EP0753588A1 - Herstellungsverfahren eines kornorientiertes Elektrostahlbleches mit einer Spiegeloberfläche und mit geringen Eisenverlusten - Google Patents

Herstellungsverfahren eines kornorientiertes Elektrostahlbleches mit einer Spiegeloberfläche und mit geringen Eisenverlusten Download PDF

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EP0753588A1
EP0753588A1 EP95111069A EP95111069A EP0753588A1 EP 0753588 A1 EP0753588 A1 EP 0753588A1 EP 95111069 A EP95111069 A EP 95111069A EP 95111069 A EP95111069 A EP 95111069A EP 0753588 A1 EP0753588 A1 EP 0753588A1
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Prior art keywords
annealing
steel sheet
final
grain
oriented electrical
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French (fr)
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EP0753588B1 (de
EP0753588B2 (de
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Shuichi c/o Nippon Steel Corporation Yamazaki
Yoshiyuki C/O Nippon Steel Corporation Ushigami
Hiroyasu c/o Nippon Steel Corporation Fujii
Kenichi c/o Nippon Steel Corporation Murakami
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Nippon Steel Corp
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Priority to EP95111069A priority Critical patent/EP0753588B2/de
Priority to DE1995613811 priority patent/DE69513811T3/de
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
    • C21D8/1277—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties involving a particular surface treatment
    • C21D8/1283—Application of a separating or insulating coating

Definitions

  • the present invention relates to a method for the production of a grain-oriented electrical steel sheet used as an iron core of a transformer or other electric appliances. More particularly, the present invention relates to a method for the production of a grain-oriented electrical steel sheet in which core loss is reduced by imparting it with a mirror surface and keeping it free of precipitates at the surface region.
  • Grain-oriented electrical steel sheet material for use in various types of electric equipment mainly transformers, contains 0.8 - 4.8% Si and has a crystal texture preferentially aligned in the ⁇ 110 ⁇ 001 ⁇ orientation.
  • the required characteristics of a grain-oriented electrical steel sheet are a high magnetic flux density and a low core loss, which are represented by B 8 and W 17/50 , respectively.
  • Core loss can be subdivided into eddy current loss and hysterisis loss.
  • the former decreases in proportion to reductions in the width of the magnetic domains of the steel sheet, and the later can be reduced by eliminating hindrances to the movement of magnetic domain walls.
  • Primary causes of this hindrance are uneven or rough surfaces of the steel sheet and the presence of precipitates near the steel surface.
  • An inner oxide layer mainly composed of SiO 2 and a glass film mainly composed of forsterite (Mg 2 SiO 4 ) are present on the surface of a grain-oriented electrical steel sheet produced by the current production process.
  • the inner oxide layer is formed on the steel surface by decarburization annealing.
  • the glass film is formed on the above inner oxide layer during the final annealing, which reacts SiO 2 with MgO, to avoid having windings of the coil stick to each other.
  • this glass film is formed based on the above inner oxide layer, the interface between the glass film and the steel sheet is not smooth because of the presence of precipitates. As a result, these precipitates become a hindrance to movement of the magnetic domains.
  • This phenomenon is well known from the various reports, for example, by S. D. Washko, T. H. Shen and W. G. Morris, Journal of Applied Physics., vol. 53, pp 8296 - 8298. Since then, there have been proposed various methods for dealing with this phenomenon. For example, one of the methods is to prevent glass film formation during the final annealing, and another is to obtain an even and smooth steel surface by chemical or mechanical polishing after removal of the glass film.
  • a primary object of the present invention is to provide a grain-oriented electrical steel sheet having a mirror surface and reduced core loss, free of precipitates directly below the surface.
  • a further object of the present invention is to provide a simplified process that lowers production cost by elimination of the acid pickling step.
  • the present inventors conducted numerous experiments aimed at overcoming the defects of the conventional techniques and attaining the foregoing object, to develop a more effective production process for obtaining a miller steel surface free of precipitates directly below the surface of the grain-oriented electrical steel sheet products.
  • the present inventors found that if the amount of impurities contained in the oxide used as an annealing separator, especially the concentration of alkali metals, is controlled in accordance with the amount of oxygen which is contained in the steel sheet during the decarburization annealing, the formation of precipitates, which increases core loss, can be prevented from the start and furthermore, formation of a mirror surface can be promoted in the final annealing step.
  • a grain-oriented electrical steel sheet having a mirror surface with low core loss by means of using an annealing separator mainly composed of non-hydrating oxides and controlling the concentration of alkali metal impurities in the annealing separator and the oxygen amount in the steel sheet just prior to the final annealing, for achieving a decreased core loss.
  • a mirror surface is obtained by satisfying the relationship: [A] > 0.2 ⁇ [O],
  • the present invention provides a non-hydrating oxide contained in an annealing separator mainly composed of alumina for obtaining a mirror steel surface and reduced core loss.
  • the above mentioned alkali metal impurities consist of at least one of Li, Na and K.
  • the annealing separator further contains at least one of hydroxide, nitrate, sulfate, chloride or acetate of Li, Na or K.
  • a mirror steel surface free of precipitates directly below the surface can be easily obtained by a simplified process for decreasing core loss, especially hysterisis loss.
  • Figure 1 shows the results of X-ray diffraction (CuK ⁇ ) microscopy of a grain-oriented electrical steel sheet, coated with alumina as an annealing separator, and then given a final annealing.
  • CuK ⁇ X-ray diffraction
  • (a) shows an example of the results of X-ray diffraction analysis (CuK ⁇ ) in the case of using high purity alumina.
  • (b) shows an example of the results of X-ray diffraction analysis (CuK ⁇ ) of in the case of using alumina containing 0.2 weight % of Na as impurity.
  • Figure 2 is a diagram illustrating the relationship between the amount of Na in alumina as an annealing separator and the oxygen content of the steel sheet during the decarburization annealing, and the formation of precipitates directly below the steel surface. "o” indicates absence of precipitates and “ ⁇ ” indicates presence of precipitates.
  • Figure 3 is a micrograph showing a cross sectional view of a grain-oriented electrical steel sheet which was coated by alumina as an annealing separator, and then final annealed.
  • (a) shows an example of the case of using high purity alumina.
  • (b) shows an example of the case of using alumina containing 0.2 weight % of Na as impurity.
  • the present inventors used various kinds of alumina, the oxide which is commonly used as an annealing separator, and found that Na as an impurity contained in alumina influenced the formation of precipitates and the mirror condition of the steel surface. This is because when a large amount of Na is present, the mirror surface can be obtained even if an oxide film exists. In addition, no precipitates are observed directly below the steel surface when the steel surface exhibits the mirror condition. The present inventors have not ascertained the reason for this. It is thought that reduction of SiO 2 formed during the decarburization annealing may be accelerated in the final annealing step because of the existence of Na. If the reduction of SiO 2 easily occurs in the final annealing step, the precipitates directly below the steel surface, once formed, decrease and disappear. Otherwise they are not formed from the start. As a result, a mirror steel surface can be easily obtained.
  • carbon is an essential element for obtaining the required crystal texture in the intermediate product so as to preferentially promote ⁇ 110 ⁇ 001 ⁇ crystal orientation in the final product. Though this carbon must be included in the required amount in the early production stage, the carbon remaining in the final product increases the core loss. Accordingly, a primary recrystallization annealing is carried out in a wet hydrogen/nitrogen mixed atmosphere for decaburization. This primary recrystallization annealing is ordinarily called decaburization annealing. The concentration of the remaining carbon in the final product must be limited to less than 30 ppm.
  • the speed of the decarburizing reaction depends upon the reaction potential of the oxygen in the decarburization atmosphere.
  • the reaction potential of the oxygen becomes low, the decarburizing reaction slows down.
  • the reaction oxygen potential can be increased to form an inner oxide layer, mainly composed of SiO 2 , on the surface of the electrical steel sheet.
  • decarburized annealed steel sheets treated under normal conditions have inevitably included an inner oxide layer mainly composed of SiO 2 .
  • an inner oxide layer mainly composed of SiO 2 .
  • a coat of coarse and high purity alumina is applied to the decarburized steel sheet having the inner oxide layer, and given a final annealing, a grain-oriented electrical steel sheet having no oxide film on the surface can be obtained.
  • the thus obtained steel sheet not only exhibits a mirror steel surface but also has precipitates present directly below the steel surface. These precipitates are clearly observed in the microscopic sectional view of the steel surface as shown in Fig. 3(a).
  • the origin of the SiO 2 contained among these precipitates is thought to be the inner oxide layer containing SiO 2 formed during the decarburization annealing.
  • the origin of the Al 2 O 3 contained among the precipitates is assumed to be the sol Al contained in the steel sheet for controlling the secondary recrystallization, and to be the alumina used as an annealing separator. This is because the precipitates are not exposed on the steel surface.
  • the SiO 2 inner oxide layer formed during the decarburization annealing remains directly below the steel surface, so that this SiO 2 is not reduced by the reducing atmosphere during the final annealing.
  • sol Al when sol Al is contained in the steel sheet, this sol Al reacts with the SiO 2 and forms mullite directly below the steel surface. Since these precipitates are present inside the steel sheet, they are not reduced under the condition of the reducing atmosphere at a high temperature in the latter half of the final annealing. If these precipitates are not present at the steel surface, atomic diffusion is vigorously promoted so that the formation of a mirror finish is accelerated. On the other hand, if these precipitates are present directly below the steel surface, the promotion of atomic diffusion is prevented so that the formation of a mirror finish is also prevented during the final annealing.
  • the present invention can be basically applied to the production of all kinds of grain-oriented electrical steel sheet on the premise of the above mentioned conditions (1) - (3).
  • the present inventors used various kinds of alumina, the oxide which is commonly used as an annealing separator, containing different amounts of impurities such as Na, K or Li and/or their compounds, and found that when Na is contained in alumina as an impurity, it influences the formation of precipitates and the condition of the mirror brightness, even if an oxide film is present. In addition, this phenomenon depends upon the amount of Na. Accordingly, when alumina containing a large amount of Na was used as an annealing separator, no precipitates were found directly below the steel surface, and a mirror surface was obtained. This phenomenon is clearly observed in the microscopic views of Fig. 3(a) and Fig. 1(b). The present inventors have not yet clarified the reason for this.
  • Carbon is an element required for ⁇ phase formation, and is necessary for controlling the primary recrystallization texture prior to the final annealing for ensuring an appropriate secondary recrystallization. Therefore, carbon must be contained in the cold rolled steel sheet in the range of 0.02 - 0.1%. If the carbon content is more than 0.1%, the primary recrystallized texture deteriorates and a long period of time is required for decarburization.
  • Silicon is an important element for increasing electric resistance and decreasing core loss. If the silicon content is less than 0.8%, ⁇ to ⁇ transformation occurs during final annealing and the crystal structure and the orientation are impaired, while if the silicon content is more than 4.8%, cold rolling becomes difficult because of cracking.
  • the preferred silicon content is from 0.8% to 4.8%.
  • Manganese and sulfur form an inhibitor which suppresses primary grain growth.
  • the manganese and sulfur contents must each be limited to the range of 0.005 - 0.04%.
  • Acid soluble aluminum is a basic element which combines with nitrogen to form AlN or (Al, Si)N as an inhibitor for obtaining a high magnetic flux density.
  • the preferred acid soluble alumina content is from 0.012 to 0.05%.
  • Nitrogen is also a basic element which combines with the acid soluble aluminum to form an inhibitor. If the nitrogen content is more than 0.01%, blisters are undesirably formed in the final product. The preferred nitrogen content is not more than 0.01%.
  • inhibitors such as B, Bi, Pb, S, Se, Sn or Ti, in addition to the acid soluble aluminum.
  • a hot rolled steel strip adjusted to the composition range mentioned above by a known process is cold rolled directly or with hot rolled band annealing in a short period of time.
  • This hot rolled band annealing is effective for improving the magnetic properties of the final product, and is carried out at a temperature between 750°C and 1200°C for 30 seconds to 30 minutes.
  • the annealing conditions are determined based on the desired product quality or cost.
  • the cold rolling is carried out at a reduction rate of more than 80% to the final thickness by a known cold rolling process as described in Japanese Patent Publication (Kokoku) No. Sho 40-15644.
  • the condition of the cold rolling is of course variable depending upon the inhibitors used.
  • the decarburization annealing is carried out on the cold rolled steel strip in a wet atmosphere at a temperature between 750°C and 900°C for primary recrystallization and the removal of carbon from the cold rolled steel strip.
  • the nitriding treatment is carried out following the decarburization annealing in the case of using (Al, Si)N as the main inhibitor.
  • the nitriding treatment is carried out in an atmospheric gas containing NH 3 having nitriding capability.
  • the nitriding amount is more than 0.005% to the total amount of nitrogen contained in the steel sheet, preferably more than the aluminum equivalent of the steel sheet.
  • an annealing separator is coated on the decarburized or nitrided steel strip to form a glass film during the final annealing and prevent sticking.
  • the annealing separator can be used in the present invention is an oxide which is hard to hydrate. If an oxide which is easy to hydrate, like MgO, is used, peroxidation occurs at the steel surface during the final annealing or an oxide layer forms on the steel surface by reaction with the oxide film formed by decarburizing, so that a mirror surface cannot be obtained.
  • the annealing separator is a stable oxide having a non-hydrating characteristic, it is not limited to a specific oxide.
  • An oxide like ZrO 2 or Y 2 O 3 can be used.
  • Alumina is a suitable oxide for the present invention because of its non-hydrating characteristic and low cost. It is advisable to use inexpensive alumina because it contains a large amount of sodium.
  • This annealing separator is applied as a slurry in the conventional way or by electrostatic coating. When the annealing separator is suspended in water, it is desirable to add an anti-corrosion agent to the suspension, to prevent rusting of the steel surface during the coating. In the case of using relatively coarse oxide particles suspended in water, a caking agent such as methylcellulose is added to improve the coating ability and adhesibility.
  • the specific requirement for obtaining a mirror surface according to the present invention is that the condition defined as follows must be satisfied during the decarburization annealing and the coating with the annealing separator.
  • the condition is the relationship; [A] > 0.2 ⁇ [O] , where [O] is the amount of oxygen (g/m 2 ) contained in the steel sheet just prior to the final annealing and [A] is the total concentration of alkali metal impurities (weight %) in the annealing separator.
  • the oxygen content in the steel sheet can be reduced by a light acid pickling treatment after the decarburization annealing.
  • this method is not recommendable from the point of view of production cost because it requires an additional step.
  • the non-hydrating oxide containing the alkali metal impurity as the annealing separator can be used in accordance with the amount of generated oxygen contained in the steel sheet when the decarburization is almost completed, and selecting an appropriate atmosphere and annealing period which prevent the oxidation of the steel sheet.
  • the following means can be used for securing the necessary concentration of the alkali metal impurity of the non-hydrating oxide as the annealing separator.
  • the commercial low priced alumina generally used naturally contains Na as an impurity, approximately in an amount of 0.2%, due to its production process. Therefore, this inexpensive commercial alumina is very useful as the annealing separator for achieving the object of the present invention.
  • an alkali metal chloride (or salt) is added to the oxide powder or an alkali metal chloride (or salt) is dissolved in the necessary amount in the slurry for making the annealing separator.
  • a water soluble salt selected from the group consisting of hydroxide, nitrate, sulfate, chloride or acetate of Na, K, or Li etc.
  • the final annealing is carried out for secondary recrystallization and purification after the annealing separator is coated.
  • a specific heating cycle which maintains a constant temperature for promoting the secondary recrystallization during the heating step is effective for increasing the magnetic flux density as described in Japanese Unexamined Patent Publication (Kokai) No. 2-258929.
  • the heated steel strip is kept at a temperature higher than 1100°C in a 100% hydrogen atmosphere for the purification of nitride and a mirror conditioning the steel surface.
  • An insulation coating is applied to the steel strip for imparting a tensioning effect and reducing core loss.
  • magnetic domain refining treatment by the laser irradiation may be applied for further reducing core loss.
  • the present invention will now be described in detail with reference to the following examples, that by no means limit the scope of the invention.
  • the present invention will be applicable to other steel compositions or other production process as already described as far as satisfying the following conditions independently or altogether; (1) the steel contains Si, (2) decarburization annealing is necessary, and (3) a mirror surface is formed without glass film containing forsterite during the final annealing in the production of a grain-oriented electrical steel sheet.
  • the nitriding treatment was carried out in an NH 3 atmosphere gas bringing the nitrogen content in the steel sheet to 0.025% for strengthening inhibitors.
  • an annealing separator was coated onto the nitrided steel sheet.
  • Conventional MgO was applied to several steel sheets, and alumina containing different kinds of alkali metal as impurities and different concentrations in the slurry state were applied to the remaining steel sheets.
  • final annealing was carried out by heating the steel sheets to 1200°C at a constant heating rate of 10 °C/hr in an atmosphere of 100% nitrogen gas, and by maintaining them at a temperature of 1200°C for 20 hours in an atmosphere of 100% hydrogen gas.
  • the atmosphere gas was switched from nitrogen to hydrogen at 1200°C.
  • insulation coating and the magnetic domain refinement treatment by laser irradiation were applied to the finally annealed sheets.
  • the resultant products had the magnetic properties as shown in Table 1.
  • an annealing separator was applied to the decarburized steel strip.
  • Conventional MgO was applied to several steel sheets, and alumina containing different kinds of alkali metal as impurities and different concentrations in the slurry is applied to the remaining steel sheets.
  • final annealing was carried out by heating the steel sheets to 1200°C at a constant heating rate of 15° C/hr in a mixed atmosphere comprising 15% nitrogen and 85% hydrogen gas, and further maintaining the steel at a temperature of 1200°C for 20 hours in an atmosphere of 100% hydrogen gas. The atmosphere gas was switched from nitrogen to hydrogen at 1200°C.
  • insulation coating and the magnetic domain refining treatment by laser irradiation were applied to the final annealed strip.
  • the resultant products had the magnetic properties as shown in Table 2.

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EP95111069A 1995-07-14 1995-07-14 Verfahren zum herstellen eines kornorientierten elektrostahlblechs mit einer spiegeloberflache und mit geringem kernverlust Expired - Lifetime EP0753588B2 (de)

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EP95111069A EP0753588B2 (de) 1995-07-14 1995-07-14 Verfahren zum herstellen eines kornorientierten elektrostahlblechs mit einer spiegeloberflache und mit geringem kernverlust
DE1995613811 DE69513811T3 (de) 1995-07-14 1995-07-14 Verfahren zum herstellen eines kornorientierten elektrostahlblechs mit einer spiegeloberflache und mit geringem kernverlust

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EP95111069A EP0753588B2 (de) 1995-07-14 1995-07-14 Verfahren zum herstellen eines kornorientierten elektrostahlblechs mit einer spiegeloberflache und mit geringem kernverlust

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EP0753588A1 true EP0753588A1 (de) 1997-01-15
EP0753588B1 EP0753588B1 (de) 1999-12-08
EP0753588B2 EP0753588B2 (de) 2005-04-27

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1006207A1 (de) * 1998-03-11 2000-06-07 Nippon Steel Corporation Unidirektional magnetisches stahlblech
EP1464712A1 (de) * 2002-01-08 2004-10-06 Nippon Steel Corporation Verfahren zur herstellung von kornorientierten siliciumstahlplatten mit spiegeloberfläche

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3785882A (en) * 1970-12-21 1974-01-15 Armco Steel Corp Cube-on-edge oriented silicon-iron having improved magnetic properties and method for making same
EP0305966A1 (de) * 1987-08-31 1989-03-08 Nippon Steel Corporation Verfahren zur Herstellung von kornorientierten Stahlblechen mit Metallglanz und ausgezeichneter Stanzbarkeit
JPH0617132A (ja) * 1992-07-02 1994-01-25 Nippon Steel Corp 磁束密度の極めて高い超低鉄損方向性電磁鋼板及びその製造方法
JPH0639123A (ja) * 1993-04-30 1994-02-15 Daiichi Shokai Co Ltd パチンコ機の管理装置
EP0607440A1 (de) * 1992-05-08 1994-07-27 Nippon Steel Corporation Verfahren zur herstellung elektrisch gerichteter spiegelnder bleche

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Publication number Priority date Publication date Assignee Title
IT1127263B (it) † 1978-11-28 1986-05-21 Nippon Steel Corp Sostanza di separazione da utilizzare nella fase di ricottura di strisce di acciaio al silicio a grani orientati
JPH0756048B2 (ja) † 1990-11-30 1995-06-14 川崎製鉄株式会社 被膜特性と磁気特性に優れた薄型方向性けい素鋼板の製造方法

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Publication number Priority date Publication date Assignee Title
US3785882A (en) * 1970-12-21 1974-01-15 Armco Steel Corp Cube-on-edge oriented silicon-iron having improved magnetic properties and method for making same
EP0305966A1 (de) * 1987-08-31 1989-03-08 Nippon Steel Corporation Verfahren zur Herstellung von kornorientierten Stahlblechen mit Metallglanz und ausgezeichneter Stanzbarkeit
EP0607440A1 (de) * 1992-05-08 1994-07-27 Nippon Steel Corporation Verfahren zur herstellung elektrisch gerichteter spiegelnder bleche
JPH0617132A (ja) * 1992-07-02 1994-01-25 Nippon Steel Corp 磁束密度の極めて高い超低鉄損方向性電磁鋼板及びその製造方法
JPH0639123A (ja) * 1993-04-30 1994-02-15 Daiichi Shokai Co Ltd パチンコ機の管理装置

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Title
PATENT ABSTRACTS OF JAPAN vol. 18, no. 226 (C - 1194) 25 April 1994 (1994-04-25) *
PATENT ABSTRACTS OF JAPAN vol. 9, no. 166 (C - 290) 11 July 1985 (1985-07-11) *

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1006207A1 (de) * 1998-03-11 2000-06-07 Nippon Steel Corporation Unidirektional magnetisches stahlblech
EP1006207A4 (de) * 1998-03-11 2005-01-05 Nippon Steel Corp Unidirektional magnetisches stahlblech
EP1728885A1 (de) * 1998-03-11 2006-12-06 Nippon Steel Corporation Kornorientiertes Elektrostahlblech und dessen Herstellungsverfahren
EP1464712A1 (de) * 2002-01-08 2004-10-06 Nippon Steel Corporation Verfahren zur herstellung von kornorientierten siliciumstahlplatten mit spiegeloberfläche
EP1464712A4 (de) * 2002-01-08 2006-08-09 Nippon Steel Corp Verfahren zur herstellung von kornorientierten siliciumstahlplatten mit spiegeloberfläche
US7364629B2 (en) 2002-01-08 2008-04-29 Nippon Steel Corporation Method for manufacturing grain-oriented silicon steel sheets with mirror-like surface
EP2319944A1 (de) * 2002-01-08 2011-05-11 Nippon Steel Corporation Methode zur Herstellung von Stahlblechen mit spiegelähnlicher Oberfläche und orientierten Körnern

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EP0753588B1 (de) 1999-12-08
DE69513811T3 (de) 2005-09-22
DE69513811D1 (de) 2000-01-13
EP0753588B2 (de) 2005-04-27
DE69513811T2 (de) 2000-04-27

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