JP2007169726A - Low iron loss grain oriented silicon steel sheet and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To propose a low iron loss grain oriented silicon steel sheet having stress relieving annealing resistance characteristics free from iron loss deterioration due to stress relieving annealing and an inexpensive method for manufacturing the same. <P>SOLUTION: The method for manufacturing the low iron loss grain oriented silicon steel sheet having the excellent stress relieving annealing resistance characteristics is characterized in that through-holes of 0.2 to 50 pieces per 1 cm<SP>2</SP>, are formed in the steel sheet randomly, preferably in a honeycomb or grid form in either process of forming an insulation film after final cold rolling through secondary recrystallization annealing in a manufacturing direction of the grain oriented silicon steel sheet containing 1.5 to 7.0 mass% Si. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a grain-oriented electrical steel sheet used for an iron core or the like of a transformer or a generator, and more particularly to a low iron loss grain-oriented electrical steel sheet without iron loss deterioration due to strain relief annealing and a method for manufacturing the same.

  A grain-oriented electrical steel sheet composed of crystal grains (goth grains) containing 1.5 to 7.0 mass% of Si and oriented in the (110) [001] orientation (goth orientation) has excellent soft magnetic properties. Since it shows, it is widely used as various iron core materials used in a commercial frequency band.

As the characteristics required for the electromagnetic steel sheet, the magnetic flux density B ₈ (T) at a magnetizing force of 800 A / m is high, and the iron loss W ₁₇ when magnetized at a frequency of 50 Hz and a maximum magnetic flux density of 1.7 T. _{/ 50} (W / kg) is low.

  Generally, it is known that the magnetic flux density of the grain-oriented electrical steel sheet depends on the degree of integration in the Goss direction, and the higher the degree of integration, the higher the magnetic flux density. Further, grain oriented electrical steel sheets having a high magnetic flux density often have low hysteresis loss and are generally excellent in iron loss characteristics. However, when the degree of accumulation in the (110) [001] direction is increased, goss grains become coarse, and the magnetic domain width increases accordingly, so that another eddy current loss constituting the iron loss increases. As a result, the reduction in hysteresis loss is offset and no further improvement in iron loss can be expected.

  Accordingly, various techniques for subdividing the magnetic domains have been developed in order to further improve the iron loss of the directional electrical steel sheet having a high magnetic flux density. For example, Patent Document 1 discloses a method of introducing a linear micro strain in a direction perpendicular to the cold rolling direction on a surface of a finish-annealed steel sheet, and Patent Document 2 irradiates a laser on the surface of a steel sheet that has been subjected to finish annealing. Thus, a method of introducing linear distortion is disclosed, and Patent Document 3 discloses a method of linearly irradiating a plasma flame. However, the strain introduced by these methods has poor thermal stability, and there is a problem that the effect disappears by strain relief annealing performed at a temperature of about 800 ° C.

Therefore, various techniques for physically forming grooves have been proposed as magnetic domain refinement methods that do not lose their effects even with strain relief annealing. For example, Patent Document 4 discloses a method for forming a groove by applying a load to a surface of a finish-annealed steel plate using a gear-type roll with a protrusion. Further, Patent Document 5 discloses a method of forming a groove by pattern-applying a hardly soluble resist on the surface and etching the base iron partly with an acid, or etching by electrolysis. Further, Patent Document 6 discloses a method of forming a groove by etching after breaking an insulating film with a laser.
Japanese Patent Publication No.58-5968 Japanese Patent Publication No.57-2252 Japanese Patent Publication No. 07-72300 JP-A 62-53579 Japanese Patent Publication No. 08-6140 JP-A-61-253380

  However, the method disclosed in Patent Document 4 is a ceramic coating mainly composed of forsterite present on the surface of a finish-annealed steel sheet. In addition to being unsuitable for production, there is a problem in that the space factor is lowered due to local deformation of the steel sheet. Further, the method disclosed in Patent Document 5 is excellent in that the space factor is not reduced and the groove depth can be uniformly controlled, but there is a drawback that the manufacturing cost including the resist removal step is high. Further, the method disclosed in Patent Document 6 has a problem in that the coating film may remain due to the variation in the thickness of the insulating coating, and the groove depth varies and the iron loss reduction effect cannot be obtained stably. .

  Furthermore, since any of the above groove forming methods forms a groove in a direction substantially perpendicular to the rolling direction, there is a problem that the magnetic flux density is lowered. To avoid this, the depth of the groove to be formed is set to a plate. There is an essential problem that it must be limited to about 10% of the thickness.

  Accordingly, an object of the present invention is to propose a grain-oriented electrical steel sheet having a low iron loss which is excellent in anti-distortion annealing characteristics without deterioration of iron loss due to stress relief annealing, and an advantageous manufacturing method thereof.

  The inventors have intensively studied in order to solve the above-mentioned problems of the prior art. As a result, the inventors have conceived that a large number of micro holes penetrating the plate thickness are formed on the surface of the steel plate. As a result of further investigation, when a through hole is formed, the problem of variation in the iron loss reduction effect due to a change in groove depth, as in the case of groove formation, can not occur essentially. Thus, the present inventors have found that since the flow of magnetic flux is two-dimensionally distributed on a plane, the magnetic flux density hardly decreases. Furthermore, by properly controlling the distribution pattern and surface density of the through holes, it has been found that the effect of magnetic domain subdivision can be expressed without incurring a decrease in magnetic flux density, and as a result, low iron loss can be achieved. I let you.

That is, the present invention is a grain-oriented electrical steel sheet containing 1.5 to 7.0 mass% of Si, wherein 0.2 to 50 through holes are formed in the steel sheet per 1 cm ^2. It is a low iron loss grain-oriented electrical steel sheet with excellent annealing characteristics.

  The through holes in the electrical steel sheet of the present invention are characterized by being distributed in a honeycomb shape, a lattice shape, or randomly.

  Further, the present invention provides any process from the final cold rolling to the secondary recrystallization annealing until the formation of the insulating coating in the production direction of the grain-oriented electrical steel sheet containing 1.5 to 7.0 mass% of Si. The method for producing a low iron loss directional electrical steel sheet having excellent anti-strain annealing characteristics, wherein the through hole is formed in the steel sheet.

  In the production method of the present invention, the through holes are formed in a honeycomb shape, a lattice shape, or randomly distributed.

  ADVANTAGE OF THE INVENTION According to this invention, the low iron loss directional electrical steel sheet which performed the magnetic domain refinement process which is excellent in the anti-distortion annealing characteristic can be easily and cheaply manufactured, without damaging magnetic flux density almost.

  The grain-oriented electrical steel sheet according to the present invention is a conventionally known manufacturing method, that is, a steel slab containing 1.5 to 7.0 mass% of Si is hot-rolled into a hot-rolled sheet, and if necessary, a hot-rolled sheet After annealing, cold-rolled sheet with the final thickness is obtained by cold rolling twice or once with intermediate annealing, and then primary recrystallization annealing also serves as decarburization in a wet hydrogen atmosphere. Then, it can be manufactured by a manufacturing method in which an annealing separator is applied, coiled into a coil, and subjected to finish annealing for secondary recrystallization, and then an insulating coating is formed on the surface of the steel sheet. And in the manufacturing process of the above-mentioned series of grain-oriented electrical steel sheets, the present invention provides a through-hole having a small diameter over the entire surface of the steel sheet using a method such as laser irradiation between the last cold rolling and before the formation of the insulating coating. It is characterized in that it is formed and the magnetic domain is subdivided.

First, an experiment that triggered the development of the present invention will be described.
C: 0.07 mass%, Si: 3.3 mass%, Mn: 0.07 mass%, S: 0.025 mass%, acid-soluble Al: 0.026 mass%, N: 0.008 mass%, Sn: 0.1 mass% A hot-rolled sheet having a thickness of 2.0 mm containing the material was annealed at 1120 ° C. for 2 minutes and then cold-rolled to obtain a cold-rolled sheet having a final thickness of 0.23 mm. This cold-rolled sheet is subjected to primary recrystallization annealing that also serves as decarburization at 850 ° C. for 90 seconds in a mixed gas atmosphere of nitrogen and hydrogen, and then using a CO ₂ laser used for cutting and the like of the steel sheet, Through holes were formed over the entire surface of the steel plate. The distribution of the through holes was two types, the triangular lattice pattern A and the honeycomb pattern B shown in FIG. 1, and the surface density of the through holes was variously changed. When the formed through hole was observed with an optical microscope, the diameter of the through hole was about 30 μm, and deformation of the steel sheet due to drilling, adhesion of a molten mass around the hole, and the like were not observed. Thereafter, a slurry of an annealing separator mainly composed of MgO is applied and dried, followed by secondary recrystallization annealing in which the temperature is raised to 1180 ° C. at 25 ° C./hr in an atmosphere of 75 vol% hydrogen and 25 vol% nitrogen. Was given.

With respect to the steel sheet after secondary recrystallization obtained as described above, the magnetic flux density B ₈ and the iron loss W _17/50 were measured. FIG. 2 shows the relationship between the surface density of the through holes, the magnetic flux density B ₈ and the iron loss W _17/50 for the measurement results. From FIG. 2, regardless of the distribution pattern of the through holes, the effect of decreasing the iron loss W _17/50 value by magnetic domain subdivision can be obtained when the surface density is 0.2 pieces / cm ² or more, while the surface density is 50 It has been found that when it is larger than the number of pieces / cm ² , the iron loss reduction effect is saturated and the magnetic flux density is greatly reduced.

  Furthermore, as a result of observing the magnetic domain width with and without through holes using the same material, it was confirmed that the magnetic domain was subdivided by the through holes. The cause of the magnetic domain fragmentation due to the formation of the through hole is not sufficiently clear, but is considered to be related to the demagnetizing field effect caused by the magnetic pole appearing on the side surface of the through hole. In addition, when holes are formed before the finish annealing, fine grains are formed in the vicinity of the through holes, which may contribute to magnetic domain subdivision.

As for the relationship between the secondary recrystallized grain size and the surface density of the through-holes, it is sufficient that at least one through-hole is formed in the secondary recrystallized grains, and there are few through-holes. Even when the number of holes formed in the crystal grains is about one, the magnetic domain refinement effect of the present invention is sufficiently obtained as long as it is in the range of 0.2 to 50 per cm ² . In addition, even if there are grains in which no through hole is formed, if a through hole is formed in an adjacent grain and magnetic domain is subdivided, the magnetic domain is subdivided due to the continuity of the flow of magnetic flux at the grain boundary. It has been confirmed that Therefore, the effect of the surface density of the through holes on the magnetic domain refinement is not greatly affected by the size of the secondary recrystallized grains.

Next, a method for forming a through hole, which is a feature of the present invention, will be described.
As a method for forming the through hole, a laser irradiation method is simple. This is because a large number of through holes can be formed simultaneously by arranging a large number of mirrors. However, there is no problem even if mechanical processing such as drilling or punching is used.

  The diameter of the through hole to be formed is preferably in the range of 5 μm to 2 mm. If the thickness is less than 5 μm, the effect of reducing the iron loss is small. On the other hand, if it exceeds 2 mm, it is not preferable because the yield of the material is remarkably reduced and the load for hole formation increases.

Regarding the distribution pattern of the through holes to be formed, a triangular lattice shape or a honeycomb shape pattern as shown in FIG. 1, a square lattice shape, a rhombus lattice shape, or the like is preferable because it is easy to form industrially. In addition, the surface density may not be locally less than 0.2 / cm ² or more than 50 / cm ² in this case. is necessary.

  By the way, in the conventional magnetic domain subdivision technique, it has been common to form grooves and minute strain regions in the form of lines or broken lines. However, according to the examination results of the inventors, when the through holes are arranged in a row, adjacent through holes approach each other, and the iron loss reduction effect is insufficient or the iron loss reduction effect is on the contrary. It became clear that it was damaged. The reason is presumed that when the through holes are formed in a row, the magnetic domain motion between adjacent through holes is disturbed. In addition, it was also found that the arrangement of the through holes in a row causes a decrease in strength or rigidity in a specific direction of the steel sheet, and therefore the magnetostrictive vibration tends to increase and noise tends to increase.

  In this regard, the grain-oriented electrical steel sheet of the present invention does not form through holes in a row in a specific direction, as described above, but is dispersed in a honeycomb or various lattices or randomly. There is no risk of problems such as

  The step of forming the through hole in the steel plate needs to be any step after the final cold rolling step and before the formation of the insulating coating. Performing rolling after drilling not only increases the load of drilling, but also changes the shape of the hole and loses the magnetic domain refinement effect, or makes the rolling itself difficult. On the other hand, when the through-hole is formed after the insulating coating is formed, the corrosion resistance, the insulation, and the like are deteriorated, so that a repair process such as re-application of the insulating coating is required.

  The magnetic domain refinement technique of the present invention is not limited to the grain-oriented electrical steel sheet on which an insulating film is formed. For example, a mineral mainly composed of forsterite is prepared by adjusting the component of the separating agent during finish annealing. Needless to say, the present invention is effective even when applied to a steel sheet in which a quality film is not intentionally formed, or a steel sheet in which the formed forsterite film is removed and the surface is smoothed.

Next, the desirable component composition of the grain-oriented electrical steel sheet of the present invention will be described.
The grain-oriented electrical steel sheet of the present invention preferably contains Si in a range of 1.5 to 7.0 mass% and Mn in a range of 0.03 to 2.5 mass%. Si and Mn are effective components for increasing the electric resistance of the steel sheet and reducing iron loss, and it is preferable to contain 1.5 mass% or more and 0.03 mass% or more, respectively. However, if Si exceeds 7.0 mass%, the hardness becomes too high, making manufacture and processing difficult, and if M exceeds 2.5 mass%, γ transformation is induced at the time of heat treatment to induce magnetic transformation. This is because the characteristics may be deteriorated.

  In addition to the Si and Mn, the grain-oriented electrical steel sheet of the present invention includes Al, B, Bi, Sb, Mo, Te, Sn, P, Ge, as an inhibitor component essential for causing secondary recrystallization. It is preferable to contain elements such as As, Nb, Cr, Ti, Cu, Pb, Zn, and In alone or in combination depending on the characteristics of each element.

  Further, in the grain-oriented electrical steel sheet of the present invention, impurity components such as C, S, and N all have a harmful effect on magnetic properties, and particularly deteriorate iron loss. Therefore, C: 0.003 mass%, respectively. Hereinafter, it is preferable to set S: 0.002 mass% or less and N: 0.002 mass% or less.

  The insulating coating formed on the surface of the grain-oriented electrical steel sheet of the present invention is preferably of a tension imparting type. As the tension-imparting type insulating coating, a phosphate-colloidal silica-chromic acid type conventionally used as an insulating coating of a grain-oriented electrical steel sheet having a forsterite coating is used in terms of magnetic properties, From the viewpoint of manufacturability such as uniform processability and cost. The thickness of the insulating coating is preferably in the range of 0.3 to 10 μm from the viewpoints of tension application effect, space factor, coating adhesion, and the like. The tension imparting type insulating coating is not limited to the above-mentioned phosphate-colloidal silica-chromic acid system. For example, JP-A-6-65754, JP-A-6-65555, An oxide-based film such as boric acid-alumina proposed in Japanese Patent Laid-Open No. 8-299366 can also be applied.

A cold-rolled sheet of grain oriented electrical steel sheet containing 3 mass% of Si and having a thickness of 0.20 mm is subjected to primary recrystallization annealing that also serves as decarburization, and then penetrates the entire surface of the sample using a CO ₂ laser with a diameter of 50 μm. The holes were formed by changing the surface density in four patterns as shown in FIG.
After that, the material is divided into two, one is the application of an annealing separator mainly composed of MgO, the final finishing annealing including the secondary recrystallization process and the purification process, and the directional electromagnetic having a forsterite film A steel plate was used. The other is to apply an annealing separator containing MgO as the main component and lead chloride to obtain a final finish annealing plate having a smooth surface without a forsterite film, followed by electrolysis in a NaCl aqueous solution for smoothing treatment. Then, a TiN film was deposited with a thickness of 1 μm per side using a CVD method to obtain a grain-oriented electrical steel sheet.
Thereafter, an aqueous treatment liquid mainly composed of magnesium phosphate, colloidal silica and magnesium chromate is applied to both steel plates, and baked at 800 ° C. to form an insulating coating having an adhesion amount of about 8.0 g / m ^2. The magnetic flux density B ₈ (T) and the iron loss W _17/50 (W / kg) were measured.

The results of the measurement are shown in Table 1 together with the surface state of the steel sheet, the distribution pattern of the through holes, and the surface density. From these results, it was found that the surface density of the through holes was less than 0.2 / cm ² regardless of the distribution pattern of the through holes. The steel sheets Nos. 1 and 7 were not able to obtain the effect of reducing iron loss, while the surface density of No. 1 exceeding 50 / cm ² . It can be seen that the steel plates of 5, 6 and 10 have a large decrease in magnetic flux density and accompanying this, the deterioration of iron loss has also occurred. On the other hand, No. 1 satisfying the conditions of the present invention (surface density: 0.2 to 50 / cm ² ). It can be seen that the steel sheets 2-4, 8 and 9 have achieved a reduction in iron loss while maintaining a high magnetic flux density. These steel sheets were annealed at 800 ° C. for 180 minutes corresponding to strain relief annealing, and then the magnetic flux density and iron loss were measured. No deterioration was observed in any of the properties.

It is a figure explaining the distribution pattern of the through-hole used for experiment. It is a graph which shows the influence which the surface density of a through hole exerts on the magnetic characteristics (magnetic flux density, iron loss) of a grain-oriented electrical steel sheet. It is a figure explaining the distribution pattern of the through-hole used in the Example.

Claims (4)

In a grain-oriented electrical steel sheet containing 1.5 to 7.0 mass% of Si, the steel sheet is formed with 0.2 to 50 through-holes per 1 cm ^2. Iron loss-oriented electrical steel sheet. 2. The low iron loss directional electrical steel sheet according to claim 1, wherein the through holes are formed in a honeycomb shape, a lattice shape, or randomly distributed. In the production direction of the grain-oriented electrical steel sheet containing 1.5 to 7.0 mass% of Si, 1 cm ² is applied to the steel sheet in any step from the final cold rolling to the formation of the insulating coating through secondary recrystallization annealing. A method for producing a low iron loss directional electrical steel sheet having excellent anti-strain annealing characteristics, wherein 0.2 to 50 through holes are formed per one. The method for producing a low iron loss grain-oriented electrical steel sheet according to claim 3, wherein the through holes are formed in a honeycomb shape, a lattice shape, or randomly distributed.

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