Non-oriented electrical steel sheet and its manufacturing method

Abstract

A non-oriented electromagnetic steel sheet 1 of the present embodiment is provided with: a base material steel sheet 10; and an insulating film 20 formed on a surface of the base material steel sheet 10. The insulating film 20 contains: a phosphoric acid metal salt; an organic resin; and a nitrite. The nitrogen content of the insulating film 20 is 0.05 to 5.00 mass%.

Description

[Technical Field]

[0001] The present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same. [Background technology]

[0002] Non-oriented electrical steel sheets are used in drive motors for small home appliances such as audio equipment, and in iron cores (motor cores (rotor cores, stator cores)) for drive motors for hybrid cars and electric vehicles.

[0003] An insulating coating is formed on the surface of a non-oriented electrical steel sheet. The insulating coating ensures insulation between the electrical steel sheets stacked together to form, for example, a stator core. In other words, the insulating coating is required to have excellent insulating properties. The insulating coating is also required to have good adhesion to the steel sheet. Therefore, the insulating coating is required to have both insulating properties and adhesion.

[0004] Insulation coatings for non-oriented electrical steel sheets that have excellent insulation properties and adhesion are proposed, for example, in International Publication No. 2016 / 136515 (Patent Document 1), Japanese Patent Application Laid-Open No. 2017-141480 (Patent Document 2), and Japanese Patent Application Laid-Open No. 2013-249486 (Patent Document 3).

[0005] The electrical steel sheet disclosed in Patent Document 1 has an insulating coating on the surface of the steel sheet, the insulating coating comprising a binder composed of 100 parts by mass of a metal phosphate and 1 to 50 parts by mass of an organic resin having an average particle size of 0.05 to 0.50 μm, and a carboxylic acid compound having 2 to 50 carbon atoms, the content of which is 0.1 to 10.0 parts by mass per 100 parts by mass of the solid content of the binder, the organic resin being one or more selected from acrylic resin, epoxy resin, and polyester resin. Patent Document 1 states that this insulating coating, even if it does not contain a chromium compound, has excellent insulation properties as well as adhesion, corrosion resistance, appearance, and edge rust prevention properties after punching.

[0006] The electrical steel sheet disclosed in Patent Document 2 has an insulating coating on its surface composed of 100 parts by mass of metal phosphate as a main component, 1 to 50 parts by mass of an acrylic resin with an average particle size of 0.05 to 0.50 μm and utilizing a reactive emulsifier, and 0.5 to 10 parts by mass of a polyhydric alcohol, wherein the metal elements of the metal phosphate are a mixture of at least divalent and trivalent metal elements, with the mixture ratio of the divalent metal elements being 30 to 80 mass% relative to the total mass of the metal elements of the metal phosphate. Patent Document 2 also describes that this insulating coating has good uniformity, no problems with insulation, and excellent adhesion to resins during electrodeposition coating and molding, even when applied thinly.

[0007] Patent Document 3 discloses a treatment solution for forming an insulating film on electrical steel sheet, characterized by containing, in an aqueous medium, a primary phosphate of a polyvalent metal containing Al and / or Mg as the main component, a nitric acid compound selected from nitric acid and polyvalent metal nitrates, and a chelating agent selected from phosphonic acid compounds and pyrophosphoric acid. Patent Document 3 states that the insulating coating obtained from this treatment solution has improved resistance to whitening immediately after production, whitening during storage, and adhesion after bluing treatment. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2016 / 136515 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-141480 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-249486 Summary of the Invention [Problem to be solved by the invention]

[0009] The manufacturing method for a stator core using non-oriented electrical steel sheets is as follows: The non-oriented electrical steel sheets are punched into a predetermined shape. The punched steel sheets (core blanks) are then stacked and fixed to produce a laminated core. Coils are placed in the slots of the stator core. During the punching process, processing strain is imparted to the punched non-oriented electrical steel sheets, which deteriorates their magnetic properties. For this reason, stress relief annealing is sometimes performed to remove the processing strain. Stress relief annealing is performed at high temperatures of 700°C or higher. The insulating coating heated during stress relief annealing may generate decomposition products due to the heat.

[0010] As mentioned above, the insulating coating of non-oriented electrical steel sheets is required to have excellent adhesion even after stress relief annealing. If the adhesion after stress relief annealing is poor, pieces of the coating that peel off from the steel sheet will get between the stator core and the rotor core, hindering the rotation of the stator core and the rotor core. In some cases, this could cause damage to the rotor core.

[0011] An object of the present invention is to provide a non-oriented electrical steel sheet provided with an insulating coating that exhibits excellent adhesion after stress relief annealing, and a method for manufacturing a non-oriented electrical steel sheet provided with an insulating coating that exhibits excellent adhesion after stress relief annealing. [Means for solving the problem]

[0012] The non-oriented electrical steel sheet of the present invention is A base steel plate; an insulating coating formed on the surface of the base steel sheet, The insulating coating is a metal phosphate; An organic resin, Contains nitrite, The insulating coating has a nitrogen content of 0.05 to 5.00 mass %.

[0013] The method for producing a non-oriented electrical steel sheet of the present invention comprises: a step of applying a surface treatment agent containing a metal phosphate, an organic resin, and a nitrite to a surface of a base steel sheet; and a step of heating the base steel sheet to which the surface treatment agent has been applied under the conditions of a heat treatment temperature of 200 to 450°C, a dew point of -30 to 30°C, and a heat treatment time of 10 to 120 seconds to form an insulating coating having a nitrogen content of 0.05 to 5.00 mass%. [Effects of the Invention]

[0014] The non-oriented electrical steel sheet of the present invention has an insulating coating that exhibits excellent adhesion after stress relief annealing. The method for producing a non-oriented electrical steel sheet of the present invention can produce a non-oriented electrical steel sheet that has an insulating coating that exhibits excellent adhesion after stress relief annealing. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a cross-sectional view parallel to the sheet thickness direction of a non-oriented electrical steel sheet according to this embodiment. [Figure 2] FIG. 2 is an enlarged cross-sectional view of the insulating coating 20 in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present inventors have investigated and examined the adhesion of insulating coatings on non-oriented electrical steel sheets after stress relief annealing.

[0017] The present inventors first investigated means for improving the adhesion of insulating coatings on non-oriented electrical steel sheets. The above-mentioned Patent Documents 1 and 2 describe that insulating coatings containing metal phosphate and organic resin have excellent adhesion. Therefore, the present inventors investigated means for further improving the adhesion of insulating coatings containing metal phosphate and organic resin.

[0018] The insulating coating of non-oriented electrical steel sheet is manufactured as follows: A surface treatment agent containing a metal phosphate and an organic resin is applied to the base steel sheet. The base steel sheet with the surface treatment agent applied is then heated to form the insulating coating. The process of heating the base steel sheet with the surface treatment agent applied to form the insulating coating is called the baking process.

[0019] As a result of investigations by the present inventors, it was found that in the case of an insulating coating containing the above-mentioned metal phosphate and organic resin, coarse bubbles may be generated during the baking process. In an insulating coating containing coarse bubbles, the insulating coating is thin on the surface of the coarse bubbles. The strength of the insulating coating in the thin portions is low. When exposed to high temperatures during stress relief annealing, stress is generated in the insulating coating due to thermal expansion of the organic resin, etc. The stress during stress relief annealing causes the insulating coating in the thin portions to peel off. An insulating coating with peeled parts has low strength and reduced adhesion. The present inventors believed that the above mechanism may cause the adhesion of an insulating coating containing a metal phosphate and an organic resin to be reduced after stress relief annealing.

[0020] The inventors therefore believed that suppressing the formation of coarse bubbles during the baking process would improve the adhesion of the insulating coating after stress relief annealing. After extensive research, the inventors discovered that adding a nitrite to an insulating coating containing a metal phosphate and an organic resin is effective. While the reason for this is unclear, it is thought to be as follows.

[0021] Nitrites decompose when heated, generating gases containing N or O. If nitrites are included in the surface treatment agent, they will partially decompose and generate gas during the baking process. The gas is contained in the insulating coating as fine bubbles. By generating a small amount of gas uniformly, gas concentration during the baking process is suppressed, and as a result, coarse bubbles can be suppressed.

[0022] On the other hand, adding nitrite to an insulating coating containing organic resin raises concerns that the organic resin may be degraded. Degradation of the organic resin would reduce the adhesiveness of the insulating coating after stress relief annealing. For this reason, previous studies have avoided adding nitrite to insulating coatings containing organic resin.

[0023] However, as a result of investigations by the present inventors, it was found that if the nitrogen content of the nitrite in the insulating coating is 0.05 to 5.00 mass %, it is possible to suppress deterioration of the organic resin while generating fine gas during the baking process. In other words, the present inventors' investigations were the first to discover that if the nitrogen content of the nitrite is 0.05 to 5.00 mass %, it is possible to improve the adhesion of the insulating coating after stress relief annealing.

[0024] The non-oriented electrical steel sheet of this embodiment has been completed based on the above-mentioned technical concept, and its gist is as follows.

[0025] [1] A base steel plate; an insulating coating formed on the surface of the base steel sheet, The insulating coating is a metal phosphate; An organic resin, Contains nitrite, The nitrogen content in the insulating coating is 0.05 to 5.00 mass%. Non-oriented electrical steel sheet.

[0026] [2] The metal phosphate salt is One or more selected from the group consisting of Zn phosphate, Mn phosphate, Al phosphate, and Mo phosphate, [1] The non-oriented electrical steel sheet according to [1].

[0027] [3] The organic resin is One or more resins selected from the group consisting of epoxy resins, acrylic resins, and melamine resins. [1] or [2].

[0028] [4] The nitrite is one or more selected from the group consisting of lithium nitrite, calcium nitrite, potassium nitrite, sodium nitrite, and ammonium nitrite; The non-oriented electrical steel sheet according to any one of [1] to [3].

[0029] [5] The insulating coating is Relative to 100 parts by mass of the metal phosphate, The organic resin is contained in an amount of 3 to 50 parts by mass. The non-oriented electrical steel sheet according to any one of [1] to [4].

[0030] [6] The base steel plate comprises, in mass%, Si: 2.5 to 4.5% Al: 0.1 to 1.5%, Mn: Contains 0.2 to 4.0% The non-oriented electrical steel sheet according to any one of [1] to [5].

[0031] The non-oriented electrical steel sheet can be manufactured by the following manufacturing method, for example.

[0032] [7] A method for producing a non-oriented electrical steel sheet according to any one of [1] to [6], a step of applying a surface treatment agent containing a metal phosphate, an organic resin, and a nitrite to a surface of a base steel sheet; and heating the base steel sheet coated with the surface treatment agent under conditions of a heat treatment temperature of 200 to 450°C, a dew point of -30 to 30°C, and a heat treatment time of 10 to 120 seconds to form an insulating coating having a nitrogen content of 0.05 to 5.00 mass%. Manufacturing method for non-oriented electrical steel sheets.

[0033] The non-oriented electrical steel sheet of this embodiment will be described in detail below.

[0034] [Composition of non-oriented electrical steel sheets] Fig. 1 is a cross-sectional view parallel to the sheet thickness direction of a non-oriented electrical steel sheet of this embodiment. Referring to Fig. 1, the non-oriented electrical steel sheet 1 includes a base steel sheet 10 and an insulating coating 20. The insulating coating 20 is formed on the surface of the base steel sheet 10. In Fig. 1, the insulating coating 20 is formed on both the upper and lower surfaces of the base steel sheet 10. However, the insulating coating 20 may be formed on only one surface of the base steel sheet 10. The base steel sheet 10 and the insulating coating 20 will be described below.

[0035] [Base material steel plate 10] The base steel sheet 10 can be appropriately selected from known steel sheets used as non-oriented electrical steel sheets 1. In other words, the base steel sheet 10 is not particularly limited as long as it is a known steel sheet used as the non-oriented electrical steel sheet 1. Whether the steel sheet is oriented or non-oriented electrical steel sheet 1 can be determined by measuring the magnetic flux density of the steel sheet. The magnetic flux density can be measured using a known Tesla meter.

[0036] The chemical composition of the base steel sheet 10 is not directly related to the nitrogen content in the insulating coating. Therefore, in the non-oriented electrical steel sheet 1 according to this embodiment, there are no particular restrictions on the chemical composition of the base steel sheet 10. However, it is preferable that the chemical composition of the base steel sheet 10 contains basic elements, optional elements as needed, with the balance consisting of Fe and impurities. The chemical composition of the base steel sheet 10 contains, for example, the following elements. Hereinafter, unless otherwise specified, "%" means % by mass.

[0037] [Basic elements] The base steel sheet 10 preferably contains Si, Al, and Mn as basic elements in its chemical composition. These elements will be described below.

[0038] Si: 2.5 to 4.5% Silicon (Si) increases the electrical resistance of steel and reduces eddy current loss. As a result, iron loss of steel sheet decreases. Si also increases the strength of steel. If the Si content is less than 2.5%, the above effects cannot be sufficiently obtained. On the other hand, if the Si content exceeds 4.5%, the workability of the steel decreases. Therefore, the Si content is 2.5 to 4.5%. The lower limit of the Si content is preferably 2.6%, more preferably 2.7%. The upper limit of the Si content is preferably 4.3%, more preferably 4.2%.

[0039] Al: 0.1 to 1.5% Aluminum (Al) increases the electrical resistance of steel and reduces eddy current loss. As a result, iron loss of the steel sheet decreases. If the Al content is less than 0.1%, the above effects cannot be sufficiently obtained. On the other hand, if the Al content exceeds 1.5%, the saturation magnetic flux density decreases. Therefore, the Al content is 0.1 to 1.5%. The lower limit of the Al content is preferably 0.15%, and more preferably 0.2%. The upper limit of the Al content is preferably 1.4%, and more preferably 1.3%.

[0040] Mn: 0.2 to 4.0% Manganese (Mn) increases the electrical resistance of steel and reduces eddy current loss. As a result, the iron loss of steel sheet decreases. Mn also has unfavorable {111} <112> The formation of texture is suppressed. If the Mn content is less than 0.2%, the above effect cannot be sufficiently obtained. On the other hand, if the Mn content exceeds 4.0%, the texture changes and hysteresis loss deteriorates. Therefore, the Mn content is 0.2 to 4.0%. The lower limit of the Mn content is preferably 0.3%, and more preferably 0.4%. The upper limit of the Mn content is preferably 3.8%, and more preferably 3.6%.

[0041] In this embodiment, the chemical composition of the base steel plate 10 contains impurities. Here, the impurities refer to elements that are mixed in from raw materials such as ore or scrap, or from the manufacturing environment, when the base steel plate 10 is industrially produced. Examples of impurities include elements such as C, P, S, and N.

[0042] The chemical composition of the base steel sheet 10 can be measured by a known chemical analysis method. For example, the chemical composition of the base steel sheet 10 may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry).

[0043] [Insulating coating 20] As described above, the insulating coating 20 is formed on the surface of the base steel sheet 10. The non-oriented electrical steel sheet 1 is processed into a core blank, which is then laminated to form a motor core. The insulating coating 20 reduces eddy currents between the steel sheets (between the core blanks) after lamination. As a result, eddy current loss in the motor core can be reduced.

[0044] Fig. 2 is an enlarged cross-sectional view of insulating coating 20 in Fig. 1. Referring to Fig. 2, insulating coating 20 contains metal phosphate 201 and organic resin 202. Note that insulating coating 20 does not contain chromium oxide. Metal phosphate 201, organic resin 202, and nitrite will be described below.

[0045] [Metal phosphate 201] The metal phosphate 201 functions as a binder for the insulating coating 20. The metal phosphate 201 is a solid obtained by drying an aqueous solution (insulating coating solution) containing phosphoric acid and metal ions. There are no particular limitations on the type of phosphoric acid, and known phosphoric acids can be used. Preferred phosphoric acids are one or more selected from the group consisting of orthophosphoric acid, metaphosphoric acid, and polyphosphoric acid.

[0046] The metal ions affect the corrosion resistance and adhesion of the insulating coating 20. There are no particular limitations on the type of metal ions, and the metal ions may be one or more selected from the group consisting of Li, Al, Zn, Mg, Ca, Sr, Ti, Co, Mn, and Ni, for example.

[0047] Preferably, the metal phosphate 201 contains one or more selected from the group consisting of Zn phosphate, Mn phosphate, Al phosphate, and Mo phosphate. Zn phosphate effectively improves the corrosion resistance of the insulating coating 20. Mn phosphate improves the heat resistance of the insulating coating 20. Al phosphate improves the adhesion of the insulating coating 20 to the base steel sheet 10 and also improves the heat resistance of the insulating coating 20. Mo phosphate improves the heat resistance of the insulating coating 20. The metal phosphate may further contain, in addition to Al and Zn, the above-mentioned other metal elements other than Al and Zn.

[0048] [Metal phosphate content] There are no particular restrictions on the content of metal phosphate 201. Preferably, the content of metal phosphate 201 in insulating coating 20 is 50% or more by mass. If the content of metal phosphate 201 is 50% or more, the function as a binder can be sufficiently ensured. The content of metal phosphate 201 is more preferably 60% or more. Note that the substantial upper limit of the content of metal phosphate 201 is 95%.

[0049] Furthermore, the phosphorus content in the insulating coating 20 is preferably 35% or more by mass in terms of H2PO4, more preferably 40% or more, even more preferably 45% or more, and even more preferably 50% or more.

[0050] The content of metal phosphate 201 and phosphorus can be determined by measuring the content of P and metal elements using scanning electron microscope-energy dispersive X-ray analysis (SEM-EDS). P is calculated as phosphoric acid in H2PO4 and its content is calculated. In addition, metal phosphate is calculated as M(H2PO4) x (where M is the metal element, and x is the valence of the metal element), and the sum of the calculated metal element and phosphoric acid is the content of the metal phosphate.

[0051] [Organic Resin 202] 2, organic resin 202 is dispersed in metal phosphate 201, which functions as a binder. Organic resin 202 inhibits metal phosphate 201 from growing coarse and promotes polycrystallization of metal phosphate 201. Organic resin 202 forms dense insulating coating 20.

[0052] The organic resin 202 is not particularly limited, and any known organic resin can be used. Preferred organic resins 202 are one or more selected from the group consisting of acrylic resin, polystyrene resin, vinyl acetate resin, epoxy resin, polyester resin, polyurethane resin, polyamide resin, phenolic resin, melamine resin, silicone resin, polypropylene resin, and polyethylene resin. More preferably, organic resin 202 is one or more selected from the group consisting of epoxy resin, acrylic resin, and melamine resin.

[0053] Preferably, the organic resin 202 is an epoxy resin. Epoxy resins have excellent insulating properties and corrosion resistance. The type of epoxy resin is not particularly limited. For example, the epoxy resin may be one or more types selected from the group consisting of bisphenol A, F, B type, alicyclic type, glycidyl ether type, glycidyl ester type, biphenyl type, naphthalene type, phenol novolac type, orthocresol novolac type, tetraphenylol ethane type, and trishydroxyphenylmethane type.

[0054] More specifically, the epoxy resin is, for example, one or more selected from the group consisting of bisphenol A diglycidyl ether, a caprolactone ring-opening adduct of bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, bisphenol S diglycidyl ether, novolac glycidyl ether, dimer acid glycidyl ether, glycidyl ether derivatives, hexahydrophthalic acid polyglycidyl ester, dimer acid glycidyl ester, and glycidyl ester derivatives.

[0055] [Method for measuring metal phosphate 201 and organic resin 202 in insulating coating 20] The metal phosphate 201 and organic resin 202 in the insulating coating 20 can be measured by the following method. The gas generation behavior when the non-oriented electrical steel sheet 1 on which the insulating coating 20 is formed is heated is analyzed using pyrolysis-gas chromatography / mass spectrometry (Py-GC / MS) (hereinafter referred to as "GC / MS") to identify the presence or absence of organic resin 202 and the type of organic resin 202. The organic resin may be identified by using the above-mentioned GC / MS method in combination with Fourier transform infrared spectroscopy (FT-IR).

[0056] Furthermore, chemical analysis is performed on the insulating coating 20 using energy dispersive X-ray spectroscopy (EDS) or ICP-AES, and if P and metal elements (Zn, Al, etc.) are detected, it is determined that the insulating coating 20 contains metal phosphate.

[0057] [Organic resin content] Preferably, the insulating coating 20 contains 3 to 50 parts by mass of organic resin 202 per 100 parts by mass of metal phosphate 201. When the content of organic resin 202 is 3 parts by mass or more, coarsening of the metal phosphate 201 can be sufficiently suppressed. In this case, adhesion of the insulating coating 20 to the base steel sheet 10 is more stably improved. On the other hand, when the content of organic resin 202 is 50 parts by mass or less, excessive inclusion of organic resin in the insulating coating is suppressed. In this case, adhesion of the insulating coating 20 to the base steel sheet 10 is more stably improved. Therefore, the content of the organic resin in the surface treatment agent is preferably 3 to 50 parts by mass per 100 parts by mass of metal phosphate.

[0058] The lower limit of the content of organic resin 202 is more preferably 5 parts by mass, even more preferably 10 parts by mass, even more preferably 15 parts by mass, and even more preferably 20 parts by mass per 100 parts by mass of metal phosphate 201. The upper limit of the content of organic resin 202 is more preferably 45 parts by mass, even more preferably 40 parts by mass, even more preferably 35 parts by mass, and even more preferably 30 parts by mass per 100 parts by mass of metal phosphate 201. The content of organic resin 202 in insulating coating 20 is less than the content of metal phosphate 201.

[0059] The content of organic resin 202 can be determined by the following method. First, the type of organic resin 202 is identified by FT-IR and / or GC / MS. The carbon content of organic resin 202 is calculated from the identified chemical structure of organic resin 202. Next, the surface of insulating coating 20 is measured using SEM-EDS. Measurement points are any multiple locations on the surface of insulating coating 20.

[0060] The carbon (C) concentration is determined by elemental analysis. The arithmetic mean of the carbon concentrations at multiple measurement locations is defined as the carbon concentration of the insulating coating 20. Next, the weight of the insulating coating 20 peeled off from the base steel sheet 10 is determined using an alkaline solution. The absolute value of the carbon content in the insulating coating 20 is calculated from the weight of the insulating coating 20 and the carbon concentration of the insulating coating 20. The content of the organic resin 202 in the insulating coating 20 can be calculated from the absolute value of the carbon content in the insulating coating 20 and the carbon content of the organic resin 202.

[0061] [Nitrite] The insulating coating 20 contains nitrite. The nitrite is a nitrite ion (NO - ) as an anion. Nitrite generates a small amount of gas during the baking process. By uniformly generating a small amount of gas, gas concentration during the baking process is suppressed. As a result, it is believed that the generation of large bubbles is suppressed and the adhesion of the insulating coating 20 is improved.

[0062] The nitrite is, for example, one or more selected from the group consisting of lithium nitrite, calcium nitrite, potassium nitrite, sodium nitrite, ammonium nitrite, magnesium nitrite, strontium nitrite, barium nitrite, cesium nitrite, silver nitrite, nickel nitrite, zinc nitrite, lead (II) dinitrite, copper (II) dinitrite, and cobalt (II) nitrite. Preferably, the nitrite is one or more selected from the group consisting of lithium nitrite, calcium nitrite, potassium nitrite, sodium nitrite, and ammonium nitrite.

[0063] Nitrites are chemically completely different from nitrates. As a result of the inventors' investigations, it was found that nitrates do not have the effect of suppressing coarse bubbles. Therefore, in this embodiment, nitrites are used.

[0064] [How to identify nitrites] The nitrite in the insulating coating 20 can be identified by the following method. A portion of the insulating coating 20 is collected and pulverized in a mortar. Distilled water is added to the mortar containing the pulverized insulating coating 20 to obtain a suspension. Arsanilic acid is added to the suspension, causing a reaction between the arsanilic acid and the nitrite in the suspension. This synthesizes a diazonium compound. Naphthylethylenediamine is then added to the suspension, causing a reaction between the naphthylethylenediamine and the diazonium compound. This synthesizes an azo dye. If the azo dye is synthesized, the suspension becomes colored. The color of the suspension is confirmed with a colorimeter (colorimetric method). This identifies that an azo dye has been synthesized in the suspension. The above method identifies the presence of nitrite in the insulating coating.

[0065] [Nitrite content] The insulating coating 20 contains nitrite. However, it is quite difficult to quantify the amount of nitrite in the insulating coating 20. However, the amount of nitrite can be substituted for the amount of nitrogen in the insulating coating 20. Therefore, in the present disclosure, the amount of nitrite is substituted for the amount of nitrogen in the insulating coating 20.

[0066] [Nitrogen content in insulating coating 20] In the insulating coating 20 of this embodiment, which contains metal phosphate 201 and organic resin 202, if the nitrogen content is less than 0.05 mass%, the nitrite content is too low. As a result, a sufficient amount of fine gas is not generated during the baking process, and the adhesiveness of the insulating coating 20 after stress relief annealing is not improved. On the other hand, in the insulating coating 20 of this embodiment, which contains metal phosphate 201 and organic resin 202, if the nitrogen content is more than 5.00 mass%, the nitrite content is too high. As a result, excessive gas is generated during the baking process, and the adhesiveness of the insulating coating 20 after stress relief annealing is not improved. Therefore, the nitrogen content of the insulating coating 20 is 0.05 to 5.00 mass%. The lower limit of the nitrogen content of the insulating coating 20 is preferably 0.10 mass%, more preferably 0.15 mass%. The lower limit of the nitrogen content of the insulating coating 20 is even more preferably 0.50 mass%, and even more preferably 1.00 mass%. The upper limit of the nitrogen content in the insulating coating 20 is preferably 4.80 mass %, more preferably 4.50 mass %, even more preferably 4.00 mass %, and even more preferably 3.00 mass %.

[0067] [Method for measuring nitrogen content in insulating coating 20] The nitrogen content in the insulating coating 20 is measured by the following method. The content of each element in the insulating coating 20 is measured using EDS for the non-oriented electrical steel sheet 1 on which the insulating coating 20 is formed. The analysis is performed on the surface of five arbitrary locations of the non-oriented electrical steel sheet 1 (insulating coating 20). From the analysis results, the peak intensity of iron (Fe) is excluded, and the total of the peaks of the remaining elements is taken as 100 mass % to determine the nitrogen content (mass %).

[0068] Insulating coating 20 may be made of metal phosphate 201, organic resin 202, and nitrite. Insulating coating 20 may further contain other components. That is, insulating coating 20 may be made of metal phosphate 201, organic resin 202, nitrite, and other components.

[0069] [Other ingredients] The insulating coating 20 may contain other components. Examples of the other components include water-soluble organic compounds. Examples of the water-soluble organic compounds include one or more selected from the group consisting of surfactants, emulsifiers, antifoaming agents, and leveling agents. The content of the other components is 5.0 parts by mass or less per 100 parts by mass of the metal phosphate 201. The upper limit of the content of the other components is preferably less than 5.0 parts by mass, more preferably 4.5 parts by mass, even more preferably 4.0 parts by mass, even more preferably 3.5 parts by mass, and even more preferably 3.0 parts by mass per 100 parts by mass of the metal phosphate 201. The lower limit of the content of the other components may be 0%. The lower limit of the content of the other components is, for example, 0.1%.

[0070] The content of water-soluble organic compounds can be measured using the GC-MS method described above. More specifically, the content of water-soluble organic compounds is measured by thermally decomposing the water-soluble organic compounds contained in the insulating coating at 800°C in an analyzer, at which point the organic matter is burned and sublimated.

[0071] [Preferable film thickness of insulating coating 20] There are no particular limitations on the thickness of the insulating coating 20. A preferred thickness of the insulating coating 20 is 0.20 to 1.60 μm. If the thickness is 0.20 to 1.60 μm, the insulating coating 20 exhibits even better insulating properties. However, even if the thickness of the insulating coating 20 is outside the range of 0.20 to 1.60 μm, the insulating coating 20 exhibits excellent adhesion after stress relief annealing.

[0072] As described above, the non-oriented electrical steel sheet 1 of this embodiment includes a base steel sheet 10 and an insulating coating 20 formed on the surface of the base steel sheet 10. The insulating coating 20 contains a metal phosphate 201, an organic resin 202, and a nitrite. The nitrogen content in the insulating coating 20 is 0.05 to 5.00 mass %. Therefore, the insulating coating 20 exhibits excellent adhesion after stress relief annealing.

[0073] [Manufacturing method] An example of a method for manufacturing the non-oriented electrical steel sheet 1 of this embodiment will be described. The manufacturing method described below is one example for manufacturing the non-oriented electrical steel sheet 1. Therefore, the non-oriented electrical steel sheet 1 may be manufactured by a manufacturing method other than the manufacturing method described below. However, the manufacturing method described below is a suitable example of a method for manufacturing the non-oriented electrical steel sheet 1.

[0074] An example of a method for manufacturing the non-oriented electrical steel sheet 1 of this embodiment includes a step (application step) of applying a surface treatment agent containing a metal phosphate, an organic resin, and a nitrite to the surface of the base steel sheet 10, and a step (baking step) of heating the base steel sheet 10 to which the surface treatment agent has been applied to form the insulating coating 20. Each step will be described below.

[0075] [Coating process] In the coating step, the surface treatment agent is coated on the surface of the base steel sheet 10. The coating method is not particularly limited, and known coating methods can be applied. For example, the coating method is a roll coater method, a spray method, a dipping method, etc.

[0076] [About surface treatment agents] The surface treatment agent contains a metal phosphate, an organic resin, and a nitrite. Here, the metal phosphate, organic resin, and nitrite in the surface treatment agent are the metal phosphate 201, organic resin 202, and nitrite described above. When preparing the metal phosphate solution, it is preferable to mix at least one of an oxide, carbonate, and hydroxide of a metal ion with various phosphoric acids such as orthophosphoric acid.

[0077] [About the organic resin content in surface treatment agents] The content of the organic resin in the surface treatment agent may be the same as the content of the organic resin 202 in the insulating coating 20. In other words, the content of the organic resin in the surface treatment agent is preferably 3 to 50 parts by mass per 100 parts by mass of the metal phosphate.

[0078] The lower limit of the organic resin content in the surface treatment agent is more preferably 5 parts by mass, even more preferably 10 parts by mass, even more preferably 15 parts by mass, and even more preferably 20 parts by mass, per 100 parts by mass of the metal phosphate. The upper limit of the organic resin content is more preferably 45 parts by mass, even more preferably 40 parts by mass, even more preferably 35 parts by mass, and even more preferably 30 parts by mass, per 100 parts by mass of the metal phosphate. The content of the organic resin in the surface treatment agent is less than the content of the metal phosphate.

[0079] [Nitrite content in surface treatment agents] Preferably, the content of the nitrite in the surface treatment agent is 2 to 80 parts by mass per 100 parts by mass of the metal phosphate.

[0080] The lower limit of the nitrite content is more preferably 3 parts by mass, even more preferably 5 parts by mass, even more preferably 8 parts by mass, even more preferably 10 parts by mass, and even more preferably 15 parts by mass, relative to 100 parts by mass of the metal phosphate. The upper limit of the nitrite content is more preferably 70 parts by mass, even more preferably 60 parts by mass, even more preferably 50 parts by mass, even more preferably 40 parts by mass, and even more preferably 30 parts by mass, relative to 100 parts by mass of the metal phosphate.

[0081] [About the hardener] The surface treatment agent may contain a curing agent in addition to the metal phosphate and the organic resin. The curing agent cures the organic resin. For example, the curing agent may be one or more selected from the group consisting of polyamine-based curing agents, acid anhydride-based curing agents, and methylol group-containing precondensates.

[0082] The polyamine-based curing agent is, for example, one or more selected from the group consisting of aliphatic polyamines, alicyclic polyamines, aromatic polyamines, polyamide polyamines, and modified polyamines.

[0083] The acid anhydride curing agent is, for example, one or more selected from the group consisting of monofunctional acid anhydrides (phthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, chlorendic anhydride, etc.), bifunctional acid anhydrides (pyromellitic anhydride, benzophenone tetracarboxylic anhydride, ethylene glycol bis(anhydrotrimate), methylcyclohexene tetracarboxylic anhydride, etc.), and free acid anhydrides (trimellitic anhydride, polyazelaic anhydride, etc.).

[0084] The methylol group-containing precondensate is, for example, one or more selected from the group consisting of novolac or resol phenolic resins, urea resins, and melamine resins.

[0085] When a curing agent is contained, the content of the curing agent in the surface treatment agent is 0 to 50.0 parts by mass per 100 parts by mass of the metal phosphate. When a curing agent is contained in the surface treatment agent, the curing agent promotes the curing of the organic resin. When the content of the curing agent is 50.0 parts by mass or less, the adhesion of the insulating coating 20 to the base steel sheet 10 is more stably improved. Therefore, when a curing agent is contained, the content of the curing agent in the surface treatment agent is 0 to 50.0 parts by mass per 100 parts by mass of the metal phosphate.

[0086] The preferred lower limit of the curing agent content is 0.5 parts by mass, more preferably 1.0 parts by mass, and even more preferably 2.0 parts by mass, per 100 parts by mass of the metal phosphate, and the preferred upper limit of the curing agent content is 45.0 parts by mass, more preferably 40.0 parts by mass, and even more preferably 35.0 parts by mass, per 100 parts by mass of the metal phosphate.

[0087] The organic resin and curing agent in the surface treatment agent undergo a baking process, which will be described later, and ultimately become organic resin 202 in insulating coating 20. Therefore, the total content of the organic resin and curing agent in the surface treatment agent is preferably 0 to 50.0 parts by mass per 100 parts by mass of the metal phosphate.

[0088] [Baking process] In the baking step, the base steel sheet 10 coated with the surface treatment agent is heated to form the insulating coating 20. The baking conditions are a heat treatment temperature of 200 to 450°C, a dew point of -30 to 30°C, and a heat treatment time of 10 to 120 seconds.

[0089] Heat treatment temperature: 200~450℃ If the heat treatment temperature is below 200°C, the dehydration reaction of the metal phosphate does not proceed sufficiently, and therefore the insulating coating 20 cannot be formed properly. On the other hand, if the heat treatment temperature exceeds 450°C, the organic resin will thermally decompose, and therefore the insulating coating 20 cannot be formed properly. Therefore, the heat treatment temperature is 200 to 450°C. The preferred lower limit of the heat treatment temperature is 250°C, more preferably 280°C, and even more preferably 300°C. The preferred upper limit of the heat treatment temperature is 430°C, more preferably 400°C, even more preferably 380°C, even more preferably 350°C, and even more preferably 320°C.

[0090] Dew point: -30~30℃ If the dew point is lower than -30°C, there is a risk of voids occurring due to bumping. On the other hand, if the dew point is higher than 30°C, evaporation of water takes time, which may slow down the progress of crystallization of the metal phosphate. Therefore, the dew point is -30 to 30°C. The lower limit of the dew point is preferably -15°C, and more preferably -10°C. The upper limit of the dew point is preferably 20°C.

[0091] Heat treatment time: 10 to 120 seconds If the heat treatment time is less than 10 seconds, the metal phosphate will not crystallize sufficiently. As a result, the insulating coating 20 will not be formed properly. On the other hand, if the heat treatment time is more than 120 seconds, the organic resin will melt due to excessive heating. If the heat treatment time is more than 120 seconds, the organic resin may thermally decompose, which may cause the insulating coating 20 to powder. Therefore, the heat treatment time is 10 to 120 seconds. The preferred lower limit of the heat treatment time is 15 seconds, more preferably 20 seconds, even more preferably 25 seconds, and even more preferably 30 seconds. The preferred upper limit of the heat treatment time is 100 seconds, more preferably 90 seconds, even more preferably 80 seconds, even more preferably 70 seconds, and even more preferably 60 seconds.

[0092] For example, the surface treatment agent may contain metal phosphate, organic resin, and 5 to 80 parts by mass of nitrite per 100 parts by mass of metal phosphate. By heat treating this surface treatment agent while appropriately adjusting the baking conditions within the above-mentioned range, an insulating coating 20 with a nitrogen content of 0.05 to 5.00% by mass can be formed. By appropriately controlling the conditions in the baking step, it is possible to suppress the volatilization of nitrogen contained in the nitrite and control the nitrogen content within the above-mentioned range.

[0093] Through the above manufacturing steps, the non-oriented electrical steel sheet 1 is manufactured. [Example]

[0094] The effects of the non-oriented electrical steel sheet of this embodiment will be described more specifically using examples. The conditions in the following examples are one example of conditions adopted to confirm the feasibility and effects of the non-oriented electrical steel sheet of this embodiment. Therefore, the non-oriented electrical steel sheet of this embodiment is not limited to this one example of conditions.

[0095] A base steel sheet (non-oriented electrical steel sheet) with a thickness of 0.25 mm was prepared. The base steel sheet contained, by mass%, 3.1% Si, 0.6% Al, 0.2% Mn, with the remainder being Fe and impurities. A coating process was carried out on the prepared base steel sheet. Specifically, a surface treatment agent with the composition shown in Table 1 was applied to the surface of the base steel sheet using a rubber roll coating device.

[0096] [Table 1]

[0097] The "Metal Phosphate (100 parts by mass)" column in Table 1 shows the type of metal phosphate contained in the surface treatment agent and the mass ratio within the metal phosphate. For example, in Test No. 1, the metal phosphate consists of aluminum phosphate. In Test No. 3, the metal phosphate contains aluminum phosphate and magnesium phosphate in a mass ratio of 5:5. In Test No. 4, the metal phosphate contains aluminum phosphate and magnesium phosphate in a mass ratio of 6:4.

[0098] The "Types" A to E in the "Nitrite" column in Table 1 are as follows: A: Lithium nitrite (LiNO2) B: Sodium nitrite (NaNO2) C: Calcium nitrite (Ca(NO2)2) D: Potassium nitrite (KNO2) E: Ammonium nitrite (NH4NO2)

[0099] The "Amount blended" in the "Nitrite" column in Table 1 indicates the parts by mass of nitrite per 100 parts by mass of metal phosphate. A "-" indicates that no nitrite was contained in the surface treatment agent.

[0100] In Table 1, the "types" a to c in the "organic resin" column are as follows: a: A bisphenol A type epoxy resin with an epoxy equivalent of 5000 is modified with methacrylic acid and ethyl acrylate to form an acrylic-modified epoxy resin, which is then emulsified by reacting with dimethylethanolamine to form an amine-containing epoxy resin emulsion. b: A self-emulsifying epoxy resin obtained by modifying a phenol novolac epoxy resin with an ethylene propylene block copolymer and nonylphenyl ether ethylene oxide. c: Epoxy resin emulsion made by emulsifying bisphenol A type epoxy resin with an epoxy equivalent of 300 with forced stirring using an emulsifier.

[0101] In Table 1, the "amount blended" in the "organic resin" column indicates the parts by mass of the organic resin when the metal phosphate is taken as 100 parts by mass.

[0102] The surface treatment agent of each number was applied in an amount of 0.8 g / m 2 The base steel sheet was coated with the surface treatment agent so that the coating was uniform. A baking treatment was then carried out on the base steel sheet to which the surface treatment agent had been applied. The heat treatment temperature for each test number was 300°C, the dew point was 30°C, and the heat treatment time was 60 seconds. Through the above process, a non-oriented electrical steel sheet was manufactured in which an insulating coating was formed on the surface of the base steel sheet.

[0103] [Table 2]

[0104] [Evaluation Test 1] The manufactured non-oriented electrical steel sheets were subjected to tests to measure the content of metal phosphates and phosphorus, a nitrogen content measurement test using EDS, an insulation evaluation test, a corrosion resistance evaluation test, a leaching evaluation test, a content identification test using GC / MS, and a nitrite identification test.

[0105] [Metal phosphate and phosphorus content measurement test] The contents of P and metal elements were measured by SEM-EDS. The P content was calculated as phosphoric acid in H2PO4. The metal phosphate salts were calculated as M(H2PO4) x (where M is the metal element, and x is the valence of the metal element), and the sum of the calculated metal element and phosphoric acid was taken as the content of metal phosphate.

[0106] [Nitrogen content measurement test using EDS] The nitrogen content in the insulating coating of the non-oriented electrical steel sheet of each test number was measured using the following method. The content of each element in the insulating coating was measured for the non-oriented electrical steel sheet on which the insulating coating was formed using an energy dispersive X-ray analyzer. The analysis was performed on the surface of five randomly selected locations on the non-oriented electrical steel sheet (insulating coating). From the analysis results, the peak intensity of iron (Fe) was excluded, and the nitrogen content (mass%) was calculated using the sum of the peaks of the remaining elements as 100 mass%. The results are shown in the "Properties [N] concentration (%) before stress relief annealing" column in Table 2.

[0107] [Insulation evaluation test] The insulation properties of the non-oriented electrical steel sheets with each test number were evaluated using the following method. The interlaminar resistance of the non-oriented electrical steel sheets of each test number was measured in accordance with C2550-4:2019. Based on the obtained interlaminar resistance values, the insulation properties were evaluated as follows.

[0108] A: Interlayer resistance is 30 Ω·cm 2 / or more B: Interlayer resistance is 10 Ω·cm 2 / sheet or more 30Ω·cm 2 Less than / C: Interlayer resistance is 3 Ω cm 2 / sheet or more 10Ω·cm 2 Less than / D: Interlayer resistance is 3 Ω cm 2 Less than / The obtained insulation evaluation results are shown in the "Insulation properties before stress relief annealing" column in Table 2. Evaluations A and B were considered to be acceptable.

[0109] [Corrosion resistance evaluation test] The corrosion resistance of each non-oriented electrical steel sheet was evaluated using the following method. A steel sheet sample measuring 30 mm in width and 300 mm in length was taken from each non-oriented electrical steel sheet. In accordance with the salt spray test described in JIS Z2371:2015, a 5% NaCl aqueous solution was allowed to fall naturally onto the steel sheet sample for 7 hours in a 35°C atmosphere. After that, the area ratio of the area where rust occurred on the surface of the steel sheet sample (hereinafter referred to as the "rust area ratio") was determined. Corrosion resistance was evaluated using the following 10-point scale based on the determined rust area.

[0110] 10: Rust area rate is 0% 9: Rust area rate is 0.10% or less 8: Rust area ratio is over 0.10% and 0.25% or less 7: Rust area ratio is over 0.25% and 0.50% or less 6: Rust area ratio is over 0.50% and 1.00% or less 5: Rust area rate is over 1.00% and 2.50% or less 4: Rust area ratio is over 2.50% and 5.00% or less 3: Rust area rate is over 5.00% and 10.00% or less 2: Rust area rate is over 10.00% and 25.00% or less 1: Rust area rate is over 25.00% and 50.00% or less The obtained corrosion resistance is shown in the "Properties before stress relief annealing: Corrosion resistance" column in Table 2. A score of 5 or more was considered to be acceptable.

[0111] [Elution resistance evaluation test] The elution resistance of the non-oriented electrical steel sheets of each test number was evaluated by the following method. Steel sheet samples of 30 mm width and 300 mm length were taken from each non-oriented electrical steel sheet of each test number. The steel sheet samples were boiled in boiling pure water for 10 minutes. The amount of phosphoric acid eluted in the pure water (solution) after boiling was measured. Specifically, the boiled pure water (solution) was cooled. The solution was diluted with pure water, and the phosphoric acid concentration in the solution was measured by ICP-AES. The amount of phosphoric acid eluted (mg / m ) was calculated from the dilution ratio. 2 The results are shown in the "Properties before stress relief annealing - Dissolution" column in Table 2. The amount of dissolved phosphoric acid was 140 mg / m 2 If the resistance was less than this, the sample was judged to be acceptable (excellent in resistance to elution).

[0112] [GC / MS content identification test] The organic resin in the insulating coating for each test number was identified using the following method. The presence or absence of organic resin and the type of organic resin were identified by analyzing the gas generation behavior when the non-oriented electrical steel sheet with the insulating coating was heated using GC / MS. As a result, it was confirmed that the insulating coating for each test number contained epoxy resin.

[0113] [Specific test for nitrite] The nitrite in the insulating coating of each test number was identified by the following method. A portion of the insulating coating was collected and crushed in a mortar. Distilled water was added to the mortar containing the crushed insulating coating to obtain a suspension. Arsanilic acid was added to the suspension, causing a reaction between the arsanilic acid and the nitrite in the suspension. This resulted in the synthesis of a diazonium compound. Furthermore, naphthylethylenediamine was added to the suspension, causing a reaction between the naphthylethylenediamine and the diazonium compound. This resulted in the synthesis of an azo dye. The synthesis of the azo dye was identified by confirming the color of the suspension with a colorimeter (colorimetric method). Using the above method, the presence of nitrite in the suspension was identified. As a result, it was confirmed that the insulating coatings of test numbers 1 to 9 contained nitrite.

[0114] [Evaluation Test 2] An adhesion evaluation test was carried out on the non-oriented electrical steel sheets with each test number.

[0115] [Adhesion evaluation test] The adhesion of each non-oriented electrical steel sheet was evaluated using the following method. A steel sheet sample measuring 30 mm in width and 300 mm in length was taken from each non-oriented electrical steel sheet. Strain relief annealing was performed on the steel sheet sample. Strain relief annealing was performed in a nitrogen gas flow at an annealing temperature of 800°C for 2 hours. After strain relief annealing, adhesive tape was applied to the insulating coating of the steel sheet sample. The steel sheet sample with the adhesive tape applied was wrapped around a metal rod with a diameter of 10 mm. The steel sheet sample was then separated from the metal rod. In other words, the steel sheet sample was bent to a diameter of 10 mm. The adhesive tape was then peeled off the steel sheet sample, and the proportion (area ratio) of the insulating coating that remained unpeeled from the base steel sheet was measured. Based on the obtained area ratio, adhesion was evaluated as follows.

[0116] A: The area ratio of the remaining insulating coating was 100%. In other words, the insulating coating did not peel off. B: The area ratio of the remaining insulating coating was 90% or more but less than 100%. C: The area ratio of the remaining insulating coating was 50% or more but less than 90%. D: The area ratio of the remaining insulating coating was 25% or more but less than 50%. E: The area ratio of the remaining insulating coating was less than 25%. The obtained adhesion evaluation results are shown in the "Specific adhesion after stress relief annealing" column in Table 2. Evaluations A and B were considered to be acceptable.

[0117] [Evaluation results] The evaluation results are shown in Table 2. Referring to Table 2, the insulating coatings of the non-oriented electrical steel sheets of test numbers 1 to 7 contained metal phosphate, organic resin, and nitrite. Furthermore, the nitrogen content in the insulating coating was 0.05 to 5.00 mass%. As a result, the insulating coatings of test numbers 1 to 7 showed excellent adhesion after stress relief annealing.

[0118] On the other hand, in Test No. 8, the nitrite content was too low. As a result, the nitrogen content in the insulating coating was less than 0.05 mass %. As a result, the insulating coating of Test No. 8 did not have improved adhesion after stress relief annealing.

[0119] The insulating coating of Test No. 9 contained too much nitrite. As a result, the nitrogen content in the insulating coating exceeded 5.00 mass %. As a result, the insulating coating of Test No. 9 was unable to improve adhesion after stress relief annealing.

[0120] The insulating coating of test number 10 did not contain nitrite, and as a result, the insulating coating of test number 10 was unable to improve adhesion after stress relief annealing.

[0121] The embodiments of the present disclosure have been described above. However, the above-described embodiments are merely examples for implementing the present disclosure. Therefore, the present disclosure is not limited to the above-described embodiments, and can be implemented by appropriately modifying the above-described embodiments within the scope of the present disclosure. [Explanation of symbols]

[0122] 1 Non-oriented electrical steel sheet 10 Base steel plate 20 Insulating coating 201 Metal phosphates 202 Organic Resin

Claims

1. A base steel plate; an insulating coating formed on the surface of the base steel sheet, The insulating coating is a metal phosphate; An organic resin, Contains nitrite, The insulating coating has a nitrogen content of 0.05 to 5.00 mass % and a phosphorus content of 35 mass % or more in terms of H 2 PO 4 . Non-oriented electrical steel sheet.

2. The metal phosphate salt is One or more selected from the group consisting of zinc phosphate, manganese phosphate, aluminum phosphate, and molybdenum phosphate; The non-oriented electrical steel sheet according to claim 1.

3. The organic resin is One or more resins selected from the group consisting of epoxy resins, acrylic resins, and melamine resins; The non-oriented electrical steel sheet according to claim 1.

4. A non-oriented electrical steel sheet, The nitrite is one or more selected from the group consisting of lithium nitrite, calcium nitrite, potassium nitrite, sodium nitrite, and ammonium nitrite; The non-oriented electrical steel sheet according to claim 1.

5. The insulating coating is Relative to 100 parts by mass of the metal phosphate, Contains 3 to 50 parts by mass of the organic resin, The non-oriented electrical steel sheet according to claim 1.

6. The base steel plate comprises, in mass%, Si: 2.5-4.5%, Al: 0.1-1.5%, Mn: Contains 0.2 to 4.0%; The non-oriented electrical steel sheet according to claim 1.

7. A method for producing a non-oriented electrical steel sheet according to any one of claims 1 to 6, a step of applying a surface treatment agent containing a metal phosphate, an organic resin, and a nitrite to a surface of a base steel sheet; and heating the base steel sheet coated with the surface treatment agent under conditions of a heat treatment temperature of 200 to 450°C, a dew point of -30 to 30°C, and a heat treatment time of 10 to 120 seconds to form an insulating coating having a nitrogen content of 0.05 to 5.00 mass%. Manufacturing method for non-oriented electrical steel sheets.

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