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

Abstract

A method for producing a grain-oriented electrical steel sheet, in which a steel raw material is hot-rolled to form a hot-rolled sheet, the hot-rolled sheet is cold-rolled once or cold-rolled twice or more with intermediate annealing interposed therebetween to form 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 final annealing is performed, in the temperature rise process of the decarburization annealing, rapid heating is performed at an average temperature rise rate of 250 DEG C / s or more from 400 DEG C to a temperature T (DEG C) between 700 DEG C and 900 DEG C, and the time for which the temperature rise rate is 2 / 3 or less of the average temperature rise rate at any temperature between 500 DEG C and 700 DEG C in the temperature rise process is 0.10 s or more and less than 1.00 s. Thus, a grain-oriented electrical steel sheet having excellent magnetic properties is produced. In addition, rapid heating of the decarburization annealing is performed using a transverse induction heating device.

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 electromagnetic steel sheet is a soft magnetic material widely used as the core material of transformers and generators. It is a steel sheet with excellent magnetic properties. The steel sheet has a crystal structure in which the {110}<001> orientation (Gauss orientation), which is the easy magnetization axis of iron, is highly consistent with the rolling direction of the steel sheet.

[0003] As one of the means to achieve 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, it is important 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 structure of a steel sheet after primary recrystallization, for example, Patent Document 1 discloses the following method: a cold-rolled sheet is subjected to heat treatment at a low temperature during cold rolling and subjected to aging treatment. In addition, Patent Document 2 discloses the following method: during the intermediate annealing before annealing of a hot-rolled sheet or cold rolling (final cold rolling) to a final sheet thickness, the cooling rate is set to 30°C / s or more, and then the steel sheet is subjected to 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 the following technology: by conducting warm rolling in which the temperature of the steel sheet during cold rolling is increased and rolling is performed, dynamic strain aging is effectively utilized in which the dislocations introduced during rolling are immediately fixed with C and N.

[0006] The technologies of the above-mentioned patent documents 1 to 3 are all to 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 by cold rolling, inhibit the movement of dislocations, thereby promoting shear deformation in subsequent rolling and improving the rolling texture. This is based on the idea 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, a method of rapid heating during the heating process of decarburization annealing is disclosed in Patent Document 4. 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 in the processed structure by subsequent cold rolling, have the following problems: if excessive shear bands are introduced, although the Gossian oriented grains increase, the {111}<112> oriented grains in the primary recrystallization structure decrease excessively, and sharp Gossian oriented grains are difficult to grow during the secondary recrystallization. Therefore, there is a limit to the improvement of magnetic properties for the techniques of Patent Documents 1 to 3, 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 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 present inventors have focused on the holding treatment conditions during the rapid heating of the decarburization annealing disclosed in the above-mentioned Patent Document 5, and have repeatedly conducted in-depth studies on measures to form Goss-oriented grains and {111}<112>-oriented grains as a matrix in a balanced and high-frequency manner in the primary recrystallization structure. As a result, they have found that the above problems can be solved by optimizing the holding treatment conditions during the rapid heating in the temperature rise process of the decarburization annealing, and have developed the present invention.

[0022] The present invention based on the above findings proposes a method for manufacturing a grain-oriented electrical steel sheet, wherein a steel raw material is hot-rolled to form a hot-rolled sheet, the hot-rolled sheet is cold-rolled once or twice or more with intermediate annealing to form 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 a final annealing, the manufacturing method being characterized in that in the heating process of 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 that at any temperature between 500°C and 700°C in the heating process, the time during which the heating rate is less than 2 / 3 of the average heating rate is set to be greater than 0.10s and less than 1.00s.

[0023] 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:

[0024] Group A: Contains 0.01 to 0.10 mass % of C, 2.0 to 4.5 mass % of Si, 0.01 to 0.50 mass % of Mn, 0.0100 to 0.0400 mass % of Al, 0.0050 to 0.0120 mass % of N, and at least one of S and Se: 0.01 to 0.05 mass % in total;

[0025] 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.

[0026] In addition, the following is a feature: the above-mentioned steel raw material used in the above-mentioned method for manufacturing the oriented electrical steel sheet of the present invention, in addition to the above-mentioned component composition, 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.

[0027] 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.

[0028] In addition, the present invention is an induction heating device, which is a transverse induction heating device used in the method for manufacturing a grain-oriented electromagnetic steel sheet described above, characterized in that the heating coil has a rounded rectangular shape consisting of two parallel lines of equal length along the sheet width direction and two semicircles, and the maximum inner diameter of the heating coil in the sheet width direction is set to R 1 (m), the maximum inner diameter of the heating coil in the plate passing direction is set to R 2 (m), the width of the steel plate is set to w (m) and the speed of the steel plate is set to v (m / s), satisfying R 1 ≥w and R 2 <v relationship.

[0029] Effects of the Invention

[0030] According to the present invention, a grain-oriented electrical steel sheet having excellent magnetic properties can be stably produced, thus greatly contributing to energy saving of electric equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] 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.

[0032] 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.

[0033] Figure 3 The figures show an example of a horizontal 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.

[0034] 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.

[0035] 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.

[0036] Figure 6 This is a diagram showing the influence of the rapid heating end temperature T on the iron loss. DETAILED DESCRIPTION

[0037] First, the experiment that led to the development of the present invention will be described.

[0038] To solve the above problems of the prior art, the present 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.

[0039] <Experiment 1>

[0040] A steel slab having a composition containing no inhibitor-forming components, including 0.035 mass % C, 3.4 mass % Si, 0.05 mass % Mn, 0.0086 mass % Al, 0.0050 mass % N, 0.0031 mass % S and 0.0031 mass % Se, with the balance being Fe and inevitable impurities, 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.×60 s, and then cold-rolled once using five tandem rolling mills to produce a cold-rolled plate with a final plate thickness (product plate thickness) of 0.20 mm.

[0041] 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 while baking the coating and correcting the shape, thereby producing a product sheet.

[0042] Epstein test pieces were cut 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).

[0043]

[0044] As shown in Table 1, the iron loss W is 0.0447 W / cm2 under the condition that the average heating rate from 400°C to 750°C is set to 250°C / s or more during the decarburization annealing process and the heating rate is temporarily reduced in the middle of the above rapid heating. 17 / 50 Here, the iron loss value of 0.89 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.

[0045] As described above, the reason why the 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 yet fully understood, but it is believed that 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.

[0046] Next, the present 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.

[0047] Experiment 2

[0048] The cold-rolled sheet produced in the above-mentioned <Experiment 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 100 s. 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 0.50 s. 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 was performed, and a flattening annealing was performed to produce a product sheet. An Epstein test piece was cut from the product sheet to measure the iron loss W. 17 / 50 .

[0049] The above measurement results are compared with the average heating rate from 400℃ to 750℃ and the heating rate reduced by only 0.10s and the iron loss W 17 / 50 The relationship is shown in Figure 1 In the figure, the case indicated by "○" indicates the iron loss W 17 / 50 The reference value is 0.89W / kg or less (good iron loss). The case indicated by "▲" indicates the iron loss W 17 / 50 Higher than the reference value of 0.89W / kg (iron loss difference).

[0050] 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 when the heating rate of the steel plate is reduced to less than 2 / 3 of the average heating rate between 400 and 750°C at 600°C, the iron loss W is reduced. 17 / 50 Reduced to below the baseline value of 0.89W / kg.

[0051] Furthermore, the present inventors conducted the following experiment to investigate the time required to reduce the heating rate in order to reduce iron loss during the heating process of decarburization annealing.

[0052] <Experiment 3>

[0053] 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 when the temperature of the steel sheet reached 600°C, the heating rate was reduced to 50°C / s or 150°C / s. At this time, the time for reducing the heating rate was varied between 0 and 1.2s. Next, 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 was performed, and a flattening annealing was performed to produce a product sheet, and an Epstein test piece was cut from the product sheet to measure the iron loss W. 17 / 50 .

[0054] 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 Reduced to below the baseline value of 0.89W / kg.

[0055] The present invention has been completed through further studies based on the above-mentioned new findings.

[0056] Next, the component composition of the steel material for producing the grain-oriented electrical steel sheet of the present invention will be described.

[0057] 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 within the following ranges from the viewpoint of stably producing a grain-oriented electrical steel sheet having excellent magnetic properties.

[0058] C: 0.01-0.10% by mass

[0059] 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 steel billet structure is not sufficiently refined. On the other hand, when it exceeds 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%.

[0060] Si: 2.0-4.5 mass%

[0061] Si is an element that is 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 exceeds 4.5% by mass, the processability is significantly reduced, and rolling manufacturing is difficult. 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.

[0062] Mn: 0.01-0.50 mass%

[0063] 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 exceeds 0.50 mass%, it is possible that the primary recrystallization texture deteriorates, 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%.

[0064] In addition, when AlN is used as an inhibitor in the occurrence of secondary recrystallization in the final annealing, the steel raw 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 the above-mentioned upper limit is exceeded, the dispersion state of the precipitated inhibitor becomes uneven, and it is still difficult to obtain the expected inhibitor effect.

[0065] In addition to the above-mentioned inhibitor AlN, Mn sulfides (MnS, Cu 2 S, etc.), selenides (MnSe, Cu 2 Se, etc.) as an inhibitor. In addition, the above-mentioned sulfides and selenides can also be used in combination. When using Mn sulfides and selenides as additional inhibitors, it is preferred that at least one of S and Se is contained in a total range of 0.01 to 0.05 mass %. When the total content of S and Se is lower than the above lower limit, it is difficult to fully obtain the effect as an inhibitor. On the other hand, when the above upper limit is exceeded, the dispersion of the precipitates becomes uneven, and it is still difficult to fully obtain the inhibitor effect.

[0066] 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 the inhibitor 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.

[0067] 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 components. The above 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 ranges, 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.

[0068] In addition, in the steel material used in the present invention, the balance other than the above-mentioned components is Fe and inevitable impurities.

[0069] Next, a method for producing a grain-oriented electrical steel sheet according to the present invention will be described.

[0070] The steel raw material (steel billet) used for the oriented electrical steel sheet of the present invention is preferably manufactured by melting the steel having the component composition described above by a commonly known refining process in which molten steel obtained by a converter, an electric furnace, etc. is subjected to secondary refining such as vacuum degassing, and then by a commonly known continuous casting method, ingot casting-blowing rolling method, etc.

[0071] Next, the steel raw material (steel billet) is heated to a predetermined temperature and then hot-rolled to form a hot-rolled plate. Regarding the heating temperature of the steel billet, 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 the upper limit of the heating temperature is not particularly limited, but when it exceeds 1450°C, it is too close to the melting point of the steel, and it is difficult to maintain the shape of the steel billet, 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.

[0072] 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.

[0073] 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.

[0074] 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 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.

[0075] The reduction ratio of the above-mentioned final cold rolling is not particularly limited, 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 is insufficient, and during secondary recrystallization, it is difficult for Goss-oriented grains to grow. On the other hand, when it exceeds 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, not only does the productivity decrease, but also 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 exceeds 1.0 mm, the eddy current loss becomes larger and the iron loss increases, so it is not preferred.

[0076] It should be noted that in the above-mentioned cold rolling, especially the final cold rolling, in order to form a large number of recrystallization nuclei of Goss-oriented grains in the primary recrystallization structure, it is preferred to perform heat treatment such as interpass aging, or adopt warm rolling, as described in Patent Documents 1 to 3 of the prior art.

[0077] 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 difficult to cause magnetic aging. The decarburization conditions (heat soaking conditions) in the decarburization annealing can be any known conditions and are not particularly limited. For example, annealing at 750 to 950°C for 30 to 180 seconds is preferably performed in a wet hydrogen atmosphere.

[0078] Here, it is important in the present invention that in the decarburization annealing, it is necessary to perform rapid heating with an average heating rate of 250°C / s or more until the temperature T (°C) from 400°C to 700-900°C in the heating process 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 is 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 in the present invention is a heating rate including the time for temporarily reducing the heating rate described later.

[0079] In addition, the temperature T (°C) at which the above-mentioned rapid heating is terminated 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 is insufficient, and the effect of rapid heating cannot be obtained. On the other hand, when it exceeds 900°C, the decomposition of the inhibitor (AlN) occurring at high temperature hinders the secondary recrystallization, and thus good iron loss characteristics cannot be obtained. The preferred temperature T is in the range of 700 to 850°C.

[0080] Furthermore, during the heating process of the decarburization annealing, the time required to reduce the heating rate to below the average heating rate from 400°C to T (°C) at any temperature between 500°C and 700°C during the rapid heating is set to be greater than 0.10 s and less than 1.00 s.

[0081] If the temperature at which the heating rate is reduced is lower than 500°C, the recrystallization driving force of the Goss-oriented nuclei is reduced due to recovery, so the recrystallization of the Goss-oriented grains is insufficient and good iron loss characteristics cannot be obtained. On the other hand, if the temperature exceeds 700°C, the recrystallization rate is already high, so even if the heating rate is reduced, the effect of promoting the development of {111}<112> oriented grains cannot be fully obtained.

[0082] In addition, by Figure 2 It 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 is still not obtained. It is preferably greater than 0.20s and less than 0.70s.

[0083] 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 the heating rate cannot be improved. It is preferably less than 1 / 2. It should be noted that the lower limit of the reduced heating rate is not particularly limited, but since the average heating rate from 400°C to T (°C) needs to be more than 250°C / s, it needs to be appropriately determined, 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 at a high speed and performing time differentiation on the measured temperature.

[0084] 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 by arranging two or more rapid heating devices such as electric heating devices, solenoid induction heating devices, etc. in series on the production line, setting any one of the above-mentioned two or more devices as the temperature rise rate reduction interval, and appropriately adjusting the output power of the above-mentioned rapid heating device and the steel plate passing speed (line speed).

[0085] However, installing more than two rapid heating devices as described above requires more 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 along the shape of the heating coil in the plate surface, and the induced current does not flow in the portion of the steel plate opposite to the iron core. Therefore, when the steel plate passes through the iron core portion, the heating rate is temporarily reduced. In addition, the reduction in the heating rate occurs in one induction heating device, so there is no problem with the installation space. Therefore, the transverse induction heating device is preferably suitable for the present invention.

[0086] The shape of the heating coil of the horizontal induction heating device may be any of circular, rectangular, elliptical, etc., and is not particularly limited. 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 type induction heating device having such a heating coil is used, the maximum inner diameter of the heating coil in the plate width direction is set to R 1 (m), the maximum inner diameter of the heating coil in the plate passing direction ( Figure 3 R is the inner diameter of the central part of the steel plate width. 2(m), the width of the steel plate is w (m), and the speed of the steel plate is v (m / s), preferably, R 1 ≥w and R 2 <v. 1 ≥w is a necessary condition for generating induced current on the entire surface of the steel plate. In addition, R 2 <v is a necessary condition for suppressing the temperature increase rate decrease time to less than 1.00 s.

[0087] Next, for the cold rolled sheet subjected to the above decarburization annealing, an annealing separator is applied to 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, a annealing separator having MgO as the main component and TiO added as needed can be mentioned. 2 Annealing separators with additives such as SiO 2 、Al 2 O 3 Annealing separator as the main component, etc.

[0088] The steel sheet subjected to the above-mentioned final annealing is preferably coated with 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 the above-mentioned coating is baked and flattened annealing is performed to correct the shape of the steel sheet deteriorated by the final annealing, so as to form a product sheet. It should be noted that the coating of the insulating coating can be carried out by other production lines. 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 preferably coated with 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, etc., and baked at a temperature of about 800°C.

[0089] It should be noted that when further low 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 a strain area on the surface of the steel plate after the final annealing, or forming a thermal strain area by irradiating a laser beam, electron beam, etc.

[0090] Example 1

[0091] A steel slab having a composition containing inhibitor-forming components, which includes 0.06 mass % of C, 3.4 mass % of Si, 0.06 mass % of Mn, 0.0250 mass % of Al, 0.0090 mass % of N, 0.01 mass % of S, and 0.01 mass % of Se, with 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. Subsequently, the hot-rolled plate was first cold-rolled to produce an intermediate plate with a plate thickness of 1.2 mm, and then cold-rolled at N 2 : 75 volume % + H 2 The steel sheet was subjected to intermediate annealing at 1100° C.×80 s in an atmosphere of 25% by volume and a dew point of 46° C., and then subjected to a second cold rolling (final cold rolling) to obtain a cold rolled sheet having a final sheet thickness of 0.20 mm.

[0092] 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, in the heating process of the decarburization annealing, the average heating rate between 400°C and 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 to 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 while baking the coating and correcting the shape, thereby producing a product sheet.

[0093] Epstein test pieces were cut 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.

[0094] It was 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 0.89W / kg.

[0095]

[0096] Example 2

[0097] The cold rolled sheet of the final sheet 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 0.10s 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, after removing the unreacted annealing separator from the surface of the steel sheet after the final annealing, an insulating coating solution 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 product sheet.

[0098] Epstein test pieces were cut 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 relationship between the average heating rate from 400°C to 800°C during decarburization annealing and the heating rate when it was reduced by only 0.10s and the iron loss. Figure 4 It should be noted that in the figure, the case indicated by "○" indicates the iron loss W 17 / 50 The iron loss W is below the reference value of 0.89W / kg. The case indicated by “▲” 17 / 50 Higher than the benchmark value of 0.89W / kg.

[0099] 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 in 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 less than 2 / 3 of the average heating rate during the heating process. 17 / 50 Reduced to below the baseline value of 0.89W / kg.

[0100] Example 3

[0101] 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. Furthermore, 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 carried out. Next, after removing the unreacted annealing separator from the surface of the steel sheet after the final annealing, an insulating coating solution 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 product sheet.

[0102] Epstein test pieces were cut 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 steel sheets in which the heating rate is reduced for a period of time of 0.10 s or more and less than 1.00 s during the rapid heating of the decarburization annealing all have a lower iron loss W 17 / 50 Reduced to below the baseline value of 0.89W / kg.

[0103] Example 4

[0104] 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.

[0105] 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 components

[0106] Steel slab B: A steel slab containing inhibitor-forming components having a composition comprising 0.06 mass % C, 3.4 mass % Si, 0.06 mass % Mn, 0.0250 mass % Al, 0.0095 mass % N, 0.01 mass % S, and 0.01 mass % Se, with the balance being Fe and unavoidable impurities

[0107] Next, a test piece was cut from the hot rolled sheet produced from the above-mentioned steel slab A, and the hot rolled sheet was annealed at 1000°C for 60 seconds, and then a cold rolling (final cold rolling) was performed using a tandem rolling mill to produce a cold rolled sheet with a final sheet thickness of 0.20 mm. On the other hand, a test piece was also cut from the hot rolled sheet produced from the above-mentioned steel slab B, and the first cold rolling was performed to make the intermediate sheet thickness 1.2 mm, and the cold rolling was performed at N 2 : 75 volume % + H 2 The steel sheet was subjected to intermediate annealing at 1100° C.×80 s in an atmosphere of 25% by volume and a dew point of 46° C., and then subjected to a second cold rolling (final cold rolling) using a Sendzimir mill to obtain a cold-rolled sheet having a final sheet thickness of 0.20 mm.

[0108] Next, the cold-rolled sheet is subjected to a decarburization annealing which also serves as a primary recrystallization annealing with the soaking temperature set to 840°C and the soaking time set to 100s. At this time, during the heating process of the decarburization annealing, rapid heating is performed from 400°C to temperature T at an average heating rate of 300°C / s, and the temperature T is varied in the range of 650°C to 950°C. In addition, when the sheet temperature reaches 550°C in the middle of the rapid heating, the output power of the heating device is adjusted to set the heating rate to 100°C / s for 0.2s. It should be noted that, under the condition that the temperature T is above 860°C, after rapid heating to temperature T, the steel sheet is cooled to 840°C by nitrogen and then soaked at 840°C for 100s.

[0109] Next, similarly to Example 1, an annealing separator was applied to the surface of the cold-rolled sheet after decarburization annealing, and then final annealing was performed to perform secondary recrystallization. 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 × 30s to produce a product sheet.

[0110] Epstein test pieces were cut 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, when the above-mentioned rapid heating end temperature T is set between 700 and 900°C, the steel sheets heated have a core loss W of 17 / 50 Reduced to below the baseline value of 0.89W / kg.

[0111] Example 5

[0112] 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 3, the balance consisting of Fe and inevitable impurities, and no inhibitor-forming components was melted to form a steel slab. Then, the steel slab was heated to 1210°C and 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-rolled plate with a final plate thickness of 0.20 mm was formed by primary cold rolling (final cold rolling) using a tandem rolling mill.

[0113] 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 at an average heating rate of 260°C / s from 400°C to 710°C, 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 after the above-mentioned decarburization annealing, and a final annealing for secondary recrystallization is performed. Then, after removing the unreacted annealing separator from the surface of the steel plate after the final annealing, 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 product plate.

[0114] Epstein test pieces were cut 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, the product sheets which were rapidly heated under the conditions of 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 the raw material and which was rapidly heated using a transverse induction heating device in the temperature raising process of decarburization annealing, all had iron loss W 17 / 50 It is below the standard value of 0.82W / kg and has excellent magnetic properties.

[0115]

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 decarburization annealing which also serves as primary recrystallization annealing, and then subjected to final annealing, The manufacturing method is characterized in that In the heating process of 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 during which the heating rate is 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 0.10 s or more and less than 1.00 s.

2. The method for manufacturing a grain-oriented electrical steel sheet according to claim 1, 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 to 0.10 mass % of C, 2.0 to 4.5 mass % of Si, 0.01 to 0.50 mass % of Mn, 0.0100 to 0.0400 mass % of Al, 0.0050 to 0.0120 mass % of N, and at least one of S and Se: 0.01 to 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.

3. The method for producing a grain-oriented electrical steel sheet according to claim 2, 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.

4. The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 3, characterized in that: The rapid heating in the decarburization annealing is performed using a lateral induction heating device.

5. 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 4, 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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