JP5063902B2 - Oriented electrical steel sheet and method for treating insulating film - Google Patents

Description

  The present invention relates to a grain-oriented electrical steel sheet having a high-strength insulating coating that does not contain chromate, and a method for treating the insulating coating.

  Usually, the surface coating of grain-oriented electrical steel sheets is applied to a forsterite layer called a primary coating formed during high-temperature finish annealing and a treatment liquid mainly composed of phosphate to heat flatten the steel sheet. It is formed from two layers of a phosphate coating layer that is sometimes baked. Phosphate coating is necessary for imparting electrical insulation to grain-oriented electrical steel sheets, reducing eddy current loss and improving iron loss. In addition to insulation, corrosion resistance, heat resistance, Various film properties such as slipperiness and adhesion are required.

  That is, in order to process a grain-oriented electrical steel sheet into an iron core such as a transformer, it goes through various manufacturing processes. However, when this iron core is manufactured, heat resistance, slipping property, and adhesion are inferior. If it is, the film peels off during strain relief annealing, and the original performance cannot be exhibited, or the steel sheets cannot be laminated smoothly and workability is deteriorated.

  Furthermore, one of the important characteristics of the insulating coating of the grain-oriented electrical steel sheet is that it exerts the effect of imparting tension to the steel sheet and improving the magnetic properties of the grain-oriented electrical steel sheet. This is to improve the iron loss of the grain-oriented electrical steel sheet by imparting tension to the grain-oriented electrical steel sheet, thereby facilitating the domain wall movement. The noise of the transformer manufactured using the grain-oriented electrical steel sheet as the iron core. It is known that it is also effective in reducing magnetostriction, which is one of the main causes.

  In Patent Document 1, an insulating film treatment liquid mainly composed of phosphate, chromate, and colloidal silica having a specific composition is applied onto a forsterite film formed on the surface of a steel sheet after finish annealing, and baked. Thus, a method has been disclosed in which an insulating coating having high tension is formed on the surface of a steel sheet to reduce iron loss and magnetostriction of the grain-oriented electrical steel sheet.

  Patent Document 2 discloses that a high tension of an insulating coating is obtained by applying and baking a treatment liquid containing ultrafine colloidal silica having a particle size of 8 μm or less, a primary phosphate, and a chromate in a specific ratio. And a method for improving the lubricity of the coating is disclosed.

  Further, Patent Document 3 discloses a directional electromagnetic wave having a high-strength insulating coating having a specific amount of an insulating coating composed mainly of colloidal silica having a phosphate, chromate and glass transition point of 950 to 1200 ° C. Techniques relating to steel sheets are disclosed.

  Although various film properties are remarkably excellent and the film tension is improved as compared with the prior art by the techniques disclosed in the above-mentioned patent documents, both have been mixed with a chromate which is a chromium compound. Close-up and there is a need to prohibit and limit the use of compounds such as lead, chromium and cadmium.

As a technique not containing a chromium compound, Patent Document 4 discloses that colloidal silica is 20 parts by weight of SiO ₂ , aluminum phosphate is 10 to 120 parts by weight, boric acid is 2 to 10 parts by weight, and Mg, Al, Fe, Co, Ni. An insulating film treatment method is disclosed in which a treatment liquid containing 4 to 40 parts by weight of one or two kinds selected from the respective sulfates of Zn is baked at 300 ° C. or higher.

  Patent Document 5 discloses a technique related to a coating material for forming a grain-oriented electrical steel sheet coating, which contains a mixture of boric acid and alumina sol and an organic solvent compatible with water.

  Furthermore, in Patent Document 6, as an organic acid salt selected from Ca, Mn, Fe, Zn, Co, Ni, Cu, B and Al, formate, acetate, oxalate, tartrate, lactate, citric acid A technique related to a surface treatment agent for grain-oriented electrical steel sheets, characterized by adding one or more organic acid salts selected from salts, succinates and salicylates, is disclosed.

  However, the technique disclosed in Patent Document 4 has a problem of a decrease in corrosion resistance due to sulfate ions in the sulfate, and the technique disclosed in Patent Document 5 has a corrosion resistance and a baking temperature that are too high. There is a problem that it is easy to attach, and the technique disclosed in Patent Document 6 has a problem in discoloration and liquid stability due to an organic acid in an organic acid salt, and in any case, further improvement is necessary.

Patent Document 7 discloses that “when baking is performed in an atmosphere where P _H2O / P _H2 is less than 10 ⁻² , a part of the coating crystallizes and minute cracks are generated”. However, in the technique disclosed in Patent Document 7, there is no intention to control crystallization, and a dry atmosphere that does not crystallize is defined only to prevent the occurrence of cracks, and crystallization is insufficient.

Japanese Patent Publication No.53-28375 Japanese Patent Laid-Open No. 61-41778 Japanese Patent Laid-Open No. 11-071683 Japanese Patent Publication No.57-9631 JP-A-7-278828 JP 2000-178760 A Japanese Patent Laid-Open No. 9-78253

  The present invention improves the properties of the insulating film formed on the surface by applying and baking to the steel sheet in the final process of producing the grain-oriented electrical steel sheet, has various film properties such as adhesion, and is much more than before. An object is to obtain a grain-oriented electrical steel sheet having an excellent “high-strength coating film containing no chromium compound”.

  The gist of the present invention is as follows.

(1) A direction characterized by having a high-strength insulating coating containing, as a main component, a metal phosphate and colloidal silica and containing no chromium and having a crystallinity of 2 to 40%. Electrical steel sheet.

  (2) The directionality according to (1), wherein the metal phosphate is one or more selected from Ni, Co, Mn, Zn, Fe, Al, Mg, and Ba. Electrical steel sheet.

  (3) The grain-oriented electrical steel sheet according to (1) or (2), wherein the colloidal silica has an average particle size of 5 to 35 nm.

  (4) The grain-oriented electrical steel sheet contains 0.005% or less of C, 2.5 to 7.0% of Si, an average crystal grain size of 1 to 10 mm, and a crystal orientation of (110) [ The grain-oriented electrical steel sheet according to any one of (1) to (3), which has a deviation of an orientation of 8 ° or less in the rolling direction as an average value with respect to the ideal orientation of 001].

(5) When forming a high-tensile film by applying a treatment liquid mainly composed of a metal phosphate and colloidal silica to the surface of a grain-oriented electrical steel sheet, an average particle size of 5 to 5 is used as an insulating film treatment agent. 100 parts by weight of 35 nm colloidal silica in terms of solid content, and one or more of Ni, Co, Mn, Zn, Fe, Al, Mg, Ba phosphates with respect to 100 parts by weight. A treatment liquid containing 155 to 250 parts by weight of a solid content was applied, and a heating rate V (° C./second), a baking soaking temperature C (° C.), a soaking rate satisfying the following conditional expressions (1) to (6): An insulating coating treatment method for grain- oriented electrical steel sheets, characterized in that a high-strength insulating coating not containing chromium having a heat retention time S (seconds) and a crystallinity of the metal phosphate of 2 to 40% is formed.
30 ≦ V (1)
10 ≦ S (2)
800 ≦ C ≦ 1000 (3)
S ≦ 2V-40 (4)
C ≦ 5 / 3V + 900 (5)
S ≦ −4 / 5C + 820 (6)

  (6) The grain-oriented electrical steel sheet contains 0.005% or less of C, 2.5 to 7.0% of Si, an average crystal grain size of 1 to 10 mm, and a crystal orientation of (110) [001 ] In the method for insulating film treatment of grain-oriented electrical steel sheet according to (5), the average orientation has a deviation of an orientation of 8 ° or less in the rolling direction.

  According to the present invention, it is possible to obtain a grain-oriented electrical steel sheet having a high coating tension applied to the surface of the steel sheet, good adhesion of the iron core material in transformer production, and good magnetic properties.

  Hereinafter, the present invention will be described in detail.

  First, in order for the insulating coating of the grain-oriented electrical steel sheet to apply tension to the steel plate, it is necessary that there is a difference in the thermal expansion coefficient between the steel plate and the insulating coating. When the thermal expansion coefficient of the insulating coating is smaller than that of the steel plate, the shrinkage of the steel plate is larger than that of the insulating coating when the insulating coating is baked, so that the steel plate is subjected to tensile stress and compressive stress is applied to the coating. Become. Therefore, the tensile stress applied to the steel sheet can be further increased by reducing the thermal expansion coefficient of the insulating coating.

  In addition, the insulating coating of the grain-oriented electrical steel sheet needs to have excellent adhesion because it does not peel even when tension is applied to such a steel sheet. A mixture of phosphate, colloidal silica, and chromate is generally used to form such an insulating coating.

  The present inventors have intensively studied to obtain an insulating coating that does not contain chromic acid, that is, a so-called environmental problem, and that retains the high tension required for the grain-oriented electrical steel sheet. As a result, in the insulating coating mainly composed of phosphate and colloidal silica, the crystallinity of the phosphate is greatly related to the thermal expansion coefficient of the insulating coating, and the crystallinity of the phosphate is 60%. It has been found that the film tension can be remarkably increased by controlling the following.

  Normally, when chromate is removed with a composition mainly composed of phosphate and colloidal silica, the insulating film has a porous structure, the film tension is low, and adhesion, corrosion resistance, and hygroscopicity are also achieved. It is inferior and cannot be used as it is. The reason why such a porous structure is formed is that there are many gaps between the crystals of phosphate. Therefore, by controlling the crystallization, the formation of a porous film can be prevented. Form.

  It can be easily known that the insulating coating has a crystal structure by analyzing the grain-oriented electrical steel sheet having the insulating coating with an X-ray structure analyzer. For the calculation of crystallinity by X-ray diffraction, a profile fitting method, a quantitative analysis method, and the like are known. Although not particularly limited, profile fitting by peak separation is simple.

  However, in the case of profile fitting, since the insulating coating as in the present invention is in a mixed state of colloidal silica and metal phosphate, in the calculation of crystallinity, colloidal silica or the like alone is previously used. Care must be taken that heat treatment is performed and the diffraction pattern is measured and excluded.

  FIG. 1 illustrates a typical X-ray diffraction measurement chart (using a Cu radiation source). In the case of FIG. 1, a treatment liquid containing 225 parts by weight of Ni phosphate and 100 parts by weight of colloidal silica having a particle size of 12 nm is heated to 900 ° C. at a temperature increase rate of 60 ° C./second and held at 900 ° C. for 25 seconds. An X-ray diffraction chart was measured using the prepared samples. The amorphous component appears as an amorphous halo around 2θ = 20 °, and Ni phosphate appears as a main peak around 30 °.

From these peaks, the background is separated to determine the scattering intensity, and the crystallinity X is calculated by the following equation.
X = C / (C + A) × 100
Here, C: crystalline scattering intensity, A: amorphous scattering intensity

  In addition, since colloidal silica also contains an amorphous component, when calculating the crystallinity of the phosphate, the colloidal silica was previously heat-treated under the same conditions to remove the amorphous halo.

  It is also possible to calculate the degree of crystallinity simply and quickly by calculating the contribution of amorphous halo from the colloidal silica content and calculating the amorphous component of the metal phosphate. .

  Furthermore, although the accuracy is inferior, if the amount of insulating coating deposited, the content of metal phosphate and the type of metal can be specified, the peak of the forsterite coating formed on the surface of the grain-oriented electrical steel sheet can be compared. If the peak of the acid metal salt is sufficiently small, it can be estimated that it contains an amorphous component of the metal phosphate.

  Next, the reason for limitation of the present invention will be described. First, a feature of the present invention is that an insulating film is formed of a metal phosphate and colloidal silica, and the crystallinity of the metal phosphate is 60% or less. When the degree of crystallinity exceeds 60%, a dense film cannot be formed, and the film tension decreases or the corrosion resistance deteriorates. Preferably it is 2 to 40% of range, More preferably, it is 5 to 20% of range.

  When the degree of crystallinity is low, a film having a smooth surface, high film tension, and excellent corrosion resistance can be obtained. When the degree of crystallinity is less than 2%, an insulating film is formed depending on the type of metal phosphate. The polycondensation reaction proceeds later, and as a result, excessive phosphoric acid may be generated to absorb moisture or deteriorate the corrosion resistance.

  As a result of investigations by the present inventors, the crystal system varies depending on the type of metal phosphate, but when heated at a high temperature, Al phosphate is mainly hexagonal, tetragonal or monoclinic. It tends to be monoclinic and orthorhombic with Ni phosphate. Co phosphate and Mn phosphate are likely to be monoclinic or orthorhombic, and are not particularly limited, but the crystal system of the metal phosphate is symmetric such as monoclinic or orthorhombic. A crystal system having low properties is preferred.

  It is presumed that when the symmetry of the crystal system is low, it is presumed that the continuity with the amorphous state is good and unevenness is not easily formed, and a smooth surface state is easily obtained. Ni phosphate or Mg phosphate This is because a good surface appearance can be obtained.

  Further, in the present invention, for example, the details of the reason why Ca phosphate cannot be used are not clear. However, as the present inventors have studied, Ca phosphate tends to form spherulites, and the volume increases as the temperature rises. This is because the film changes greatly, and film defects such as cracks occur. A metal phosphate having such physical properties cannot be used.

  Next, the type of metal phosphate is limited to one or a mixture of two or more phosphates of Ni, Co, Mn, Zn, Fe, Al, Mg, and Ba. More preferably, when one or a mixture of two or more of Ni, Zn, Al, and Mg is used and these metal phosphate salts are used, the mechanism disclosed in the present invention appears. In the case of a metal salt having low solubility of phosphate such as phosphoric acid Ba, Ni, Co, etc., it may be an acidic solution, a colloidal solution, or a dispersion.

  In addition, phosphoric acid metal salts other than the above, such as Ca salt, are likely to produce apatite-based hydrous minerals, and have poor corrosion resistance of the coating, similar to alkali metal salts such as Na salt and K salt, Sr salt, Ba A salt or the like has a very low solubility, and the stability of the colloidal solution is poor, so that a uniform film cannot be formed.

  Further, boric acid, sodium boride, various oxides such as titanium oxide and molybdenum oxide, pigments, and inorganic compounds such as barium titanate may be added to the treatment liquid. In particular, inorganic compounds such as pigments are effective not only for coloring but also for increasing the film hardness and making the insulating film less susceptible to wrinkles.

Next, 2-7 g / m < ² > is suitable for the amount of insulation coating of the product. If the amount of the insulating coating is less than 2 g / m ^2, it is difficult to obtain a high tension, and the insulation and corrosion resistance also decrease. On the other hand, if the amount exceeds 7 g / m ² , the space factor decreases. Transformer characteristics deteriorate.

  Next, the reason for limitation according to the manufacturing method of the present invention will be described. First, the blend of colloidal silica and phosphate used in the present invention is phosphoric acid of Ni, Co, Mn, Zn, Fe, Al, Mg, Ba with respect to 100 parts by weight of colloidal silica in terms of solid content. 155 to 250 parts by weight of salt is blended. If the phosphate is less than 155 parts by weight, powdering by colloidal silica occurs, so the lower limit is limited to 155 parts by weight. On the other hand, if it exceeds 250 parts by weight, the tension effect by colloidal silica cannot be sufficiently exhibited. The amount is preferably 175 to 235 parts by weight, and in this range, an insulating coating having a beautiful surface appearance can be obtained.

  The colloidal silica used in the present invention preferably has an average particle size of 5 to 35 nm. If the average particle size is less than 5 nm, the stability of the liquid is poor, whereas if it exceeds 35 nm, the reactivity is poor, and the ability to fix phosphate is not sufficient, so the hygroscopicity is poor.

  Further, a colloidal silica of 12 to 25 nm is preferable, and the surface is subjected to chemical treatment with aluminum. In addition, from the viewpoint of film-forming properties, it is preferable that the silica is continuous in an indefinite shape or a bead shape, not a spherical shape.

  Next, the insulating film forming method in the present invention will be described. In applying the present invention, the grain-oriented electrical steel sheet after finish annealing may be either a steel sheet having a normal forsterite film or a steel sheet not having a forsterite film. Regardless of which steel plate is used, after removing the excess annealing separator with water, it is subjected to pickling treatment with a sulfuric acid bath, water washing treatment, surface cleaning and surface activation, and then an insulating coating composition liquid is applied. To do.

  In the present invention, in order to obtain a mixed state of an amorphous structure and a crystalline structure, a heating rate V (° C./second), a soaking temperature C (° C.), a soaking time S (second), and these The relationship is very important. As a result of intensive studies by the present inventors, it has been found that the crystallinity of the metal phosphate can be achieved only when all of the following conditional expressions (1) to (6) are satisfied.

30 ≦ V (1)
10 ≦ S (2)
800 ≦ C ≦ 1000 (3)
S ≦ 2V-40 (4)
C ≦ 5 / 3V + 900 (5)
S ≦ −4 / 5C + 820 (6)

  First, if the temperature rising rate V (° C./second) is 30 ° C./second or more, preferably 50 ° C./second or more, more preferably 70 ° C./second or more, and 50 ° C./second or more, the crystallinity is easily obtained. When the temperature is 70 ° C./second, a very beautiful appearance can be obtained. When the temperature is less than 30 ° C./second, crystallization proceeds and a sufficient amorphous structure cannot be obtained.

  Next, the soaking soaking temperature C (° C.) is the ultimate plate temperature, and a range of 800 ° C. or higher and 1000 ° C. or lower is necessary. If the temperature is lower than 800 ° C., sufficient tension is not exhibited. When it exceeds, a crack will arise in a film and film tension will fall or insulation will fall.

  Further, the soaking time S (second) is required to be 10 seconds or more, and if it is less than 10 seconds, seizure is insufficient and the hygroscopicity tends to deteriorate, preferably 20 seconds or more.

Furthermore, in the present invention, in order to control the crystallinity, the rate of temperature rise, the soaking temperature, and the soaking time are:
S ≦ 2V−40, C ≦ 5 / 3V + 900, S ≦ −4 / 5C + 820
It is necessary to satisfy each conditional expression.

  This is because when the heating rate is high, the material is likely to be amorphous, and the higher the soaking temperature, the easier it is to crystallize as the soaking time is longer. In this case, crystallization proceeds and the crystallinity becomes too large.

  Incidentally, the grain-oriented electrical steel sheet produced by using the technique disclosed in Japanese Patent Application Laid-Open No. 7-268567 as the insulating film treatment, that is, C is 0.005% or less, and Si is 2.5 to 7.0. A grain-oriented electrical steel sheet having an average crystal grain size of 1 to 10 mm and a deviation of an orientation of 8 ° or less in the rolling direction as an average value with respect to the ideal orientation of (110) [001]. The effect of further reducing the iron loss was obtained by applying to.

  Next, examples will be described.

(Example 1) A sample having a width of 7 cm and a length of 30 cm was cut out from the same coil after final finishing annealing of a 0.23 mm-thick directional electrical steel sheet, and the annealing separator remaining on the surface was washed with water and lightly pickled. And removing the glass film to leave a glass coating, followed by strain relief annealing. Next, after preparing the insulating film treatment liquid at the blending ratio shown in Table 1, it was applied to the steel sheet and baked under the conditions shown in Table 2 so that the coating amount was 4.5 g / m ^2. Characteristics were evaluated. The results are shown in Table 3.

  In Comparative Example 1, since the crystallinity is large and Ca salt is used as the phosphate, cracking occurs in the coating and the adhesiveness deteriorates. In Comparative Example 2, the crystallinity is large and the particle size of the colloidal silica is large. Was too small to form a porous film with a large gap, and the adhesion was also lowered. In Comparative Example 3, since colloidal silica having a large crystallinity and a particle size that was too large was used, cracks were also generated in the coating, resulting in a decrease in adhesion. In Comparative Example 4, since the proportion of phosphoric acid was too low, crystallization progressed and adhesion decreased.

  In Comparative Example 5, the degree of crystallinity was large and the rate of temperature increase was too low to cause swelling of the film. In Comparative Example 6, the soaking temperature was too low to cause swelling and the film tension was deteriorated. In Comparative Example 7, the degree of crystallinity was large and the soaking temperature was too high, resulting in a porous film with many gaps, and the adhesion deteriorated. In Comparative Example 8, the relationship between the soaking time and the temperature raising rate was compared, and in Comparative Example 9, the relationship between the temperature raising rate and the soaking temperature did not match, so that crystallization progressed and a porous film was formed, and the adhesion deteriorated.

  (Example 2) Using the technique disclosed in Japanese Patent Application Laid-Open No. 7-268567, a molten steel containing 3.25% of Si is cast, and after slab heating, hot rolling is performed at 1100 ° C for 5 minutes. The hot-rolled sheet was annealed and then made 0.22 mm thick by cold rolling. The steel sheet was heated to 850 ° C. at a heating rate of 400 ° C./second, then decarburized and annealed, applied with an annealing separator, and subjected to finish annealing at 1200 ° C. for 20 hours.

Similar to Example 1 from the same coil having an average grain size of 9.5 mm and a crystal orientation of 4.4 ° on average from the ideal orientation of (110) [001]. Then, using the solution shown in Table 4, the coating was applied to the steel sheet and baked under the conditions shown in Table 5 so that the coating amount was 4.5 g / m ² , and then the coating properties and magnetic properties were evaluated. The results are shown in Table 6.

  In Comparative Example 10, since the crystallinity is large and Ca salt is added to the phosphate, cracking occurs in the coating and adhesion deteriorates. In Comparative Example 11, the crystallinity is large and the particle size of colloidal silica is large. Was too small to form a porous film with a large gap, and the adhesion was also lowered. In Comparative Example 12, since colloidal silica having a large crystallinity and a particle size that was too large was used, cracks were also generated in the coating, resulting in a decrease in adhesion.

  In Comparative Example 13, since the soaking temperature was too high, crystallization progressed and adhesion decreased. In Comparative Examples 14 and 15, the relationship between the rate of temperature rise, the soaking temperature, and the soaking time was poor, and crystallization progressed and the adhesion deteriorated.

  As a result of this test, an insulating coating using a specific metal phosphate and controlled to have a crystallinity of 60% or less has higher tension and superior adhesion than the comparative example, and has a good effect of improving magnetic properties. It was.

  According to the present invention, it is possible to obtain a grain-oriented electrical steel sheet having a high coating tension applied to the surface of the steel sheet, good adhesion of the iron core material in transformer production, and good magnetic properties. Therefore, the present invention has high applicability in industries that use electromagnetic steel sheets.

It is a figure which shows a typical X-ray-diffraction chart (using Cu source).

Claims (6)

A grain-oriented electrical steel sheet comprising a high-strength insulating coating containing, as a main component, a metal phosphate and colloidal silica on the surface, and containing no chromium and having a crystallinity of 2 to 40% .
  The grain-oriented electrical steel sheet according to claim 1, wherein the metal phosphate is at least one selected from Ni, Co, Mn, Zn, Fe, Al, Mg, and Ba.   The grain-oriented electrical steel sheet according to claim 1 or 2, wherein the colloidal silica has an average particle diameter of 5 to 35 nm.   The grain-oriented electrical steel sheet contains 0.005% or less of C and 2.5 to 7.0% of Si, an average crystal grain size of 1 to 10 mm, and a crystal orientation of (110) [001]. The grain oriented electrical steel sheet according to any one of claims 1 to 3, which has a deviation of an orientation of 8 ° or less in the rolling direction as an average value with respect to the ideal orientation. A colloid having an average particle size of 5 to 35 nm as an insulating coating treatment agent when a high-tensile coating film is formed on a surface of a grain-oriented electrical steel sheet by applying a treatment liquid mainly composed of metal phosphate and colloidal silica. 100 parts by weight of solid silica in terms of solid content, and one or more of Ni, Co, Mn, Zn, Fe, Al, Mg, Ba phosphates in solid content with respect to 100 parts by weight A treatment liquid containing 155 to 250 parts by weight is applied, and a temperature rising rate V (° C./second), a baking soaking temperature C (° C.), and a soaking hold time satisfying the following conditional expressions (1) to (6) An insulating coating treatment method for grain- oriented electrical steel sheets, characterized in that a high-strength insulating coating not containing chromium having a crystallinity of 2 to 40% is formed in S (seconds).
30 ≦ V (1)
10 ≦ S (2)
800 ≦ C ≦ 1000 (3)
S ≦ 2V-40 (4)
C ≦ 5 / 3V + 900 (5)
S ≦ −4 / 5C + 820 (6)
  The grain-oriented electrical steel sheet contains 0.005% or less of C and 2.5 to 7.0% of Si, an average crystal grain size of 1 to 10 mm, and a crystal orientation of (110) [001]. 6. The method for treating an insulating film on a grain-oriented electrical steel sheet according to claim 5, wherein an average value has a deviation of an orientation of 8 [deg.] Or less in the rolling direction with respect to the ideal orientation.

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