JPH11254136A - Magnetic stir-welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the ultrasonic permeability of the joint weld zone of an austenitic stainless steel. SOLUTION: When welding a groove 4 for joint, which is formed between base materials 3 consisting of the austenitic stainless steel, a stirring force F by magnetism is given to a melting pool 5a by setting a magnetic frequency from 4 to 10 Hz. Consequently, since the stirring frequency of the melting pool 5a can be increased and sufficient stirring can be performed without being affected by gravity, the texture of the joint weld zone 5 can be micronized even by welding in any welding position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic stir welding method capable of improving the ultrasonic permeability by making the structure of a joint weld finer.

[0002]

2. Description of the Related Art Ultrasonic flaw detection is generally considered to be more difficult in austenitic stainless steel joint welds than in carbon steel or the like because the columnar crystal structure grows remarkably and has sonic anisotropy. I have.

That is, as shown in FIGS. 7A and 7B,
When performing an ultrasonic inspection of a base material a made of austenitic stainless steel, if there is no joint weld in the middle of the base material a, the ultrasonic beam c is emitted via the probe b to perform angle beam inspection. For example, it is possible to detect an echo that returns after hitting the defective portion d at the bottom as a large noise and obtain the distance W1 to the defective portion d. As shown in the figure, when a joint weld e is interposed in the middle of the base material a and a defect d is detected at a position where the ultrasonic beam c passes through the joint weld e, the columnar shape of the joint weld e is determined. Due to the presence of the crystal structure, the ultrasonic beam c is curved or a pseudo echo is generated, so that the distance to the defective portion d is determined as W2 longer than W1, and it is difficult to perform the flaw detection inspection with high accuracy. Can not.

[0004] In order to improve the ultrasonic permeability of the welded portion of austenitic stainless steel, it is necessary to refine the structure of the welded portion of the joint. There is known a magnetic stir welding method in which welding is performed while applying a magnetic stirring force to the formed molten pool (Japanese Patent Application Laid-Open No. 3-27878).

[0005]

However, in the conventional magnetic stir welding method described above, in a normal downward welding position, for example, the mechanical oscillation and the magnetic frequency are synchronized by synchronizing the former at 1 Hz and the latter at 2 Hz. By controlling the agitation state of the pool, it is possible to improve the ultrasonic characteristics of the welded joint.However, if the welding posture changes to a vertical upward, vertical downward, upward, etc. Since the shape changes due to the effect of gravity, it becomes difficult to stir the molten metal when it solidifies. Also, the degree of improvement in the ultrasonic characteristics varies depending on other construction conditions (speed, amount of wires, etc.).

Therefore, the present invention is intended to improve the ultrasonic characteristics of a welded portion of austenitic stainless steel by obtaining a large stirring effect without being restricted by the welding position. is there.

[0007]

In order to solve the above-mentioned problems, the present invention provides a magnetic stirrer in which a molten pool formed in a joint groove of a base material is welded while applying a magnetic stirring force. In the welding method, the magnetic frequency for stirring the molten pool is set to 4 to 10 Hz to form a joint weld.

[0008] When the magnetic frequency is increased to 4 to 10 Hz, the number of times of stirring of the molten pool increases, so that the molten pool is sufficiently stirred without being affected by gravity regardless of the welding posture, so that the welded portion of the joint is welded. Is refined.
Therefore, the ultrasonic characteristics of the joint weld can be improved.

Further, by changing the welding direction every time one layer of weld bead to be a joint weld is formed, the growth of the structure in the same direction can be suppressed.
The ultrasonic characteristics can be further improved.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 (a) and 1 (b) show an embodiment of the present invention, in which a welding device equipped with an electromagnetic coil 2 at the outer peripheral position of the tip of a welding torch 1 is used to form an austenitic stainless steel. An unillustrated wire is melted by an arc emitted from the tip of the welding torch 1 in the joint groove 4 of the base material 3 to form a molten pool 5a.
In the magnetic stirring welding method in which a magnetic field is applied to the vicinity of the welded portion by the electromagnetic coil 2 to apply welding force F by Lorentzka to the molten pool 5a, the magnetic frequency for stirring the molten pool 5a is set to 4 The frequency is set to 10 to 10 Hz to form the joint weld 5 having a fine structure.

Also, a weld bead 5 serving as the joint weld 5 is provided.
Each time b is formed in one layer (one pass), the welding direction (the traveling direction of the welding torch 1) is changed in the opposite direction.

In the present invention, when the joint groove 4 between the base materials 3 is welded to form the joint weld 5, the magnetic frequency is set to 4.
Since the magnetic stirring welding is performed at a high frequency of 10 to 10 Hz, the number of times of stirring of the molten pool 5a can be increased when the molten metal solidifies and the structure grows. This allows the molten pool 5a to be sufficiently stirred without being affected by gravity regardless of the welding position, so that it is not necessary to synchronize with the mechaosylate, and the joint welding portion 5 can be easily formed. The structure can be miniaturized. That is, when the welding posture and the working conditions change, the solidification rate changes and the timing of stirring is greatly affected. However, if the number of times of stirring is large, the stirring is sufficiently performed, and the influence of gravity is less likely. Therefore, the ultrasonic permeability of the joint weld 5 can be improved, and the ultrasonic characteristics can be improved.

In addition, the joint welded portion 5 performs multi-pass welding in which the weld beads 5b are stacked in multiple layers from the bottom layer to the upper layer in the groove 4 for joint. Since the welding direction is changed every time the weld bead 5b is formed in one layer (one pass), the growth of the structure in the same direction can be suppressed, and the structure can be further refined. Thus, the ultrasonic characteristics can be further improved.

[0015]

Next, the results of the ultrasonic transmission test performed by the present invention will be described.

First, as shown in FIG. 2, SUS316 steel having a thickness of 10 mm is used as a base material 3 ', and a groove 4' of 60 ° is formed on the base material 3 'while leaving a thickness of 2.5 mm and a width of 6 mm. Is established,
At the groove 4 ', a joint welded portion 5' is formed by magnetic stirring welding (multi-layer pass) in each welding position (downward, vertical upward, vertical upward, downward) using a stainless steel material (Y316L). Formed. For comparison, a test piece by normal welding without magnetic stirring was also manufactured.

After confirming by microscopic observation that the structure has been refined by magnetic stirring welding, the front and back surfaces are ground to 1 mm so that the thickness of the joint welded portion 5 ′ is 8 mm, and an ultrasonic permeability test is performed. A piece was made.

Next, all the test pieces were evaluated for ultrasonic permeability at 2 MHz oblique flaw detection at a refraction angle of 45 degrees. As shown in FIGS. 3 (a), 3 (b) and 3 (c), the test method is such that the transmitting probe 6a is fixed to the back surface of the joint welded portion 5 ', and the receiving probe 6b is scanned on the front surface side. The transmitted sound pressure was measured at the probe position where the maximum transmitted sound pressure (echo height) was obtained by direct irradiation. The measurement was performed at two positions on the bead center line, that is, the bead direction and the direction opposite to the bead, and the measurement was performed at three positions in the same direction.

FIG. 4 shows a comparison result of ultrasonic permeability between a test piece which was subjected to normal welding (downward) and a case where magnetic stirring was performed with a magnetic frequency of 1 Hz in each welding position.
Fig. 7 shows the comparison results of ultrasonic permeability between a test piece which was normally welded and a case where magnetic stirring was performed at a magnetic frequency of 6 Hz in each welding position.

As is apparent from FIGS. 4 and 5, when the transmittance of the shear wave ultrasonic wave is set to 100%, about 20% is obtained by ordinary welding.
%, While in magnetic stir welding,
In any of the welding positions, the permeability of the ultrasonic wave is improved. However, when the magnetic frequency is 1 Hz, the degree of improvement is low at about 30% when the welding position is upright and downward and upward. In contrast,
When the magnetic frequency is 6 Hz, the transmittance is greatly improved to 40% or more in any welding position. This is considered to be because when the magnetic frequency is increased, the molten pool is constantly stirred and becomes less affected by gravity.

FIG. 6 shows the results of a similar test performed using a test piece having a thickness of 20 mm. In the ordinary welding, the ultrasonic transmission was greatly attenuated to about 5%, but the magnetic stirring was performed. It can be seen that the transmittance is about 25% or more in the welding, and the transmittance is improved about 5 times or more compared to the normal welding. This is considered that in magnetic stirring welding, the microstructure is refined and the microstructure grows in the same direction, so that even when the plate thickness is increased, the attenuation of the ultrasonic wave is small.

According to the test conducted by the present inventors, when the magnetic frequency is set to 3 Hz or less, the magnetic head is susceptible to the influence of the welding posture almost as in the case of 1 Hz. However, it has been confirmed that the molten pool becomes difficult to move due to the influence of inertia, and conversely, the stirring effect is reduced.

As described above, by using magnetic stir welding, even in the welding of austenitic stainless steel joints, the structure can be refined by setting the magnetic frequency to 4 to 10 Hz, and the ultrasonic permeability can be improved. It was confirmed that it could be improved. In particular, when the magnetic frequency is 6 Hz,
It was found that there was no effect of the welding position and the ultrasonic transmission was improved stably.

[0024]

As described above, according to the magnetic stir welding method of the present invention, the following excellent effects are exhibited. (1) In a magnetic stir welding method in which the molten pool formed in the joint groove of the base material is welded while applying a magnetic stirring force, the magnetic frequency for stirring the molten pool is set to 4 to 10 Hz. Since the joint weld is formed, the number of times of stirring of the molten pool can be increased, so that the molten pool can be sufficiently stirred without being affected by gravity in any welding posture. The microstructure of the weld can be refined, and therefore, even in the case of austenitic stainless steel joint welds where ultrasonic testing was conventionally difficult, ultrasonic permeability can be improved, The sound characteristics can be improved. (2) Each time one layer of weld bead to be the joint weld is formed,
By changing the welding direction, the growth of the structure in the same direction can be suppressed, so that the ultrasonic characteristics can be further improved.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention, in which (a) is a schematic view showing a state in which a joint weld is formed, and (b) is a view taken along the line AA of (a).

FIG. 2 is a schematic view of a test piece.

3A and 3B show a state in which an ultrasonic permeability test is being performed, wherein FIG. 3A is a plan view, FIG.
(C) is a view taken along the line CC of (A).

FIG. 4 is a view showing a comparison result of ultrasonic permeability between a case where normal welding is performed by a test with a plate thickness of 10 mm and a case where magnetic stirring is performed with a magnetic frequency of 1 Hz in each welding position.

FIG. 5 is a diagram showing comparison results of ultrasonic permeability between a case where normal welding is performed by a test with a plate thickness of 10 mm and a case where magnetic stirring is performed with a magnetic frequency of 6 Hz in each welding position.

FIG. 6 is a diagram showing a comparison result of ultrasonic transmission between a case where normal welding is performed by a test with a plate thickness of 20 mm and a case where magnetic stirring is performed with a magnetic frequency of 6 Hz in each welding position.

FIGS. 7A and 7B show an ultrasonic inspection method of a base material at a position where there is no joint weld, wherein FIG. 7A is a side view and FIG.

8A and 8B show an ultrasonic inspection method for a base material at a position where a joint weld is interposed, wherein FIG. 8A is a side view and FIG. 8B is a diagram showing an example of an inspection result.

[Explanation of symbols]

 3 Base Material 4 Joint Groove 5 Joint Weld 5a Melt Pool 5b Weld Bead F Stirring Force

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuji Yasuda 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Toshibauchi Co., Ltd. (72) Inventor Kenji Hirano 1 Shin-Nakahara-cho, Isogo-ku, Yokohama-shi, Kanagawa Ishikawajima-Harima Heavy Industries Inside the Technical Research Institute Co., Ltd. (72) Inventor Norihiro Arakawa 1 Shinnakahara-cho, Isogo-ku, Yokohama-shi, Kanagawa Ishikawashima-Harima Heavy Industries Co., Ltd. (72) Inventor Iwaaki Tamaki 1515 Kamihamacho, Tsu-shi, Mie Pref.

Claims (2)

[Claims] In a magnetic stir welding method in which a molten pool formed in a joint groove of a base material is welded while applying a magnetic stirring force, a magnetic frequency for stirring the molten pool is 4 to 10 Hz. A magnetic stir welding method characterized by forming a joint weld. 2. The magnetic stir welding method according to claim 1, wherein the welding direction is changed every time one layer of a weld bead to be a joint weld is formed.