JP2019178378A - Manufacturing method of oriented electromagnetic steel sheet - Google Patents

Abstract

To provide a manufacturing method of an oriented electromagnetic steel sheet capable of achieving excellent magnetic property and excellent coated film adhesiveness.SOLUTION: The manufacturing method conducts hot rolling and cold rolling on a slab consisting of by mass%, C:0.020 to 0.100%, Si:3.30 to 3.75%, Mn:0.010 to 0.300%, S and/or Se: total 0.001 to 0.050%, sol.Al:0.010 to 0.065%, N:0.002 to 0.015%, and the balance:Fe with impurities, and then annealing treatment on the steel sheet before final cold rolling. Further the steel sheet after the cold rolling process is decarbonization annealed at a decarbonization annealing temperature of 800 to 950°C. In the decarbonization annealing process, temperature rise rate in a temperature range of 500 to 600°C S1 is 300 to 1500°C/sec., temperature rise rate in a temperature range of 600 to 700°C S2 is 300 to 750°C/sec., and the temperature rise rate S1 and the temperature rise rate S2 satisfy the formula (1). 0.50≤S2/S1≤0.90 (1).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a grain-oriented electrical steel sheet.

  A grain-oriented electrical steel sheet is a steel sheet containing about 0.5 to 7% by mass of Si and having crystal orientations accumulated in {110} <001> orientation (Goth orientation). Directional electrical steel sheets are used as soft magnetic materials in iron core materials for transformers and other electrical equipment. A catastrophic grain growth phenomenon called secondary recrystallization is used to control the crystal orientation of grain-oriented electrical steel sheets.

  The manufacturing method of a grain-oriented electrical steel sheet is as follows. The slab is heated and hot-rolled to produce a hot-rolled steel sheet. The hot-rolled steel sheet is annealed as necessary. The hot-rolled steel sheet is pickled as necessary. Cold rolling is performed on the hot rolled steel sheet after pickling by cold rolling at a cold rolling rate of 80% or more. Decarburization annealing is performed on the cold-rolled steel sheet to develop primary recrystallization. Finish annealing is performed on the cold-rolled steel sheet after decarburization annealing to develop secondary recrystallization. A grain-oriented electrical steel sheet is manufactured by the above process.

The grain-oriented electrical steel sheet is required to have magnetic characteristics, and in particular, excellent excitation characteristics and iron loss characteristics are required. As an index indicating the excitation characteristics of the grain-oriented electrical steel sheet, for example, B8, which is a magnetic flux density at a magnetic field strength of 800 A / m, is used. Further, as an index indicating the iron loss characteristic of the grain-oriented electrical steel sheet, for example, W _17/50 which is an iron loss per unit mass when magnetized to 1.7 T at 50 Hz is used.

  In recent years, there has been an increasing demand for further improvement of iron loss characteristics of grain-oriented electrical steel sheets. This is because the efficiency of the generator and the transformer is increased by further reducing the iron loss of the grain-oriented electrical steel sheet.

  Iron loss consists of hysteresis loss and eddy current loss. The hysteresis loss is affected by the purity, internal strain, crystal orientation, and the like of the grain-oriented electrical steel sheet. Eddy current loss is affected by the electrical resistance, thickness, grain size, magnetic domain size, tension of the coating formed on the surface of the steel sheet, and the like.

  Increasing the Si content increases the electrical resistance of the steel sheet, thereby reducing eddy current loss. Therefore, it is considered effective to increase the Si content in order to reduce the iron loss. However, when the Si content is increased, desired iron loss characteristics depending on the Si content may not be obtained.

  Techniques for improving iron loss characteristics in grain-oriented electrical steel sheets with an increased Si content have been proposed in Japanese Patent Application Laid-Open No. 2001-192733 (Patent Document 1) and Japanese Patent Application Laid-Open No. 5-345921 (Patent Document 2). Yes.

  In the method for producing a unidirectional electrical steel sheet disclosed in Patent Document 1, in mass%, Si: 3.0 to 3.8%, Mn: 0.03 to 0.45%, S, Se: single or composite And heating an electromagnetic steel slab containing 0.15% or less, acid-soluble Al: 0.015 to 0.035%, and N: 0.0035 to 0.012% to a temperature of 1250 ° C. or less. Hot-rolled sheet annealing is performed, the final sheet thickness is obtained by cold rolling, and then decarburization annealing, nitriding treatment, and finish annealing are performed. Then, assuming that the thickness of the hot-rolled sheet is tA (mm) and the thickness of the final cold-rolled sheet is tC (mm), tA / tC is 3 according to the Si content (Si (%)). .57−0.43 × Si (%) ≦ ln (tA / tC) ≦ 4.58−0.64 × Si (%) In Patent Document 1, by adjusting the cold rolling rate (tA / tC) within the range of the above formula, the Goth orientation in the primary recrystallization is effectively increased, so that the Goth orientation integration degree in the secondary recrystallization is increased. It is described that, as a result, iron loss characteristics corresponding to the Si content can be obtained.

  In the method for producing a unidirectional electrical steel sheet disclosed in Patent Document 2, in mass%, C: 0.090% or less, Si: 2.5-4.5%, Mn: 0.03-0.15% , S: 0.010 to 0.050%, acid-soluble Al: 0.010 to 0.050%, N: 0.0045 to 0.012%, Sn: 0.03 to 0.5%, Cu: 0 0.02 to 0.3%, Ni: 0.05 to 1.0%, and the steel slab composed of the remaining Fe and inevitable impurities is heated to 1250 ° C. or higher and then hot-rolled and subjected to precipitation annealing. Cold rolling with a cold rolling rate of 80% or more, decarburization annealing, and finish annealing are performed. In Patent Document 2, it is described that magnetic properties (magnetic flux density and iron loss) are increased by further containing Ni in the chemical composition of the grain-oriented electrical steel sheet having a high Si content.

JP 2001-192733 A Japanese Patent Laid-Open No. 5-345921

By the way, in the manufacturing process of grain-oriented electrical steel sheets, an annealing separator containing magnesium oxide (MgO) is applied to the steel sheet surface before the finish annealing process, and forsterite (Mg ₂ SiO ₄ ) is the main component in the finish annealing process. To form a primary coating. Further, an insulating film is formed on the primary film. The primary coating imparts tension to the steel sheet to reduce iron loss or increase insulation. The primary coating further plays a role of ensuring the adhesion of the insulating coating formed on the primary coating to the steel plate. Hereinafter, the adhesion of the insulating coating to the steel sheet is referred to as “coating adhesion”.

  However, when a grain-oriented electrical steel sheet having a Si content of 3.30% or more is produced by the methods of Patent Document 1 and Patent Document 2, both excellent magnetic properties and excellent film adhesion cannot be obtained sufficiently. There is a case.

  An object of the present disclosure is to provide a method for producing a grain-oriented electrical steel sheet capable of achieving both excellent magnetic properties and excellent film adhesion even when the Si content is 3.30% or more.

A method for producing a grain-oriented electrical steel sheet according to the present disclosure includes a hot rolling process, a cold rolling process, an annealing process before the final cold rolling, a decarburizing annealing process, an annealing separator coating process, and a finish annealing process. Is provided.
In the hot rolling process, the chemical composition is mass%, C: 0.020 to 0.100%, Si: 3.30 to 3.75%, Mn: 0.010 to 0.300%, S and / or Se: 0.001 to 0.050% in total, sol. Al: 0.010 to 0.065%, N: 0.002 to 0.015%, Sn: 0 to 0.500%, Cr: 0 to 0.500%, Cu: 0 to 0.500%, Bi A steel plate is manufactured by performing hot rolling on a slab composed of: 0 to 0.0100% and the balance: Fe and impurities.
In the cold rolling process, cold rolling is performed one or more times on the steel sheet after the hot rolling process.
In the annealing process before the final cold rolling, the annealing process is performed on the steel sheet before the final cold rolling out of one or a plurality of cold rollings.
The decarburization annealing process includes a temperature raising process and a decarburization process. In the temperature raising step, the steel sheet after the cold rolling step is heated to the decarburization annealing temperature. In the temperature raising step, the temperature raising rate S1 in the temperature range of 500 to 600 ° C. is 300 to 1500 ° C./second, and the temperature raising rate S2 in the temperature range of 600 to 700 ° C. is 300 to 750 ° C./second. The temperature increase rate S1 and the temperature increase rate S2 satisfy the formula (1).
0.50 ≦ S2 / S1 ≦ 0.90 (1)
In the decarburization step, the steel plate is held at a decarburization annealing temperature of 800 to 950 ° C. and decarburization annealing is performed.
In the annealing separator application process, the annealing separator is applied to the surface of the steel sheet after the decarburization annealing process.
In the finish annealing step, finish annealing is performed on the steel sheet to which the annealing separator is applied.

  The method for producing a grain-oriented electrical steel sheet according to the present disclosure can achieve both excellent magnetic properties and excellent film adhesion even when the Si content is 3.30% or more.

FIG. 1 is a flowchart showing the manufacturing process of the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment. FIG. 2 is a schematic diagram showing a heat pattern in the decarburization annealing process in FIG. 1.

  The present inventors investigated and examined the reason why magnetic properties and film adhesion may be lowered in a grain-oriented electrical steel sheet having a Si content of 3.30% or more. As a result, the present inventors obtained the following knowledge.

  When the Si content increases, the primary recrystallization structure deteriorates, and the secondary recrystallization may become unstable in the final annealing step. In this case, the degree of integration in the Goth direction is lowered, and the magnetic characteristics are lowered.

  The following reasons can be considered as the reason why the primary recrystallization structure deteriorates. If the Si content increases, the ferrite ratio in the structure increases. In this case, an α fiber orientation group that is a stable rolling orientation develops at the center of the steel plate during hot rolling. Here, the α fiber orientation group means a crystal grain group in which the <110> axis of the crystal is along the rolling direction. The α fiber orientation group generated in the hot rolling process also remains in the steel sheet after the cold rolling process. This α fiber orientation group degrades the primary recrystallization structure, and as a result, suppresses the selective growth of Goth orientation during the secondary recrystallization in the final annealing step. As a result, it is considered that the degree of integration in the Goth direction decreases and the magnetic characteristics deteriorate.

  Accordingly, the present inventors have studied a method for obtaining excellent magnetic properties when the Si content is as high as 3.30% or more. As a result, the following knowledge was obtained.

  In the decarburization annealing process in the manufacturing process of the grain-oriented electrical steel sheet, the temperature increase rate up to the decarburization annealing temperature is made faster than the conventional temperature increase rate. In this case, the primary recrystallized structure is improved, the degree of integration of the goth orientation of the grain-oriented electrical steel sheet is increased, and the magnetic properties are improved.

  The reason for this is not clear, but the following reasons can be considered. By increasing the rate of temperature increase, the primary recrystallization changes the form of recrystallization from the α fiber orientation group (primary recrystallization), and increases the selective growth of the Goss orientation from the α fiber orientation group. Recrystallization orientation grains such as ({411} <148>) increase. The Σ9-compatible grain increases the selective growth of the Goth grain. Therefore, it is considered that the degree of integration of Goss orientation increases in secondary recrystallization, and excellent magnetic properties can be obtained. The above-described improvement in magnetic characteristics is particularly effective when the temperature rising rate at 500 ° C. or higher is set to 300 ° C./second or higher, which is a conventional temperature rising rate.

  As described above, in the temperature raising step up to the decarburization annealing temperature in the decarburization annealing step, excellent magnetic properties can be obtained by increasing the temperature rising rate of 500 ° C. or higher. However, it has been newly found that if the decarburization annealing temperature is increased while the heating rate is increased, the adhesion of the directional electromagnetic steel sheet to the steel sheet (hereinafter referred to as film adhesion) decreases.

  Therefore, the present inventors further examined the reason why the film adhesion is lowered. As a result, the following knowledge was obtained.

The oxide film formed by the decarburization annealing process reacts with the annealing separator applied to the surface of the steel sheet in the final annealing process to form a primary film mainly composed of forsterite (Mg ₂ SiO ₄ ). A primary film has a role which improves the adhesiveness (film adhesiveness) with respect to the steel plate of the insulating film formed on a primary film after a finish annealing process. The more complex the interface structure between the primary coating and the ground iron (steel plate), the better the coating adhesion. However, if the heating rate is increased in the temperature raising step during the decarburization annealing step, the interface between the oxide film formed on the steel sheet surface and the ground iron is smoothed and is not complicated. As a result, film adhesion may be reduced.

  Based on the above examination results, the present inventors further manufacture a grain-oriented electrical steel sheet capable of achieving both excellent magnetic properties and excellent film adhesion even when the Si content is as high as 3.30% or more. The method was examined.

  As described above, it is particularly effective to improve the primary recrystallization structure by increasing the temperature rising rate in the temperature range of 500 ° C. or higher. On the other hand, oxidation of the steel sheet surface layer becomes significant at 500 to 700 ° C. Therefore, the present inventors tried to achieve both improvement of the primary recrystallization structure and complication of the oxide film structure by precisely controlling the temperature rising rate at 500 to 700 ° C. As a result, the primary recrystallization structure is improved by increasing the heating rate in the temperature range of 500 to 600 ° C, and the heating rate is made slower in the temperature range of 600 to 700 ° C than in the case of 500 to 600 ° C. Therefore, the oxide film structure can be complicated.

Based on the above examination, the present inventors examined the optimum rate of the temperature increase rate S1 in the temperature range of 500-600 degreeC and the temperature increase rate S2 in the temperature range of 600-700 degreeC. As a result, the chemical composition is mass%, C: 0.020-0.100%, Si: 3.30-3.75%, Mn: 0.010-0.300%, S and / or Se: total 0.001 to 0.050%, sol. Al: 0.010 to 0.065%, N: 0.002 to 0.015%, Sn: 0 to 0.500%, Cr: 0 to 0.500%, Cu: 0 to 0.500%, Bi : When producing a grain-oriented electrical steel sheet using a slab composed of 0 to 0.0100% and the balance: Fe and impurities, a temperature raising rate of 500 to 600 ° C. in the temperature raising step of the decarburization annealing step If S1 is 300-1500 ° C./sec, 600-700 ° C. temperature rise rate S2 is 300-750 ° C./sec, and temperature rise rates S1 and S2 satisfy the following formula (1), then the Si content It has been found that even if the content is increased to 3.30% or more, both excellent magnetic properties and excellent film adhesion can be achieved.
0.50 ≦ S2 / S1 ≦ 0.90 (1)

The method of manufacturing the grain-oriented electrical steel sheet according to the present embodiment completed based on the above knowledge includes a hot rolling process, a cold rolling process, a final cold rolling annealing process, a decarburizing annealing process, and annealing separation. An agent coating step and a finish annealing step.
In the hot rolling process, the chemical composition is mass%, C: 0.020 to 0.100%, Si: 3.30 to 3.75%, Mn: 0.010 to 0.300%, S and / or Se: 0.001 to 0.050% in total, sol. Al: 0.010 to 0.065%, N: 0.002 to 0.015%, Sn: 0 to 0.500%, Cr: 0 to 0.500%, Cu: 0 to 0.500%, Bi A steel plate is manufactured by performing hot rolling on a slab composed of: 0 to 0.0100% and the balance: Fe and impurities.
In the cold rolling process, cold rolling is performed one or more times on the steel sheet after the hot rolling process.
In the annealing process before the final cold rolling, the annealing process is performed on the steel sheet before the final cold rolling out of one or a plurality of cold rollings.
The decarburization annealing process includes a temperature raising process and a decarburization process. In the temperature raising step, the steel sheet after the cold rolling step is heated to the decarburization annealing temperature. In the temperature raising step, the temperature raising rate S1 in the temperature range of 500 to 600 ° C. is 300 to 1500 ° C./second, and the temperature raising rate S2 in the temperature range of 600 to 700 ° C. is 300 to 750 ° C./second. The temperature increase rate S1 and the temperature increase rate S2 satisfy the formula (1).
0.50 ≦ S2 / S1 ≦ 0.90 (1)
In the decarburization step, the steel plate is held at a decarburization annealing temperature of 800 to 950 ° C. and decarburization annealing is performed.
In the annealing separator application process, the annealing separator is applied to the surface of the steel sheet after the decarburization annealing process.
In the finish annealing step, finish annealing is performed on the steel sheet to which the annealing separator is applied.

  The chemical composition of the slab is selected from the group consisting of Sn: 0.005 to 0.500%, Cr: 0.010 to 0.500%, and Cu: 0.010 to 0.500%. It may contain seeds or more. Moreover, the chemical composition of the slab may contain Bi: 0.0010 to 0.0100%.

  Hereinafter, the manufacturing method of the grain-oriented electrical steel sheet according to the present embodiment will be described in detail. In the present specification, “%” relating to the element content means “% by mass” unless otherwise specified.

[Manufacturing process flow]
FIG. 1 is a flowchart of a method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment. With reference to FIG. 1, this manufacturing method is performed one or more times with respect to the hot rolling process (S1) which performs hot rolling with respect to a slab, and the steel plate (hot-rolled steel sheet) after a hot rolling process. The cold rolling step (S2) for performing the cold rolling (S20) and the final cold rolling for performing the annealing treatment on the steel plate before the final cold rolling among one or a plurality of cold rollings. Pre-annealing step (S3), decarburization annealing step (S4) for performing decarburization annealing on the steel plate after cold rolling (cold rolled steel plate), and annealing separation on the surface of the steel plate after decarburization annealing step An annealing separator coating step (S5) for applying the agent, and a final annealing step (S6) for performing the final annealing on the steel sheet coated with the annealing separator. Hereinafter, each process S1-S6 is demonstrated.

[Hot rolling process (S1)]
A hot rolling process (S1) implements hot rolling with respect to the prepared slab, and manufactures a hot-rolled steel plate. The chemical composition of the slab contains the following elements:

[Essential elements in the chemical composition of the slab]
C: 0.020 to 0.100%
Carbon (C) is effective in controlling the structure until the decarburization annealing process is completed during the manufacturing process. However, if the C content is less than 0.020%, the above effects cannot be obtained sufficiently. On the other hand, if the C content exceeds 0.100%, even if a decarburization annealing process described later is performed, decarburization becomes insufficient and magnetic aging occurs. In this case, sufficient iron loss characteristics cannot be obtained. Therefore, the C content is 0.020 to 0.100%. The minimum with preferable C content is 0.030%, More preferably, it is 0.040%. The upper limit with preferable C content is 0.090%, More preferably, it is 0.080%.

Si: 3.30-3.75%
Silicon (Si) increases the electrical resistance of the grain-oriented electrical steel sheet and reduces eddy current loss among iron losses. If the Si content is less than 3.30%, the above effect cannot be obtained sufficiently. On the other hand, if the Si content exceeds 3.75%, the cold workability of the steel decreases. Therefore, the Si content is 3.30 to 3.75%. The minimum with preferable Si content is 3.35%, More preferably, it is 3.40%. The upper limit with preferable Si content is 3.70%, More preferably, it is 3.60%.

Mn: 0.010-0.300%
Manganese (Mn) increases the specific resistance of the grain-oriented electrical steel sheet and reduces iron loss. Mn further improves hot workability and suppresses the occurrence of cracks in hot rolling. Further, Mn combines with S and / or Se in the annealing step before the final cold rolling to form fine MnS and / or fine MnSe. Fine MnS and fine MnSe serve as precipitation nuclei for fine AlN utilized as inhibitors. Therefore, if the amount of fine MnS and fine MnSe deposited is large in the annealing process before the final cold rolling, a sufficient amount of fine AlN can be obtained. If the Mn content is less than 0.010%, a sufficient amount of fine MnS and fine MnSe will not precipitate. On the other hand, if the Mn content exceeds 0.300%, the magnetic flux density of the grain-oriented electrical steel sheet decreases. Therefore, the Mn content is 0.010 to 0.300%. The minimum with preferable Mn content is 0.020%, More preferably, it is 0.030%. The upper limit with preferable Mn content is 0.200%, More preferably, it is 0.150%.

S and / or Se: 0.001 to 0.050% in total
Sulfur (S) and selenium (Se) combine with Mn during the manufacturing process to form the above-mentioned fine MnS and / or fine MnSe. Fine MnS and fine MnSe serve as precipitation nuclei for fine AlN utilized as inhibitors. Therefore, if the amount of fine MnS and fine MnSe deposited is large in the annealing process before the final cold rolling, a sufficient amount of fine AlN can be obtained. If the total content of S and / or Se is less than 0.001%, a sufficient amount of fine MnS and fine MnSe cannot be obtained. On the other hand, if the total content of S and / or Se exceeds 0.050%, MnS and / or MnSe may remain in the steel sheet after the finish annealing step. In this case, the magnetic characteristics are deteriorated. Therefore, the total content of S and / or Se is 0.001 to 0.050%. A preferable lower limit of the total content of S and / or Se is 0.005%. The upper limit with preferable total content of S and / or Se is 0.040%, More preferably, it is 0.030%.

sol. Al: 0.010 to 0.065%
Aluminum (Al) combines with N to form AlN during the manufacturing process of the grain-oriented electrical steel sheet, and functions as an inhibitor. sol. If the Al content is less than 0.010%, a sufficient amount of AlN that functions as an inhibitor cannot be obtained. On the other hand, sol. If the Al content exceeds 0.065%, AlN coarsens and the inhibitor strength decreases. Therefore, sol. Al content is 0.010 to 0.065%. sol. The minimum with preferable Al content is 0.015%, More preferably, it is 0.020%. sol. The upper limit with preferable Al content is 0.055%, More preferably, it is 0.045%. In this specification, sol. Al means acid-soluble Al. Therefore, sol. The Al content is the content of acid-soluble Al.

N: 0.002 to 0.015%
Nitrogen (N) combines with Al to form AlN during the manufacturing process of the grain-oriented electrical steel sheet, and functions as an inhibitor. In order to make the N content less than 0.002%, excessive refining is required in the steel making process, and in this case, the production cost becomes high. Therefore, the lower limit of the N content is 0.002%. On the other hand, if the N content in the steel material exceeds 0.015%, a large number of blisters (holes) are likely to be generated in the steel sheet during cold rolling. Therefore, the N content is 0.002 to 0.015%. The minimum with preferable N content is 0.004%, More preferably, it is 0.006%. The upper limit with preferable N content is 0.012%, More preferably, it is 0.0010%.

  The balance of the chemical composition of the slab according to the present embodiment is composed of Fe and impurities. Here, the impurities, when industrially manufacturing a slab that is a material of the grain-oriented electrical steel sheet, is mixed from ore, scrap, or production environment as a raw material, It means that it is allowed as long as it does not adversely affect the grain-oriented electrical steel sheet manufactured by the manufacturing method.

[Any element in the chemical composition of the slab]
The chemical composition of the above slab may contain one or more selected from the group consisting of Sn, Cr, and Cu instead of a part of Fe.

Sn: 0 to 0.500%
Tin (Sn) is an optional element and may not be contained. That is, the Sn content may be 0%. When contained, Sn improves the properties of the oxide layer produced during the decarburization annealing step, and also improves the properties of the primary coating produced using this oxide layer during the finish annealing step. Furthermore, Sn improves the magnetic characteristics of the grain-oriented electrical steel sheet by suppressing the formation of the oxide layer and the primary film, and suppresses variations in the magnetic characteristics. Sn is also a grain boundary segregation element and stabilizes secondary recrystallization. However, if the Sn content exceeds 0.500%, the surface of the steel sheet becomes difficult to be oxidized, and the formation of the primary film may be insufficient. Therefore, the Sn content is 0 to 0.500%. The minimum with preferable Sn content is more than 0%, More preferably, it is 0.005%, More preferably, it is 0.010%, More preferably, it is 0.020%. The upper limit with preferable Sn content is 0.300%, More preferably, it is 0.200%.

Cr: 0 to 0.500%
Chromium (Cr) is an optional element and may not be contained. That is, the Cr content may be 0%. When contained, Cr improves the properties of the oxide layer produced during the decarburization annealing step, and also improves the properties of the primary coating produced using this oxide layer during the finish annealing step. Furthermore, Cr improves the magnetic characteristics of the grain-oriented electrical steel sheet by suppressing the formation of the oxide layer and the primary film, and suppresses variations in the magnetic characteristics. However, if the Cr content exceeds 0.500%, the formation of the primary film may become unstable. Therefore, the Cr content is 0 to 0.500%. The minimum with preferable Cr content is more than 0%, More preferably, it is 0.010%, More preferably, it is 0.020%. The upper limit with preferable Cr content is 0.200%, More preferably, it is 0.150%.

Cu: 0 to 0.500%
Copper (Cu) is an optional element and may not be contained. That is, the Cu content may be 0%. When contained, Cu promotes the precipitation of fine MnS, which is the formation nucleus of AlN. However, if the Cu content is too high, CuS precipitates may be deposited, and the CuS precipitates may remain after finish annealing. If CuS precipitates remain in the steel, the magnetic properties of the grain-oriented electrical steel sheet will deteriorate. Therefore, the Cu content is 0 to 0.500%. The minimum with preferable Cu content is more than 0%, More preferably, it is 0.010%, More preferably, it is 0.030%, More preferably, it is 0.050%. The upper limit with preferable Cu content is 0.400%, More preferably, it is 0.300%.

The chemical composition of the above slab may contain Bi instead of a part of Fe.
Bi: 0 to 0.0100%
Bismuth (Bi) is an optional element and may not be contained. That is, the Bi content may be 0%. When contained, Bi stabilizes precipitates such as sulfides and enhances the function as an inhibitor. However, if the Bi content is too high, the primary film may not be stably formed. Therefore, the Bi content is 0 to 0.0100%. The minimum with preferable Bi content is more than 0%, More preferably, it is 0.0010%, More preferably, it is 0.0020%. The upper limit with preferable Bi content is 0.0080%, More preferably, it is 0.0060%.

[Method for producing slab having the above chemical composition]
An example of a method for producing a slab having the above chemical composition is as follows. A molten steel having the above chemical composition is manufactured (melted). A slab is manufactured by continuous casting using molten steel.

[Hot rolling process using the slab (S1)]
The prepared slab having the chemical composition is hot-rolled using a hot rolling mill to produce a steel plate (hot rolled steel plate). First, the slab is heated. For example, the slab is charged in a known heating furnace or a known soaking furnace and heated. The preferable heating temperature of a slab is 1300-1400 degreeC, More preferably, it is 1320-1380 degreeC.

  The heated slab is hot-rolled using a hot rolling mill to produce a steel plate (hot rolled steel plate). The hot rolling mill includes a rough rolling mill and a finish rolling mill disposed downstream of the rough rolling mill. The rough rolling mill includes one or a plurality of rough rolling stands arranged in a line. Each rough rolling stand includes a plurality of rolls arranged vertically. The rough rolling mill may be a reverse rolling mill or a tandem rolling mill. Similarly, the finish rolling mill includes one or a plurality of finish rolling stands arranged in a line. Each finish rolling stand includes a plurality of rolls arranged up and down. The finish rolling mill may be a reverse rolling mill or a tandem rolling mill. After the heated slab is rolled by a roughing mill, it is further rolled by a finish rolling mill to produce a hot rolled steel sheet.

  The thickness of the hot-rolled steel sheet manufactured by hot rolling is not particularly limited, and can be a known thickness. The finishing temperature in the hot rolling process (the steel plate temperature on the exit side of the finish rolling stand that finally squeezes the steel plate in the finish rolling mill) is, for example, 900 to 1100 ° C. The finishing temperature is the surface temperature (° C.) of the steel sheet obtained by a thermometer arranged on the exit side of the finishing rolling stand that performs the final reduction. A steel plate is manufactured by the above rolling process.

[Cold rolling process (S2)]
In the cold rolling step (S2), one or more cold rollings are performed on the manufactured steel sheet. Cold rolling is performed using a cold rolling mill. The cold rolling mill includes one or a plurality of cold rolling stands arranged in a row. Each cold rolling stand includes a plurality of cold rolling rolls. The cold rolling mill may be a reverse rolling mill or a tandem rolling mill.

  As shown in FIG. 1, in the cold rolling step, the cold rolling may be performed only by one cold rolling (S20) or multiple times of cold rolling (S20). When performing cold rolling several times, after performing cold rolling using said cold rolling mill, you may implement the intermediate annealing process aiming at the softening of a steel plate. In this case, the following cold rolling is performed after the intermediate annealing treatment. That is, you may implement an intermediate annealing process during cold rolling.

  In this specification, “perform one cold rolling” means that a cold rolled steel sheet having a desired final plate thickness is obtained by a plurality of rolling operations including one or more reciprocations using a reverse rolling mill. Alternatively, using a tandem rolling mill, the steel sheet is passed from the first rolling stand to the last rolling stand of the cold rolling stands arranged in a row and rolled into a cold rolled steel sheet having a desired final thickness. Means. In addition, after performing cold rolling, when performing intermediate annealing and further performing cold rolling, it is equivalent to "implementing two cold rollings." That is, in the case of “performing one cold rolling”, the rolling is performed a plurality of times without interposing intermediate annealing.

  The conditions for the intermediate annealing process performed between the cold rolling and the next cold rolling may be known conditions. The annealing temperature in the intermediate annealing treatment is, for example, 900 to 1200 ° C., and the holding time at the annealing temperature is 30 to 180 seconds. The intermediate annealing treatment reduces the distortion introduced into the steel sheet in the cold rolling of the previous stage (softening the steel sheet), and then performs the cold rolling of the next stage.

  In addition, when performing cold rolling several times, without performing an intermediate annealing process in the middle, in a manufactured grain-oriented electrical steel sheet, it may be difficult to obtain a uniform characteristic. On the other hand, when cold rolling is performed a plurality of times and intermediate annealing is performed during each cold rolling, the magnetic flux density may be lowered in the produced grain-oriented electrical steel sheet. Therefore, the number of cold rolling and the presence / absence of the intermediate annealing treatment are determined according to characteristics and manufacturing cost required for the grain-oriented electrical steel sheet to be finally manufactured.

  In the cold rolling process, as described above, only one cold rolling may be performed.

A preferable cumulative cold rolling rate in one or more cold rollings is 80 to 95%. Here, the cumulative cold rolling rate (%) is defined as follows.
Cold rolling rate (%) = 100−plate thickness of cold rolled steel sheet after final cold rolling / sheet thickness of steel sheet before start of first cold rolling × 100

  In the cold rolling process, when only one cold rolling is performed, the cold rolling rate is a cold rolling rate in only one cold rolling. The steel plate manufactured by the cold rolling process is wound into a coil shape.

[Annealing process before final cold rolling (S3)]
In the annealing process before the final cold rolling (S3), the steel sheet before the final cold rolling (S20) among the one or more cold rollings (S20) in the cold rolling process (S2) is the final. An annealing process before cold rolling is performed. The conditions of the annealing process before the final cold rolling are the same as the conditions in the above-described intermediate annealing process. The annealing temperature in the annealing process before the final cold rolling is, for example, 900 to 1200 ° C., and the holding time at the annealing temperature is 30 to 180 seconds.

[Decarburization annealing step (S4)]
In the decarburization annealing step (S4), the steel plate (cold rolled steel plate) after the cold rolling step (S2) is subjected to decarburization annealing to develop primary recrystallization.

  FIG. 2 is a schematic diagram showing a heat pattern in the decarburization annealing step (S4). Referring to FIG. 2, the decarburization annealing step (S4) includes a temperature raising step (S41), a decarburization step (S42), and a cooling step (S43). In the temperature raising step (S41), the steel sheet is heated to the decarburization annealing temperature Ta. In the decarburization step (S42), decarburization annealing is performed on the steel sheet heated to the decarburization annealing temperature Ta to develop primary recrystallization. In the cooling step (S43), the steel plate after the decarburization step (S42) is cooled by a known method.

  In the present embodiment, in the temperature raising step (S41), the primary recrystallization structure is improved by raising the temperature at a temperature raising rate S1 in the temperature range of 500 to 600 ° C., and the temperature raising rate is changed to S1 at 600 ° C. to 700 ° C. By slowing from S2 to S2, the interface structure between the oxide film and the ground iron is complicated at 600 to 700 ° C., and the film adhesion is improved. Hereinafter, details of each process will be described.

[Temperature raising step (S41)]
In the temperature raising step (S41), first, the steel plate after the cold rolling step is charged into a heat treatment furnace. In the heat treatment furnace for decarburization annealing in the present embodiment, the temperature of the cold-rolled steel sheet is raised to the decarburization annealing temperature, for example, by high frequency induction heating. Referring to FIG. 2, in the temperature raising step, the temperature rising rate in the temperature range of 500 to 600 ° C. is defined as S1 (° C./second), and the temperature rising rate in the temperature range of 600 to 700 ° C. is defined as S2 ( (° C / second). In the temperature raising step, the temperature raising rates S1 and S2 are set as follows.

[Raising rate S1 at 500 to 600 ° C.]
The temperature increase rate S1 in the temperature range of 500 to 600 ° C. is set to 300 to 1500 ° C./second. The primary recrystallized structure is improved by increasing the heating rate in the temperature range of 500 to 600 ° C. and performing rapid heating. Hereinafter, these points will be described.

  In the heating step of the decarburization annealing step, when rapid heating is performed at a heating rate S1 at 500 to 600 ° C. of 300 to 1500 ° C./second, the primary recrystallized structure can be improved, and the secondary recrystallization In the crystal, the degree of integration in the Goth direction can be increased. If the heating rate S1 is less than 300 ° C./second, the recrystallization orientation grains such as the Σ9 orientation do not increase sufficiently in the primary recrystallization, and as a result, the degree of integration of the Goss orientation is sufficient in the secondary recrystallization. It will not be high. On the other hand, if the temperature rising rate S1 exceeds 1500 ° C./second, the temperature rising rate S2 at 600 to 700 ° C. is 300 to 750 ° C./second, and even if S2 / S1 satisfies the formula (1), decarburization is performed. The interface between the oxide film and the ground iron after the process is smoothed, and the interface structure is not complicated. Therefore, good film adhesion cannot be obtained. If the heating rate S1 in the temperature range of 500 to 600 ° C. is 300 to 1500 ° C./second, the recrystallization orientation grains such as the Σ9 orientation are sufficiently increased in the primary recrystallization, and the Goss orientation in the secondary recrystallization. The degree of integration increases. Furthermore, if the temperature rising rate S2 at 600 to 700 ° C. is 300 to 750 ° C./second and S2 / S1 satisfies the formula (1), the interface structure between the oxide film and the ground iron after the decarburization process is complicated. To improve the film adhesion. A preferable lower limit of the temperature increase rate S1 is 350 ° C./second, and more preferably 400 ° C./second. A preferable upper limit of the temperature increase rate S1 is 1450 ° C./second, and more preferably 1400 ° C./second.

[Temperature increase rate S2 at 600 to 700 ° C.]
After raising the temperature from 500 to 600 ° C. at the temperature raising rate S1, the temperature raising rate S2 in the temperature range from 600 to 700 ° C. is set to 300 to 750 ° C./second.

  In the temperature range of 600 to 700 ° C., the interface structure between the oxide film and the ground iron is mainly complicated. As described above, the oxide film is necessary for generating a primary coating mainly composed of forsterite, and improves the adhesion of the primary coating to the steel sheet. Therefore, the adhesion (coating adhesion) of the insulating coating formed on the primary coating to the steel plate is also improved.

  If the heating rate S2 is less than 300 ° C./second, good magnetic properties cannot be obtained even if the heating rate S1 is increased. This is considered to be related to the amount of crystal orientation grains having the Σ9 corresponding orientation in the primary recrystallization structure described above. On the other hand, if the temperature rising rate S2 exceeds 750 ° C./second, the interface structure between the oxide film and the ground iron is smoothed. In this case, it is considered that the interface strength between the primary coating formed in the finish annealing step and the ground iron is lowered, and as a result, coating adhesion is lowered. Therefore, the temperature increase rate S2 is set to 300 to 750 ° C./second. A preferable lower limit of the temperature increase rate S2 is 320 ° C./second, more preferably 340 ° C./second. A preferable upper limit of the temperature increase rate S2 is 740 ° C./second, more preferably 720 ° C./second.

[Relationship between heating rate S1 and S2]
The heating rates S1 and S2 further satisfy the following formula (1).
0.50 ≦ S2 / S1 ≦ 0.90 (1)

  The ratio of the temperature rising rate S2 to the temperature rising rate S1 is considered to affect the thickness of the oxide film to be formed and the interface structure between the oxide film and the ground iron. Even if the temperature rising rate S1 is in the range of 300 to 1500 ° C./second and the temperature rising rate S2 is in the range of 300 to 750 ° C./second, the coating film is sufficient if S2 / S1 is less than 0.50. Adhesion deteriorates. The cause of this is not clear, but when S2 / S1 is less than 0.50, an external oxide film is likely to be formed between 500-700 ° C. The external oxide film suppresses further oxidation of the steel sheet, and as a result, the oxide film after the decarburization annealing process becomes thin. As a result, the formation of the primary film is insufficient, and the film adhesion is considered to deteriorate. On the other hand, even if the temperature rising rate S1 is in the range of 300 to 1500 ° C./second and the temperature rising rate S2 is in the range of 300 to 750 ° C./second, if S2 / S1 exceeds 0.90. The film adhesion deteriorates. The cause is considered as follows. If S2 / S1 exceeds 0.90, the interface structure between the oxide film and the ground iron is smoothed, and is not complicated. Therefore, it is considered that the interface strength between the primary coating formed in the finish annealing step and the ground iron is lowered, and as a result, the coating adhesion is lowered. Therefore, S2 / S1 is 0.50 to 0.90. The preferable lower limit of S2 / S1 is 0.55, and more preferably 0.60. The upper limit with preferable S2 / S1 is 0.85, More preferably, it is 0.80.

[Regarding the rate of temperature increase in a temperature range other than 500 to 700 ° C. in the temperature increasing step]
The rate of temperature rise in other temperature ranges other than 500 to 700 ° C. in the temperature raising step (normal temperature to less than 500 ° C. and over 700 ° C. to decarburization annealing temperature) is not particularly limited. For example, you may hold | maintain about several seconds within the range of normal temperature-less than 500 degreeC. The temperature increase rate in these temperature ranges may be appropriately selected within a range of 300 to 1500 ° C./second, for example.

The atmosphere during the temperature raising step is, for example, a dry nitrogen atmosphere having an oxygen potential (P _H2O / P _H2 ) of 0.1 or less. Preferably, the oxygen potential (P _H2O / P _H2 ) of the atmosphere in the temperature range of at least 500 to 700 ° C. during the temperature raising step is set to 0.001 or less.

  The temperature increase rate S1 and the temperature increase rate S2 are measured by the following method. A plurality of thermometers for measuring the surface temperature of the steel plate are installed in the heat treatment furnace. The plurality of thermometers are arranged from the upstream to the downstream of the heat treatment furnace. Based on the temperature of the steel plate measured by the thermometer and the time taken for the steel plate temperature to rise to 500 to 600 ° C., the temperature increase rate S1 is obtained. Moreover, temperature rising rate S2 is calculated | required based on the temperature of the steel plate measured with the thermometer, and the time taken for the steel plate temperature to rise to 600-700 degreeC.

[Decarburization step (S42)]
In the decarburization step (S42) in the decarburization annealing step (S4), the steel plate after the temperature raising step (S41) is held at the decarburization annealing temperature Ta, and decarburization annealing is performed. Thereby, primary recrystallization is expressed in the steel sheet. The atmosphere during the decarburization process may be a well-known atmosphere, for example, a wet nitrogen-hydrogen mixed atmosphere containing hydrogen and nitrogen. By performing decarburization annealing, carbon in the steel sheet is removed from the steel sheet, and primary recrystallization occurs. The manufacturing conditions in the decarburization process are as follows.

Decarburization annealing temperature Ta: 800-950 ° C
As described above, the decarburization annealing temperature Ta corresponds to the furnace temperature of the heat treatment furnace that performs the decarburization annealing, and corresponds to the temperature of the steel sheet during the decarburization annealing. If decarburization annealing temperature Ta is less than 800 degreeC, the crystal grain of the steel plate after primary recrystallization expression is too small. In this case, secondary recrystallization is not sufficiently developed in the finish annealing step (S6). On the other hand, if the decarburization annealing temperature Ta exceeds 950 ° C., the crystal grains of the steel sheet after the primary recrystallization is too large. Also in this case, secondary recrystallization is not sufficiently developed in the finish annealing step (S6). If decarburization annealing temperature Ta is 800-950 degreeC, the crystal grain of the steel plate after primary recrystallization will become an appropriate size, and secondary recrystallization will fully express in a finish annealing process (S6).

  Note that the holding time at the decarburization annealing temperature Ta in the decarburization step (S42) is not particularly limited. The holding time at the decarburization annealing temperature Ta is, for example, 15 to 150 seconds.

[Cooling step (S43)]
In the cooling step (S43), the steel plate after the decarburization step (S42) is cooled to room temperature by a well-known method. The cooling method may be cooling or water cooling. Preferably, the steel plate after the decarburizing step is allowed to cool. In the decarburization annealing step (S4) through the above steps, a decarburization annealing process is performed on the steel sheet.

[Annealing Separator Application Step (S5)]
An annealing separator application step (S5) is performed on the steel sheet after the decarburization annealing step (S4). In the annealing separator application step (S5), an annealing separator is applied to the steel sheet surface. Specifically, an aqueous slurry containing an annealing separator is applied to the steel sheet surface. The aqueous slurry is prepared by adding water to the annealing separator and stirring. The annealing separator contains magnesium oxide (MgO). Preferably, MgO is the main component of the annealing separator. Here, “main component” means that the MgO content in the annealing separator is 60.0% or more by mass%. The annealing separator may contain known additives in addition to MgO. For example, together with MgO, a Ca compound, Ce compound, La compound, Pr compound, Nd compound, Sc compound, Y compound, and the like may be contained.

  In the annealing separator application step, an aqueous slurry annealing separator is applied on the surface of the steel sheet. The steel sheet having the surface coated with the annealing separator is wound and coiled. After making a steel plate into a coil shape, a finish annealing process (S6) is implemented.

  In addition, after apply | coating the annealing separator of aqueous slurry on the steel plate surface and making a steel plate into a coil shape, you may implement a baking process before implementing a finish annealing process. In the baking process, the coiled steel plate is charged and held in a furnace maintained at 400 to 1000 ° C. (baking process). Thereby, the applied annealing separator is dried. The holding time is, for example, 10 to 90 seconds.

  You may implement a finish annealing process with respect to the coil-shaped steel plate with which the annealing separation agent was apply | coated, without implementing a baking process.

[Finishing annealing process (S6)]
A final annealing process (S6) is implemented with respect to the steel plate after an annealing separation agent application process (S5), and a secondary recrystallization is expressed. The final annealing process is performed using a heat treatment furnace. The manufacturing conditions in the finish annealing step are, for example, as follows. In addition, the furnace atmosphere in finish annealing is a known atmosphere.

Finish annealing temperature: 1150-1250 ° C
Holding time at the final annealing temperature: 5 to 30 hours If the final annealing temperature is less than 1150 ° C., sufficient secondary recrystallization does not occur, and sufficient purification to remove precipitates used in the secondary recrystallization is sufficient. is not. Therefore, the magnetic properties of the manufactured grain-oriented electrical steel sheet are lowered. On the other hand, even if the finish annealing temperature exceeds 1250 ° C., the effect on secondary recrystallization and purification is low, and problems such as deformation of the steel sheet occur. If the finishing temperature is 1150 to 1250 ° C., sufficient secondary recrystallization is developed on the premise that the holding time is appropriate, and the magnetic properties are enhanced. Furthermore, the temperature increase rate S1 and S2 in the above-mentioned decarburization annealing process is suitable, and the primary film containing forsterite (Mg ₂ SiO ₄ ) on the steel sheet surface is provided on condition that the formula (1) is satisfied. It is formed stably.

  In addition, each element of the chemical composition of the steel sheet is removed to some extent from the steel components by the finish annealing step (S6). In particular, S, Al, N, etc. that function as inhibitors are greatly removed.

  Through the above manufacturing process, the grain-oriented electrical steel sheet according to the present embodiment is manufactured. The produced grain-oriented electrical steel sheet has excellent magnetic properties even though the Si content is as high as 3.30% or more. Furthermore, since the primary coating is stably formed, excellent coating adhesion is exhibited when the insulating coating is formed by an insulating coating forming process described later.

[Insulating film forming process]
In the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment, an insulating film forming step may be performed after the finish annealing step (S6). In the insulating coating forming step, an insulating coating treatment agent is applied on the primary coating of the grain-oriented electrical steel sheet after cooling in the finish annealing step.

  The insulating film treating agent mainly contains colloidal silica and phosphate.

  The colloidal silica of this embodiment may be a well-known colloidal silica. Colloidal silica becomes a solid content when the insulating film treating agent as a solution is dried, and functions as a binder. The particle size of the colloidal silica is not particularly limited, and a known particle size is sufficient. The average particle diameter of the colloidal silica is, for example, 5 nm to 200 nm.

  The phosphate of this embodiment has phosphoric acid and metal ions as main components. The phosphate becomes a solid content when the aqueous solution is dried, and functions as a binder. The form of phosphoric acid is not particularly limited. Examples of phosphoric acid used for the insulating film treating agent include orthophosphoric acid, metaphosphoric acid, polyphosphoric acid, and phosphonic acid. It does not specifically limit as a metal component (kind of a metal ion) of a phosphate. Examples of the metal component of the phosphate include Mg, Ca, Ba, Sr, Ni, Co, Mn, Zn, Fe, Al, and Mn.

  The above-mentioned insulating coating treatment agent is applied on the primary coating of the steel plate. The application method is not particularly limited. The coating method may be a roll coater method, or a coating method such as a spray method or a dip method.

  The applied insulating film treating agent is heated and dried to form an insulating film. The heating method for heating and drying the insulating film treating agent is not particularly limited. The heating method may be heating in a normal radiation furnace or hot air furnace, or heating using electricity such as an induction heating method. The drying conditions are, for example, a baking time of 10 to 120 seconds in a range where the plate temperature of the electrical steel sheet coated with the insulating film treating agent is 800 ° C. to 980 ° C. However, the drying conditions are not limited to this. In the insulating film forming step, flattening annealing for applying tension to the steel plate during baking may be performed. The planarization annealing may be performed under known conditions. The annealing temperature in planarization annealing is 800-950 degreeC, for example.

  Through the above steps, a grain-oriented electrical steel sheet having an insulating coating formed on the primary coating is manufactured.

[Other processes]
[Magnetic domain segmentation process]
The grain-oriented electrical steel sheet according to the present embodiment may further perform a magnetic domain subdivision processing step after the finish annealing step or the insulating film forming step, if necessary. In the magnetic domain refinement process, the surface of the grain-oriented electrical steel sheet is irradiated with laser light having a magnetic domain refinement effect, or a groove is formed on the surface. In this case, a grain-oriented electrical steel sheet that is further excellent in magnetic properties can be produced.

  Hereinafter, embodiments of the present invention will be specifically described with reference to examples. These examples are examples for confirming the effects of the present invention, and do not limit the present invention.

[Manufacture of grain-oriented electrical steel sheets for each test number]
The chemical composition is mass%, C: 0.075%, Si: 3.45%, Mn: 0.075%, S: 0.028%, sol. A slab containing Al: 0.028%, N: 0.008%, with the balance being Fe and impurities was prepared.

  Each test number slab was heated to 1350 ° C. in a heating furnace. A hot rolling process was performed on the heated slab to produce a hot-rolled steel sheet having a thickness of 2.3 mm. The finish rolling temperature (° C.) was in the range of 1000 to 1100 ° C. in any test number.

  An annealing process before final cold rolling was performed on the hot-rolled steel sheet. In the annealing process before the final cold rolling, the hot-rolled steel sheet was heated to 1120 ° C., and then the steel sheet was annealed at an annealing temperature of 900 ° C. and a holding time at the annealing temperature of 40 seconds.

One cold rolling (final cold rolling) was performed on the steel sheet after the annealing process before the final cold rolling to produce a cold rolled steel sheet having a thickness of 0.23 mm. A decarburization annealing process was performed on the cold-rolled steel sheet after the cold rolling process. In the decarburization annealing step, the decarburization annealing temperature was set to 830 ° C. The atmosphere in the heat treatment furnace for performing the decarburization annealing treatment was a well-known wet nitrogen-hydrogen mixed atmosphere containing hydrogen and nitrogen. Then, the oxygen potential (P _H2O / P _H2 ) in the atmosphere in the temperature raising step was set to 0.1. Furthermore, in the temperature raising step, the temperature raising rate S1 in the temperature range of 500 to 600 ° C. and the temperature raising rate S2 in the temperature range of 600 to 700 ° C. are as shown in Table 1.

  The surface of the steel sheet after decarburization annealing was coated with an annealing separator (aqueous slurry) mainly composed of MgO, and then wound into a coil shape. Finish annealing was implemented with respect to the steel plate wound up by the coil shape. The finish annealing temperature was 1150 ° C., and the holding time at the finish annealing temperature was 10 hours. The steel plate after finish annealing was allowed to cool.

  After the coiled steel sheet after the final annealing process was washed with water, an insulating film forming process was performed. In the insulating coating forming step, an insulating coating treatment agent mainly composed of colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheet after the finish annealing step. The insulating film treating agent was mainly composed of aluminum phosphate and colloidal silica. After applying the insulating film treating agent to the steel sheet surface, flattening annealing was performed. In flattening annealing, it was kept at 900 ° C. for 30 seconds. The grain-oriented electrical steel sheet of each test number was manufactured from the above manufacturing process.

[Evaluation test]
[Magnetic property evaluation test]
The magnetic properties (magnetic flux density B8 and iron loss W _17/50 ) of the _grain- oriented electrical steel sheets of each test number were evaluated according to JIS C2556: 2015 by the following method. Specifically, a magnetic field of 800 A / m was applied to each sample, and the magnetic flux density B8 (T) was measured. Saturation magnetic flux density Bs (T) was calculated | required with the following formula | equation using Si content (mass%).
Bs = 2.2032-0.0581Si
Based on the obtained magnetic flux density B8 and the saturated magnetic flux density Bs, the Goss orientation integration degree (B8 / Bs), which is the ratio of the magnetic flux density B8 to the saturated magnetic flux density Bs, was obtained.

Table 1 shows the obtained magnetic flux density B8, Goss direction integration degree B8 / Bs, and iron loss W _17/50 .

[Coating adhesion evaluation test]
A test piece of 30 mm × 80 mm × plate thickness was collected from the center position of the width of the grain-oriented electrical steel sheet of each test number. The test piece was wound around a cylinder with a diameter of 20 mm and bent 180 °. The area ratio (%) of the insulating film remaining on the test piece bent by 180 ° was obtained from the following equation.
Area ratio = area of insulating film remaining on test piece / area of test piece × 100
When the obtained area ratio was 95.0% or more, it was judged that the film adhesion was very excellent (“VG” in the table). When the obtained area ratio was 90.0 or more and less than 95.0%, it was judged that the film adhesion was excellent (“G” in the table). When the obtained area ratio was 85.0 to less than 90.0%, the film adhesion was judged to be good (“F” in the table). When the obtained area ratio was less than 80.0%, it was judged that the film adhesion was low (“B” in the table). In addition, when cracks are confirmed in the steel sheet during the manufacturing process, and when secondary recrystallization after the finish annealing process is defective (that is, when the Goss orientation integration degree B8 / Bs is low), the coating adheres. A sex assessment test was not performed. When the obtained area ratio was 80.0% or more, it was judged that the film adhesion was excellent.

[Test results]
The test results obtained are shown in Table 1. Referring to Table 1, in test numbers 11, 12, 17, 18, 23-25, 30-32, 37 and 40, the chemical composition of the slab is appropriate, and the conditions in each manufacturing process are It was appropriate. As a result, in any test number, the magnetic flux density B8 was as high as 1.910 T or more, and the Goss direction integration degree B8 / Bs was as high as 0.954 or more. Furthermore, the iron loss W _17/50 was as low as 0.831 W / kg or less. In the film adhesion evaluation test, the area ratio was 80.0% or more, and excellent film adhesion was exhibited.

On the other hand, in the test numbers 1 to 3, the heating rate S1 at 500 to 600 ° C. was too slow. Therefore, the Goss direction integration degree B8 / Bs was less than 0.954. Therefore, the magnetic flux density B8 was less than 1.910 T, and the iron loss W _17/50 also exceeded 0.831 W / kg.

In test number 42, the temperature increase rate S1 at 500 to 600 ° C. was too fast. Therefore, the Goss orientation integration degree B8 / Bs is as high as 0.954 or more, the magnetic flux density B8 is 1.910 T or more, and the iron loss W _17/50 is 0.831 W / kg or less. It was low.

In the test numbers 6-8, 13, 19, 20, 26, and 39, the heating rate S2 at 600 to 700 ° C. was too slow. Therefore, the Goss direction integration degree B8 / Bs was less than 0.954. Therefore, the magnetic flux density B8 was less than 1.910 T, and the iron loss W _17/50 also exceeded 0.831 W / kg.

In test numbers 27 and 34 to 36, the temperature increase rate S2 was too fast. Therefore, the Goss orientation integration degree B8 / Bs is as high as 0.954 or more, the magnetic flux density B8 is 1.910 T or more, and the iron loss W _17/50 is 0.831 W / kg or less. It was low.

In test numbers 4, 5, 9, 10, 14, 15, 16, 21, 22, 28, 29, 33, 38, and 41, the temperature increase rate S1 and the temperature increase rate S2 did not satisfy the formula (1). Therefore, the Goss orientation integration degree B8 / Bs is as high as 0.953 or more, the magnetic flux density B8 is 1.910 T or more, and the iron loss W _17/50 is 0.831 W / kg or less. It was low.

[Manufacture of grain-oriented electrical steel sheets for each test number]
Chemical composition is mass%, C: 0.075%, Mn: 0.075%, S: 0.028%, sol. A slab containing Al: 0.028%, N: 0.008%, further containing Si (% by mass) shown in Table 2, and the balance being Fe and impurities was prepared.

  Each test number slab was heated to 1350 ° C. in a heating furnace. A hot rolling process was performed on the heated slab to produce a hot-rolled steel sheet having a thickness of 2.3 mm. The finish rolling temperature (° C.) was in the range of 1000 to 1100 ° C. in any test number.

  An annealing process before final cold rolling was performed on the hot-rolled steel sheet. In the annealing process before the final cold rolling, the hot-rolled steel sheet was heated to 1120 ° C., and then the hot-rolled steel sheet was annealed at an annealing temperature of 900 ° C. and a holding time at the annealing temperature of 40 seconds. One cold rolling (final cold rolling) was performed on the steel sheet after the annealing process before the final cold rolling to produce a cold rolled steel sheet having a thickness of 0.23 mm.

One cold rolling (final cold rolling) was performed on the steel sheet after the annealing process before the final cold rolling to produce a cold rolled steel sheet having a thickness of 0.23 mm. A decarburization annealing process was performed on the cold-rolled steel sheet after the cold rolling process. In the decarburization annealing step, the decarburization annealing temperature was set to 830 ° C. The atmosphere in the heat treatment furnace for performing the decarburization annealing treatment was a well-known wet nitrogen-hydrogen mixed atmosphere containing hydrogen and nitrogen. Then, the oxygen potential (P _H2O / P _H2 ) in the atmosphere in the temperature raising step was set to 0.1. Furthermore, in the temperature raising step, the temperature raising rate S1 in the temperature range of 500 to 600 ° C. and the temperature raising rate S2 in the temperature range of 600 to 700 ° C. are as shown in Table 2.

  On the surface of the steel plate after decarburization annealing, the same annealing separator (aqueous slurry) containing MgO as the main component as in Example 1 was applied, and then wound into a coil shape. Finish annealing was implemented with respect to the steel plate wound up by the coil shape. The finish annealing temperature was 1150 ° C., and the holding time at the finish annealing temperature was 10 hours. The steel plate after finish annealing was allowed to cool.

  After the coiled steel sheet after the final annealing process was washed with water, an insulating film forming process was performed. In the insulating coating forming step, an insulating coating treatment agent mainly composed of colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheet after the finish annealing step. The same insulating film treating agent as in Example 1 was used. After applying the insulating film treating agent to the steel sheet surface, flattening annealing was performed. In flattening annealing, it was kept at 900 ° C. for 30 seconds. The grain-oriented electrical steel sheet of each test number was manufactured from the above manufacturing process.

[Evaluation test]
By the same method as Example 1, magnetic flux density B8 of each test number, Goss direction integration degree B8 / Bs, iron loss _W17 / ₅₀ , and film adhesion were evaluated.

[Test results]
The test results obtained are shown in Table 2. Referring to Table 2, in test numbers 12-14, 16, 20-22, 24, 28-30, 32, 36-38 and 40, the chemical composition of the slab is appropriate, and each production process The conditions at were also appropriate. As a result, in any test number, the magnetic flux density B8 was as high as 1.901 T or more, and the Goss direction integration degree B8 / Bs was as high as 0.954 or more. Furthermore, the iron loss W _17/50 was as low as 0.831 W / kg or less. In the film adhesion evaluation test, the area ratio was 80.0% or more, and excellent film adhesion was exhibited.

On the other hand, in test numbers 1 to 8, the Si content was less than 3.30%. Therefore, the iron loss W _17/50 was less than 0.831 W / kg.

  In test numbers 41 to 48, the Si content was too high. Therefore, in the test numbers 42, 45, and 46, cracks occurred in the steel plate during cold rolling. Moreover, in the test numbers 41, 43, 44, 47, and 48, the magnetic flux density B8 was less than 1.901T, and the Goth orientation integration degree B8 / Bs was less than 0.954.

In test numbers 9, 10, 17, 18, 25, 26, 33, and 34, the temperature increase rate S2 at 600 to 700 ° C. was too slow. Therefore, the Goss direction integration degree B8 / Bs was less than 0.954. Therefore, the magnetic flux density B8 was less than 1.900 T, and the iron loss W _17/50 also exceeded 0.831 W / kg.

In test numbers 15, 23, 31, and 39, the temperature increase rate S2 was too fast. Therefore, the Goss orientation integration degree B8 / Bs is as high as 0.954 or more, the magnetic flux density B8 is 1.900 T or more, and the iron loss W _17/50 is 0.831 W / kg or less, but the film adhesion is good. It was low.

In test numbers 11, 19, 27, and 35, the heating rate S1 and the heating rate S2 did not satisfy the formula (1). Therefore, the Goss orientation integration degree B8 / Bs is as high as 0.954 or more, the magnetic flux density B8 is 1.900 T or more, and the iron loss W _17/50 is 0.831 W / kg or less, but the film adhesion is good. It was low.

[Manufacture of grain-oriented electrical steel sheets for each test number]
The chemical composition is mass%, C: 0.075%, Si: 3.45%, Mn: 0.075%, S: 0.028%, sol. A slab containing Al: 0.028%, N: 0.008%, Sn: 0.110%, Cu: 0.070%, Cr: 0.035%, with the balance being Fe and impurities was prepared.

  Each test number slab was heated to 1350 ° C. in a heating furnace. A hot rolling process was performed on the heated slab to produce a hot-rolled steel sheet having a thickness of 2.3 mm. The finish rolling temperature (° C.) was in the range of 1000 to 1100 ° C. in any test number.

  An annealing process before final cold rolling was performed on the hot-rolled steel sheet. In the annealing process before the final cold rolling, the hot-rolled steel sheet was heated to 1120 ° C., and then the hot-rolled steel sheet was annealed at an annealing temperature of 900 ° C. and a holding time at the annealing temperature of 40 seconds. One cold rolling (final cold rolling) was performed on the steel sheet after the annealing process before the final cold rolling to produce a cold rolled steel sheet having a thickness of 0.23 mm.

One cold rolling (final cold rolling) was performed on the steel sheet after the annealing process before the final cold rolling to produce a cold rolled steel sheet having a thickness of 0.23 mm. A decarburization annealing process was performed on the cold-rolled steel sheet after the cold rolling process. In the decarburization annealing step, the decarburization annealing temperature was set to 830 ° C. The atmosphere in the heat treatment furnace for performing the decarburization annealing treatment was a well-known wet nitrogen-hydrogen mixed atmosphere containing hydrogen and nitrogen. Then, the oxygen potential (P _H2O / P _H2 ) in the atmosphere in the temperature raising step was set to 0.1. Furthermore, in the temperature raising step, the temperature raising rate S1 in the temperature range of 500 to 600 ° C. and the temperature raising rate S2 in the temperature range of 600 to 700 ° C. are as shown in Table 3.

  On the surface of the steel plate after decarburization annealing, the same annealing separator (aqueous slurry) containing MgO as the main component as in Example 1 was applied, and then wound into a coil shape. Finish annealing was implemented with respect to the steel plate wound up by the coil shape. The finish annealing temperature was 1150 ° C., and the holding time at the finish annealing temperature was 10 hours. The steel plate after finish annealing was allowed to cool.

  After the coiled steel sheet after the final annealing process was washed with water, an insulating film forming process was performed. In the insulating coating forming step, an insulating coating treatment agent mainly composed of colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheet after the finish annealing step. The same insulating film treating agent as in Example 1 was used. After applying the insulating film treating agent to the steel sheet surface, flattening annealing was performed. In flattening annealing, it was kept at 900 ° C. for 30 seconds. The grain-oriented electrical steel sheet of each test number was manufactured from the above manufacturing process.

[Evaluation test]
By the same method as Example 1, magnetic flux density B8 of each test number, Goss direction integration degree B8 / Bs, iron loss _W17 / ₅₀ , and film adhesion were evaluated.

[Test results]
The test results obtained are shown in Table 3. Referring to Table 3, in test numbers 11, 12, 17, 18, 23-25, 30-32, 37 and 40, the chemical composition of the slab is appropriate, and the conditions in each manufacturing process are It was appropriate. As a result, in any of the test numbers, the magnetic flux density B8 was as high as 1.915 T or more, and the Goss direction integration degree B8 / Bs was as high as 0.956 or more. Furthermore, the iron loss W _17/50 was as low as 0.806 W / kg or less. In the film adhesion evaluation test, the area ratio was 80.0% or more, and excellent film adhesion was exhibited.

On the other hand, in the test numbers 1 to 3, the heating rate S1 at 500 to 600 ° C. was too slow. Therefore, the Goss direction integration degree B8 / Bs was less than 0.956. Therefore, the magnetic flux density B8 was less than 1.915 T, and the iron loss W _17/50 also exceeded 0.806 W / kg.

In test number 42, the temperature increase rate S1 at 500 to 600 ° C. was too fast. Therefore, the Goss orientation integration degree B8 / Bs is as high as 0.956 or more, the magnetic flux density B8 is 1.915 T or more, and the iron loss W _17/50 is 0.806 W / kg or less. It was low.

In the test numbers 6-8, 13, 19, 20, 26, and 39, the heating rate S2 at 600 to 700 ° C. was too slow. Therefore, the Goss direction integration degree B8 / Bs was less than 0.956. Therefore, the magnetic flux density B8 was less than 1.910 T, and the iron loss W _17/50 also exceeded 0.806 W / kg.

In test numbers 27 and 34 to 36, the temperature increase rate S2 was too fast. Therefore, the Goss orientation integration degree B8 / Bs is as high as 0.956 or more, the magnetic flux density B8 is 1.915 T or more, and the iron loss W _17/50 is 0.806 W / kg or less. It was low.

In test numbers 4, 5, 9, 10, 14 to 16, 21, 22, 28, 29, 33, 38, and 41, the temperature increase rate S1 and the temperature increase rate S2 did not satisfy the formula (1). Therefore, the Goss orientation integration degree B8 / Bs is as high as 0.956 or more, the magnetic flux density B8 is 1.915 T or more, and the iron loss W _17/50 is 0.806 W / kg or less. It was low.

[Manufacture of grain-oriented electrical steel sheets for each test number]
Chemical composition is mass%, C: 0.075%, Si: 3.50%, Mn: 0.075%, S: 0.028%, sol. Al: 0.028%, N: 0.008%, Sn: 0.110%, Cu: 0.070%, Cr: 0.035%, and Bi: 0.0020%, the balance being Fe And the slab which is an impurity was prepared.

  Each test number slab was heated to 1350 ° C. in a heating furnace. A hot rolling process was performed on the heated slab to produce a hot-rolled steel sheet having a thickness of 2.3 mm. The finish rolling temperature (° C.) was in the range of 1000 to 1100 ° C. in any test number.

  An annealing process before final cold rolling was performed on the hot-rolled steel sheet. In the annealing process before the final cold rolling, the hot-rolled steel sheet was heated to 1120 ° C., and then the hot-rolled steel sheet was annealed at an annealing temperature of 900 ° C. and a holding time at the annealing temperature of 40 seconds. One cold rolling (final cold rolling) was performed on the steel sheet after the annealing process before the final cold rolling to produce a cold rolled steel sheet having a thickness of 0.23 mm.

One cold rolling (final cold rolling) was performed on the steel sheet after the annealing process before the final cold rolling to produce a cold rolled steel sheet having a thickness of 0.23 mm. A decarburization annealing process was performed on the cold-rolled steel sheet after the cold rolling process. In the decarburization annealing step, the decarburization annealing temperature was set to 830 ° C. The atmosphere in the heat treatment furnace for performing the decarburization annealing treatment was a well-known wet nitrogen-hydrogen mixed atmosphere containing hydrogen and nitrogen. Then, the oxygen potential (P _H2O / P _H2 ) in the atmosphere in the temperature raising step was set to 0.1. Furthermore, in the temperature raising step, the temperature raising rate S1 in the temperature range of 500 to 600 ° C. and the temperature raising rate S2 in the temperature range of 600 to 700 ° C. are as shown in Table 4.

  On the surface of the steel plate after decarburization annealing, the same annealing separator (aqueous slurry) containing MgO as the main component as in Example 1 was applied, and then wound into a coil shape. Finish annealing was implemented with respect to the steel plate wound up by the coil shape. The finish annealing temperature was 1150 ° C., and the holding time at the finish annealing temperature was 10 hours. The steel plate after finish annealing was allowed to cool.

  After the coiled steel sheet after the final annealing process was washed with water, an insulating film forming process was performed. In the insulating coating forming step, an insulating coating treatment agent mainly composed of colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheet after the finish annealing step. The same insulating film treating agent as in Example 1 was used. After applying the insulating film treating agent to the steel sheet surface, flattening annealing was performed. In flattening annealing, it was kept at 900 ° C. for 30 seconds. The grain-oriented electrical steel sheet of each test number was manufactured from the above manufacturing process.

[Evaluation test]
By the same method as Example 1, magnetic flux density B8 of each test number, Goss direction integration degree B8 / Bs, iron loss _W17 / ₅₀ , and film adhesion were evaluated. In addition, with respect to the sample whose magnetic flux density B8 is 1.90 T or more, the magnetic domain fragmentation process was performed by laser irradiation, and then the iron loss W _17/50 was measured by the same method as in Example 1.

[Test results]
The obtained test results are shown in Table 4. Referring to Table 4, in test numbers 11, 12, 17, 18, 23-25, 30-32, 37 and 40, the chemical composition of each slab is appropriate, and the conditions in each manufacturing process are It was appropriate. As a result, in any of the test numbers, the magnetic flux density B8 was as high as 1.926 T or more, and the Goss direction integration degree B8 / Bs was as high as 0.963 or more. Furthermore, the iron loss W _17/50 after laser irradiation was as low as 0.741 W / kg or less. In the film adhesion evaluation test, the area ratio was 80.0% or more, and excellent film adhesion was exhibited.

  On the other hand, in the test numbers 1 to 3, the heating rate S1 at 500 to 600 ° C. was too slow. Therefore, the Goss direction integration degree B8 / Bs was less than 0.963. Therefore, the magnetic flux density B8 was less than 1.926T.

In test number 42, the temperature increase rate S1 at 500 to 600 ° C. was too fast. Therefore, the Goss orientation integration degree B8 / Bs is as high as 0.963 or more, the magnetic flux density B8 is 1.926 T or more, and the iron loss W _17/50 after laser irradiation is 0.741 W / kg or less, The film adhesion was low.

  In the test numbers 6-8, 13, 19, 20, 26, and 39, the heating rate S2 at 600 to 700 ° C. was too slow. Therefore, the Goss direction integration degree B8 / Bs was less than 0.963. Therefore, the magnetic flux density B8 was less than 1.926T.

In test numbers 27 and 34 to 36, the temperature increase rate S2 was too fast. Therefore, the Goss orientation integration degree B8 / Bs is as high as 0.963 or more, the magnetic flux density B8 is 1.926 T or more, and the iron loss W _17/50 after laser irradiation is 0.741 W / kg or less, The film adhesion was low.

In test numbers 4, 5, 9, 10, 14, 15, 16, 21, 22, 28, 29, 33, 38, and 41, the temperature increase rate S1 and the temperature increase rate S2 did not satisfy the formula (1). Therefore, the Goss orientation integration degree B8 / Bs is as high as 0.963 or more, the magnetic flux density B8 is 1.926 T or more, and the iron loss W _17/50 after laser irradiation is 0.741 W / kg or less, The film adhesion was low.

The embodiment of the present invention has been described above. However, the above-described embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately changing the above-described embodiment without departing from the spirit thereof.

Claims (3)

The chemical composition is
% By mass
C: 0.020 to 0.100%,
Si: 3.30 to 3.75%,
Mn: 0.010 to 0.300%,
S and / or Se: 0.001 to 0.050% in total,
sol. Al: 0.010 to 0.065%,
N: 0.002 to 0.015%,
Sn: 0 to 0.500%,
Cr: 0 to 0.500%
Cu: 0 to 0.500%,
Bi: 0 to 0.0100%, and
Balance: Fe and impurities,
A hot rolling process for producing a steel sheet by performing hot rolling on a slab comprising:
A cold rolling step of performing cold rolling one or more times on the steel sheet after the hot rolling step;
Among the one or more times of the cold rolling, an annealing process before the final cold rolling for performing an annealing process on the steel plate before the final cold rolling,
Including a temperature raising step for heating the steel plate after the cold rolling step to a decarburizing annealing temperature, and a decarburizing step for holding the steel plate at a decarburizing annealing temperature of 800 to 950 ° C. and performing decarburizing annealing. Decarburization annealing process,
An annealing separator application step for applying an annealing separator to the surface of the steel sheet after the decarburization annealing step,
And a final annealing step for performing a final annealing on the steel sheet coated with the annealing separator,
In the temperature raising step of the decarburization annealing step,
The temperature increase rate S1 in the temperature range of 500 to 600 ° C. is 300 to 1500 ° C./second,
The temperature rising rate S2 in the temperature range of 600 to 700 ° C. is 300 to 750 ° C./second,
The temperature increase rate S1 and the temperature increase rate S2 satisfy the formula (1).
A method for producing grain-oriented electrical steel sheets.
0.50 ≦ S2 / S1 ≦ 0.90 (1) It is a manufacturing method of the grain-oriented electrical steel sheet according to claim 1,
The chemical composition of the slab is
Sn: 0.005 to 0.500%,
Cr: 0.010 to 0.500%, and
Cu: 0.010 to 0.500%,
Containing one or more selected from the group consisting of:
A method for producing grain-oriented electrical steel sheets. It is a manufacturing method of the grain-oriented electrical steel sheet according to claim 1 or 2,
Bi: 0.0010 to 0.0100%,
Containing
A method for producing grain-oriented electrical steel sheets.

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