Hot-rolled and annealed steel sheet for grain-oriented electrical steel sheets

Abstract

This hot-rolled and annealed steel sheet for a grain-oriented electromagnetic steel sheet satisfies the following conditions with regard to a particle size-detection intensity distribution of precipitates having a circle equivalent diameter D of 50-1,000 nm: a most frequent diameter Dp is 50-350 nm; a number density f(Dp) of the most frequent diameter is 1,000,000 particles / g or greater; and a value Wp / Dp obtained by dividing a half-value width Wp of the most frequent diameter by the most frequent diameter Dp is 0.75-2.25. Additionally, when the most frequent diameter of Al-based precipitates is denoted by DpAl in units of nm, and the most frequent diameter of Nb-based precipitates is denoted by DpNb in units of nm, the hot-rolled and annealed steel sheet for a grain-oriented electromagnetic steel sheet satisfies the condition that DpAl - DpNb is 22-100 nm.

Description

[Technical Field]

[0001] This invention relates to a hot-rolled and annealed steel sheet for grain-oriented electrical steel sheets. This application claims priority based on Japanese Patent Application No. 2024-034150, filed in Japan on March 6, 2024, and the contents of that application are incorporated herein by reference. [Background technology]

[0002] Grain-oriented electrical steel sheet contains 7% by mass or less of Si, {110} <001> It has a secondary recrystallized texture concentrated in the orientation (Goss orientation). <001> Orientation refers to the orientation in which the {110} planes of the crystal are aligned parallel to the rolling plane, and the crystal is <001> This means that the axis is positioned parallel to the rolling direction.

[0003] The magnetic properties of grain-oriented electrical steel sheets are {110} <001> It is greatly influenced by the degree of concentration in a particular direction. In particular, the rolling direction of the steel sheet, which is the main magnetization direction when the steel sheet is used, and the crystal, which is the easy magnetization direction. <001> The relationship with direction is considered important. Therefore, in recent practical grain-oriented electrical steel sheets, the crystal structure <001> The angle between the direction of movement and the rolling direction is controlled to fall within a range of approximately 5°.

[0004] Such precise crystal orientation control is achieved by appropriately dispersing fine precipitates called inhibitors in the steel before finish annealing, and by holding the steel sheet at a high temperature during finish annealing. For example, the inhibitors enhance the selective growth of Goss-oriented grains, and as a result, secondary recrystallization proceeds so that Goss-oriented grains preferentially grow during finish annealing. To date, attempts have been made to highly control inhibitors with the aim of precisely controlling crystal orientation.

[0005] For example, Patent Document 1 discloses the use of MnS as an inhibitor and the performance of two cold rolling processes. Patent documents 2 and 3 disclose controlling MnS+AlN and MnS(and / or MnSe)+Sb as inhibitors, respectively. Patent Document 4 discloses a technique for preferably controlling an inhibitor in order to lower the slab heating temperature for the purpose of reducing manufacturing costs.

[0006] Patent Document 5 discloses controlling the primary recrystallized grain size related to the inhibitor and its dispersion. Patent Documents 6 to 8 disclose adding Nb, V, etc. to a grain-oriented electrical steel sheet.

[0007] Also, Patent Documents 9 to 11 disclose a technique for improving magnetic strain by forming sub-grain boundaries in secondary recrystallized grains by precisely controlling the atmosphere and residence time during finish annealing. These techniques show a technical concept of expanding the temperature range in which secondary recrystallization proceeds to form sub-grain boundaries, and at the same time, it is shown that an improvement in magnetic flux density can be expected.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Patent Document 9

Patent Document 10

[0009] In recent years, in the global movement for environmental conservation such as power and energy reduction, the demand for higher efficiency of transformers has been increasing. Under such a social environment, there is also a demand for improving the performance of grain-oriented electrical steel sheets used for transformer core materials and the like. In particular, it is required to increase the magnetic flux density of grain-oriented electrical steel sheets.

[0010] As a result of the study by the present inventors, it was found that the conventional inhibitor control techniques disclosed in Patent Documents 1 to 8 above do not fully meet the requirements for grain-oriented electrical steel sheets, and further increase in magnetic flux density is necessary.

[0011] One aspect of the present invention has been made in view of the above problems. One aspect of the present invention aims to provide a hot-rolled annealed steel sheet for grain-oriented electrical steel sheets capable of increasing the magnetic flux density, based on the current situation where an increase in the magnetic flux density of grain-oriented electrical steel sheets is required. [Means for Solving the Problems]

[0012] The gist of the present invention is as follows.

[0013] (1) The hot-rolled annealed steel sheet for grain-oriented electrical steel sheets according to one aspect of the present invention is by mass%, C: More than 0.0050% ~0.10%, Si: 2.0 to 7.0%, Mn: 0.050 to 1.0%, S: 0 to 0.0350%, Se: 0 to 0.0350%, Total content of S + Se: 0.0030 to 0.0350%, Al: 0.010 to 0.0650% N: 0.0040~0.0120%, Nb: 0.0030~0.030%, V: 0~0.030%, Mo: 0~0.030%, Ta: 0~0.030%, W: 0~0.030%, Cu: 0~0.40%, Bi: 0~0.010%, B: 0~0.080%, P: 0-0.50% Ti: 0~0.0150%, Sn: 0~0.10%, Sb: 0~0.10%, Cr: 0~0.30%, Ni: 0~1.0%, It contains and has a chemical composition consisting of Fe and impurities as the remainder, Precipitates which are the residue obtained by electrolytic extraction of the aforementioned hot-rolled annealed steel sheet. Based on a calibration curve created from six types of standard particles with particle sizes of 29 nm, 48 nm, 100 nm, 200 nm, 300 nm, and 500 nm. Particle size-number density distribution measure , Let Dp be the most frequent diameter in nm. Let f(Dp) be the number density of the most mode diameter in units of particles / g. When the full width at half maximum of the most mode diameter is denoted as Wp in units of nm, Dp is 50~350nm, f(Dp) is 1,000,000 particles / g or more. Wp / Dp is 0.75~2.25. Satisfying the conditions, Precipitates which are the residue obtained by electrolytic extraction of the aforementioned hot-rolled annealed steel sheet. Based on a calibration curve created from six types of standard particles with particle sizes of 29 nm, 48 nm, 100 nm, 200 nm, 300 nm, and 500 nm. Particle size-detection intensity distribution measure , The most frequent diameter of Al-based precipitates in units of nm (Dp). Al year, The most frequent diameter of Nb precipitates in units of nm (Dp) Nb In that case, Dp Al -Dp Nb 22~100nm, It satisfies the condition. (2) The hot-rolled annealed steel sheet for grain-oriented electrical steel sheets described in (1) above may contain, as the chemical composition, at least one selected from the group consisting of Nb, V, Mo, Ta, and W in a total amount of 0.0030 to 0.030 mass%. [Effects of the Invention]

[0014] According to the above embodiment of the present invention, a hot-rolled and annealed steel sheet for grain-oriented electrical steel sheets is provided that can increase the magnetic flux density. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic diagram of the particle size-number density distribution of precipitates with an equivalent circle diameter D of 50-1000 nm. [Figure 2] This is a schematic diagram of the particle size-detection intensity distribution of precipitates with an equivalent circle diameter D of 50-1000 nm. [Figure 3] This is a flowchart illustrating a method for manufacturing a hot-rolled and annealed steel sheet for grain-oriented electrical steel sheets according to one embodiment of the present invention. [Modes for carrying out the invention]

[0016] A preferred embodiment of the present invention will be described in detail. However, the present invention is not limited to the configuration disclosed in this embodiment, and various modifications are possible without departing from the spirit of the invention. Furthermore, the numerical limits described below include both lower and upper limits. Numerical values ​​indicated as "greater than" or "less than" are not included in the numerical range. Also, "%" in relation to chemical composition means "mass%" unless otherwise specified.

[0017] Furthermore, in the following description, regarding the precipitates in the steel that are characteristic of this embodiment, the term "inhibitor" will be used mainly in descriptions related to the secondary recrystallization mechanism, and the term "precipitate" will be used mainly in descriptions related to the compound phase observed in the microstructure. However, in this embodiment, the terms "inhibitor" and "precipitate" are not used with the intention of strictly distinguishing between them.

[0018] As mentioned above, there is currently a need to increase the magnetic flux density of grain-oriented electrical steel sheets.

[0019] Therefore, the inventors focused on the technical concept of "expanding the secondary recrystallization temperature range" disclosed in the above-mentioned Patent Documents 9 to 11. These Patent Documents 9 to 11 primarily utilize this "expanding the secondary recrystallization temperature range" technique for the formation of subgrain boundaries within secondary recrystallized grains and the associated noise reduction. The inventors considered that further improvement in magnetic flux density would be possible if this "expanding the secondary recrystallization temperature range" technique were optimized to enhance the selectivity of crystal orientation.

[0020] Specifically, we investigated how to effectively expand the secondary recrystallization temperature range by appropriately controlling the inhibitor morphology in the steel, and how to preferentially grow grains with a desirable crystal orientation during the secondary recrystallization process within the expanded temperature range. As a result, we found that by optimally controlling the morphology of precipitates contained in the hot-rolled and annealed steel sheet during the manufacturing process of grain-oriented electrical steel sheets, the secondary recrystallization temperature range expands during finish annealing, Goss-oriented grains grow preferentially, and the magnetic flux density of the final grain-oriented electrical steel sheet can be increased beyond that of conventional techniques.

[0021] Generally, inhibitors are fine precipitates in steel with a diameter of approximately 1000 nm or less. These inhibitors have a grain boundary pinning effect, suppressing grain growth. When the temperature exceeds approximately 1000°C during finish annealing, these inhibitors dissolve into the αFe phase, the matrix phase, and the grain boundary pinning effect weakens. As a result, abnormal grain growth occurs, a phenomenon known as secondary recrystallization.

[0022] For example, sulfides and selenides are used as Mn-based precipitates, and nitrides are used as Al-based precipitates, serving as major inhibitors. Mn-based inhibitors and Al-based inhibitors (Al-based inhibitors controlled before cold rolling) are mainly used in manufacturing methods where the slab heating temperature before hot rolling is 1300°C or higher (hereinafter sometimes referred to as the "high-temperature slab heating process"). Al-based inhibitors (Al-based inhibitors controlled after cold rolling) are mainly used in manufacturing methods where the slab heating temperature before hot rolling is 1280°C or lower, and nitriding is performed between cold rolling and finish annealing (hereinafter sometimes referred to as the "low-temperature slab heating process"). In addition to the above inhibitors, carbides and nitrides of Nb, V, Mo, Ta, W, etc., are sometimes used as auxiliary inhibitors.

[0023] Traditionally, in order to form inhibitors with appropriate functions within steel, the steel composition and manufacturing conditions have been controlled during the production of grain-oriented electrical steel sheets. In particular, the steel composition, hot rolling conditions, and decarburization annealing conditions have been recognized as manufacturing conditions that greatly influence the morphology of the inhibitors, and these conditions have been precisely controlled.

[0024] In this embodiment, by controlling the size and distribution of precipitates (inhibitors) contained in the hot-rolled annealed steel sheet to an appropriate range, the secondary recrystallization temperature range is expanded during the subsequent finish annealing process, and the selectivity of the crystal orientation associated with the progression of secondary recrystallization is enhanced. Specifically, the above effect is obtained by allowing relatively fine inhibitors and relatively coarse inhibitors to coexist in the hot-rolled annealed steel sheet in an appropriate size and distribution.

[0025] The inventors of this invention estimate that the above effect is obtained through the following mechanism.

[0026] First, let's consider the reason why the temperature range for secondary recrystallization is expanded. As mentioned above, secondary recrystallization occurs because the pinning effect of the grain boundaries weakens as the inhibitor dissolves. During finish annealing, it is thought that fine inhibitors dissolve and disappear earlier than coarse inhibitors. Therefore, when fine and coarse inhibitors coexist, it is thought that the fine inhibitors preferentially disappear early in the heating process of finish annealing. In particular, when Nb is added, it becomes possible to favorably control the decomposition of fine inhibitors, which decompose at lower temperatures than conventional inhibitors such as AlN.

[0027] As fine inhibitors dissolve, coarse inhibitors may grow, similar to Ostwald growth. However, the increase in pinning force due to the growth of coarse inhibitors is thought to have a smaller impact than the decrease in pinning force due to the disappearance of fine inhibitors. Therefore, if fine and coarse inhibitors coexist, and the fine inhibitors dissolve earlier than the coarse inhibitors, secondary recrystallization is thought to begin at a relatively low temperature during the heating process of the finish annealing.

[0028] In addition, it is thought that coarse inhibitors remain non-equilibrium dissolved until relatively high temperatures during the heating process of the finish annealing, and that their pinning effect is maintained up to high temperatures. Therefore, when fine and coarse inhibitors coexist, and the coarse inhibitors remain until high temperatures, it is thought that the pinning effect is maintained up to high temperatures, and secondary recrystallization continues up to relatively high temperatures.

[0029] In other words, when fine inhibitors and coarse inhibitors coexist, secondary recrystallization starts at a relatively low temperature during the heating process of the finish annealing and continues up to a relatively high temperature, thus expanding the temperature range in which secondary recrystallization can proceed.

[0030] Next, let's consider the reason why the selectivity of crystal orientation improves. As mentioned above, secondary recrystallization proceeds with the preferential growth of Goss-oriented grains. This preferential growth of Goss-oriented grains is thought to be due to the special characteristics of the grain boundaries (grain boundary properties) and the special characteristics of the grain size (size advantage) of Goss-oriented grains.

[0031] However, the driving force for the preferential growth of Goss-oriented grains is not very strong. Therefore, if grain boundary movement occurs relatively easily even in grains other than Goss-oriented grains during secondary recrystallization, for example, if the inhibitor decomposition is rapid and the grain growth pinning effect is weak, resulting in a relatively high grain growth rate (a relatively high driving force for grain growth), then grains other than Goss-oriented grains will also grow easily. In this case, the preferential growth of Goss-oriented grains is inhibited.

[0032] Therefore, to preferentially grow Goss-oriented grains, the inhibitor decomposition rate should be kept as slow as possible, the grain growth rate during secondary recrystallization should be relatively fast relative to the inhibitor decomposition rate, and secondary recrystallization should be sustained for a long period of time. For example, the heating rate in the temperature range where the inhibitor strength weakens (the temperature range in which the inhibitor dissolves) should be slowed down, the inhibitor dissolution rate should be slowed down, and the resulting secondary recrystallized grain growth rate should be relatively fast relative to the inhibitor decomposition rate. However, this method increases the total finish annealing time, so a decrease in productivity is unavoidable.

[0033] When it is difficult to industrially extend the finish annealing time (when it is difficult to change the heating rate if the maximum temperature reached is the same), even if the heating rate is constant, if the temperature range in which secondary recrystallization proceeds can be expanded by slowing down the decomposition rate of the inhibitor, it is possible to extend the time during which secondary recrystallization proceeds, make the growth rate of secondary recrystallized grains relatively fast, and improve the preferential growth of secondary recrystallized grains without reducing productivity. For example, considering that the entire surface of the grain-oriented electrical steel sheet will eventually be covered with secondary recrystallized grains, it can be understood that extending the time during which secondary recrystallization proceeds leads to an acceleration of the growth rate of secondary recrystallized grains relative to the decomposition rate of the inhibitor.

[0034] In other words, when fine and coarse inhibitors coexist, the temperature range in which the inhibitor decomposition rate is slow expands, and the temperature range in which secondary recrystallization progresses, where the growth rate of secondary recrystallized grains is relatively fast relative to the inhibitor decomposition rate, expands. As a result, it is thought that Goss-oriented grains are more likely to grow preferentially. Consequently, it is thought that it becomes possible to ultimately increase the magnetic flux density.

[0035] In this embodiment, by comprehensively and inseparably controlling the steel composition, casting conditions, hot rolling conditions, and hot-rolled sheet annealing conditions, relatively fine precipitates and relatively coarse precipitates are made to coexist in an appropriate size and distribution in the hot-rolled annealed steel sheet after the hot-rolled sheet annealing process. Furthermore, in this embodiment, the morphology of the precipitates is preferably controlled by adding auxiliary inhibitor-forming elements.

[0036] In this embodiment, the morphology of the precipitates described above is defined based on hot-rolled and annealed steel sheet (steel sheet immediately before cold rolling).

[0037] The hot-rolled and annealed steel sheet for grain-oriented electrical steel sheets according to this embodiment will be described in detail below.

[0038] The hot-rolled and annealed steel sheet according to this embodiment is, by mass %, C: 0.0010~0.10%, Si: 2.0~7.0%, Mn: 0.050~1.0%, S: 0~0.0350%, Se: 0~0.0350%, S+Se total content: 0.0030~0.0350%, Al: 0.010~0.0650%, N: 0.0040~0.0120%, Nb: 0.0030~0.030%, V: 0~0.030%, Mo: 0~0.030%, Ta: 0~0.030%, W: 0~0.030%, Cu: 0~0.40%, Bi: 0~0.010%, B: 0~0.080%, P: 0-0.50% Ti: 0~0.0150%, Sn: 0~0.10%, Sb: 0~0.10%, Cr: 0~0.30%, Ni: 0~1.0%, It contains and has a chemical composition consisting of Fe and impurities as the remainder, Regarding the particle size-number density distribution of precipitates with an equivalent circular diameter D of 50-1000 nm, which are the residues obtained by electrolytic extraction of hot-rolled annealed steel sheets, Let Dp be the most frequent diameter in nm. Let f(Dp) be the number density of the most mode, in units of particles / g. When the full width at half maximum of the most mode is denoted as Wp in units of nm, Dp is 50~350nm, f(Dp) is 1,000,000 particles / g or more. Wp / Dp satisfies 0.75 to 2.25, Regarding the particle size-detection intensity distribution of precipitates with an equivalent circle diameter D of 50-1000 nm, which are the residues obtained by electrolytic extraction of hot-rolled annealed steel sheets, The most frequent diameter of Al-based precipitates in units of nm (Dp). Al year, The most frequent diameter of Nb precipitates in units of nm (Dp) Nb In that case, DpAl -Dp Nb 22~100nm, It satisfies the condition.

[0039] Furthermore, the hot-rolled annealed steel sheet according to this embodiment may contain, in terms of chemical composition, at least one selected from the group consisting of Nb, V, Mo, Ta, and W in a total amount of 0.0030 to 0.030% by mass.

[0040] 1.Chemical composition The chemical composition of the hot-rolled and annealed steel sheet according to this embodiment may be the same as the general chemical composition used for grain-oriented electrical steel sheets.

[0041] It should be noted that the chemical composition of hot-rolled annealed steel sheets, which are intermediate products, is rarely described in publicly available literature on grain-oriented electrical steel sheets. However, since the steel composition hardly changes during the process from slab to before decarburization and annealing, the chemical composition of hot-rolled annealed steel sheets can be considered to be basically the same as the chemical composition of slabs disclosed in publicly available literature.

[0042] The hot-rolled and annealed steel sheet according to this embodiment has a chemical composition that includes basic elements, optional elements as needed, and the remainder being Fe and impurities.

[0043] The hot-rolled and annealed steel sheet according to this embodiment contains, by mass fraction, the following basic elements (major alloying elements): C: 0.0010~0.10%, Si: 2.0~7.0%, Mn: 0.050~1.0%, total S+Se content: 0.0030~0.0350%, Al: 0.010~0.0650%, N: 0.0040~0.0120%, and Nb: 0.0030~0.030%.

[0044] C: 0.0010~0.10% Carbon (C) is an effective element for controlling the primary recrystallization structure during the manufacturing process. However, excessive C content in the final product negatively affects its magnetic properties. Therefore, the C content of hot-rolled annealed steel sheets should be between 0.0010% and 0.10%. The preferred upper limit for C content is 0.0850% and 0.0750%. Note that C is purified in the decarburization annealing and finish annealing processes described later, and after the finish annealing process, it becomes 0.0050% or less. When C is present, considering productivity in industrial production, the C content may be greater than 0% or greater than 0.0010%.

[0045] Si: 2.0~7.0% Silicon (Si) increases the electrical resistance of grain-oriented electrical steel sheets, thereby reducing iron loss. If the Si content is less than 2.0%, austenite transformation occurs during finish annealing, damaging the crystal orientation of the grain-oriented electrical steel sheet. On the other hand, if the Si content exceeds 7.0%, cold workability decreases, making the sheet more prone to cracking during cold rolling. Therefore, the Si content of hot-rolled and annealed steel sheets should be between 2.0% and 7.0%. The preferred lower limit of the Si content is 2.50%, and more preferably 3.0%. The preferred upper limit of the Si content is 4.50%, and more preferably 4.0%.

[0046] Mn: 0.050~1.0% Manganese (Mn) combines with S and Se to precipitate as MnS and MnSe, functioning as inhibitors. To favorably control the morphology of these inhibitors (precipitates), the Mn content of the hot-rolled annealed steel sheet should be between 0.050% and 1.0%. If the Mn content is below 0.050%, the amount of MnS and MnSe that function as inhibitors will be insufficient, thus inhibiting the proper progression of secondary recrystallization. Conversely, if the Mn content exceeds 1.0%, the amount of MnS and MnSe that function as inhibitors will be excessive, also inhibiting the proper progression of secondary recrystallization. In this embodiment, some of the inhibitory functions may be carried out by carbides, nitrides, or carbonitrides of Nb group elements. In this case, the amount of MnS and MnSe that precipitate as inhibitors may be controlled to be lower. Therefore, the upper limit of the Mn content is preferably 0.50%, and more preferably 0.20%.

[0047] S: 0~0.0350% Se: 0~0.0350% S+Se total content: 0.0030~0.0350% Sulfur (S) and selenium (Se) combine with manganese (Mn) to precipitate as MnS and MnSe, respectively, and function as inhibitors. To favorably control the morphology of these inhibitors (precipitates), the S content of the hot-rolled and annealed steel sheet should be 0 to 0.0350%, the Se content 0 to 0.0350%, and the total S+Se content 0.0030 to 0.0350%. A total S and Se content of 0.0030 to 0.0350% is preferable because it stabilizes secondary recrystallization. In this embodiment, some of the inhibitor functions may be carried out by carbides, nitrides, or carbonitrides of Nb group elements. In this case, the amount of MnS and MnSe precipitated as inhibitors may be controlled to be smaller. Therefore, the upper limit of the total S and Se content is preferably 0.0250%, and more preferably 0.010%. Furthermore, if S and Se remain in the steel after finish annealing, they can form compounds that degrade iron loss. Therefore, it is preferable to remove S and Se from the steel through purification during finish annealing to reduce their content.

[0048] Here, "the total content of S and Se is 0.0030 to 0.0350%" means that the hot-rolled annealed steel sheet may contain only S or Se in its chemical composition, and the content may be between 0.0030 and 0.0350%. Alternatively, it may contain both S and Se, and the total content may be between 0.0030 and 0.0350%.

[0049] Al: 0.010~0.0650% Aluminum (Al) combines with nitrogen (N) to precipitate as AlN or (Al,Si)N, functioning as inhibitors. To favorably control the morphology of these inhibitors (precipitates), the Al content of the hot-rolled and annealed steel sheet should be between 0.010% and 0.0650%. If the Al content is 0.010% or higher, AlN and (Al,Si)N precipitate in favorable forms through nitriding treatment in the low-temperature slab heating process, and secondary recrystallization is particularly stable in the high-temperature range. If the Al content is below 0.010%, the amount of AlN and (Al,Si)N that function as inhibitors precipitates is insufficient, hindering the proper progress of secondary recrystallization. If the Al content exceeds 0.0650%, the amount of AlN and (Al,Si)N that function as inhibitors precipitates is excessive, also hindering the proper progress of secondary recrystallization. The lower limit of the Al content is preferably 0.020%, and more preferably 0.0250%. From the viewpoint of stability during secondary recrystallization, the upper limit of the Al content is preferably 0.040%, and more preferably 0.030%.

[0050] N: 0.0040~0.0120% Nitrogen (N) combines with Al to precipitate as AlN or (Al,Si)N, functioning as an inhibitor. The N content of hot-rolled and annealed steel sheets should be between 0.0040% and 0.0120%. In low-temperature slab heating processes, N may be added to the steel during the manufacturing process through nitriding. If the N content exceeds 0.0120%, blistering, a type of defect, is more likely to occur in the steel sheet. The upper limit of the N content is preferably 0.010%, and more preferably 0.0090%. N is purified in the finish annealing process, and after the finish annealing process, the N content becomes 0.0050% or less.

[0051] Nb: 0.0030~0.030% Niobium (Nb) precipitates as carbides, nitrides, or carbonitrides, which act as inhibitors, and functions favorably as inhibitors. Specifically, it preferably expands the temperature range in which secondary recrystallization progresses. Therefore, the Nb content should be between 0.0030% and 0.030%. The lower limit of the Nb content is preferably 0.0040%, and more preferably 0.0050%. The upper limit of the Nb content is preferably 0.020%, and more preferably 0.010%.

[0052] The hot-rolled and annealed steel sheet according to this embodiment may contain impurities in its chemical composition. "Impurities" refer to elements that are introduced during the industrial production of steel from raw materials such as ore and scrap, or from the manufacturing environment. 。

[0053] Furthermore, the hot-rolled and annealed steel sheet according to this embodiment may contain optional elements in addition to the basic elements and impurities described above. For example, instead of a portion of the remaining Fe described above, V, Mo, Ta, W, Cu, Bi, B, P, Ti, Sn, Sb, Cr, Ni, etc. may be included as optional elements. These optional elements may be included according to their purpose. Therefore, there is no need to limit the lower limit of these optional elements, and the lower limit may be 0%. Moreover, even if these optional elements are included as impurities, the above effects will not be impaired.

[0054] V: 0~0.030% Mo: 0~0.030% Ta: 0~0.030% W: 0~0.030% Vanadium (V), molybdenum (Mo), tantalum (Ta), and tungsten (W) precipitate as auxiliary inhibitors such as carbides, nitrides, and carbonitrides, and function favorably as inhibitors. Specifically, they favorably expand the temperature range over which secondary recrystallization progresses. Therefore, the V content may be 0-0.030%, the Mo content may be 0-0.030%, the Ta content may be 0-0.030%, and the W content may be 0-0.030%.

[0055] In this embodiment, Nb, V, Mo, Ta, and / or W may be collectively referred to as "Nb group elements."

[0056] In this embodiment, the hot-rolled and annealed steel sheet preferably contains, as an Nb group element, at least one selected from the group consisting of Nb, V, Mo, Ta, and W in a total amount of 0.0030 to 0.030 mass%.

[0057] When Nb group element precipitates are used as inhibitors, if the total content of Nb group elements in the hot-rolled and annealed steel sheet is 0.030% or less (preferably 0.0030% to 0.030%), the morphology of the Nb group element precipitates is preferably controlled, and the secondary recrystallization temperature range is preferably expanded. As a result, Goss-oriented grains grow preferably, and the magnetic flux density of the resulting grain-oriented electrical steel sheet is preferably increased.

[0058] The reason why precipitates of Nb group elements function favorably as inhibitors is not clear, but it is thought to be as follows: Carbides, nitrides, or carbonitrides of Nb group elements are thought to precipitate non-equilibrium during the cooling process from high temperatures and act as precipitation nuclei for MnS and AlN that precipitate thereafter. Therefore, compared to cases where Nb group elements are not present, when Nb group elements are present, there are many more precipitation sites for MnS and AlN, and as a result, MnS and AlN are more likely to form as fine precipitates. In the hot-rolled annealed steel sheet according to this embodiment, the secondary recrystallization temperature range is expanded by allowing fine and coarse inhibitors to coexist, and precipitates of Nb group elements are thought to be particularly effective in expanding the secondary recrystallization temperature range to the lower temperature side.

[0059] The total content of Nb group elements is preferably 0.0040% or more, and more preferably 0.0050% or more. Furthermore, the total content of Nb group elements is preferably 0.020% or less, and more preferably 0.010% or less. If the total content of Nb group elements falls below 0.0030%, there will be insufficient precipitates of Nb group elements that act as precipitation nuclei, making it difficult for MnS and AlN to become finely ground. On the other hand, if the total content of Nb group elements exceeds 0.030%, the precipitation temperature range of the Nb group element precipitates will be high, and the precipitates of Nb group elements will tend to be coarse and low in density. In addition, the difference between the precipitation temperature range of Nb group element precipitates and the precipitation temperature range of MnS and AlN will be large, making it difficult for the Nb group element precipitates to effectively act as precipitation nuclei for the refinement of MnS and AlN.

[0060] Cu: 0~0.40% Bi: 0~0.010% B: 0~0.080% P: 0-0.50% Ti: 0~0.0150% Sn: 0~0.10% Sb: 0~0.10% Cr: 0~0.30% Ni: 0~1.0% Copper (Cu), bismuth (Bi), boron (B), phosphorus (P), titanium (Ti), tin (Sn), antimony (Sb), chromium (Cr), and nickel (Ni) may be included according to known purposes. There is no need to set a lower limit for the content of these selected elements, and the lower limit may be 0%.

[0061] In grain-oriented electrical steel sheets, relatively large changes in chemical composition (reduction in element content) occur through decarburization annealing and purification annealing during secondary recrystallization. For some elements, purification annealing can reduce the content to levels undetectable by general analytical methods (less than 1 ppm). However, the above chemical composition refers to that of hot-rolled annealed steel sheets. The steel composition hardly changes during the process from slab to before decarburization annealing.

[0062] The chemical composition of the hot-rolled annealed steel sheet according to this embodiment can be measured by a general method of analyzing steel. For example, the chemical composition of the hot-rolled annealed steel sheet can be measured by ICP-AES (Inductively The measurement should be performed using Coupled Plasma-Atomic Emission Spectrometry (ICP-AES). Specifically, the chemical composition can be determined by measuring a 35 mm square test specimen taken from a hot-rolled annealed steel sheet using ICP-AES under conditions based on a pre-established calibration curve. C and S can be measured using the combustion-infrared absorption method, and N can be measured using the inert gas fusion-thermal conductivity method.

[0063] 2. Precipitate Next, we will describe the precipitates contained in the hot-rolled annealed steel sheet according to this embodiment.

[0064] The precipitates (inhibitors) contained in the hot-rolled annealed steel sheet according to this embodiment may be precipitates formed from elements contained in the hot-rolled annealed steel sheet. For example, Mn precipitates (Mn-containing precipitates) may be sulfides or selenides, Al precipitates (Al-containing precipitates) may be nitrides, and Nb precipitates (Nb-containing precipitates) may be carbides, nitrides, or carbonitrides. In addition to these inhibitors, auxiliary inhibitors may include compounds of Nb group elements other than Nb, compounds of arbitrary elements such as Bi and B, or composite compounds with the above elements.

[0065] The precipitates to be controlled in the hot-rolled annealed steel sheet according to this embodiment are precipitates with an equivalent circular diameter D of 50 to 1000 nm. The "equivalent circular diameter" refers to the diameter of a circle when the area of ​​the precipitate is converted to a circle of the same area. This equivalent circular diameter is equivalent to the equivalent spherical diameter.

[0066] Precipitates with an equivalent circle diameter D smaller than 50 nm in hot-rolled annealed steel sheets currently have little effect in expanding the secondary recrystallization temperature range. The reason for this is not clear, but it is thought that precipitates with an equivalent circle diameter D smaller than 50 nm in the hot-rolled annealed steel sheet change or disappear in subsequent processes and are less likely to function as inhibitors during finish annealing. Therefore, in the hot-rolled annealed steel sheet according to this embodiment, the size and distribution of precipitates with an equivalent circle diameter D of 50 nm or more are controlled. Furthermore, by considering processes including those after the hot-rolled sheet annealing process, it is expected that precipitates with an equivalent circle diameter D smaller than 50 nm will be able to function as inhibitors in the future.

[0067] Furthermore, precipitates with an excessively large equivalent diameter D may adversely affect the growth of secondary recrystallized grains in the final stage of secondary recrystallization. Also, the formation of precipitates with an excessively large equivalent diameter D may reduce the number of precipitates (number density) contained in the hot-rolled annealed steel sheet. Moreover, precipitates with an excessively large equivalent diameter D are less likely to function as inhibitors. For this reason, it is preferable that the equivalent diameter D of the precipitates be 1000 nm or less on average. In the hot-rolled annealed steel sheet according to this embodiment, the size and distribution of precipitates with an equivalent diameter D of 50 to 1000 nm are controlled to have the effect of expanding the secondary recrystallization temperature range.

[0068] In the hot-rolled annealed steel sheet according to this embodiment, among the precipitates which are the residue obtained by electrolytic extraction of the hot-rolled annealed steel sheet, the particle size-number density distribution of precipitates with an equivalent circular diameter D of 50 to 1000 nm is as follows: Let Dp be the most frequent diameter in nm. Let f(Dp) be the number density of the most mode, in units of particles / g. When the full width at half maximum of the most mode is denoted as Wp in units of nm, Dp is 50~350nm, f(Dp) is 1,000,000 particles / g or more. Wp / Dp is 0.75~2.25. It satisfies the condition.

[0069] Figure 1 shows a schematic diagram of the particle size-number density distribution of precipitates with an equivalent circle diameter D of 50 to 1000 nm. Dp, f(Dp), and Wp are shown as examples in Figure 1.

[0070] When Dp exceeds 350 nm, it is unsuitable because there are fewer fine precipitates to expand the secondary recrystallization temperature range. The upper limit of Dp is preferably 300 nm, and more preferably 250 nm. On the other hand, when Dp is less than 50 nm, as mentioned above, the effect of expanding the secondary recrystallization temperature range is small. The lower limit of Dp is preferably 80 nm, and more preferably 130 nm.

[0071] If f(Dp) is less than 1,000,000 particles / g, there are few precipitates necessary for secondary recrystallization to occur, and the pinning effect cannot be sufficiently obtained, making it unsuitable. On the other hand, there is no particular upper limit to f(Dp), but for example, 50,000,000 particles / g would be appropriate.

[0072] If Wp / Dp is less than 0.75, the ratio of Wp to Dp is small, so the secondary recrystallization temperature range is not sufficiently expanded, which is unsuitable. The lower limit of Wp / Dp is preferably 1.0. On the other hand, if Wp / Dp is greater than 2.25, the ratio of Wp to Dp is too large, so the primary recrystallized grains grow unevenly during normal grain growth, resulting in a mixed grain structure before secondary recrystallization, which is unsuitable. The upper limit of Wp / Dp is preferably 1.75.

[0073] The particle size-number density distribution of precipitates with an equivalent circle diameter D of 50 to 1000 nm can be determined as follows.

[0074] For example, the method described in Japanese Patent No. 6572598 may be used. First, precipitates are electrolytically extracted from the hot-rolled annealed steel sheet. The electrolytic extraction conditions can be, for example, constant current electrolytic extraction (500 mA - 2 hours) using a solution prepared by adding a dispersant such as a surfactant (for example, sodium dodecyl sulfate with a molecular weight of 288.38 g / mol) to an acetylacetone-based electrolyte in advance. Electrolytic extraction should be performed such that the amount of electrolytic material extracted from the hot-rolled annealed steel sheet is 1 g or more.

[0075] The extraction residue (precipitation) should be recovered from the electrolytic extract. The size and distribution of this recovered precipitate should be measured by the Field Flow Fractionation (FFF) method. For the measurement method using the FFF method, please refer to Japanese Patent No. 6572598 mentioned above.

[0076] Note that each parameter can be changed depending on the particle size and type being measured. Here is an example: The FFF instrument should be a Wyatt Eclipse AF4 instrument (Wyatt Technology Europe, Germany). For the dispersion solution of the measurement sample, an aqueous solution of sodium dodecyl sulfate at a concentration of 300 mg / mL should be used. For the cell, an asymmetric diamond-type channel spacer with a channel length of 275 mm and a thickness of 350 μm should be used. As the separation membrane, a regenerated cellulose ultrafiltration membrane with a molecular weight of 30 kDa should be used.

[0077] Before adding the extraction residue (precipitation) recovered from the electrolytic extract, it is necessary to create a calibration curve by correlating particle size with the time until particle detection using standard samples with known particle sizes. The type and number of standard samples should be selected according to the particle size distribution of the extraction residue to be measured, but for example, standard particles of polystyrene latex with particle sizes of 29 to 500 nm can be selected.

[0078] The size of the standard particles must be directly confirmed beforehand using a TEM (Transmission Electron Microscope) or similar device. A minimum of 500 measurements should be performed. The longest side of each standard particle should be measured, and the average value should be calculated. Regarding the types of particle sizes used, for example, six different particle sizes such as 29 nm, 48 nm, 100 nm, 200 nm, 300 nm, and 500 nm can be used.

[0079] The actual separation conditions should be as follows. First, for stabilization before focusing, the eluent flow (channel flow) of the FFF instrument (hereinafter referred to as channel flow) should be 1.0 mL / min and the cross flow 0.5 mL / min for 1 minute. Then, for focusing before sample injection, the focus flow should be 3.0 mL / min for 1 minute. Next, during focusing, the sample should be injected at 0.2 mL / min for 2 minutes. The focusing time after sample injection should be 1 minute. After that, the flow path should be switched, the focus flow should be stopped, and the channel flow should be 1.0 mL / min, and the cross flow should be injected while decreasing the flow rate in direct proportion from 0.5 mL / min to 0.05 mL / min over 35 minutes. A calibration curve should be created by correlating the time from when the injection started until particles were detected with the average value of the particle size of the standard particles that had been measured in advance. The maximum time for particle detection should be 35 minutes, and the injection volume of the liquid in which the sample is dispersed should be 0.1 to 0.4 mL.

[0080] After creating the calibration curve as described above, the extraction residue (precipitate) recovered from the electrolytic extract is then added back into the apparatus. The apparatus settings parameters should be the same as described above.

[0081] In this way, the particle size of nanoparticles contained in the nanoparticle dispersion sample to be measured can be determined.

[0082] Furthermore, the effluent from the FFF instrument (a solution containing precipitates separated by size) can be subjected to component analysis using a standard ICP (Inductively Coupled Plasma) mass spectrometer.

[0083] For particle separation using the FFF method, for example, a 0.05 wt% sodium dodecyl sulfate (SDS) solution can be used as the developing solvent and flowed at a rate of 1 mL / min.

[0084] Using the particle size distribution data measured by the FFF method, the particle size is divided at 0.5 nm intervals, and the number density per unit number / g is calculated from the number of precipitates contained in this particle size range and the electrolysis amount of the extraction electrolysis, and a histogram of the particle size and the number density may be created. From this histogram, Dp, f(Dp), and Wp may be obtained.

[0085] In addition to the above, in the hot-rolled annealed steel sheet according to this embodiment, regarding the particle size-detection intensity distribution of precipitates having a circle equivalent diameter D of 50 to 1000 nm among the precipitates that are the residue after electrolytic extraction of the hot-rolled annealed steel sheet, The most frequent diameter of the Al-based precipitate is Dp in units of nm Al and The most frequent diameter of the Nb-based precipitate is Dp in units of nm Nb when Dp Al - Dp Nb is 22 to 100 nm, satisfies.

[0086] Fig. 2 shows a schematic diagram of the particle size-detection intensity distribution of precipitates having a circle equivalent diameter D of 50 to 1000 nm. In Fig. 2, Dp Al and Dp Nb are illustrated.

[0087] Dp Al - Dp Nb If the value of is less than 22 nm, the balance between relatively fine inhibitors and relatively coarse inhibitors is not preferable, so the secondary recrystallization temperature range is not sufficiently expanded and it is inappropriate. The lower limit of Dp Al - Dp Nb is preferably 22 nm, more preferably 55 nm. On the other hand, if the value of Dp Al - Dp Nb exceeds 100 nm, the coarse inhibitor is too large, so when the primary recrystallized grains grow normally, they grow unevenly, and the grain structure before secondary recrystallization becomes a mixed grain structure, which is inappropriate. The upper limit of Dp Al - Dp Nb is preferably 100 nm, more preferably 90 nm.

[0088] The particle size-detection intensity distribution of precipitates with an equivalent circle diameter D of 50 to 1000 nm can be determined as follows.

[0089] The precipitate can be collected in the same manner as described above. The size and distribution of this precipitate can then be measured using the FFF-ICP-MS (Field Flow Fractionation - Inductively Coupled Plasma - Mass Spectrometry) method.

[0090] The measurement method using the FFF method is as described above. Furthermore, the precipitate separated by size using the FFF method can be analyzed for its components using inductively coupled plasma mass spectrometry (ICP-Mass).

[0091] Using the particle size distribution data calculated from the measurement results of the FFF-ICP-MS method, a distribution of particle size and ICP-MS detection intensity (Al detection intensity and Nb detection intensity) can be created. From this particle size-detection intensity distribution, Dp Al and Dp Nb We just need to find that.

[0092] In this embodiment, the "mode diameter" corresponds to the particle diameter (particle diameter category) at which the number density value is greatest in the particle diameter-number density distribution described above, and also corresponds to the particle diameter at which the detection intensity value is greatest in the particle diameter-detection intensity distribution described above.

[0093] Note that the above Dp, f(Dp), Wp, Dp Al , Dp Nb Calculations such as these are preferably performed after smoothing the measurement data from the FFF method and FFF-ICP-MS method. For example, the simple moving average method can be used to smooth the measurement data from the FFF method and FFF-ICP-MS method. Furthermore, the value of f(Dp) can be determined by considering the first three digits of the numerical value as valid.

[0094] 3. Plate thickness The thickness of the hot-rolled annealed steel sheet according to this embodiment is not particularly limited. The hot-rolled annealed steel sheet according to this embodiment is subjected to a subsequent cold-rolling process to be ultimately finished as a grain-oriented electrical steel sheet. Therefore, considering the general manufacturing conditions for grain-oriented electrical steel sheets, the thickness of the hot-rolled annealed steel sheet can be 1.8 to 3.5 mm. However, it is not limited to this thickness, and any known thickness or a thickness that is used in practical applications may be adopted.

[0095] 4. Manufacturing method Next, a method for manufacturing a hot-rolled annealed steel sheet for grain-oriented electrical steel sheets according to one embodiment of the present invention will be described. Note that the method for manufacturing the hot-rolled annealed steel sheet according to this embodiment is not limited to the method described below. The manufacturing method described below is one example for manufacturing the hot-rolled annealed steel sheet according to this embodiment.

[0096] Figure 3 is a flowchart illustrating the manufacturing process of a hot-rolled annealed steel sheet according to this embodiment. Figure 3 also shows the manufacturing process of a grain-oriented electrical steel sheet using this hot-rolled annealed steel sheet. As shown in Figure 3, the manufacturing method of a hot-rolled annealed steel sheet according to this embodiment comprises a casting process, a hot-rolling process, and a hot-rolled sheet annealing process. The conditions controlled in these processes will be described in detail later.

[0097] Furthermore, the processes from the cold rolling process onward shown in Figure 3, namely the cold rolling process, decarburization annealing process, annealing release agent application process, and finish annealing process, are the manufacturing processes for grain-oriented electrical steel sheets (finish annealed steel sheets). The effects of the hot-rolled annealed steel sheet according to this embodiment can be confirmed in the final product, the grain-oriented electrical steel sheet, so the control conditions for these processes will also be described later.

[0098] The method for manufacturing a hot-rolled and annealed steel sheet according to this embodiment comprises a casting step, a hot-rolling step, and a hot-rolled sheet annealing step. In the casting process, In mass percent, C: 0.0010~0.10%, Si: 2.0~7.0%, Mn: 0.050~1.0%, S: 0~0.0350%, Se: 0~0.0350%, S+Se total content: 0.0030~0.0350%, Al: 0.010~0.0650%, N: 0.0040~0.0120%, Nb: 0.0030~0.030%, V: 0~0.030%, Mo: 0~0.030%, Ta: 0~0.030%, W: 0~0.030%, Cu: 0~0.40%, Bi: 0~0.010%, B: 0~0.080%, P: 0-0.50% Ti: 0~0.0150%, Sn: 0~0.10%, Sb: 0~0.10%, Cr: 0~0.30%, Ni: 0~1.0%, Molten steel having a chemical composition containing and the remainder consisting of Fe and impurities is cast and formed into a slab. In the hot rolling process, the slab after the casting process is heated, roughly rolled, and then finish-rolled to form a hot-rolled steel sheet. In the hot-rolled sheet annealing process, the hot-rolled steel sheet after the hot-rolling process is annealed to obtain a hot-rolled annealed steel sheet.

[0099] Furthermore, in the method for manufacturing hot-rolled annealed steel sheets according to this embodiment, when the total content of the group consisting of Nb, V, Mo, Ta, and W in the chemical composition of the slab is greater than 0.030% by mass, In the hot rolling process, During the slab heating process before rough rolling, the soaking temperature of the slab is set to over 1040°C but less than 1100°C to preferably dissolve a portion of the precipitates contained in the slab (for example, dissolving 14-25% by volume of precipitates based on the precipitates contained in the slab after the casting process), and in order to homogenize this dissolved state within the slab, the soaking time of the slab is set to over 2 hours. During rough rolling, the rolling temperature is set to 940-1030°C and the reduction ratio to 90-95%. When performing finish rolling, the finishing temperature should be set to 850-950°C. In the hot-rolled sheet annealing process, the average cooling rate from 750°C to 500°C during the cooling process after annealing may be set to 25 to 80°C / second.

[0100] Furthermore, in the method for manufacturing hot-rolled annealed steel sheets according to this embodiment, when the total content of the group consisting of Nb, V, Mo, Ta, and W in the chemical composition of the slab is 0.0030 to 0.030% by mass, In the hot rolling process, During the slab heating process before rough rolling, the soaking temperature of the slab is set to over 1030°C but less than 1180°C to preferably dissolve a portion of the precipitates contained in the slab (for example, dissolving 12 to 85 volume percent of precipitates based on the precipitates contained in the slab after the casting process), and in order to homogenize this dissolved state within the slab, the soaking time of the slab is set to over 70 minutes. During rough rolling, the rolling temperature is set to 940-1070°C and the reduction ratio to 82-95%. When performing finish rolling, the finishing temperature should be set to 850-950°C. In the hot-rolled sheet annealing process, the average cooling rate from 750°C to 500°C during the cooling process after annealing may be set to 25 to 80°C / second.

[0101] To control the size and distribution of precipitates in hot-rolled annealed steel sheets, it is necessary to control the steel composition, casting conditions, hot rolling conditions, and hot-rolled sheet annealing conditions. In particular, it is important to control the steel composition, slab heating conditions (solution state of precipitates before rough rolling), rough rolling temperature, rough rolling reduction ratio, finish rolling temperature, and cooling rate after hot-rolled sheet annealing. Furthermore, to control the "solution state of precipitates before rough rolling" mentioned above, it is important to control the steel composition and slab heating conditions, respectively.

[0102] Furthermore, the slab heating described above does not require temporarily increasing the heating temperature during the heating process; instead, it is sufficient to perform soaking at a predetermined temperature for a predetermined time. In this case, the soaking temperature of the slab refers to the surface temperature of the slab, and the soaking time refers to the holding time after the surface temperature of the slab reaches the soaking temperature. For example, although it is also affected by the steel composition and heating rate, if the surface temperature of the slab reaches the soaking temperature during the heating process, the solution state of precipitates on the surface of the slab is favorably controlled. Also, if the surface temperature of the slab is held for the soaking time after reaching the soaking temperature, the solution state of precipitates is favorably controlled all the way to the center of the slab.

[0103] The important manufacturing conditions for the hot-rolled and annealed steel sheet manufacturing method according to this embodiment are described below. Other manufacturing conditions can be those of conventional known grain-oriented electrical steel sheets.

[0104] (Casting process) In the casting process, a slab is prepared. As mentioned above, the chemical composition hardly changes from the slab to the process before decarburization and annealing, so the chemical composition of the slab is set to the chemical composition of the target hot-rolled annealed steel sheet (the chemical composition of the hot-rolled annealed steel sheet described above).

[0105] Furthermore, the chemical composition of the slab affects the "solution state of precipitates before rough rolling" mentioned above. As will be explained in more detail later, the chemical composition of the slab needs to be controlled in combination with other manufacturing conditions that affect the "solution state of precipitates before rough rolling," in addition to satisfying the chemical composition requirements for hot-rolled and annealed steel sheets mentioned above.

[0106] An example of a slab manufacturing method is as follows: Molten steel is produced (melted). A slab is manufactured using this molten steel. For example, the slab may be manufactured by continuous casting. Alternatively, an ingot may be manufactured using molten steel, and the ingot may be rolled into a slab. The thickness of the slab is, for example, 150 to 350 mm. Preferably, the thickness of the slab is 220 to 280 mm. A so-called thin slab with a thickness of 10 to 70 mm may be used as the slab.

[0107] (Hot rolling process) The hot rolling process involves heating a slab to a predetermined temperature and performing hot rolling (rough rolling and finish rolling) to obtain a hot-rolled steel sheet.

[0108] For example, in the hot rolling process, the slab after the casting process is heated, rough rolling is performed, and then finish rolling is performed to produce a hot-rolled steel sheet with a predetermined thickness of 1.8 to 3.5 mm. After the finish rolling is completed, the hot-rolled steel sheet is wound up at a predetermined temperature.

[0109] During the hot rolling process, when heating the slab after the casting process, the following conditions must be met.

[0110] For example, when the total content of the group consisting of Nb, V, Mo, Ta, and W in the chemical composition of the slab is greater than 0.030 mass%, when heating the slab before rough rolling, the soaking temperature of the slab should be set to more than 1040°C but less than 1100°C to preferably dissolve some of the precipitates contained in the slab (for example, dissolving 14 to 25 volume percent of precipitates based on the precipitates contained in the slab at room temperature after the casting process), and the slab should be heated for more than 2 hours to homogenize this dissolved state within the slab.

[0111] On the other hand, when the total content of the group consisting of Nb, V, Mo, Ta, and W in the chemical composition of the slab is 0.0030 to 0.030 mass%, when heating the slab before rough rolling, the soaking temperature of the slab should be set to over 1030°C and less than 1180°C to preferably dissolve some of the precipitates contained in the slab (for example, dissolving 12 to 85 volume percent of precipitates based on the precipitates contained in the slab at room temperature after the casting process), and the slab should be heated for more than 70 minutes to homogenize this dissolved state within the slab.

[0112] In the pre-rough rolling stage, it is desirable to dissolve some of the precipitates contained in the slab in order to ultimately achieve a desirable balance between the amount of relatively coarse precipitates that remain dissolved after the slab heating stage (undissolved precipitates) and the amount of relatively fine precipitates that do not precipitate during the slab heating stage but precipitate after hot rolling (re-precipitation precipitates).

[0113] Furthermore, Wp, which is the main technical feature of this embodiment, can be increased by controlling the size difference between relatively coarse precipitates that remain precipitated during the slab heating stage (undissolved precipitates) and relatively fine precipitates that do not precipitate during the slab heating stage but precipitate after hot rolling (re-precipitated precipitates).

[0114] The "solution state of precipitates before rough rolling" mentioned above refers to the "solution state of precipitates before rough rolling" in an equilibrium state, not a non-equilibrium state. In a non-equilibrium state, for example, the solution state of precipitates becomes non-uniform near the surface and near the center in the thickness direction of the sheet. If a slab in this non-equilibrium state is subjected to rough rolling, it becomes difficult to control the size and distribution of precipitates contained in the steel sheet after the hot-rolled sheet annealing process.

[0115] For example, in order to bring the solution state of the precipitates closer to equilibrium, it is preferable to keep the value obtained by subtracting the slab center temperature from the slab surface temperature within the range of greater than -10°C and less than 50°C during slab heating and extraction. In particular, if the above temperature difference is less than -10°C, the steel plate surface becomes less expandable, and the occurrence of defects becomes significant. Also, if the above temperature difference is greater than 50°C, the solution state of the precipitates becomes non-uniform in the thickness direction of the plate, making it difficult to control the size of the precipitates.

[0116] Although different from the slab heating method in this embodiment, the heating temperature may be temporarily increased during the slab heating process to shorten the soaking time. In this case, it is effective to keep the difference between the surface temperature at the time of maximum temperature attainment and the surface temperature at the time of slab extraction from the heating furnace to 80°C or less. In this case, it is preferable to hold the slab in the lower temperature region of the slab heating furnace for at least 20 minutes after it has cooled from the maximum temperature attainment, so that the difference between the surface temperature and the core temperature at the time of extraction from the slab heating furnace is less than 50°C. More preferably, the difference between the surface temperature and the core temperature of the slab should be between 0 and 30°C.

[0117] In conventional techniques that perform slab heating at temperatures below 1280°C, known as low-temperature slab heating processes, there was no technical concept of dissolving only a specific proportion of precipitates contained in the slab, nor was there any knowledge that it was necessary to bring this dissolution of precipitates closer to an equilibrium state. In the method for manufacturing hot-rolled annealed steel sheets according to this embodiment, the dissolution state of precipitates is favorably controlled, and a slab in which the dissolution of precipitates is in an equilibrium state is subjected to rough rolling.

[0118] The "solution state of precipitates before rough rolling" described above is a characteristic that is influenced by both the steel composition and the hot rolling conditions (slab heating conditions). To control this "solution state of precipitates before rough rolling," it is necessary to control each of the above manufacturing conditions in a complex and inseparable manner, taking into account the influence of each manufacturing condition on the "solution state of precipitates." For example, a person skilled in the art can perform material control including precipitation behavior, so if they understand that each of the above conditions affects the "solution state," they can control the "solution state" by combining the above conditions.

[0119] For example, the "solution state of precipitates before rough rolling" may be controlled as described above by temporarily increasing the heating temperature during the slab heating process and then holding it for a certain period of time after cooling. However, in the manufacturing method of hot-rolled annealed steel sheets according to this embodiment, one example is shown of controlling the "solution state of precipitates before rough rolling" by performing soaking at a predetermined temperature for a predetermined time without temporarily increasing the heating temperature during the slab heating process.

[0120] For example, if the total content of the group consisting of Nb, V, Mo, Ta, and W in the chemical composition of the slab is greater than 0.030 mass%, the soaking temperature during slab heating should be greater than 1040°C but less than 1100°C, and the soaking time should be greater than 2 hours. In this case, it is preferable to dissolve a portion of the precipitates contained in the slab (for example, based on the precipitates contained in the slab at room temperature after the casting process, it is preferable to dissolve 14 to 25 volume percent of the precipitates).

[0121] When the content of Nb group elements is within the above range, setting the soaking temperature during slab heating to below 1100°C makes it easier to ultimately control the size and distribution of precipitates. For example, if the slab heating temperature is 1100°C or higher, as in the conventional technique, the solutionization of precipitates progresses too much, making it difficult to control the solutionization state favorably (for example, it is difficult to control the precipitate solutionization rate to 25% by volume or less). In this case, the size of the precipitates re-precipitation in subsequent processes becomes larger, making it difficult to have fine inhibitors and coarse inhibitors coexist. As a result, the size difference of precipitates, which is the main technical feature of this embodiment, becomes smaller. Therefore, it is necessary to control the temperature to a lower level than in the conventional technique, as described above.

[0122] Furthermore, if the soaking temperature during slab heating is below 1040°C, the temperature is too low, making it difficult for the precipitates to dissolve and thus difficult to control the dissolution state favorably (for example, it is difficult to control the precipitate dissolution rate to 14% by volume or more). In this case, the amount of precipitates that re-precipitation in subsequent processes will be small, making it difficult to allow fine inhibitors and coarse inhibitors to coexist. As a result, the size difference of the precipitates, which is a key technical feature of this embodiment, becomes smaller.

[0123] In this embodiment, the secondary recrystallization temperature range is expanded by controlling the size difference between the relatively coarse precipitates that remain precipitated during the slab heating stage (undissolved precipitates) and the relatively fine precipitates that precipitate after hot rolling (re-precipitated precipitates) to be large. Therefore, when the content of Nb group elements is within the above range, it is important to set the soaking temperature during slab heating to more than 1040°C but less than 1100°C. This soaking temperature is preferably 1050°C to 1080°C.

[0124] Furthermore, when the Nb group element content is within the above range, a soaking time of 2 hours or less is too short, making it difficult to control the solution state of the precipitate to an equilibrium state. While there is no particular upper limit to the soaking time, it may be set to 3 hours considering productivity in industrial production.

[0125] On the other hand, when the total content of the group consisting of Nb, V, Mo, Ta, and W in the chemical composition of the slab is 0.0030 to 0.030 mass%, the soaking temperature during slab heating should be greater than 1030°C but less than 1180°C, and the soaking time should be greater than 70 minutes. In this case, it is preferable to dissolve a portion of the precipitates contained in the slab (for example, based on the precipitates contained in the slab at room temperature after the casting process, it is preferable to dissolve 12 to 85 volume percent of the precipitates).

[0126] When the Nb group element content is within the above range, the slab heating temperature before hot rolling and the rough rolling conditions described later are preferably relaxed. Specifically, even if the slab heating temperature is 1100°C or higher, it is ultimately possible to have both fine and coarse inhibitors coexist. For example, if the slab heating temperature is high and the solution treatment of AlN and MnS is promoted during the slab heating stage, these AlN and MnS tend to reprecipitate coarsely in subsequent processes. However, when the Nb group element content is within the above range, the Nb group element precipitates act as precipitation nuclei for MnS and AlN, reducing the size of the reprecipitated AlN and MnS. Furthermore, since the precipitation nose of Nb group element precipitates (carbonitrides) is at a lower temperature than the precipitation nose of AlN and MnS, the Nb group element precipitates themselves tend to precipitate as even finer precipitates than AlN and the like.

[0127] Therefore, when the content of Nb group elements is within the above range, the upper limit temperature during slab soaking is relaxed to less than 1180°C. While higher soaking temperatures promote the solubilization of precipitates, when the content of Nb group elements is within the above range, the controllable solubilization state of the precipitates is also relaxed (for example, the upper limit of the precipitate solubilization rate is relaxed to 85% by volume). Even with these relaxed conditions, the effect of the Nb group element precipitates makes it easier to achieve the coexistence of fine and coarse inhibitors.

[0128] Similarly, when the Nb group element content is within the above range, the lower limit temperature for slab soaking is relaxed to over 1030°C. While a lower soaking temperature also suppresses precipitate solution formation, when the Nb group element content is within the above range, the controllable precipitate solution state is also relaxed (for example, the lower limit for precipitate solution rate is relaxed to 12% by volume). Even with these relaxed conditions, it is ultimately possible to achieve coexistence of fine and coarse inhibitors.

[0129] The mechanism by which the above effects are obtained is thought to be related to the fact that precipitates of Nb group elements (carbonitrides) precipitate more easily than MnS and AlN (in particular, MnS is difficult to precipitate without support such as dislocation proliferation due to rolling, and when it does precipitate, it becomes larger in size), and that precipitates of Nb group elements function as precipitation nuclei in the precipitation of MnS and AlN, suppressing the coarsening of re-precipitated AlN and MnS.

[0130] Furthermore, when the Nb group element content is within the above range, a soaking time of 70 minutes or less is too short, making it difficult to control the solution state of the precipitate to an equilibrium state. While the upper limit of the soaking time is not particularly limited, it may be set to 2 hours considering productivity in industrial production.

[0131] Controlling the "solution state of precipitates before rough rolling" to the above conditions is necessary to ultimately achieve a favorable balance between the amount of relatively coarse precipitates that remain precipitated during the slab heating stage (undissolved precipitates) and the amount of relatively fine precipitates that precipitate after hot rolling (re-precipitation precipitates).

[0132] The soaking temperature of the slab mentioned above represents the surface temperature of the slab, and the soaking time of the slab represents the holding time after the surface temperature of the slab reaches the soaking temperature. For example, although it is also affected by the steel composition and heating rate, if the surface temperature of the slab reaches the soaking temperature mentioned above during the heating of the slab, the solution state of precipitates on the surface of the slab will be favorably controlled. Furthermore, if the surface temperature of the slab is held for the soaking time mentioned above after reaching the soaking temperature, the solution state of precipitates will be favorably controlled all the way to the center of the slab.

[0133] The specific solution treatment rate is not particularly limited. As described above, the "solution treatment state of precipitates before rough rolling" can be favorably controlled by controlling the steel composition and slab heating conditions, respectively. However, if necessary, a specific solution treatment rate can be determined using integrated thermodynamic calculation software. For example, "Thermo-Calc" is a commonly available integrated thermodynamic calculation software. In this embodiment, "Thermo-Calc" (2019a ver.) was used to calculate the solution treatment rate from the chemical composition and temperature of the slab, and this was used as a reference.

[0134] In the hot rolling process, hot rolling is carried out following the slab heating described above. Generally, hot rolling is divided into rough rolling and finish rolling. In this embodiment, in order to control the size and distribution of precipitates contained in the steel sheet after the hot-rolled sheet annealing process, it is important to control the rough rolling temperature, the rough rolling reduction ratio, and the finish rolling completion temperature after controlling the "solution state of precipitates before rough rolling" described above.

[0135] In the hot rolling process, the following conditions must be met when rough rolling is performed after heating the slab.

[0136] For example, if the total content of the group consisting of Nb, V, Mo, Ta, and W in the chemical composition of the slab is greater than 0.030 mass%, then when rough rolling the heated slab, the rolling temperature should be controlled to 940-1030°C and the reduction ratio to 90-95%.

[0137] On the other hand, when the total content of the group consisting of Nb, V, Mo, Ta, and W in the chemical composition of the slab is 0.0030 to 0.030 mass%, when rough rolling the heated slab, the rolling temperature should be controlled to 940 to 1070°C and the reduction ratio to 82 to 95%.

[0138] By setting the reduction ratio within the above range, processing-induced precipitation occurs, making it possible to precipitate fine and abundant precipitates. If the reduction ratio for rough rolling is smaller than the lower limit above, the introduction of dislocations due to the rolling process will decrease, and the number of precipitation sites that can undergo processing-induced precipitation will decrease, resulting in larger particle sizes for the precipitates and a lower Wp value. On the other hand, there is no particular upper limit to the reduction ratio for rough rolling, but it is reasonable to set it at 95% considering the performance of the rolling mill, etc.

[0139] The reduction ratio for rough rolling mentioned above refers to the cumulative reduction ratio during rough rolling. Specifically, the reduction ratio for rough rolling is defined as follows: Rough rolling reduction ratio (cumulative reduction ratio) (%) = (1 - "steel plate thickness after rough rolling" / "steel plate thickness before rough rolling") × 100

[0140] Furthermore, if the rolling temperature for rough rolling is higher than the upper limit mentioned above, precipitates of MnS, AlN, and Nb group elements will precipitate at a higher temperature than or near the precipitation nose, resulting in a larger critical radius for precipitation of precipitates that re-precipitation during hot rolling. Consequently, the size difference between these precipitates and the relatively coarse precipitates (undissolved precipitates) that have precipitated since the slab heating stage becomes smaller, and the Wp value decreases. On the other hand, there is no particular lower limit to the rolling temperature for rough rolling, but since the slab hardens and its rollability decreases at lower temperatures, it is advisable to roll at, for example, 940°C or higher. The rough rolling temperature is defined as the average value of the start and end temperatures of rough rolling.

[0141] Furthermore, when the chemical composition preferably contains Nb group elements, during rough rolling, precipitates of Nb group elements (especially carbides and nitrides) precipitate in addition to MnS and AlN. These Nb group element precipitates act as precipitation nuclei for MnS and AlN that precipitate later, resulting in finer reprecipitation of MnS and AlN. Therefore, when the chemical composition preferably contains Nb group elements, the control conditions that need to be controlled in the hot rolling process, such as the solution state of the precipitates (e.g., the solution rate of the precipitates before rough rolling), the rough rolling temperature, and the rough rolling reduction rate, are relaxed.

[0142] The reason why the control conditions for the solution state of precipitates are relaxed when Nb group elements are suitably included, compared to when Nb group elements are not suitably included, is thought to be as follows: When Nb group elements are included, MnS and AlN are re-precipitated more finely due to the precipitates of Nb group elements, so Dp is smaller compared to when Nb group elements are not included. On the other hand, even if Nb group elements are included, the value of Wp does not change significantly. Therefore, when Nb group elements are included, Wp / Dp becomes larger. For these reasons, it is thought that the control conditions for the solution state of precipitates are relaxed.

[0143] For example, if the solution state of precipitates is not favorably controlled when Nb group elements are present (for example, if the "solution rate of precipitates before rough rolling" is lower than 12 volume%), the precipitates will not be sufficiently dissolved at the time of slab heating, similar to the case where Nb group elements are not present, resulting in fewer fine precipitates re-precipitation during hot rolling. Consequently, Wp becomes smaller, and the secondary recrystallization temperature range cannot be sufficiently expanded during finish annealing. Also, if the solution state of precipitates is not favorably controlled when Nb group elements are present (for example, if the "solution rate of precipitates before rough rolling" is higher than 85 volume%), most of the precipitates will be dissolved at the time of slab heating, similar to the case where Nb group elements are not present, resulting in fewer relatively coarse precipitates (undissolved precipitates) in the slab. Consequently, the secondary recrystallization temperature range cannot be sufficiently expanded during finish annealing.

[0144] Furthermore, the reason why the control conditions for the rough rolling reduction rate are relaxed when Nb group elements are suitably included, compared to when Nb group elements are not suitably included, is thought to be as follows: When Nb group elements are included, precipitates of Nb group elements tend to precipitate finely in the steel, so the number of fine precipitates contained in the steel even before rough rolling is greater compared to when Nb group elements are not included. Therefore, when Nb group elements are included, there are more precipitation sites for precipitates, and processing-induced precipitation is more likely even when the reduction rate is reduced. For these reasons, it is thought that the control conditions for the rough rolling reduction rate are relaxed.

[0145] When Nb group elements are present, if the reduction ratio during rough rolling is less than 82%, similar to when Nb group elements are not present, the introduction of dislocations due to the rolling process will decrease, and the number of precipitation sites that can be precipitated by the process will decrease. As a result, the particle size of the precipitate will increase, and the Wp value will decrease. When Nb group elements are present, the upper limit of the reduction ratio during rough rolling is preferably 93%.

[0146] Furthermore, the reason why the control conditions for rough rolling temperature are relaxed when Nb group elements are suitably included, compared to when Nb group elements are not suitably included, is thought to be as follows: When Nb group elements are included, as mentioned above, the number of fine precipitates contained in the steel even before rough rolling is greater compared to when Nb group elements are not included. Therefore, when Nb group elements are included, there are more precipitation sites for precipitates, and the precipitates that re-precipitation during hot rolling tend to be finer. For these reasons, it is thought that the control conditions for rough rolling temperature are relaxed.

[0147] When Nb group elements are present, if the rough rolling temperature is higher than 1070°C, all precipitates, including MnS, AlN, and Nb group elements, will undergo processing-induced precipitation at a temperature higher than the precipitation nose of the precipitates. As a result, the critical precipitation radius of the precipitates re-precipitationd during hot rolling becomes larger. Therefore, the size difference between the relatively coarse precipitates (undissolved precipitates) that have precipitated since the slab heating stage becomes smaller, and the Wp value decreases. When Nb group elements are present, the upper limit of the rough rolling temperature is preferably 1065°C, and more preferably 1040°C.

[0148] Furthermore, although the reason why Nb group elements promote the fine precipitation of precipitates is not clear, it is thought to be as follows.

[0149] During rough rolling, the steel sheet temperature drops rapidly over time. Therefore, the rough rolling process is considered to be in a non-equilibrium state. Even in temperature ranges where all MnS and AlN would precipitate in an equilibrium state, dissolved MnS and AlN may exist in a non-equilibrium state. For example, because the rough rolling process is in a non-equilibrium state, dissolved MnS and AlN are thought to exist even in temperature ranges where Nb group elements precipitate. Therefore, when Nb group elements precipitate during rough rolling, these precipitates are thought to act as precipitation nuclei for MnS and AlN that precipitate later, causing fine precipitates of MnS and AlN. Specifically, compared to the case where Nb group element precipitates are not present, the presence of Nb group element precipitates many more precipitation sites for MnS and AlN, resulting in finer precipitates of MnS and AlN.

[0150] Furthermore, when precipitates of Nb group elements that acted as precipitation nuclei for MnS and AlN are covered with MnS or AlN, the further growth of those Nb group element precipitates is suppressed. In this case, the Nb group elements that would have been consumed in the growth of the precipitates are thought to precipitate as new, fine precipitates. These new, fine precipitates of Nb group elements are thought to act as new precipitation nuclei for MnS and AlN, contributing to the further fine precipitation of MnS and AlN. Thus, precipitates of Nb group elements are thought to synergistically contribute to the fine precipitation of MnS and AlN.

[0151] Furthermore, the slab soaking temperature during slab heating before rough rolling, and the rolling temperature during rough rolling, as described above, are temperatures that are controlled with a specific purpose. These temperatures are not due to the natural temperature drop that occurs when the slab is removed from the slab heating furnace and subjected to rough rolling. For example, in general operation, the slab soaking temperature and rough rolling temperature are not controlled with a specific purpose. Normally, if the slab soaking temperature is high, the rough rolling temperature will also be high, and if the slab soaking temperature is low, the rough rolling temperature will also be low. On the other hand, in this embodiment, the slab soaking temperature and rough rolling temperature described above are controlled with a specific purpose. For example, even if the slab soaking temperature is high within the above range, the rough rolling temperature is controlled to remain within the above range, and similarly, even if the slab soaking temperature is low within the above range, the rough rolling temperature is controlled to remain within the above range.

[0152] Furthermore, in the hot rolling process, the following conditions must be met during the finish rolling.

[0153] The finishing rolling temperature should be set to 850-950°C.

[0154] By setting the end temperature of the finish rolling within the above range, rolling can be performed at a temperature higher than 850°C, which is the precipitation nose for Al-based precipitates (such as AlN). As a result, the particle size of the Al-based precipitates newly precipitated during the finish rolling is large, i.e., Dp Al The value of becomes larger. As a result, among the precipitates contained in the steel sheet after the hot-rolled sheet annealing process, the Dp of precipitates with an equivalent circle diameter D of 50 to 1000 nm Al -Dp Nb The value can be preferably controlled to 22-100 nm.

[0155] Furthermore, there are no particular limitations on the finishing rolling conditions other than those mentioned above; normal hot rolling conditions may be used.

[0156] (Hot-rolled sheet annealing process) The hot-rolled sheet annealing process is a process in which hot-rolled steel sheets are annealed after the hot-rolling process to obtain hot-rolled annealed steel sheets. Hot-rolled sheet annealing is generally performed to control the steel sheet structure, such as the recrystallization rate, residual strain, and grain size, and to favorably adjust the morphology of precipitates in the steel.

[0157] The annealing conditions in the hot-rolled sheet annealing process can be those described later. In this embodiment, the precipitates contained in the hot-rolled annealed steel sheet after the hot-rolled sheet annealing process are controlled to the above-described precipitate morphology (size and distribution).

[0158] For example, in this embodiment, in the hot-rolled sheet annealing process, the average cooling rate of 750 to 500°C during the cooling process after the completion of annealing (after the second stage of annealing) should be 25 to 80°C / second.

[0159] The average cooling rate is preferably 25°C / second or higher, more preferably 30°C / second or higher, and even more preferably 40°C / second or higher. There is no particular upper limit to the average cooling rate, but to prevent fracture during cold rolling, the upper limit should be 80°C / second.

[0160] When the average cooling rate after annealing is within the above range, the Nb-based precipitates (such as NbC) that precipitate mainly during this cooling process become smaller in diameter, resulting in a Dp Nb The value of becomes smaller. As a result, among the precipitates contained in the steel sheet after the hot-rolled sheet annealing process, the Dp of precipitates with an equivalent circle diameter D of 50 to 1000 nm Al -Dp Nb The value of can be controlled to a desirable degree. Note that the average cooling rate mentioned above refers to the value obtained by dividing the temperature range from the annealing temperature (second-stage annealing temperature) to 500°C by the time required for cooling.

[0161] Furthermore, in this embodiment, the hot-rolled sheet annealing conditions other than those described above are not particularly limited, and ordinary hot-rolled sheet annealing conditions may be used.

[0162] For example, in this embodiment, the hot-rolled steel sheet after the hot-rolling process is heated and recrystallized in a first-stage annealing process at a temperature range of 1000 to 1150°C, followed by a second-stage annealing process at a lower temperature range of 800 to 1000°C, and then the steel sheet is cooled. The first-stage annealing temperature is preferably 1020 to 1130°C. The second-stage annealing temperature is preferably 800 to 950°C. The heating rate to reach the first-stage annealing temperature is preferably an average of 5°C / second or more. Furthermore, it is preferable to hold the steel sheet for 20 seconds or more during the second-stage annealing.

[0163] As described above, the method for manufacturing a hot-rolled annealed steel sheet according to this embodiment comprises a casting step, a hot-rolling step, and a hot-rolled sheet annealing step. In the hot-rolled annealed steel sheet manufactured by comprehensively controlling the above conditions in each step, the size and distribution of precipitates are preferably controlled, and the particle size-number density distribution and particle size-detection intensity distribution of the precipitates are controlled within the above range. As a result, the secondary recrystallization temperature range is expanded during finish annealing, the selective growth of Goss-oriented grains is enhanced, and the magnetic flux density of the grain-oriented electrical steel sheet is improved.

[0164] For example, as described above, in the manufacturing method of hot-rolled annealed steel sheets according to this embodiment, the amount of relatively coarse precipitates (undissolved precipitates) that remain precipitated during the slab heating stage is controlled mainly by the slab soaking temperature and slab soaking time during slab heating before rough rolling, and the amount of relatively fine precipitates (re-precipitated precipitates) is controlled by the subsequent manufacturing conditions, thereby controlling each characteristic of the hot-rolled annealed steel sheet within the above range. As a result, the secondary recrystallization temperature range is expanded during finish annealing, the selective growth of Goss-oriented grains is improved, and the magnetic flux density of the grain-oriented electrical steel sheet is increased.

[0165] 5. How to use hot-rolled annealed steel sheets The effects of the hot-rolled annealed steel sheet according to this embodiment can be confirmed in the final product, the grain-oriented electrical steel sheet. Therefore, from the perspective of how to use the hot-rolled annealed steel sheet according to this embodiment, the manufacturing process of the grain-oriented electrical steel sheet following the hot-rolled sheet annealing process will be described.

[0166] The manufacturing method for grain-oriented electrical steel sheets includes a cold rolling process, a decarburization annealing process, an annealing separation agent application process, and a finish annealing process. Additionally, an insulating film formation process and a magnetic domain control process may be included as needed. These processes can utilize known general process conditions. Below, a manufacturing method applying nitriding treatment as a low-temperature slab heating process will be described as an example.

[0167] (Cold rolling process) The cold rolling process involves taking the hot-rolled and annealed sheet obtained in the hot-rolled sheet annealing process and subjecting it to multiple cold rolling processes (two or more times) via one cold rolling or annealing (intermediate annealing) to a total cold rolling rate of 80-95%, thereby obtaining a cold-rolled steel sheet with a thickness of, for example, 0.10-0.50 mm.

[0168] (Decarburization annealing process) The decarburization annealing process involves performing decarburization annealing (for example, at 700-900°C for 1-3 minutes) on the cold-rolled steel sheet obtained in the cold-rolling process to obtain a decarburized annealed steel sheet in which primary recrystallization has occurred. By performing decarburization annealing on the cold-rolled steel sheet, carbon contained in the cold-rolled steel sheet is removed. Decarburization annealing is preferably performed in a humid atmosphere in order to remove the carbon contained in the cold-rolled steel sheet.

[0169] (nitriding treatment) Nitriding is performed to adjust the strength of the inhibitor during secondary recrystallization. In nitriding, the nitrogen content of the steel sheet can be increased to approximately 40-300 ppm at any time between the start of the decarburization annealing described above and the start of secondary recrystallization during the finish annealing described later. Examples of nitriding treatments include annealing the steel sheet in an atmosphere containing a gas with nitriding ability such as ammonia, or finishing annealing a decarburized annealed steel sheet coated with an annealing separator containing a powder with nitriding ability such as MnN.

[0170] (Annealing separating agent application process) The annealing separation agent application process involves applying an annealing separation agent to a decarburized annealed steel sheet. Examples of annealing separation agents that can be used include those primarily composed of MgO or alumina.

[0171] After applying the annealing release agent, the decarburized annealed steel sheet is wound into a coil and then finished annealed in the next finish annealing process.

[0172] (Finishing annealing process) The finish annealing process involves applying a finish annealing to a decarburized annealed steel sheet coated with an annealing separating agent to induce secondary recrystallization. This process allows secondary recrystallization to proceed while the growth of primary recrystallized grains is suppressed by an inhibitor, thus {110} <001> This method prioritizes the growth of azimuthal particles, thereby improving magnetic flux density.

[0173] When using the hot-rolled and annealed steel sheet according to this embodiment, the secondary recrystallization temperature range is expanded during finish annealing, resulting in a level of {100} not previously seen. <011> Preferential growth of oriented grains occurs, resulting in a dramatic increase in magnetic flux density. Additionally, abnormal grain growth of secondary recrystallized grains occurs during finish annealing, and after finish annealing, these secondary recrystallized grains occupy the entire surface of the plate. The few secondary recrystallized grains cover the entire surface of the steel plate, and the grain size of each secondary recrystallized grain increases.

[0174] Furthermore, in the finish annealing process, the finish annealing conditions for "expanding the secondary recrystallization temperature range" disclosed in the above-mentioned Patent Documents 9 to 11 may be applied as needed. By using the hot-rolled annealed steel sheet according to this embodiment and applying the finish annealing conditions disclosed in Patent Documents 9 to 11, the secondary recrystallization temperature range can be further preferably expanded.

[0175] The following insulating film formation and magnetic domain control steps use the crystal orientation {110}. <001> From the perspective of integration, this process is not necessary. However, it is a process that is commonly used in grain-oriented electrical steel sheets to improve practical magnetic properties. (Insulating film formation process) The insulating coating formation process is a process of forming an insulating coating on grain-oriented electrical steel sheets (finish-annealed steel sheets) after the finish annealing process. An insulating coating mainly composed of phosphate and colloidal silica, or an insulating coating mainly composed of alumina sol and boric acid, can be formed on the steel sheet after finish annealing.

[0176] (Magnetic domain control process) The magnetic domain control process is a process that subdivides the magnetic domains of the grain-oriented electrical steel sheet. This process is carried out at an appropriate time after cold rolling. For example, local minute strains or local grooves can be formed in the grain-oriented electrical steel sheet using known methods such as laser, plasma, mechanical methods, or etching.

[0177] 6. Grain-oriented electrical steel sheet obtained using the hot-rolled and annealed steel sheet according to this embodiment A grain-oriented electrical steel sheet manufactured using the hot-rolled and annealed steel sheet according to this embodiment will be briefly described.

[0178] In the hot-rolled annealed steel sheet according to this embodiment, relatively fine precipitates and relatively coarse precipitates coexist in a favorable size and distribution. Therefore, in the grain-oriented electrical steel sheet obtained using the hot-rolled annealed steel sheet according to this embodiment, Goss-oriented grains preferentially grow, and the magnetic flux density is favorably increased. Furthermore, since the grain-oriented electrical steel sheet manufactured using the hot-rolled annealed steel sheet according to this embodiment does not suffer deterioration of other properties due to the increased magnetic flux density, it can be used for the same applications as conventional materials.

[0179] The grain-oriented electrical steel sheet manufactured using the hot-rolled and annealed steel sheet according to this embodiment contains, by mass fraction, Si (silicon): 2.0 to 7.0% as a basic element (major alloying element).

[0180] Furthermore, impurities may be present. "Impurities" refer to elements that are introduced during the industrial production of steel, either from the raw materials (ore or scrap) or from the manufacturing environment. 。

[0181] Furthermore, in addition to the basic elements and impurities mentioned above, optional elements may also be included. For example, instead of a portion of the remaining Fe mentioned above, optional elements such as Nb, V, Mo, Ta, W, C, Mn, S, Se, Al, N, Cu, Bi, B, P, Ti, Sn, Sb, Cr, Ni, etc., may be included. These optional elements may be included according to their purpose. Therefore, there is no need to limit the lower limit of these optional elements, and the lower limit may be 0%. Also, these optional elements may be included as impurities.

[0182] In grain-oriented electrical steel sheets, relatively large changes in chemical composition (reduction in content) occur through decarburization annealing and purification annealing during secondary recrystallization. Depending on the element, the content may be reduced to a level undetectable by general analytical methods (less than 1 ppm) through purification annealing. Generally, the chemical composition of the final product differs from that of the starting material slab. However, the arbitrary elements mentioned above are elements that remained in the final product from those contained in the slab, and the content of each element will not exceed the aforementioned content range for the slab, but will be within the content range corresponding to the content in the slab and subsequent manufacturing processes.

[0183] The above chemical composition is that of grain-oriented electrical steel sheet. If the grain-oriented electrical steel sheet used as a measurement sample has an insulating coating or the like on its surface, the coating or the like should be removed by a known method before measuring the chemical composition.

[0184] The grain-oriented electrical steel sheet manufactured using the hot-rolled annealed steel sheet according to this embodiment may have an intermediate layer disposed in contact with the grain-oriented electrical steel sheet (silicon steel sheet) and an insulating coating disposed in contact with the intermediate layer.

[0185] For example, the above-mentioned intermediate layer may be a layer mainly composed of oxides, a layer mainly composed of carbides, a layer mainly composed of nitrides, a layer mainly composed of borides, a layer mainly composed of silicides, a layer mainly composed of phosphides, a layer mainly composed of sulfides, or a layer mainly composed of intermetallic compounds. These intermediate layers are formed primarily to ensure adhesion between the silicon steel sheet and the insulating coating, and may be known to be formed by heat treatment in an atmosphere with controlled oxidation-reduction properties, chemical vapor deposition (CVD), physical vapor deposition (PVD), etc.

[0186] Furthermore, typical examples of the above-mentioned insulating coatings include those mainly composed of phosphate and colloidal silica with an average thickness of 0.1 to 10 μm, and those mainly composed of alumina sol and boric acid with an average thickness of 0.5 to 8 μm. [Examples]

[0187] Next, the effects of the present invention will be specifically described in detail with reference to examples. The conditions in the examples are just one example of conditions adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to this one example of conditions. The present invention can adopt various conditions as long as they do not depart from the spirit of the invention and achieve the objectives of the present invention.

[0188] Hot-rolled annealed steel sheets were manufactured using slabs with the chemical compositions shown in Tables 1 and 2. The chemical composition of the manufactured hot-rolled annealed steel sheets was equivalent to that of the slabs shown in Tables 1 and 2. These chemical compositions were measured using the method described above. In Tables 1 and 2, "-" indicates that the content was not controlled or measured during manufacturing, and therefore the content was not measured.

[0189] Furthermore, the hot-rolled annealed steel sheets described above were manufactured based on the manufacturing conditions shown in Tables 3 to 10. Slab heating was performed by soaking at a predetermined temperature for a predetermined time without temporarily increasing the heating temperature during the slab heating process. In the tables, the soaking temperature represents the surface temperature of the slab after heating, and the soaking time represents the slab heating time from the time the slab surface temperature reached the soaking temperature.

[0190] Although not shown in the table, when the total content of Nb group elements exceeds 0.030 mass%, setting the slab soaking temperature to over 1040°C but less than 1100°C and the soaking time to over 2 hours will cause 14-25 volume percent of precipitates to be dissolved, based on the precipitates contained in the slab after the casting process. Furthermore, when the total content of Nb group elements is between 0.0030 and 0.030 mass%, setting the slab soaking temperature to over 1030°C but less than 1180°C and the soaking time to over 70 minutes will cause 12-85 volume percent of precipitates to be dissolved, based on the precipitates contained in the slab after the casting process.

[0191] In the hot-rolled sheet annealing process, the hot-rolled steel sheet was annealed after the hot-rolling process. In all examples except No. 119, the hot-rolled steel sheet was heated and recrystallized in a first-stage annealing at a temperature of 1100°C, followed by a second-stage annealing at a lower temperature of 900°C, after which the steel sheet was cooled. The heating rate to the first-stage annealing temperature was set to an average of 5°C / second or more, and the holding time for the second-stage annealing was set to 20 seconds or more. In example No. 119, the same annealing conditions as above were used, but the second-stage annealing was omitted.

[0192] The precipitate morphology was investigated using the hot-rolled annealed steel sheets manufactured, based on the method described above. The size and distribution of precipitates with an equivalent circle diameter D of 50 to 1000 nm are shown in Tables 11 to 18. In the table, for precipitates with an equivalent circle diameter D of 50 to 1000 nm, Dp represents the most frequent diameter of the precipitate, f(Dp) represents the number density of the most frequent diameter of the precipitate, Wp represents the full width at half maximum of the most frequent diameter of the precipitate, and Dp Al This represents the most frequent diameter of Al-based precipitates, and Dp Nb The most frequent diameter of Nb precipitates is represented in the table. Al -Dp Nb This represents the difference between the most frequent diameter of Al-based precipitates and the most frequent diameter of Nb-based precipitates.

[0193] Furthermore, cold rolling and decarburization annealing were performed on the manufactured hot-rolled annealed steel sheets under known conditions. For cold rolling, the reduction ratio was 90.7% and the sheet thickness was 0.26 mm. For decarburization annealing, the steel sheets were annealed for 90 seconds at a temperature in the range of 830°C to 860°C. After decarburization annealing, the steel sheets were subjected to nitriding treatment (nitriding annealing) in a mixed atmosphere of hydrogen, nitrogen, and ammonia, resulting in a nitrogen content of 0.020 to 0.023 mass% (200 ppm to 230 ppm) in the steel sheets.

[0194] Furthermore, an annealing separation agent mainly composed of MgO was applied to the steel plate, and finish annealing was performed. In the final stage of finish annealing, the steel plate was held at 1200°C in a hydrogen atmosphere for 20 hours (purification annealing) and then allowed to cool naturally.

[0195] A coating solution for forming an insulating film, mainly composed of phosphate and colloidal silica and containing chromium, was applied to the primary film (intermediate layer) formed on the surface of the manufactured grain-oriented electrical steel sheet (finish annealed steel sheet). The sheet was then heated and held in an atmosphere of hydrogen:nitrogen at 75% by volume:25% by volume, and then cooled to form an insulating film.

[0196] The manufactured grain-oriented electrical steel sheet, when viewed from a cross-section parallel to the thickness direction, had an intermediate layer placed in contact with the grain-oriented electrical steel sheet (silicon steel sheet) and an insulating coating placed in contact with this intermediate layer. The intermediate layer was a forsterite coating with an average thickness of 2 μm, and the insulating coating was an insulating coating mainly composed of phosphate and colloidal silica with an average thickness of 1 μm.

[0197] The obtained grain-oriented electrical steel sheets were evaluated for various properties. The evaluation results are shown in Tables 11-18.

[0198] (1) Magnetic properties of grain-oriented electrical steel sheets The magnetic properties of the grain-oriented electrical steel sheets were measured based on the Single Sheet Tester (SST) method specified in JIS C 2556:2015.

[0199] As magnetic properties, the magnetic flux density B8 (T) in the rolling direction of the steel sheet when excited at 800 A / m was measured. When the magnetic flux density B8 was 1.945 T or more, it was judged as qualified. Also, for reference, under the conditions of an AC frequency of 50 Hz and an excitation magnetic flux density of 1.7 T, the iron loss W 17 / 50 (W / kg) defined as the power loss per unit weight (1 kg) of the steel sheet was measured.

[0200] Among No.1 to No.122, in the examples of the present invention, the precipitates contained in the hot-rolled annealed steel sheet were preferably controlled, and all showed excellent magnetic flux density as a grain-oriented electrical steel sheet. On the other hand, among No.1 to No.122, in the comparative examples, the precipitates contained in the hot-rolled annealed steel sheet were not preferably controlled, and a preferable magnetic flux density as a grain-oriented electrical steel sheet could not be obtained.

[0201] [Table 1]

[0202] [Table 2]

[0203] [Table 3]

[0204] [Table 4]

[0205] [Table 5]

[0206] [Table 6]

[0207] [Table 7]

[0208] Table 8

[0209] Table 9

[0210] Table 10

[0211] Table 11

[0212] Table 12

[0213] Table 13

[0214] Table 14

[0215] Table 15

[0216] Table 16

[0217] Table 17

[0218] [Table 18] [Industrial applicability]

[0219] According to the above aspects of the present invention, it is possible to provide a hot-rolled annealed steel sheet for grain-oriented electrical steel sheets that can increase magnetic flux density, thus having high industrial applicability.

Claims

1. In hot-rolled and annealed steel sheets for grain-oriented electrical steel sheets, The aforementioned hot-rolled annealed steel sheet is, by mass%, C: more than 0.0050% to 0.10%, Si: 2.0 to 7.0%, Mn: 0.050 to 1.0%, S: 0 to 0.0350%, Se: 0 to 0.0350%, S+Se total content: 0.0030-0.0350%, Al: 0.010-0.0650%, N: 0.0040-0.0120%, Nb: 0.0030 to 0.030%, V: 0 to 0.030%, Mo: 0 to 0.030%, Ta: 0 to 0.030%, W: 0-0.030%, Cu: 0 to 0.40%, Bi: 0 to 0.010%, B: 0 to 0.080%, P: 0-0.50%, Ti: 0 to 0.0150%, Sn: 0 to 0.10%, Sb: 0 to 0.10%, Cr: 0 to 0.30%, Ni: 0-1.0%, It contains and has a chemical composition consisting of Fe and impurities as the remainder, The precipitate, which is the residue obtained by electrolytic extraction of the aforementioned hot-rolled annealed steel sheet, had its particle size-number density distribution measured based on a calibration curve created from six types of standard particles with particle sizes of 29 nm, 48 nm, 100 nm, 200 nm, 300 nm, and 500 nm. Let Dp be the most frequent diameter in nm. Let the number density of the most mode diameter be f(Dp) in units of particles / g. When the full width at half maximum of the most frequent diameter is denoted as Wp in units of nm, Dp is 50-350 nm, f(Dp) is 1,000,000 particles / g or more. Wp / Dp is 0.75 to 2.

25. Satisfying the conditions, The precipitate, which is the residue obtained by electrolytic extraction of the aforementioned hot-rolled annealed steel sheet, was analyzed by measuring the particle size-detection intensity distribution based on a calibration curve created from six types of standard particles with particle sizes of 29 nm, 48 nm, 100 nm, 200 nm, 300 nm, and 500 nm. The most frequent diameter of Al-based precipitates in nanometers (Dp) Ａｌ year, The most frequent diameter of Nb precipitates in units of nm (Dp) Ｎｂ In that case, Dp Ａｌ -Dp Ｎｂ 22-100 nm, Satisfying A hot-rolled, annealed steel sheet for grain-oriented electrical steel sheets, characterized by the following features.

2. The aforementioned chemical composition contains a total of 0.0030 to 0.030% by mass of at least one element selected from the group consisting of Nb, V, Mo, Ta, and W. The hot-rolled annealed steel sheet for grain-oriented electrical steel sheets according to feature 1.

Images