JP6424875B2 - Directional electromagnetic steel sheet and method of manufacturing the same - Google Patents

Description

  The present invention is directed to a oriented electrical steel sheet used mainly for a transformer, and a very low iron loss can be obtained by applying a high tensile tension to the base iron by means of a ceramic coating formed on the base iron. The invention also relates to a grain-oriented electrical steel sheet having very good film adhesion even after high-temperature annealing such as strain relief annealing, and further having excellent workability.

A directional magnetic steel sheet excellent in magnetic properties is mainly used as an iron core material inside a transformer, and its reduction in iron loss is required to improve the energy usage efficiency of the transformer. In addition to methods such as sharpening of crystal grains to the Goss orientation, increase in film tension, and thinning, methods for surface processing of steel plates are known for reducing iron loss in grain-oriented electrical steel sheets.
The grain-oriented electrical steel sheet obtained by this method can be roughly divided into two types: heat-resistant type in which low iron loss is maintained even if heat treated at several hundred degrees or more and non-heat-resistant type in which iron loss is deteriorated after heat treatment. When the transformer core is wound, heat-resistant characteristics are often required. The reason is that, in many cases, the strain that causes deterioration of the iron loss, which is generated inside the steel sheet in producing the wound core, is often removed by high-temperature strain relief annealing.

  With respect to a method of reducing iron loss by surface processing of a steel plate, a method of introducing a linear groove in a cold rolled sheet before forming a film is shown in response to the requirement of a heat-resistant low iron loss material. For example, in Patent Document 1, after a resist ink is applied to a cold-rolled sheet before decarburizing annealing, a groove is formed on the surface of the steel sheet by etching, and a directional iron sheet having low core loss even after strain relief annealing The method is shown. This method has the advantage of high maintainability because there is little mechanical wear of the device that occurs when forming grooves by stamping.

  On the other hand, in response to the demand for non-heat resistant low iron loss materials, for example, Patent Document 2 shows a method of locally introducing distortion into a steel plate after secondary recrystallization by an electron beam or a laser, Very low core losses have been achieved. However, in recent years, the technology for reducing iron loss by these methods tends to be saturated, and it is becoming difficult to dramatically improve the magnetic characteristics.

On the other hand, from the viewpoint of surface modification, techniques to further reduce iron loss are known. For example, Patent Document 3 shows that by smoothing the surface of the base iron, extremely excellent magnetic properties can be obtained. As to the detailed mechanism, there are still many unclear points, but reducing the roughness of the base iron suppresses energy loss accompanying the movement of the domain wall, thereby reducing hysteresis loss and increasing permeability. For example, the magnetic flux density B ₈ can achieve a value of up to about 1.96 T. However, according to this method, although the hysteresis loss which is a part of the total iron loss is reduced, the eddy current loss is not sufficiently reduced. However, in this respect, by applying tensile tension to the base iron, even if the tensile strength is the same, even if the material has a low roughness, the eddy current is more than in the material having a high roughness. It has been found that losses can be reduced.

  In addition, if a higher tension is applied, it is possible to realize an extremely low iron loss which has not been achieved conventionally. For this reason, high tension coatings have been developed in order to provide high tension to the ground iron. For example, Patent Document 4 discloses that a very high tensile tension is formed by forming a TiN film on base steel by PVD or CVD.

Patent No. 2942074 gazette International Publication No. 2013/099258 Japanese Patent Publication No. 52-24499 Patent No. 4192818 JP 2002-356751 A JP 2003-301246 A

"Functionalization of steel surface by vapor phase coating" (Japan Iron and Steel Institute, Ed., 1995, pp. 141-148)

There are three problems in the formation of the above-mentioned ceramic coating.
The first problem is that the manufacturing cost for film formation is high. In the case of film formation by PVD or CVD, the cost of the metal element (for example, Ti) serving as the evaporation source is high, and the film formation yield is also low. Therefore, although it is desirable to form the ceramic coating as thin as possible, low iron loss is difficult to obtain in this case.

The second problem is the adhesion of the film after annealing. When the steel sheet with the ceramic film is subjected to strain relief annealing, the adhesion of the film is impaired, and the film may be stripped or discolored black. This tendency was remarkable especially when the ceramic coating was a thin film.
In the conventional findings, FeP formed at the interface with the base iron due to P present in the film is also considered to be a cause of deterioration in film adhesion, but it is a case where a film not containing P is formed. Even in the same case, the film adhesion may be impaired. Therefore, there may be other causes, but there are many unclear points in detail.

  The third problem is processability. The above-mentioned ceramic coatings are generally high in hardness, and when a steel sheet is subjected to a shearing process for a transformer core, the shearing machine wears rapidly, which causes a loss in productivity. In addition, when processed with a worn shear, burrs etc. occur in the iron core material, which causes the characteristic of the transformer to be disturbed.

  Until now, attempts have been made to reduce the film thickness as much as possible in order to reduce the film formation cost. For example, Patent Document 5 shows that even if the total film thickness is thin, the film adhesion is improved and low iron loss is obtained by forming a composite film, that is, forming a SiNx film on top of TiNO. ing. However, when the ceramic film is multilayered, there is a problem that the apparatus becomes excessively large and equipment cost increases because the appropriate film forming conditions differ between different film forming species.

  Further, Patent Document 6 discloses a technique for reducing the hardness of a ceramic coating to improve processability. According to this technique, a low core loss oriented silicon steel sheet excellent in cutting characteristics is obtained without impairing the film quality and adhesion of the ceramic film.

  However, according to the experiments of the present inventors, when the hardness is lowered, a tendency of the Young's modulus to be lowered simultaneously is recognized. The hardness of the ceramic coating may be affected by the frequency of presence of defects and the like inherent in the coating, and it is considered that the material having many defects has a low hardness and a low Young's modulus. Since the Young's modulus of the film is considered to be proportional to the magnitude of the tension applied to the base iron, lowering the Young's modulus is in principle not preferable in terms of iron loss.

  The present invention advantageously solves the above-mentioned problems, and in the case of achieving low iron loss with a relatively thin ceramic coating, there is little deterioration in the adhesion of the coating after stress relief annealing, and also excellent processability. The purpose is to propose a grain-oriented electrical steel sheet with its advantageous manufacturing method.

Now, as a result of repeating experiments and studies to solve the above problems, the inventors of the present invention have found that the grain size and the surface condition of the base iron are necessary for reducing iron loss and improving adhesion by the ceramic coating. I found it to have a strong influence.
That is, for the ground iron
・ The average grain size is 16 mm or more, and the etching depth at grain boundaries is less than 10 μm,
・ Surface roughness Ra is 0.3 μm or less,
It was experimentally proved that it is important that the area ratio of the crystal grain including the etch pit portion be 30% or less.

FIG. 1 shows the results of investigations on film adhesion and iron loss using materials having average crystal grain sizes of 13 mm, 16 mm, and 33 mm, in which the average crystal orientations are substantially the same. Here, the investigation is a phosphate-based coating obtained by depositing a 0.3 μm thick TiN film by PVD on a ground iron smoothed by the method of electropolishing and nitric acid polishing and baking the treatment liquid of the inorganic substance. Then, it was carried out on a steel sheet subjected to strain relief annealing at 850 ° C. for 3 h. In all of these, grain boundaries were preferentially polished during electrolytic polishing and nitric acid polishing, and the grain boundaries were polished about 2 μm deeper than in the grains.
In addition, coating film adhesiveness evaluated the minimum bending diameter which coating peeling does not produce, when a steel plate is wound around the round bar of diameter: 50, 40, 30, 25, 20, 15, 10, 5 mm. The average crystal grain size D was evaluated by Di Di x Ai (i: 1 to 50) using the area ratio Ai of one crystal grain and the RD grain size Di. Here, the RD grain size is the grain size of crystal grains in the rolling direction (RD).

  It can be seen from FIG. 1 that the larger the average grain size, the better the core loss and the film adhesion. On the other hand, when the average grain size was smaller than 16 mm, it was observed that the film adhesion, in particular, was rapidly deteriorated.

Next, using a material with an average crystal grain size of 16 mm, the polishing depth of grain boundaries is changed by changing the nitric acid concentration and immersion time, and the grain boundary polishing depth affects film adhesion and core loss. We investigated the impact. The obtained result is shown in FIG.
As shown in the figure, when the polishing depth of the grain boundary with respect to the grain is 10 μm in ND, although the iron loss is almost equal, the film adhesion is deteriorated. Here, ND means the rolling surface normal direction. A more preferable polishing depth is 5 μm or less.
Although the details regarding the influence of the number of grain boundaries and the deeply-pierced grain boundaries on the film properties are not clear, it is thought that the ceramic film grows epitaxially with respect to the base iron, so voids and lattice defects It is considered that some defects or defects exist in the ceramic coating grown on the surface of the contained grain boundary portion.

In addition, as shown in the conventional findings, it is the same in the present invention that lower surface roughness is advantageous for reducing iron loss.
FIG. 3 shows that the surface of a material having an average crystal grain size of 16 mm is subjected to strain relief annealing at 800 ° C. for a material whose surface roughness Ra is changed by changing the concentration of electrolytic polishing and nitric acid polishing, and immersion time. It investigated about the iron loss after applying. Here, the polishing depth of the grain boundary portion was 0.4 to 0.9 μm.
As shown in the figure, particularly low iron loss is obtained when Ra is 0.3 μm or less.

Polishing by a chemical method using hydrochloric acid, nitric acid or the like is known as an effective means for producing a steel sheet surface having a low surface roughness.
Therefore, when the present inventors tried polishing by a chemical method using hydrochloric acid, nitric acid, etc., in the case of this method, adhesion of the film was observed depending on the appearance of the etch pit formed on the surface of the base iron. Sex and iron loss were found to be worse.

  FIG. 4 shows an example of a photograph of the surface of a steel plate observed after depositing TiN to a thickness of 0.3 μm. The three square parts in the center are the etch pits. If the thickness of the formed film is thin, it can be confirmed as shown in the photograph, but if it is relatively thick, the surface is roughened and it is difficult to check. Therefore, it is preferable to selectively remove the ceramic coating to check.

FIG. 5 shows the _core loss W _17/50 after strain relief annealing at 850 ° C. for 3 hours in relation to the area ratio of crystal grains including etch pits. In the experiment, a TiN film having a thickness of 0.4 μm was formed by PVD on a base iron surface having an average crystal grain size of 20 mm and a surface roughness Ra of 0.15 μm, and then a phosphate-based coating was applied. It is performed to the steel plate which performed strain relief annealing. Here, the surface roughness was measured at a portion not including the etch pit. The etch pits were observed by an optical microscope before the formation of the ceramic film. Further, the fact that the etch pits are contained in the crystal grains means that the existing area ratio of the etch pits in the crystal grains is 2% or more. The area ratio of the etch pits was evaluated as the average value of the area ratio within the field of view of 1 mm × 1 mm in the interior of the crystal grain. The number of crystal grains observed was about 200 arbitrarily selected.
As shown in the figure, it can be seen that when the area ratio of crystal grains including etch pits exceeds 30%, the iron loss after stress relief annealing rapidly deteriorates.

  In the present invention, the ceramic coating has a film thickness of 1.0 μm or less for cost reduction, and the type thereof is TiN, TiCN, or TiC, which is highly effective in reducing iron loss. In addition, Ti oxides (TiOx, x: 1 to 2) may be mixed. However, when TiOx is contained, if TiOx is present at the film-base iron interface, the film adhesion is impaired. Therefore, it is preferable that the film be present more on the surface side of the film.

FIG. 6 shows the effect of oxygen distribution on the minimum bending diameter. The horizontal axis of the figure is the ratio of the depth from the surface of the ceramic coating, at which the oxygen detection strength measured by GDS is 1/2 of that of the insulating oxide coating, with respect to the thickness of the ceramic coating (here 0.3 μm) Is shown.
As shown in the figure, when this value is 0.5 or more, it is quantitatively understood that the film adhesion deteriorates.

The minimum value of the average film thickness of the ceramic coating is 0.3 μm. The reason is that when the film is formed at less than 0.3 μm, sufficient iron loss can not be achieved.
The ceramic coating desirably has a ratio of surface roughness Rz to average film thickness of 0.3 or less. It is known that TiN and the like grow like islands, but depending on the film forming conditions, as shown in Fig. 7 (a surface photograph of TiN with a thickness of 0.3 μm immediately after film forming), especially when the film thickness is thin. In addition, the thickness of TiN is partially changed. In this case, the film adhesion deteriorates at portions where the film thickness is thin (portions where the ratio of the surface roughness Rz to the average film thickness is large). Rz was derived from the cross-sectional observation image of the SEM.

  The result of having investigated about the adhesiveness of the ceramic film which changed the ratio (Rz / t) with respect to the average film thickness t of surface roughness Rz in Table 1 is changed is shown.

  As shown in the table, as the ratio of the surface roughness Rz to the average film thickness t decreases, the adhesion is improved, and in particular, good results can be obtained when the ratio is 0.3 or less.

  Furthermore, the present inventors have found that the hardness of the ceramic coating and the roughness of the ceramic coating are important for the reduction of iron loss and the improvement of the coating adhesion by the ceramic coating. And it became clear that it was effective to make the crystal size of a ceramic film smaller in order to increase the hardness of a ceramic film. The hardness of the ceramic coating was at most 2000 HV as shown in the conventional example of Patent Document 6. Moreover, in Patent Document 6, it is shown that it is rather important to set the value to 1500 HV or less from the viewpoint of improvement in processability.

As described separately, since the hardness of the ceramic coating is also affected by the material to be deposited, exact comparison can not be made, but as shown in Non-Patent Document 1, TiN deposited on the same steel material, SUS, is used. Hardness of about 1500 HV.
The inventors of the present invention have found that, as described below, by increasing the hardness of the ceramic coating more than before, both the coating adhesion after annealing and the iron loss can be remarkably improved.

FIGS. 8 and 9 show the results of investigation of the influence of the hardness of the ceramic coating (TiN coating) on the coating adhesion and the core loss, respectively. Here, the film hardness was a value measured immediately after depositing TiN by the PVD method. The film thickness was 0.4 μm, and the crystal orientation angle β of the ground iron was 2 °. The hardness was converted to Vickers hardness (HV) by multiplying the value of 92.6 by the indentation hardness value measured by a Berkovich indenter based on the ISO 14577 standard.
In addition, film adhesion and iron loss were measured after forming a TiN film, applying a phosphate-based coating to which a treatment liquid of an inorganic substance was baked and then performing stress relief annealing (also referred to as SRA) at 800 ° C. for 3 hours. . In addition, coating film adhesiveness was evaluated by the minimum bending diameter which coating peeling does not produce, when a steel plate is wound around the round bar of diameter 50, 40, 30, 25, 20, 15, 10, 5 mm. Moreover, the numbers attached to the plot points in FIG. 9 are Young's modulus (unit: GPa) measured at the same timing as the hardness measurement. Here, the Young's modulus of the film was determined by the following equation with the Poisson's ratio of the film being 0.3.
1 / E _r = (1-ν ² ) / E _IT + (1-ν _i ² ) / E _i
Where E _IT = elastic modulus of the film (Young's modulus)
E _r = complex modulus
E _i = elastic modulus of indenter (diamond)
= = Poisson's ratio of film
_{i i} = Poisson's ratio of indenter (diamond)

  As apparent from FIGS. 8 and 9, it is possible to improve both the core loss and the film adhesion by increasing the hardness, and it is possible to achieve extremely good iron loss by making the hardness higher than ever before. found.

On the other hand, when the above-described high hardness ceramic film is formed, there is a problem that the processability is deteriorated. In this regard, as a result of repeating the experiment for achieving both high hardness and processability, the present inventors have found that it is important to control the structure of the ceramic coating in order to achieve both high hardness and processability. .
That is, in order to increase the hardness without deteriorating the processability, it is useful to set the RD average crystal grain size of the ceramic coating to 0.1 μm or less and to form a columnar structure in which single grains are elongated to ND. I found out. The average grain size is smaller than ever before, and it is estimated that this affects the high hardness as described above. Here, the columnar shape can be measured by the EBSD method. Although there is also an example in which the structure is observed by a frozen fractured surface, it is not preferable because accurate crystal size can not always be measured. The EBSD measurement can not be performed well, probably because a large amount of strain is introduced at the ground iron interface, so crystal orientation analysis is performed in the range of 1/2 from the surface layer, and 50% or more of the tissue clearly measured. If it is a pillar having a major axis at the ND, it is judged to be a pillar.

In order to confirm the effect of forming a columnar structure, a plate with TiN formed as a film was sheared under the same conditions with a shearing machine, and the generation ratio of the burrs of the sheared part of 3 μm or more was examined.
The obtained results are shown in Table 2.

  As shown in Table 2, by forming the structure into a columnar structure, it was possible to significantly reduce the incidence of burrs in the sheared portion.

The present invention is based on the above findings, and the gist configuration is as follows.
1. A directional electromagnetic steel sheet having an insulating oxide film containing O or P in the outermost layer, and a ceramic coating on the lower layer thereof and on the base iron,
The local iron is
・ The average grain size is 16 mm or more, and the etching depth at grain boundaries is less than 10 μm,
・ Surface roughness Ra is 0.3 μm or less,
The area ratio of crystal grains including the etch pit portion is 30% or less, and the ceramic coating is
Any of TiN, TiCN or TiC having an average film thickness of 0.3 μm or more and 1.0 μm or less
The position from the surface where the detection strength of oxygen is 1/2 of that of the upper insulating oxide film is on the surface side of the center of the film in the thickness direction,
-A grain-oriented electrical steel sheet characterized in that the hardness of the ceramic film measured from the surface layer is 2100 HV or more.

2. It is the directionality electromagnetic steel sheet according to the above 1, and
The ceramic coating is
A directional electrical steel sheet characterized in that the ratio of the surface roughness Rz to the average film thickness is 0.3 or less.

3. The directional electromagnetic steel sheet according to 1 or 2 above,
The ceramic coating is
-A grain-oriented electrical steel sheet characterized in that it has a columnar structure with an average crystal grain size of RD in the surface layer of less than 0.1 μm and extended to ND.

4. It is the directionality electromagnetic steel sheet according to any one of 1 to 3 above,
-A grain-oriented electrical steel sheet characterized in that in the average crystal orientation of the ground iron, the angle β between the <100> axis of the secondary recrystallized grains facing the rolling direction of the steel sheet and the rolling surface is less than 3 °.

5. It is a method of manufacturing the directionality electromagnetic steel sheet according to any one of 1 to 4 above,
The insulating oxide film according to any one of the above 1 to 4 is formed into a film by a coating roll, and in that case, the line tension at the time of baking the insulating oxide film is 7 MPa or more. Method of manufacturing steel plate.

6. It is a method of manufacturing the directionality electromagnetic steel sheet according to any one of 1 to 4 above,
In smoothing the surface of the base iron which forms the ceramic film according to any one of the above 1 to 4, after the base iron is polished with hydrochloric acid, nitric acid or an acid containing them, the base iron is further subjected to electrolytic polishing or chemical polishing. A method of manufacturing a grain-oriented electrical steel sheet, comprising: polishing by 8 μm or more and smoothing.

7. It is a method of manufacturing the directionality electromagnetic steel sheet according to any one of 1 to 4 above,
In forming the ceramic film according to any one of 1 to 4 above, Ti ions accelerated at a voltage of 500 V or more collide with the surface of the base iron for 10 seconds or more to remove the oxide film on the surface, and then ion accelerated. A method of manufacturing a grain-oriented electrical steel sheet characterized by forming a film at a voltage of 100 V or more.

8. It is a method of manufacturing the directionality electromagnetic steel sheet according to any one of 1 to 4 above,
In addition to the above-described 7, when a strain introduction type magnetic domain fragmentation treatment is not performed, in a step after the ceramic film deposition step, and when a strain introduction type magnetic domain fragmentation treatment is performed, a ceramic coating film deposition step and A method of manufacturing a grain-oriented electrical steel sheet characterized in that annealing is performed at 750 ° C. or more and 15 s or more in any of the steps during the strain introduction type magnetic domain refining step.

9. It is a method of manufacturing the directionality electromagnetic steel sheet according to any one of 1 to 4 above,
In forming the ceramic film in any one of said 1-4, the film-forming speed | rate of a ceramic film is 1 nm / s or more, The manufacturing method of the directionality electromagnetic steel sheet characterized by the above-mentioned.

According to the present invention, even in the case of achieving low iron loss of a grain-oriented electrical steel sheet by forming a single-layer ceramic film, the film adhesion after strain relief annealing is significantly improved compared to the prior art. be able to. In addition, it is possible to suppress the deterioration in processability caused by the increase in hardness of the ceramic coating, which has hitherto been concerned.
Therefore, the use of the grain-oriented electrical steel sheet manufactured according to the present invention for a transformer can reduce energy use efficiency, which is industrially useful.

It is a graph which shows the relationship between the crystal grain size of base iron, film | membrane adhesiveness, and an iron loss. It is a graph which shows the relationship between the grain boundary grinding | polishing depth of a base iron surface, film | membrane adhesiveness, and an iron loss. It is a graph which shows the relationship between surface roughness Ra of a base iron, and an iron loss. It is a microscope picture (magnification: 200 times) of the steel plate surface after forming a film into a TiN of 0.3 micrometer in thickness. It is a graph which shows the relationship between the area ratio of the crystal grain containing the etch pit of the base iron surface, and the iron loss after strain relief annealing. It is a graph which shows the relation between the ratio of the depth from the surface of the ceramic film whose oxygen detection intensity is 1/2 of the thickness of the insulating oxide film to the film thickness of the ceramic film, and the minimum bending diameter. It is a microscope picture (magnification: 20,000 times) of the steel plate surface immediately after forming TiN into a film with a thickness of 0.3 micrometer. It is a graph which shows the relationship between the hardness of ceramic coating film, and film adhesion. It is a graph which shows the relationship between the hardness of a ceramic coating, and an iron loss.

Hereinafter, the present invention will be specifically described.
First, the grain-oriented electrical steel sheet prior to the formation of the ceramic film will be described.
The grain-oriented electrical steel sheet preferably contains C: 300 mass ppm or less, Si: 1 to 7 mass%, P: 0.1 mass% or less, Mn: 0.1 mass% or less and S: less than 10 mass ppm as a steel composition . With respect to the other components, there is no problem even if a component is added such that the crystal orientation after secondary recrystallization is sharpened to the Goss orientation based on the conventional findings, but in the case of forming a forsterite film, It is preferable that the amount of Cr for developing the anchor be as small as possible, and 0.1 mass% or less. Moreover, it is preferable that secondary recrystallization annealing is performed and it is the structure | tissue which accumulated in the vicinity of Goss orientation.
The average grain size is set to 16 mm or more as the secondary recrystallized structure. The reason is that if the average crystal grain size is less than 16 mm, as shown in FIG. 1 above, the core loss and the film adhesion, particularly the film adhesion, are rapidly deteriorated.
In addition, as shown in the examples described later, the iron loss improvement effect increases as the angle β formed between the <100> axis of the secondary recrystallized grains facing the rolling direction of the steel sheet and the rolling surface decreases, so the β angle Is preferably less than 3 °.

  If a forsterite film is formed on the surface of the base iron, it must be removed in advance using an acid or the like. Although the film may be removed by a mixture of hydrochloric acid and hydrogen fluoride, an etch pit appears. Therefore, it is further chemically polished by electrolytic polishing or a mixed solution of hydrogen peroxide water and hydrogen fluoride water to reduce the thickness by 8 μm or more, and the area ratio of crystal pits having an etch pit ratio of more than 2% is 30%. It needs to be reduced to The reason is that if the area ratio of crystal grains whose etch pit presence ratio is larger than 2% exceeds 30%, as shown in FIG. Further, it is necessary to smooth the surface of the base iron by the above-mentioned electrolytic polishing or chemical polishing to make the surface roughness Ra 0.3 μm or less. The reason is that when the surface roughness Ra of the base iron exceeds 0.3 μm, as shown in FIG. 3, the iron loss is deteriorated. However, since too much polishing reduces the yield of base iron, the removal amount after film removal is preferably within 10% of the plate thickness.

  On the other hand, even when the forsterite film is not formed, an unavoidable oxide may be formed on the surface layer during secondary recrystallization annealing, so the thickness is reduced by several μm by electrolytic polishing or chemical polishing. It is good to do. In the case of nitric acid polishing or electrolytic polishing, grain boundaries tend to be preferentially etched, but the etching depth at the grain boundaries needs to be limited to less than 10 μm by adjusting the nitric acid concentration, immersion time, and current density. The reason is that when the etching depth at grain boundaries is 10 μm or more, as shown in FIG.

Next, the ceramic coating formed on the surface of the base iron will be described.
Before the formation of the ceramic coating, it is necessary that no visible rust has been generated on the surface of the base iron, but if the occurrence of rust is recognized, chemical reaction such as hydrochloric acid pickling It needs to be removed by the method. However, since extremely fine oxides are inevitably formed in the surface layer, it is advantageous to remove them by ion cleaning in a vacuum of 10 Pa or less in advance. As cleaning, it is advantageous to cause ions accelerated at a voltage of 500 V or more to collide with the surface of the ground iron for 10 seconds or more. The ions used here are preferably Ti ions which are film forming elements. Desirably, acceleration voltage: 800 V or more. This improves the adhesion of the ceramic coating. If coarse impurities such as oxides remain on the surface of the base iron, there is a disadvantage that the ceramic coating is peeled off therefrom. However, when the acceleration voltage is excessively increased, the upper limit is preferably 2000 V in order to give distortion to the base iron and to increase iron loss.

Deposition of the ceramic coating is performed by PVD. For example, in the thermal CVD method, since the film formation temperature is high, the film formation structure tends to grow and soften, which is not preferable.
The PVD method includes the HCD method and the AIP method as representative film forming methods, but either of them can be applied. However, in the case of the AIP method, it is preferable to adjust the cathode so that droplets do not occur. Droplets and other defects promote the diffusion of O from the insulating oxide film and degrade the film.

In order to increase the adhesion to the ground iron, it is preferable to apply the HCD method or the AIP method, and set the ionization rate of the film forming element to 50% or more. The film forming species is either TiN, TiCN or TiC, which has an excellent iron loss reduction effect. The evaporation source Ti uses a high purity material. In addition, the film thickness of the ceramic coating is 0.3 to 1.0 μm. This is because if the thickness of the ceramic coating is less than 0.3 μm, the tension of the ceramic coating is low, while if it exceeds 1.0 μm, not only the cost for forming the film is high but also the processability is deteriorated. Here, a preferable average film thickness is 0.4 μm or more.
Note that the film formation temperature is set to 300 ° C. or more and 500 ° C. or less. If it is excessively low, the deposition rate will decrease, and if it increases, the coating structure will become coarse.

  In addition, the position from the surface where the detection strength of oxygen in the ceramic coating is 1/2 of that of the insulating oxide coating in the upper layer is on the surface side of the center in the thickness direction of the coating, that is, the oxygen detection strength is the insulating oxide The ratio of the depth from the surface of the ceramic coating to the film thickness of the ceramic coating needs to be within 0.5, which is 1/2 of the coating. This is because when this ratio is 0.5 or more, the film adhesion is degraded as shown in FIG.

  Furthermore, in order to make the ceramic coating a fine structure, the deposition rate is preferably 1 nm / s or more. The deposition rate can be easily increased by increasing the evaporation source. More preferably, it is 5 nm / s or more. Note that if the deposition rate is high, island-like structures tend to be formed as shown in FIG. 8 above, but in this case, the film thickness may be increased or the accelerating voltage during deposition may be increased. The ratio of the surface roughness Rz to the average film thickness may be 0.3 or less.

  The acceleration voltage of the evaporation source ions at the time of film formation is set to 100 V or more. This is because defects in the ceramic coating tend to be reduced and hardness increased by increasing the accelerating voltage. The upper limit is preferably set to 1000 V because the film forming rate tends to decrease as the acceleration voltage increases. The flow rate of nitrogen gas and methane gas, and the degree of vacuum may be suitably determined so as to form the above-mentioned film with conventionally known values, but in particular, the ceramic film is parallel to the rolling surface and the {111} crystal plane It is preferable to adjust the conditions so as to obtain a preferentially oriented tissue. The crystal orientation of {111} is likely to form a columnar structure. However, the vacuum sheet passing device has a differential pressure type structure of two or more stages. Since water is adsorbed to the steel plate before vapor deposition, it is necessary to remove it in the first stage vacuum chamber. More preferably, a three-stage differential pressure structure is used. The presence of moisture causes defects in the ceramic coating, resulting in reduced hardness and reduced coating adhesion.

The hardness of the ceramic coating formed by the above method can be 2100 HV or more. In the case of using TiCN as a film forming species, it is possible to set it to 2600 HV or more. By setting the hardness of the ceramic coating to 2100 HV or more, the coating adhesion and the core loss are effectively improved as shown in FIGS.
In addition, by forming the ceramic film by the above-described method, it is possible to form a columnar structure elongated to ND with an average crystal grain size of RD of 0.1 μm or less at the interface opposite to the base iron side except TiC. . Although the average grain size of RD seems to be finer at the interface on the base iron side, it could not be clearly confirmed by the above-mentioned EBSD method.

Next, the insulating oxide film formed on the ceramic film will be described.
Since the above-mentioned ceramic coatings such as TiN have conductivity, it is necessary to form an insulating coating on the surface in order to be used as a transformer core application. In the present invention, an insulating oxide film containing O or P is used as the insulating film. This is because insulating oxide films containing O or P are inexpensive and advantageous in high temperature heat resistance and high tension generation. Here, as content of O and P, about 10-70 mass% is suitable.
Examples of such an insulating oxide include magnesium phosphate and aluminum phosphate.

  Such an insulating film may be formed by a PVD method, but the cost is preferably a method of forming an oxide film by baking after application by a roll. Baking is usually performed at a high temperature of 300 ° C. or higher, but at this time, the yield point of the base iron is lowered, and the film is deformed by the tension of the film being formed to introduce unnecessary distortion into the base iron There is sex. In order to prevent this deformation, the line tension at the time of baking is preferably 7 MPa or more. The upper limit is preferably set to 12 MPa from the viewpoint of suppressing creep deformation of the steel plate. When ion irradiation is performed at a high voltage before the formation of the ceramic film, a small amount of distortion may be present in the steel sheet, so it is more preferable that annealing can be performed at 750 ° C. or more and 15 s or more.

In the present invention, magnetic domain refinement processing can be further performed.
In the case of forming a groove on the surface of the base iron to carry out magnetic domain fragmentation, the groove forming process is preferably performed before the formation of the ceramic film. In the case of forming the groove after the formation of the ceramic film, it is not preferable because an additional cost is required to remove the film. Further, the non-heat resistant magnetic domain fragmentation treatment may be performed after the formation of the insulating oxide film. Depending on the insulating oxide film, since there is a film formed at a high temperature of 700 ° C. or more, even if distortion is introduced by an electron beam or the like before the formation of the insulating oxide film, the distortion disappears at the time of baking. This is because the effect of magnetic domain fragmentation is reduced.
Further, as a non-heat-resistant magnetic domain refining method, the electron beam method is preferable to the laser method. In the case of a laser, it is reflected by the smoothed surface, resulting in low energy irradiation efficiency.

  When the strain introduction type magnetic domain fragmentation treatment is not performed, in the step after the ceramic film deposition step, and when the strain introduction type magnetic domain fragmentation treatment is performed, the ceramic coating film deposition step and the strain introduction magnetic domain It is advantageous to apply annealing at 750 ° C. or more and 15 s or more in any step during the subdivision step. This is to remove a slight amount of strain introduced into the steel plate when the ions are irradiated at a high voltage before the formation of the ceramic film. There is no problem if this annealing is combined with the baking of the insulating oxide film described above.

Example 1
As a steel plate, two types of secondary recrystallized plates (plate thickness: 0.22 mm, average grain size: different in manufacturing conditions) with a forsterite film containing 20 mass ppm of C and 3.4 mass% of Si in ground iron 28-35 mm) was used. After removing the forsterite film with a mixture of hydrochloric acid, hydrogen fluoride and nitric acid, this steel plate was mixed with hydrogen fluoride water (47%) and hydrogen peroxide water (34.5%) at a ratio of 1:20. By chemical polishing with an aqueous solution, the thickness of the plate was reduced to 0.20 mm, and a smooth surface having a surface roughness Ra of 0.1 μm or less was obtained. The etching depth of the grain boundary at this time was 0.5 μm or less.
Next, the surface oxide was removed by ions accelerated at a voltage of 1000 V, and a TiN film having an average film thickness of 0.6 μm was formed at a deposition voltage of 200 V and a deposition rate of 1.5 nm / s. The hardness of TiN was 2550 HV. In addition, the ratio of the surface roughness Rz to the average film thickness was 0.14, and the RD average crystal grain size was 0.05 μm, which was a columnar structure extending in parallel to ND.
Next, a phosphate-based insulating tension film was baked after roll application at 800 ° C. for 60 seconds. The line tension at this time was 10 MPa. Thereafter, magnetic domain refinement processing was performed by the electron beam method.

Crystal orientation angle β, area ratio of crystal grains including etch pits, iron loss W _17/50 and adhesion of film after SRA in N ₂ atmosphere for 3 hours, in thus obtained grain-oriented electrical steel sheet Table 3 shows the results of examining the properties (minimum bending diameter) and the iron loss increase amount ΔW _17/50 by SRA.
In addition, the ground iron smoothing method A shown in the table is a mixed solution of hydrochloric acid, hydrogen fluoride and nitric acid, and when the thickness is reduced to 0.205 mm and then reduced to 0.197 mm by the chemical polishing method, The ground iron smoothing method B is a case of reducing the thickness to 0.202 mm with a mixed solution of hydrochloric acid, hydrogen fluoride and nitric acid, and then reducing the thickness to 0.197 mm by a chemical polishing method.

  It is understood that it is possible to significantly reduce the iron loss by setting the crystal orientation angle β to 3 ° or less. In addition, it is possible to improve film adhesion and iron loss after annealing (after SRA) at 850 ° C. for 3 hours by polishing at least 8 μm by chemical polishing using method A as a method of smoothing the base iron I know that there is.

(Example 2)
As a steel plate, grooves extending in the width direction with a depth of 30 μm are periodically formed at intervals of 3 mm in the rolling direction, and 2 with a forsterite film containing 20 mass ppm of C and 3.4 mass% of Si 2 The following recrystallization plate (plate thickness: 0.22 mm, average grain size: 30 mm, angle β: 2 °) was used. The forsterite film is removed with a mixed solution of hydrochloric acid, hydrogen fluoride and nitric acid and the thickness is reduced to 0.210 mm, and then the thickness is reduced to 0.200 mm by electropolishing using an aqueous solution of NaCl as an electrolyte. In addition, the surface roughness Ra was a smooth surface of 0.1 μm or less. At this time, the etching depth of grain boundaries was 0.5 μm or less, and the area ratio of crystal grains including etch pits was 3%.
Then, the surface oxide was removed by ions accelerated at a voltage of 1000 V, and TiN or TiCN having an average film thickness of 0.6 μm was formed under the conditions shown in Table 4. The ratio of the surface roughness Rz to the average film thickness was 0.15, and the structure was a columnar structure extending parallel to ND except No. 4.
Thereafter, a phosphate-based insulation tension film was baked after roll application at 800 ° C. for 60 seconds. The line tension at this time was 10 MPa.

RD grain size of the ceramic coating measured before SRA, hardness of the ceramic coating, iron loss W _17/50 after SRA in Ar atmosphere, and coating adhesion in Ar atmosphere in the thus-obtained grain-oriented electrical steel sheet Table 4 also shows the results of examining the properties (minimum bending diameter) and the number of burrs generated in the sheared part.

  As shown in Table 4, according to the present invention, it can be seen that excellent iron loss, film adhesion, and processability can be established under the condition that the hardness of the ceramic film becomes high.

(Example 3)
As a steel plate, grooves extending in the width direction with a depth of 30 μm are periodically formed at intervals of 3 mm in the rolling direction, and 2 with a forsterite film containing 20 mass ppm of C and 3.4 mass% of Si 2 The following recrystallization plate (plate thickness: 0.22 mm, average grain size: 25 mm, angle β: 2 °) was used. The forsterite film is removed with a mixed solution of hydrochloric acid, hydrogen fluoride and nitric acid and the thickness is reduced to 0.210 mm, and then the thickness is reduced to 0.200 mm by electropolishing using an aqueous solution of NaCl as an electrolyte. In addition, the surface roughness Ra was a smooth surface of 0.1 μm or less. At this time, the etching depth of grain boundaries was 0.5 μm or less, and the area ratio of crystal grains including etch pits was 3%.
Next, the surface oxide was removed by Ti ions accelerated at each voltage shown in Table 5, and TiN was formed to a film thickness of 0.7 μm under each condition. The ratio of the surface roughness Rz to the average film thickness was 0.1, and the structure was a columnar structure extending in parallel to the ND.
Thereafter, by holding for 15 seconds at each temperature shown in Table 5, the oxide insulating tension film applied by the roll was baked.

Table 5 also shows the results of examining the iron loss W _17/50 and the film adhesion (minimum bending diameter) after SRA in Ar atmosphere at 800 ° C. for 3 hours in the directionality steel sheet thus obtained. .

  As shown in Table 5, it can be seen that raising the baking temperature and line tension at the time of baking the insulating oxide film together with raising the cleaning voltage is effective in improving the core loss and the film adhesion.

Claims (9)

A directional electromagnetic steel sheet having an insulating oxide film containing O or P in the outermost layer, and a ceramic coating on the lower layer thereof and on the base iron,
The local iron is
The average crystal grain size is 16 mm or more, and the etching depth in the rolling surface normal direction at grain boundaries with respect to the smoothed surface of the base iron is less than 10 μm.
・ Surface roughness Ra is 0.3 μm or less,
The area ratio of crystal grains including the etch pit portion is 30% or less, and the ceramic coating is
Any of TiN, TiCN or TiC having an average film thickness of 0.3 μm or more and 1.0 μm or less
The position from the surface where the detection strength of oxygen is 1/2 of that of the upper insulating oxide film is on the surface side of the center of the film in the thickness direction,
-A grain-oriented electrical steel sheet characterized in that the hardness of the ceramic film measured from the surface layer is 2100 HV or more. The directional electrical steel sheet according to claim 1, wherein
The ceramic coating is
A directional electrical steel sheet characterized in that the ratio of the surface roughness Rz to the average film thickness is 0.3 or less. It is the directionality electromagnetic steel sheet according to claim 1 or 2,
The ceramic coating is
A grain-oriented electrical steel sheet characterized in that it has a columnar structure elongated in ND with an average crystal grain size of RD in the surface layer of less than 0.1 μm . It is a grain-oriented electrical steel sheet according to any one of claims 1 to 3,
-A grain-oriented electrical steel sheet characterized in that in the average crystal orientation of the ground iron, the angle β between the <100> axis of the secondary recrystallized grains facing the rolling direction of the steel sheet and the rolling surface is less than 3 °. A method of manufacturing a grain-oriented electrical steel sheet according to any one of claims 1 to 4,
The insulating oxide film according to any one of claims 1 to 4 is formed into a film by a coating roll, and in that case, the line tension at the time of baking the insulating oxide film is 7 MPa or more. Method of manufacturing electromagnetic steel sheet. A method of manufacturing a grain-oriented electrical steel sheet according to any one of claims 1 to 4,
In smoothing the surface of the base iron which forms the ceramic film according to any one of claims 1 to 4, after the base iron is polished with hydrochloric acid, nitric acid or an acid containing them, the base is further electropolished or chemically polished. A method of manufacturing a grain-oriented electrical steel sheet characterized by polishing and smoothing iron by 8 μm or more. A method of manufacturing a grain-oriented electrical steel sheet according to any one of claims 1 to 4,
In forming the ceramic film according to any one of claims 1 to 4, after Ti ions accelerated at a voltage of 500 V or more collide with the surface of the base iron for 10 seconds or more to remove the oxide film on the surface, ions are then formed. A method of manufacturing a grain-oriented electrical steel sheet characterized by forming a film with an accelerating voltage of 100 V or more. A method of manufacturing a grain-oriented electrical steel sheet according to any one of claims 1 to 4,
In addition to the seventh aspect, in the case where the strain introduction type magnetic domain fragmentation treatment is not performed, in the subsequent step of the ceramic film deposition step, and when the strain introduction type magnetic domain fragmentation treatment is performed, the ceramic coating film deposition step A method of manufacturing a grain-oriented electrical steel sheet, characterized in that annealing is performed at 750 ° C. or more and 15 s or more in any of the steps between the first and second magnetic domain refining steps. A method of manufacturing a grain-oriented electrical steel sheet according to any one of claims 1 to 4,
The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 4, wherein the deposition rate of the ceramic coating is 1 nm / s or more.