JP2016138333A - Electromagnetic steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic steel sheet capable of obtaining excellent rust resistance without using hexavalent chromium as a raw material for an insulation coat.SOLUTION: An electromagnetic steel sheet 1 has a base metal 2 for a silicon steel, and an insulation coat 3 formed on the surface of the base metal 2, and containing a polyvalent metal phosphate. When expressing each mass of Fe, Fecontained in the insulation coat 3 as [Fe], [Fe], the value of a parameter Q [Q=[Fe]/([Fe]+[Fe])] is 0.50 or less, and the mass of Feper 1 mof the base metal 2 is 100 mg or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electromagnetic steel sheet.

  Electrical steel sheets are used or transported in corrosive environments. For example, electrical steel sheets are used in hot and humid areas or transported by sea. When transporting by sea, a large amount of salt comes in. For this reason, the electromagnetic steel sheet is required to have rust resistance. In order to obtain rust resistance, an insulating coating is formed on the surface of the electromagnetic steel sheet. Examples of the insulating coating include chromate-based insulating coatings. Although chromate-based insulating coatings exhibit excellent rust resistance, hexavalent chromium used as a raw material for chromate-based insulating coatings has carcinogenic properties. For this reason, development of the insulation film which can be formed without using hexavalent chromium as a raw material is requested | required.

  Examples of insulating coatings that can be formed without using hexavalent chromium as a raw material include phosphate insulating coatings, silica insulating coatings, and zirconium insulating coatings (Patent Documents 1 to 12). However, these insulating coatings do not provide the same level of rust resistance as chromate-based insulating coatings. If the insulating film is thickened, the rust resistance is improved. However, the thicker the insulating film is, the lower the weldability and caulking properties are.

Japanese Examined Patent Publication No. 53-028375 JP 05-078855 A Japanese Patent Laid-Open No. 06-330338 JP-A-11-131250 JP-A-11-152579 JP 2001-107261 A JP 2002-047776 A International Publication No. 2012/057168 JP 2002-47576 A JP 2008-303411 A JP 2002-249881 A JP 2002-317277 A

  An object of the present invention is to provide an electrical steel sheet that can obtain excellent rust resistance without using hexavalent chromium as a raw material for an insulating coating.

  The present inventors have intensively studied to solve the above problems. As a result, it was revealed that excellent rust resistance can be obtained when the presence form of Fe contained in the insulating coating is appropriate. It has also become clear that it is important to use a coating solution containing a chelating agent for the formation of such an insulating coating.

  As a result of further intensive studies based on such knowledge, the present inventors have conceived various aspects of the invention described below.

(1)
With the base material of electromagnetic steel,
An insulating film 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 ³⁺ ]) ”, the value of 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 electrical 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. . For this reason, it is also possible to avoid a decrease in weldability and caulking properties accompanying the increase in the thickness of the insulating coating.

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

As shown in FIG. 1, the electrical steel sheet 1 according to the embodiment of the present invention includes a base material 2 of the electrical steel and an insulating coating 3 formed on the surface of the base material 2 and containing a polyvalent metal phosphate. It is. 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 coating 3 are [Fe ²⁺ ] and [Fe ³⁺ ], respectively, “Q = [Fe ³⁺ ] / ([Fe ²⁺ ] + [Fe 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. Multivalent metal phosphates include, for example, Al, Zn, Mg or Ca, or any combination thereof. Hereinafter, Al, Zn, Mg, Ca, or any combination thereof may be represented by M.

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

The mass of Fe contained in the insulating coating 3 can be specified as follows, for example. In this method, the insulating coating 3 is separated from the base material 2 by the iodine-methanol method and pulverized. The powder is subjected to alkali melting and acid decomposition, and the obtained sample solution is subjected to inductively coupled plasma (ICP) analysis. I do. The value of the parameter Q can be specified as follows, for example. 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 analyzed by Mossbauer spectroscopy. For example, a ⁵⁷ Co / Rh matrix is used as a radiation source, and the powder of the insulating coating 3 is spread on the surface of a filter paper to obtain a sample. Then, the sample development surface is irradiated with γ-rays extracted from the radiation source, the intensity of 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⁺ are Identify. The value of the parameter Q can be specified based on the absorption curve at each identified Doppler shift. Mossbauer spectroscopy uses the Mossbauer effect, which is a phenomenon in which a nucleus emits gamma rays and the other same nucleus resonates and absorbs the gamma rays, and it is well known that Fe has a large effect. Mossbauer spectroscopy makes it possible to obtain information on the state of Fe in the sample because the absorption energy changes according to the atomic state of Fe, that is, the valence, spin state, coordination number, etc. . Although the mass of Fe ^{2+ and} the mass of Fe ³⁺ can be used by X-ray photoelectron spectroscopy, etc., this method is a method of analyzing the state of the pole surface only, and grasps the entire state of the insulating coating 3・ It is insufficient as a method of analysis.

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

  In a conventional method for manufacturing an electrical steel sheet, an aqueous solution of polyvalent metal phosphate is applied to a base material of the electrical steel and baked. Examples of the polyvalent metal phosphate include monoaluminum phosphate, monobasic zinc phosphate, monobasic magnesium phosphate and monobasic calcium phosphate. Hereinafter, aluminum phosphate, zinc phosphate, magnesium phosphate, and calcium phosphate represent primary aluminum phosphate, primary zinc phosphate, primary magnesium phosphate, and primary calcium phosphate, 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 taken into the insulating coating. Various factors affect the phosphate cross-linking reaction. To improve corrosion resistance, especially rust resistance, the phosphate cross-linking reaction is promoted and water, salt, etc. that cause corrosion penetrate. It is important to form a difficult, dense and uniform cross-linked state (film structure). However, the conventional manufacturing method cannot form a dense and uniform cross-linked state (film structure).

  As a result of various tests conducted by the inventors paying attention to such problems, an insulating film is formed under predetermined conditions using a coating solution composed of a polyvalent metal phosphate, a chelating agent and water. Thus, it was found that excellent rust resistance can be obtained.

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

  Examples of the test for evaluating the rust resistance of the electrical steel sheet include a wet test specified in JIS K 2246 and a salt spray test specified in JIS Z 2371. However, the corrosive environment in these tests is greatly different from the corrosive environment in which rust is generated in the electromagnetic steel sheet, and it cannot be said that the rust resistance of the electromagnetic steel sheet can be properly evaluated.

  Therefore, the present inventors examined a method that can appropriately evaluate rust resistance in a corrosive environment in which rust is generated on an electromagnetic steel sheet. As a result, it was found that the rust resistance can be appropriately evaluated by the following method. In this method, 0.5 μl droplets of sodium chloride aqueous solution having different concentrations are attached to the surface of an electrical steel sheet having an insulating coating and dried, and the temperature is 50 ° C. and the relative humidity RH is 90%. The magnetic steel sheet is kept in the atmosphere for 48 hours. A constant temperature and humidity chamber may be used. Then, the presence or absence of rust is confirmed, and the density | concentration of the sodium chloride which does not generate | occur | produce rust in the said magnetic steel sheet is specified. And rust resistance is evaluated based on the density | concentration of sodium chloride which rust does not generate | occur | produce.

  That is, in this method, the magnetic steel sheet is exposed to a humid atmosphere after the droplets of sodium chloride aqueous solution are attached and dried. Such a process is similar to the corrosive environment to 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. . As the concentration of sodium chloride increases, the amount of sodium chloride remaining after drying increases and rust is likely to occur. Therefore, if observation is performed while gradually reducing the concentration of the sodium chloride aqueous solution and a concentration at which rust does not occur (hereinafter sometimes referred to as “limit sodium chloride concentration”) is specified, based on this limit sodium chloride concentration The rust resistance in a corrosive environment where the electromagnetic steel sheet is actually exposed can be quantitatively evaluated.

  2A to 2E show examples of test results obtained by the above method. In this test, the sodium chloride concentration was adjusted to 1.0 mass% (FIG. 2 (a)), 0.3 mass% (FIG. 2 (b)), 0.1 mass% (FIG. 2 (c)), 0. It was set to 03% by mass (FIG. 2 (d)) or 0.01% by mass (FIG. 2 (e)). And as shown to FIG.2 (a)-(e), rust is confirmed when the density | concentration of sodium chloride is 1 mass%, 0.3 mass%, 0.1 mass%, or 0.03 mass%, Rust was not confirmed when the concentration of sodium chloride was 0.01% by mass. For this reason, the limit sodium chloride concentration of this electrical steel sheet is 0.01% by mass. The present inventors have confirmed that such a rusting state hardly changes even when the holding time in a constant temperature and humidity atmosphere exceeds 48 hours.

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

  As described above, when the insulating film is formed using the coating liquid containing the chelating agent, the limit sodium chloride concentration is higher and superior than when the insulating film is formed using the coating liquid not containing the chelating agent. Rust resistance is obtained.

  As described above, when a coating solution containing no chelating agent is used, the crosslinking reaction does not proceed sufficiently and a dense and uniform crosslinked state (film structure) is not formed in the insulating film. On the other hand, when a coating solution containing a chelating agent is used, excellent rust resistance is obtained. In consideration of the fact that Fe elutes from the base material and is taken into the insulating film during the formation of the insulating film, the state of Fe in the insulating film is dense in the cross-linked state (film structure) formed by the cross-linking reaction of phosphate. And is considered to affect the uniformity.

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

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

For example, although the valence of Fe eluted from the base material and contained in the insulating coating is 2 or 3, the proportion of trivalent Fe was higher in the chelating agent-free coating than in the chelating agent-added coating. That is, when the amount of the coating solution applied to the base material is equal, when 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. In addition, the amount of Fe contained in the chelating agent-free coating was greater than the amount of Fe contained in the chelating agent-added coating. The reason why the rust resistance is low when the value of parameter Q is large is not clear, but due to the expansion due to the oxidation of Fe, the denseness of the insulating film is hindered, and the penetration of corrosion factors such as water, salt, chloride ions, etc. It is considered that the rust resistance decreases due to the easy structure.

In an example of the measurement performed by the present inventors, the following results were obtained. In the coating film without addition of a chelating agent, 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 was 0.32.

  Thus, it was confirmed that the amount of Fe contained in the insulating coating excellent in rust resistance was small and the value of the parameter Q was small. Based on these findings, the inventors have arrived at an embodiment of the present invention.

If the value of 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. As will be described in detail later, the higher the proportion of Fe ²⁺ , in other words, the lower the proportion of Fe ³⁺ , the better the rust resistance, so even if the value of 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.

  Next, a method for manufacturing the electromagnetic steel sheet 1 will be described. In this method, a coating liquid composed 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 monobasic aluminum phosphate, monobasic zinc phosphate, monobasic magnesium phosphate and monobasic calcium phosphate. Hereinafter, aluminum phosphate, zinc phosphate, magnesium phosphate, and calcium phosphate represent primary aluminum phosphate, primary zinc phosphate, primary magnesium phosphate, and primary calcium phosphate, respectively.

When the coating solution is baked, the phosphate ends are cross-linked by a dehydration condensation reaction to form an insulating film. When an insulating film is formed by applying and baking a coating solution mainly containing a phosphate aqueous solution on a base material, Fe eluted from the base material into the coating solution is ionized according to Chemical Formula 1. Then, it is considered that it is oxidized to Fe ³⁺ according to the chemical formula 2 and mainly becomes ferric phosphate or ferric hydroxide and 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 solution is oxidized to Fe ³⁺ (Chemical formula 2), a large amount of ferric phosphate or ferric hydroxide (Fe ³⁺ ) is present in the insulating coating, and the parameters The value of Q increases. Since the expansion due to the oxidation of Fe inhibits the denseness of the insulating film, the presence of a large amount of ferric phosphate or ferric hydroxide (Fe ³⁺ ) causes a decrease in the rust resistance of the insulating film.

On the other hand, in the chelating agent-added film, the rust resistance is improved and the value of the parameter Q is small compared to the chelating agent-free film (the oxidation of Fe up to Fe ³⁺ is suppressed). with reference to the fact, illustrated in formula 3, by the reaction of the chelating agent (HO-R-OH) Fe ²⁺ (reaction R-OH group and Fe ^2+), a number of Fe ^2+, the Fe ²⁺ It is considered that the rust resistance of the insulating coating is improved.
HO—R—OH + Fe ²⁺ → HO—R—O—Fe ²⁺ —O—R—OH (Chemical Formula 3)

The reaction of Chemical Formula 3 is a reaction between Fe ²⁺ ionized from Fe eluted from the base material and the R—OH group of the chelating agent. Therefore, before this reaction occurs, other metal ions and R—OH groups are reacted with each other. Upon reaction, the chelating agent loses activity and the reaction of Formula 3 is less likely to occur. As a result, Fe eluted from the base material is oxidized to Fe ³⁺ and the rust resistance of the insulating coating is lowered.

  Therefore, in order to keep the activity of the chelating agent high, metals other than the metal contained in the phosphate are prevented from reacting with the chelating agent before the baking of the coating solution is completed. For this reason, it is preferable that the density | concentration of the metal ion with 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 decreases or the rust resistance decreases. Therefore, the total concentration of Ca ions and Mg ions in water is 100 ppm or less, preferably 50 ppm or less. The fewer alkaline earth metal ions other than Ca ions and Mg ions, the better.

The chelating agent has a hydroxyl group at the terminal, and the hydroxyl group easily takes an association state (hydrogen bond) represented by Chemical Formula 4.
R-OH ... O = R (Chemical Formula 4)

When the degree of association of the hydroxyl group of the chelating agent (the degree of hydrogen bonding) increases, the chelating agent that takes in Fe ²⁺ loses activity, and the reaction between the chelating agent represented by Formula 3 and Fe ²⁺ hardly occurs. For this reason, it is preferable to apply the coating solution so that the degree of association is as small as possible. For example, when performing application (roll coating) using a roller, it is preferable to apply the application liquid while reducing the degree of association of the chelating agent by applying a shearing force to the application liquid. By reducing the diameter of the roller and increasing the moving speed of the base material, it is possible to apply a shearing force appropriate for solving the association state. For example, it is preferable that the moving speed of the base material is 60 m / min or more using a roller having a diameter of 700 mm or less, and the moving speed of the base material is 70 m / min or more using a roller having a diameter of 500 mm or less. 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 oxycarboxylic acid chelating agents include malic acid, glycolic acid and lactic acid. Examples of dicarboxylic acid-based chelating agents include oxalic acid, malonic acid, and succinic acid. Examples of the phosphonic acid chelating agent include aminotrimethylene phosphonic acid, hydroxyethylidene monophosphonic acid and hydroxyethylidene diphosphonic acid.

The amount of the chelating agent contained in the coating solution is 1% by mass to 30% by mass with respect to the mass of the insulating coating after baking. Since the coating solution containing phosphate is acidic, the drying of the coating solution is not completed, and while the coating solution is kept acidic, Fe elutes from the base material into the coating solution. And when Fe elutes excessively and exceeds the reaction limit of the chelating agent, the reaction of Chemical Formula 2 is promoted, mainly ferric phosphate and ferric hydroxide are generated, and sufficient rust resistance is achieved. I can't get it. Such a phenomenon is remarkable when the reaction between the chelating agent and Fe ²⁺ is insufficient, particularly 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 coating after baking. On the other hand, if the amount of the chelating agent exceeds 30% by mass, the phosphate in the coating solution is less than 70% by mass, and sufficient heat resistance cannot be obtained for the insulating coating. Therefore, the amount of the chelating agent is 30% by mass or less based on the mass of the insulating coating after baking.

  The coating solution 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, a temperature increase rate from about 30 ° C. to 100 ° C. (first temperature increase rate) is 8 ° C./second or more And the temperature increase rate (second temperature increase rate) from 150 ° C. to 250 ° C. is set lower than the first temperature increase rate. The temperature at the time of application is substantially equal to the temperature of the application liquid.

The aforementioned progress of the association of the chelating agent will not occur if the fluidity of the coating solution is lost. Therefore, in order to make the degree of association as low as possible, it is preferable to increase the first temperature increase rate up to the boiling point of water (100 ° C.). When the first rate of temperature rise is less than 8 ° C./second, the degree of association of the chelating agent increases rapidly during the temperature rise, and the reaction between the chelating agent represented by Chemical Formula 3 and Fe ²⁺ hardly occurs. Therefore, the first heating rate is 8 ° C./second or more.

The reaction of the chelating agent of Formula 3 with Fe ²⁺ occurs in the temperature range of 150 ° C to 250 ° C. For this reason, by making the 2nd temperature increase rate from 150 degreeC to 250 degreeC small, reaction of a chelating agent and Fe ^<2+> can be accelerated ^| stimulated, suppressing decomposition | disassembly of a chelating agent. However, a decrease in the heating rate may cause a decrease in productivity. On the other hand, the crosslinking reaction of the chelating agent varies depending on the degree of association of the aforementioned chelating agent. Therefore, if the first temperature increase rate is increased and the association degree of the chelating agent is decreased, the crosslinking reaction between the phosphate and the chelating agent can be promoted even if the second temperature increase rate is increased. . On the other hand, when the first heating rate is small and the degree of association of the chelating agent is large, the crosslinking reaction between the chelating agent and the phosphate is sufficiently advanced unless the second heating rate is lowered accordingly. I can't. According to the study of the present inventors, if the first temperature rising rate is 8 ° C./second or more and the second temperature rising rate is lower than the first temperature rising rate, the phosphate and the chelate are selected according to the degree of association of the chelating agent. It has been found that the crosslinking reaction with the agent proceeds and excellent rust resistance can be obtained. However, when the second temperature rising rate is excessively large, for example, when it exceeds 18 ° C./second, the crosslinking is not sufficiently completed even when the first temperature rising rate is 8 ° C./second or more, and excellent rust resistance. Cannot be obtained. Therefore, the second heating rate is set to 18 ° C./second or less. On the other hand, the lower the second heating rate, the lower the productivity, and becomes remarkable at less than 5 ° C./second. Therefore, the second heating rate is preferably 5 ° C./second or more.

When 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. When the time from reaching 100 ° C. to the end of baking exceeds 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, and preferably 50 seconds or less.

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

  The coating solution may contain an organic resin. The organic resin contained in the coating solution has an action of suppressing the wear of the punching die. For this reason, the punching workability of the electrical steel sheet is improved by using a coating liquid containing an organic resin. The organic resin is preferably used as a water-dispersible organic emulsion. When a water-dispersible organic emulsion is used, the smaller the amount of alkaline earth metal ions such as Ca ions and Mg ions contained therein, the better. Examples of the organic resin include acrylic resin, acrylic styrene resin, alkyd resin, polyester resin, silicone resin, fluorine resin, 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 electromagnetic steel sheet 1 exhibits sufficient rust resistance even in a high-flying salinity environment such as during ocean transportation or in a high-temperature and high-humidity environment corresponding to a subtropical or tropical environment. Since it is not necessary to form the insulating coating 3 thickly, it is possible to avoid a decrease in weldability and caulking properties.

  The above-described embodiments are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed in a limited manner. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

  Next, examples of the present invention will be described. The conditions in the examples are one condition example adopted to confirm the feasibility and effects 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 object of the present invention is achieved without departing from the gist of the present invention.

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

  Next, measurement of the amount of Fe contained in the insulating coating, calculation of the value of parameter Q, and evaluation of rust resistance and weldability were performed.

  In the measurement of the amount of Fe contained in the insulating coating, the insulating coating is separated from each magnetic steel sheet by the iodine-methanol method and pulverized, charged in a crucible in which lithium borate is melted and dissolved, and the entire molten salt is treated with acid. Disassembled. Then, ICP analysis of the obtained sample solution 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 calculating the value of the parameter Q, the insulating film produced as described above was analyzed by Mossbauer spectroscopy. Here, a ⁵⁷ Co / Rh matrix was used as the radiation source, and the insulating coating powder was spread on the surface of the filter paper to prepare a sample. Then, the sample development surface is irradiated with γ-rays extracted 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⁺ Identified. Based on the absorption curve at each identified Doppler shift, 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. Note that “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 magnetic steel sheet, 0.5 μl of sodium chloride aqueous solution having a different concentration is attached to the surface of the test piece and dried, and the temperature is 50 ° C. and relative humidity. The test piece was held in a constant temperature and humidity atmosphere with 90% RH for 48 hours. The concentration of the sodium chloride aqueous solution is 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%. 0.0 mass%. Then, the presence or absence of rust was confirmed and the limit sodium chloride (NaCl) density | concentration of each test piece was specified. The results are also shown in Table 2.

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

  As shown in Table 2, sample Nos. Within the scope of the present invention. 6-No. 11, no. 13, no. 16-No. 20, no. 24-No. In No. 26, both a limiting sodium chloride concentration of 0.10% by mass and a welding speed 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. In No. 33, the limit sodium chloride concentration was 0.03% by mass or less, and the welding speed was 50 cm / min. That is, rust resistance or weldability or both were low.

1: Electromagnetic steel sheet 2: Base material 3: Insulation coating

Claims (2)

With the base material of electromagnetic steel,
An insulating film 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 ³⁺ ]) ”, the value of 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 electrical steel sheet according to claim 1, wherein the insulating coating contains an organic resin.