Manufacturing method of grain-oriented electrical steel sheet and rolling equipment for manufacturing grain-oriented electrical steel sheet

Abstract

The present invention provides a method for manufacturing an oriented electromagnetic steel sheet with which it is possible to manufacture, in a stable manner, a low-iron-loss oriented electromagnetic steel sheet with little variation in iron loss, using a tandem rolling mill. The present invention is a method for manufacturing an oriented electromagnetic steel sheet in which a steel material is hot-rolled to produce a hot-rolled steel sheet, the hot-rolled steel sheet is cold-rolled once or twice or more interposed by intermediate annealing to produce a cold-rolled sheet having the final sheet thickness, then the cold-rolled sheet is subjected to decarburization annealing followed by secondary recrystallization annealing, wherein in the final cold rolling, a tandem rolling mill is used and the steel sheet is heated to a temperature range of 70-200°C (inclusive) and then introduced into the first pass of the tandem rolling mill, the rolling in the first pass being such that the biting temperature T(°C) and the strain rate e(s-1) satisfy relationship (1).　0.0378e2 + 0.367e + 37.2 > T [relationship 1]

Description

[Technical field]

[0001] The present invention relates to a method for producing grain-oriented electrical steel sheet and rolling equipment for producing grain-oriented electrical steel sheet used in this method. [Background technology]

[0002] Grain-oriented electrical steel is a soft magnetic material used as the core material for transformers and generators. It has an easy magnetization axis of iron, {110} <001> This steel sheet has excellent magnetic properties and a crystal structure in which the orientation (Goss orientation) is highly aligned in the rolling direction of the steel sheet.

[0003] As a method for increasing the concentration in the Goss orientation, for example, Patent Document 1 discloses a method in which a cold-rolled sheet is heat-treated at a low temperature during cold rolling and then aged. Patent Document 2 discloses a technique in which the cooling rate during hot-rolled sheet annealing or intermediate annealing before final cold rolling is set to 30°C / s or more, and interpass aging for 2 minutes or more is performed at a sheet temperature of 150 to 300°C at least twice during final cold rolling. Patent Document 3 discloses a technique that utilizes dynamic strain aging in which dislocations introduced during rolling are immediately fixed with C or N by warm rolling at a high steel sheet temperature during rolling.

[0004] The techniques described in Patent Documents 1 to 3 all aim to improve the rolling texture by maintaining the steel sheet temperature at an appropriate temperature before cold rolling, during rolling, or between rolling passes, thereby diffusing solute elements carbon (C) and nitrogen (N) at low temperatures, fixing dislocations introduced by cold rolling, preventing dislocation movement in subsequent rolling, and inducing more shear deformation. By applying these techniques, many Goss orientation seed crystals are formed at the time of the primary recrystallized sheet. The grain growth of these Goss orientation seed crystals during secondary recrystallization can increase the concentration of Goss orientation after secondary recrystallization.

[0005] Patent Document 4 discloses a technique for further enhancing the effect of the above-mentioned strain aging, in which fine carbides are precipitated in steel in an annealing process immediately prior to the final cold rolling in the cold rolling process, and the final rolling is divided into a first half and a second half, with the first half being rolled at a low temperature of 140°C or lower with a reduction ratio of 30-75%, and the second half being rolled at least two reduction passes at a high temperature of 150-300°C with a total reduction ratio of 80-95% for the first and second half. Patent Document 5 also discloses a technique for obtaining a material highly concentrated in the Goss orientation in a stable manner, by applying a 0.5 kg / mm 2 A technique is disclosed in which fine carbides are precipitated in steel by carrying out a heat treatment at 50 to 150° C. for 30 seconds to 30 minutes while applying the above tension. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 50-016610 [Patent Document 2] Japanese Patent Application Publication No. 08-253816 [Patent Document 3] Japanese Patent Application Publication No. 01-215925 [Patent Document 4] Japanese Patent Application Publication No. 09-157745 [Patent Document 5] Japanese Patent Application Publication No. 04-120216 Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, the demand for low-core-loss grain-oriented electrical steel sheets has been increasing due to societal demand for energy conservation, and there is a need to develop technology for the stable mass production of low-core-loss grain-oriented electrical steel sheets.

[0008] Tandem rolling mills have a larger throughput per hour than reverse mills such as Sendzimir mills, and are therefore advantageous for mass production of grain-oriented electrical steel sheets. The techniques of interpass aging during rolling disclosed in Patent Documents 1 and 2 cannot achieve the desired effect when the distance between passes is short and the line speed is fast, as in tandem rolling. Furthermore, the method of heating and rolling at the entry side of the tandem rolling mill disclosed in Patent Document 3 was insufficient in terms of iron loss improvement. The reasons for this are as follows. Primary recrystallized Goss orientation grains are oriented in the {111} <112> It is believed that they nucleate from shear bands introduced into the matrix structure. {111} <112> Since the matrix structure develops by cold rolling at low temperatures, the method of heating and rolling at the inlet side of the tandem rolling mill does not produce {111} <112> It is believed that the matrix structure could not be sufficiently developed, resulting in an insufficient amount of primary recrystallized Goss-oriented grains.

[0009] In addition, in the technology described in Patent Documents 4 and 5 in which carbide precipitation treatment is performed in the annealing process before final cold rolling, the carbides coarsen over the time that elapses between the precipitation treatment and final cold rolling, and the texture changes with time fluctuation, resulting in a problem of large variation in iron loss in the product coil.

[0010] Therefore, an object of the present invention is to provide a method for producing grain-oriented electrical steel sheet which solves the problems of the above-mentioned conventional techniques and enables grain-oriented electrical steel sheet with low iron loss and little variation in iron loss to be stably produced using a tandem rolling mill, and rolling equipment used in this method. [Means for solving the problem]

[0011] In order to solve the above problems, the inventors have conducted extensive research into a method for performing heat treatment before cold rolling in a series of processes for manufacturing grain-oriented electrical steel sheets. The experimental results that led to the present invention are described below.

[0012] A steel slab containing, by mass%, 0.037% C, 3.4% Si, and 0.05% Mn, 31 ppm S and 31 ppm Se, 50 ppm N, and 85 ppm sol.Al, with the balance being Fe and unavoidable impurities, was heated to 1210°C and then hot-rolled to obtain a hot-rolled sheet having a thickness of 2.0 mm. The hot-rolled sheet was subjected to hot-rolled sheet annealing at 1000°C for 60 seconds, and then cooled from 800°C to 350°C at 20°C / s, and then wound into a coil. The obtained hot-rolled annealed sheet was tandem-rolled to a cold-rolled sheet having a thickness of 0.20 mm by one tandem rolling using a tandem rolling mill (roll diameter 300 mm, number of stands 5).

[0013] At that time, the hot-rolled annealed sheet was heated to various temperatures between 50°C and 250°C as shown in Table 1 by a heating device installed between the payoff reel of the rolling mill and the rolling stand of the first pass. After heating, the sheet was heated at a strain rate of 25 s -1 The roll speed was adjusted so that the coil speed was 100 rpm, and two types of coils were produced: one in which the steel sheet was inserted into the rolling stand for the first pass at that temperature, and one in which the steel sheet was cooled to room temperature (25°C) before being inserted. A coil was also produced in which the steel sheet was inserted into the rolling stand for the first pass at room temperature without being heated.

[0014] The cold-rolled sheet was then subjected to primary recrystallization annealing, which also served as decarburization annealing, with a soaking temperature of 840°C and a soaking time of 100 seconds, after which an annealing separator mainly composed of MgO was applied to the steel sheet surface, and then finish annealing was performed to cause secondary recrystallization. A coating solution containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 was applied to the steel sheet surface after the finish annealing, and planarization annealing was performed at 800°C for 30 seconds to produce a product coil.

[0015] The iron loss of 10 coils manufactured under the same conditions was measured for each product coil, and the average value and standard deviation were calculated. The iron loss was measured by cutting a sample from the longitudinal center of the coil so that the total weight was 500g or more and performing an Epstein test. The results of this iron loss measurement are shown in Table 1 together with the heating temperature and the first pass clamping temperature mentioned above.

[0016] [Table 1]

[0017] From Table 1, it can be seen that when the steel sheet is heated to a temperature range of 70°C to 200°C before being unloaded from the pay-off reel during cold rolling and bitten into the first pass (when heating to 200°C, when the first pass biting temperature is 25°C), the variation in iron loss is small. Furthermore, it can be seen that when the steel sheet is heated to a temperature range of 70°C to 200°C and then the biting temperature when bitten into the first pass is set to a low temperature (25°C), even lower iron loss is achieved.

[0018] Although the mechanism by which the iron loss was reduced and the variation in iron loss was improved in the above experiment is unclear, the inventors believe it to be as follows. The mechanism by which the variation in iron loss was improved is thought to be that by heating the steel sheet after it is removed from the payoff reel during cold rolling and before it is engaged in the first pass, the time from heating to being engaged in the first pass is constant, and the change over time of fine carbides precipitated by heating is suppressed. In addition, the mechanism by which low iron loss occurs when the steel sheet temperature is lowered after heating and before being engaged in the first pass is thought to be as follows. The primary recrystallized Goss orientation grains are one of the stable rolling orientations, {111} <112> It is believed that they nucleate from shear bands induced within the matrix structure.

[0019] Therefore, as in the above experiment, by heating the steel plate to cause fine carbide precipitation and keeping the temperature at the time of biting low, the {111} <112> It is believed that while creating a matrix structure, the fine carbides promote the local formation of shear bands, effectively increasing the number of Goss-oriented grains.

[0020] In addition, the inventors have also investigated the relationship between the bite temperature in the first pass of final cold rolling and the strain rate in the first pass. The details of the experiment are described below. That is, the hot-rolled sheet produced in the above experiment was subjected to hot-rolled sheet annealing at 1000°C for 60 seconds, then cooled from 800°C to 350°C at 20°C / s, and then wound into a coil. The obtained hot-rolled annealed sheet was made into a cold-rolled sheet with a thickness of 0.20 mm by one tandem rolling using a tandem rolling mill (roll diameter 300 mm, number of stands 5). At that time, the steel sheet was heated to 100°C by a heating device installed between the payoff reel of the rolling mill and the rolling stand of the first pass. Thereafter, the biting temperature was changed variously from 20°C to 180°C, and the strain rate in the first tandem pass was changed from 0 to 50 s. -1 In addition, a coil was also made in which the steel sheet was not heated but was still at room temperature when it was inserted in the first pass.

[0021] The cold-rolled sheet was then subjected to primary recrystallization annealing, which also served as decarburization annealing, with a soaking temperature of 840°C and a soaking time of 100 seconds, after which an annealing separator mainly composed of MgO was applied to the steel sheet surface, and then finish annealing was performed to cause secondary recrystallization. A coating solution containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 was applied to the steel sheet surface after the finish annealing, and planarization annealing was performed at 800°C for 30 seconds to produce a product coil.

[0022] The iron loss of 10 coils manufactured under the same conditions was measured for each product coil, and the average value and standard deviation were calculated. The iron loss was measured by cutting a sample from the longitudinal center of the coil so that the total weight was 500g or more and performing an Epstein test. The iron loss measurement results were compared with the above-mentioned bite temperature T (℃) and strain rate e (s -1 ) are shown in Figure 1. The average iron loss value is 0.9 W / kg or less and the standard deviation is 0.05 W / kg or less, and the rest are shown as "○", and "×".

[0023] From Figure 1, the strain rate e(s -1 ) and the first pass bite temperature T (℃) is calculated using the following formula: 0.0378e 2 +0.367e+37.2>T When the above condition was satisfied, the iron loss was low and the variation in iron loss between coils was small. Based on these findings, further investigations were carried out and the present invention was completed.

[0024] That is, the gist of the present invention is as follows. [1] A method for producing a grain-oriented electrical steel sheet, comprising the steps of hot rolling a steel material to obtain a hot-rolled steel sheet, cold rolling the hot-rolled steel sheet once or twice or more times with intermediate annealing to obtain a cold-rolled sheet having a final thickness, and then subjecting the cold-rolled sheet to decarburization annealing and then secondary recrystallization annealing, When the cold rolling is defined as the final cold rolling in the case of the one or two or more cold rollings, and the final cold rolling in the case of the two or more cold rollings, The final cold rolling is performed by heating the steel sheet to a temperature range of 70°C to 200°C using a tandem rolling mill, and then introducing it into the first pass of the tandem rolling mill. The first pass of rolling is performed at a bite temperature T (°C) and a strain rate e (s -1 ) satisfies the following formula (1). 0.0378e 2 +0.367e+37.2>T (1)

[0025] [2] The method for producing a grain-oriented electrical steel sheet according to [1], wherein the decarburization annealing is performed by heating to a temperature range of 400° C. to 700° C. at a heating rate of 200° C. / s or more.

[0026] [3] The steel material comprises, in mass%, C: 0.01 to 0.10%, Si: 2.0-4.5%, Mn: 0.01 to 0.50%, Al: 0.0100~0.0400%, S and / or Se: 0.01 to 0.05% in total, and N: 0.0050~0.0120% and the remainder being Fe and unavoidable impurities.

[0027] [4] The steel material comprises, in mass%, C: 0.01 to 0.10%, Si: 2.0-4.5%, Mn: 0.01 to 0.50%, Al: less than 0.0100%, S: 0.0070% or less, Se: 0.0070% or less and N: 0.0050% or less and the remainder being Fe and unavoidable impurities.

[0028] [5] The steel material further comprises, in mass%, Sb: 0.005 to 0.500%, Cu: 0.01-1.50%, P: 0.005-0.500%, Cr: 0.01 to 1.50%, Ni: 0.005 to 1.500%, Sn: 0.01 to 0.50%, Nb: 0.0005~0.0100%, Mo: 0.01 to 0.50%, B: 0.0010~0.0070% and Bi: 0.0005 to 0.0500% The method for producing a grain-oriented electrical steel sheet according to the above [3] or [4], comprising one or more selected from the group consisting of:

[0029] [6] A rolling facility for producing grain-oriented electrical steel sheet, comprising: a tandem rolling mill arranged on a production line for grain-oriented electrical steel sheet; and a heating device and a cooling device arranged in this order from the upstream side of the production line at the entry side of a first stand of the tandem rolling mill.

[0030] [7] The rolling equipment for manufacturing grain-oriented electrical steel sheet described in [6] above, wherein the heating device has a function of spraying a high-temperature liquid onto the steel sheet on the production line, and the cooling device has a function of spraying a low-temperature liquid onto the steel sheet on the production line. Effect of the Invention

[0031] According to the present invention, grain-oriented electrical steel sheet having excellent magnetic properties and little variation in iron loss between coils can be stably produced using a tandem rolling mill. [Brief description of the drawings]

[0032] [Figure 1] 1 is a graph showing the results of iron loss measurement, arranged in relation to bite temperature T (° C.) and strain rate e (s−1). [Diagram 2] 1 is a graph showing the results of iron loss measurement, arranged in relation to bite temperature T (° C.) and strain rate e (s−1).

[0033] The present invention will be described in detail below. <Steel material> In the manufacturing method of the present invention, the steel material may be a slab, bloom or billet. For example, the steel slab may be one manufactured by a known manufacturing method. Examples of manufacturing methods for the steel material include steelmaking-continuous casting and ingot making-bloom rolling. In steelmaking, molten steel obtained in a converter or electric furnace can be refined to a desired composition through secondary refining such as vacuum degassing.

[0034] The composition of the steel material may be a composition for producing grain-oriented electrical steel sheets, and may be a known composition for grain-oriented electrical steel sheets. From the viewpoint of producing grain-oriented electrical steel sheets having excellent magnetic properties, it is preferable for the steel material to contain C, Si, and Mn. Suitable contents of C, Si, and Mn include the following. Here, the "%" indication regarding the composition means "% by mass" unless otherwise specified.

[0035] C: 0.01 to 0.10% C is an element that contributes to improving the primary recrystallization texture by precipitating fine carbides. If it exceeds 0.10%, it may be difficult to reduce the carbon content to 0.0050% or less at which magnetic aging does not occur by decarburization annealing. On the other hand, if it is less than 0.01%, the amount of precipitated fine carbides may be insufficient, and the texture improving effect may be insufficient. Therefore, the C content is preferably 0.01 to 0.10%, and more preferably 0.01 to 0.08%.

[0036] Silicon: 2.0 to 4.5% Silicon is an element effective in increasing the electrical resistance of steel and improving iron loss. If the silicon content exceeds 4.5%, the workability is significantly reduced, and it may be difficult to manufacture the steel by rolling. On the other hand, if the silicon content is less than 2.0%, it may be difficult to obtain a sufficient iron loss reduction effect. Therefore, the silicon content is preferably 2.0 to 4.5%, and more preferably 2.5 to 4.5%.

[0037] Mn: 0.01 to 0.50% Mn is an element necessary for improving hot workability. If the Mn content exceeds 0.50%, the primary recrystallized texture may deteriorate, and it may be difficult to obtain secondary recrystallized grains in which the Goss orientation is highly accumulated. On the other hand, if the Mn content is less than 0.01%, it may be difficult to obtain sufficient hot rolling workability. Therefore, the Mn content is preferably 0.01 to 0.50%, and more preferably 0.03 to 0.50%.

[0038] The steel material may contain, in addition to the above-mentioned C, Si, and Mn, Al: 0.0100-0.0400% and N: 0.0050-0.0120% as inhibitor components in secondary recrystallization. That is, if the Al content and N content are below the above lower limits, it may be difficult to obtain the desired inhibitor effect. On the other hand, if they exceed the above upper limits, the dispersion state of the precipitates may become non-uniform, and it may also be difficult to obtain the desired inhibitor effect.

[0039] Furthermore, in addition to Al and N, one or both of S and Se may be contained in a total amount of 0.01 to 0.05% as inhibitor components. By containing these, sulfides (MnS, Cu 2 S, etc.), selenides (MnSe, Cu 2 In addition, sulfides and selenides (e.g., Se) can be formed. Sulfides and selenides may be precipitated in combination. If the S content and Se content are below the lower limit, it may be difficult to obtain a sufficient inhibitor effect. On the other hand, if they exceed the upper limit, the dispersion of the precipitates becomes non-uniform, and it may also be difficult to obtain a sufficient inhibitor effect.

[0040] In addition, the Al content of the composition can be suppressed to less than 0.0100% to be suitable for an inhibitor-less system. In this case, the N content can be 0.0050% or less, the S content can be 0.0070% or less, and the Se content can be 0.0070% or less.

[0041] Furthermore, in order to improve the magnetic properties, in addition to the above-mentioned composition, one or more selected from the group consisting of Sb: 0.005-0.500%, Cu: 0.01-1.50%, P: 0.005-0.500%, Cr: 0.01-1.50%, Ni: 0.005-1.500%, Sn: 0.01-0.50%, Nb: 0.0005-0.0100%, Mo: 0.01-0.50%, B: 0.0010-0.0070%, and Bi: 0.0005-0.0500% may be contained. Sb, Cu, P, Cr, Ni, Sn, Nb, Mo, B, and Bi are elements useful for improving the magnetic properties, and since the magnetic properties improving effect can be sufficiently obtained without inhibiting the development of secondary recrystallized grains, it is preferable to make them within the above ranges when they are contained. The remainder of the composition of the steel material other than the above-mentioned components is Fe and unavoidable impurities.

[0042] <Manufacturing process> In the manufacturing method of the present invention, for example, a steel slab is hot-rolled to obtain a hot-rolled sheet. The steel slab can be heated before being subjected to hot rolling. The heating temperature at that time is preferably about 1050°C or higher from the viewpoint of ensuring hot rolling properties. There is no particular upper limit to the heating temperature, but a temperature above 1450°C is close to the melting point of steel and it is difficult to maintain the shape of the slab, so it is preferably 1450°C or lower. Other hot rolling conditions are not particularly limited, and known conditions can be applied.

[0043] In addition, when the above-mentioned cold rolling is performed twice or more, the hot-rolled sheet may be subjected to hot-rolled sheet annealing as necessary. At that time, the annealing conditions are not particularly limited, and known conditions may be applied as necessary. After the hot-rolled sheet annealing is performed as necessary, descaling may be performed by pickling or the like before cold rolling.

[0044] In the cold rolling process, a cold-rolled sheet of the final thickness may be obtained by one cold rolling, or two or more cold rollings with intermediate annealing may be performed to obtain a cold-rolled sheet of the final thickness. The total reduction of the cold rolling is not particularly limited and may be 70% or more and 95% or less. In the present invention, the final cold rolling needs to be controlled as described below. The reduction of the final cold rolling is not particularly limited and may be 60% or more and 95% or less. The final thickness is not particularly limited and may be, for example, 0.1 mm or more and 1.0 mm or less.

[0045] Here, the term "final cold rolling" refers to the cold rolling that is performed last among the one or more cold rollings. For example, in the case of a one-step method in which cold rolling is performed only once, the one cold rolling is the final cold rolling. In the case of a two-step method in which cold rolling is performed twice, the second cold rolling is the final cold rolling. Similarly, in the case of performing cold rolling three or more times, the last cold rolling is the final cold rolling.

[0046] Final cold rolling is performed in a tandem rolling mill. When the steel sheet is taken off the payoff reel and introduced to the first pass of final cold rolling, the steel sheet is heated to 70°C or higher and 200°C or lower before being inserted into the first pass. The rolling in the first pass is performed at a strain rate e(s-1 ) and biting temperature T (°C) must satisfy the following formula (1). 0.0378e 2 +0.367e+37.2>T (1)

[0047] First, the heating temperature of the steel sheet for the final cold rolling is 70°C or more and 200°C or less. That is, if the heating temperature is less than 70°C, fine carbides do not precipitate sufficiently, while if it exceeds 200°C, the diffusion speed of carbon becomes too high and coarse carbides precipitate, so that the effect of improving the texture by strain aging is lost and the magnetic property deteriorates. The heating temperature is preferably 100°C or more and 170°C or less.

[0048] Furthermore, the rolling in the first pass is performed at a strain rate of e(s -1 It is essential that the rolling temperature T (℃) and the biting temperature T satisfy the above formula (1). In other words, by the rolling in the first pass satisfying the above formula (1), rolling at a low temperature or a high strain rate is realized, and as a result, the rolling stable orientation {111} <112> The matrix structure can be created. Under rolling conditions that do not satisfy the above formula (1), the {111} <112> The matrix structure cannot be sufficiently developed, and the effect of improving the texture is lost.

[0049] Here, the bite temperature T (unit: °C) in the above formula (1) is the temperature of the steel sheet just before it is bitten into the rolling mill, and can be obtained by measuring with a contact thermometer or a radiation thermometer. Also, the strain rate e (unit: s -1 ) is the amount of change in nominal strain with time during rolling, and can be simply calculated by the following formula.

number

[0050] The method for heating the steel sheet before final cold rolling is not particularly limited, and examples thereof include air bath, oil bath, sand bath, induction heating, and injection of heated lubricating oil or hot water onto the steel sheet, but since the heating is performed on the entry side of the tandem rolling mill, a method capable of heating in a short time is preferable. The heating temperature is the steel sheet temperature on the exit side of the heating device.

[0051] The cooling method after heating before final cold rolling is not particularly limited, and examples include spraying with coolant, cooling rolls, and oil baths. Since cooling is performed on the entry side of the tandem rolling mill, cooling in a short period of time is required.

[0052] In order to carry out the above-mentioned cold rolling, the tandem rolling mill used in the present invention must be equipped with a heating device on the inlet side of the first stand and a cooling device on the outlet side of the heating device. The heating type of the heating device is not particularly limited, but it is preferable to spray heated lubricating oil or hot water, which is a high-temperature liquid, onto the steel sheet, since this is easy to implement. Similarly, the cooling device is not particularly limited, but it is preferable to spray a coolant liquid, which is a low-temperature liquid, since this is easy to implement.

[0053] Although a heat treatment such as aging treatment or warm rolling may be inserted during cold rolling, the method described in the above-mentioned Patent Document 4, in which the final rolling is divided into two parts, a first half and a second half, and the first half is rolled at a low temperature and the second half is rolled at a high temperature, is preferable. This is because the primary recrystallized Goss orientation grains are in the {111} <112> It is believed that they nucleate from shear bands introduced into the matrix structure. {111} <112> Since the matrix structure develops by cold rolling at low temperatures, the {111} <112> By creating a large amount of matrix structure and then rolling at high temperature, Goss orientation recrystallization nuclei can be efficiently created.

[0054] In the method for producing a grain-oriented electrical steel sheet of the present invention, the cold-rolled sheet finished to the final thickness as described above is subjected to decarburization annealing and then secondary recrystallization annealing to obtain a grain-oriented electrical steel sheet (product sheet). After secondary recrystallization annealing, an insulating coating may be formed.

[0055] The conditions of the decarburization annealing are not particularly limited. In general, decarburization annealing often doubles as primary recrystallization annealing, and can also double as primary recrystallization annealing in the manufacturing method of the present invention. In this case, by heating at a temperature increase rate of 200°C / s or more between 400°C and 700°C in the temperature increase process, the Goss orientation grains formed in the final cold rolling process are efficiently recrystallized, so that the texture improvement effect of the present invention can be further enhanced. Other conditions are not particularly limited, and known conditions can be applied. For example, annealing conditions of 800°C x 2 minutes in a warm hydrogen atmosphere can be mentioned.

[0056] After the cold-rolled steel sheet is subjected to decarburization annealing, it is subjected to finish annealing for secondary recrystallization. Before the finish annealing, an annealing separator can be applied to the surface of the steel sheet. The annealing separator is not particularly limited, and a known one can be used. For example, a quenching separator containing MgO as the main component and TiO as necessary can be used. 2 Addition of SiO 2 Or Al 2 O 3 The main components include:

[0057] After the finish annealing, it is preferable to apply an insulating coating to the surface of the steel sheet, bake it, and, if necessary, perform planarization annealing to adjust the shape of the steel sheet. The type of insulating coating is not particularly limited, and when forming an insulating coating that imparts tensile tension to the surface of the steel sheet, it is preferable to use a coating liquid containing phosphate-colloidal silica as described in JP-A-50-79442, JP-A-48-39338, JP-A-56-75579, etc., and bake it at about 800°C. Example 1

[0058] A steel slab containing, by mass%, C: 0.037%, Si: 3.4%, and Mn: 0.05%, and further containing, by mass ppm, S and Se: 31 ppm each, N: 50 ppm, sol. Al: 85 ppm, with the balance being Fe and unavoidable impurities, was heated to 1210°C and then hot-rolled to form a hot-rolled sheet with a thickness of 2.0 mm.

[0059] The hot-rolled sheet was subjected to hot-rolled sheet annealing at 1000°C for 60 seconds, then cooled from 800°C to 350°C at 20°C / s, and then wound into a coil. The obtained hot-rolled annealed sheet was tandem-rolled once using a tandem rolling mill (roll diameter 300 mm, number of stands 5) to produce a cold-rolled sheet with a thickness of 0.20 mm. At that time, the sheet was inserted into the rolling stand for the first pass at the heating temperature, strain rate, and first pass biting temperature shown in Table 2. The heating temperature, strain rate, and first pass biting temperature were all within the range of the present invention.

[0060] The cold-rolled steel sheets were then subjected to primary recrystallization annealing, which also served as decarburization annealing, with a soaking temperature of 840°C and a soaking time of 100 seconds. During the temperature rise process of the primary recrystallization annealing, the temperature rise rates in the temperature range of 400°C to 700°C were either 50°C / s or 300°C / s. An annealing separator mainly composed of MgO was then applied to the surface of the steel sheet, which was then subjected to finish annealing to cause secondary recrystallization.

[0061] A coating solution containing phosphate-chromate-colloidal silica in a weight ratio of 3:1:2 was applied to the steel sheet surface after the secondary recrystallization annealing, and the steel sheet was subjected to flattening annealing at 800°C for 30 seconds to obtain a product coil.

[0062] The iron loss of 10 coils manufactured under the same conditions was measured for the product coil, and the average value and standard deviation were calculated. The iron loss was measured by cutting a sample from the longitudinal center of the coil so that the total weight was 500g or more and performing an Epstein test. The results of this iron loss measurement are shown in Table 2 together with the heating temperature, strain rate, and first pass bite temperature mentioned above.

[0063] [Table 2]

[0064] From Table 2, it can be seen that when the heating rate for decarburization annealing is set to 300°C / s, the core loss is further reduced. Example 2

[0065] A steel slab containing, by mass%, 0.06% C, 3.4% Si, and 0.06% Mn, 90 ppm N, 250 ppm sol. Al, 0.02% S and 0.02% Se each, and the remainder being Fe and unavoidable impurities, was heated to 1400°C and then hot rolled to form a hot-rolled sheet having a thickness of 2.0 mm.

[0066] The hot-rolled sheet was subjected to hot-rolled sheet annealing at 1000°C for 60 seconds, then cooled from 800°C to 350°C at 10°C / s, and then wound into a coil. The obtained hot-rolled sheet was subjected to a first cold rolling in a tandem rolling mill (roll diameter 300 mm, number of stands 5), and then N 2 75vol%+H 2 The steel sheet was subjected to intermediate annealing at 1100°C for 80 seconds in an atmosphere with a 25 vol% Cr content and a dew point of 46°C, and then cooled at a cooling rate of 25°C / s during the cooling process from 800°C to 350°C. Next, the final cold rolling was performed in a tandem rolling mill (roll diameter 300 mm, number of stands 5) to obtain a cold-rolled sheet with a thickness of 0.20 mm. During the final cold rolling, the steel sheet was heated to the temperature shown in Table 3 by a steel sheet heating equipment installed between the payoff reel of the rolling mill and the first pass rolling stand, and after heating, the steel sheet was inserted into the first pass rolling stand at the first pass biting temperature shown in Table 3, and rolled at the strain rate shown in Table 3. In addition, a steel sheet was also produced that was inserted into the first pass rolling stand at various strain rates and first pass biting temperatures shown in Figure 2 at a heating temperature of 100°C.

[0067] The cold-rolled sheet was then subjected to primary recrystallization annealing, which also served as decarburization annealing, with a soaking temperature of 840°C and a soaking time of 100 seconds, after which an annealing separator mainly composed of MgO was applied to the steel sheet surface, and then finish annealing was performed to cause secondary recrystallization. A coating solution containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 was applied to the steel sheet surface after the secondary recrystallization annealing, and flattening annealing was performed at 800°C for 30 seconds to produce a product coil.

[0068] For the product coils, the iron loss of 10 coils manufactured under the same conditions was measured, and the average value and standard deviation were calculated. The iron loss was measured by cutting a sample from the longitudinal center of the coil so that the total weight was 500g or more, and carrying out an Epstein test. The iron loss measurement results are shown in Table 3 together with the heating temperature, strain rate, and first pass bite temperature mentioned above. The iron loss measurement results are also shown in Table 3 as a function of the bite temperature T (℃) and strain rate e (s -1 The results of sorting the relationship between the average iron loss and the standard deviation are shown in Figure 2. The average iron loss value is 0.9 W / kg or less and the standard deviation is 0.05 W / kg or less, and is shown as "◯" (examples of the invention), while the rest are shown as "×" (comparative examples).

[0069] [Table 3]

[0070] As shown in Table 3, when a steel slab containing a large amount of inhibitor is used and intermediate annealing is performed in the cold rolling process, if the final cold rolling is performed under specified conditions, the iron loss is good and the variation is small. Also, from Figure 2, it can be seen that by satisfying the above formula (1), the average iron loss is 0.9 W / kg or less and the standard deviation is 0.05 W / kg or less. Example 3

[0071] A steel containing, by mass%, 0.036% C, 3.4% Si, and 0.06% Mn, and, by mass ppm, 50 ppm N, 72 ppm sol. Al, 31 ppm S, and 31 ppm Se each, and other added elements, Sb, Cu, P, Cr, Ni, Sn, Nb, Mo, B, and Bi, in the composition shown in Table 4, with the balance being Fe and unavoidable impurities, was melted and formed into a steel slab, which was heated to 1210°C and then hot-rolled to a hot-rolled sheet having a thickness of 2.0 mm.

[0072] The hot-rolled sheet was annealed at 1000°C for 60 seconds, then cooled from 800°C to 350°C at 20°C / s, and wound into a coil. The obtained hot-rolled annealed sheet was rolled in a tandem rolling mill (roll diameter 300 mm, number of stands 5) once to produce a cold-rolled sheet with a thickness of 0.20 mm. During the final cold rolling, the steel sheet was heated to 100°C by a steel sheet heating device installed between the payoff reel of the rolling mill and the rolling stand of the first pass, cooled to 25°C after heating, and rolled at a strain rate of 25 s. -1 Then, it was inserted into the rolling stand for the first pass.

[0073] Thereafter, the cold-rolled sheet was subjected to primary recrystallization annealing, which also served as decarburization annealing, with a soaking temperature of 840°C and a soaking time of 100 seconds. Then, an annealing separator mainly composed of MgO was applied to the surface of the steel sheet, and then the steel sheet was subjected to finish annealing to cause secondary recrystallization.

[0074] A coating solution 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-mentioned finish annealing, and flattening annealing was performed at 800°C for 30 seconds to obtain a product coil. The iron loss of 10 product coils manufactured under the same conditions was measured to determine the average value and standard deviation. The iron loss was measured by cutting a sample from the longitudinal center of the coil so that the total weight was 500g or more and performing an Epstein test. The results of this iron loss measurement are shown in Table 4 together with the composition of the above-mentioned added components.

[0075] [Table 4]

[0076] As shown in Table 4, steel sheets containing one or more of Sb, Cu, P, Cr, Ni, Sn, Nb, Mo, B, and Bi had reduced iron loss to 0.80 W / kg or less, and also had small variation in properties along the length of the coil.

Claims

1. In mass percent, C: 0.01 to 0.10%, Si: 2.0 to 4.5%, Mn: 0.01 to 0.50%, Al: 0.0100-0.0400%, S and Se: 0.01 to 0.05% in total, and N: 0.0050-0.0120% A method for producing a grain-oriented electrical steel sheet, comprising the steps of hot rolling a steel material having a composition containing 0.1% by mass and the balance being Fe and unavoidable impurities, cold rolling the hot rolled steel sheet once or at least two times with intermediate annealing therebetween to produce a cold rolled sheet having a final sheet thickness, and then subjecting the cold rolled sheet to decarburization annealing and then secondary recrystallization annealing, When the cold rolling is defined as the final cold rolling in the case of the one or two or more cold rollings, and the final cold rolling in the case of the two or more cold rollings, The final cold rolling is performed by heating the steel sheet to a temperature range of 70° C. or more and 200° C. or less using a tandem rolling mill, and then introducing the steel sheet into the first pass of the tandem rolling mill. The first pass of rolling is performed at a bite temperature T (° C.) and a strain rate e (s －１ ) satisfies the following formula (1). 0.0378e ２ +0.367e+37.2>T ・・・・(1)

2. In mass percent, C: 0.01 to 0.10%, Si: 2.0 to 4.5%, Mn: 0.01 to 0.50%, Al: less than 0.0100%, S: 0.0070% or less, Se: 0.0070% or less; N: 0.0050% or less and the balance being Fe and unavoidable impurities, is hot-rolled to obtain a hot-rolled steel sheet, the hot-rolled steel sheet is cold-rolled once or at least twice with intermediate annealing to obtain a cold-rolled sheet having a final sheet thickness, and the cold-rolled sheet is then subjected to decarburization annealing and then secondary recrystallization annealing, When the cold rolling is defined as the final cold rolling in the case of the one or two or more cold rollings, and the final cold rolling in the case of the two or more cold rollings, The final cold rolling is performed by heating the steel sheet to a temperature range of 70° C. or more and 200° C. or less using a tandem rolling mill, and then introducing the steel sheet into the first pass of the tandem rolling mill. The first pass of rolling is performed at a bite temperature T (° C.) and a strain rate e (s －１ ) satisfies the following formula (1). 0.0378e ２ +0.367e+37.2>T ・・・・(1)

3. The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2, wherein the decarburization annealing is performed by heating to a temperature range of 400° C. to 700° C. at a temperature increase rate of 200° C. / s or more.

4. The steel material further comprises, in mass%, Sb: 0.005-0.500%, Cu: 0.01 to 1.50%, P: 0.005-0.500%, Cr: 0.01-1.50%, Ni: 0.005-1.500%, Sn: 0.01-0.50%, Nb: 0.0005 to 0.0100%, Mo: 0.01-0.50%, B: 0.0010 to 0.0070% and Bi: 0.0005-0.0500% The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2, further comprising:

5. The steel material further comprises, in mass%, Sb: 0.005-0.500%, Cu: 0.01 to 1.50%, P: 0.005-0.500%, Cr: 0.01-1.50%, Ni: 0.005-1.500%, Sn: 0.01-0.50%, Nb: 0.0005 to 0.0100%, Mo: 0.01-0.50%, B: 0.0010 to 0.0070% and Bi: 0.0005-0.0500% The method for producing a grain-oriented electrical steel sheet according to claim 3, further comprising the step of:

6. A rolling facility for manufacturing grain-oriented electromagnetic steel sheets which is applicable to the manufacturing method of grain-oriented electromagnetic steel sheets described in claim 1 or 2, comprising a tandem rolling mill arranged on a manufacturing line for grain-oriented electromagnetic steel sheets, and a heating device and a cooling device arranged in that order from the upstream side of the manufacturing line at the entry side of a first stand of the tandem rolling mill.

7. A rolling facility for manufacturing grain-oriented electromagnetic steel sheets which is applicable to the manufacturing method of grain-oriented electromagnetic steel sheets described in claim 3, comprising a tandem rolling mill arranged on a manufacturing line for grain-oriented electromagnetic steel sheets, and a heating device and a cooling device arranged in that order from the upstream side of the manufacturing line at the entry side of a first stand of the tandem rolling mill.

8. A rolling facility for manufacturing grain-oriented electromagnetic steel sheets which is applicable to the manufacturing method of grain-oriented electromagnetic steel sheets described in claim 4, comprising a tandem rolling mill arranged on a manufacturing line for grain-oriented electromagnetic steel sheets, and a heating device and a cooling device arranged in that order from the upstream side of the manufacturing line at the entry side of a first stand of the tandem rolling mill.

9. A rolling facility for manufacturing grain-oriented electromagnetic steel sheets which is applicable to the manufacturing method of grain-oriented electromagnetic steel sheets described in claim 5, comprising a tandem rolling mill arranged on a manufacturing line for grain-oriented electromagnetic steel sheets, and a heating device and a cooling device arranged in that order from the upstream side of the manufacturing line at the entry side of a first stand of the tandem rolling mill.

Images