JP2010100885A - Method for manufacturing grain-oriented electrical steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a grain-oriented electrical steel sheet having high grade stable magnetic characteristic by using a component system having no inhibitor. <P>SOLUTION: When the grain-oriented electrical steel sheet is manufactured by using a slab composed of the component system which does not contain the inhibitor consisting of, by mass%, ≤0.10% C, 2.0-8.0% Si, 0.005-1.0% Mn, ≤100 ppm Al and respectively, ≤50 ppm N, S and Se and the balance Fe with inevitable impurities; the mass-ratio of Al content and N content in the slab, is made to ≥1.4 and further, in this slab, one kind or more kinds selected among B, Ta, Nb and V of 10-150 ppm are contained in total. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a grain-oriented electrical steel sheet that is suitable for applications such as iron core materials for transformers.

For grain-oriented electrical steel sheets, it is known as a general technique to preferentially recrystallize grains having Goss orientation during final finish annealing using precipitates called inhibitors. . For example, Patent Document 1 shows a method using AlN and MnS as inhibitors, and Patent Document 2 shows a method using MnS and MnSe as inhibitors, which are industrially put into practical use.
Further, for the purpose of enhancing 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, A method using V, Cr, and Mo is disclosed.

  Although the method using an inhibitor is an effective method for stably developing secondary recrystallized grains, slab heating at a high temperature of 1300 ° C. or higher is necessary to finely disperse the inhibitor in steel. . Furthermore, since the inhibitor causes the magnetic properties to deteriorate after the secondary recrystallization, a purification annealing process is necessary to remove the inhibitor, and the process controls the annealing atmosphere at a high temperature of 1100 ° C. or higher. There is a need.

  On the other hand, Patent Document 5 proposes a method for producing a grain-oriented electrical steel sheet using a component system that does not contain an inhibitor component. This method eliminates the inhibitor component as much as possible, and reveals the grain boundary orientation angle dependence of the grain boundary energy of the grain boundary at the time of primary recrystallization, thereby preventing grains having Goth orientation without using an inhibitor. Is a technology for secondary recrystallization, and the effect is called the texture inhibition effect. In the method of Patent Document 5, the step of purifying the inhibitor is not necessary, and therefore it is not necessary to increase the temperature of the final finish annealing. Furthermore, since it is not necessary to finely disperse the inhibitor in the steel, it is a method having great merit in terms of manufacturing cost and equipment maintenance, such as not requiring high-temperature slab heating.

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

However, in a component system that does not contain an inhibitor as shown in Patent Document 5, since there are few precipitates that suppress grain growth, the grain growth tends to increase due to grain growth during annealing, and the dependence on annealing temperature is strong. . For this reason, the grain size after hot-rolled sheet annealing or after recrystallization annealing also fluctuates due to slight process condition fluctuations, specifically, annealing temperature fluctuations, and the magnetic characteristics of the product coil over its entire length vary. The problem that good magnetic properties cannot be obtained as a whole has become apparent.
The present invention advantageously solves the above problems, and proposes a method of manufacturing a grain-oriented electrical steel sheet that can achieve high stability of product magnetic properties.

Now, as a result of intensive studies focusing on elements that seem to have an influence on particle size control in order to solve the above problems, the inventors have regulated the ratio of Al and N within a predetermined range. The inventors have found that good and stable magnetic characteristics can be obtained by adding a small amount of a specific element. Hereinafter, experiments that have made the present invention successful will be described.
In the following description, “%” means “% by mass” unless otherwise specified.

(Experiment 1)
C: 0.012 to 0.073%, Si: 3.15 to 3.33%, Mn: 0.06 to 0.09%, Cr: 0.02 to 0.06%, Sb: 0.018 to 0.045%, Al: 35 to 100 ppm, N: 14 to 70 ppm, S: 11 Steel slab with ~ 25ppm and Nb: 20 ~ 50ppm, composition of balance Fe and unavoidable impurities is manufactured by continuous casting, heated at 1250 ° C and heated to 2.3mm thickness by hot rolling It was a sheet. Next, hot-rolled sheet annealing was performed at 1050 ° C. for 15 seconds, and then finished to a sheet thickness of 0.23 mm by cold rolling. Further, after recrystallization annealing at 850 ° C. for 60 seconds, an annealing separator mainly composed of MgO was applied, and then finish annealing was held at 1200 ° C. for 10 hours. Finally, planarization annealing was performed at 900 ° C. for 15 seconds, which also served as the formation of a tension-imparting coating mainly composed of magnesium phosphate and boric acid, to produce a grain-oriented electrical steel sheet.

The magnetic flux density B ₈ of the resulting samples was measured according to the method of JIS C2550. Although the obtained magnetic flux density seemed to vary at first glance, a very good correlation was obtained when arranged by the ratio of Al and N of steel slab components.
The results are shown in FIG.
As shown in the figure, it can be seen that when Al / N is small, the magnetic flux density tends to decrease, and especially when Al / N <1.4, the variation becomes large. Further, in the range of 1.4 ≦ Al / N <2, the magnetic flux density is stable, but a tendency to slightly decrease is recognized.

  Therefore, the reason why Al / N has a correlation with the magnetic flux density was examined. As a result, in the above-described experiment 1, Al and N present in the sample steel sheet form AlN due to the change in magnetic flux density near Al / N = 2 (Al / N is 27/14 in mass ratio). It was estimated that this behavior of nitrogen compounds is involved. In order to pursue this estimation, experiments were conducted in which various nitride forming elements were further added.

(Experiment 2)
C: 0.045 to 0.062%, Si: 3.20 to 3.31%, Mn: 0.04 to 0.16%, Cr: 0.03 to 0.11%, Sb: 0.015 to 0.037%, Mo: 0.03 to 0.05%, Al: 55 to 97 ppm, N: A steel slab containing 20 to 49 ppm, Al / N: 1.98 to 3.10 and S: 17 to 27 ppm, further containing about 50 ppm each of Zr, Ti, B, Ta, Nb and V, and the balance being Fe and inevitable impurities Steel slabs that do not contain these trace elements (Zr, Ti, B, Ta, Nb, and V) were each manufactured by continuous casting, heated at 1250 ° C, and hot rolled to a thickness of 2.2 mm by hot rolling. A board was used. Subsequently, after hot-rolled sheet annealing was performed at 1100 ° C. for 60 seconds, it was finished to a sheet thickness of 0.23 mm by cold rolling. Furthermore, after applying recrystallization annealing at 840 ° C. for 80 seconds, an annealing separator mainly composed of MgO was applied, and then finish annealing was carried out at 1200 ° C. for 10 hours. Finally, planarization annealing was performed at 900 ° C. for 15 seconds, which also served as the formation of a tension-imparting coating mainly composed of magnesium phosphate and boric acid, to produce a grain-oriented electrical steel sheet.

The magnetic flux density B ₈ of the resulting samples was measured according to the method of JIS C2550.
The result is shown in FIG.
As shown in the figure, it can be seen that the magnetic flux density obtained varies greatly depending on the types of added Zr, Ti, B, Ta, Nb and V. That is, the sample to which Zr and Ti were added had a low magnetic flux density and did not develop secondary recrystallization. On the other hand, when B, Ta, Nb, and V were added, it became clear that the magnetic flux density was higher than when not added.
The reason why the magnetic properties are improved by adding B, Ta, Nb and V is not necessarily clear as described above, but the inventors consider as follows.

The thermodynamic stability of nitrides in additives and impurities has been investigated in detail, and it has been found that the stability varies depending on the element bonded to nitrogen. In the experiment described above, the stability of the nitride of the added element is Zr, Ti, Al, Ta, B, Nb, and V from the stable side.
Zr and Ti, which have a lower magnetic flux density, are more stable in nitride than Al nitride, whereas B, Ta, Nb, and V, which have higher magnetic flux density, are less nitrided than Al nitride. It is stable. This suggests the possibility that ZrN and TiN, which are more stable than AlN, are formed in the steel sheet containing Zr and Ti, and that the formed ZrN and TiN have reduced magnetic properties.

Furthermore, in Experiment 1, when Al / N was low, the magnetic flux density was low even in the presence of Nb. This is presumably because Al / N is low, and therefore N is stoichiometrically excessive with respect to Al, and Nb is combined with excess N to form a nitride.
From the above considerations, it is presumed that an increase in trace element nitrides diminishes the texture inhibition effect using the grain boundary energy difference of the crystal grains in the steel sheet as a driving force.

On the other hand, when Ta, B, Nb and V are added, since AlN is formed preferentially, nitrides of Ta, B, Nb and V are not formed. It has also been found that when B, Ta, Nb and V are present in the steel sheet, the crystal grain size after recrystallization annealing is fine and uniform.
Thus, there is no formation of nitrides of trace elements (except for Al), and the uniformity of the crystal grain size realized by the presence of trace elements is not affected by the size of the grain size. It is presumed that the hibition effect was exhibited, and as a result, the magnetic flux density was improved. In other words, the effect of this trace element is considered to improve the variation in magnetic properties within the same sample, which is a problem of the conventional component system not containing an inhibitor.

  Through the experiments and considerations as described above, the inventors regulate the ratio of Al and N present in the grain-oriented electrical steel sheet to a component system that does not contain an inhibitor, and in addition, Ta, B, Nb, and V It was concluded that good magnetic properties can be obtained by adding a small amount of.

That is, the gist configuration of the present invention is as follows.
(1) C: 0.10% or less, Si: 2.0 to 8.0% and Mn: 0.005 to 1.0%, Al is 100 ppm or less, N, S and Se are 50 ppm or less, respectively, and the balance Fe and unavoidable impurities After slab is hot-rolled and hot-rolled sheet annealing is performed as necessary, it is cold-rolled once or twice with intermediate annealing, and finished to the final thickness, followed by recrystallization annealing. After applying, in the manufacturing method of grain oriented electrical steel sheet consisting of a series of steps to finish annealing,
The ratio of the amount of Al and N contained in the slab is 1.4 or more in terms of mass ratio, and one or more selected from B, Ta, Nb and V are further added to the slab. A method for producing a grain-oriented electrical steel sheet, characterized by containing 10 to 150 ppm.

  (2) In the slab, Ni: 0.010 to 1.50%, Cr: 0.01 to 0.50%, Cu: 0.01 to 0.50%, P: 0.005 to 0.50%, Sn: 0.005 to 0.50%, Sb: 0.005 to 0.50 %, Bi: 0.005 to 0.50% and Mo: 0.005 to 0.10%. The method for producing a grain-oriented electrical steel sheet according to (1) above, comprising at least one selected from the group consisting of 0.005 to 0.10%.

  According to the present invention, it is possible to obtain a grain-oriented electrical steel sheet having highly stable magnetic properties in a component system that does not substantially contain an inhibitor.

  Next, the reason for limitation in the constituent requirements of the present invention will be described.

C: 0.10% or less When the amount of C exceeds 0.10%, it is difficult to reduce to 50 ppm or less where magnetic aging does not occur even when decarburization is performed. Therefore, it is desirable that C is small, but up to 0.10% is acceptable.

Si: 2.0-8.0%
Si is an element necessary to increase the specific resistance of steel and improve iron loss, but if it is less than 2.0%, its effect is poor, while if it exceeds 8.0%, workability deteriorates and rolling is difficult. Therefore, the Si amount is set to 2.0 to 8.0%.

Mn: 0.005 to 1.0%
Mn is an element necessary for improving the hot workability, but if it is less than 0.005%, its effect is poor, while if it exceeds 1.0%, the magnetic flux density of the product plate decreases, so the amount of Mn is 0.005 to 1.0%.

In the present invention, the amount of Al is 100 ppm or less, and the amount of N, S and Se is 50 ppm or less, respectively, in order to satisfactorily recrystallize the steel sheet. It is desirable to reduce these components as much as possible from the viewpoint of magnetic properties. However, since the reduction of these components increases the cost, there is no problem even if they are left within the above range.
Of the elements described above, it is more desirable that Al is 80 ppm or less and Se is 20 ppm or less. In addition, it is difficult to completely remove N and S light elements at the time of adjusting the components before producing the steel slab, and when no special treatment is performed, 20 ppm each remains in the steel plate.

  Among these elements, it is essential for the above-mentioned reason that the ratio of Al and N is 1.4 or more. In particular, when the ratio of Al and N is 2 or more, the magnetic characteristics are further improved, which is more preferable. . Further, as described above, since it is difficult to completely remove N, addition of Al in the range of 100 ppm or less is not prevented in order to satisfy Al / N ≧ 1.4.

Furthermore, in order to sufficiently obtain the effect of improving the magnetic characteristics in the present invention, it is necessary to add 10 ppm or more of Ti, Nb, B and V.
If the addition amount is less than 10 ppm, the addition effect is small. Moreover, each is preferably 20 ppm or more, more preferably 50 ppm or more.
However, since these trace additive elements remain in the base iron even in the final product and cause deterioration of iron loss, the total amount is limited to 150 ppm or less. From the viewpoint of suppressing deterioration of iron loss, the total amount is desirably 100 ppm or less.
As described above, the essential elements and the suppressing elements have been described. However, in the present invention, the following elements can be appropriately contained as elements for improving the magnetic properties.

Ni: 0.01 to 1.50%
Ni can be added to improve the hot rolled sheet structure and improve the magnetic properties. If the addition amount is less than 0.01%, the effect of addition is small. On the other hand, if it exceeds 1.50%, secondary recrystallization becomes unstable and the magnetic properties deteriorate.

Cr: 0.01 to 0.50%, Cu: 0.01 to 0.50%, P: 0.005 to 0.50%
All of these elements are useful elements for improving iron loss, but if they are less than the lower limit, the effect of addition is poor, while if the upper limit is exceeded, the development of secondary recrystallized grains is suppressed, and rather magnetic Degradation of characteristics is caused.
Sn: 0.005 to 0.50%, Sb: 0.005 to 0.50%, Bi: 0.005 to 0.50%, Mo: 0.005 to 0.10%
These elements are also useful elements for improving the magnetic properties, but if they are less than the lower limit, the effect of addition is poor. On the other hand, if the upper limit is exceeded, the development of secondary recrystallized grains is suppressed, rather the magnetic properties deteriorate. Invite.

Next, the manufacturing process of the present invention will be described.
The molten steel adjusted to a suitable composition of the above components is made into a slab by a normal ingot-making method or a continuous casting method. Moreover, it is good also as a thin cast piece of thickness of 100 mm or less by a direct casting method. In the case of a slab, it is heated and hot-rolled by a normal method, but it may be hot-rolled immediately without being heated after casting. In the case of a thin slab, hot rolling may be performed, or hot rolling may be omitted and used as it is for the subsequent steps.
The slab heating temperature before hot rolling is a slab that does not substantially contain inhibitor components with reduced Al, N, S, and Se, and therefore high temperature annealing is required to dissolve the inhibitor, which has been required in the past. However, the temperature can be lowered to 1250 ° C. or lower, which is desirable in terms of cost.

  Then, hot-rolled sheet annealing is performed as necessary. The hot-rolled sheet annealing temperature for obtaining good magnetic properties is preferably 800 to 1150 ° C. When the hot-rolled sheet annealing temperature is less than 800 ° C., a band structure in hot rolling remains, making it difficult to achieve a sized primary recrystallized structure and inhibiting the development of secondary recrystallization. On the other hand, when the hot-rolled sheet annealing temperature exceeds 1150 ° C., the grain size after the hot-rolled sheet annealing is excessively coarsened, which is extremely disadvantageous for realizing a sized primary recrystallized structure.

  After hot-rolled sheet annealing, after one or two or more cold rollings with intermediate annealing, recrystallization annealing is performed, and the temperature of the cold rolling is increased to 100 ° C to 300 ° C. In addition, it is advantageous to improve the magnetic properties by performing the aging treatment at 100 to 300 ° C. once or a plurality of times during the cold rolling.

  The recrystallization annealing is performed in a wet atmosphere when decarburization is required, but may be performed in a dry atmosphere when decarburization is not required. After recrystallization annealing, a technique for increasing the amount of Si by a siliconization method may be used in combination.

Thereafter, when forming a forsterite film with an emphasis on iron loss, a secondary recrystallized structure is developed by applying an annealing separator mainly composed of MgO, followed by a final annealing, and forsterite. A coating can be formed.
In the case where the forsterite film is not formed with emphasis on the punching processability, an annealing separator is not used or even if it is used, silica, alumina, or the like that inhibits the formation of the forsterite film is used as a main component. When applying the above-mentioned annealing separator, it is effective to perform electrostatic coating without bringing in moisture, and a heat-resistant inorganic material sheet (silica, alumina, mica) may be used.

The finish annealing is desirably performed at 800 ° C. or higher in order to develop secondary recrystallization. In order to complete the secondary recrystallization, it is desirable to hold at a temperature of 800 ° C. or higher for 20 hours or longer.
If the forsterite film is not formed with emphasis on punchability, secondary recrystallization should be completed, so the holding temperature is preferably 850-950 ° C, and finish annealing can be completed at the holding stage. is there.
When placing importance on iron loss or forming a forsterite film to reduce transformer noise, it is desirable to raise the temperature to about 1200 ° C.

  After the finish annealing, water washing, brushing, pickling, etc. are performed in order to remove the unreacted annealing separator adhering. Thereafter, it is effective to correct the shape by performing flattening annealing in order to reduce iron loss.

  In the case where the steel plates are laminated and used, it is effective to apply an insulating coating to the steel plate surface for the purpose of improving iron loss before or after the flattening annealing. This insulation coating is desirably a coating that can impart tension to the steel sheet in order to reduce iron loss. Inorganic coatings are deposited on the steel sheet surface by a tension coating application method using a binder, physical vapor deposition, or chemical vapor deposition. If the coating method is adopted, excellent coating film adhesion and iron loss reduction effect can be obtained.

<Example 1>
C: 0.018-0.023%, Si: 3.20-3.40%, Mn: 0.10-0.15%, Cr: 0.03-0.05%, Al: 30-140ppm and N: 29-50ppm, Al / N ratio as described in Table 1 Further, a steel slab containing Nb amounts shown in Table 1 and the balance being Fe and inevitable impurities was produced by continuous casting. Subsequently, the slab was heated at 1200 ° C., and a hot rolled sheet having a thickness of 2.2 mm was formed by hot rolling. Next, hot-rolled sheet annealing was performed at 1060 ° C. for 40 seconds and finished to a thickness of 0.23 mm by one cold rolling. Furthermore, after applying recrystallization annealing at 850 ° C. for 100 seconds, after applying an annealing separator mainly composed of MgO, it was held at 900 ° C. for 50 hours for secondary recrystallization, The forsterite film was formed by holding at 1200 ° C. for 10 hours. Finally, flattening annealing was performed at 1200 ° C. for 60 seconds, and then TiN was vapor-deposited on the steel sheet surface by chemical vapor deposition to form a coating.

Here, the collection of the magnetic property measurement sample and the measurement of the magnetic property in this example were performed according to the following procedure.
First, the iron loss is measured over the entire length of the coil by an in-line iron loss meter installed on the exit side of the annealing furnace of the flattening annealing line, and the iron loss profile in the coil longitudinal direction is acquired. Next, after TiN coating, samples were taken from a total of 5 locations, from the location where the iron loss in the iron loss profile was high, to 3 locations in the plate width direction and 2 locations in the coil longitudinal direction (center in the width direction). The magnetic properties were collected and measured according to the method of JIS C2550.
Of the above five locations, the magnetic flux density B ₈ and W _17/50 in the sample having the worst magnetic characteristics are _used as the representative values of the coil. We evaluated whether or not.
The above measurement evaluation results are also shown in Table 1.

  As shown in the table, according to the present invention, it was possible to obtain a grain-oriented electrical steel sheet having good magnetic properties over the entire coil length in a component system that does not contain an inhibitor.

<Example 2>
A steel slab containing the components shown in Table 2 with the balance being Fe and inevitable impurities was produced by continuous casting. Subsequently, the slab was heated at 1250 ° C., and a hot-rolled sheet having a thickness of 2.3 mm was formed by hot rolling. Next, hot-rolled sheet annealing was performed at 1000 ° C. for 35 seconds, and a steel sheet having a thickness of 0.82 mm was obtained by the first cold rolling. Then, after intermediate annealing at 1000 ° C. for 40 seconds, a final thickness of 0.23 mm was obtained by the second cold rolling. Subsequently, recrystallization annealing was performed at 850 ° C. for 60 seconds, an annealing separator mainly composed of MgO was applied, and final annealing was performed at 1250 ° C. for 10 hours. At this time, Ar atmosphere was set for the latter half 5 hours out of 10 hours holding, and hydrogen atmosphere was set for the rest. Finally, flattening annealing was performed at 900 ° C. for 15 seconds, which also served to form a tension-imparting coating mainly composed of magnesium phosphate and boric acid.

The magnetic properties of the obtained samples were measured and evaluated for the steel plates after annealing according to the same procedure as in Example 1.
The results are also shown in Table 2.

  As shown in the table, according to the present invention, it was possible to obtain a grain-oriented electrical steel sheet having good magnetic properties over the entire coil length in a component system that does not contain an inhibitor.

  According to the present invention, in a component system that does not contain an inhibitor, it is possible to obtain a grain-oriented electrical steel sheet having excellent magnetic properties over the entire length and width of the coil. It is extremely effective when used for such applications.

It is a diagram showing the relationship between the ratio Al / N and the magnetic flux density B ₈ of Al and N in the steel. It is a diagram comparatively showing relations between the type and the magnetic flux density B ₈ of the added trace elements in the steel.

Claims (2)

In mass%, C: 0.10% or less, Si: 2.0-8.0%, and Mn: 0.005-1.0%, Al is 100 ppm or less, N, S, and Se are 50 ppm or less respectively, the remainder Fe and inevitable impurities The slab made of is hot-rolled and, if necessary, hot-rolled sheet annealing is performed, then cold rolling is performed once or two or more times with intermediate annealing between them to finish to the final thickness, and then recrystallization annealing In the method for producing a grain-oriented electrical steel sheet comprising a series of steps of performing finish annealing,
The ratio of the amount of Al and N contained in the slab is set to 1.4 or more in terms of mass ratio, and one or more selected from B, Ta, Nb and V are further added to the slab. A method for producing a grain-oriented electrical steel sheet, characterized by containing 10 to 150 ppm.   In the slab, Ni: 0.01 to 1.50%, Cr: 0.01 to 0.50%, Cu: 0.01 to 0.50%, P: 0.005 to 0.50%, Sn: 0.005 to 0.50%, Sb: 0.005 to 0.50 2. The method for producing a grain-oriented electrical steel sheet according to claim 1, comprising at least one selected from%, Bi: 0.005 to 0.50%, and Mo: 0.005 to 0.10%.

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