JP2567708B2 - High current density gas shielded arc welding steel wire - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a steel wire for gas shielded arc welding, and more specifically, it provides stable droplet transferability and good penetration shape in high current density welding. Steel wire used.

(Prior Art) Recently, the gas shielded arc welding method is more and more widely used due to the automation and high efficiency of welding. As a means for increasing efficiency, it is generally adopted to increase the current density to increase the melting rate (deposition amount) of the wire. However, in high current density welding, many problems occur, such as frequent occurrence of spatter, deterioration of porosity resistance, crack resistance and fusion failure.

That is, in CO ₂ welding in which carbon dioxide is used as the shielding gas, the amount of spatter increases sharply when the current density is increased. In Ar-CO ₂ mixed gas welding where the amount of spatter generated is small, when the current density exceeds a certain level, a so-called "finger-like" penetration shape is formed in which excessive penetration is formed in the center by the pinch force. Since the central portion of the penetration has a high cooling rate, not only solidification and cracking easily occur but also gas easily remains, which is one of the causes of blowholes.

In addition, in the lamination welding and the welding of butt joints, there is a problem that a shape defect such as fusion failure often occurs due to a small penetration width.

All of these problems are ameliorated by changing the penetration shape from a finger shape to a circular shape,
As a solution, a welding method in which He is added to a shield gas, for example, Japanese Patent Laid-Open No. 59-45084, proposes a welding method using a mixed gas of four kinds of Ar—He—CO ₂ —O ₂ .

However, since this method also contains 25-60% of He, it is necessary to keep the current value extremely high in order to obtain a stable circular penetration, and as a result, excessive welding heat input is applied, resulting in a weld zone. In addition to the fact that the crystal grains of Co become coarse and the impact toughness decreases, and in addition to practical restrictions such as the narrow range of conditions that can be selected, especially in Japan, the gas cost becomes high, so it leaves an economic problem. It was

Thus, although some studies have been made on the welding method, almost no studies have been made on steel wires in the past, and there is a strong demand for wires suitable for high current density welding.

(Problems to be Solved by the Invention) The present invention solves various problems of the conventional high current density welding, and the rotational fine grain transferability of droplets is good and stable even at a relatively low current. It is intended to provide a steel wire for high current density welding, which has a circular shape penetration and is excellent in the resistance to blowholes.

(Means for Solving the Problems) The gist of the present invention is that Ti (weight%, the same applies hereinafter): 0.050 to 0.35%, S: 0.010 to 0.040% are contained, and the electrical resistivity of the wire at room temperature ( ρ) is 25 to 65 (μΩcm)
Steel wire for high current density gas shielded arc welding (where K = 505
・ S (%) ＋ 0.41 ・ ρ (μΩcm))

(Operation) Generally, when the welding current is increased in the droplet transfer form of MAG welding, as shown in Fig. 1, (a) granular transfer, (b) fine particle transfer, (c) rotary fine particle transfer and three types It is known to exhibit the form of That is, it is a transition form of the low current region (a)
In the granular transfer, the droplet 2a at the tip of the wire 1 grows into large particles and transfers to the molten pool 4 because the pushing force of the arc 3 is weak.
When the current is increased, the arc 3 is squeezed by the pinch force, and the droplet 2b becomes fine particles (b), which is fine particle transfer. When the electric current further increases, the droplet pushing force of the arc causes the droplets 2c and 2c 'to start to rotate (c), which results in the transfer of rotating fine particles.

The high current density welding in the present invention includes (c)
It refers to the range showing rotational fine grain transfer. The rotary fine grain transfer is a transfer of droplets while the softening portion at the tip of the wire and the droplet rotate about the wire vertical axis as a rotation axis by an arc force.

The present inventors, in such high current density welding,
In order to stabilize the phenomenon that the droplet transfer morphology changes from fine grain transfer to rotating fine grain transfer, it is important that the pushing force due to the arc acting on the droplet be constant, and the arc at the droplet tip is Focusing on three points, that is, the generation point is stable, the softened portion at the tip of the wire is stably generated, and the droplet transfer is performed stably, the droplet transfer characteristics and the wire characteristics will be described in detail. Various studies were conducted.

As a result, the Ti content is limited, and the resistivity and S
By limiting the amount and a certain range, a steel wire suitable for high current density welding was reached, and the present invention was completed.

That is, the greatest feature of the present invention is stabilization of the softened portion of the wire tip by limiting the specific resistance of the wire, and further S, Ti
The best effect in high current density welding is to be achieved by measuring the well-balanced improvement of droplet transferability by adjusting.

 The reasons for limitation in the present invention will be described below.

When the specific resistance (ρ) of the wire is less than 25 (μΩcm), the transition current value increases rapidly. Also, when it exceeds 65 (μΩcm), the effect of reducing the transition current value is not remarkable, the weight of the softened part at the wire tip is not constant, and the phenomenon of scattering with rotation is intensified, resulting in frequent occurrence of large spatter. .

The S content of the wire has the effects of lowering the transition current value, reducing the transition current width, and maintaining the droplet size appropriately.
If it is less than 0.010%, such an effect cannot be obtained, and if it exceeds 0.040%, there is an adverse effect such as a marked decrease in the weld metal's resistance to wear, so 0.040% was made the upper limit.

Further, even if the specific resistance ρ and S content of the wire are within the above ranges, stable rotary fine grain transfer may not be performed under certain conditions where ρ and S are low or high. Understand, and as a result of further detailed examination,
It was found necessary to limit 505 × S (%) + 0.41 × ρ (μΩcm) to the range of 20-40.

Ti stabilizes the arc point on the droplet and exerts a remarkable effect on the reduction of the transition current value and the current width in which the transition morphology changes from the fine grain transition to the rotary fine grain transition by the addition of an extremely small amount.

FIG. 2 shows an arc observation result by a high-speed video about the relationship between the Ti content of the wire and the transition current in which the droplet transfer form changes from the fine grain transfer to the rotating fine particle transfer as an example of the examination result. . From the figure, it can be seen that when the Ti content is 0.050% or more, the transition current sharply decreases, and the width of the transition current value that changes from the fine grain transition to the rotary grain transition becomes narrow, and the rotary fine grain transition becomes stable. . However, the Ti amount is 0.15
%, The effect on the transition current tends to be saturated, and when the Ti content exceeds 0.35%, not only the tensile strength of the weld metal becomes too high, but also its impact toughness decreases sharply. 0.35% because the harmful effects such as
Was set as the upper limit.

The transition current value changes depending on the peripheral conditions such as the shield gas composition, wire diameter or wire protrusion length, welding speed, etc. The effect is demonstrated.

In this case, the composition system of the wire is 0.07 to 0.09% C-0.
7-0.9% Si-1.4-0.6% Mn-0.015-0.020% S,
Wire diameter is 1.2 mmφ, shielding gas: Ar-10% CO ₂ (Flow rate:
25 / min), the welding position is downward flat plate, the distance between the tip and the base metal (Ext): 25 mm, and the welding speed is 40 cm / min.

 Next, the effects of the present invention will be specifically described with reference to examples.

(Example) Example 1 Steel having the composition shown in Table 1 was melted, and after forging, wire drawing, plating, and wire drawing to finish a wire of 1.2 mmφ, the method shown in FIG. 3 was used. The electrical resistance was measured. Third
In the figure, a constant current voltage is applied by a constant current generator 5 to both ends of a wire 1 having a length of 10 m, and a switch 9 is connected to the wire 1 side to obtain a voltage value (V) and a current value (I) at that time. Was read and recorded by a voltmeter 7 and an ammeter 8, respectively, and the specific resistance (ρ) was calculated from the result and the measured value of the wire diameter [D (cm)] by the following formula. These measurements were performed at room temperature (20 ° C.), and the standard resistance 6 was used for checking the voltage value and current value.

Perform welding by welding condition indicating specific resistance ^{(ρ) = 10 6 · π} · V · D 2/400 · I [μΩcm] Each of these wires in Table 2, high-speed video camera that arc condition (1/1000 Second, the droplet transfer state was measured, and the results shown in Table 3 were obtained.

From the video image, the droplet transfer property is the number of rotation transfer times of every 10 msec of the data of 500 points every 1 msec [2c in Fig. 1 (c)].
→ 2c '→ number of changes to 2c] to obtain the average number of rotations of the data at each 50 points and its standard deviation, and the average number of rotations at the current value for which stable fine grain transfer is performed in advance. The ratio of the rotation speed was 50% or less, and it was determined to be defective.

In the bead X-ray transmission test, the number of defects and the number of pores of the film were measured, and JIS grade 3 or lower was determined to be unacceptable. The penetration shape and the bead cross-section macro were sampled to measure the penetration shape. In the penetration shape, as shown in Fig. 4,
It was judged that the penetration width at half the maximum penetration depth was 50% or more of the maximum penetration width.

As shown in Fig. 5, the bead-on-plate welding in which the welding bead 11 is placed on the base material 12 from which the oxide scale layer on the surface is removed is performed by the bead-on-plate welding. Welding spatter collected by welding 3 times (1 min each for welding time) into a copper collection container (200 mm w x 150 mm h x 600 mm l) covering the weight, and evaluating the average value, the value is 2.5 (G / min) or less was judged to be good.

It should be noted that those attached to the inner surface of the torch 10 and the base material 12 were excluded.

In Table 3, wires No. 9 and No. 12 are wires whose K value is out of the limited range of the present invention. No. 9 is good in rotation transfer, X-ray performance, and penetration shape, but a large amount of spatter is generated. No. 12 has a small amount of spatter generation, but has poor rotational transfer, X-ray performance and penetration shape. Thus, even if the Ti amount, the S amount, and the specific resistance are within the limit ranges, good performance cannot be obtained if the K value does not satisfy the limit range.

Wire Nos. 11 and 13 have an S content outside the range of the present invention. No. 11, which has a high S content, has a relatively high average rotation transfer rate, but lacks stability. Therefore, there are problems in the X-ray and the penetration shape, and in No. 13, the S content is too low, so the rotational transferability, the X-ray performance, and the penetration shape are poor. A crack was found in the center of the finger portion.

Wires Nos. 15 and 18 have Ti contents outside the range of the present invention. In No. 15 with low Ti, almost no rotational transfer was performed, so that it had a finger-like penetration shape, and broholes were observed in the vicinity of its tip. Also, many fine spatters were generated. Further, in No. 18 having a high Ti content, since the rotational transition is too violent, a phenomenon in which large-sized spatters are scattered around due to the rotation of the droplets is observed, and the spatter generation amount is very large.

The wire Nos. 14 and 16 are wires whose specific resistance (ρ) is out of the limit range of the present invention. No. 14, which has a low specific resistance, has a relatively small amount of spatter, but the rotation transfer is insufficient, and as a result, both the X-ray performance and the penetration shape are poor. On the other hand, No. 16, which has too high specific resistance, has a rotational transfer rate of over 50% but lacks stability, the arc length fluctuates greatly, and large spatters frequently occur. Wire No. 10 has a Ti content and a specific resistance, and No. 20 has an S content and a specific resistance, which are outside the limits of the present invention. Therefore, good results cannot be obtained in all items except the penetration shape of wire No. 10. Wire No. 19 had S content, Ti content, and K value outside the limits of the present invention, and the rotational transferability was extremely unstable. Especially, the shape of the droplet tip was not constant and scattered around as it rotated. Large spatter is generated.

Wire No. 17 had all the amounts of S, Ti, specific resistance, and K value outside the limits of the present invention, almost no transfer of rotary fine particles was observed, and the penetration shape showed a remarkable finger shape and X The line performance is also poor. As described above, any wire that does not satisfy the limited range of the present invention cannot obtain good high current density welding performance.

On the other hand, the wire Nos. 1 to 8 of the present invention all show good performance in all items, and stable high current density welding is performed.

Example 2 Among the wires in Table 1, No. 1 and No. 15 were used to variously change the shielding gas composition and the rotary fine particle transfer rate was changed under the welding conditions in Table 2 by the same method as in Example 1. The examined results are shown in Table 4.

Wire No. 1 of the present invention shows stable rotary fine grain transfer at low current in any shield gas composition as compared with Comparative Wire No. 15, and it can be seen that the applicable current range is wide.

Example 3 Using No. 1 and No. 10 of the wires in Table 1, the mechanical properties of the deposited metal were examined by the steel plate and groove shape shown in FIG. 6 and the welding conditions shown in Table 5. The results shown in Table 6 were obtained. Incidentally, these tests were carried out according to JIS Z 3312.

The wire No. 1 of the present invention shows excellent mechanical performance of the deposited metal under any high current density welding condition.

(Effects of the Invention) As described above, according to the wire of the present invention, a stable rotation transfer is performed, and as a result, a good penetration shape, porosity resistance, an extremely small amount of spatter are generated, and a wide welding condition range. And high current density welding is performed, which results in a weld metal having good performance.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the migration form of droplets, FIG. 2 is a diagram showing the relationship between the Ti amount of the wire and the transition current, FIG. 3 is a diagram showing a method for measuring the electric resistance of the wire, and FIG. The figure which shows the penetration shape of a bead, FIG. 5 is a figure which shows the sampling method of spatter, and FIG. 6 is a figure which shows the groove shape of a weld metal test. 1 ... Wire, 2a, 2b, 2c, 2c '... Droplet, 3 ... Arc, 4 ... Melting pool, 5 ... Constant current generator, 6 ...
Standard resistance, 7 ... voltmeter, 8 ... ammeter, 9 ... switch, 10 ... torch nozzle, 11 ... bead, 12 ... base metal,
13 ... Copper collection box.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Kawabe 3-5-4 Tsukiji, Chuo-ku, Tokyo Inside Nittetsu Welding Industry Co., Ltd. (56) Reference JP-A-3-35881 (JP, A)

Claims (1)

(57) [Claims] 1. Ti (% by weight, the same applies hereinafter): 0.050 to 0.35%,
S: Contains 0.010 to 0.040%, the electrical resistivity (ρ) of the wire at room temperature (hereinafter simply referred to as the specific resistance) is 25 to 65 (μΩcm), and the parameter K shown in the following equation is 20 to 40 High current density gas shielded arc welding steel wire. However, K = 505 · S (%) + 0.41 · ρ (μΩcm)