Title of invention: Non-oriented electrical steel sheet and its manufacturing method
Technical field
[0001]
The present invention relates to a non-oriented electrical steel sheet and its manufacturing method.
Background technology
[0002]
Non-oriented electrical steel sheets are used as a core material for rotating machines in the form of so-called laminates, which are composed of multiple layers of steel sheets. When a non-oriented electrical steel sheet is used as an iron core for a rotating machine, if an electric current called eddy current is induced in the normal direction to the surface of the laminated steel sheets, the efficiency of the rotating machine will decrease. . Therefore, in order to prevent the occurrence of eddy currents, an insulating film is generally formed on the surface of the non-oriented electrical steel sheet.
[0003]
In addition to preventing the generation of eddy currents, this insulating film also has the function of protecting the non-oriented electrical steel sheet itself, which is composed mainly of iron elements, from rusting, that is, from corrosion. For this reason, it has been common to form a chromate-based film having a strong corrosion-preventing action on the surface of a non-oriented electrical steel sheet.
[0004]
However, in recent years, with the rise of environmental awareness, many insulating films that do not use chromate compounds have been proposed. Among them, a technique has been proposed in which "Zn" is used as one of the metal components in the coating liquid, which is the material of the insulating film.
[0005]
For example, Patent Document 1 discloses the use of a coating agent containing one or more of Al phosphate, Ca phosphate, and Zn phosphate as inorganic substances. In Patent Document 2, Al 2 O 3 /H 3 PO 4 molar ratio, CaO/H 3 PO 4 molar ratio, and ZnO/H 3 PO 4 are used as inorganic compounds in the film for Al phosphate, Ca phosphate, and Zn phosphate, respectively. It is disclosed to define the molar ratio. Patent Document 3 discloses the use of Al monophosphate and organic acid salts of Al, Mg, Ca and Zn. Patent Documents 4 to 6 disclose the use of a metal phosphate containing a Zn component.
[0006]
The above-mentioned technology relates to the inorganic components among the constituent components of the film. On the other hand, as a technique focusing on the organic components of the film constituents, proposals have been made to use chelate-forming compounds such as phosphonic acids as the film constituents.
[0007]
For example, Patent Document 7 discloses a technique of adding a phosphonic acid-based or carboxylic acid-based chelate-forming compound to a coating liquid. Patent Document 8 discloses a technique of using a phosphonic acid-based or carboxylic acid-based chelate-forming compound as an anti-yellowing agent. Patent Document 9 discloses a technique using titanium hydrofluoric acid or zircon hydrofluoric acid in addition to a phosphonic acid-based or carboxylic acid-based chelate-forming compound.
[0008]
Patent Document 10 discloses a technique of adding a phosphonic acid-based or carboxylic acid-based chelate-forming compound to a coating liquid. Patent Literature 11 discloses a technique using a titanium chelate or the like. Patent Document 12 discloses a technique of using a phosphonic acid-based or carboxylic acid-based chelate compound after applying Ni plating prior to coating. Patent Document 13 discloses a technique of adding a polyamine to a coating liquid in addition to a phosphonic acid-based or carboxylic acid-based chelate-forming compound.
[0009]
Furthermore, recently, the following proposals have been made that further define the film structure on the premise of using a phosphonic acid compound as a component of the coating liquid for forming the film.
[0010]
For example, Patent Document 14 discloses defining the Fe area fraction in the cross section of the film obtained using a transmission electron microscope or the like. Patent Literature 15 discloses defining the relationship between the proportion of P in the coating obtained by X-ray photoelectron spectroscopy and the proportion of Fe bound to O. Patent Literature 16 discloses defining the ratio of Fe/P in the coating. Patent Document 17 discloses defining the integrated intensity fraction of P in nuclear magnetic resonance spectroscopy. Patent Literature 18 discloses stipulating that the film contains a carboxylic acid. Patent Literature 19 discloses that the amount of phosphoric acid in the film is specified for each type. Patent Literature 20 discloses defining the ratio of Fe 3+ to the total Fe in the coating. Patent Literature 21 discloses defining the amount of enrichment of the divalent metal in the coating.
[0011]
By applying the above-mentioned technique using "Zn" to form an insulating film on the non-oriented electrical steel sheet, it is possible to ensure a considerable degree of corrosion resistance in terms of film formation. However, in recent years, there have been an increasing number of cases where non-oriented electrical steel sheets are processed in high-temperature, high-humidity environments and environments where sea salt adheres, as typified by Southeast Asian countries. In such a severe steel sheet processing environment with high temperature, high humidity and salt adhesion, high corrosion resistance is required not only for the surface where the insulation film is formed, but also for the "cut surface of the steel sheet" where the insulation film is not formed. It's here.
[0012]
In the process of manufacturing various rotating machines from electromagnetic steel sheets, first, the electromagnetic steel sheets are formed into a predetermined shape. The most common forming method is a method of punching out an electromagnetic steel sheet using a die. Since the base material steel plate is exposed at the cut surface of the electrical steel plate, the rust preventive effect of the insulating film cannot be obtained.
[0013]
In this punching process, "punching oil" is used to reduce wear on the mold. The punching oil also adheres to the cut surface of the punched steel plate and exerts a certain degree of rust prevention. Recently, however, so-called "quick-drying oil" has come to be used frequently in consideration of the influence in the process after punching. The quick-drying oil evaporates from the cut surface of the steel plate and disappears within a very short time after punching. Such quick-drying oils are less likely to exhibit antirust properties.
[0014]
Also, depending on the type of rotating machine, etc., the cut surface of the magnetic steel sheet may be stored as it is for a considerably long period of time after punching until the magnetic steel sheet is transferred to the next process. Corrosion of the cut surfaces may occur during this storage.
[0015]
In this way, it has been desired not only to ensure corrosion resistance on the surface where the film is formed, but also to improve corrosion resistance on the cut surface of the steel plate.
[0016]
Regarding the improvement of the corrosion resistance of steel plate cut surfaces, Patent Document 22 proposes a method of adding a carboxylic acid compound having 2 to 50 carbon atoms to a coating solution for forming an insulating film.
prior art documents
patent literature
[0017]
Patent document 1: JP-A-07-041913
Patent document 2: JP-A-07-166365
Patent document 3: JP-A-11-131250
Patent Document 4: JP-A-11-080971
Patent Document 5: JP-A-2001-129455
Patent Document 6: JP-A-2002-069657
Patent document 7: JP-A-2002-47576
Patent Document 8: JP-A-2005-314725
Patent Document 9: JP-A-2008-303411
Patent document 10: JP 2009-155707 A
Patent Document 11: Japanese Patent Publication No. 2009-545674
Patent Document 12: Japanese Patent Application Laid-Open No. 2010-7140
Patent Document 13: JP 2010-261063 A
Patent Document 14: International Publication No. 2016/104404
Patent Document 15: International Publication No. 2016/104405
Patent Document 16: International Publication No. 2016/104407
Patent Document 17: International Publication No. 2016/104512
Patent document 18: JP 2016-125141 A
Patent document 19: JP 2016-125142 A
Patent document 20: JP 2016-138333 A
Patent Document 21: International Publication No. 2016/194520
Patent Document 22: International Publication No. 2016/136515
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0018]
By applying the above-described technique using a carboxylic acid compound having 2 to 50 carbon atoms to form an insulating film on a non-oriented electrical steel sheet, it is possible to ensure a certain degree of corrosion resistance even on the cut surface of the steel sheet. However, as a result of repeated studies by the present inventors, it was found that even when a chelate compound such as a carboxylic acid compound is used, it is sometimes difficult to improve the corrosion resistance of the cut surface of the steel sheet.
[0019]
In addition, when using a chelate compound as a component of a coating liquid for film formation, there is also the problem of an increase in cost. The price competition for non-oriented electrical steel sheets is fierce, and the cost that can be spent on coating liquids for forming insulating films is extremely limited. Therefore, raw materials used for film formation are inevitably desired to be low in cost.
[0020]
Against the background of these problems, the present inventors have developed a non-metallic material that can stably exhibit the excellent corrosion resistance of Zn even on the "steel plate cut surface" without using a costly carboxylic acid-based compound or the like. We worked on the development of grain-oriented electrical steel sheets and their manufacturing methods.
[0021]
The present invention solves the above-mentioned problems, and does not use chromate-based compounds, which are substances of environmental concern, and does not use expensive organic compounds such as carboxylic acid-based compounds. An object of the present invention is to provide a non-oriented electrical steel sheet having excellent corrosion resistance on the cut surface of the steel sheet and a method for producing the same.
Means to solve problems
[0022]
The present invention has been made to solve the above problems, and the gist thereof is the following non-oriented electrical steel sheet and its manufacturing method.
[0023]
(1) A non-oriented electrical steel sheet according to one embodiment of the present invention includes a base steel sheet and a composite coating of a Zn-containing phosphate and an organic resin formed on the surface of the base steel sheet. , the Zn content in the composite coating is 10 mg/m 2 or more per side, and the product of the amount of oxygen in the base steel plate and the thickness of the base steel plate is 50 ppm·mm or less.
[0024]
(2) In the non-oriented electrical steel sheet described in (1) above, the composite coating may further contain one or more selected from the group consisting of Al, Mg, and Ca.
[0025]
(3) In the non-oriented electrical steel sheet according to (1) or (2) above, the organic resin is an acrylic resin, a styrene resin, an acrylic-styrene resin, an epoxy resin, a polyester resin, a phenol resin, or a urethane resin. It may contain one or more selected from the group consisting of.
[0026]
(4) A method for manufacturing a non-oriented electrical steel sheet according to another embodiment of the present invention includes the steps of: applying a coating liquid containing a Zn-containing phosphate and an organic resin to the surface of a base steel sheet; Baking the liquid in an atmosphere with an oxygen concentration of 30% or less under conditions where the maximum temperature is within the range of 250 to 450 ° C. and the tensile strength imparted to the base steel plate is 15 to 60 N / mm 2, forming a composite coating having a Zn content of 10 mg/m 2 or more per side.
[0027]
(5) In the method for manufacturing a non-oriented electrical steel sheet described in (4) above, the coating liquid may further contain one or more selected from the group consisting of Al, Mg, and Ca.
[0028]
(6) In the method for producing a non-oriented electrical steel sheet according to (4) or (5) above, the organic resin includes an acrylic resin, a styrene resin, an acrylic-styrene resin, an epoxy resin, a polyester resin, a phenol resin, and It may contain one or more selected from the group consisting of urethane resins.
Effect of the invention
[0029]
According to the present invention, even without using environmentally hazardous substances such as chromate-based compounds and expensive organic compounds typified by carboxylic acid-based compounds as coating materials, the excellent corrosion resistance of Zn can be applied to the cut surface of a steel sheet. It is possible to manufacture a non-oriented electrical steel sheet that can demonstrate
MODE FOR CARRYING OUT THE INVENTION
[0030]
The inventors of the present invention have made intensive studies on methods for improving the corrosion resistance of steel plate cut surfaces, and as a result, have obtained the following knowledge.
[0031]
First, we examined the state of the "steel plate cut surface" when a non-oriented electrical steel sheet with a film on the surface was cut with a shear or punched with a die.
[0032]
When cutting with a shear or punching with a die, the film formed on the surface of the steel sheet may adhere to the cut surface of the steel sheet. This is called the "sagging effect"”. The present inventors paid attention to the relationship between the "sagging effect" and the corrosion resistance of the cut surface of the steel sheet, and conducted further research.
[0033]
When a steel plate cut surface is exposed to a saltwater corrosion environment, moisture and salt come into contact with the cut surface. It is presumed that the moisture in contact with the cut surface dissolves the components contained in the film or the like adhering to the cut surface, and the eluted components form some kind of corrosion product.
[0034]
It is believed that the corrosion resistance of steel sheets is determined by the presence or absence of these corrosion products and their quality. That is, when a corrosion product that inhibits permeation of moisture and salt is formed on the cut surface of the steel sheet, contact/intrusion of moisture and salt into the steel sheet itself is blocked. Therefore, the corrosion of the steel plate itself is suppressed, and as a result, the generation of rust is suppressed in the salt spray test.
[0035]
As a result of investigations from this point of view, when the film contains more than a predetermined amount of Zn, when it comes into contact with water or salt, Zn will elute from the film adhering to the cut surface, and corrosion will occur with excellent corrosion resistance. It was found that a substance can be formed and the generation of red rust and the like can be suppressed on the cut surface.
[0036]
On the other hand, if the above "sagging effect" is not sufficiently obtained, the formation of corrosion products will be insufficient. As described above, the coating may contain a chelate compound for the purpose of improving the adhesion between the coating and the base steel sheet. However, it has been found that if the adhesiveness is too high, the coating is less likely to peel off and the "sagging effect" is less likely to be obtained.
[0037]
Also, even if the "sagging effect" is obtained, if corrosion products with low moisture and salt permeation suppression are generated on the cut surface of the steel sheet, moisture and salt will come in contact with/infiltrate the steel sheet itself one after another. end up Therefore, the corrosion of the steel sheet itself progresses, and as a result, in the salt spray test, the base iron dissolves and the generation of rust becomes conspicuous.
[0038]
As a result of the study by the present inventors, it was found that the corrosion resistance of the cut surface deteriorates when an oxide layer is formed on the surface of the base steel plate. From this, if an oxidized layer exists on the surface of the base steel sheet, the oxidized layer peels off and adheres to the cut surface during cutting with a shear or punching with a die. It is presumed that when placed in a moist environment containing, it forms a corrosion product that is easily permeable to water and salt and has poor corrosion resistance.
[0039]
Furthermore, as a result of investigating a method for suppressing the formation of an oxide layer on the surface of the base steel sheet, it is important to control the conditions when the base steel sheet is coated with the coating solution for forming the film and then baked. I found something. Specifically, it is important to keep the tension applied to the steel sheet in the baking furnace within a predetermined range and reduce the oxygen concentration in the furnace.
[0040]
The present invention has been made based on the above findings. Each requirement of the present invention will be described below.
[0041]
1. Non-oriented electrical steel sheet
A non-oriented electrical steel sheet according to the present embodiment includes a base steel sheet and an insulating coating formed on the surface of the base steel sheet. In general, the insulating coatings of non-oriented electrical steel sheets are roughly classified into all-organic coatings (all coatings are composed of organic substances), inorganic coatings (all coatings are composed of inorganic substances), and composite coatings ( The film is composed of a combination of organic and inorganic substances, and is also called a semi-organic film). The insulating coating of the non-oriented electrical steel sheet according to this embodiment is a composite coating.
[0042]
In addition, phosphate, colloidal silica, alumina sol, zirconia sol, etc. have been proposed as inorganic substances in the composite coating. In the present invention, only phosphate is contained as an inorganic substance, and inorganic substances other than phosphate such as colloidal silica, alumina sol and zirconia sol are not contained. As described above, the present invention is based on the technical concept of improving the corrosion resistance by eluting the Zn component adhering to the cut surface, so the Zn-containing phosphate is essential. That is, in the present invention, the composite film contains a Zn-containing phosphate and an organic resin.
[0043]
2. Composite coating
　In the non-oriented electrical steel sheet according to the present embodiment, the Zn content in the composite coating is 10 mg/m2 or more per side. Here, the Zn content per side means the average value of the Zn content per unit area (mg/m 2 ) of the composite coating on both the front side and the back side of the base steel sheet.
[0044]
When the Zn content in the composite coating is less than 10 mg/m 2 , Zn-containing corrosion products with good corrosion resistance are less likely to form from the coating that drips onto the cut surface of the steel plate. As a result, the corrosion resistance of the cut surface of the steel sheet is deteriorated, and red rust occurs frequently. On the other hand, by setting the Zn content in the composite coating to 10 mg/m 2 or more, a sufficient amount of Zn is eluted from the coating that drips onto the cut surface of the steel sheet. As a result, a corrosion product containing Zn having good corrosion resistance is formed, and the cut surface of the steel plate has excellent corrosion resistance, so red rust is reduced.
[0045]
The Zn content in the composite coating is preferably 20 mg/m2 or more per side, more preferably 30 mg/m2 or more.
[0046]
　In the present invention, the Zn content in the composite coating is measured by the following method. First, a non-oriented electrical steel sheet having a composite coating is immersed in a methanol solution containing 5% by mass of bromine. Next, by irradiating the non-oriented electrical steel sheet immersed in the solution with ultrasonic waves, the base material steel sheet is dissolved, and the composite film component is filtered as a residue.
[0047]
The resulting residue is completely dissolved by the acid dissolution-alkali dissolution method to form an aqueous solution. Next, this aqueous solution is analyzed by ICP (High Frequency Inductively Coupled Plasma) emission spectroscopy to quantify the amount of Zn. Finally, the quantified amount of Zn is divided by the sample area of ​​the non-oriented electrical steel sheet (the total area of ​​the front and back surfaces of the base material steel sheet) to convert it into the amount per unit area. JIS K 0116:2014 "General Rules for Emission Spectroscopic Analysis" can be used for the ICP analysis of the composite film component collected by filtration.
[0048]
In addition, in the non-oriented electrical steel sheet according to the present embodiment, the product of the amount of oxygen in the base material steel sheet and the thickness of the base material steel sheet is 50 ppm·mm or less. Here, the oxygen content of the base material steel sheet is a value obtained by analyzing the oxygen content of the steel sheet after removing the composite film of the non-oriented electrical steel sheet by a predetermined means, and the unit is ppm. The thickness of the base material steel sheet is the thickness of the steel sheet after removing the composite coating from the non-oriented electrical steel sheet, and its unit is mm.
[0049]
As described above, the present inventors found that the corrosion resistance of the cut surface deteriorates when an oxide layer is formed on the surface of the base steel plate. In particular, it was found that there is a good correlation between the salt spray corrosion resistance and the product of the base material steel sheet oxygen content and thickness.
[0050]
The surface of the base material steel plate is not oxidized before the coating solution for forming the composite film is applied and baked. This is because the base steel sheet before being coated with the treatment liquid is annealed in a low oxidizing atmosphere. Therefore, the oxygen measured as the amount of oxygen in the base steel plate is generated by oxidizing the base steel plate when the coating solution is baked.
[0051]
It should be noted here that the amount of oxygen in the base steel sheet is the mass ratio of oxygen in the sample to the total amount of the base steel sheet (that is, the average oxygen content in the sample). Oxygen is contained on the surface of the base material steel sheet of the non-oriented electrical steel sheet due to surface oxidation during baking, but almost no oxygen is contained inside the base material steel sheet. Therefore, when the oxygen content of a thin base steel plate and a thick base steel plate subjected to baking under the same conditions (that is, the degree of oxidation of the surface is almost the same) is measured by the above-described method, the thin base metal The amount of oxygen in the steel sheet is calculated to be larger than the amount of oxygen in the thin base steel sheet.
[0052]
Therefore, the present inventors decided to use the value obtained by multiplying the thickness (mm) of the base steel sheet by the amount of oxygen in the base steel sheet as an index for evaluating the degree of oxidation of the surface of the base steel sheet. did. By multiplying the measured oxygen content by the plate thickness, the influence of the plate thickness of the base steel plate on the measured value of the oxygen content of the base steel plate can be corrected.
[0053]
By setting the product of the amount of oxygen in the base material steel sheet and the thickness of the base material steel sheet to 50 ppm mm or less, the sagging of the oxide layer to the cut surface is suppressed, and the corrosion product containing Zn with good corrosion resistance. It is possible to promote the formation of The product of the amount of oxygen in the base steel sheet and the thickness of the base steel sheet is preferably 40 ppm·mm or less, more preferably 30 ppm·mm or less.
[0054]
In the present invention, the oxygen content of the base steel sheet is measured by the following method. First, the non-oriented electrical steel sheet is boiled in a 50% sodium hydroxide aqueous solution for 30 minutes to remove the composite film from the base steel sheet. Next, the oxygen content of the remaining steel sheet is measured by JIS G 1239:2014 "Iron and steel--oxygen determination method--inert gas melting--infrared absorption method".
[0055]
In the present invention, when calculating the product of the oxygen content of the base steel plate and the thickness of the base steel plate, the measurement accuracy of the oxygen content is taken into consideration, and the result is rounded to a multiple of 5. shall be displayed.
[0056]
In addition to Zn, the composite coating may contain, for example, one or more selected from the group consisting of Al, Mg, and Ca. These elements, like Zn, are desired to be contained as phosphates. In consideration of the environmental load, it is not preferable that the composite coating contains a chromic acid-based compound and substances derived therefrom. The content of chromic acid-based compounds and substances derived therefrom should be reduced as much as possible so as to comply with environmental standards, preferably 0% by mass.
[0057]
Also, the organic resin is not particularly limited, but is exemplified by one or more selected from the group consisting of acrylic resins, styrene resins, acrylic-styrene resins, epoxy resins, polyester resins, phenol resins, and urethane resins.
[0058]
There are no particular restrictions on other ingredients. However, as described above, when a chelate compound such as a phosphonic acid-based compound or a carboxylic acid-based compound is included, the adhesion between the coating and the base steel sheet is improved, the coating is less likely to peel off, and the "sagging effect" occurs. may be difficult to obtain. Therefore, the composite film of the present invention does not contain a chelate compound.
[0059]
3. Base material steel plate
The base material steel sheet of the non-oriented electrical steel sheet according to this embodiment is not particularly limited. This is because the improvement in corrosion resistance, which is a problem of the non-oriented electrical steel sheet according to the present embodiment, is achieved by the above characteristics of the insulating coating. The base material steel sheet can be appropriately selected from ordinary steel sheets used as base material steel sheets for non-oriented electrical steel sheets.
[0060]
4. Production method
A non-oriented electrical steel sheet according to the present embodiment is manufactured by applying a coating liquid to the surface of a base steel sheet, and then baking the coating liquid to form a composite coating on the base steel sheet. can be manufactured by
[0061]
4-1. Coating liquid
The coating liquid applied to the surface of the base steel sheet contains a phosphate aqueous solution and an organic resin aqueous dispersion. Also, the metal component in the phosphate aqueous solution contains a Zn component. The components of the coating solution should be adjusted so that the Zn content per side is 10 mg/m 2 or more after baking. In addition to Zn, for example, one or more selected from the group consisting of Al, Mg, and Ca may be further included, but is not limited thereto.
[0062]
The type of organic resin is not particularly limited. Any type can be used as long as it does not form coarse aggregates when mixed with an aqueous phosphate solution. Preferred organic resins include one or more selected from the group consisting of acrylic resins, styrene resins, acrylic-styrene resins, epoxy resins, polyester resins, phenol resins, urethane resins, and the like.
[0063]
The ratio of the phosphate aqueous solution and the organic resin aqueous dispersion can be arbitrarily selected. A non-oriented electrical steel sheet on which an insulating film is formed using a coating liquid that does not contain an organic resin aqueous dispersion tends to be inferior in punchability. Therefore, the organic resin aqueous dispersion is used as the coating liquid.It is better to include The blending ratio of the phosphate aqueous solution and the organic resin aqueous dispersion may be determined in consideration of the respective solid content concentrations. As long as the blending ratio is controlled so that the Zn content is within a predetermined range, the insulating coating should contain a sufficient amount of Zn to ensure corrosion resistance of the cut surface regardless of the blending ratio. Become.
[0064]
From the viewpoint of reducing the environmental burden, it is not preferable to include chromate-based compounds in the coating liquid.
[0065]
4-2. baking conditions
As described above, it is necessary to suppress the formation of an oxide layer on the surface of the base steel plate when baking the coating liquid. Therefore, in the present invention, it is important to control the baking conditions.
[0066]
　Usually, the coating liquid is baked on a continuous line. At this time, in order to suppress the formation of an oxide layer, it is necessary to adjust the tension applied to the steel sheet within an appropriate range. mm2. The tensile strength is preferably 20 N/mm 2 or more and preferably 50 N/mm 2 or less.
[0067]
Although the mechanism is not clear, if the tensile strength imparted to the steel sheet is too low, the steel sheet may meander and come into contact with equipment in the baking furnace. It is presumed that since the coating is not applied to the surface, there will be areas that are easily oxidized. On the other hand, it is thought that even if the tensile strength is excessive, the grain boundaries expand and the material is easily oxidized.
[0068]
Also, even if the tension applied to the base steel sheet is within the above range, it is difficult to suppress the formation of an oxide layer when the oxygen concentration in the furnace atmosphere is too high. Therefore, the oxygen concentration in the atmosphere in the baking furnace is set to 30% or less. The oxygen concentration is preferably 20% or less.
[0069]
Furthermore, if the maximum temperature reached during baking is too low, baking will be insufficient and stickiness will occur. On the other hand, if the maximum temperature reached is too high, it becomes difficult to suppress the formation of an oxide layer, and the corrosion resistance of the cut surface deteriorates. Therefore, the maximum temperature reached during baking should be within the range of 250 to 450°C.
[0070]
The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.
Example
[0071]
(Example 1) Tension during baking
An annealed non-oriented electrical steel sheet (that is, a base material steel sheet) having a thickness of 0.5 mm was prepared before forming the composite coating. Since the annealing was performed in a low oxidizing atmosphere, the surfaces of these base steel sheets were not oxidized. For this base material steel plate, 100 g of an aqueous phosphate solution with a solid content concentration of 50%, in which the Zn molar ratio is adjusted to 20% with a mixture of Al phosphate and Zn phosphate, and an acrylic/styrene resin with a concentration of 40% A mixture of 20 g of water dispersion was applied. Then, a composite film was formed with an atmospheric oxygen concentration of 20% and a maximum temperature of 340° C. while applying various tensions.
[0072]
The composite coating amount was set to 1.5 g/m2 per side. The composite coating was provided on both sides of the base steel sheet, and the amount and composition of the composite coating were substantially the same on both sides. Then, the Zn content per one side of the composite film was determined by the above-mentioned "dissolution in bromine/methanol liquid-acid/alkali fusion preparation-ICP analysis method". As a result, the Zn content of each composite film was 10 mg/m 2 per side.
[0073]
In addition, the non-oriented electrical steel sheet on which the composite coating was formed was boiled in an aqueous solution of sodium hydroxide having a concentration of 50% for 30 minutes, and the non-oriented electrical steel sheet from which the composite coating was removed was JIS G 1239:2014 "Iron and steel--oxygen determination method--inert gas fusion--infrared absorption method" to measure the oxygen content. Then, by multiplying the measured value by the plate thickness, the product (ppm·mm) of the amount of oxygen in the base steel plate and the plate thickness of the base steel plate was obtained.
[0074]
Then, the non-oriented electrical steel sheet with the composite coating was cut into 20 mm x 50 mm dimensions with a shear. Twenty pieces of cut non-oriented electrical steel sheets were laminated so that the total height of the cut surface was about 10 mm. Corrosion resistance evaluation was performed by a salt spray method on one cut laminated face of 10 mm×50 mm of this laminated body. The salt spray corrosion resistance test was performed according to "JIS Z 2371". The NaCl concentration of the aqueous salt solution for testing was 5 mass %. The temperature near the specimen holder in the spray chamber was 35°C. The quality of corrosion resistance was determined by the red rust area ratio of the cut laminated surface of each non-oriented electrical steel sheet at the time when the spraying time was 8 hours, and classified as follows. The case where the determination was A or B was regarded as a pass.
[0075]
(Criteria for evaluation of corrosion resistance by salt spray method)
・When the red rust area ratio is less than 10%: A
· When the red rust area ratio is 10% or more and less than 20%: B
· When the red rust area ratio is 20% or more and less than 30%: C
· When the red rust area ratio is 30% or more and less than 40%: D
・If the red rust area ratio is 40% or more: E
[0076]
Table 1 shows the above results.
[0077]
[table 1]

[0078]
From Table 1, it can be seen that by setting the tensile strength imparted to the steel sheet during baking within the range of 15 to 60 N/mm 2 , the formation of an oxide layer is suppressed and the salt spray corrosion resistance of the cut surface of the steel sheet is good. I understand.
[0079]
(Example 2) Zn content and oxygen concentration
An annealed non-oriented electrical steel sheet (that is, a base material steel sheet) having a thickness of 0.5 mm was prepared before forming the composite coating. Since the annealing was performed in a low oxidizing atmosphere, the surfaces of these base steel sheets were not oxidized. For these base material steel sheets, 100 g of an aqueous phosphate solution with a solid content concentration of 50%, in which the Zn molar ratio is adjusted in the range of 0 to 100% with Al phosphate, Zn phosphate, or a mixture thereof, A mixture of 15 g of a 40% acryl-styrene organic resin aqueous dispersion was applied. Then, composite coatings were formed at various atmospheric oxygen concentrations and with a maximum temperature of 340°C.
[0080]
The tensile strength imparted to the steel plate during baking was set to 22 N/mm2. The amount of composite coating was adjusted to 1 g/m 2 per side. The composite coating was provided on both sides of the base steel sheet, and the amount and composition of the composite coating were substantially the same on both sides. Various analyzes and evaluations were performed according to the same criteria as in Example 1. Results are shown in Tables 2 and 3.
[0081]
[Table 2]

[0082]
[Table 3]

[0083]
From Tables 2 and 3, the Zn content of the composite coating is 10 mg/m 2 or more per side, and the product of the oxygen amount and the plate thickness of the base steel plate is 50 ppm mm. It can be seen that the salt spray corrosion resistance is good.
[0084]
(Example 3) Zn/Mg phosphate
An annealed non-oriented electrical steel sheet (that is, a base material steel sheet) having a thickness of 0.5 mm was prepared before forming the composite coating. Since the annealing was performed in a low oxidizing atmosphere, the surfaces of these base steel sheets were not oxidized. For this base steel plate, 100 g of an aqueous phosphate solution with a solid content concentration of 50%, in which the Zn molar ratio is adjusted in the range of 0 to 100% with Mg phosphate, Zn phosphate, or a mixture thereof, and a concentration of 40 % acrylic-styrene organic resin aqueous dispersion of 10 g. Then, a composite film was formed with an atmospheric oxygen concentration of 20% and a maximum temperature of 340°C.
[0085]
The tensile strength imparted to the steel plate during baking was set to 22 N/mm2. The amount of composite coating was adjusted to 1 g/m 2 per side. The composite coating was provided on both sides of the base steel sheet, and the amount and composition of the composite coating were substantially the same on both sides. Various analyzes and evaluations were performed according to the same criteria as in Example 1. Table 4 shows the results.
[0086]
[Table 4]

[0087]
From Table 4, when the Zn content of the composite coating is 10 mg/m 2 or more per side and the product of the oxygen content and the plate thickness of the base steel plate is 50 ppm mm, the metal component of the phosphate is It can be seen that even in the Zn/Mg system, the cut surface of the steel sheet has good salt spray corrosion resistance.
[0088]
(Example 4) Zn/Ca phosphate
An annealed non-oriented electrical steel sheet (that is, a base material steel sheet) having a thickness of 0.35 mm was prepared before forming the composite coating. Since the annealing was performed in a low oxidizing atmosphere, the surfaces of these base steel sheets were not oxidized. For these base material steel sheets, 100 g of an aqueous phosphate solution with a solid content concentration of 50%, in which the Zn molar ratio is adjusted in the range of 0 to 100% with Ca phosphate or Zn phosphate, or a mixture thereof, A mixture of 20 g of a 40% acryl-styrene organic resin aqueous dispersion was applied. Then, a composite film was formed with an atmospheric oxygen concentration of 30% and a maximum temperature of 340°C.
[0089]
The tensile strength imparted to the steel plate during baking was set to 22 N/mm2. The amount of composite coating was adjusted to 1 g/m 2 per side. The composite coating was provided on both sides of the base steel sheet, and the amount and composition of the composite coating were substantially the same on both sides. Various analyzes and evaluations were performed according to the same criteria as in Example 1. Table 5 shows the results.
[0090]
[Table 5]

[0091]
From Table 5, if the Zn content of the composite coating is 10 mg/m 2 or more per side and the product of the oxygen amount and the plate thickness of the base steel plate is 50 ppm mm or less, the metal component of the phosphate It can be seen that even if is a Zn/Ca system, the salt spray corrosion resistance at the cut surface of the steel sheet is good.
[0092]
(Example 5) Organic resin
An annealed non-oriented electrical steel sheet (that is, a base material steel sheet) having a thickness of 0.5 mm was prepared before forming the composite coating. Since the annealing was performed in a low oxidizing atmosphere, the surfaces of these base steel sheets were not oxidized. For these base material steel sheets, 100 g of a phosphate aqueous solution with a solid content concentration of 50%, in which the Zn molar ratio is adjusted to 70% with a mixture of Al phosphate and Zn phosphate, and a concentration of 40%. A mixture of 15 g of an organic resin aqueous dispersion was applied. Then, a composite film was formed with an atmospheric oxygen concentration of 5% and a maximum temperature of 340°C.
[0093]
The tensile strength imparted to the steel plate during baking was set to 22 N/mm2. The amount of composite coating was adjusted to 0.8 g/m 2 per side. The composite coating was provided on both sides of the base steel sheet, and the amount and composition of the composite coating were substantially the same on both sides. Various analyzes and evaluations were performed according to the same criteria as in Example 1. Table 6 shows the results. The Zn content per one side of the composite coating was 15 mg/m 2 in each case.
[0094]
[Table 6]

[0095]
From Table 6, if the Zn content of the composite coating is 10 mg/m 2 or more per side and the oxygen content of the base steel sheet in terms of the thickness of 1 mm is 50 ppm mm or less, any organic resin can be used. It can also be seen that the steel plate cut surface has good salt spray corrosion resistance.
[0096]
(Example 6) Baking temperature
An annealed non-oriented electrical steel sheet (that is, a base material steel sheet) having a thickness of 0.5 mm was prepared before forming the composite coating. Since the annealing was performed in a low oxidizing atmosphere, the surfaces of these base steel sheets were not oxidized. For this base material steel plate, 100 g of an aqueous phosphate solution with a solid content concentration of 50%, in which the Zn molar ratio is adjusted to 20% with a mixture of Al phosphate and Zn phosphate, and an acrylic/styrene resin with a concentration of 40% A mixture of 20 g of water dispersion was applied. Composite coatings were formed at various maximum temperatures with an atmospheric oxygen concentration of 1%.
[0097]
The tensile strength imparted to the steel plate during baking was set to 22 N/mm2. The composite coating amount was set to 1.5 g/m 2 per side. The composite coating was provided on both sides of the base steel sheet, and the amount and composition of the composite coating were substantially the same on both sides. Various analyzes and evaluations were performed according to the same criteria as in Example 1. Table 7 shows the results. The Zn content of each composite film was 10 mg/m 2 per side.
[0098]
[Table 7]

[0099]
From Table 7, if the maximum temperature reached is 250°C to 450°C, the salt on the cut surface of the steel plate It can be seen that the water spray corrosion resistance is good.
[0100]
　Composite coatings produced under the conditions of a maximum temperature of 200°C were not sufficiently baked on the base steel plate, resulting in stickiness, and the corrosion resistance of the cut surface could not be evaluated. When the highest temperature reached 510° C., the rust area ratio was 35% and the corrosion resistance was poor due to the formation of an oxide layer.
Industrial applicability
[0101]
According to the present invention, even without using environmentally hazardous substances such as chromate-based compounds and expensive organic compounds typified by carboxylic acid-based compounds as coating materials, the excellent corrosion resistance of Zn can be applied to the cut surfaces of steel sheets. It is possible to manufacture a non-oriented electrical steel sheet that can demonstrate Therefore, the non-oriented electrical steel sheet according to the present invention can suppress the generation of red rust on the cut surface of the steel sheet even when exposed to a severe environment such as flying marine salt.
The scope of the claims
[Claim 1]
　Base material steel plate and
A composite film of Zn-containing phosphate and an organic resin formed on the surface of the base steel plate,
A non-oriented electrical steel sheet comprising
　The Zn content in the composite coating is 10 mg/m2 or more per side,
The product of the amount of oxygen in the base steel plate and the thickness of the base steel plate is 50 ppm mm or less,
　Non-oriented electrical steel sheet.
[Claim 2]
The composite coating further contains one or more selected from the group consisting of Al, Mg, and Ca,
The non-oriented electrical steel sheet according to claim 1.
[Claim 3]
The organic resin contains one or more selected from the group consisting of acrylic resin, styrene resin, acrylic-styrene resin, epoxy resin, polyester resin, phenol resin, and urethane resin,
The non-oriented electrical steel sheet according to claim 1 or claim 2.
[Claim 4]
A step of applying a coating liquid containing a Zn-containing phosphate and an organic resin to the surface of the base steel plate;
The coating solution is applied in an atmosphere with an oxygen concentration of 30% or less, the maximum temperature is within the range of 250 to 450 ° C., and the tensile strength imparted to the base steel plate is 15 to 60 N / mm 2. Baking, forming a composite coating having a Zn content of 10 mg/m2 or more per side,
　Method for manufacturing non-oriented electrical steel sheets.
[Claim 5]
The coating liquid further contains one or more selected from the group consisting of Al, Mg, and Ca,
A method for manufacturing the non-oriented electrical steel sheet according to claim 4.
[Claim 6]
The organic resin contains one or more selected from the group consisting of acrylic resin, styrene resin, acrylic-styrene resin, epoxy resin, polyester resin, phenol resin, and urethane resin,
A method for manufacturing the non-oriented electrical steel sheet according to claim 4 or claim 5.