JP5982883B2 - Evaluation method of grain-oriented electrical steel sheet - Google Patents

Description

The present invention relates to a method for producing a grain-oriented electrical steel sheet excellent in quality stability suitable for use as a core material of a transformer.
Moreover, this invention relates to the evaluation method of the grain-oriented electrical steel sheet which judges the quality of the magnetic property of the grain-oriented electrical steel sheet obtained in a slab stage or a hot-rolled sheet stage.

  When manufacturing grain-oriented electrical steel sheets, it is known as a general technique to preferentially recrystallize goth-oriented grains during finish annealing using precipitates called inhibitors. For example, Patent Document 1 discloses a method using AlN and MnS, and Patent Document 2 discloses a method using MnS and MnSe, both of which are put into practical use. Has been.

  The methods using these inhibitors usually require slab heating at a high temperature of 1300 ° C or higher in order to finely disperse the precipitates, but they are extremely useful for developing secondary recrystallized grains stably. Met.

  Furthermore, as a method for strengthening the action of these inhibitors, Patent Document 3 discloses a method using Pb, Sb, Nb, Te, and Patent Document 4 discloses Zr, Ti, B, Nb, Ta, V, Cr, Mo. A method of using each is disclosed.

  However, the method using these inhibitors is a useful method for stably developing secondary recrystallized grains, but the presence of the inhibitor causes deterioration of the magnetic properties after final finish annealing. . For this reason, it has been necessary to remove precipitates such as inhibitors from the ground iron by setting the finish annealing to a high temperature of 1100 ° C. or higher and controlling the atmosphere.

In order to solve the above problems, a method for producing a grain-oriented electrical steel sheet using a material that contains as little inhibitor component as possible has been developed (for example, Patent Document 5). In this method, the inhibitor component is eliminated as much as possible, and the goss-oriented grains are secondary recrystallized by revealing the grain boundary orientation angle dependence of the grain boundary energy of the grain boundaries at the time of primary recrystallization. is there.
Since this method does not require fine dispersion of the inhibitor in steel and does not require high-temperature slab heating, which has been essential until now, it is a method having great advantages both in terms of cost and maintenance.
However, when using a material that suppresses the addition of inhibitor components, so-called inhibitorless materials, there are few precipitates that suppress grain growth, so the grain growth during annealing varies greatly depending on the annealing temperature. Therefore, the crystal grain size fluctuates due to slight variations in process conditions, especially the annealing temperature during hot-rolled sheet annealing and recrystallization annealing, and as a result, the magnetic properties of the product coil fluctuate over the entire length of the coil. There was a problem.

  With respect to this problem, the inventors previously mentioned that in an inhibitorless material, it is effective to contain a slight amount of AlN in order to suppress particle size fluctuations during hot-rolled sheet annealing and recrystallization annealing. This was found and disclosed in Patent Document 6.

Japanese Patent Publication No.40-15644 Japanese Patent Publication No.51-13469 Japanese Patent Publication No.38-8214 JP-A-52-24116 JP 2000-129356 JP JP 2010-100885 gazette

As described above, even when an inhibitorless material is used, by containing a slight amount of AlN in the steel, particle size fluctuations during hot-rolled sheet annealing and recrystallization annealing can be suppressed and stabilized. Good magnetic properties can be obtained.
However, even when Al and N are contained in an amount sufficient to form an appropriate amount of AlN in the steel, the desired magnetic properties may not be obtained.

The present invention advantageously solves the above problems, and when producing grain-oriented electrical steel sheets using an inhibitorless material, it effectively suppresses the particle size fluctuation that has been a concern in the past, and is stably desired. It aims at proposing the advantageous manufacturing method of the grain-oriented electrical steel sheet excellent in quality stability which can express the magnetic characteristic of this.
Another object of the present invention is to propose a method for evaluating a grain-oriented electrical steel sheet that can determine whether magnetic properties are good or bad at the slab stage or hot-rolled sheet stage when the grain-oriented electrical steel sheet is manufactured. .

When manufacturing grain-oriented electrical steel sheets using an inhibitorless material, even when a proper amount of Al and N is contained in the steel as a particle size fluctuation inhibitor, fluctuations in the particle size occur, resulting in variations in magnetic properties. As described above, it sometimes occurred.
Therefore, the inventors investigated the distribution of precipitates before the first recrystallization annealing of the steel sheet in which the variation in magnetic characteristics occurred and the steel sheet in which the variation did not occur, in order to investigate the cause. This experiment was conducted by collecting a part of each test coil before the primary recrystallization annealing.

As a result, it was found that a relatively large amount of CaS was deposited on all the steel sheets with variations in magnetic properties. Therefore, it is considered that CaS is responsible for the deterioration of the magnetic characteristics.
However, even when a relatively large amount of CaS is precipitated, there are steel sheets that have good magnetic properties.

Then, the inventors paid attention to S and investigated the state of S in steel.
As a result, it was found that in the steel sheet having poor magnetic properties, most of S is present as CaS and the amount of precipitation as MnS is extremely small.
On the other hand, it was found that a relatively large amount of MnS was precipitated on the steel sheet having good magnetic properties regardless of the amount of CaS precipitated.

Furthermore, as a new finding, AlN was found to be formed using MnS as a nucleus.
Therefore, in order to obtain a desired amount of AlN, an appropriate amount of MnS is necessary. However, when Ca is mixed in the steel, S preferentially binds to Ca to form CaS, and the amount of MnS is accordingly increased. The amount formed decreases.
That is, in order to obtain a desired amount of AlN, an appropriate amount of MnS is required, but conventionally no consideration has been given to a decrease in the amount of MnS due to Ca having a high sulfide-forming ability. It was found that the desired amount of AlN was not obtained, and as a result, the magnetic properties were deteriorated.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1 . In mass% or mass ppm, C: 0.002 to 0.10%, Si: 2.0 to 8.0% and Mn: 0.005 to 1.0%, Al is reduced to 100 ppm or less, N, S, Se is reduced to 50 ppm or less, and the balance A slab composed of Fe and inevitable impurities is hot-rolled and, if necessary, hot-rolled sheet annealing is performed, followed by one or more cold rollings sandwiching intermediate annealing and finishing to the final thickness Then, after performing recrystallization annealing that also serves as decarburization, when producing a grain-oriented electrical steel sheet by performing finish annealing,
In the slab stage or hot-rolled sheet stage, the amount of S and Ca in the steel is analyzed, and the analyzed amount of S and Ca is expressed by the following formula (1) ′
8 + Ca (ppm) × 0.7 <S (ppm) --- (1) '
A method for evaluating a grain-oriented electrical steel sheet, wherein the quality of magnetic properties is determined based on whether or not the above relationship is satisfied.

2 . In mass% or mass ppm, C: 0.002 to 0.10%, Si: 2.0 to 8.0% and Mn: 0.005 to 1.0%, Al is reduced to 100 ppm or less, N, S, Se is reduced to 50 ppm or less, and the balance A slab composed of Fe and inevitable impurities is hot-rolled and, if necessary, hot-rolled sheet annealing is performed, followed by one or more cold rollings sandwiching intermediate annealing and finishing to the final thickness Then, after performing recrystallization annealing that also serves as decarburization, when producing a grain-oriented electrical steel sheet by performing finish annealing,
In the hot-rolled plate stage, a residue obtained by dissolving a small amount of hot-rolled plate is filtered on a filter, and a predetermined area on the filter is observed by SEM , and particles containing 10% by mass or more of particles having a particle size of 250 nmφ or less are obtained. Measured as MnS particles, the number of MnS particles and the total number of precipitates are expressed by the following formula (2)
(Number of precipitated MnS particles / total number of precipitates) x 100 ≥ 10% --- (2)
A method for evaluating a grain-oriented electrical steel sheet, wherein the quality of magnetic properties is determined by whether or not the above relationship is satisfied.

  According to the present invention, when AlN is used to stabilize secondary recrystallization, Ca, which is an element that inhibits the formation of MnS, which is the precipitation nucleus of AlN, can be effectively detoxified. Thus, it is possible to stably obtain a grain-oriented electrical steel sheet having excellent magnetic properties without variation.

FIG. 5 is a diagram showing the relationship between the annealing temperature, the type of precipitates, and the amount of precipitation in a component system in which Ca is not mixed. It is the figure which showed the relationship between the annealing temperature in the component type | system | group in the case of mixing 5 mass ppm of Ca, the kind of precipitation, and the precipitation amount. It is the figure which showed the influence which Ca and S have on a magnetic characteristic. It is a diagram showing the relationship of the MnS precipitation ratio (%) and magnetic flux density B ₈ and (T).

Hereinafter, the present invention will be specifically described.
In the grain-oriented electrical steel sheet targeted by the present invention, although an inhibitorless material is used, in order to suppress the fluctuation of the crystal grain size during the primary recrystallization annealing, 45% of the steel is in the steel before the primary recrystallization annealing. It is necessary to contain about 150 ppm by mass of AlN. For this purpose, MnS of about 25 to 75 ppm by mass is required, and at least about 10 ppm by mass of S is required to form such an amount of MnS.

Therefore, good magnetic properties should be obtained if at least 10 ppm by mass of S is contained and the necessary amount of MnS and the necessary amount of AlN are secured. In the plate, there was a case where the magnetic characteristics varied.
The reason is that when Ca is mixed into the steel for some reason, S is preferentially combined with Ca to form CaS, and the amount of MnS formed is reduced accordingly. It is as follows.

Figure 1 shows the precipitation behavior of MnS and AlN in steel sheets containing C: 0.023%, Si: 3.25%, Mn: 0.05%, S: 13ppm, Al: 60ppm, N: 40ppm in mass% or mass ppm. The results are shown.
As shown in the figure, it can be seen that MnS starts to precipitate at a temperature of slightly over 1000 ° C., and a sufficient amount of MnS is present at an annealing temperature of about 900 ° C. It can also be seen that AlN is present in a sufficient amount.

Next, FIG. 2 shows the results of examining the precipitation behavior of MnS, CaS and AlN when 5 mass ppm of Ca is further added to the same components as in FIG.
As is clear from the figure, the precipitation form of sulfide fluctuates when Ca is mixed in, and as a result of Ca preferentially producing sulfide, the amount of MnS precipitation decreases, and at an annealing temperature of about 900 ° C. It can be seen that there is almost no MnS. Moreover, it turns out that the precipitation amount of AlN also decreases in connection with this.

Therefore, the inventors investigated the amount of Ca mixed in normal operation and the effect on the magnetic properties.
As a result, the amount of Ca mixed in the normal operation was around 2 mass ppm, and when the amount mixed was around 2 mass ppm, there was no adverse effect due to Ca.
However, when the amount of Ca mixed is 3 mass ppm or more, there may be variations in magnetic properties.

Then, the inventors investigated the influence of the amount of S and Ca in the steel on the magnetic properties. The obtained results are shown in FIG. In FIG. 3, the circles indicate that there was almost no variation in magnetic properties on the product plate, and the crosses indicated that the variation in magnetic properties was large.
Specifically, the difference between the maximum value and the minimum value of iron loss W _17/50 (W / kg) when taking a sample (n = 10) from any place on the product plate and measuring it is _0.6 W / The case where it is kg or less and the difference between the maximum value and the minimum value of the magnetic flux density B ₈ (T) is 0.1 T or less is marked with ◯, and the other, that is, the characteristic fluctuation width is marked with x.
As shown in FIG. 3, the amount of S and the amount of Ca are expressed by the following formula (1) ′
8 + Ca (ppm) × 0.7 <S (ppm) --- (1) '
If the above relationship is satisfied, it has been found that no adverse effects caused by Ca occur.
As is clear from the above (1) ', when the amount of Ca mixed is about 2 ppm by mass, there is no problem as long as about 10 ppm by mass of S is contained in the steel.

However, in actual operation, when 3 mass ppm or more of Ca is mixed, deterioration of magnetic characteristics is inevitable with a normal amount of S of about 10 mass ppm.
Therefore, the inventors further investigated the Ca mixing route.
As a result, Ca contamination is due to Ca being eluted from the refractory on the inner wall of the furnace in the steelmaking stage, particularly in the deoxidation process, and for some reason (for example, refractory peeling off). It was investigated that the magnetic properties deteriorate due to an increase in the amount of Ca mixed in the molten steel.

Therefore, in the present invention, the amount of S in the slab is expressed by the following formula (1) according to the amount of mixed Ca.
8 + Ca (ppm) × 0.7 <S (ppm) ≦ 50 (ppm) --- (1)
Therefore, the quality stability of the grain-oriented electrical steel sheet is improved by adjusting the range to satisfy the above relationship.

Next, the reason why the slab component is limited to the above range in the present invention will be described. The unit of the content of the component elements is “mass%” or “mass ppm”, but hereinafter, unless otherwise specified, it is simply indicated by “%” or “ppm”.
C: 0.002 to 0.10%
C is an element useful for improving the magnetic properties. However, if the content exceeds 0.10%, it is difficult to reduce it to 0.005% or less where no magnetic aging occurs even if decarburization annealing is performed. On the other hand, if it is less than 0.002%, texture control becomes difficult and causes deterioration of magnetic properties. Therefore, the C content is limited to a range of 0.002 to 0.10%.

Si: 2.0-8.0%
Si is an element necessary for increasing the specific resistance of steel and reducing iron loss. For that purpose, at least 2.0% is required, but if it exceeds 8.0%, the workability of the steel deteriorates and rolling becomes difficult, so Si is limited to the range of 2.0 to 8.0%.

Mn: 0.005 to 1.0%
In the present invention, Mn is an important element for securing MnS as a precipitation nucleus of AlN. It is also an element necessary for improving hot workability. However, if the content is less than 0.005%, the effect of addition is poor. On the other hand, if it exceeds 1.0%, the magnetic flux density of the product plate decreases, so the Mn content is in the range of 0.005 to 1.0%.

Al: 100 ppm or less, N, S, Se: 50 ppm or less
Reduction of Al to 100 ppm or less and N, S, and Se to 50 ppm or less is a basic condition for satisfactorily recrystallizing the steel sheet in the present invention. Conventionally, it has been desirable from the viewpoint of magnetic properties to reduce such components as much as possible. However, in the present invention, AlN is used as a particle size variation inhibitor, and MnS is used as a precipitation nucleus of such AlN. As will be described later, a necessary amount of S needs to be contained.

Ca: 3-15ppm
Ca is an element that is eluted from the furnace wall refractories and the like in the steelmaking stage, particularly in the deoxidation process, and is inevitably mixed in the steel. The amount of Ca mixed in normal operation is about 2 ppm, and there is no particular problem with this amount of mixed calcium. However, if the Ca content is 3 ppm or more, the magnetic properties may be adversely affected. Therefore, in the present invention, the lower limit of the Ca content is 3 ppm. On the other hand, when the Ca content exceeds 15 ppm, inclusions in the steel increase and surface defects called “hege” may occur during production, so the upper limit of the Ca content is 15 ppm.

In the present invention, S is an important element for securing a predetermined amount of MnS as a precipitation nucleus of AlN, but when Ca is mixed in steel, S preferentially bonds with Ca, The formation of minute MnS is inhibited.
Therefore, in the present invention, the amount of S is represented by the following formula (1) according to the amount of Ca.
8 + Ca (ppm) × 0.7 <S (ppm) ≦ 50 (ppm) --- (1)
It was decided to adjust the range to satisfy the above relationship.

A predetermined amount of MnS can be ensured by adjusting the S amount to a range satisfying the above expression (1) according to the Ca amount, and as a result, a necessary amount of AlN can be secured.
Here, in order to secure the necessary amount of AlN, the lower limit of Al is preferably 30 ppm, and the lower limit of N is preferably 20 ppm.

Although the basic components of the present invention have been described above, the present invention can appropriately contain other elements described below.
That is, for the purpose of reducing iron loss, Cr, Cu and P may be added individually or in combination in the range of Cr: 0.01 to 0.50%, Cu: 0.01 to 0.50%, P: 0.005 to 0.50%, respectively. it can.
For the purpose of improving the magnetic flux density, Nb, Ni, Sb, Sn, Bi, Mo, B, V, and Ta are set to Nb: 0.001 to 0.015%, Ni: 0.001 to 0.015%, and Sb: 0.005 to 0.50%, respectively. , Sn: 0.005-0.50%, Bi: 0.005-0.50%, Mo: 0.005-0.100%, B: 2-25ppm, V: 0.001-0.010%, Ta: 0.001-0.010% can do.
If the addition amount is less than the lower limit, the effect of improving the magnetic properties is poor. On the other hand, if the addition amount exceeds the upper limit, the development of secondary recrystallized grains is suppressed and the magnetic properties are degraded.

Next, the manufacturing method of this invention is demonstrated.
In this invention, there is no restriction | limiting in particular except adjusting the amount of S in steel according to the amount of mixing Ca, The conventionally well-known manufacturing process of inhibitorless steel can be applied.
That is, the molten steel having the above components may be slabd by an ingot casting method or a continuous casting method, or a thin cast piece having a thickness of 100 mm or less may be produced by a direct casting method.
The slab is heated and hot-rolled by a normal method, but may be immediately subjected to hot rolling without being heated after casting. In the case of a thin slab, hot rolling may be performed, or hot rolling may be omitted and the subsequent process may proceed as it is. Since the slab heating temperature before hot rolling is an inhibitor-less component system, it is not necessary to heat to a high temperature of 1300 ° C. or higher for dissolving the inhibitor, which has been indispensable in the past, and is desirable in terms of cost.
Next, after performing hot-rolled sheet annealing as necessary, it was cold-rolled twice or more, including one or intermediate annealing, and finished to the final sheet thickness, and then subjected to recrystallization annealing that also served as decarburization. Then, if necessary, after applying an annealing separator mainly composed of MgO, finish annealing is performed.
After finishing annealing, it is advantageous to perform water washing, brushing, and pickling to remove excess annealing separator. After that, flattening annealing is effective to reduce the iron loss. It is.

As described above, in the present invention, a grain-oriented electrical steel sheet having excellent magnetic properties without variation can be obtained by adjusting the S content within a predetermined range in accordance with the amount of Ca mixed therein.
Therefore, in the slab stage or hot-rolled sheet stage, the amount of S and Ca in steel is analyzed, and the analyzed amount of S and Ca is expressed by the following formula (1) ′
8 + Ca (ppm) × 0.7 <S (ppm) --- (1) '
By determining whether or not the above relationship is satisfied, it is possible to determine the quality of the magnetic properties of the product plate.

Furthermore, it has been clarified that the determination of the variation in magnetic characteristics due to the variation in grain size during production can also be achieved by directly measuring fine MnS precipitated in the hot rolling stage. It was known that the magnetic characteristics varied at the coil sampling position of the product, and this was recognized as a variation in the characteristics. However, in the manufacturing process, the waiting time for hot-rolled sheet annealing was newly set at the beginning and end of the coil. It was found that the amount of MnS deposited in the same coil of the same component also changes depending on various manufacturing factors such as
As described above, AlN that acts as a particle size fluctuation suppressor generates MnS as a nucleus, but the residue obtained by electrolytic extraction at the stage of hot-rolled sheet is measured using SEM, and 250 nmφ or less for all measured precipitates By measuring the precipitation ratio of the MnS particles, it is possible to determine the quality of the magnetic properties regardless of the position of the slab.

That is, for example, a small amount of hot-rolled sheet is electrolytically extracted, and a solution obtained by removing cementite from the obtained residue with a magnet is filtered through an alumina filter. Next, a predetermined area (for example, 100 μm × 100 μm) on the filter is observed with an SEM, and EDS analysis is performed on those recognized as particles by binarization. In addition, about 1-2 g is sufficient for the quantity of the hot-rolled sheet to be electrolytically extracted.
Among the obtained particles, those having an equivalent circle particle diameter of 250 nmφ or less and Mn ≧ 10% by EDS determination are defined as MnS particles, and the number of corresponding particles is counted. Further, the total number of precipitates is recognized as particles by the above binarization.
Then, the number of MnS particles deposited with respect to the total number of precipitates (total number of precipitates) was determined, and these were calculated by the following formula (2)
(Number of precipitated MnS particles / total number of precipitates) x 100 ≥ 10 (%) --- (2)
If the above relationship is satisfied, a sufficient amount of MnS is precipitated as AlN precipitation nuclei, so that good magnetic properties can be obtained.
Therefore, the ratio of (number of precipitated MnS particles / total number of precipitates) is obtained by the above method, and the magnetic ratio is determined regardless of the position of the slab depending on whether the number ratio satisfies the relationship of the above equation (2). The quality of the characteristic can be determined.

Example 1
A steel slab having the composition shown in Table 1 was made into a slab by continuous casting, heated to a slab at 1240 ° C., and then hot-rolled into a 2.7 mm thick hot-rolled sheet. Next, after heating at 1025 ° C for 30 seconds, annealing was performed at 45 ° C / s from 900 ° C to 600 ° C, followed by cold rolling to a final thickness of 0.30 mm (reduction rate: 88.9%) Finished. Then, recrystallization annealing was performed at 830 ° C. for 60 seconds in a 40% N ₂ -60% H ₂ humid atmosphere. At this time, the time for which the steel plate was maintained at a temperature of 800 ° C. or higher was about 150 seconds. Then, after applying an annealing separator mainly composed of MgO, purification annealing was performed at 1200 ° C. for 6 hours. Thereafter, flattening annealing was performed under the conditions of 870 ° C. for 15 seconds, which also served as a tension-imparting coating mainly composed of magnesium phosphate and boric acid.
The magnetic properties of the product plate thus obtained were measured according to the method described in JIS C 2550. The magnetic properties (W _17/50 , B ₈ ) are indicated by the average value of samples (n = 10) taken from any location on the product plate. Further, the difference ΔW _17/50 and ΔB ₈ between the maximum and minimum values of W _17/50 and B ₈ (T) were also measured.
The obtained results are shown in Table 2.

As is apparent from Table 2, when manufactured according to the present invention (Nos. 1 to 3 and 13 to 18), it is possible to obtain a grain-oriented electrical steel sheet excellent in product stability without variation in magnetic properties. I understand.
On the other hand, No. 4 with excessive C, No. 5 with excessive Si, No. 6 with excessive Mn, No. 7 with excessive S, No. 8 with excessive Al, No. 8 with N excessive. 9, No. 10 with excessive Se, No. 11 with excessive Ca, and No. 12 containing no S corresponding to the amount of Ca were inferior in both characteristics of magnetic flux density and iron loss. .

Example 2
Of the steel ingots in Table 1, No. 1, 2, 3, 11, and 12 steel types with different amounts of S, the amount of fine MnS deposited at the hot-rolled sheet stage was measured by the SEM particle analysis method. Samples were taken from the head (TE) and tail (LE) of the hot-rolled sheet, and 1 g was electrolyzed after removing the scale by double-side grinding, and the solution obtained by removing cementite from the resulting residue with a magnet was obtained. Filtered to an alumina filter. The obtained filter paper is set in a holder for SEM measurement, C deposition is performed to ensure conductivity, and an area of 100 μm × 100 μm is observed with an 80-field backscattered electron image at 8000 times, and binarized particles EDS analysis was performed on those recognized as such.
Of the obtained particles, those with Mn ≧ 10% were defined as MnS from the EDS quantitative value of particles with an equivalent circle diameter of 250 nmφ or less, and the number of corresponding particles was counted. Moreover, what was recognized as particle | grains by the said binarization was made into the total number of precipitates.
Table 3 shows the results of measuring the number of precipitates and the total number of precipitates of MnS particles of 250 nmφ or less by the above method. Table 3 also shows the results of examining the magnetic characteristics (B ₈ ) of the part.
Furthermore, FIG. 4 shows the results of examining the correlation with the magnetic flux density B ₈ (T), where (number of MnS particles deposited / total number of precipitates) × 100 is MnS precipitation ratio (%).

As shown in Table 3, the MnS precipitation ratio may be lower depending on the location of the hot-rolled sheet in the invention example, regardless of the comparative material, but the MnS precipitation ratio obtained by the above formula is 10% or more. If this is the case, it is clear that the magnetic characteristics are good, and it can be seen that this is effective as a further evaluation method.
Further, as apparent from FIG. 4, it can be seen that when the value of the MnS precipitation ratio is 10% or more, the magnetic properties (B ₈ ) are greatly improved.

Claims (2)

In mass% or mass ppm, C: 0.002 to 0.10%, Si: 2.0 to 8.0% and Mn: 0.005 to 1.0%, Al is reduced to 100 ppm or less, N, S, Se is reduced to 50 ppm or less, and the balance A slab composed of Fe and inevitable impurities is hot-rolled and, if necessary, hot-rolled sheet annealing is performed, followed by one or more cold rollings sandwiching intermediate annealing and finishing to the final thickness Then, after performing recrystallization annealing that also serves as decarburization, when producing a grain-oriented electrical steel sheet by performing finish annealing,
In the slab stage or hot-rolled sheet stage, the amount of S and Ca in the steel is analyzed, and the analyzed amount of S and Ca is expressed by the following formula (1) ′
8 + Ca (ppm) × 0.7 <S (ppm) --- (1) '
A method for evaluating a grain-oriented electrical steel sheet, wherein the quality of magnetic properties is determined based on whether or not the above relationship is satisfied. In mass% or mass ppm, C: 0.002 to 0.10%, Si: 2.0 to 8.0% and Mn: 0.005 to 1.0%, Al is reduced to 100 ppm or less, N, S, Se is reduced to 50 ppm or less, and the balance A slab composed of Fe and inevitable impurities is hot-rolled and, if necessary, hot-rolled sheet annealing is performed, followed by one or more cold rollings sandwiching intermediate annealing and finishing to the final thickness Then, after performing recrystallization annealing that also serves as decarburization, when producing a grain-oriented electrical steel sheet by performing finish annealing,
In the hot-rolled plate stage, a residue obtained by dissolving a small amount of hot-rolled plate is filtered on a filter, and a predetermined area on the filter is observed by SEM , and particles containing 10% by mass or more of particles having a particle size of 250 nmφ or less are obtained. Measured as MnS particles, the number of MnS particles and the total number of precipitates are given by the following formula (2)
(Number of precipitated MnS particles / total number of precipitates) x 100 ≥ 10% --- (2)
A method for evaluating a grain-oriented electrical steel sheet, wherein the quality of magnetic properties is determined based on whether or not the above relationship is satisfied.

Images