JP2000323318A - Directional silicon steel lamination with low core-loss value - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a core-loss value by forming a tension anisotropic coating on the surface of a directional silicon steel lamination, wherein Young's modulus in the rolling direction divided by coefficient of thermal expansion is greater than Young's modulus perpendicular to the rolling direction divided by coefficient of thermal expansion. SOLUTION: After plating with Cr a finally finished annealed steal plate including Si at 3 weight percent and formed of a directional silicon steel lamination having a thickness of 0.23 mm, it anneals at a different temperature to evaluate magnetic properties. A tension imparted to the steel plate is calculated from a warp of sample steal plated on either side with Cr. In accordance with the calculated result, Young's modulus becomes about 1.4 times when a Cr plated film is directed to the orientation <001> in the rolling direction, and then an obtained stress also becomes about 1.4 times. A coating imparting a greater tension in the rolling direction may be any of anisotropic coatings in which Young's modulus in the rolling direction divided by coefficient of thermal expansion (EL/αL) is greater than Young's modulus perpendicular to the rolling direction divided by coefficient of thermal expansion (Ec/αc).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grain-oriented silicon steel sheet used for an iron core of a transformer or a power generator, and more particularly to a steel sheet by imparting tensile anisotropy to a film covering the surface of the steel sheet. It is intended to further reduce the loss value.

[0002]

2. Description of the Related Art Si is contained and the crystal orientation is (110).
Oriented silicon steel sheets oriented in the [001] direction are widely used as various iron core materials in the commercial frequency range because of their excellent soft magnetic properties. A particularly important characteristic of such a silicon steel sheet is a low iron loss represented by W _17/50 (W / kg), which is a loss when magnetized to 1.7 T at a frequency of 50 Hz.

Among the iron losses, effective methods for reducing eddy current loss (We) include a method of increasing electric resistance by adding Si, a method of reducing the thickness of a steel sheet, and a method of reducing a crystal grain size. As a method of reducing the hysteresis loss (W _h ), a method of highly aligning the <001> axis in the rolling direction is known. Among the above-mentioned methods, the method of containing a large amount of Si has its own limit because it causes a decrease in the saturation magnetic flux density and causes an increase in the size of the iron core. In addition, the method of aligning the crystal orientations is similar to the method in which the magnetic flux density
Products with excellent values of 1.96T and 1.97T for ₈ have been obtained, leaving little room for further improvement. Further, the method of reducing the thickness of the product is not industrially practical because an extremely thin product is difficult to roll.

[0004] Other effective methods for reducing iron loss include:
A method of applying tension to a steel sheet is known, and industrially, tension is applied to the steel sheet by forming a coating made of a material having a smaller thermal expansion coefficient than that of the steel sheet. That is, in the final refining annealing step, which combines the secondary recrystallization to finally align the crystal orientation and the purification of the steel sheet, the oxide on the steel sheet surface (mainly SiO ₂ ) and the annealing separator (MgO) applied to the steel sheet surface Reacts with the main component) to form a coating containing forsterite (Mg ₂ SiO ₄ ) as a main component, but this coating has a large tension applied to the steel sheet and is effective in reducing iron loss. Further, in order to increase the tension effect, a low thermal expansion coating (tensile type insulating coating) is overcoated on the forsterite coating,
Generally, it is a product.

At present, as a tension imparting type insulating coating applied to a grain oriented silicon steel sheet having a forsterite film, a phosphate of Al or alkaline earth metal and colloidal silica, chromic anhydride or chromate are mainly used. Many are formed by applying and baking a treatment liquid as a component. The mechanism of applying tension by this coating is based on the difference in thermal expansion between the ground iron and the insulating coating by baking the coating containing a large amount of inorganic substances having a smaller thermal expansion coefficient than that of the ground iron represented by colloidal silica at a high temperature. Thus, at room temperature, a phenomenon in which tension is applied to a steel sheet is used. The insulating coating formed by this method has a large effect of imparting tension to the steel sheet, and is extremely effective in reducing iron loss. A typical method of forming such an insulating film is disclosed in, for example, Japanese Patent Publication No. 53-28375 and Japanese Patent Publication No. 56-52117.

[0006]

It is known that when a tension is applied to a steel sheet by utilizing a difference in thermal expansion coefficient between the steel sheet and the coating, the tension value σ is expressed by the following equation (1). (Eg, Japanese Patent No. 2664323). σ = 2E _coa · A _coa (T−T ₀ ) (α _met −α _coa ) ÷ A _m --- (1) where, E _coa : Young's modulus of the coating A _coa , A _met : _{Cutting of} coating, steel plate Area T: Coating temperature (softening temperature) T ₀ : Measurement temperature (room temperature) α _coa , α _met : Coefficient of thermal expansion of coating and steel plate According to the above equation (1), the Young's modulus of the coating is high, The lower the coefficient of thermal expansion compared to that of a steel sheet, the greater the tension value. However, a desired low iron loss could not be obtained even if the Young's modulus or the coefficient of thermal expansion of the coating was changed more than at present.

Hereinafter, the reason will be described. Whether it's a primary coating of minerals based on forsterite or a top-coating, low thermal expansion, tensioning coating,
The stress generated by the coating is isotropic in two dimensions, and uniformly applies tension in all directions in the plane. By forming these coatings on the steel sheet, the effect of magnetic domain refining is exhibited and the iron loss value is reduced because the crystal of the secondary recrystallized directional silicon steel sheet is (110) [001] with respect to the rolling direction. ]
This is because they are accumulated in the direction. This is because a grain-oriented silicon steel sheet which is oriented and oriented closer to a single crystal is composed of a crystal group having a <100> axis in the rolling direction and a <110> axis in a direction perpendicular to the rolling direction. Body-centered cubic lattice (B
Metals having CC) generally have the lowest Young's modulus in the <100> orientation. As shown by the following Young's modulus definition equation (2), when the same stress σ is applied, the smaller the Young's modulus, the larger the amount of deformation of the material. Additional stress σ = Young's modulus E × deformation △ L --- (2)

Therefore, even when a uniform stress is applied isotropically to the grain-oriented silicon steel sheet, the steel sheet undergoes the most stretching deformation, particularly in the rolling direction. When tension is applied in the rolling direction, magnetic domains substantially parallel to the rolling direction are subdivided, and the iron loss value is reduced. Conversely, when tension is applied perpendicular to the rolling direction, the magnetic domain pattern is disturbed or disappears, resulting in an increase in iron loss value. However, even with a coating that imparts isotropic tension, such as forsterite or a topcoat, the iron loss value is reduced because the tensile effect in the rolling direction is maximized due to the anisotropy of the steel sheet itself as described above. You do it.

As is apparent from the above formula (1), it is possible to increase the applied stress by increasing the thickness of the coating, increasing the Young's modulus, or decreasing the coefficient of thermal expansion. However, this method also increases the rolling component and the tensile component in the perpendicular direction, which are detrimental to magnetic domain refining, so that simply changing various parameters of the coating having isotropic properties saturates the iron loss reducing effect. The effect of reducing iron loss was not obtained. For the reasons mentioned above,
In recent years, no new development has been recognized in the technology for reducing iron loss by applying tension to a steel sheet.

[0010]

Means for Solving the Problems The inventors of the present invention have made various studies to overcome the above-mentioned limitations, and as a result, have obtained a completely new idea of imparting tensile anisotropy to the coating itself. In other words, as a result of diligent research to reduce the effect of applying tension in the direction perpendicular to rolling that is detrimental to reducing iron loss, and to increase the application of tension in the rolling direction more effectively, a new film that has its own tension application anisotropy was developed. And completed the present invention.

That is, the gist configuration of the present study is as follows. 1. The value obtained by dividing the Young's modulus in the rolling direction by the coefficient of thermal expansion ( _EL
/ Α _L ) having an anisotropic coating larger than the value (E _C / α _C ) obtained by reducing the Young's modulus in the direction perpendicular to the rolling direction by the coefficient of thermal expansion (E _C / α _C ). Silicon steel sheet.

2. 2. The grain-oriented silicon steel sheet having a low iron loss value according to the above 1, wherein the grain-oriented silicon steel sheet has a film oriented in the rolling direction of the steel sheet.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described specifically. A final finish-annealed sheet of a grain oriented silicon steel sheet containing 3 wt% Si and having a final sheet thickness of 0.23 mm was pickled with H ₂ SO ₄ to remove forsterite on the surface. The obtained steel sheet was treated with Cr using a general Sargent bath consisting of hexavalent chromium and sulfuric acid.
Plated. Thereafter, annealing was performed at various temperatures, and the magnetic properties were evaluated. Further, the tension applied to the steel sheet was calculated from the amount of warpage of a sample in which only one side of the steel sheet was plated with Cr.

FIG. 1 shows the relationship between the annealing temperature and the iron loss value. As shown in the figure, the iron loss W _17/50 value is remarkably reduced as the annealing temperature increases.

FIG. 2 shows the relationship between the annealing temperature and the stress generated in the Cr plating film. The dotted line in the figure is the theoretical value obtained by substituting the Young's modulus, coefficient of thermal expansion, and plating thickness of Cr into Equation (1) .When the annealing temperature was 600 ° C or higher, a stress higher than expected was obtained. . When the crystal orientation of the Cr film was measured for a sample in which a stress exceeding the expected value was generated, the Cr crystal was (110) [001] in the rolling direction, similarly to the base steel sheet.
It was found that the orientation was aligned so that the orientations were aligned.

Table 1 shows the Young's modulus of the polycrystal of Fe and Cr and the Young's modulus in each of the basic orientations of the single crystal. As described above, the Young's modulus of Fe is the smallest in the <001> orientation. The same applies to silicon steel containing about 3 wt% of Si. On the other hand, the Young's modulus of Cr is the largest in the <001> orientation.

[0017]

[Table 1]

As described above, the Cr plating film is less than <0 in the rolling direction as compared with the case where a polycrystalline film generates isotropic tension.
When the <01> orientation is oriented, the Young's modulus is about 1.4 times, and thus the obtained stress is estimated to be about 1.4 times. From the above, it is considered that by applying a coating having anisotropic applied stress on the surface of the steel sheet, the magnetic domains were effectively subdivided, and as a result, a remarkable reduction in iron loss was achieved.

By the way, as a film giving a greater effect of imparting tension in the rolling direction, a film having a low coefficient of thermal expansion in the rolling direction may be used as long as it does not have an anisotropic Young's modulus. That is, the value obtained by dividing the Young's modulus in the rolling direction by the coefficient of thermal expansion (E _L / α _L ) is equal to that in the direction perpendicular to the rolling (E _L / α _L ).
_C / α _C ).

In the case of BCC metal, Group 6 elements such as Mo and W have a large Young's modulus in the <001> orientation, so that the <001> orientation may be aligned with the rolling direction.
1> The direction may be aligned. Similar considerations apply to FCC and HCP metals. Of course, not only the metal film but also a ceramic film may be used as long as the film has an anisotropy such that the coefficient of thermal expansion in the rolling direction of the steel sheet is small or the Young's modulus is large.

In an amorphous or cubic crystal, the coefficient of thermal expansion is constant, but in other hexagonal, triclinic and orthorhombic systems, the a-axis and the c-axis perpendicular to it have a different thermal expansion coefficient. Different expansion coefficients. For example, CaCO ₃ (aragonite) has α = 10 × 10 ⁻⁶ / K in the a-axis direction, α = 33 × 10 ⁻⁶ / K in the c-axis direction, and α = 13 × 10 ⁻⁶ / K in Fe. As compared with, the a-axis direction is small and the c-axis direction is large. Therefore, when the a-axis is aligned with the rolling direction, it is possible to apply a tensile stress in the rolling direction and a compressive stress in the direction perpendicular to the rolling direction according to the formula (1). .

Further, even if the matrix of the coating has an isotropic property, it has a fibrous structure which is parallel to the rolling direction and exhibits anisotropy. There may be. For example, instead of randomly dispersing glass fiber fibers in a matrix, by continuously uniaxially orienting the glass fiber fibers, the Young's modulus in that direction can be increased.

The thickness of such an anisotropic film is not particularly limited, but is preferably about 0.05 to 20 μm in consideration of film adhesion and space factor.

Next, the preferred composition of the silicon steel sheet of the present invention will be described. As the components of the steel sheet used in the present invention, Si is 1.5 to 7.0 wt%, and Mn is 0.03 to 2.5 wt%.
It is desirable to contain about wt%. That is, Si or Mn
Is an effective component to increase the electrical resistance of products and reduce iron loss. However, if Si exceeds 7.0 wt%, its hardness will increase and it will be difficult to manufacture and process, while Mn will be 2.5 wt% If it exceeds, there is a possibility that γ transformation is induced during the heat treatment to deteriorate the magnetic properties. Further, in steel, in addition to the above elements, Al, B, Bi, Sb, Mo, Te, Sn, P, Ge, As, which are known as inhibitor components suitable for the production of grain-oriented silicon steel sheets.
Nb, Cr, Ti, Cu, Pb, Zn, In and the like can be contained alone or in combination. Further, impurities such as C, S, and N all have harmful effects on magnetic properties and particularly deteriorate iron loss. Therefore, C: 0.003 wt% or less, S: 0.002 wt% or less, and N: 0.002 wt%. % Is desirable.

The method for manufacturing the silicon steel sheet is not particularly limited, and may be manufactured according to a conventional method. Regarding the surface after finish annealing, when forming an anisotropic film by a plating method, even if forsterite is present, it is only necessary that the resistance value is low enough to allow conduction, and of course, it may not be present. . In addition, although it is effective on a ground iron surface in which an inorganic coating such as forsterite is simply removed, it is more effective to reduce the iron loss by performing a smoothing treatment on the surface. For example, there may be mentioned a mirror-finished surface having a surface roughness as small as possible by thermal etching or chemical polishing or a graining-like surface obtained by crystal orientation enhancement treatment by electrolysis in an aqueous halide solution. In particular, the latter surface of the 3 wt% Si-FeSi (110) surface where the terraces and steps are alternately arranged is different from the mirror surface in that not only the adhesion is improved due to the high roughness, but also the deposition rate of the individual secondary Since it does not depend on the plane orientation of the crystal grains, there is no variation in the bonding force that affects the thickness and adhesion of the plating layer, so that the film characteristics are stable and it can be said that this is a more excellent processing method.

There is no particular limitation on the surface properties except for the plating method. However, in the case where anisotropy is obtained by using epitaxial growth by vacuum evaporation, necessary surface treatment should be performed. . In the case of the plating method, since there is no insulating film, an insulating coating is formed on the electrodeposited layer. As the insulating coating, it is more effective to reduce the iron loss value if it has a tension imparting effect, but a general coating may be used as long as it has insulating properties.

As the kind of the tension coating, a phosphate-colloidal silica-chromic acid type coating which has been conventionally used for a grain oriented silicon steel sheet having a forsterite film, and the like, its effect, cost, uniform processing property, etc. It is preferable from the point of view. The thickness of the coating should be 0.3
It is preferably about 10 μm. Further, as the tension coating, other than this, JP-A-6-65754,
It is also possible to apply an oxide coating such as boric acid-alumina proposed in JP-A-6-65755 and JP-A-6-299366. The combination of these isotropic tension films and the anisotropic tension film of the present invention did not particularly reduce the effect of anisotropy.

Even if the magnetic domain is subdivided by irradiating the steel sheet thus obtained with a laser or a plasma flame for the purpose of further reducing iron loss, there is no problem in the adhesion of the insulating coating. . Further, at any stage of the production process of the grain-oriented silicon steel sheet of the present invention, by forming linear grooves at regular intervals by etching or tooth-shaped rolls on the surface for magnetic domain refinement, the iron loss is further reduced. It is effective as a means.

[0029]

Example: Si: 3.4 wt%, C: 0.07 wt%, Mn 0.07 wt%,
Se: 0.02 wt%, Sb: 0.04 wt%, Al: 0.03 wt% and N:
A steel slab containing 0.09 wt% and the remainder having a substantially Fe composition was hot-rolled and then cold-rolled according to a conventional method.
Finished into a cold-rolled sheet with a final sheet thickness of 0.20 mm. Next, the obtained cold-rolled sheet is subjected to a magnetic domain refining treatment for forming a linear groove in a direction substantially perpendicular to the rolling direction, and then subjected to decarburization and primary recrystallization annealing, and then to MgO as a main component, After applying an annealing separating agent to which lead chloride was added, final annealing including a secondary recrystallization process and a purification process was performed to produce a grain-oriented silicon steel sheet without a forsterite film. In addition to annealing while the material that does not perform smoothing processing, two types of pre-processing of the specular treatment by chemical polishing in an electrolytic due to crystal orientation-intensifying treatment, and HF-H ₂ 0 ₂ bath in the aqueous solution of NaCl And the surface was magnetically smoothed.

After the steel sheet thus obtained was plated with Cr, it was annealed at various temperatures, and the iron loss value (W _17/50 ) of the obtained steel sheet and the crystal orientation of the Cr plated grains were measured. did. Further, the ratio (E _L / E _C ) of the Young's modulus in the direction perpendicular to the rolling direction (L direction) and the rolling direction (C direction) was calculated from the amount of warpage of the steel sheet in the corresponding direction. Since chromium is BCC, the coefficient of thermal expansion is constant and isotropic in all directions and α =
8.4 × 10 ⁻⁶ / K. The plating bath used was a fluorosilicic bath composed of hexavalent chromium, sulfuric acid, and sodium fluorosilicate. Table 2 shows the obtained results.

[0031]

[Table 2]

As is clear from the table, when the orientation appeared in the Cr plating film by the annealing treatment, the iron loss value was remarkably reduced. On the other hand, in Comparative Examples (Sample Nos. 1, 4, and 7) in which the plating layer was not oriented, the iron loss value was not sufficiently reduced.
In particular, it is presumed that the iron loss value of Sample No. 7 was significantly deteriorated due to the strain considered to be caused by the electrodeposition stress introduced during plating.

[0033]

Thus, according to the present invention, on the surface of a grain-oriented silicon steel sheet, a tension component parallel to the rolling direction effective for magnetic domain refining is larger than a harmful perpendicular direction tension component. By forming a coating having the above, the iron loss value can be reduced remarkably as compared with the prior art, and the industrial advantage is extremely large.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between an annealing temperature after Cr plating and iron loss.

FIG. 2 is a graph showing a relationship between an annealing temperature after Cr plating and a generated stress.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seiji Okabe 1-chome, Kawasaki-dori, Mizushima, Kurashiki-shi, Okayama Pref. Inside the Mizushima Works, Kawasaki Steel Corporation (72) Mitsumasa Kurosawa 1, Kawasaki-dori Mizushima, Kurashiki-shi, Okayama Chome (without address) Mizushima Works, Kawasaki Steel Corporation (72) Inventor Michio Komatsubara 1-chome, Mizushima Kawasaki-dori, Kurashiki-shi, Okayama Prefecture (without address) Mizushima Works, Kawasaki Steel Corporation F-term (reference) 5E041 AA02 BC01 CA02

Claims (2)

[Claims] The value obtained by dividing the Young's modulus in the rolling direction by the coefficient of thermal expansion (E _L / α _L ) is the value obtained by reducing the Young's modulus in the direction perpendicular to the rolling direction by the coefficient of thermal expansion (E _C / α _C ). A grain-oriented silicon steel sheet having a low iron loss value, having a larger anisotropic coating. 2. The grain-oriented silicon steel sheet having a low iron loss value according to claim 1, wherein the steel sheet has a film oriented in the rolling direction of the steel sheet.