Method for producing grain-oriented electrical steel sheet

Abstract

This method for producing a grain-oriented electrical steel sheet has a tension-imparted insulating coating film formation step that includes: an insulating coating film chemical solution application step in which an insulating coating film formation solution is applied to the surface of a surface-treated steel sheet, the surface of which has been pickled; and a baking step in which a tension-imparting insulating coating is formed on the surface of the surface-treated steel sheet by heat-treating the surface-treated steel sheet to which the insulating coating-forming liquid has been applied, the heat treatment in the baking step having a temperature-raising step in which the tension-imparting insulating coating is applied, and a soaking step in which the tension-imparting insulating coating is applied on the surface of the surface-treated steel sheet. The average temperature rise rate of the steel sheet in the steel sheet temperature range of 100 DEG C to 600 DEG C is set to 10 DEG C / sec to 400 DEG C / sec in an atmosphere having an oxygen concentration of 1 vol% to 21 vol% and a dew point of 0 DEG C to 30 DEG C; the holding time at a constant steel sheet temperature in the range of 800 DEG C to 1000 DEG C is set to 5 seconds to 200 seconds in a soaking atmosphere in which the hydrogen concentration is 1-15% and the atmosphere dew point is a constant value in the range of-20 DEG C to + 40 DEG C.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet.

[0002] This application claims priority based on Japanese Patent Application No. 2023-013747 filed on February 1, 2023, and incorporates its content herein. Background Art

[0003] A grain-oriented electrical steel sheet is a steel sheet containing about 0.5% to 7% by mass of silicon (Si), and the crystal orientations are aggregated in the {110}<001> orientation (Goss orientation) by a phenomenon called secondary recrystallization. It is mainly used as a soft magnetic material in the iron cores of transformers and the like. Since the characteristics of the grain-oriented electrical steel sheet have a great influence on the performance of the transformer, in-depth research has been carried out on the grain-oriented electrical steel sheet to achieve good excitation characteristics and low iron loss.

[0004] A general method for manufacturing a grain-oriented electrical steel sheet is as follows.

[0005] First, a steel slab having a predetermined chemical composition is heated and hot-rolled to manufacture a hot-rolled steel sheet. For the obtained hot-rolled steel sheet, after hot-rolled sheet annealing as needed, the hot-rolled steel sheet is pickled. The pickled hot-rolled steel sheet is cold-rolled to manufacture a cold-rolled steel sheet. The obtained cold-rolled steel sheet is decarburized and annealed to exhibit primary recrystallization.

[0006] After that, an aqueous slurry containing an annealing parting agent mainly composed of MgO is coated on the surface of the cold-rolled steel sheet after decarburization annealing and dried. Then, the steel sheet is wound into a coil and subjected to final annealing to exhibit secondary recrystallization. At the time of final annealing, while the secondary recrystallization in the steel sheet is exhibited, MgO in the annealing parting agent reacts with SiO2 in the internal oxide layer formed on the surface of the cold-rolled steel sheet during decarburization annealing, and a glass film mainly composed of forsterite (Mg2SiO4) (hereinafter, also referred to as "primary film") is formed on the surface of the base steel sheet.

[0007] After final annealing (after the formation of the primary film), a tension-imparting insulating film (hereinafter, also referred to as "secondary film") is formed by coating a liquid medicine mainly composed of silica and phosphate, for example, on the upper layer of the primary film and baking it.

[0008] In addition to functioning as an insulating film, the above-mentioned primary film also has the function of improving the adhesion of the secondary film formed on the upper layer of the primary film. Moreover, due to the tension generated by both the primary film and the secondary film, the iron loss is reduced. However, since the primary film is a non-magnetic phase, it is not preferred from the viewpoint of magnetic properties. In addition, the interface between the base material steel plate and the primary film has an embedding structure in which the root of the primary film penetrates into the base material steel plate, and sometimes an increase in iron loss is caused due to the hindrance of the movement of magnetic domain walls.

[0009] Prior Art Documents

[0010] Patent Documents

[0011] Patent Document 1: Japanese Patent Laid-Open No. 8-269560

[0012] Patent Document 2: International Publication No. 2019 / 182149

[0013] Patent Document 3: International Publication No. 2020 / 149345 Summary of the Invention

[0014] Problems to be Solved by the Invention

[0015] Due to the above background, many inventions regarding non-oriented electrical steel sheets without a primary film have been made. For example, in Patent Document 1 mentioned above, a manufacturing method is disclosed in which, in the annealing separation agent coating step before the secondary recrystallization annealing step, the generation and peeling of the primary film are suppressed by adding a chloride to the annealing separation agent. This manufacturing method has high industrial value due to its simplicity.

[0016] However, due to the non-formation of the primary film, the adhesion of the secondary film is still insufficient. Therefore, for example, in Patent Document 2 mentioned above, unevenness is formed on the surface of the base material steel plate before the coating and baking step of the secondary film after the secondary recrystallization annealing. According to this manufacturing method, the film adhesion is ensured by the anchoring effect generated at the interface between the base material steel plate and the secondary film. However, the unevenness of this interface becomes an obstacle to the movement of magnetic domain walls when the non-oriented electrical steel sheet is magnetized, and sometimes becomes a factor that hinders the reduction of iron loss.

[0017] In Patent Document 3 mentioned above, intermediate annealing is performed on the base material steel plate before the coating of the secondary film solution. This manufacturing method generates an oxide film on the surface of the base material steel plate and uses it as a buffer layer when the secondary film is adhered, and can achieve both high magnetic properties and high film adhesion. However, since the intermediate annealing step is set as essential during manufacturing, there is another problem of high manufacturing load.

[0018] The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for manufacturing a grain-oriented electrical steel sheet having high film adhesion (secondary film adhesion) without impairing magnetic properties without performing intermediate annealing.

[0019] Means for Solving the Problem

[0020] In order to solve the above problems and achieve the above object, the present invention adopts the following solutions.

[0021] (1) The method for manufacturing a grain-oriented electrical steel sheet according to one aspect of the present invention includes the following steps:

[0022] Hot rolling step: A hot-rolled steel sheet is obtained by heating a slab and performing hot rolling. The chemical composition of the slab contains, by mass%:

[0023] C: 0.020% to 0.150%,

[0024] Si: 3.00% to 4.00%,

[0025] Mn: 0.01% to 0.50%,

[0026] S: 0.0010% to 0.0400%,

[0027] Acid-soluble Al: 0.010% to 0.050%,

[0028] N: 0.002% to 0.020%,

[0029] Bi: 0.0000% to 0.0200%,

[0030] P: 0.000% to 0.100%,

[0031] Sn: 0.00% to 0.50%,

[0032] Cu: 0.00% to 0.50%,

[0033] Cr: 0.00% to 0.50%,

[0034] Sb: 0.00% to 0.20%,

[0035] Mo: 0.00% to 0.10%,

[0036] Nb: 0.0000% to 0.0200%,

[0037] B: 0.0000% to 0.0200%,

[0038] Te: 0.0000% to 0.0200%,

[0039] Ni: 0.00% to 0.20%,

[0040] Se: 0.0000% to 0.0200%,

[0041] The balance is Fe and impurities;

[0042] Hot-rolled sheet annealing process: After subjecting the above hot-rolled steel sheet to hot-rolled sheet annealing to obtain a hot-rolled sheet annealed sheet, the above hot-rolled sheet annealed sheet is immersed in a pickling solution;

[0043] Cold rolling process: A cold-rolled steel sheet is obtained by cold-rolling the above hot-rolled sheet annealed sheet;

[0044] Decarburizing annealing process: A decarburized annealed sheet is obtained by subjecting the above cold-rolled steel sheet to decarburizing annealing;

[0045] Release agent coating process: An annealing release agent containing MgO, Al2O3 and chloride is coated on the surface of the above decarburized annealed sheet;

[0046] Final annealing process: A final annealed sheet is obtained by subjecting the above decarburized annealed sheet coated with the above annealing release agent to final annealing;

[0047] Surface treatment process: The surface of the above final annealed sheet is pickled to obtain a surface-treated steel sheet; and

[0048] Tension-imparting insulating film forming process: It includes: Insulating film forming liquid coating process: An insulating film forming liquid containing 80% by mass or more of aluminum phosphate and silicon dioxide in total is coated on the surface of the above surface-treated steel sheet; and Baking process: By heat-treating the above surface-treated steel sheet coated with the above insulating film forming liquid, a tension-imparting insulating film is formed on the surface of the above surface-treated steel sheet,

[0049] Among them, the heat treatment in the above baking process has a heating process and a soaking process,

[0050] In the above heating process, the average heating rate of the steel sheet in the steel sheet temperature range of 100°C to 600°C is set to 10°C / second to 400°C / second in an atmosphere with an oxygen concentration of 1% to 21% by volume and a dew point of 0°C to 30°C,

[0051] In the above soaking process, the holding time at a constant steel sheet temperature in the range of 800°C to 1000°C is set to 5 seconds to 200 seconds in a soaking atmosphere with a constant value in the range of a hydrogen concentration of 1 to 15% by volume and an atmosphere dew point of -20 to +40°C.

[0052] (2) According to the manufacturing method of the directional electromagnetic steel sheet described in the above (1), among which, it is also possible that:

[0053] In the above annealing parting agent, the content of the above MgO is 0.0 mass% or more and 79.5 mass% or less, the content of the above Al2O3 is 20.0 mass% or more and 99.5 mass% or less, and the balance is the above chloride.

[0054] (3) According to the method for manufacturing a grain-oriented electromagnetic steel sheet described in the above (1) or (2), it is also possible that:

[0055] In the above surface treatment step, the above final annealed sheet is immersed in a treatment liquid containing at least one of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, with a total acid concentration of 1 vol% to 20 vol% and a liquid temperature of 50°C to 90°C for 3 seconds to 60 seconds.

[0056] (4) According to the method for manufacturing a grain-oriented electromagnetic steel sheet described in any one of the above (1) to (3), it is also possible that:

[0057] The above chemical composition of the above slab contains, by mass%, at least one selected from the group consisting of the following elements:

[0058] Bi: more than 0.0000% and 0.0200% or less,

[0059] P: more than 0.000% and 0.100% or less,

[0060] Sn: more than 0.00% and 0.50% or less,

[0061] Cu: more than 0.00% and 0.50% or less,

[0062] Cr: more than 0.00% and 0.50% or less,

[0063] Sb: more than 0.00% and 0.20% or less,

[0064] Mo: more than 0.00% and 0.10% or less,

[0065] Nb: more than 0.0000% and 0.0200% or less,

[0066] B: more than 0.0000% and 0.0200% or less,

[0067] Te: more than 0.0000% and 0.0200% or less,

[0068] Ni: more than 0.00% and 0.20% or less, and

[0069] Se: more than 0.0000% and 0.0200% or less.

[0070] Advantages of the Invention

[0071] According to the above aspects of the present invention, it is possible to manufacture a grain-oriented electromagnetic steel sheet having high film adhesion (secondary film adhesion) without impairing magnetic properties without performing intermediate annealing. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 FIG. is a cross-sectional schematic view of a grain-oriented electromagnetic steel sheet obtained by a method for manufacturing a grain-oriented electromagnetic steel sheet according to an embodiment of the present invention.

[0073] Figure 2 FIG. is a flowchart showing a method for manufacturing a grain-oriented electromagnetic steel sheet according to this embodiment.

[0074] Figure 3 FIG. is a diagram for explaining a baking process in this manufacturing method, where the horizontal axis represents time and the vertical axis represents the temperature of the base metal steel sheet. DETAILED DESCRIPTION OF THE INVENTION

[0075] Hereinafter, a method for manufacturing a grain-oriented electromagnetic steel sheet according to an embodiment of the present invention will be described. However, the present invention is not limited to the configurations and processes disclosed in this embodiment, and various modifications can be made without departing from the gist of the present invention. In addition, for the numerical limit ranges described below, the lower limit value and the upper limit value are included in the range. On the other hand, for values expressed as "exceeding" or "lower than", the value is not included in the numerical range. In addition, unless otherwise specified, % of chemical components refers to mass %.

[0076] Figure 1 FIG. is a cross-sectional schematic view of a grain-oriented electromagnetic steel sheet (grain-oriented electromagnetic steel sheet according to this embodiment) obtained by the method for manufacturing a grain-oriented electromagnetic steel sheet according to this embodiment. As Figure 1 shown in FIG., the grain-oriented electromagnetic steel sheet 1 according to this embodiment, when observed in a cross-sectional view where the cutting direction is parallel to the plate thickness direction, has a base metal steel sheet 2 and an insulating film, i.e., a secondary film 3, disposed on the surface of the base metal steel sheet 2. At the interface between the base metal steel sheet 2 and the secondary film 3, only an oxide layer 4 containing a Fe-Al-P-O compound is formed, and substantially no glass film (hereinafter, also referred to as "primary film") exists.

[0077] As the average plate thickness of the base metal steel sheet 2, 0.17 mm to 0.29 mm can be exemplified. In addition, as the average film thickness of the secondary film 3, 1.0 μm to 6.0 μm can be exemplified.

[0078] In order to improve the iron loss characteristics, it is effective to make the surface of the base steel sheet 2 smooth to facilitate the movement of magnetic domain walls. In addition, it is effective to make the base steel sheet 2 closely adhere to the secondary coating 3, apply tension to the base steel sheet 2, and ensure electrical insulation between multiple sheets of grain-oriented electrical steel sheets 1 that overlap each other. In the grain-oriented electrical steel sheet 1 according to the present embodiment, the surface smoothness of the base steel sheet 2 is ensured by disposing it on the base steel sheet 2 in contact with the secondary coating 3 (there is no primary coating). In addition, as described in the manufacturing method below, by controlling the atmosphere conditions, the average steel sheet heating rate, the holding time of the soaking temperature, etc. in the baking process of the secondary coating 3, an Fe-Al-P-O compound is formed at the interface between the base steel sheet 2 and the secondary coating 3 to ensure the adhesion. Therefore, the grain-oriented electrical steel sheet 1 according to the present embodiment has excellent iron loss characteristics and coating adhesion.

[0079] In the Fe-Al-P-O compound, Fe is derived from the base metal component of the base steel sheet 2, and Al and P are derived from the insulating film forming liquid (insulating film chemical solution). From the base metal side toward the film side, Fe ions diffuse to the film side. On the other hand, from the film side toward the base metal side, Al and P ions diffuse / concentrate. By the association of Fe ions with Al or P ions, chemical bonds are generated, and as a result, an Fe-Al-P-O compound is formed. That is, as a result of the chemical bonding between the ions in the film and the base metal (as a result of the film closely adhering to the base metal), an Fe-Al-P-O compound is observed at the interface between the film and the base metal.

[0080] Next, use Figure 2 and Figure 3 to describe the manufacturing method of the grain-oriented electrical steel sheet according to the present embodiment. The following manufacturing method is an example, and appropriate changes can be made as long as it does not affect the formation of the Fe-Al-P-O compound. Figure 2 is a flowchart showing the manufacturing method of the grain-oriented electrical steel sheet according to the present embodiment. Figure 3 is a diagram for explaining the baking process in this manufacturing method, where the horizontal axis is time and the vertical axis represents the temperature of the base steel sheet.

[0081] The manufacturing method of the directional electromagnetic steel sheet according to this embodiment mainly includes the following processes: Hot rolling process: A hot-rolled steel sheet is obtained by heating a slab (steel ingot) having a specified chemical composition and performing hot rolling; Hot-rolled sheet annealing process: After performing hot-rolled sheet annealing on the hot-rolled steel sheet to obtain a hot-rolled sheet annealed sheet, the hot-rolled sheet annealed sheet is immersed in a pickling solution for pickling; Cold rolling process: A cold-rolled steel sheet is obtained by performing cold rolling on the hot-rolled sheet annealed sheet; Decarburizing annealing process: A decarburized annealed sheet is obtained by performing decarburizing annealing on the cold-rolled steel sheet; Release agent coating process: A release agent for annealing is coated on the surface of the decarburized annealed sheet; Final annealing process: A final annealed sheet is obtained by performing final annealing on the decarburized annealed sheet coated with the release agent for annealing; Surface treatment process: A surface-treated steel sheet is obtained by pickling the surface of the final annealed sheet; and Tension-imparting insulating film forming process: It includes an insulating film chemical solution coating process for coating an insulating film forming solution and a heating-up process and a soaking process performed after the heating-up process, and a tension-imparting insulating film containing aluminum phosphate and silicon dioxide is formed on the surface of the surface-treated steel sheet.

[0082] Moreover, in the above heating-up process, the average heating rate of the steel sheet in the steel sheet temperature range of 100°C to 600°C is set to 10°C / second to 400°C / second in an atmosphere with an oxygen concentration of 1% by volume to 21% by volume and a dew point of 0°C to 30°C. Further, in the above soaking process, the holding time at a constant steel sheet temperature in the range of 800°C to 1000°C is set to 5 seconds to 200 seconds in a soaking atmosphere with a hydrogen concentration of 1 to 15% by volume and an atmosphere dew point in the range of -20 to +40°C.

[0083] The details of the above processes will be further described below. In the following description, if the conditions of each process are not described, well-known conditions can be appropriately applied.

[0084] [Hot rolling process]

[0085] In the hot rolling process, a steel ingot (for example, a slab such as a steel slab) having a specified chemical composition is hot rolled. For example, the chemical composition of the slab (steel ingot) supplied to the hot rolling process contains, by mass%:

[0086] C: 0.020% to 0.150%,

[0087] Si: 3.00% to 4.00%,

[0088] Mn: 0.01% to 0.50%,

[0089] S: 0.0010% to 0.0400%,

[0090] Acid-soluble Al: 0.010% to 0.050%,

[0091] N: 0.002% to 0.020%,

[0092] Bi: 0.0000% to 0.0200%,

[0093] P: 0.000% to 0.100%,

[0094] Sn: 0.00% to 0.50%,

[0095] Cu: 0.00% to 0.50%,

[0096] Cr: 0.00% to 0.50%,

[0097] Sb: 0.00% to 0.20%,

[0098] Mo: 0.00% to 0.10%,

[0099] Nb: 0.0000% to 0.0200%,

[0100] B: 0.0000% to 0.0200%,

[0101] Te: 0.0000% to 0.0200%,

[0102] Ni: 0.00% to 0.20%,

[0103] Se: 0.0000% to 0.0200%,

[0104] The balance may contain Fe and impurities.

[0105] In addition, the chemical composition of the above slab (bloom) may also contain at least one selected from the group consisting of the following elements in mass%:

[0106] Bi: more than 0.0000% and 0.0200% or less,

[0107] P: more than 0.000% and 0.100% or less,

[0108] Sn: more than 0.00% and 0.50% or less,

[0109] Cu: more than 0.00% and 0.50% or less,

[0110] Cr: more than 0.00% and 0.50% or less,

[0111] Sb: more than 0.00% and 0.20% or less,

[0112] Mo: more than 0.00% and 0.10% or less,

[0113] Nb: More than 0.0000% and 0.0200% or less,

[0114] B: More than 0.0000% and 0.0200% or less,

[0115] Te: More than 0.0000% and 0.0200% or less,

[0116] Ni: More than 0.00% and 0.20% or less,

[0117] Se: More than 0.0000% and 0.0200% or less.

[0118] C: 0.020% - 0.150%

[0119] C (carbon) is a basic element for the steel billet (slab). C is contained for the purpose of increasing the aggregation degree of Goss orientation in secondary recrystallization. The C content required for improving magnetic properties is 0.020% or more as a slab, preferably 0.040% or more, and more preferably 0.050% or more. However, if C remains in excess in the final product, it can become a factor for deterioration of iron loss. Therefore, decarburization treatment is required using a decarburization annealing process. As a slab, when the C content exceeds 0.150%, decarburization treatment becomes difficult, so the C content of the slab is 0.150% or less, preferably 0.120% or less, and more preferably 0.100% or less.

[0120] Si: 3.00% - 4.00%

[0121] Si (silicon) is a basic element for the steel billet (slab). If the Si content is less than 3.00%, eddy current loss cannot be sufficiently reduced, so good magnetic properties cannot be obtained. Therefore, the Si content is set to 3.00% or more. The Si content is preferably 3.10% or more, and more preferably 3.20% or more. On the other hand, if the Si content exceeds 4.00%, the steel plate becomes brittle and the plate passing property during manufacturing deteriorates significantly. Therefore, the Si content is set to 4.00% or less. The Si content is preferably 3.80% or less, and more preferably 3.60% or less.

[0122] Mn: 0.01% - 0.50%

[0123] Mn (Manganese) is an essential element for steel billets (slabs). If the Mn content is less than 0.01%, it is difficult to form MnS (MnSe in the case of using Se as part of S) that functions as an inhibitor, and secondary recrystallization does not proceed sufficiently, resulting in poor magnetic properties. Therefore, the Mn content is set at 0.01% or more. The Mn content is preferably 0.03% or more, more preferably 0.06% or more. On the other hand, if the Mn content exceeds 0.50%, the steel undergoes a phase change during final annealing, and secondary recrystallization does not proceed sufficiently, resulting in poor magnetic properties. Therefore, the Mn content is set at 0.50% or less. The Mn content is preferably 0.30% or less, more preferably 0.20% or less.

[0124] S: 0.0010% - 0.0400%

[0125] Se: 0.0000 - 0.0200%

[0126] S (Sulfur) is an essential element for steel billets (slabs). S is an element that forms MnS as an inhibitor. The S content is 0.0010% or more as a slab, preferably 0.0100% or more, more preferably 0.0150% or more. On the other hand, as a slab, if the S content exceeds 0.0400%, it becomes a cause of hot brittleness, and sometimes hot rolling becomes difficult. The S content is 0.0400% or less as a slab, preferably 0.0350% or less, more preferably 0.0300% or less. If S also remains in excess in the final product, it can be a cause of magnetic degradation. Therefore, S also needs to be removed (purified) from the base steel plate during final annealing.

[0127] Se (Selenium) is also an element that forms MnSe, so Se can also be used for a part of S (the Se content can also exceed 0.0000%). In the case where Se is present in excess, secondary recrystallization becomes unstable, which may be a cause of magnetic degradation. Therefore, the Se content must be set at 0.0000% or more and 0.0200% or less. The Se content is preferably 0.0000% or more and 0.0150% or less, more preferably 0.0000% or more and 0.0100% or less.

[0128] Acid-soluble Al: 0.010% - 0.050%

[0129] Acid-soluble Al is an essential element for steel billets (slabs). Acid-soluble Al is an element necessary for forming AlN as an inhibitor and improving magnetic properties. The acid-soluble Al content is 0.010% or more, preferably 0.015% or more, and more preferably 0.020% or more for slabs. On the other hand, when the acid-soluble Al is excessively contained in the slab, embrittlement sometimes becomes significant. The acid-soluble Al content is 0.050% or less, preferably 0.040% or less, and more preferably 0.030% or less for slabs. Similar to N, acid-soluble Al needs to be removed (purified) from the base steel plate during final annealing.

[0130] N: 0.002% - 0.020%

[0131] N (nitrogen) is an essential element for steel billets (slabs). N is an element required for forming AlN as an inhibitor and increasing the aggregation degree of Goss orientation during secondary recrystallization. The N content required for inhibitor formation is 0.002% or more, preferably 0.004% or more, and more preferably 0.006% or more for slabs. On the other hand, as a slab, if the N content exceeds 0.020%, blisters (voids) are generated in the steel plate during cold rolling, and the strength of the steel plate increases, sometimes deteriorating the through-feedability during manufacturing. The N content is 0.020% or less, preferably 0.015% or less, and more preferably 0.010% or less for slabs. Similar to C, if N remains excessively in the final product, it can cause magnetic degradation. Therefore, N needs to be removed (purified) during final annealing.

[0132] P: 0.000% - 0.100%

[0133] P (phosphorus) is a selective element for steel billets (slabs). If the P content exceeds 0.100%, sometimes the workability of the steel plate is significantly reduced. Therefore, the P content only needs to be 0.100% or less. The P content is preferably 0.070% or less, and more preferably 0.030% or less. On the other hand, the lower limit value of the P content is not particularly limited and can also be 0.000%. However, since P has the effect of improving the texture and magnetic properties of the steel plate, the P content can also be set to exceed 0.000%, or can be set to 0.005% or more.

[0134] Bi: 0.0000% - 0.0200%

[0135] Bi is a selectable element for steel billets (slabs). If the Bi content exceeds 0.0200%, the sheet passing property during cold rolling may sometimes deteriorate. In addition, if the purification during final annealing is insufficient and Bi remains in excess, it may sometimes have an adverse effect on magnetic properties. Therefore, the Bi content only needs to be 0.0200% or less. The Bi content is preferably 0.0150% or less, more preferably 0.0100% or less. On the other hand, the lower limit value of the Bi content is not particularly limited and can also be 0.0000%. However, since Bi has the effect of improving magnetic properties, the Bi content can also be set to exceed 0.0000% or can be set to 0.0005% or more.

[0136] Sn: 0.00% to 0.50%

[0137] Sn is a selectable element for steel billets (slabs). If the Sn content exceeds 0.50%, secondary recrystallization becomes unstable and may sometimes have an adverse effect on magnetic properties. Therefore, the Sn content only needs to be 0.50% or less. The Sn content is preferably 0.40% or less, more preferably 0.30% or less. On the other hand, the lower limit value of the Sn content is not particularly limited and can also be 0.00%. However, since Sn has the effect of improving the aggregation degree of Goss orientation and improving magnetic properties, the Sn content can also be set to exceed 0.00% or can be set to 0.01% or more, and further can be set to 0.03% or more.

[0138] Cu: 0.00% to 0.50%

[0139] Cu is a selectable element for steel billets (slabs). If the Cu content exceeds 0.50%, the steel sheet may sometimes embrittle during hot rolling. Therefore, the Cu content only needs to be 0.50% or less. The Cu content is preferably 0.40% or less, more preferably 0.30% or less. On the other hand, the lower limit value of the Cu content is not particularly limited and can also be 0.00%. However, since Cu has the effect of improving the aggregation degree of Goss orientation and improving magnetic properties, the Cu content can also be set to exceed 0.00% or can be set to 0.01% or more, and further can be set to 0.03% or more.

[0140] Cr: 0.00% to 0.50%

[0141] Cr (chromium) is a selective element for steel billets (slabs). If the Cr content exceeds 0.50%, Cr oxides are formed, which sometimes have an adverse effect on magnetic properties. Therefore, the Cr content only needs to be 0.50% or less. The Cr content is preferably 0.40% or less, more preferably 0.30% or less. On the other hand, the lower limit value of the Cr content is not particularly limited and can also be 0.00%. However, since Cr has the effect of improving the aggregation degree of the Goss orientation and thus improving magnetic properties, the Cr content can also be set to exceed 0.00%, can also be set to 0.01% or more, and further can also be set to 0.03% or more.

[0142] Sb: 0.00% - 0.20%

[0143] Sb (antimony) is a selective element for steel billets (slabs). If the Sb content exceeds 0.20%, it sometimes has an adverse effect on magnetic properties. Therefore, the Sb content only needs to be 0.20% or less. The Sb content is preferably 0.15% or less, more preferably 0.10% or less. On the other hand, the lower limit value of the Sb content is not particularly limited and can also be 0.00%. However, since Sb has the effect of stabilizing secondary recrystallization by functioning as an inhibitor, the Sb content can also be set to exceed 0.00%, and can also be set to 0.01% or more.

[0144] Mo: 0.00% - 0.10%

[0145] Mo (molybdenum) is a selective element for steel billets (slabs). If the Mo content exceeds 0.10%, sometimes problems occur in the rollability of the steel sheet. Therefore, the Mo content only needs to be 0.10% or less. The Mo content is preferably 0.05% or less, more preferably 0.03% or less. On the other hand, the lower limit value of the Mo content is not particularly limited and can also be 0.00%. However, since Mo has the effect of improving the aggregation degree of the Goss orientation and thus improving magnetic properties, the Mo content can also be set to exceed 0.00%, and can also be set to 0.01% or more.

[0146] Nb: 0.0000% - 0.0200%

[0147] Nb (niobium) is a selective element for steel billets (slabs). If the Nb content exceeds 0.0200%, sometimes secondary recrystallization becomes unstable. Therefore, the Nb content only needs to be 0.0200% or less. The Nb content is preferably 0.0100% or less, more preferably 0.0050% or less. On the other hand, the lower limit value of the Nb content is not particularly limited and can also be 0.0000%. However, since Nb has the effect of stabilizing secondary recrystallization, the Nb content can also be set to exceed 0.0000%, and can also be set to 0.0005% or more.

[0148] B: 0.0000% to 0.0200%

[0149] B (boron) is a selectable element for steel billets (slabs). If the B content exceeds 0.0200%, sometimes the secondary recrystallization becomes unstable. Therefore, the B content only needs to be 0.0200% or less. The B content is preferably 0.0100% or less, more preferably 0.0050% or less. On the other hand, the lower limit value of the B content is not particularly limited and can also be 0.0000%. However, since B has the effect of stabilizing the secondary recrystallization, the B content can also be set to exceed 0.0000% or can be set to 0.0005% or more.

[0150] Te: 0.0000% to 0.0200%

[0151] Te (tellurium) is a selectable element for steel billets (slabs). If the Te content exceeds 0.0200%, sometimes it fractures during hot rolling and cold rolling. Therefore, the Te content only needs to be 0.0200% or less. The Te content is preferably 0.0150% or less, more preferably 0.0100% or less. On the other hand, the lower limit value of the Te content is not particularly limited and can also be 0.0000%. However, since Te has the effect of stabilizing the secondary recrystallization, the Te content can also be set to exceed 0.0000% or can be set to 0.0005% or more.

[0152] Ni: 0.00% to 0.20%

[0153] Ni (nickel) is a selectable element for steel billets (slabs). Ni is an effective element for influencing the crystal orientation rotation generated during cold rolling and obtaining a texture preferred for secondary recrystallization. In addition, it is also an effective element for increasing the specific resistance and reducing iron loss. Therefore, it can also be contained. When containing Ni, in order to obtain these effects, it is preferably to set the Ni content to exceed 0.00%, more preferably to set it to 0.01% or more.

[0154] On the other hand, when the Ni content exceeds 0.20%, sometimes the secondary recrystallization becomes unstable. Therefore, when contained, the Ni content is set to 0.20% or less. The Ni content is preferably 0.15% or less, more preferably 0.10% or less.

[0155] The steel billets (slabs) for the hot rolling process can also contain impurities. "Impurities" refer to elements mixed in from ores, scrap iron as raw materials or from the manufacturing environment, etc. during the industrial production of steel.

[0156] The chemical composition of the steel billet (slab) for the hot rolling process can be determined by general analytical methods. For example, it can be determined using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). For acid-soluble Al, it can be determined by subjecting the filtrate obtained by heating and decomposing the sample with acid to ICP-AES. In addition, C and S can be determined by combustion-infrared absorption method, and N can be determined by inert gas fusion-thermal conductivity method.

[0157] In the hot rolling process, first, the slab (steel billet) is subjected to a heating treatment. The heating temperature can be set, for example, to 1200 °C or higher and 1600 °C or lower. The heating temperature is preferably 1280 °C or higher and preferably 1500 °C or lower. Next, the heated slab is hot rolled. The thickness of the hot rolled steel sheet after hot rolling is preferably in the range of 2.0 mm or more and 3.0 mm or less, for example.

[0158] [Hot rolled sheet annealing process]

[0159] In the hot rolled sheet annealing process, the hot rolled steel sheet obtained in the hot rolling process is annealed. Through this hot rolled sheet annealing, recrystallization occurs in the steel sheet, and finally good magnetic properties can be achieved. The conditions for hot rolled sheet annealing are not particularly limited, but for example, it is sufficient to anneal the hot rolled steel sheet in the temperature range of 900 °C to 1200 °C for 10 seconds to 5 minutes.

[0160] Immediately after this hot rolled sheet annealing process, pickling is carried out. In this pickling, the surface of the hot rolled steel sheet after hot rolled sheet annealing is immersed in a pickling solution and pickled to obtain a hot rolled sheet annealed sheet.

[0161] [Cold rolling process]

[0162] In the cold rolling process, the hot rolled sheet annealed sheet after the hot rolled sheet annealing process is subjected to single cold rolling or multiple cold rollings with intermediate annealing in between. Here, the so-called "single time" means carrying out single pass or multiple passes of cold rolling or intermediate annealing once. When intermediate annealing is carried out between cold rollings, the heating method for intermediate annealing is not particularly limited. In addition, cold rolling can be carried out in more than 3 times with intermediate annealing in between, but since the manufacturing cost increases, it is preferably set to single or double cold rolling.

[0163] The final cold rolling reduction ratio in cold rolling (the cumulative cold rolling ratio without intermediate annealing, or the cumulative cold rolling ratio after the last intermediate annealing in the case of intermediate annealing) may be set, for example, in the range of 80% or more and 95% or less. By setting the final cold rolling reduction ratio within the above range, the aggregation degree in the {110}<001> orientation can ultimately be increased, and the destabilization of secondary recrystallization can be suppressed. The thickness of the cold rolled steel sheet after cold rolling usually becomes the thickness of the base steel sheet (final thickness) of the finally manufactured grain-oriented electrical steel sheet. The thickness of the cold rolled steel sheet after cold rolling is preferably, for example, in the range of 0.15 mm or more and 0.30 mm or less.

[0164] [Decarburizing annealing process]

[0165] In the decarburizing annealing process, the cold rolled steel sheet obtained in the cold rolling process is subjected to decarburizing annealing. Through this decarburizing annealing, C contained in the cold rolled steel sheet is removed, and primary recrystallization occurs. In order to remove C contained in the cold rolled steel sheet, the decarburizing annealing is preferably carried out in a humid atmosphere. For example, in a humid atmosphere, annealing can be carried out in the temperature range of 700 °C to 1000 °C for 10 seconds to 10 minutes. In addition, from the viewpoint of magnetic property improvement, in the heating process, the temperature range of 500 °C to 800 °C can also be set to be 100 °C / second or more and 3000 °C / second or less.

[0166] In addition, before coating the annealing separating agent after decarburizing annealing, nitriding treatment can also be carried out. In the nitriding treatment, the decarburized annealing sheet after decarburizing annealing is subjected to nitriding treatment to manufacture a nitriding treated steel sheet. For example, in an atmosphere containing gases with nitriding ability such as hydrogen, nitrogen, and ammonia, annealing can be carried out in the temperature range of 700 °C to 850 °C for 10 seconds to 60 seconds.

[0167] [Coating process of separating material]

[0168] In the coating process of separating material, in order to prevent the steel sheet rolled into a coil shape from sintering during the subsequent final annealing process, before the final annealing process, an annealing separating agent is coated on the decarburized annealing sheet obtained in the decarburizing annealing process (further subjected to nitriding treatment as required) and dried.

[0169] The annealing separating agent contains magnesium oxide (MgO), aluminum oxide (Al2O3), and chloride. The total content of MgO and Al2O3 in each component of the annealing separating agent is preferably 80.0 mass% or more and 99.5 mass% or less in terms of solid component conversion, and the remaining part is chloride. That is, the content of chloride in the annealing separating agent is the value obtained by subtracting the total content of MgO and Al2O3 from 100 mass%, and is preferably 0.5 mass% or more and 20.0 mass% or less. In the above remaining part, impurities may sometimes be included.

[0170] In the annealing release agent, the content obtainable as elemental MgO is preferably 0.0 mass% or more and 79.5 mass% or less, and the content obtainable as elemental Al₂O₃ is preferably 20.0 mass% or more and 99.5 mass% or less.

[0171] The total content of MgO and Al₂O₃ is more preferably 85.0 mass% or more, and further preferably 90.0 mass% or more. In addition, the total content of MgO and Al₂O₃ is more preferably 99.0 mass% or less, and further preferably 95.0 mass% or less.

[0172] On the other hand, the content of the remaining chloride is more preferably 1.0 mass% or more, and further preferably 5.0 mass% or more. In addition, the chloride content is more preferably 15.0 mass% or less, and further preferably 10.0 mass% or less.

[0173] There is no special designation for the chloride, for example, bismuth oxychloride (BiOCl), bismuth trichloride (BiCl₃), calcium chloride, iron chloride, cobalt chloride, nickel chloride, etc. are considered.

[0174] [Final annealing process]

[0175] In the final annealing process immediately following the release material coating process, final annealing is performed on the decarburized annealing sheet pre-coated with the annealing release agent. The final annealing is performed by annealing the steel sheet in a coiled state for a long time.

[0176] The annealing conditions for the final annealing are not particularly limited, and known conditions can be suitably used. For example, in the final annealing, the decarburized annealing sheet after coating the annealing release agent and drying is held in a temperature range of 1000 °C or more and 1300 °C or less for 10 hours or more and 60 hours or less. The atmosphere during the final annealing is set to a nitrogen atmosphere or a mixed atmosphere of nitrogen and hydrogen, for example. In addition, after the final annealing, the surface of the final annealed sheet can be washed with water to remove powder.

[0177] Through this final annealing, secondary recrystallization is caused in the steel sheet, and the crystal orientation proceeds along the {110}<001> orientation. The easy magnetization axis of this secondary recrystallized structure is aligned in the rolling direction, and the grains are coarse. Due to this secondary recrystallized structure, excellent magnetic properties can be obtained. In this embodiment, since the annealing release agent contains chloride, the formation of the primary film can be suppressed, and the surface of the final annealed sheet becomes smooth.

[0178] In addition, the atmosphere during the final annealing can be changed to a hydrogen atmosphere for purification treatment. Through this purification treatment, elements such as Al, N, S (when Se is used as part of S, Se is also included) contained as steel components in the steel sheet are discharged outside the system, and the steel sheet is purified.

[0179] After obtaining the final annealed sheet through this final annealing process, the surface treatment process is carried out without intermediate annealing.

[0180] [Surface treatment process]

[0181] In this process, the surface of the final annealed sheet obtained in the final annealing process is pickled to obtain a surface-treated steel sheet. The pickling conditions at this time are not particularly specified. For example, the final annealed sheet may be immersed in an acid (treatment solution) of a specific concentration. Preferably, the treatment solution contains at least one of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, the total acid concentration is 1 vol% to 20 vol%, and the liquid temperature is 50°C to 90°C. It is preferable to use this treatment solution to perform surface treatment on the final annealed sheet for 3 seconds to 60 seconds.

[0182] In this process, the removal of the annealing release agent attached to the surface of the final annealed sheet is carried out. At this time, it is preferable to perform surface treatment under conditions where erosion pits are not generated on the surface of the final annealed sheet. For this purpose, the above-mentioned conditions can be controlled comprehensively and inseparably. For example, if the pickling intensity is increased for a certain condition among the above conditions, it can be changed in such a way that the pickling intensity is weakened for other conditions among the above conditions, so as to ensure the smooth state of the surface. As long as those skilled in the art can perform surface control including pickling behavior, as long as the influence of the above-mentioned conditions on the pickling intensity is considered, the above-mentioned conditions can be combined to control the surface state.

[0183] If the total acid concentration of the treatment solution is less than 1 vol%, it is difficult to remove the annealing release agent on the surface of the final annealed sheet. When the annealing release agent remains on the surface, it is difficult to form internal oxidized SiO2 in the subsequent tension-imparting insulating film forming process. On the other hand, if the total acid concentration of the treatment solution exceeds 20 vol%, erosion pits are likely to be formed on the surface of the final annealed sheet. Similarly, if the liquid temperature of the treatment solution is lower than 50°C, an active surface state cannot be obtained. In addition, if the liquid temperature of the treatment solution exceeds 90°C, erosion pits are likely to be formed. Similarly, if the treatment time of the surface treatment is less than 3 seconds, an active surface state cannot be obtained. In addition, if the treatment time of the surface treatment exceeds 60 seconds, erosion pits are likely to be formed.

[0184] [Tension-imparting insulating film forming process]

[0185] The tension-imparting insulating film forming process is carried out following the surface treatment process. This tension-imparting insulating film forming process is a process of forming a tension-imparting insulating film containing aluminum phosphate and silica on the surface of the surface-treated steel sheet, and has an insulating film coating solution coating process and a baking process.

[0186] In the insulating film liquid coating process, an insulating film forming liquid containing aluminum phosphate and silica (hereinafter, also referred to as "insulating film liquid medicine") is coated on the surface of the surface-treated steel sheet. The total content of aluminum phosphate and silica is 80% by mass or more. The total content of aluminum phosphate and silica is preferably 90% by mass or more, and more preferably 95% by mass or more. In the insulating film liquid medicine, chromium is preferably not contained.

[0187] The silica is not limited to silica of a specific property. The particle size is also not limited to a specific particle size, but is preferably 200 nm (number average particle diameter) or less. For example, 5 nm to 30 nm is sufficient. If the particle size exceeds 200 nm, it may settle in the coating liquid.

[0188] In the baking process following the insulating film liquid coating process, by performing heat treatment on the surface-treated steel sheet coated with the insulating film liquid medicine, an insulating film (secondary film 3) is formed on the surface of the surface-treated steel sheet. This insulating film (tension-imparting insulating film) reduces the iron loss as a single steel sheet by imparting tension to the oriented electrical steel sheet, and when the oriented electrical steel sheets are laminated and used, it reduces the iron loss as a core by ensuring electrical insulation between the steel sheets.

[0189] For the heat treatment performed in the baking process, use Figure 3 is described. Figure 3 It is a diagram illustrating the baking process, where the horizontal axis is time and the vertical axis represents the temperature of the base steel sheet.

[0190] The baking process includes a heating process P1 in which the surface-treated steel sheet is heated to raise its temperature and a soaking process P2 performed after the heating process P1.

[0191] <Heating process P1>

[0192] The heating process P1 is an important process for controlling the interaction between the surface of the surface-treated steel sheet and the interface of the insulating film liquid medicine in contact with this surface. In the heating process P1, the average heating rate of the steel sheet in the steel sheet temperature range of 100 °C to 600 °C is set to 10 °C / second to 400 °C / second in an atmosphere with an oxygen concentration of 1% by volume to 21% by volume and a dew point of 0 °C to 30 °C.

[0193] In the heating process P1, by setting the atmosphere during heating within the above range, the reduction of Al(PO)4 and SiO2 in the insulating film liquid medicine can be suppressed, and thus high film adhesion can be obtained.

[0194] During the heating process P1, Fe dissolves from the surface-treated steel sheet into the insulating film chemical solution, and Fe atoms gradually diffuse into the insulating film chemical solution. Fe is dissolved in Al(PO)4, and nuclei of Fe-Al-P-O compounds are formed on the surface of the base steel sheet. If the average heating rate of the steel sheet during the heating process P1 exceeds 400 °C / second, Fe-Al-P-O compounds will not be formed. Therefore, the average heating rate of the steel sheet is set to 400 °C / second or less.

[0195] On the contrary, if the heating process P1 is set to slow heating and the average heating rate of the steel sheet is set to less than 10 °C / second, FeO and Fe3O4 are formed at the interface between the insulating film chemical solution and the surface of the base steel sheet. These FeO and Fe3O4 become the starting points of film peeling and thus are factors that hinder the improvement of film adhesion. Therefore, the average heating rate of the steel sheet is set to 10 °C / second or more. The average heating rate of the steel sheet is preferably 20 °C / second or more, and more preferably 50 °C / second or more.

[0196] The temperature of the steel sheet at which FeO and Fe3O4 precipitate is 400 °C to 600 °C. Therefore, it is considered to control the average heating rate of the steel sheet in the range of 10 °C / second to 400 °C at least in the temperature range of 400 °C to 600 °C. However, in order to control the average heating rate of the steel sheet only in such a narrow temperature range as 400 °C to 600 °C, special equipment is required. Therefore, the start of control of the average heating rate of the steel sheet can also be set to a relatively low temperature range of about 100 °C. However, in this case, the average heating rate of the steel sheet in the temperature range of 400 °C to 600 °C is also controlled in the range of 10 °C / second to 400 °C.

[0197] In addition, if the oxygen concentration in the atmosphere is less than 1% by volume, oxide films of Fe2SiO4 and SiO2 are formed at the interface between the insulating film chemical solution and the steel sheet. These oxide films have the effect of inhibiting the formation of Fe-Al-P-O, so the film adhesion becomes poor. On the other hand, if the oxygen concentration exceeds 21% by volume, FeO and Fe3O4 are formed at the interface between the insulating film chemical solution and the steel sheet, and the film adhesion becomes poor.

[0198] In addition, if the dew point of the atmosphere is less than 0 °C, oxide films of Fe2SiO4 and SiO2 are formed at the interface, so the film adhesion becomes poor. On the other hand, if the dew point exceeds 30 °C, FeO and Fe3O4 are formed at the interface, and the film adhesion becomes poor.

[0199] At the moment when the temperature of the steel plate reaches 600°C, nuclei of Fe-Al-P-O compounds necessary in sufficient amounts are formed on the surface of the base steel plate. Moreover, the thermal cycle from the moment when this 600°C is reached until the start of the soaking process P2 has little effect on the nuclei of the Fe-Al-P-O compounds. Therefore, it is also possible to temporarily lower the temperature to room temperature after the temperature of the steel plate reaches 600°C and then start reheating to perform the soaking process P2. Or, as shown in Figure 3 , after the temperature of the steel plate reaches 600°C, the temperature is also continued to be raised and heated to the soaking temperature T1 (a constant steel plate temperature within the range of 800°C to 1000°C), and then the soaking process P2 is directly continued. In either of these cases, the temporarily generated nuclei of the Fe-Al-P-O compounds remain directly on the surface of the base steel plate.

[0200] <Soaking process P2>

[0201] In the subsequent soaking process P2, the temperature of the steel plate is maintained at Figure 3 the soaking temperature T1. Specifically, the soaking temperature T1 is a constant steel plate temperature selected from the range of 800°C to 1000°C. Moreover, in the soaking process P2, the soaking atmosphere is, for example, an inert gas (nitrogen or argon), a mixed gas of hydrogen and water vapor. At this time, the hydrogen concentration in the soaking atmosphere is set to 1 to 15 vol%, and the dew point is set to -20 to +40°C. Moreover, the temperature holding time of the soaking process P2 is set within the range of 5 seconds to 200 seconds.

[0202] If the holding time is less than 5 seconds, the time required for the formation of the nuclei of the Fe-Al-P-O compounds generated in the heating process P1 cannot be ensured, and the film adhesion becomes poor. On the other hand, if it exceeds 200 seconds, the secondary film crystallizes, and thus the film adhesion becomes poor.

[0203] This soaking process P2 is an important process for growing the nuclei of the Fe-Al-P-O compounds generated in the heating process P1. In particular, the control of both the soaking temperature and the soaking atmosphere is important. When the soaking temperature T1 is lower than 800°C, the nuclei of the Fe-Al-P-O compounds cannot grow sufficiently, and as a result, sufficient film adhesion cannot be ensured. Therefore, the soaking temperature T1 is set to 800°C or higher. The soaking temperature T1 is preferably 820°C or higher, more preferably 840°C or higher.

[0204] On the contrary, when the soaking temperature T1 exceeds 1000°C, the generated secondary film crystallizes, and there is a concern about film peeling. Therefore, from the viewpoint of preventing deterioration of the film adhesion, the soaking temperature T1 is set to 1000°C or lower. The soaking temperature T1 is preferably 950°C or lower, more preferably 900°C or lower.

[0205] For the above reasons, it is necessary to control the soaking temperature T1 in the soaking process P2 to a constant steel plate temperature within the range of 800°C to 1000°C.

[0206] In addition, in the soaking process P2, the control of the soaking atmosphere is also important. Specifically, it is controlled such that the hydrogen concentration in the annealing atmosphere is set to 1 to 15 vol%, and the atmosphere dew point becomes a substantially constant value (e.g., ±5°C) within the range of -20 to +40°C. Through this control, the nuclei of the Fe-Al-P-O compound generated in the heating process P1 grow most stably. If the soaking process P2 is carried out with a hydrogen concentration lower than 1%, there is a concern about the deterioration of the film adhesion factor, i.e., Fe-based oxides such as FeO. Therefore, the hydrogen concentration is set to 1 vol% or more. The hydrogen concentration is preferably 2 vol% or more, and more preferably 3 vol% or more.

[0207] In addition, when the atmosphere dew point is lower than -20°C, the nuclei of the Fe-Al-P-O compound generated in the heating process P1 are reduced, so the film adhesion deteriorates. The atmosphere dew point is set to -20°C or more. The atmosphere dew point is preferably 0°C or more, and more preferably 15°C or more.

[0208] On the other hand, when the hydrogen concentration in the atmosphere exceeds 15 vol%, FeP may be generated from the Fe-Al-P-O compound. FeP causes the formation of voids in the secondary film. If a large number of voids are generated in the secondary film, it becomes the cause of film peeling, significantly reducing the film adhesion. Therefore, the hydrogen concentration is set to 15 vol% or less. The hydrogen concentration is preferably 10 vol% or less, and more preferably 5 vol% or less.

[0209] In addition, when the atmosphere dew point exceeds +40°C, there is a concern about the deterioration of the film adhesion factor, i.e., Fe-based oxides such as FeO. Therefore, the atmosphere dew point is +40°C or less. The atmosphere dew point is preferably +35°C or less, and more preferably +30°C or less.

[0210] Through the above respective processes, the Figure 1 directional electromagnetic steel sheet 1 shown in

[0211] After the formation of the secondary film, flattening annealing for shape correction may also be carried out as needed. By performing flattening annealing on the steel sheet, the iron loss can be further reduced.

[0212] In addition, before or after the secondary film formation process, magnetic domain control treatment may also be carried out as needed. By performing magnetic domain control treatment, the iron loss of the directional electromagnetic steel sheet can be further reduced.

[0213] When performing the magnetic domain control treatment before the secondary film formation process, it is sufficient to form linear or dot-shaped groove portions extending in a direction intersecting the rolling direction at a prescribed interval along the rolling direction. Further, when performing the magnetic domain control treatment after the secondary film formation process, it is sufficient to form linear or dot-shaped stress and strain portions extending in a direction intersecting the rolling direction at a prescribed interval along the rolling direction. By the magnetic domain control treatment, the width of the 180° magnetic domain becomes narrow (the 180° magnetic domain is refined).

[0214] When forming the groove portions, a mechanical groove formation method using gears or the like, a chemical groove formation method using electrolytic etching, a thermal groove formation method using laser irradiation, etc. can be applied. Further, when forming the stress and strain portions, laser beam irradiation, electron beam irradiation, etc. can be applied.

[0215] According to the method for manufacturing a grain-oriented electrical steel sheet described above, a grain-oriented electrical steel sheet having high magnetic properties and high film adhesion can be manufactured without setting the intermediate annealing process, which has been necessary in the past, as essential.

[0216] Examples

[0217] Next, the effects of one aspect of the present invention will be described more specifically by way of examples. However, the various conditions in these examples are illustrations adopted for confirming the feasibility and effects of the present invention, and the present invention is not limited only to these illustrations. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

[0218] First, in the hot rolling process, slabs (steel billets) No. a to l having the chemical compositions shown in Table 1 below were prepared.

[0219]

[0220] Specifically, in all of slabs No. a to l, the chemical composition was set to include, by mass%:

[0221] C: 0.020% to 0.150%,

[0222] Si: 3.00% to 4.00%,

[0223] Mn: 0.01% to 0.50%,

[0224] S: 0.0010% to 0.0400%,

[0225] Acid-soluble Al: 0.010% to 0.050%,

[0226] N: 0.002% to 0.020%,

[0227] The remaining part contains Fe and impurities.

[0228] In addition, in slabs No. c to l, the chemical composition further contains at least one selected from the group consisting of the following elements by mass%:

[0229] Bi: 0.0200% or less,

[0230] P: 0.100% or less,

[0231] Sn: 0.50% or less,

[0232] Cu: 0.50% or less,

[0233] Cr: 0.50% or less,

[0234] Sb: 0.20% or less,

[0235] Mo: 0.10% or less,

[0236] Nb: 0.0200% or less,

[0237] B: 0.0200% or less,

[0238] Te: 0.0200% or less,

[0239] Ni: 0.20% or less,

[0240] Se: 0.0200% or less.

[0241] Moreover, these slabs No. a to l are heated to 1350 °C and subjected to hot rolling to produce a hot-rolled steel sheet with a thickness of 2.3 mm.

[0242] Next, in the hot-rolled sheet annealing process, the hot-rolled steel sheet obtained in the hot-rolling process is annealed at 1100 °C for 120 seconds, and pickling is further performed by immersing its surface in a pickling solution. In this way, a hot-rolled sheet annealed sheet is obtained.

[0243] Next, in the cold-rolling process, the hot-rolled sheet annealed sheet after the hot-rolled sheet annealing process is subjected to single cold rolling or multiple cold rollings with intermediate annealing to produce a cold-rolled steel sheet with a final thickness shown in Tables 2A to 2C and Tables 3A to 3C.

[0244] Next, in the decarburizing annealing process, the cold-rolled steel sheet obtained in the cold-rolling process is subjected to decarburizing annealing at 830 °C for 100 seconds in a wet hydrogen atmosphere.

[0245] Next, in the release agent coating process, a release agent for annealing containing the components shown in Tables 2A to 2C and Tables 3A to 3C is coated on the surface of the decarburized annealed sheet and dried.

[0246] Next, in the final annealing process, final annealing is performed on a decarburized annealing sheet pre-coated with an annealing release agent.

[0247] After obtaining the final annealed sheet through this final annealing process, intermediate annealing is not performed, and then a surface treatment process is carried out.

[0248] In the surface treatment process, surface treatment is performed by immersing the final annealed sheet in a treatment liquid for 3 to 60 seconds to obtain a surface-treated steel sheet. The treatment liquid used at this time contains sulfuric acid, the total acid concentration is 3 to 5 vol%, and the liquid temperature is 70 to 90 °C. However, for Test No. 35, the surface treatment process is carried out under the conditions of an acid concentration of 5 vol% and a liquid temperature of 30 °C.

[0249] In the subsequent tension-imparting insulating film forming process, an insulating film coating process and a baking process are carried out. In the insulating film coating process, an insulating film coating liquid containing 100% by mass of silica and aluminum phosphate in terms of solid content is coated on the surface of the surface-treated steel sheet.

[0250] In the baking process immediately following the insulating film coating process, heat treatment is applied to the surface-treated steel sheet coated with the insulating film coating liquid to form an insulating film (secondary film 3) on the surface of the surface-treated steel sheet. This baking process is set to include a heating process P1 in which the surface-treated steel sheet is heated to raise its temperature and a soaking process P2 carried out after the heating process P1.

[0251] Moreover, in the heating process P1, the average heating rate, dew point, and oxygen concentration of the steel sheet are set to the conditions shown in Tables 2A to 2C and Tables 3A to 3C described later.

[0252] Similarly, in the soaking process P2, the annealing temperature, annealing time, hydrogen concentration, and atmosphere dew point are set to the conditions shown in Tables 2A to 2C and Tables 3A to 3C described later.

[0253] The film adhesion, iron loss, and magnetic flux density of the test piece obtained through the above tension-imparting insulating film forming process are evaluated. In any example, the average film thickness of the secondary film is 1.0 to 5.0 μm.

[0254] Regarding the film adhesion, specifically, first, the test piece is wound around a cylinder with a diameter of 20 mm, and evaluated by the film remaining area ratio when bent 180°. The area ratio of the remaining film surface to the steel sheet area in contact with the cylinder is calculated. The steel sheet area in contact with the cylinder is obtained by calculation. The area of the remaining surface is obtained by taking a photo of the steel sheet after the test and performing image analysis on the photo image.

[0255] When the film remaining area ratio is 90% or more, it is evaluated as Very Good (VG); when it is 85% or more and less than 90%, it is evaluated as Good (G); when it is 80% or more and less than 85%, it is evaluated as Fair (F); when it is less than 80%, it is evaluated as Poor (P). When the film remaining area ratio is 80% or more, the film adhesion is judged to be excellent.

[0256] Next, the iron loss characteristics are evaluated for the test piece according to the single sheet magnetic property test method (SST: Single Sheet Tester). Under the conditions of alternating current frequency: 50 Hz and excitation magnetic flux density: 1.7 T, the iron loss W17 / 50 (W / kg) defined as the power loss per unit weight (1 kg) of the steel sheet is measured.

[0257] When the iron loss W17 / 50 is less than 0.75 W / kg, the iron loss characteristics are judged to be excellent.

[0258] The magnetic flux density is measured by applying a magnetic field of 800 A / m to the test piece and measuring the magnetic flux density B8 (T) in the rolling direction.

[0259] The above results are shown in Tables 2A to 2C and Tables 3A to 3C.

[0260] [Table 2A]

[0261]

[0262] [Table 2B]

[0263]

[0264] [Table 2C]

[0265]

[0266] [Table 3A]

[0267]

[0268] [Table 3B]

[0269]

[0270] [Table 3C]

[0271]

[0272] First, in the results of Tables 2A to 2C, in all of Test Nos. 1 to 12 as inventive examples, the manufacturing conditions of the heating process P1 and the soaking process P2 were set within the ranges described in the above embodiments. That is, in the heating process P1, the average heating rate of the steel sheet within the steel sheet temperature range of 100°C to 600°C was set to 10°C / sec to 400°C / sec in an atmosphere with an oxygen concentration of 1 vol% to 21 vol% and a dew point of 0°C to 30°C. Further, in the soaking process P2, the holding time at a constant steel sheet temperature within the range of 800°C to 1000°C was set to 5 seconds to 200 seconds in a soaking atmosphere having a constant value within the range of a hydrogen concentration of 1 to 15 vol% and an atmosphere dew point of -20 to +40°C.

[0273] In the examples of Tables 2A to 2C, various changes were made to the steel components. However, since the manufacturing conditions satisfied the above ranges, relatively good film adhesion was obtained. However, since the average heating rate of the steel sheet in the heating process P1, and the annealing temperature and annealing atmosphere (hydrogen concentration, atmosphere dew point) in the soaking process P2 deviated from the preferred ranges, the evaluation was only "F".

[0274] On the other hand, regarding the iron loss W17 / 50, as shown in Tables 2A to 2C, it became less than 0.75 W / kg in all of Test Nos. 1 to 12.

[0275] In addition, as shown in Tables 2A to 2C, in all of Test Nos. 1 to 12, no significant decrease in the magnetic flux density was observed. Thus, without impairing the magnetic flux density, both the film adhesion and the iron loss resulted in meeting the acceptance criteria.

[0276] Next, in the results of Tables 3A to 3C in which both the manufacturing conditions and the steel components were changed, the results differed depending on the manufacturing conditions.

[0277] First, in Test Nos. 21 to 26 and 35 as inventive examples, in all of the heating process P1, the average heating rate of the steel sheet within the steel sheet temperature range of 100°C to 600°C was set within the range of 10°C / sec to 400°C / sec in an atmosphere with an oxygen concentration of 1 vol% to 21 vol% and a dew point of 0°C to 30°C. Further, in all of Test Nos. 21 to 26 and 35, in the soaking process P2, the holding time at a constant steel sheet temperature within the range of 800°C to 1000°C was set within the range of 5 seconds to 200 seconds in a soaking atmosphere having a constant value within the range of a hydrogen concentration of 1 to 15% and an atmosphere dew point of -20 to +40°C.

[0278] As a result, in all of these Tests No. 21 to 26 and 35, both the film adhesion and the iron loss became results that met the acceptance criteria. In particular, in Tests No. 23 to 26, high film adhesion was shown, and Tests No. 25 and 26 exhibited the highest film adhesion.

[0279] In addition, as shown in Tables 3A to 3C, in all of Tests No. 21 to 26, no significant decrease in the magnetic flux density was observed. Thus, without impairing the magnetic flux density, both the film adhesion and the iron loss are excellent.

[0280] On the other hand, in Test No. 27 as a comparative example, the average heating rate of the steel sheet in the heating process P1 was 5 °C / second, which was lower than the lower limit value of the present invention range, i.e., 10 °C / second. As a result, both the film adhesion and the iron loss were insufficient.

[0281] In Test No. 28 as a comparative example, the average heating rate of the steel sheet in the heating process P1 was 450 °C / second, which exceeded the upper limit value of the present invention range, i.e., 400 °C / second. As a result, both the film adhesion and the iron loss were insufficient.

[0282] In Test No. 29 as a comparative example, the dew point in the heating process P1 was -22 °C, which was lower than the lower limit value of the present invention range, i.e., -20 °C. As a result, although the iron loss met the acceptance criteria, the film adhesion was insufficient.

[0283] In Test No. 30 as a comparative example, the dew point in the heating process P1 was 32 °C, which exceeded the upper limit value of the present invention range, i.e., 30 °C. As a result, both the film adhesion and the iron loss were insufficient.

[0284] In Test No. 31 as a comparative example, the annealing temperature in the soaking process P2 was 780 °C, which was lower than the lower limit value of the present invention range, i.e., 800 °C. As a result, both the film adhesion and the iron loss were insufficient.

[0285] In Test No. 32 as a comparative example, the annealing temperature in the soaking process P2 was 1,020 °C, which exceeded the upper limit value of the present invention range, i.e., 1,000 °C. As a result, although the iron loss met the acceptance criteria, the film adhesion was insufficient.

[0286] In Test No. 33 as a comparative example, the atmosphere dew point in the soaking process P2 was -30 °C, which was lower than the lower limit value of the present invention range, i.e., -20 °C. As a result, although the iron loss met the acceptance criteria, the film adhesion was insufficient.

[0287] In Test No. 34 as a comparative example, the atmosphere dew point in the soaking process P2 was +45°C, exceeding the upper limit value of +40°C within the scope of the present invention. As a result, although the iron loss satisfied the acceptance criteria, the film adhesion was insufficient.

[0288] From the above results, it was confirmed that in order to achieve excellent film adhesion and iron loss, the conditions of both the heating process P1 and the soaking process P2 should be appropriately controlled. Specifically, in the heating process P1, the average heating rate of the steel sheet within the steel sheet temperature range of 100°C to 600°C should be set to 10°C / sec to 400°C / sec in an atmosphere with an oxygen concentration of 1 vol% to 21 vol% and a dew point of 0°C to 30°C. In addition, in the soaking process P2, the holding time at a constant steel sheet temperature within the range of 800°C to 1000°C should be set to 5 seconds to 200 seconds in a soaking atmosphere with a constant value within the range of a hydrogen concentration of 1 to 15% and an atmosphere dew point of -20 to +40°C.

[0289] Industrial Applicability

[0290] According to the present invention, it is possible to manufacture a grain-oriented electrical steel sheet with high film adhesion (secondary film adhesion) without sacrificing magnetic properties without performing intermediate annealing. Therefore, the industrial applicability is high.

[0291] Explanation of Reference Numerals

[0292] 1 Grain-oriented electrical steel sheet

[0293] 2 Base steel sheet

[0294] 3 Secondary film (tension-imparting insulating film)

[0295] 4 Oxide layer

[0296] P1 Heating process

[0297] P2 Soaking process

Claims

1. A manufacturing method of a directional electromagnetic steel sheet, characterized in that, It has the following processes: Hot rolling process: A hot-rolled steel sheet is obtained by heating a slab and performing hot rolling. The chemical composition of the slab contains, by mass%: C：0.020％～0.150％、 Si: 3.00% - 4.00%, Mn: 0.01% - 0.50%, S：0.0010％～0.0400％、 Acid-soluble Al: 0.010% - 0.050%, N：0.002％～0.020％、 Bi: 0.0000% - 0.0200%, P：0.000％～0.100％、 Sn: 0.00% - 0.50%, Cu: 0.00% - 0.50%, Cr：0.00％～0.50％、 Sb: 0.00% - 0.20%, Mo: 0.00% - 0.10%, Nb: 0.0000% - 0.0200%, B：0.0000％～0.0200％、 Te: 0.0000% - 0.0200%, Ni: 0.00% - 0.20%, Se: 0.0000% - 0.0200%, The balance is Fe and impurities; Hot-rolled sheet annealing process: After performing hot-rolled sheet annealing on the hot-rolled steel sheet to obtain a hot-rolled sheet annealed sheet, the hot-rolled sheet annealed sheet is immersed in a pickling solution; Cold rolling process: A cold-rolled steel sheet is obtained by performing cold rolling on the hot-rolled sheet annealed sheet; Decarburizing annealing process: A decarburized annealed sheet is obtained by performing decarburizing annealing on the cold-rolled steel sheet; Release agent coating process: An annealing release agent containing MgO, Al2O3, and chloride is coated on the surface of the decarburized annealed sheet; Final annealing process: A final annealed sheet is obtained by performing final annealing on the decarburized annealed sheet coated with the annealing release agent; Surface treatment process: The surface of the final annealed sheet is pickled to obtain a surface-treated steel sheet; and Tension-imparting insulating film forming process: It includes: Insulating film liquid coating process: An insulating film forming liquid containing 80 mass% or more of aluminum phosphate and silica in total is coated on the surface of the surface-treated steel sheet; and Baking process: By performing heat treatment on the surface-treated steel sheet coated with the insulating film forming liquid, a tension-imparting insulating film is formed on the surface of the surface-treated steel sheet, wherein the heat treatment in the baking process has a heating-up process and a soaking process, In the heating-up process, the average heating rate of the steel sheet in the steel sheet temperature range of 100°C to 600°C is set to 10°C / second to 400°C / second in an atmosphere with an oxygen concentration of 1 volume% to 21 volume% and a dew point of 0°C to 30°C, In the soaking process, the holding time at a constant steel sheet temperature in the range of 800°C to 1000°C is set to 5 seconds to 200 seconds in a soaking atmosphere with a constant value in the range of a hydrogen concentration of 1 to 15 volume% and an atmosphere dew point of -20 to +40°C.

2. The manufacturing method of the directional electromagnetic steel sheet according to claim 1, characterized in that, In the annealing release agent, the content of MgO is 0.0 mass% or more and 79.5 mass% or less, the content of Al2O3 is 20.0 mass% or more and 99.5 mass% or less, and the balance is the chloride.

3. The manufacturing method of the directional electromagnetic steel sheet according to claim 1 or 2, characterized in that, In the surface treatment process, the final annealed sheet is immersed in a treatment liquid containing at least one of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid and having a total acid concentration of 1 volume% to 20 volume% and a liquid temperature of 50°C to 90°C for 3 seconds to 60 seconds.

4. The manufacturing method of the directional electromagnetic steel sheet according to claim 1 or 2, characterized in that, The chemical composition of the slab contains, by mass%, at least one selected from the group consisting of the following elements: Bi: more than 0.0000% and 0.0200% or less, P: more than 0.000% and 0.100% or less, Sn: more than 0.00% and 0.50% or less, Cu: more than 0.00% and 0.50% or less, Cr: more than 0.00% and 0.50% or less, Sb: more than 0.00% and 0.20% or less, Mo: more than 0.00% and 0.10% or less, Nb: more than 0.0000% and 0.0200% or less, B: more than 0.0000% and 0.0200% or less, Te: more than 0.0000% and 0.0200% or less, Ni: more than 0.00% and 0.20% or less, and Se: more than 0.0000% and 0.0200% or less.

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