WO2023068236A1

WO2023068236A1 - Grain-oriented electromagnetic steel sheet and method for producing same

Info

Publication number: WO2023068236A1
Application number: PCT/JP2022/038635
Authority: WO
Inventors: 誠渡邉; 拓弥山田; 敬寺島
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2021-10-20
Filing date: 2022-10-17
Publication date: 2023-04-27
Also published as: JPWO2023068236A1

Abstract

The present invention provides a grain-oriented electromagnetic steel sheet which is free from defects such as cracking and chipping due to twinning deformation even if applied to a winding core or an iron core of a small power generator or the like, thereby being subjected to intense processing, and which is also free from deterioration in the magnetic characteristics. This grain-oriented electromagnetic steel sheet has a component composition that contains 2.8 mass% to 3.5 mass% of Si and 0.01 mass% to 1.0 mass% of Mn, with the balance being made up of Fe and unavoidable impurities, while having a base coating film that is mainly composed of forsterite and contains Ti, and a top coating film that is formed on the base coating film. With respect to this grain-oriented electromagnetic steel sheet, the base coating film has an oxygen weight per square meter of 3.8 g/m² or more and a Ti weight per square meter of 0.06 g/m² or less.

Description

Grain-oriented electrical steel sheet and manufacturing method thereof

The present invention is a grain-oriented electrical steel sheet mainly used for iron cores of transformers, electric motors, generators, etc., especially iron cores of small generators and small electric motors, or winding cores and EI cores. The present invention relates to a grain-oriented electrical steel sheet in which twinning is unlikely to occur even when subjected to shearing or the like, and a method for producing the same.

Grain-oriented and non-oriented electrical steel sheets are widely used as iron core materials for various transformers, electric motors, generators, etc. Of these, grain-oriented electrical steel sheets are highly concentrated in the {110}<001> orientation known as the Goss orientation, so they have high magnetic flux density and low iron loss. It is characterized by having good iron loss characteristics, which directly leads to the reduction of energy loss.

When such grain-oriented electrical steel sheets are used to manufacture iron cores for small generators and small electric motors, or EI cores, etc., they are subjected to a leveler process for correcting the shape of the coil, followed by punching or shearing. often do However, during the leveler treatment, punching, and shearing, the steel sheet may undergo twinning deformation, resulting in cracking, chipping, or warping, which may cause manufacturing troubles. Also, when manufacturing a wound core, twinning may occur when a steel sheet is wound and deformed into a core shape, degrading the magnetic properties.

Therefore, various techniques have been proposed to improve workability.
For example, in Patent Document 1, by reducing S and N in the raw material components and adding 0.5 to 5.0 mass% of the SO ₃ component mass of the SO ₃ compound to the annealing separator, twinning is achieved. Techniques for suppressing the generation have been proposed.

In addition, Patent Document 2 describes a technique for forming a forsterite coating with excellent coating properties by including a Ti compound in an annealing separator, wherein the Ti concentration of the steel sheet including the forsterite coating is 1 with respect to the N concentration. Techniques have been proposed to prevent cracking during shearing and bending by reducing N in the steel to a range of 0.0 to 2.0 times.

Patent Document 3 discloses a technique for reducing the number of origins of twinning by refining the secondary recrystallized grain size in the direction perpendicular to rolling (C direction) and reducing the unevenness of the film/base iron interface. It is

JP-A-2000-256810 JP-A-06-179977 Japanese Patent Publication No. 2013-58239

Although the workability can be improved without degrading the magnetic properties of the grain-oriented electrical steel sheet by applying the above-described prior art, further improvement is required for suppressing the occurrence of twins.
For example, when the technique described in Patent Document 1 is applied, although the twinning rate is greatly reduced, the twinning rate may be as high as about 10%, although it is within the range of variation. improvement is required.

In addition, although the bending workability is improved by optimizing the concentration ratio of Ti and N according to Patent Document 2, twins that occur during bending have not been studied, so the rate of twinning is reduced. In order to achieve this, further consideration is required.

Refining the secondary grain size in the direction perpendicular to rolling, as described in Patent Document 3, is effective in reducing twins. , the secondary recrystallized grains are coarsened, so there is room for improvement in that strict control is required.

The present invention has been made in view of the above-mentioned circumstances of the prior art. Provided is a grain-oriented electrical steel sheet that does not suffer from cracking or chipping due to twinning deformation even in applications that undergo strong processing, such as iron cores and winding cores of small generators, and that does not deteriorate in magnetic properties. to propose.

In order to solve the above problems, the inventors have developed a grain-oriented electrical steel sheet having good coating properties, which has a Ti-containing forsterite coating as a base coating formed by applying an annealing separator containing a Ti compound. Extensive experiments were conducted, and measures to reduce the twinning rate compared to the conventional technology were examined. As a result, it was found that the oxygen basis weight of the undercoat and the amount of Ti contained in the undercoat have a great effect on the occurrence of twins. The inventors have newly found that it is effective to increase the oxygen basis weight and limit the amount of Ti in the undercoat, and have developed the present invention.
That is, the gist and configuration of the present invention are as follows.

1. A component composition containing Si: 2.8 to 3.5 mass% and Mn: 0.01 to 1.0 mass%, the balance being Fe and unavoidable impurities, and a base coat containing Ti and mainly composed of forsterite and and a topcoat formed on the undercoat, wherein the undercoat has an oxygen basis weight of 3.8 g/m ² or more and a Ti basis weight of 0.06 g/m ² or less. .

2. The component composition further includes Al: more than 0 mass% and 0.015 mass% or less, N: more than 0 mass% and 0.007 mass% or less, Cu: more than 0 mass% and 0.14 mass% or less, Ni: more than 0 mass% and 0.3 mass% or less. , Cr: more than 0 mass% and 0.06 mass% or less, Sb: more than 0 mass% and 0.04 mass% or less, Sn: more than 0 mass% and 0.04 mass% or less, Mo: more than 0 mass% and 0.1 mass% or less, B: more than 0 mass% 0.01 mass% or less, P: more than 0 mass% and 0.06 mass% or less, Nb: more than 0 mass% and 0.02 mass% or less, Bi: more than 0 mass% and 0.01 mass% or less, Ge: more than 0 mass% and 0.05 mass% or less, One selected from As: more than 0 mass% and 0.05 mass% or less, Te: more than 0 mass% and 0.02 mass% or less, Ti: more than 0 mass% and 0.04 mass% or less, and V: more than 0 mass% and 0.03 mass% or less Or the grain-oriented electrical steel sheet according to 1 above containing two or more kinds.

3. C: 0.001 to 0.10 mass%, Si: 2.8 to 3.5 mass%, Mn: 0.01 to 1.0 mass%, one or two selected from S and Se in total 0 A steel slab having a chemical composition containing 0.005 to 0.03 mass% and the balance being Fe and unavoidable impurities is hot-rolled to form a hot-rolled sheet, and the hot-rolled sheet is subjected to one or intermediate annealing. A cold-rolled sheet is obtained by sandwiching and cold-rolling two or more times, and the cold-rolled sheet is subjected to primary recrystallization annealing, then an annealing separator is applied, and then finish annealing is performed to obtain a finish-annealed sheet. A method for producing a grain-oriented electrical steel sheet, comprising applying a coating liquid to an annealed sheet and performing flattening annealing to obtain a grain-oriented electrical steel sheet,
The oxygen basis weight on the surface of the steel sheet after the primary recrystallization annealing is 1.5 g/m ² or more and 2.1 g/m ² or less, and as the annealing separator, TiO ₂ is 0.6 per 100 parts by mass of MgO. A method for producing a grain-oriented electrical steel sheet, characterized by using an annealing separator containing up to 2.7 parts by mass, and setting the rate of temperature increase between 700 to 950°C in the final annealing to 15°C/h or more. .

4. The chemical composition of the steel slab further includes Al: 0.003 to 0.015 mass%, N: 0.001 to 0.007 mass%, Cu: 0.01 to 0.14 mass%, Ni: 0.01 to 0. .3 mass%, Cr: 0.01 to 0.06 mass%, Sb: 0.004 to 0.04 mass%, Sn: 0.005 to 0.04 mass%, Mo: 0.01 to 0.1 mass%, B: 0.001 to 0.01mass%, P: 0.005 to 0.06mass%, Nb: 0.002 to 0.02mass%, Bi: 0.001 to 0.01mass%, Ge: 0.001 to 0.01mass% 05 mass%, As: 0.005 to 0.05 mass%, Te: 0.005 to 0.02 mass%, Ti: 0.005 to 0.04 mass% and V: 0.005 to 0.03 mass% 3. The method for producing a grain-oriented electrical steel sheet according to 3 above, containing one or more of

According to the present invention, it is possible to provide a grain-oriented electrical steel sheet that is less likely to undergo twinning deformation and has less deterioration in magnetic properties even when used for applications that require strong working. Therefore, by using the grain-oriented electrical steel sheet of the present invention, it is possible not only to reduce troubles such as cracks and chips when processing iron cores and wound cores of small generators, but also to reduce energy loss in generators, transformers, etc. enables the production of

First, the experimental results leading to the present invention will be described.
C: 0.04 mass%, Si: 2.9 mass%, Mn: 0.06 mass%, Se: 0.01 mass% and Sb: 0.01 mass%, the balance being Fe and unavoidable impurities The steel slab having the steel sheet was hot-rolled by a known method to obtain a hot-rolled sheet, and then hot-rolled sheet annealing was performed at 850° C. for 30 seconds. After that, cold rolling was performed twice or more with intermediate annealing at 900° C. for 1 minute to finish a cold-rolled sheet having a final thickness of 0.30 mm. Next, the cold-rolled sheets were subjected to primary recrystallization annealing, which also serves as decarburization annealing, at 840° C. for 140 seconds in various atmospheres with a PH ₂ O/PH ₂ ratio of 0.39 to 0.61. At this time, as shown in Table 1, the oxygen basis weight on the surface of the cold-rolled sheet after the primary recrystallization annealing (hereinafter also referred to as decarburization-annealed sheet) was variously changed. After that, an annealing separator was applied to both the front and back surfaces of the decarburized annealed sheet. As the annealing separating agent, a powder obtained by changing the amount of TiO ₂ added to 100 parts by mass of MgO as shown in Table 1 was slurried, and the amount of hydration was 2.0 mass%. It was applied at 15 g/m ² so as to be After the application, it was dried, wound into a coil, and subjected to final annealing. In the final annealing, the temperature was raised from 700 to 950°C at a temperature elevation rate of 15°C/h, followed by holding treatment at 1160°C for 5 hours for purification. In this final finish annealing, an undercoat was formed on the surface of the decarburized annealed sheet. After that, a coating solution consisting of magnesium phosphate, colloidal silica, and chromic anhydride is applied to the undercoating, and then baked and flattened to correct the shape of the steel plate. steel plate) was obtained. In this flattening annealing, a top coat was formed on the base coat.

For each steel sheet thus obtained, the oxygen basis weight of the decarburized annealed sheet after primary recrystallization annealing (hereinafter also referred to as the oxygen basis weight after decarburization annealing), the oxygen basis weight and the Ti basis weight of the undercoat Table 1 shows the measurement results of , and the investigation results of the magnetic flux density and twinning rate in the steel sheet.

Here, the above oxygen basis weight can be measured by a melting-infrared absorption method. Similarly, the Ti basis weight can be measured by emission spectroscopy.

In addition, the magnetic flux density is the magnetic flux density when excited at 800 A / m: B ₈ (T) according to JISIt was measured according to the method specified in C2550.

Furthermore, the twinning rate was measured by taking 60 or more JIS No. 5 test pieces (samples) from each steel plate, subjecting each JIS No. 5 test piece to a tensile test at room temperature at a tensile speed of 10 m / min, and then pickling it. The macro-etched surface is visually observed, and a sample in which twin lines are observed is determined to be a twinned sample. It is a ratio (%).

From Table 1, it can be seen that in the undercoating, if the oxygen basis weight is 3.8 g/m ² or more and the Ti basis weight is 0.06 g/m ² or less, the twinning rate is effectively 1.5% or less. It turns out that it is decreasing.

Furthermore, as shown in Table 1, in order to control the oxygen basis weight of the undercoat to 3.8 g/m ² or more, the oxygen basis weight after decarburization annealing should be increased, and the amount of TiO ₂ in the annealing separator should be increased. Both increasing the amount contributes. However, when the oxygen basis weight after decarburization annealing was increased too much, the oxygen basis weight of the undercoat decreased rapidly. In addition, both the oxygen basis weight after decarburization annealing and the TiO ₂ amount in the annealing separator also contribute to the control of the Ti basis weight of the undercoat, reducing the Ti basis weight, especially 0.06 g /m ² or less, it was effective not only to reduce the TiO ₂ content in the annealing separator, but also to reduce the oxygen basis weight after decarburization annealing.

Although the reason why such a result was obtained is not clear, the present inventors consider as follows.
In grain-oriented electrical steel sheets, the orientation of secondary recrystallized grains is highly concentrated in {110}<001>. The sliding system of <111> works to cause deformation twinning. However, the twinning deformation occurs only when the strain rate is high or when the deformation is performed at a low temperature because the deformation energy is high. In general, such twins are reduced by, for example, reducing coarse inclusions or refining the crystal grain size to reduce local stress concentration, or by reducing impurities to reduce strength against material deformation. is considered valid. In relation to the coating, the strength of the coating is increased by introducing S into the coating as described in Patent Document 1 above, or by adjusting the ratio of Ti and N as described in Patent Document 2. It is known that increasing In contrast, the above findings suggest that factors other than film strength are involved. That is, the present inventors considered that it is important not to directly transmit the coating tension due to the overcoat to the steel substrate. In other words, the top coat applies stress in the tensile direction to the steel sheet, and under this condition, twinning occurs when deformation stress is further applied. Conversely, if the film stress is not applied, twins are unlikely to occur even with some deformation stress.

Then, when the oxygen basis weight of the undercoating is increased by a certain amount or more, the stress of the overcoating coating in the upper layer is relaxed in the undercoating, and the stress applied to the base steel is reduced. Further, as the Ti content in the undercoat increases, the tension in the undercoat itself increases, so twinning is more likely to occur.

Next, a method for controlling the oxygen basis weight of the undercoat will be described.
Since the oxygen basis weight of the undercoating generally correlates with the oxygen basis weight of the surface of the steel sheet after decarburization annealing, increasing this increases the oxygen basis weight of the undercoating. However, if the oxygen basis weight after decarburization annealing is too high, the amount of the undercoat formed will be too large, and the undercoat will partially peel off, thereby decreasing the oxygen basis weight of the undercoat. Therefore, there is an appropriate range for the oxygen basis weight after decarburization annealing.

Furthermore, in addition to adjusting the oxygen basis weight after decarburization annealing, the oxygen basis weight of the undercoating can also be increased by increasing the amount of TiO ₂ in the annealing separator. That is, TiO ₂ decomposes during final annealing to generate oxygen, which oxidizes the steel sheet and increases the amount of undercoating formed.

Furthermore, a method for controlling the Ti weight per unit area of the undercoat will be described.
Since the Ti source is TiO ₂ in the annealing separator, the Ti basis weight is almost correlated with the amount of TiO ₂ added. Besides adjusting the amount of TiO ₂ , the basis weight of oxygen after decarburization annealing also has an effect. This is because when the oxygen basis weight after decarburization annealing is high, oxides present in the subscale surface layer, such as Fe ₂ SiO ₄ , and TiO ₂ undergo a substitution reaction to form FeTiO ₃ . It is considered that the amount of Ti in the coating increases because Ti easily penetrates into the coating.

As described above, both the oxygen basis weight after decarburization annealing and the amount of _TiO2 added in the annealing separator affect both the oxygen basis weight and the Ti basis weight of the undercoat. By optimizing the basis weight and the amount of TiO ₂ added in the annealing separator, respectively, the oxygen basis weight and the Ti basis weight of the undercoat can be kept within appropriate ranges, and the twinning rate can be reduced.

The present invention will be specifically described below. First, the grain-oriented electrical steel sheet targeted by the present invention will be described.
The grain-oriented electrical steel sheet targeted by the present invention contains Si: 2.8 to 3.5 mass%, Mn: 0.01 to 1.00 mass%, and the balance is Fe and unavoidable impurities. It has an undercoat containing Ti and mainly composed of forsterite and a top coat formed on the undercoat.

In this grain-oriented electrical steel sheet, it is essential that the undercoating has an oxygen basis weight of 3.8 g/m ² or more and a Ti basis weight of 0.06 g/m ² or less. This is based on the above-described new knowledge that strain due to tension in the overcoat promotes twinning, and that if the stress caused by the overcoat is relieved by the undercoat, the occurrence of twins can be suppressed.
That is, when the oxygen basis weight of the undercoat is less than 3.8 g/m ² , the ability of the undercoat to relax the tension of the coating decreases, resulting in an increase in twinning rate. On the other hand, if the Ti basis weight exceeds 0.06 g/m ² , the tension of the undercoat itself increases, so the twinning rate also increases. Therefore, in the undercoating, the oxygen basis weight should be 3.8 g/m ² or more and the Ti basis weight should be 0.06 g/m ² or less.

On the other hand, it is not necessary to limit the upper limit of the oxygen basis weight and the lower limit of the Ti basis weight in the undercoating. However, from the viewpoint of film adhesion, the oxygen basis weight of the undercoat is preferably 5.0 g/m ² or less. From the same point of view, it is preferable that the Ti basis weight in the undercoating is 0.01 g/m ² or more.

For the overcoat to be formed on the undercoat, any type of overcoat can be applied as a topcoat for grain-oriented electrical steel sheets. For example, a tension-imparting coating obtained by coating and baking a coating liquid consisting of magnesium phosphate-colloidal silica-titanium sulfate can be applied.

Furthermore, the grain-oriented electrical steel sheet targeted by the present invention preferably has a magnetic flux density of 1.88 T or less at _B8 . The reason why it is desirable to lower the magnetic flux density is that when the magnetic flux density is high, the secondary recrystallized grain size usually becomes large, the grain boundary density decreases, and twin crystals are likely to develop. If the secondary recrystallized grain size is made finer by setting the magnetic flux density to a lower value, it is possible to prevent the strain imparted during working from being locally concentrated, making it easier to prevent twinning deformation. Therefore, the present invention cannot be applied to, for example, a technique in which a coil is annealed under a temperature gradient to elongate secondary recrystallized grains. Also, the technique of growing secondary recrystallized grains by holding in the secondary recrystallization temperature range during final annealing is not suitable for the present invention.

The chemical composition of the grain-oriented electrical steel sheet is further selected from Al, N, Cu, Ni, Cr, Sb, Sn, Mo, B, P, Nb, Bi, Ge, As, Te, Ti and V. You may contain 1 type(s) or 2 or more types. Specifically, the chemical composition of the grain-oriented electrical steel sheet is as follows: Al: more than 0 mass% and 0.015 mass% or less, N: more than 0 mass% and 0.007 mass% or less, Cu: more than 0 mass% and 0.14 mass% or less, Ni: 0 mass% % to 0.3 mass%, Cr: 0 mass% to 0.06 mass%, Sb: 0 mass% to 0.04 mass%, Sn: 0 mass% to 0.04 mass%, Mo: 0 mass% to 0.1 mass% Below, B: more than 0 mass% and 0.01 mass% or less, P: more than 0 mass% and 0.06 mass% or less, Nb: more than 0 mass% and 0.02 mass% or less, Bi: more than 0 mass% and 0.01 mass% or less, Ge: 0 mass% More than 0.05 mass% or less, As: more than 0 mass% and 0.05 mass% or less, Te: more than 0 mass% and 0.02 mass% or less, Ti: more than 0 mass% and 0.04 mass% or less, and V: more than 0 mass% and 0.03 mass% or less You may contain 1 type(s) or 2 or more types chosen from the inside.

Next, a method for manufacturing the grain-oriented electrical steel sheet will be described.
First, the chemical composition of the steel slab will be explained.

C: 0.001 to 0.10 mass%
C is a component necessary for generating Goss-oriented crystal grains, and should be contained in an amount of 0.001 mass% or more in order to exhibit such an effect. On the other hand, addition exceeding 0.10 mass% makes it difficult to decarburize to a level that does not cause magnetic aging in the subsequent decarburization annealing. Therefore, the C content should be in the range of 0.001 to 0.10 mass%. The content of C is preferably 0.015 mass% or more, and preferably 0.08 mass% or less.

Si: 2.8-3.5 mass%
Si is a necessary component for increasing the electrical resistance of steel to reduce core loss, stabilizing the BCC structure, and enabling high-temperature heat treatment, and should be added in an amount of at least 2.8 mass%. However, addition of more than 3.5 mass% lowers the workability and makes it difficult to manufacture by cold rolling. Therefore, the Si content should be in the range of 2.8 to 3.5 mass%. Including the effect of preventing the occurrence of twins, the Si content is preferably 2.8 mass% or more and preferably 3.3 mass% or less.

Mn: 0.01 to 1.0 mass%
Mn is effective in improving the hot shortness of steel, and when it contains S and Se, it forms precipitates such as MnS and MnSe, and is an element that functions as an inhibitor. is. The above effect can be obtained by addition of 0.01 mass% or more. However, if it is added in excess of 1.0 mass%, precipitates such as MnSe become coarse, and the inhibitor effect is lost. Therefore, the content of Mn should be in the range of 0.01 to 1.0 mass%. The content of Mn is preferably 0.03 mass% or more and preferably 0.50 mass% or less.

S, Se: 0.005 to 0.03 mass% in total of 1 type or 2 types
S and Se are useful components that combine with Mn and Cu to form MnSe, MnS, Cu _2-x Se, and Cu _2-x S, precipitate as dispersed second phases in steel, and exhibit inhibitory action. be. If the total content of S and Se is less than 0.005 mass%, the above addition effect is not sufficient. becomes. Therefore, the amount of these elements to be added should be in the range of 0.005 to 0.03 mass%, whether they are added singly or in combination. The total content of S and Se is preferably 0.006 mass% or more and preferably 0.020 mass% or less.

In addition to the above chemical composition, the steel slab used for manufacturing the grain-oriented electrical steel sheet of the present invention further contains Al (sol. Al): 0.003 to 0.015 mass%, N: 0.001 to 0.007 mass%. %, Cu: 0.01 to 0.14 mass%, Ni: 0.01 to 0.3 mass%, Cr: 0.01 to 0.06 mass%, Sb: 0.004 to 0.04 mass%, Sn: 0.04 mass%. 005-0.04mass%, Mo: 0.01-0.1mass%, B: 0.001-0.01mass%, P: 0.005-0.06mass%, Nb: 0.002-0.02mass% , Bi: 0.001 to 0.01 mass%, Ge: 0.001 to 0.05 mass%, As: 0.005 to 0.05 mass%, Te: 0.005 to 0.02 mass%, Ti: 0.005 0.04 mass% and one or more selected from V: 0.005 to 0.03 mass%.

Al, N, Cu, Ni, Cr, Sb, Sn, Mo, B, P, Nb and Bi segregate on the grain boundaries and on the surface of the steel sheet and act as auxiliary inhibitors to improve the magnetic properties. can be added as necessary. However, in order to prevent the magnetic flux density from being excessively increased above a certain level as in the present invention, it is necessary to reduce the amount of addition as compared with the prior art. Therefore, when it is added, it is preferable to set it as the above range.

In addition, since each element of Ge, As, Te, Ti, and V has a stable inhibitory effect (inhibiting power), even in processes such as slab heating and finish annealing, where temperature variations occur within the steel sheet, Since it can be present in the coil, it has the effect of stabilizing the magnetic flux density over the entire length of the coil, so it can be added as necessary.

Among the components described above, C is decarburized during the manufacturing process and removed from the steel, and S and Se are purified and removed from the steel in the final annealing. The content is also at the level of unavoidable impurities.

Next, manufacturing conditions for the grain-oriented electrical steel sheet according to the present invention will be described in detail.
The grain-oriented electrical steel sheet of the present invention is produced by melting steel having the chemical composition described above by a conventionally known refining process, and using a continuous casting method or an ingot casting-slabbing rolling method or the like to form a steel material (steel slab). After that, the steel material is hot-rolled to obtain a hot-rolled sheet, and if necessary, hot-rolled sheet annealing is performed, and cold rolling is performed once or twice or more with intermediate annealing. The cold-rolled sheet shall be thick. For the purpose of refining secondary grains and suppressing the occurrence of twins without excessively increasing the magnetic flux density, as in the present invention, a lower final cold rolling reduction is desirable. Specifically, the final cold rolling reduction is preferably 50 to 70%, more preferably 55 to 66%.

Next, the cold-rolled sheet is subjected to primary recrystallization annealing or primary recrystallization annealing that also serves as decarburization annealing. Moreover, at this time, nitriding treatment may be performed as necessary. It is the first feature of the present invention and one of the main elements of the present invention to adjust the oxygen basis weight (of the oxide film) formed at this time to be higher than before.
That is, at least one of the temperature, time and atmosphere in the primary recrystallization annealing is adjusted so that the oxygen basis weight on the steel sheet surface after the primary recrystallization annealing is 1.5 to 2.1 g/m ² . Here, the reason why the oxygen basis weight on the surface of the steel sheet after primary recrystallization annealing is 1.5 to 2.1 g/m ² is to set the oxygen basis weight and the Ti basis weight in the undercoating to appropriate ranges. . In particular, when the oxygen basis weight is less than 1.5 g/m ² , the formation of the undercoat becomes insufficient, and when the oxygen basis weight exceeds 2.1 g/m ² , the formation of the undercoat becomes excessive. In the end, point-like peeling occurs, and a sufficient effect cannot be obtained.

As the conditions for the primary recrystallization annealing to set the oxygen basis weight after the primary recrystallization annealing within the above range, the annealing temperature is preferably 700 to 900° C. and the annealing time is preferably 30 to 300 seconds. If the annealing temperature is less than 700° C. or the annealing time is less than 30 seconds, the desired oxygen basis weight cannot be secured or decarburization becomes insufficient. On the other hand, if the annealing temperature exceeds 900° C. or the annealing time exceeds 300 seconds, the oxygen basis weight becomes excessive. Also, the decarburization annealing is performed in a wet hydrogen atmosphere. The dew point is in the range of 45 to 60° C., and the H ₂ concentration is a conventional method, which can be in the range of 40% to 80%. By adjusting the atmosphere oxidizing PH ₂ O/PH ₂ from the dew point and the H ₂ concentration, the oxygen basis weight can be adjusted. This PH ₂ O/PH ₂ is desirably in the range of 0.40 to 0.55. It is also possible to change at each stage of the heating zone and soaking zone.

The soaking area can be divided into two stages, a front stage and a rear stage. Both or one of the soaking temperature and the atmospheric oxidizing PH ₂ O/PH ₂ conditions are different between the former stage and the latter stage. When the soaking temperature is changed, the temperature difference between the former stage and the latter stage shall be 20°C or more. If oxidizing, change the PH ₂ O/PH ₂ difference by 0.2 or more. In general, the temperature is not particularly limited, but the latter stage should be higher than the former stage. Regarding atmospheric oxidizability, PH ₂ O/PH ₂ is often lower in the latter stage than in the former stage, and this can be followed in the present invention. Furthermore, it is also possible to divide the preceding stage into a plurality of stages, in which case the temperature and/or PH ₂ O/PH ₂ difference between the final stage and the preceding stage is within the above range. The final soaking region when changing the temperature or PH ₂ O/PH ₂ in this manner is defined as the final stage.

In addition, in order to realize the high oxygen basis weight specified in the present invention, it is possible to devise the pretreatment of the primary recrystallization annealing. For example, when cleaning a rolled sheet (cold-rolled sheet), electrolytic degreasing is performed with a degreasing solution (electrolytic solution) containing sodium silicate. As a result, the SiO ₂ compound is electrodeposited on the surface of the steel sheet, which serves as a starting point for oxidation during decarburization annealing, and can increase the oxygen basis weight.

Since the oxygen basis weight after the primary recrystallization annealing changes depending on the material composition and the previous process, it is necessary to adjust the annealing conditions according to each process. For example, if the Si content in the steel material is as low as 3 mass% or less, the oxygen basis weight tends to decrease, so the dew point is set high. In addition, if the steel sheet surface before primary recrystallization annealing has a high oxygen basis weight of 0.1 g/m ² or more, it is effective to set the dew point to a lower value.

Furthermore, in order to increase the oxygen basis weight after the primary recrystallization annealing, it is possible to set the dew point of the heating area higher and the dew point of the soaking area lower. These treatments are not particularly limited, and any conditions may be used as long as the oxygen basis weight can be kept within the desired range.

After the primary recrystallization annealing, the surface of the steel sheet is coated with an annealing separator containing MgO as a main component. At this time, the annealing separating agent used is one to which TiO ₂ is added. The reason why TiO ₂ is added here is mainly from the viewpoint of enhancing film adhesion, and this addition of TiO ₂ has been conventionally performed. The second feature of the present invention is that the amount of TiO ₂ added is kept to a very small amount. That is, the amount of TiO ₂ added to the annealing separator used in the present invention is in the range of 0.6 to 2.7 parts by mass when MgO is 100 parts by mass. If the amount (content) of TiO ₂ added to the annealing separating agent is less than 0.6 parts by mass, the film adhesion is lowered, and the underlying pattern is generated. On the other hand, when the amount of TiO ₂ added to the annealing separator is higher than 2.7 parts by mass, the amount of Ti contained in the undercoating exceeds 0.06 g/m ² in terms of Ti basis weight, and the twinning rate increases. will do.

The conditions of the annealing separator other than the amount of TiO ₂ added may be as known. For example, in addition to _TiO2 , additives for the annealing separator include borates such as Li, Na, K, Mg, Ca, Sr, Sn, Sb, Cr, Fe, and Ni, sulfates, carbonates, and water. Oxides, chlorides and the like can be added singly or in combination. Also, the amount of the annealing separator applied to the surface of the steel sheet is preferably 8 to 16 g/m ² on both sides, and the hydration amount is preferably in the range of 0.5 to 3.7 mass%. Further, the annealing separating agent is usually made into a slurry with water, coated with a roll coater, and then dried. This method can also be used in the present invention.

After applying the annealing separator, finish annealing is applied. A third feature of the present invention is to specify the rate of temperature increase at this time. That is, the rate of temperature increase between 700 and 950° C. in the final annealing must be 15° C./h or more. This temperature range is the temperature range in which the formation of the undercoating begins in earnest, and is also the temperature range immediately before TiO ₂ in the annealing separator decomposes and Ti penetrates into the undercoating. If the rate of temperature rise in this temperature range is slow, the substitution reaction that forms _FeTiO3 from _Fe2SiO4 proceeds _too much, Ti penetrates too much into the film, and the Ti content in the undercoat increases. In addition, as a result of the loss of MgO activity at this temperature, subsequent film reaction is less likely to proceed, and the oxygen basis weight of the undercoat also decreases. Furthermore, as a result of promoting the growth of secondary recrystallized grains at this temperature, the grain size becomes coarse. Therefore, the rate of temperature increase between 700 and 950° C. in the final annealing should be 15° C./h or more, preferably 20° C./h or more.

Other conditions in the finish annealing may be as usual. For example, the atmosphere may be H ₂ , N ₂ , Ar, or a mixture of these. The final annealing (retaining treatment) is generally performed at a temperature of 1150° C. or higher and 1250° C. or lower for a time of 3 hours or longer and 50 hours or shorter, and the present invention is also within this range. If the temperature is lower than 1150° C. or the time is shorter than 3 hours, purification may be insufficient and precipitates may remain, resulting in an increased twinning rate. On the other hand, if the temperature is higher than 1250° C. or the time is longer than 50 hours, the coil may buckle and the yield may decrease.

Further, after the final annealing, an insulating coating is applied and flattening annealing, which also serves as baking, is performed.
As described above, it is possible to obtain a grain-oriented electrical steel sheet in which twinning is less likely to occur even if it is subjected to heavy working by manufacturing with a manufacturing method consisting of a series of steps.

Contains C: 0.05 mass%, Si: 3.2 mass%, Mn: 0.06 mass%, S: 0.01 mass%, Al: 0.006 mass%, N: 0.004 mass% and Mo: 0.01 mass% Then, a steel slab having a chemical composition in which the balance is Fe and unavoidable impurities is heated at 1410 ° C. for 30 minutes, hot-rolled to a hot-rolled sheet with a thickness of 2.5 mm, and heated at 1000 ° C. for 1 minute. The hot-rolled sheet was annealed. After that, it was cold-rolled to a thickness of 0.9 mm, subjected to intermediate annealing at 980° C. for 1 minute, and then cold-rolled to a final thickness of 0.35 mm.

Next, primary recrystallization annealing, which also serves as decarburization annealing, was performed at 850° C. for 120 seconds in an atmosphere with a PH ₂ O/PH ₂ ratio of 0.51. At this time, the oxygen basis weight of the decarburized annealed sheet was set to 2.0 g/m ² . Further, after that, powder obtained by adding 2.4 parts by mass of TiO ₂ and 0.1 part by mass of Li ₂ SO ₄ to 100 parts by mass of MgO as an annealing separator was made into a slurry, and the amount of hydration was 1.0 parts by mass. It was coated on both sides of the steel sheet at 11 g/m ² so as to be 3 mass%. After the application, it was dried, wound into a coil, and subjected to final annealing. In the final annealing, the temperature was raised between 700 and 950° C. at various heating rates shown in Table 2, followed by holding treatment at 1160° C. for 5 hours for purification.

After that, a coating liquid consisting of magnesium phosphate-colloidal silica-titanium sulfate was applied, and flattening annealing was performed for both baking and shape correction of the steel sheet to obtain a product coil (grain-oriented electrical steel sheet).
The steel sheets thus obtained were examined for magnetic flux density _B8 and twinning rate. The results are shown in Table 2 together with the oxygen basis weight and Ti basis weight of the undercoat. The oxygen basis weight, Ti basis weight, magnetic flux density _B8 , and twinning rate of the undercoat were measured according to the above-described measurement method.

From Table 2, it can be seen that when the heating rate is slow, the oxygen basis weight of the undercoat decreases, the Ti content increases, and the twinning rate increases accordingly.

A steel slab containing the various components shown in Table 3, with the balance being Fe and unavoidable impurities, was heated at 1380 ° C. for 60 minutes and then hot rolled to a thickness of 2.2 mm. A hot-rolled sheet was annealed at 1000° C. for 1 minute. After that, it was cold rolled to an intermediate plate thickness of 0.8 mm, subjected to intermediate annealing at 1000° C. for 2 minutes, and further cold rolled to obtain a cold rolled plate having a final thickness of 0.27 mm. This was subjected to electrolytic degreasing at 10 C/dm ² with an electrolytic solution containing 2% sodium silicate, and then decarburization annealing at 820° C. for 100 seconds in an atmosphere of PH ₂ O/PH ₂ of 0.46. Also, primary recrystallization annealing was performed. Further, after that, a powder obtained by adding 1.5 parts by mass of TiO ₂ and 2.5 parts by mass of calcium hydroxide to 100 parts by mass of MgO as an annealing separator was made into a slurry, and the hydration amount was 1.0 mass%. 10 g/m ² was applied to both sides of the steel plate so that After the application, it was dried, wound into a coil, and subjected to final annealing. In the final annealing, the temperature was raised from 700 to 950°C at a temperature elevation rate of 20°C/h, followed by holding treatment at 1180°C for 10 hours for purification. After that, a coating liquid consisting of magnesium phosphate-colloidal silica-titanium sulfate was applied, and flattening annealing was performed for both baking and shape correction of the steel sheet to obtain a product coil (grain-oriented electrical steel sheet).

The steel sheets thus obtained were examined for magnetic flux density _B8 and twinning rate. The results are shown in Table 3 together with the oxygen basis weight after primary recrystallization annealing, the oxygen basis weight in the undercoat and the Ti basis weight. The oxygen basis weight after the primary recrystallization annealing, the oxygen basis weight and Ti basis weight in the undercoat, the magnetic flux density _B8 and the twinning rate were measured according to the measurement method described above.

From Table 3, under the conditions in which electrolytic degreasing is performed and the oxygen basis weight after primary recrystallization annealing is within an appropriate range, the oxygen basis weight of the undercoating increases and the Ti basis weight decreases regardless of the steel sheet composition. It can be seen that the twinning rate is improved accordingly.

Claims

A component composition containing Si: 2.8 to 3.5 mass% and Mn: 0.01 to 1.0 mass%, the balance being Fe and unavoidable impurities, and a base coat containing Ti and mainly composed of forsterite and and a topcoat formed on the undercoat, wherein the undercoat has an oxygen basis weight of 3.8 g/m 2 or more and a Ti basis weight of 0.06 g/m 2 or less. .
The component composition further includes Al: more than 0 mass% and 0.015 mass% or less, N: more than 0 mass% and 0.007 mass% or less, Cu: more than 0 mass% and 0.14 mass% or less, Ni: more than 0 mass% and 0.3 mass% or less. , Cr: more than 0 mass% and 0.06 mass% or less, Sb: more than 0 mass% and 0.04 mass% or less, Sn: more than 0 mass% and 0.04 mass% or less, Mo: more than 0 mass% and 0.1 mass% or less, B: more than 0 mass% 0.01 mass% or less, P: more than 0 mass% and 0.06 mass% or less, Nb: more than 0 mass% and 0.02 mass% or less, Bi: more than 0 mass% and 0.01 mass% or less, Ge: more than 0 mass% and 0.05 mass% or less, One selected from As: more than 0 mass% and 0.05 mass% or less, Te: more than 0 mass% and 0.02 mass% or less, Ti: more than 0 mass% and 0.04 mass% or less, and V: more than 0 mass% and 0.03 mass% or less Or the grain-oriented electrical steel sheet according to claim 1, containing two or more kinds.
C: 0.001 to 0.10 mass%, Si: 2.8 to 3.5 mass%, Mn: 0.01 to 1.0 mass%, one or two selected from S and Se in total 0 A steel slab having a chemical composition containing 0.005 to 0.03 mass% and the balance being Fe and unavoidable impurities is hot-rolled to form a hot-rolled sheet, and the hot-rolled sheet is subjected to one or intermediate annealing. A cold-rolled sheet is obtained by sandwiching and cold-rolling two or more times, and the cold-rolled sheet is subjected to primary recrystallization annealing, then an annealing separator is applied, and then finish annealing is performed to obtain a finish-annealed sheet. A method for producing a grain-oriented electrical steel sheet, comprising applying a coating liquid to an annealed sheet and performing flattening annealing to obtain a grain-oriented electrical steel sheet,
The oxygen basis weight on the surface of the steel sheet after the primary recrystallization annealing is 1.5 g/m 2 or more and 2.1 g/m 2 or less, and as the annealing separator, TiO 2 is 0.6 per 100 parts by mass of MgO. A method for producing a grain-oriented electrical steel sheet, characterized by using an annealing separator containing up to 2.7 parts by mass, and setting the rate of temperature increase between 700 to 950°C in the final annealing to 15°C/h or more. .
The chemical composition of the steel slab further includes Al: 0.003 to 0.015 mass%, N: 0.001 to 0.007 mass%, Cu: 0.01 to 0.14 mass%, Ni: 0.01 to 0. .3 mass%, Cr: 0.01 to 0.06 mass%, Sb: 0.004 to 0.04 mass%, Sn: 0.005 to 0.04 mass%, Mo: 0.01 to 0.1 mass%, B: 0.001 to 0.01mass%, P: 0.005 to 0.06mass%, Nb: 0.002 to 0.02mass%, Bi: 0.001 to 0.01mass%, Ge: 0.001 to 0.01mass% 05 mass%, As: 0.005 to 0.05 mass%, Te: 0.005 to 0.02 mass%, Ti: 0.005 to 0.04 mass% and V: 0.005 to 0.03 mass% The method for producing a grain-oriented electrical steel sheet according to claim 3, which contains one or more of the