Method for manufacturing grain-oriented electrical steel sheet

Abstract

A method for manufacturing an oriented electromagnetic steel sheet of the present invention is a method for manufacturing an oriented electromagnetic steel sheet by heating a steel billet having a composition containing, in mass%, C: 0.02 to 0.10%, Si: 2.5 to 5.5%, Mn: 0.01 to 0.30%, sol. Al: 0% or more but less than 0.010%, N: 0% or more but less than 0.006%, and at least one of S and Se: 0% or more but less than 0.010%, the remainder being Fe and inevitable impurities, to a temperature of 1300°C or lower, performing hot rolling, performing cold rolling once or twice or more with intermediate annealing to produce a cold-rolled sheet having a final sheet thickness, performing primary recrystallization annealing serving as decarburization annealing, applying an annealing separator, and performing final annealing, wherein, in an annealing step before the cold rolling to produce the cold-rolled sheet having the final sheet thickness, after soaking, cooling is performed at an average cooling rate of 15°C / s or more from 800°C to 400°C, and then low-temperature heat treatment is performed at a temperature of 60 to 100°C for a temperature retention time of 30 to 600 seconds.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing so-called oriented electromagnetic steel sheets in which the grains {110} are highly concentrated on the sheet surface and <001> are highly concentrated in the rolling direction, according to the Miller index. Background Technology

[0002] Oriented magnetic steel sheets are soft magnetic materials with excellent magnetic properties such as low iron loss and high magnetic flux density, achieved through secondary recrystallization, which concentrates the grains highly in the {110}<001> orientation (hereinafter referred to as "Goss orientation"). This is because they possess these properties through secondary recrystallization. Therefore, they are mainly used as core materials for electrical equipment such as transformers. It should be noted that the magnetic properties of oriented magnetic steel sheets are generally expressed using the magnetic flux density B8(T) at a magnetic field strength of 800 (A / m) and the iron loss W per 1 kg of steel sheet magnetized to 1.7 (T) in an AC magnetic field with an excitation frequency of 50 (Hz). 17 / 50 (W / kg)

[0003] As a method for manufacturing the aforementioned oriented electromagnetic steel sheet, a common approach is to preferentially grow grains in the Goss orientation by precipitating fine precipitates, known as inhibitors, during the final annealing process, thereby imparting a mobility difference to the grain boundaries. For example, Patent Document 1 discloses a method using AlN and MnS as inhibitors, and Patent Document 2 discloses a method using MnS and MnSe as inhibitors; both of these methods have been industrially applied.

[0004] Ideally, these methods using inhibitors require a uniform and finely dispersed state of the inhibitor. Therefore, the steel billet, used as the raw material, needs to be heated to a high temperature of over 1300°C before hot rolling. Consequently, these methods suffer from problems such as increased oxide scale loss due to high-temperature heating, reduced yield, increased thermal energy costs, higher equipment costs, and more complex equipment maintenance. Therefore, they cannot fully meet the requirement of reducing manufacturing costs.

[0005] On the other hand, as a technology to solve the above problems, manufacturing methods that do not use inhibitors (inhibitor-free methods) have also been proposed. For example, Patent Document 3, etc., proposes a technology that uses high-purity steel billets that do not contain inhibitor-forming components. This technology significantly increases the grain boundary orientation difference angle dependence of the grain boundary energy during primary recrystallization by eliminating impurities such as inhibitor components as much as possible, and preferentially recrystallizes Goss orientation grains in the secondary crystallization without using inhibitors. It should be noted that the above effect is called "texture suppression effect". Since this method does not require high-temperature billet heating, it has many advantages in manufacturing compared to methods that use inhibitors.

[0006] In addition, as a method to improve magnetic flux density by controlling the recrystallization aggregate structure, Patent Document 4 discloses the following technique: by controlling the temperature history of the steel sheet from the annealed steel coil before final cold rolling to the start of cold rolling, it is attempted to prevent cracks at the edge of the steel sheet and improve magnetic properties.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Publication No. 40-015644

[0010] Patent Document 2: Japanese Patent Publication No. 51-013469

[0011] Patent Document 3: Japanese Patent Application Publication No. 2000-129356

[0012] Patent Document 4: Japanese Patent Application Publication No. 2003-253335 Summary of the Invention

[0013] However, in the techniques disclosed in Patent Document 3 and others, which use billets without inhibitor-forming components, although high-temperature billet heating is not required and oriented electromagnetic steel sheets can be manufactured at low cost, the lack of inhibitor-forming components results in insufficient inhibition of normal grain growth (first-stage recrystallization grain growth). This leads to low orientation concentration of the Goss grains grown during secondary recrystallization, and a tendency for the magnetic flux density of the product to deteriorate compared to materials using inhibitors. Therefore, to manufacture products with high magnetic flux density, it is crucial to strictly control the aggregate structure of the first-stage recrystallization grains before secondary recrystallization. Furthermore, even when the technique in Patent Document 4 is applied in the aforementioned technologies, the improvement in the magnetic flux density of the product sheet is insufficient.

[0014] The present invention was made in view of the above-mentioned problems existing in the prior art, and its object is to propose a method for manufacturing orientation electromagnetic steel sheets with high magnetic flux density inexpensively and stably using steel billets that do not contain inhibitor-forming components.

[0015] The inventors conducted repeated and in-depth research on methods to solve the above-mentioned problems. As a result, they discovered that by performing a rapid cooling process after heat treatment in the annealing process before cold rolling (final cold rolling) to achieve the final plate thickness, followed by a low-temperature heat treatment that maintains the temperature, or by further applying strain to the steel plate before or during the aforementioned low-temperature heat treatment and by properly managing the time between the completion of the aforementioned low-temperature heat treatment and the start of final cold rolling, it is possible to increase the magnetic flux density of the product plate compared to the past, thereby developing the present invention.

[0016] Based on the above insights, the present invention proposes a method for manufacturing an orientation-oriented electromagnetic steel sheet, comprising the following steps: heating a steel billet having at least one of S and Se containing C: 0.02–0.10 wt%, Si: 2.5–5.5 wt%, Mn: 0.01–0.30 wt%, further containing sol.Al: 0 wt% or more and less than 0.010 wt%, N: 0 wt% or more and less than 0.006 wt%, totaling 0 wt% or more and less than 0.010 wt%, with the remainder consisting of Fe and unavoidable impurities, to a temperature below 1300°C. Afterwards, hot rolling is performed, followed by annealing of the hot-rolled sheet, or by one cold rolling or two or more cold rollings with intermediate annealing without hot rolling to produce a cold-rolled sheet of the final thickness. Then, a recrystallization annealing is performed, which also serves as decarburization annealing. An annealing separating agent is applied, and a final annealing is performed. The manufacturing method of the above-mentioned orientation electromagnetic steel sheet is characterized in that, in the annealing process before producing the cold-rolled sheet of the final thickness, after homogenization heat treatment, the sheet is cooled from 800°C to 400°C at an average cooling rate of 15°C / s or more, and then subjected to a low-temperature heat treatment at a temperature between 60°C and 100°C for 30 to 600 s.

[0017] The method for manufacturing the above-described orientation-oriented electromagnetic steel sheet of the present invention is characterized in that, in the annealing process prior to cold rolling to achieve the above-described final sheet thickness, after homogenization heat treatment, before cooling from 800°C to 400°C at an average cooling rate of 15°C / s or more and before performing low-temperature heat treatment at a temperature between 60°C and 100°C for 30 to 600 s, or during the low-temperature heat treatment at a temperature between 60°C and 100°C for 30 to 600 s, strain is imparted to the steel sheet.

[0018] Furthermore, the method for manufacturing the oriented electromagnetic steel sheet of the present invention is characterized in that the method of imparting strain to the steel sheet is at least one of the following: a method of bending the steel sheet at an angle of 90° or more by winding it around a roll at least once, and a method of rolling with a small reduction.

[0019] Furthermore, the manufacturing method of the above-mentioned oriented electromagnetic steel sheet of the present invention is characterized in that, after completing the above-mentioned low-temperature heat treatment, the final cold rolling is started within 300 hours.

[0020] Furthermore, the manufacturing method of the above-mentioned orientation-oriented electromagnetic steel sheet of the present invention is characterized by having a step that satisfies the following conditions:

[0021] • In the hot rolling process, the steel billet is heated and rough rolled in a temperature range of 900 to 1200°C for one or more passes, and then finished rolled in a temperature range of 700 to 1000°C for two or more passes to produce a hot rolled plate, which is then wound into a steel coil at a winding temperature of 400 to 750°C.

[0022] • In the hot-rolled plate annealing process, the hot-rolled plate is annealed and then kept in the temperature range of 800 to 1250°C for more than 5 seconds, and then cooled from 800°C to 400°C at a rate of 5 to 100°C / s.

[0023] • Intermediate annealing process: During intermediate annealing, the temperature is maintained in the range of 800 to 1250°C for more than 5 seconds, and then cooled from 800°C to 400°C at a rate of 5 to 100°C / s.

[0024] • The cold rolling process results in a final total reduction rate of 80-92%.

[0025] • The primary recrystallization annealing process, which also serves as decarburization annealing, is carried out in a humid atmosphere containing H2 and N2 with a dew point of 20–80°C, and held at a temperature range of 750–950°C for more than 10 seconds.

[0026] • Annealing release agent coating process: Apply 2.5g / m² of annealing release agent to each side of the steel plate. 2 The above are annealing separating agents with MgO as the main component;

[0027] The final annealing process includes purification treatment at a temperature of 1050–1300°C for at least 3 hours, and a portion of the atmosphere in the temperature range above 800°C is an H2-containing atmosphere.

[0028] Furthermore, the steel billet used in the manufacturing method of the oriented electromagnetic steel sheet of the present invention is characterized in that, in addition to the above-mentioned composition, it further contains at least one component selected from Ni: 0-1.00 wt%, Sb: 0-0.50 wt%, Sn: 0-0.50 wt%, Cu: 0-0.50 wt%, Cr: 0-0.50 wt%, P: 0-0.50 wt%, Mo: 0-0.50 wt%, Nb: 0-0.020 wt%, V: 0-0.010 wt%, B: 0-0.0025 wt%, Bi: 0-0.50 wt%, and Zr: 0-0.10 wt%.

[0029] Furthermore, the steel billet used in the above-described method for manufacturing the oriented electromagnetic steel sheet of the present invention is characterized in that, in addition to the above-described composition, it further contains at least one component selected from Co: 0 to 0.0500% by mass and Pb: 0 to 0.0100% by mass.

[0030] Furthermore, the steel billet used in the above-described method for manufacturing the oriented electromagnetic steel sheet of the present invention is characterized in that, in addition to the above-described composition, it further contains at least one component selected from As: 0 to 0.0200 wt%, Zn: 0 to 0.0200 wt%, W: 0 to 0.0100 wt%, Ge: 0 to 0.0050 wt%, and Ga: 0 to 0.0050 wt%.

[0031] According to the method for manufacturing oriented electromagnetic steel sheets of the present invention, oriented electromagnetic steel sheets with high magnetic flux density can be manufactured inexpensively and stably. Attached Figure Description

[0032] Figure 1 This is a graph showing the effect of cooling rate, low-temperature heat treatment conditions, and time from low-temperature heat treatment to the start of final cold rolling on the magnetic flux density of the product plate during the annealing process before final cold rolling.

[0033] Figure 2 This is a graph showing the effect of low-temperature heat treatment conditions and strain applied to the steel plate on the magnetic flux density of the product plate. Detailed Implementation

[0034] First, the experiments used to develop this invention will be described.

[0035] <Experiment 1>

[0036] A steel billet containing 0.03 wt% C, 3.2 wt% Si, 0.08 wt% Mn, 0.005 wt% sol.Al, 0.004 wt% N, and 0.005 wt% S, with the remainder consisting of Fe and unavoidable impurities, is manufactured. This billet is heated to 1200°C and then hot-rolled to produce a 2.5 mm thick hot-rolled plate. It is then water-cooled and coiled at 600°C. Next, the hot-rolled plate undergoes the following hot-rolled annealing: after a homogenization heat treatment at 1000°C for 60 s, it is water-cooled at three levels with average cooling rates varying from 800°C to 400°C: 5°C / s, 15°C / s, and 50°C / s, and further cooled to below 40°C. Then, after removing the oxide scale from the surface of the steel plate, it undergoes low-temperature heat treatment at temperatures of 40°C, 60°C, 80°C, 100°C, and 120°C, held at each temperature for 0s, 30s, 300s, 600s, and 900s, followed by water cooling and rewinding into steel coils. After completing the aforementioned low-temperature heat treatment, it is then cold-rolled for 50hr, 300hr, and 500hr to produce a cold-rolled sheet with a final thickness (product thickness) of 0.27mm.

[0037] Next, the cold-rolled sheet was subjected to a primary recrystallization annealing at 820°C for 60 seconds under a humid atmosphere containing H2 and N2 at a dew point of 45°C. This annealing also served as a decarburization annealing. The surface of the steel sheet was then treated with a single-sided coating of 3 g / m². 2An annealing separator primarily composed of MgO is applied, dried, and then recrystallized a second time before undergoing a final annealing process at 1200°C for 5 hours to purify the material. It should be noted that during this final annealing, the temperature range above 1100°C is set in an atmosphere primarily composed of H2. Next, after removing the unreacted annealing separator from the surface of the steel sheet after the final annealing, a phosphate-based tension-imparting insulating film is applied, followed by a planarization annealing process that serves both as sintering of the film and planarization of the steel sheet, thereby producing the product sheet.

[0038] From the product plate thus obtained, a test piece for magnetic property measurement was taken, and the magnetic flux density B8 at a magnetization of 800 A / m was measured using the method described in JIS C 2550-1 (2011). The results are summarized and presented below. Figure 1 As shown in the figure, to obtain a good magnetic flux density of B8 ≥ 1.86T, it is necessary to perform cooling from 800℃ to 400℃ at an average cooling rate of 15℃ / s or more during the cooling process after the homogenization heat treatment of the hot-rolled plate after annealing, followed by a low-temperature heat treatment at 60-100℃ for 30-600s. Furthermore, it can be seen that by starting the final cold rolling within 300 hours after completing the above low-temperature heat treatment, an even better magnetic flux density of B8 ≥ 1.87T can be obtained.

[0039] As described above, the average cooling rate from 800°C to 400°C during the annealing process of the hot-rolled plate is 15°C / s or more, and then a low-temperature heat treatment is performed at a temperature between 60°C and 100°C for 30 to 600 s, or further, the final cold rolling is started within 300 hours after the completion of the above-mentioned low-temperature heat treatment. As a result, the magnetic flux density of the product plate is increased. Although the reason is not yet fully clear, the inventors believe that it is due to the following reasons.

[0040] First, after homogenization treatment via hot-rolled sheet annealing, rapid cooling is performed within a temperature range of 800°C to 400°C. This prevents dissolved carbon (C) in the steel from precipitating as carbides, instead leaving it in a solid solution state. Furthermore, rapid cooling introduces numerous lattice defects such as dislocations and vacancies into the steel sheet. When low-temperature heat treatment is performed under these conditions, the dissolved C is fixed to these lattice defects, suppressing carbide precipitation. However, if the temperature of the low-temperature heat treatment is too low or the holding time is too short, the aforementioned fixation effect cannot be fully achieved. Conversely, if the temperature of the low-temperature heat treatment is too high or the holding time is too long, carbide precipitation occurs.

[0041] However, the steel sheet after the aforementioned low-temperature heat treatment still contains dissolved carbon that is not fixed to lattice defects and can move freely. Therefore, by limiting the time until the start of final cold rolling and performing cold rolling before the dissolved carbon precipitates in the form of carbides, dissolved carbon can also remain in the steel sheet after final cold rolling. As described in Patent Document 4, billets containing a large amount of dissolved carbon have the effect of improving the primary recrystallization aggregate structure formed in subsequent cold rolling and decarburization annealing. As a result, in the primary recrystallized grains, only grains with the ideal Goss orientation can grow into secondary recrystallized grains during final annealing, and the magnetic flux density of the product sheet is increased.

[0042] <Experiment 2>

[0043] A steel billet containing 0.06 wt% C, 3.5 wt% Si, 0.10 wt% Mn, 0.003 wt% sol.Al, 0.002 wt% N, and 0.008 wt% S, with the remainder consisting of Fe and unavoidable impurities, is heated to 1280°C and hot-rolled to a thickness of 2.8 mm. This hot-rolled sheet is then water-cooled and coiled at 600°C. Next, after removing the oxide scale from the steel sheet surface, it undergoes a first cold rolling to an intermediate thickness of 1.5 mm. Following this, it is subjected to a homogenization heat treatment at 1050°C for 120 s, then water-cooled from 800°C to 400°C at an average cooling rate of 30°C / s, and further cooled to below 40°C. Then, after removing the oxide scale from the steel plate surface, a portion of the steel coil undergoes a bending process by being wound onto a 1000mm φ roll at a through speed of 30m / min and angles of 60°, 90°, and 180°. Following this, it undergoes low-temperature heat treatment at 50°C, 70°C, 90°C, and 110°C for 20s, 200s, 400s, 600s, and 800s respectively, followed by water cooling and rewinding into a steel coil. After completing the aforementioned low-temperature heat treatment, it undergoes a second cold rolling (final cold rolling) after 50 hours to produce a cold-rolled plate with a final thickness of 0.27mm.

[0044] Next, after a primary recrystallization annealing at 880°C for 100s, which also serves as a decarburization annealing, is performed in a humid atmosphere containing H2 and N2 at a dew point of 50°C, the steel plate surface is then treated with a single-sided mid-grain annealing of 7.5 g / m². 2 An annealing release agent with MgO as the main component is applied, dried, and then recrystallized a second time before undergoing a final annealing process at 1180°C for 20 hours for purification. It should be noted that during this final annealing, the temperature range above 900°C is in an atmosphere primarily composed of H2. Next, after removing the unreacted annealing release agent from the surface of the steel sheet after the final annealing, a phosphate-based tension-imparting insulating film is applied, followed by a planarization annealing process that serves both as sintering of the film and planarization of the steel strip to produce the product sheet.

[0045] The magnetic flux density B8 at a magnetization of 800 A / m was measured using a test piece for magnetic property testing from the product plate obtained in this way, according to the method described in JIS C 2550-1 (2011). The results were compiled and presented. Figure 2 As shown in the figure, in the annealing process before the final cold rolling, after cooling from 800℃ to 400℃ at an average cooling rate of 15℃ / s or more and before performing low-temperature heat treatment at 60-100℃ for 30-600s, the steel plate is bent at an angle of 90° or more to impart strain, thereby obtaining an excellent magnetic flux density of B8≥1.89T.

[0046] As described above, in the annealing process before final cold rolling, the steel sheet is cooled from 800°C to 400°C at an average cooling rate of 15°C / s or more. Before the low-temperature heat treatment of holding the temperature between 60°C and 100°C for 30 to 600 seconds, the steel sheet is bent at an angle of 90° or more to impart strain. As a result, the magnetic flux density of the product sheet is further increased. Although the reason is not yet fully clear, the inventors believe that the following is the reason.

[0047] The effects of rapid cooling during intermediate annealing and subsequent low-temperature heat treatment are described in Experiment 1. However, it is believed that by applying strain to the steel plate through bending at an angle of 90° or more around a roll, the density of lattice defects in the steel plate increases. In the subsequent low-temperature heat treatment, the amount of C in solid solution fixed to the lattice defects increases, resulting in improved primary recrystallization aggregate structure and further improved magnetic flux density of the product plate.

[0048] Next, the composition of the steel billet (bill) used in the manufacture of the oriented electromagnetic steel sheet of the present invention will be described.

[0049] C: 0.02–0.10% by mass

[0050] Carbon (C) is a necessary component for improving the microstructure of hot-rolled steel sheets by utilizing the austenite-ferrite phase transformation that occurs during hot rolling and homogenization during annealing. However, if the C content is less than 0.02% by mass, there is a risk of losing the grain boundary strengthening effect provided by C and causing cracks in the billet, thus hindering manufacturing. On the other hand, if the C content exceeds 0.10% by mass, not only does the load on the decarburization annealing process increase, but decarburization itself becomes incomplete, also contributing to magnetic aging in the finished product. Therefore, the C content is in the range of 0.02 to 0.10% by mass, preferably in the range of 0.03 to 0.08% by mass.

[0051] Si: 2.5–5.5% by mass

[0052] Si is an extremely effective component for increasing the resistivity of steel and reducing eddy current losses, which constitute part of iron loss. However, if the Si content is less than 2.5% by mass, the resistivity is low, and good iron loss characteristics cannot be obtained. On the other hand, although the resistivity of steel increases monotonically until the Si content reaches 11% by mass, if it exceeds 5.5% by mass, the workability decreases significantly, making rolling difficult. Therefore, the Si content is in the range of 2.5% to 5.5% by mass, preferably in the range of 3.0% to 4.0% by mass.

[0053] Mn: 0.01~0.30% by mass

[0054] Mn is an effective component for improving hot workability. However, if the content is less than 0.01% by mass, the above-mentioned effect cannot be fully obtained; on the other hand, if it exceeds 0.30% by mass, the magnetic flux density of the product plate decreases. Therefore, the Mn content is in the range of 0.01 to 0.30% by mass, preferably in the range of 0.05 to 0.20% by mass.

[0055] sol.Al: 0% by mass or more and less than 0.010% by mass; N: 0% by mass or more and less than 0.006% by mass; at least one of S and Se: total 0% by mass or more and less than 0.010% by mass.

[0056] In this invention, to express the technique of secondary recrystallization without using inhibitors, but rather through texture inhibition to induce secondary recrystallization in the Goss orientation, it is necessary to minimize the content of Al, N, S, and Se, which are inhibitor-forming components. Therefore, it is necessary to use steel billets with Al content less than 0.010 wt% (sol.Al, acid-soluble Al), N content less than 0.0060 wt%, and at least one of S and Se reduced to a combined content less than 0.010 wt%. Preferably, the sol.Al content is 0–0.008 wt%, N content is 0–0.0050 wt%, and the combined content of at least one of S and Se is 0–0.007 wt%. However, reducing these components increases manufacturing costs, so it is not necessarily necessary to reduce them to 0 wt%.

[0057] In addition to the basic components described above, the steel billet used in this invention may further contain at least one component selected from Ni: 0-1.00 wt%, Sb: 0-0.50 wt%, Sn: 0-0.50 wt%, Cu: 0-0.50 wt%, Cr: 0-0.50 wt%, P: 0-0.50 wt%, Mo: 0-0.50 wt%, Nb: 0-0.020 wt%, V: 0-0.010 wt%, B: 0-0.0025 wt%, Bi: 0-0.50 wt%, and Zr: 0-0.10 wt% in order to improve magnetic properties. If the content of any component exceeds the above-mentioned upper limit, there is a risk that the development of secondary recrystallized grains will be suppressed, resulting in a deterioration of magnetic properties. It should be noted that, from the viewpoint of further improving magnetic properties, it is preferable to contain Ni: 0.01% by mass or more, Sb: 0.005% by mass or more, Sn: 0.005% by mass or more, Cu: 0.01% by mass or more, Cr: 0.01% by mass or more, P: 0.005% by mass or more, Mo: 0.005% by mass or more, Nb: 0.001% by mass or more, V: 0.001% by mass or more, B: 0.0002% by mass or more, Bi: 0.005% by mass or more, and Zr: 0.001% by mass or more.

[0058] In addition to the above-mentioned composition, the steel billet used in this invention may further contain at least one component selected from Co: 0 to 0.0500 wt% and Pb: 0 to 0.0100 wt% to improve magnetic properties. If the content of each component exceeds the above-mentioned upper limit, the development of secondary recrystallized grains is suppressed, resulting in a deterioration of magnetic properties. It should be noted that, from the viewpoint of further improving magnetic properties, it is preferable to contain Co: 0.0020 wt% or more and Pb: 0.0001 wt% or more.

[0059] In addition to the above-mentioned composition, the steel billet used in this invention may further contain at least one component selected from As: 0-0.0200 wt%, Zn: 0-0.0200 wt%, W: 0-0.0100 wt%, Ge: 0-0.0050 wt%, and Ga: 0-0.0050 wt% to improve magnetic properties. If the content of each component exceeds the above-mentioned upper limit, the development of secondary recrystallized grains is suppressed, resulting in a deterioration of magnetic properties. It should be noted that, from the viewpoint of further improving magnetic properties, it is preferable to contain As: 0.0010 wt% or more, Zn: 0.0010 wt% or more, W: 0.0010 wt% or more, Ge: 0.0001 wt% or more, and Ga: 0.0001 wt% or more.

[0060] The steel billet used in this invention, excluding the aforementioned components, consists of Fe and unavoidable impurities. Here, unavoidable impurities refer to those that inevitably mix in during the smelting of the billet from raw materials, scrap, the smelting pot, the external environment, etc. It should be noted that Ti, contained as an unavoidable impurity, is a harmful component that forms nitrides and hinders the secondary recrystallization of Goss grains. However, excessive reduction leads to an increase in refining costs, but it is permissible if it is below 0.010% by mass. Preferably, it is below 0.0020% by mass.

[0061] Next, the manufacturing method of the oriented electromagnetic steel sheet of the present invention will be described.

[0062] The billet material for the oriented electromagnetic steel sheet of the present invention is preferably steel having the above-mentioned composition, which is then smelted using a commonly known refining process and manufactured by a commonly known ingot casting method or continuous casting method. It should be noted that thin castings with a thickness of 100 mm or less can also be manufactured by direct casting.

[0063] The steel billet (billet, thin casting) obtained as described above is heated to a specified temperature by conventional methods and then supplied for hot rolling. However, it can also be hot rolled immediately after casting without heating. It should be noted that since the billet does not contain inhibitory components, from the viewpoint of cost reduction, the heating temperature of the billet before hot rolling is preferably below 1300°C.

[0064] From the viewpoint of controlling the microstructure of hot-rolled steel, the subsequent hot rolling is preferably performed in a temperature range of 900–1200°C with at least one pass of rough rolling, followed by a temperature range of 700–1000°C with at least two passes of finish rolling. Furthermore, from the viewpoint of preventing defects such as cracks, the winding temperature of the hot-rolled steel coil is preferably in the range of 400–750°C. A more preferred winding temperature is in the range of 500–700°C.

[0065] Then, the hot-rolled steel sheet can be subjected to hot-rolled annealing as needed. By performing hot-rolled annealing, the microstructure can be homogenized, and deviations in magnetic properties can be reduced. When performing hot-rolled annealing, from the viewpoint of homogenizing the microstructure, it is preferable to perform a homogenization heat treatment at a temperature of 800–1250°C for at least 5 seconds. More preferably, it is preferable to perform a temperature treatment at 900–1150°C for 10–180 seconds. Furthermore, from the viewpoint of controlling the morphology of the second phase and precipitates, the cooling after the homogenization heat treatment is preferably performed at a cooling rate from 800°C to 400°C in the range of 5–100°C / s. More preferably, the cooling rate is in the range of 15–80°C / s.

[0066] Next, in order to remove the oxide scale generated on the surface of the steel plate during hot rolling, it is preferable to use methods such as pickling with heated acid or mechanical removal of oxide scale for descaling.

[0067] Next, the hot-rolled sheet with descaled surface is subjected to one cold rolling or two or more cold rolling processes with intermediate annealing to produce a cold-rolled sheet of the final thickness (product thickness). When intermediate annealing is performed, from the viewpoint of microstructure control, it is preferable to perform a homogenization treatment at a temperature range of 800–1250°C for at least 5 seconds. Furthermore, from the viewpoint of controlling the morphology of the second phase and precipitates, the cooling after the homogenization treatment is preferably performed at a cooling rate in the range of 5–100°C / s from 800°C to 400°C. A more preferred cooling rate is in the range of 15–80°C / s. It should be noted that when intermediate annealing is performed, it is preferable to clean the sheet beforehand to remove rolling oil from the previous process. Furthermore, after intermediate annealing, it is preferable to remove the oxide scale generated on the surface of the steel sheet using the above method. It should be noted that in this invention, the cold-rolled sheet that produces the final thickness is referred to as "final cold rolling."

[0068] Here, the most important aspect of this invention is that in the annealing process prior to final cold rolling, during the cooling process after homogenization heat treatment, cooling is performed from 800°C to 400°C at an average cooling rate of 15°C / s or more, followed by a low-temperature heat treatment held at 60-100°C for 30-600 seconds. Here, the aforementioned annealing process prior to final cold rolling refers to hot-rolled plate annealing when cold rolling to the final plate thickness (product plate thickness) is performed in one cold rolling pass, and to intermediate annealing prior to final cold rolling when cold rolling is performed in two or more passes with intermediate annealing. Therefore, when the hot-rolled plate annealing process or intermediate annealing process described above is equivalent to the annealing process prior to final cold rolling, the aforementioned cooling conditions (cooling rate from 800°C to 400°C: 5-100°C / s) need to be adapted to the aforementioned cooling conditions (average cooling rate from 800°C to 400°C: 15°C / s or more).

[0069] It should be noted that after the above-mentioned annealing process, the low-temperature heat treatment process, which involves holding the temperature between 60 and 100°C for 30 to 600 seconds, can be continued on the same annealing line, or it can be cooled to below 100°C and temporarily wound into a steel coil before being carried out on another line. Preferred low-temperature heat treatment conditions are holding the temperature between 70 and 90°C for 60 to 300 seconds. It should be noted that, as long as the holding temperature and holding time are within the above ranges, the above-mentioned low-temperature heat treatment can be carried out concurrently (simultaneously) with other processes such as pickling.

[0070] Another important aspect of this invention is the application of strain to the steel sheet before or during the aforementioned low-temperature heat treatment. Common methods for applying strain include bending the sheet around a roll or performing light cold rolling. When bending is used, it is preferable to wind the sheet around a roll with a diameter of 200 to 2500 mmφ at an angle of 90° or more, performing at least one bending operation, more preferably two to ten. The roll can be a dedicated roll for applying strain, but it can also be replaced by deflection rolls, pinch rolls, or the like provided in the production line. Furthermore, the application of strain can be performed in an annealing line, a pickling line, or on another production line for the purpose of applying strain. On the other hand, when performing low-reduction rolling, it is preferable, for example, to perform low-reduction rolling with a reduction rate of 0.5% to 10%, more preferably 1% to 5%, in a surface finishing mill.

[0071] Furthermore, another important aspect of this invention is that after the aforementioned low-temperature heat treatment, final cold rolling is initiated within 300 hours. If the time exceeds 300 hours, the amount of dissolved carbon remaining in the steel sheet decreases, the primary recrystallization aggregate structure deteriorates, leading to a deterioration in the magnetic properties of the product sheet. More preferably, it is 100 hours or less.

[0072] It should be noted that, from the viewpoint of obtaining a good primary recrystallization aggregate structure before secondary recrystallization, the final total reduction rate of cold rolling is preferably in the range of 80% to 92%. Furthermore, from the viewpoint of improving the magnetic properties by improving the recrystallization aggregate structure, it is preferable to perform warm rolling by raising the steel plate temperature to 100 to 300°C during cold rolling, or to perform one or more aging treatments at a temperature of 100 to 300°C during cold rolling. In addition, in the above-mentioned cold rolling, from the viewpoint of reducing rolling load and controlling rolling shape, it is preferable to use a lubricant such as rolling oil.

[0073] The cold-rolled sheet, after reaching its final thickness, is degreased and pickled as needed to clean the surface. Then, a primary recrystallization annealing, which also serves as a decarburization annealing, is performed. The decarburization annealing is preferably conducted at a temperature range of 750–950°C for at least 10 seconds. Furthermore, the atmosphere during decarburization annealing is preferably a humid atmosphere containing H2 and N2, with a dew point of 20–80°C for part or all of the decarburization annealing process. More preferably, it is conducted in a humid atmosphere with a dew point of 40–70°C at a temperature range of 800–900°C for 30–180 seconds. By performing the above-described decarburization annealing, the carbon content in the steel is reduced to below 0.0050% by mass, making magnetic aging less likely.

[0074] Then, the steel plate after the above decarburization annealing is preferably coated with a single-sided coating of 2.5 g / m. 2The above coating uses an annealing separating agent primarily composed of MgO. MgO can be coated onto the steel sheet in slurry form or by dry coating using electrostatic coating. When using a slurry, it is preferable to maintain the slurry solution at a temperature below 15°C to suppress viscosity increase. Furthermore, to maintain a constant slurry concentration, it is preferable to manage the slurry solution separately in a mixing tank and a tank for coating. Here, "primarily composed of MgO" means that the MgO content in the annealing separating agent is 60% by mass or more.

[0075] The steel sheet coated with the aforementioned annealing separating agent is subjected to final annealing while coiled, which promotes secondary recrystallization and the formation of a magnesium olivine film on the steel sheet surface. To achieve secondary recrystallization, heating to a temperature of 800°C or higher is preferred, and to form the magnesium olivine film, heating to a temperature of 1050°C or higher is preferred. Furthermore, to remove impurities such as inhibitor-forming components from the steel and obtain good magnetic properties, a purification treatment is preferably performed, maintaining the temperature range of 1050–1300°C for at least 3 hours, and ensuring that part or all of the temperature range above 800°C is in an atmosphere containing H2. By performing this purification treatment, inhibitor-forming components can be reduced to impurity levels. It should be noted that since final annealing is a high-temperature and long-duration heat treatment, the steel coil is generally annealed in an inverted state. However, to prevent loosening of the outer winding of the steel coil, it is preferable to pre-wrap binding tape or similar material around the steel coil before final annealing.

[0076] Subsequently, in order to reduce iron loss, the steel plate after final annealing is preferably further subjected to water washing, brushing, pickling and other processes to remove the unreacted annealing separating agent remaining on the surface of the steel plate, and then a planarization annealing is performed to correct the winding characteristics of the steel plate and the shape defects caused during final annealing.

[0077] It should be noted that electromagnetic steel sheets are mostly used in laminated form; therefore, to ensure insulation, it is preferable to form an insulating film on the surface of the steel sheet. To reduce iron loss, the aforementioned insulating film is preferably a tension-imposing type film that applies tension to the steel sheet. This insulating film can be formed by applying a coating solution before planarization annealing and sintering it during planarization annealing, or it can be done on other production lines. Furthermore, if a tension-imposing film is formed using an adhesive, or if an inorganic film is deposited on the surface of the steel sheet using physical or chemical vapor deposition, a film with excellent adhesion and a significant reduction in iron loss can be obtained.

[0078] Furthermore, from the perspective of further reducing iron loss, in any process after cold rolling, grooves can be formed on the surface of the steel plate by etching, or thermal strain regions can be formed by irradiating the surface of the steel plate with heat energy beams such as lasers or plasma after forming an insulating film, or a processing strain region can be formed by pressing a roller with protrusions onto the surface of the steel plate, thereby implementing magnetic domain refinement treatment.

[0079] Example 1

[0080] A steel billet containing 0.03 wt% C, 3.1 wt% Si, 0.14 wt% Mn, 0.008 wt% sol.Al, 0.004 wt% N, and 0.002 wt% S, with the remainder consisting of Fe and unavoidable impurities, is heated to 1250°C and then hot-rolled to produce a hot-rolled sheet with a thickness of 2.5 mm. This sheet is then wound into coils at 600°C. Next, the hot-rolled sheet undergoes a homogenization heat treatment at 950°C for 60 seconds, followed by water annealing from 800°C to 400°C at an average cooling rate of 30°C / s. Next, after removing the oxide scale from the surface of the steel plate, it is cold rolled for the first time to produce an intermediate plate with a thickness of 1.8 mm. After a homogenization heat treatment at 1050℃ for 30 s, the average cooling rate from 800℃ to 400℃ is varied to three levels: 10℃ / s, 35℃ / s, and 80℃ / s, and then water-cooled. The cooling continues until it is below 40℃, thus performing intermediate annealing.

[0081] Then, while pickling, a low-temperature heat treatment was performed at 80°C for 200 seconds, followed by water cooling, and then the steel was wound into a coil again. At this time, the steel plate was subjected to strain under the conditions A to E shown in Table 1. Specifically, condition A is the condition of not imparting strain; condition B is the condition of performing one bending process at a 90° angle on a roll with a diameter of 1000mmφ at a through-plate speed of 50m / min after the above intermediate annealing and before low-temperature heat treatment; condition C is the condition of performing three bending processes at a 180° angle on a roll with a diameter of 2000mmφ at a through-plate speed of 50m / min after the above intermediate annealing and before low-temperature heat treatment; condition D is the condition of performing one small reduction rolling with a reduction rate of 2% at a through-plate speed of 50m / min on a surface finishing mill with a work roll with a diameter of 1000mmφ at a through-plate speed of 50m / min after the above intermediate annealing and before low-temperature heat treatment; and condition E is the condition of performing one bending process at a 90° angle on a roll with a diameter of 1000mmφ at a through-plate speed of 50m / min during the above low-temperature heat treatment (after holding for 100s).

[0082] Then, after 200 hours of the aforementioned low-temperature heat treatment, the steel sheet is subjected to a second cold rolling (final cold rolling) to produce a cold-rolled sheet with a final thickness of 0.18 mm. Next, the cold-rolled sheet is subjected to a first recrystallization annealing at 800°C for 60 seconds in a humid atmosphere containing H2 and N2 at a dew point of 40°C, which also serves as a decarburization annealing. Finally, the steel sheet surface is treated with a single-sided thickness of 5 g / m². 2An annealing separator primarily composed of MgO is applied, dried, and then recrystallized a second time before undergoing a final annealing process at 1160°C for 5 hours for purification. It should be noted that during this final annealing, the temperature range above 1100°C is in an atmosphere primarily composed of H2. Next, after removing the unreacted annealing separator from the surface of the steel sheet after the final annealing, a phosphate-based tension-imparting insulating film is applied, followed by a planarization annealing process that serves both as sintering of the film and planarization of the steel sheet to produce the finished product sheet.

[0083] The magnetic flux density B8 at a magnetization of 800 A / m was measured using test pieces for magnetic property testing of the product plates obtained in this way, according to the method described in JIS C2 550-1 (2011). The results are listed in Table 1. These results show that steel plates manufactured under the conditions conforming to this invention all achieve a good magnetic flux density of B8 ≥ 1.87 T. In particular, steel plates with an intermediate annealing cooling rate of 80 °C / s achieve an even better magnetic flux density of B8 ≥ 1.89 T.

[0084]

[0085] Example 2

[0086] A steel billet containing the various components shown in Table 2, with the remainder consisting of Fe and unavoidable impurities, is manufactured. After heating to 1250°C, it is hot-rolled to produce a 2.0 mm thick hot-rolled sheet, water-cooled, and wound into coils at 500°C. Next, each hot-rolled sheet undergoes the following hot-rolled annealing: after a homogenization heat treatment at 1050°C for 30 seconds, it is water-cooled from 800°C to 400°C at an average cooling rate of 50°C / s, and further cooled to below 40°C. Then, while pickling, it undergoes a low-temperature heat treatment at 90°C for 60 seconds, followed by water cooling and coiling. At this point, after the above-mentioned hot-rolled sheet annealing and before the low-temperature heat treatment, it undergoes three bending processes at a 90° angle on a roll with a diameter of 1000 mmφ, with a through-plate speed of 80 m / min.

[0087] Next, after 20 hours following the aforementioned low-temperature heat treatment, a second cold rolling (final cold rolling) is performed to produce a cold-rolled sheet with a final thickness of 0.23 mm. Then, a primary recrystallization annealing, also serving as a decarburization annealing, is carried out at 840°C for 100 seconds in a humid atmosphere containing H2 and N2 at a dew point of 55°C, with a single-sided thickness of 5 g / m². 2An annealing separator primarily composed of MgO is applied and dried. Then, after secondary recrystallization, a final annealing process is performed at 1200°C for 20 hours to purify the steel. It should be noted that during this final annealing, the temperature range above 1000°C is in an atmosphere primarily composed of H2. Next, after removing the unreacted annealing separator from the surface of the steel sheet after the final annealing, a phosphate-based tension-imparting insulating film is applied, followed by planarization annealing, which serves both as sintering of the film and planarization of the steel sheet, to produce the product sheet.

[0088] The magnetic flux density B8 at a magnetization of 800 A / m was measured using test pieces for magnetic property testing from the product sheet obtained in this way, according to the method described in JIS C 2550-1 (2011). The results are shown in Table 2. The results show that steel sheets manufactured using steel billets (billets) with a composition conforming to the present invention and under conditions conforming to the present invention all achieve a good magnetic flux density of B8 ≥ 1.89 T. In particular, steel sheets with appropriate amounts of any additive components achieve an excellent magnetic flux density of B8 ≥ 1.91 T.

[0089]

[0090]

Claims

1. A method for manufacturing an orientation-oriented electromagnetic steel sheet, characterized in that, The process includes the following steps: A steel billet with the following composition is heated to a temperature below 1300°C and then hot-rolled. After hot-rolled annealing, it undergoes one cold rolling to produce a cold-rolled sheet of the final thickness, or it undergoes two or more cold rolling processes with intermediate annealing without hot rolling to produce a cold-rolled sheet of the final thickness. It then undergoes a recrystallization annealing that also serves as decarburization annealing, is coated with an annealing separating agent, and finally undergoes final annealing. The steel billet is composed of at least one of the following: C: 0.02–0.10 wt%, Si: 2.5–5.5 wt%, Mn: 0.01–0.30 wt%, and further contains sol.Al: 0 wt% and less than 0.010 wt%, N: 0 wt% and less than 0.006 wt%, and a total of 0 wt% and less than 0.010 wt% of S and Se. Furthermore, it may contain at least one of the following A to C: A: Selected from at least one of the following: Ni: 0–1.00 wt%, Sb: 0–0.50 wt%, Sn: 0–0.50 wt%, Cu: 0–0.50 wt%, Cr: 0–0.50 wt%, P: 0–0.50 wt%, Mo: 0–0.50 wt%, Nb: 0–0.020 wt%, V: 0–0.010 wt%, B: 0–0.0025 wt%, Bi: 0–0.50 wt%, and Zr: 0–0.10 wt%. B: Selected from at least one of Co: 0–0.0500% by mass and Pb: 0–0.0100% by mass. C: Selected from at least one of As: 0–0.0200 wt%, Zn: 0–0.0200 wt%, W: 0–0.0100 wt%, Ge: 0–0.0050 wt%, and Ga: 0–0.0050 wt%. The remainder consists of Fe and unavoidable impurities; In the annealing process prior to cold rolling to achieve the final plate thickness, after homogenization heat treatment, the plate is cooled from 800°C to 400°C at an average cooling rate of 15°C / s or more, and then subjected to low-temperature heat treatment at a temperature between 60°C and 100°C for 30 to 600 s.

2. The method for manufacturing the oriented electromagnetic steel sheet according to claim 1, characterized in that, In the annealing process prior to cold rolling to achieve the final plate thickness, after homogenization heat treatment, before cooling from 800°C to 400°C at an average cooling rate of 15°C / s or more and before performing low-temperature heat treatment at a temperature between 60°C and 100°C for 30 to 600 s, or during low-temperature heat treatment at a temperature between 60°C and 100°C for 30 to 600 s, strain is imparted to the steel plate.

3. The method for manufacturing the oriented electromagnetic steel sheet according to claim 2, characterized in that, The method of applying strain to the steel plate is at least one of the following: bending at least once by winding the steel plate around a roll at an angle of 90° or more, and rolling with a small reduction.

4. The method for manufacturing the oriented electromagnetic steel sheet according to any one of claims 1 to 3, characterized in that, After the low-temperature heat treatment is completed, the final cold rolling begins within 300 hours.

5. The method for manufacturing the oriented electromagnetic steel sheet according to any one of claims 1 to 3, characterized in that, A process that meets the following conditions: Hot rolling process: The steel billet is heated and rough rolled in a temperature range of 900-1200℃ for more than one pass, and then finished rolled in a temperature range of 700-1000℃ for more than two passes to produce a hot rolled plate, which is then wound into a steel coil at a winding temperature of 400-750℃. The hot-rolled sheet annealing process in the case of hot-rolled sheet annealing is as follows: after holding the temperature range of 800 to 1250°C for more than 5 seconds, it is cooled from 800°C to 400°C at a rate of 5 to 100°C / second. Intermediate annealing process in the case of intermediate annealing: after holding in the temperature range of 800 to 1250°C for more than 5 seconds, cool from 800°C to 400°C at a rate of 5 to 100°C / second. Cold rolling process: The final total reduction rate of cold rolling is in the range of 80-92%; The recrystallization annealing process, which also serves as decarburization annealing, involves holding the anneal at a temperature range of 750–950°C for more than 10 seconds in a humid atmosphere containing H2 and N2 with a dew point of 20–80°C. Annealing release agent coating process: Apply 2.5 g / m² to one side of the steel plate surface. 2 The above coating is an annealing separating agent with MgO as the main component; Final annealing process: includes at least a purification process that is maintained at a temperature of 1050–1300°C for more than 3 hours, and the atmosphere in a portion of the temperature range above 800°C is an H2-containing atmosphere.

6. The method for manufacturing an orientation-oriented electromagnetic steel sheet according to claim 4, characterized in that, A process that meets the following conditions: Hot rolling process: The steel billet is heated and rough rolled in a temperature range of 900-1200℃ for more than one pass, and then finished rolled in a temperature range of 700-1000℃ for more than two passes to produce a hot rolled plate, which is then wound into a steel coil at a winding temperature of 400-750℃. The hot-rolled sheet annealing process in the case of hot-rolled sheet annealing is as follows: after holding the temperature range of 800 to 1250°C for more than 5 seconds, it is cooled from 800°C to 400°C at a rate of 5 to 100°C / second. Intermediate annealing process in the case of intermediate annealing: after holding in the temperature range of 800 to 1250°C for more than 5 seconds, cool from 800°C to 400°C at a rate of 5 to 100°C / second. Cold rolling process: The final total reduction rate of cold rolling is in the range of 80-92%; The recrystallization annealing process, which also serves as decarburization annealing, involves holding the anneal at a temperature range of 750–950°C for more than 10 seconds in a humid atmosphere containing H2 and N2 with a dew point of 20–80°C. Annealing release agent coating process: Apply 2.5 g / m² to one side of the steel plate surface. 2 The above coating is an annealing separating agent with MgO as the main component; Final annealing process: includes at least a purification process that is maintained at a temperature of 1050–1300°C for more than 3 hours, and the atmosphere in a portion of the temperature range above 800°C is an H2-containing atmosphere.

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