JPH09184017A - Forsterite film of grain oriented silicon steel sheet with high magnetic flux density and its formation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably produce the applied tension effect of a forsterite film and to effectively improve iron loss by specifying the required conditions of a forsterite film of a silicon steel sheet. SOLUTION: This silicon steel sheet is a grain oriented silicon sheet having >=1.90T magnetic flux density, and the forsterite film on its surface satisfies the following required conditions: coating weight of oxygen, (2.5 to 4.5)g/m<2> ; coating weiqht of Ti, (0.25 to 0.90)g/m<2> ; T/N by mole, <=1.2; and the average grain size of the forsterite grains, <=0.5/μm. Although the effects of these required conditionss are confirmed experimentally their function and mechanism are not made clear yet. However, it is considered, e.g. as possibility, that the mechanical properties of the film are improved by the synergistic effect of these respective required conditions and the coefficient of thermal expansion of the film is further lowered by the incorporation of Ti and N. Moreover, at a guess, these required conditions contribute greatly to the recovery of iron loss after stress relief annealing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention proposes a forsterite coating and a method for forming the forsterite coating, which contributes to the improvement of the quality of a high magnetic flux density unidirectional silicon steel sheet, and particularly to the reduction of iron loss.

[0002]

2. Description of the Related Art Oriented silicon steel sheets are used as soft magnetic materials.
It is mainly used as an iron core material of a transformer or a rotating machine, and is required to have high magnetic flux density and small iron loss and magnetostriction as magnetic characteristics. For that purpose, the <001> axis, which is the axis of easy magnetization, is highly aligned in the rolling direction.
It is necessary to create a so-called goth orientation texture by secondary recrystallization. Such grain-oriented silicon steel sheet has an inhibitor necessary for secondary recrystallization, such as MnS or MnS.
After the directional slabs of directional silicon steel containing e, AlN, etc. are hot-rolled by heating, they are annealed as necessary and then cold-rolled once or twice with an intermediate anneal between them to obtain the final product sheet. After thickening and then decarburizing annealing, the steel sheet was MgO
It is produced by applying an annealing separator such as the above and then performing finish annealing. On the surface of this grain-oriented silicon steel sheet, except for special cases, forsterite (Mg ₂ Si
O ₄ ) A high quality insulating film is formed. This coating not only electrically insulates the surface, but also effectively reduces iron loss and magnetostriction by applying tensile stress to the steel sheet by utilizing its low thermal expansion property.

This forsterite coating is formed during finish annealing, and the coating formation behavior of MnS in steel is
Since it affects the behavior of inhibitors such as MnSe and AlN, it also affects secondary recrystallization itself, which is an essential process for obtaining excellent magnetic properties. That is, the forsterite formation reaction starts from the temperature rising process of finish annealing, but when the forsterite coating formed during this finish annealing becomes porous or when the formation of this coating progresses unevenly, the annealing atmosphere Since O and N easily penetrate into the steel, the inhibitor in the steel decomposes, coarsens, or becomes excessive. As a result, the obtained secondary recrystallized structure has a low degree of integration in the Goss orientation, and therefore the magnetic characteristics are deteriorated. In addition, the forsterite coating substantially concentrates the steel by forming the coating so that the unnecessary inhibitor component is concentrated near the coating. This also contributes to the further improvement of the magnetic properties of the steel sheet. Therefore, controlling the film formation process to form a forsterite film uniformly is one of the important points that affect the product quality of grain-oriented silicon steel sheets.

Furthermore, the formed coating film must naturally be uniform and free from defects, and must have excellent adhesiveness capable of withstanding shearing, punching, bending, and the like, and the user's strain relief The deterioration of magnetic properties due to annealing should be small, the surface should be smooth, and a high space factor should be exhibited when laminated as an iron core.

In order to form a forsterite insulating coating on a grain-oriented silicon steel sheet, first, a cold-rolled sheet cold-rolled to a desired final thickness is continuously annealed in wet hydrogen at a temperature of 700 to 900 ° C. As a result, the structure after cold rolling is primary recrystallized so that proper secondary recrystallization occurs, and the secondary recrystallization after that is completely performed to improve the magnetic properties by 0.01 to 0.01%. Decarbonize about 0.10% of carbon to about 0.003% or less. Furthermore, by substituting this annealing in an oxidizing atmosphere, a subscale containing SiO ₂ as a main component is generated on the surface layer of the steel sheet.

After that, an annealing separator containing MgO as a main component is applied to the steel sheet, wound into a coil, and subjected to secondary recrystallization annealing and purification annealing at a maximum of 1200 in a reducing or non-oxidizing atmosphere. By performing high-temperature finish annealing at a temperature of about ° C, a forsterite insulating coating is formed mainly by a solid-phase reaction represented by the following formula. 2MgO ＋ SiO ₂ → Mg ₂ SiO ₄ --- (1)

The grain-oriented silicon steel sheet using AlN as the inhibitor is advantageous in producing a product having a high magnetic flux density because a sharp Goss orientation is easily obtained due to a strong suppressing force. In addition, since this AlN-based grain-oriented silicon steel sheet has well-aligned crystal orientations, it is characterized in that the iron loss improving effect is large because the 180 ° magnetic domain width is narrowed by the tension. Therefore, in order to increase the tension applied to the forsterite-coated steel sheet of this AlN-based grain-oriented silicon steel sheet (hereinafter simply referred to as the coating tension),
Several techniques have been proposed. For example, Japanese Patent Publication Sho 63-
No. 3007 (Method for forming forsterite insulating coating on unidirectional silicon steel sheet) and JP-B-63-24046 (Method for producing unidirectional electrical steel sheet with excellent magnetic properties) show Mn activity and finish annealing. A method of increasing the applied tension of the coating by the combination with the partial pressure of oxygen at the time is disclosed. Further, JP-A-5-140637 (annealing separator for grain-oriented silicon steel sheet) discloses a method for increasing the applied tension of a film by adding cordierite powder to the separator, and further disclosed in JP-A-7-62443.
In the gazette (a method of manufacturing a grain-oriented electrical steel sheet having a high-strength glass coating and having excellent magnetic properties), after decarburizing annealing and nitriding treatment, an annealing separator containing an Sb compound is applied,
Proposals and methods for increasing the applied tension of the coating film subjected to finish annealing under specific temperature rising conditions are proposed and disclosed.

[0008]

However, in each of the above-mentioned techniques, although the iron loss reducing effect by the applied tension of the coating film is recognized to some extent, variations are caused and the iron loss reducing effect is industrially sufficiently stable. However, the recovery of the iron loss after the strain relief annealing, which is performed when the user manufactures the transformer, is insufficient.

Therefore, the present invention stably exerts the effect of applied tension of the coating on the high magnetic flux density unidirectional silicon steel sheet, effectively improves the iron loss, and at the same time, the iron after the strain relief annealing by the user. The purpose of the present invention is to propose a forsterite coating and a method for forming the same, in which loss recovery is sufficient.

[0010]

[Means for Solving the Problems] The inventors have shown that the tension effect of the coating is stably exerted and the iron loss is effectively improved, and in particular, the iron loss recovery after the strain relief annealing is significantly improved. The present invention has been accomplished by newly discovering a forsterite coating that can be improved. That is, the gist of the present invention is as follows.

A unidirectional silicon steel sheet having a forsterite coating on its surface and having a magnetic flux density B ₈ of 1.90 T or more, wherein the forsterite coating has an oxygen basis weight of 2.5.
To 4.5 g / m ² , Ti basis weight: 0.25 to 0.90 g / m ² , Ti / N molar ratio: 1.2 or less, and average particle size of forsterite particles: 0.5 μm or less, high magnetic flux. A forsterite coating on a density unidirectional silicon steel sheet (first invention).

A unidirectional silicon steel sheet having a forsterite coating on its surface and having a magnetic flux density B ₈ of 1.90 T or more, wherein the forsterite coating has an oxygen basis weight of 2.5.
~ 4.5g / m ² , Ti basis weight: 0.25 ~ 0.90g / m ² , Sr basis weight: 0.
03-0.20 g / m ² , Ti / N molar ratio: 1.2 or less and average particle size of forsterite particles: 0.5 μm or less, forsterite coating of high magnetic flux density unidirectional silicon steel sheet (Second invention).

[0013] A material for unidirectional silicon steel sheet is hot-rolled, then cold-rolled, and then decarburized and annealed to obtain a decarburization annealed material having an oxygen basis weight of 0.9 to 2.5 g / m ^2. An annealing separator containing Ti compounds in the range of 6.0 to 30.0% by weight in terms of TiO _{2 and} having a composition of substantially MgO was applied to the surface of the plate, and then secondary annealing was performed by finish annealing. After annealing, 1150
High magnetic flux density unidirectional silicon carbide characterized by performing purification annealing at a temperature of ℃ or more and annealing in the H ₂ -N ₂ mixed atmosphere with N ₂ concentration: 10% or more for at least 30 minutes during the purification annealing. A method for forming a forsterite coating on a bare steel sheet (third invention).

The material for unidirectional silicon steel sheet is hot-rolled, then cold-rolled, and then decarburized and annealed to obtain a decarburization annealed material having an oxygen basis weight of 0.9 to 2.5 g / m ^2. on the surface of the plate, a 6.0 to 30.0 wt% and Sr compound Ti compound in terms of TiO ₂ contained in the range of 0.1 to 4.0 wt% in terms of SrO, the remainder being coated with an annealing separating agent consisting essentially composition of MgO Then, after secondary recrystallization annealing by finish annealing, purification annealing is performed at a temperature of 1150 ° C or higher, and at least 30 times during the purification annealing.
A method for forming a forsterite coating on a high magnetic flux density unidirectional silicon steel sheet, which comprises annealing in a H ₂ —N ₂ mixed atmosphere having a N ₂ concentration of 10% or more for 4 minutes (the fourth invention).

In the third or fourth invention, the decarburized annealed sheet has a pickling weight loss of 0.3 g / m ² or less when pickling is performed for 60 seconds at a temperature of 70 ° C. using a 5% HCl aqueous solution. A method for forming a forsterite coating on a high magnetic flux density unidirectional silicon steel sheet, which is characterized by (5th invention).

In the third, fourth or fifth invention, a silicon compound is adhered to the steel sheet before decarburization annealing, and the adhered amount is changed to Si.
A method for producing a high magnetic flux density unidirectional silicon steel sheet, characterized in that it is in the range of 0.5 to 7.0 mg / m ^{2 in} terms of weight (sixth invention).

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION First, experimental results relating to the present invention.
The results will be described below. As an inhibitor, AlN,
 Final cold pressure to 0.23mm, containing MnSe and Sb
Rolled 3.3% silicon steel sheet in a wet hydrogen atmosphere at 840 ° C.
Decarburized and annealed. After that, TiO was added to MgO._TwoAnd Sr (OH)_Two
Annealing Separator added with, then 1200 ℃ × 5 hours
H_TwoA final finish annealing in gas was applied. At this time,
Oxygen basis weight of forsterite coating and forstery
Decarburization annealing time for the purpose of changing the particle size and the fineness of
In the range of 15 to 300 seconds, and the atmospheric oxidizability during the heating process.
, PH _TwoO / PH_TwoIn the range of 0.10 to 0.70 and soaking process
The atmospheric oxidizability of each is changed in the range of 0.40 to 0.80.
Was. Furthermore, the Ti basis weight in the forsterite coating can be changed.
TiO in the annealing separator_Two0.5 ~ 50wt%
The Ti / N molar ratio in the coating in addition to
Sr (OH) in the annealing separator_TwoAddition amount is 0-10wt
%, And 1200 ° C retention in final finish annealing
At the beginning of the 1 hour atmosphere N_TwoConcentration in the range of 0-50%,
Each was changed. About the product thus obtained Iron
Coating tension and oxygen basis weight as indicators of loss reduction effect
Amount, Ti basis weight, Ti / N molar ratio and forsterite grains
The average particle size of the child was investigated.

The relationship between the applied tension of the coating and the oxygen areal weight and the Ti areal weight are shown in FIGS. 1 to 3 for each forsterite particle size and Ti / N molar ratio. Here, FIG.
Forsterite average particle size: 0.4 μm, Ti / N molar ratio: 0.9-1.1, FIG. 2 shows forsterite average particle size: 0.4 μm, Ti / N molar ratio: 1.4-1.6, FIG. 3 shows forsterite average particle. Diameter: 0.8 μm, Ti / N molar ratio:
This is the case of 0.9 to 1.1. Here, the applied tension of the coating was calculated from the warpage of the steel sheet when the coating on one surface was removed by pickling.

From FIG. 1, the forsterite particle size is 0.4 μ.
m, and when Ti / N molar ratio of 0.9 to 1.1, oxygen basis weight 2.5 g / m ² or more, Ti basis weight in the range of ^{0.25~0.9g / m 2, 0.6kgf / mm} 2 higher than It can be seen that the applied tension of the film can be obtained. On the other hand, the Ti / N molar ratio is 1.4-
Figure 2 which is as large as 1.6, or forsterite particle size
In FIG. 3, which is as large as 0.80 μm, it is clear that the applied tension of the coating is inferior to that in FIG. The iron loss _{17/50 of} the products in which the applied tension of the coating showed a value of 0.6 kgf / mm ² or more was a low value of 0.80 W / kg or less.

Generally, the coefficient of linear thermal expansion of 3% Si-Fe is about 13
X10 ^-6 / ℃, forsterite that is 10 ~ 11 x
It is said to be 10 ^-6 / ° C. The factor that the forsterite coating film exerts the tension on the steel sheet is due to the difference in the coefficient of thermal expansion. Therefore, when the coating amount is large, the tension increases.
However, the tension is not necessarily determined only by the coating amount, and as can be seen from the comparison between FIG. 1 and FIG.
It can be seen that the particle size of forsterite also has a large effect, and that fine particles give greater tension. Further, as can be seen from the comparison between FIG. 1 and FIG. 2, the Ti basis weight in the coating and the Ti / N molar ratio are also important factors affecting the applied tension of the coating.

Although the mechanism of the effect that the particle size of the forsterite coating, the Ti / N molar ratio in the coating, and the Ti basis weight affect the applied tension of the coating, it has not been clarified yet. It is conceivable that these may synergistically improve the mechanical properties of the coating, and that the thermal expansion coefficient of the coating may be further reduced by containing Ti, N, etc. It is considered that this also greatly contributes to the recovery of iron loss after stress relief annealing. In addition, the forsterite coating that imparts high tension to the steel sheet exerts a great effect on reducing iron loss in high-flux-density grain-oriented silicon steel sheets having a magnetic flux density B ₈ of 1.90 T or more,
When the applied tension of the coating is less than 0.6 kgf / mm ² or the magnetic flux density B ₈ is less than 1.90 T, the iron loss reducing effect is relatively reduced. Therefore, in order to reduce iron loss by imparting tension of the coating may be the magnetic flux density B ₈ is applied to the above oriented silicon steel sheet 1.90T, unidirectional present invention also the magnetic flux density B ₈ is not less than 1.90T It shall be applied to silicon steel sheets.

Next, the reasons for limitation and the preferred range of the present invention will be described. In a high magnetic flux density unidirectional silicon steel sheet with a magnetic flux density B ₈ of 1.90 T or more, in order to effectively reduce the iron loss due to the applied tension of the forsterite coating, the applied tension of the coating is 0.6 kgf / mm ² The above is preferable. The various characteristics of the forsterite coating for effectively obtaining this reduction in iron loss are listed below.・ Oxygen basis weight: 2.5-4.5g / m ² Oxygen basis weight is 2.5g to obtain sufficient reduction of iron loss.
Requires / m ² or more. However, if it exceeds 4.5 g / m ² , the coating becomes excessively thick, the space factor when laminating steel sheets is reduced, and the adhesion of the coating is deteriorated, and the iron loss reducing effect is impaired. Therefore, the oxygen basis weight is
The range is 2.5 to 4.5 g / m ² .

Ti basis weight: 0.25 to 0.90 g / m ² Ti basis weight is, in order to obtain a sufficient iron loss reducing effect,
0.25g / m ² or more is required. However, if it exceeds 0.90 g / m ² , the forsterite coating tends to coarsen as if there was a gap, rather the applied tension of the coating decreases and the iron loss increases, or the iron loss deteriorates after strain relief annealing. Become a trend. Therefore, the Ti basis weight is set in the range of 0.25 to 0.90 g / m ² .

Ti / N molar ratio: 1.2 or less and average particle size: 0.5 μm or less In order to increase the applied tension of the coating and effectively reduce iron loss, Ti
It is important that the / N molar ratio is 1.2 or less and the average particle size of the forsterite coating is 0.5 μm or less. Note that Ti
If the / N molar ratio exceeds 1.2, iron loss deteriorates after strain relief annealing.

[0025] · Sr basis weight: 0.02~0.30g / m ² Sr unit weight, by entering 0.02 g / m ² or more, it was found that applying tension coating is more stable and higher levels. This phenomenon seems to be due to some catalytic action, but when Sr is added, the Ti / N molar ratio falls to a low range of 1.2 or less,
Further, the Ti basis weight is stabilized at a high level of 0.25 g / m ² or more.
This seems to be the cause of stabilizing the applied tension of the coating at a high level and effectively reducing the iron loss. In addition,
When Sr exceeds 0.30 g / m ² , the coating becomes rather rough and the applied tension decreases. Therefore, the Sr weight is 0.02-0.30g /
A range of m ² is good.

Such oxygen basis weight, Ti basis weight, Ti / N
Forsterite coatings that regulate the molar ratio and average particle size, and in addition to these, forsterite coatings that regulate the Sr basis weight, obtain a stable and high level of applied tension of the coating to effectively reduce iron loss. Not to mention, it has a special effect on recovery of iron loss after stress relief annealing.

Next, a method of forming the forsterite coating film of the present invention will be described. First, the preferred component composition of the grain-oriented silicon steel sheet material according to the present invention will be described.
The preferable ranges of the contents of C, Si and Mn are C: 0.
02 to 0.12 wt% (hereinafter wt% is simply expressed as%), Si:
2.0 to 5.0%, Mn: 0.03 to 0.30%. The reason is,
C is necessary for improving the hot rolled structure, but if it is too large, it becomes difficult to decarburize, so it is set to about 0.02 to 0.12%. If Si is too small, the electric resistance will be small and good iron loss characteristics will not be obtained. On the other hand, if it is too large, cold rolling will be difficult, so the range of 2.0 to 5.0% is preferable. Mn is necessary as an inhibitor component, but if it is too large, the inhibitor size becomes coarse, which is not preferable. Therefore, the range of 0.03 to 0.30% is preferable.

In the steel of the present invention, the inhibitors include AlN type, AlN-MnS type, AlN-MnSe type, and M type.
Although any inhibitor species such as nSe type and MnS type can be used, a system using AlN 3 is particularly preferable.
The reason is that it is easy to obtain a product with a high magnetic flux density, and N in steel derived from AlN moves to the surface during finish annealing, which is effective in lowering the Ti / N molar ratio in the coating. . In addition, it is easy to obtain a forsterite having a small particle size.

In this case, if the Al content is too small, the magnetic flux density will be low, and if it is too large, the secondary recrystallization will be unstable. Therefore, the Al content is preferably in the range of 0.01 to 0.05%. N is 0.00
If it is less than 4%, the amount of AlN is insufficient, and if it exceeds 0.012%, blisters occur in the product, so the content is 0.004 ~.
It is preferable to set it in the range of 0.012%.

S and / or Se is an inhibitor component, but if it exceeds 0.05%, purification by purification annealing becomes difficult, while if it is less than 0.01%, the amount of the inhibitor is insufficient, so 0.01 to 0.05% in total. It is preferable to contain in the range of.

In addition to the above components, in order to suppress the oxidation of the inhibitor in finish annealing, it is effective to further contain Sb and utilize the segregation effect of Sb on the steel sheet surface in order to improve the magnetic properties. is there. Further, since Cu generally has the effect of reinforcing the inhibitor, this also exerts an advantageous effect in improving the magnetic properties. Further, Sn has the effect of improving iron loss by reducing the secondary recrystallized grain size. Therefore, it becomes possible to further improve the magnetic characteristics by including at least one of these. In this case, if the content thereof is less than 0.01%, the effect is small, while if it exceeds 0.30%, deterioration of toughness and adverse effect on the coating film occur, so the content is
The range of 0.01 to 0.30% is preferable.

In addition to these, inhibitor reinforcing components such as Nb, Te, Cr, Bi, B and Ge can be added as appropriate. Also,
Mo may be added to prevent surface defects due to hot brittleness.

Next, the manufacturing process will be described. A silicon steel slab or ingot made of the above steel components is sized and heated, and then hot rolled. The hot-rolled sheet is annealed at, for example, 900 to 1200 ° C., rapidly cooled, and then cold-rolled once or twice with an intermediate annealing. In the case of AlN-based inhibitors, it is advantageous to apply the final reduction rate of 80% or more. This is because the primary recrystallized structure for exerting the strong suppressing power of AlN cannot be obtained at a rolling reduction of less than 80%.

After the final cold rolling, the surface of the steel sheet is cleaned by degreasing or pickling, and then decarburized and annealed. The decarburization annealing condition is that the oxygen basis weight of the annealed sheet after decarburizing and annealing is set so that the oxygen basis weight after finish annealing is in the range of 2.5 to 4.5 g / m ^2.
It is preferably in the range of 0.9 to 2.5 g / m ² . this is,
Forsterite coating, the main oxide SiO ₂ formed in decarburization annealing as one raw material, MgO which is the main component of the annealing separator as the other raw material is generated by the above formula (1), This is because the oxygen basis weight of the forsterite coating is greatly influenced by the oxygen basis weight of the annealed sheet after decarburization annealing.

However, even during the finish annealing, the steel sheet undergoes a certain amount of additional oxidation due to the moisture generated from the annealing separator. This is because the annealing separator is applied as a water slurry and dried, but part of MgO gradually releases hydrated water up to around 800 ° C. Therefore, the oxygen basis weight of the forsterite coating is not uniquely determined by the oxygen basis weight of the annealed sheet after decarburization annealing, but if the oxygen basis weight of the decarburized annealed sheet is low, this additional oxidation Tends to increase. Therefore, the oxygen basis weight after decarburization annealing is 0.9-
By setting it in the range of 2.5 g / m ² , the oxygen basis weight after finish annealing comes to fall within the limited range of the present invention (2.5 to 4.5 g / m ² ).

Further, in order to make the forsterite coating finer with an average particle size of 0.5 μm or less, a decarburization annealed plate of 5%, an aqueous solution of HCl was used as a qualitative index of the subscale formed by decarburization annealing. It is important that the pickling weight loss when evaluated by pickling at 70 ° C for 60 seconds is 0.3 g / m ² or less.

This pickling weight loss is an index of the chemical activity of the surface, and the surface of the steel sheet, which has a large amount, is more reactive. Therefore, the additional oxidation during the finish annealing increases. The additional oxidation mainly produces iron oxide or iron silicate on the surface. When the amount of these is large, forsterite nucleation is hindered, so that a film having a large particle size, coarseness, poor uniformity, and weak applied tension is formed.

When the TiO ₂ concentration in the annealing separator is as high as 6% or more, H ₂ O produced by the reaction of TiO ₂ + 2H ₂ → Ti + 2H ₂ O --- (2) during finish annealing. However, it becomes an additional oxidation factor, and makes the forsterite particle size easy to coarsen. It is important to reduce the pickling loss of the decarburized annealed sheet to 0.3 g / m ² or less in order to suppress these additional oxidations and form a dense forsterite film.

The additional oxidation is an inhibitor, AlN.
It also causes the oxidation of MnSe and MnSe, resulting in a decrease in the suppression force and deterioration of magnetic properties. In order to prevent such a harmful effect, it is important to keep the pickling weight loss low.

The decarburized annealed sheet having the above-mentioned oxygen basis weight and pickling loss can be manufactured as follows. The decarburization annealing temperature may be in the range of normal decarburization and primary recrystallization temperature of 700 to 900 ° C. Further, the annealing time can be selected from the range of about 30 to 300 seconds so that the oxygen basis weight after decarburization annealing is in the range of 0.9 to 2.5 g / m ² .

Next, in order to reduce the pickling loss of the decarburized and annealed sheet to 0.3 g / m ² or less, it is important to select the oxidizing property of the atmosphere, and the degree of oxidation P (H ₂ O) of the atmosphere in the preceding stage of the soaking process is important. / P (H ₂ ) 0.7
It is important that the temperature is less than the above, and the degree of oxidation P (H ₂ O) / P (H ₂ ) of the atmosphere in the temperature raising process up to the soaking process is lower than that in the soaking process. The reason why the pickling weight loss can be lowered by lowering the oxidizing property in the temperature rising process to that in the soaking process is considered to be that FeSiO _{3 which} is chemically low in activity is produced in large amounts. The preferred range of the degree of oxidation during the temperature rising process is 0.05 to 0.50, although it depends on the degree of oxidation during the soaking process.

In the soaking process, if the degree of oxidation is 0.7 or more, the pickling weight loss increases. This is thought to be due to the formation of FeO 3 when considering the equilibrium diagram of the temperature of 3% silicon steel in wet hydrogen and the oxide formed on the surface of the steel sheet. FeO is an oxide that is generated not by the internal diffusion of oxygen but by the external diffusion of Fe atoms, and it is thought that once such oxide is generated, the surface protective property deteriorates. Therefore, in the present invention, the degree of oxidation before the soaking process is preferably less than 0.7. A more preferable range is 0.
It is about 30 to 0.65.

Further, by setting the degree of oxidation of the atmosphere at the latter stage of the soaking process within the range of 0.2 to 0.005, the subscale protection property is improved and the pickling weight loss can be reduced. It is considered that this is because the surface oxide is changed to a chemically stable state by the reduction effect. This degree of oxidation
If it exceeds 0.2, this change is small and the effect is considered to be small. On the other hand, when it is less than 0.005, on the contrary, the oxidative weight loss increases sharply, which seems to be because the reduction proceeds too much.

Further, before decarburization annealing, the Si compound was changed to Si.
By making it adhere in the range of 0.5 to 7.0 mg / m ² , it is possible to more reliably reduce the amount of pickling. This is due to the change in the form or composition of the initial oxide formed by decarburization annealing, and the oxide layer formed in the subsequent soaking process,
It is thought that it will be more precise. As the Si compound, it is effective to attach a silicon compound essentially consisting of Si, O, H or a silicon compound essentially consisting of Si, O, that is, a compound represented by the form of SiO ₂ .xH ₂ O. Ortho silicic acid (H ₄ SiO _4), metasilicate _{(H 2 SiO 3), SiO} 2 electrodepositing when such water like ultra fine SiO ₂ colloidal silica, and a steel sheet with silicate alkaline aqueous solution was electrolyzed , Or a compound or the like in which H ₂ O is bound to this, corresponds to this.

The amount of such Si compound deposited is 0.5 mg / Si
If it is less than m ² , the desired effect is difficult to obtain, and if the amount of Si compound attached exceeds 7 mg / m ² as Si, the oxygen basis weight suddenly decreases. It is considered that this is because a film that is dense and does not easily transmit oxygen is formed on the surface. In addition, decarburization tends to be poor with the reduction of the oxygen basis weight. In the case of grain-oriented silicon steel, this poor decarburization has a great adverse effect on the magnetic properties. Therefore, in the present invention, the upper limit of the amount of Si compound deposited is set to 7 mg.
The reason for setting / m ² is as described above. Note that Si
A more preferable range of the amount of compound attached is 0.7 to 6.0 mg / Si as Si.
a m ^2.

To deposit the Si compound on the steel plate surface,
It can be roughly classified into two methods, a method by coating and a method by electrolytic treatment. First of all, when selecting the coating method, it is important to degrease the surface of the grain-oriented silicon steel sheet after the final cold rolling in advance so that the coating solution does not repel and to improve the wettability sufficiently. Is. As the coating agent, colloidal silica having a particle size of 4 to 50 μm, or silicic acid (SiO ₂ · xH ₂₎ having a low solubility in water
O) etc. can be used. The specific means for coating and the components and concentrations after coating are not particularly limited, but for example, if a coating roll having grooves at intervals of 0.5 to 2.0 mm is used, the coating liquid concentration and roll pressure It is preferable because the coating amount can be controlled arbitrarily by selecting the force.

Next, a method by electrolytic treatment will be described. For grain-oriented silicon steel sheets, the rolling oil that has adhered to the surface after the final cold rolling, the iron powder, etc. to remove the particles of scale formed in various steps prior to the final cold rolling to obtain a clean surface. Perform cleaning.

As this cleaning method, immersion degreasing,
In addition to spray degreasing, brushing degreasing, etc., there is so-called electrolytic degreasing in which a steel sheet is electrolytically treated in an alkaline degreasing bath. For this electrolytic degreasing, usually caustic soda, sodium carbonate,
An aqueous solution containing one or more of sodium phosphate, sodium silicate, etc. is adopted as the degreasing bath.However, if the steel sheet is electrolytically degreased using a degreasing bath containing silicate, the surface of the steel sheet will be silicic acid or silica. A chemical compound containing an acid salt or a hydrated oxide of iron and iron is electrodeposited. This phenomenon is particularly remarkable in the cathode. Therefore, the grain-oriented silicon steel sheet after the final cold rolling is electrolytically degreased in a degreasing bath containing silicate,
Attaching an electrode for electrolysis to the end of normal immersion degreasing
It is extremely advantageous because a Si compound convenient for the present invention can be attached simultaneously with the degreasing treatment. Further, it is also an advantage that the amount of Si compound deposited can be arbitrarily selected by controlling the amount of electricity.

As the silicate used in the electrolytic bath for this electrolytic treatment, sodium silicate, that is, sodium orthosilicate (Na ₄ SiO ₄ ), sodium metasilicate (Na ₂ SiO ₃ ).
Alternatively, so-called water glass, which is a liquid mixture of various sodium silicates, is suitable. It is also possible to use potassium or lithium silicate. In either case, the molar ratio of metal ion and Si does not matter.

The composition of the electrolytic bath is not limited as long as it contains the above-mentioned silicic acid compound, regardless of the presence and concentration of other components such as NaOH and Na ₂ CO ₃ , but the concentration of the silicate is not limited. If it is about 0.5 to 5%, it is possible to achieve the desired target in both degreasing and adhesion of Si, which is advantageous. In addition, the Si compound can be electrodeposited by electrolytically treating the steel sheet in a suspension of colloidal silica.

The electrolysis method and conditions, that is, the energization method, the current density, the electrolysis time, the electrolysis temperature and the like may be appropriately selected within a known range.

Oxygen basis weight after decarburization annealing is 0.9
Apply an annealing separator containing MgO as a main component to steel plates in the range of up to 2.5 g / m ² . It is important to add a Ti compound to this annealing separator so that the coating weight of Ti in the film after finish annealing is 0.25 to 0.9 g / m ² . In this case, if the Ti compound content is 6.0% by weight or less as TiO ₂ , the target Ti
If the weight is less than 30% by weight, the Ti weight exceeds the target weight, so the Ti compound should be 6 to 30 as TiO _2.
It is good to add in the range of%. Ti as a Ti compound
_{O 2, Ti (OH) 4} , TiO 3 · H 2 O, TiO · (OH) 2 and the like. Furthermore, by adding SrCO ₃ or Sr (OH) ₂ to the separating agent in an amount of 0.1 to 4.0% by weight as SrO, the Ti basis weight in the coating can be stably secured and the Ti / N molar ratio can be 1.2 or less. It is effective in the above. In particular, when SrO is added in the range of 1.0 to 4.0% by weight, Sr is contained in the coating in the range of 0.03 to 0.20 g / m ² , and the tension applied to the coating can be made more stable and higher.

After applying the annealing separator, the steel sheet is subjected to finish annealing. The finish annealing is performed by a secondary recrystallization annealing and, subsequently, a heat pattern in which purification annealing is a series of steps for purifying the inhibitor components such as N, S, and Se in the unnecessary steel. Be seen. In grain-oriented silicon steel sheets using AlN as an inhibitor, secondary recrystallization annealing usually suppresses the decomposition of AlN, so N ₂ : 5 to 50 vol.
% Including, in N ₂ -H ₂ mixed atmosphere heating rate 7 to 50 ° C. /
It is carried out by heating up to around 1150 ° C at a heating rate of about hr. Subsequent purification annealing is carried out in the temperature range of 1150 to 1250 ° C. by holding in H ₂ for 3 to 20 hours.

In the present invention, the Ti / N molar ratio in the coating is 1.
In order to make it 2 or less
It is important to anneal for at least 30 minutes in a H ₂ —N ₂ mixed atmosphere with an N ₂ concentration of 10% or more. The reason why the Ti / N molar ratio is lowered by doing so is considered to be that the formation of nitrides in the film is promoted. The preferable range of the N ₂ concentration during this purification annealing is 20 to 50%, and the preferable range of the annealing time in this atmosphere is 1 to 10 hours, depending on the N ₂ concentration.

After finish annealing, an insulating coating is applied if necessary to obtain a product.

[0056]

【Example】

Example 1 C: 0.069%, Si: 3.33%, Mn: 0.073%, Se: 0.022
%, Sol.Al: 0.026%, N: 0.0083% and Sb: 0.024
% Of grain-oriented silicon steel material is hot-rolled to a thickness of 2.3 mm, homogenized at 1000 ℃, and then cold-rolled twice with an intermediate anneal at 1100 ℃ to obtain a 0.23 mm plate thickness. did.
Next, decarburization annealing was performed at 840 ° C for 180 seconds in an H ₂ —N ₂ —H ₂ O atmosphere. At the time of this decarburization annealing, the atmospheric oxidizability of the temperature rising process and the soaking process is controlled independently, and P (H ₂ O)
Each value was adjusted as shown in Table 1 as P (H ₂ ).

[0057]

[Table 1]

Then, an annealing separator containing MgO ₂ containing TiO ₂ and Sr (OH) ₂ at the values shown in Table 1 was applied as a slurry at an application amount of 9.0 g / m ² and dried. After that, secondary recrystallization annealing is performed in a mixed atmosphere of N ₂ : 20vol% and H ₂ : 80vol% at a heating rate of 20 ° C / hr to 1180 ° C, and subsequently at a temperature of 1180 ° C for 10 hours. Purification annealing was performed. At this time, in the initial stage of annealing, the N ₂ % H ₂ —N ₂ mixed atmosphere shown in Table 1 was maintained for the time shown in Table 1, and thereafter H ₂ 100
It was held in the atmosphere of%.

Thereafter, a coating containing magnesium phosphate and colloidal silica as main components was applied. During this step, a part of the samples after the decarburization annealing was analyzed for the oxygen basis weight, and the pickling weight loss in the pickling at 5% HCl / 70 ° C / 60 seconds was measured. Also, in some samples after finish annealing,
The oxygen areal weight, Ti areal weight, Sr areal weight, and Ti / N molar ratio of the forsterite coating were analyzed, and the average particle diameter of the forsterite particles and the applied tension of the coating were measured.

Further, the obtained product was plastically processed into a toroidal shape and further linearly stretched, and then dried in N ₂ .
Strain relief annealing was performed at 800 ° C for 3 hours. For the products before and after strain relief annealing, the magnetic flux density (B
₈ values), iron loss at 1.7 T, 50 Hz (W _17/50 value), bending adhesion of the coating, and appearance of the coating. The flexural adhesion of this coating was indicated by the minimum diameter at which the test piece was wound around round rods having various diameters at 5 mm intervals and the coating did not peel off. These results are collectively shown in Table 1.

As is clear from Table 1, all of the sample Nos. 1 to 9 which are suitable examples of the present invention have a forsterite coating film having a high applied tension of 0.6 kgf / mm ² or more, and have excellent iron loss. As shown, no iron loss deterioration was observed after the strain relief annealing, and the coating properties were naturally excellent. On the other hand, the sample weights of oxygen and the average particle diameter of the forsterite coating are Comparative Examples Nos. 10 and 11 in which the average particle size is outside the scope of the present invention, and the sample weights of Comparative Examples in which the Ti basis weight is outside the scope of the present invention. 12, 13, Ti / N
Sample No. 14, 1 of Comparative Example in which the molar ratio is outside the scope of the present invention
6, 17, Sr areal weight and average particle size are out of the range of the present invention, the sample No. 15 of Comparative Example has a low coating tension and inferior iron loss.

Further, in the comparative examples of sample Nos. 18 and 19, even though the applied tension of the coating was 0.6 Kgf / mm ² or more, the oxygen basis weight, the Ti basis weight, the Ti / N molar ratio or the average particle Since any of the diameters is out of the range of the present invention, the iron loss is inferior to that of the conforming example of the present invention, and the iron loss recovery after the strain relief annealing is not sufficient.

Example 2 The same cold rolled steel sheet as in Example 1 having a final thickness of 0.23 mm was electrolytically degreased in an electrolytic degreasing bath containing 3% sodium orthosilicate as a main component, and the surface A Si compound was attached to. At this time, the amount of adhesion as Si was adjusted to the value shown in Table 2 by changing the electric field electric amount.

[0064]

[Table 2]

After that, the same treatment as in Example 1 was conducted, and the same investigation as in Example 1 was conducted. These treatment conditions and the survey results are also shown in Table 2 together. As is clear from Table 2, sample Nos. 1 to 5 which are the application examples of the present invention.
Have a forsterite coating with a high applied tension of 0.7 kgf / mm ² or more, and show excellent iron loss.
Excellent coating properties. On the other hand, in the sample Nos. 6 and 7 of Comparative Examples in which the amount of deposited Si is more than the range of the present invention, the average particle diameter is excessively large, the applied tension of the coating is weak, and the iron loss and the coating properties are poor.

In addition, in the comparative examples of sample Nos. 8 and 9, although the applied tension of the coating is 0.6 Kgf / mm ² or more, the oxygen basis weight, the Ti basis weight or the Ti / N molar ratio is the same as that of the present invention. The iron loss is inferior to that of the conforming example of the present invention because it is out of the range.

[0067]

EFFECT OF THE INVENTION The present invention provides an oxygen basis weight, a Ti basis weight of a forsterite coating of a high magnetic flux density unidirectional silicon steel sheet,
It defines the Ti / N molar ratio and the average particle size,
According to this invention, the applied tension effect of the coating film can be stably exhibited, and the iron loss can be effectively improved. In particular, the recovery of the iron loss in the strain relief annealing by the user can be significantly improved,
It also has excellent coating properties.

[Brief description of the drawings]

[Fig. 1] Average particle size of forsterite: 0.4 μm, Ti
3 is a graph showing the relationship between the applied tension of the coating and the oxygen areal weight and the Ti areal weight when the / N molar ratio is 0.9 to 1.1.

[Figure 2] Forsterite average particle size: 0.4 μm, Ti /
3 is a graph showing the relationship between the applied tension of the coating and the oxygen basis weight and the Ti basis weight when the N molar ratio is 1.4 to 1.6.

[Fig. 3] Forsterite average particle size: 0.8 μm, Ti /
6 is a graph showing the relationship between the applied tension of the coating and the oxygen basis weight and the Ti basis weight when the N molar ratio is 0.9 to 1.1.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location H01F 1/16 H01F 1/16 B (72) Inventor Hiroshi Yamaguchi 1-chome, Kawashima-dori, Kurashiki, Okayama (No street number) Inside Kawashima Steel Co., Ltd. Mizushima Steel Works (72) Inventor Masako Kuda 1-chome, Mizushima Kawasaki Dori, Kurashiki City, Okayama Prefecture (No street number) Inside Kawashima Steel Co., Ltd. Mizushima Steel Works

Claims (6)

[Claims] 1. A unidirectional silicon steel sheet having a forsterite coating on the surface and having a magnetic flux density B ₈ of 1.90 T or more, wherein the forsterite coating has an oxygen basis weight: 2.5 to 4.5 g / m ² , High magnetic flux density unidirectional silicon steel sheet characterized by satisfying Ti basis weight: 0.25 to 0.90 g / m ² , Ti / N molar ratio: 1.2 or less, and average particle size of forsterite particles: 0.5 μm or less Forsterite film. 2. A unidirectional silicon steel sheet having a forsterite coating on its surface and a magnetic flux density B ₈ of 1.90 T or more, wherein the forsterite coating has an oxygen basis weight of 2.5 to 4.5 g / m ² . Ti basis weight: 0.25 to 0.90 g / m ² , Sr basis weight: 0.03 to 0.20 g / m ² Ti / N molar ratio: 1.2 or less, and average particle diameter of forsterite particles: 0.5 μm or less Forsterite coating of high magnetic flux density unidirectional silicon steel sheet. 3. A material for unidirectional silicon steel sheet is hot-rolled, then cold-rolled, and then decarburized and annealed to obtain an oxygen basis weight in the range of 0.9 to 2.5 g / m ^2. The surface of the charcoal-annealed plate was coated with an annealing separator containing Ti compound in the range of 6.0 to 30.0% by weight in terms of TiO ₂ and the balance being substantially MgO, and then subjected to secondary annealing by finish annealing. After recrystallization annealing, 1150 ℃
A high magnetic flux density unidirectional silicon characterized by performing purification annealing at the above temperature and annealing in the H ₂ -N ₂ mixed atmosphere with N ₂ concentration: 10% or more for at least 30 minutes during the purification annealing. Method for forming forsterite coating on steel sheet. 4. A material for unidirectional silicon steel sheet is hot-rolled, then cold-rolled, and then decarburized and annealed to obtain an oxygen basis weight in the range of 0.9 to 2.5 g / m ^2. on the surface of the coal annealed sheet, a 6.0 to 30.0 wt% and Sr compound Ti compound in terms of TiO ₂ contained in the range of 0.1 to 4.0 wt% in terms of SrO, the remainder annealing separator consisting essentially composition of MgO Then, after secondary recrystallization annealing by finish annealing, purification annealing is performed at a temperature of 1150 ° C. or higher, and N ₂ concentration: 10% or more of H ₂ —N ₂ for at least 30 minutes during the purification annealing. A method for forming a forsterite coating on a high magnetic flux density unidirectional silicon steel sheet, characterized by annealing in a mixed atmosphere. 5. The pickling reduction amount according to claim 3 or 4, when the decarburized annealed sheet is pickled with a 5% HCl aqueous solution at a temperature of 70 ° C. for 60 seconds, the pickling loss is 0.3 g / m ^2. A method for forming a forsterite coating on a high magnetic flux density unidirectional silicon steel sheet, characterized in that: 6. The silicon compound according to claim 3, 4 or 5, wherein a silicon compound is adhered to the steel sheet before decarburization annealing, and the adhered amount is in the range of 0.5 to 7.0 mg / m ^{2 in} terms of Si weight. Method for producing high magnetic flux density unidirectional silicon steel sheet.