Method for producing grain-oriented electrical steel sheet, and induction heating device

Abstract

When producing a grain-oriented electrical steel sheet in which a steel raw material having a prescribed component composition is hot-rolled and cold-rolled to obtain a cold-rolled sheet having a final sheet thickness, the cold-rolled sheet is subjected to decarburization annealing that also serves as primary recrystallization annealing, and then the cold-rolled sheet is subjected to final annealing, in the final cold rolling of the cold rolling, the thickness of the cold-rolled sheet is greater than the thickness of the cold-rolled sheet. Rolling is performed at least one pass in a temperature range in which the steel plate temperature is 150-350 DEG C, and in the decarburization annealing, rapid heating is performed at an average temperature increase rate of 250 DEG C / s or more from 400 DEG C to a temperature T (DEG C) in the temperature increase process of 700-900 DEG C; and setting the time for which the temperature increase rate is equal to or less than 2 / 3 of the average temperature increase rate at any temperature between 500 DEG C and 700 DEG C in the temperature increase process to 0.10 s or more and less than 1.00 s, thereby obtaining a grain-oriented electromagnetic steel sheet having excellent magnetic properties. In addition, a transverse induction heating device is used in the rapid heating.

Description

Technical Field

[0001] The present invention relates to a method for producing a grain-oriented electrical steel sheet and an induction heating device for decarburization annealing used in the method. Background Art

[0002] Grain-oriented electrical steel sheets are soft magnetic materials widely used as core materials for transformers and generators. They have a crystal structure in which the {110}<001> orientation (Goss orientation), which is the easy magnetization axis of iron, is highly consistent with the rolling direction of the steel sheet, and have excellent magnetic properties.

[0003] As one of the methods for achieving low iron loss of grain-oriented electrical steel sheets, there is a method of making the grains after secondary recrystallization annealing highly aggregated in Goss orientation. In order to increase the aggregation of secondary recrystallized grains in Goss orientation, it is important to pre-form a large number of Goss-oriented grains in the steel sheet structure at the time of primary recrystallization and to make the grain boundary mobility different in such a way that only sharp Goss-oriented grains preferentially grow, that is, to pre-optimize the texture of the steel sheet after primary recrystallization.

[0004] As primary recrystallization structures that can preferentially grow only sharp Goss-oriented grains, there are {111}<112> oriented grains and {411}<148> oriented grains. By making them exist in a balanced and high frequency, Goss-oriented grains can be highly concentrated in the rolling direction during secondary recrystallization annealing.

[0005] In addition, as a method for increasing the existence ratio of Goss-oriented grains in the steel sheet structure after primary recrystallization, for example, Patent Document 1 discloses a method of heat treating a cold-rolled sheet during cold rolling at a low temperature and performing an aging treatment. In addition, Patent Document 2 discloses a method of making the cooling rate of the intermediate annealing before annealing the hot-rolled sheet or cold rolling (final cold rolling) to the final sheet thickness 30°C / s or more, and performing inter-pass aging at a temperature of 150 to 300°C for more than 2 minutes during the final cold rolling. In addition, Patent Document 3 discloses a technique of performing warm rolling by increasing the temperature of the steel sheet during cold rolling, and effectively utilizing dynamic strain aging in which the dislocations introduced during rolling are immediately fixed with C and N.

[0006] The technologies in the above-mentioned patent documents 1 to 3 all increase the temperature of the steel plate to an appropriate temperature before, during or between cold rolling passes, promote the diffusion of dissolved carbon (C) and nitrogen (N) to fix the dislocations introduced during cold rolling, inhibit the movement of dislocations, thereby promoting shear deformation in subsequent rolling and improving the rolling texture. This is based on the consideration that the cores of the Gossian-oriented grains in the primary recrystallization structure are introduced into the shear bands in the processed structure with the {111}<112> orientation. By applying these technologies, a large number of shear bands can be introduced into the {111}<112> processed structure, and a large number of Gossian-oriented grains can be formed in the primary recrystallization structure.

[0007] In addition, by increasing the heating rate of the heating process of decarburization annealing, the formation of Goss-oriented grains in the primary recrystallization structure can also be promoted. For example, Patent Document 4 discloses a method of rapid heating during the heating process of decarburization annealing. This technology uses electric heating or induction heating to raise the temperature from room temperature to near the recrystallization temperature in a short time, thereby suppressing the development of the γ fiber structure ({111} / / ND) that is preferentially formed at the usual heating rate, and promoting the generation of Goss-oriented grains that become the core of the secondary recrystallization grains.

[0008] In addition, Patent Document 5 discloses a method in which rapid heating is performed at an average heating rate of 50°C / s or more between 550°C and 700°C during the heating process of decarburization annealing, and a holding treatment is performed for 1 to 10 seconds in any temperature range between 250°C and 550°C to reduce the heating rate to 10°C / s or less. This technology promotes the recovery of the {111} processed structure and suppresses recrystallization by holding for a short time between 250°C and 550°C as the recovery temperature range, thereby relatively increasing the existence ratio of Goss-oriented grains.

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent Application Laid-Open No. 50-016610

[0012] Patent Document 2: Japanese Patent Application Laid-Open No. 08-253816

[0013] Patent Document 3: Japanese Patent Application Laid-Open No. 01-215925

[0014] Patent Document 4: Japanese Patent Application Laid-Open No. 04-160114

[0015] Patent Document 5: Japanese Patent Application Publication No. 2014-152393 Summary of the invention

[0016] Problems to be solved by the invention

[0017] However, the techniques disclosed in the above-mentioned Patent Documents 1 to 3, which fix the dislocations in the {111}<112> processed structure with C and N in the middle of cold rolling and introduce a large number of shear bands into the processed structure through subsequent cold rolling, have the following problems: when excessive shear bands are introduced, although the number of Goss-oriented grains increases, the number of {111}<112>-oriented grains in the primary recrystallization structure decreases excessively, and it becomes difficult for sharp Goss-oriented grains to grow during secondary recrystallization. Therefore, the techniques in Patent Documents 1 to 3 have a limit in improving magnetic properties, and it is difficult to fully respond to the increasingly stringent requirements for energy saving in recent years.

[0018] In addition, for the method disclosed in Patent Document 4, which performs rapid heating during decarburization annealing, although the number of Goss-oriented grains increases, the number of {111}<112>-oriented grains decreases, so the improvement effect of magnetic properties is still insufficient. In addition, for the technology disclosed in Patent Document 5, depending on the holding conditions, the recrystallization of the Goss-oriented grains in the {111}<112> processed structure is sometimes hindered, and there is a problem that the desired improvement effect of magnetic properties cannot be stably obtained.

[0019] The present invention has been made in view of the above-mentioned problems existing in the prior art, and its object is to solve the above-mentioned various problems, propose a method for manufacturing a oriented electrical steel sheet that can stably manufacture a oriented electrical steel sheet with excellent magnetic properties, and provide an induction heating device for decarburization annealing used in the method.

[0020] Methods used to solve problems

[0021] In order to solve the above problems, the inventors have repeatedly conducted in-depth studies on the scheme of forming Goss-oriented grains and {111}<112>-oriented grains as a matrix in a balanced and high-frequency manner in the primary recrystallization structure, focusing on the aging conditions in the cold rolling process disclosed in the above patent documents 1 to 3 and the holding treatment conditions performed in the middle of the rapid heating of the decarburization annealing disclosed in the above patent document 5. As a result, it was found that the above problems can be solved by optimizing the aging conditions in the final cold rolling process and optimizing the holding treatment conditions performed in the middle of the rapid heating in the temperature rise process of the decarburization annealing, and the present invention was developed.

[0022] The present invention based on the above findings provides a method for manufacturing a grain-oriented electrical steel sheet, wherein a steel raw material is hot-rolled to obtain a hot-rolled sheet, the hot-rolled sheet is cold-rolled once or twice or more with intermediate annealing interposed therebetween to obtain a cold-rolled sheet of a final sheet thickness, the cold-rolled sheet is subjected to a decarburization annealing which also serves as a primary recrystallization annealing, and then subjected to a final annealing, the method for manufacturing a grain-oriented electrical steel sheet being characterized in that, in the final cold rolling of the cold rolling, at least one pass or more of rolling is performed within a temperature range of 150°C to 350°C inclusive of the steel sheet temperature, in the decarburization annealing, rapid heating is performed at an average heating rate of 250°C / s or more from 400°C in the heating process to a temperature T (°C) between 700 and 900°C, and the time for the heating rate to become less than 2 / 3 of the average heating rate at any temperature between 500°C and 700°C in the heating process is set to be 0.10s to less than 1.00s.

[0023] The characteristic lies in that in the final cold rolling in the method for manufacturing the oriented electrical steel sheet of the present invention, after at least one rolling pass is performed in a temperature range of 30°C to 130°C, at least one rolling pass is performed in a temperature range of 150°C to 350°C.

[0024] Furthermore, the steel material used in the method for producing the grain-oriented electrical steel sheet of the present invention has a composition containing the following components of Group A or Group B, with the balance being Fe and inevitable impurities.

[0025] Group A: Contains 0.01-0.10 mass % of C, 2.0-4.5 mass % of Si, 0.01-0.50 mass % of Mn, 0.0100-0.0400 mass % of Al, 0.0050-0.0120 mass % of N, and at least one of S and Se: 0.01-0.05 mass % in total;

[0026] Group B: C: 0.01 to 0.10 mass%, Si: 2.0 to 4.5 mass%, Mn: 0.01 to 0.50 mass%, Al: less than 0.0100 mass%, N: 0.0050 mass% or less, S: 0.0070 mass% or less, and Se: 0.0070 mass% or less.

[0027] In addition, it is characterized in that the above-mentioned steel raw material used in the manufacturing method of the above-mentioned grain-oriented electrical steel sheet of the present invention further contains at least one of Sb: 0.500 mass% or less, Cu: 1.50 mass% or less, P: 0.500 mass% or less, Cr: 1.50 mass% or less, Ni: 1.500 mass% or less, Sn: 0.50 mass% or less, Nb: 0.0100 mass% or less, Mo: 0.50 mass% or less, B: 0.0070 mass% or less and Bi: 0.0500 mass% or less in addition to the above-mentioned component composition.

[0028] Furthermore, the method for producing the grain-oriented electrical steel sheet according to the present invention is characterized in that the rapid heating in the decarburization annealing is performed using a transverse induction heating device.

[0029] In addition, the present invention is an induction heating device, which is a horizontal induction heating device used in the manufacturing method of the oriented electromagnetic steel plate described above, characterized in that the heating coil has a rounded rectangular shape composed of two parallel lines of equal length along the plate width direction and two semicircles, and when the maximum inner diameter of the heating coil in the plate width direction is set to R1 (m), the maximum inner diameter of the heating coil in the plate passing direction is set to R2 (m), the width of the steel plate is set to w (m) and the plate passing speed of the steel plate is set to v (m / s), the relationship R1≥w and R2<v is satisfied.

[0030] Effects of the Invention

[0031] According to the present invention, a grain-oriented electrical steel sheet having excellent magnetic properties can be stably manufactured, thus greatly contributing to energy saving of electric equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a diagram showing the influence of the average temperature increase rate and the temporarily reduced temperature increase rate on the iron loss during decarburization annealing.

[0033] Figure 2 This is a diagram showing the effect of the time for temporarily reducing the heating rate during rapid heating in decarburization annealing on the iron loss.

[0034] Figure 3 The figures show an example of a transverse induction heating device used for rapid heating in decarburization annealing, wherein (a) is a plan view and (b) is a cross-sectional view in the width direction.

[0035] Figure 4 This is another diagram showing the influence of the average temperature increase rate and the temporarily reduced temperature increase rate on the iron loss during decarburization annealing.

[0036] Figure 5 This is another diagram showing the effect of the time for temporarily reducing the heating rate during rapid heating in decarburization annealing on the iron loss.

[0037] Figure 6 This is a diagram showing the influence of the rapid heating end temperature T on the iron loss. DETAILED DESCRIPTION

[0038] First, the experiment that led to the development of the present invention will be described.

[0039] To solve the above problems of the prior art, the inventors conducted the following experiment to investigate the temperature increase conditions of decarburization annealing for forming Goss-oriented grains and {111}<112>-oriented grains as a matrix in a steel sheet structure after primary recrystallization in a balanced and high-frequency manner.

[0040] <Experiment 1>

[0041] A steel slab having a composition containing C: 0.035 mass%, Si: 3.4 mass%, Mn: 0.05 mass%, Al: 0.0086 mass%, N: 0.0050 mass%, S: 0.0031 mass% and Se: 0.0031 mass% and the balance consisting of Fe and inevitable impurities, and containing no inhibitor-forming components, was heated to 1210°C and then hot-rolled to produce a hot-rolled plate with a plate thickness of 2.0 mm. Next, a test piece cut from the hot-rolled plate was subjected to hot-rolled plate annealing at 1000°C × 60s, and then cold-rolled once using 5 tandem rolling mills to produce a cold-rolled plate with a final plate thickness (product plate thickness) of 0.20 mm. At this time, the third pass was set as warm rolling in which the steel plate temperature at the inlet side was increased to 200°C and rolled.

[0042] Next, the cold rolled sheet was subjected to decarburization annealing which also served as primary recrystallization annealing with an absorptive temperature of 840°C and an absorptive time of 100 seconds. At this time, as shown in Table 1, the average heating rate from 400°C to 750°C was varied in various ways during the heating process of the decarburization annealing, and for a part, the heating rate was temporarily reduced under the conditions shown in Table 1 when the temperature reached 600°C. Next, an annealing separator containing MgO as the main component was applied to the surface of the steel sheet after the decarburization annealing, and then a final annealing was performed to perform secondary recrystallization. Next, the unreacted annealing separator was removed from the surface of the steel sheet after the final annealing, and then an insulating coating liquid containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 was applied, and a flattening annealing of 800°C×30 seconds was performed to simultaneously perform baking of the coating and shape correction, thereby producing a finished sheet.

[0043] Epstein test pieces were cut out from the product sheets thus obtained, and the iron loss W was measured in accordance with JIS C 2550. 17 / 50 The results are shown in Table 1 (iron loss per unit mass at a frequency of 50 Hz and a maximum magnetic flux density of 1.7 T).

[0044]

[0045] As shown in Table 1, under the conditions of rapid heating from 400°C to 750°C with an average heating rate of 250°C / s or more and temporarily reducing the heating rate in the middle of the rapid heating, the iron loss W 17 / 50 Here, the iron loss value of 0.87 W / kg is the reference value of the present invention for judging whether the iron loss characteristics of a grain-oriented electromagnetic steel sheet with a thickness of 0.20 mm are acceptable or not. The reference value depends on the sheet thickness, and the thicker the sheet thickness, the larger the reference value.

[0046] As described above, the reason why iron loss is reduced by setting the average heating rate to above 250°C / s during the heating process of decarburization annealing and temporarily reducing the heating rate in the middle of the above-mentioned rapid heating is not fully understood at present, but it is believed that this is because, by reducing the heating rate for a short time in the middle of rapid heating, the promotion of recrystallization of Goss-oriented grains brought about by rapid heating and the development of recrystallized {111}<112> oriented grains are balanced.

[0047] Next, the inventors conducted the following experiment to investigate the influence of the average heating rate of rapid heating in the heating process of decarburization annealing and the heating rate reduced in the middle of the rapid heating on the iron loss characteristics.

[0048] Experiment 2

[0049] The cold-rolled sheet produced in the above-mentioned <Experiment 1> was subjected to decarburization annealing which also served as primary recrystallization annealing with the soaking temperature set to 840°C and the soaking time set to 100s. At this time, the average heating rate from 400°C to 750°C during the heating process of the decarburization annealing was varied between 200 and 500°C / s, and when the temperature of the steel sheet reached 600°C, the heating rate was varied within the range of 25 to 500°C / s for only 0.50s. Next, similarly to the above-mentioned <Experiment 1>, an annealing separator was applied to the steel sheet after the above-mentioned decarburization annealing, and then a final annealing and a flattening annealing were performed to produce a finished sheet. An Epstein test piece was cut from the finished sheet to measure the iron loss W. 17 / 50 .

[0050] The above measurement results are compared with the average heating rate from 400℃ to 750℃ and the heating rate reduced by only 0.50s and the iron loss W 17 / 50 The relationship is shown in Figure 1 In the figure, the case marked with "○" indicates the iron loss W 17 / 50The reference value is 0.87W / kg or less (good iron loss). The case marked with "▲" indicates the iron loss W 17 / 50 Higher than the reference value of 0.87W / kg (iron loss difference).

[0051] Depend on Figure 1 It can be seen that when the average heating rate from 400°C to 750°C is set to 250°C / s or more and the heating rate of the steel plate is reduced to less than 2 / 3 of the average heating rate from 400°C to 750°C at 600°C, the iron loss W 17 / 50 All were reduced to below the benchmark value of 0.87W / kg.

[0052] Furthermore, the inventors conducted the following experiment to investigate the time required to reduce the heating rate in order to reduce the iron loss during the heating process of decarburization annealing.

[0053] Experiment 3

[0054] When the cold-rolled sheet produced in the above-mentioned <Experiment 1> was subjected to decarburization annealing which also served as primary recrystallization annealing with the soaking temperature set to 840°C and the soaking time set to 100s, during the heating process, the average heating rate from 400°C to 750°C was changed between two levels of 250°C / s and 300°C / s, and the heating rate was reduced to 50°C / s or 150°C / s when the temperature of the steel sheet reached 600°C. At this time, the time for reducing the above-mentioned heating rate was varied between 0 and 1.2s. Next, in the same manner as in the above-mentioned <Experiment 1>, an annealing separator was applied to the steel sheet after the above-mentioned decarburization annealing, and then a final annealing and a flattening annealing were performed to produce a finished sheet, and an Epstein test piece was cut from the finished sheet to measure the iron loss W 17 / 50 .

[0055] The results of the above measurements are shown in Figure 2 As can be seen from the figure, by reducing the heating rate to a time of 0.10s or more and less than 1.00s, the iron loss W 17 / 50 It has dropped below the baseline value of 0.87W / kg.

[0056] The present invention has been completed through further research based on the above-mentioned new findings.

[0057] Next, the component composition of the steel material used for producing the grain-oriented electrical steel sheet of the present invention will be described.

[0058] The steel material used in the present invention is not particularly limited as long as it has a component composition known for use in grain-oriented electrical steel sheets, but preferably contains C, Si and Mn in the following ranges from the viewpoint of stably producing a grain-oriented electrical steel sheet having excellent magnetic properties.

[0059] C: 0.01-0.10% by mass

[0060] C is an austenite forming element and is an element useful for increasing the maximum fraction of the γ phase and refining the steel billet structure. However, when the C content is less than 0.01 mass%, the γ phase fraction decreases and the refinement of the steel billet structure becomes insufficient. On the other hand, when it is greater than 0.10 mass%, it is difficult to reduce it to less than 0.0050 mass% by decarburization annealing where magnetic aging does not occur. Therefore, the C content is preferably set in the range of 0.01 to 0.10 mass%. More preferably, it is in the range of 0.02 to 0.08 mass%.

[0061] Si: 2.0-4.5 mass%

[0062] Si is an element effective in increasing the resistivity of steel and reducing iron loss. However, when the Si content is less than 2.0% by mass, the above-mentioned iron loss reduction effect cannot be fully obtained. On the other hand, when it is greater than 4.5% by mass, the workability is significantly reduced, and it is difficult to manufacture by rolling. Therefore, the Si content is preferably set in the range of 2.0 to 4.5% by mass. More preferably, it is in the range of 2.5 to 4.0% by mass.

[0063] Mn: 0.01-0.50 mass%

[0064] Mn is an element required to improve hot workability. When the Mn content is less than 0.01 mass%, the above-mentioned improvement effect of hot workability cannot be fully obtained. On the other hand, when it is greater than 0.50 mass%, the primary recrystallization texture may deteriorate, and it is difficult to obtain a secondary recrystallization structure that is highly aggregated in the Goss orientation. Therefore, the Mn content is preferably set to a range of 0.01 to 0.50 mass%. More preferably, it is in the range of 0.03 to 0.30 mass%.

[0065] In addition, when AlN is used as an inhibitor in the occurrence of secondary recrystallization in the final annealing, the steel material used in the present invention preferably contains Al: 0.0100-0.0400 mass% and N: 0.0050-0.0120 mass% as inhibitor-forming elements in addition to the above-mentioned C, Si and Mn. When the Al content and the N content are lower than the above-mentioned lower limit, it is difficult to fully obtain the desired inhibitor effect. On the other hand, when it is greater than the above-mentioned upper limit, the dispersion state of the precipitated inhibitor becomes uneven, and it is still difficult to obtain the expected inhibitor effect.

[0066] In addition, on the basis of the above-mentioned inhibitor AlN, Mn sulfide (MnS, Cu2S, etc.) and selenide (MnSe, Cu2Se, etc.) can also be used as an inhibitor. In addition, the above-mentioned sulfide and selenide can also be used in combination. When using Mn sulfide and selenide as additional inhibitors, it is preferred to contain at least one of S and Se in a total range of 0.01 to 0.05 mass%. When the total content of S and Se is lower than the above-mentioned lower limit, it is difficult to fully obtain the effect as an inhibitor. On the other hand, when it is greater than the above-mentioned upper limit, the dispersion of the precipitate becomes uneven, and it is still difficult to fully obtain the inhibitor effect.

[0067] On the other hand, when an inhibitor is not used in the occurrence of secondary recrystallization in the final annealing, it is preferable to reduce the components that form inhibitors as much as possible. Specifically, it is preferable to set Al: less than 0.0100 mass%, N: 0.0050 mass% or less, S: 0.0070 mass% or less, and Se: 0.0070 mass% or less.

[0068] In addition, the steel material used in the present invention may contain at least one selected from Sb: 0.500 mass % or less, Cu: 1.50 mass % or less, P: 0.500 mass % or less, Cr: 1.50 mass % or less, Ni: 1.500 mass % or less, Sn: 0.50 mass % or less, Nb: 0.0100 mass % or less, Mo: 0.50 mass % or less, B: 0.0070 mass % or less, and Bi: 0.0500 mass % or less in addition to the above-mentioned components. The above-mentioned Sb, Cu, P, Cr, Ni, Sn, Nb, Mo, B, and Bi are all elements useful for improving magnetic properties. If they are within the above-mentioned range, the effect of improving magnetic properties can be obtained without hindering the development of secondary recrystallized grains. It should be noted that in order to reliably obtain the above-mentioned addition effect, it is preferred to add Sb: 0.005 mass % or more, Cu: 0.01 mass % or more, P: 0.005 mass % or more, Cr: 0.01 mass % or more, Ni: 0.005 mass % or more, Sn: 0.01 mass % or more, Nb: 0.0005 mass % or more, Mo: 0.01 mass % or more, B: 0.0010 mass % or more and Bi: 0.0005 mass % or more respectively.

[0069] In addition, in the steel material used in the present invention, the balance other than the above-mentioned components is Fe and inevitable impurities.

[0070] Next, a method for producing a grain-oriented electrical steel sheet according to the present invention will be described.

[0071] The steel raw material (steel billet) used in the oriented electrical steel sheet of the present invention is preferably manufactured by melting the steel having the component composition described above through a commonly known refining process in which the molten steel obtained by a converter, an electric furnace, etc. is subjected to secondary refining such as vacuum degassing, and then manufactured by a commonly known continuous casting method, ingot casting-blowing rolling method, etc.

[0072] Next, the above-mentioned steel raw material (steel slab) is heated to a predetermined temperature and then hot-rolled to form a hot-rolled plate. Regarding the heating temperature of the above-mentioned steel slab, when no inhibitor-forming component is contained, it is preferably set to about 1050°C or more from the viewpoint of ensuring hot rolling properties. In addition, when an inhibitor-forming component is contained, it is preferably set to about 1200°C or more from the viewpoint of dissolving the inhibitor-forming component in the steel. It should be noted that there is no particular restriction on the upper limit of the heating temperature, but when it is higher than 1450°C, it is too close to the melting point of the steel, and it is difficult to maintain the shape of the steel slab or the oxide scale loss increases, so it is preferably set to below 1450°C. The other hot rolling conditions can be set to generally known conditions without any particular restrictions.

[0073] Next, the hot-rolled steel sheet (hot-rolled sheet) may be subjected to hot-rolled sheet annealing as necessary. The hot-rolled sheet annealing may be performed under known conditions and is not particularly limited.

[0074] Next, the hot rolled sheet or the steel sheet after hot rolled sheet annealing is descaled by pickling or the like, and then cold rolled to obtain a cold rolled sheet of the final sheet thickness (product sheet thickness). The cold rolling may be performed once to obtain a cold rolled sheet of the final sheet thickness, or may be performed twice or more with intermediate annealing to obtain a cold rolled sheet of the final sheet thickness.

[0075] It should be noted that in the present invention, the cold rolling to obtain the above-mentioned final plate thickness is referred to as "final cold rolling". Specifically, when the final plate thickness is obtained by one cold rolling, the cold rolling is referred to as "final cold rolling". In addition, when the final plate thickness is obtained by two or more cold rollings with intermediate annealing, the last cold rolling is referred to as "final cold rolling". In addition, the rolling mill used in the cold rolling is not particularly limited, and a well-known rolling mill such as a tandem rolling mill, a single reversing rolling mill, a Sendzimir rolling mill, and a planetary rolling mill can be used.

[0076] There is no particular restriction on the reduction rate of the above-mentioned final cold rolling, but from the viewpoint of improving the primary recrystallization texture, it is preferably set to be greater than 60% and less than 95%. When it is less than 60%, the development of {111}<112> oriented grains in the primary recrystallization texture becomes insufficient, and it is difficult for Goss-oriented grains to grow during secondary recrystallization. On the other hand, when it is greater than 95%, it is difficult to perform cold rolling due to work hardening. In addition, the above-mentioned final plate thickness (product plate thickness) is preferably set to a range of 0.1 to 1.0 mm. When it is less than 0.1 mm, productivity is reduced, and there is no rigidity when the product plate is made, and the operation becomes difficult when it is processed into the core of the transformer. On the other hand, when it is greater than 1.0 mm, the eddy current loss becomes larger and the iron loss increases, so it is not preferred.

[0077] Here, it is important in the present invention that at least one warm rolling is performed in the temperature range of 150°C to 350°C in the above-mentioned final cold rolling. By performing the final cold rolling at the above-mentioned temperature, the diffusion of the solid solution C and N and the fixation to the dislocation can be promoted, and the shear bands that become the nucleation sites of the Goss-oriented grains can be efficiently introduced into the primary recrystallization structure. As described later, the present invention is a developed technology that takes into account both the Goss-oriented grains and the {111}<112>oriented grains in the primary recrystallization structure by optimizing the heating conditions of the heating process of the decarburization annealing. Therefore, it is extremely important to make the final cold rolling a warm rolling that is effective in increasing the nucleation sites of the Goss-oriented grains. When the temperature of the steel plate in the above-mentioned warm rolling is lower than 150°C, the fixation of the dislocations by the solid solution C and N becomes insufficient, and the increase of the Goss-oriented grains in the primary recrystallization structure cannot be expected. On the other hand, when the temperature is higher than 350°C, excessive shear bands are introduced into the {111}<112> processed structure, so the {111}<112> oriented grains after primary recrystallization cannot be avoided, and the magnetic properties of the finished sheet are deteriorated. It should be noted that the preferred warm rolling temperature (steel sheet temperature) is in the range of 180°C to 300°C.

[0078] In addition, by performing at least one pass of rolling in the temperature range of 30°C to 130°C in the above-mentioned final cold rolling, and then performing at least one pass of rolling in the temperature range of 150°C to 350°C, the number of Goss-oriented grains in the primary recrystallization structure can be further increased. Here, the temperature range of 30°C to 130°C in the final cold rolling is defined as the "low temperature range", and the temperature range of 150°C to 350°C is defined as the "high temperature range". Since the {111}<112> orientation is a rolling-stable orientation in which the crystal orientation is not easily changed by rolling, by performing rolling in the low temperature range to develop the {111}<112> structure, and then performing rolling in the high temperature range, it is possible to more effectively introduce shear bands that become nucleation sites of Goss-oriented grains through primary recrystallization into the {111}<112> processed structure. However, when the rolling temperature in the low temperature range is lower than 30°C, cracks are easily generated in the steel sheet during rolling, and productivity is reduced. On the other hand, when the temperature is higher than 130° C., the effect of developing the {111}<112> structure cannot be obtained. The temperature in the preferred low temperature range is in the range of 40° C. to 100° C.

[0079] It should be noted that the combination of rolling in the above-mentioned low temperature range and then rolling in the high temperature range only needs to exist in at least one of the final cold rolling, and the pass positions of rolling in the low temperature range and rolling in the high temperature range are not particularly limited. For example, in the case of three passes of final cold rolling, rolling in the order of low temperature range-high temperature range-high temperature range or high temperature range-low temperature range-high temperature range is appropriate, but rolling in the order of high temperature range-low temperature range-low temperature range, high temperature range-high temperature range-low temperature range, and high temperature range-high temperature range-high temperature range cannot be expected to further increase the effect of Goss-oriented grains.

[0080] Here, there is no particular limitation on the method of heating the steel sheet to the high temperature range of 150°C or more and 350°C or less, and examples thereof include: a method of utilizing the processing heat generated by rolling; a method of using induction heating or electric heating; a method of passing the steel sheet through a radiation heating furnace; or a method of contacting with a heating roller, etc. In addition, there is no particular limitation on the method of cooling the steel sheet to the low temperature range of 30°C or more and 130°C or less, and examples thereof include: a method of adjusting the temperature of the cooling water or coolant during rolling; a method of extending the time between rolling passes; or a method of adjusting the pass schedule to reduce the processing heat, etc.

[0081] Next, the cold rolled sheet having the final sheet thickness is subjected to a decarburization annealing which also serves as a primary recrystallization annealing to reduce the C content to 0.0050 mass % or less, which is less likely to cause magnetic aging. The decarburization conditions (heat soaking conditions) in the decarburization annealing are not particularly limited as long as known conditions are applied. For example, annealing at 750 to 950°C for 30 to 180 seconds is preferably performed in a wet hydrogen atmosphere.

[0082] Here, what is important in the present invention is that in the decarburization annealing, it is necessary to perform rapid heating with an average heating rate of 250°C / s or more in the heating process from 400°C to a temperature T (°C) between 700 and 900°C until the above-mentioned soaking temperature is reached. When the above-mentioned average heating rate is less than 250°C / s, the primary recrystallization of the Goss-oriented grains becomes insufficient and good iron loss cannot be obtained. The preferred average heating rate is 300°C / s or more. It should be noted that the above-mentioned average heating rate of the present invention is a heating rate including the time for temporarily reducing the heating rate described later.

[0083] In addition, the temperature T (°C) for ending the above-mentioned rapid heating is set between 700 and 900°C because, when the upper limit of the rapid heating interval is lower than 700°C, the primary recrystallization of the Goss-oriented grains becomes insufficient and the effect of rapid heating cannot be obtained. On the other hand, when it is higher than 900°C, the decomposition of the inhibitor (AlN) occurring at high temperature hinders the secondary recrystallization, so good iron loss characteristics cannot be obtained. The preferred temperature T is in the range of 700 to 850°C.

[0084] In addition, during the heating process of the above-mentioned decarburization annealing, it is necessary to set the time for reducing the heating rate to below the average heating rate from 400°C to T (°C) at any temperature between 500°C and 700°C in the middle of the above-mentioned rapid heating to be greater than 0.10s and less than 1.00s.

[0085] When the temperature at which the heating rate is reduced is lower than 500°C, the driving force for recrystallization of the Goss-oriented nuclei is reduced due to recovery, so that the recrystallization of the Goss-oriented grains becomes insufficient and good iron loss characteristics cannot be obtained. On the other hand, when the temperature is higher than 700°C, since the recrystallization rate is already high, even if the heating rate is reduced, the effect of promoting the development of {111}<112> oriented grains cannot be fully obtained.

[0086] In addition, by Figure 2It can be seen that the time for reducing the heating rate needs to be set to be greater than 0.10s and less than 1.00s. When it is less than 0.10s, the reduction time is too short and the effect of reducing the heating rate cannot be obtained. On the other hand, when it is greater than 1.00s, the development of {111}<112> oriented grains becomes excessive, hindering the subsequent recrystallization of Goss oriented grains, so good iron loss still cannot be obtained. It is preferably in the range of greater than 0.20s and less than 0.70s.

[0087] In addition, the above-mentioned temporarily reduced heating rate needs to be less than 2 / 3 of the average heating rate from 500°C to T(°C). When the heating rate is higher than this, the effect of promoting the development of {111}<112> oriented grains brought about by the reduction in heating rate cannot be improved. It is preferably less than 1 / 2. It should be noted that there is no special restriction on the lower limit of the reduced heating rate, but since the average heating rate from 400°C to T(°C) needs to be set to more than 250°C / s, it is necessary to appropriately determine the time including the time for reducing the heating rate. The preferred lower limit of the heating rate is 0°C / s. It should be noted that the above-mentioned temporarily reduced heating rate can be obtained by measuring the temperature of the steel plate during the heating process using a thermocouple, radiation thermometer, etc. that can respond quickly and performing time differentiation on the measured temperature.

[0088] Here, regarding the rapid heating during the temperature rise process of the above-mentioned decarburization annealing and the temporary reduction of the temperature rise rate in the middle, it can be implemented in the following manner: two or more rapid heating devices such as electric heating devices, solenoid induction heating devices, etc. are arranged in series on the production line, and any one of the above-mentioned two or more devices is used as the temperature rise rate reduction interval, and the output power of the above-mentioned rapid heating device and the steel plate passing speed (line speed) are appropriately adjusted.

[0089] However, installing more than two rapid heating devices as described above requires a lot of space. Therefore, as a rapid heating device, it is preferred to use a transverse induction heating device, in which the heating coils wound on the iron core are arranged above and below the steel plate, so that the alternating magnetic flux generated in the iron core passes through the thickness direction of the steel plate, and the steel plate is heated by the effect of the magnetic field. In this induction heating device, the induced current flows in the shape of the heating coil within the plate surface, and the induced current does not flow through the portion of the steel plate opposite to the iron core. Therefore, when the steel plate passes through the iron core portion, a phenomenon of temporary reduction in the heating rate occurs. In addition, since the reduction in the heating rate occurs in one induction heating device, there will be no problem with the installation space. Therefore, the transverse induction heating device is preferably suitable for the present invention.

[0090] The shape of the heating coil of the horizontal induction heating device may be any of circular, rectangular, elliptical, etc., without particular limitation. Figure 3 , a heating coil having a rounded rectangular shape consisting of two parallel lines of equal length and two semicircles is shown as an example. When a horizontal induction heating device using a heating coil having such a shape is used, the maximum inner diameter of the heating coil in the plate width direction is set to R1(m), and the maximum inner diameter of the heating coil in the plate passing direction (in Figure 3 When R1 is the inner diameter of the central part of the width of the steel plate) and the width of the steel plate is w (m) and the speed of the steel plate is v (m / s), it is preferred to satisfy the relationship of R1≥w and R2<v. R1≥w is a necessary condition for generating an induced current on the entire surface of the steel plate, and R2<v is a necessary condition for suppressing the reduction time of the heating rate to less than 1.00s.

[0091] Next, for the cold rolled sheet subjected to the above decarburization annealing, an annealing separator is applied on the surface of the steel sheet, and then a final annealing for secondary recrystallization is performed. As the annealing separator, a known annealing separator can be used without particular limitation, for example, an annealing separator with MgO as the main component and additives such as TiO2 added as needed; an annealing separator with SiO2 and Al2O3 as the main components, etc.

[0092] For the steel sheet subjected to the above-mentioned final annealing, it is preferred to apply an insulating coating liquid on the surface of the steel sheet after removing the unreacted annealing separator remaining on the surface of the steel sheet, and simultaneously carry out baking of the above-mentioned coating and flattening annealing to correct the shape of the steel sheet that has deteriorated due to the final annealing to produce a finished plate. It should be noted that the coating of the insulating coating can be carried out by another production line. The type of the above-mentioned insulating coating is not particularly limited. In the case of forming a tension-imparting insulating coating that imparts tensile tension on the surface of the steel sheet, it is preferred to apply a phosphate-colloidal silica slurry disclosed in Japanese Patent Publication No. 50-79442, Japanese Patent Publication No. 48-39338, and Japanese Patent Publication No. 56-75579, and bake it at a temperature of about 800°C.

[0093] It should be noted that when lower iron loss is desired, magnetic domain refinement treatment can be implemented by known methods such as forming grooves on the surface of the steel plate in any process after the above-mentioned cold rolling, or mechanically forming strain areas on the surface of the steel plate after final annealing, or forming thermal strain areas by irradiating laser beams, electron beams, etc.

[0094] Example 1

[0095] A steel slab having a composition containing inhibitor-forming components, including C: 0.06 mass%, Si: 3.4 mass%, Mn: 0.06 mass%, Al: 0.0250 mass%, N: 0.0090 mass%, S: 0.01 mass% and Se: 0.01 mass% and the balance being Fe and inevitable impurities, was heated to 1400°C and then hot-rolled to produce a hot-rolled plate with a plate thickness of 2.0 mm. Next, the hot-rolled plate was first cold-rolled using a tandem rolling mill to produce an intermediate plate thickness of 1.2 mm, and intermediate annealing was performed at 1100°C × 80s in an atmosphere of N2: 75 volume% + H2: 25 volume% and a dew point of 46°C. Next, a second cold rolling (final cold rolling) was performed using a Sendzimir rolling mill to produce a cold-rolled plate with a final plate thickness of 0.20 mm. At this time, the final cold rolling was performed in 6 passes, and the fourth pass was warm rolling with the steel sheet temperature at the inlet side being 250°C.

[0096] Next, the cold rolled sheet was subjected to decarburization annealing which also served as primary recrystallization annealing with an absorptive temperature of 840°C and an absorptive time of 100s. At this time, in the heating process of the decarburization annealing, the average heating rate from 400°C to 770°C was varied as shown in Table 2. In addition, for some cold rolled sheets, when the temperature of the steel sheet reached 550°C, the heating rate of the steel sheet was temporarily reduced as shown in Table 2. Next, for the cold rolled sheet subjected to the decarburization annealing, an annealing separator containing MgO as the main component was applied on the surface of the steel sheet, and then a final annealing for secondary recrystallization was performed. Next, the unreacted annealing separator was removed from the surface of the steel sheet after the final annealing, and then an insulating coating liquid containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 was applied, and a flattening annealing of 800°C×30s was performed to simultaneously bake the coating and correct the shape, thereby producing a finished sheet.

[0097] Epstein test pieces were cut out from the product sheets thus obtained, and the iron loss W was measured in accordance with JIS C 2550. 17 / 50 , and the results are shown in Table 2.

[0098] It is confirmed from Table 2 that even when a grain-oriented electrical steel sheet is produced using a steel billet containing an inhibitor-forming component and when intermediate annealing is performed in the cold rolling process, the iron loss W can be reduced by setting the average heating rate from 400°C to 770°C in the decarburization annealing heating process to 250°C / s or more and reducing the heating rate for a short period of time of 0.10s or more and less than 1.00s during the above heating process. 17 / 50 Reduced to below the baseline value of 0.87W / kg.

[0099]

[0100] Example 2

[0101] The cold rolled sheet of the final thickness prepared in Example 1 was subjected to decarburization annealing which also served as primary recrystallization annealing with an absorptive temperature of 840°C and an absorptive time of 100s. At this time, during the heating process of the decarburization annealing, the average heating rate from 400°C to 800°C was varied in the range of 200 to 500°C / s, and when the temperature of the steel sheet reached 650°C, the heating rate was reduced to various rates of only 0.30s between 25 and 500°C / s. Next, an annealing separator containing MgO as the main component was applied to the surface of the cold rolled sheet after the decarburization annealing, and a final annealing for secondary recrystallization was performed. Next, the unreacted annealing separator was removed from the surface of the steel sheet after the final annealing, and then an insulating coating liquid containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 was applied, and a flattening annealing of 800°C×30s was performed to produce a finished sheet.

[0102] Epstein test pieces were cut out from the product sheets thus obtained, and the iron loss W was measured in accordance with JIS C 2550. 17 / 50 The results are shown in the form of the average heating rate from 400°C to 800°C during decarburization annealing and the relationship between the heating rate and iron loss when the heating rate was reduced by only 0.30s. Figure 4 It should be noted that in the figure, the case marked with "○" represents the iron loss W 17 / 50 The iron loss W is below the reference value of 0.87W / kg. The case marked with “▲” indicates the iron loss W 17 / 50 Higher than the benchmark value of 0.87W / kg.

[0103] Depend on Figure 4 It can be seen that even when a steel billet containing inhibitor-forming components is used and intermediate annealing is performed during the cold rolling process, the iron loss W can be reduced by setting the average heating rate from 400°C to 800°C in the decarburization annealing to 250°C / s or more and reducing the heating rate to 2 / 3 or less of the average heating rate during the heating process. 17 / 50 Reduced to below the baseline value of 0.87W / kg.

[0104] Example 3

[0105] The cold rolled sheet of the final sheet thickness produced in the above-mentioned Example 1 was subjected to a decarburization annealing which also served as a primary recrystallization annealing with an absorptive temperature of 840°C and an absorptive time of 100s. At this time, the average heating rate from 400°C to 750°C during the heating process of the decarburization annealing was set to two conditions of 250°C / s and 300°C / s. In addition, when the temperature of the steel sheet reached 500°C during the above-mentioned heating process, the heating rate was reduced to 50°C / s or 100°C / s, and the time for reducing the above-mentioned heating rate was varied in the range of 0 to 1.2s. Next, an annealing separator having MgO as the main component was applied to the steel sheet surface of the cold rolled sheet after the above-mentioned decarburization annealing, and a final annealing for secondary recrystallization was performed. Next, the unreacted annealing separator was removed from the surface of the steel sheet after the final annealing, and then an insulating coating liquid containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 was applied and planarization annealing was performed at 800°C for 30 seconds to obtain a finished steel sheet.

[0106] Epstein test pieces were cut out from the product sheets thus obtained, and the iron loss W was measured in accordance with JIS C 2550. 17 / 50 , and the results are shown in Figure 5 As can be seen from the figure, the iron loss W of the steel sheet is reduced by setting the time for reducing the heating rate during the rapid heating of the decarburization annealing to be greater than 0.10s and less than 1.00s. 17 / 50 All were reduced to below the benchmark value of 0.87W / kg.

[0107] Example 4

[0108] The following two types of steel billets A and B were heated to 1300° C. respectively, and then hot-rolled to produce hot-rolled plates with a thickness of 2.0 mm.

[0109] Steel billet A: A steel billet having a composition containing 0.035 mass % C, 3.3 mass % Si, 0.05 mass % Mn, 0.0084 mass % Al, 0.0051 mass % N, 0.0031 mass % S and 0.0031 mass % Se, with the balance being Fe and unavoidable impurities, and containing no inhibitor-forming component

[0110] Steel slab B: A steel slab having a composition containing 0.06 mass % of C, 3.4 mass % of Si, 0.06 mass % of Mn, 0.0250 mass % of Al, 0.0095 mass % of N, 0.01 mass % of S, and 0.01 mass % of Se, with the balance being Fe and unavoidable impurities, and containing inhibitor-forming components

[0111] Next, a test piece was cut from the hot-rolled sheet made from the above-mentioned billet A, and the hot-rolled sheet was annealed at 1000°C × 60s, and then a cold-rolled sheet with a final thickness of 0.20mm was made by a single cold rolling (final cold rolling) using a Sendzimir rolling mill. On the other hand, a test piece was also cut from the hot-rolled sheet made from the above-mentioned billet B, and the first cold rolling was performed using a tandem rolling mill to make an intermediate sheet thickness of 1.2mm, and an intermediate annealing of 1100°C × 80s was performed in an atmosphere of N2: 75 volume % + H2: 25 volume %, dew point 46°C. Then, a second cold rolling (final cold rolling) was performed using a tandem rolling mill to make a cold-rolled sheet with a final thickness of 0.20mm. At this time, each final cold rolling was performed in 4 passes, and the steel sheet temperature at the entrance side of each pass was changed in various ways as shown in Table 3.

[0112] Next, the cold rolled sheet was subjected to a decarburization annealing which also served as a primary recrystallization annealing with a soaking temperature of 840°C and a soaking time of 100 seconds. Figure 3 The horizontal induction heating device shown in the figure performs rapid heating at an average heating rate of 260°C / s from 400°C to 710°C. When the plate temperature reaches 550°C, the output power of the induction heating device is adjusted so that the time for the heating rate to be 100°C / s is set to 0.2s.

[0113] Next, for the cold rolled sheet after decarburization annealing, an annealing separator was applied to the surface of the steel sheet, and then final annealing was performed to perform secondary recrystallization in the same manner as in Example 1. Then, the unreacted annealing separator was removed from the surface of the steel sheet after final annealing, and then an insulating coating liquid containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 was applied, and flattening annealing was performed at 800°C for 30s to produce a finished sheet.

[0114] Epstein test pieces were cut out from the product sheets thus obtained, and the iron loss W was measured in accordance with JIS C 2550. 17 / 50 The results are shown in Table 3. As can be seen from the table, when the final cold rolling is performed at least once in the temperature range of 150°C to 350°C, the iron loss W 17 / 50 It can also be seen that after at least one pass of rolling in the temperature range of 30°C to 130°C in the final cold rolling, at least one pass of rolling in the temperature range of 150°C to 350°C, the iron loss W 17 / 50 Both were further reduced to below 0.82W / kg.

[0115]

[0116]

[0117]

[0118]

[0119]

[0120]

[0121]

[0122]

[0123] Example 5

[0124] The billets A and B used in the above-mentioned Example 4 were used as raw materials, and final cold rolling was performed under the conditions of No. 17 (using billet A) and No. 178 (using billet B) shown in Table 3 (the inlet side steel plate temperature of the first pass: 300°C, the inlet side steel plate temperature of the second to fourth passes: 100°C) to obtain cold-rolled plates with a plate thickness of 0.20 mm. The cold-rolled plates were subjected to decarburization annealing which also served as primary recrystallization annealing with an ambulation temperature of 840°C and an ambulation time of 100 s. At this time, in the temperature increase process of the above-mentioned decarburization annealing, rapid heating was performed from 400°C to temperature T at an average temperature increase rate of 300°C / s, and the above-mentioned temperature T was varied in the range of 650°C to 950°C. In addition, when the plate temperature reached 550°C in the middle of the above-mentioned rapid heating, the output power of the heating device was adjusted so that the time for which the temperature increase rate was 100°C / s was set to 0.2s. It should be noted that, under the condition that the temperature T is 860° C. or higher, after rapid heating to the temperature T, the steel plate is cooled to 840° C. using nitrogen, and then soaked at 840° C. for 100 s.

[0125] Next, for the cold-rolled sheet after decarburization annealing, an annealing separator was applied to the surface of the steel sheet, and then final annealing was performed to perform secondary recrystallization in the same manner as in Example 1. Next, the unreacted annealing separator was removed from the surface of the steel sheet after final annealing, and then an insulating coating liquid containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 was applied, and flattening annealing was performed at 800°C for 30s to produce a finished sheet.

[0126] Epstein test pieces were cut out from the product sheets thus obtained, and the iron loss W was measured in accordance with JIS C 2550. 17 / 50 , and the results are shown in Figure 6 As can be seen from the figure, the iron loss W of the steel plate after heating when the above-mentioned rapid heating end temperature T is set between 700 and 900°C is 17 / 50All were reduced to below the benchmark value of 0.87W / kg.

[0127] Example 6

[0128] Steel having a composition containing C: 0.036 mass%, Si: 3.4 mass%, Mn: 0.06 mass%, Al: 0.0072 mass%, N: 0.0050 mass%, S: 0.0031 mass% and Se: 0.0031 mass%, Sb, Cu, P, Cr, Ni, Sn, Nb, Mo, B and Bi as other components in the composition shown in Table 4, and the balance consisting of Fe and inevitable impurities, and not containing inhibitor-forming components, was melted to form a steel slab. Then, the steel slab was heated to 1210°C and then hot-rolled to form a hot-rolled plate with a plate thickness of 2.0 mm. Then, the hot-rolled plate was subjected to hot-rolled plate annealing at 1000°C × 60s, and then a cold rolling (final cold rolling) was performed using a tandem rolling mill to form a cold-rolled plate with a final plate thickness of 0.20 mm. At this time, the final cold rolling was set as warm rolling with the steel plate temperature at the inlet side of all passes being 170°C.

[0129] Next, the cold rolled sheet was subjected to a decarburization annealing which also served as a primary recrystallization annealing with a soaking temperature of 840°C and a soaking time of 100 seconds. Figure 3 The induction heating device of the horizontal type shown performs rapid heating from 400°C to 710°C at an average heating rate of 260°C / s, and when the temperature of the steel plate reaches 550°C, the time for reducing the heating rate to 100°C / s is adjusted to only 0.2s. Next, an annealing separator containing MgO as the main component is applied to the surface of the steel plate of the cold-rolled plate after the above decarburization annealing, and a final annealing for secondary recrystallization is performed. Then, the unreacted annealing separator is removed from the surface of the steel plate after the final annealing, and then an insulating coating liquid containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 is applied, and a flattening annealing of 800°C×30s is performed to produce a finished plate.

[0130] Epstein test pieces were cut out from the product sheets thus obtained, and the iron loss W was measured in accordance with JIS C 2550. 17 / 50 The results are shown in Table 4. As can be seen from the table, the iron loss W of the product sheet which was rapidly heated in the temperature rise process of decarburization annealing using a horizontal induction heating device under the conditions according to the present invention using a steel billet to which at least one selected from Sb, Cu, P, Cr, Ni, Sn, Nb, Mo, B and Bi was added as a raw material is 17 / 50 All are below the standard value of 0.80W / kg, and have excellent magnetic properties.

[0131]

Claims

1. A method for manufacturing a grain-oriented electrical steel sheet, wherein: A steel raw material is hot-rolled to obtain a hot-rolled sheet, the hot-rolled sheet is cold-rolled once or twice or more with intermediate annealing to obtain a cold-rolled sheet having a final sheet thickness, the cold-rolled sheet is subjected to a decarburization annealing which also serves as a primary recrystallization annealing, and then subjected to a final annealing. The method for producing the grain-oriented electrical steel sheet is characterized in that: In the final cold rolling of the cold rolling, at least one pass of rolling is performed within a temperature range of 150° C. to 350° C. on the steel sheet. In the decarburization annealing, rapid heating is performed from 400°C to a temperature T (°C) between 700 and 900°C at an average heating rate of 250°C / s or more, and The time for the heating rate to become less than 2 / 3 of the average heating rate at any temperature between 500° C. and 700° C. in the heating process is set to be greater than or equal to 0.10 s and less than 1.00 s.

2. The method for manufacturing a grain-oriented electrical steel sheet according to claim 1, wherein: In the final cold rolling, after rolling is performed at least once in a temperature range of 30° C. to 130° C., rolling is then performed at least once in a temperature range of 150° C. to 350° C.

3. The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2, wherein: The steel material has a composition containing the following components of Group A or Group B, with the balance being Fe and inevitable impurities. Group A: Contains 0.01-0.10 mass % of C, 2.0-4.5 mass % of Si, 0.01-0.50 mass % of Mn, 0.0100-0.0400 mass % of Al, 0.0050-0.0120 mass % of N, and at least one of S and Se: 0.01-0.05 mass % in total; Group B: C: 0.01 to 0.10 mass%, Si: 2.0 to 4.5 mass%, Mn: 0.01 to 0.50 mass%, Al: less than 0.0100 mass%, N: 0.0050 mass% or less, S: 0.0070 mass% or less, and Se: 0.0070 mass% or less.

4. The method for manufacturing a grain-oriented electrical steel sheet according to claim 3, wherein: In addition to the above-mentioned component composition, the steel raw material also contains at least one of Sb: 0.500 mass %, Cu: 1.50 mass % or less, P: 0.500 mass % or less, Cr: 1.50 mass % or less, Ni: 1.500 mass % or less, Sn: 0.50 mass % or less, Nb: 0.0100 mass % or less, Mo: 0.50 mass % or less, B: 0.0070 mass % or less and Bi: 0.0500 mass % or less.

5. The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 4, characterized in that: The rapid heating in the decarburization annealing is performed using a lateral induction heating device.

6. An induction heating device, which is a transverse induction heating device used in the method for producing a grain-oriented electrical steel sheet according to claim 5, characterized in that: The heating coil has a rounded rectangular shape consisting of two parallel lines of equal length along the plate width direction and two semicircles. When the maximum inner diameter of the heating coil in the plate width direction is set to R1 (m), the maximum inner diameter of the heating coil in the plate passing direction is set to R2 (m), the width of the steel plate is set to w (m) and the plate passing speed of the steel plate is set to v (m / s), the relationship R1≥w and R2<v is satisfied.

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