WO2021054409A1 - 方向性電磁鋼板 - Google Patents
方向性電磁鋼板 Download PDFInfo
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- WO2021054409A1 WO2021054409A1 PCT/JP2020/035339 JP2020035339W WO2021054409A1 WO 2021054409 A1 WO2021054409 A1 WO 2021054409A1 JP 2020035339 W JP2020035339 W JP 2020035339W WO 2021054409 A1 WO2021054409 A1 WO 2021054409A1
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- steel sheet
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- glass film
- base steel
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Definitions
- the present invention relates to grain-oriented electrical steel sheets.
- grain-oriented electrical steel sheets are mainly used as iron cores of transformers, it is desired that their magnetization characteristics, especially iron loss, are low. For that purpose, it is important to highly align the crystal grains accumulated in the ⁇ 110 ⁇ ⁇ 001> orientation, to contain Si to increase the intrinsic resistance, and to reduce impurities.
- Magnetic domain control technology can be broadly divided into non-heat resistant type and heat resistant type technology.
- Non-heat resistant magnetic domain control technique for example, as disclosed in Patent Documents 1 and 2, a method of forming a linear thermal strain region on the surface layer of a steel sheet by irradiating the steel sheet with a laser beam is known. ing. In this method, the magnetic domain width is narrowed by the thermal strain region, so that iron loss is reduced.
- the grain-oriented electrical steel sheet to which the non-heat-resistant magnetic domain control technology is applied cannot be used for a transformer that requires strain removal and annealing after processing such as a wound steel core. Therefore, there is a problem that the usage of the grain-oriented electrical steel sheet is limited.
- grain-oriented electrical steel sheets with heat-resistant magnetic domain control technology have the advantage of not being restricted by their use.
- a heat-resistant magnetic domain control technique for example, a method of forming a groove by electrolytic etching as disclosed in Patent Document 3 is known.
- a glass film is first formed on the surface of the steel sheet after secondary recrystallization. Then, the glass film on the surface of the steel sheet is linearly removed by a laser or a mechanical method, and a groove is formed in the portion where the base iron is exposed by etching. Therefore, this method complicates the process and increases the manufacturing cost. Furthermore, there is a limit to the processing speed.
- Patent Document 4 a method of forming a groove on the surface of a steel sheet by a mechanical tooth mold press is known.
- about 3% by mass of Si is often added to the electromagnetic steel sheet for the purpose of increasing the electric resistance. Since such an electromagnetic steel sheet is very hard, the method disclosed in Patent Document 4 may cause wear and damage of the tooth profile. Further, the groove depth may vary, and the iron loss improving effect may also vary.
- Patent Documents 5 and 6 disclose a technique for devising the shape of the steel plate surface and the groove shape as a heat-resistant magnetic domain control technique, but a fundamental solution to each of the above problems possessed by the heat-resistant magnetic domain control technique. Has not been reached.
- the tension exerted on the steel sheet by the insulating film or the glass film (hereinafter, also referred to as "film tension") is extremely important.
- the insulating film for example, one formed by applying an aqueous coating solution containing a phosphate and colloidal silica to a steel sheet is known.
- the glass film which will be described in detail later, for example, a glass film containing an oxide containing forsterite as a main component is known.
- Patent Documents 7 and 8 disclose techniques for increasing the tension of the glass film.
- Patent Document 7 discloses an electromagnetic steel sheet in which spinel (for example, MgAl 2 O 4 ) in forsterite (that is, in a glass film) is 5% or more.
- Patent Document 8 discloses an electromagnetic steel sheet in which the emission intensities of Al and Fe obtained by glow discharge emission analysis satisfy a predetermined condition.
- Patent Document 9 discloses a technique for improving the adhesion of the glass film (preventing peeling during bending during transformer manufacturing).
- Patent Document 9 discloses an electromagnetic steel sheet in which the emission intensity of B obtained by glow discharge emission analysis satisfies a predetermined condition.
- Patent Documents 7 to 9 can be expected to improve the tension or adhesion of the glass film, these techniques alone cannot obtain the magnetic domain subdivision effect. That is, the techniques disclosed in Patent Documents 7 to 9 are premised on the heat-resistant magnetic domain control technique described above. Therefore, even with these techniques, the problem that the iron loss reduction effect cannot be sufficiently obtained cannot be sufficiently solved.
- the heat-resistant magnetic domain control technology has a problem that the iron loss reduction effect cannot be sufficiently obtained.
- the non-heat-resistant magnetic domain control technology can enhance the iron loss reduction effect as compared with the heat-resistant magnetic domain control technology, further improvement of the iron loss reduction effect has been required.
- the present invention has been developed in view of the above circumstances, and even in heat-resistant magnetic domain control in which the iron loss before magnetic domain control is further improved and the iron loss improving effect cannot be sufficiently obtained, the iron loss is sufficiently improved. It is an object of the present invention to provide a grain-oriented electrical steel sheet to which an effect can be obtained.
- the present inventor has made extensive studies to solve the above problems. Specifically, the present inventor repeated an experiment in which heat-resistant magnetic domain control was performed on a grain-oriented electrical steel sheet having the same magnetic flux density and various iron loss characteristics before magnetic domain control. As a result, the present inventor has found that the better the iron loss in the state before the magnetic domain control, the better the iron loss after the magnetic domain control. Then, as a result of investigating the characteristics of the steel sheet having good iron loss before the magnetic domain control, the present inventor has a structure in which the glass film is fitted into the surface layer of the base steel sheet (hereinafter, "glass film fitting" in any of the steel sheets. It was clarified that the structure (also called "structure”) was developed. The present inventor came up with the present invention based on such findings.
- the gist of the present invention is as follows.
- it is a grain-oriented electrical steel sheet containing a base steel sheet and a glass film formed on the surface of the base steel sheet, and the base steel sheet has a chemical component of mass%.
- C 0.010% or less
- Si 2.00 to 4.00%
- Mn 0.05 to 1.00%
- Al 0.010 to 0.065% or less
- N 0.004% or less
- S Containing 0.010% or less
- the balance is composed of Fe and impurities
- the oxygen concentration contained in the glass film and the base steel sheet is 2500 ppm or less
- the directional electromagnetic steel sheet is analyzed by glow discharge emission from the surface of the glass film.
- the concentration profile of Al obtained by (GDS) has at least two peaks, and each peak of Al is set as the first peak and the second peak in order from the side closest to the surface of the glass film, and the first peak of Al is set. strength of the I Al_1, when the second peak intensity of Al was set to I Al_2, oriented electrical steel sheet characterized by satisfying the relation of equation (1) is provided. I Al_1 ⁇ I Al_1 ... Equation (1)
- the region within the range from the surface of the glass film to the depth of 10 ⁇ m in the direction of the center of the plate thickness has a diameter equivalent to a circle of 1 ⁇ m or more.
- Al-containing precipitates may be scattered in the rolling direction at an average frequency of 50 pieces / mm or more.
- the vertical cross section refers to a cross section parallel to the normal direction of the surface of the steel sheet.
- the relationship of the mathematical formula (1) is satisfied.
- the condition of the mathematical formula (1) is satisfied, the inset structure of the glass film is greatly developed, and a large amount of Al precipitates are formed in the surface layer portion of the base steel sheet. Since these Al precipitates form magnetic poles, the magnetic domain subdivision effect can be sufficiently enhanced by these Al precipitates.
- the magnetic domain control may be further applied to the grain-oriented electrical steel sheet according to the present invention. Therefore, according to the present invention, the iron loss before the magnetic domain control is further improved, and the iron loss improving effect can be sufficiently obtained even in the heat-resistant magnetic domain control in which the iron loss improving effect cannot be sufficiently obtained.
- GDS glow discharge emission analysis
- the subdivision of magnetic domains can be realized by generating new magnetic poles on the surface layer of the base steel sheet. More specifically, such magnetic poles increase the static energy of the surface layer portion of the base steel sheet. Then, in the surface layer portion of the base steel sheet, a new 180 ° domain wall is generated in order to reduce the static magnetic energy. As a result, the magnetic domain is subdivided. In other words, the magnetic domain width becomes narrower.
- the present inventor examined fitting the glass film into the surface layer portion of the base steel sheet. This is because the fitting structure of the glass film forms magnetic poles at the surface layer portion of the base steel sheet, so that subdivision of magnetic domains can be realized. Although the details will be described later, the inset structure of the glass film contains Al precipitates, which form the magnetic poles.
- the present inventor has repeatedly studied for maximizing the effect of subdividing the magnetic domain by the fitting structure of the glass film, and found that the fitting structure is formed by forming a glass film satisfying a predetermined condition on the surface of the base steel sheet. It was found that it can be controlled and the magnetic domain subdivision effect can be enjoyed to the maximum.
- the oxygen concentration contained in the glass film and the base steel sheet is 2500 ppm or less.
- the concentration profile of Al obtained by performing glow discharge emission analysis (GDS) on the directional electromagnetic steel plate as shown in FIG. 1, the intensity of the first peak 1 of Al (first peak intensity) is set to I Al_1.
- the intensity of the second peak 2 of Al is I Al_2
- the structure of the glass film is controlled so that the relationship of I Al_1 ⁇ I Al_2 (formula (1)) is satisfied. As shown in FIGS.
- the region within a range of 10 ⁇ m from the surface of the glass film a toward the center of the plate thickness is a circle.
- Precipitates b containing Al having an equivalent diameter of 1 ⁇ m or more are preferably scattered in the rolling direction at an average frequency of 50 pieces / mm or more.
- the grain-oriented electrical steel sheet according to the present embodiment includes a base steel sheet and a glass film formed on the surface of the base steel sheet. An insulating film may be further formed on the surface of the glass film.
- the glass film has an fitting structure that fits into the base steel sheet, and the fitting structure is very well developed. That is, the inset structure has a complicated three-dimensional network structure. Therefore, the glass film is classified into a covering portion that covers most of the surface layer of the base steel sheet and an fitting structure that is fitted into the inside of the surface layer portion of the base steel sheet from the covering portion. Further, the inset structure contains a large amount of Al-containing precipitates.
- FIG. 2 and 3 show an example of a vertical cross section parallel to the rolling direction of the grain-oriented electrical steel sheet according to the present embodiment.
- FIG. 2 is a schematic view
- FIG. 3 is a photomicrograph of a cross section.
- ND indicates the plate thickness direction (normal direction of the steel plate surface), and RD indicates the rolling direction.
- the grain-oriented electrical steel sheet includes the base steel sheet c and the glass film a formed on the surface of the base steel sheet c.
- the glass film a has an fitting structure that fits into the base steel plate c, and the fitting structure is very developed.
- the inset structure contains Al precipitate b.
- Al precipitates appear to be scattered in FIGS. 2 and 3, the Al precipitates are present on the plane of the paper surface (that is, in the rolling direction of the steel sheet) as shown in FIGS. 2 and 3. Not only exists only on a parallel cross section), but actually extends in a direction intersecting the paper surfaces of FIGS. 2 and 3 (for example, perpendicular to the paper surface) (that is, in the plate width direction of the steel plate), and extends to the covering portion.
- the fitting structure generally appears to fit from the covering portion toward the surface layer portion of the base steel plate (that is, extends in the plate thickness direction), but the fitting structure extends in the rolling direction and the plate width direction. In some cases.
- a long fitting structure is observed on the left and right (in the rolling direction and the plate width direction). Details of the inset structure and Al precipitate will be described later.
- the coated portion of the glass coating is a portion that covers most of the surface layer of the base steel plate, and is a portion that is connected to the fitting structure that is fitted inside the surface layer portion of the base steel plate.
- the covering portion and the fitting structure can be classified by the Al concentration profile as described later.
- the base steel sheet has C: 0.010% or less, Si: 2.00 to 4.00%, Mn: 0.05 to 1.00%, Al: 0.010 to 0 in mass% as chemical components. It contains .065% or less, N: 0.004% or less, S: 0.010% or less, and the balance is composed of Fe and impurities.
- % related to the component composition shall mean mass% with respect to the total mass of the base steel sheet.
- C (C: 0.010% or less) C is an element that is effective in controlling the primary recrystallization structure, but since it adversely affects the magnetic properties, it is an element that is removed by decarburization annealing before finish annealing. If the C concentration in the final product exceeds 0.010%, C will age-harden and the hysteresis loss will deteriorate. Therefore, the C concentration should be 0.010% or less.
- the C concentration is preferably 0.007% or less, more preferably 0.005% or less.
- the lower limit of the C concentration includes 0%, but if the C concentration is reduced to less than 0.0001%, the manufacturing cost will increase significantly, so 0.0001% is a practical lower limit on the practical steel sheet. In grain-oriented electrical steel sheets, the C concentration is usually reduced to about 0.001% or less by decarburization annealing.
- Si is an element that increases the electrical resistance of a steel sheet and improves the iron loss characteristics. If the Si concentration is less than 2.00%, ⁇ transformation of the iron structure occurs during finish annealing and the crystal orientation of the steel sheet is impaired. Therefore, the Si concentration is set to 2.00% or more. The Si concentration is preferably 2.50% or more, more preferably 3.00% or more. On the other hand, if the Si concentration exceeds 4.00%, the workability of the grain-oriented electrical steel sheet deteriorates and cracks occur during rolling, so the Si concentration is set to 4.00% or less. The Si concentration is preferably 3.50% or less.
- Mn 0.05 to 1.00%)
- Mn is an element that prevents cracking during hot rolling and combines with S to produce MnS that functions as an inhibitor. If the Mn concentration is less than 0.05%, the effect of adding Mn is not sufficiently exhibited, so the Mn concentration is set to 0.05% or more.
- the Mn concentration is preferably 0.07% or more, more preferably 0.09% or more.
- the Mn concentration exceeds 1.00%, the precipitation and dispersion of MnS become non-uniform, the required secondary recrystallization structure cannot be obtained, and the magnetic flux density decreases, so that the Mn concentration is 1.00% or less.
- the Mn concentration is preferably 0.80% or less, more preferably 0.60% or less.
- Al is an element that binds to N to produce (Al, Si) N or AlN that functions as an inhibitor. If the Al concentration is less than 0.010%, the effect of adding Al is not sufficiently exhibited and the secondary recrystallization does not proceed sufficiently. Therefore, the Al concentration is set to 0.010% or more.
- the Al concentration is preferably 0.015% or more, more preferably 0.020% or more.
- the Al concentration exceeds 0.065%, the precipitation and dispersion of the inhibitor become non-uniform, the required secondary recrystallization structure cannot be obtained, and the magnetic flux density decreases, so that the Al concentration is 0.065% or less. And.
- the Al concentration is preferably 0.050% or less, more preferably 0.040% or less.
- N is an element that binds to Al to form AlN that functions as an inhibitor.
- the N concentration of the final product exceeds 0.004%, N in the steel sheet is precipitated as AlN, which deteriorates the hysteresis loss. Therefore, the N concentration is set to 0.004% or less.
- the lower limit of the N concentration includes 0%, but if the N concentration is reduced to less than 0.0001%, the manufacturing cost will increase significantly, so 0.001% is a practical lower limit on the practical steel sheet. In the grain-oriented electrical steel sheet, the N concentration is usually reduced to about 0.001% or less by finish annealing.
- S is an element that binds to Mn to produce MnS that functions as an inhibitor.
- S concentration exceeds 0.010% in the final product, S in the steel sheet is precipitated as MnS, which deteriorates the hysteresis loss. Therefore, the S concentration is set to 0.010% or less.
- the lower limit of the S concentration includes 0%, but if the S concentration is reduced to less than 0.0001%, the manufacturing cost will increase significantly, so 0.0001% is a practical lower limit on the practical steel sheet.
- the S concentration is usually reduced to about 0.005% or less by finish annealing.
- the balance excluding the above elements is Fe and impurities.
- Impurities are basically unavoidable impurities, but when the base steel sheet contains optional additive elements described later, the impurities are composed of these optional additive elements in addition to the unavoidable impurities.
- the unavoidable impurities are elements that are unavoidably mixed from the steel raw material and / or in the steelmaking process, and are permissible elements as long as they do not impair the characteristics of the grain-oriented electrical steel sheet according to the present embodiment.
- the base steel sheet Cr: 0.30% or less, Cu: 0.40% or less, P: 0.50% for the purpose of not inhibiting the magnetic characteristics and enhancing other characteristics.
- Ni 1.00% or less
- Sn 0.30% or less
- Sb 0.30% or less
- B 0.0100% or less
- Mo 0.1% or less
- Bi 0.01% or less.
- One or more of the above may be added as an optional additive element. Since these elements are optional additives, the lower limit of the concentration may be 0%.
- Cr is an element that improves the oxide layer of decarburization annealing and is effective for forming a glass film. Therefore, Cr may be added to the base steel sheet in the range of 0.30% or less. If the Cr concentration exceeds 0.30%, the decarburization property is significantly inhibited. Therefore, the upper limit of the Cr concentration is preferably 0.30%.
- Cu is an element effective in increasing the specific resistance of the base steel sheet and reducing iron loss. If the C concentration exceeds 0.40%, the iron loss reduction effect is saturated and causes surface defects such as "copper hesitation" during hot spreading. Therefore, the upper limit of the C concentration is preferably 0.40%.
- P 0.50% or less
- P is an element effective for increasing the specific resistance of the base steel sheet and reducing the iron loss. If the P concentration exceeds 0.50%, a problem will occur in rollability. Therefore, the upper limit of the P concentration is preferably 0.50%.
- Ni is an element effective in increasing the specific resistance of the base steel sheet and reducing iron loss. Ni is also an effective element for controlling the iron structure of the hot-rolled plate and improving the magnetic properties. However, if the Ni concentration exceeds 1.00%, secondary recrystallization becomes unstable, so the upper limit of the Ni concentration is preferably 1.00%.
- Sn and Sb are well-known intergranular segregation elements. Since the base steel sheet according to the present embodiment contains Al, Al may be oxidized by the moisture released from the annealing separator depending on the finish annealing conditions, and the inhibitor strength may fluctuate at the coil position. As a result, the magnetic characteristics may fluctuate depending on the coil position. As one of the countermeasures, there is a method of preventing the oxidation of Al by adding these intergranular segregation elements, and for that purpose, Sn and Sb may be added to the base steel sheet at a concentration of 0.30% or less, respectively. ..
- the concentration of these elements exceeds 0.30%, Si is less likely to be oxidized during decarburization annealing, the formation of a glass film becomes insufficient, and the decarburization annealing is significantly inhibited. Therefore, the upper limit of the concentration of these elements is preferably 0.30%.
- B is an element that binds to N in the base steel sheet and complex-precipitates with MnS to form BN that functions as an inhibitor.
- the lower limit of the B concentration is not particularly limited, and may be 0% as described above. However, in order to fully exert the effect of adding B, the lower limit of the B concentration is preferably 0.0005%.
- the B concentration is preferably 0.001% or more, more preferably 0.0015% or more.
- the B concentration is preferably 0.0100% or less.
- the B concentration is preferably 0.0080% or less, more preferably 0.0060% or less, and more preferably 0.0040% or less.
- Mo 0.1% or less
- Mo is an element effective for improving the surface texture during hot spreading. However, if the Mo concentration exceeds 0.1%, the Mo addition effect is saturated, so the upper limit of the Mo concentration is preferably 0.1%.
- Bi 0.01% or less
- Bi has the effect of stabilizing precipitates such as sulfides and strengthening the function as an inhibitor.
- the upper limit of the Bi concentration is preferably 0.01%.
- the total oxygen concentration in the glass film and the base steel sheet is 2500 ppm or less. Most of the oxygen is contained in the glass film, and the oxygen contained in the steel sheet is about 10 to 100 ppm.
- the grain-oriented electrical steel sheet contains an insulating film described later, the oxygen concentration is measured after the insulating film is removed from the grain-oriented electrical steel sheet. That is, the insulating film is not included in the measurement target of the oxygen concentration.
- the insulating film is removed using, for example, an aqueous sodium hydroxide solution.
- the oxygen analysis method uses a gas analysis method in which a sample is placed in a graphite crucible, the sample is melted and heated, and CO and CO 2 are measured by an infrared absorption method.
- the oxygen concentration exceeds 2500 ppm, the magnetic flux density of the base steel sheet decreases (more specifically, the amount of magnetic iron decreases), and the iron loss deteriorates. Therefore, the upper limit of the oxygen concentration is 2500 ppm.
- the lower limit of the oxygen concentration is not particularly limited, but when the oxygen concentration is extremely low as 500 ppm or less, a glass film is not actually formed on the surface of the base steel sheet, and the inset structure of the glass film does not develop. Therefore, the iron loss becomes inferior. Furthermore, the adhesion of the insulating film may decrease. Therefore, the oxygen concentration is preferably more than 500 ppm, more preferably 1000 ppm or more. The oxygen concentration is measured using a gas analyzer that uses the principle of the inert gas melting method.
- the method for setting the oxygen concentration to 2500 ppm or less include decarburization annealing conditions, particularly a method for adjusting the dew point.
- the oxygen concentration can be set to 2500 ppm or less by adjusting the dew point while considering the annealing time and annealing temperature.
- GDS analysis requires appropriate condition adjustment according to the sample, and the adjustment is within the range of normal practice for those skilled in the art. Therefore, the measurement conditions of GDS are not limited, but for example, the output is 35 W, and the data is taken in at intervals of 0.01 to 0.10 seconds.
- the Al concentration profile has at least two peaks.
- the peaks of each Al are designated as the first peak, the second peak, and so on in order from the side closer to the surface of the glass film.
- FIG. 1 shows an example of the Al concentration profile.
- the Al concentration profile shown in FIG. 1 has two peaks, that is, a first peak 1 and a second peak 2.
- the number of peaks is preferably two.
- the peaks may partially overlap or may be separated from each other.
- the first peak is derived from the Al precipitate in the coated portion of the glass film
- the second peak is derived from the Al precipitate in the inlaid structure of the glass film.
- the Al precipitate from which each peak is derived is, for example, Mg 2 Al 2 O 4 in which Si of forsterite (Mg 2 SiO 4) constituting the glass film is replaced with Al.
- MgAl 2 O 4 has a similar composition of constituent elements to forsterite (Mg 2 SiO 4 ), has a polymorphic relationship, and is easily produced.
- the Al precipitate is not necessarily limited to Mg 2 Al 2 O 4 , and is not particularly limited as long as it constitutes a magnetic pole in the surface layer portion of the base steel sheet. Examples of other Al precipitates assumed in the present embodiment include precipitates in which other elements are substituted and solid-solved in MgAl 2 O 4 , Al 2 O 3 and the like.
- the first peak intensity of Al is I Al_1 and the second peak intensity of Al is I Al_1
- the relationship of the equation (1) is satisfied.
- each peak intensity is defined as the maximum intensity of Al emission intensity at each peak (in other words, the maximum peak height).
- the equation (1) may be modified so that the ratio of the first peak intensity to the second peak intensity is less than 1. That is, the relation of the mathematical formula (1)'is satisfied.
- the first peak intensity may be 0, and the lower limit of the peak ratio may be 0.
- the lower limit of the peak ratio is 0.1 or more or more than 0.1, 0.2 or more or more than 0.2, 0.3 or more or more than 0.3, 0.4 or more or more than 0.4, 0. 5 or more or more than 0.5, 0.6 or more or more than 0.6, 0.7 or more or more than 0.7, 0.8 or more or more than 0.8, 0.9 or more or more than 0.9. You may. On the other hand, in general, the stronger the second peak intensity, the closer the peak ratio is to 1, which is preferable. Therefore, the upper limit of the peak ratio is 0.9 or less or less than 0.9, 0.8 or less or less than 0.8, 0.7 or less or less than 0.7, 0.6 or less or less than 0.6, 0. It may be 5 or less or less than 0.5, 0.4 or less or less than 0.4.
- FIGS. 2 and 3 show an example of the surface state of the grain-oriented electrical steel sheet according to the present embodiment.
- the grain-oriented electrical steel sheet includes a base steel sheet c and a glass film a formed on the surface of the base steel sheet c.
- the glass film a has an fitting structure that fits into the base steel plate c, and the fitting structure is very developed.
- the inset structure contains Al precipitate b.
- the inset structure has a very complex three-dimensional network structure.
- Al precipitates appear to be scattered in FIGS. 2 and 3
- the Al precipitates are present on the plane of the paper surface (that is, in the rolling direction of the steel sheet) as shown in FIGS. 2 and 3.
- the fitting structure generally appears to fit from the covering portion toward the surface layer portion of the base steel plate (that is, extends in the plate thickness direction), but the fitting structure extends in the rolling direction and the plate width direction. In some cases. When observing the vertical cross section of this portion, a long fitting structure is observed on the left and right (in the rolling direction and the plate width direction).
- the "surface layer portion of the base steel plate” in the present embodiment means a region from the surface of the base steel plate (the interface between the coated portion of the glass film and the base steel plate) to a predetermined depth in the base steel plate.
- the portion where the fitting structure of the glass film is formed may be used as the surface layer portion of the base steel sheet.
- the surface of the base steel sheet (the interface between the coated portion of the glass film and the base steel plate) generally corresponds to the boundary between the coated portion of the glass film and the fitting structure, and the boundary is determined by the Al concentration profile. Can be classified.
- the predetermined depth may be 10 ⁇ m from the surface of the glass coating toward the center of the plate thickness in consideration of the thickness of the glass coating on a general grain-oriented electrical steel sheet.
- a part of the inset structure is composed of Al precipitates.
- Al precipitates are abundantly distributed at the tip of the inset structure.
- the tip end portion of the fitting structure means an end portion extending in the depth direction on the inner side of the steel sheet in observation in a two-dimensional cross section as shown in FIG. 3, for example.
- FIGS. 2 and 3 it can be seen that a large amount of Al precipitates are formed at the tip of the inset structure.
- Al precipitates appearing to be scattered substantially spherically in the base steel plate are at the tip of the fitting structure extending in the direction intersecting the paper surface (that is, the plate width direction of the steel plate). It is formed.
- the Al precipitate may be present at a portion other than the tip of the inset structure.
- the specific three-dimensional network structure of the inset structure is not particularly limited, but the more complicated the inset structure is, the more Al precipitates are generated in the inset structure and trapped and stay there.
- the fitting structure since the fitting structure forms a very complicated three-dimensional network structure, many Al precipitates are present in the fitting structure.
- most of the Al precipitates are formed by the inset structure and are trapped there, so that not so much is deposited on the coated portion of the glass film.
- the first peak is derived from the Al precipitate in the coating portion of the glass film
- the second peak is derived from the Al precipitate in the inlaid structure of the glass film. Therefore, in the grain-oriented electrical steel sheet according to the present embodiment, the second peak intensity is larger than the first peak intensity, and the mathematical formula (1) is satisfied. From this, the boundary between the coated portion of the glass film and the inset structure can be classified by the Al concentration profile.
- the Al precipitate forms an interface on the surface layer of the base steel sheet that has a different magnetic permeability from that of the steel sheet. That is, the Al precipitate having the fitted structure fitted into the surface layer portion of the base steel sheet constitutes the magnetic pole.
- many Al precipitates, that is, magnetic poles are formed on the surface layer portion of the base steel sheet, so that the magnetic domain is further subdivided.
- the case where the mathematical formula (1) is not satisfied is, for example, a case where the inset structure is not developed and the amount of Al precipitates deposited is small.
- An example of such a grain-oriented electrical steel sheet is shown in FIG.
- the meaning of each reference numeral in FIG. 4 is the same as that in FIGS. 2 and 3.
- the inset structure is hardly developed, and therefore the Al precipitate is present almost only in the glass film (the portion corresponding to the coating portion).
- the fitting structure is not developed, and Al precipitates serving as magnetic poles are hardly formed on the surface layer portion of the base steel sheet, so that the magnetic domain subdivision effect cannot be enjoyed.
- the inlaid structure of the glass film is the portion fitted into the surface layer portion of the base steel sheet, and the Al precipitate contained in the inlaid structure is the portion of the surface layer portion of the base steel sheet from the surface of the glass film to a depth of 10 ⁇ m.
- the Al precipitate can be observed by the following method. That is, of the vertical cross section parallel to the rolling direction of the surface layer portion of the base steel plate, the region from the surface of the glass film to a depth of 10 ⁇ m (hereinafter, also referred to as “observation region”) is defined by an optical microscope or FE-SEM (field electron emission). Observe with a emission scanning electron microscope) or the like.
- the composition of the observation region is analyzed by EDS (energy dispersive X-ray spectroscopy), EPMA (electron probe microanalyzer), or the like.
- EDS energy dispersive X-ray spectroscopy
- EPMA electron probe microanalyzer
- the size and precipitation frequency of Al precipitates which will be described later, can be measured.
- the precipitation frequency for example, a plurality of photographs of the observation area may be taken, and the precipitation frequency measured in each photograph may be arithmetically averaged.
- Al precipitates having a diameter equivalent to a circle and having a diameter of 1 ⁇ m or more are scattered in the observation region at an average frequency of 50 pieces / mm or more in the rolling direction. In this case, the magnetic domain subdivision effect can be further enhanced.
- the presence of Al precipitates having a circle-equivalent diameter of less than 1 ⁇ m does not adversely affect the characteristics of the base steel sheet, it is considered that such Al precipitates are unlikely to contribute to the magnetic domain refinement effect.
- the upper limit of the equivalent circle diameter of the Al precipitate is not particularly limited. However, if the Al precipitates are too large, the number density of the Al precipitates is relatively reduced, and the iron loss improving effect may be reduced. Therefore, for example, the equivalent circle diameter is preferably 10 ⁇ m or less.
- the precipitation frequency of Al precipitates is less than 50 pieces / mm, the frequency of occurrence of magnetic poles decreases, so that the magnetic domain subdivision effect may be slightly reduced.
- the upper limit of the precipitation frequency is not particularly limited, but if the precipitation frequency is too high, the Al precipitates may hinder the domain wall movement itself. In this case, the iron loss may be impaired, so the precipitation frequency is preferably 100 pieces / mm or less.
- the grain- oriented electrical steel sheet according to the present embodiment when the first peak intensity of Al is I Al_1 and the second peak intensity of Al is I Al_1 , the relationship of the mathematical formula (1) is satisfied. Is done.
- the condition of the formula (1) is satisfied, the inlaid structure of the glass film is greatly developed, and many Al precipitates are formed in the inlaid structure, in other words, in the surface layer portion of the base steel sheet. Since these Al precipitates form magnetic poles, the magnetic domain subdivision effect can be sufficiently enhanced by these Al precipitates.
- the magnetic domain control described later may be further applied to the grain-oriented electrical steel sheet according to the present embodiment. Therefore, according to the present embodiment, the iron loss before the magnetic domain control is further improved, and the iron loss improving effect can be sufficiently obtained even in the heat-resistant magnetic domain control in which the iron loss improving effect cannot be sufficiently obtained. ..
- Manufacturing method of grain-oriented electrical steel sheet > Next, an example of the method for manufacturing the grain-oriented electrical steel sheet according to the present embodiment will be described.
- the manufacturing method of the grain-oriented electrical steel sheet according to the present embodiment is not limited to the manufacturing method described below, and any manufacturing method can be used as long as it can manufacture the grain-oriented electrical steel sheet according to the present embodiment. You may.
- the method for manufacturing the directional electromagnetic steel sheet according to the present embodiment includes a steel slab preparation step, a reheating step, a hot rolling step, a hot rolling plate annealing step, a cold rolling step, a decarburization annealing step, a nitrided step, and a quench separation. Includes agent coating step, finish annealing step, purification annealing step, and cooling step. Hereinafter, each step will be described in detail.
- a steel slab is prepared. Specifically, steel is melted by, for example, a converter or an electric furnace. The molten steel thus obtained is subjected to vacuum degassing treatment as necessary, and then continuously cast or ingot and then block-rolled. This gives a steel slab.
- the thickness of the steel slab is not particularly limited, but is usually cast in the range of 150 to 350 mm, preferably 220 to 280 mm. However, the steel slab may be a so-called thin slab having a thickness range of 30 to 70 mm. When a thin slab is used, there is an advantage that it is not necessary to roughen the intermediate thickness when manufacturing the hot-rolled plate.
- the chemical composition of the steel slab is the same as that of the base steel sheet described above except for the mass% of N. Here, only the mass% of N will be described.
- N is an element that binds to Al to form AlN that functions as an inhibitor. However, N is also an element that forms blisters (vacancy) in the steel sheet during cold rolling. If the mass% of N is less than 0.004%, the formation of AlN is insufficient, so the N concentration is set to 0.004% or more. It is preferably 0.006% or more, more preferably 0.007% or more. If the N concentration exceeds 0.012%, many blisters may be formed in the steel sheet during cold rolling, so the N concentration is set to 0.012% or less.
- the steel slab is reheated.
- the reheating temperature of the steel slab is preferably 1280 ° C. or lower.
- the reheating temperature exceeds 1280 ° C., the amount of molten scale increases.
- the decarburization annealing temperature it is necessary to set the decarburization annealing temperature to more than 900 ° C. in order to obtain the desired primary recrystallization grain size. Therefore, in this embodiment, it is preferable to reheat the steel slab at 1280 ° C. or lower.
- the lower limit of the reheating temperature is not particularly limited, but may be, for example, 1100 ° C.
- Hot rolling process hot rolled sheet annealing process
- the steel slab after reheating is hot-rolled.
- the hot-rolled plate annealing step the iron structure is recrystallized by heating the hot-rolled plate obtained by the hot rolling step to the first stage temperature of 1000 to 1150 ° C. Then, the hot-rolled plate is annealed at 850 to 1100 ° C. and at the second stage temperature lower than the first stage temperature.
- This hot-rolled plate annealing step is mainly performed for the purpose of homogenizing the non-uniform structure generated during hot-rolling.
- the upper limit of the first stage temperature in this case has a great influence on the inhibitor. For example, when the temperature of the first stage exceeds 1150 ° C., the inhibitor is finely precipitated in the subsequent steps. Therefore, the upper limit of the temperature of the first stage is set to 1150 ° C. On the other hand, when the temperature of the first stage is less than 1000 ° C., recrystallization is insufficient and the iron structure after hot spreading cannot be made uniform. Therefore, the lower limit of the first stage temperature is set to 1000 ° C.
- the upper limit of the temperature of the second stage also has a great influence on the inhibitor. For example, when the temperature of the second stage exceeds 1100 ° C., the inhibitor is finely precipitated in the subsequent step. Therefore, the upper limit of the temperature of the second stage is set to 1100 ° C. When the temperature of the second stage is less than 850 ° C., the ⁇ phase is not generated, so that the iron structure cannot be made uniform. Therefore, the lower limit of the second stage temperature is set to 850 ° C. Further, the temperature of the second stage needs to be controlled to a value lower than the temperature of the first stage.
- the hot-rolled plate After performing the hot-rolled plate annealing step, the hot-rolled plate is subjected to one cold rolling or two or more cold rollings (cold rolling) with intermediate annealing sandwiched between them. As a result, the final cold-rolled plate is produced.
- Each cold rolling may be carried out at room temperature, or may be hot rolling in which the temperature of the steel sheet is raised to a temperature higher than room temperature, for example, about 200 ° C.
- the decarburization annealing step first, a heating step of heating the steel plate (cold-rolled plate) after the cold-rolling step from an inlet temperature t0 ° C. to a soaking temperature t2 higher than the inlet temperature, and a heating step of equalizing the temperature of the cold-rolled plate. It includes a soaking step of maintaining a heat temperature of t2 ° C. for a predetermined time.
- the decarburization annealing step is performed in a moist atmosphere.
- the inlet temperature t0 ° C. is the temperature at which the cold-rolled plate is introduced into the annealing furnace, and is generally 600 ° C. or lower.
- the soaking temperature is a temperature within the range of 700 to 900 ° C.
- the decarburization annealing soaking step (the process of maintaining a temperature of 700 to 900 ° C. for a predetermined time) is performed for the purpose of removing carbon in steel and controlling the primary recrystallization grain size to a desired grain size.
- the soaking step is preferably carried out at a soaking temperature of t2 ° C. in a temperature range of 700 ° C. to 900 ° C. for a time such that the primary recrystallization particle size is 15 ⁇ m or more. If the soaking temperature t2 ° C. is less than 700 ° C., the desired primary recrystallization particle size cannot be achieved, and if the soaking temperature t2 exceeds 900 ° C., the primary recrystallization exceeds the desired particle size.
- the primary recrystallization texture (specifically, the crystal orientation in the texture) can be controlled by controlling the heating rate in the heating process.
- the ease of recrystallization differs depending on the crystal orientation, and the ⁇ 411 ⁇ orientation grains are most likely to recrystallize at a heating rate of around 100 ° C./sec, and the Goth orientation grains are more likely to recrystallize in proportion to the heating rate. .. Therefore, in the present embodiment, the heating rate HR1 from t0 ° C., which is 600 ° C. or lower, to t2 ° C.
- thermo in the tropics which is in the range of 700 to 900 ° C.
- temperature in the tropics is set to 40 ° C./sec or more, preferably 75 ° C. It is preferable to heat at a heating rate of / sec or more, more preferably 75 to 125 ° C./sec. This makes it possible to reduce the ⁇ 111 ⁇ orientation grains and increase the ⁇ 411 ⁇ orientation grains and the Goth orientation grains.
- HR1 is an average heating rate from t0 ° C. to t2 ° C., and the heating rate may fluctuate in a part of the heating process and temporarily become less than 40 ° C./sec.
- the decarburization and annealing steps include a heating step of heating the cold-rolled plate from an inlet temperature t0 ° C. below 600 ° C. to a soaking temperature t2 ° C. higher than the inlet temperature t0 ° C. and a temperature of the cold-rolled plate.
- the temperature of the cold-rolled plate is within the range of the inlet temperature t0 ° C. to 700 to 900 ° C. and the soaking temperature.
- the heating rate hr1 until the ultimate temperature t1 ° C. lower than t2 ° C. is set to 40 ° C./sec or more, and the heating rate hr2 until the temperature of the cold-rolled plate reaches the soaking temperature t2 ° C. from the ultimate temperature t1 ° C. It may be over 15 ° C./sec to 30 ° C./sec.
- the temperature of the cold-rolled plate reaches the ultimate temperature t1 ° C., which is within the range of the inlet temperature t0 ° C. to 700 to 900 ° C. and lower than the soaking temperature t2 ° C. ( That is, the heating rate hr1 in the rapid heating temperature range) is set to 40 ° C./sec or more, and the heating rate hr2 from the reaching temperature t1 ° C. to the soaking temperature t2 ° C. is set to 15 ° C./sec. It may be super to 30 ° C./sec.
- the inlet temperature t0 ° C. to the ultimate temperature t1 Heating in the temperature range of ° C. can be performed by an induction heating device.
- the heating rate hr1 may be 40 ° C./sec or higher, preferably 75 to 125 ° C./sec.
- the heating rate hr1 from the inlet temperature t0 ° C. to the soaking heat t1 ° C. is set to 40 ° C./sec or more. This makes it possible to reduce the ⁇ 111 ⁇ orientation grains and increase the ⁇ 411 ⁇ orientation grains and the Goth orientation grains.
- the heating rate hr1 is preferably 75 ° C./sec or higher, and more preferably 75 to 125 ° C./sec.
- the heating rate hr2 from the ultimate temperature t1 ° C. to the soaking temperature t2 ° C. may be set to more than 15 ° C./sec to 30 ° C./sec.
- the lower limit of the heating rate hr2 is preferably 16 ° C./sec.
- the heating rate hr2 after the temperature of the cold-rolled plate reaches the ultimate temperature t1 ° C. may be set to a relatively high value of more than 15 ° C./sec to 30 ° C./sec.
- the reason why the above effect is obtained when the heating rate hr2 is controlled to more than 15 ° C./sec to 30 ° C./sec is not clear, but the present inventor considers the reason as follows. .. That is, in the temperature range from the ultimate temperature t1 ° C. of rapid heating to the soaking temperature t2 ° C., which is 700 to 900 ° C., recrystallization of unrecrystallized grains and grain growth of crystal grains that have already been recrystallized occur. At the soaking temperature of t2 ° C., all the unrecrystallized grains are recrystallized grains.
- the recrystallized grains enter the grain growth mode, the azimuth grains having a small grain size are slaughtered, and the azimuth grains having a large grain size have a large diameter.
- the Goth orientation grains have completed recrystallization at an ultimate temperature of t1 ° C. or lower. Goth that has already completed recrystallization by controlling the heating rate hr2 from the ultimate temperature t1 ° C. to the soaking temperature t2 ° C. to more than 15 ° C./sec to 30 ° C., preferably 16 ° C./sec or more and 30 ° C./sec or less. Grain growth of oriented grains is promoted. That is, since the Goth azimuth grains are already large-diameter crystal grains at the start of the heat equalizing step, they can exist without being eaten by other azimuth grains in the heat soaking step.
- the heating rate hr2 is 15 ° C./sec or less, the growth of the crystal grains in the orientation of recrystallization after the reaching temperature t1 ° C. and the growth of the Goth orientation grains compete with each other, and the Goth orientation grains cannot grow sufficiently. ..
- the frequency of Goth orientation grains decreases in the primary recrystallized grain aggregate structure, and an electromagnetic steel sheet having good iron loss characteristics cannot be obtained.
- the heating rate hr2 exceeds 30 ° C./sec, the frequency and crystal grain size of the goth-oriented grains become extremely large in the primary recrystallized grain aggregate structure, and the grain size (uniformity) of the entire structure is significantly impaired. It will be lost.
- the upper limit of hr2 may be 25 ° C. or lower or less than 25 ° C.
- the range of hr2 can be heated by various heating devices as described in detail later, but if hr2 becomes large and overshoots the soaking temperature t2, it may lead to subsequent secondary recrystallization failure. Therefore, it is preferable that the upper limit of hr2 is 25 ° C. or lower or less than 25 ° C., because it is possible to prevent overshooting the soaking temperature t2.
- Heating in the heating process of decarburization annealing may be performed by induction heating.
- the degree of freedom of the heating rate is high, the steel sheet can be heated in a non-contact manner, and the effect of being relatively easy to install in the decarburization annealing furnace can be obtained.
- the cold-rolled plate is heated from the inlet temperature t0 ° C. only by the induction heating device. It can be rapidly heated to the ultimate temperature t1 ° C.
- heating from the ultimate temperature t1 ° C. to the soaking temperature t2 ° C. and the soaking heat treatment in the subsequent soaking step may be performed using a heating device using a radiant heat source such as a radiant tube. It is difficult to heat after the Curie point with an induction heating device, but a heating device using a radiant heat source can stably heat a cold-rolled plate even in such a temperature range. Further, heating by radiant heat has an advantage that it is easy to control within the range of the heating rate hr2 (within the range slower than the heating rate hr1).
- the heating method is not particularly limited.
- the heating method may be a method using a new high-energy heat source such as a laser or plasma, a method using an energization heating device, or the like. It is also possible to combine these as appropriate.
- a new high-energy heat source such as a laser or plasma
- an energization heating device or the like. It is also possible to combine these as appropriate.
- an induction heating device or a heating device using a radiant heat source there is an advantage that the cold rolling plate can be heated without the heating device coming into direct contact with the cold rolling plate.
- the method for measuring the heating rate of HR1, HR2 (described later), hr1, hr2, etc. is not particularly limited, but it can be calculated by measuring the temperature of the steel sheet using, for example, a radiation thermometer or the like. However, if it is difficult to measure the steel plate temperatures t0, t1, t2, etc., and it is difficult to estimate the exact locations of the start and end points of HR1, HR2, hr1, hr2, etc., each heat in the temperature rise process These locations may be estimated by analogizing the pattern.
- the steel sheet After decarburization annealing, the steel sheet is nitrided so that the nitrogen concentration of the steel sheet is 40 ppm or more and 1000 ppm or less. If the nitrogen concentration of the steel sheet after the nitriding treatment is less than 40 ppm, AlN is not sufficiently precipitated in the steel sheet, and AlN does not function as an inhibitor. Therefore, the nitrogen concentration of the steel sheet is set to 40 ppm or more. On the other hand, when the nitrogen concentration of the steel sheet exceeds 1000 ppm, excess AlN is present in the steel sheet even after the completion of secondary recrystallization in finish annealing. Such AlN causes deterioration of iron loss. Therefore, the nitrogen concentration of the steel sheet is set to 1000 ppm or less.
- an annealing separator is applied to the surface of the steel sheet.
- Finish annealing which will be described later, may be performed in a state where the steel sheet is wound into a coil. When finish annealing is performed in such a state, the coil may be seized and it may be difficult to unwind the coil. Therefore, in the present embodiment, an annealing separator is applied so that the coil can be unwound after finish annealing.
- the main component of the annealing separator is MgO, and MgO in the annealing separator undergoes a solid-phase reaction with SiO 2 in the internal oxide layer during finish annealing to form forsterite (Mg 2 SiO 4 ), resulting in a glass film. To form.
- the finish annealing step is annealing, which is also called a secondary recrystallization annealing step, and is a process for promoting secondary recrystallization of the iron structure.
- the steel sheet is heated to about 1200 ° C., which will be described later.
- the heating rate HR2 is 15 ° C./h or less in the temperature range of at least 1000 ° C. to 1100 ° C.
- heating rate HR2 is too fast (more than 15 ° C./h), crystal grains having a crystal orientation other than the Goth orientation will grow.
- the heating rate in other temperature ranges is not particularly limited and may be about the same as that of the conventional finish annealing.
- the finish annealing process is performed in a mixed atmosphere of nitrogen and hydrogen. Further, in the present embodiment, the nitrogen concentration (nitrogen partial pressure) is controlled to be gradually lowered in the heating process. Specifically, when the temperature range of 700 to 900 ° C. is T2, the temperature range of 800 to 1000 ° C. is T3, and the temperature range of 900 to 1200 ° C. is T4, the partial pressure of nitrogen from room temperature to T2 (T2 or less) P0 is 60 to 90%, nitrogen partial pressure P1 from T2 to T3 (more than T2 and T3 or less) is 40 to 60%, and nitrogen partial pressure P2 from T3 to T4 (more than T3 and T4 or less) is 10 to 40%. ..
- T4 is set to a temperature lower than 1200 ° C.
- the nitrogen partial pressure P2 at T4 to 1200 ° C. is 0% (hydrogen partial pressure 100%).
- the precipitates (AlN, MnS, etc.) used as inhibitors are detoxified by purifying after the completion of the secondary recrystallization. This makes it possible to reduce the hysteresis loss in the final magnetic characteristics.
- the purification annealing step for example, it is preferable to retain the steel sheet at 1200 ° C. for 10 hours or more in a hydrogen atmosphere.
- the steel sheet is cooled.
- the cooling rate (temperature lowering rate) CR in the temperature range (T5) of 1200 to 1000 ° C. is 30 to 100 ° C./h.
- the cooling rate CR is more preferably 30 to 50 ° C./h.
- the grain-oriented electrical steel sheet according to the present embodiment can be produced.
- the reason why the grain-oriented electrical steel sheet according to the present embodiment can be produced by each of the above-mentioned steps is not clear, but the present inventor generally considers the reason as follows.
- forsterite (Mg 2 SiO 4 ) is produced by the solid-phase reaction between SiO 2 in the internal oxide layer and MgO in the annealing separator. Then, forsterite is accumulated on the surface of the steel sheet to form a glass film. As a result, a glass film is formed on the surface of the steel sheet (base steel sheet).
- the nitrogen partial pressure is gradually lowered from a high partial pressure to a low partial pressure at 700 to 1200 ° C.
- MgO in the annealing separator reacts stably with SiO 2 existing at a deeper position in the internal oxide layer to generate forsterite.
- the glass film is fitted into the surface layer portion of the base steel sheet, and the fitting structure is formed. Furthermore, the Ostwald growth of the generated Ostwald develops the inset structure. Specifically, the three-dimensional network structure of the inset structure becomes complicated, and the branches constituting the inset structure become thicker.
- the Al precipitates that are abundantly distributed in this inlaid structure correspond to the second peak of the Al concentration profile.
- the Al precipitate present in this glass film corresponds to the first peak of the Al concentration profile. Therefore, the second peak derived from the Al precipitate of the inlaid structure is larger than the first peak derived from the Al precipitate of the glass film.
- the Al precipitate grows in the inset structure and develops in the surface layer portion of the base steel sheet so that the mathematical formula (1) is satisfied.
- 2 and 3 show an example in which the inset structure is developed (that is, the equation (1) is satisfied), and
- FIG. 4 shows an example in which the inset structure is not developed (that is, the equation (1) is not satisfied).
- the lower the cooling rate CR the more the fitting structure develops. That is, the lower the cooling rate CR, the higher the precipitation frequency of Al precipitates, and by extension, 50 pieces / mm or more.
- an insulating film coating step and a magnetic domain control step may be further performed.
- the type of the insulating film is not particularly limited, and any conventionally known insulating film is suitable for the grain-oriented electrical steel sheet of the present embodiment.
- the insulating film include a film formed by applying an aqueous coating solution containing a phosphate and colloidal silica.
- examples of the phosphate include phosphates such as Ca, Al, and Sr. Of these, the aluminum phosphate salt is more preferable.
- Colloidal silica is not particularly limited, and its particle size can be used as appropriate.
- a particularly preferable particle size (average particle size) is 200 nm or less. Even if the particle size is less than 100 nm, there is no problem in dispersion, but the manufacturing cost becomes high and it may not be realistic. If the particle size exceeds 200 nm, it may settle in the treatment liquid.
- the insulating film coating liquid it is preferable to apply the insulating film coating liquid to the surface of the steel sheet by a wet coating method such as a roll coater and bake it in an atmospheric atmosphere at a temperature of 800 to 900 ° C. for 10 to 60 seconds to form a tension insulating film. ..
- the specific processing method of the magnetic domain control step is not particularly limited, and lower iron loss can be obtained by performing magnetic domain control by, for example, laser irradiation, electron beam, etching, or a groove forming method using a gear.
- the iron loss is greatly improved in the grain-oriented electrical steel sheet according to the present embodiment even before the magnetic domain control. Therefore, even if the heat-resistant magnetic domain control is performed in which the iron loss improving effect cannot be sufficiently obtained, the iron loss improving effect can be sufficiently obtained.
- the conditions in the examples are one condition example adopted for confirming the feasibility and effect of the present invention, and the present invention is not limited to this one condition example.
- the present invention can adopt various conditions as long as the gist of the present invention is not deviated and the object of the present invention is achieved.
- Example 1> In Example 1, the steel slab having the composition shown in Table 1 was heated to 1150 ° C. and then subjected to hot rolling to obtain a hot-rolled plate having a plate thickness of 2.6 mm. Then, the hot-rolled plate was annealed by setting the temperature of the first stage to 1100 ° C. and the temperature of the second stage to 900 ° C. Then, the hot-rolled plate was subjected to one cold-rolling or a plurality of times of cold-rolling sandwiching intermediate annealing to prepare a cold-rolled plate having a final plate thickness of 0.23 mm.
- the cold-rolled plate having a final plate thickness of 0.23 mm was subjected to decarburization annealing and nitriding treatment (annealing to increase the amount of nitrogen in the steel plate).
- the heating rate HR1 in decarburization annealing was set to 100 ° C./s.
- the heating method was a radiant tube method.
- t0 was 550 ° C and t2 was 840 ° C. In the tropics, the temperature t2 was maintained for 100 seconds.
- the nitrogen concentration is 200 to 25.
- the range was set to 0 ppm, and analysis was performed by the method described in JIS G 1228.
- an annealing separator containing magnesia (MgO) as a main component was applied to the surface of the steel sheet, and finish annealing was performed.
- the steel sheet was heated to 1200 ° C.
- the heating temperature in the temperature range of 1000 to 1100 ° C. was set to 10 ° C./h.
- the nitrogen partial pressure P0 up to 800 ° C. (up to T2) is 80%
- the nitrogen partial pressure P1 up to 1000 ° C. (up to T3) is 50%
- P2 was set to 20%.
- the annealing atmosphere of Comparative Examples b10 and b11 was the atmosphere described later. Purification was at 1200 ° C. for 10 hours.
- the steel sheet was cooled at a cooling rate CR of 60 ° C./h in the temperature range (T5) from 1200 ° C. to 1000 ° C.
- the cooling rate CR of Comparative Examples b12 and b13 was set to a value described later.
- a grain-oriented electrical steel sheet was produced by the above steps.
- the oxygen concentration of the grain-oriented electrical steel sheet was measured, and the Al concentration profile was further measured by GDS.
- the oxygen concentration was analyzed by the method described in JIS G 1239.
- the GDS had an output of 35 W, and data was acquired at 0.01 second intervals. The results are shown in Table 2.
- the iron loss is 0.85 W / kg or less, which is good magnetism. The characteristics have been obtained.
- Comparative Examples b1, b2, b4, and b5 since a steel slab in which the mass% of a part of the component composition was out of the range of the present embodiment was used, secondary recrystallization did not occur and the iron loss was 1.0 W / W /. It exceeded kg and was significantly inferior.
- Comparative Examples b3 and b9 since the steel slab in which the mass% of a part of the component composition was less than the range of this embodiment was used, the intrinsic resistance was small and the iron loss was 0.9 W / kg or more, which was inferior.
- Comparative Examples b6 and b7 since steel slabs having a mass% of some component compositions exceeding the range of this embodiment were used, impurities remained and the iron loss was inferior to 0.9 W / kg or more.
- Comparative Example b8 since a steel slab in which the mass% of a part of the component composition was out of the range of the present embodiment was used, the steel sheet after reheating became brittle and rolling had to be stopped.
- the nitrogen partial pressure P0 up to 800 ° C. (up to T2) was 50%
- the nitrogen partial pressure P1 up to 1000 ° C. (up to T3) was 50%
- up to 1200 ° C. (up to T4) with respect to the finish annealing atmosphere.
- the nitrogen partial pressure P2 was set to 50%. That is, the partial pressure of nitrogen was kept constant. Therefore, the fitting structure of the glass film was not developed, and the iron loss was inferior to more than 0.85 W / kg.
- the cooling rate CR in the temperature range (T5) from 1200 ° C. to 1000 ° C. was set to 150 ° C./h in the cooling step after finish annealing. Therefore, the inlaid structure of the glass film, particularly Al precipitates, did not develop, and the iron loss was inferior to more than 0.85 W / kg.
- Example 2 In Example 2, the steel slab having the composition shown in Table 1 was heated to 1150 ° C. and then subjected to hot rolling to obtain a hot-rolled steel sheet having a plate thickness of 2.6 mm. Then, the hot-rolled plate was annealed by setting the temperature of the first stage to 1100 ° C. and the temperature of the second stage to 900 ° C. Then, the hot-rolled plate was subjected to one cold-rolling or a plurality of times of cold-rolling sandwiching intermediate annealing to prepare a cold-rolled plate having a final plate thickness of 0.23 mm.
- the cold-rolled steel sheet having a final thickness of 0.23 mm was subjected to decarburization annealing and nitriding treatment (annealing to increase the amount of nitrogen in the steel sheet).
- the heating rate HR in decarburization annealing was 100 ° C./s.
- the heating method was a radiant tube method.
- t0 was 580 ° C.
- t2 was 860 ° C.
- the temperature t2 was maintained for 120 seconds.
- the nitrogen concentration is 220-26.
- the range was set to 0 ppm, and analysis was performed by the method described in JIS G 1228.
- an annealing separator containing magnesia (MgO) as a main component was applied to the surface of the steel sheet, and finish annealing was performed.
- the steel sheet was heated to 1200 ° C.
- the heating temperature in the temperature range of 1000 to 1100 ° C. was set to 10 ° C./h.
- the annealing atmosphere and the cooling rate CR in the subsequent cooling step were changed for each invention example. Specifically, regarding the annealing atmosphere of Invention Examples C1 to C3 (see Table 3), the nitrogen partial pressure P0 up to 800 ° C. (up to T2) is 90%, and the nitrogen partial pressure P1 up to 1000 ° C. (up to T3) is set.
- the nitrogen partial pressure P2 up to 60% and 1200 ° C. (up to T4) was set to 30%.
- the cooling rate CR in the temperature range (T5) from 1200 ° C. to 1000 ° C. was set to 100 ° C./h.
- the nitrogen partial pressure P0 up to 800 ° C. (up to T2) was 75%
- the nitrogen partial pressure P1 up to 1000 ° C. (up to T3) was 50%
- the nitrogen partial pressure P2 up to 1200 ° C. (up to T4) was set to 30%.
- the cooling rate CR in the temperature range (T5) from 1200 ° C. to 1000 ° C. was set to 40 ° C./h.
- the oxygen concentration of the grain-oriented electrical steel sheet was measured in the same manner as in Example 1, and the Al concentration profile was further measured by GDS.
- the oxygen concentration was analyzed by the method described in JIS G 1239.
- the cross section of the grain-oriented electrical steel sheet was also observed. Specifically, in the vertical cross section parallel to the rolling direction of the surface layer portion of the base steel sheet, a region from the surface of the glass film to a depth of 10 ⁇ m, that is, an observation region was photographed with an optical microscope. The magnification at the time of photographing was 400 times, and 10 images were photographed for each sample. Then, the composition of the observation region in each image was analyzed by SEM-EDS to identify the composition in the observation region.
- the iron loss of Invention Examples C4 to C17 satisfying the precipitation frequency of Al precipitates of 50 pieces / mm or more is higher than that of Invention Examples C1 to C3 in which the precipitation frequency of Al precipitates is less than 50 pieces / mm. It was even better at 0.80 W / kg or less. Since the cooling rates in Invention Examples C4 to C17 are lower than the cooling rates in Invention Examples C1 to C3, it is presumed that such a result was obtained.
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Abstract
Description
IAl_1<IAl_2 ・・・ 式(1)
以下に添付図面を参照しながら、本発明の好適な実施の形態について詳細に説明する。まず、本発明の概要について説明する。本発明者は、さらなる鉄損の低減のために、磁区細分化を促進する技術について鋭意検討した。磁区が細分化されると、磁区幅が狭くなる。磁区幅が狭くなると鋼板が磁化された際の磁壁の移動距離が短くなるので、磁壁移動時のエネルギーロスが低減する。すなわち鉄損が低減される。
(2-1.全体構成)
本実施形態に係る方向性電磁鋼板は、母材鋼板と、母材鋼板の表面に形成されたグラス皮膜とを含む。グラス皮膜の表面にはさらに絶縁皮膜が形成されていてもよい。グラス皮膜は母材鋼板に嵌入する嵌入構造を有しており、嵌入構造が非常に発達している。すなわち、嵌入構造は複雑な3次元ネットワーク構造を有している。したがって、グラス皮膜は、母材鋼板の表層の大部分を被覆する被覆部分と、当該被覆部分から母材鋼板の表層部の内部に嵌入した嵌入構造とに区分される。さらに、嵌入構造はAlを含む析出物を多く含む。
母材鋼板は、化学成分として、質量%で、C:0.010%以下、Si:2.00~4.00%、Mn:0.05~1.00%、Al:0.010~0.065%以下、N:0.004%以下、S:0.010%以下を含有し、残部がFe及び不純物からなる。以下、成分組成に係る%は、母材鋼板の総質量に対する質量%を意味するものとする。
Cは、一次再結晶組織の制御に有効な元素であるが、磁気特性に悪影響を及ぼすので、仕上げ焼鈍前に脱炭焼鈍で除去される元素である。最終製品でC濃度が0.010%を超えると、Cが時効析出し、ヒステリシス損が劣化するので、C濃度は0.010%以下とする。C濃度は好ましくは0.007%以下、より好ましくは0.005%以下である。C濃度の下限は0%を含むが、C濃度を0.0001%未満に低減しようとすると、製造コストが大幅に上昇するので、実用鋼板上、0.0001%が実質的な下限である。なお、方向性電磁鋼板において、C濃度は、脱炭焼鈍によって通常0.001%程度以下に低減される。
Siは、鋼板の電気抵抗を高めて、鉄損特性を改善する元素である。Si濃度が2.00%未満では、仕上げ焼鈍時に鉄組織のγ変態が生じ、鋼板の結晶方位が損なわれるので、Si濃度は2.00%以上とする。Si濃度は、好ましくは2.50%以上、より好ましくは3.00%以上である。一方、Si濃度が4.00%を超えると、方向性電磁鋼板の加工性が低下し、圧延時に割れが発生するので、Si濃度は4.00%以下とする。Si濃度は好ましくは3.50%以下である。
Mnは、熱間圧延時の割れを防止するとともに、Sと結合して、インヒビターとして機能するMnSを生成する元素である。Mn濃度が0.05%未満では、Mnの添加効果が十分に発現しないので、Mn濃度は0.05%以上とする。Mn濃度は、好ましくは0.07%以上、より好ましくは0.09%以上である。一方、Mn濃度が1.00%を超えると、MnSの析出分散が不均一になり、所要の二次再結晶組織が得られず、磁束密度が低下するので、Mn濃度は1.00%以下とする。Mn濃度は好ましくは0.80%以下、より好ましくは0.60%以下である。
Alは、Nと結合して、インヒビターとして機能する(Al、Si)NまたはAlNを生成する元素である。Al濃度が0.010%未満では、Alの添加効果が十分に発現せず、二次再結晶が十分に進行しないので、Al濃度は0.010%以上とする。Al濃度は好ましくは0.015%以上、より好ましくは0.020%以上である。一方、Al濃度が0.065%を超えると、インヒビターの析出分散が不均一になり、所要の二次再結晶組織が得られず、磁束密度が低下するので、Al濃度は0.065%以下とする。Al濃度は好ましくは0.050%以下、より好ましくは0.040%以下である。なお、詳細は後述するが、母材鋼板中のAlは嵌入構造が発達したグラス皮膜と反応し、Al析出物を形成するという機能も有する。
Nは、Alと結合して、インヒビターとして機能するAlNを形成する元素である。ただし、最終製品でN濃度が0.004%を超えると鋼板中のNがAlNとして析出し、ヒステリシス損を劣化させるので、N濃度は0.004%以下とする。N濃度の下限は0%を含むが、N濃度を0.0001%未満に低減しようとすると、製造コストが大幅に上昇するので、実用鋼板上、0.001%が実質的な下限である。なお、方向性電磁鋼板において、N濃度は、仕上げ焼鈍によって通常0.001%程度以下に低減される。
Sは、Mnと結合して、インヒビターとして機能するMnSを生成する元素である。ただし、最終製品においてS濃度が0.010%を超えると鋼板中のSがMnSとして析出し、ヒステリシス損を劣化させるので、S濃度は0.010%以下とする。S濃度の下限は0%を含むが、S濃度を0.0001%未満に低減しようとすると、製造コストが大幅に上昇するので、実用鋼板上、0.0001%が実質的な下限である。なお、方向性電磁鋼板において、S濃度は、仕上げ焼鈍によって通常、0.005%程度以下に低減される。
Crは、脱炭焼鈍の酸化層を改善し、グラス皮膜形成に有効な元素である。このため、Crを0.30%以下の範囲で母材鋼板に添加してもよい。Cr濃度が0.30%を超えると、脱炭性を著しく阻害するので、Cr濃度の上限は0.30%であることが好ましい。
Cuは母材鋼板の比抵抗を高めて鉄損を低減させることに有効な元素である。C濃度が0.40%を超えると鉄損低減効果が飽和するとともに、熱延時に「カッパーヘゲ」なる表面疵の原因になるため、C濃度の上限は0.40%であることが好ましい。
Pは母材鋼板の比抵抗を高めて鉄損を低減させることに有効な元素である。P濃度が0.50%を超えると圧延性に問題を生じるため、P濃度の上限は0.50%であることが好ましい。
Niは母材鋼板の比抵抗を高めて鉄損を低減させることに有効な元素である。また、Niは熱延板の鉄組織を制御して磁気特性を向上させるうえで有効な元素でもある。しかしながら、Ni濃度が1.00%を超えると二次再結晶が不安定になるため、Ni濃度の上限は1.00%であることが好ましい。
SnとSbは、良く知られている粒界偏析元素である。本実施形態に係る母材鋼板はAlを含有しているため、仕上げ焼鈍の条件によっては焼鈍分離剤から放出される水分によりAlが酸化されてコイル位置でインヒビター強度が変動する場合がある。この結果、磁気特性がコイル位置で変動する場合がある。この対策の一つとして、これらの粒界偏析元素の添加によりAlの酸化を防止する方法があり、そのためにSn及びSbをそれぞれ0.30%以下の濃度で母材鋼板に添加してもよい。一方、これらの元素の濃度が0.30%を超えると脱炭焼鈍時にSiが酸化されにくく、グラス皮膜の形成が不十分となるとともに、脱炭焼鈍性を著しく阻害する。このため、これらの元素の濃度の上限は0.30%であることが好ましい。
Bは母材鋼板中のNと結合し、MnSと複合析出して、インヒビターとして機能するBNを形成する元素である。B濃度の下限は特に制限されず、上述したように0%でもよい。ただし、Bの添加効果を十分に発揮するためには、B濃度の下限は0.0005%であることが好ましい。B濃度は好ましくは0.001%以上、より好ましくは0.0015%以上である。一方、B濃度が0.0100%を超えると、BNの析出分散が不均一になり、所要の二次再結晶組織が得られず、磁束密度が低下する。このため、B濃度は0.0100%以下であることが好ましい。B濃度は好ましくは0.0080%以下、より好ましくは0.0060%以下、より好ましくは0.0040%以下である。
Moは熱延時の表面性状を改善することに有効な元素である。ただし、Mo濃度が0.1%を超えるとMo添加効果が飽和してしまうため、Mo濃度の上限は0.1%であることが好ましい。
Biは硫化物などの析出物を安定化してインヒビターとしての機能を強化する効果がある。しかしながら、Bi濃度が0.01%を超えるとBiがグラス皮膜形成に悪影響を及ぼすため、Bi濃度の上限は0.01%であることが好ましい。
グラス皮膜及び母材鋼板中の合計の酸素濃度は2500ppm以下とされる。酸素の殆どはグラス皮膜に含まれ、鋼板中に含まれる酸素は10~100ppm程度である。なお、方向性電磁鋼板が後述する絶縁皮膜を含む場合、酸素濃度は、方向性電磁鋼板から絶縁皮膜を除去した後に測定される。つまり、絶縁皮膜は酸素濃度の測定対象には含まれない。絶縁皮膜は、例えば水酸化ナトリウム水溶液等を用いて除去される。
本実施形態に係る方向性電磁鋼板をグロー放電発光分析(GDS)した場合、板厚方向にAlの発光強度分布(Al濃度プロファイル)が観測される。なお、方向性電磁鋼板が後述する絶縁皮膜を含む場合、Al濃度プロファイルは、方向性電磁鋼板から絶縁皮膜を除去した後に測定される。つまり、絶縁皮膜はAl濃度プロファイルの測定対象には含まれない。GDSによる測定は、グラス皮膜の表面から行われる。
IAl_1<IAl_2 ・・・ 式(1)
つまり、第2ピーク強度は第1ピーク強度よりも大きくなる。ここで、各ピーク強度は、各ピークにおけるAl発光強度の最高強度(言い換えれば最高ピーク高さ)として定義される。
また、数式(1)を変形して、第1ピーク強度と第2ピーク強度の比が1未満であってもよい。すなわち、数式(1)’の関係を満たす。
IAl_1/IAl_2 <1・・・ 式(1)’
第1ピーク強度は0であってもよく、ピーク比の下限は0であってもよい。また、ピーク比の下限は、0.1以上または0.1超、0.2以上または0.2超、0.3以上または0.3超、0.4以上または0.4超、0.5以上または0.5超、0.6以上または0.6超、0.7以上または0.7超、0.8以上または0.8超、0.9以上または0.9超、であってもよい。
一方、概して第2ピーク強度が強いほど、ピーク比は1に近づき好ましい。従って、ピーク比の上限は、0.9以下または0.9未満、0.8以下または0.8未満、0.7以下または0.7未満、0.6以下または0.6未満、0.5以下または0.5未満、0.4以下または0.4未満であってもよい。
上述したように、第2ピーク強度は第1ピーク強度よりも大きくなる。これは、母材鋼板の表層部にグラス皮膜の嵌入構造が形成されており、後述で詳細に説明するとおりAl析出物が嵌入構造に多く分布するからである。そこで、図2及び図3を参照して、グラス皮膜の嵌入構造について説明する。上述したように、図2及び図3は本実施形態に係る方向性電磁鋼板の表面状態の一例を示す。これらの例では、方向性電磁鋼板は、母材鋼板cと、母材鋼板cの表面に形成されたグラス皮膜aとを含む。グラス皮膜aは母材鋼板cに嵌入する嵌入構造を有しており、嵌入構造が非常に発達している。嵌入構造はAl析出物bを含む。
グラス皮膜の嵌入構造は母材鋼板の表層部に嵌入した部分であり、その嵌入構造に含まれるAl析出物は、母材鋼板の表層部のうち、グラス皮膜の表面から深さ10μmまでの部分に多く存在する。このため、Al析出物は以下の方法で観察可能である。すなわち、母材鋼板の表層部の圧延方向に平行な垂直断面のうち、少なくともグラス皮膜の表面から深さ10μmまでの領域(以下、「観察領域」とも称する)を光学顕微鏡やFE-SEM(電界放出型走査電子顕微鏡)等で観察する。ついで、観察領域の組成をEDS(エネルギー分散型X線分光法)やEPMA(電子線マイクロアナライザ)等で分析する。これにより、観察領域内のAl析出物を同定することができる。例えば、後述するAl析出物のサイズ、析出頻度を測定することができる。なお、析出頻度に関しては、例えば観察領域の写真を複数枚撮影し、各写真で測定された析出頻度を算術平均してもよい。
上記観察領域内には、円相当径で1μm以上のAl析出物が圧延方向に平均で50個/mm以上の頻度で点在することが好ましい。この場合、磁区細分化効果をより高めることができる。
次に、本実施形態に係る方向性電磁鋼板の製造方法の一例を説明する。なお、本実施形態に係る方向性電磁鋼板の製造方法は以下に説明する製造方法に限定されず、本実施形態に係る方向性電磁鋼板を製造できる製造方法であればどのような製造方法であってもよい。
本実施形態に係る方向性電磁鋼板の製造方法は、鋼スラブ準備工程、再加熱工程、熱間圧延工程、熱延板焼鈍工程、冷間圧延工程、脱炭焼鈍工程、窒化処理工程、焼鈍分離剤塗布工程、仕上げ焼鈍工程、純化焼鈍工程、及び冷却工程を含む。以下、各工程について詳細に説明する。
この工程では、鋼スラブを準備する。具体的には、例えば転炉または電気炉等により鋼を溶製する。これにより得られた溶鋼を必要に応じて真空脱ガス処理した後、連続鋳造もしくは造塊後分塊圧延する。これにより鋼スラブが得られる。鋼スラブの厚さは特に制限されないが、通常は150~350mmの範囲、好ましくは220~280mmの厚みで鋳造される。ただし、鋼スラブは30~70mmの厚さ範囲のいわゆる薄スラブであっても良い。薄スラブを使用する場合、熱延板を製造する際に中間厚みに粗加工を行う必要がないという利点がある。
Nは、Alと結合して、インヒビターとしての機能するAlNを形成する元素である。ただし、Nは冷間圧延時に鋼板中にブリスター(空孔)を形成する元素でもある。Nの質量%が0.004%未満では、AlNの形成が不十分となるので、N濃度は0.004%以上とする。好ましくは0.006%以上、より好ましくは0.007%以上である。N濃度が0.012%を超えると、冷間圧延時に鋼板中に多くのブリスターを形成する可能性があるので、N濃度は0.012%以下とする。
この工程では、鋼スラブを再加熱する。鋼スラブの再加熱温度は1280℃以下が好ましい。再加熱温度が1280℃を超える場合、溶融スケール量が多くなる。さらに、MnSが鋼スラブに完全固溶し、その後の工程で微細に析出するため、所望の一次再結晶粒径を得るための脱炭焼鈍温度を900℃超とする必要がある。このため、本実施形態では、鋼スラブを1280℃以下で再加熱することが好ましい。再加熱温度の下限値は特に制限されないが、例えば1100℃であってもよい。
熱間圧延(熱延)工程では、再加熱後の鋼スラブを熱延する。熱延板焼鈍工程では、上記熱間圧延工程により得られた熱延板を1000~1150℃の1段目温度まで加熱することで、鉄組織を再結晶させる。ついで、熱延板を850~1100℃かつ1段目温度より低い2段目温度で焼鈍する。この熱延板焼鈍工程は主に熱延時に生じた不均一組織の均一化を目的として行われる。
熱延板焼鈍工程を行った後、熱延板に1回の冷間圧延または中間焼鈍を挟む2回以上の冷間圧延(冷延)を施す。これにより、最終冷延板を作製する。各冷間圧延は、常温で行ってもよいし、常温より高い温度たとえば200℃程度に鋼板温度を上げて圧延する温間圧延としてもよい。
脱炭焼鈍工程では、まず、冷延工程後の鋼板(冷延板)を入側温度t0℃から入側温度よりも高い均熱温度t2まで加熱する加熱工程と、冷延板の温度を均熱温度t2℃に所定時間維持する均熱工程とを含む。脱炭焼鈍工程は湿潤雰囲気で行われる。ここで、入側温度t0℃は冷延板が焼鈍炉に導入される際の温度であり、概ね600℃以下である。均熱温度は700~900℃の範囲内の温度とされる。
一実施形態では、脱炭焼鈍工程は、冷延板を600℃以下の入側温度t0℃から入側温度t0℃よりも高い均熱温度t2℃まで加熱する加熱工程と、冷延板の温度を均熱温度t2℃で維持する均熱工程と、を含み、脱炭焼鈍工程の加熱工程では、冷延板の温度が入側温度t0℃から700~900℃の範囲内でかつ均熱温度t2℃よりも低い到達温度t1℃に到達するまでの加熱速度hr1を40℃/秒以上とし、冷延板の温度が到達温度t1℃から均熱温度t2℃に到達するまでの加熱速度hr2を15℃/秒超~30℃/秒としてもよい。
本実施形態では、冷延板の温度が入側温度t0℃から均熱t1℃に到達するまでの加熱速度hr1を40℃/秒以上とする。これにより、{111}方位粒を減らし、{411}方位粒およびゴス方位粒を増やすことができる。加熱速度hr1は、好ましくは75℃/秒以上、さらに好ましくは75~125℃/秒である。
また、hr2の上限は、25℃以下または25℃未満としてもよい。hr2の範囲は、後段で詳述するとおり、種々の加熱装置で加熱することができるが、hr2が大きくなり均熱温度t2をオーバーシュートすると、その後の二次再結晶不良につながることがある。そのため、hr2の上限は、25℃以下または25℃未満とすることにより、均熱温度t2をオーバーシュートすることを防ぐことができ、好ましい。
脱炭焼鈍の加熱過程における加熱は誘導加熱で行ってもよい。この場合、加熱速度の自由度が高く、鋼板と非接触に加熱でき、さらに、脱炭焼鈍炉内への設置が比較的容易であるなどの効果が得られる。
脱炭焼鈍後、鋼板の窒素濃度が40ppm以上1000ppm以下となるように、鋼板に窒化処理を施す。窒化処理後の鋼板の窒素濃度が40ppm未満では鋼板内にAlNが十分に析出せず、AlNがインヒビターとして機能しない。このため、鋼板の窒素濃度は40ppm以上とする。一方、鋼板の窒素濃度が1000ppm超となった場合、仕上げ焼鈍において二次再結晶完了後も鋼板内に過剰にAlNが存在する。このようなAlNは鉄損劣化の原因となる。このため、鋼板の窒素濃度は1000ppm以下とする。
窒化処理工程後、鋼板の表面に焼鈍分離剤を塗布する。後述する仕上げ焼鈍は鋼板をコイル状に巻き取った状態で行われる場合がある。このような状態で仕上げ焼鈍を行った場合、コイルが焼き付いてコイルを巻きほどくことが困難になることがある。そこで、本実施形態では、仕上げ焼鈍後にコイルを巻きほどくことができるように、焼鈍分離剤を塗布する。ここで、焼鈍分離剤の主成分はMgOであり、焼鈍分離剤中のMgOが仕上げ焼鈍時に内部酸化層中のSiO2と固相反応し、フォルステライト(Mg2SiO4)が生成、グラス皮膜を形成する。
仕上げ焼鈍工程は、二次再結晶焼鈍工程とも称される焼鈍であり、鉄組織の二次再結晶を促す処理である。仕上げ焼鈍工程では、鋼板を後述する1200℃程度まで加熱する。ここで、加熱過程において、少なくとも1000℃~1100℃の温度範囲では、加熱速度HR2を15℃/h以下とすることが好ましい。また、加熱速度の制御に代えて、1000℃~1100℃の温度範囲内に10時間以上保持することも有効である。つまり、この温度域での加熱速度を極めて遅くする。これにより、ゴス方位の優先成長(二次再結晶)を促すことができる。加熱速度HR2が速すぎる(15℃/hを超える)場合、ゴス方位以外の結晶方位の結晶粒が成長してしまう。他の温度域における加熱速度は特に制限されず、従来の仕上げ焼鈍と同程度であればよい。
仕上げ焼鈍工程に続く純化焼鈍工程では、二次再結晶完了後に純化を行うことで、インヒビターとして利用した析出物(AlN、MnS等)の無害化を行う。これにより最終磁気特性におけるヒステリシス損を低減することが可能となる。純化焼鈍工程では、例えば、水素雰囲気下、1200℃で10時間以上鋼板の保定を行うことが好ましい。
純化焼鈍工程後、鋼板を冷却する。ここで、1200~1000℃の温度範囲(T5)の冷却速度(降温速度)CRを30~100℃/hとすることが好ましい。冷却速度CRは、より好ましくは30~50℃/hである。詳細は後述するが、冷却速度CRを低くすることで、嵌入構造をより発達させることができる。
冷却工程後の鋼板表面に、さらに絶縁皮膜コーティングを塗布し、焼き付ける。絶縁皮膜の種類については、特に限定されることはなく、従来公知のあらゆる絶縁皮膜が本実施形態の方向性電磁鋼板に適合する。絶縁皮膜の例としては、リン酸塩とコロイダルシリカを含む水系塗布溶液を塗布して形成される皮膜が挙げられる。この場合、リン酸塩としては、例えば、Ca、Al、Sr等のリン酸塩が挙げられる。中でも、リン酸アルミニウム塩がより好ましい。コロイダルシリカは特に限定はなく、その粒子サイズも適宜使用することができる。特に好ましい粒子サイズ(平均粒径)は、200nm以下である。粒子サイズが100nm未満でも分散に問題はないが製造コストが高くなって現実的でない場合がある。粒子サイズが、200nmを超えると処理液中で沈降する場合がある。
磁区制御工程の具体的な処理方法は特に制限されず、例えばレーザー照射、電子ビーム、エッチング、歯車による溝形成法にて、磁区制御を施すことで、より低鉄損が得られる。なお、上述したように、磁区制御前であっても、本実施形態に係る方向性電磁鋼板では、鉄損が大きく改善している。したがって、仮に鉄損改善効果が十分に得られない耐熱性の磁区制御を行う場合であっても、十分に鉄損改善効果を得ることができる。
実施例1では、表1に示す成分組成の鋼スラブを1150℃に加熱した後に熱間圧延に供し、板厚2.6mmの熱延板とした。ついで、該熱延板に1段目温度を1100℃、2段目温度を900℃として熱延板焼鈍を施した。ついで、熱延板に一回の冷間圧延又は中間焼鈍を挟む複数回の冷間圧延を施し、最終板厚0.23mmの冷延板を作製した。
0ppmの範囲とし、JIS G 1228に記載の手法にて分析した。
実施例2では、表1に示す成分組成の鋼スラブを1150℃に加熱した後に熱間圧延に供し、板厚2.6mmの熱延鋼板とした。ついで、該熱延板に1段目温度を1100℃、2段目温度を900℃として熱延板焼鈍を施した。ついで、熱延板に一回の冷間圧延又は中間焼鈍を挟む複数回の冷間圧延を施し、最終板厚0.23mmの冷延板を作製した。
0ppmの範囲とし、JIS G 1228に記載の手法にて分析した。
2:Alの第2ピーク
a:グラス皮膜(Mg2SiO4)
b:Al析出物
c:母材鋼板
Claims (2)
- 母材鋼板と、
前記母材鋼板の表面に形成されたグラス皮膜と、を含む方向性電磁鋼板であって、
前記母材鋼板は、化学成分として、質量%で、C:0.010%以下、Si:2.00~4.00%、Mn:0.05~1.00%、Al:0.010~0.065%以下、N:0.004%以下、S:0.010%以下を含有し、残部がFe及び不純物からなり、
前記グラス皮膜及び前記母材鋼板に含まれる酸素濃度が2500ppm以下であり、
前記グラス皮膜の表面から前記方向性電磁鋼板をグロー放電発光分析(GDS)することで得られるAlの濃度プロファイルが少なくとも2つのピークを有し、
各々のAlのピークを前記グラス皮膜の表面に近い側から順に第1ピーク、第2ピークとし、Alの第1ピークの強度をIAl_1、Alの第2ピーク強度をIAl_2としたとき、数式(1)の関係を満たすことを特徴とする方向性電磁鋼板。
IAl_1<IAl_2 ・・・ 式(1) - 前記母材鋼板の表層部の圧延方向に平行な垂直断面のうち、前記グラス皮膜の表面から板厚中心部方向への深さ10μmまでの範囲内の領域には、円相当径で1μm以上のAlを含有する析出物が圧延方向に平均で50個/mm以上の頻度で点在することを特徴とする、請求項1記載の方向性電磁鋼板。
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