Method for manufacturing a grain-oriented electromagnetic steel sheet and induction heating apparatus

Abstract

When manufacturing a grain-oriented electrical steel sheet by hot-rolling a steel material into a hot-rolled sheet, cold-rolling the hot-rolled sheet into a cold-rolled sheet with the final sheet thickness, subjecting the cold-rolled sheet to decarburizing annealing that also serves as primary recrystallization annealing, and then performing finish annealing for secondary recrystallization, in the above decarburizing annealing, the average heating rate T (°C / s) during the temperature increase process between 500°C and 700°C is set to 250°C / s or more, and the time for reducing the heating rate to 150°C / s or less between 500°C and 700°C is varied according to the value of x / w (x: distance from the center of the sheet width (mm), w: half of the sheet width (mm)) at each position in the sheet width direction, thereby proposing a method for manufacturing a grain-oriented electrical steel sheet having uniform and excellent magnetic properties in the sheet width direction, and providing an induction heating device used for the decarburizing annealing of the above method.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet and an induction heating device used in decarburizing annealing of the manufacturing method.

Background Art

[0002] The grain-oriented electrical steel sheet is a soft magnetic material mainly used for core materials of transformers, generators, etc. Since it has a crystal structure in which the {110}<001> orientation (Goss orientation), which is the easy magnetization axis of iron, is highly aligned in the rolling direction of the steel sheet, it is a steel sheet with excellent magnetic properties of low iron loss and high magnetic flux density.

[0003] As a means for further reducing the iron loss of the grain-oriented electrical steel sheet, highly accumulating the crystal grains after secondary recrystallization annealing in the Goss orientation can be mentioned. In order to increase the degree of accumulation of the secondary recrystallized grains in the Goss orientation, a large number of Goss orientation grains should be formed in the steel sheet structure at the time after primary recrystallization, and in secondary recrystallization, a difference in grain boundary mobility should be provided so that only sharp Goss orientation grains preferentially grow, that is, it is important to optimize the aggregate structure of the steel sheet after primary recrystallization.

[0004] Examples of the primary recrystallized structure in which only sharp Goss orientation grains can preferentially grow include {111}<112> orientation grains and {411}<148> orientation grains. By presenting these in a well-balanced manner and at a high frequency in the primary recrystallized structure, the Goss orientation grains can be highly accumulated in the rolling direction in secondary recrystallization annealing.

[0005] As a method for increasing the existing ratio of Goss orientation grains in the primary recrystallized structure, for example, Patent Document 1 discloses a method of heat-treating a cold-rolled sheet during cold rolling at a low temperature to perform aging treatment. Further, Patent Document 2 discloses a method in which the cooling rate during intermediate annealing before hot-rolled sheet annealing or cold rolling (final cold rolling) to the final sheet thickness is 30°C / s or more, and further, inter-pass aging in which the steel sheet is held at a temperature of 150 to 300°C for 2 minutes or more during final cold rolling is performed two or more times. Further, Patent Document 3 discloses a technique of performing warm rolling in which the temperature of the steel sheet during cold rolling is increased for rolling.

[0006] The technologies of the above Patent Documents 1 to 3 all raise the temperature of the steel sheet to an appropriate temperature before cold rolling, during cold rolling, or between cold rolling passes to promote the diffusion of solid solution elements such as carbon (C) and nitrogen (N), fix the dislocations introduced by cold rolling, suppress the movement of dislocations in subsequent rolling, and promote shear deformation, thereby attempting to improve the rolling texture. This is based on the idea that the nuclei of Goss-oriented grains in the primary recrystallized structure appear from shear bands introduced into the worked structure having the {111}<112> orientation. By applying these technologies, it becomes possible to introduce a large number of shear bands into the {111}<112> worked structure, and a large number of Goss-oriented grains can be formed in the primary recrystallized structure.

[0007] Also, by increasing the heating rate during the heating process of decarburizing annealing, it is also possible to promote the formation of Goss-oriented grains in the primary recrystallized structure. For example, Patent Document 4 discloses a method of rapidly heating during the heating process of decarburizing annealing. This technology attempts to suppress the development of the γ-fiber texture ({111} / / ND) that is preferentially formed at a normal heating rate by heating from room temperature to near the recrystallization temperature in a short time using electric heating or induction heating, etc., and promote the generation of Goss-oriented grains that become the nuclei of secondary recrystallized grains.

[0008] Also, Patent Document 5 discloses a method of rapidly heating the temperature range between 550 and 700 °C during the heating process of decarburizing annealing at an average heating rate of 50 °C / s or more, and holding the heating rate at 10 °C / s or less for 1 to 10 s in any temperature range between 250 and 550 °C. This technology attempts to promote the recovery of the {111} worked structure and suppress recrystallization by holding for a short time in the recovery temperature range of 250 to 550 °C, and relatively increase the existence ratio of Goss-oriented grains.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

[0010] By the way, the primary recrystallized grain structure is often not uniform in the width direction of the steel sheet. The causes include non-uniform reduction ratio in the cold rolling in the width direction of the sheet due to edge drops formed in the hot rolling, inability to uniformly heat the width direction of the sheet in hot rolled sheet annealing, etc., and non-uniform crystal grain size in the width direction of the steel sheet before cold rolling. Also, when warm rolling is applied to cold rolling as in the technologies disclosed in Patent Documents 1 to 3 above, a large temperature drop occurs at the end of the steel sheet due to heat dissipation, and a difference in the diffusion distance of carbon and nitrogen occurs in the width direction of the sheet, which is also considered to be one of the reasons for the change in the grain structure.

[0011] When the primary recrystallized grain structure is different in the width direction of the sheet, the secondary recrystallization behavior will also be different in the width direction of the sheet, which causes fluctuations in the magnetic properties of the final product in the width direction of the sheet. To prevent this, trimming and removing the end of the steel sheet after hot rolling or after cold rolling, etc. can be considered, but a reduction in yield is inevitable.

[0012] The present invention has been made in view of the above problems of the prior art, and its purpose is to propose a method for manufacturing a grain-oriented electrical steel sheet having uniform and excellent magnetic properties in the width direction, and to provide an induction heating device for decarburization annealing used in the method. [Means for Solving the Problems]

[0013] In order to solve the above problems, the inventors have intensively studied a method for homogenizing the primary recrystallized structure in the plate width direction. As a result, in the final cold rolling of cold rolling, the steel plate temperature is set to 150 °C or higher and rolled for at least 1 pass or more. In the decarburization annealing that also serves as primary recrystallization annealing, when rapidly heating between 500 °C and 700 °C during the heating process, the heating rate is temporarily decreased in the middle, and the time of the decrease is changed in the plate width direction, and it has been found that the primary recrystallized structure after decarburization annealing can be made uniform in the plate width direction, and the present invention has been developed.

[0014] Based on the above findings, the present invention hot-rolls a steel material to obtain a hot-rolled sheet, subjects the hot-rolled sheet to two or more cold rollings with one cold rolling or intermediate annealing interposed therebetween to obtain a cold-rolled sheet having a final plate thickness, and after subjecting the cold-rolled sheet to decarburization annealing that also serves as primary recrystallization annealing, performs finish annealing for secondary recrystallization. In the manufacturing method of the grain-oriented electrical steel sheet, in the above decarburization annealing, the average heating rate T (°C / s) during the heating process between 500 °C and 700 °C is set to 250 °C / s or higher, and in any temperature range between 500 °C and 700 °C, the heating rate at each position in the plate width direction of the steel sheet is adjusted according to the value of x / w at each position by the following formula (1); 200 / T×0.2(1 - x / w) ≦ t ≦ 200 / T×0.8(1 - x / w) ···(1) Here, x: distance from the center of the plate width (mm), w: 1 / 2 of the plate width (mm), provided that 0 ≦ x ≦ 0.9w A manufacturing method of a grain-oriented electrical steel sheet is proposed, which is characterized in that the temperature is lowered to 150 °C / s or lower for a time t (s) that satisfies the above conditions.

[0015] The above steel material used in the manufacturing method of the grain-oriented electrical steel sheet of the present invention contains C: 0.01 to 0.10 mass%, Si: 2.0 to 4.5 mass%, Mn: 0.01 to 0.50 mass%, Al: 0.0100 to 0.0400 mass% and N: 0.0050 to 0.0120 mass%, and further contains at least one of S and Se: a total of 0.01 to 0.05 mass%, and the balance consists of Fe and unavoidable impurities.

[0016] In addition, the steel material used in the method for manufacturing the above-described grain-oriented electromagnetic steel sheet of the present invention has a component composition containing 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: less than 0.0100 mass%, and Se: less than 0.0100 mass%, with the balance being Fe and inevitable impurities.

[0017] In addition, the steel material used in the method for manufacturing the above-described grain-oriented electromagnetic steel sheet of the present invention further contains at least one component selected from Sb: 0.005 to 0.500 mass%, Cu: 0.01 to 1.50 mass%, P: 0.005 to 0.500 mass%, Cr: 0.01 to 1.50 mass%, Ni: 0.005 to 1.500 mass%, Sn: 0.01 to 0.50 mass%, Nb: 0.0005 to 0.0100 mass%, Mo: 0.01 to 0.50 mass%, B: 0.0010 to 0.0070 mass%, and Bi: 0.0005 to 0.0500 mass% in addition to the above component composition.

[0018] In addition, the method for manufacturing the above-described grain-oriented electromagnetic steel sheet of the present invention is characterized in that the rapid heating in the decarburizing annealing is performed using a transverse induction heating device.

[0019] In addition, the present invention is a transverse induction heating device used for rapid heating in the decarburizing annealing in the method for manufacturing the above-described grain-oriented electromagnetic steel sheet.

Effects of the Invention

[0020] According to the present invention, it becomes possible to stably manufacture a grain-oriented electromagnetic steel sheet having uniform and excellent magnetic properties in the sheet width direction of the steel sheet, which greatly contributes to improving the quality and yield of the product sheet.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0022] First, the experiments that led to the development of the present invention will be described. <Experiment 1> A steel slab having a component composition containing C: 0.033 mass%, Si: 3.4 mass%, Mn: 0.07 mass%, sol.Al: 0.0081 mass%, N: 0.0052 mass%, S: 0.0030 mass%, and Se: 0.0030 mass% and the balance being Fe and inevitable impurities was heated to 1220°C and then hot-rolled into a hot-rolled sheet with a thickness of 2.0 mm. Next, the above hot-rolled sheet was subjected to hot-rolled sheet annealing at 1000°C for 60 s and then cold-rolled once into a cold-rolled sheet with a final thickness of 0.20 mm. Then, a sample material was taken from the above cold-rolled sheet, and when the distance from the center of the sheet width was x (mm) (x = 0 at the center of the sheet width) and half the width of the sheet width was w (mm), a plurality of samples of the size of Epstein test pieces (30 mm × length 280 mm) were taken from five positions of x = 0, 0.2w, 0.4w, 0.6w, and 0.8w in the sheet width direction of the above sample material.

[0023] Next, each of the above samples was subjected to decarburization annealing that also served as primary recrystallization annealing with a soaking temperature of 850°C and a soaking time of 100 s. At this time, the average heating rate from 500°C to 700°C during the heating process of the decarburization annealing was set to 300°C / s. Furthermore, under some conditions, when reaching 600°C, the heating rate was decreased to 120°C / s for the time shown in Table 1. Next, after applying an annealing separation agent mainly composed of MgO to the surface of the sample after the decarburization annealing, finish annealing was performed to cause secondary recrystallization. Thereafter, an insulating coating liquid containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 was applied to the surface of the sample after the finish annealing, and heat treatment simulating flattening annealing at 800°C × 30 s was performed for baking to obtain product plate samples. Note that the average heating rate of 300°C / s from 500°C to 700°C is the average heating rate of the time excluding the time when the heating rate is decreased.

[0024] Regarding the product plate samples with the Epstein test piece size obtained as described above, the iron loss W 17 / 50 was measured in accordance with JIS Z 2550, and the difference between the maximum value and the minimum value of the iron loss values in the plate width direction was determined, and the results are shown in Table 1.

[0025]

Table 1

[0026] From Table 1, when rapidly heating between 500 and 700°C, by providing a time during which the heating rate is temporarily decreased between the above temperatures, and making the time during which the heating rate is decreased longer at the center of the plate width and shorter at the end side of the plate width, it was found that the difference between the maximum value and the minimum value of the iron loss values in the plate width direction becomes 0.04 W / kg or less, and uniform magnetic properties in the plate width direction can be obtained.

[0027] Regarding the reason why uniform magnetic properties in the plate width direction were obtained under the condition of making the time during which the heating rate is temporarily decreased longer at the center of the plate width and shorter at the end side of the plate width when rapidly heating as described above, the inventor considers as follows.

[0028] On the side of the sheet width end, the cold rolling reduction ratio is lower than that in the central part of the sheet width due to edge drop or the like during hot rolling. This means that the amount of deformation during cold rolling is small on the side of the sheet width end. Also, the temperature of the steel sheet during cold rolling is more likely to be lower due to heat dissipation on the side of the sheet width end than in the central part of the sheet width. Due to these factors, the diffusion distances of carbon and nitrogen in the steel on the side of the sheet width end become smaller, and it becomes difficult for the dislocations formed during rolling to be fixed. Therefore, in the cold rolled structure on the side of the sheet width end, the amount of introduction of the shear band, which becomes the formation site of the cube-oriented grains by primary recrystallization, is less than that in the central part of the sheet width. Therefore, on the side of the sheet width end, it is better to shorten the time for reducing the heating rate in order to promote the recrystallization of the cube-oriented grains. Conversely, in the central part of the sheet width, it is better to lengthen the time for reducing the heating rate in order to suppress the recrystallization of the cube-oriented grains. As a result, it is considered that the number of cube-oriented grains after primary recrystallization annealing is made uniform in the sheet width direction.

[0029] Next, based on the above experimental results, the inventors conducted an experiment to investigate the appropriate time for reducing the heating rate according to the position in the sheet width direction. <Experiment 2> Samples of five types of Epstein test piece sizes with different positions in the sheet width direction of the cold rolled sheet collected in Experiment 1 were subjected to decarburization annealing that also served as primary recrystallization annealing with a soaking temperature of 850°C and a soaking time of 100 s. At this time, the average heating rate from 500°C to 700°C during the heating process of the decarburization annealing was set to 300°C / s, and when reaching 650°C, the time in the sheet width direction for reducing the heating rate to 110°C / s was changed to the eight conditions shown in FIG. 1. Next, an annealing release agent mainly composed of MgO was applied to the surface of the sample after the above decarburization annealing, and finish annealing was performed to cause secondary recrystallization. Next, an insulating coating liquid containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 was applied to the surface of the sample after the above finish annealing, and heat treatment simulating flattening annealing at 800°C × 30 s was performed for baking to obtain a product sheet sample.

[0030] Regarding the product sheet samples of the Epstein test piece sizes obtained as described above, the iron loss W 17 / 50 was measured in accordance with JIS Z 2550, and the difference between the maximum value and the minimum value of the iron loss values in the sheet width direction is shown in Table 2.

[0031]

Table 2

[0032] From Table 2, the time t for reducing the temperature rise temperature at each position of x = 0, 0.2w, 0.4w, 0.6w, and 0.8w in the plate width direction is given by the following formula (1); 200 / T × 0.2(1 - x / w) ≤ t ≤ 200 / T × 0.8(1 - x / w) ···(1) Here, x: distance from the center of the plate width (mm), w: 1 / 2 of the plate width (mm), provided that 0 ≤ x ≤ 0.9w Under the condition that this is satisfied, it was found that the difference between the maximum value and the minimum value of the iron loss value in the plate width direction is 0.04 W / kg or less, and uniform magnetic properties in the plate width direction are obtained. The present invention was completed by further study based on the above new findings.

[0033] Next, the component composition that the steel material (slab) used for manufacturing the oriented electrical steel sheet of the present invention should have will be described. As the steel material used in the present invention, conventionally known ones used for manufacturing oriented electrical steel sheets can be used, but from the viewpoint of obtaining excellent magnetic properties, it is preferably one having the following component composition.

[0034] C: 0.01 to 0.10 mass% C is an element that contributes to improving the primary recrystallized grain structure by precipitating as fine carbides. However, if the C content is less than 0.01 mass%, the precipitation amount of fine carbides is insufficient, and there is a risk that the improvement effect on the above grain structure becomes insufficient. On the other hand, if it exceeds 0.10 mass%, it may be difficult to reduce it to 0.0050 mass% or less where magnetic aging does not occur during decarburization annealing. Therefore, the C content is preferably in the range of 0.01 to 0.10 mass%. More preferably, it is in the range of 0.015 to 0.08 mass%.

[0035] Si: 2.0 to 4.5 mass% Si is an element effective in increasing the specific resistance of steel and improving iron loss. However, when the Si content is less than 2.0 mass%, the above iron loss reduction effect cannot be sufficiently obtained. On the other hand, when it exceeds 4.5 mass%, the workability is significantly reduced, and it becomes difficult to manufacture by rolling. Therefore, the Si content is preferably in the range of 2.0 to 4.5 mass%. More preferably, it is in the range of 2.5 to 4.0 mass%.

[0036] Mn: 0.01 - 0.50 mass% Mn is an element necessary for improving hot workability. When the Mn content is less than 0.01 mass%, it becomes difficult to obtain the above hot workability improvement effect. On the other hand, when it exceeds 0.50 mass%, there is a risk that the primary recrystallized grain structure deteriorates and it becomes difficult to obtain secondary recrystallized grains with a high concentration of Goss orientation. Therefore, the Mn content is preferably in the range of 0.01 to 0.50 mass%. More preferably, it is in the range of 0.03 to 0.45 mass%.

[0037] Regarding the components other than the above C, Si, and Mn, it differs depending on whether an inhibitor is used for secondary recrystallization or not. Specifically, when an inhibitor is used for secondary recrystallization and AlN is used as the above inhibitor, in addition to the above-mentioned C, Si, and Mn, it is preferable to contain Al and N in the ranges of Al: 0.0100 to 0.0400 mass% and N: 0.0050 to 0.0120 mass%. When the Al content and the N content are less than the above lower limit values, it becomes difficult to obtain a predetermined inhibitor effect. On the other hand, when it exceeds the above upper limit values, the dispersion state of the precipitates becomes non-uniform, and it also becomes difficult to obtain a predetermined inhibitor effect.

[0038] Also, as inhibitors, in addition to the above AlN, sulfides (MnS, Cu 2 S, etc.) and selenides (MnSe, Cu 2When using S, Se, etc., in addition to the above-mentioned Al and N, it is preferable to contain at least one selected from S and Se in a total amount in the range of 0.0100 to 0.0500 mass%. If the total content of S and Se is less than the above lower limit value, it becomes difficult to sufficiently obtain the effect as an inhibitor. On the other hand, if it exceeds the above upper limit value, the dispersion of the precipitate becomes non-uniform, and it also becomes difficult to sufficiently obtain the inhibitor effect. Note that the above sulfide and selenide may be precipitated in combination.

[0039] On the other hand, when not using an inhibitor for secondary recrystallization, it is preferable to reduce the components forming the inhibitor as much as possible. Specifically, it is preferable that Al is less than 0.0100 mass%, N is 0.0050 mass% or less, S is less than 0.0100 mass%, and Se is less than 0.0100 mass%.

[0040] The steel material used for manufacturing the grain-oriented electrical steel sheet of the present invention has the balance other than the above basic components substantially composed of Fe and unavoidable impurities. However, for the purpose of improving magnetic properties, in addition to the above components, at least one selected from Sb: 0.005 to 0.500 mass%, Cu: 0.01 to 1.50 mass%, P: 0.005 to 0.500 mass%, Cr: 0.01 to 1.50 mass%, Ni: 0.005 to 1.500 mass%, Sn: 0.01 to 0.50 mass%, Nb: 0.0005 to 0.0100 mass%, Mo: 0.01 to 0.50 mass%, B: 0.0010 to 0.0070 mass%, and Bi: 0.0005 to 0.0500 mass% may be contained. Sb, Cu, P, Cr, Ni, Sn, Nb, Mo, B, and Bi are elements useful for improving magnetic properties, and within the above ranges, the effect of improving magnetic properties can be obtained without inhibiting the growth of secondary recrystallized grains.

[0041] Next, the manufacturing method of the grain-oriented electrical steel sheet of the present invention will be described. The steel material (slab) used in the production of the directionally electromagnetic steel sheet of the present invention is melted into steel having the above-described component composition by a generally known refining process in which secondary refining such as vacuum degassing is performed on the molten steel obtained in a converter, an electric furnace, or the like, and then it is preferably made into a steel material by a generally known continuous casting method, an ingot-blooming rolling method, or the like.

[0042] Next, the above steel material (slab) is heated to a predetermined temperature and then hot-rolled into a hot-rolled sheet. From the viewpoint of ensuring hot workability, the heating temperature of the slab is preferably about 1050°C or higher. The upper limit of the heating temperature is not particularly limited, but if it exceeds 1450°C, it becomes difficult to maintain the shape of the slab as it approaches the melting point of the steel, so it is preferably 1450°C or lower. For the hot rolling following the slab heating, generally known conditions can be applied and are not particularly limited.

[0043] Next, the above hot-rolled steel sheet (hot-rolled sheet) may be subjected to hot-rolled sheet annealing as necessary. When performing hot-rolled sheet annealing, generally known conditions can be applied and are not particularly limited.

[0044] The above hot-rolled steel sheet or the steel sheet after hot-rolled sheet annealing is descaled by pickling, mechanical methods, or the like as necessary and then cold-rolled into a cold-rolled sheet with the final plate thickness (product plate thickness). The above cold rolling may be a cold-rolled sheet with the final plate thickness in one cold rolling, or a cold-rolled sheet with the final plate thickness in two or more cold rollings with intermediate annealing in between. The above final plate thickness is preferably in the range of 0.1 mm or more and 1.0 mm or less.

[0045] Also, among the above cold rollings, the reduction ratio of the final cold rolling is preferably in the range of 60% or more and 95% or less. Here, the above final cold rolling refers to the cold rolling performed last among one or two or more cold rollings. For example, when cold rolling is performed only once, the single rolling is the final cold rolling, and when cold rolling is performed two or more times, the final rolling is the final cold rolling.

[0046] In the cold rolling described above, in order to form a large number of recrystallization nuclei of Goss-oriented grains in the primary recrystallized structure to improve magnetic properties, as described in Patent Documents 1 to 3 of the prior art, it is preferable to perform heat treatment such as inter-pass aging or to employ warm rolling.

[0047] Next, the cold-rolled sheet with the final sheet thickness is subjected to decarburization annealing that also serves as primary recrystallization annealing. Regarding the decarburization conditions (conditions during soaking) in this decarburization annealing, known conditions may be applied and there is no particular limitation. For example, it is preferable to set the conditions to 720 to 870 °C × 60 to 150 s in a wet hydrogen atmosphere. By this decarburization annealing, C contained in the steel sheet is reduced to 0.0050 mass% or less where magnetic aging does not occur.

[0048] However, in this decarburization annealing, it is important that the heating during the temperature rising process from 500 °C to 700 °C until reaching the above soaking temperature is rapid heating with an average temperature rising rate of 250 °C / s or more. Here, the average temperature rising rate between 500 and 700 °C in the present invention is the average temperature rising rate of the time excluding the time when the temperature rising rate temporarily decreases, which will be described later. If the above average temperature rising rate is less than 250 °C / s, the Goss-oriented grains after primary recrystallization will be insufficient and good iron loss cannot be obtained. The preferable average temperature rising rate is 300 °C / s or more. Note that rapid heating may be performed in a range other than the temperature range of 500 °C to 700 °C.

[0049] Also, in the temperature rising process of the above decarburization annealing, it is necessary to provide a time for temporarily reducing the temperature rising rate to 150 °C / s or less at any temperature between 500 and 700 °C where the above rapid heating is performed. If the temperature of the steel sheet at which the temperature rising rate is reduced is less than 500 °C, even if the temperature rising rate is lowered, there is no change in the recrystallization behavior of the Goss-oriented grains, and the effect of adjusting the number of Goss-oriented grains in primary recrystallization cannot be obtained. On the other hand, when it exceeds 700 °C, since recrystallization is almost complete even if the temperature rising rate is lowered, the effect of adjusting the number of Goss-oriented grains in primary recrystallization cannot be obtained either.

[0050] Furthermore, in the present invention, it is necessary to vary the time for temporarily reducing the heating rate according to the position in the plate width direction. The present invention is a technique for eliminating the difference in the steel plate structure in the plate width direction caused by various manufacturing conditions up to decarburizing annealing by varying the time for temporarily reducing the heating rate in the plate width direction during the rapid heating of decarburizing annealing, so that the recrystallization of Goss-oriented grains in primary recrystallization occurs uniformly in the plate width direction.

[0051] During the above-mentioned rapid heating, the time t for temporarily reducing the heating rate to 150 °C / s or less should be longer on the side of the center of the plate width and shorter on the side of the plate width end. Specifically, the following formula (1): 200 / T×0.2(1 - x / w) ≦ t ≦ 200 / T×0.8(1 - x / w) ···(1) Here, x: distance from the center of the plate width (mm), w: 1 / 2 of the plate width (mm), provided that 0 ≦ x ≦ 0.9w It is important to vary while satisfying this. If t is shorter than the left side of the above formula (1), the number of Goss-oriented grains in that part will be too large, and the iron loss will decrease partially. Conversely, if t is longer than the right side of the above formula (1), the recrystallization of Goss-oriented grains in that part will be suppressed, and the iron loss will increase partially. As a result, uniform magnetic properties in the plate width direction cannot be obtained. The reason for setting the plate width range satisfying the above formula (1) as (0 ≦ x ≦ 0.9w) is that when using transverse induction heating for rapid heating, the induced current concentrates and flows at the plate width end, so there is a possibility that the entire width cannot satisfy formula (1). Of course, it is preferable to satisfy the above formula (1) over the entire width.

[0052] Also, the heating rate to be temporarily reduced needs to be 150 °C / s or less. At a heating rate higher than this, the recrystallization suppression effect of Goss-oriented grains becomes insufficient. The lower limit of the heating rate to be reduced is not particularly limited, but preferably 10 °C / s or more. The above-mentioned time for temporarily reducing the heating rate can be obtained by measuring the temperature of the steel plate during the heating process with a thermocouple or the like and differentiating the time of the steel plate temperature at each time.

[0053] Here, in the heating-up process of the decarburizing annealing, the rapid heating and the decrease in the heating-up rate during the process can be achieved by arranging two or more rapid heating devices, such as an electric heating device or a solenoid-type induction heating device, in series in the plate passing direction of the steel plate, designating any section between the two or more devices as the section with a decreased heating-up rate, and appropriately adjusting the output of the rapid heating device and the plate passing speed (line speed) of the steel plate. Further, from the viewpoint of preventing heat dissipation at the plate width ends, an edge heater or the like may be provided in the section with a decreased heating-up rate.

[0054] As described above, installing two or more rapid heating devices in series has the problem of requiring a lot of cost and space. However, as a rapid heating device, for example, as schematically shown in FIG. 3, heating coils wound around the core are arranged above and below the steel plate, and the alternating magnetic flux generated in the core is passed through the thickness direction of the steel plate, and when a transverse type induction heating device that heats the steel plate by the action of the magnetic field is used, the induced current flows in the plate surface along the shape of the heating coil, and no induced current flows in the steel plate portion facing the core. Therefore, when the steel plate passes through the core portion, the heating-up rate temporarily decreases, and by utilizing this phenomenon, it is possible to lower the heating-up rate. Further, by changing the output of the induction heating device and the line speed, the time of the decrease in the heating-up rate can be adjusted. Also, since induced current flows at the plate width ends, heat dissipation at the plate width ends can also be suppressed. Moreover, since the decrease in the heating-up rate occurs within one induction heating device, there is no problem in terms of space. Therefore, the transverse type induction heating device can be preferably used in the present invention.

[0055] Also, in the above transverse type induction heating device, to change the time of the decrease in the heating-up rate in the plate width direction, the coil diameter in the plate passing direction may be made larger at the center of the plate width and gradually smaller toward the plate width ends. Further, the shape of the heating coil of the above transverse type induction heating device may be any of a circular shape, a rectangular shape, an elliptical shape, etc., but as described above, it is preferable to change the coil diameter in the plate passing direction in the plate width direction.

[0056] Next, the cold-rolled sheet that has undergone the decarburization annealing is subjected to finish annealing for secondary recrystallization after applying an annealing release agent to the steel sheet surface. As the annealing release agent, known ones can be used and are not particularly limited. For example, those with MgO as the main component and additives such as TiO 2 added as auxiliary agents, or those with SiO 2 or Al 2 O 3 as the main component, etc., can be mentioned.

[0057] The steel sheet that has undergone the above finish annealing is, after removing the unreacted annealing release agent remaining on the steel sheet surface, coated with an insulating coating liquid on the steel sheet surface, and baked by flattening annealing that also serves to correct the deteriorated steel sheet shape in the finish annealing to obtain a product sheet. Note that the formation of the insulating coating may be performed on a separate line. The type of the insulating coating is not particularly limited. However, when forming a tension-applying type insulating coating that applies tensile stress to the steel sheet surface, it is preferable to apply a slurry containing phosphate - colloidal silica disclosed in, for example, JP-A-50-79442, JP-A-48-39338, and JP-A-56-75579 and bake it at a temperature of about 800°C.

[0058] In addition, when further aiming for lower iron loss, a magnetic domain refinement treatment may be performed by a known method such as forming grooves on the steel sheet surface in any process after the cold rolling, forming a mechanically strained region on the steel sheet surface after the finish annealing, or forming a thermally strained region by irradiating a laser beam, an electron beam, etc.

Example

[0059] A steel slab having a component composition containing C: 0.035 mass%, Si: 3.3 mass%, Mn: 0.05 mass%, sol.Al: 0.0084 mass%, N: 0.0051 mass%, S: 0.0031 mass%, and Se: 0.0031 mass% with the balance being Fe and unavoidable impurities was heated to 1260°C and then hot-rolled to obtain a hot-rolled sheet with a thickness of 2.0 mm. Next, the above hot-rolled sheet was subjected to hot-rolled sheet annealing at 1000°C for 60 s and then cold-rolled once to obtain a cold-rolled sheet with a final thickness of 0.20 mm.

[0060] Next, the cold-rolled sheet was subjected to decarburization annealing that also served as primary recrystallization annealing with a soaking temperature of 850°C and a soaking time of 100 s. At this time, in the heating-up process of the decarburization annealing, as shown in Table 3, the average heating-up rate T (°C / s) between 500°C and 700°C was varied in various ways. In some steel sheets, when reaching 620°C, the following formula (2); t = 200 / T × 0.5 × (1 - x / w) ···(2) where x: distance from the center of the sheet width (mm), w: 1 / 2 of the sheet width (mm), provided that 0 ≤ x ≤ 0.9w For a time t represented by this, the heating-up rates at each position in the sheet-width direction were decreased so as to obtain the "decreased heating-up rate" shown in Table 3. Next, an annealing release agent mainly composed of MgO was applied to the surface of the steel sheet after the above decarburization annealing, and finish annealing was carried out to cause secondary recrystallization. Next, an insulating coating liquid containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 was applied to the surface of the steel sheet after the above finish annealing, and flattening annealing at 800°C × 30 s was carried out for baking to obtain a product sheet.

[0061] Thus, Epstein test pieces with a width of 30 mm and a length of 280 mm were sampled from each of the positions x = 0, 0.2w, 0.4w, 0.6w, and 0.8w (x: distance from the center of the sheet width (mm), w: 1 / 2 of the sheet width (mm)) in the sheet-width direction of the obtained product sheet, and the iron loss W 17 / 50 was measured in accordance with JIS Z 2550. The average value of the iron loss values in the sheet-width direction, and the difference between the maximum value and the minimum value were obtained, and the results were also shown in Table 3. From Table 3, it can be seen that under the condition that the average heating-up rate is 250°C / s or more and the decreased heating-up rate is 150°C / s or less, the average value of the iron loss is as low as 0.87 W / kg or less, and the iron loss difference is suppressed to 0.04 W / kg or less.

[0062]

Table 3-1

[0063]

Table 3-2

[0064]

Table 3-3

Example

[0065] A steel slab containing inhibitor-forming components, having a component composition consisting of C: 0.06 mass%, Si: 3.4 mass%, Mn: 0.06 mass%, sol.Al: 0.0250 mass%, N: 0.0090 mass%, S: 0.01 mass% and Se: 0.01 mass%, with the balance being Fe and inevitable impurities, was heated to 1400 °C and then hot-rolled to obtain a hot-rolled sheet with a thickness of 2.0 mm. Next, the above hot-rolled sheet was cold-rolled once to an intermediate thickness of 1.2 mm. Next, N 2 : 75 vol% + H 2 : 25 vol%, and after being subjected to intermediate annealing at 1100 °C for 80 s in an atmosphere with a dew point of 46 °C, it was cold-rolled a second time (final cold rolling) using a tandem rolling mill to obtain a cold-rolled sheet with a final thickness of 0.20 mm.

[0066] Next, the above cold-rolled sheet was subjected to decarburization annealing that also served as primary recrystallization annealing with a soaking temperature of 850 °C and a soaking time of 100 s. In the heating-up process of the above decarburization annealing, a transverse-type induction heating device was used, and it was rapidly heated with an average heating-up rate of 300 °C / s between 500 °C and 700 °C. At this time, when the steel plate temperature reached 650 °C during the above induction heating, the output of the induction heating device, the line speed, etc. were adjusted so that the time in the plate width direction at which the heating-up rate T became 100 °C / s would be the 6 conditions shown in Figure 2. Next, an annealing separating agent mainly composed of MgO was applied to the surface of the steel plate after decarburization annealing, and finish annealing was performed to cause secondary recrystallization. Next, an insulating coating liquid containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 was applied to the surface of the steel plate after finish annealing, and flattening annealing at 800 °C for 30 s was performed to bake it into a product sheet.

[0067] From the positions of the product plate obtained in this way at x = 0, 0.2w, 0.4w, 0.6w, and 0.8w in the plate width direction (x: distance from the center of the plate width (mm), w: 1 / 2 of the plate width (mm)), Epstein test pieces with a width of 30 mm × a length of 280 mm were sampled, and the iron loss W 17 / 50 was measured. The average value of the iron loss values in the plate width direction and the difference between the maximum value and the minimum value were obtained, and the results were also shown in Table 4. From Table 4, at all positions in the plate width direction of the steel sheet, the following formula (1); 200 / T×0.2(1 - x / w) ≦ t ≦ 200 / T×0.8(1 - x / w) ···(1) Here, x: distance from the center of the plate width (mm), w: 1 / 2 of the plate width (mm), provided that 0 ≦ x ≦ 0.9w For the steel sheet whose heating rate was decreased during rapid heating under the condition of satisfying the above, the difference between the maximum value and the minimum value of the iron loss values in the plate width direction was all 0.04 W / kg or less. Therefore, it can be seen that even when manufacturing a grain-oriented electrical steel sheet using a material containing an inhibitor-forming component, by applying the present invention, the magnetic properties in the plate width direction can be made uniform.

[0068]

Table 4

Example

[0069] A steel having a component composition containing C: 0.036 mass%, Si: 3.4 mass%, Mn: 0.06 mass%, sol.Al: 0.0072 mass%, N: 0.0050 mass%, S: 0.0031 mass%, and Se: 0.0031 mass%, and containing Sb, Cu, P, Cr, Ni, Sn, Nb, Mo, B, and Bi in the compositions shown in Table 5 as other components, with the balance being Fe and inevitable impurities and not containing an inhibitor-forming component, was melted and made into a steel slab. Next, the above steel slab was heated to 1210°C and then hot-rolled into a hot-rolled sheet with a thickness of 2.0 mm. Next, the above hot-rolled sheet was subjected to hot-rolled sheet annealing at 1000°C × 60 s, and then cold-rolled once (final cold rolling) using a tandem rolling mill into a cold-rolled sheet with a final thickness of 0.20 mm.

[0070] Subsequently, the cold-rolled sheet was subjected to decarburization annealing that also served as primary recrystallization annealing with a soaking temperature of 850°C and a soaking time of 100 s. At this time, in the heating-up process of the decarburization annealing, a transverse-type induction heating device was used in the same manner as in Example 2, and rapid heating was performed with an average heating-up rate of 300°C / s between 500°C and 700°C. The time in the plate width direction for reducing the heating-up rate to 110°C / s when the steel plate temperature reached 650°C was set to be the same as the condition of No. 1 in Fig. 2. Subsequently, after applying an annealing separating agent mainly composed of MgO to the surface of the steel plate after the decarburization annealing, finish annealing was performed to cause secondary recrystallization. Subsequently, an insulating coating liquid containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 was applied to the surface of the steel plate after the finish annealing, and flattening annealing at 800°C × 30 s was performed for baking to obtain a product plate.

[0071] Thus, Epstein test pieces with a width of 30 mm and a length of 280 mm were sampled from each position at positions x = 0, 0.2w, 0.4w, 0.6w, and 0.8w in the plate width direction of the obtained product plate (x: distance from the center of the plate width (mm), w: 1 / 2 of the plate width (mm)), and the iron loss W 17 / 50 was measured. The average value of the iron loss values in the plate width direction of the product plate, and the difference between the maximum value and the minimum value were determined, and the results are also shown in Table 5. From Table 5, it can be seen that product plates manufactured under the conditions in accordance with the method of the present invention using a slab added with at least one selected from Sb, Cu, P, Cr, Ni, Sn, Nb, Mo, B, and Bi as the steel material and using a transverse-type induction heating device in the heating-up process of the decarburization annealing all have an average value of the iron loss value in the plate width direction of 0.82 W / kg or less, and the difference between the maximum value and the minimum value of the iron loss value in the plate width direction of 0.04 W / kg or less, indicating that they are uniform in the plate width direction and have excellent magnetic properties.

[0072]

Table 5

Claims

1. A steel sheet comprising: C: 0.01-0.10 mass%, Si: 2.0-4.5 mass%, Mn: 0.01-0.50 mass%, Al: 0.0100-0.0400 mass%, and N: 0.0050-0.0120 mass%, and further comprising at least one of S and Se: 0.01-0.05 mass% in total; Optionally, at least one component selected from Sb: 0.005 to 0.500 mass%, Cu: 0.01 to 1.50 mass%, P: 0.005 to 0.500 mass%, Cr: 0.01 to 1.50 mass%, Ni: 0.005 to 1.500 mass%, Sn: 0.01 to 0.50 mass%, Nb: 0.0005 to 0.0100 mass%, Mo: 0.01 to 0.50 mass%, B: 0.0010 to 0.0070 mass%, and Bi: 0.0005 to 0.0500 mass%, A method for producing a grain-oriented electrical steel sheet, comprising the steps of hot rolling a steel material having a composition with the balance being Fe and unavoidable impurities to obtain a hot rolled sheet, cold rolling the hot rolled sheet once or cold rolling two or more times with intermediate annealing in between to obtain a cold rolled sheet of a final sheet thickness, subjecting the cold rolled sheet to decarburization annealing which also serves as primary recrystallization annealing, and then to finish annealing for secondary recrystallization, a temperature rise rate T (°C / s) between 500°C and 700°C during the heating process is set to 250°C / s or more, and the heating rate at each position in the sheet width direction of the steel sheet is reduced to 150°C / s or less for a time t (s) that satisfies the following formula (1) in accordance with the value of x / w at each position, in any temperature range between 500°C and 700°C during the heating process: Note 200 / T×0.2(1-x / w)≦t≦200 / T×0.8(1-x / w)...(1) Here, x is the distance from the center of the plate width (mm), w is 1 / 2 of the plate width (mm), where 0≦x≦0.9w

2. A steel sheet comprising: 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: less than 0.0100 mass%, and Se: less than 0.0100 mass%, Optionally, Sb: 0.005 to 0.500 mass%, Cu: 0.01 to 1.50 mass%, P: 0.005 to 0.500 mass%, Cr: 0.01 to 1.50 mass%, Ni: 0.005 to 1.500 mass%, Sn: 0.01 to 0.50 mass%, Nb: 0.0005 to 0.0100 mass%, Mo: 0.01 to 0.50 mass%, B: 0.0010 to 0.0070 mass%, and Bi: A method for producing a grain-oriented electrical steel sheet, comprising the steps of hot rolling a steel material having a composition containing at least one component selected from 0.0005 to 0.0500 mass% of an alloy containing at least one element, the balance being Fe and unavoidable impurities, to obtain a hot rolled sheet, cold rolling the hot rolled sheet once or cold rolling two or more times with intermediate annealing in between to obtain a cold rolled sheet having a final sheet thickness, subjecting the cold rolled sheet to decarburization annealing which also serves as primary recrystallization annealing, and then subjecting the cold rolled sheet to finish annealing for secondary recrystallization, In the decarburization annealing, the average heating rate T (°C / s) between 500°C and 700°C during the heating process is set to 250°C / s or more, and the heating rate at each position in the sheet width direction of the steel sheet is reduced to 150°C / s or less for a time t (s) that satisfies the following formula (1) depending on the value of x / w at each position in any temperature range between 500°C and 700°C during the heating process. A method for producing a grain-oriented electrical steel sheet comprising the steps of: Note 200 / T×0.2(1-x / w)≦t≦200 / T×0.8(1-x / w)...(1) Here, x is the distance from the center of the plate width (mm), w is 1 / 2 of the plate width (mm), where 0≦x≦0.9w

3. 3. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the rapid heating in the decarburization annealing is carried out using a transverse type induction heating device.

4. 3. A transverse type induction heating device used for rapid heating in the decarburization annealing in the method for producing grain-oriented electrical steel sheet according to claim 1 or 2.

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