Hot-rolled annealed steel sheet for grain-oriented magnetic steel sheet

Abstract

The hot-rolled annealed steel sheet for the grain-oriented electromagnetic steel sheet satisfies, for a particle diameter-strength distribution of precipitates having an equivalent circle diameter D of 50 to 1000 nm, 22 to 100 nm when Dp Al , the mode diameter of Al-based precipitates, per unit nm, is set as Dp Nb , and Dp Al -Dp Nb .

Description

Technical Field

[0001] This invention relates to hot-rolled annealed steel sheets for oriented electromagnetic steel sheets.

[0002] This application claims priority based on Japanese Patent Application No. 2024-034150, filed in Japan on March 6, 2024, the contents of which are incorporated herein by reference. Background Technology

[0003] Oriented electromagnetic steel sheets contain less than 7% by mass of Si and have properties in {110} <001> Secondary recrystallization texture with Goss orientation aggregation. It should be noted that {110} <001> Orientation refers to the arrangement of the {110} plane of the crystals parallel to the rolling surface, and the crystals... <001> The shaft is arranged parallel to the rolling direction.

[0004] The magnetic properties of oriented electromagnetic steel sheets are affected by {110} <001> The degree of aggregation of orientation has a significant impact. In particular, the rolling direction of the steel sheet, which is considered to be the main magnetization direction when used in steel sheets, is related to the crystallization direction, which is an easy magnetization direction. <001> The orientation relationship is important. Therefore, in the practical application of orientation-oriented electromagnetic steel sheets in recent years, crystalline... <001> The angle between the rolling direction and the rolling direction is controlled to be within a range of about 5°.

[0005] Such precise control of crystal orientation is achieved by moderately dispersing fine precipitates, known as inhibitors, in the steel up to the final annealing stage, and by maintaining the steel sheet at a high temperature during the final annealing. For example, by increasing the selective growth of Goss-oriented grains through inhibitors, secondary recrystallization occurs in a manner that preferentially promotes the growth of Goss-oriented grains during the final annealing. To date, attempts have been made to highly control the inhibitors with the aim of achieving dense control over crystal orientation.

[0006] For example, Patent Document 1 discloses the use of MnS as an inhibitor for two cold rolling processes.

[0007] Patent documents 2 and 3 disclose the control of MnS+AlN and MnS (and / or MnSe)+Sb as inhibitors, respectively.

[0008] Patent document 4 discloses a technique for preferentially controlling inhibitors in order to reduce the heating temperature of slabs in order to reduce manufacturing costs.

[0009] Patent document 5 discloses the control of the primary recrystallization particle size and its dispersion associated with the inhibitor.

[0010] Patent documents 6-8 disclose the addition of Nb, V, etc. to oriented electromagnetic steel sheets.

[0011] Furthermore, patent documents 9-11 disclose techniques for improving magnetostriction by precisely controlling the atmosphere and residence time during final annealing to form subgrain boundaries within the secondary recrystallized grains. These techniques demonstrate a concept of expanding the temperature range for secondary recrystallization to form subgrain boundaries, while also showing the potential for increased magnetic flux density.

[0012] Existing technical documents Patent documents Patent Document 1: Japanese Patent Publication No. 30-3651 Patent Document 2: Japanese Patent Publication No. 40-15644 Patent Document 3: Japanese Patent Publication No. 51-13469 Patent Document 4: Japanese Patent Application Publication No. 62-40315 Patent Document 5: Japanese Patent Application Publication No. 2008-261022 Patent Document 6: Japanese Patent Application Publication No. 52-024116 Patent Document 7: Japanese Patent Application Publication No. 02-200732 Patent Document 8: Japanese Patent No. 4962516 Patent Document 9: International Publication No. 2020 / 027215 Patent Document 10: International Publication No. 2020 / 027218 Patent Document 11: International Publication No. 2020 / 027219 Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] In recent years, amidst global trends towards energy conservation and environmental protection, the demands for higher efficiency in transformers have increased significantly. In this context, there are also requirements for improved performance in oriented electromagnetic steel sheets used in transformer cores, particularly regarding magnetic flux density.

[0015] The inventors determined through their research that the prior inhibitor control technologies disclosed in the aforementioned patent documents 1 to 8 cannot fully meet the requirements of oriented electromagnetic steel sheets, and further high magnetic flux density is needed.

[0016] The present invention was made in view of the above-mentioned problems. One aspect of the present invention is to provide a hot-rolled annealed steel sheet for oriented electromagnetic steel sheets that can improve the magnetic flux density, in view of the current requirement to improve the magnetic flux density of oriented electromagnetic steel sheets.

[0017] means for solving problems

[0018] The main points of this invention are as follows.

[0019] (1) A hot-rolled annealed steel sheet for oriented electromagnetic steel sheet according to one aspect of the present invention has the following chemical composition: Contains, by weight % C: 0.0010~0.10% Si: 2.0~7.0% Mn: 0.050~1.0%, S: 0~0.0350%, Se: 0~0.0350% Total S+Se 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%, The balance includes Fe and impurities; The particle size-number density distribution of precipitates with an equivalent circular diameter D of 50~1000 nm in the precipitates obtained from the electrolytic extraction of the hot-rolled annealed steel sheet. When the mode path is set to Dp in nm, The number density of the modal paths is defined as f(Dp) in units of 1 / g. When the half-value width of the mode path is set to Wp in nm, Satisfying DP values ​​of 50~350nm f(Dp) is 1,000,000 or more per gram. Wp / Dp ranges from 0.75 to 2.25. For the particle size-detection intensity distribution of precipitates with an equivalent circular diameter D of 50~1000 nm in the precipitates obtained from the electrolytic extraction of the hot-rolled annealed steel sheet. The modal diameter of Al-based precipitates is set as Dp in nm. Al , The modal diameter of Nb-based precipitates is denoted as Dp in nm. Nb hour, Satisfy Dp Al -Dp Nb The wavelength range is 22~100nm.

[0020] (2) The hot-rolled annealed steel sheet for oriented electromagnetic steel sheet described in (1) above may contain, as the above chemical composition, at least one of the following selected from the group consisting of Nb, V, Mo, Ta and W, in a total of 0.0030 to 0.030% by mass.

[0021] Invention Effects

[0022] According to the above-described manner of the present invention, a hot-rolled annealed steel sheet for oriented electromagnetic steel sheets capable of improving magnetic flux density is provided. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the particle size-number density distribution of precipitates with an equivalent circular diameter D of 50~1000nm.

[0024] Figure 2 This is a schematic diagram of the particle size-detection intensity distribution of precipitates with an equivalent circular diameter D of 50~1000nm.

[0025] Figure 3 This is a flowchart of a method for manufacturing a hot-rolled annealed steel sheet for oriented electromagnetic steel sheet according to one embodiment of the present invention. Detailed Implementation

[0026] A preferred embodiment of the present invention will be described in detail below. However, the present invention is not limited to the configuration disclosed in this embodiment, and various modifications can be made without departing from the spirit of the invention. Furthermore, in the numerical ranges described below, the lower and upper limits are included within the range. Values ​​marked "more than" or "less than" are not included in the numerical range. Additionally, unless otherwise specified, "%" in relation to chemical composition refers to "mass %".

[0027] Furthermore, in the following description, the term "inhibitor" is primarily used in the description related to the secondary recrystallization mechanism for precipitates in the steel that are characteristic of this embodiment, while the term "precipitate" is primarily used in the description related to the compounds observed in the microstructure. However, in this embodiment, the terminology is not intended to strictly distinguish between "inhibitor" and "precipitate".

[0028] As mentioned above, there is a current demand to increase the magnetic flux density of oriented electromagnetic steel sheets.

[0029] Therefore, the inventors focused on the technical concept of "expanding the temperature range for secondary recrystallization" disclosed in Patent Documents 9-11. In these Patent Documents 9-11, the technique of "expanding the temperature range for secondary recrystallization" is mainly used for the formation of subgrain boundaries within the secondary recrystallized grains and the associated noise reduction. The inventors believe that if this technique of "expanding the temperature range for secondary recrystallization" is optimized to improve the selectivity of crystal orientation, the magnetic flux density can be further increased.

[0030] Specifically, the study investigated how to more effectively expand the temperature range for secondary recrystallization by appropriately controlling the morphology of inhibitors in steel, and how to preferentially grow grains with preferred crystal orientations during the secondary recrystallization process within this expanded temperature range. The results showed that, in the manufacture of oriented electromagnetic steel sheets, if the morphology of the precipitates contained in the hot-rolled annealed steel sheet is optimally controlled, the temperature range for secondary recrystallization during final annealing is expanded, and Goss-oriented grains preferentially grow, enabling the magnetic flux density of the final oriented electromagnetic steel sheet to be improved beyond that of existing technologies.

[0031] Typically, inhibitors are fine precipitates in steel with a diameter of less than 1000 nm. These inhibitors have a grain boundary pinning effect, inhibiting grain growth. Then, during final annealing at temperatures above approximately 1000°C, the inhibitor dissolves in the parent α-Fe phase, weakening the grain boundary pinning effect. This results in what is known as secondary recrystallization, a process of abnormal grain growth.

[0032] For example, sulfides, selenides, and nitrides, which are Al-based precipitates, are used as the main inhibitors. Mn-based inhibitors and Al-based inhibitors (Al-based inhibitors controlled up to cold rolling) are mainly used in manufacturing methods where the slab heating temperature before hot rolling is set to 1300°C or higher (hereinafter, sometimes referred to as "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 set to 1280°C or lower, and nitriding treatment is performed from cold rolling until final annealing (hereinafter, sometimes referred to as "low-temperature slab heating process"). In addition to the above inhibitors, carbides and nitrides such as Nb, V, Mo, Ta, and W are sometimes effectively utilized as auxiliary inhibitors.

[0033] In the past, steel composition and manufacturing conditions were controlled during the production of oriented electromagnetic steel sheets in order to form inhibitors with appropriate functions in steel. In particular, steel composition, hot rolling conditions, and decarburization annealing conditions were identified as manufacturing conditions that have a significant impact on the morphology of inhibitors, and these conditions were precisely controlled.

[0034] In this embodiment, by controlling the size and distribution of the precipitates (inhibitors) contained in the hot-rolled annealed steel sheet within an appropriate range, the temperature range for secondary recrystallization is expanded during the final annealing process, which is a subsequent step, and the selectivity of the crystal orientation accompanying secondary recrystallization is improved. Specifically, the above-mentioned effects are achieved by allowing relatively fine inhibitors and relatively coarse inhibitors to coexist in the hot-rolled annealed steel sheet at an appropriate size and distribution.

[0035] The inventors presume that the above-mentioned effects can be achieved in the following manner.

[0036] First, we speculate on the reasons for the expanded temperature range of secondary recrystallization. As mentioned above, secondary recrystallization occurs due to the weakening of grain boundary pinning effect accompanying the melting of inhibitors. It is believed that during final annealing, fine inhibitors melt and disappear earlier than coarse inhibitors. Therefore, it is assumed that when fine and coarse inhibitors coexist, the fine inhibitors preferentially disappear in the early stages of the final annealing heating process. Especially with the addition of Nb, it is preferable to control the decomposition of fine inhibitors at a lower temperature than conventional inhibitors such as AlN.

[0037] As fine inhibitors melt, coarse inhibitors may grow, similar to Ostwald growth. However, the increase in pinning force accompanying the growth of coarse inhibitors is considered to have a smaller impact than the decrease in pinning force accompanying the disappearance of fine inhibitors. Therefore, it is believed that when fine and coarse inhibitors coexist, and the fine inhibitors melt earlier than the coarse inhibitors, secondary recrystallization begins at a lower temperature during the final annealing heating process.

[0038] Furthermore, it is believed that the pinning effect of coarse inhibitors, which undergo non-equilibrium melting and remain until the final annealing process reaches a relatively high temperature, is maintained at this temperature. Therefore, it is assumed that fine and coarse inhibitors coexist, and when coarse inhibitors remain at a high temperature, the pinning effect is maintained, and secondary recrystallization continues to a relatively high temperature.

[0039] That is, it is believed that when fine inhibitors and coarse inhibitors coexist, secondary recrystallization starts from a relatively low temperature in the final annealing heating process and continues to a relatively high temperature, thus expanding the temperature range for secondary recrystallization.

[0040] Next, we speculate on the reasons for the increased selectivity of crystal orientation. As mentioned above, secondary recrystallization preferentially grows Goss-oriented grains. It is believed that the preferential growth of these Goss-oriented grains is due to the special characteristics of the grain boundaries (grain boundary properties) and the special characteristics of the grain size (size advantage) of the Goss-oriented grains.

[0041] However, the driving force for the preferential growth of Goss-oriented grains is not that strong. Therefore, during secondary recrystallization, grain boundary movement is relatively easy to occur even outside of Goss-oriented grains. For example, due to the rapid decomposition of inhibitors, the pinning effect of grain growth weakens, and when the grain growth rate is relatively high (the driving force for grain growth is relatively high), grains outside of Goss-oriented grains are also prone to grow. In this case, the preferential growth of Goss-oriented grains is hindered.

[0042] Therefore, to promote preferential growth of Goss-oriented grains, the decomposition rate of the inhibitor should be kept as low as possible, the grain growth rate during secondary recrystallization should be relatively high compared to the inhibitor decomposition rate, and the secondary recrystallization should be sustained for a long time. For example, this can be achieved by slowing down the heating rate in the temperature region where the inhibitor strength weakens (the temperature region where the inhibitor melts), reducing the inhibitor melting rate, and ensuring that the growth rate of the accompanying secondary recrystallized grains is relatively faster than the inhibitor decomposition rate. However, in this method, a decrease in productivity cannot be avoided because the total final annealing time is longer.

[0043] In industrial applications where it's difficult to extend the final annealing time (where the heating rate is difficult to change if the maximum reached temperature is the same), even with a constant heating rate, as long as the temperature range for secondary recrystallization can be expanded by delaying the decomposition rate of the inhibitor, the time for secondary recrystallization can be extended without reducing productivity. This allows for a faster growth rate of the secondary recrystallized grains and improves their preferential growth. For example, if we consider that the entire surface of the final oriented electromagnetic steel sheet is occupied by secondary recrystallized grains, it can be understood that a longer secondary recrystallization time is related to the faster growth rate of the secondary recrystallized grains relative to the decomposition rate of the inhibitor.

[0044] That is, it is believed that when fine and coarse inhibitors coexist, the temperature range where the inhibitor decomposes slowly expands, and the growth rate of secondary recrystallized grains becomes relatively high relative to the inhibitor decomposition rate, leading to a wider temperature range for secondary recrystallization. Therefore, Goss-oriented grains tend to grow preferentially. As a result, it is believed that the magnetic flux density can ultimately be increased.

[0045] 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 coexist in the hot-rolled annealed steel sheet after the hot-rolled sheet annealing process at appropriate sizes and distributions. Furthermore, in this embodiment, the morphology of the precipitates is preferably controlled by adding auxiliary inhibitory elements.

[0046] In this embodiment, the morphology of the precipitates described above is defined based on the hot-rolled annealed steel sheet (the steel sheet before cold rolling).

[0047] The following describes in detail the hot-rolled annealed steel sheet for oriented electromagnetic steel sheet according to this embodiment.

[0048] The hot-rolled annealed steel sheet of this embodiment has the following chemical composition: Contains, by weight % C: 0.0010~0.10% Si: 2.0~7.0% Mn: 0.050~1.0%, S: 0~0.0350%, Se: 0~0.0350% Total S+Se 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%, The balance includes Fe and impurities; The particle size-number density distribution of precipitates with an equivalent circular diameter D of 50~1000 nm in the precipitates obtained from the electrolytic extraction of hot-rolled annealed steel sheets. When the mode path is set to Dp in nm, The number density of the mode path is set as f(Dp) in units of 1 / g. When the half-width of the mode path is set to Wp in nm, Satisfying DP values ​​of 50~350nm f(Dp) is 1,000,000 or more per gram. Wp / Dp ranges from 0.75 to 2.25. For the particle size-intensity distribution of precipitates with an equivalent circular diameter D of 50~1000 nm in the precipitates obtained from the electrolytic extraction of hot-rolled annealed steel sheets. The modal diameter of Al-based precipitates is set as Dp in nm. Al , The modal diameter of Nb-based precipitates is denoted as Dp in nm. Nb hour, Satisfy Dp Al -Dp Nb The wavelength range is 22~100nm.

[0049] In addition, the hot-rolled annealed steel sheet of this embodiment may contain, as a chemical composition, at least one of the following selected from the group consisting of Nb, V, Mo, Ta and W, in a total of 0.0030 to 0.030% by mass.

[0050] 1. Chemical composition

[0051] The chemical composition of the hot-rolled annealed steel sheet in this embodiment is the same as that used in oriented electromagnetic steel sheets.

[0052] It should be noted that in publicly available literature related to oriented electromagnetic steel sheets, there are few records of the chemical composition of hot-rolled annealed steel sheets as intermediate products. However, the steel composition remains almost unchanged in the process from slab to decarburization annealing, so 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.

[0053] The hot-rolled annealed steel sheet of this embodiment contains basic elements as its chemical composition, selective elements as needed, and the balance includes Fe and impurities.

[0054] The hot-rolled annealed steel sheet of this embodiment contains, by mass fraction, C: 0.0010~0.10%, Si: 2.0~7.0%, Mn: 0.050~1.0%, S+Se total content: 0.0030~0.0350%, Al: 0.010~0.0650%, N: 0.0040~0.0120%, and Nb: 0.0030~0.030% as basic elements (main alloying elements).

[0055] C: 0.0010~0.10% Carbon (C) is an effective element for controlling the primary recrystallization structure during manufacturing. However, excessive C content in the final product negatively impacts magnetic properties. Therefore, the C content of hot-rolled annealed steel sheets should be between 0.0010% and 0.10%. The preferred upper limits for C content are 0.0850% and 0.0750%. It should be noted that C is purified in the decarburization annealing and final annealing processes described later, and is below 0.0050% after the final annealing process. When C is present, considering productivity in industrial production, the C content can exceed 0% or be above 0.0010%.

[0056] Si: 2.0~7.0% Silicon (Si) increases the electrical resistance of grain-oriented electromagnetic steel sheets, thereby reducing iron loss. If the Si content is less than 2.0%, an austenitic phase transformation occurs during final annealing, impairing the crystal orientation of the grain-oriented electromagnetic steel sheet. On the other hand, if the Si content exceeds 7.0%, cold workability is poor, and cracking is prone to occur during cold rolling. Therefore, a Si content of 2.0% to 7.0% is suitable for hot-rolled annealed steel sheets. The preferred lower limit of Si content is 2.50%, more preferably 3.0%. The preferred upper limit of Si content is 4.50%, more preferably 4.0%.

[0057] Mn: 0.050~1.0% Manganese (Mn) combines with S and Se to precipitate as MnS and MnSe, which function as inhibitors. To optimally control the morphology of these inhibitors (precipitates), the Mn content of the hot-rolled annealed steel sheet should be only 0.050~1.0%. When the Mn content is below 0.050%, the amount of MnS and MnSe precipitated as inhibitors is insufficient, thus hindering proper secondary recrystallization. Conversely, when the Mn content is above 1.0%, the amount of MnS and MnSe precipitated as inhibitors is excessive, also hindering proper secondary recrystallization. Furthermore, in this embodiment, Nb group carbides, nitrides, carbonitrides, etc., can also partially perform the inhibitor function. In this case, the amount of MnS and MnSe precipitated can be reduced. Therefore, the upper limit of the Mn content is preferably 0.50%, and more preferably 0.20%.

[0058] S: 0~0.0350% Se: 0~0.0350% Total S+Se content: 0.0030~0.0350% Sulfur (S) and selenium (Se) combine with Mn to precipitate as MnS or MnSe, functioning as inhibitors. To optimally control the morphology of these inhibitors (precipitates), the hot-rolled annealed steel sheet only needs to have an S content of 0-0.0350%, a Se content of 0-0.0350%, and a total S+Se content of 0.0030-0.0350%. If the total S and Se content is 0.0030-0.0350%, secondary recrystallization is stable, which is preferred. Alternatively, in this embodiment, carbides, nitrides, carbonitrides, etc., of Nb group elements can also perform part of the inhibitor function. In this case, the amount of MnS and MnSe precipitated can be reduced. Therefore, the upper limit of the total S and Se content is preferably 0.0250%, and more preferably 0.010%. It should be noted that if S and Se remain in the steel after final annealing, they may sometimes form compounds, deteriorating iron loss. Therefore, it is preferable to remove S and Se from the steel and reduce their content through purification during the final annealing.

[0059] Here, "the total content of S and Se is 0.0030~0.0350%" means that the hot-rolled annealed steel sheet contains only either S or Se as a chemical component, and its content can be 0.0030~0.0350%. Alternatively, the hot-rolled annealed steel sheet may also contain both S and Se, and its total content is 0.0030~0.0350%.

[0060] Al: 0.010~0.0650% Aluminum (Al) combines with nitrogen (N) to precipitate as AlN and (Al,Si)N, which function as inhibitors. To optimally control the morphology of these inhibitors (precipitates), the Al content of the hot-rolled 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 preferred morphologies through nitriding treatment in a low-temperature slab heating process, particularly stabilizing secondary recrystallization at high temperatures. When the Al content is below 0.010%, the amount of AlN and (Al,Si)N precipitated as inhibitors is insufficient, thus hindering proper secondary recrystallization. Conversely, when the Al content is above 0.0650%, the amount of AlN and (Al,Si)N precipitated as inhibitors is excessive, also hindering proper secondary recrystallization. The lower limit of the Al content is preferably 0.020%, more preferably 0.0250%. From the viewpoint of stability of secondary recrystallization, the upper limit of the Al content is preferably 0.040%, more preferably 0.030%.

[0061] N: 0.0040~0.0120% Nitrogen (N) combines with Al to precipitate AlN and (Al, Si)N, acting as an inhibitor. The N content of hot-rolled annealed steel sheets should be between 0.0040% and 0.0120%. It should be noted that in low-temperature slab heating processes, N is sometimes introduced into the steel through nitriding treatment midway through manufacturing. If the N content exceeds 0.0120%, blistering, a type of defect, is easily generated in the steel sheet. The upper limit of the N content is preferably 0.010%, more preferably 0.0090%. N is purified in the final annealing process, becoming below 0.0050% after the final annealing.

[0062] Nb: 0.0030~0.030% Niobium (Nb) precipitates as an inhibitor of carbides, nitrides, and carbonitrides, and preferably functions as an inhibitor. Specifically, it is preferable to broaden the temperature range for secondary recrystallization. Therefore, an Nb content of 0.0030 to 0.030% is sufficient. The lower limit of the Nb content is preferably 0.0040%, more preferably 0.0050%. Furthermore, the upper limit of the Nb content is preferably 0.020%, more preferably 0.010%.

[0063] The hot-rolled annealed steel sheet of this embodiment may contain impurities as part of its chemical composition. It should be noted that "impurities" refer to elements introduced during the industrial manufacturing of steel from raw materials such as ore, waste, or the manufacturing environment. The total content of impurities may be capped at, for example, 5%.

[0064] Furthermore, in the hot-rolled annealed steel sheet of this embodiment, in addition to the basic elements and impurities described above, selective elements may also be included. For example, instead of Fe, which is part of the balance mentioned above, V, Mo, Ta, W, Cu, Bi, B, P, Ti, Sn, Sb, Cr, Ni, etc., may be included as selective elements. These selective elements can be included according to their purpose. Therefore, it is not necessary to limit the lower limit value of these selective elements, and the lower limit value can also be 0%. In addition, even if these selective elements are included as impurities, the above-mentioned effects will not be compromised.

[0065] 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 carbides, nitrides, and carbonitrides, preferably functioning as inhibitors. Specifically, it is preferable to broaden the temperature range for secondary recrystallization. Therefore, a V content of 0-0.030%, a Mo content of 0-0.030%, a Ta content of 0-0.030%, and a W content of 0-0.030% are all acceptable.

[0066] In this embodiment, Nb, V, Mo, Ta and / or W are sometimes collectively referred to as "Nb group elements".

[0067] The hot-rolled annealed steel sheet of this embodiment preferably contains at least one element selected from the group consisting of Nb, V, Mo, Ta and W as the Nb group element, with a total mass percentage of 0.0030 to 0.030%.

[0068] When Nb group element precipitates are used as inhibitors, and the total Nb group element content in the hot-rolled annealed steel sheet is 0.030% or less (preferably 0.0030% or more and 0.030% or less), the morphology of the Nb group element precipitates is preferably controlled, and the temperature range for secondary recrystallization is preferably expanded. As a result, Goss orientation grains preferably grow, and the magnetic flux density of the final oriented electromagnetic steel sheet is preferably increased.

[0069] The rationale for the preferred function of Nb group element precipitates as inhibitors is not yet clear, but it is believed that: Nb group element carbides, nitrides, or carbonitrides precipitate non-equilibrium during cooling from high temperatures, acting as precipitation nuclei for subsequently precipitated MnS and AlN. Therefore, compared to the case without Nb group elements, the presence of Nb group elements increases the number of MnS and AlN precipitation sites, resulting in a greater likelihood of MnS and AlN forming fine precipitates. In the hot-rolled annealed steel sheet of this embodiment, the coexistence of fine and coarse inhibitors expands the secondary recrystallization temperature range, but Nb group element precipitates are considered particularly effective in expanding the secondary recrystallization temperature range towards lower temperatures.

[0070] The total content of Nb group elements is preferably 0.0040% or more, more preferably 0.0050% or more. Furthermore, the total content of Nb group elements is preferably 0.020% or less, more preferably 0.010% or less. When the total content of Nb group elements is less than 0.0030%, the precipitates of Nb group elements that function as precipitation nuclei are insufficient, making it difficult for MnS and AlN to become finer. On the other hand, when the total content of Nb group elements is greater than 0.030%, the precipitation temperature range of Nb group element precipitates becomes high, resulting in coarse precipitates that tend to be low in density. Additionally, the deviation between the precipitation temperature range of Nb group element precipitates and that of MnS and AlN becomes larger, making it difficult for Nb group element precipitates to function effectively as precipitation nuclei for refining MnS and AlN.

[0071] 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 for the purposes known to the public. There is no need to set a lower limit for the content of these selected elements; the lower limit can be 0%.

[0072] It should be noted that in oriented electromagnetic steel sheets, the decarburization annealing and purification annealing during secondary recrystallization cause significant changes in chemical composition (lower content). Depending on the element, sometimes the content can be reduced to levels undetectable by conventional analytical methods (below 1 ppm) through purification annealing. However, the chemical composition described above refers to that of hot-rolled annealed steel sheets. In the processes from slab to before decarburization annealing, the steel composition remains almost unchanged.

[0073] The chemical composition of the hot-rolled annealed steel sheet in this embodiment can be determined using general analytical methods for steel. For example, the chemical composition of the hot-rolled annealed steel sheet can be determined using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Specifically, using ICP-AES, the chemical composition is determined by measuring a 35 mm square test piece collected from the hot-rolled annealed steel sheet under conditions based on a pre-prepared standard curve. It should be noted that C and S are determined using the combustion-infrared absorption method, and N is determined using the inert gas melting-thermal conductivity method.

[0074] 2. Precipitates

[0075] Next, the precipitates contained in the hot-rolled annealed steel sheet of this embodiment will be described.

[0076] The precipitates (inhibitors) contained in the hot-rolled annealed steel sheet of this embodiment can be any precipitates formed from elements contained in the hot-rolled annealed steel sheet. For example, sulfides and selenides can be Mn-based precipitates (containing Mn precipitates), nitrides can be Al-based precipitates (containing Al precipitates), and carbides, nitrides, and carbonitrides can be Nb-based precipitates (containing Nb precipitates). In addition to these inhibitors, as auxiliary inhibitors, compounds of Nb group elements other than Nb, compounds of any element such as Bi and B, and composite compounds with the above elements may also be included.

[0077] In this embodiment, the precipitates to be controlled in the hot-rolled annealed steel sheet are precipitates with an equivalent circle diameter D of 50~1000 nm. It should be noted that "equivalent circle diameter" refers to the diameter of a circle whose area is converted to the area of ​​the precipitate. This equivalent circle diameter is the same as the equivalent sphere diameter.

[0078] Precipitates with an equivalent circle diameter D of less than 50 nm in hot-rolled annealed steel sheets have a limited effect on expanding the temperature range for secondary recrystallization at the current time point. The reason for this is not yet clear, but it is believed that precipitates with an equivalent circle diameter D of less than 50 nm at the time of hot rolling annealing may change or disappear in subsequent processes, making it difficult for them to function as inhibitors during final annealing. Therefore, in the hot-rolled annealed steel sheet of this embodiment, the size and distribution of precipitates with an equivalent circle diameter D of 50 nm or more are controlled. It should be noted that through research including processes after the hot-rolled annealing process, it is expected that precipitates with an equivalent circle diameter D of less than 50 nm will function as inhibitors in the future.

[0079] Furthermore, precipitates with excessively large equivalent circle diameters (D) can sometimes negatively impact the growth of secondary recrystallized grains in the final stage of secondary recrystallization. Additionally, when precipitates with excessively large equivalent circle diameters (D) are generated, the number of precipitates (number density) in the hot-rolled annealed steel sheet can sometimes decrease. Moreover, precipitates with excessively large equivalent circle diameters (D) are less effective as inhibitors. Therefore, the average equivalent circle diameter (D) of the precipitates is preferably 1000 nm or less. In the hot-rolled annealed steel sheet of this embodiment, the size and distribution of precipitates with an equivalent circle diameter (D) of 50 to 1000 nm are controlled as precipitates that have the effect of expanding the temperature range for secondary recrystallization.

[0080] In the hot-rolled annealed steel sheet of this embodiment, the particle size-number density distribution of precipitates with an equivalent circular diameter D of 50 to 1000 nm in the precipitates that are the residue obtained by electrolytic extraction of the hot-rolled annealed steel sheet is as follows: When the mode path is set to Dp in nm, The number density of the mode path is set as f(Dp) in units of 1 / g. When the half-width of the mode path is set to Wp in nm, Satisfying DP values ​​of 50~350nm f(Dp) is 1,000,000 or more per gram. Wp / Dp ranges from 0.75 to 2.25.

[0081] Figure 1 A schematic diagram showing the particle size-number density distribution of precipitates with an equivalent circular diameter D of 50–1000 nm. Figure 1 Examples of Dp, f (Dp), and Wp are shown in the example.

[0082] When Dp exceeds 350 nm, the amount of fine precipitates used to expand the secondary recrystallization temperature range decreases, making it unsuitable. 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 described 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.

[0083] When f(Dp) is less than 1,000,000 precipitates / g, the amount of precipitate required for secondary recrystallization is insufficient to achieve the pinning effect, thus it is inappropriate. On the other hand, there is no specific upper limit for f(Dp), for example, it can be set to 50,000,000 precipitates / g.

[0084] When Wp / Dp is less than 0.75, Wp is small relative to Dp, therefore 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, when Wp / Dp exceeds 2.25, Wp is too large relative to Dp, resulting in uneven growth during normal primary recrystallization, and the grain structure before secondary recrystallization becomes a mixed-crystal structure, which is also unsuitable. The upper limit of Wp / Dp is preferably 1.75.

[0085] The particle size-number density distribution of precipitates with an equivalent circular diameter D of 50~1000nm can be calculated as follows.

[0086] For example, the method described in Japanese Patent No. 6572598 can be used. First, the precipitate is extracted from the hot-rolled annealed steel sheet by electrolysis. The electrolytic extraction conditions can be, for example, a solution of a surfactant or other dispersant (e.g., sodium dodecyl sulfate with a molecular weight of 288.38 g / mol) is added appropriately to an acetylacetone-based electrolyte, and electrolytic extraction is carried out at a constant current (500 mA - 2 hours). Electrolytic extraction only needs to be performed to achieve an electrolytic amount of 1 g or more of the hot-rolled annealed steel sheet.

[0087] The extraction residue (precipitate) can be recovered from the electrolytic extraction solution. The size and distribution of the recovered precipitate can be determined by the FFF (Field Flow Fractionation) method. The determination method based on the FFF method is the same as described in Japanese Patent No. 6572598.

[0088] It should be noted that the parameters can be adjusted according to the particle size and type being measured. An example is shown below. A Wyatt Eclips AF4 apparatus (Wyatt Technology Europe, Germany) can be used for the FFF test. For the sample dispersion solution, a sodium dodecyl sulfate aqueous solution at a concentration of 300 mg / mL is sufficient. The flow channel can use a 275 mm long channel with a 350 μm thick asymmetric diamond channel spacer. A regenerated cellulose ultrafiltration membrane with a molecular weight of 30 kDa can be used as the separation membrane.

[0089] Before adding the extraction residue (precipitate) recovered from the electrolytic extract, a standard curve needs to be constructed using standard samples with known particle sizes to correlate the particle size with the time until particle detection. The type and quantity of standard samples can be selected based on the particle size distribution of the extraction residue to be measured; for example, standard particles with a particle size of 29–500 nm from polystyrene latex particles can be used.

[0090] The size of the standard particles needs to be confirmed beforehand using a TEM (Transmission Electron Microscope) or similar instrument. At least 500 samples should be measured. Measure the long side of each standard particle and derive its average value. Regarding the types of standard particle sizes, six sizes can be used, for example: 29nm, 48nm, 100nm, 200nm, 300nm, and 500nm.

[0091] The actual separation conditions are as follows. First, for stabilization before focusing, simply set the eluent flow rate of the FFF device (hereinafter referred to as the channel flow) to 1.0 mL / min, the crossflow rate to 0.5 mL / min, and the time to 1 minute. Then, during focusing before sample injection, set the focusing flow rate to 3.0 mL / min and the time to 1 minute. Next, during focusing, inject the sample at 0.2 mL / min for 2 minutes. The focusing time after sample injection is 1 minute. Then, switch the flow path, stop the focusing flow, and feed the sample at the channel flow rate of 1.0 mL / min and the crossflow rate, decreasing proportionally from 0.5 mL / min to 0.05 mL / min over 35 minutes. Using the start of feeding as a reference, construct a standard curve by correlating the time from that point to particle detection with the pre-determined average particle size of the standard particles. It should be noted that the maximum particle detection time is 35 minutes, and the injection volume of the liquid containing the sample is 0.1~0.4 mL.

[0092] After preparing the standard curve as described above, re-introduce the extraction residue (precipitate) recovered from the electrolytic extractant into the device. Set the device parameters as described above.

[0093] In this way, it is possible to determine the particle size of the nanoparticles contained in the nanoparticle dispersion sample that is the object of the test.

[0094] In addition, it is possible to perform component analysis on the effluent (containing a solution of precipitates separated into different sizes) from the FFF unit using a conventional ICP (Inductively Coupled Plasma) quality analysis device.

[0095] Particle separation conditions using the FFF method can be achieved by using a 0.05 wt% sodium dodecyl sulfate (SDS) solution as the developing solvent and allowing it to flow at a rate of 1 mL / min.

[0096] Using particle size distribution data determined by the FFF method, particle sizes are divided into 0.5 nm widths. The number density is calculated in units of particles / g based on the number of precipitates contained within this particle size width and the amount of electrolysis during extraction. A histogram of particle size and number density is then constructed. Dp, f(Dp), and Wp can be determined from this histogram.

[0097] Furthermore, in the hot-rolled annealed steel sheet of this embodiment, the particle size-detection intensity distribution of precipitates with an equivalent circular diameter D of 50 to 1000 nm, which are precipitates obtained as residues from electrolytic extraction of hot-rolled annealed steel sheet, is further analyzed. The modal diameter of Al-based precipitates is set as Dp in nm. Al , The modal diameter of Nb-based precipitates is denoted as Dp in nm. Nb hour, Dp Al -Dp Nb It meets the requirements of 22~100nm.

[0098] Figure 2 A schematic diagram showing the particle size-detection intensity distribution of precipitates with an equivalent circular diameter D of 50~1000nm. Figure 2 Example Dp in Al and Dp Nb .

[0099] If Dp Al -Dp Nb If the value is less than 22 nm, the balance between finer and coarser inhibitors is not optimal, and therefore the secondary recrystallization temperature range is not sufficiently expanded, which is unsuitable. Al -Dp Nb The lower limit is preferably 22nm, and more preferably 55nm. On the other hand, if Dp Al -Dp NbIf the value exceeds 100nm, the inhibitor is too large, resulting in uneven growth during the normal grain growth of the first recrystallization. The grain structure before the second recrystallization becomes a mixed-crystal structure, which is inappropriate. Dp Al -Dp Nb The upper limit is preferably 100nm, and more preferably 90nm.

[0100] The particle size-detection intensity distribution of precipitates with an equivalent circular diameter D of 50~1000nm can be calculated as follows.

[0101] The precipitates can be recovered in the same manner as described above. The size and distribution of the precipitates can be determined by FFF-ICP-MS (Field Flow Fractionation-Inductively Coupled Plasma-Mass Spectrometry).

[0102] The determination method based on the FFF method is as described above. Furthermore, inductively coupled plasma mass spectrometry (ICP-Mass) can be used to analyze the composition of the precipitates that have undergone size separation using the FFF method.

[0103] Using the particle size distribution data calculated based on the 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 prepared. Dp can then be calculated from this particle size-detection intensity distribution. Al and Dp Nb That's all.

[0104] It should be noted that in this embodiment, the "mode diameter" corresponds to the particle size (particle size classification) when the number density value is the largest in the particle size-number density distribution mentioned above, and also corresponds to the particle size when the detection intensity value is the largest in the particle size-detection intensity distribution mentioned above.

[0105] It should be noted that the above Dp, f(Dp), Wp, and Dp Al , Dp Nb The calculations are preferably performed after smoothing the measurement data from the FFF and FFF-ICP-MS methods. The smoothing method for the FFF and FFF-ICP-MS measurement data can be, for example, using a simple moving average method. Furthermore, the value of f(Dp) can be obtained by considering the top three digits of the numerical value as valid.

[0106] 3.Plate thickness

[0107] The thickness of the hot-rolled annealed steel sheet in this embodiment is not particularly limited. The hot-rolled annealed steel sheet of this embodiment is supplied to the subsequent cold rolling process for final finishing into an orientation-oriented electromagnetic steel sheet. Therefore, considering the general manufacturing conditions of orientation-oriented electromagnetic steel sheets, a thickness of 1.8 to 3.5 mm is sufficient. It should be noted that this thickness is not limited; any known or practically applicable thickness can be used.

[0108] 4. Manufacturing method

[0109] Next, a method for manufacturing a hot-rolled annealed steel sheet for oriented electromagnetic steel sheets according to one embodiment of the present invention will be described. It should be noted that the method for manufacturing the hot-rolled annealed steel sheet of this embodiment is not limited to the method described below. The following manufacturing method is an example for manufacturing the hot-rolled annealed steel sheet of this embodiment.

[0110] Figure 3 This is a flowchart illustrating the manufacturing process of the hot-rolled annealed steel sheet according to this embodiment. Figure 3 The manufacturing process of the oriented electromagnetic steel sheet using this hot-rolled annealed steel sheet is also shown. For example... Figure 3 As shown, the manufacturing method of the hot-rolled annealed steel sheet of this embodiment includes 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.

[0111] in addition, Figure 3 The processes following the cold rolling process, namely the cold rolling process, decarburization annealing process, annealing separator coating process, and final annealing process, are the manufacturing processes of the oriented electromagnetic steel sheet (final annealed steel sheet). The effect of the hot-rolled annealed steel sheet of this embodiment can be confirmed by the oriented electromagnetic steel sheet as the final product, therefore the conditions controlled in these processes will also be described later.

[0112] The method for manufacturing hot-rolled annealed steel sheets according to this embodiment includes a casting process, a hot rolling process, and a hot-rolled sheet annealing process. In the casting process, molten steel with the following chemical composition is cast and formed into a slab: Contains, by weight % C: 0.0010~0.10% Si: 2.0~7.0% Mn: 0.050~1.0%, S: 0~0.0350%, Se: 0~0.0350% Total S+Se 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%, The balance includes Fe and impurities; In the hot rolling process, the slab after the casting process is heated, rough rolled, and finish rolled to form a hot-rolled steel plate; In the hot-rolled steel plate annealing process, the hot-rolled steel plate after the hot rolling process is annealed to obtain the hot-rolled annealed steel plate.

[0113] Furthermore, in the method for manufacturing hot-rolled annealed steel sheet according to this embodiment, when the total content of the group consisting of Nb, V, Mo, Ta, and W, which constitutes the chemical composition of the slab, exceeds 0.030% by mass, In the hot rolling process, During the heating of the slab before rough rolling, the homogenization temperature of the slab is made to exceed 1040°C but below 1100°C, thereby preferably dissolving a portion of the precipitates contained in the slab (for example, based on the precipitates contained in the slab after the casting process, dissolving 14 to 25% by volume of the precipitates). Furthermore, to ensure that this solution state is homogeneous within the slab, the homogenization time is made to exceed 2 hours. During rough rolling, the rolling temperature is set at 940~1030℃, and the reduction rate is set at 90~95%. During finish rolling, the finishing temperature should be 850~950℃; In the annealing process of hot-rolled steel plates, the average cooling rate of 750℃~500℃ during the cooling process after annealing is 25~80℃ / second.

[0114] Furthermore, in the method for manufacturing hot-rolled annealed steel sheet of this embodiment, when the total content of the group consisting of Nb, V, Mo, Ta, and W, which constitutes the chemical composition of the slab, is 0.0030 to 0.030% by mass, In the hot rolling process, During the heating of the slab before rough rolling, the homogenization temperature of the slab is made to exceed 1030°C and fall below 1180°C, thereby preferably dissolving a portion of the precipitates contained in the slab (for example, based on the precipitates contained in the slab after the casting process, dissolving 12 to 85% by volume of the precipitates), and in order to ensure that this solution state is homogeneous within the slab, the homogenization time of the slab is made to exceed 70 minutes. During rough rolling, the rolling temperature is set at 940~1070℃, and the reduction rate is set at 82~95%. During finish rolling, the finishing temperature should be 850~950℃; In the annealing process of hot-rolled steel plates, the average cooling rate of 750℃~500℃ during the cooling process after annealing is 25~80℃ / second.

[0115] To control the size and distribution of precipitates in hot-rolled annealed steel sheets, it is necessary to separately control the steel composition, casting conditions, hot rolling conditions, and hot-rolled annealing conditions. Particularly important is the separate control of the steel composition, slab heating conditions (the solution state of the precipitates before rough rolling), rough rolling temperature, rough rolling reduction rate, finishing rolling end temperature, and cooling rate after annealing. Furthermore, to control the aforementioned "solution state of the precipitates before rough rolling," separate control of the steel composition and slab heating conditions becomes crucial.

[0116] It should be noted that the above-mentioned slab heating only requires homogenization at a specified temperature for a specified time without temporarily increasing the heating temperature during the heating process. Here, the homogenization temperature refers to the surface temperature of the slab, and the homogenization time refers to the holding time after the surface temperature reaches the above-mentioned homogenization temperature. For example, the steel composition and heating rate are also affected, but if the surface temperature of the slab reaches the above-mentioned homogenization temperature during the slab heating process, it is preferable to control the solid solution state of the precipitates on the surface of the slab. Furthermore, if the surface temperature of the slab is held at the above-mentioned homogenization temperature for the above-mentioned homogenization time, it is preferable to control the solid solution state of the precipitates to the center of the slab.

[0117] The following describes the important manufacturing conditions in the method for manufacturing hot-rolled annealed steel sheets according to this embodiment. Other manufacturing conditions can be applied using the manufacturing conditions for conventionally known oriented electromagnetic steel sheets.

[0118] (Casting process)

[0119] In the casting process, slabs are prepared. As mentioned above, the chemical composition remains almost unchanged from the slab to the decarburization annealing stage, therefore the chemical composition of the slab is the same as that of the target hot-rolled annealed steel sheet (the chemical composition of the hot-rolled annealed steel sheet mentioned above).

[0120] It should be noted that the chemical composition of the slab affects the "solid solution state of precipitates before rough rolling" mentioned above. Details will be discussed later. In addition to meeting the requirements for the chemical composition of the hot-rolled annealed steel sheet, the chemical composition of the slab also needs to be controlled in combination with other manufacturing conditions that affect the "solid solution state of precipitates before rough rolling".

[0121] An example of a method for manufacturing a slab is described below. Molten steel is produced (smelted). A slab is then manufactured using this molten steel. For example, a slab can also be manufactured by continuous casting. Alternatively, an ingot can be made using molten steel, and the ingot can be rolled to produce a slab. The thickness of the slab is, for example, 150 to 350 mm. A preferred thickness is 220 to 280 mm. Thin slabs with a thickness of 10 to 70 mm can also be used as slabs.

[0122] (Hot rolling process)

[0123] The hot rolling process is the process of heating a slab to a specified temperature and then hot rolling (rough rolling and finish rolling) to obtain a hot-rolled steel plate.

[0124] For example, in the hot rolling process, the slab after the casting process is heated, rough rolled, and then finish rolled to produce a hot-rolled steel plate with a specified thickness of 1.8~3.5mm. After the finish rolling is completed, the hot-rolled steel plate is coiled at a specified temperature.

[0125] In the hot rolling process, when heating the slab after the casting process, the following conditions must be met.

[0126] For example, when the total content of the group consisting of Nb, V, Mo, Ta and W in the chemical composition of the slab exceeds 0.030% by mass, during the heating of the slab before rough rolling, the slab is heated to a temperature exceeding 1040°C and below 1100°C, so that a portion of the precipitates contained in the slab are preferably dissolved (for example, based on the precipitates contained in the slab at room temperature after the casting process, 14 to 25% by volume of the precipitates are dissolved), and in order to make this solution state homogeneous in the slab, the slab is heated in such a way that the heating time exceeds 2 hours.

[0127] On the other hand, when the total content of the group consisting of Nb, V, Mo, Ta and W in the slab chemical composition is 0.0030 to 0.030% by mass, during the heating of the slab before rough rolling, the slab is heated to a temperature exceeding 1030°C and below 1180°C, so that a portion of the precipitates contained in the slab are preferably dissolved (for example, based on the precipitates contained in the slab at room temperature after the casting process, 12 to 85% by volume of the precipitates are dissolved), and in order to make this solution state homogeneous in the slab, the slab is heated in such a way that the slab is heated for a time exceeding 70 minutes.

[0128] As a state before rough rolling, it is desirable to preferably solidify a portion of the precipitates contained in the slab. This requires the optimal balance between the amount of relatively coarse precipitates (melting residue precipitates) precipitated during the slab heating stage and the relatively fine precipitates (re-precipitated precipitates) precipitated after hot rolling but not precipitated during the slab heating stage.

[0129] Furthermore, Wp, a key technical feature of this embodiment, is increased by controlling the size difference between relatively coarse precipitates (melting residue precipitates) that remain in the precipitated state during the slab heating stage and relatively fine precipitates that do not precipitate during the slab heating stage but precipitate after hot rolling (re-precipitated precipitates).

[0130] The aforementioned "solution state of precipitates before rough rolling" refers to the equilibrium state of the precipitates before rough rolling, not the non-equilibrium state. In the non-equilibrium state, for example, near the surface and center in the thickness direction, the solid solution state of the precipitates becomes uneven. When this non-equilibrium slab is supplied for rough rolling, it becomes difficult to control the size and distribution of the precipitates contained in the steel plate after the hot-rolled annealing process.

[0131] For example, to ensure the solid solution state of the precipitates is close to equilibrium, it is preferable that the value obtained by subtracting the center temperature of the slab from the surface temperature during slab heating extraction is within a range greater than -10°C and less than 50°C. In particular, if the temperature difference is below -10°C, the steel plate surface is difficult to extend, thus the formation of defects becomes significant. Furthermore, if the temperature difference is above 50°C, the solid solution of the precipitates becomes uneven along the thickness direction, making it difficult to control the size of the precipitates.

[0132] It should be noted that although the slab heating method differs from that in this embodiment, the heating temperature is sometimes temporarily increased midway through the slab heating process in order to shorten the homogenization time. In this case, it is effective to set the difference between the surface temperature at the highest temperature and the surface temperature at the time of slab extraction to be below 80°C. In this case, after cooling down from the highest temperature, the slab is kept in the low-temperature region of the slab heating furnace for at least 20 minutes, and the difference between the surface temperature and the center temperature at the time of slab extraction from the slab heating furnace is preferably set to be less than 50°C. More preferably, the difference between the surface temperature and the center temperature of the slab is 0~30°C.

[0133] In existing technologies, such as the low-temperature slab heating process that heats slabs at temperatures below 1280°C, there is no concept of a technology that allows only a specific proportion of precipitates contained in the slab to be dissolved, nor is there any insight into the need to bring the solid solution of these precipitates close to equilibrium. In the method for manufacturing hot-rolled annealed steel sheets of this embodiment, it is preferable to control the solid solution state of the precipitates and to supply a slab in which the solid solution of the precipitates is in equilibrium to the roughing mill.

[0134] The aforementioned "solution state of precipitates before rough rolling" is a characteristic influenced by both the steel composition and the hot rolling conditions (slab heating conditions). To control this "solution state of precipitates before rough rolling," each manufacturing condition can be controlled in a composite and inseparable manner, taking into account the influence of the aforementioned manufacturing conditions on the "solution state of precipitates." For example, those skilled in the art can perform material control including precipitation behavior; therefore, as long as the influence of the aforementioned conditions on the "solution state" is understood, the aforementioned conditions can be combined to control the "solution state."

[0135] For example, regarding the "solution state of precipitates before rough rolling," as mentioned above, the heating temperature can be temporarily increased during the slab heating process, and then maintained for a certain period of time after cooling to control the "solution state." However, in the method for manufacturing hot-rolled annealed steel sheet of this embodiment, as an example, a method is shown to control the "solution state of precipitates before rough rolling" by performing homogenization at a specified temperature for a specified time without temporarily increasing the heating temperature during the slab heating process.

[0136] For example, when the total content of the group consisting of Nb, V, Mo, Ta, and W in the slab's chemical composition exceeds 0.030% by mass, it is sufficient to heat the slab to a homogenization temperature exceeding 1040°C and below 1100°C for a homogenization time exceeding 2 hours. In this case, it is preferable to readily 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 readily dissolveable to 14-25% by volume).

[0137] When the Nb group element content is within the aforementioned range, by keeping the homogenization temperature during slab heating below 1100°C, it is ultimately easier to control the size and distribution of the precipitates. For example, as in the prior art, when the slab heating temperature is set above 1100°C, excessive solid solution of the precipitates occurs, making it difficult to optimally control the solid solution state (e.g., it is difficult to control the solid solution rate of the precipitates below 25% by volume). In this case, the size of the precipitates that re-precipitate in subsequent processes becomes larger, making it difficult for 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. Therefore, as described above, it is necessary to control the temperature to a lower level than in the prior art.

[0138] Furthermore, when the homogenization temperature during slab heating is below 1040°C, the temperature is too low, making it difficult to dissolve the precipitates and optimize the solution state (for example, it is difficult to control the solubility of the precipitates to 14% by volume or more). In this case, the amount of precipitates that re-precipitate in subsequent processes is reduced, making it difficult for fine inhibitors and coarse inhibitors to coexist. As a result, the size difference of the precipitates, a key technical feature of this embodiment, is reduced.

[0139] In this embodiment, the secondary recrystallization temperature range is expanded by controlling the temperature to increase the size difference between the relatively coarse precipitates (melting residue precipitates) that remain in the precipitated state during the slab heating stage and the relatively fine precipitates (re-precipitated precipitates) that precipitate after hot rolling. Therefore, when the Nb group element content is within the above-mentioned range, it is important to ensure that the homogenization temperature during slab heating exceeds 1040°C and is below 1100°C. This homogenization temperature is preferably 1050°C to 1080°C.

[0140] Furthermore, when the Nb group element content is within the above range, a soaking time of less than 2 hours is too short to control the solid solution state of the precipitate to an equilibrium state. It should be noted that there is no specific upper limit to the above soaking time, but considering productivity in industrial production, it can also be set to 3 hours.

[0141] On the other hand, when the total content of the group consisting of Nb, V, Mo, Ta, and W in the slab's chemical composition is 0.0030 to 0.030% by mass, it is sufficient to heat the slab to a homogenization temperature exceeding 1030°C and below 1180°C for a homogenization time exceeding 70 minutes. In this case, it is preferable to readily 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 readily dissolveable to 12 to 85% by volume).

[0142] When the Nb group element content is within the aforementioned range, it is preferable to moderate the slab heating temperature before hot rolling and the rough rolling conditions described later. Specifically, even if the slab heating temperature is above 1100°C, it is ultimately possible for fine inhibitors and coarse inhibitors to coexist. For example, if a high slab heating temperature promotes the solid solution of AlN, MnS, etc., during the slab heating stage, these AlN and MnS tend to coarsely redefine in subsequent processes. However, when the Nb group element content is within the aforementioned range, the Nb group element precipitates act as precipitation nuclei for MnS and AlN, reducing the size of the reprecipitated AlN and MnS. Furthermore, the precipitation front (nose) of the Nb group element precipitates (carbonitrides) is located at a lower temperature compared to the precipitation front of AlN and MnS, therefore, the Nb group element precipitates themselves are more likely to precipitate as finer precipitates compared to AlN, etc.

[0143] Therefore, when the Nb group element content is within the above range, the upper limit temperature for slab homogenization is moderated to below 1180°C. It should be noted that while the solid solution of precipitates is promoted as the homogenization temperature increases, the controllable solid solution state of the precipitates is also moderated when the Nb group element content is within the above range (e.g., the upper limit of the solid solution rate of the precipitates is moderated to 85% by volume). Even with these moderated conditions, the effects of the Nb group element precipitates described above ultimately make it easy for fine inhibitors and coarse inhibitors to coexist.

[0144] Similarly, when the Nb group element content is within the above range, the lower limit temperature for slab homogenization is moderated to above 1030°C. It should be noted that while the solid solution of precipitates is suppressed as the homogenization temperature decreases, the controllable solid solution state of the precipitates is also moderated when the Nb group element content is within the above range (e.g., the lower limit of the solid solution rate of precipitates is moderated to 12% by volume). Even with these moderated conditions, it is ultimately possible for fine inhibitors and coarse inhibitors to coexist.

[0145] Regarding the mechanism of the above-mentioned effects, it is believed that precipitates of Nb group elements (carbonitrides) are easier to precipitate than MnS and AlN (especially MnS, which is difficult to precipitate without the support of dislocation multiplication caused by rolling, and the size of the precipitate becomes larger). Nb group element precipitates function as precipitation nuclei in the precipitation of MnS and AlN, thereby inhibiting the coarsening of AlN and MnS that are re-precipitated.

[0146] Furthermore, when the Nb group element content is within the above range, a soaking time of less than 70 minutes is too short to control the solid solution state of the precipitate to an equilibrium state. It should be noted that there is no specific upper limit to the above soaking time, but considering productivity in industrial production, it can also be set to 2 hours.

[0147] To control the "solid solution state of precipitates before rough rolling" to the above conditions, it is necessary to achieve an optimal balance between the amount of relatively coarse precipitates (melting residue precipitates) precipitated during the slab heating stage and the relatively fine precipitates (re-precipitated precipitates) precipitated after hot rolling.

[0148] It should be noted that the above-mentioned slab homogenization temperature refers to the surface temperature of the slab, and the slab homogenization time refers to the holding time after the surface temperature of the slab reaches the above-mentioned homogenization temperature. For example, the steel composition and heating rate are also affected, but when the slab is heated, if the surface temperature of the slab reaches the above-mentioned homogenization temperature, it is preferable to control the solid solution state of the precipitates on the surface of the slab. In addition, if the surface temperature of the slab is held at the above-mentioned homogenization temperature for the above-mentioned homogenization time, it is preferable to control the solid solution state of the precipitates to the center of the slab.

[0149] There is no particular limitation on the specific value of the solution rate. As mentioned above, by controlling the steel composition and slab heating conditions separately, the "solution state of the precipitates before rough rolling" can be optimally controlled. However, a specific solution rate value can also be determined using integrated thermodynamic calculation software as needed. For example, "Thermo-Calc" is a commonly used integrated thermodynamic calculation software. In this embodiment, "Thermo-Calc" (2019a ver.) is used to calculate the solution rate based on the chemical composition and temperature of the slab, and is used as a reference.

[0150] In the hot rolling process, the slab described above is then heated and hot rolled. Hot rolling is typically divided into roughing and finishing rolling. In this embodiment, in order to control the size and distribution of precipitates in the steel sheet after the hot-rolled annealing process, it is important to control the roughing temperature, roughing reduction rate, and finishing temperature based on controlling the "solid solution state of the precipitates before roughing" mentioned above.

[0151] In the hot rolling process, when rough rolling is performed after the slab is heated, the following conditions must be met.

[0152] For example, if the total content of the group consisting of Nb, V, Mo, Ta and W in the chemical composition of the slab exceeds 0.030% by mass, the rolling temperature can be controlled at 940~1030℃ and the reduction rate can be controlled at 90~95% when rough rolling the heated slab.

[0153] On the other hand, when the total content of the group consisting of Nb, V, Mo, Ta and W in the slab is 0.0030~0.030% by mass, the rolling temperature can be controlled at 940~1070℃ and the reduction rate can be controlled at 82~95% when rough rolling the heated slab.

[0154] By setting the reduction rate within the aforementioned range, processing-induced precipitation occurs, resulting in fine and abundant precipitates. When the roughing reduction rate is lower than the aforementioned lower limit, fewer dislocations are introduced due to rolling, resulting in fewer precipitation sites for processing-induced precipitation. Consequently, the precipitate particle size increases, and the Wp value decreases. On the other hand, there is no particular upper limit to the roughing reduction rate; it can be set to 95% considering factors such as mill performance.

[0155] It should be noted that the reduction rate of roughing rolling mentioned above refers to the cumulative reduction rate during roughing rolling. Specifically, the reduction rate of roughing rolling is defined as follows. The reduction rate (cumulative reduction rate) of rough rolling (%) = (1 - "thickness of steel plate after rough rolling" / "thickness of steel plate before rough rolling") × 100

[0156] Furthermore, when the roughing rolling temperature exceeds the aforementioned upper limit, precipitation is induced at or near the high-temperature edge of the precipitation front for elements such as MnS, AlN, and Nb. Therefore, the critical precipitation radius of the precipitates that re-precipitate during hot rolling increases. Consequently, the size difference between the precipitates and the relatively coarse precipitates (melting residues) precipitated from the slab heating stage decreases, and the Wp value decreases. On the other hand, there is no particular limitation on the lower limit of the roughing rolling temperature. If the temperature is too low, the slab hardens, and its rollability decreases. Therefore, rolling at, for example, 940°C or higher is acceptable. It should be noted that the roughing rolling temperature is defined as the average of the start and end temperatures of the roughing roll.

[0157] It should be noted that, as a chemical composition, when Nb group elements are appropriately contained, in addition to MnS and AlN, Nb group element precipitates (especially carbides and nitrides) are also precipitated during rough rolling. These Nb group element precipitates act as nuclei for the subsequent precipitation of MnS and AlN, resulting in the further fine re-precipitation of MnS and AlN. Therefore, when Nb group elements are appropriately contained as a chemical composition, the control conditions for the solid solution state of the precipitates (e.g., the solid solution rate of the precipitates before rough rolling), rough rolling temperature, and rough rolling reduction rate, which need to be controlled in the hot rolling process, are mitigated.

[0158] The reason why the control conditions for the solid solution state of the precipitates are eased when Nb group elements are appropriately present, compared to when Nb group elements are inappropriately present, is as follows: When Nb group elements are present, MnS and AlN, due to Nb group element precipitation, are redeprecipitated more finely, thus Dp decreases compared to the case without Nb group elements. On the other hand, even with Nb group elements, the value of Wp does not change significantly. Therefore, Wp / Dp increases when Nb group elements are present. It is believed that the control conditions for the solid solution state of the precipitates are eased for these reasons.

[0159] For example, in the case of Nb group elements, if the solid solution state of the precipitates is not optimally controlled (e.g., the solid solution rate of precipitates before rough rolling is less than 12% by volume), then, similarly to the case without Nb group elements, the precipitates will not fully dissolve during slab heating, resulting in fewer fine precipitates re-precipitated during hot rolling. Consequently, Wp decreases, and the temperature range for secondary recrystallization cannot be sufficiently expanded during final annealing. Furthermore, in the case of Nb group elements, if the solid solution state of the precipitates is not optimally controlled (e.g., the solid solution rate of precipitates before rough rolling is greater than 85% by volume), then, similarly to the case without Nb group elements, most of the precipitates dissolve during slab heating, resulting in fewer coarser precipitates (melted residual precipitates) in the slab. Consequently, the temperature range for secondary recrystallization cannot be sufficiently expanded during final annealing.

[0160] Furthermore, the reason why the control conditions for rough rolling reduction are relaxed when Nb group elements are appropriately present, compared to when Nb group elements are inappropriately present, is as follows: When Nb group elements are present, Nb group element precipitates tend to precipitate finely in the steel, thus increasing the number of fine precipitates even before rough rolling compared to when Nb group elements are absent. Therefore, with the presence of Nb group elements, the number of precipitate sites increases, making processing-induced precipitation more likely even with a reduced reduction rate. It is believed that the control conditions for rough rolling reduction are relaxed for these reasons.

[0161] When Nb group elements are present, a roughing reduction ratio of less than 82% results in fewer dislocation introductions due to rolling, similar to the case without Nb group elements. This reduces the number of precipitation sites that can induce processing, leading to larger precipitate particle sizes and a smaller Wp value. When Nb group elements are present, the upper limit of the roughing reduction ratio is preferably 93%.

[0162] Furthermore, the reason why the control conditions for rough rolling temperature are relaxed when Nb group elements are appropriately present, compared to when Nb group elements are inappropriately present, is as follows: When Nb group elements are present, as mentioned above, the number of fine precipitates in the steel even before rough rolling increases compared to when Nb group elements are not present. Therefore, when Nb group elements are present, the precipitation sites for precipitates increase, and precipitates that re-precipitate during hot rolling tend to become finer. It is believed that the control conditions for rough rolling temperature are relaxed for these reasons.

[0163] When Nb group elements are present, if the roughing rolling temperature is higher than 1070°C, precipitation is induced at a higher temperature than the precipitation front of all precipitates, including those from MnS, AlN, and Nb group elements. Therefore, the critical precipitation radius of the precipitates re-precipitated during hot rolling increases. Consequently, the size difference between the precipitates and the relatively coarse precipitates (melting residues) precipitated from the slab heating stage decreases, and the Wp value decreases. When Nb group elements are present, the upper limit of the roughing rolling temperature is preferably 1065°C, and more preferably 1040°C.

[0164] Furthermore, the reason why Nb group elements promote the fine precipitation of precipitates is not yet clear, but it is believed to be as follows.

[0165] During rough rolling, the steel plate temperature decreases sharply over time. Therefore, the rough rolling process is considered a non-equilibrium state. If it were an equilibrium state, even in the temperature range where all MnS and AlN precipitate, dissolved MnS and AlN may still exist in a non-equilibrium state. For example, since the rough rolling process is non-equilibrium, it is believed that dissolved MnS and AlN exist even in the temperature range where Nb group element precipitates. Therefore, it is considered that when Nb group element precipitates during rough rolling, these precipitates act as nuclei for subsequent MnS and AlN precipitation, resulting in fine MnS and AlN precipitation. Specifically, compared to the case where Nb group element precipitates are absent, the presence of Nb group element precipitates increases the number of MnS and AlN precipitation sites, resulting in fine MnS and AlN precipitation.

[0166] Furthermore, when precipitates of Nb group elements, which act as precipitation nuclei for MnS and AlN, are covered by MnS and AlN, further growth of these Nb group element precipitates is inhibited. In this case, it is believed that the Nb group elements that should be consumed by the growth of precipitates precipitate finely as new precipitates. These fine precipitates of new Nb group elements are considered to act as new precipitation nuclei for MnS and AlN, contributing to the further fine precipitation of MnS and AlN. Thus, it is believed that the precipitates of Nb group elements synergistically contribute to the fine precipitation of MnS and AlN.

[0167] It should be noted that the slab homogenization temperature during the pre-rough rolling heating and the rolling temperature during rough rolling are controlled with a specific purpose. These temperatures are not caused by the natural temperature drop that occurs when the slab is removed from the slab heating furnace for rough rolling. For example, in normal operation, the slab homogenization temperature and rough rolling temperature are not controlled with a specific purpose. Generally, if the slab homogenization temperature is high, the rough rolling temperature will also be high, and if the slab homogenization temperature is low, the rough rolling temperature will also be low. On the other hand, in this embodiment, the slab homogenization temperature and the rough rolling temperature are controlled in a specific manner. For example, even if the slab homogenization temperature is within the aforementioned range, the rough rolling temperature is also controlled to be within the aforementioned range; similarly, even if the slab homogenization temperature is within the aforementioned range, the rough rolling temperature is also controlled to be within the aforementioned range.

[0168] In addition, during the hot rolling process, the following conditions need to be met when performing finish rolling.

[0169] The finishing temperature of the finishing rolling can be 850~950℃.

[0170] By setting the finishing rolling temperature to the aforementioned range, rolling can be performed in a temperature range above 850°C, which is the precipitation front of Al-based precipitates (AlN, etc.). Therefore, the newly precipitated Al-based precipitates in the finishing rolling have a large particle size, i.e., Dp. Al The value increases. As a result, it is possible to reduce the Dp of precipitates with an equivalent circular diameter D of 50~1000nm in the precipitates contained in the steel sheet after the hot-rolled annealing process. Al -Dp Nb The value is preferably controlled to be 22~100nm.

[0171] It should be noted that there are no special restrictions on the finishing rolling conditions other than those mentioned above; as long as the usual hot rolling conditions are used, they are acceptable.

[0172] (Hot-rolled plate annealing process)

[0173] The hot-rolled sheet annealing process is a process of annealing hot-rolled steel sheets after the hot-rolling process to obtain hot-rolled annealed steel sheets. Hot-rolled sheet annealing is usually carried out by annealing the hot-rolled steel sheets after the hot-rolling process to control the recrystallization rate, residual strain, crystal grain size and other steel sheet microstructures. In addition, it is carried out to optimize and adjust the morphology of precipitates in the steel.

[0174] The annealing conditions in the hot-rolled sheet annealing process can be the same as 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 have the above-described precipitate morphology (size and distribution).

[0175] For example, in this embodiment, during the annealing process of hot-rolled plate, the average cooling rate of 750~500°C after the annealing (after the second stage of annealing) is 25~80°C / second.

[0176] 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; however, to prevent breakage during cold rolling, an upper limit of 80°C / second is acceptable.

[0177] When the average cooling rate after annealing is within the above range, in order to precipitate at a faster cooling rate than usual, the Nb-based precipitates (NbC, etc.) that mainly precipitate during this cooling become smaller in diameter, Dp. Nb The value decreases. As a result, it is possible to optimally control the Dp of precipitates with an equivalent circular diameter D of 50~1000nm in the precipitates contained in the steel sheet after the hot-rolled annealing process. Al -Dp Nb The value is [value missing]. It should be noted 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.

[0178] In addition, in this embodiment, there are no particular limitations on the annealing conditions of hot-rolled plates other than those described above; any ordinary annealing conditions for hot-rolled plates may be used.

[0179] For example, in this embodiment, the hot-rolled steel sheet after the hot-rolling process is heated to undergo a first-stage annealing at a temperature range of 1000~1150°C for recrystallization, followed by a second-stage annealing at a lower temperature range of 800~1000°C, and then the steel sheet is cooled. The first-stage annealing temperature is preferably 1020~1130°C. The second-stage annealing temperature is preferably 800~950°C. Furthermore, the heating rate up to the first-stage annealing temperature is preferably an average of 5°C / second or more. Additionally, during the second-stage annealing, the steel sheet is preferably held for at least 20 seconds.

[0180] As described above, the method for manufacturing hot-rolled annealed steel sheets according to this embodiment includes a casting process, a hot rolling process, and a hot-rolled sheet annealing process. The size and distribution of precipitates in the hot-rolled annealed steel sheets manufactured by controlling the above conditions in each process are preferably controlled, and the particle size-number density distribution and particle size-detection intensity distribution of the precipitates are controlled within the aforementioned ranges. As a result, the temperature range for secondary recrystallization during final annealing is expanded, the selective growth of Goss-oriented grains is improved, and the magnetic flux density of the oriented electromagnetic steel sheet is increased.

[0181] For example, as described above, in the manufacturing method of hot-rolled annealed steel sheet of this embodiment, the amount of relatively coarse precipitates (melting residue precipitates) precipitated during the slab heating stage is mainly controlled by the slab homogenization temperature and slab homogenization time during slab heating before rough rolling. Based on subsequent manufacturing conditions, the amount of relatively fine precipitates (re-precipitated precipitates) is controlled, thereby controlling the various characteristics of the hot-rolled annealed steel sheet within the aforementioned range. As a result, the temperature range for secondary recrystallization during final annealing is expanded, the selective growth of Goss orientation grains is improved, and the magnetic flux density of the orientation-oriented electromagnetic steel sheet is increased.

[0182] 5. Application Method of Hot-Rolled Annealed Steel Plate

[0183] The effectiveness of the hot-rolled annealed steel sheet of this embodiment can be confirmed by the oriented electromagnetic steel sheet as the final product. Therefore, from the viewpoint of using the hot-rolled annealed steel sheet referred to in this embodiment, the manufacturing process of the oriented electromagnetic steel sheet immediately following the hot-rolled sheet annealing process will be described.

[0184] The manufacturing method of oriented electromagnetic steel sheets includes a cold rolling process, a decarburization annealing process, an annealing separating agent coating process, and a final annealing process. Additionally, depending on the requirements, an insulating film formation process and a magnetic domain control process may also be included. These processes can be performed using known, general process conditions. The following describes an example of a manufacturing method that uses nitriding treatment as a low-temperature slab heating process.

[0185] (Cold rolling process)

[0186] The cold rolling process is a process in which the hot-rolled annealed sheet obtained in the hot-rolled sheet annealing process is subjected to multiple (more than 2) cold rolling processes (e.g., the total cold rolling rate is 80~95%) by means of one cold rolling or annealing (intermediate annealing) to obtain a cold-rolled steel sheet with a thickness of, for example, 0.10~0.50 mm.

[0187] (Decarburization annealing process)

[0188] The decarburizing annealing process involves decarburizing the cold-rolled steel sheet obtained from the cold rolling process (e.g., at 700-900°C for 1-3 minutes) to obtain a decarburized annealed steel sheet that has undergone one recrystallization. By performing decarburizing annealing on the cold-rolled steel sheet, the carbon (C) contained in the sheet is removed. To remove carbon from the cold-rolled steel sheet, decarburizing annealing is preferably performed in a humid atmosphere.

[0189] (Nitriding treatment)

[0190] Nitriding is performed to adjust the strength of the inhibitor in secondary recrystallization. During nitriding, the nitrogen content of the steel sheet is increased to approximately 40-300 ppm at any point during the period from the start of the decarburization annealing described above to the start of secondary recrystallization in the final annealing described later. Examples of nitriding treatments include annealing the steel sheet in an atmosphere containing a nitriding gas such as ammonia, and performing final annealing on decarburized annealed steel sheets coated with an annealing separating agent containing powders with nitriding capabilities such as MnN.

[0191] (Annealing release agent coating process)

[0192] The annealing release agent coating process is a process of applying an annealing release agent to a decarburized annealed steel plate. For example, annealing release agents with MgO as the main component or with alumina as the main component can be used.

[0193] After being coated with annealing separating agent, the decarburized annealed steel sheet is rolled into a coil and then subjected to final annealing in the subsequent final annealing process.

[0194] (Final annealing process)

[0195] The final annealing process is a process that involves subjecting a decarburized annealed steel sheet coated with an annealing separating agent to final annealing, resulting in secondary recrystallization. This process involves allowing secondary recrystallization to occur while the growth of primary recrystallized grains is suppressed using an inhibitor, thereby achieving {110} <001> Oriented grains grow preferentially, which increases magnetic flux density.

[0196] When using the hot-rolled annealed steel sheet of this embodiment, the temperature range for secondary recrystallization during final annealing expands, resulting in an unprecedented {100}. <011> The preferential growth of oriented grains results in a dramatic increase in magnetic flux density. Furthermore, abnormal grain growth of secondary recrystallized grains occurs during the final annealing process, resulting in these secondary recrystallized grains occupying the entire surface of the plate after final annealing. A small number of secondary recrystallized grains cover the entire steel plate surface, and the grain size of each secondary recrystallized grain is increased.

[0197] Furthermore, in the final annealing process, the final annealing conditions for "expanding the temperature range for secondary recrystallization" disclosed in Patent Documents 9-11 can be applied as needed. Based on the hot-rolled annealed steel sheet of this embodiment, if the final annealing conditions disclosed in Patent Documents 9-11 are applied, the temperature range for secondary recrystallization can be further expanded.

[0198] The following insulating coating formation process and magnetic domain control process cause the crystal orientation to aggregate in {110} <001> From a technical standpoint, this is not a necessary step. However, it is a step used in general oriented electromagnetic steel sheets to improve practical magnetic properties.

[0199] (Insulation coating formation process)

[0200] The insulating coating formation process is the process of forming an insulating coating on the oriented electromagnetic steel sheet (final annealed steel sheet) after the final annealing process. This can be achieved by forming an insulating coating primarily composed of phosphate and colloidal silica, or an insulating coating primarily composed of alumina sol and boric acid, on the final annealed steel sheet.

[0201] (Magnetic domain control process)

[0202] The magnetic domain control process is a procedure that refines the magnetic domains of the oriented electromagnetic steel sheet. This process is performed at an appropriate time after cold rolling. For example, known methods such as laser, plasma, mechanical methods, and etching can be used to create localized micro-deformations or localized grooves on the oriented electromagnetic steel sheet.

[0203] 6. Oriented electromagnetic steel sheet obtained using the hot-rolled annealed steel sheet of this embodiment.

[0204] A brief description will be given of the orientation-oriented electromagnetic steel sheet manufactured using the hot-rolled annealed steel sheet of this embodiment.

[0205] The hot-rolled annealed steel sheet of this embodiment has both relatively fine and relatively large precipitates of preferred size and distribution. Therefore, in the oriented electromagnetic steel sheet obtained using the hot-rolled annealed steel sheet of this embodiment, Goss orientation grains preferentially grow, and the magnetic flux density is preferably increased. In addition, the oriented electromagnetic steel sheet manufactured using the hot-rolled annealed steel sheet of this embodiment does not suffer from deterioration of other properties due to the increase in magnetic flux density, and therefore can be used for the same applications as before.

[0206] The oriented electromagnetic steel sheet manufactured using the hot-rolled annealed steel sheet of this embodiment contains 2.0 to 7.0% Si (silicon) as a basic element (the main alloying element) by mass fraction.

[0207] Additionally, it may contain impurities. It should be noted that "impurities" refer to elements introduced during the industrial manufacturing of steel from raw materials such as ore, waste, or the manufacturing environment. The total impurity content can be capped at, for example, 5%.

[0208] Furthermore, in addition to the basic elements and impurities mentioned above, selective elements may also be included. For example, instead of Fe, which is the balance mentioned above, Nb, V, Mo, Ta, W, C, Mn, S, Se, Al, N, Cu, Bi, B, P, Ti, Sn, Sb, Cr, Ni, etc., may be included as selective elements. These selective elements are included according to their purpose. Therefore, there is no need to limit the lower value of these selective elements, and the lower limit can also be 0%. In addition, these selective elements are sometimes included as impurities.

[0209] It should be noted that in oriented electromagnetic steel sheets, the decarburization annealing and purification annealing during secondary recrystallization cause significant changes in chemical composition (lower content). Depending on the element, sometimes purification annealing reduces the content to levels undetectable by conventional analytical methods (below 1 ppm). Typically, the chemical composition of the final product differs from that of the slab used as the starting raw material. However, any of the aforementioned elements present in the slab remain in the final product, and the content of each element in the slab does not exceed the aforementioned range, forming the content range in the slab and corresponding to the content range in subsequent manufacturing processes.

[0210] It should be noted that the above chemical composition refers to the composition of the oriented electromagnetic steel sheet. When the oriented electromagnetic steel sheet used as the test sample has an insulating coating or the like on its surface, the chemical composition is determined after removing the coating or the like using known methods.

[0211] The orientation-oriented electromagnetic steel sheet manufactured using the hot-rolled annealed steel sheet of this embodiment can have an intermediate layer disposed on the orientation-oriented electromagnetic steel sheet (silicon steel sheet) and an insulating coating disposed on the intermediate layer.

[0212] For example, the aforementioned intermediate layer can be any layer primarily composed of oxides, carbides, nitrides, borides, silicides, phosphides, sulfides, or intermetallic compounds. These intermediate layers are primarily formed to ensure the tight adhesion between the silicon steel sheet and the insulating coating, and can be any known intermediate layer formed through heat treatment, chemical vapor deposition (CVD), or physical vapor deposition (PVD) in a controlled redox atmosphere.

[0213] In addition, the aforementioned insulating films can be exemplified by insulating films mainly composed of phosphate and colloidal silica with an average thickness of 0.1 to 10 μm, and insulating films mainly composed of alumina sol and boric acid with an average thickness of 0.5 to 8 μm.

[0214] Example

[0215] Next, the effects of the present invention will be specifically illustrated through examples. The conditions in the examples are one example used to confirm the feasibility and effects of implementing the present invention, and the present invention is not limited to this one example. Various conditions can be used as long as they do not depart from the spirit of the present invention and achieve the purpose of the present invention.

[0216] 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 identical to that of the slabs shown in Tables 1 and 2. It should be noted that these chemical compositions were determined based on the methods described above. In Tables 1 and 2, "-" indicates that no conscious content control or manufacturing was performed, and no content determination was carried out.

[0217] Furthermore, the hot-rolled annealed steel sheets described above are manufactured based on the manufacturing conditions shown in Tables 3-10. During the slab heating process, the heating temperature is not temporarily increased, but rather homogenized at a specified temperature for a specified time. It should be noted that the homogenization temperature shown in the tables represents the surface temperature of the slab after heating, and the homogenization time shown in the tables represents the slab heating time required for the surface temperature to reach the homogenization temperature.

[0218] Although not shown in the table, when the total content of Nb group elements exceeds 0.030% by mass, the slab's homogenization temperature exceeds 1040°C but is below 1100°C, and the homogenization time exceeds 2 hours, resulting in 14-25% by volume of precipitates dissolved in the slab after the casting process. Furthermore, when the total content of Nb group elements is 0.0030-0.030% by mass, the slab's homogenization temperature exceeds 1030°C but is below 1180°C, and the homogenization time exceeds 70 minutes, resulting in 12-85% by volume of precipitates dissolved in the slab after the casting process.

[0219] It should be noted that in the hot-rolled sheet annealing process, the hot-rolled steel sheet after the hot rolling process is annealed. In embodiments other than No. 119, the hot-rolled steel sheet is heated and subjected to a first-stage annealing at a temperature range of 1100°C to allow recrystallization, followed by a second-stage annealing at a lower temperature range of 900°C, and then the steel sheet is cooled. In this case, the heating rate up to the first-stage annealing temperature is set to an average of 5°C / second or more, and the holding time in the second-stage annealing is set to 20 seconds or more. In the embodiment of No. 119, the same annealing conditions are used, but the second-stage annealing is not performed.

[0220] Using the manufactured hot-rolled annealed steel sheet, the precipitation morphology of the precipitates was investigated based on the method described above. The size and distribution of precipitates with an equivalent circle diameter D of 50–1000 nm are shown in Tables 11–18. It should be noted that, for precipitates with an equivalent circle diameter D of 50–1000 nm, in the tables, Dp represents the modal diameter of the precipitate, f(Dp) represents the number density of the modal diameter of the precipitate, and Wp represents the half-value width of the modal diameter of the precipitate. Al Dp represents the modal path of Al-based precipitates. Nb This represents the modal path of Nb-based precipitates. Additionally, in the table, Dp... Al -Dp Nb This represents the difference between the mode diameter of Al-based precipitates and the mode diameter of Nb-based precipitates.

[0221] Furthermore, the hot-rolled annealed steel sheet manufactured was subjected to cold rolling and decarburization annealing under known conditions. During cold rolling, the sheet thickness was reduced to 0.26 mm with a reduction rate of 90.7%. The decarburization annealing temperature was within the range of 830°C to 860°C for 90 seconds. The decarburized steel sheet was then 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% by mass (200 ppm to 230 ppm).

[0222] Next, an annealing separating agent with MgO as the main component is coated on the steel plate, and final annealing is carried out. In the final annealing process, the steel plate is held at 1200°C in a hydrogen atmosphere for 20 hours (purification annealing) and then naturally cooled.

[0223] On the surface of the manufactured oriented electromagnetic steel sheet (final annealed steel sheet), a coating solution for forming an insulating coating, mainly composed of phosphate and colloidal silica and containing chromium, is applied. The coating is heated and held in an atmosphere of 75 vol%: 25 vol% hydrogen and nitrogen, and then cooled to form an insulating coating.

[0224] When viewed from a cross-section parallel to the thickness direction, the manufactured oriented electromagnetic steel sheet has an intermediate layer grounded on the oriented electromagnetic steel sheet (silicon steel sheet) and an insulating coating grounded on the intermediate layer. It should be noted that the intermediate layer is a forsterite coating with an average thickness of 2 μm, and the insulating coating is primarily composed of phosphate and colloidal silica with an average thickness of 1 μm.

[0225] The obtained oriented electromagnetic steel sheets were evaluated for various properties. The evaluation results are shown in Tables 11-18.

[0226] (1) Magnetic properties of oriented electromagnetic steel sheets

[0227] The magnetic properties of the oriented electromagnetic steel sheet were determined based on the Single Sheet Tester (SST) method specified in JIS C 2556:2015.

[0228] As a magnetic property, the magnetic flux density B8 (T) in the rolling direction of the steel plate under excitation of 800 A / m was measured. A magnetic flux density B8 of 1.945 T or higher was considered acceptable. Additionally, as a reference, under AC frequency of 50 Hz and excitation magnetic flux density of 1.7 T, the iron loss W, defined as the electrical loss per unit weight (1 kg) of the steel plate, was measured. 17 / 50 (W / kg).

[0229] In Examples No. 1 to 122, the present invention preferably controls the precipitates contained in the hot-rolled annealed steel sheet, all exhibiting excellent magnetic flux density as orientation-oriented electromagnetic steel sheets. On the other hand, in Comparative Examples No. 1 to 122, the precipitates contained in the hot-rolled annealed steel sheet were not preferably controlled, and the magnetic flux density preferred as an orientation-oriented electromagnetic steel sheet could not be obtained.

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[0248] Industrial availability According to the above-described manner of the present invention, a hot-rolled annealed steel sheet for oriented electromagnetic steel sheets that can improve magnetic flux density can be provided, thus having high potential for industrial application.

Claims

1. A hot-rolled annealed steel sheet for use in oriented electromagnetic steel sheets, characterized in that, The hot-rolled annealed steel sheet has the following chemical composition: Contains, by weight % C：0.0010~0.10%、 Si: 2.0~7.0% Mn: 0.050~1.0%, S：0~0.0350%、 Se: 0~0.0350% Total S+Se 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%, The balance includes Fe and impurities; The particle size-number density distribution of precipitates with an equivalent circular diameter D of 50~1000 nm in the precipitates obtained from the electrolytic extraction of the hot-rolled annealed steel sheet. When the mode path is set to Dp in nm, The number density of the modal paths is defined as f(Dp) in units of 1 / g. When the half-value width of the mode path is set to Wp in nm, Dp is 50~350nm. f(Dp) is 1,000,000 or more per gram. Wp / Dp ranges from 0.75 to 2.

25. For the particle size-detection intensity distribution of precipitates with an equivalent circular diameter D of 50~1000 nm in the precipitates obtained from the electrolytic extraction of the hot-rolled annealed steel sheet. The modal diameter of Al-based precipitates is set as Dp in nm. Al , The modal diameter of Nb-based precipitates is denoted as Dp in nm. Nb hour, Dp Al -Dp Nb It meets the requirements of 22~100nm.

2. The hot-rolled annealed steel sheet for oriented electromagnetic steel sheet according to claim 1, characterized in that, As the chemical composition, it contains at least one of the following selected from the group consisting of Nb, V, Mo, Ta and W, in a total mass percentage of 0.0030 to 0.030%.

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