JP3482221B2 - Manufacturing method of strip-like ultrahigh silicon electrical steel sheet - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention efficiently uses a super high silicon magnetic steel sheet used as a soft magnetic material for an iron core of an electric device.
The present invention also relates to a stable manufacturing method.

[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 transformer or a rotating machine. In this kind of soft magnetic material, the iron loss characteristic is improved (the iron loss value is lowered) as the Si content increases. In particular, when the Si content is around 6.5%, the iron loss characteristics are good, and the magnetostriction approaches zero, so that the magnetic permeability is further improved, and it can be a magnetic material having a new function that has never been seen before.

In recent years, as a new magnetic material having a low iron loss value and capable of satisfying various requirements for magnetic properties of electric equipment for the purpose of energy saving, ultra high silicon containing 6.5% or near Si. Steel has begun to be reviewed. However, since the ultra-high silicon steel sheet is extremely brittle, it has many problems in industrial mass production and has not yet been put into practical use.

The first technical problem in industrially mass producing ultra-high silicon electromagnetic steel sheets is that when the ultra-high silicon electromagnetic steel strips are run on various processing lines, the strips are broken or cracked. Is a problem.

Conventionally, industrial mass production of electromagnetic steel sheets has been carried out by a series of steps in the manufacturing process of hot rolled sheets or cast strips, such as pickling line, cold rolling mill, degreasing line, annealing line and insulating film coating line. It is made by passing through the processing line. The passing capacity and configuration of these processing lines are designed to maximize production efficiency. Therefore, it is possible to industrially mass-produce the ultra-high silicon steel sheet only after it can be passed through these processing lines.

By the way, in these processing lines, there are many places where the strip is bent, and bending stress is generated in the strip at these bent portions. The ultra-high silicon magnetic steel sheet has an elongation at room temperature of only about 0.5%, and it is extremely difficult to pass through the treatment line because it breaks or cracks at the location where the bending is applied. Therefore, a hot rolled plate or a cast thin plate of ultra-high silicon steel cannot be pickled even in a normal line.

Even if the ultra-high silicon magnetic steel sheet is pickled by some method, it cannot be attached to the tension reel during rolling because of the low elongation of ultra-high silicon at room temperature as described above. For this reason, as for the method of attaching to the tension reel, Japanese Patent Publication No. 63-22
Japanese Patent No. 0902 proposes a method in which a leader strip made of a metal material having excellent workability is connected to both ends of an ultra-high silicon steel sheet, and the leader strip is attached to a tension reel.

According to the present invention, since the ultra-high silicon steel sheet cannot be welded, the leader strip and the ultra-high silicon steel strip are fastened and connected via a connecting plate. However, in the connecting method disclosed in the present invention, a thick plate portion is formed at the connecting portion between the leader strip and the ultra high silicon steel sheet strip. For this reason, when wound around a tension reel, unnecessary bending stress is applied to the ultra-high silicon steel sheet at the connection portion having a different plate thickness, and the ultra-high silicon steel is broken at the connection portion during rolling and may be cracked in some cases. There was a problem.

Further, when the rolled ultra-high silicon electromagnetic steel strip is annealed and passed through an insulating film coating line, the ultra-high silicon steel sheet is connected to the ultra-high silicon steel sheet at a connecting portion having a different thickness at a portion where the strip is bent. There was a problem that excessive bending stress was applied and the ultra-high silicon steel was broken or cracked.

The second technical problem in processing the ultra-high silicon steel sheet in a strip state and performing industrial mass production is a material (strip) generated when the ultra-high silicon steel sheet is hot-rolled or cold-rolled. It is a strip edge crack called fracture or harshness. Edge cracks are generated by hot rolling even in magnetic steel sheets that currently contain about 3% by weight and are mass-produced. However, if such hot rolled sheet is cold rolled as it is, edge cracks develop and strip breakage occurs. Will cause. For this reason, a strip edge that causes an edge crack in a state after hot rolling is cut (edge cut) with a round blade.
However, since the ultra-high-silicon electrical steel sheet is inferior in cold workability, when the edge is cut by this method, the strip edge is rather cracked.

By the way, even in the currently mass-produced silicon electromagnetic steel sheets, if the cold workability is relatively poor, a method of raising the temperature of the cutting portion with a burner or the like before cutting may be used. However, if this method is applied to ultra-high-silicon electrical steel sheets, the temperature at which cracks can be prevented becomes high, which significantly shortens the life of the round blade and increases the frequency of round blade replacement, thus increasing productivity. However, there was a problem that

[0012]

DISCLOSURE OF THE INVENTION The present invention provides a method for making extremely brittle ultra-high silicon electrical steel sheet capable of being rolled so that various processing lines can be passed therethrough, thereby enabling industrial mass production. With the goal.

[0013]

The gist of the present invention is as follows. The first invention is, by weight ratio, C ≤ 0.006%, Si: 4.3 to 7.1%, S ≤ 0.007%, total N ≤ 0.0035%, and the balance: Fe and unavoidable impurities. Both ends of the hot rolled plate or cast thin plate have a surface
Scale in a state attached to the ultra-high-silicon steel welds
Was connected by welding a leader strip heated to below the preheating temperature of 600 ° C. 175 ° C. or higher, after welding 0.99 ° C. or less
Hold for 0.5 minutes or more and 10 minutes or less at the above temperature, and make the cooling rate slower as the holding time approaches the lower limit within the range of 0.1 ℃ / SEC or more and 100 ℃ / SEC or less. After cutting the side edge of the strip obtained after cooling by adjusting the retention time and cooling rate to (laser cutting),
A method for producing a strip-shaped ultra-high silicon electromagnetic steel sheet, characterized in that warm rolling is performed while the scale is still attached to the surface . A second invention is the first invention, wherein the side end portion of the strip is A method for producing a strip-shaped ultra-high silicon magnetic steel sheet, characterized in that the cutting is replaced by laser cutting and water jet cutting (edge cutting) is performed.

The present invention will be described in detail below. The first technical problem that must be solved when industrially mass-producing an extremely brittle ultra-high silicon steel sheet is to pass through various treatment lines without causing breaks and cracks in the strip. The second technical problem is to prevent the material (strip) from breaking during cold rolling.

As a method for solving the above-mentioned various problems of the prior art at once, the inventors directly warm-rolled a hot-rolled plate made of ultra-high silicon steel to reduce the plate thickness. After that, it was considered to pass it through various treatment lines such as a pickling line.

Therefore, first, the inventors tried to butt-weld a super-high silicon steel hot-rolled sheet with the scale adhered to the surface thereof with a leader strip having a thickness approximately the same as this hot-rolled sheet. It was However, in the welded part of the ultra-high silicon electrical steel sheet, lateral cracks occur at low temperature during cooling,
It was not possible to connect the leader strip to the ultra-high silicon magnetic steel sheet by the usual welding method.

The inventors of the present invention have conducted extensive studies and have carried out ultra-high silicon steel welding.
Part is heated to a preheating temperature of 175 ° C. or more and 600 ° C. or less to weld the leader strip, and after welding, the temperature is maintained at 150 ° C. or more for 0.5 minutes or more and 10 minutes or less. The cooling rate is 0.1 ℃ / SEC or more and 100 ℃ / SEC or less,
It was confirmed that by increasing the cooling rate as the holding time becomes longer, the occurrence of cracks in the welded part can be prevented.

Hereinafter, this knowledge will be described in detail. Elongation at room temperature of ferrite single-phase ultra-high silicon steel sheet is small, but if it is heated above the toughness transition temperature at which sufficient elongation can be expected in advance, local heat input by welding and subsequent solidification and shrinkage of molten metal It can be expected that the steel material can be welded without cracking even when stress is generated. Since the toughness transition temperature is about 150 ° C. for Si: 4 to 7.1 wt% steel, it is considered that preheating at 150 ° C. or higher is necessary. Experiments show that the minimum required preheating temperature is Si:
It was 175 ° C. in 4.3 to 7.1 wt% steel.

At this time, if preheating over 600 ° C. is performed,
Not only is it uneconomical, but because the growth of crystal grains occurs and the mechanical properties of the weld deteriorate, the preheating temperature is 60
It shall be 0 ° C or lower. However, this preheating alone could not prevent lateral cracking that occurs at low temperature during cooling.

Therefore, as a result of further study, the occurrence of cracks in the welded portion can be prevented by maintaining the temperature near the preheating temperature even after welding, managing the cooling rate after completion of the retaining operation, and completing the connection process. I was able to. The reason why the retention and the control of the cooling rate after the completion of the retention are effective in preventing the occurrence of cracks is not yet clear, and the following examples will be explained.

Table 1 shows the irradiation output of 4 kW after preheating to 200 ° C.,
This shows the quality of the welded portion when the cooling rate was changed after laser welding was performed at a welding speed of 4 m / min. The test materials used were Si: 6.23% and C: 0.0 by weight.
03%, Mn: 0.17%, P: 0.005%, S:
It is a hot-rolled steel sheet with a scale of 0.001%, total N: 0.0015%, the balance being substantially Fe and having a thickness of 2 mm.

[0022]

[Table 1]

When the holding time is 1 minute, the cooling rate is 2 ° C./SEC or less, the same 5 minutes, the same 20 ° C./SEC or less, and the same 10 minutes, the same 10
It was possible to prevent cracking at 0 ° C / SEC or less. Table 1
From this, it is understood that the cooling rate can be increased if the retention time is increased. By the way, when the retention time is 1 minute,
Reducing the cooling rate after the end of retention to less than 0.1 ° C./SEC is uneconomical because it takes too much time, and the retention time of 10 minutes or more is meaningless.

By the way, since the holding time required for preventing the occurrence of cracks is as long as 0.5 minutes or more, the holding is not necessary only for making the temperature distribution of the welded portion uniform, and the metallurgical reaction is required. Is effective for causing In fact
In laser welding, the temperature distribution in the welded portion is uniform about 0.5 minutes after the laser irradiation is completed.

Further, conventionally, it has been said that it is necessary to remove the scale at the time of welding, because the scale at the portion to be welded causes a welding defect such as a blowhole. However, in the ultra-high silicon steel sheet, the scale did not cause welding defects.

Further, the holding temperature does not necessarily have to be exactly the same as the preheating temperature unless it is lower than 150 ° C.
Almost the same effect can be obtained by making the holding temperature extremely higher or lower than the preheating temperature. However, in order to make the holding temperature extremely higher or lower than the preheating temperature, a considerable heating device or cooling device is required, which is uneconomical. Therefore, it is desirable to set the holding temperature to a temperature near the preheating temperature. .

Further, this result is almost the same in plasma welding, TIG welding, and MIG welding regardless of the welding method. In order to perform warm rolling after connecting the leader strip to the ultra-high silicon magnetic steel sheet by the above-mentioned welding method, it is necessary to prepare the ultra-high silicon magnetic steel sheet strip edge that has been roughened by hot rolling.

Therefore, as described in the prior art, when a cutting with a round blade was tried, a cutting surface that could not withstand rolling was obtained after cutting for about 10 m. It is considered that this is because the scale on the surface of the ultra-high silicon steel plate worked as an abrasive and the life of the round blade was remarkably shortened. That is, it has been clarified that the edge cutting with the round blade is usually performed after the pickling, but the edge cutting with the round blade cannot be industrially performed on the steel plate with scale targeted by the present invention. As a result of repeated studies by the inventors, it has been clarified that laser cutting or water jet cutting can obtain edge-cutting quality that can withstand rolling.

Hereinafter, this finding will be described in detail. As disclosed in Japanese Patent Laid-Open No. 55-70492, slag or dross is likely to remain in the lower part of the cutting groove in laser cutting of a silicon steel sheet. In the above patent, the cutting gas is made to flow coaxially with the laser gas, and the same gas is made to flow from behind the cutting portion. Here, the dross adhesion was avoided by setting the supply pressure of the gas flowing coaxially with the laser light to be high. Table 2 shows the dross adhesion state when cutting was performed at a laser irradiation output of 1.5 kW and a cutting speed of 1 m / min. At this time, the diameter of the cutting nozzle hole was 1.5 mm and the gap between the nozzle and the steel plate was 1 mm. It can be seen that nitrogen is a wider cutting gas than oxygen, and a wider range of conditions can be cut without dross sticking.

[0030]

[Table 2]

By the way, if a large amount of dross adheres during cutting,
In the laser cutting, there is a problem that the strip breaks during rolling, the peeled dross mixes with the rolling oil, or the dross adheres to the rolling rolls, causing scratches on the surface of the rolled material. The absence of dross attachment is a necessary condition for cutting the edge.

Further, when a steel plate having a constant thickness is cut by using a water jet, if the cutting speed is too fast, a trag line (periodic undulations peculiar to water jet cutting) occurs on the lower surface of the cutting surface to smooth the cutting surface. It gets worse.
If the cutting speed is slowed down, a smooth cut surface can be obtained, but if the cutting speed is too slow, the cutting width of the lower surface becomes wider than the cutting width of the upper surface. Then, it was clarified that there exists an optimum cutting speed that can obtain a smooth cut surface with equal upper and lower cutting widths.

That is, as shown in Table 3, the plate thickness is 1.8.
The cutting width for water jet cutting of ultra high silicon electromagnetic steel sheet of mm is 5 to 15% of the limit cutting speed (maximum cutting speed for cutting a given steel sheet), so that the cutting width of the upper and lower surfaces in the plate thickness direction is It was possible to obtain the same and a good cut surface shape. Furthermore, only by selecting such cutting conditions, strip breakage could be prevented in rolling.

[0034]

[Table 3]

Next, the warm rolling of ultra-high silicon steel with scale attached to the surface will be described in detail. Normal,
In the silicon steel manufacturing process, the hot-rolled sheet is subjected to pickling to remove surface scale, and then cold-rolled. According to conventional knowledge, for example, Japanese Patent Publication No. 59-289 and Japanese Patent Publication No. 60-
As disclosed in Japanese Patent No. 40921, when a hot-rolled plate having a scale attached to its surface is directly cold-rolled,
The scale is crushed and peeled off, which has been a problem, and such rolling has not been performed on an industrial mass production scale.

The inventors have developed ultra-high silicon strips from 150 to
We have discovered an epoch-making phenomenon that rolling in the temperature range of 450 ° C. allows rolling without any peeling of the scale on the surface of hot rolling. By weight ratio, Si: 6.52%, C: 0.
003%, Mn: 0.16%, P: 0.005%, S:
0.001%, total N: 0.0013%, balance: 50 kg steel ingot consisting essentially of Fe is heated to 1200 ° C., and then finish hot rolling is started at 800 ° C., and 2.3 in 6 passes.
mm thickness. The rolling finishing temperature was 690 ° C.

For this coil, with the surface scale still attached, material temperature: 1) room temperature (about 23 ° C.), 2) 15
It rolled at 0 degreeC, 3) 270 degreeC, 4) 440 degreeC. Table 4 shows the cracking state of the material (strip) and the degree of peeling of the surface scale at this time.

[0038]

[Table 4]

When rolled at room temperature, the surface scale is crushed and peeled off significantly, and the peeled scale may be mixed with rolling oil or adhered to the rolling rolls, resulting in scratches on the surface of the rolled material. occured. Rolling temperature is 150 ℃, 2
When the temperature was raised to 70 ° C. and 440 ° C., crushing and peeling of the surface scale were completely eliminated, and rolling was performed smoothly.

As described above, when rolling was carried out at 150 to 450 ° C. in a temperature range which is usually performed, it was possible to carry out warm rolling without scale peeling even in a state with surface scale . At this time, the leader strip was connected according to the procedure described above, and the strip was wound on a tension reel and rolled using this, but when laser welding and plasma welding were used as the welding method, it was possible to roll including the welded part. , Was effective in increasing the yield.

In the conventional general strip processing equipment, the diameter of the bent portion of the strip is about 200 mm in most cases. Whether or not the ultra-high silicon electromagnetic steel strip can be passed through such equipment is considered to depend on the thickness of the steel sheet. Therefore, the effect of the bending diameter on the number of times of bending until cracking occurred at room temperature was investigated for the 0.5 mm thick strip obtained by the warm rolling method. For comparison, as-finished hot-rolled 2.0
The same investigation was carried out for a mm-thick hot rolled steel sheet and a steel sheet warm-rolled to a thickness of 1.2 mm by warm rolling.

Table 5 shows the results. 0.5 mm from Table 5
It can be seen that the ultra-high silicon magnetic steel sheet warm- rolled to a thickness has sufficient mechanical properties to pass through conventional strip processing equipment.

[0043]

[Table 5]

Further, according to the present invention, since the leader strips are connected to both ends of the ultra high silicon steel sheet strip, the leader strip can be easily welded to other steel sheets when passing through the conventional strip processing equipment. It is convenient. That is, according to the present invention, it is possible to roll an ultra-high silicon steel sheet in a strip state and reduce the thickness of the steel sheet so that it can be passed through various treatment lines such as pickling.

[0045]

【Example】

(Example 1) Si: 6.51%, C: 0.0 by weight ratio
04%, Mn: 0.16%, P: 0.005%, S:
0.001%, total N: 0.0013%, balance: 5000 kg steel ingot consisting essentially of Fe is heated to 1200 ° C. and then finish hot rolling is started at 1090 ° C., and it is 1.8 mm thick in 6 passes. It was a strip of fish. Rolling finishing temperature is 9
It was 70 ° C.

The weight ratio of Si:
A 1.8 mm thick leader strip containing 3.2% was butted and laser welded. A carbon dioxide laser oscillator was used as the laser oscillator. At this time, the abutting end faces were formed by laser cutting using an irradiation output of 1.5 kW, a cutting speed of 1 m / min, and nitrogen as a cutting gas.

In welding, the welded portion was heated to 200 ° C. in advance and kept at the same temperature, and then laser butt welding was performed at an irradiation output of 1.8 kW and a welding speed of 1 m / min. After welding, it was held at 200 ° C for 5 minutes, and after the holding, it was left to cool to a cooling rate of 2 ° C / SEC to complete the connection process.

With the leader strip thus connected, the irradiation output was 1.5 kW, the cutting speed was 1 m / min, and the strip edge was 1 from the edge using nitrogen as the cutting gas.
Laser cutting was performed at a position of 0 mm. In this state, the leader strip was used to wind the strip on a tension reel, and the strip was rolled at a plate temperature of 200 ° C. to a thickness of 0.325 mm including the connecting portion with the leader strip while the scale was kept. Then, pass through a long pickling line with a total length of about 70 m, and further with an annealing line with a total length of about 100 m at 820 ° C x
It was annealed at 30 SEC.

Further, using a rolling roll polished with a # 1000 grindstone, it was rolled at room temperature (about 25 ° C.) to a thickness of 0.30 mm, passed through a degreasing line, and coated with a chromic acid type insulating film. A product free from cracks was obtained in rolling, pickling, annealing and coating line passing. The magnetic properties of this electromagnetic steel sheet are B ₈ = 1.36T, W _10/50 =
0.69w / kg, W10 / ₄₀₀ = 9.8w / kg, and the occupancy rate was also good. Note that the surface after final annealing has R _a = 0.8.
μm, R _max = 8.0 μm.

(Example 2) Si: 6.53 by weight ratio
%, C: 0.003%, Mn: 0.17%, P: 0.0
04%, S: 0.001%, total N: 0.0013
%, Balance: 5000 kg steel ingot consisting essentially of Fe
After heating to 200 ° C., finish hot rolling was started at 1100 ° C., and a strip having a thickness of 1.8 mm was formed by 6 passes. The rolling finishing temperature was 980 ° C.

The weight ratio of Si:
A 1.8 mm thick leader strip containing 3% was butted and plasma welded. Plasma welding condition is welding current 2
00 Amp, nozzle hole diameter 2 mmφ, nozzle steel sheet distance (standoff) 1 mm, welding speed 1 m / min. At this time, the butted end faces were formed by hot shear cutting. In addition, at the time of welding, the welded portion is heated to 200 ° C. in advance, kept at the same temperature, and plasma-welded.
It was held at 0 ° C. for 5 minutes, and after the holding was completed, it was left to cool to cool at a cooling rate of 2 ° C./SEC to complete the connection process.

With the leader strip thus connected, the water pressure was 3000 kgf / cm ² , the nozzle diameter was 1.2 mm,
Under the cutting conditions of a distance between nozzles of 2 mm and a cutting speed of 3 m / min, the strip edge was water jet cut at a position 10 mm from the edge. At this time, # 60 as an abrasive
Garnet sand of.

In this state, the strip is wound around the tension reel by using the leader strip, and the plate temperature is set to 2
It was rolled to a thickness of 0.325 mm including the connecting portion with the leader strip at 00 ° C with the scale attached. afterwards,
Through a long pickling line with a total length of about 70 m, and a total length of about 1
Annealing was performed at 820 ° C. × 30 SEC on a 00 m annealing line.

Further, by using a rolling roll polished with a # 1000 grindstone, it was rolled to a thickness of 0.30 mm at room temperature (about 25 ° C.), passed through a degreasing line, and coated with a chromic acid type insulating film. A product free from cracks was obtained in rolling, pickling, annealing and coating line passing. The magnetic properties of this electromagnetic steel sheet are B ₈ = 1.35T, W _10/50 =
0.68w / kg, W10 / ₄₀₀ = 9.8w / kg, and the occupancy rate was also good. Note that the surface after final annealing has R _a = 0.8.
μm, R _max = 8.0 μm.

[0055]

Industrial Applicability According to the present invention, it is extremely brittle, and it is difficult to mass-produce industrially because it causes material cracking in cold rolling and material breakage or cracking in a bent portion when passing through a processing line. An ultra-high silicon electromagnetic steel sheet is warm-rolled in a striped state and is used industrially on a processing line that has been conventionally generally used for producing an electromagnetic steel sheet, without causing material breakage or cracking in a bent portion. Since it can be mass-produced, the industrial value of the present invention is very high.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI H01F 1/16 H01F 1/16 A (72) Inventor Shuji Kitahara 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Co., Ltd. Within the Development Headquarters (72) Inventor Yozo Suga 20-1 Shintomi, Futtsu City, Chiba Nippon Steel Co., Ltd.Technical Development Headquarters (72) Inventor Toshiya Kuroki 20-1 Shintomi, Futtsu City, Chiba Nippon Steel Co., Ltd. ceremony Corporate Technology Development Division (56) Reference JP-A-5-293684 (JP, A) JP-A-61-79729 (JP, A) JP-A-63-220902 (JP, A) (58) Fields investigated ( Int.Cl. ⁷ , DB name) C21D 8/12 C21D 9/46 501 C22C 38/00-38/60 B21K 3/02 B23K 31/00 H01F 1/16

Claims (2)

(57) [Claims] 1. C: 0.006% by weight, Si: 4.3 to 7.1%, S ≤ 0.007%, total N ≤ 0.0035%, balance: Fe and inevitable impurities Both ends of the hot rolled plate or cast thin plate have a surface
Scale in a state attached to the ultra-high-silicon steel welds
Was connected by welding a leader strip heated to below the preheating temperature of 600 ° C. 175 ° C. or higher, after welding 0.99 ° C. or less
Hold for 0.5 minutes or more and 10 minutes or less at the above temperature, and make the cooling rate slower as the holding time approaches the lower limit within the range of 0.1 ℃ / SEC or more and 100 ℃ / SEC or less. After cooling by adjusting the holding time and cooling rate, the side edge of the obtained strip is laser-cut (cutting), and then warm-rolled with the scale still attached to the surface. A method for manufacturing a strip-shaped ultra-high-silicon electrical steel sheet. 2. C: 0.006% by weight, Si: 4.3 to 7.1%, S ≤ 0.007%, total N ≤ 0.0035%, balance: Fe and inevitable impurities Both ends of the hot rolled plate or cast thin plate have a surface
Scale in a state attached to the ultra-high-silicon steel welds
To a preheating temperature of 175 ° C. or higher and 600 ° C. or lower to weld the leader strip, and after welding, hold at a temperature of 150 ° C. or higher for 0.5 minutes or more and 10 minutes or less, and set the cooling rate after holding to 0.1. In the range of ℃ / SEC or more and 100 ℃ / SEC or less, connect the ultra-high silicon steel and the leader strip so that the cooling rate becomes slower as the holding time approaches the lower limit.
A method for producing a strip-shaped ultra-high silicon electrical steel sheet, which comprises performing water jet cutting (edge cutting) on a side end portion of the thus-produced strip, and then performing warm rolling with the scale still attached to the surface .