JP6931968B2 - 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 amount of phosphoric acid 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 film formed on the surface of the base material, containing polyvalent metal phosphate, and not using hexavalent chromium as a raw material.
Have,
The total amount of orthophosphoric acid, pyrophosphoric acid and tripolyphosphoric acid contained in the insulating coating is 20 mg / m ² or less in terms of phosphorus.
The total amount of pyrophosphoric acid and tripoliphosphoric acid contained in the insulating coating is 10 mg / m ² or less in terms of phosphorus, and
An electromagnetic steel sheet having a critical sodium chloride concentration of 0.10% by mass or more.
The amounts of orthophosphoric acid, pyrophosphoric acid, and tripolyphosphoric acid are exchanged, for example, when the electromagnetic steel plate having the insulating film is immersed in ion-exchanged water and boiled in the air at 100 ° C. for 20 minutes or more. It can be obtained by quantifying each chemical species in the liquid eluted in water.

(2)
In an electromagnetic steel sheet made of polyvalent metal phosphate and having an insulating film that does not use hexavalent chromium as a raw material,
(I) When the electromagnetic steel plate having the above insulating coating is immersed in ion-exchanged water and boiled in the air at 100 ° C. for 20 minutes or more, the phosphorus eluted in the ion-exchanged water is orthophosphoric acid (Chemical Species A). And, it is phosphorus derived from one or two kinds (chemical species B) of pyrophosphoric acid and tripoliphosphoric acid.
(Ii-1) The elution amount of phosphorus derived from Chemical Species A and B is 20 mg / m ² or less in terms of steel plate area as phosphorus.
(Ii-2) The elution amount of phosphorus derived from chemical species B is 10 mg / m ² or less in terms of steel plate area as phosphorus, and
An electromagnetic steel sheet provided with an insulating film having excellent rust resistance, characterized in that the critical sodium chloride concentration is 0.10% by mass or more.

(3)
The electromagnetic steel sheet according to (1) or (2), wherein the insulating coating contains an organic resin.

According to the present invention, chromium-free phosphate is used in the insulating coating, and the amount of phosphoric acid contained in the insulating coating, which is highly soluble in water, is controlled. Therefore, hexavalent is obtained. Excellent rust resistance can be obtained without using 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. The total amount of orthophosphoric acid, pyrophosphoric acid and tripolyphosphoric acid ^{contained in the insulating coating 3 is 20 mg / m 2} or less in terms of phosphorus, and the total amount of pyrophosphoric acid and tripolyphosphoric acid contained in the insulating coating 3 is , 10 mg / m ² or less in terms of phosphorus. 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.

The details will be described later, but the insulating coating 3 as described above 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 amount of phosphorus contained in the insulating film 3 can be specified, for example, as follows. In this method, the insulating coating 3 is immersed in ion-exchanged water, boiled in air at 100 ° C. for 20 minutes or more, and then eluted in ion-exchanged water, the amount of phosphorus derived from orthophosphoric acid, and pyrophosphorus. The total amount of phosphorus derived from acid or tripolyphosphoric acid is measured. The amount of these phosphorus can be measured by ion chromatography, color analysis using the molybdenum blue method, or inductively coupled plasma analysis. However, in order to distinguish and quantify orthophosphoric acid, pyrophosphoric acid and tripolyphosphoric acid, measurement by ion chromatography is most preferable.

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, not all the phosphates in the aqueous solution undergo a cross-linking reaction to be polymerized, but some phosphates are orthophosphates that are not dehydrated and condensed, and dimeric compounds in which two phosphate molecules are dehydrated and condensed. Pyrrolic acid or trimolecular phosphoric acid is dehydrated and condensed to remain in the insulating coating as a trimeric tripolyphosphoric acid.

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, in an insulating coating containing a large amount of orthophosphoric acid, pyrophosphoric acid and / or tripolyphosphoric acid, the cross-linking reaction of the phosphate is insufficient, and sufficient rust resistance cannot be obtained.

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.

As a test for evaluating the rust resistance of an electromagnetic steel sheet, a wet test specified in JIS K 2246 and a salt spray test specified in JIS Z 2371 are exemplified. 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 sheet having an insulating film and dried, and the temperature is 50 ° C. and the relative humidity RH is 90%. Hold the electrical steel sheet 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. 3A shows an example of the 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. 3B 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 liquid 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 liquid containing no chelating agent. Rust resistance can be obtained.

As described above, when a coating liquid containing no chelating agent is used, the cross-linking reaction is difficult to proceed sufficiently, and orthophosphoric acid, pyrophosphoric acid and / or tripolyphosphoric acid remain in the insulating coating to insulate. A dense and uniform crosslinked state (coating structure) is not formed in the coating.

If a dense crosslinked state (coating structure) is formed in the insulating coating, it is assumed that the amounts of orthophosphoric acid, pyrophosphoric acid and tripoliphosphoric acid in the insulating coating are small.

Therefore, the present inventors investigated the relationship between the amount of orthophosphoric acid, pyrophosphoric acid and tripolyphosphoric acid contained in the insulating coating and the rust resistance. In this investigation, the amounts of orthophosphoric acid, pyrophosphoric acid and tripolyphosphoric acid were measured by the above-mentioned method using ion-exchanged water.

As a result, the elution amount of phosphorus derived from orthophosphoric acid in the insulating film formed by using the coating liquid containing no chelating agent was 20 mg / m ² in terms of phosphorus, and pyrophosphoric acid or tripolyphosphoric acid. The total amount of phosphorus derived from Phosphorus was 12 mg / m ² in terms of phosphorus. That is, the total amount of orthophosphoric acid, pyrophosphoric acid and tripolyphosphoric acid ^{contained in this insulating coating is 32 mg / m 2} in terms of phosphorus, and the total amount of pyrophosphoric acid and tripolyphosphoric acid contained in this insulating coating is Was 12 mg / m ² in terms of phosphorus.

On the other hand, the elution amount of phosphorus derived from orthophosphoric acid in the insulating film formed by using the coating liquid containing a chelating agent is 7 mg / m ² in terms of phosphorus, and is derived from pyrophosphoric acid or tripolyphosphoric acid. The total amount of phosphoric acid eluted was 0 mg / m ² . That is, the total amount of orthophosphoric acid, pyrophosphoric acid and tripolyphosphoric acid ^{contained in this insulating coating is 7 mg / m 2} in terms of phosphorus, and the total amount of pyrophosphoric acid and tripolyphosphoric acid contained in this insulating coating is Was 0 mg / m ² in terms of phosphorus.

As described above, it was confirmed that the amount of phosphoric acid contained in the insulating film having excellent rust resistance was small, and in particular, the amounts of pyrophosphoric acid and tripoliphosphoric acid were very small. Based on these findings, the present inventors have come up with an embodiment of the present invention.

If the total amount of orthophosphoric acid, pyrophosphoric acid and tripolyphosphoric acid contained in the insulating film is ^{more than 20 mg / m 2} in terms of phosphorus, the cross-linking reaction of the phosphate is not sufficient and the insulating film is cross-linked. It means that the state (coating structure) has low density and uniformity, and the rust resistance is inferior. Therefore, this total amount is 20 mg / m ² or less, preferably 15 mg / m ² or less. Since it is preferable that the amount of phosphorus contained in the insulating film is small, the total amount may be 0 mg / m ² .

If the total amount of pyrophosphoric acid and tripolyphosphoric acid contained in the insulating coating exceeds 10 mg / m ² in terms of phosphorus, many dew condensation starting points may be formed on the surface of the insulating coating, and the rust resistance may be lowered. Therefore, this total amount is 10 mg / m ² or less, preferably 5 mg / m ² or less. Since it is preferable that the amount of phosphorus contained in the insulating film is small, the total amount may be 0 mg / m ² .

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. The following is exemplified as a reaction formula of the dehydration condensation reaction. Here, the chelating agent is described as "HO-R-OH" and the metal is described as "M".
P-OH + HO-P → P-OP (Chemical formula 1)
P-OH + HO-P + HO-R-OH → P-O-R-OP (Chemical formula 2)
P-OH + HO-P + HO-R-OH + M
→ P-O-M-O-R-O-P (Chemical formula 3)
P-OH + HO-P + HO-R-OH + 2M
→ P-O-M-O-R-O-M-O-P (Chemical formula 4)

On the other hand, when a coating liquid composed of polyvalent metal phosphate and water and containing no chelating agent is used, the reaction of Chemical Formula 1 occurs, but the reaction of Chemical Formulas 2 to 4 does not occur. Therefore, when a coating liquid containing a chelating agent is used, more cross-linking points are present in the insulating coating than when a coating liquid containing no chelating agent is used, and high rust resistance can be obtained. The larger the number of bonds of the chelating agent, the larger the number of cross-linking points, and higher rust resistance can be obtained.

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 the 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, iron phosphate and iron hydroxide are produced, and sufficient rust resistance cannot be obtained. Such a phenomenon is remarkable 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 coating after baking.

Chelating agents are active compounds, but when they react with metals, they become energetically stable and do not show sufficient activity. The reaction between the chelating agent and the metal is represented by, for example, Chemical Formula 5.
HO-R-OH + 2M → MO-R-OM (Chemical formula 5)

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.

Further, the alkaline earth metal contained in the insulating film, in combination with pyrophosphoric acid and tripoliphosphoric acid in the insulating film, lowers the rust resistance of the insulating film. Pyrophosphoric acid and tripolyphosphoric acid have the property of binding to and solidifying cationic species (Na, K, Ca, Mg) in a corrosive environment, and in particular, have the property of remarkably solidifying when combined with Ca and Mg. As a result, the corrosion resistance of the insulating film is reduced by this solidification. That is, calcium pyrophosphate, magnesium pyrophosphate, calcium tripolyphosphate and magnesium tripolyphosphate, which are hard deposited on the surface of the insulating coating, serve as dew condensation points on the surface of the insulating coating and easily capture salt and water in a corrosive environment. Therefore, the rust resistance of the insulating film tends to decrease.

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 70 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 6.
R-OH ・ ・ ・ O = R (Chemical formula 6)

When the degree of association of hydroxyl groups (degree of hydrogen bonding) of the chelating agent is high, the cross-linking reaction represented by Chemical Formulas 2 to 4 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 apply the coating liquid while reducing the degree of association of the chelating agent. 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.

The coating liquid is baked at a temperature of 250 ° C. or higher, and the temperature of the base material at the time of coating, for example, the heating rate from room temperature of about 30 ° C. to 100 ° C. (first heating rate) is set to 8 ° C./sec or higher. The heating rate from 150 ° C. to 250 ° C. (second heating rate) is made lower than the first heating 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 cross-linking reaction represented by Chemical Formulas 2 to 4 is less likely to occur. Therefore, the first heating rate is set to 8 ° C./sec or more.

The cross-linking reaction of the phosphate and the chelating agent of Chemical Formulas 1 to 4 and the decomposition and volatilization of the chelating agent occur in the temperature range of 150 ° C. to 250 ° C. Therefore, by reducing the second temperature rising rate from 150 ° C. to 250 ° C., the cross-linking reaction 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 are chelated according to 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.

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 a 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 subtropical or tropical areas. 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. In the present invention, various conditions can be adopted 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., and the second heating rate is a heating rate from 150 ° C. to 250 ° C. The base material contained 0.3% by mass of Si, and the thickness of the base material was 0.5 mm. Sample No. In 24, for reference, an insulating coating was formed using chromate instead of phosphate.

Next, the amount of phosphoric acid contained in the insulating coating was measured, and the rust resistance and weldability were evaluated.

To measure the amount of phosphoric acid contained in the insulating film, a test piece is cut out from each electromagnetic steel plate, the test piece is immersed in ion-exchanged water, and boiled in the air at 100 ° C. for 20 minutes or more, and then ion-exchanged water. The amount of phosphorus derived from orthophosphoric acid and the total amount of phosphorus derived from pyrophosphoric acid or tripolyphosphoric acid eluted in the above were measured by ion chromatography. A DX-600 manufactured by DIONEX was used as an ion chromatography analyzer, an IonPac AG11-HC manufactured by DIONEX was used as a separation column, and an electric conductivity detector was used as a detector. A 1 mmol / L to 35 mmol / L potassium hydroxide aqueous solution was used as the eluent, and the eluate flow rate was 0.38 mL / min.

Chromography was measured in advance at various concentrations using sodium orthophosphate, sodium pyrophosphate and sodium tripolyphosphate as standard substances, and the concentration and conductivity at the time of detection were measured at the retention time corresponding to each standard substance. After clarifying the relationship, the phosphoric acid contained in each test piece was quantified. 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 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. 10, No. 12, No. 15-No. At 22, 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. 11, No. 13-No. 14, No. 23, No. 25-No. At 28, 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 (3)

The base material of electrical steel and
An insulating film formed on the surface of the base material, containing polyvalent metal phosphate, and not using hexavalent chromium as a raw material.
Have,
The total amount of orthophosphoric acid, pyrophosphoric acid and tripolyphosphoric acid contained in the insulating coating is 20 mg / m ² or less in terms of phosphorus.
The total amount of pyrophosphoric acid and tripoliphosphoric acid contained in the insulating coating is 10 mg / m ² or less in terms of phosphorus, and
An electromagnetic steel sheet having a critical sodium chloride concentration of 0.10% by mass or more. In an electromagnetic steel sheet made of polyvalent metal phosphate and having an insulating film that does not use hexavalent chromium as a raw material,
(I) When the electromagnetic steel plate having the above insulating coating is immersed in ion-exchanged water and boiled in the air at 100 ° C. for 20 minutes or more, the phosphorus eluted in the ion-exchanged water is orthophosphoric acid (Chemical Species A). And, it is phosphorus derived from one or two kinds (chemical species B) of pyrophosphoric acid and tripoliphosphoric acid.
(Ii-1) The elution amount of phosphorus derived from chemical species A and B is 20 mg / m ² or less in terms of steel plate area as phosphorus.
(Ii-2) The elution amount of phosphorus derived from chemical species B is 10 mg / m ² or less in terms of steel plate area as phosphorus, and
An electromagnetic steel sheet provided with an insulating film having excellent rust resistance, characterized in that the critical sodium chloride concentration is 0.10% by mass or more. The electromagnetic steel sheet according to claim 1 or 2, wherein the insulating coating contains an organic resin.

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