JP5533159B2 - Annealing separator for grain-oriented electrical steel sheet and method for producing grain-oriented electrical steel sheet - Google Patents

Description

  The present invention relates to an annealing separator for grain-oriented electrical steel sheets, and a method for producing a grain-oriented electrical steel sheet in which finish annealing is performed using the annealing separator.

  The grain-oriented electrical steel sheet is mainly used as a power transformer core material, and therefore must have low iron loss. The grain-oriented electrical steel sheet has a process of forming a film on the steel sheet surface after performing decarburization annealing on the cold-rolled steel sheet having the final thickness, followed by finish annealing for the purpose of secondary recrystallization and purification. It is manufactured after.

  The grain-oriented electrical steel sheet thus obtained is composed of a Si-containing steel sheet having a sharp (110) [001] texture (Goss orientation) and an inorganic coating having a thickness of several microns formed on the surface thereof.

  It is indispensable for the steel sheet to have Goth orientation to achieve the low iron loss characteristics of grain-oriented electrical steel sheets. To achieve this structure, Goss orientation grains grow selectively during finish annealing. Grain growth called secondary recrystallization is used.

In order to stably cause secondary recrystallization, grain oriented electrical steel sheets utilize fine precipitates in the steel called inhibitors. Inhibitors during finish annealing, at low temperature section, and suppress grain growth, in the above certain temperature, lose pinning effect by decomposition or coarsening, an action which you provoked the secondary recrystallization. As the inhibitor, sulfide or nitride is generally used.

  In order to obtain the desired structure, it is necessary to keep the inhibitor at a certain temperature. If it is a sulfide, the sulfur partial pressure of the final annealing should be controlled, and if it is a nitride, the nitrogen partial pressure should be controlled. The purpose can be achieved.

  Although sulfides and nitrides used as inhibitors are necessary for secondary recrystallization that occurs in the course of temperature rising during finish annealing, if they remain in the product, the iron loss of the product is significantly worsened. In order to remove the influence of sulfides and nitrides from the steel, after secondary recrystallization is completed, it is held for a long time at around 1200 ° C. in pure hydrogen. This is called purification annealing.

  On the other hand, the inorganic film of the grain-oriented electrical steel sheet is composed of a glass film and a secondary film, and the magnetic domain control effect is obtained by the tension applied to the steel sheet by these films, and the low iron loss characteristics are improved.

In general, during finish annealing, SiO ₂ in the steel sheet reacts with MgO as the main component of the annealing separator to form a glass film on the steel sheet. The glass coating has two functions.

  One of them is that the glass film adheres firmly to the steel sheet, and itself has the effect of imparting tension to the steel sheet, and the adhesion to the steel sheet when forming a tension film formed in the post-finish annealing process. It functions as an intermediate layer to ensure The other is the function of preventing excessive strength reduction of the inhibitor and stabilizing secondary recrystallization during finish annealing.

  Therefore, in order to stably manufacture a grain-oriented electrical steel sheet having good magnetic properties, it is necessary to form a healthy glass film without defects.

  In the glass film, defects of about 0.1 to 1 mm where the film is not formed in a dotted shape may occur densely. In such a case, it is not only a problem in appearance but also good magnetic properties cannot be obtained.

  Conventionally, in order to obtain a good glass film, Patent Documents 1 and 2 disclose that the CAA (Citric acid activity) value or the particle size distribution is an optimum value and the reactivity between the annealing separator and the steel sheet is improved. It is disclosed.

  Patent Document 3 discloses forming a sound film by controlling the hydration amount of the annealing separator. Patent Document 4 discloses that a sound film is formed by adding chloride to an annealing separator. However, in any case, a sufficient effect is not necessarily obtained for suppressing defects in the vicinity of the steel plate end portion that is easily affected by the annealing atmosphere.

  Patent Document 5 discloses a method for suppressing defects in the glass film by controlling the atmosphere, but this method can achieve a target atmosphere uniformly including the steel plate end and the steel plate interior. There are problems such as difficulty in controlling the atmosphere because it may be difficult or it may be necessary to humidify.

  As described above, various techniques have been disclosed so far, but the film defects have not been completely suppressed.

Japanese Patent Laid-Open No. 10-088423 Japanese Patent Application Laid-Open No. 07-188937 JP 2002-194445 A JP 08-199239 A JP 2006-161106 A

Yasuaki Uno et al., Clay Science, 32, 129 (1992) Kishibe, thermal measurement, 34, 87 (2007) Takahiko Sasaki et al., Abstracts of Clay Science Discussion Meeting, 34, 148 (1990)

  An object of the present invention is to provide means for stably producing a grain-oriented electrical steel sheet having no film defects and good magnetic properties.

The present inventors have studied a method for effectively suppressing film defects. As a result, the addition of talc to one or both of smectite and sepiolite, or any of these to the annealing separator for finish annealing is effective in suppressing film defects. I found out that

  Since the present invention is less susceptible to non-uniformity problems in each part of the steel sheet coil than the method of controlling the finish annealing atmosphere by mixing nitrogen-hydrogen ratio or steam, the film is more effective than the above method. Defects can be suppressed.

  According to the present invention, it is possible to stably obtain a grain-oriented electrical steel sheet having a glass film with excellent properties and good magnetic properties.

  The present invention will be described in detail below. Although the present invention relates to a finish annealing process, a steel sheet for finish annealing is manufactured through the following processes.

  First, a molten metal having a predetermined composition containing C: 0.03 to 0.1% by mass and Si: 2.5 to 4.5% by mass was cast into a slab shape, and this was hot-rolled by a known method. Then, it heat-processes and cold-rolls. Cold-rolled sheets contain trace additives added to improve the magnetic properties, mechanical properties, and film properties of the final product, and elements that are inevitably mixed.

  The steel plate having the final thickness obtained in this way is subjected to heat treatment and decarburized to obtain a decarburized annealed plate for the next finish annealing step. The decarburized annealed plate contains an inhibitor for developing secondary recrystallization. For example, AlN, MnS, MnSe, and the like are known as inhibitors, but in the present invention, the type of the inhibitor is not particularly limited.

Usually, the outermost layer of the decarburized annealed plate has an oxide layer mainly composed of SiO ₂ formed during decarburization. Since this SiO ₂ reacts with MgO contained in the annealing separator to form a glass film made of forsterite, it is necessary to control the SiO ₂ amount of the decarburized annealing plate in order to obtain a good film. It becomes.

When SiO ₂ is too small, the formation of the glass coating film becomes poor and adhesion of the coating is impaired. On the other hand, if the amount of SiO ₂ is too large, the glass film becomes unnecessarily thick, and the magnetic properties of the product plate deteriorate. Therefore, the amount of SiO ₂ is preferably 400 to 1500 ppm, more preferably 600 to 1100 ppm in terms of oxygen amount.

  The purpose of applying the annealing separator to the decarburized annealed plate is to form a glass film while preventing seizure between the steel plates during finish annealing. The annealing separator contains MgO as a main component, but may contain a known trace additive element for improving the film characteristics and magnetic characteristics.

  As a method for applying the annealing separator, any known method such as a method of applying and drying as a slurry with water or the like, or an electrostatic application method can be used. The decarburized and annealed plate after the application of the annealing separator may be a cut plate or the like, and may be subjected to finish annealing. However, if it is wound in a coil shape and finish annealing is performed, workability is good.

Here, the present inventors examined various compounds for the purpose of finding an additive that optimizes the oxygen potential immediately above the steel sheet during finish annealing. As a result, when one or both of smectite and sepiolite, or a compound obtained by adding talc to any one of these is used as an additive for the annealing separator, good results for suppressing film defects are obtained. It was. Based on this result, in the present invention, a compound obtained by further adding talc to one or both of smectite and sepiolite, or any of these, is added to the annealing separator.

  In the addition of these additives, if the addition amount is too small, there is no effect of addition, and if it is too much, the film properties are deteriorated. Therefore, an appropriate addition amount is 2 to 30% by mass, preferably 5 to 25% by mass, based on 100 parts by mass of the main component MgO of the annealing separator.

  It is estimated that the film defect inhibitory effect by the said additive expresses for the following reasons. In general, when heated, smectite, sepiolite, and talc are dehydrated in a high temperature range and release a gas containing oxygen. The weight loss due to dehydration is estimated to be 2% or more in the temperature range of 500 to 950 ° C. This is reported in Non-Patent Documents 1 to 3.

  When the oxygen-containing gas is generated from the additive of the annealing separator in the above temperature range (500 to 950 ° C.), the reduction of the oxygen potential directly above the steel sheet is suppressed, and the atmosphere directly above the steel sheet contributes to the formation of the glass film. As a result, it is presumed that a film defect suppressing effect can be obtained.

  When selecting an additive, the one having a large weight loss due to generation of a gas containing oxygen in a temperature range of 500 to 950 ° C. is selected. The weight loss should be 2% or more. If the weight loss is less than 2%, the amount of additive added becomes too large, adversely affecting the film formation, and a healthy glass film cannot be obtained.

  Even if the temperature range where the weight loss of the additive is 2% or more due to the generation of the gas containing oxygen is too low or too high, the film defect suppressing effect is not exhibited.

  Even if oxygen-containing gas is generated at a temperature lower than 500 ° C. and the oxygen potential directly above the steel plate is increased, there is no effect in improving the film in this temperature range. Therefore, the lower limit of the temperature range where the weight loss of the additive is 2% or more due to the generation of the gas containing oxygen is 500 ° C. Preferably it is 600 degreeC or more, and the further favorable film | membrane improvement effect is acquired in this temperature range.

  On the other hand, when a large amount of oxygen-containing gas is generated from the annealing separator in a temperature range exceeding 950 ° C., film defects are likely to occur, and the magnetic properties are also deteriorated. Therefore, the upper limit of the temperature range where the weight loss of the additive is 2% or more due to the generation of gas containing oxygen is 950 ° C. The temperature is preferably 850 ° C. or less, and a better film improving effect can be obtained in this temperature range.

  As described above, the decarburized annealed plate is subjected to finish annealing, and after secondary recrystallization, it is subjected to purification annealing and cooled to room temperature, and a steel sheet having a secondary recrystallized structure and having a glass film formed thereon. Can be obtained.

  Next, examples of the present invention will be described. The conditions in the examples are one example of conditions used for confirming the feasibility and effects of the present invention, and the present invention is based on this one example of conditions. It is not limited. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

Example 1
Si: 3.2 mass%, Mn: 0.12 mass%, S: 0.005 mass%, C: 0.05 mass%, acid-dissolvable Al: 0.026 mass%, N: 0.008 mass% Using a slab containing slab as a raw material, it was hot-rolled by a known method, then subjected to hot-rolled sheet annealing, and then cold-rolled to obtain a cold-rolled sheet having a thickness of 0.23 mm.

  Thereafter, the cold-rolled sheet was annealed in a humidified hydrogen-nitrogen atmosphere, and the nitrogen content of the steel sheet was adjusted to approximately 200 ppm to obtain a decarburized annealed sheet. An annealing separator mainly composed of MgO was applied to the decarburized annealing plate, and then wound into a coil shape.

The annealing separator was added with 200 ppm of FeCl ₂ with respect to 100 parts by mass of MgO and 5 parts by mass of TiO ₂ , and further added with 10% by mass of the additives shown in Table 1 in each example. Is. The steel plate coated with such an annealing separator was annealed in a hydrogen stream at 1200 ° C. for 20 hours. Table 1 also shows the film properties and magnetic properties (magnetic flux density B8 (T) and iron loss W17 / 50 (w / kg)) of the obtained steel sheet.

The meanings of the evaluation symbols for film properties are as follows. ○ The above is acceptable.
A: There is no defect on the entire surface of the steel sheet, and the glass film has a uniform color over the entire area of the steel sheet.
◯: A glass film with no unevenness in color near the edge of the steel sheet and near the center of the steel sheet, although there is no defect on the entire surface of the steel sheet.
(Triangle | delta): It is a glass membrane | film | coat with which a dotted | punctate defect is scattered in the steel plate edge part vicinity.

  From Table 1, it can be seen that when an annealing separator added with smectite, sepiolite, or talc is used, a good film without defects can be obtained and satisfactory magnetic properties can be obtained.

  An annealing separator added with palygorskite with crystal water has no effect of improving the film. This is because, as is clear from Non-Patent Document 3, there is no loss of 2% or more at 500 to 950 ° C. Further, even in Comparative Examples 4 to 6 using an annealing separator to which 10% by mass of smectite, sepiolite, or talc added by heat treatment at 1000 ° C. is removed, there is no effect of improving the film.

(Example 2)
Si: 3.2 mass%, Mn: 0.12 mass%, S: 0.005 mass%, C: 0.05 mass%, acid-dissolvable Al: 0.026 mass%, N: 0.008 mass% Using a slab containing slab as a raw material, it was hot-rolled by a known method, then subjected to hot-rolled sheet annealing, and then cold-rolled to obtain a cold-rolled sheet having a thickness of 0.23 mm.

  Thereafter, the cold-rolled sheet was annealed in a humidified hydrogen-nitrogen atmosphere, and the nitrogen content of the steel sheet was adjusted to approximately 200 ppm to obtain a decarburized annealed sheet. An annealing separator mainly composed of MgO was applied to the decarburized annealing plate, and then wound into a coil shape.

The annealing separator was added with 200 ppm of FeCl ₂ with respect to 100 parts by mass of MgO and 5 parts by mass of TiO ₂ , and the additives shown in Table 2 were added in respective addition amounts in each case. It is a thing. The steel plate coated with such an annealing separator was annealed in a hydrogen stream at 1200 ° C. for 20 hours. Table 2 shows the film properties and magnetic properties (magnetic flux density B8 (T) and iron loss W17 / 50 (w / kg)) of the obtained steel sheet.

The meanings of the evaluation symbols for film properties are as follows. ○ The above is acceptable.
A: There is no defect on the entire surface of the steel sheet, and the glass film has a uniform color over the entire area of the steel sheet.
A: A glass film having a slight unevenness in color near the edge of the steel plate and near the center of the steel plate, although there is no defect on the entire surface of the steel plate.
(Triangle | delta): It is a glass membrane | film | coat with which a dotted | punctate defect is scattered in the steel plate edge part vicinity.
X: A glass film having a point defect near the edge of the steel plate and having a discolored portion.

  From Table 2, it can be seen that when an annealing separator added with smectite, sepiolite, or talc is used, a good film without defects can be obtained and satisfactory magnetic properties can be obtained.

(Example 3)
Si: 3.2 mass%, Mn: 0.12 mass%, S: 0.005 mass%, C: 0.05 mass%, acid-dissolvable Al: 0.026 mass%, N: 0.008 mass% Using a slab containing slab as a raw material, it was hot-rolled by a known method, then subjected to hot-rolled sheet annealing, and then cold-rolled to obtain a cold-rolled sheet having a thickness of 0.23 mm.

  Thereafter, the cold-rolled sheet was annealed in a humidified hydrogen-nitrogen atmosphere, and the nitrogen content of the steel sheet was adjusted to approximately 200 ppm to obtain a decarburized annealed sheet. An annealing separator mainly composed of MgO was applied to the decarburized annealing plate, and then wound into a coil shape.

The annealing separator is added with 200 ppm of FeCl ₂ with respect to MgO: 100 parts by mass and TiO ₂ : 5 parts by mass, and further, the additives shown in Table 3 are added in respective addition amounts. It is a thing. The steel plate coated with such an annealing separator was annealed in a hydrogen stream at 1200 ° C. for 20 hours. Table 3 shows the film properties and magnetic properties (magnetic flux density B8 (T) and iron loss W17 / 50 (w / kg)) of the obtained steel sheet.

The meanings of the evaluation symbols for film properties are as follows. ○ The above is acceptable.
(Double-circle): There is no defect on the whole surface of the steel sheet, and the glass film has a uniform color throughout the steel sheet.
○: A glass film having no defects on the entire surface of the steel sheet, but having some unevenness in color near the edge of the steel sheet and near the center of the steel sheet.
(Triangle | delta): It is a glass membrane | film | coat with which a dotted | punctate defect is scattered in the steel plate edge part vicinity.
X: A glass film having a point defect near the edge of the steel plate and having a discolored portion.

From Table 3, smectites, and, either one or both of the sepiolite, or one of them, the use of further annealing separating agent was added pressure to the compound added talc, good without defects It can be seen that a film is obtained and satisfactory magnetic properties are obtained.

  As described above, according to the present invention, a grain-oriented electrical steel sheet having a glass film with excellent properties and good magnetic properties can be stably obtained. Therefore, the present invention has high applicability in the electrical steel sheet manufacturing industry.

Claims (4)

When heated in a nitrogen-hydrogen mixed gas stream at normal pressure, a gas containing oxygen is released , and a smectite containing crystal water whose weight loss due to the gas release in a temperature range of 500 to 950 ° C. is 2% or more , and An annealing separator for grain-oriented electrical steel sheets comprising 2 to 30% by mass of a compound obtained by further adding talc to any one or both of sepiolite or any of them . The annealing separator for grain-oriented electrical steel sheets according to claim 1, wherein the annealing separator is mainly composed of MgO. The annealing separator for grain-oriented electrical steel sheets according to claim 2 , wherein the annealing separator contains 2 to 30% by mass of the compound as an additive with respect to 100 parts by mass of MgO. In the manufacturing method for grain-oriented electrical steel sheets, the cold-rolled sheet of the final thickness is subjected to decarburization annealing, and after nitriding, finish annealing is performed to produce a grain-oriented electrical steel sheet. Alternatively, when performing finish annealing in a coil state, the annealing separator for the grain-oriented electrical steel sheet according to any one of claims 1 to 3 is applied to a cold-rolled plate to perform finish annealing. A method for producing grain-oriented electrical steel sheets.