Production method for grain-oriented electrical steel sheet

Abstract

Provided is a method for producing a grain-oriented electrical steel sheet having good magnetic properties, when using a continuous process in which steps from casting a molten steel to producing a hot-rolled sheet are performed with a series of equipment lines. A molten steel having a given composition is continuously cast to produce a slab having a thickness of 30-80 mm. Thereafter, the slab is heated under given conditions and then hot-rolled to obtain a hot-rolled sheet having a thickness of 1.0-3.5 mm. Thereafter, hot-rolled sheet annealing (optional), one-pass cold rolling or at least two-pass cold rolling with process annealing therebetween, decarburization annealing doubling as primary recrystallization annealing, and finish annealing as secondary recrystallization annealing are performed. An annealing separator to be used in the finish annealing consists mainly of MgO and contains one or more compounds selected from the group consisting of sulfides, sulfuric acid salts, selenides, selenic acid salts, sulfurous acid salts, selenious acid salts, and thiosulfuric acid salts.

Description

Manufacturing method of grain-oriented electrical steel sheets

[0001] This invention relates to a method for manufacturing grain-oriented electrical steel sheets.

[0002] Grain-oriented electrical steel sheets are soft magnetic materials used as core materials for transformers and large generators, and have a texture in which the <001> axis of the crystal orientation, which is the easy magnetization axis of iron, is highly aligned in the rolling direction of the steel sheet. Such a texture is achieved by secondary recrystallization, which preferentially causes the growth of crystal grains with the {110}<001> orientation, called the Goss orientation.

[0003] A common manufacturing method for grain-oriented electrical steel sheets involves using precipitates called inhibitors to induce secondary recrystallization of grains with a Goss orientation during secondary recrystallization annealing. Examples include the method using AlN described in Patent Document 1 and the method using MnS or MnSe described in Patent Document 2, both of which have been put into practical industrial use. These inhibitor-based methods require heating the slab at a high temperature of 1300°C or higher for complete solid solution of the inhibitor components, but they are extremely useful for stably developing secondary recrystallized grains.

[0004] On the other hand, a technique for developing Goss-oriented crystal grains through secondary recrystallization in materials that do not contain inhibitor components has been disclosed in Patent Document 3, etc. This technique aims to eliminate impurities such as inhibitor components as much as possible, thereby making the dependence of grain boundary energy on the grain boundary orientation difference angle during primary recrystallization apparent, and allowing for secondary recrystallization of grains with Goss orientation without the use of inhibitors. This effect is called the texture inhibition effect. This method does not require fine dispersion of inhibitors in the steel, and therefore does not require the high-temperature slab heating that was previously essential, offering significant advantages in terms of both cost and maintenance.

[0005] The manufacturing method of grain-oriented electrical steel sheets using secondary recrystallization as described above has the drawback of requiring many steps and having a relatively high manufacturing cost compared to other steel products. For this reason, in recent years, in order to reduce costs, techniques have been developed to reduce the slab thickness and directly hot-roll the cast slab. For example, Patent Document 4 discloses a method for obtaining uniform magnetic properties by producing thin slabs with a thickness of about 50 to 100 mm and strictly controlling the hot-rolling conditions.

[0006] Japanese Patent Publication No. 40-15644, Japanese Patent Publication No. 51-13469, Japanese Patent Publication No. 2000-129356, Japanese Patent Publication No. 2013-512332

[0007] However, when the inventors conducted manufacturing studies on a lab scale, which is smaller than the actual machine, they found that when hot-rolled coils were continuously obtained from slabs cast thinner than usual using a continuous process that carries out everything from molten steel casting to the production of hot-rolled sheets using a series of equipment, the expected magnetic properties could not be obtained.

[0008] Therefore, in view of the above problems, the present invention aims to provide a method for manufacturing grain-oriented electrical steel sheets that can produce grain-oriented electrical steel sheets having good magnetic properties when using a continuous process in which the process from casting molten steel to manufacturing hot-rolled sheets is carried out using a series of equipment.

[0009] To solve the above problems, the inventors diligently studied a method for stably obtaining good magnetic properties in a series of processes for grain-oriented electrical steel sheets, including a continuous process (hereinafter also referred to as the casting and hot-rolling continuous process) in which a series of equipment is used to carry out everything from casting molten steel to manufacturing hot-rolled sheets. As a result, they first found that secondary recrystallization occurs and the sheet can have the properties of grain-oriented electrical steel sheets if the following conditions (A) to (C) are met in the casting and hot-rolling continuous process. (A) The slab thickness in the casting process is 30 mm or more and 80 mm or less. (B) After casting, heating is performed under predetermined conditions (heating time: 5 minutes or more and 30 minutes or less, maximum temperature reached: 1000°C or more and 1290°C or less). (C) A hot-rolled sheet with a thickness of 1.0 mm or more and 3.5 mm or less is obtained by hot rolling.

[0010] By satisfying all of the above conditions (A) to (C), it was possible to manufacture a hot-rolled sheet by a continuous casting and hot-rolling process, and subsequently induce secondary recrystallization. However, the magnetic properties obtained after secondary recrystallization were not necessarily sufficient compared to the case where a general slab reheating process was adopted. Therefore, the inventors conducted further investigations and found that by optimizing the composition of the annealing separating agent applied to the decarburized annealed sheet, it was possible to ultimately manufacture a grain-oriented electrical steel sheet with excellent magnetic properties.

[0011] The experiments that led to the completion of this invention will be described below.

[0012] <Experiment 1> Molten steel with a composition of C: 0.04%, Si: 3.3%, Mn: 0.07%, sol. Al: 0.007%, N: 0.003%, and S: 0.002% by mass, with the remainder being Fe and unavoidable impurities, was prepared in a laboratory vacuum melting furnace and poured into a mold to obtain a 60 mm thick slab. While the cast slab was still hot, it was heated for 10 minutes under conditions that the maximum surface temperature reached was 1250°C. Subsequently, the slab was hot-rolled to obtain a 2.7 mm thick hot-rolled plate. During this process, the surface temperature T at the center of the slab in the width direction at the entry side of the hot-rolling was adjusted within the range of 800 to 1200°C. The surface temperature of the slab was adjusted by blowing high-pressure air or water, which also served as descaling.

[0013] Subsequently, the hot-rolled sheet was annealed at a soaking temperature of 1050°C for 30 seconds, scale was removed by pickling, and then cold-rolled to a final thickness of 0.27 mm. This cold-rolled sheet was then annealed at 840°C for 150 seconds at 55% H. ２ -45%N ２ The material was then annealed in a humid atmosphere with a dew point of 60°C for decarburization and primary recrystallization to obtain a decarburized annealed plate. Subsequently, an annealing separating agent mainly composed of MgO was applied to the surface of the decarburized annealed plate. ４ By not adding or adding S, the S content [S] Ｂ Annealing separating agents were used, with their concentration adjusted in various ways within the range of 0.0 to 3.0% by mass. The application amount p of the annealing separating agent was also varied from 5 to 30 g / m². ２Various modifications were made within the scope. Next, finish annealing for secondary recrystallization was performed under the conditions of a maximum reached temperature of 1200°C and a soaking time of 5 hours to obtain a finish-annealed sheet. An insulating coating composed of colloidal silica and aluminum phosphate was applied to the surface of the finish-annealed sheet and baked at 820°C to obtain a final grain-oriented electrical steel sheet.

[0014] For the obtained grain-oriented electrical steel sheet, the magnetic flux density (B at an exciting magnetic field of 800 A / m and an exciting frequency of 50 Hz was measured in accordance with JIS C2550-1:2011 ８ ) was measured. The horizontal axis represents the surface temperature T at the center in the width direction of the slab on the entry side of hot rolling, and the vertical axis represents the S content [S] in the annealing separator Ｂ and the product of the coating amount p of the annealing separator, and the results of organizing the magnetic flux density (B ８ ) are shown in Figure 1. From Figure 1, it can be seen that by adding MgSO ４ to increase the S content in the annealing separator, good magnetic properties of 1.900 T or higher can be obtained. It is also found that by satisfying the following inequality, better magnetic properties of 1.910 T or higher can be obtained. [S] Ａ ×1530×{1.4 + (900 - T) / 300} < [S] Ｂ ×p [S] Ａ : S content of slab (mass%) T: surface temperature at the center in the width direction of the slab on the entry side of hot rolling (°C) [S] Ｂ : S content in the annealing separator (mass%) p: coating amount of the annealing separator (g / m ２ )

[0015] <Experiment 2> A molten steel having a chemical composition containing, by mass%, C: 0.02 to 0.08%, Si: 3.0 to 3.5%, Mn: 0.05 to 0.09%, sol. Al: 0.005 to 0.025%, N: 0.002 to 0.008%, and S and Se: 0.001 to 0.025% in total, with the balance being Fe and unavoidable impurities was produced in a laboratory vacuum melting furnace and poured into a mold to obtain a slab with a thickness of 80 mm. The S content (mass%) and Se content (mass%) of the slab are respectively [S] Ａ and [Se] Ａ , [S] Ａ , [Se] Ａ , and CＳ (= [S] Ａ +0.405[Se] Ａ Table 1 shows the results. The cast slab was heated for 20 minutes while it was still hot, under conditions that the maximum surface temperature reached was 1200°C. After that, the slab was hot-rolled to obtain a hot-rolled sheet with a thickness of 2.7 mm. At that time, the surface temperature T at the center of the width direction of the slab on the hot-rolling entry side was adjusted to the value shown in Table 1. The surface temperature of the slab was adjusted by blowing high-pressure air or water, which also served as descaling.

[0016] Subsequently, the hot-rolled sheet was annealed at a soaking temperature of 950°C for 10 seconds, scale was removed by pickling, and then cold-rolled to a final thickness of 0.23 mm. This cold-rolled sheet was then annealed at 840°C for 150 seconds at 60% H. ２ -40%N ２ The material was then annealed in a humid atmosphere with a dew point of 45°C for decarburization and primary recrystallization to obtain a decarburized annealed plate. Subsequently, an annealing separation agent mainly composed of MgO was applied to the surface of the decarburized annealed plate. ４ and K ２ SeO ３ By not adding or adding S, the S content [S] Ｂ and Se content [Se] Ｂ An annealing separating agent was used, adjusted to the values ​​shown in Table 1 (by mass%). Ｓ (= [S] Ｂ +0.405[Se] Ｂ The values ​​for ) are shown in Table 1. Also, the application amount p (g / m) of the annealing separating agent is shown. ２ The values ​​shown in Table 1 were used. Next, finish annealing for secondary recrystallization was performed under conditions of a maximum temperature of 1200°C and a soaking time of 5 hours to obtain a finish annealed sheet. An insulating coating consisting of colloidal silica and aluminum phosphate was applied to the surface of the finish annealed sheet and baked at 850°C to obtain the final grain-oriented electrical steel sheet.

[0017] For the obtained grain-oriented electrical steel sheet, the magnetic flux density (B) at an excitation magnetic field of 800 A / m and an excitation frequency of 50 Hz was measured in accordance with JIS C2550-1:2011. ８ The magnetic flux density (B) obtained was measured. ８ ) are listed in Table 1. From Table 1, SrSO４ and K ２ SeO ３ In the inventive example where the S and Se content in the annealing separating agent is increased by adding [a certain substance], it can be seen that good magnetic properties of 1,900 T or more can be obtained. Furthermore, in the inventive example that satisfies the following formula (1), it can be seen that even better magnetic properties of 1,910 T or more can be obtained. C Ｓ ×1530×{1.4+(900-T) / 300} < S Ｓ ×p...(1) C Ｓ = [S] Ａ +0.405[Se] Ａ [S] Ａ Sodium content of the slab (mass%) [Se] Ａ : Se content of the slab (mass%) T: Surface temperature of the center of the slab in the width direction at the entry side of hot rolling (°C) Ｓ = [S] Ｂ +0.405[Se] Ｂ [S] Ｂ : S content (mass%) in annealing separating agent [Se] Ｂ : Se content in the annealing separating agent (mass%) p: Amount of annealing separating agent applied (g / m²) ２ ) Note that C Ｓ and S Ｓ In the calculation, the reason for multiplying the Se content by 0.405 is to convert Se to S equivalent.

[0018]

[0019] <Discussion> In the manufacturing method of grain-oriented electrical steel sheets, which includes a continuous casting and hot-rolling process, the reason why good magnetic properties can be obtained by increasing the content of S and Se in the annealing separating agent is not entirely clear, but the inventors believe it to be as follows.

[0020] MnS and MnSe primarily precipitate using dislocations introduced during hot rolling as nucleation sites. When precipitation occurs before this, there are fewer nucleation sites, resulting in coarse precipitation. In such cases, when MnS and MnSe are used as inhibitors, the expected grain growth inhibitory effect is not fully realized. When slabs are manufactured in a continuous casting and hot rolling process, the surface must be rapidly cooled before hot finish rolling to prevent breakout, which is thought to make it easier for MnS and MnSe to precipitate coarsely on the surface of the slab. In addition, when the slab thickness is reduced, the proportion of the area where MnS and MnSe precipitate coarsely increases relative to the total thickness of the slab, which is thought to make coarse precipitation on the surface more likely. Under such circumstances, it is thought that increasing the content of S and Se in the annealing separating agent may have had the effect of replenishing the MnS and MnSe that had been coarsely precipitated before hot rolling, by having S and Se penetrate the surface layer of the steel sheet during finish annealing and react with Mn in the base metal to form new MnS and MnSe.

[0021] The above is considered to apply not only to cases where MnS and MnSe are used as inhibitors, but also to inhibitor-free slabs. This is because even in inhibitor-free slabs, it is difficult to remove S and Se from the steel, and trace amounts remain. Furthermore, the inventors believe that in inhibitor-free slabs, because the S and Se content in the steel is low, the effect of coarse precipitation of MnS and MnSe during the continuous casting and hot rolling process becomes greater.

[0022] Based on the above findings, the gist of the present invention is as follows. [1] A process to produce a slab with a thickness of 30 mm to 80 mm by continuously casting molten steel having a composition in mass%, containing C: 0.10% or less, Si: 1.5% to 4.5%, Mn: 0.02% to 0.30%, acid-soluble Al: 0.040% or less, N: 0.015% or less, and one or both of S and Se: 0.025% or less in total, with the remainder being Fe and unavoidable impurities; a heating process thereafter, heating the slab for a heating time of 5 minutes to 30 minutes and the maximum temperature reached on the surface of the slab being 1000°C to 1290°C; a hot rolling process thereafter, hot rolling the slab to obtain a hot-rolled sheet with a thickness of 1.0 mm to 3.5 mm; and an optional process thereafter, hot-rolled sheet annealing. A method for producing grain-oriented electrical steel sheets, comprising the steps of: subjecting the hot-rolled sheet to cold rolling once or two or more times with an intermediate annealing in between to obtain a cold-rolled sheet having a final thickness; subjecting the cold-rolled sheet to decarburization annealing which also serves as primary recrystallization annealing to obtain a decarburized annealed sheet; and subjecting the decarburized annealed sheet to an annealing separating agent mainly composed of MgO and performing finish annealing as secondary recrystallization annealing, wherein the annealing separating agent contains one or more selected from the group consisting of sulfides, sulfates, selenides, selenates, sulfites, selenites, and thiosulfates.

[0023] [2] A method for manufacturing grain-oriented electrical steel sheets as described in [1] above, satisfying the following formula (1). C Ｓ ×1530×{1.4+(900-T) / 300} < S Ｓ ×p ... (1) Here, C Ｓ = [S] Ａ +0.405[Se] Ａ However, [S] Ａ and [Se] Ａ These are the S content (mass%) and Se content (mass%) in the component composition of the slab, respectively, and T is the surface temperature (°C) at the center of the width direction of the slab on the entry side of the hot rolling process, and S Ｓ = [S] Ｂ +0.405[Se] ＢHowever, [S] Ｂ and [Se] Ｂ These are the S content (mass%) and Se content (mass%) in the annealing separating agent, respectively, and p is the amount of the annealing separating agent applied (g / m²). ２ )

[0024] [3] A method for producing grain-oriented electrical steel sheet as described in [1] above, wherein the component composition is: acid-soluble Al: 0.0020% or more and less than 0.0120%, N: 0.0010% or more and less than 0.0060%, S: less than 0.0050%, and Se: less than 0.0050%.

[0025] [4] A method for producing grain-oriented electrical steel sheet as described in [2] above, wherein the component composition is: acid-soluble Al: 0.0020% or more and less than 0.0120%, N: 0.0010% or more and less than 0.0060%, S: less than 0.0050%, and Se: less than 0.0050%.

[0026] [5] A method for manufacturing a grain-oriented electrical steel sheet according to any one of the above [1] to [4], comprising the step of performing a nitriding treatment on the cold-rolled sheet during the decarburization annealing, or on the decarburized annealed sheet after the decarburization annealing and before the finish annealing.

[0027] [6] The component composition is: [Group A] one or more selected from the group consisting of Sb: 0.500% or less, Sn: 0.500% or less, Cr: 0.500% or less, Cu: 0.50% or less, Ni: 0.50% or less, Bi: 0.500% or less, P: 0.200% or less, Mo: 0.500% or less, and Co: 0.500% or less, in mass% or mass ppm; [Group B] one or more selected from the group consisting of B: 25.0 ppm or less, Nb: 0.020% or less, Ti: 0.0400% or less, V: 0.020% or less, and W: 0.020% or less, in mass% or mass ppm. A method for manufacturing grain-oriented electrical steel sheets according to any one of the above [1] to [5], comprising: [Group C] one or more groups selected from a group consisting of one or more selected from the

[0028] According to the method for manufacturing grain-oriented electrical steel sheets of the present invention, it is possible to manufacture grain-oriented electrical steel sheets with good magnetic properties when using a continuous process in which the process from casting molten steel to manufacturing hot-rolled sheets is carried out using a series of equipment.

[0029] The horizontal axis represents the surface temperature T at the center of the slab in the width direction at the entry side of hot rolling, and the vertical axis represents the sulfur content [S] in the annealing separating agent. Ｂ The magnetic flux density (B) is calculated as the product of the amount of annealing separating agent applied p. ８ This is a graph that summarizes the data.

[0030] [Method for Manufacturing Grain-Grain Electrical Steel Sheets] A method for manufacturing grain-grain electrical steel sheets according to one embodiment of the present invention comprises the steps of: continuously casting molten steel having a predetermined component composition to produce a slab; then a heating step of heating the slab under predetermined conditions; then a hot rolling step of hot rolling the slab under predetermined conditions to obtain a hot-rolled sheet; then an optional step of annealing the hot-rolled sheet; then a cold rolling step of one or two or more times with an intermediate annealing step in between; a decarburization annealing step; and a finish annealing step to obtain grain-grain electrical steel sheets as product steel sheets.

[0031] (Composition of Molten Steel and Slabs) First, the composition of molten steel and slabs will be explained. Unless otherwise specified, "%" in relation to the components means mass percent. Similarly, unless otherwise specified, "ppm" refers to mass ppm.

[0032] C: 0.10% or less. If carbon (C) remains in the final product plate, it causes magnetic aging and leads to magnetic degradation. If the C content of the molten steel and slab exceeds 0.10%, it becomes difficult to reduce the C content to 0.005% or less, which prevents magnetic aging, through decarburization annealing. Therefore, the C content of the molten steel and slab should be 0.10% or less, preferably 0.08% or less. On the other hand, carbon (C) has the effect of improving the texture after decarburization annealing and improving the final magnetism. From this viewpoint, a C content of 0.025% or more is preferable.

[0033] Si: 1.5% to 4.5% Si is an element that reduces iron loss by increasing electrical resistance. From the viewpoint of obtaining this effect, the Si content should be 1.5% or more, preferably 2.5% or more. On the other hand, if the Si content is too high, cold rolling becomes extremely difficult, so the Si content should be 4.5% or less, preferably 4.0% or less.

[0034] Mn: 0.02% or more and 0.30% or less. In this embodiment, Mn is an essential element for forming MnS and MnSe when S and Se in the annealing separating agent penetrate into the steel. Furthermore, Mn is an element that has the effect of improving the hot workability of steel. From the viewpoint of obtaining these effects to the fullest, the Mn content is set to 0.02% or more, preferably 0.05% or more. On the other hand, if the Mn content is too high, the magnetic flux density of the product plate will decrease. Therefore, the Mn content is set to 0.30% or less, preferably 0.15% or less.

[0035] Acid-soluble Al: 0.040% or less, N: 0.015% or less, S and Se (either or both): 0.025% or less in total. By including acid-soluble Al, N, and either or both S and Se within the above content ranges, precipitates containing these elements can act as inhibitors, improving the final magnetic properties. If the upper limits of each content are exceeded, there is a concern that the precipitates will become too coarse and will not be able to exert a sufficient pinning effect. When using such inhibitors, the content of acid-soluble Al is preferably 0.004% or more, the N content is preferably 0.002% or more, and the content of either or both S and Se is preferably 0.002% or more in total.

[0036] Furthermore, this embodiment is particularly effective in inhibitor-free slabs. When applying this embodiment to the inhibitor-free method, it is preferable that the acid-soluble Al content be 0.0020% or more and less than 0.0120%, N content be 0.0010% or more and less than 0.0060%, S content be less than 0.0050%, and Se content be less than 0.0050%. In addition, there is no particular lower limit to the S content and Se content, but since the presence of trace amounts of S and Se is unavoidable, the S content and Se content may each be 0.0001% or more.

[0037] The remainder of the components other than those listed above consists of Fe and unavoidable impurities. Unavoidable impurities are impurities that are inevitably mixed in from raw materials, manufacturing processes, or manufacturing equipment, and are permissible to be included in a range that does not hinder the purpose of the present invention. Examples of raw materials include iron ore, reduced iron, or scrap. Examples of unavoidable impurities include elements that are mixed in unintentionally. These elements may be inevitably present in amounts of about 0.010% or less. Furthermore, for the purpose of further improving performance, the component composition of the molten steel and slab may optionally contain the following elements.

[0038] [Group A] By including one or more of the following in mass%, the recrystallized texture is improved, and the final magnetic properties can be improved. If the content of each exceeds the upper limit, the effect saturates and becomes a cost-increasing factor. While there are no particular limitations on the lower limit of the content of each element, in order to obtain the above effects, the preferred content of each element is as follows: Sb: 0.005% or more, Sn: 0.005% or more, Cr: 0.005% or more, Cu: 0.01% or more, Ni: 0.01% or more, Bi: 0.005% or more, P: 0.005% or more, Mo: 0.005% or more, and Co: 0.001% or more.

[0039] [Group B] In mass%, or in mass ppm, B: 25.0 ppm or less, Nb: 0.020% or less, Ti: 0.0400% or less, V: 0.020% or less, and W: 0.020% or less. By including one or more of the above, carbides and nitrides of these elements are formed finely, and the grain size after annealing is refined, improving the bending characteristics and suppressing sheet threading problems. If the content of each exceeds the upper limit, the effect saturates and becomes a factor that increases costs. There is no particular lower limit for the content of each element, but in order to obtain the above effect, the preferred content of each element is B: 0.1 ppm or more, Nb: 0.001% or more, Ti: 0.0005% or more, V: 0.001% or more, and W: 0.001% or more.

[0040] [Group C] By including one or more elements selected from the above, these elements can be concentrated or compounded at the grain boundaries, thereby strengthening the grain boundaries and suppressing defects caused by grain boundary fracture. If the content of each element exceeds the upper limit, the effect saturates, leading to increased costs. While there are no particular limitations on the lower limit of the content of each element, in order to obtain the above effects, the preferred content of each element is as follows: Zn: 0.0005% or more, Zr: 0.001% or more, Pb: 0.0001% or more, As: 0.001% or more, Ag: 0.001% or more, Au: 0.001% or more, Ga: 0.0001% or more, Ge: 0.0001% or more, Ca: 0.0005% or more, Mg: 0.0005% or more, REM: 0.0005% or more, and Hf: 0.001% or more.

[0041] (Casting Process) In this embodiment, first, molten steel having the above-mentioned component composition is continuously cast to produce slabs with a thickness of 30 mm to 80 mm. Optimizing the slab thickness makes it possible to achieve sufficient microstructure control during subsequent hot rolling. While thicker slabs are generally more effective, in this embodiment, where the final thickness of the hot-rolled sheet is determined by a series of hot rolling processes without dividing it into rough rolling and finish rolling, it is extremely difficult to directly roll slabs cast to a thickness exceeding 80 mm during manufacturing. Therefore, the slab thickness is set to 80 mm or less. Furthermore, if the slab thickness is less than 30 mm, it is not possible to set a sufficient reduction ratio during hot rolling, resulting in insufficient introduction of dislocations that serve as inhibitor precipitation nuclei. Therefore, the slab thickness is set to 30 mm or more.

[0042] (Heating Process) Next, the slab obtained in the casting process is subjected to the heating process directly, i.e., in a continuous process. In the heating process, the slab is heated for a heating time of 5 minutes or more and 30 minutes or less, and the maximum temperature reached on the surface of the slab is between 1000°C and 1290°C. In the slab state, the surface temperature is low and the temperature in the center of the plate thickness is high, so if hot rolling is performed afterward, many surface defects will occur due to temperature unevenness. To reduce this temperature unevenness, a heat treatment is performed before hot rolling. Furthermore, since it is generally difficult to perform casting at high speed, in processes that perform casting and hot rolling in a continuous manner, a certain amount of time is often required before hot rolling. If it takes about 10 minutes or more from the start of casting until hot rolling, precipitates such as sulfides, selenides, and nitrides containing MnS and MnSe may precipitate coarsely. To avoid this coarse precipitation, it was effective to heat the slab for 5 to 30 minutes before hot rolling, until the surface temperature of the slab reached between 1000°C and 1290°C. In addition, starting the heating process before the slab surface temperature fell below 750°C was even more effective in avoiding coarse precipitation.

[0043] Heating time: 5 minutes or more and 30 minutes or less. If the heating time is less than 5 minutes, temperature unevenness in the thickness direction of the plate remains, and the occurrence of surface defects cannot be suppressed. Therefore, the heating time should be 5 minutes or more, preferably 8 minutes or more. On the other hand, if the heating time exceeds 30 minutes, the line length must be increased in the continuous casting and hot rolling process, which is inefficient, and scale formation is likely to progress in the temperature range of the heating process, which is undesirable from the viewpoint of yield. Therefore, the heating time should be 30 minutes or less, preferably 20 minutes or less. Note that "heating time" means the time during which heat is applied to the slab by the heating device. If the heating device is a tunnel furnace, it means the time during which the slab is inside the tunnel furnace. If the heating device is an induction heating device, it means the time during which the slab is under the influence of the magnetic field of the induction heating device.

[0044] Maximum surface temperature of the slab: 1000°C or higher and 1290°C or lower. If the maximum surface temperature of the slab during the heating process is less than 1000°C, the influence of coarsely precipitated MnS and MnSe on the surface becomes very large, causing the recrystallized grain size to become non-uniform at the stage of primary recrystallization, making secondary recrystallization impossible. Therefore, the maximum surface temperature should be 1000°C or higher, preferably 1100°C or higher. On the other hand, if the maximum surface temperature exceeds 1290°C, problems may arise such as breakout during subsequent hot rough rolling, or the deformation resistance of the steel becoming too low, making it difficult to control the shape after hot rolling. Therefore, the maximum surface temperature should be 1290°C or lower, preferably 1250°C or lower.

[0045] The heating process is preferably carried out in a non-oxidizing atmosphere with an oxygen concentration of 3.0 volume% or less. This is because if the oxygen concentration in the atmosphere is high, carbon in the steel on the slab surface will be decarburized as CO by the oxygen in the atmosphere, promoting grain coarsening near the surface and potentially causing bleed defects. The oxygen concentration may be 0.0 volume%. The non-oxidizing atmosphere is not particularly limited and may include carbon-based combustion gases, ammonia-based combustion gases, and N2, which are by-products of the steelworks. ２ It can be composed of one or more gases selected from the group consisting of inert gases such as Ar. In particular, when using carbon-based combustion gas or ammonia-based combustion gas, which are by-products of steel mills, oxygen or air is introduced to generate the combustion gas, but CO, CO ２ No, no ２ It is preferable that the amount of unreacted oxygen in the total gas volume, including the above, be 3.0% by volume or less.

[0046] Since the slabs are continuously supplied to the next process, it is preferable to use an open furnace such as a tunnel furnace in the heating process. Furthermore, from the viewpoint of further improving temperature uniformity, it is also preferable that the heating process includes an induction heating process using an induction heating device capable of rapid heating.

[0047] Furthermore, the above heating process can be a two-stage heating process consisting of a first heating step in which a first heating device is used to raise the surface temperature of the slab to 950°C or higher and 1150°C or lower, and a second heating step in which a second heating device different from the first heating device is used to raise the surface temperature of the slab to a maximum temperature of 1000°C or higher and 1290°C or lower. The advantage of this two-stage heating is that the heating rate of the first heating step and the second heating step can be controlled individually. In the case of two-stage heating, a heating time of 5 minutes or more and 30 minutes or less refers to the total heating time of the first heating step and the second heating step.

[0048] During the heating process, when the surface temperature of the slab exceeds 1100°C, the oxides on the surface begin to liquefy, and when the temperature exceeds 1150°C, almost the entire surface of the slab becomes covered with liquid-phase scale. This liquid-phase scale can be a cause of baldness defects. Therefore, in the second heating process, which aims for a maximum temperature of 1000°C to 1290°C, it is preferable to use an induction heating device capable of rapid heating. For example, it is preferable to use a tunnel furnace for the first heating process and an induction heating device for the second heating process. By making the second heating process rapid, grain growth, which tends to progress especially in the high-temperature range, can be suppressed, and texture deterioration caused by coarse grains can be more effectively suppressed, and as a result, baldness defects can also be suppressed.

[0049] (Hot Rolling Process) Next, the slab is hot-rolled under predetermined conditions to obtain a hot-rolled sheet with a thickness of 1.0 mm or more and 3.5 mm or less. Descaling may be performed before hot rolling. The descaling method may be any known method.

[0050] The surface temperature T (°C) at the center of the slab in the width direction at the entry side of hot rolling is not particularly limited as long as it satisfies formula (1), but it is preferably in the range of 750°C to 1200°C. If it is 750°C or higher, the deformation resistance does not become too high, so rolling does not become difficult, and if it is 1200°C or lower, surface defects are less likely to occur during rolling, so manufacturability does not deteriorate easily.

[0051] Hot-rolled sheet thickness: 1.0 mm to 3.5 mm. During the hot-rolling process, the temperature is relatively low, and dislocations are introduced into the steel sheet. Since dislocations function as nuclei for precipitation, the precipitation of MnS and MnSe progresses. If hot-rolling is attempted to reduce the thickness of the hot-rolled sheet to less than 1.0 mm, the edges (ear shape) of the hot-rolled sheet tend to deteriorate, and it becomes difficult to ensure a uniform thickness throughout the entire length and width. Therefore, the thickness of the hot-rolled sheet should be 1.0 mm or more. On the other hand, if the thickness of the hot-rolled sheet exceeds 3.5 mm, the reduction ratio of cold rolling becomes relatively high, the primary recrystallized texture deteriorates, and the magnetic properties deteriorate. Therefore, the thickness of the hot-rolled sheet should be 3.5 mm or less.

[0052] The number of hot rolling passes is not particularly limited, but from the viewpoint of improving the accuracy of the final plate thickness, multiple passes are preferable, and specifically, three to seven passes are preferable.

[0053] (Cooling and winding processes) After hot rolling, the hot-rolled sheet can be cooled and then wound up to obtain a hot-rolled coil. In this process, it is preferable to cool the hot-rolled sheet within 200 seconds after the completion of hot rolling, under conditions that the surface temperature of the hot-rolled sheet is 650°C or lower. After hot rolling, dislocations disappear due to recovery and grain growth of MnS and MnSe occurs, making it easy for precipitates to become coarse. If the cooling time from the end of hot rolling until the surface temperature of the hot-rolled sheet reaches 650°C is 200 seconds or less, the coarsening of MnS and MnSe can be suppressed. The lower limit of this cooling time is not particularly limited, and cooling may be started immediately after the completion of hot rolling if there are no constraints on the equipment configuration.

[0054] (Hot-rolled sheet annealing process) After that, the hot-rolled sheet is subjected to hot-rolled sheet annealing as necessary. As described above, in order to reduce the <100> / / ND orientation caused by the columnar crystal structure as much as possible in order to improve the magnetic properties, it is desirable to perform hot-rolled sheet annealing. In that case, it is preferable to set the soaking temperature (the highest temperature reached by the hot-rolled sheet) in the hot-rolled sheet annealing to 900°C or higher so that recrystallization occurs. There is no particular upper limit to the soaking temperature in the hot-rolled sheet annealing. However, in order to suppress deterioration of surface quality due to pickup, it is preferable that the soaking temperature in the hot-rolled sheet annealing is 1200°C or lower. There is no particular limit to the holding time at the soaking temperature (soaking time), but it is preferable to be 10 seconds or more in order to reduce the <100> / / ND orientation, and 240 seconds or less in order to suppress deterioration of surface quality due to pickup.

[0055] (Cold Rolling Process) Subsequently, the hot-rolled sheet is subjected to cold rolling once or two or more times with an intermediate annealing in between to obtain a cold-rolled sheet. Descaling by pickling or the like may be performed before cold rolling. This cold rolling includes not only general cold rolling performed at room temperature, but also warm rolling in which the temperature of the hot-rolled sheet is raised to a higher temperature than room temperature, for example, between 100°C and 300°C. Furthermore, performing aging treatment once or multiple times in the range of 100°C to 300°C during cold rolling is effective in changing the recrystallized texture and improving the magnetic properties.

[0056] From the viewpoint of improving the microstructure, the soaking temperature in intermediate annealing is preferably 900°C or higher, and more preferably 1000°C or higher. Furthermore, to suppress deterioration of surface quality due to picking, the soaking temperature is preferably 1200°C or lower. From the viewpoint of improving the microstructure, the holding time at the soaking temperature in intermediate annealing is preferably 30 seconds or higher, and more preferably 60 seconds or higher. Furthermore, to suppress deterioration of surface quality due to picking, the holding time at the soaking temperature is preferably 240 seconds or lower.

[0057] (Decarburization Annealing Process) Subsequently, the cold-rolled sheet is subjected to decarburization annealing to obtain a decarburized annealed sheet. This decarburization annealing is also called primary recrystallization annealing. That is, the primary purpose of this annealing is to primary recrystallize the cold-rolled sheet having a rolled structure and adjust it to the primary recrystallized grain size which is optimal for secondary recrystallization. The second purpose of this annealing is to decarburize the carbon contained in the steel by using a wet hydrogen nitrogen or wet hydrogen argon atmosphere with a dew point of 20°C to 80°C, and at the same time form an oxide film on the surface by the above annealing atmosphere. For this reason, it is desirable that the annealing temperature (holding temperature) for decarburization annealing be 800°C to 900°C. The holding time at the annealing temperature is preferably 30 seconds to 240 seconds. Furthermore, it is preferable that the heating rate to the holding temperature in decarburization annealing be 50°C / s to 1000°C / s in order to obtain good magnetic properties.

[0058] Nitriding treatment may be applied to the cold-rolled sheet during the decarburization annealing process, or to the decarburized annealed sheet after the decarburization annealing process. Nitriding treatment can further improve the magnetic properties. The nitriding treatment can be performed using the conventional methods used for grain-oriented electrical steel sheets. As an example of performing nitriding treatment during the decarburization annealing process, the decarburization annealing process may be held in a humid hydrogen nitrogen atmosphere (e.g., 75% H). ２ +25%N ２ Methods include performing the process under the specified conditions and, after holding, blowing ammonia gas onto the steel plate while maintaining the same atmosphere, or introducing the plate into a mixed gas atmosphere of hydrogen, nitrogen, and ammonia after holding. Another method for performing nitriding after decarburization annealing is to first cool the decarburized annealed plate to room temperature, then raise the temperature again to between 400°C and 900°C, and anneal it with a mixed gas of hydrogen, nitrogen, and ammonia.

[0059] (Finish Annealing Process) Next, an annealing separator is applied to the surface of the decarburized annealed sheet. Magnesia (MgO) can be used as the main component of the annealing separator in order to form a forsterite film on the surface of the steel sheet after finish annealing. In this embodiment, it is essential that the annealing separator contains one or more compounds selected from the group consisting of sulfides, sulfates, selenides, selenates, sulfites, selenites, and thiosulfates. These compounds penetrate into the steel during finish annealing and form fine MnS and MnSe, thereby compensating for the MnS and MnSe that precipitated coarsely on the slab surface between casting and hot rolling and no longer function as inhibitors. The amount of these compounds added is not particularly limited, but from the viewpoint of obtaining a sufficient magnetic improvement effect, it is preferable that the total amount be 0.01 parts by mass or more per 100 parts by mass of MgO. Furthermore, there is no particular upper limit to the amount of these compounds added, but if the amount added is too large, the film peelability may deteriorate, so it is preferable that the total amount of these compounds added is 30 parts by mass or less per 100 parts by mass of MgO.

[0060] Furthermore, by incorporating the compound into the annealing separating agent so as to satisfy the following formula (1), further improvement in magnetic properties can be expected. C Ｓ ×1530×{1.4+(900-T) / 300} < S Ｓ ×p ... (1) Here, C Ｓ = [S] Ａ +0.405[Se] Ａ However, [S] Ａ and [Se] Ａ These are the S content (mass%) and Se content (mass%) in the slab's composition, respectively, and T is the surface temperature (°C) at the center of the slab's width direction on the entry side of hot rolling. Ｓ = [S] Ｂ +0.405[Se] Ｂ However, [S] Ｂ and [Se] Ｂ These are the S content (mass%) and Se content (mass%) in the annealing separating agent, respectively, and p is the amount of annealing separating agent applied (g / m²). ２ )

[0061] S relating to the annealing separator Ｓ is not particularly limited as long as the above formula (1) is satisfied, and may be within the range of 0.001% by mass or more and 5% by mass or less. S Ｓ is too small, the effect of forming MnS and MnSe cannot be sufficiently obtained, and S Ｓ is excessive, there is a risk that coating detachability may deteriorate. In addition, the coating amount p of the annealing separator is not particularly limited as long as it satisfies the above formula (1), and is 3 g / m ２ or more and 40 g / m ２ or less. When p is too small, the coil fuses during secondary recrystallization annealing, and manufacturability significantly deteriorates. Further, even if p is excessive, the effect of forming MnS and MnSe is saturated, and a magnetic property improvement effect commensurate with the cost increase cannot be obtained. In order to avoid forsterite coating defects, it is preferable to satisfy Ss×p≦5.

[0062] As sulfides, for example, Na ２ S, K ２ S, CaS, MnS, FeS, CdS, MoS ２ , MgS, SrS, and Al ２ S ３ One or more selected from the group consisting of the above and the like can be used. As sulfates, for example, Na ２ SO ４ , K ２ SO ４ , BaSO ４ , SrSO ４ , PbSO ４ , CaSO ４ , Ag ２ SO ４ , and MgSO ４ One or more selected from the group consisting of the above and the like can be used. As selenides, Na ２ Se, K ２ Se, MnSe, SrSe, CaSe, MoSe ２ , and Al ２ Se ３ One or more selected from the group consisting of the above and the like can be used. As selenates, Na ２ SeO ４ , K ２ SeO ４,BaSeO ４ , SrSeO ４ , PbSeO ４ CaSeO ４ , and Ag ２ SeO ４ One or more can be selected from the group consisting of the following:

[0063] Examples of sulfites include CuSO4. ３ ZnSO ３ MgSO ３ _K ２ SO ３ , and Na ２ SO ３ One or more can be selected from the group consisting of the following. As for selenite, Na ２ SeO ３ _K ２ SeO ３ , and MgSeO ３ One or more selected from the group consisting of the following can be used. As the thiosulfate, MgS ２ O ３ Na ２ S ２ O ３ _K ２ S ２ O ３ CaS ２ O ３ , and SrS ２ O ３ You can use one or more selected from the group consisting of the following.

[0064] In addition to one or more substances selected from the group consisting of sulfides, sulfates, selenides, selenates, sulfites, selenites, and thiosulfates, adding an appropriate amount of Ti oxide or Sr compound to the annealing separation agent can favorably facilitate the formation of a forsterite film. In particular, the addition of an aid that promotes the uniform formation of the forsterite film is also advantageous for improving the peeling properties of the film. The method of applying the annealing separation agent is not particularly limited, and methods such as applying a solution in which the annealing separation agent is dissolved in a solvent, or attaching a sheet of the annealing separation agent that has been prepared in advance, can be used as appropriate.

[0065] Next, finish annealing is performed for secondary recrystallization and forsterite film formation. The annealing atmosphere is N ２ Ar, H ２ , or any of these mixed gases are suitable. In finish annealing, it is desirable to hold the steel sheet at 1100°C to 1280°C for 3 to 50 hours in order to remove (purify) inhibitor components from the steel sheet. More preferably, it is 1150°C or higher for 10 hours or more. Furthermore, H ２ Because the purification is accelerated by the atmosphere, H ２ It is desirable to create an atmosphere containing 50% or more of [the substance].

[0066] After the secondary recrystallization annealing described above, it is useful to perform either water washing, brushing, or pickling to remove any adhering annealing separator. Subsequently, performing planar annealing to correct the shape is effective in reducing iron loss. Furthermore, to improve iron loss, it is effective to apply an insulating coating to the surface of the steel sheet before or after planar annealing. The coating may also be baked on during this planar annealing. In this case, it is desirable from the viewpoint of reducing iron loss to use a coating that can impart tension to the steel sheet. It is desirable to deposit inorganic materials onto the surface of the steel sheet using physical vapor deposition or chemical vapor deposition, as this provides excellent coating adhesion and a significant effect in reducing iron loss.

[0067] [Example 1] Molten steel having a composition of C: 0.04%, Si: 3.2%, Mn: 0.10%, sol. Al: 0.008%, N: 0.003%, and Se: 0.004% by mass, with the remainder being Fe and unavoidable impurities, was prepared in a laboratory vacuum melting furnace. A casting process, a heating process, and a hot rolling process were carried out in succession under the conditions shown in Table 2 to obtain a hot-rolled sheet. At that time, the surface temperature T at the center of the width direction of the slab on the entry side of the hot rolling process was adjusted to the value shown in Table 2. The surface temperature of the slab was adjusted by blowing high-pressure air or water, which also served as descaling.

[0068] Subsequently, the hot-rolled sheet was subjected to hot-rolled sheet annealing at a soaking temperature of 1025°C for 30 seconds, scale was removed by pickling, and then cold-rolled to a final sheet thickness of 0.23 mm. This cold-rolled sheet was then subjected to annealing at 840°C for 100 seconds at 50% H. ２-50%N ２ The material was then annealed in a humid atmosphere with a dew point of 45°C for decarburization and primary recrystallization to obtain a decarburized annealed plate. Subsequently, an annealing separating agent mainly composed of MgO was applied to the surface of the decarburized annealed plate. At this time, MgS and Al ２ See ３ By not adding or adding S, the S content [S] Ｂ and Se content [Se] Ｂ An annealing separation agent was used, adjusted to the values ​​shown in Table 2 (mass %). Ｓ (= [S] Ｂ +0.405[Se] Ｂ The values ​​for ) are shown in Table 2. Also, the application amount p (g / m) of the annealing separating agent is shown. ２ The values ​​shown in Table 2 were used. Next, finish annealing for secondary recrystallization was performed under conditions of a maximum temperature of 1200°C and a soaking time of 5 hours to obtain a finish annealed sheet. An insulating coating consisting of colloidal silica and aluminum phosphate was applied to the surface of the finish annealed sheet and baked at 860°C to obtain the final grain-oriented electrical steel sheet.

[0069] For the obtained grain-oriented electrical steel sheet, the magnetic flux density (B) at an excitation magnetic field of 800 A / m and an excitation frequency of 50 Hz was measured in accordance with JIS C2550-1:2011. ８ The magnetic flux density (B) obtained was measured. ８ The following is shown in Table 2. As is clear from Table 2, good magnetic properties were obtained in grain-oriented electrical steel sheets manufactured under the conditions according to the present invention.

[0070]

[0071] [Example 2] Molten steel having a composition of C: 0.03%, Si: 3.3%, Mn: 0.10%, sol. Al: 0.008%, N: 0.002%, and Se: 0.004% by mass, with the remainder being Fe and unavoidable impurities, was prepared in a laboratory vacuum melting furnace. A casting process, a heating process, and a hot rolling process were carried out in succession under the conditions shown in Table 3 to obtain a hot-rolled sheet. At that time, the surface temperature T at the center of the width direction of the slab on the entry side of the hot rolling process was adjusted to the value shown in Table 3. The surface temperature of the slab was adjusted by blowing high-pressure air or water, which also served as descaling.

[0072] Subsequently, the hot-rolled sheet was subjected to hot-rolled sheet annealing at a soaking temperature of 1025°C for 30 seconds, scale was removed by pickling, and then cold-rolled to a final thickness of 0.20 mm. This cold-rolled sheet was then subjected to annealing at 840°C for 150 seconds at 50% H. ２ -50%N ２ Then, annealing for decarburization and primary recrystallization was performed in a humid atmosphere with a dew point of 45°C to obtain a decarburized annealed plate.

[0073] Subsequently, as shown in Table 3, nitriding treatment was performed on some of the invention examples. In the "intermediate nitriding" described in Table 3, immediately after the 150-second holding period at 840°C for decarburization annealing, the temperature was reduced to 750°C and left at 60% H for 20 seconds. ２ +20%N ２ +20%NH ３ The material was introduced into a mixed gas atmosphere. In the "additional nitriding" described in Table 3, after decarburization annealing was completed and the temperature was cooled to room temperature, it was again heated to 750°C for 20 seconds at 60% H. ２ +20%N ２ +20%NH ３ The mixture was introduced into a mixed gas atmosphere. The increase in nitrogen content at this time was 0.013% in the intermediate nitriding process and 0.012% in the additional nitriding process.

[0074] Subsequently, an annealing separation agent mainly composed of MgO was applied to the surface of the decarburized annealed plate. At that time, MgS and Al ２ See ３ Adding one or both of these increases the S content [S] Ｂ and Se content [Se] Ｂ An annealing separation agent was used, adjusted to the values ​​shown in Table 3 (by mass%). Ｓ (= [S] Ｂ +0.405[Se] Ｂ The values ​​for ) are shown in Table 3. Also, the application amount p (g / m) of the annealing separating agent is shown. ２ The values ​​shown in Table 3 were used. Next, finish annealing for secondary recrystallization was performed under conditions of a maximum temperature of 1200°C and a soaking time of 5 hours to obtain a finish annealed sheet. An insulating coating consisting of colloidal silica and aluminum phosphate was applied to the surface of the finish annealed sheet and baked at 860°C to obtain the final grain-oriented electrical steel sheet.

[0075] For the obtained grain-oriented electrical steel sheet, the magnetic flux density (B) at an excitation magnetic field of 800 A / m and an excitation frequency of 50 Hz was measured in accordance with JIS C2550-1:2011. ８ The magnetic flux density (B) obtained was measured. ８ The following is shown in Table 3. As is clear from Table 3, grain-oriented electrical steel sheets manufactured from hot-rolled sheets manufactured under the conditions of the present invention exhibited good magnetic properties, and even better magnetic properties were obtained by nitriding treatment.

[0076]

[0077] [Example 3] Molten steel having a composition consisting of the elements shown in Table 4, with the remainder being Fe and unavoidable impurities, was prepared in a laboratory vacuum melting furnace and poured into a mold to obtain a slab with a thickness of 50 mm. While the cast slab was still hot, it was heated for 10 minutes under conditions that the maximum surface temperature reached was 1200°C. Subsequently, the slab was hot-rolled to obtain a hot-rolled plate with a thickness of 1.5 mm. At that time, the surface temperature T at the center of the width direction of the slab on the hot-rolling entry side was adjusted to 870°C. The surface temperature of the slab was adjusted by blowing high-pressure air or water, which also served as descaling.

[0078] Subsequently, the hot-rolled sheet was subjected to hot-rolled sheet annealing at a soaking temperature of 1000°C for 20 seconds, scale was removed by pickling, and then cold-rolled to a final thickness of 0.23 mm. This cold-rolled sheet was then subjected to annealing at 830°C for 120 seconds at 45% H. ２ -55%N ２ The material was then annealed in a humid atmosphere with a dew point of 55°C for decarburization and primary recrystallization to obtain a decarburized annealed plate. Subsequently, an annealing separation agent mainly composed of MgO was applied to the surface of the decarburized annealed plate. At that time, MgSO was used as the annealing separation agent. ４ and SrSeO ４ By adding [S], the S content [S] Ｂ 2.0% by mass, Se content [Se] Ｂ It is 3.7% by mass, S Ｓ A 3.5% by mass annealing separation agent was used. Furthermore, the application amount p of the annealing separation agent was set to 18 g / m². ２These conditions satisfy equation (1). Next, finish annealing for secondary recrystallization was performed under conditions of a maximum temperature of 1180°C and a soaking time of 10 hours to obtain a finish annealed sheet. An insulating coating consisting of colloidal silica and aluminum phosphate was applied to the surface of the finish annealed sheet and baked at 840°C to obtain the final grain-oriented electrical steel sheet.

[0079] For the obtained grain-oriented electrical steel sheet, the magnetic flux density (B) at an excitation magnetic field of 800 A / m and an excitation frequency of 50 Hz was measured in accordance with JIS C2550-1:2011. ８ The magnetic flux density (B) obtained was measured. ８ The components are listed in Table 4. As is clear from Table 4, good magnetic properties were obtained by using a slab having a component composition according to the present invention.

[0080]

[0081] This invention can be applied to the manufacture of grain-oriented electrical steel sheets.

Claims

1. A process to produce a slab with a thickness of 30 mm to 80 mm by continuously casting molten steel having a composition in mass%, containing C: 0.10% or less, Si: 1.5% to 4.5%, Mn: 0.02% to 0.30%, acid-soluble Al: 0.040% or less, N: 0.015% or less, and one or both of S and Se: 0.025% or less in total, with the remainder being Fe and unavoidable impurities; a heating process thereafter, in which the slab is heated for a heating time of 5 minutes to 30 minutes and the maximum temperature reached on the surface of the slab is 1000°C to 1290°C; a hot rolling process thereafter, in which the slab is hot-rolled to obtain a hot-rolled sheet with a thickness of 1.0 mm to 3.5 mm; and an optional process thereafter, in which the hot-rolled sheet is hot-rolled sheet annealed. A method for producing grain-oriented electrical steel sheets, comprising the steps of: then subjecting the hot-rolled sheet to cold rolling once or two or more times with an intermediate annealing in between to obtain a cold-rolled sheet having a final thickness; then subjecting the cold-rolled sheet to decarburization annealing which also serves as primary recrystallization annealing to obtain a decarburized annealed sheet; and then applying an annealing separating agent mainly composed of MgO to the decarburized annealed sheet and performing finish annealing as secondary recrystallization annealing, wherein the annealing separating agent contains one or more selected from the group consisting of sulfides, sulfates, selenides, selenates, sulfites, selenites, and thiosulfates.

2. The method for producing a grain-oriented electrical steel sheet according to claim 1, which satisfies the following formula (1): C Ｓ ×1530×{1.4 + (900 - T) / 300} < S Ｓ ×p ・・・(1) wherein, C Ｓ = [S] Ａ + 0.405 [Se] Ａ ; wherein [S] Ａ and [Se] Ａ are respectively the S content (mass%) and Se content (mass%) in the component composition of the slab, T is the surface temperature (°C) at the center in the width direction of the slab on the entry side of the hot rolling, and S Ｓ = [S] Ｂ + 0.405 [Se] Ｂ ; wherein [S] Ｂ and [Se] Ｂ are respectively the S content (mass%) and Se content (mass%) in the annealing separator, and p is the coating amount (g / m ２ ) of the annealing separator.

3. The method for producing grain-oriented electrical steel sheet according to claim 1, wherein the component composition is: acid-soluble Al: 0.0020% or more and less than 0.0120%, N: 0.0010% or more and less than 0.0060%, S: less than 0.0050%, and Se: less than 0.0050%.

4. The method for producing grain-oriented electrical steel sheets according to claim 2, wherein the component composition is: acid-soluble Al: 0.0020% or more and less than 0.0120%, N: 0.0010% or more and less than 0.0060%, S: less than 0.0050%, and Se: less than 0.0050%.

5. A method for manufacturing a grain-oriented electrical steel sheet according to any one of claims 1 to 4, comprising the step of performing a nitriding treatment on the cold-rolled sheet during the decarburization annealing process, or on the decarburized annealed sheet after the decarburization annealing and before the finish annealing.

6. The component composition is: [Group A] One or more selected from the group consisting of Sb: 0.500% or less, Sn: 0.500% or less, Cr: 0.500% or less, Cu: 0.50% or less, Ni: 0.50% or less, Bi: 0.500% or less, P: 0.200% or less, Mo: 0.500% or less, and Co: 0.500% or less, in mass% or mass ppm; [Group B] One or more selected from the group consisting of B: 25.0 ppm or less, Nb: 0.020% or less, Ti: 0.0400% or less, V: 0.020% or less, and W: 0.020% or less, in mass% or mass ppm. A method for manufacturing grain-oriented electrical steel sheets according to any one of claims 1 to 5, comprising one or more groups selected from the group consisting of one or more selected from the group consisting of Zn: 0.0200% or less, Zr: 0.020% or less, Pb: 0.0100% or less, As: 0.020% or less, Ag: 0.050% or less, Au: 0.050% or less, Ga: 0.0050% or less, Ge: 0.0050% or less, Ca: 0.0200% or less, Mg: 0.0200% or less, REM: 0.0200% or less, and Hf: 0.020% or less, in mass%,

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