JP4258402B2 - Method for producing grain-oriented electrical steel sheet with good magnetic properties - Google Patents

Description

  The present invention relates to a method for producing a grain-oriented electrical steel sheet having good magnetic properties, and in particular, when a grain-oriented electrical steel sheet is produced without using an inhibitor, a forsterite film is effectively formed on the steel sheet surface. It is intended to improve the magnetic characteristics advantageously.

In the production of grain-oriented electrical steel sheets, it is common to preferentially recrystallize {110} <001> oriented grains called goth oriented grains during final finish annealing using precipitates called inhibitors. It is used as a technical technique.
For example, a method using AlN and MnS as an inhibitor (see Patent Document 1) and a method using MnS and MnSe as an inhibitor (see Patent Document 2) have already been put into practical use industrially.
In addition, a technique using CuSe and BN as inhibitors (see Patent Document 3) and a method using Ti, Zr, and V nitrides (see Patent Document 4) are also known.

Although the method using these inhibitors is a useful method for developing secondary recrystallized grains stably, it is necessary to finely disperse the precipitates, so the slab heating before hot rolling is 1300 ° C or higher. It is required to be performed at a high temperature.
However, the high-temperature heating of the slab not only increases the equipment cost in realizing the heating, but also increases the amount of scale generated during hot rolling, resulting in a decrease in yield and complicated maintenance of the equipment. is there.

On the other hand, various methods for producing grain-oriented electrical steel sheets without using inhibitors have been proposed. What is common to these technologies is that the {110} plane grows preferentially using surface energy as a driving force.
In order to effectively use such a surface energy difference due to crystal orientation as a driving force, it is inevitably required to reduce the plate thickness in order to increase the contribution of the surface.
For example, in Patent Document 5, the thickness of the steel plate is limited to 0.2 mm or less, and in Patent Document 6, the thickness is limited to 0.15 mm or less.
However, since the thickness of the grain-oriented electrical steel sheet currently used is almost 0.20 mm or more, it is difficult to produce a normal grain-oriented electrical steel sheet by the method using the surface energy as described above.

In this regard, the inventors have previously developed a technique for expressing secondary recrystallization using a grain boundary migration inhibitory effect of solute nitrogen in a high-purity material that does not contain an inhibitor component. Disclosed.
However, the electrical steel sheet obtained by the technique of Patent Document 7 has a problem that the magnetic flux density is lower than the technique using an existing inhibitor.

Therefore, the inventors further perform secondary recrystallization annealing in a state where C remains in a method for producing a grain-oriented electrical steel sheet having no forsterite film using a material that does not contain the inhibitor component described above. By obtaining the knowledge that the magnetic flux density is improved by this, a suitable amount of C is left before the secondary recrystallization, and after the completion of the secondary recrystallization, the C is removed by performing flattening annealing that also serves as decarburization annealing. Was newly developed and disclosed in Patent Document 8.
However, since the electrical steel sheet obtained by the technique of Patent Document 8 does not have an oxide film on its surface, it can be used for applications that require a surface oxide film such as a forsterite film, such as a large transformer. In addition, problems were left where iron loss was inferior.

Japanese Patent Publication No.40-15644 (Claims) Japanese Patent Publication No. 51-13469 (Claims) Japanese Patent Publication No. 58-42244 (Claims, Examples) Japanese Examined Patent Publication No. 46-40855 (Claims) JP-A-64-55339 (Claims) JP-A-2-57635 (Claims) JP 2000-129356 A (Claims) JP 2003-34821 A (Claims)

  The present invention advantageously solves the above problem, and when producing a grain-oriented electrical steel sheet without using an inhibitor, by effectively forming a forsterite coating, a large transformer or the like can be obtained. It is an object of the present invention to propose an advantageous method for producing a grain-oriented electrical steel sheet that can be suitably used and has excellent magnetic properties.

That is, the gist configuration of the present invention is as follows.
(1) By mass%, C: 0.08% or less, Si: 2.0-8.0% and Mn: 0.005-3.0%, Al: 100 ppm or less, N, S, Se amount reduced to 50 ppm or less respectively The remainder is a slab composed of Fe and inevitable impurities , hot-rolled, and then subjected to cold rolling twice or more with intermediate or intermediate annealing and finished to the final sheet thickness, followed by recrystallization annealing, The amount of C in the steel after recrystallization annealing is adjusted to a range of 0.005 to 0.025%, followed by secondary recrystallization annealing at a temperature of 800 ° C or higher, and then 0.05g / m ² or more for the obtained steel plate. 2. After surface grinding that brings about a weight loss of less than O g / m ² , decarburization annealing is performed, and then an annealing separator mainly composed of MgO is applied to the steel sheet surface, and then subjected to forging at a temperature of 1000 ° C or higher. method for producing oriented electrical steel sheets towards you characterized by applying final annealing to form a stellite coating.

(2) The slab is further in% by mass: Ni: 0.005 to 1.50%, Sn: 0.01 to 0.50%, Sb: 0.005 to 0.50%, Cu: 0.01 to 0.50%, P: 0.005 to 0.50% and Cr: 0.01 The method for producing a grain-oriented electrical steel sheet according to (1) above, wherein the composition contains one or more selected from ˜1.50%.

According to the present invention, by using a material that does not use an inhibitor, the magnetic flux density is improved by secondary recrystallization with C remaining, and the secondary recrystallization step and the forsterite film forming step are separated. The grain-oriented electrical steel sheet having a forsterite coating with excellent magnetic flux density and iron loss is obtained by forming a forsterite coating with a surface and further improving the decarburization performance by surface grinding before decarburization annealing. be able to.
The present invention is a method of developing secondary recrystallization without using an inhibitor, and it is possible to omit high-temperature purification annealing at about 1200 ° C. for high-temperature heating of the slab for inhibitor solid solution and removal of the inhibitor. High magnetic flux density and low iron loss can be obtained with a simple manufacturing process.

Hereinafter, the experiment that led to the present invention will be described. Unless otherwise specified, “%” in relation to ingredients means mass%.
Inhibitor component containing C: 0.036%, Si: 3.2% and Mn: 0.05%, Al: 30 ppm, N: 29 ppm, S: 15 ppm, Se: 2 ppm, other components: each reduced to 30 ppm or less The slab which does not contain was manufactured by continuous casting. Then, after heating to 1200 ° C., the thickness was 2.4 mm by hot rolling. The hot-rolled sheet was soaked in a nitrogen atmosphere at 1020 ° C. for 60 seconds and then rapidly cooled. Then, a final thickness of 0.30 mm was obtained by cold rolling. This steel sheet was subjected to recrystallization annealing at 900 ° C. and soaking for 30 seconds in an atmosphere having various dew points with hydrogen: 30 vol% and nitrogen: 70 vol%. Subsequently, secondary recrystallization annealing was performed. This secondary recrystallization annealing was performed in a nitrogen atmosphere with a dew point of −20 ° C. under the condition that the temperature was increased from room temperature to 900 ° C. at a rate of 50 ° C./h and held for 50 hours. Subsequently, decarburization annealing was performed in an atmosphere of hydrogen: 50 vol%, nitrogen: 50 vol%, dew point: 60 ° C, 825 ° C, soaking: 120 seconds.

FIG. 1 shows the results of examining the relationship between the amount of C in steel after recrystallization annealing and after decarburization annealing and the atmospheric dew point during recrystallization annealing.
As is apparent from the figure, the amount of C in the steel after recrystallization annealing and after decarburization annealing varies greatly depending on the atmospheric dew point during recrystallization annealing.

Next, MgO containing 2% of TiO ₂ was applied as an annealing separator, and final annealing for forming a forsterite film was performed in a hydrogen atmosphere at 1100 ° C.
FIG. 2 shows the results of examining the influence of the atmospheric dew point during recrystallization annealing on the magnetic properties of the product plate.
As shown in the figure, the magnetic flux density B ₈ is generally good by securing the C content after recrystallization annealing, that is, before secondary recrystallization annealing, in the range of 0.005 to 0.025%. .
However, the iron loss W _17/50 is good only when the dew point during recrystallization annealing, which is a condition for reducing the C content to 30 ppm, is 25 ° C. Under conditions where the dew point is 20 ° C. or lower, the amount of C remains at 50 ppm or more after decarburization annealing, and the iron loss is deteriorated because carbides are precipitated. On the other hand, when the dew point is 40 ° C or higher, the amount of C after recrystallization annealing decreases to 50 ppm or less, so the effect of improving the degree of integration of secondary recrystallization orientation due to C residual decreases and the magnetic flux density decreases. It is thought that.

Thus, when a secondary recrystallization process and a forsterite film formation process are isolate | separated, a subscale has already produced | generated by the recrystallization annealing before a decarburization annealing process, and a secondary recrystallization annealing process. Since this subscale acts as a barrier against C diffusion and inhibits decarburization, there is a problem that suitable conditions for decarburization annealing are extremely narrow and it is extremely difficult to complete decarburization stably.
In addition, when secondary recrystallization annealing is performed with C remaining, the precipitation of chemically stable graphite on the surface of the steel sheet after annealing is considered to promote the decarburization deterioration.

Therefore, in order to improve the decarburization by removing the subscale and graphite generated on the surface layer of the steel plate, double-side grinding with a grinding brush with abrasive grains is performed under various conditions before decarburization annealing, and the decarburization and magnetic properties are improved. The effect on characteristics was investigated.
FIG. 3 shows the results of examining the relationship between the grinding amount and the residual C after decarburization annealing when the grinding amount is variously changed.
As is clear from the figure, the decarburization is remarkably improved by surface grinding.

Moreover, in FIG. 4, the investigation result about the change of the iron loss characteristic with respect to each grinding amount is shown.
As shown in the figure, the iron loss was remarkably improved in a range where the grinding amount was small, and when the grinding amount increased, the iron loss tended to deteriorate rather.

Therefore, when the surface condition after grinding was investigated, when the grinding amount was small, only the outermost surface layer of the subscale was removed, whereas when the grinding amount was large, the surface of the iron rail was partially Was exposed and wrinkled.
From the results of this survey, it was found that an excellent iron loss improvement effect can be obtained by performing relatively light grinding that removes only the outermost layer of the subscale without completely removing the subscale. .

  The reason why the decarburization improves by subjecting the steel sheet surface to relatively mild grinding before decarburization annealing is not necessarily clearly understood, but the precipitation of graphite is concentrated on the outermost layer. It is considered that the oxide that inhibits the decarburization reaction and becomes a barrier against C diffusion is the densest outermost layer portion.

  As described above, when a grain-oriented electrical steel sheet is manufactured using a material that does not use an inhibitor, the magnetic flux density is improved by applying secondary recrystallization annealing in a state where C remains, and a secondary recrystallization step is performed. It is possible to form a forsterite film by separating the forsterite film formation process, and it is possible to improve the decarburization deterioration due to subscale formation and graphite precipitation before decarburization annealing by relatively mild surface grinding. Based on this finding, the present invention has been completed.

Next, the reason why the component composition of the slab is limited to the above range in the present invention will be described.
C: 0.08% or less When the amount of C exceeds 0.08%, it is difficult to reduce to 0.025% or less, which is the amount that exhibits the C-containing effect during recrystallization annealing of the present invention. C content was limited to 0.08% or less.
If the C content is less than 0.005%, the magnetic flux density decreases. Therefore, the lower limit of the C content is preferably 0.005%.

Si: 2.0 to 8.0%
Si is a useful element that improves iron loss by increasing electrical resistance. However, if the content is less than 2.0%, the effect of addition is poor. On the other hand, if it exceeds 8.0%, the cold rolling property deteriorates significantly. , Si was limited to the range of 2.0-8.0%.

Mn: 0.005 to 3.0%
Mn is an element necessary for improving the hot workability. However, if the content is less than 0.005%, the effect of addition is poor. On the other hand, if it exceeds 3.0%, the magnetic flux density decreases, so Mn is 0.005 to Limited to a range of 3.0%.

Al: 100 ppm or less, N, S, Se: 50 ppm or less Each of the present invention is intended for a method of developing secondary recrystallization without using a conventionally known inhibitor such as AlN, MnSe, etc. By omitting high-temperature heating of the slab for solid solution and high-temperature purification annealing for removing the inhibitor, low iron loss is obtained by a simple manufacturing process.
Therefore, Al is reduced to 100 ppm or less, and N, S, and Se are each reduced to 50 ppm or less.
In addition, it is advantageous to reduce the iron loss by reducing other nitride forming elements such as Ti, Nb, B, Ta, and V to 50 ppm or less.

Although the essential components have been described above, in the present invention, in addition to the above, the following elements can be appropriately contained as components that improve the magnetic characteristics more stably industrially.
Ni can be added to improve the hot rolled sheet structure and improve the magnetic properties. However, if the Ni addition amount is less than 0.005%, the effect of improving the magnetic properties is small. On the other hand, if it exceeds 1.50%, secondary recrystallization becomes unstable and the magnetic properties deteriorate, so the addition amount is set to 0.005 to 1.50%.
In addition, for the purpose of improving iron loss, Sn: 0.01 to 0.50%, Sb: 0.005 to 0.50%, Cu: 0.01 to 0.50%, P: 0.005 to 0.50%, and Cr: 0.01 to 1.5% 1 Seeds or two or more can be added. About these elements, when the addition amount is less than the lower limit amount, the effect of improving iron loss is small, while when the upper limit amount is exceeded, the development of secondary recrystallized grains is suppressed.

Next, the manufacturing method of this invention is demonstrated.
The slab adjusted to the above suitable component composition range is produced by a normal ingot-making method and a continuous casting method. Further, a thin cast piece having a thickness of 100 mm or less may be manufactured by a direct casting method.
The obtained slab is subjected to hot rolling after heating, but high-temperature heating at 1300 ° C. or higher is not necessary in the composition of the present invention.
Next, hot-rolled sheet annealing is performed as necessary. In order to develop a goth structure on the product plate to a high degree, the hot-rolled sheet annealing temperature is preferably in the range of 800 to 1100 ° C.
After hot-rolled sheet annealing, it is subjected to cold rolling at least once with intermediate or intermediate annealing, and finished to the final sheet thickness, followed by recrystallization annealing. In this cold rolling, it is necessary to raise the rolling temperature to 100 to 250 ° C., and to perform aging treatment in the range of 100 to 250 ° C. one or more times during the cold rolling. It is effective in developing the tissue.

The recrystallization annealing after the cold rolling is preferably performed in the range of 800 to 1000 ° C.
In the present invention, after the recrystallization annealing, adjusting the C content to a range of 0.005 to 0.025% is the most important point in securing a high magnetic flux density. If the amount of C after recrystallization annealing is less than 0.005%, the effect of improving the magnetic flux density by solute C cannot be obtained. Conversely, if it exceeds 0.025%, secondary recrystallized grains do not develop due to γ transformation. Magnetic properties are greatly degraded.
In addition, as a method for controlling the C amount, the method of controlling the C amount in this range in the steelmaking stage and performing all subsequent annealing processes in a non-decarburized atmosphere is the simplest, but it is difficult to reduce in the steelmaking stage. In such a case, a method of decarburizing by hot-rolled sheet annealing, intermediate annealing or recrystallization annealing in a wet hydrogen atmosphere until secondary recrystallization annealing, and adjusting the C content to a range of 0.005 to 0.025%. It may be used.

  Subsequently, secondary recrystallization annealing is performed, but it is necessary to perform at a temperature of 800 ° C. or higher for the secondary recrystallization. The residence time at 800 ° C. or higher is preferably secured for 20 hours or longer sufficient for the development of the secondary recrystallization structure.

After secondary recrystallization annealing, before decarburization annealing, 0.05 g / m ² or more, subjected to surface grinding results in a weight reduction of less 2.O g / m ² for improving the decarburizing. This technique is the basis of the present invention. Here, the grinding amount is less than 0.05 g / m ² decarburization improving effect small, whereas 2.0 g / m ² by weight, the iron loss contain flaws in the base steel surface is deteriorated.
The grinding method is not particularly limited, and for example, a method of removing the subscale and graphite in the surface layer portion using a grinding brush containing abrasive grains, an elastic grindstone roll, a belt sander or the like is suitable. Further, the grinding effect may be enhanced by using hydrochloric acid pickling, electrolytic degreasing and the like together. However, if the surface roughness after grinding is too large, the magnetic properties will be deteriorated.
In grinding, the number of grinding passes is not particularly limited, but it is economically advantageous that the number of passes is as small as possible in actual operation. On the other hand, it is advantageous in terms of iron loss to reduce the grinding force as much as possible and increase the grinding time and the number of grinding passes.
In consideration of reducing grinding unevenness, 2 to 4 passes are realistic. In this case, it is possible to further stabilize the quality by performing rough grinding using a material having a low grindstone count in the previous stage and performing finish grinding using a material having a high grindstone count in the subsequent stage.
The process of grinding needs to be performed after secondary recrystallization annealing and between decarburization annealing, and it may be performed only by grinding, but it is practically performed at the pretreatment stage of decarburization annealing. Efficient.

Decarburization annealing is performed in a wet hydrogen atmosphere in the range of 750 to 900 ° C., and the C content is reduced to 50 ppm or less, desirably 30 ppm or less.
After decarburization annealing, an annealing separator mainly composed of MgO is applied, followed by final annealing for forming a forsterite film. The final annealing temperature must be 1000 ° C. or higher for forming the forsterite film.
After the final annealing, flattening annealing is performed to correct the shape. It is preferable to apply an insulating coating to the surface after planarization annealing. In order to obtain good iron loss, it is advantageous to apply a tension coating in which phosphate and colloidal silica are mixed.

C: 0.040%, Si: 3.2%, Mn: 0.04% and Sb: 0.04%, Al: 20ppm, N: 25ppm, other components: each reduced to 30ppm or less After heating to ° C., a hot-rolled sheet having a thickness of 2.4 mm was formed by hot rolling. Subsequently, hot-rolled sheet annealing was performed at 980 ° C. under conditions of soaking: 60 seconds, and then finished to a final thickness of 0.30 mm by cold rolling at room temperature.
Subsequently, recrystallization annealing was performed in an atmosphere of hydrogen: 25 vol%, nitrogen: 75 vol%, dew point: 30 ° C, 900 ° C, soaking: 10 seconds. The amount of C after recrystallization annealing was 190 ppm. Subsequently, secondary recrystallization annealing was performed by heating up to 875 ° C. at 50 ° C./h in a nitrogen atmosphere without applying an annealing separator and switching to an Ar atmosphere and holding for 50 hours.
After secondary recrystallization annealing, double-side grinding was performed under the conditions shown in Table 1 using a grinding brush containing abrasive grains, then in an atmosphere of hydrogen: 50 vol%, nitrogen: 50 vol%, dew point: 60 ° C. Decarburization annealing was performed at ℃, soaking: 100 seconds.
Then, an annealing separator containing 5% TiO ₂ added to MgO was applied, and a final annealing was performed at 1100 ° C. for 10 hours in a hydrogen atmosphere.
After the final annealing, flattening annealing was performed at 850 ° C. for 30 seconds in a dry nitrogen hydrogen mixed atmosphere to correct the shape.
The product plate thus obtained was measured for the magnetic flux density (B ₈ ) and iron loss (W _17/50 ) in the rolling direction.
The obtained results are also shown in Table 1.

  As is clear from the table, by performing surface grinding before decarburization annealing to improve decarburization, it is possible to obtain a grain-oriented electrical steel sheet having a forsterite coating with excellent magnetic flux density and iron loss. It was.

A slab having the component composition shown in Table 2 was heated to 1125 ° C., and then hot rolled into a 2.6 mm thick hot rolled sheet. All the components not shown in Table 2 were reduced to 50 ppm or less.
Next, after annealing to 1000 ° C, soaking: hot-rolled sheet for 30 seconds, and finished to a final thickness of 0.30mm by cold rolling, atmosphere of hydrogen: 50 vol%, nitrogen: 50%, dew point: -20 ° C Inside, recrystallization annealing was performed at 900 ° C. for 20 seconds. Next, secondary recrystallization annealing was performed in which the temperature was raised to 900 ° C. at 20 ° C./h in a nitrogen atmosphere without applying an annealing separator, and the Ar atmosphere was maintained for 75 hours. After secondary recrystallization annealing, after performing two-pass double-sided grinding using a # 240 abrasive brush, in an atmosphere of hydrogen: 40 vol%, nitrogen: 60 vol%, dew point: 55 ° C 820 Decarburization annealing was performed at 120 ° C. for 120 seconds. After decarburization annealing, an annealing separator containing 2% TiO ₂ added to MgO was applied, and a final annealing was performed at 1150 ° C. for 5 hours in a hydrogen atmosphere. After this final annealing, flattening annealing was performed at 850 ° C. for 30 seconds in a dry nitrogen hydrogen mixed atmosphere to correct the shape.
The product plate thus obtained was measured for the magnetic flux density (B ₈ ) and iron loss (W _17/50 ) in the rolling direction.
The obtained results are also shown in Table 2.

  As is clear from the table, by performing surface grinding before decarburization annealing to improve decarburization, it is possible to obtain a grain-oriented electrical steel sheet having a forsterite coating with excellent magnetic flux density and iron loss. It was.

  The application of the grain-oriented electrical steel sheet according to the present invention is mainly a large-scale transformer, does not use an inhibitor as a material, and does not need to be subjected to high-temperature heating and high-temperature purification annealing of a slab, so that mass production is possible at low cost. There is a big advantage.

It is the figure which showed the relationship between the dew point of recrystallization annealing atmosphere, and the amount of C after recrystallization annealing and after decarburization annealing. It is a diagram illustrating a relationship between the recrystallization annealing dew point and after the final annealing (B ₈₎ and iron loss (W _17/50). It is the figure which showed the relationship between grinding amount and C amount after decarburization annealing. It is the figure which showed the relationship between the grinding amount and the iron loss ( _{W17 / 50} ) of a product board.

Claims (2)

In mass%, C: 0.08% or less, Si: 2.0-8.0% and Mn: 0.005-3.0%, Al: 100ppm or less, N, S, Se amount reduced to 50ppm or less respectively , the balance being Fe After slabs made of unavoidable impurities are hot-rolled, then cold rolled twice or more with intermediate or intermediate annealing, finished to the final sheet thickness, and then recrystallized and annealed. The amount of C in the steel was adjusted to a range of 0.005 to 0.025%, followed by secondary recrystallization annealing at a temperature of 800 ° C or higher. Next, 0.05g / m ² or more, 2.O g After surface grinding that brings about a weight reduction of less than / m ² , decarburization annealing is performed, then an annealing separator mainly composed of MgO is applied to the steel sheet surface, and then a forsterite film is formed at a temperature of 1000 ° C or higher method for producing oriented electrical steel sheets towards you characterized by applying final annealing to.   The slab is further in% by mass: Ni: 0.005 to 1.50%, Sn: 0.01 to 0.50%, Sb: 0.005 to 0.50%, Cu: 0.01 to 0.50%, P: 0.005 to 0.50% and Cr: 0.01 to 1.50% The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the composition contains one or more selected from among the above.

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