JP6844110B2 - Manufacturing method of grain-oriented electrical steel sheet and manufacturing method of original sheet for grain-oriented electrical steel sheet - Google Patents

Description

The present invention relates to a manufacturing method for obtaining a unidirectional electrical steel sheet having improved film adhesion and rust resistance.

Normally, a two-layer film is formed on the surface of a unidirectional electromagnetic steel sheet, and tension is applied to the steel sheet to improve the magnetic properties as a single sheet and between the steel sheets when laminated to form a magnetic member. The insulation is improved to improve the magnetic efficiency of the members. Of the films, the glass film, which is the base film on the mother steel plate side, is an oxide mainly composed of forsterite, which itself contributes to tension application and insulation, but ensures the adhesion of the upper insulation film. Has an important role. Regarding this glass film, it is known that the structure of the glass film in the formed state such as unevenness, roots, and film thickness is closely related to the adhesion.

In addition, when products are delivered to overseas customers, they are often stored for a long period of time in a harsh transportation environment for steel sheets such as temperature and humidity. As a result, rust or the like is generated, and there are often concerns from consumers about not only the appearance but also the magnetism of the product. This has low adhesion of the film, and there are problems such as slight cracks that occur in the film when handling the product board, and it also functions as a protective film from a wet environment such as the density and uniformity of the film against moisture permeation. It becomes important.

As an existing technique relating to a glass film, for example, in Patent Document 1 (Japanese Unexamined Patent Publication No. 62-156226), a hydrated layer is formed by treating only the outermost layer of MgO fired at a high temperature in a gas phase to form an MgO. There is a technical disclosure that the insulation property is improved by increasing the reactivity of the above and reducing the water content. Further, as a means for improving rust resistance, in Patent Document 2 (Japanese Unexamined Patent Publication No. 9-256164), when forming a film mainly composed of aluminum borate on the steel surface, alkali metal compounds and alkaline earth metal compounds are used. A technique for adding one or two of them and a mixture of a rare earth metal compound and one or more of zirconium and hafnium is disclosed.
However, in these conventional techniques, there is room for improvement in both tension (magnetic characteristics), adhesion, and rust resistance.

Japanese Unexamined Patent Publication No. 62-156226 Japanese Unexamined Patent Publication No. 9-256164

An object of the present invention is to provide a method for producing a unidirectional electrical steel sheet and a method for producing an original sheet for grain-oriented electrical steel sheet, which controls the structure of the glass film and has both applied tension, adhesion and rust resistance. To do.

The present inventor examined the relationship between the manufacturing process and the film properties, and found that heat treatment as a pretreatment for decarburization annealing may improve adhesion and rust resistance. Further examination of the pretreatment conditions in detail revealed that the properties related to the film were improved, especially when the heat treatment was performed for a short time at a high dew point. And this effect changes the morphology of the oxide layer formed in the whole decarburization annealing, especially when the oxidation behavior at the initial stage of oxidation during decarburization annealing is changed, and it becomes the morphology of the glass film formed in the subsequent finish annealing. It was thought to be due to the influence. Considering the means to carry out this heat treatment industrially, it was found that the same effect can be obtained by raising the temperature of decarburization annealing at a high dew point and rapid heating, and then performing the initial decarburization at a low dew point and a high temperature for a short time. After confirmation, the present invention was completed. Specifically, it is as follows.

( 1 )
A forsterite-based film having an average particle size of 0.6 μm or more and 2.0 μm or less is provided between the insulating film and the mother steel sheet, and the standard deviation of the forsterite particle size distribution of the forsterite-based film is A method for manufacturing a unidirectional electromagnetic steel sheet having a size of 0.6 μm or less.
One-way manufacturing by hot-rolling steel slabs, annealing hot-rolled plates if necessary, cold-rolling to final product thickness, decarburization annealing, nitriding annealing if necessary, final finish annealing, insulation coating treatment In the manufacturing process of sex electromagnetic steel sheets, the temperature rise by decarburization annealing is performed at an atmosphere of PH ₂ O / PH ₂ : 0.65 to 3.0, a heating rate of ≥100 ° C / s, and a heating temperature of ≥800 ° C. The decarburization was continued with the residence time at 750 ° C. or higher ≤ 5 seconds, and the atmosphere P (H ₂ O) / P (H ₂ ): 0.25 to 0.6, the maximum temperature reached Y: 700 to. 900 ° C., residence time ≦ 4 seconds at Y-30 ° C. greater, characterized in that as in a residence time ≧ 10 seconds at Y-30 ℃ ~Y-85 ℃ after maximum temperature, unidirectional Manufacturing method of electromagnetic steel plate.

( 2 )
The surface of the base steel sheet has a forsterite-based film with an average particle size of 0.6 μm or more and 2.0 μm or less, and the standard deviation of the forsterite particle size distribution of the forsterite-based film is 0.6 μm. The following method for manufacturing a unidirectional electromagnetic steel sheet original plate.
Original plate for unidirectional electromagnetic steel plate manufactured by hot-rolling a steel slab, annealing the hot-rolled plate if necessary, cooling it to the final product thickness, decarburizing and annealing, nitriding and annealing if necessary, and final finish annealing. In the manufacturing process of, the temperature rise by decarburization annealing is _{adjusted to P (H 2} O) / P (H ₂ ) in the atmosphere: 0.65 to 3.0, heating rate ≥ 100 ° C / s, heating temperature ≥ 800. It was carried out at ℃ or higher, and the residence time at 750 ℃ or higher was ≤5 seconds, and then decarburization was continued with P (H ₂ O) / P (H ₂ ) in the atmosphere: 0.25 to 0.6, and the maximum temperature reached Y. : The period of stay at 700 to 810 ° C. and above Y-30 ° C. ≤ 4 seconds, and the residence time at Y-30 ° C. to Y-85 ° C. after reaching the maximum temperature ≥ 10 seconds . Manufacturing method of original plate for unidirectional electromagnetic steel plate.

According to the present invention, a unidirectional electrical steel sheet having a dense and uniform glass film and having both applied tension, adhesion and rust resistance, a master plate for unidirectional electrical steel sheet, and a method for producing the same can be obtained.

It is a figure which shows the glass film structure.

Hereinafter, embodiments of the present invention will be described.
(Product features)
As an observation example of the steel of the present invention, FIG. 1 shows an example of observing the surface structure of the steel sheet in the conventional steel and the invention steel (the right figure is the conventional steel and the left figure is the invention steel). In FIG. 1, an annealing separator was applied to a decarburized plate in which the temperature of decarburization annealing was raised at a dew point of 80 ° C. or 0 ° C. at a heating rate of 180 ° C./s or 50 ° C./s, and finish annealing was performed. It is the surface structure of the steel sheet after it is carried out. The surface of the steel sheet is covered with a glass film formed by the reaction of _{the SiO 2-based oxide formed by decarburization annealing and MgO contained in the applied annealing separator.}

Although the details are unknown, it is considered that such a change in the glass film is caused by a change in the morphology of oxides such as _{SiO 2 formed on the surface layer of the decarburized plate due to oxidation during decarburization.} Regarding the decarburized plate, the amount of oxygen by gas analysis does not change significantly to about 1000 ppm regardless of the dew point and heating rate. However, the decarburized plate having a high dew point and a high heating rate _{tends to have a thicker oxide layer in which oxides such as SiO 2} are present, and the form of the oxides tends to be complicated. It is considered that such a change was caused by the rapid introduction of oxygen to the surface of the steel sheet in the high temperature state in the heat treatment at a high temperature, and as a result, the oxidation behavior was changed. It is believed that such changes in the oxide film on the decarburized plate contribute to the formation of a dense and uniform structure of the glass film formed by finish annealing as a result. The reason why the fineness and uniformity of the glass film affects the adhesion is not always clear, but when the particle size of the glass film becomes small and it is formed of dense and uniform forsterite, the interface between the glass film and the mother steel sheet It is expected that the micro-concavities and convexities will be fine and uniform, the contact area will increase, the stress concentration during steel plate deformation will decrease, and the peeling resistance will improve. Denseness is considered to be an important factor for controlling the film characteristics, in addition to the depth of macro unevenness at the interface between the glass film and the mother steel sheet, which has been known and controlled in the past, and the thickness of the film itself. ..

With such a glass film, not only the applied tension is large and it contributes to the improvement of magnetic characteristics, but also the adhesion of the glass film to the mother steel plate is high, and the adhesion of the insulating film applied on the glass film is also improved. As a result, an insulating film that generates high tension can be applied, and defects such as cracks in the film can be avoided, and moisture permeation can be suppressed to improve rust resistance.

In the present invention, the product plate (unidirectional steel sheet) has an intermediate product (unidirectional steel sheet) having a film mainly composed of forsterite having a particle size of 2.0 μm or less between the insulating film and the mother steel sheet. The original sheet) is characterized by having a film mainly composed of forsterite having a particle size of 2.0 μm or less on the surface of the base steel sheet.

Here, the "film mainly composed of forsterite" is generally called a "glass film", and in the present invention, it may be simply described as a "glass film". The glass film is composed of a composite oxide such as _{forsterite (Mg 2} SiO ₄ ), spinel (Mg Al ₂ O ₄ ), or cordierite (Mg _{2 Al 4} Si ₅ O _16). The details will be described later, but the glass film is a film formed to prevent seizure of the steel sheet in the finish annealing step, which is one of the manufacturing processes of the unidirectional electromagnetic steel sheet.

In the present invention, including these unavoidably formed composite oxides, a "forsterite-based film" is defined, and in the observation of the film, what is observed as the particle size is "forsterite particle size". ".

In the present invention, "mainly forsterite" means that the ratio of forsterite in the film is 50% or more. The method for confirming the ratio of forsterite is that when the particle size observation surface of the film is mapped for Mg, Mn, Si, Al, and O by SEM-EDS, Mg, Si, and O are detected at the same time (Al and Mn are also detected). The area (which may be) is determined to be "forsterite", and when the area ratio of this area is 50% or more, it is determined to be "mainly forsterite". There is no particular regulation on the content and form of spinel, cordierite, etc. that are not judged to be forsterite.

In the product, this glass film is formed between the insulating film formed on the upper layer and the mother steel sheet. This configuration itself is not particularly newly defined in the present invention, but is a general configuration.

The insulating film contains, for example, colloidal silica and phosphate, and plays a role of imparting not only electrical insulation but also tension, corrosion resistance, heat resistance and the like to the steel sheet. This is also not particularly limited in the present invention, and any known insulating film may be used.

Of particular importance in the present invention is the form of the glass film. In the present invention, the average particle size of the glass film is 2.0 μm or less. It is preferably 0.01 to 1.5 μm, more preferably 0.05 to 1.0 μm. This is small compared to normal glass film particles of around 5 μm. In the present invention, it is considered that the tension, adhesion, and rust resistance are improved by increasing the density and uniformity of the glass film, and therefore, the finer the thickness, the more preferable. On the other hand, practical atmosphere control and heating rate control become difficult, so the lower limit is set to 0.01 μm or 0.05 μm.

The standard deviation of the particle size distribution shall be 0.6 μm or less. This is because the glass film has a more dense structure, moisture permeation from the atmosphere after steel sheet production is suppressed, and rusting from the mother steel sheet is suppressed. It is preferably 0.4 μm or less, more preferably 0.2 μm or less.

Here, the glass film structure is as follows: For unidirectional electromagnetic steel sheets (product plates), for steel sheets from which the insulating film on the surface has been peeled off, for unidirectional electromagnetic steel sheets (intermediate product plates), for steel sheets immediately after finish annealing. Observe the glass film on the surface with SEM.

The insulating film is, for example, a grain-oriented electrical steel sheet having an insulation coating, NaOH: _10% by mass ₊ H 2 O: to 90% by weight aqueous sodium hydroxide, 15 minutes at 80 ° C., washed immersed in. Finally, it can be removed by a method of drying with a warm air blower for a little less than 1 minute. As for the glass film surface observed on the steel sheet after the insulating film is peeled off in this way, the state of the glass film before forming the insulating film is observed almost as it is with respect to the characteristics specified in the present invention. That is, the state of the glass film obtained on the product plate in the present invention is achieved in the steel sheet after finish annealing, which is an intermediate product before forming the insulating film.

The particle size is determined as the equivalent circle diameter by a general line segment method or image processing that traces the grain boundaries with an SEM image. The standard deviation is calculated by a general calculation method for obtaining the square root of the variance.

(About mother steel plate)
The unidirectional electromagnetic steel sheet of the present invention is a grain steel sheet (material steel) whose crystal orientation is controlled so that the easily magnetized axis of the crystal grains and the rolling direction coincide with each other by a combination of cold rolling treatment and annealing treatment. , A glass film formed on the surface of the mother steel sheet and an insulating film formed on the surface of the glass film are provided.

The base steel plate has chemical components such as C: more than 0% to 0.003%, Si: 2.5% to 4.0%, acid-soluble Al: 0% to 0.065%, N. : 0% to 0.003%, Mn: 0% to 3.0%, Cr: 0% to 0.3%, Cu: 0% to 0.4%, P: 0% to 0.5%, Sn : 0% to 0.30%, Ni: 0% to 1%, S: 0% to 0.030%, and the balance is composed of Fe and impurities.

The above chemical component is a preferable chemical component for controlling the crystal orientation to a Goss texture integrated in the {110} <001> orientation. Among the above elements, Si and C are basic elements, and acid-soluble Al, N, Mn, Cr, Cu, P, Sn, Ni and S are selective elements. Since the above-mentioned selective element may be contained according to its purpose, it is not necessary to limit the lower limit value, and the lower limit value may be 0%. In addition, even if an element known as a known technique is contained as the selective element, or even if these selective elements are contained as impurities, the effect of the present embodiment is not impaired. In the above-mentioned mother steel sheet, the balance of the above-mentioned basic element and selective element may be composed of Fe and impurities. The term “impurity” means an element that is inevitably mixed with ore as a raw material, scrap, or the manufacturing environment when the base steel sheet is industrially manufactured.

C causes magnetic aging and deteriorates magnetic properties, so it should be 0.003% or less. Although the effect of the present invention is not lost even if it does not exist, the lower limit is preferably 0.0001% from the viewpoint of reduction cost.

The amount of Si added should be 2.5% or more in order to increase the natural resistance and improve the iron loss characteristics. However, it is an oxidative element, and it is preferably 4.0% or less in order to appropriately control the oxidation behavior at the initial stage of decarburization annealing, which is a feature of the present invention.

Acid-soluble Al is an element that is contained in a trace amount as an impurity, so it is difficult to completely eliminate it. Practically, it is 0.003% or more. If it is contained at 0.065% or more, the adhesion of the glass film is lowered.

Since N is an element that is contained in a trace amount as an impurity, it is difficult to completely eliminate it. Practically, it is 0.0030% or less. If it is contained in excess of 0.030%, it becomes difficult to obtain a dense and uniform glass film.

Mn increases the intrinsic resistance and improves the iron loss characteristics. It does not have to be contained at all, but the content that functions as a practical precipitate is 0.01% or more and less than 3.0%. If it exceeds 3.0%, γ transformation occurs during finish annealing and inhibits good secondary recrystallization.

Cr is an element effective for improving the oxide film of decarburization annealing and forming a glass film, and is added in the range of 0.3% or less. If it exceeds 0.3%, the adhesion of the film will be adversely affected.

Cu is an element effective in increasing the natural resistance and reducing the iron loss. If the amount added exceeds 0.4%, the iron loss reduction effect will be saturated and it will cause surface defects such as "copper hesitation" during heat spreading.

If the amount of P added exceeds 0.5%, there is a problem in rollability.

With respect to Sn, depending on the finish annealing conditions, Al is oxidized by the water released from the annealing separator and the inhibitor strength changes. Therefore, the magnetic characteristics may fluctuate due to the difference in coil position. As one of the countermeasures, there is a method of preventing oxidation by adding an element that easily causes grain boundary segregation. Therefore, Sn can be added in the range of 0.30% or less. On the other hand, if it exceeds 0.30%, it is difficult to be oxidized during decarburization annealing, the formation of a glass film becomes insufficient, and the decarburization property is significantly inhibited.

Ni is an element that is effective in increasing the natural resistance and reducing iron loss, and is an element that is effective in controlling the metallographic structure of the hot-rolled plate and improving the magnetic properties. However, if the amount added exceeds 1%, the secondary recrystallization becomes unstable.

S may not be contained at all, but is preferably contained in an amount of 0.0030% or more and 0.030% or less. A dense and uniform glass film, which is also a feature of the present invention, cannot be obtained. It does not have to be contained at all, but since it is an element that is contained in a trace amount as an impurity, it is difficult to completely eliminate it, and it is practically 0.0001% or more.

In addition, electrical steel sheets generally undergo purification annealing during secondary recrystallization. In the purification annealing, the inhibitor-forming element is discharged to the outside of the system. In particular, the concentrations of N and S are significantly reduced to 50 ppm or less. Under normal purified annealing conditions, it reaches 9 ppm or less, further 6 ppm or less, and if purified annealing is sufficiently performed, it reaches a level that cannot be detected by general analysis (1 ppm or less).

The chemical composition of the mother steel sheet may be measured by a general method for analyzing steel. For example, the chemical composition of the mother steel sheet may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrum). Specifically, by measuring a 35 mm square test piece from the center position of the steel sheet 2 after removing the film with a Shimadzu ICPS-8100 or the like (measuring device) under conditions based on a calibration curve prepared in advance. Can be identified. In addition, C and S may be measured by using the combustion-infrared absorption method, and N may be measured by using the inert gas melting-thermal conductivity method.

(About the manufacturing method)
Next, a method for manufacturing the unidirectional electromagnetic steel sheet according to the present embodiment will be described. Needless to say, the steel sheet of the present invention is not limited to the steel sheet obtained by the following manufacturing method.

The steel of the present invention is a generally known method for producing a unidirectional electromagnetic steel sheet, such as melting, hot-rolling, hot-rolled sheet annealing, pickling, cold-rolling, decarburization annealing, and nitriding annealing as required. It can be manufactured by the steps of applying an annealing separator and finish annealing. First, a general manufacturing method for grain-oriented electrical steel sheets is shown below.

In the first casting step, C: more than 0% to 0.10%, Si: 2.5% to 7%, acid-soluble Al: 0% to 0.065%, N: 0% to 0 in terms of mass fraction. .012%, Mn: 0% to 3.0%, Cr: 0% to 0.3%, Cu: 0% to 0.4%, P: 0% to 0.5%, Sn: 0% to 0 A molten steel containing .30%, Ni: 0% to 1%, S: 0% to 0.050%, and having a chemical component consisting of Fe and impurities as the balance is supplied to the continuous casting machine, and the slab is continuous. Is produced.

Subsequently, in the hot rolling step, the slab obtained from the casting step is heated to a predetermined temperature (for example, 1150 to 1400 ° C.), and then hot rolling is performed on the slab. As a result, for example, a hot-rolled steel sheet having a thickness of 1.8 to 3.5 mm can be obtained.

Subsequently, when hot-rolled sheet is annealed, the hot-rolled steel sheet obtained from the hot-rolling step is annealed under predetermined temperature conditions (for example, heating at 750 to 1200 ° C. for 30 seconds to 10 minutes). The process is carried out. Subsequently, in the cold rolling step, after the pickling treatment is performed, the hot-rolled steel sheet is cold-rolled. As a result, for example, a cold-rolled steel sheet having a thickness of 0.15 to 0.35 mm can be obtained.

Subsequently, in the decarburization annealing step, the cold-rolled steel sheet obtained from the cold rolling step is heat-treated (that is, under the condition of heating at 700 to 900 ° C. for 1 to 3 minutes) under predetermined temperature conditions (for example, heating at 700 to 900 ° C. for 1 to 3 minutes). Decarburization annealing treatment) is carried out. When such a decarburization annealing treatment is carried out, carbon is reduced to a predetermined amount or less in the cold-rolled steel sheet, and a primary recrystallization structure is formed. _{Further, in the decarburization annealing step, an oxide layer containing silica (SiO 2} ) as a main component is formed on the surface of the cold-rolled steel sheet.

Subsequently, in the annealing separating agent coating step, an annealing separating agent containing magnesia (MgO) as a main component is applied to the surface of the cold-rolled steel sheet (the surface of the oxide layer). Subsequently, in the finish annealing step, the cold-rolled steel sheet coated with the annealing separator is heat-treated (that is, finish annealing) under predetermined temperature conditions (for example, conditions of heating at 1100 to 1300 ° C. for 20 to 24 hours). Processing) is carried out. When such a finish annealing treatment is carried out, secondary recrystallization occurs in the cold-rolled steel sheet and the cold-rolled steel sheet is purified. As a result, a base material of a unidirectional electromagnetic steel sheet having the above-mentioned chemical composition of the grain steel sheet and whose crystal orientation is controlled so that the easily magnetized axis of the crystal grains and the rolling direction coincide with each other can be obtained.

Further, when the finish annealing treatment as described above is carried out, the oxide layer containing silica as a main component reacts with the annealing separator containing magnesia as a main component, and forsterite (Mg) is formed on the surface of the steel sheet. ₂ A glass film containing a composite oxide such as SiO _{4) is formed.} In the finish annealing step, the finish annealing treatment is performed with the steel sheet wound in a coil shape. By forming a glass film on the surface of the steel sheet during the finish annealing treatment, it is possible to prevent seizure from occurring on the coiled steel sheet.

In the final insulating film forming step, an insulating coating liquid containing, for example, colloidal silica and phosphate is applied over the glass film onto the surface of the steel sheet on which the glass film is formed. Then, the heat treatment is carried out under a predetermined temperature condition (for example, 840 to 920 ° C.) to finally obtain a unidirectional electromagnetic steel sheet having a glass film and an insulating film.

The mother steel plate of the unidirectional electromagnetic steel plate manufactured as described above has Si: 2.5% to 7%, C: more than 0% to 0.10%, and acid-soluble Al as chemical components. : 0% to 0.065%, N: 0% to 0.012%, Mn: 0% to 3%, Cr: 0% to 0.3%, Cu: 0% to 0.4%, P: 0 It contains% to 0.5%, Sn: 0% to 0.3%, Ni: 0% to 1%, S: 0% to 0.050%, and the balance is composed of Fe and impurities.

(Characteristics of manufacturing method)
In the present invention, a good glass film is formed by controlling the oxidation behavior on the surface of the base steel until the glass film is formed. Decarburization annealing is an important process for controlling this oxidation behavior. In particular, the temperature rise, which is the initial process of oxidation, should be carried out at a high dew point and rapid heating, and the initial decarburization should be carried out at a high temperature for a short time. Is effective. In the present invention, "partial pressure of H ₂ O" in the atmosphere of temperature increase of decarburization annealing / a "partial pressure of H _2" P (H ₂ O) / P a (H ₂₎ 0.65~3 0.0, preferably 1.0 to 2.5, heating rate ≥ 100 ° C / s, preferably 200 ° C / s or higher, more preferably 400 ° C / s or higher, heating temperature ≥ 800 ° C or higher, 750 ° C or higher. Stay time ≤ 5 seconds. At the same time, continued decarburization of the atmosphere P (H2 O) / P (H ₂₎
): 0.25 to 0.6, preferably 0.30 to 0.5, maximum temperature reached Y: 700 to 900 ° C, preferably 81 to 890 ° C, staying time above Y-30 ° C ≤ 4 seconds, The effect of the invention can be sufficiently obtained by preferably setting the residence time at Y-30 ° C to Y-85 ° C after reaching the maximum temperature to 3 seconds or less, preferably 20 seconds or more.

The reason why the above heat treatment is effective is not clear, but when oxidation is performed with the above thermal history and atmosphere, preferential oxidation of the decarburized plate is likely to occur, especially near the surface, and the final glass The interface structure between the film and the base steel plate becomes complicated and the adhesion is improved. Then, the particle size of the forsterite of the glass film formed by the subsequent finish annealing becomes fine and uniform, and the fineness is improved.

Further, the amount of oxygen at the time after decarburization annealing is one index of the effect of the present invention. In the present invention, the effect of the invention is likely to appear when the oxygen content of the decarburized annealing plate is 9 to 12 g / m2.

Hereinafter, examples of the present invention will be described. The conditions adopted in the examples are examples for confirming the feasibility and effect of the present invention, and the present invention is not limited thereto. Various conditions can be adopted as long as the object of the present invention is achieved without departing from the present invention.

(Example) C: 0.004%, Si: 3.8%, S: 0.002%, Al: 0.003%, N: 0.0080%, Mn: 0.4%, and the rest is Fe molten steel as a 2.6 mm thick hot-rolled plate.

Anneal the hot-rolled plate at 1000 ° C for 30 seconds, and then cold-roll to 0.23 mm. The decarburization annealing process is performed so that the heating rate is 125 ° C / s, the maximum temperature reaches 720 to 911 ° C, and the holding within 5 s is 665 to 825 ° C. Anneal for ~ 20 seconds. The material coated with the annealing separator mainly composed of MgO is annealed at 1200 ° C for 20 hours by deheating while blowing a nitridable gas. Further, an insulating coating liquid containing colloidal silica and phosphate was applied, and a phosphate-based insulating film was formed by baking at 880 ° C. The characteristic of the glass film is the result of measurement after peeling the insulating film.

Film appearance: The smoothness, cracking, and glossiness of the coating film were observed with the naked eye and evaluated according to the following criteria.
◯: There is no abnormality in the coating film and it is good.
Δ: Smoothness or glossiness is slightly inferior, but cracks are not observed.
X: Cracks are observed, or smoothness or glossiness is significantly inferior.

The rust resistance of the film is evaluated by immersing the steel sheet on which the film is formed as it is in 100 ml of boiling water for 10 minutes and changing the weight before and after that. The result is a weight change of less than 5 mg per 50 cm2 steel sheet. Further, as shown in Table 1, the rust resistance shows rust resistance for 48 hours or more in an atmosphere of a temperature of 80 ° C. and a humidity of 98%, which is a very good result. Table 1 shows the manufacturing conditions and characteristics adopted in the examples.

The steel of the present invention having an average particle size of 2.0 μm or less and a standard deviation of the particle size distribution of 0.6 μm or less had excellent rust resistance of the film and low iron loss. The state of the glass film obtained on the product plate is achieved on the steel sheet after finish annealing, which is an intermediate product before forming the insulating film.

Claims (2)

A forsterite-based film having an average particle size of 0.6 μm or more and 2.0 μm or less is provided between the insulating film and the mother steel sheet, and the standard deviation of the forsterite particle size distribution of the forsterite-based film is A method for manufacturing a unidirectional electromagnetic steel sheet having a size of 0.6 μm or less.
The steel slab hot rolled, annealed hot-rolled sheet as required, cold rolled to a final product thickness, decarburization annealing, nitriding necessary annealing, final finish annealing, the one that is produced by insulating film treatment In the manufacturing process of directional electromagnetic steel sheet, the temperature rise by decarburization annealing is _{adjusted to PH 2} O / PH ₂ : 0.65 to 3.0, heating rate ≥ 100 ° C / s, heating temperature ≥ 800 ° C. With a staying time of 750 ° C. or higher ≤ 5 seconds, decarburization was continued in the atmosphere of P (H ₂ O) / P (H ₂ ): 0.25 to 0.6, and the maximum temperature reached: Y :. 700-810 ° C., characterized by that in at Y-30 ° C. residence time ≦ 4 seconds at greater residence time ≧ 10 seconds at Y-30 ℃ ~Y-85 ℃ after maximum temperature, single Manufacturing method of directional electromagnetic steel plate. The surface of the base steel sheet has a forsterite-based film with an average particle size of 0.6 μm or more and 2.0 μm or less, and the standard deviation of the forsterite particle size distribution of the forsterite-based film is 0.6 μm. The following method for manufacturing a unidirectional electromagnetic steel sheet original plate.
The steel slab hot rolled, annealed hot-rolled sheet as required, cold rolled to a final product thickness, decarburization annealing, nitriding necessary annealing, final finish annealing and the grain-oriented electromagnetic steel sheet is produced by In the manufacturing process of the original plate, the temperature rise by decarburization annealing is _{adjusted to P (H 2} O) / P (H ₂ ): 0.65 to 3.0, heating rate ≥ 100 ° C / s, heating temperature ≥ It was carried out at 800 ° C or higher, and the residence time at 750 ° C or higher was ≤5 seconds. Then, decarburization was continued, and the atmosphere P (H ₂ O) / P (H ₂ ): 0.25 to 0.6 reached the maximum. The feature is that the temperature Y: 700 to 810 ° C., the residence time above Y-30 ° C. ≤4 seconds, and the residence time at Y-30 ° C. to Y-85 ° C. after reaching the maximum temperature ≥10 seconds. A method for manufacturing an original plate for a unidirectional electromagnetic steel plate.