JP6056675B2 - Method for producing grain-oriented electrical steel sheet - Google Patents

Description

  The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent magnetic characteristics, which can obtain a grain-oriented electrical steel sheet having excellent magnetic characteristics at a low cost, and a cold for grain-oriented electrical steel sheet obtained by using the production method. It relates to a hot rolled sheet.

  A grain-oriented electrical steel sheet is a soft magnetic material used as a core material for transformers and generators, and has a crystal structure in which the <001> orientation, which is the easy axis of iron, is highly aligned in the rolling direction of the steel sheet. . Such a texture preferentially grows grains of the {110} <001> orientation called the Goss orientation during secondary recrystallization annealing during the production process of grain-oriented electrical steel sheets. Formed through secondary recrystallization.

  Conventionally, such a grain-oriented electrical steel sheet is heated to 1300 ° C or higher by heating a slab containing about 4.5 mass% or less of Si and an inhibitor component such as MnS, MnSe, and AlN to once dissolve the inhibitor component. After that, it is hot-rolled and subjected to hot-rolled sheet annealing as necessary, to obtain the final sheet thickness by one or more cold rollings sandwiching intermediate annealing, followed by primary recrystallization annealing in a wet hydrogen atmosphere After performing primary recrystallization and decarburization, and then applying an annealing separator mainly composed of magnesia (MgO), the secondary recrystallization and the inhibitor component are purified at 1200 ° C. for about 5 hours. It has been manufactured by performing final finish annealing (for example, Patent Document 1, Patent Document 2, and Patent Document 3).

  As described above, when manufacturing conventional grain-oriented electrical steel sheets, precipitates (inhibitor components) such as MnS, MnSe, and AlN are included in the slab stage, and these are heated at a high temperature exceeding 1300 ° C. The step of causing secondary recrystallization by once dissolving the inhibitor component of this compound and then precipitating it finely in a subsequent step has been adopted.

  In this way, the conventional manufacturing process of grain-oriented electrical steel sheets required slab heating at a high temperature exceeding 1300 ° C, so the manufacturing cost must be extremely high, and there has been a demand for reduction in manufacturing costs in recent years. I was left with a problem where I couldn't respond.

  In order to solve such a problem, for example, in Patent Document 4, 0.010 to 0.060% of acid-soluble Al (sol. Al) is contained, slab heating is suppressed to a low temperature, and an appropriate nitriding atmosphere is used in the decarburization annealing process. A method has been proposed in which (Al, Si) N is precipitated during secondary recrystallization by nitriding and used as an inhibitor. (Al, Si) N functions as an effective inhibitor by being finely dispersed in the steel, but since the inhibitor strength is determined by the Al content, it is sufficient if the accuracy of Al in steelmaking is insufficient. In some cases, it was not possible to obtain a sufficient grain growth inhibiting force. Many methods have been proposed in which nitriding treatment is performed in the middle of the process and (Al, Si) N or AlN is used as an inhibitor. Recently, however, a manufacturing method in which the slab heating temperature exceeds 1300 ° C has been disclosed. ing.

On the other hand, as a technique for causing secondary recrystallization without including an inhibitor component in the slab, Patent Document 5 discloses a technique (inhibitorless method) capable of performing secondary recrystallization without containing an inhibitor component. ing.
Here, the inhibitorless method is a technique in which secondary recrystallization is manifested by texture (control of texture) using higher-purity steel. However, the inhibitorless method does not require high-temperature slab heating and enables production of grain-oriented electrical steel sheets at a low cost. As a result, there is a disadvantage that the magnetic characteristics of the product are likely to vary.

  In addition, since texture control is an important factor for magnetic properties, many conditions have been proposed for warm rolling and the like in which texture control is performed. When this texture control cannot be performed sufficiently, the degree of integration in the Goth orientation ({110} <001>) after secondary recrystallization is low and the magnetic flux density is low as compared with the technique using an inhibitor.

U.S. Patent No. 1965559 Japanese Patent Publication No. 40-15644 Japanese Patent Publication No.51-13469 Japanese Patent No. 2782086 Japanese Unexamined Patent Publication No. 2000-129356

As described above, it has often been difficult to stably achieve good magnetic properties in the method of manufacturing grain-oriented electrical steel sheets that has been proposed so far.
In contrast, the inventors deposited silicon nitride instead of AlN by applying a nitriding treatment while avoiding high-temperature slab heating using a component according to an inhibitorless component in which Al was suppressed to less than 300 ppm. Thus, by making this silicon nitride function as a suppressive force for normal grain growth, the inventors have come up with a method for producing grain-oriented electrical steel sheets that have significantly reduced variations in magnetic properties and have industrially stable and good properties.

As described above, for the precipitate control, since secondary recrystallization occurs conveniently, it needs to be finely controlled. However, in conventional grain-oriented electrical steel sheets, high temperature slab heating is essential. There were restrictions on the manufacturing method in the process.
On the other hand, with respect to texture control, due to the restrictions on the conventional grain-oriented electrical steel sheet manufacturing as described above, it was impossible to use manufacturing conditions advantageous for improving the magnetic flux density.

  In view of the current situation, the inventors added nitrogen to the steel in the latter half of the manufacturing process and used the technique of controlling the precipitation of nitrides, thereby restricting the manufacturing method of the grain-oriented electrical steel sheet. I thought there might be a way to ease the formation of an ideal texture.

  That is, as an ideal texture for improving the magnetic flux density, the structure before the secondary recrystallization is as small as possible in the direction near the oblique Cube. The orientation in the vicinity of the oblique Cube is because the Goss orientation that grows during secondary recrystallization is an orientation that is extremely difficult to phagocytose, and thus the Goss orientation sharpness is significantly degraded.

  Here, it is known that the oblique Cube orientation has already been generated in the hot rolling stage. This is because this orientation is a very stable orientation with respect to rolling, and is formed particularly when the amount of carbon is small and the ferrite phase fraction is high.

  On the other hand, for the oblique Cube orientation, the annealing, after cold rolling, recrystallization, the more oblique Cube orientation before rolling, the more oblique Cube orientation after annealing tends to remain, the absolute amount I found out that the phenomenon decreased. In addition, from this finding, it was found that the oblique Cube orientation can be reduced by adding a recrystallization step.

  The present invention was developed based on the above findings, and in a grain-oriented electrical steel sheet that adds nitrogen to a steel sheet before secondary recrystallization for the purpose of forming silicon nitride, an oblique Cube orientation is obtained by adding a recrystallization process. An object of the present invention is to provide a method for producing a grain-oriented electrical steel sheet having good magnetic properties and a cold-rolled sheet for grain-oriented electrical steel sheet obtained by using the production method.

The gist of the present invention is as follows.
1. In mass%, C: 0.08% or less, Si: 2.0 to 4.5%, and Mn: 0.5% or less, S, Se, and O are each less than 50 mass ppm, and sol.Al is the nitrogen content in steel (mass (ppm): [ppmN] ([ppmN] / 14) * 26 ppm by mass or more and 300 ppm by mass or less, N is 80 ppm by mass or less, and the balance is a steel slab with a composition of Fe and inevitable impurities. , Without reheating or after reheating, after normal hot rolling or in normal hot rolling, using a rolling mill having an n-stage rolling stand, the sheet thickness: 4 mm or less under the following conditions After that, a cold rolled sheet having a final thickness is formed by annealing and rolling, and then a nitriding treatment in which the nitrogen increase becomes 50 mass ppm to 1000 mass ppm during the primary recrystallization annealing or after annealing is performed at a temperature of 800 ° C. or less. in, or after being subjected to 30 seconds at 800 ° C. greater than the temperature, the annealing separator was applied Secondary recrystallization annealing, and
Random orientation ratio {001} <110> strength at plate thickness 1/2 after the primary recrystallization annealing: I and carbon content (% by mass) in steel: [% C]: I ≦ 4- A method for producing a grain-oriented electrical steel sheet, characterized by satisfying a relationship of 50 × [% C] .
Rolling conditions:
Roll at one or more rolling stands at a temperature of 750 ° C or lower,
And,
When the equivalent plastic strain (≈ -2 / Sqrt (3) * Ln (t _i / t _0i )) due to the i-th rolling of the n-stage rolling stand at 750 ° C or lower is pi, Sum of each rolling stand up to ith above 750 ° C: _Σ pi
_Σ pi ≧ 0.45
The equivalent plastic strain (≒ -2 / Sqrt (3) * Ln (t _j / t _0j )) qj from the j-th rolling of the rolling stand above 800 ° C in the n-stage rolling stand,
qj ≧ 0.35.
Here, j indicates a stand number. T _0i is the i-th and t _0j is the steel plate thickness before rolling at the j-th rolling stand, t _i is the i-th thickness and t _j is the steel plate thickness after the rolling at the j-th rolling stand. means.

2. In mass%, C: 0.08% or less, Si: 2.0 to 4.5% and Mn: 0.5% or less, S, Se and O are each less than 50 ppm by mass, sol.Al is 50 to 300 ppm by mass, N Is controlled to 25 mass ppm or less, and [ppmN] ≦ ([ppmTi] / 48 + [ppmB] /10.8) * 14 ≦ [ppmN] +10 massppm (however, [ppmX] is contained in steel of element X) Ti and / or B is added so that the mass ppm), and the remainder is a composition of Fe and inevitable impurities, without reheating or after reheating, after normal hot rolling, or In hot rolling, using a rolling mill having an n-stage rolling stand, the sheet thickness is set to 4 mm or less under the following conditions, and then a cold rolled sheet having a final sheet thickness is formed by annealing and rolling, followed by primary recrystallization. A nitriding treatment in which the nitrogen increase is 50 mass ppm or more and 1000 mass ppm or less during annealing or after annealing is performed at 800 ° C. or less. After applying a temperature, or less than 30 seconds at 800 ° C. greater than the temperature, the annealing separator was applied, and secondary recrystallization annealing, and
Random orientation ratio {001} <110> strength at plate thickness 1/2 after the primary recrystallization annealing: I and carbon content (% by mass) in steel: [% C]: I ≦ 4- A method for producing a grain-oriented electrical steel sheet, characterized by satisfying a relationship of 50 × [% C] .
Rolling conditions:
Roll at one or more rolling stands at a temperature of 750 ° C or lower,
And,
When the equivalent plastic strain (≈ -2 / Sqrt (3) * Ln (t _i / t _0i )) due to the i-th rolling of the n-stage rolling stand at 750 ° C or lower is pi, Sum of each rolling stand up to ith above 750 ° C: _Σ pi
_Σ pi ≧ 0.45
The equivalent plastic strain (≒ -2 / Sqrt (3) * Ln (t _j / t _0j )) qj from the j-th rolling of the rolling stand above 800 ° C in the n-stage rolling stand,
qj ≧ 0.35.
Here, j indicates a stand number. T _0i is the i-th and t _0j is the steel plate thickness before rolling at the j-th rolling stand, t _i is the i-th thickness and t _j is the steel plate thickness after the rolling at the j-th rolling stand. means.

3. Furthermore, the said steel slab is mass%,
Ni: 0.005-1.50%,
Sn: 0.01 to 0.50%,
Sb: 0.005-0.50%,
Cu: 0.01 to 0.50%,
Cr: 0.01 to 1.50%
P: 0.0050 to 0.50% and
Mo: 0.01-0.50%
The method for producing a grain-oriented electrical steel sheet according to 1 or 2 above, comprising one or more selected from among the above.

4). Furthermore, the said steel slab is mass%,
V: 0.0005-0.0100% and
Nb: 0.0005-0.0100%
The method for producing a grain-oriented electrical steel sheet according to any one of the above 1 to 3, which comprises one or two selected from among the above.

  According to the present invention, even if high temperature slab heating is not performed, the magnetic property variation is greatly reduced, and a grain-oriented electrical steel sheet having industrially stable and good characteristics can be obtained.

It is a figure explaining the heat history of steel and the technical idea of this invention in rolling processes, such as after hot rolling.

Hereinafter, the present invention will be specifically described.
First, the reason for limiting the component composition of the steel slab in the present invention will be described. Unless otherwise specified, “%” and “ppm” in relation to ingredients mean mass% and mass ppm, respectively.
C: 0.08% or less C is an element useful for improving the primary recrystallization texture. However, if the content exceeds 0.08%, the primary recrystallization texture is deteriorated. % Or less. A desirable addition amount from the viewpoint of magnetic properties is in the range of 0.01 to 0.06%. If the required magnetic property level is not so high, C may be set to 0.01% or less in order to omit or simplify the decarburization in the primary recrystallization annealing.

Si: 2.0-4.5%
Si is a useful element that improves iron loss by increasing electric resistance. However, if the content exceeds 4.5%, the cold rolling property deteriorates remarkably, so Si is limited to 4.5% or less. In the present invention, Si needs to function as a nitride-forming element, so it is important to contain 2.0% or more. In addition, the desirable addition amount from the viewpoint of iron loss is in the range of 2.0 to 4.5%.

Mn: 0.5% or less
Since Mn has the effect of improving hot workability during production, it is preferable to contain 0.05% or more. However, if the content exceeds 0.5%, the primary recrystallization texture deteriorates and the magnetic properties are increased. Since the characteristics are deteriorated, Mn is limited to 0.5% or less.

S, Se, and O: less than 50 ppm each When the amount of S, Se, and O is 50 ppm or more, it becomes difficult to obtain a desired secondary recrystallization. This is because coarse oxides and MnS and MnSe coarsened by slab heating make the primary recrystallized structure non-uniform. Accordingly, S, Se, and O are all suppressed to less than 50 ppm.

Although the basic components have been described above, in the present invention, a predetermined amount of elements are added together with the rolling conditions described later.
That is, as a measure to improve the magnetic properties more stably industrially, the steel plate component is not only in the range shown below, but also after normal hot rolling or in normal hot rolling, It is important that the conditions for rolling applied to are as described below.

[Effect of low temperature and high strain in hot rolling]
In conventional hot rolling, a high Si steel with a high ferrite phase ratio has a large amount of rolling with ferrite, and the oblique Cube orientation, which is a stable rolling orientation, tends to become conspicuous with each rolling. In addition, in many cases, the grain-oriented electrical steel sheet sandwiches an annealing process after hot rolling and before cold rolling, but the inclined Cube orientation tends to be further increased by this annealing process.

  The inventors considered that the above phenomenon may be due to the fact that the oblique Cube orientation stabilized by rolling remains recovered or strain-induced grain growth without recrystallization. And if this growth was suppressed and the structure was recrystallized, it was thought that the recrystallization orientation could devour the oblique Cube orientation and reduce the oblique Cube orientation.

  And, in the subsequent examination, in order to promote recrystallization of the orientation that tends to engulf the oblique Cube orientation in the hot rolling process, it is important to suppress the recovery of the oblique Cube orientation. It has been conceived that it is necessary to introduce strain into steel at an increased amount of strain or at a low temperature (750 ° C. or lower, preferably 500 ° C. or higher considering rolling properties). It has also been found that the addition of Nb, V, or the like can develop a recovery delay in the oblique Cube orientation.

  It was also found that even if the rolling amount is the same, it is effective to reduce the amount of dissolved nitrogen as much as possible in order to make it easy to grow the direction of erosion of the oblique Cube orientation during recrystallization. Specifically, it is effective to reduce the amount of nitrogen in the slab, and it should be 80 ppm or less. More desirably, it is 25 ppm or less. In addition, although there is no restriction | limiting in particular in the lower limit of nitrogen amount, about 5 ppm is preferable at the point of productivity.

  Moreover, it is necessary to add Al having a strong affinity for nitrogen to N equivalents or more. This is because Al, which has a high oxygen affinity, reduces the amount of dissolved oxygen in steel by adding a small amount in steelmaking, and has the effect of reducing oxide inclusions that lead to the deterioration of steel sheet properties. This is because it can be suppressed. Therefore, the lower limit of Al needs to be ([ppmN] / 14) * 26 or more using the mass number of nitrogen 14 and the mass number 26 of Al and the nitrogen content (ppm) [ppmN] in the steel. On the other hand, when Al is added excessively, AlN deposited in the subsequent nitriding treatment (nitrogen increase) step adversely affects the magnetism after secondary recrystallization, so it is necessary to make it 300 ppm or less.

  On the other hand, in the present invention, a nitride may be formed at a high temperature by adding Ti and / or B. When fixing N with Ti and B, Al does not easily form nitrides, but AlN is considered to contribute effectively as an inhibitor of secondary recrystallization. Therefore, Al must be added in an amount of 50 ppm or more. It is desirable that AlN is deposited later. On the other hand, when Al is added excessively, AlN precipitated in the subsequent nitriding treatment process adversely affects the magnetism after the secondary recrystallization, so it is necessary to make it 300 ppm or less. Moreover, N needs to be 25 ppm or less. This is because when TiN or BN is excessively present in the steel sheet after secondary recrystallization, the magnetic properties are remarkably impaired. Furthermore, the formation of TiN and BN also has the effect of suppressing grain growth and reducing the crystal grain size. Since the above-mentioned orientation that erodes the oblique Cube orientation occurs from a high strain region near the crystal grain boundary, it is considered that reducing the grain size is effective in eliminating the oblique Cube orientation. In addition, although there is no restriction | limiting in particular in the lower limit of nitrogen amount, about 5 ppm is preferable at the point of productivity.

[[PpmN] ≤ ([ppmTi] / 48 + [ppmB] /10.8) * 14≤ [ppmN] + 10ppm] (However, [ppmX] is the elemental content of element X in steel)]
In the present invention, as described above, Ti and / or B can be added in order to improve the magnetic properties. In this case, [ppmN] ≦ ([ppmTi] / 48 + [ppmB] / 10.8) * 14 ≦ [ppmN] + 10ppm The relationship must be satisfied. This is because if ([ppmTi] / 48 + [ppmB] /10.8) * 14 is not set to [ppmN] or more, all solid solution N cannot be precipitated with Ti or B, while ([ppmTi ] / 48 + [ppmB] /10.8) * 14 unless [ppmN] +10 mass ppm or less, excessively added Ti or B forms TiC or TiN or BN during nitridation, resulting in magnetism This is because it deteriorates.

Although the essential components have been described above, in the present invention, the following elements can be appropriately contained as components that improve the magnetic properties more stably industrially. The balance is Fe and inevitable impurities.
Ni: 0.005-1.50%
Ni works to improve the magnetic properties by increasing the uniformity of the hot-rolled sheet structure, and for that purpose, it is preferable to contain 0.005% or more, but if the content exceeds 1.50%, the desired secondary Since it becomes difficult to obtain recrystallization and the magnetic properties deteriorate, it is desirable to contain Ni in the range of 0.005 to 1.50%.

Sn: 0.01-0.50%
Sn is a useful element that suppresses nitriding and oxidation of steel sheets during secondary recrystallization annealing and promotes secondary recrystallization of grains having good crystal orientation to improve magnetic properties. However, if it exceeds 0.50%, the cold rolling property deteriorates, so it is desirable to contain Sn in the range of 0.01 to 0.50%.

Sb: 0.005-0.50%
Sb is a useful element that effectively suppresses nitridation and oxidation of steel sheets during secondary recrystallization annealing, promotes secondary recrystallization of grains with good crystal orientation, and effectively improves magnetic properties. For the purpose, it is preferable to contain 0.005% or more, but if it exceeds 0.50%, the cold rolling property deteriorates, so Sb is preferably contained in the range of 0.005 to 0.50%.

Cu: 0.01-0.50%
Cu suppresses oxidation of the steel sheet during secondary recrystallization annealing, promotes secondary recrystallization of grains having a good crystal orientation, and effectively improves magnetic properties. However, if it exceeds 0.50%, the hot rolling property is deteriorated, so it is desirable to contain Cu in the range of 0.01 to 0.50%.

Cr: 0.01 to 1.50%
Cr has a function of stabilizing the formation of the forsterite film, and for that purpose, it is preferable to contain 0.01% or more, but when the content exceeds 1.50%, a desired secondary recrystallization can be obtained. Since it becomes difficult and the magnetic properties deteriorate, it is desirable to contain Cr in the range of 0.01 to 1.50%.

P: 0.0050 ~ 0.50%
P has a function of stabilizing the formation of the forsterite film. For that purpose, P is preferably contained in an amount of 0.0050% or more. However, if the content exceeds 0.50%, the cold rolling property deteriorates, so P is 0.0050 to It is desirable to make it contain in 0.50% of range.

Mo: 0.01-0.50%
Mo has an effect of suppressing sag after hot rolling through suppression of cracking due to temperature change during slab heating. If Mo is not contained in an amount of 0.01% or more, the effect of suppressing the hege is small. On the other hand, if it exceeds 0.50%, it will cause iron loss deterioration when remaining in the final product, such as by forming carbides and nitrides. It is desirable to be in the above-mentioned range.

V: 0.0005-0.0100%
V has the effect of delaying the recovery of the oblique Cube orientation. Therefore, if V is not contained above the lower limit, the recovery delay effect is poor. On the other hand, if the upper limit is exceeded, the magnetism of the steel sheet deteriorates due to the formation of carbides and nitrides. It is desirable to do.

Nb: 0.0005-0.0100%
Nb, like V, has the effect of delaying the recovery of the oblique Cube orientation. Therefore, Nb is poor recovery delay effect if not contained above the lower limit, on the other hand, exceeding the upper limit, the formation of carbides and nitrides, the magnetism of the steel sheet deteriorates, the range described above It is desirable to do.

Next, the manufacturing method of this invention is demonstrated.
The steel slab adjusted to the above preferred component composition range is subjected to the next step such as hot rolling without being reheated or after being reheated. When the slab is reheated, the reheating temperature is preferably about 1000 ° C. or higher and 1300 ° C. or lower. This is because slab heating above 1300 ° C is meaningless for the present invention, which contains almost no inhibitor in the steel at the slab stage, and only increases costs. On the other hand, when the slab is heated at a temperature lower than 1000 ° C., the rolling load at the time of hot rolling becomes high and it becomes difficult to perform rolling.

Thereafter, the steel slab has a thickness of 4 mm or less under the following conditions using a rolling mill having an n-stage rolling stand after normal hot rolling or in normal hot rolling.
Rolling conditions:
Roll at one or more rolling stands at a temperature of 750 ° C or lower,
And,
When the equivalent plastic strain (≈ -2 / Sqrt (3) * Ln (t _i / t _0i )) due to the i-th rolling of the n-stage rolling stand at 750 ° C or lower is pi, Each at 750 ℃ or less
The sum of the rolling stands up to the above i: Σpi is set to Σpi ≧ 0.45.
The equivalent plastic strain (≒ -2 / Sqrt (3) * Ln (t _j / t _0j )) qj from the j-th rolling of the rolling stand above 800 ° C in the n-stage rolling stand,
qj ≧ 0.35.
Here, j indicates a stand number. T _0i is the i-th and t _0j is the steel plate thickness before rolling at the j-th rolling stand, t _i is the i-th thickness and t _j is the steel plate thickness after the rolling at the j-th rolling stand. means.

[Σpi ≧ 0.45]
In the present invention, rolling is performed at a temperature of 750 ° C. or lower in one or more rolling stands of the n-stage rolling stand, and the i-th rolling of the rolling stand at 750 ° C. or lower among the n-stage rolling stands. When the equivalent plastic strain (≒ -2 / Sqrt (3) * Ln (t _i / t _0i )) is pi, the sum up to the i-th of the rolling stand at 750 ° C or lower: Σpi is 0.45 or more There is a need. This is because the driving force of recrystallization sufficient to reduce the oblique Cube orientation cannot be obtained unless Σpi is 0.45 or more. On the other hand, the upper limit of Σpi is not particularly limited, but about 1.5 is preferable industrially.

The term “750 ° C. or lower” in the present invention means that the outlet side plate temperature of the rolling stand is 750 ° C. or lower. Further, the lower limit of the rolling temperature is not particularly limited, but is preferably about 500 ° C. in consideration of rollability.
Note that Σpi is the sum of the first to i-th equivalent plastic strains of the rolling stand at 750 ° C or lower, but there is a rolling stand above 750 ° C between the rolling stands at 750 ° C or lower. Needless to say, that rolling stand is not counted.

[Qj ≧ 0.35]
In the present invention, among the rolling stands at 800 ° C. or higher in the n-stage rolling stand,
The equivalent plastic strain (≈−2 / Sqrt (3) * Ln (t _j / t _0j )) qj by the j-th rolling needs to be 0.35 or more. This is because, if qj is not 0.35 or more, a band-like structure that easily deteriorates magnetism tends to remain. On the other hand, the upper limit of qj is not particularly limited, but is preferably about 1.05 industrially.

The term “800 ° C. or higher” in the present invention means that the outlet side plate temperature of the rolling stand is 800 ° C. or higher. Moreover, although the upper limit of the said rolling temperature is not specifically limited, About 950 degreeC is preferable from a viewpoint on an installation.
In the present invention, it is not essential to provide a rolling stand at 800 ° C. or higher, but it is desirable to provide it from the viewpoint of process stability.

In addition, even when Ti and / or B is contained, after normal hot rolling or in normal hot rolling, a sheet thickness is obtained under the conditions shown below using a rolling mill having an n-stage rolling stand. : 4 mm or less steel plate. The numerical ranges of Σpi and qj and the reasons for limiting the numerical values are as described in the above paragraphs [0047] and [0049].
Rolling conditions:
Roll at one or more rolling stands at a temperature of 750 ° C or lower,
And,
When the equivalent plastic strain (≈ -2 / Sqrt (3) * Ln (t _i / t _0i )) due to the i-th rolling of the n-stage rolling stand at 750 ° C or lower is pi, Each at 750 ℃ or less
The sum of the rolling stands up to the above i: Σpi is set to Σpi ≧ 0.45.
The equivalent plastic strain (≒ -2 / Sqrt (3) * Ln (t _j / t _0j )) qj from the j-th rolling of the rolling stand above 800 ° C in the n-stage rolling stand,
qj ≧ 0.35.
Here, j indicates a stand number. T _0i is the i-th and t _0j is the steel plate thickness before rolling at the j-th rolling stand, t _i is the i-th thickness and t _j is the steel plate thickness after the rolling at the j-th rolling stand. means.

The series of steel thermal history and the technical idea of the present invention are summarized in FIG. This figure is an example of a four-stage rolling stand (r1 to r4). In the figure, r1 to r4 represent the temperatures when rolled on the respective rolling stands on the vertical axis. That is, in this example, the equivalent plastic strain at r1 is q1, and the equivalent plastic strain at r3 and r4 is p1 and p2, respectively.
Therefore, if q1 is 0.35 or more and Σpi = p1 + p2 is 0.45 or more, the present invention will be satisfied. The above figure is a simplified illustration that gives priority to easy understanding. Steps that are not necessary for the description of the present invention, such as a pickling step, are appropriately omitted.

  Next, the hot-rolled sheet is annealed and rolled to obtain a cold-rolled sheet having a final thickness. Specifically, after performing hot-rolled sheet annealing, it is subjected to one cold rolling or two or more cold rolling sandwiching the intermediate annealing to obtain a final cold-rolled sheet. This cold rolling may be performed at normal temperature, or may be warm rolling in which the steel sheet temperature is raised to a temperature higher than normal temperature, for example, about 250 ° C.

[{001} <110> Strength I: I ≦ 4-50 × [% C]]
I means the intensity of the oblique Cube orientation ({001} <110>) at a thickness of 1/2 to the X-ray diffraction intensity of a sample with a random crystal orientation.
In the cold-rolled sheet for grain-oriented electrical steel sheets in the present invention, when the carbon content (%) in steel is [% C], the primary recrystallized sheet obtained by annealing it is I ≦ 4-50 ×. It is important to satisfy the relationship [% C].
As described above, the oblique Cube tends to decrease as the amount of carbon increases, and thus the above relationship is derived using C as a parameter.
In addition, the above-described rolling steel composition satisfying the above-described composition of the steel sheet, that is, in the n-stage rolling stand, one or more rolling stands are rolled at 750 ° C. or less, and the sum of the pi: Σpi If the equivalent plastic strain qj of the rolling stand at 800 ° C. or higher is set to 0.35 or higher, a cold rolled sheet for grain-oriented electrical steel sheets that satisfies the above relational expression can be effectively obtained.

  Subsequently, primary recrystallization annealing is performed on the cold-rolled sheet. The purpose of this primary recrystallization annealing is to adjust the primary recrystallization grain size optimal for secondary recrystallization by primary recrystallization of a cold rolled sheet having a rolled structure. For that purpose, it is desirable to set the annealing temperature of the primary recrystallization annealing to about 800 ° C. or more and less than 950 ° C. Note that the annealing atmosphere at this time may be wet hydrogen nitrogen or wet hydrogen argon atmosphere, and may also serve as decarburization annealing.

  In the present invention, by using a component according to the inhibitorless component and performing nitriding treatment while avoiding high-temperature slab heating, silicon nitride having an average diameter of about 100 nm is deposited instead of AlN. It is also characterized by functioning as a suppressive force for normal grain growth.

The nitriding treatment for increasing the nitrogen is performed after cold rolling and after the primary recrystallization annealing and before applying the annealing separator. The method of nitriding is not particularly limited as long as the amount of nitriding to be increased can be controlled. However, for example, a method of performing gas nitriding using an NH ₃ atmosphere gas in a coil form or a running strip has been implemented in the past. A technique of nitriding continuously can be adopted. It is also preferable to use salt bath nitriding, which has a higher nitriding ability than gas nitriding.

In the nitriding process, an important point is to form a nitride layer on the surface layer. In particular, it is desirable to perform nitriding at a temperature of 800 ° C. or lower in order to suppress diffusion into the steel, but by reducing the time to a short time (for example, about 30 seconds), the nitride is applied to the surface even at high temperatures. A layer can be formed. In addition, it is important that the nitrogen increase by nitriding is 50 ppm or more and 1000 ppm or less.
This is because if the nitrogen increase is less than 50 ppm, the effect cannot be obtained sufficiently, while if it exceeds 1000 ppm, the amount of silicon nitride deposited becomes excessive and secondary recrystallization does not occur. Desirably, it is 200 ppm or more and less than 1000 ppm. Note that the nitrogen concentration is a value averaged to the average in the thickness direction of the steel plate even if it is concentrated in a part of the steel plate.

After the nitriding treatment, a water slurry of an annealing separator is applied to the steel sheet surface and dried. In addition, as long as the annealing separator in this invention is a conventionally well-known annealing separator for grain-oriented electrical steel sheets, all can use it conveniently.
Following the application of the annealing separator, secondary recrystallization annealing is performed. Any secondary recrystallization annealing condition in the present invention can be suitably used as long as it is a conventionally known annealing separator for grain-oriented electrical steel sheets.

After the secondary recrystallization annealing, an insulating film can be further applied and baked on the steel sheet surface. The type of the insulating coating is not particularly limited, and any conventionally known insulating coating is suitable. For example, a coating solution containing phosphate-chromate-colloidal silica described in JP-A-50-79442 and JP-A-48-39338 is applied to a steel plate and baked at about 800 ° C. The attaching method is suitable.
Further, the shape of the steel sheet can be adjusted by flattening annealing, and this flattening annealing can also be combined with the baking treatment of the insulating film.

Example 1
A silicon steel sheet slab containing chemical compositions represented by symbols B, D, E and I in Table 1 is heated at 1100 ° C. for 30 minutes, and then hot rolled into a hot rolled sheet having a thickness of 2.4 mm. After annealing for 1 minute, it was cold rolled to a final thickness of 0.27 mm, and a sample of 100 mm x 400 mm size was taken from the center of the obtained cold rolled coil and subjected to primary recrystallization in the laboratory. Annealing combined with annealing, decarburization, and nitriding (continuous nitriding treatment) was performed. Moreover, the intensity | strength with respect to the X-ray-diffraction intensity | strength of the sample with a random crystal orientation of the diagonal Cube direction ({001} <110>) in a 1/2 thickness was measured. 20 steel sheets with the same conditions were prepared per condition, and an annealing separator containing MgO as a main component and containing 5% of TiO ₂ was made into a water slurry, applied, dried, and baked on the steel sheet. Further, final annealing was performed.
Subsequently, a phosphate-based insulating tension coating was applied and baked, and the magnetic flux density (B ₈ , T) at a magnetizing force of 800 A / m was evaluated. The magnetic properties were evaluated with an average value of 20 sheets for each SST condition.
Sum of equivalent plastic strain from 1st to i-th of rolling stand at 750 ° C or lower: Σpi, suitability of equivalent plastic strain qi of rolling stand above 800 ° C, strength of ({001} <110>) Table 2 shows the results of measurement and evaluation of the increased amount of nitrogen in the steel after nitriding and the magnetic flux density.

  As shown in the table, it can be seen that in the inventive examples according to the present invention, the Cube orientation of the primary recrystallized plate is reduced compared to those manufactured under conventional rolling conditions, and as a result, the magnetic properties are improved.

(Example 2)
In Table 1, silicon steel slabs containing components indicated by symbols A, C, F, G, H, I, J, K, L, and M were heated at 1050 ° C. for 20 minutes and hot-rolled to 2.2. A hot-rolled sheet with a thickness of mm is annealed at 1000 ° C. for 1 minute, and then a final sheet thickness of 0.23 mm is obtained by cold rolling, and then an annealing temperature in an atmosphere of PH ₂ O / PH ₂ = 0.3: Decarburization annealing was performed by maintaining the temperature at 830 ° C. for 2 minutes. Here, test no. Each sample was sampled, and the intensity of the oblique Cube orientation ({001} <110>) in the 1/2 layer thickness with respect to the X-ray diffraction intensity of a sample with a random crystal orientation was measured. Then, nitriding treatment (under NH ₃ atmosphere) is performed by batch processing, and after increasing the amount of N in steel, an annealing separator containing 10% TiO ₂ containing MgO as the main component is mixed with water to form a slurry. After the coating, the coil was wound up and annealed at a rate of temperature increase during which the residence time between 300-800 ° C. was 30 hours during the temperature increase process of secondary recrystallization annealing. Subsequently, the product was subjected to flattening annealing for the purpose of applying and baking a phosphate-based insulating tension coating and flattening the steel strip.
An Epstein specimen was taken from the product coil thus obtained, and the magnetic flux density (B ₈ ) was measured. In addition, 20 samples of the same conditions were produced per condition.
Table 3 shows the compatibility of Σpi and qi during hot rolling, the strength of ({001} <110>), the amount of increased nitrogen in the steel after nitriding and the magnetic flux density, and the evaluation results.

As shown in the table, it can be seen that in the inventive examples according to the present invention, the Cube orientation of the primary recrystallized plate is reduced compared with those manufactured under conventional rolling conditions, and as a result, the magnetic properties are improved. Moreover, even if the steel sheet slab deviating from the composition of the present invention is subjected to rolling and nitriding treatment according to the present invention, the average value of 20 sheets causes magnetic characteristics due to the variation. It turns out that it is inferior to.

Claims (4)

In mass%, C: 0.08% or less, Si: 2.0 to 4.5%, and Mn: 0.5% or less, S, Se, and O are each less than 50 mass ppm, and sol.Al is the nitrogen content in steel (mass (ppm): [ppmN] ([ppmN] / 14) * 26 ppm by mass or more and 300 ppm by mass or less, N is 80 ppm by mass or less, and the balance is a steel slab with a composition of Fe and inevitable impurities. , Without reheating or after reheating, after normal hot rolling or in normal hot rolling, using a rolling mill having an n-stage rolling stand, the sheet thickness: 4 mm or less under the following conditions After that, a cold rolled sheet having a final thickness is formed by annealing and rolling, and then a nitriding treatment in which the nitrogen increase becomes 50 mass ppm to 1000 mass ppm during the primary recrystallization annealing or after annealing is performed at a temperature of 800 ° C. or less. Or after applying for 30 seconds or less at a temperature above 800 ° C, apply an annealing separator. Secondary recrystallization annealing and the random orientation ratio {001} <110> strength at half the plate thickness after the primary recrystallization annealing: strength of I and carbon content in steel (mass%): [% C ] Satisfies the relationship of I ≦ 4-50 × [% C].
Rolling conditions:
Roll at one or more rolling stands at a temperature of 750 ° C or lower,
And,
When the equivalent plastic strain ( = -2 / Sqrt (3) * Ln (t _i / t _0i )) due to the i-th rolling of the n-stage rolling stand at 750 ° C or lower is pi, Each at 750 ℃ or less
The sum of the rolling stands up to the above i: Σpi is set to Σpi ≧ 0.45.
The equivalent plastic strain ( = -2 / Sqrt (3) * Ln (t _j / t _0j )) qj due to the j-th rolling of the rolling stand above 800 ° C in the n-stage rolling stand,
qj ≧ 0.35.
Here, j indicates a stand number. T _0i is the i-th and t _0j is the steel plate thickness before rolling at the j-th rolling stand, t _i is the i-th thickness and t _j is the steel plate thickness after the rolling at the j-th rolling stand. means. In mass%, C: 0.08% or less, Si: 2.0 to 4.5% and Mn: 0.5% or less, S, Se and O are each less than 50 ppm by mass, sol.Al is 50 to 300 ppm by mass, N Is controlled to 25 mass ppm or less, and [ppmN] ≦ ([ppmTi] / 48 + [ppmB] /10.8) * 14 ≦ [ppmN] +10 massppm (however, [ppmX] is contained in steel of element X) Ti and / or B is added so that the mass ppm), and the remainder is a composition of Fe and inevitable impurities, without reheating or after reheating, after normal hot rolling, or In hot rolling, using a rolling mill having an n-stage rolling stand, the sheet thickness is set to 4 mm or less under the following conditions, and then a cold rolled sheet having a final sheet thickness is formed by annealing and rolling, followed by primary recrystallization. A nitriding treatment in which the nitrogen increase is 50 mass ppm or more and 1000 mass ppm or less during annealing or after annealing is performed at 800 ° C. or less. After applying for 30 seconds or less at a temperature or at a temperature above 800 ° C., an annealing separator is applied, secondary recrystallization annealing is performed, and the ratio of random orientation to the thickness 1/2 of the plate thickness after the primary recrystallization annealing is applied. {001} <110> Strength: I and carbon content (% by mass) in steel: [% C] satisfy the relationship of I ≦ 4-50 × [% C]. A method for producing electrical steel sheets.
Rolling conditions:
Roll at one or more rolling stands at a temperature of 750 ° C or lower,
And,
When the equivalent plastic strain ( = -2 / Sqrt (3) * Ln (t _i / t _0i )) due to the i-th rolling of the n-stage rolling stand at 750 ° C or lower is pi, Each at 750 ℃ or less
The sum of the rolling stands up to the above i: Σpi is set to Σpi ≧ 0.45.
The equivalent plastic strain ( = -2 / Sqrt (3) * Ln (t _j / t _0j )) qj due to the j-th rolling of the rolling stand above 800 ° C in the n-stage rolling stand,
qj ≧ 0.35.
Here, j indicates a stand number. T _0i is the i-th and t _0j is the steel plate thickness before rolling at the j-th rolling stand, t _i is the i-th thickness and t _j is the steel plate thickness after the rolling at the j-th rolling stand. means. Furthermore, the said steel slab is mass%,
Ni: 0.005-1.50%,
Sn: 0.01 to 0.50%,
Sb: 0.005-0.50%,
Cu: 0.01 to 0.50%,
Cr: 0.01 to 1.50%
P: 0.0050 to 0.50% and
Mo: 0.01-0.50%
The method for producing a grain-oriented electrical steel sheet according to claim 1, comprising one or more selected from among the above. Furthermore, the said steel slab is mass%,
V: 0.0005-0.0100% and
Nb: 0.0005-0.0100%
The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 3, further comprising one or two selected from among them.

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