JPH11335742A - Mgo annealing separation agent for production of grain oriented silicon steel sheet excellent in primary film forming and production of grain oriented silicon steel sheet using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a primary film having a low film defect area rate over a coil whole length/width by dissolving a metal element of a specified quantity into in MgO to form a solid solution and conducting finish annealing to a silicon steel sheet with using a solid solution type MgO annealing separating agent having a specified CAA value and a specified particle distribution. SOLUTION: The grain oriented silicon steel sheet having a low iron loss is obtained by coating/drying a MgO annealing separation agent on a silicon steel sheet subjected to annealing and primary recrystallization with <=100 ppm carbon quantity, subjecting the sheet to being wound up into a coil, annealing and secondary recrystallization and allowing it to form primary film of an inorganic mineral substance essentially comprising forsterite. The MgO annealing separation agent contains a bivalent and/or a trivalent metal element with a solid solution content rate of 0.1-<1.0 mol.% based on Mg, has a CAA value of 100-600 sec. of 30 deg.C and contains secondary grains of >=5 μm size at a ratio of 1-50%. An annealing separation agent excellent in a primary film reaction is obtained. The bivalent metals are preferably Ca, Ba, Mn, Zn, Ni, etc., and the trivalent metals are preferably Al, Cr, Ti, Bi, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for forming a primary film by applying MgO as an annealing separating agent to an annealed silicon-containing steel plate which performs both decarburization and primary recrystallization, followed by annealing. The present invention relates to a method for manufacturing a grain-oriented silicon steel sheet.

[0002]

2. Description of the Related Art As a general method for producing a grain-oriented silicon steel sheet, annealing (hereinafter, referred to as decarburization annealing) which combines recrystallization and decarburization from steel in a cold-rolled silicon-containing steel sheet is known. Then, an annealing separator mainly composed of MgO is applied to the surface of the steel sheet, dried, and then wound into a coil. next,
The coiled steel sheet is annealed in pure hydrogen for about 20 hours (hereinafter referred to as finish annealing). Secondary recrystallization proceeds in this finish annealing step, and a solid-phase reaction occurs between SiO2 generated on the steel sheet surface during decarburizing annealing and a part of MgO applied as an annealing separating agent, forsterite ( A film (hereinafter, referred to as a primary film) of an inorganic mineral substance mainly composed of 2 (MgO) .SiO2 is generated.

[0003] Next, a coating solution mainly composed of colloidal silica, chromic acid and phosphate is applied on the primary film, dried, and baked at a temperature of about 800 ° C. A product is formed by forming a film (hereinafter, referred to as a secondary film). Conventionally, the primary coating has been referred to as a glass coating. However, since the primary coating shows a clear diffraction line in X-ray diffraction analysis and clearly shows a crystal phase, it is easy to distinguish the primary coating from the secondary coating described later in the present invention. For this reason, the name of primary coating is adopted.

[0004] The unidirectional silicon steel sheet manufactured as described above is processed into predetermined dimensions by shearing, punching, or the like, laminated, and then fixed to become an electric component for voltage conversion such as an iron core. When a product such as an iron core is manufactured, the most important characteristic is a heat energy loss at the time of voltage conversion. This heat energy loss is called iron loss. Iron loss is greatly affected by the eddy current generated in the steel sheet. In order to suppress the generation of eddy current, it is effective to increase the insulating property of the steel sheet surface.
Various types of films are formed to enhance the insulation. In particular, the forsterite primary coating, which is the base coat on the steel sheet side, also affects the adhesion of the upper secondary coating, so it is extremely important to form this primary coating uniformly and without defects on the steel sheet surface. That is.

Recently, as a method for forming a uniform primary film, Japanese Patent Application Laid-Open Nos. 7-310188 and 8-350
No. 14, JP-A-9-41153, JP-A-7-41
Japanese Patent No. 316831 discloses a method for forming a good forsterite film by using MgO in which a divalent or trivalent element is dissolved in MgO. First,
Japanese Patent Application Laid-Open No. 7-310188 discloses that the solid solution ratio of divalent and trivalent metals is 0.01 or more and 0.40 or less (1 mol% or more and 40 or less).
mol% or less) and a method for producing a unidirectional silicon steel sheet using the same. Then, Japanese Patent Application Laid-Open No. 8-35014 discloses that the solid solution ratio of divalent and trivalent metals is 0.01 or more and 0.40 or less (1 mol% or more and 40 mol or less).
% Or less) and F, Cl, Br, CO3, SiO3, P
A solid solution type MgO containing O3, CrO3 and the like and a method for producing a unidirectional silicon steel sheet using the same have been proposed. Further, Japanese Patent Application Laid-Open No. 9-41153 discloses an annealing separator containing a composite hydroxide composed of divalent and trivalent metal elements in the range of 0.5 to 15 parts by weight with respect to general MgO. A method for producing a unidirectional silicon steel sheet using the same has been disclosed.
Further, Japanese Patent Application Laid-Open No. Hei 7-316831 has proposed a ceramic film forming agent for a metal material and the like containing a solid solution of a multi-element oxide containing Mg as an effective component.

[0006]

Here, the concept and measures for improving the conventional primary film will be described. When film defects such as shimo-furi occur in the finish annealing coil,
Until now, it has been determined that the reactivity in the initial stage of film formation is insufficient, and improvements have been made based on the idea of increasing the reactivity. First, for MgO, measures have been taken to increase the solid solution fraction of solid solution elements having a film formation promoting effect. In addition, since the primary film forming reaction is relatively good when the atmosphere oxidizing property is high in the final annealing low-temperature stage, a measure of using fine-grain MgO to increase the amount of water brought in and to suppress the water flow between the plates. Has been taken.

[0007] The present inventors have applied these techniques and expanded field tests, and as a result, it has been found that a primary film cannot always be formed stably by the above-mentioned conventional techniques alone. In particular, the tendency was remarkable in the outer edge portion of the finish annealing coil.
The present inventors applied the conventional technology and repeated on-site tests with coils of several tons to several tens of tons, and analyzed in detail the state of primary film formation over the entire length and width of the finish-annealed coils. As a result, when the element solid solution type MgO is applied, a very good primary film forming portion can be obtained locally as compared with the case of using the conventional MgO containing no solid solution element. It has been found that the occurrence of a so-called Shimofuri type film defect in which the film is partially lost and the metal surface is exposed is conversely revealed depending on the part. Such a film formation situation is described in, for example, JP-A-8-3
The specific surface area of MgO disclosed in US Pat.
5 m ² / g is set to 200 meters ² / g from and 30 or the measured CAA value in the range from 100 to 30 seconds at ° C., or water of MgO as proposed in JP-A 7-197707 JP Even if the total water content was narrowed down to a range of 3% or less, no improvement was obtained. That is, it has been found that simply applying the conventional technique is not necessarily advantageous when viewed in terms of the film defect occurrence area rate which directly affects the product yield and is important in industrial production. Here, the film defect occurrence area ratio is a ratio of the area where the film defect occurs to the entire area of the finish annealing coil.

[0008]

Means for Solving the Problems The present invention has been made to solve the above problems, and its gist is as follows: (1) MgO contains a divalent and / or trivalent metal element
0.1 mol% or more and 1.0 m in total solid solution fraction to g
ol% and a CAA value at 30 ° C. of 10
An MgO annealing separator for producing a grain-oriented silicon steel sheet having excellent primary coating reactivity, characterized by containing a primary particle having a secondary particle diameter of not less than 0 second and not more than 600 seconds and a particle diameter of not less than 5 μm in an amount of from 1% to 50%. .

However, the solid solution metal element in MgO is a divalent metal such as Fe, Ca, Ba, Mn, Zn, Ni, Co,
Be, Sr, Sn, and trivalent metals such as Al, Mn, and F
e, Co, Cr, Ni, Ti, Bi, and Sb. (2) An annealing separator mainly composed of MgO is applied to a silicon-containing steel sheet which has been primarily recrystallized at a carbon content of 100 ppm or less in steel,
A method for producing a unidirectional silicon steel sheet in which secondary recrystallization and formation of a forsterite-based inorganic mineral substance film are performed by drying, winding up in a coil shape, and then performing finish annealing, and having a physical property value of (1). A method for producing a grain-oriented silicon steel sheet, comprising using MgO for an annealing separator.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION
Focusing on the specificity of the
And repeated the review. Here, first, unidirectional silicon steel sheet
Atmosphere between plates in finish annealing coil in manufacturing process
The uniqueness of will be described. As described above, unidirectional silica
The primary coating of the base steel sheet is coated with MgO on the decarburized annealed sheet,
After drying, wind it into a coil and apply finish annealing.
And formed by At this time, MgO is in the form of water slurry
After being prepared in a state, it is applied to a steel plate. Therefore, M
Some of the gO undergoes a hydration reaction and magnesium hydroxide
(Mg (OH) _Two). MgO slurry applied
Is dried on steel plate, but in the form of magnesium hydroxide
The part brought between the coil plates has a temperature of about 350 ° C
At that time, it is converted to MgO, at which time moisture is released between the coil plates.
Will be issued. Dehydration of such magnesium hydroxide
Progresses from the particle surface, but Mg
(OH)_TwoIf the area remains, the dehydration reaction is completely completed
In order to do_TwoMust diffuse inside the grains in the form of O etc.
And requires a large amount of diffusion energy. That
The dehydration reaction continues to about 1000 ° C.

On the other hand, regarding the form of annealing, finish annealing is a tight coil type box annealing. The shape of unidirectional silicon steel sheet, that is, its flatness, greatly affects the product characteristics. In finish annealing at a maximum temperature of 1200 ° C., the coil is so-called loosely wound to prevent thermal deformation and buckling of the steel sheet. Can not do it. In the case of the tight coil type, the space between the plates becomes very narrow, and the heat transfer and air permeability become extremely poor. In addition, since the heat input is performed from the outer edge of the coil, the temperature of the outer edge of the coil reaches a relatively high temperature relatively quickly, but the temperature does not rise easily in the interior, resulting in a situation where the temperature deviation depending on the part is very large. As described above, the above-mentioned dehydration reaction proceeds between the plates of the finish-annealed coil in which the temperature deviation between the coil portions is very large and the heat conductivity and the air permeability are not good.

The dehydration reaction occurring between the plates based on the above-mentioned temperature raising characteristics is as follows. As the annealing time elapses, the coil outer edge temperature increases. Then, heat is transferred to the inside of the coil and the temperature rises, and a dehydration reaction starts inside the coil. The generated moisture diffuses between the plates of the coil toward the edge side in the width direction of the coil, and after passing through the edge portion, diffuses out of the coil. Since the finish-annealed coil takes the above-described oxidation history, especially the coil edge portion is constantly exposed to moisture diffused from the inside of the coil. In other words, the outer edge has moisture in the atmosphere between the plates in a very wide temperature range,
That is, a history of high oxidizability is obtained. The present inventors considered that this was the cause of the film defect.

Therefore, an approach completely opposite to the conventional idea, that is, if the primary film forming ability is somewhat reduced, the oxidizing property between the plates is reduced, and the flowability of the atmosphere is improved, the primary film primary coil can be used. In particular, it was thought that the defective film portion at the outer edge could be significantly improved. Therefore, attention was paid to the following three points, and improvements were made. First, in order to adjust the primary film-forming ability, the amount of the divalent and / or trivalent metal that controls the reactivity was reduced. In addition, in order to reduce the amount of water carried between the coil plates, adjustment was made so that the CAA time became longer. Furthermore, the fraction of MgO particles having a relatively large particle diameter of 5 μm or more was adjusted so that air permeability between the coil plates could be secured.

The CAA value is an index representing the hydration of MgO, and is a 0.4N citric acid aqueous solution (100 ml).
When 2 g of MgO powder was added to
Is a numerical value representing the time required to reach to in seconds. The secondary particle diameter was determined by measuring a dispersion of MgO powder in water or alcohol by a laser diffraction method or the like. Experiments were conducted on a field coil using MgO having various solid solution contents and conventional MgO which were produced as trials. Table 1 shows the composition, physical properties and film defect area ratio of the solid solution MgO used.

[0015]

[Table 1]

From Table 1, under the conditions of Comparative Examples 2 to 6 in which the total fraction of the divalent and / or trivalent solid-solution elements is 1 mol% or more (comparative example), the primary film defect generation area ratio Is 1.7% to 2.4%, and the solid solution content is 0.1mo.
Under the conditions of Experimental Examples 14 to 18 (Comparative Example) in which the defect rate is less than 1%, the defect rate is 1.7% to 2.4%, which is better than that of the conventional MgO, but is 1.7% or more. Film defects occur at an area ratio of. On the other hand, under the conditions of Experimental Examples 7 to 13 in which the solid solution fraction was 0.1 mol% or more and less than 1.0 mol%, the film defect rate was 1.2%.
The following is better than conditions outside this range. However, the solid solution content is 0.1 mol% or more and 1.0 mol%.
If the CAA value is less than 100 seconds (Experimental Example 8: Comparative Example) or more than 600 seconds (Experimental Example 9: Comparative Example), or the proportion of particles having a secondary particle diameter of 5 μm or more is 50%
Above (Experimental Example 12: Comparative Example) and 1% or less (Experimental Example 13:
Under the conditions of Comparative Example), the film defect rate was 1.2%,
It is relatively high at 1.1%, 1.2% and 1.1%. On the other hand, the condition that the solid solution fraction is 0.1 mol% or more and less than 1.0 mol%, the CAA value is more than 100 seconds and 600 seconds or less, and the fraction of secondary particles 5 μm or more is 1% or more and 50% or less. (Experimental Examples 7, 10, and 11: Examples) In Example, the film defect rate was 0.4%.
It is extremely low as below and is good. That is, the solid solution content is 0.1%.
1 mol% or more and less than 1.0 mol% and a CAA value of 1
Manufacture of unidirectional silicon steel sheet with extremely low primary film defect area ratio by using solid-solution type MgO with a condition of more than 00 seconds and not more than 600 seconds and a secondary particle size of 5 μm or more and a fraction of 1% or more and 50% or less it can. These are the conventional ideas for improving the film in MgO, that is, an increase in the solid solution element fraction that has a film formation promoting effect, an increase in hydratability to enhance atmospheric oxidizability, and a suppression of inter-plate flowability. This suggests that micronization was not always appropriate. It also shows that the in-situ finish-annealed coil, particularly its outer edge, had higher oxidizability than previously expected, proving that the inventors' predictions were correct.

Next, a method for producing the solid solution type MgO used in the present invention will be described. The magnesium substance used as a raw material may be a method of directly collecting from seawater (seawater method), MgCl ₂ (by bittern method) by-produced during salt production, or inexpensive high-temperature firing MgO. First, mixing such a raw material magnesium substance and salts containing a solid solution type element,
Let react. At this time, a hydrothermal reaction may be used.

The composite hydroxide thus prepared is filtered through a filter, roughly dried, and fired in a firing furnace.
There is no particular limitation on the firing atmosphere, and firing can be performed in an air atmosphere. As the firing furnace, a continuous rotary firing furnace or a batch type muffle furnace can be used. The heating method of the firing furnace may be a direct type or an indirect type. The firing temperature is from 800 ℃ to 1100 ℃
The temperature before and after is suitable, but the optimum temperature varies depending on the type of the solid solution element. Therefore, the temperature is adjusted while checking the solid solution amount, the CAA value, and the ratio of the secondary particle diameter of 5 μm or more. 1mo solid solution
When the content is 1% or more, the reactivity is too high.
When the content is less than 1%, the reactivity becomes insufficient and the film defect rate increases, so that the solid solution amount is 0.1 mol% or more and 1.0 mol% or less.
It must be less than mol%. Also, the CAA value is 1
If it is less than 00 seconds, the moisture content is too high, while if it is more than 600 seconds, it is too low, and the film defect rate becomes high. Therefore, the CAA value is set to be in the range of more than 100 seconds to 600 seconds or less. Furthermore, if the ratio of the secondary particle size is 5 μm or more is less than 1%, the inter-plate permeability is too low, and if it is more than 50%, the gas permeability is too high. The range is from 1% to 50%.

Next, a method of preparing an MgO water slurry to be applied to a steel sheet will be described. First, the solid solution type MgO produced as described above and water are mixed. Next, in order to uniformly disperse MgO, a propeller blade type stirrer, a closed homomixer, a colloid mill, a bead mill, or the like is used. At this time, a borate, a sulfate, or the like may be added to adjust the primary film reactivity. Further, an oxide such as TiO2 may be added in order to finely adjust the inter-plate oxidation property of the finish annealing coil.

Next, the steel plate used will be described. After the cold rolling of the silicon-containing steel sheet, the steel sheet is annealed at a temperature of about 850 ° C. to cause primary recrystallization. However, the carbon content in steel is 100pp
If it exceeds m, it will remain in the product after the finish annealing and further deteriorate the magnetic properties with time, so that the carbon content in the steel of the steel sheet before the application of MgO is decarbonized to 100 ppm or less in a wet hydrogen atmosphere.

The above-described steel sheet is coated with solid solution type MgO, wound up in a coil shape, and subjected to finish annealing. In the first half, the final annealing atmosphere is preferably a nitrogen-containing atmosphere at least up to the secondary recrystallization start temperature from the viewpoint of controlling the decomposition of a nitride-based inhibitor such as AlN. On the other hand, if nitrides and sulfides remain in the product, they hinder domain wall movement and degrade magnetic properties. Therefore, they must be annealed at about 1200 ° C. for about 20 hours in a dry hydrogen atmosphere and removed from steel.

[0022]

Example 1 <Example 1> A material having a Si content of 3.25% and a decarburized carbon concentration of 12 ppm in steel and having a thickness of 0.225 mm and having a primary recrystallized unidirectional silicon steel sheet is shown in Table 2. The following three kinds of annealing separators were applied, dried, wound up in a coil shape, and subjected to finish annealing. After removing excess MgO by washing with water, the three primary film defect generation area ratios were compared. Table 2 also shows the composition and physical properties of the used annealing separator, and the film defect rate.
Shown in

[0023]

[Table 2]

Table 2 shows that conventional MgO containing no solid solution element
(Experiment No. 1: Comparative Example) and the solid solution type MgO having too much Fe solid solution (Experiment No. 2: Comparative Example) have film defect rates of 3.5% and 2.2%, respectively. In the case of solid solution type MgO having an appropriate solubility and physical properties (Experiment No. 3: Example), the film defect rate is as good as 0.3%. <Example 2> Three types of materials shown in Table 3 were used for a material for a primary recrystallized unidirectional silicon steel sheet containing Si: 3.20% and decarbonized to a carbon concentration of 10 ppm in steel and having a thickness of 0.30 mm and having been subjected to primary recrystallization. An annealing separator was applied, dried, wound into a coil, and subjected to finish annealing. After removing excess MgO by washing with water, the three primary film defect generation area ratios were compared. Table 3 also shows the composition and physical properties of the used annealing separator, and the film defect rate.

[0025]

[Table 3]

Table 3 shows that the conventional MgO containing no solid solution element
(Experiment No. 1: Comparative example) or solid solution type Mg with too much solid solution
In the case of O (Experiment No. 2: Comparative Example), the film defect rates were 3.4% and 1.9%, respectively, whereas the solid solution amount and physical properties of the solid solution type MgO (Experiment No. 3: Example) In the case of ()), the film defect rate is extremely good at 0.2%.

[0027]

As described above, based on the specificity of the in-situ finish-annealed coil, from the viewpoint of minimizing the area ratio of film defect occurrence to the entire area of the coil, the physical properties are completely different from the conventional ones. New solid solution type annealing separator M with adjusted value
gO was developed. This new MgO has excellent primary film forming ability, and the primary film on the finished annealed plate manufactured using the same is good over the entire length of the coil, and the film defect area ratio is extremely low as compared with the conventional method. This can greatly improve the product yield.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Norihiro Yamamoto 1-1 Niwahata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture Nippon Steel Corporation Yawata Works (72) Inventor Shingo Okada Tobata-ku, Tobata-ku, Fukuoka Prefecture 1-1 Nippon Steel Corporation Yawata Works (72) Inventor Go Hamaya 1-1 Nichihatacho, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture Nippon Steel Corporation Yawata Works

Claims (2)

[Claims] Claims 1. A MgO containing a divalent and / or trivalent metal element in a total solid solution fraction of 0.1 mol% or more and less than 1.0 mol% with respect to Mg, and CAA at 30 ° C.
MgO annealing for producing a unidirectional silicon steel sheet excellent in primary coating reactivity, characterized by containing a value of more than 100 seconds to 600 seconds or less and a secondary particle size of 5 μm or more in a ratio of 1% to 50%. Separating agent. However, the solid solution metal element in MgO is Fe, Ca, Ba, Mn, Zn, Ni, as a divalent metal.
Co, Be, Sr, Sn, and trivalent metals such as Al, M
n, Fe, Co, Cr, Ni, Ti, Bi, and Sb. 2. A primary recrystallized silicon-containing steel sheet having a carbon content of 100 ppm or less is coated with an annealing separator mainly composed of MgO, dried, wound into a coil, and then subjected to finish annealing to perform a secondary annealing. A method for producing a grain-oriented silicon steel sheet for forming an inorganic mineral substance film mainly composed of crystals and forsterite, the M for an annealing separator having physical properties according to claim 1.
A method for producing a grain-oriented silicon steel sheet, comprising using gO.