JP6901826B2 - Electrical steel sheet - Google Patents

Description

The present invention relates to electrical steel sheets.

Electrical steel sheets are used or transported in a corrosive environment. For example, electrical steel sheets are used in hot and humid areas or transported by sea. A large amount of salt comes flying during marine transportation. Therefore, the electromagnetic steel sheet is required to have rust resistance. An insulating film is formed on the surface of the electrical steel sheet in order to obtain rust resistance. Examples of the insulating film include a chromate-based insulating film. Chromate-based insulating coatings show excellent rust resistance, but hexavalent chromium used as a raw material for chromate-based insulating coatings has carcinogenicity. Therefore, there is a demand for the development of an insulating film that can be formed without using hexavalent chromium as a raw material.

Examples of the insulating film that can be formed without using hexavalent chromium as a raw material include a phosphate-based insulating film, a silica-based insulating film, and a zirconium-based insulating film (Patent Documents 1 to 12). However, these insulating coatings do not have the same level of rust resistance as the chromate-based insulating coatings. The thicker the insulating film, the better the rust resistance, but the thicker the insulating film, the lower the weldability and caulking property.

Special Publication No. 53-028375 Japanese Unexamined Patent Publication No. 05-078855 Japanese Unexamined Patent Publication No. 06-330338 Japanese Unexamined Patent Publication No. 11-131250 Japanese Unexamined Patent Publication No. 11-152579 Japanese Unexamined Patent Publication No. 2001-107261 Japanese Unexamined Patent Publication No. 2002-047576 International Publication No. 2012/05/71168 JP-A-2002-47576 Japanese Unexamined Patent Publication No. 2008-303411 Japanese Unexamined Patent Publication No. 2002-249881 JP-A-2002-317277

An object of the present invention is to provide an electromagnetic steel sheet capable of obtaining excellent rust resistance without using hexavalent chromium as a raw material for an insulating coating.

The present inventors have made diligent studies to solve the above problems. As a result, it was clarified that excellent rust resistance can be obtained when the presence form of Fe contained in the insulating film is appropriate. It was also clarified that it is important to use a coating liquid containing a chelating agent for forming such an insulating film.

As a result of further diligent studies based on such findings, the present inventors have come up with various aspects of the invention shown below.

(1)
The base material of electrical steel and
An insulating coating formed on the surface of the base material and containing a polyvalent metal phosphate,
Have,
When the masses of ^{Fe 2+} and Fe ³⁺ contained in the insulating film ^{are [Fe 2+} ] and [Fe ³⁺ ], respectively, "Q = [Fe ³⁺ ] / ([Fe ²⁺ ] + [Fe 2+]" ³⁺ ]) ”, the value of the parameter Q is 0.50 or less, and the mass of ^{Fe 3+} is 100 mg or less per ^{1 m 2 of the base material.}

(2)
The electromagnetic steel sheet according to (1), wherein the insulating coating contains an organic resin.

According to the present invention, since the amount and existence form of Fe having a specific valence contained in the insulating coating are appropriate, excellent rust resistance can be obtained without using hexavalent chromium as a raw material for the insulating coating. .. Therefore, it is possible to avoid deterioration of weldability and caulking property due to the thickening of the insulating film.

It is sectional drawing which shows the structure of the electromagnetic steel sheet which concerns on embodiment of this invention. It is a figure which shows the example of the test result of the rust resistance. It is a figure which shows the example of the test result of the rust resistance.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing the structure of an electromagnetic steel sheet according to an embodiment of the present invention.

As shown in FIG. 1, the electromagnetic steel sheet 1 according to the embodiment of the present invention includes an electromagnetic steel base material 2 and an insulating coating 3 formed on the surface of the base material 2 and containing a polyvalent metal phosphate. Is done. The base material 2 has a composition suitable for a grain-oriented electrical steel sheet or a non-oriented electrical steel sheet. When the masses of ^{Fe 2+} and Fe ³⁺ contained in the insulating film 3 ^{are [Fe 2+} ] and [Fe ³⁺ ], respectively, "Q = [Fe ³⁺ ] / ([Fe ²⁺ ] + [Fe 2+]" The value of the parameter Q represented by " ³⁺ ])" is 0.50 or less, and the mass of ^{Fe 3+} is 100 mg or less per ^{1 m 2 of the base material.} Polyvalent metal phosphates include, for example, Al, Zn, Mg or Ca or any combination thereof. Hereinafter, Al, Zn, Mg or Ca or any combination thereof may be represented by M.

Although the details will be described later, the above-mentioned insulating coating 3 is denser than the insulating coating contained in the conventional electrical steel sheet, and has excellent rust resistance. Therefore, according to the electrical steel sheet 1, excellent rust resistance can be obtained without using hexavalent chromium as a raw material for the insulating coating 3 and without lowering the weldability and caulking property.

The mass of Fe contained in the insulating coating 3 can be specified, for example, as follows. In this method, the insulating coating 3 is separated from the base material 2 by the iodine-methanol method and pulverized, and the powder is alkali-melted and acid-decomposed, and the obtained sample solution is subjected to inductively coupled plasma (ICP) analysis. I do. The value of the parameter Q can be specified, for example, as follows. In this method, the insulating coating 3 is separated from the base material 2 by the iodine-methanol method and powdered, and the powder is analyzed by Mesbower spectroscopy. ^{For example, a 57} Co / Rh matrix is used as a radiation source, and the powder of the insulating coating 3 is developed on the surface of a filter paper to prepare a sample. Then, the sample developing surface is irradiated with γ-rays taken out from the radiation source, the intensity of the γ-rays emitted from the back surface of the sample developing surface is measured, the Doppler shift with respect to pure iron is obtained, and Fe ³⁺ and Fe ²⁺ are obtained. To identify. The value of the parameter Q can be specified based on the absorption curve at each Doppler shift identified. Mesbauer spectroscopy utilizes the Mesbauer effect, which is a phenomenon in which an atomic nucleus emits gamma rays and the other same atomic nucleus resonates and absorbs the gamma rays, and it is well known that Fe has a large effect. By Mesbower spectroscopy, the absorbed energy changes according to the atomic state of Fe, that is, the valence, spin state, coordination number, etc., so it is possible to obtain information on the state of Fe in the sample. .. X-ray photoelectron spectroscopy or the like can also be used for the mass of Fe ^{2+ and} the mass of Fe ³⁺ , but this method is a method of analyzing the state of only the polar surface, and grasps the overall state of the insulating coating 3.・ It is not enough as a method of analysis.

Here, the background to the idea of the embodiment of the present invention will be described.

In the conventional method for manufacturing electrical steel sheets, an aqueous solution of polyvalent metal phosphate is applied to the base metal of electrical steel and baked. Examples of the phosphate of the polyvalent metal include aluminum monophosphate, zinc monophosphate, magnesium monophosphate and calcium monophosphate. Hereinafter, aluminum phosphate, zinc phosphate, magnesium phosphate, and calcium phosphate refer to aluminum primary phosphate, zinc primary phosphate, magnesium monophosphate, and calcium monophosphate, respectively.

When the aqueous solution is baked, the phosphate is crosslinked by a dehydration condensation reaction to form an insulating film. At this time, Fe is eluted from the base material, and this Fe is also incorporated into the insulating film. Various factors affect the cross-linking reaction of phosphate, but in order to improve corrosion resistance, especially rust resistance, the cross-linking reaction of phosphate is promoted and water, salt, etc. that cause corrosion permeate. It is important to form a difficult, dense and uniform crosslinked state (coating structure). However, with the conventional manufacturing method, it is not possible to form a dense and uniform crosslinked state (coating structure).

As a result of conducting various tests focusing on such problems, the present inventor forms an insulating film under predetermined conditions using a coating liquid consisting of a polyvalent metal phosphate, a chelating agent and water. As a result, it was found that excellent rust resistance can be obtained.

Here, a method for evaluating rust resistance will be described.

Examples of tests for evaluating the rust resistance of electrical steel sheets include a wetness test specified in JIS K 2246 and a salt spray test specified in JIS Z 2371. However, the corrosive environment in these tests is significantly different from the corrosive environment in which rust occurs on the electromagnetic steel sheet, and it cannot always be said that the rust resistance of the electromagnetic steel sheet can be appropriately evaluated.

Therefore, the present inventors have investigated a method capable of appropriately evaluating the rust resistance in a corrosive environment in which an electromagnetic steel sheet is rusted. As a result, it was found that the rust resistance can be appropriately evaluated by the following method. In this method, 0.5 μl of droplets of sodium chloride aqueous solution having different concentrations are attached to the surface of an electromagnetic steel plate having an insulating film and dried, and the temperature is 50 ° C. and the relative humidity RH is 90%. Hold the electromagnetic steel plate in the atmosphere for 48 hours. A constant temperature and humidity bath may be used. After that, the presence or absence of rust is confirmed, and the concentration of sodium chloride that does not generate rust in the electromagnetic steel sheet is specified. Then, the rust resistance is evaluated based on the concentration of sodium chloride that does not generate rust.

That is, in this method, the electrical steel sheet is exposed to a moist atmosphere after the droplets of the sodium chloride aqueous solution are attached and dried. Such a process is similar to the corrosive environment in which the electrical steel sheet is exposed, in which salt adheres to the surface of the electrical steel sheet during storage, transportation and use, and then the humidity rises and the salt deliquesces. .. The higher the concentration of sodium chloride, the larger the amount of sodium chloride remaining after drying, and the more likely it is that rust will occur. Therefore, if observation is performed while gradually reducing the concentration of the sodium chloride aqueous solution and the concentration at which rust does not occur (hereinafter, may be referred to as "limit sodium chloride concentration") is specified, it is based on this limit sodium chloride concentration. , The rust resistance in the corrosive environment where the electromagnetic steel plate is actually exposed can be quantitatively evaluated.

FIGS. 2 (a) to 2 (e) show examples of test results by the above method. In this test, the sodium chloride concentration was 1.0% by mass (Fig. 2 (a)), 0.3% by mass (Fig. 2 (b)), 0.1% by mass (Fig. 2 (c)), 0. It was set to 03% by mass (FIG. 2 (d)) or 0.01% by mass (FIG. 2 (e)). Then, as shown in FIGS. 2 (a) to 2 (e), rust was confirmed when the concentration of sodium chloride was 1% by mass, 0.3% by mass, 0.1% by mass or 0.03% by mass. No rust was confirmed when the concentration of sodium chloride was 0.01% by mass. Therefore, the critical sodium chloride concentration of this electromagnetic steel sheet is 0.01% by mass. The present inventors have confirmed that such a rusting situation hardly changes even if the holding time in a constant temperature and humidity atmosphere exceeds 48 hours.

FIG. 3 (a) shows an example of test results by the above method for an electromagnetic steel sheet in which an insulating film is formed using a coating liquid containing no chelating agent, and FIG. 3 (b) shows a coating liquid containing a chelating agent. An example of the test result by the above method is shown for an electromagnetic steel sheet on which an insulating film is formed by using. Both coating liquids contain aluminum phosphate as a polyvalent metal phosphate. Rust was confirmed on the electrical steel sheet in which the insulating film was formed using the coating liquid containing no chelating agent, as shown in FIG. 3A, when an aqueous sodium chloride solution having a concentration of 0.03% by mass was used. .. On the other hand, as shown in FIG. 3 (b), rust was confirmed on the electromagnetic steel sheet in which the insulating film was formed by using the coating liquid containing the chelating agent, even when the sodium chloride aqueous solution having a concentration of 0.2% by mass was used. There wasn't.

As described above, when the insulating film was formed using the coating solution containing the chelating agent, the critical sodium chloride concentration was higher and superior to the case where the insulating film was formed using the coating solution containing no chelating agent. Rust resistance can be obtained.

As described above, when the coating liquid containing no chelating agent is used, the cross-linking reaction is difficult to proceed sufficiently, and a dense and uniform cross-linked state (coating structure) is not formed in the insulating film. On the other hand, when a coating liquid containing a chelating agent is used, excellent rust resistance can be obtained. Considering that Fe is eluted from the base material and incorporated into the insulating film when the insulating film is formed, the state of Fe in the insulating film is the denseness of the crosslinked state (coating structure) formed by the cross-linking reaction of phosphate. And it is considered that it affects the uniformity.

Therefore, the present inventors focused on Fe that was eluted from the base material and contained in the insulating film, and considered that the presence or absence of the chelating agent affected the state of Fe in the insulating film. The relationship with rust resistance was investigated. In this investigation, the mass of Fe and the value of parameter Q per ^{1 m 2 of the} base material contained in the insulating coating were measured by the above separation by the iodine-methanol method and the analysis by ICP analysis or Mesbauer spectroscopy. From the mass of Fe and the value of the parameter Q, the mass of Fe ^{2+ and} the mass of Fe ^{3+ per 1 m 2 of the} base material contained in the insulating coating can also be calculated.

As a result of this measurement, when the insulating coating formed by using the coating liquid containing no chelating agent and the insulating coating formed by using the coating liquid containing a chelating agent are compared, the amount of Fe and the valence of Fe between them are compared. It became clear that the conditions were different. Hereinafter, an insulating film formed by using a coating liquid containing no chelating agent may be referred to as a “chelating agent-free coating”, and an insulating coating formed by using a coating liquid containing a chelating agent is referred to as a “chelating agent-added coating”. Sometimes.

For example, the valence of Fe eluted from the base metal and contained in the insulating coating was 2 or 3, but the chelating agent-free coating had a higher proportion of trivalent Fe than the chelating agent-added coating. That is, when the amounts of the coating liquids applied to the base material are the same, and the masses of ^{Fe 2+} and Fe ^{3+ contained in the insulating film are [Fe 2+} ] and [Fe ³⁺ ], respectively, "Q = [ The value of the parameter Q represented by "Fe ³⁺ ] / ([Fe ²⁺ ] + [Fe ³⁺ ])" was larger in the chelating agent-free coating than in the chelating agent-added coating. Further, the amount of Fe contained in the chelating agent-free coating film was larger than the amount of Fe contained in the chelating agent-added coating film. The reason why the rust resistance is low when the value of the parameter Q is large is not clear, but the expansion due to the oxidation of Fe hinders the denseness of the insulating film and allows the permeation of corrosion factors such as water, salt and chloride ions. It is considered that the rust resistance is lowered due to the simple structure.

In an example of the measurements made by the present inventors, the following results were obtained. In the chelating agent-free coating, the amount of Fe: 211 mg / m ² , ^{the amount of Fe 2+} : 99 mg / m ² (47% by mass), ^{the amount of Fe 3+} : 112 mg / m ² (53% by mass), and the parameters. Q: 0.53, and in the chelating agent-added coating, the amount of Fe: 123 mg / m ² , ^{the amount of Fe 2+} : 84 mg / m ² (68% by mass), ^{the amount of Fe 3+} = 39 mg / m ² ( 32% by mass), and the parameter Q: 0.32.

As described above, it was confirmed that the amount of Fe contained in the insulating film having excellent rust resistance was small and the value of the parameter Q was small. Based on these findings, the present inventors have come up with an embodiment of the present invention.

If the value of the parameter Q exceeds 0.50, sufficient rust resistance cannot be obtained. Therefore, the value of the parameter Q is 0.50 or less, preferably 0.40 or less. Details will be described later, but the higher the proportion of ^{Fe 2+ , in other words, the lower the proportion of Fe 3+} , the better rust resistance can be obtained. Therefore, even if the value of the parameter Q is 0, Good. The mass of Fe ³⁺ is 100 mg or less per ^{1 m 2 of the base material.} As will be described later, Fe ³⁺ lowers the denseness of the insulating film and lowers the rust resistance. Therefore, the smaller the amount, the better, and the value may be 0.

Next, a method of manufacturing the electromagnetic steel sheet 1 will be described. In this method, a coating liquid consisting of a polyvalent metal phosphate containing M, a chelating agent, and water is applied to a base material of electrical steel and baked. As the water, water having a total concentration of Ca ions and Mg ions of 100 ppm or less is used. Examples of the polyvalent metal phosphate include aluminum monophosphate, zinc monophosphate, magnesium monophosphate and calcium monophosphate. Hereinafter, aluminum phosphate, zinc phosphate, magnesium phosphate, and calcium phosphate refer to aluminum primary phosphate, zinc primary phosphate, magnesium monophosphate, and calcium monophosphate, respectively.

When the coating liquid is baked, the ends of the phosphate are crosslinked by a dehydration condensation reaction to form an insulating film. When a coating liquid mainly composed of a phosphate aqueous solution is applied to a base material and baked to form an insulating film, Fe eluted from the base material into the coating liquid is ionized according to Chemical Formula 1. After that, according to Chemical Formula 2, ^{it is considered that it is oxidized to Fe 3+} and mainly becomes ferric phosphate or ferric hydroxide, which is fixed in the insulating coating.
Fe → Fe ²⁺ + 2e ^- (Formula 1)
Fe ²⁺ + O → Fe ³⁺ (Chemical formula 2)

When Fe eluted in the coating liquid is ^{oxidized to Fe 3+} (chemical formula 2), a large amount of ferric phosphate or ferric hydroxide (Fe ³⁺ ) becomes present in the insulating film, and the parameter The value of Q becomes large. ^{The presence of a large amount of ferric phosphate or ferric hydroxide (Fe 3+} ) causes a decrease in the rust resistance of the insulating coating, because expansion due to oxidation of Fe hinders the denseness of the insulating coating.

On the other hand, in the chelating agent-added coating, the rust resistance is improved and the parameter Q value is small ( ^{the oxidation of Fe up to Fe 3+} is suppressed) as compared with the chelating agent-free coating. Taking this into consideration, due to the reaction between the chelating agent (HO-R-OH) and Fe ²⁺ (reaction between the R-OH group and Fe ²⁺ ) shown in Chemical Formula 3, many Fe ²⁺ are ^{converted to Fe 2+} . It is considered that the insulation film is maintained as it is and the rust resistance of the insulating film is improved.
HO-R-OH + Fe ²⁺ → HO-R-O-Fe ²⁺ -O-R-OH (Chemical formula 3)

Since the reaction of Chemical Formula 3 is a reaction ^{between Fe 2+} in which Fe eluted from the base metal is ionized and the R-OH group of the chelating agent, other metal ions and the R-OH group are formed before this reaction occurs. Upon reaction, the chelating agent loses its activity and the reaction of Chemical Formula 3 is less likely to occur. As a result, Fe eluted from the base metal is ^{oxidized to Fe 3+,} and the rust resistance of the insulating film is lowered.

Therefore, in order to maintain high activity of the chelating agent, metals other than the metal contained in the phosphate are prevented from reacting with the chelating agent before the baking of the coating liquid is completed. Therefore, it is preferable that the concentration of metal ions having high reactivity with the chelating agent in water is low. Examples of such metal ions include Ca ions and Mg ions.

When the total concentration of Ca ions and Mg ions exceeds 100 ppm, the activity of the chelating agent is lowered and the rust resistance is lowered. Therefore, the total concentration of Ca ions and Mg ions in water is 100 ppm or less, preferably 50 ppm or less. The smaller the amount of alkaline earth metal ions other than Ca ions and Mg ions, the more preferable.

The chelating agent has a hydroxyl group at the terminal, and the hydroxyl group tends to take an associated state (hydrogen bond) represented by the chemical formula 4.
R-OH ・ ・ ・ O = R (Chemical formula 4)

When the degree of hydroxyl group association (degree of hydrogen bond) of the ^{chelating agent becomes high, the chelating agent that takes in Fe 2+} loses its activity, and the reaction between the chelating agent represented by the chemical formula 3 and Fe ^{2+ is unlikely to occur.} Therefore, it is preferable to apply the coating liquid so that the degree of association is as small as possible. For example, when coating using a roller (roll coating), it is preferable to apply a shearing force to the coating liquid to reduce the degree of association of the chelating agent while applying the coating liquid. By reducing the diameter of the roller and increasing the moving speed of the base metal, it is possible to apply an appropriate shearing force to break the association state. For example, it is preferable to use a roller having a diameter of 700 mm or less to set the moving speed of the base material to 60 m / min or more, and to use a roller having a diameter of 500 mm or less to set the moving speed of the base material to 70 m / min or more. More preferred.

As the chelating agent, for example, an oxycarboxylic acid-based, dicarboxylic acid-based or phosphonic acid-based chelating agent is used. Examples of the oxycarboxylic acid-based chelating agent include malic acid, glycolic acid and lactic acid. Examples of the dicarboxylic acid chelating agent include oxalic acid, malonic acid and succinic acid. Examples of the phosphonic acid-based chelating agent include aminotrimethylene phosphonic acid, hydroxyethylidene monophosphonic acid and hydroxyethylidene diphosphonic acid.

The amount of the chelating agent contained in the coating liquid is 1% by mass to 30% by mass with respect to the mass of the insulating film after baking. Since the coating liquid containing phosphate is acidic, Fe elutes from the base material into the coating liquid while the coating liquid is not completely dried and the coating liquid is kept acidic. When Fe is excessively eluted and exceeds the reaction limit of the chelating agent, the reaction of Chemical Formula 2 is promoted to mainly produce ferric phosphate and ferric hydroxide, and sufficient rust resistance is obtained. I can't get it. Such a phenomenon is ^{remarkable when the reaction between the chelating agent and Fe 2+} is insufficient, especially when the amount of the chelating agent is less than 1% by mass. Therefore, the amount of the chelating agent is 1% by mass or more with respect to the mass of the insulating film after baking. On the other hand, when the amount of the chelating agent exceeds 30% by mass, the phosphate in the coating liquid is less than 70% by mass, and sufficient heat resistance cannot be obtained for the insulating film. Therefore, the amount of the chelating agent is 30% by mass or less with respect to the mass of the insulating film after baking.

The coating liquid is baked at a temperature of 250 ° C. to 350 ° C., and the temperature of the base material at the time of coating, for example, the temperature rise rate from room temperature of about 30 ° C. to 100 ° C. (first temperature rise rate) is 8 ° C./sec or more. The temperature rise rate from 150 ° C. to 250 ° C. (second temperature rise rate) is set to be lower than the first temperature rise rate. The temperature at the time of coating is substantially equal to the temperature of the coating liquid.

The progress of the above-mentioned association of chelating agents does not occur when the fluidity of the coating liquid is lost. Therefore, in order to reduce the degree of association as much as possible, it is preferable to increase the first heating rate up to the boiling point (100 ° C.) of water. If the first temperature rise rate is less than 8 ° C./sec, the degree of association of the chelating agent rapidly increases during the temperature rise, so that the reaction between the ^{chelating agent represented by the chemical formula 3 and Fe 2+ is unlikely to occur.} Therefore, the first heating rate is set to 8 ° C./sec or more.

The reaction between the chelating agent of Chemical Formula 3 and Fe ²⁺ occurs in the temperature range of 150 ° C to 250 ° C. Therefore, by reducing the second heating rate from 150 ° C. to 250 ° C., the reaction between the ^{chelating agent and Fe 2+ can be promoted while suppressing the decomposition of the chelating agent.} However, a decrease in the rate of temperature rise may lead to a decrease in productivity. On the other hand, the cross-linking reaction of the chelating agent changes depending on the degree of association of the chelating agent described above. Therefore, if the first heating rate is increased and the degree of association of the chelating agent is decreased, the cross-linking reaction between the phosphate and the chelating agent can be promoted even if the second heating rate is increased. .. On the other hand, when the first temperature rising rate is low and the degree of association of the chelating agent is large, the cross-linking reaction between the chelating agent and the phosphate is sufficiently advanced unless the second temperature rising rate is lowered accordingly. Can't. According to the study by the present inventors, if the first temperature rise rate is 8 ° C./sec or more and the second temperature rise rate is lower than the first temperature rise rate, the phosphate and the chelate depend on the degree of association of the chelating agent. It has been found that the cross-linking reaction with the agent proceeds and excellent rust resistance can be obtained. However, when the second temperature rise rate is excessively high, for example, when the temperature exceeds 18 ° C./sec, even if the first temperature rise rate is 8 ° C./sec or more, the cross-linking is not sufficiently completed and the excellent rust resistance. Cannot be obtained. Therefore, the second temperature rising rate is set to 18 ° C./sec or less. On the other hand, the lower the second heating rate, the lower the productivity, which becomes remarkable at less than 5 ° C./sec. Therefore, the second heating rate is preferably 5 ° C./sec or higher.

If the baking temperature is less than 250 ° C. ^{, the reaction between the chelating agent and Fe 2+} becomes insufficient or the productivity decreases. When the baking temperature exceeds 350 ° C., ^{the oxidation of Fe 2+} (chemical formula 2) is promoted, and excellent rust resistance cannot be obtained. Therefore, the baking temperature is 250 ° C. to 350 ° C., preferably 250 ° C. to 320 ° C. If the time from reaching 100 ° C. to the end of baking is more than 60 seconds, ^{the oxidation of Fe 2+} (chemical formula 2) is promoted, and excellent rust resistance cannot be obtained. Therefore, the time from reaching 100 ° C. to the end of baking is 60 seconds or less, preferably 50 seconds or less.

The electromagnetic steel sheet 1 can be manufactured through the coating and baking of the coating liquid on the base material of the electromagnetic steel.

The coating liquid may contain an organic resin. The organic resin contained in the coating liquid has an effect of suppressing wear of the punching die. Therefore, by using a coating liquid containing an organic resin, the punching workability of the electromagnetic steel sheet is improved. The organic resin is preferably used as a water-dispersible organic emulsion. When an water-dispersible organic emulsion is used, it is preferable that the amount of alkaline earth metal ions such as Ca ions and Mg ions contained therein is small. Examples of the organic resin include acrylic resin, acrylic styrene resin, alkyd resin, polyester resin, silicone resin, fluororesin, polyolefin resin, styrene resin, vinyl acetate resin, epoxy resin, phenol resin, urethane resin and melamine resin.

According to the electromagnetic steel sheet 1 according to the present embodiment, excellent rust resistance can be obtained without using hexavalent chromium as a raw material for the insulating coating 3. For example, the electrical steel sheet 1 exhibits sufficient rust resistance even in a high-flying salt environment such as during marine transportation and in a high-temperature and high-humidity environment corresponding to subtropics or tropics. Since it is not necessary to form the insulating film 3 thickly, it is possible to avoid deterioration of weldability and caulking property.

It should be noted that all of the above embodiments merely show examples of embodiment in carrying out the present invention, and the technical scope of the present invention should not be construed in a limited manner by these. That is, the present invention can be implemented in various forms without departing from the technical idea or its main features.

Next, examples of the present invention will be described. The conditions in the examples are one condition example adopted for confirming the feasibility and effect of the present invention, and the present invention is not limited to this one condition example. The present invention can adopt various conditions as long as the gist of the present invention is not deviated and the object of the present invention is achieved.

The present inventors prepared a coating liquid consisting of a phosphate, a chelating agent, an organic resin and water shown in Table 1, and applied this to both sides of a base material of an electromagnetic steel and baked it. Table 1 also shows the total concentration of Ca ions and Mg ions contained in water (total ion concentration). Table 1 also shows the coating conditions and the baking conditions. The first heating rate is a heating rate from 30 ° C. to 100 ° C., the second heating rate is a heating rate from 150 ° C. to 250 ° C., and the holding time reaches 100 ° C. before baking. It is the time to finish. When the reached temperature is lower than 250 ° C., the temperature rise rate is from 150 ° C. to the temperature. The base material contained 0.3% by mass of Si, and the thickness of the base material was 0.5 mm. Sample No. In 29, for reference, an insulating coating was formed using chromate instead of phosphate.

Next, the amount of Fe contained in the insulating coating was measured, the value of the parameter Q was calculated, and the rust resistance and weldability were evaluated.

In measuring the amount of Fe contained in the insulating film, the insulating film is separated from each electrical steel sheet by the iodine-methanol method and powdered, and lithium borate is charged into a melted crucible to dissolve it, and the entire molten salt is acidified. Disassembled. Then, ICP analysis of the obtained sample liquid was performed. The results are shown in Table 2. The underline in Table 2 indicates that the numerical value is out of the scope of the present invention.

In the calculation of the value of the parameter Q, the analysis of the insulating coating prepared as described above was performed by Mesbauer spectroscopy. ^{Here, a 57} Co / Rh matrix was used as the radiation source, and the powder of the insulating coating was developed on the surface of the filter paper to prepare a sample. Then, the sample development surface is irradiated with γ-rays taken out from the radiation source, the intensity of the γ-rays emitted from the back surface of the sample development surface is measured, the Doppler shift with respect to pure iron is obtained, and Fe ³⁺ and Fe ²⁺ The existence was identified. Based on the absorption curve at each Doppler shift identified, ^{the abundance ratio of Fe 3+} and Fe ²⁺ was determined, and the value of parameter Q was determined. The results are also shown in Table 2. The underline in Table 2 indicates that the numerical value is out of the scope of the present invention. ^{“Fe 3+} (mg / m ² )” in Table 2 is obtained by multiplying the amount of Fe by the value of the parameter Q.

In the evaluation of rust resistance, a test piece is prepared from each electromagnetic steel plate, and 0.5 μl of droplets of sodium chloride aqueous solution having different concentrations are attached to the surface of the test piece and dried, and the temperature is 50 ° C. and the relative humidity is relative humidity. The test piece was held for 48 hours in a constant temperature and humidity atmosphere with a RH of 90%. The concentrations of the aqueous sodium chloride solution are 0.001% by mass, 0.01% by mass, 0.02% by mass, 0.03% by mass, 0.10% by mass, 0.20% by mass, 0.30% by mass and 1 It was set to 0.0% by mass. Then, the presence or absence of rust was confirmed, and the critical sodium chloride (NaCl) concentration of each test piece was specified. The results are also shown in Table 2.

In the evaluation of weldability, the welding current is 120 A, La-W (2.4 mmφ) is used as the electrode, the gap is 1.5 mm, the Ar gas flow rate is 6 l / min, and the tightening pressure is 50 kg / cm ^2. , Welding was performed at various welding speeds. Then, the maximum welding speed at which blow holes do not occur was specified. The results are also shown in Table 2.

As shown in Table 2, the sample No. within the scope of the present invention. 6 to No. 11, No. 13, No. 16-No. 20, No. 24-No. At 26, both a critical sodium chloride concentration of 0.10% by mass or higher and a welding rate of 100 cm / min were obtained. That is, excellent rust resistance and weldability were obtained.

Sample No. 1-No. 5, No. 12, No. 14-No. 15, No. 21-No. 23, No. 27-No. 28, No. 30-No. At 33, the critical sodium chloride concentration was 0.03% by mass or less, and the welding speed was 50 cm / min. That is, rust resistance and / or weldability were low.

1: Electrical steel sheet 2: Base material 3: Insulation film

Claims (2)

The base material of electrical steel and
An insulating coating formed on the surface of the base material and containing a polyvalent metal phosphate,
Have,
When the masses of ^{Fe 2+} and Fe ³⁺ contained in the insulating film ^{are [Fe 2+} ] and [Fe ³⁺ ], respectively, "Q = [Fe ³⁺ ] / ([Fe ²⁺ ] + [Fe 2+]" ³⁺ ]) ”, the value of the parameter Q is 0.50 or less, and the mass of ^{Fe 3+} is 100 mg or less per ^{1 m 2 of the base material.} The electromagnetic steel sheet according to claim 1, wherein the insulating coating contains an organic resin.

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