JPH07173641A - Directional electromagnetic steel sheet - Google Patents

Abstract

PURPOSE:To provide the directional eletromagnetic steel sheet of low core loss. CONSTITUTION:The directional electromagnetic steel sheet of low core loss where the metallic coating layer of 0.005-5mum in thickness is provided on the surface, and the linear coefficient of thermal expansion after heat treatment of the metallic coating layer is lower than that before heat treatment by >=3X10<-6>K<-1> is provided. This directional electromagnetic steel sheet is provided with the tension-applied metallic coating layer which is not peeled off after the heat treatment at high temperature, and is excellent in the thermal stability without deteriorating the core loss.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grain-oriented electrical steel sheet having extremely good magnetic properties relating to magnetic flux density and iron loss,
In particular, the present invention relates to a grain-oriented electrical steel sheet in which iron loss is reduced and magnetic flux density is increased by improving the surface of the steel sheet to improve magnetic properties.

[0002]

2. Description of the Related Art Recently, in grain-oriented electrical steel sheets, a technique for applying a tension to the steel sheet by surface modification to reduce the iron loss value has been actively developed. The first of these is laser irradiation on the surface of a steel sheet ["Iron and Steel", 69 (1983), p. 895 and Japanese Patent Publications Nos. 57-2252, 57-53419 and 58-24605).
No. 58-24606) or plasma irradiation
(Japanese Patent Laid-Open Nos. 62-96617, 62-151511, and 62-151516
No. 62-151517) and introduces local strain to subdivide the magnetic domain to reduce iron loss.

However, while the above-mentioned magnetic domain refinement technique is effective for the transformer material for laminated iron cores that is not subjected to strain relief annealing, in the wound core material transformer material that is subjected to strain relief annealing, the local strain introduced with great care during annealing is used. Since it is released and the magnetic domain width is widened, there is a drawback that the irradiation effect of laser or plasma disappears.

As a method for preventing the magnetic domain refining effect from deteriorating even when subjected to such high temperature annealing, for example, a method of forming grooves or serrations on the surface of the finish annealed sheet (Japanese Patent Publication No. 50-35679). JP 59-28525
No. 59-197520), a method of forming a fine crystal grain region on the surface of a finish annealed plate (see Japanese Patent Laid-Open No. 56-130454), and forming a different thickness or defect region in a forsterite film. Method (JP-A-60-92481, JP-A-60-258479)
(See each publication), and a method of forming a different composition region in a base metal, a forsterite film, or a tension insulating film.
(See JP-A-60-103124 and JP-A-60-103182). However, with these methods, the cost is significantly increased, and the degree of decrease in iron loss is small,
These have not been adopted industrially.

After finishing annealing of the grain-oriented electrical steel sheet, the surface of the steel sheet is mirror-finished, or thin metal plating or a ceramic thin film is formed on the mirror-finished surface (Japanese Patent Publication No. 52-2449).
No. 9, Japanese Patent Publication No. 56-4150), and a method of manufacturing an ultra-low iron loss grain-oriented electrical steel sheet by coating an insulating film on it is also proposed.

[0006] However, the iron loss improving method by mirror finishing not only significantly increases the cost but also does not sufficiently contribute to the iron loss reduction. Further, in the method of forming a ceramic thin film, there is a problem in the adhesion with the steel sheet after performing stress relief annealing at 600 ° C. or higher for a long time,
These methods have not been adopted in the present manufacturing process either.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation, and an object of the present invention is to have a tension-applying coating layer on the surface of a steel sheet, which reduces iron by magnetic domain refinement. It is an object of the present invention to provide a low iron loss grain-oriented electrical steel sheet in which the loss does not deteriorate even when subjected to heat treatment at a high temperature such as strain relief annealing, and the coating layer does not peel off.

[0008]

The gist of the present invention resides in the following low iron loss grain-oriented electrical steel sheet.

A metal coating layer having a thickness of 0.005 to 5 μm is formed on the surface, and the linear thermal expansion coefficient of the metal coating layer after heat treatment is lower than that before heat treatment by 3 × 10 ^-6 K ^-1 or more. Characteristic low iron loss grain-oriented electrical steel sheet.

As described above, conventionally, there has been known a method of applying tension to a steel sheet by utilizing the difference in thermal expansion between the ceramic coated on the surface of the steel sheet and the steel sheet. However, this method has not yet been put to practical use because the ceramic layer easily peels off during subsequent strain relief annealing.

On the other hand, when the coating on the surface of the steel sheet is metal plating, a part of the interface is alloyed during annealing for strain relief or phase equilibration of the steel sheet, so that peeling is difficult. Further, according to plating, a completely different structure from that in the case of melting and solidification appears in the plating layer, and a history may appear in the thermal expansion curve of the plating layer during heating and cooling of the above annealing of the steel sheet, In such a case, it is considered that the state and degree of the tension applied to the steel sheet and the degree of difficulty of peeling also differ.

As a result of the examination from such a viewpoint, the present inventors have obtained the following findings, particularly when Fe-Ni alloy plating is used as the surface coating layer of the electromagnetic steel sheet.

In the as-plated plating layer, in addition to the γ phase,
The α phase, which is difficult to appear in the normal melting and solidification process, appears and becomes two phases of α + γ, whereas it becomes a γ single phase after annealing.

In the plated layer in which the appearance and change of the phases as described above appear, an extremely large tensile stress can be applied to the steel sheet due to an extremely large difference in thermal expansion between the plated layer and the steel sheet during annealing.

The above-mentioned properties (1) to (3) are brought about by the Invar characteristics (the coefficient of thermal expansion in the room temperature region is close to zero) in the Fe-Ni system alloy.

As a result of alloying at the interface between the plating layer and the steel sheet during annealing, adhesion is improved and a surface film that is difficult to peel off is obtained.

Therefore, there may be cases where the above effects (1) to (4) are obtained even in alloys other than Fe-Ni alloys, and further, even in the simple metal plating layer, the F content in the steel sheet is increased.
It has also been clarified that similar effects may be obtained since alloying with e, Mn, etc. is performed.

[0018]

The reason why the grain-oriented electrical steel sheet of the present invention has the above metal coating layer on its surface will be described.

(1) Coating layer: metal In order to prevent the coating layer from peeling off even after high temperature heat treatment such as annealing after forming the metal coating layer, a metal-based coating layer that may alloy with the steel sheet component And need to.
Furthermore, in order to apply an appropriate tensile stress to the steel sheet by the coating layer, the volume fraction of the phase with a large thermal expansion coefficient decreases and the volume fraction of the β phase with a small thermal expansion coefficient increases during the annealing process. As a result, it is desirable to use a metal that has a large thermal expansion coefficient of the entire plated layer during heating and a small thermal expansion coefficient of the entire plated layer during cooling.

With the metal coating layer having such properties, a large tensile stress can be applied between the coating layer and the steel sheet during cooling, and the tensile stress can be applied by alloys other than the Fe-Ni system alloy. It is possible to obtain the same without sticking to the Invar phase.

Examples of the alloys as described above include Invar alloys (Fe-Ni series, Fe-Ni-Co series, Fe-Co-Cr series, Fe-
B system, Fe-Cr-Mn system, Fe-Mn-Ge system, Mn-Ge system, etc.).

Of these, Mn-Ge containing 20 to 25 at% Ge
The binary alloys are antiferromagnetic and form a hexagonal ε phase in the temperature range of 860 K (587 ° C) or higher. This phase is on the high temperature side above 773 K (500 ° C.) in the equilibrium diagram, and at temperatures below that, it is supposed to be the ε ₁ phase of ferrimagnetic fct. However, when the surface of the steel sheet was coated with this alloy as a plating layer, the temperature of 860 K (587 ° C) or higher was
If cooled at a rate of 19 × 10 ⁻³ K / s or more, the ε phase can be stably obtained at room temperature, and excellent invar characteristics are exhibited in the temperature range below its magnetic transformation point (about 100 ° C.). Therefore, this Mn-Ge-based binary alloy can also be used as a metal coating layer having desired properties, like the Fe-Ni alloy.

As the non-invar alloy, Zn-
Ni-based, Zn-Fe-based, Zn-Cr-based, Cu-Pb-based, Co-Cu-based, Ni-
P system, Ni-Sn system, Ni-S system, Fe-Mo system, Co-Mo system, Ni-
There are Mo-based and W-based alloys. In such alloy plating, the phases in the plated layer differ between the as-plated and after-annealing, and a history of the thermal expansion curve occurs, causing a large tensile stress between the coating layer and the steel sheet during cooling. I know this is going to happen. Among them, Zn-Ni type and
Since Zn-Fe-based and other products already have production lines for surface-treated steel sheets for automobiles, they are easy to put into practical use.

Other coating layers include Cr, Mn, Fe, Co, N
It may be composed of two or more metals selected from i, Cu, Zn, B, Ge, Cd, and In.

The elemental metals include Cr, Mn, Fe, Co, Ni,
One selected from Cu, Zn, B, Ge, Cd, and In is preferable.

(2) Thickness of coating layer: 0.005 to 5 μm If the thickness is less than 0.005 μm, sufficient tension cannot be applied to the steel sheet.
On the other hand, if it exceeds 5 μm, a problem occurs in the space factor, so the range is set to 0.005 to 5 μm.

(3) Coefficient of linear thermal expansion before and after annealing the coating layer: 3
× 10 ⁻⁶ K ⁻¹ or more decrease As shown in FIG. 5 of the example described later, when the difference in linear thermal expansion coefficient before and after annealing of the coating layer is 3 × 10 ⁻⁶ K ⁻¹ or more,
Iron loss W _17/50 is decreased by 0.10 W / kg, and the grade is increased as a product.

The steel sheet of the present invention and the electromagnetic steel sheet as a raw material thereof are manufactured by the following method.

The material magnetic steel sheet may be a normal grain-oriented magnetic steel sheet having a highly integrated crystal orientation in the Goss orientation shown by the {110} <001> orientation formed by secondary recrystallization.

As an example, as shown in Japanese Patent Application Laid-Open No. 5-9666, Si: 1.5 to 3.0% and Mn: 1.0 to 3.
0%, acid-soluble Al: 0.003 to 0.030%, and (Si-
0.5 × Mn) ≦ 2.0, the balance consists of Fe and unavoidable impurities, and the total amount of C and N as impurities is 0.00
It is a grain-oriented electrical steel sheet with 20% or less and S of 0.01% or less. This steel plate, in% by weight, C: 0.01% or less, N: 0.001
A steel slab containing .about.0.010% (other composition is the same as above) is processed by the following steps.

The step of hot rolling, as hot rolling, or after annealing after hot rolling, 1
Step of performing cold rolling two or more times with single or intermediate annealing, step of causing primary recrystallization by continuous annealing, 4 to 100 in a temperature range of 825 to 925 ℃ in an atmosphere containing N _2.
Hold for a period of time to induce secondary recrystallization, in a temperature range from 925 ° C to 1050 ° C in a H ₂ atmosphere.
Hold for ~ 100 hours and purify.

It is desirable that the steel sheet manufactured by the above steps be subjected to pretreatment prior to forming the metal coating layer. That is, in order to remove the surface oxide film formed up to annealing, the surface is subjected to pickling with an aqueous solution of HCl or H ₂ SO ₄ , or the surface is subjected to flattening treatment by chemical polishing or electrolytic polishing.

The steel sheet thus obtained is coated with the above-mentioned metal. As the method, any method may be used as long as it is within the range generally called plating. For example, electroplating from an aqueous solution, hot dip plating, molten salt electrolytic plating, vapor deposition, CVD, PVD, ion plating, ion plantation and the like. A surface coating layer having a thickness of 0.005 to 5 μm may be formed by any of these methods.

After that, annealing heat treatment is performed to obtain the low iron loss grain oriented electrical steel sheet of the present invention. Originally, the purpose of this annealing was to remove the strain from the steel sheet after the user punched it into a predetermined shape or after stacking them. However, here are two purposes.

The metal of the plating layer and the steel sheet are alloyed to improve the adhesion at the interface.

By changing the as-plated structure containing a phase that does not appear on the equilibrium diagram (or a phase that does not appear in a normal melting / solidification process) to become a phase on the equilibrium diagram, The coefficient of thermal expansion of the entire plated layer is changed before and after annealing to obtain a desired difference in thermal expansion between heating and cooling, whereby tension is applied to the steel sheet.

To obtain the above effect, the annealing temperature is 400 ° C.
It is desirable to set it as above. Below 400 ° C, the strain relief effect, alloying and phase change cannot be obtained in a short time. A desirable annealing time is 10 minutes or more.

[0038]

【Example】

(Example 1) In% by weight, C: 0.0030%, N: 0.0042%,
Si: 2.35%, Mn: 1.53%, acid-soluble Al: 0.010%, S:
A steel slab containing 0.002% and the balance Fe and unavoidable impurities was hot-rolled at a heating temperature of 1240 ° C and a finishing temperature of 820 ° C to finish a plate having a thickness of 2 mm. Then at 880 ° C
After hot-rolled sheet annealing for soaking for 40 seconds, it was descaled by pickling and cold-rolled once to give a sheet having a thickness of 0.30 mm.

This cold-rolled sheet was subjected to continuous annealing in a non-decarburized atmosphere of 78% N ₂ + 22% H ₂ at 880 ° C. for 30 seconds so that it was primary recrystallized, and then annealed and separated. Coating and finish annealing were performed.

Finish annealing is performed in an atmosphere of 75% N ₂ + 25% H ₂
The first annealing was soaked at 885 ° C. for 24 hours, and then the atmosphere was changed to H ₂ atmosphere, and the second annealing (purified annealing) was performed at soaked at 950 ° C. for 24 hours. When the iron loss of this electromagnetic steel sheet was measured, W _17/50 was 1.11 W / kg.

Next, using the above-mentioned purified and annealed magnetic steel sheet, its surface was pickled with a 10% HCl aqueous solution and further electroplated (electrolyte solution: FeSO ₄ .7H ₂ O and NiSO ₄ .7H ₂ O). Ni ratio x (at%) by changing mixed solution, constant current electrolysis
After performing Fe _100-X Ni _x alloy plating treatment (0 ≦ x ≦ 100), annealing was performed for 2 hours while changing the annealing temperature.

Table 1 shows the results after plating for each plating composition and further.
Table 2 shows the ratio of the ε phase after annealing at 900 ° C for 2 hours and the iron loss value at each annealing temperature, and the linear thermal expansion coefficient measured at 20 ° C and its change.

[0043]

[Table 1]

[0044]

[Table 2]

As can be seen from Table 1, in the as-plated state (without annealing), the compressive stress is usually applied to the steel sheet, so that the iron loss is deteriorated. However, when Ni is 24.5 to 44.3 at% and the annealing temperature is
Iron loss is low above 600 ° C. When the Ni content is 50.5 at% and the annealing temperature is 800 ° C or lower, the phase change is small and the iron loss is low. As can be seen from Table 2, Ni is 24.5-44.3 at
%, The linear thermal expansion coefficient decreases and the difference between the as-plated condition and the as-plated condition is 3 × 10 ^-6 K.
^-1 or more, and the iron loss value is lower than that of a steel sheet not plated.

FIG. 1 is a diagram showing the influence of the annealing temperature and the Ni ratio on the linear thermal expansion coefficient of the Fe—Ni alloy plated layer at 20 ° C. As shown in the figure, the annealing at 400 ° C has a slightly lower linear thermal expansion coefficient than that of as-plated, but the linear thermal expansion coefficient decreases as the annealing temperature increases, and the difference from that of as-plated becomes large.

FIG. 2 is a diagram showing the effect of the Ni ratio on the iron loss after Fe-Ni alloy plating and annealing at 400 ° C. and 900 ° C. As shown, Ni is 24.5-50.5
Even in the at% range, the decrease in iron loss value is small at 400 ° C, which is not much different from the iron loss value of the steel sheet before plating, but it is low at 900 ° C.

No peeling of the plating layer was observed after any annealing.

(Example 2) 10% of the surface of the magnetic steel sheet (iron loss value is the same as in Example 1) after purification annealing manufactured in Example 1 was used.
After pickling with an aqueous HCl solution to remove the surface oxide film, HF
The surface was mirror-finished by chemical polishing with + H ₂ O ₂ aqueous solution.

Since the Mn-Ge system binary alloy containing 20 to 25 at% of Ge has the above-mentioned characteristics, Mn _100-x Ge _x (10.1 ≤ x ≤ 30.1) is formed on the mirror-finished surface of the steel sheet. ) The thickness of alloy is changed to 3 by changing the Ge ratio (at%) and by ion plating.
After forming a film with a thickness of μm, the annealing temperature was changed and annealing was performed for 2 hours.

Table 3 shows the results after plating for each plating composition and further.
Table 4 shows the ratio of the ε phase after annealing at 900 ° C for 2 hours and the iron loss value at each annealing temperature, and Table 4 shows the linear thermal expansion coefficient measured at 20 ° C and its change. No peeling of the plating layer was observed after any annealing.

[0052]

[Table 3]

[0053]

[Table 4]

As can be seen from Table 3, the iron loss as plated is almost the same as that of the steel sheet not plated. But,
When Ge is in the range of 19.5 to 22.9 at%, the iron loss is low at an annealing temperature of 500 ° C or higher. As can be seen from Table 4, Ge is 19.5
By annealing at 900 ℃ in the range of ~ 22.9at%, the ratio of ε phase increases and the coefficient of linear thermal expansion decreases, resulting in a difference of as-plated 3
The iron loss value is more than × 10 ^-6 K ^-1 , which is lower than that of a steel sheet not plated.

FIG. 3 is a diagram showing the influence of the annealing temperature and the Ge ratio on the linear thermal expansion coefficient at 20 ° C. of the Mn-Ge alloy plating layer. As shown in the figure, the linear thermal expansion coefficient at 20 ° C. decreases as the ε-phase ratio increases. As shown in the figure, the coefficient of linear thermal expansion is slightly lower in the case of annealing at 400 ° C than that in the as-plated state, but the linear thermal expansion coefficient becomes lower as the annealing temperature becomes higher, and the difference from that in the as-plated state increases.

FIG. 4 is a diagram showing the effect of the Ge ratio on the iron loss after Mn-Ge alloy plating and annealing at 400 ° C. and 900 ° C. As shown, Ge is 19.5 to 22.9
Even in the at% range, the decrease in iron loss value is small at 400 ° C, which is not much different from the iron loss value of the steel sheet before plating, but it is low at 900 ° C.

FIG. 5 is a diagram showing an example of the relationship between the core loss of the grain-oriented electrical steel sheet and the amount of change in the linear thermal expansion coefficient of the plating layer based on the results of Tables 1 to 4. Fig. 5 shows that the annealing temperature is 900
This is the case of ° C. As shown in the figure, when the difference in the coefficient of linear thermal expansion before and after annealing of the plated layer is 3 × 10 ^-6 K ^-1 or more, the iron loss value is 0.10 W / kg or more lower than that of the as-plated product It is possible to obtain an elevated grain-oriented electrical steel sheet with low iron loss.

[0058]

EFFECT OF THE INVENTION The grain-oriented electrical steel sheet of the present invention is a tension-imparting metal that does not peel even after high-temperature heat treatment such as annealing for the purpose of strain relief (stress relaxation by phase equilibration) and alloying. It has a coating layer and is excellent in thermal stability without deterioration of iron loss.

[Brief description of drawings]

FIG. 1 is a diagram showing an influence of an annealing temperature and a Ni ratio on a linear thermal expansion coefficient of a Fe—Ni alloy plated layer at 20 ° C.

[Fig. 2] Fe-Ni alloy plating is applied, and then at 400 ℃ and 90
It is a figure which shows the influence of Ni ratio on iron loss after annealing at 0 degreeC.

FIG. 3 is a diagram showing the influence of the annealing temperature and the Ge ratio on the linear thermal expansion coefficient at 20 ° C. of the Mn-Ge alloy plated layer.

[Fig. 4] Mn-Ge alloy plating is applied, and then at 400 ℃ and 90
It is a figure which shows the influence of Ge ratio on iron loss after annealing at 0 degreeC.

FIG. 5 is a diagram showing an example of the relationship between the iron loss of the grain-oriented electrical steel sheet and the amount of change in the linear thermal expansion coefficient of the plating layer.

Claims (1)

[Claims] 1. A metal coating layer having a thickness of 0.005 to 5 μm is formed on the surface, and the linear thermal expansion coefficient of the metal coating layer after heat treatment is 3 × 10 ^-6 K ^-1 or more lower than that before heat treatment. A low iron loss grain-oriented electrical steel sheet characterized by the above.