it is considered that when the C content decreases, the amount of O in the droplet relatively increases. . It is known that an increase in the amount of O in molten steel lowers its surface tension. Since the surface tension acting on the constricted portion of the droplet acts in the direction of releasing the droplet, the reduction of the surface tension is not a preferable direction for the droplet detachment of pulsed mag welding.

In other words, C is an element that influences the droplet detachment phenomenon in pulsed mag welding, and there is an optimum content range depending on the physical properties of the droplet (such as surface tension) determined by the chemical composition including other elements. Found out.

Similarly, the main components of deoxidizing elements Si, Mn, Ti, O,
Welding wires with various contents of N impurities were prototyped, the formation and separation phenomena of droplets were compared, and the time from the start of holding the peak current to the separation of droplets was short, that is,
The optimum content range that enables stable welding under high frequency pulse conditions was investigated and found.

The chemical composition of the wire of the present invention was adjusted based on the results of the above welding test. The reasons for limiting the chemical components in the present invention are shown below.

Si: 0.20 to 0.50% When the Si content increases, it becomes difficult to form the constricted part itself, which is an important phenomenon for melt release.
The time from formation to separation is extremely long, so the upper limit is 0.50%. On the other hand, if the Si content is less than 0.20%,
Since deoxidation becomes insufficient and defects such as pits and blow holes occur in the weld bead, the lower limit is 0.20%.

C: 0.07 to 0.12% C also influences the above-mentioned phenomenon of droplet detachment and is an important element for realizing pulsed mag welding without a short circuit phenomenon. If the content is low, it is easy to form the necked portion,
The lower limit of the C content is set to 0.07% because it requires time to release. C is also an element that hardens the welded portion and enhances the strength of the joint, but particularly in high-speed welding, it induces hot cracking, so 0.12% is the upper limit.

Mn: 1.0 to 1.5% Mn is also a deoxidizing element and has the same effect as Si on the physical properties of the droplets and molten pool, but if it exceeds 1.5%, it becomes difficult to separate the droplets and it takes time. Become. On the other hand, if it is less than 1.0%, the amount of Si is suppressed to a low level and deoxidation becomes insufficient, resulting in defects in the welding beads.

Ti: 0.01 to 0.05% Ti is also a strong deoxidizing element. As described above, as a result of suppressing the amount of Si in order to improve the detachability of the droplets, deoxidation of only Mn is not sufficient to improve the generation of blowholes, and it is necessary to add Ti. . If its content exceeds 0.06%, the detachment of droplets is inhibited, and conversely, if it is less than 0.01%, defects due to insufficient deoxidation such as blowholes occur as in the case of no addition.

Inevitable impurities: O and N are known as elements that lower the surface tension of molten steel, but if too much, it takes time from droplet formation to detachment,
Moreover, since the detachment of droplets becomes insufficient, the content of each is 80
It should be below ppm. Since the Si content is suppressed to a low level, blowholes are easily generated when O and N exceed 80 ppm.

Potassium compound on the surface of the welding wire: Further, in the present invention, not only the chemical composition of the above-mentioned welding wire but also the presence of the potassium compound on the surface of the welding wire is an important factor.

In this regard, attempts have been made to apply a potassium compound having a low ionization voltage to the surface of the welding wire to stabilize the welding arc and prevent spatter (JP-A-58).
No. 3797), this proposal aims to increase the length of the arc by applying a compound to the surface of the wire to prevent a short circuit between the welding wire tip and the molten pool.
This is contrary to the intention of the present invention, that is, the idea of preventing a short arc.

Therefore, although the present inventors did not take this technology into consideration at the beginning of the research, in the process of investigating and forming the formation / detachment phenomenon of droplets in pulse welding, a substance having a low ionization voltage was found to be a part of the welding wire unmelted portion. It has been found that it has a great influence on the formation of the neck between the droplet and the droplet. That is, while a high current (300A to 500A) is supplied and an arc is generated, droplets are formed at the tip of the welding wire, but at this time, the arc is not concentric with the welding wire and is biased. Can occur at the location. In this case, a high-speed camera image confirmed that a constriction was less likely to occur between the unmelted portion of the welding wire and the droplet, and that it took time to separate the droplet.

On the other hand, when a potassium compound with a low ionization voltage is applied to the welding wire surface, when a high pulse current is supplied,
An arc is generated symmetrically with respect to the center line of the welding wire,
Also, the droplets were likely to be formed symmetrically (see FIG. 5). It is considered that this is because the presence of a substance having a low ionization voltage on the surface of the welding wire eliminated the bias in the arc generation point at the tip of the welding wire. As a result, the droplets are uniformly heated by the arc, the droplets are formed symmetrically with respect to the center line of the welding wire, and the constriction can be stably formed.

As an example, for a welding wire in which a potassium compound is applied at 5 ppm on the surface of the wire, the time from the start of holding a high current to the detachment of droplets can be measured as shown in FIG.
When the content was changed, the results shown in FIG. 6 were obtained.

According to FIG. 6, it is understood that not only is the time until the droplets separated until the droplets can be transferred one pulse at a high pulse frequency, but there is also no variation in time. This indicates that the size of the droplet is constant, and the presence of potassium compounds with a low ionization voltage causes the arc to break in high-current and low-current pulse welding. It is effective in stabilizing the generation and maintenance of.

Based on the above experimental results, in the present invention, K
In terms of conversion, 0.5 to 7 ppm of the total weight of the welding wire is attached to the surface of the welding wire. If the potassium compound is less than 0.5 ppm, the effect of application is not recognized, and if it is applied more than 7 ppm, the arc becomes long as in the prior art, and the low arc spattering in the short arc aimed at by the present invention does not occur. Not done. Examples of the potassium compound include potassium stearate and potassium carbonate. The effect of applying the potassium compound is closely related to the amount of oxygen in the wire, and when the O / K is 10 or more, the effect of applying the potassium compound becomes remarkable. But O /
When K exceeds 80, the amount of oxygen becomes relatively large, and blowholes tend to increase slightly. Therefore, O / K is 10-80
Is desirable.

Next, examples of the present invention will be described (Examples) Using a trial welding wire, a welding test was performed under the welding conditions shown in Table 2. The welding test results are shown in Table 3.

In Table 3, Fcr represents the optimum pulse frequency band for one pulse / one droplet transfer when the corresponding prototype welding wire is used, and the larger this value is, the better.

From Table 3, the following is considered.

Comparative wires No. 10 to No. 13 are commercially available as gas shield welding wires and have a general chemical composition. In order to perform pulsed mag welding using these welding wires, the pulse frequency must be 160 to 200 Hz at a wire feeding speed of 7 m / min, and one pulse droplet transfer does not occur, and spatter still occurs.

On the other hand, with the wire of the present invention, even if the pulse frequency is increased to 240 to 280 Hz, one pulse per droplet continues to transfer, spatter does not occur, and blow holes do not occur.

Since the comparative wire No. 14 has a high Si content and requires a long time to form and separate droplets, it is unavoidable to set a low pulse frequency for one pulse per droplet transfer.

Comparative wires No. 15 to No. 16 are wires having a low C content, and comparative wires No. 17 to No. 18 are wires having a high oxygen content.
In both cases, the surface tension / viscosity of the droplets seems to have decreased, but it takes time when the droplets separate from the tip of the wire, so the frequency for one pulse / one droplet transfer is at a low level.

The comparative wires No. 19 to No. 20 are examples in which the original level of the welding wire contains a high level of nitrogen, and blowholes were detected as a result of the X-ray transmission test of the welding beads.

Comparative wire No. 21 does not contain Ti but contains C, Si, Mn,
This is an example in which the amounts of O and N were within the range of the present invention, but blowholes were detected as a result of the X-ray transmission test of the weld beads.

Comparative wires No. 24 to No. 25 are wires No. 3 and N of the wire of the present invention.
It is a wire that has the same chemical composition as o.8, but does not apply a small amount or no potassium compound. The optimum pulse frequency was lower than when the potassium compound was applied, and spatter frequently occurred under the condition of low welding voltage.

Comparative wire No. 26 is an example in which about 9 ppm of potassium compound was applied in K conversion, but the arc spreads widely and welding defects called undercut beads in which the edge of the bead is recessed from the base metal occur. did.

Further, in order to confirm the low spatter effect of the welding wire according to the present invention, FIG. 7 shows the result of investigating the spatter generation amount in the state where the welding voltage is lowered and the arc length is shortened. From the same figure, it was confirmed that in the welding wire having the chemical composition of the present invention, the amount of spatter generated was small without short-circuiting the droplet and the molten pool even when the arc was shortened.

(Effect of the Invention) As described in detail above, according to the present invention, since the chemical composition of the wire is adjusted and a predetermined amount of the potassium compound is adhered to the wire surface, stable welding can be performed under high frequency pulse conditions. This makes it possible to provide a welding wire having a characteristic that one pulse / one droplet transfer is continuously performed and a short circuit phenomenon does not occur, and the effect is remarkable.

[Brief description of drawings]

Fig. 1 is a schematic diagram of droplet transfer and current waveform in pulse welding, Fig. 2 is a diagram for explaining holding start point and peak current value holding time under pulse conditions, and Fig. 3 is from peak current start to droplet detachment. Showing the relationship between the time and the C content in the wire, FIGS. 4 (a) and 4 (b) are explanatory views showing the shape of the constricted portion immediately before the detachment of the droplet, and FIG. 4 (a) shows a small C content. If
(B) shows the case where the C content is large, FIGS. 5 (a) and 5 (b) are explanatory views showing the arc generation state at the tip of the wire, (a) shows the case of the arc deviation,
FIG. 7B shows the case of a concentric arc, and FIG. 6 is a diagram showing the relationship between the time from the start of peak current holding by the wire coated with a potassium compound to the detachment of droplets and the C content in the wire, FIG. The figure shows the relationship between the amount of spatter generation and the welding voltage in the example.

Claims (1)

[Claims] 1. In weight% (hereinafter the same), C: 0.07 to 0.12
%, Si: 0.20 to 0.50%, Mn: 1.0 to 1.5% and Ti: 0.01 to 0.0
6%, the balance consists of Fe and inevitable impurities,
O (oxygen) and N (nitrogen) in the unavoidable impurities are
A solid wire for pulse mag welding, wherein 80 ppm or less, and further 0.5 to 7 ppm of potassium compound in terms of K per total weight of the welding wire are attached to the surface of the welding wire.