JPH06297182A - Welding method for high silicon electromagnetic steel sheets - Google Patents

Abstract

PURPOSE:To easily weld the high silicon steel sheets without causing a crack during welding. CONSTITUTION:A weld zone of the electromagnetic steel sheets l and 2 consisting of, by weight, 4.3-7.1% Si and having thickness of 0.07-0.8mm is heated to a preheating temperature of 150-600 deg.C to perform welding and after welding, the cooling speed while the weld zone is cooled from 150 to 5 deg.C is regulated to 0.1 to 2 deg.C/SEC.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention prevents the occurrence of lateral cracks at a low temperature in a welded portion when melt-welding a high silicon steel sheet in the production of a high silicon steel sheet or in the manufacture of an iron core such as a transformer or a motor. The present invention relates to a welding method for obtaining joint characteristics.

[0002]

2. Description of the Related Art Since a steel sheet containing Si has excellent soft magnetic properties, it is used as an iron core of a power converter or a rotating machine. In this kind of soft magnetic material, when the Si content increases, the iron loss characteristics are good and the magnetostriction approaches zero, so the magnetic permeability is further improved, and it can be a new magnetic material that has never existed before. In recent years, for the purpose of energy saving, Si has been used as a new magnetic material having a low iron loss value and capable of satisfying various magnetic property requirements of electric devices.
High silicon steel containing 5% or near 5% has begun to be reviewed.

Conventionally, for welding steel containing silicon, TIG welding, MIG welding, laser welding, and flash butt welding have been used particularly for coil joint welding during the production of silicon steel. For example, in Japanese Unexamined Patent Publication No. 56-19994, a heat source having a high energy density is used for butt welding a silicon steel strip containing 3.5 wt% or less of Si, or a silicon steel strip containing Al up to 1 wt%. Is used to limit the welding heat input to 10,000 J / cm ² or less.

However, when the silicon concentration exceeds 4.3 wt%, almost no plastic elongation is exhibited at room temperature. Therefore, if the conventional welding technique as described above is applied, the strain generated at the time of welding causes the welded portion to be welded at a low temperature. A crack will occur.
Here, the high silicon steel in the present invention has a silicon concentration of 4.3 wt.
% And 7.1 wt% or less of silicon steel, and the welded portion means a heat affected zone due to welding and a portion re-solidified after melting. At this time, normal fusion welding is possible with a silicon steel sheet whose silicon concentration does not exceed 4.3 wt%, and when the silicon concentration of the steel sheet exceeds 7.1 wt%, the soft magnetic properties begin to deteriorate and the elongation, etc. Since the processing characteristics at room temperature are extremely poor, it has no industrial value and is not a target of application of the present invention.

On the other hand, it is often attempted to prevent the occurrence of cracks by applying preheating and postheating during welding. For example, according to the laser welding method disclosed in Japanese Patent Laid-Open No. 61-79729, when butt-welding steel plates that are susceptible to weld cracking, each end of the butt-welding steel plates is continuously or immediately before welding until immediately after welding is completed. The temperature of the welded part and its vicinity immediately after welding is 80 ° C to
It is said that the temperature is maintained at 400 ° C., and then tempering heat treatment is performed.

However, the tempering temperature required for improving the weld properties is usually much higher than the preheating temperature,
As seen in the above patent specifications, the temperature is about 700 ° C. In order to perform post-heating at such a high temperature, not only a dedicated post-heating device is required, but also thermal strain occurs due to post-heating, and if this method is applied to welding in product processing, dimensional accuracy will deteriorate. Therefore, the product characteristics are deteriorated. Further, when post-heating at about 700 ° C. is performed, there is a problem that crystal grains grow unnecessarily in the welded portion and mechanical properties and magnetic characteristics of the welded portion deteriorate.

Regarding the welding of silicon steel, in Japanese Patent Laid-Open No. 62-61790, a part of the laser beam energy is used to remove the insulating coating before the welding and the energy of the laser beam welding after the welding. 55-7
It is said that 5% is used to irradiate the butt welded portion to prevent cracking of the welded portion and to improve bending strength.
However, the present invention is intended to prevent the occurrence of hot cracking due to the segregation of P, and is not considered to be useful for preventing cold cracking which is a problem in welding high silicon steel sheets. In fact, in this method, the silicon concentration exceeds 4.3 wt%,
Welding of high silicon steel with wt% or less could not suppress the occurrence of cracks in the weld.

Further, in Japanese Patent Laid-Open No. 63-220902, since a high silicon steel plate cannot be welded, one end of the weldable connecting plate is superposed on the high silicon steel plate to form a fastening member in connection with the leader strip. It is said that they are fastened and the other end is welded to the leader strip.

[0009]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above problems, and suppresses cracking at low temperature caused by strain generated in a welded portion, particularly when high-silicon steel is melt-welded. In addition, it is an object of the present invention to provide a welding technique that is economically excellent in that the weld heat affected zone is narrowed to obtain a weld close to the base metal characteristics, and that it can be applied to product processing in which thermal strain due to welding is a problem. .

[0010]

[Means for Solving the Problems] In high-silicon steel, there is no bainite or martensitic transformation in the weld zone and it becomes a ferrite single phase, so heat treatment such as preheating and postheating does not help prevent cracking in the weld zone. it is conceivable that. However, as a result of intensive studies by the present inventors, the plate thickness was 0.8
When welding high-silicon steel of mm or less, the temperature is maintained and maintained at a constant preheating temperature, welding is performed, and the cooling rate after welding is controlled to prevent cracking even if post-heat treatment at a significantly high temperature is not performed. We have found that we can get a good fitting.

That is, the weight ratio of Si: 4.3 to 7.1.
%, And the welded part of the electromagnetic steel thin plate having a plate thickness of 0.07 mm or more and 0.8 mm or less is heated to a preheating temperature of 150 ° C. or more and 600 ° C. or less to perform welding, and after welding, the welded part We propose a welding method for high silicon electrical steel sheet, characterized in that the cooling rate during cooling from 150 ° C to 50 ° C is 0.1 ° C / SEC or more and 2 ° C / SEC or less. Furthermore, if a laser beam is used as the welding heat source, the joint characteristics can be improved.

[0012]

The present invention will be described in detail below. Although the plastic elongation at room temperature of high silicon steel sheet which is a ferrite single phase is small, if the high silicon steel sheet is preheated to 150 ° C or more when welding, local heat input due to welding and subsequent solidification of molten metal will occur. The steel sheet can be deformed without cracking due to the stress caused by shrinkage. At this time, the preheating temperature is 60
If the temperature exceeds 0 ° C, not only the amount of heat required for preheating increases and it is uneconomical, but also the crystal grains of the welded portion become coarse and the mechanical properties and magnetic properties of the welded portion deteriorate.

Further, after the welding is completed, the welded part is cooled from 150 ° C. to 50 ° C. so that the cooling rate is 2 ° C./SEC or less so that a sound welded part without cracks can be realized. it can. Since it is not necessary to carry out post heat treatment at an extremely high temperature, it is possible to prevent deterioration of mechanical properties due to coarsening of crystal grains in the welded portion and deformation of the steel sheet due to occurrence of thermal strain. Further, the cooling rate is set to 0.1 ° C./SEC or more, because in order to achieve the cooling rate higher than this, the cooling time required is extremely long, which is not suitable for practical use.

Table 1 is a summary of the relationship between the preheating temperature, the cooling rate and the quality of the welded portion when welding the small motor iron cores 2a, 2b and 2c shown in FIG. 2 using the pulse oscillation YAG. is there. Weld quality was expressed as the presence or absence of cracks in the weld. Welding conditions: frequency 100Hz, pulse output 1J / pulse, pulse width 2msec, welding speed 1m / m
is in.

[0015]

[Table 1]

As can be seen from this table, when the preheating temperature was low, cracking could not be prevented even by slowing the cooling rate. On the other hand, when the preheating temperature was 175 ° C or higher, it was possible to realize a sound weld with no cracks by setting the cooling rate to 2 ° C / SEC or less.

The plate thickness of 0.07 mm or more depends on the restrained state when the plate thickness becomes thinner than this, but welding is essentially possible without applying the present invention. Was set to 0.8 mm or less because if the plate thickness becomes thicker than this, the strain associated with welding will increase, and it will be difficult to prevent the occurrence of cracks only by controlling the cooling rate.

If a heat source having a high degree of concentration such as a laser beam is used as the welding heat source, the heat input due to welding can be reduced, so that the mechanical properties of the welded portion deteriorate due to the coarsening of crystal grains. Also, the deterioration of magnetic characteristics can be suppressed to a minimum. For this reason, it is effective for preventing coil breakage during passing of the plate and for ensuring performance of a particularly small motor.

[0019]

【Example】

(Example 1) An example of welding a high silicon cold rolled steel sheet according to the present invention will be described below. The silicon content of the steel sheet used as a test material was 6.5 wt% in weight ratio, and two steel sheets having a thickness of 0.23 mm were butted and welded. Pulse oscillation type Y for welding heat source
A pulse frequency of 100 is used as welding conditions using an AG laser.
Hz, pulse energy 10 J / pulse, pulse width 2 mse
c, Welding speed of 1.5m / min is adopted.

In welding, the temperature of the steel sheet was raised to 150 ° C. and held, and then welding was performed. After the completion of welding, slow cooling was performed at a cooling rate of 0.5 ° C / SEC, and it was confirmed that no cracking occurred. The high silicon steel sheet that had been cold rolled was welded by the above method to form a coil, which could be passed without breaking the continuous steps of annealing and coating the insulating film.

(Embodiment 2) Here, welding of an EI core for a transformer will be described. FIG. 1 schematically shows an EI core to which the present welding method is applied. 1 in FIG. 1 is E
A high silicon steel plate having a plate thickness of 0.25 mm and punched in a square shape, and a certain number of the steel plates were stacked and TIG-welded at 3 in the drawing. The welding conditions were a welding current of 40 Amp, an arc length of 1 mm and a welding speed of 1 m / min, and no filler was added. During welding, the steel sheet 1 was heated to 200 ° C. in advance. After welding, cooling rate of 2 ° C / SEC could be realized by cooling.

The preheating temperature is preferably determined in consideration of the cooling method after welding. When it is easy to increase the preheating temperature as in this example, the preheating temperature is 150 ° C.
It is advantageous to set it higher. This is because by setting the preheating temperature higher, it is not necessary to heat the member after welding, and a cooling rate of 2 ° C / SEC can be easily achieved by paying a little attention to the heat retention of the member. is there.

Reference numeral 2 in FIG. 1 denotes an I-shaped member, and welding was performed at 4 in the drawing in the same manner as the E-shaped member. After winding the coils 6 and 7 around the E-shaped member 1 shown in FIG. 1, the I-shaped member 2 shown in FIG.
Welding is performed at a and 5b. The welding conditions at this time were exactly the same as those used for welding the E-shaped member. As a result, it was confirmed that cracks did not occur at the weld and its vicinity.

Although TIG welding was used in the above-mentioned embodiment, the welding method according to the present invention is not limited to this, and is effective in this type of welding method such as plasma welding and MIG welding.

(Embodiment 3) Here, an embodiment of the present welding method will be described by taking as an example the welding of an iron core for a small motor. Figure 2
Middle 1 is a stack of punched high silicon steel sheets.
Welding is performed by pulse Y after heating the entire member 1 to 150 ° C.
Welding was performed at 2a, 2b, and 2c using AG.
The welding conditions used were a frequency of 100 Hz, a pulse output of 1 J / pulse, a pulse width of 2 msec, and a welding speed of 1 m / min. After welding, member 1 was cooled at a cooling rate of 1 ° C / SEC. As a result, it was confirmed that cracks did not occur at the weld and its vicinity.

[0026]

When the welding technique according to the present invention is used in the production of high silicon steel, the efficiency and the yield can be improved, so that the steel material having excellent magnetic properties can be manufactured at low cost. In addition, the industrial value of the present invention is extremely high, because it can efficiently produce high-quality parts when used in product processing such as manufacturing of motor cores.

[Brief description of drawings]

FIG. 1 shows a transformer manufactured by applying the present invention using a high silicon electromagnetic steel sheet as a core.

FIG. 2 shows an iron core of a small motor manufactured by applying the present invention using a high silicon electromagnetic steel plate as a core.

[Explanation of symbols]

 1 E-shaped high silicon steel plate 2 I-shaped high silicon steel plate 2a to 2c Laser welded portion 3 to 5 TIG welded portion 6, 7 Copper wire

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toru Saito 20-1 Shintomi, Futtsu City, Chiba Shin Nippon Steel Co., Ltd. Technology Development Division (72) Inventor Shuji Kitahara 20-1 Shintomi, Futtsu City, Chiba Prefecture Iron & Steel Co., Ltd.

Claims (1)

[Claims] 1. A welded part of an electromagnetic steel thin plate containing Si: 4.3 to 7.1% by weight and having a plate thickness of 0.07 mm or more and 0.8 mm or less at 150 ° C. or more and 600 ° C. or less. While welding is performed by heating to a certain preheating temperature, the welded part is 1 after welding.
The cooling rate during cooling from 50 ° C to 50 ° C is 0.1
Welding method for high silicon electromagnetic steel thin plates, characterized in that the temperature is above ℃ / SEC and below 2 ℃ / SEC.