JP2000045025A - Production of rolled silicon steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a silicon steel capable of obtaining an extremely thin sheet excellent in magnetic properties by producing a sintered body having Fe-enriched phases and Si-enriched phases, subjecting this to cold rolling and executing annealing. SOLUTION: A binder is added to silicon steel powder, which is compacted, and debinder and sintering are executed to produce a sintered body having Fe-enriched main phases and Si-enriched solid solution phases. The sintering is executed at a temp. of about 1,000 to 1,150 deg.C in an inert gas atmosphere, in a gaseous hydrogen atmosphere, in a vacuum or the like, and, preferably, the content of oxygen in the sintered body is controlled to about 3000 ppm, the content of carbon to about <=200 ppm, the sheet thickness to about <=5 mm, and the degree of parallelization to about <=0.5 mm. This sintered body stock is cold-rolled and is thereafter annealed, the annealing temp. is controlled to about 1,200 to 1,300 deg.C as to a steel sheet sintered at a low temp. and high in a rolling ratio and is controlled to about 1,150 to 1,250 deg.C as to a steel sheet sintered at a high temp. and low in a rolling ratio, the Fe-enriched phases and Si-enriched phases are perfectly allowed to enter into solid solution, and the average crystal grain size is grown to about 0.5 to 3 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a rolled silicon steel capable of cold rolling a silicon steel having a Si content of 3 to 10% by weight, which is difficult to cold-roll, and relates to a method for producing a Fe-rich steel in advance. Prime Minister
Cold-rolling is possible by producing a thin plate-shaped sintered body with a thickness of 5 mm or less composed of Fe-Si phase and plastically deforming by utilizing the excellent ductility of Fe-rich phase crystal grains. And a method for manufacturing a rolled silicon steel from which a silicon steel sheet having excellent magnetic properties can be obtained.

[0002]

2. Description of the Related Art At present, most rolled silicon steel sheets widely used for various purposes such as iron cores of transformers and rotating machines, magnetic shielding materials, electromagnets, etc. are converted into silicon ingots having a Si content of 3 wt% or less in steel. It is manufactured by repeatedly performing steps of heat treatment, hot rolling, and annealing. It is known that the magnetic permeability of silicon steel becomes maximum when the Si content is about 6 wt%.
Rolling of a silicon steel containing 3 wt% or more has been conventionally difficult due to cracking during rolling.

[0003] For this reason, a method of adding a magnetic impurity such as Mn, Ni or the like to refine the average crystal grain size of a molten mass and performing rolling (K. Narit
a and M. Enokizono: IEEE.Trans.Mag. 14 (1978) 25
8) was also proposed, but there was a problem that these magnetic impurities deteriorate the magnetic properties of the silicon steel sheet, and it was not widely used.

[0004] In addition, a molten mass containing 3 wt% of Si in Fe is rolled in a conventional process, and then is subjected to a CVD (Chemical Vapor Deposition) method.
Impregnated with Si, silicon steel sheet having the desired composition, for example
Method for producing a silicon steel sheet having a Si content of 0.5 wt% (V. Takada,.
M.Abe, .S.Masuda and J.Inagaki: J.Appl.Phys. 64 (1
988) 5367.) Has also been proposed and implemented, but the CVD method requires a large number of steps, is costly, and its use is naturally limited.

[0005]

Generally, the molten mass of silicon steel containing 3 wt% or less of Si in steel consists of a phase in which Fe and Si are completely dissolved, and the plastic deformation due to rolling mainly depends on each type. It is caused by slip deformation in crystal grains.

However, when the Si content exceeds 3 wt%, Fe and
Since the crystal grains in which Si is completely dissolved are very hard and brittle,
Cracks and cracks occurred during rolling regardless of hot rolling or cold rolling, and the rolling itself was almost impossible.

[0007] The present invention is based on Si
With the aim of realizing the rolling of silicon steel whose content exceeds 3 wt%, a Fe-rich phase remains in the silicon steel before rolling,
By effectively utilizing the excellent ductility of the Fe-rich phase, the resulting silicon steel can be continuously and uniformly cold-rolled without repeating the heat treatment, hot rolling, and annealing processes of silicon steel as before. An object of the present invention is to provide a method for manufacturing rolled silicon steel, which is made possible.

[0008]

Means for Solving the Problems The inventors have found that the Si content is reduced.
In the rolling method of silicon steel sheet exceeding 3 wt%, in the silicon steel material before rolling, using a sintered body having a Fe-rich phase remaining, utilizing the ductility of crystal grains having a Fe-rich phase We thought that cold rolling would be possible by plastic deformation.

[0009] The inventors of the present invention have conducted various studies on rolled materials of silicon steel having good cold rollability based on the above idea, and have focused on the composition in the crystal grains. Unlike the crystal grains of the phase in which Si is completely dissolved, the sintered silicon has a Fe-rich phase and a mixed phase having a Si-rich Fe-Si solid solution phase, leaving a highly extensible Fe-rich phase. It is possible to roll by producing a steel sheet and cold rolling it, and in particular, it can be relatively easily rolled by setting the plate thickness of the steel material to 5 mm or less and the parallelism to 0.5 mm or less. Thus, the present invention has been completed.

[0010] Further, the present inventors have proposed a method for producing a sintered body,
By sintering a powder mixture of Fe powder and Fe-Si powder at a predetermined ratio by powder metallurgy, it is possible to produce a sintered body with a desired average crystal grain size. Is formed by metal injection molding, compaction molding, slip cast molding in a slurry state, etc., and then sintering at a predetermined temperature, or by hot forming such as hot pressing or plasma sintering It was found that can be adopted.

[0011] Further, the present inventors have found that in annealing after rolling, the Fe-rich phase and the Si-rich phase are completely dissolved, and the average crystal grain size is coarsened to reduce the coercive force, thereby improving the magnetic properties. In order to produce a rolled thin silicon steel sheet, it was found that if a small amount of Ti, Al, V, etc. were added in advance, the average crystal grain size was likely to become coarse during annealing after rolling, and the present invention Was completed.

[0012] That is, the present invention is to add a small amount of non-magnetic metal to the raw material, further produce a sintered silicon steel sheet having a Fe-rich phase and having a thickness of 5 mm or less, and then perform cold rolling and annealing. This is a method for producing a rolled silicon steel from which a very thin sheet having excellent magnetic properties can be obtained.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Raw materials used In the present invention, the components of the target silicon steel include:
A silicon steel characterized by having a required composition in which the content of Si in the steel is 3 to 10 wt%. That is, conventionally, since rolling cannot be performed at a Si content of 3 wt% or more, the subject of the present invention is Si.
Is 3 wt% or more, but if it exceeds 10 wt%, the magnetic flux density of the material is significantly reduced, and therefore, it is in the range of 3 to 10 wt%.

In the present invention, at the time of annealing after cold rolling,
In order to completely dissolve the Fe-rich phase and the Si-rich phase and promote the growth of crystal grains, the content of Ti, Al, V as an impurity element after sintering should be 0.01 to 1.0 wt%. , A rolled silicon steel sheet having good magnetic properties can be obtained, and the added components and the added amount may be appropriately selected according to the application. Ti, Al,
If the content of V is less than 0.01 wt%, the effect of grain growth is not sufficient, and if it exceeds 1.0 wt%, the magnetic properties deteriorate, so
The range is 1.0 wt%.

[0015] As such a raw material, more Si than desired composition
Is preferable, a gas atomized powder of an Fe-Si compound having a brittle fracture-prone component or a mixed powder obtained by blending a powder obtained by roughly pulverizing an ingot having the component into a jet mill and carbonyl iron powder at a predetermined ratio.

[0016] The Fe-Si compound used is a β phase
Fe ₂ Si compound, ε phase FeSi compound, and ζβ phase Fe
Si ₂ compounds are particularly preferred because they are susceptible to brittle fracture.

[0017] The Si content in the Fe-Si compound is 20 wt% to 5 wt%.
1 wt% is preferred. If the Si content exceeds this range, it becomes very easy to oxidize, cracks and cracks are apt to occur in the subsequent cold rolling, and the magnetic properties deteriorate.

When the average particle size of the Fe-Si compound powder is less than 3 μm,
Since the powder itself contains a large amount of oxygen and the sintered body is hard and brittle, cracks and cracks are easily generated during cold rolling, and magnetic properties are deteriorated. The average particle size is
If it exceeds 100 μm, the sintered body tends to be porous and the sintered density is lowered, which also causes cracks and cracks during cold rolling. Therefore the average particle size is 3-100μm
Is most desirable.

On the other hand, the carbonyl iron powder is preferably a commercially available powder having a particle size of 3 to 10 μm and having as small an oxygen content as possible. In any case, the oxygen content of the mixed powder of the Fe powder and the Fe-Si compound powder is preferably as small as possible, but is preferably at least 3000 ppm or less.

[0020] Silicon steel before rolling [0020] Powder metallurgy can be used to produce a sintered body before rolling. However, a sintered body by metal injection molding, powder compaction, slip casting or the like, or hot pressing or plasma sintering can be used. Production of a sintered body by hot forming such as sintering is suitable. Specifically, metal injection molding, compaction molding, and slip cast molding are methods in which a binder is added to silicon steel powder and molding is performed, and after molding, the binder is removed and sintering is performed. The hot forming method is a method in which a raw material powder is placed in a carbon mold, and pressure and pressure are applied during hot (1000 ° C. to 1300 ° C.) to simultaneously perform forming and firing.

[0021] The obtained sintered silicon steel is a mixed phase having a Fe-rich main phase and a Si-rich Fe-Si solid solution phase, in which a large number of Fe-rich phases rich in ductility are formed. . Here, the case where the amount of Si in the phase exceeds 6.5% is Si-rich,
The case not exceeding this is called Fe-rich.

In general, silicon steel powder containing a large amount of Si is very easily oxidized, and especially when a binder is used for molding, it is particularly oxidized or carbonized. It is essential. Further, since the oxidized or carbonized sintered body is hard and brittle, when cold-rolled, cracks and cracks are generated, and the magnetic properties after annealing are significantly reduced. For this reason, the amount of oxygen and the amount of carbon contained in the sintered body are desirably 3000 ppm and 200 ppm or less, respectively.

The sintering temperature varies depending on the components of the mixed powder, the average particle size, the molding density, etc., but is generally from 1000 ° C. to 1150 ° C. in an inert gas atmosphere, a hydrogen gas atmosphere, a vacuum or the like. It is good to select appropriately according to. However, if deformation during sintering is not prevented as much as possible, cracks and cracks may occur during cold rolling.

In particular, it is important to perform sintering at a temperature slightly lower than the original sintering temperature in order to leave a Fe-rich phase rich in ductility after sintering. During sintering, deformation during sintering is prevented as much as possible, and the parallelism for 50 mm length is 0.5 m
When it is suppressed to m or less, generation of cracks and cracks during cold rolling can be prevented.

Rolled silicon steel is hard and brittle compared to general metals, so the roll diameter for cold rolling and its peripheral speed need to be changed depending on the thickness before rolling and its parallelism. . That is, if the sheet thickness before rolling is large and the parallelism is poor, it is desirable to perform rolling at a small roll diameter and at a low peripheral speed.

However, conversely, if the plate thickness is small and parallelism is good,
This condition is considerably relaxed. In particular, in the case of hot rolling, since the silicon steel is easily plastically deformed, the conditions of the roll diameter and the peripheral speed are greatly relaxed as compared with the cold rolling. It is effective to perform hot rolling before cold rolling, but finally, if cold rolling is not performed, rolling of a thin plate becomes impossible. This is because the surface layer is oxidized and the magnetic properties deteriorate.

In the present invention, in the case of a silicon steel having a Fe-rich phase, in a silicon steel sheet having a sheet thickness before rolling of 5 mm or less and a parallelism of 0.5 mm (for a length of 50 mm) or less, the roll diameter is 80 mm or less, Under the condition of a roll peripheral speed of 60 mm / sec or less, cold rolling can be performed without an annealing step in the cold rolling and without cracks and cracks.

In the present invention, it is desirable that the silicon steel before rolling has an average crystal grain size of 300 μm or less and a plate thickness of 5 mm or less. If the thickness of the sintered body exceeds 5 mm, rolling stress (tensile stress) is applied only to the surface, and no stress is applied to the inside of the sintered body, so cracks occur, but if the thickness is 5 mm or less, The stress applied to the surface and the inside becomes uniform, and rolling becomes possible.

In the present invention, the thickness of the silicon steel sheet is 1 m
If the diameter is less than m, rolling with a roll having a smaller roll diameter will improve the rolling efficiency and the thickness dimensional accuracy, and also tend to prevent cracks and cracks.

[0030] In particular, when the Fe-rich phase of the silicon steel disappears and completely forms a solid solution, cracks and cracks occur during rolling regardless of the roll diameter and the roll peripheral speed. In addition, Si in silicon steel
If the content exceeds 10 wt%, it becomes difficult to leave the Fe-rich phase in the silicon steel, and almost all of the solid solution forms a solid solution, so that cracks and cracks always occur during cold rolling.

The silicon steel sheet rolled by the method of the present invention described above can be processed by a cutting machine or a punching machine after rolling, so that it can be applied to products of various shapes.

[0032] The rolled silicon steel sheet utilizing plastic deformation due to the Fe-rich phase according to the present invention has a direction in which the (100) plane has a texture unlike a normal oriented silicon steel sheet having a (110) plane as a texture. It has the characteristics of a conductive silicon steel sheet.

Annealing The annealing of the rolled silicon steel according to the present invention is performed to completely dissolve the Fe-rich phase and the Si-rich phase and to coarsen the crystal grains in order to improve the magnetic properties after the completion of the rolling. Things. In other words, conventionally, annealing of a rolled silicon steel sheet is always performed after rolling several times in order to prevent cracks and cracks during rolling, but in the present invention, a grain boundary which becomes an obstacle to domain wall movement is formed. It is intended to increase the crystal grain size for the purpose of reducing the coercive force and improving the magnetic permeability and reducing the iron loss.

[0034] The annealing temperature is determined by the rolling rate (= the thickness of the sheet after rolling).
/ Thickness before rolling x 100 (%)) and the sintering temperature of the sintered body during rolling. Annealing temperature is also affected by the additive and amount of non-magnetic elements, but for a steel sheet sintered at a low temperature and a high rolling rate, 1200 to 1300 ° C is suitable, and conversely, a high temperature A slightly lower temperature of 1150 to 1250 ° C. is suitable for a rolled steel sheet having a low rolling reduction in the steel sheet sintered in the above.

[0035] If the annealing temperature is too high, the crystal grains grow excessively and the steel sheet becomes very brittle, and if the temperature is too low, the Fe-rich phase and the Si-rich phase do not form a solid solution, and Since the crystal grains do not grow, the magnetic characteristics do not improve, so the above temperature is the optimum temperature.

[0036] By annealing at the above temperature, the Fe-rich phase and the Si
The rich phase is completely dissolved, and the average grain size is about 0.5.
Can grow to ~ 3mm. It was confirmed that the magnetic properties obtained by this annealing were similar to those of a normal ingot.

In the present invention, the rolled silicon steel sheet can be cut and punched, and can be manufactured in various shapes according to various applications. This has the advantage that a silicon steel sheet with dimensional accuracy can be manufactured.

Further, the rolled silicon steel sheet of the present invention is characterized by having a higher magnetic permeability and a higher magnetic flux density than an anisotropic silicon steel sheet because it is a directional silicon steel sheet having a (100) plane as a texture. .

[0039]

EXAMPLES Example 1 As a raw material powder of sintered silicon steel, F having the components shown in Table 1 was used.
An ingot was produced by high-frequency melting so as to become an e-Si compound, then coarsely pulverized and jet-milled to produce a powder having an average particle size as shown in Table 1. Also shown as iron powder
Carbonyl iron powder having the components shown in FIG. 1 and an average particle size was used.

[0040] The Fe-Si compound powder and the carponyl iron powder were blended in the ratio shown in Table 2, and then mixed with a V cone. A PVA (polyvinyl alcohol) binder, water, and a plasticizer were added to each of the mixed powders in the amounts shown in Table 3 to form a slurry. ℃, outlet temperature 40 ℃
And granulation was performed.

The granulated powder having an average particle size of about 100 μm was pressed into a shape as shown in Table 3 with a compression press at a pressure of ² ton / cm ² , and then, as shown in Table 4 in vacuum and hydrogen. Debinding,
Sintering was performed at the sintering temperature to obtain a sintered body having the dimensions shown in Table 5. Table 5 shows the content of the Fe-rich phase, the amount of residual oxygen, the amount of residual carbon, the average crystal grain size, and the relative density of the obtained sintered body. The content of this Fe-rich phase depends on the specific maximum X-ray diffraction intensity of FeSi compound and (1) of silicon steel having a body-centered cubic structure (bcc).
10) Relative evaluation was made based on the diffraction intensity ratio.

[0042] The sintered body having the dimensions shown in Table 5 was first cold-rolled to a rolling reduction of 50% at a roll peripheral speed of 60 mm / sec by a two-stage roll of 60 mmφ, and then further rolled at the same roll peripheral speed by a four-stage roll of 20 mmφ. At 0.10 mm. Table 6 shows the rolling state. In the rolling state in Table 6, ◎ indicates very good, Δ indicates good, Δ indicates occurrence of cracks on the end face of the rolled sheet, and × indicates occurrence of cracks on the entire surface.

Further, after rolling, a ring of 20 mmφ × 10 mmφ × 0.1 mmt was punched out and heat-treated at an annealing temperature as shown in Table 6, and then the DC magnetic characteristics and the iron loss at a frequency of 5 kHz were measured. Table 7 shows the results. As a comparative example of magnetic properties, F
Table 7 shows the magnetic properties of the ingots of e-6.5Si.

[0044]

【table 1】

[0045]

[Table 2]

[0046]

[Table 3]

[0047]

[Table 4]

[0048]

[Table 5]

[0049]

[Table 6]

[0050]

[Table 7]

[0051]

According to the present invention, a silicon steel sheet which has been conventionally difficult to manufacture can be manufactured by cold rolling, and an extremely thin silicon steel can be easily mass-produced. Further, a thin plate having excellent magnetic properties equivalent to that of a smelting material having an Si content of about 6 wt%, which has the highest magnetic permeability, can be obtained. Therefore, its applications will be dramatically expanded in a wide range such as transformers and yoke materials in the future.

The rolled silicon steel sheet according to the present invention can be cut and punched after rolling, and can be made into thin sheets of various shapes according to various uses. In addition, it is possible to produce a silicon steel thin plate with high dimensional accuracy.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) // B22F 3/24 C22C 33/02 L C22C 33/02 H01F 1/16 A (72) Inventor Masao Nomi 2-15-17, Egawa, Shimamoto-cho, Mishima-gun, Osaka Prefecture Sumitomo Special Metals Co., Ltd., Yamazaki Works

Claims (5)

[Claims] 1. A step of obtaining a sintered body having a Fe-rich phase and a Si-rich Fe-Si solid solution phase, a step of cold-rolling the sintered body material, and a step of annealing the cold-rolled material. A method for producing rolled silicon steel. 2. The method for producing rolled silicon steel according to claim 1, wherein the content of Si in the sintered body is 3 to 10% by weight. 3. The method for producing a rolled silicon steel according to claim 1, wherein the sintered body contains 0.01 to 1.0 wt% of Ti, Al, V alone or in combination as a minor component. 4. The sintered body according to claim 1, wherein the thickness of the sintered body is 5 mm or less.
4. A method for producing a rolled silicon steel according to claim 3. 5. A powder metallurgy method in which the sintered body is molded and sintered by powder injection molding, green compaction, or slip casting,
5. The method for producing a rolled silicon steel according to claim 4, wherein the sintered body is produced by a hot forming method such as hot pressing or plasma sintering, and has a Fe-rich phase remaining in the sintered body.