JPS62270724A - Production of grain oriented electrical steel sheet having high magnetic flux density - Google Patents

Abstract

PURPOSE:To execute slab heating at the temp. equiv. to the heating temp. of an ordinary steel and to provide an improvement of magnetic characteristics and shortening of finish annealing time by limiting the space between coil sheets and specifying the finish annealing conditions for the coils at the time of coiling a decarburization-annealed strip having a specific compsn. CONSTITUTION:The slab consisting of 0.025-0.075wt% C, 2.5-4.5% Si, 0.010-0.060% Sol Al, 0.0030-0.0130% N, S+0.405Se<=0.014%, 0.05-0.8% Mn, and the balance iron and inevitable impurities is heated and hot rolled at <1,280 deg.C. The space between the coil sheets is maintained at >=20mum or the strip is coiled at <=0.9g/cm<3> packing of a separating material for annealing essentially consisting of magnesia between said sheets at the time of cold rolling the hot rolled slab and coiling the decarburization-annealed strip. Such coil is subjected to finish annealing at <=30 deg.C/hr heating up rate by incorporating >=5% gaseous nitrogen into the atmosphere between the temp. from a 600-700 deg.C region to 800-900 deg.C region.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention particularly relates to a unidirectional 'IIF magnetic steel sheet with a high magnetic flux density.

[Conventional technology]

Unidirectional electrical steel sheet is a soft magnetic material mainly used for transformer cores. This type of steel sheet is made of crystal grains ((110) Cool
) orientation grain ) to! , 9, and the inclusion of St increases the specific resistance and reduces core loss due to Joule heat. On its surface, there is a few micrometers of 7-orsterite MgtSiO, which is produced by a solid phase reaction between StO selectively oxidized during decarburization annealing in the steel sheet manufacturing process and MgO coated on it during final annealing. It adheres thickly and plays the role of an insulating film, subdivides magnetic domains, and plays an important role in terms of magnetic properties. Usually, it is used as a transformer core after being coated with a secondary coating mainly made of colloidal silica for the purpose of adding tension. From this point of view, unidirectional electrical steel sheets are covered with crystal grains with (110)Cool) orientation in the rolling direction, and have a ceramic coating mainly composed of 7-orsterite and a secondary coating on the surface layer. It can be said that it is a material.

Now, (110) in such a unidirectional electrical steel sheet
(The achievement of a high degree of integration of the 0013 orientation and the formation of a 7-orsterite film, which is an oxide-based ceramic, usually occur at the same time during the 13ox annealing, which is called the final annealing. It is called recrystallization (1
10) Cool) Abnormal grain growth of oriented grains, the latter achieved by SiOt-MgO solid phase reaction on the steel plate surface,
Although these two reactions are essentially completely different phenomena, the actual reactions progress while indirectly interfering with each other.

As is well known, in order to cause secondary recrystallization, fine MnS, Ai!, etc. are added to the steel sheet before final annealing. It is necessary to suppress the normal grain growth of the sheath recrystallized grains by the presence of a precipitate such as N (usually called an inhibitor). And if secondary recrystallization is properly controlled, 9 (110) (00
1) Since the degree of accumulation of oriented grains is high, a high magnetic flux density can be obtained. A typical example of the manufacturing technology for such high magnetic flux density unidirectional electrical steel sheets is the 40-1 Special Publication by Satoru Taguchi et al.
Publication No. 5644 and Special Publication No. 51-13 by Taku Imanaka et al.
There is a method described in No. 469. In the former, MnS
In the latter case, MnS, MnBe, Sb, etc. are used as main inhibitors. Therefore, in current technology, it is essential to properly control the size, morphology, and dispersion state of these precipitates that function as inhibitors. Regarding MnS, in the current process, once MnS is completely dissolved during slab heating before hot rolling,
A method is used in which it precipitates during hot rolling. A temperature of about 140,000 is required to completely dissolve the amount of MnS required for secondary recrystallization. This is 2000C or more higher than the slab heating temperature of ordinary steel, and this high temperature slab heating treatment has the following disadvantages.

1) A high-temperature slab heating furnace exclusively for grain-oriented electrical steel is required.

2) The energy consumption rate of the heating furnace is high.

3) The amount of molten scale increases, which has a large negative impact on operations as seen in so-called slag scraping.

In order to avoid such problems, the slab heating temperature can be lowered to that of ordinary steel, but this also means that the amount of MnS, which is effective as an inhibitor, must be reduced or not used at all. This inevitably leads to destabilization of secondary recrystallization. Therefore, in order to realize low-temperature slab heating, it is necessary to strengthen the nitrogen inhibitor such as precipitates other than MnS in some way to sufficiently suppress normal grain growth during final annealing. In addition to sulfides, nitrides, oxides, grain boundary precipitated elements, etc. can be considered as such inhibitors, and examples of known techniques include the following.

In Japanese Patent Publication No. 54-24685, As%Bs%
Containing grain boundary segregation elements such as ph and Sb in steel
A method for heating the slab to a range of 1050 to 1350'C has been disclosed. In JP-A No. 52-24116, in addition to M, ZrXT1% B% Nbs”% V, C
A method has been disclosed in which the heating temperature of the cis-slab is made to range from 11° C. to 126° C. by containing nitride-forming elements such as R and Mo. Furthermore, in JP-A-57-158322, low-temperature slab heating is performed by lowering the Mn content and the Mn/S ratio is 2.5 or less, and secondary recrystallization is performed by adding Cu. A technology has been disclosed to stabilize the On the other hand, a technique was also disclosed in which improvements were made from the metal structure side in combination with reinforcement of these inhibitors. That is, in JP-A-57-89433, in addition to Mn, S
By adding elements such as , Be, Sb, Bi, Pb, Sn, B, etc., and combining this with the columnar crystallinity of the slab and the secondary cold rolling reduction ratio, low-temperature slab heating of 11°C to 1250'C is realized. are doing. Furthermore, JP-A-59-1903
Publication No. 24 discloses a technology to stabilize secondary recrystallization by forming an inhibitor mainly consisting of M, B, and nitrogen in addition to S or Ss, and subjecting it to pulse annealing during primary recrystallization annealing after cold rolling. was published. In this way, in order to realize low-temperature slab heating in the production of grain-oriented electrical steel sheets,
Great efforts have been made so far.

The present inventors previously disclosed in Japanese Patent Application Laid-Open No. 59-56522 a technique that enables heating of slabs at a lower temperature than K by reducing Mn to 0.08 to 0.45 and S to 0.007 or less. did. This essentially lowers the S to the left (M
The n:1(S) product was reduced to below the solubility product given by 120,000, and the stability of secondary recrystallization was supplemented by techniques such as adding P and setting the temperature increase rate during final annealing to below 15°C/hr. It is something.

This method was subsequently advanced in the direction of stabilizing the 92nd recrystallization and improving magnetism by adding Cr in Japanese Patent Application Laid-Open No. 59-190325.

[Problems to be solved by the present invention]

As mentioned above, many researchers have made great efforts to realize low-temperature slab heating in the production of magnetic steel sheets. However, K has not been reached until the actual manufacturing process has been drastically changed. The main cause of this is destabilization of secondary recrystallization due to insufficient function of the inhibitor that replaces Mns.

Even in the composition system found in JP-A-59-56522 and JP-A-59-190325 by the present inventors mentioned above, when final finish annealing is performed with a coil having a large unit weight of 10 to 20 tons, the coil A new problem has emerged: variations in magnetic properties in the width and length directions.

As a solution to these problems, the present inventors previously proposed in Japanese Patent Application No. 60-207757 a method of stabilizing the magnetic properties of the product by limiting the oxygen partial pressure and temperature increase rate of the atmosphere during finish annealing. Disclosed. However, with this method, the temperature increase rate during final annealing cannot be made sufficiently fast, and a new problem arises in that the time required for final annealing is long, which is economically undesirable.

[Failure to solve the problem]

The purpose of the present invention is to make low-temperature slab heating possible.
The problems mentioned above in Publication No. 56522, Publication No. 59-190325, and Japanese Patent Application No. 60-207757 are removed and improved, the secondary recrystallization that occurs during finish annealing is stabilized, and the magnetic flux density of the product is increased. The object of the present invention is to provide a finish annealing method that can be completed in a short time.

That is, the present invention has c: 0.02 s to 0.0 by weight.
75%, Si: 2.5-4.5%, acid-soluble Ag: 0.
010-0.060%, N: 0.0030-0.013
0%, S+ 0.40 s Be: 0.014%
Hereinafter, in the method of producing a unidirectional electrical steel sheet by a normal method after heating a slab containing Mn: 0.05% or more and 0.8% or less, annealing separation mainly consisting of magnesia is performed. When applying the material, we apply and dry an annealing separation material in the form of a slurry to limit the amount of application to a specific range, and then apply a fixed amount of magnesia using an electrostatic coating method. By adding a specific amount of ferromanganese nitride to the annealed separation material, secondary recrystallization of the low-temperature slab heating material of the corresponding component is sufficiently stabilized even in a coil with a large unit weight, and a material with high magnetic flux density can be obtained. Since these have become possible, these are considered as constituent factors of the present invention.

The present invention will be explained in detail below.

Figure 2 shows C: 0.06%, st: 3.3%, Mn:
0.2%, S: 0.004%, P: 0.03%, u:
o, o27%, N: 0.003%, (:'r: Q,
After decarburizing the cold rolled sheet containing 10% Tie in a wet hydrogen atmosphere.

An annealing separation material whose main component is magnesia containing 5 parts by weight of is applied, and a boundary line of N: 25% and H2: 75% is shown. Figure 3 shows the secondary recrystallization temperature of the corresponding material (approximately 1
The changes in the average crystal grain size determined by the JIS transverse method are shown from the gold phase photographs at around 000°C. From this experiment, nitrogen absorption during final annealing occurs in the temperature range of 7°C to 850'C, and materials that have sufficient nitrogen absorption in this range also have good secondary recrystallization that occurs around 1000'C. It turned out to be a material with excellent magnetic properties. We continued to investigate the form of nitrogen absorbed in steel. First, inclusions at each temperature during heating were extracted using the extraction replica method, and changes in the dispersion state of these inclusions were investigated using a transmission electron microscope, and the inclusions were identified. As a result, the nitrogen recovered is A
AN, (Si,Mn)-nitrides, (Si,
M) -nitrides were found to precipitate in large quantities, especially at grain boundaries. Comparison with gold phase photographs revealed that when the amount of precipitates precipitated at grain boundaries is large, normal grain growth is sufficiently suppressed and secondary recrystallization is stable. That is, by effectively using such a grain boundary precipitation type inhibitor, Mn
The present inventors have reached the knowledge that secondary recrystallization is stable even when S is not used as an inhibitor. For this purpose, it is necessary to absorb a large amount of nitrogen. For this reason, during final annealing, the temperature range from 6°C to 7000°C, where nitrogen absorption is possible, to 8°C to 900°C.
Japanese Patent Application No. 60-207757 makes it a necessary condition to heat up to a temperature range of 15°C at a slow temperature increase rate of 15°C/hr or less. For this reason, as mentioned above, the time required for final annealing was longer than in the conventional method.

After that, the inventors conducted experiments on a production scale using a coil with a large unit weight, and found that if the following conditions were met, the temperature increase rate would be 15 to 30.
The present invention was achieved based on the finding that secondary recrystallization is stabilized uniformly over the width and length directions of the coil even at ℃/hr. Necessary conditions are l) When winding the decarburized annealed plates into a coil, the distance between the coil plates should be 20 μm or more, or the filling rate of the annealing separating material between the coil plates should be 0.9F.
2) 6°C to 700°C during final annealing
The two points are that the atmosphere between the temperature range of from . In addition, methods for controlling the distance between the coil plates and the filling rate of the annealing separation material include changing the winding tension when winding the strip into a coil, and winding thread or wire between the plates. However, it has been found that a simple and accurate method for applying the annealing separation material is to use a dry electrostatic coating method in addition to the conventional wet coating method. Therefore, this method was made a requirement of the invention. Furthermore, when applying this annealing separation material, it is necessary to contain a specific amount of ferromanganese nitride in the material of the corresponding component system.
Since it is effective in stabilizing the subsequent recrystallization, this addition of ferromanganese nitride was made a part of the invention.

These points will be explained using FIG. 4.

This figure summarizes the changes in magnetism in the width direction of the coil when the magnesia powder application method, the addition of ferromanganese nitride, and the temperature increase rate from 6°C to 900'C during final annealing are changed. Here, the distance between the coil plates can be changed depending on the amount of annealing separation material applied, the application method, and the winding tension when winding the strip into a coil.

As can be seen from this figure, even when using the electrostatic coating method, the gap between the plates is 18 μm and the MgO filling rate is 941 μm.
/cm”, the temperature increase rate for final annealing is 128C/hr.
If the heating rate is relatively slow, the magnetism is stable in the width direction of the coil, but as the temperature rise rate increases, the magnetism at the center of the coil width deteriorates. However, as shown in Fig. 4(e), such deterioration of magnetism increases the distance between the coil plates, and
This problem can be solved by lowering the filling rate of go. The reason for this is that the nitrogen necessary to generate nitrides, which function as inhibitors, is supplied from the atmosphere outside the coil, and the gap between the coil plates, which serves as a diffusion path, is 2.
This is thought to be because it has an important meaning for the stability of subsequent recrystallization.

In addition, in order to smoothly progress nitriding, it is necessary to remove (Fe) on the outermost surface of the oxide film formed during decarburization annealing.

Mn)! It is desirable to reduce the 5i04 (fayalite) layer, so the oxygen partial pressure in the atmosphere between 600°C and 900°C is PH1°/pH, ≦fayalite
5 is desirable.

As mentioned above, the secondary recrystallization of the low-temperature slab heating material of the relevant component is stable across the width and length of the coil, and the magnetic flux density (expressed as BS) is 1 across the width and length of the coil.
．． It became possible to secure 92 (T) or more. Furthermore, the temperature increase rate for the final annealing time was changed to 25° (''/hr
By taking it to a certain extent, it can be shortened to the normal MnS,
MnBe or AI! It is not much different from the final annealing of high-temperature slab heating materials containing inhibitors mainly composed of N and the like.

Next, the reasons for limiting the constituent elements of the present invention will be described.

If C is less than 0.025% by weight (hereinafter simply referred to as "C"), secondary recrystallization becomes unstable, and even when secondary recrystallization occurs, the magnetic flux density is B, t, 80 (T) L. Therefore, it was set to 0.025% or more. On the other hand, if there is too much C, the decarburization annealing time will be long and it is not economical, so 0.07
It was set to 5% or less. If Si exceeds 4.5 inches, cracking during cold rolling will become significant, so the Si thickness was set to 4.5 inches or less. Also, 2.5%
If it is less than 2.5%, the specific resistance of the material will be too low and the low core loss required as a transformer core material cannot be obtained, so it is set to 2.5% or more. It is preferably 3.2 inches or more. M and N are MN or (Si, At) necessary for stabilizing secondary recrystallization
0 as acid soluble M to ensure n1trides
．． 0.010% or more is required. Acid soluble M is o, og
If it exceeds o, the ALN of the hot-rolled sheet becomes inappropriate and the cylindrical recrystallization becomes unstable. Regarding N, it is difficult to make it 0.0030 S or more in normal steelmaking work, and it is economically undesirable to make it less than this, so 0.0030 S or more, and 0.01
If it exceeds 30%, blister formation on the surface of the steel sheet occurs, so it was set to 0.0130% or less.

AjN or (Si, AX) n1tride which is considered to have an important role in the present invention
Mn S + Mn which is an inhibitor other than s
Even if S e is present in the steel, secondary recrystallization can be stabilized by changing the nitriding treatment during final annealing. Therefore, in principle, there are no restrictions on Mn1S$Be from the point of view of secondary recrystallization. However, if S and Be are high, secondary recrystallization defects called linear fine grains tend to occur, and if nitriding is sufficient to prevent the occurrence of secondary recrystallization defects ( It is desirable that S+0.405 Be)≦0.014% or less. If the S or Be content is higher than this, the nitriding process will be difficult.
Even if n1trides are made in steel to strengthen the inhibitor, the probability of secondary recrystallization defects is high, which is not preferable. Further, the amount of 7-eromanganese nitride required for nitriding treatment, the time required for final annealing, etc. increase, and from this point of view, it is meaningless to unnecessarily increase S or Be.

The lower limit of Mn is 0.05%. If it is lower than this, the edge shape of the hot rolled sheet will be poor and the yield will be degraded. but,
From the viewpoint of forming a good 7-orsterite film, Mn is (0.05+7 (S+0.405Be))1
The above is desirable. That is, the inventors
As detailed in Application No. 59-53819, MgO-Sin, which is a reaction for forming a forsterite film,
MnO plays a catalytic role during the solid phase reaction. To ensure the necessary Mn activity in the steel, K is
S and Be in steel to be trapped in the form of nS or MnBe: More than a certain amount of Mn is required for t, and from this point of view, Mn is [0,05+7 (S+0.405
Be)) Desirably 1 or more. If the Mn content is less than this amount, the adhesion of the 7-orsterite film, which has a large crystal grain size, will deteriorate to some extent. However, usually a secondary coating mainly composed of colloidal silica is added on top of this forsterite film to produce a product, and this does not pose a problem in actual use.

If Mn is less than this value, the film deteriorates and secondary recrystallization becomes unstable, which is not preferable. The upper limit of Mn is 0
．． It was set at 8%. If Mn t increases further than this, the magnetic flux density of the finished product will deteriorate, which is undesirable.0 Slab heating temperature is because the original purpose of the present invention is to change the slab heating temperature of grain-oriented electrical steel sheet to that of ordinary copper plate. , was limited to less than 1280°C. Preferably 11
The temperature is below 50°C.

The reason for the limitation regarding nitride 7 z Romanganese, Mn1-x F”xNyK is described below.The content of Fe is x>0.8
If this happens, the dissociation temperature of nitrogen will be too low, making it difficult to achieve the original purpose of ensuring nitrogen partial pressure during final annealing, so X≦8 must be satisfied.

Furthermore, even if x=Q, that is, pure manganese nitride, it is sufficiently effective against secondary recrystallization. From this, it is assumed that the amount of Fe is in the range of Oxx≦0.8. The amount of nitrogen and the range of y were determined for the following reasons. If y<o, ot, as is clear from the consideration based on the phase diagram in Figure 1, the nitride will almost exclusively be a (Mn, Fe)-N-order solution;
Either the necessary nitrogen partial pressure cannot be secured, or the decomposition temperature is too low to make it practical as an additive. Further, nitrides with y≧0.6 are either difficult to produce or the existence of such nitrides under atmospheric pressure has not been confirmed. On the other hand, the patent application
Mn-F by the present researchers described in detail in No. 5827
From the experimental results and considerations of the phase equilibrium theory of the e-N system, this system has ζ-Mn, , N-type, ζ-Fe, N-type, δ
It is known that there are at least three phases having a -Fe4N type crystal structure, and y=0.43.0.50.0.25, respectively. (At the dormitory, each phase is spread with some degree of non-stoichiometry.) Therefore, (
M"1-zFex) Ny (0,01≦y<0.
The compound represented by s) is most generally expressed as (M
It can be said that it is a mixture composed of the n,Fe)-N-order solution and any of the three or more phases described above.

Considering the above points, the Mn 1-z Fe z of the present invention
The composition range of Ny is the region shown by ABCD in Figure 1 (
A(0% o, o i >, B(0,0,6), C(0,
8,0,6), D (area surrounded by (0,8,0,01)) Ic is limited.

After decarburization annealing, an annealing separation material mainly composed of magnesia is applied and when wound into a coil, the interval between the coil plates is 20 μm or more, and the magnesia filling rate between the plates is 0.9 f/
cm" or less. If this range is exceeded, the supply of gas, especially nitrogen gas, between the coil plates will be insufficient, and when the temperature increase rate during final annealing is increased, the central part in the width direction of the coil may The probability of occurrence of secondary recrystallization defects due to lack of inhibitor increases.During final annealing, the atmosphere between the temperature range of 6°C to 700°C to the temperature range of 8°C to 900'C is at this temperature. Because nitrogen absorption progresses during this period, it must contain 5 or more nitrogen.The heating rate during this period must be 30°C/hr or less.If it is faster than this, nitriding will not proceed sufficiently. t12 recrystallization temperature is reached, and as a result, a secondary recrystallization failure area occurs.The starting and ending temperature ranges during finish annealing that define the above are 6°C to 700°C and 8°C to 900°C, respectively. The reason was l)
The temperature at which nitrogen absorption begins and ends varies slightly depending on the material composition, decarburization annealing conditions, the type of magnesia used as an annealing separation material, and the type of additives.
2) The temperature distribution inside the 10-ton or 20-ton coil is large, and the temperature difference inside the coil is usually more than 100'C, making it impossible to ensure a uniquely uniform heating rate across all parts of the coil. This is due to two reasons.

evening.

There are various methods for achieving the above-mentioned ranges such as widening the gap between the coil plates and filling rate of the annealing separator mainly composed of magnesia, but the most reliable and effective method is to apply it in the form of a slurry. This is a method in which the amount of annealed separation material to be dried is kept below a certain amount, and electrostatically coated magnesia is applied thereon. These amounts will vary slightly depending on the winding tension when winding into a coil, but in order to satisfy the above conditions, the wet coating amount by coating and drying in a slurry form should be increased to 1 to 1 on both sides. 12 g/m2, and the coating amount by dry electrostatic coating on top of that needs to be in the range of 6 to 2097 m''.If these values are smaller, the gap between the coil plates necessary for gas diffusion will be If it is not secured or there is too much, it is not economically meaningful.

〔Example〕

Example 1: C: 0.055%, Si: 3.25%,
Mn: o, t 7%, P: 0.025%, S:
0.008%, oxidation solubility Aj: 0.029%, N
: Molten steel containing 0.0080% was made into a steel ingot by continuous casting. This slab was heated to a temperature of 1150'C and then hot rolled.2. I made OTM hot-rolled sheets. After annealing this hot-rolled plate for 1120'CX 2 min,
It was cold rolled to a final thickness of m and decarburized annealed in wet hydrogen at a temperature of 8300C. After this, Mg containing 4% TiO2
After applying O in the form of a slurry and applying and drying it and electrostatic coating method, the amount shown in Table 1 was deposited, and then wound into a coil to form a 10 ton coil. At this time, except for some coils, Mlo, 80F80.2O was added to the slurry powder.
N0.26 was added. The spacing between the plates at this time and the filling rate between the coil plates of the annealed separation material calculated based on this are also shown in the same table. These coils were heated with N between temperatures of 620°C and 870°C at a heating rate of 23°C/hr.

Finish annealing in 20%H280% atmosphere 1200'02
After holding for 0 hours, the mixture was cooled in the furnace. The magnetic permeability of the widthwise central part of the obtained coil and the upper part of the coil are shown in Table 1 in the form of B.

Below, the width between the coil plates, the filling rate of the annealing separation material, and the 7-eromanganese nitride work effectively to prevent variations in the magnetic properties of Yunichi products, especially the deterioration of the magnetic properties at the center in the width direction of the coil. I can see that you are raising your level.

Example 2 c: o, o 59%, Si: 3.33%, Mn:
0.09%, p: 0.02 s%, s: o,
o 12%, acid soluble AI: 0.026%, N: 0
．． The 0070% t-containing molten steel was made into a steel ingot by a continuous casting method. This slab was heated to a temperature of 1180° C. and then hot-rolled to obtain a hot-rolled plate having a thickness of 2.0 mm. This hot-rolled sheet was annealed at 1100'CX 2.5ml1n, then cold rolled to a final plate thickness of 20cm sail, and decarburized annealed in wet hydrogen at a temperature of 850'C.

This board 11C'l'iQ! 3-chi nitride fluorocarbon M
nO,? 5 Fe0.25 No, Mg containing 7 pieces of 25
After applying O in the form of a slurry and drying it, use the electrostatic coating method! +
MgO was applied to create a 5 ton coil. This coil is made of nitrogen 25% hydrogen 75% dew point -10℃ (PH, o/PH
.

= 0.004) in an atmosphere of 600'C to 900°C
Final annealing was performed at a temperature increase rate of 18° C./hr. Table 2 shows the average value and standard deviation of the magnetic properties of the obtained steel sheets.

It can be seen that variations in the magnetic properties of the finished product are reduced depending on the width between the coil plates and the filling rate of the annealing separation material between the coil plates.

[Effects of the Invention] As described in detail above, the present invention has the advantage that the high-temperature heating peculiar to the production of grain-oriented electrical steel sheets during slab heating prior to hot rolling can be carried out at the temperature of an ordinary copper plate. In addition to eliminating the need for a dedicated slab heating furnace for grain-oriented electrical steel sheets,
The manufacturing cost is greatly reduced due to the reduction in energy consumption and the reduction in the generation of slag, and along with the improvement in magnetic properties, there are enormous industrial benefits.

[Brief explanation of the drawing]

Figure 1 is a provisional phase diagram of the Mn-Fe-N ternary system at room temperature, Figure 2 is a diagram showing the increase in nitrogen in the steel during final annealing, and Figure 3 is the diagram used in Figure 2. 1000 of the same sample as
It is a figure showing the change of the average crystal grain size in the vicinity of 8C. Figure 4 shows the variation in magnetism in the width direction of the coil due to an increase in temperature increase rate during final annealing from 8 to -1.
Between the coil plates! !

Claims (1)

[Claims] 1. C: 0.025 to 0.075% by weight, Si: 2.
5-4.5%, acid-soluble M: 0.010-0.060%
, N: 0.0030-0.0130%, S+0.405
, Be: 0.014% or less, Mn: 0.05 to 0.8%
After heating a slab containing iron with the balance consisting of Fe and unavoidable impurities at a temperature below 1280°C, hot rolling, cold rolling, decarburization annealing in a wet hydrogen atmosphere, and application of an annealing separation material mainly composed of magnesia. In the method of creating unidirectional electrical steel sheets using the usual method of finish annealing, when winding the decarburized annealed strip, the distance (spacing) between the coil plates is 20 μm or more, or the magnesia between the plates is The filling rate of the main annealing separation material is 0.9 g/cm^3 or less,
When final annealing the coil created in this way, 60
One characterized in that the atmosphere between the temperature range of 0°C to 700°C to the temperature range of 800°C to 900°C contains 5% or more of nitrogen gas, and the temperature increase rate is 30°C/hr or less. A method for manufacturing grain-oriented electrical steel sheets. 2. Once the annealing separation material mainly composed of magnesia is made into a slurry, it is coated and dried so that the wet coating amount (undercoat coating amount) is in the range of 1 to 12 g/m^2 on both sides of the steel plate, and then The method according to claim 1, characterized in that magnesia is dry-electrostatically applied in an amount of 6 to 20 g/m^2 per both surfaces. 3. Ferromanganese nitride (Mn_1_-_xFe_xN_y) with a composition corresponding to the area surrounded by points A, B, C, and D shown in Fig. 1 in an annealed separation material mainly composed of magnesia.
The method according to claim 1 or 2, characterized in that 0.2 to 20 parts by weight of these are added alone or in a mixture.