JP3415379B2 - Insulating coating on grain-oriented silicon steel sheet and method of forming the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulating coating film formed on the surface of a grain-oriented silicon steel sheet used for an iron core or the like of a transformer or other electric equipment, and a method for forming the same. The aim is to propose a coating with its advantageous formation.

[0002]

2. Description of the Related Art In the production process of grain-oriented silicon steel sheets, a steel slab is hot-rolled, cold-rolled, then decarburized and annealed, and finally finished and annealed for secondary recrystallization. Is common. Among these steps, secondary recrystallization occurs during final finish annealing, and huge crystal grains with easy axes of magnetization aligned in the rolling direction are generated. The role of finish annealing is also related to MgO in the annealing separator and SiO ₂ formed in decarburization annealing.
There are various methods such as formation of a forsterite film by reaction with an oxide layer mainly composed of, and removal of impurities by purification.

Since the forsterite coating is formed at a high temperature during finish annealing, the steel sheet is given a tension due to the difference in coefficient of thermal expansion between the coating and the base iron after cooling to room temperature. . When tension is applied, spins are aligned in a certain direction by the magnetoelastic effect, and magnetostatic energy increases. As a result, magnetic domains are subdivided and iron loss is reduced. In addition, if the adhesion of the forsterite coating is poor or if the formation is inadequate, it becomes difficult to apply the insulating coating applied after finish annealing, or it partially peels off, resulting in poor insulation and rust resistance. It deteriorates. Therefore, the quality of the forsterite coating is an important factor that influences the magnetic characteristics and coating characteristics of grain-oriented silicon steel.

For this reason, various methods have been disclosed for improving the quality of forsterite coatings. For example, JP-A-60-197883 discloses a method of forming a better forsterite coating by specifying the dew point in the finish annealing atmosphere by the amounts of Mn, S and Se in steel. Further, in Japanese Patent Application Laid-Open No. 6-17261, a film formed during secondary recrystallization annealing is referred to as a forsterite film.
There is disclosed a method of enhancing the tension effect and improving the magnetic properties by forming the oxide film containing Al and Si. Further, Japanese Patent Application Laid-Open No. 53-5800 discloses a method for forming a uniform film by defining the particle size of the forsterite forming the forsterite insulating film.

[0005]

With these techniques,
Although the film properties and magnetic properties have improved to some extent,
It is hard to say that sufficient effects have been obtained. In particular, from decarburization annealing to finish annealing, problems in magnetic properties and film properties are likely to occur due to subtle changes in process conditions, and therefore there is a strong need to improve the glass film.

The present invention has been made in view of the above circumstances, and proposes a method for obtaining a good film without impairing the magnetic properties.

[0007]

SUMMARY OF THE INVENTION This invention is finishing a film formed on the base iron surface of the grain oriented silicon steel sheet after annealing, write no anchor portion it said coating partially enters the inside base iron
And a neck portion that connects the anchor portion and the upper portion of the coating film is formed, and when the coating film is peeled off by a bending test of a steel sheet, the residual portion of the coating film on the surface of the base metal is 8 in area ratio.
To 53% by weight, an insulating coating of a grain-oriented silicon steel sheet, and a steel containing 2-4 wt% of Si are hot-rolled,
Cold rolling is performed once or multiple times including intermediate annealing to finish to the final plate thickness, then primary recrystallization annealing, and then Mg
In the method of forming an insulating coating on the base iron surface of a steel sheet by applying an annealing separator containing O as a main component and then performing final finishing annealing, the lamellar shape in the internal oxide layer formed by primary recrystallization annealing The silica-enriched layer has a thickness of 0.2 μm or more and 3.6 μm or less, and the amount of water introduced becomes 1.0 to 3.9% when it is slurried as an annealing separator.
Is used, and the atmospheric oxidative P (H ₂ O) / P (H ₂ ) at 700 ° C. or higher and lower than 1000 ° C. during finish annealing is set to 1.5 × 10 ⁻⁴ or more and 2.0 × 10 ⁻² or less. This is a method for forming an insulating coating on a grain-oriented silicon steel sheet.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of various experiments conducted by the inventors for further improving the coating properties of grain-oriented silicon steel,
As shown in the schematic view of the surface layer of grain-oriented silicon steel in Fig. 1,
When the coating 1 formed after the finish annealing partially enters the base metal 2 and forms the anchor portion 3, and the coating is peeled off by the bending test of the steel plate,
It was newly found that the area ratio of the remaining portion (hereinafter, also referred to as “anchor neck portion”) 4 of the coating film on the surface of the base metal 2 greatly contributes to the coating adhesion. The experiments that led to the discovery of the present invention will be described below.

A silicon steel slab containing C: 0.045 wt% (hereinafter referred to simply as%), Si: 3.25%, Mn: 0.07% and Se: 0.02%, and the balance being substantially Fe at 1380 ° C.
After heating for 30 minutes at hot rolling to a plate thickness of 2.2 mm,
Cold rolling was carried out with intermediate annealing at 1050 ° C for 1 minute to finish to a final plate thickness of 0.23 mm. After decarburizing and annealing this cold rolled steel sheet,
The annealing separator in the form of a slurry was applied by a roll coater, dried and then subjected to final finish annealing. Here, the oxidizing P (H ₂ O) / P (H ₂ ) in the atmosphere during the primary recrystallization annealing is set to 0.1 to 0.
6. The thickness of the lamella-like silica layer in the internal oxide layer formed after the primary recrystallization annealing was adjusted to 0.1 μm to 5.0 μm by controlling the temperature to various values in the range of 800 to 850 ° C. Here, the lamella-like silica refers to, in the present invention, silica in which the silica extends while undulating in a direction perpendicular to the normal line of the steel sheet, as schematically shown in FIG. In addition, as an annealing separator, 2% TiO ₂ was added to MgO and made into a slurry.
By stirring at 20 ° C for 60 minutes, 1.2% of water was brought into the annealing separator. Also, during finish annealing, 700 ℃ or more
Atmospheric oxidative P (H ₂ O) / P (H ₂ ) below 1000 ° C is 2.5 × 10 ^-3
Adjusted to. The thus-obtained finish-annealed grain-oriented silicon steel coating was flexed and peeled off, and the part where the coating was peeled off was observed from the surface with an electron microscope, and an insulating coating was applied to the steel sheet after finish-annealing and baking. After performing strain relief annealing, the bending adhesion was investigated. Flexural adhesion was evaluated by wrapping a cylinder around a steel plate and using the minimum bending diameter at which the coating did not peel off. As a typical example, FIG. 3 shows a schematic view of the anchor neck portion of the coating after finishing annealing in a sample in which the thickness of the lamellar silica layer on the surface after primary recrystallization annealing is 0.1 μm and a sample in which the thickness is 2.0 μm.

From this figure, the thickness of the lamellar silica layer is 2.
It can be seen that in the sample of 0 μm, the area ratio of the anchor neck is large and the bending adhesion is also good. Therefore, the larger the neck portion, the better the bending adhesion, and the correlation between the bending adhesion and the neck portion was obtained.
The obtained results are shown in FIG. As can be seen from this figure, there is a strong correlation between the area ratio of the neck portion and the bending adhesion, and it was newly found that the bending adhesion becomes good when the area ratio of the neck portion is in the range of 8 to 53%. This led to the invention.

The reason why the coating adhesion of the steel sheet changes depending on the area ratio of the anchor neck portion is not clear, but the inventors consider it as follows. When the steel sheet is bent, tensile stress acts on the anchor portion and compressive stress acts on the upper portion of the coating on the inside of the coating. Therefore, even if the steel sheet is bent and the coating film is forcibly peeled off, the anchor portion remains and only the upper portion of the coating film is peeled off. At this time, shear stress acts on the neck connecting the upper part of the film and the anchor,
The coating is peeled off when this portion is destroyed. Therefore, by controlling the area ratio of this neck ,
It is considered that the adhesive strength of this portion is increased and the film adhesion is increased.

Japanese Patent Laid-Open No. 6-49654 discloses a technique for defining the ratio of the oxide and the base iron portion in a portion that enters a certain depth from the surface in the plate thickness direction. The purpose is to increase the magnetic domain fragmentation by setting the anchor portion to an appropriate size, and the purpose is different from the technique of the present invention for improving coating adhesion. In addition, since the glass coating actually undulates, it is the portion left from the surface after being forcibly peeled off as in the present invention that affects the coating adhesion. A film having excellent adhesion can be obtained. Further, the method disclosed in Japanese Patent Laid-Open No. 6-49654 is one-dimensional measurement by the line segment method, and even if the same sample is measured, the distribution is different from that of the two-dimensional measurement method such as the method of the present invention. A two-dimensional evaluation method of the release surface is considered to be a better index for release.

The area ratio of the anchor neck portion as described above depends on the thickness of the silica-rich layer in the internal oxide layer, the amount of MgO hydrate,
It can be controlled by the oxidizing property of the atmosphere during finish annealing. Regarding this, I think as follows. The amount of MgO hydration and the atmospheric oxidizability during finish annealing both influence the dissociation levitation and precipitation of SiO ₂ in the internal oxide layer. The higher the MgO hydration amount and the oxidizing property of the atmosphere, the more the SiO ₂ precipitates inside the film.As a result, the anchor part of the film after finish annealing develops well, and the lower the MgO hydrating amount and the oxidizing property of the atmosphere, the more the SiO ₂ The surface of the coating floats on the surface of the coating and, as a result, the anchor portion is not developed in the coating after the finish annealing.
Therefore, in order to have an appropriate anchor neck portion, it is necessary to control so that the dissociation floating and sedimentation of SiO ₂ are within a favorable range. Since the lamellar silica mainly contributes to the formation of the inside of the glass coating, the amount of forsterite forming the anchor neck may be controlled by specifying this thickness.

Next, the reasons for limitation of the present invention will be described. The insulation coating of the invention, the coating partially base steel inside <br/> containing write no anchor portion and the anchor portion and the coating film upper
The result forms a neck portion that connects, when brought into stripping the coating by bending test of the steel sheet, characterized in that the remaining portion of the coating on the base steel surface is 8-53% by area ratio.
If the area ratio of the remaining portion (anchor neck portion) deviates from this range, good film adhesion cannot be obtained.

Further, the method for forming an insulating film of the present invention is
The thickness of the lamellar silica-enriched layer in the internal oxide layer formed by primary recrystallization annealing is 0.2 μm or more and 3.6 μm or less, and the amount of water introduced by slurrying as an annealing separator is 1.0 to 3.9. % MgO,
Atmosphere Oxidizing P above 700 ℃ and below 1000 ℃ during finish annealing
It is characterized in that (H ₂ O) / P (H ₂ ) is 1.5 × 10 ⁻⁴ or more and 2.0 × 10 ⁻² or less.

The preferred composition range of the constituent elements of the silicon-containing steel which is the material of the present invention is as follows. First, regarding C, the method for producing grain-oriented silicon steel is to improve the structure by reducing the decarburization annealing at the tapping stage and not performing decarburization annealing, and then improving the structure. There is a method of removing it by annealing. In the former method, less than 0.01% is preferable to avoid the adverse effect of C, and in the latter method, the preferable range for improving the structure is 0.01% or more and less than 0.10%. Si is 2
~ 4.5%. If it is less than 2%, the effect of reducing iron loss is weakened, and if it exceeds 4.5%, the cold rolling property is impaired. Inhibitor constituent elements are added in addition to C and Si. AlN, MnS, MnSe and the like are well known as inhibitors, and any of these may be used. MnS and / or inhibitor
When using MnSe, Mn: 0.03 to 0.10%, S + Se: 0.01
~ 0.03%. A when using AlN as an inhibitor
l: 0.01 to 0.04%, N: 50 to 120 ppm. When it is lower than these ranges, the effect as an inhibitor does not work, and when it is higher than the above range, the secondary recrystallization becomes unstable. In addition to these, C
u, Sn, Cr, Sb, Ge, Mo, Te, Bi, P, V, etc. can also be used. 0.01% or more in total as effective concentration
It is 0.2% or less. Each of these inhibitors can be used alone or in combination.

These materials are hot-rolled by a known method and then cold-rolled once or a plurality of times with intermediate annealing interposed therebetween to obtain the final plate thickness. Moreover, it is also possible to perform annealing before cold rolling of the hot rolled sheet, if necessary. After these treatments, primary recrystallization annealing is performed, an annealing separator is applied, and then final finishing annealing is performed. In the present invention, such a step must be strictly controlled in order to form a good film. First, the primary recrystallization annealing is performed by controlling the atmosphere, temperature and annealing time to form the lamella in the internal oxide layer. The thickness of the silica-rich layer is 0.2 μm or more and 3.6 μm or less. This is necessary for proper formation of the neck portion of the anchor. The atmosphere, temperature, and annealing time for this purpose are not particularly limited, but the atmosphere is water vapor, hydrogen partial pressure ratio P (H ₂ O)
/ P (H ₂ ) is 0.05 or more and 0.68 or less, the temperature is 750 ° C or more and 900 ° C or less, and the annealing time is 30 seconds or more and 180 seconds or less. A method of separately controlling the atmosphere during heating of decarburization annealing and the atmosphere during soaking is known to improve the film properties, but this invention also adjusts the lamellar silica thickness by using this method. can do. Furthermore, when AlN 3 is used as an inhibitor, a method of performing nitriding treatment before, during or after primary recrystallization annealing is known, but in the present invention, such a method may be performed simultaneously. After the primary recrystallization annealing, an annealing separating agent mainly containing MgO is used.
At this time, the amount of water brought into the MgO slurry should be 1.0% or more and 3.9% or less. This is because the reactivity of MgO is controlled and the amount of water brought into the atmosphere during finish annealing is adjusted. Outside of this range, the glass film having the expected shape cannot be formed. Furthermore, during finish annealing, the atmospheric oxidative P at temperatures above 700 ° C and below 1000 ° C
(H ₂ O) / P (H ₂ ) is 1.5 × 10 ⁻⁴ or more and 2.0 × 10 ⁻² or less.
700 to 1000 for temperature, which mainly affects the shape of glass coating
The temperature is in the range of 0 ° C., and it is necessary to define the range in order to control the shape of the forsterite coating by controlling the atmospheric oxidative property at this time. By performing the above processing, the area ratio of the neck portion is reduced to 8 to 53% or less. By keeping it within this range, excellent coating adhesion can be obtained. After this series of treatments, finish annealing is performed. The finish annealing may be a known method. After that, an insulation tension coat is applied and flattening annealing is performed to finish the product. By such a treatment step, grain-oriented silicon steel having excellent magnetic properties can be obtained.

[0018]

【Example】

(Example 1) C: 0.06%, Si: 3.28%, Al: 0.02%,
N: 50ppm, Mn: 0.07%, S: 0.005%, Cu: 0.06%, the balance substantially iron is heated to 1400 ℃, hot rolled to 2.2mm thickness, 1050 ℃, 2 minutes It was cold-rolled to 0.35 mm by sandwiching the intermediate annealing of, and finished to the final plate thickness. The steam partial pressure P (H ₂ O) / P (H ₂ ) is 0.03 to 0.75, and the temperature is 700 ° C to
The thickness of the lamellar silica in the internal oxide layer was variously changed by changing the annealing time to 950 ° C and the annealing time to 20 to 240 seconds.
After that, nitriding is performed and then the slurry is used as an annealing separator, and the amount of water introduced is 2.0%.
6% TiO ₂ was added to the above, and the mixture was applied and dried. Finish annealing, 700-1000 ℃, heating rate 20 ℃ / h, atmospheric oxidization
P (H ₂ O) / P (H ₂ ) is heated at 1.5 × 10 ^-3 and then dry H ₂
Purification annealing was performed at 1150 ° C. for 5 hours in the atmosphere. Table 1 shows the results of an examination of the magnetic properties and coating adhesion of the steel sheet thus obtained. Coating adhesion is improved when the lamellar silica thickness is within the scope of the invention. In addition, the magnetic properties also take good values within the scope of the present invention.

[0019]

[Table 1]

(Example 2) C: 0.04%, Si: 3.28%, M
A slab containing n: 0.07%, Se: 0.02%, Sb: 0.025% and the balance of iron is heated to 1400 ° C, hot rolled to a thickness of 2.6 mm, and annealed at 1000 ° C for 2 minutes. It was sandwiched, cold rolled to 0.30 mm, and finished to the final plate thickness. By subjecting this to decarburization annealing under the conditions 1 and 2 in Table 2, the thickness of lamellar silica in the internal oxide layer was changed to 0.1 μm and 1.3 μm. After that, as an annealing separator, hydrated water content of MgO and 1.5% of TiO _{2 was used.}
Was added, coated and dried. After that, as finish annealing
Oxidizing P (H ₂ O) / P (H ₂ ) in the atmosphere from 700 to 1000 ° C is 1.5 ×
After holding at 10 ^-3 and 820 ℃ for 50 hours, dry H ₂ atmosphere for 11
Purification annealing was performed at 50 ° C for 5 hours. Table 3 shows the results of examining the magnetic properties of the steel sheet thus obtained. Good magnetic properties and coating properties are obtained when the hydrated water content is in the range of 1.0 to 3.9.

[0021]

[Table 2]

[0022]

[Table 3]

(Example 3) C: 0.06%, Si: 3.28%, M
n: 0.07%, Al: 0.025%, N: 80ppm, Se: 0.02% and Sb: 0.025%, the balance is made of iron, heated to 1400 ℃, hot rolled to a thickness of 2.2 mm, After intermediate annealing at 1050 ° C for 2 minutes, it was cold rolled to 0.30 mm and finished to the final thickness. By decarburizing and annealing this under the conditions of Table 2,
The thickness of lamellar silica in the inner oxide layer was 0.1 μm and 1.3 μm.
changed to μm. After that, MgO having a water content of 2.0% and TiO ₂ having a water content of 1.5% were added as annealing separators, and applied and dried. After that, as finish annealing, various changes were made to the atmospheric oxidative P (H ₂ O) / P (H ₂ ) from 700 to 1000 ° C, and at 820 ° C.
After holding for 50 hours, purification annealing was performed at 1150 ° C for 5 hours in a dry H ₂ atmosphere. Table 4 shows the results of examining the magnetic properties of the steel sheet thus obtained. Atmosphere oxidative P (H ₂ O) / P (H ₂ ) from 700 to 1000 ° C for finish annealing is 1.5 × 10 ^-4 or more 2.0 ×
Good magnetic properties and coating properties can be obtained in the range of 10 ^-2 or less.

[0024]

[Table 4]

[0025]

Effects of the Invention According to the present invention, the film enters the interior partially steel matrix write no anchor portion and the anchor portion and the coating film
Forming a neck portion connecting to the upper part, when the coating film is peeled off by a bending test of a steel plate, an insulating coating film in which the residual portion of the coating film on the surface of the base metal is 8 to 53% in area ratio, Therefore, the thickness of the lamella-like silica-enriched layer in the internal oxide layer formed by the primary recrystallization annealing is set to 0.2 μm or more and 3.6 μm or less, and the amount of water introduced by slurrying as an annealing separator is 1.0 to 3.9
% Of MgO, the atmospheric oxidative P (H ₂ O) / P (H ₂ ) at 700 ℃ or more and less than 1000 ℃ at the time of finish annealing is 1.5 × 10 ^-4 or more 2.0
By setting it to be not more than × 10 ^-2, it becomes possible to manufacture a grain-oriented silicon steel sheet having good magnetic characteristics and coating characteristics, which can greatly contribute to quality improvement.

[Brief description of drawings]

FIG. 1 is a schematic view of a surface layer portion of grain-oriented silicon steel.

FIG. 2 is a schematic view of a steel sheet surface layer portion after primary recrystallization annealing for explaining lamellar silica.

FIG. 3 is a schematic view of an anchor neck portion.

FIG. 4 is a graph showing a relationship between bending adhesion and an area ratio of an anchor neck portion.

[Explanation of symbols]

1 film 2 Chitetsu 3 Anchor part 4 Anchor neck

Continuation of the front page (56) Reference JP 62-156221 (JP, A) JP 60-197883 (JP, A) JP 59-41480 (JP, A) JP 60-221522 (JP , A) JP-A-1-119621 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C23C 22/00-22/86 C21D 9/46 501

Claims (2)

(57) [Claims] 1. A coating formed on base iron surface of the grain oriented silicon steel sheet after finish annealing, write no anchor portion and said film enters the interior partially steel matrix
A neck portion that connects the anchor portion and the coating upper portion is formed, and when the coating is peeled off by a bending test of a steel sheet, the residual portion of the coating on the surface of the base metal is 8 to 53 in area ratio.
% Insulating coating of grain-oriented silicon steel sheet. 2. A steel containing 2 to 4 wt% of Si is hot-rolled, cold-rolled once or plural times including intermediate annealing to finish to a final plate thickness, and then primary recrystallization annealing is performed. In the method of forming an insulating coating on the base steel surface of the steel sheet by applying an annealing separator containing MgO as the main component and then performing final finishing annealing, the internal oxide layer formed in the primary recrystallization annealing is The thickness of the lamella-like silica-enriched layer is set to 0.2 μm or more and 3.6 μm or less, and MgO which brings the amount of water brought into the slurry by slurrying as an annealing separator is 1.0 to 3.9% is used.
Atmosphere Oxidizing P above 700 ℃ and below 1000 ℃ during finish annealing
A method for forming an insulating coating of a grain-oriented silicon steel sheet, characterized in that (H ₂ O) / P (H ₂ ) is set to 1.5 × 10 ⁻⁴ or more and 2.0 × 10 ⁻² or less.