EP4202068A1 - Method for producing a grain-oriented electrical strip, and grain-oriented electrical strip - Google Patents

Abstract

The invention enables the production of grain-oriented electrical strips with an optimally formed and adhering forsterite layer. For this purpose, from a) decarburizing annealed; primary recrystallized cold-rolled steel strips b) those selected for which the result of a ToF-SIMS investigation in which the surface is bombarded with Cs ions with an acceleration voltage of 2keV as sputtering material and Bi ions with an acceleration voltage of 25keV as analysis ions, the following condition 1 fulfilled: The value of the quotient formed from the signal "Al bonded to Cs" and the signal "Al not bonded to Cs" is <0.01 down to a depth of 8 µm aqueous sludge with 90 - 100% by mass of MgO particles and TiO₂ particles and ≤ 0.5% by mass of additives applied. Where: (i) 0 < %TiO/%MgO < 0.12 with %TiO = TiO₂ content and %MgO = MgO content, (ii) %TiO_Anatase/%TiO_Rutil > % N x AlCs/Al_ToF-SIMS, with %TiO_Anatase and %TiO_Rutil = anatase or rutile proportions in the TiOz content of the sludge, %N = N content of the steel strip in ppm by mass and AlCs/Al_ToF-SIMS = quotient of the signals "Al bound to Cs" and "Al not bound to Cs" obtained during the ToF-SIMS investigation at a sputtering depth of 3 µm. The coated steel strip is d) annealed to form the forsterite layer (Mg₂SiO₄) from the anti-adhesive layer applied in step c).

Description

The invention relates to a method for producing a grain-oriented electrical strip that is coated with a forsterite layer, and to a grain-oriented electrical strip with very good adhesion of a forsterite film formed on it.

Grain-oriented "electrical strip" is understood to mean steel strips produced by cold rolling, which are provided in a special way with a forsterite layer and optionally with at least one layer additionally applied to the forsterite layer. The cold-rolled steel strip of a grain-oriented electrical strip is also referred to below as "steel substrate" or "steel material".

Due to their special electromagnetic properties, grain-oriented electrical steels are suitable for applications in electrical engineering where the highest demands are placed on efficiency. It goes without saying that when "electrical steel" is mentioned in the following, "electrical steel" or "plates" are meant in the same way, which can be separated from such electrical steel or have widths or lengths that differ from deviate from the dimensions typical of electrical steel.

Typically, grain-oriented electrical steels of the type in question are 0.10-0.35 mm thick.

The decarburization-annealed and primary recrystallized cold-rolled steel substrate of grain-oriented electrical strips of the type according to the invention typically consists of, in % by mass, 2.5 - 4.0% silicon ("Si"), ≤ 0.20% manganese ("Mn"), ≤ 0 50% copper ("Cu"), ≤ 0.065% aluminum ("Al"), ≤ 0.1% nitrogen ("N") and optionally one or more elements from the group "chromium ("Cr"), Nickel ("Ni"), Molybdenum ("Mo"), Phosphorus ("P"), Arsenic ("As"), Sulfur ("S"), Tin ("Sn"), Selenium ("Se"), Antimony ("Sb"), tellurium ("Te"), boron ("B") or bismuth ("Bi")" with the proviso that the contents of the elements of this group are ≤ 0.2%, the remainder being iron and unavoidable impurities.

As in detail, for example, in Leaflet 401 "Electrical steel and sheet metal", 2005 edition, published by Stahl-Informations-Zentrum, 40039 Düsseldorf, Germany and, or the WO 03/000951 A1 described, a forsterite layer is built up on the respective electrical steel sheet in conventional production methods by subjecting a steel strip cold-rolled to its final thickness, which is composed within the framework of the general alloy specification given above, to a first annealing in order to bring about primary recrystallization and decarburization of the steel substrate and the Surface of the substrate to oxidize targeted. The surface of the electrical strip treated in this way is then typically coated with a solution containing magnesium oxide (“MgO”) and suitable additives as a protection against adhesion. After the MgO coating has dried, the electrical steel is then wound into a coil and coil annealed again to effect secondary recrystallization and subsequent purification of the steel of precipitate-forming elements.

During this high-temperature annealing step, which typically takes place at 1100 °C to 1,300 °C, the anti-adhesive layer, which consists essentially of MgO, reacts with the oxides present on the surface of the steel substrate, which predominantly consist of silicon oxide, and thus forms the desired layer of forsterite ("Mg2SiO4"), also known as "glass film". This layer of forsterite merges into the steel substrate with roots, which ensures its adhesion to the steel substrate.

On the forsterite layer can in a further step, such as from the DE 22 47 269 C3 is known, a solution based on magnesium phosphate or aluminum phosphate or mixtures of both with various additives such as chromium compounds and Si oxide are applied and baked at temperatures above 350 °C. The layer system formed in this way on the electrical strip forms an insulating layer which transfers tensile stresses to the steel material, which have a favorable effect on the electromagnetic properties of the electrical strip or sheet.

In order for these tensile stresses to be safely transmitted over a long period of use under harsh operating conditions, excellent adhesion of the forsterite layer on the cold-rolled steel material of the electrical strip must be guaranteed. It must be ensured that the forsterite layer also adheres firmly to the steel substrate when the electrical steel coated with it is wound into a coil or blanks or other sheet metal parts that are required for further processing are cut from it.

The high-temperature annealing step that forms the forsterite layer typically takes 6-7 days and requires significant energy input. With conventional production methods, it is only after this long annealing period that it can be determined whether the forsterite layer has formed properly or whether it is not sufficiently adhering to the steel substrate. Interventions in the production process to eliminate a faulty formation of the forsterite layer can therefore only be made with a considerable delay. Since production continues during this time, larger quantities may also be shipped defective electrical steels are produced until the cause of the error has been remedied.

Against this background, the task was to develop a process that reliably enables the production of grain-oriented electrical steel with an optimally formed forsterite layer that adheres to the steel substrate of the respective electrical steel.

In addition, a grain-oriented electrical strip should be specified in which the forsterite layer adheres optimally firmly to the steel substrate of the electrical strip.

With regard to the method, the invention has achieved this object in that at least the work steps specified in claim 1 are completed in the production of grain-oriented electrical strips with an optimally adhering forsterite layer. It goes without saying that a person skilled in the art, when carrying out the method according to the invention and its variants and expansion options explained here, adds those work steps not explicitly mentioned here, which he knows from his practical experience that they are regularly used when carrying out such methods .

A grain-oriented electrical steel sheet which achieves the above-specified object according to the invention and is produced by the method according to the invention has at least the features specified in claim 2 .

Advantageous refinements of the invention are specified in the dependent claims and, like the general inventive concept, are explained in detail below.

With the invention, in the course of the production of grain-oriented electrical steel, it is possible to decide at a point in time based on fixed criteria whether an intermediate product obtained before high-temperature annealing is suitable for forming a forsterite layer that adheres optimally to the steel substrate of the electrical strip. The invention makes it possible to measure the subsequent adhesive strength of the forsterite layer in the process and thus provides a safe range of process parameters, which leads to perfect adhesive strength of the forsterite layer after annealing.

1. a) Bereitstellen von zwei oder mehr 0,10 - 0,35 mm dicken entkohlend geglühten und primärrekristallisierten kaltgewalzten Stahlbändern, welche aus, in Masse-%, 2,5 - 4,0 % Si, ≤ 0,30 % Mn, ≤ 0,50 % Cu, ≤ 0,065 % Al, 0,005 - 0,1 % N, ≤ 0,2 % Sn sowie jeweils optional einem Element oder mehreren Elementen aus der Gruppe "Cr, Ni, Mo, P, As, S, Sb, Se, Te, B oder Bi" mit der Maßgabe, dass die Gehalte an den Elementen dieser Gruppe jeweils ≤ 0,2 % betragen, Rest Eisen und unvermeidbaren Verunreinigungen bestehen wobei die Stahlbänder mindestens 0,05 Masse-% Cu oder mindestens 0,005 Masse-% Sn enthalten.
2. b) Auswählen desjenigen Stahlbands oder derjenigen Stahlbänder aus den im Arbeitsschritt a) bereitgestellten Stahlbändern, für das oder für die das Ergebnis einer ToF-SIMS-Untersuchung, bei der die Oberfläche des jeweiligen Stahlbands mit Cs-Ionen mit einer Beschleunigungsspannung von 2keV als Sputtermaterial und Bi-Ionen mit einer Beschleunigungsspannung von 25keV als Analyseionen beschossen wird, folgende Bedingung 1 erfüllt:

   Bedingung 1:

   Der Wert des aus dem Signal "Al an Cs gebunden" und dem Signal "Al nicht an Cs gebunden" gebildeten Quotienten "Al an Cs gebunden" / "Al nicht an Cs gebunden" ist in einem von der Oberfläche des Stahlbands bis in eine Tiefe von 8 µm reichenden Tiefenbereich kleiner als 0,01.

3. c) Auftragen einer aus einer wässrigen Schlemme, deren Festkörperanteil zu 90 - 100 Masse-% aus MgO-Partikeln, ferner TiO₂-Partikeln, optional zugegebenen weiteren Additiven mit einem Gesamtgehalt von höchstens 0,5 Masse-% besteht, gebildeten Klebschutzschicht auf das in Arbeitsschritt b) jeweils ausgewählte Stahlband, wobei die Zusammensetzung der Schlemme folgende Maßgaben (i) und (ii) erfüllt:
   1. (i) Für den aus dem Gehalt %TiO an TiO₂ der Schlemme und aus dem Gehalt %MgO an MgO der Schlemme gebildete Verhältnis %TiO/%MgO gilt: $$0<\%\mathrm{TiO}/\%\mathrm{MgO}<\mathrm{0,12}$$
      
   2. (ii) Das Mischverhältnis %TiO_Anatas/%TiO_Rutil der Anteile %TiO_Anatas und %TiO_Rutil der beiden TiO₂-Strukturen Anatas und Rutil an dem TiO₂ -Gehalt der Schlemme erfüllt folgende Bedingung 2: $$\%\mathrm{TiO}\_\mathrm{Anatas/}\%\mathrm{TiO}\_\mathrm{Rutil}>\%\mathrm{N}\times {\mathrm{AlCs/Al}}_{\mathrm{ToF}-\mathrm{SIMS}}$$
      
      mit

      %N:

      jeweiliger N-Gehalt des im Arbeitsschritt a) bereitgestellten Stahlbands in Masse-ppm und

      AlCs/AlToF-SIMS:

      Quotient der bei einer ToF-SIMS-Untersuchung, bei der die Oberfläche des jeweiligen Stahlbands mit Cs-Ionen mit einer Beschleunigungsspannung von 2keV als Sputtermaterial und Bi-Ionen mit einer Beschleunigungsspannung von 25keV als Analyseionen beschossen wird, in einer ausgehend von der Oberfläche des Stahlbands gemessenen Sputtertiefe von 3 µm die gewonnenen Signale "Al an Cs gebunden" und "Al nicht an Cs gebunden"

4. d) Glühen des Stahlbands, wobei sich über das Glühen aus der im Arbeitsschritt c) aufgetragenen Klebschutzschicht die Forsteritschicht (Mg₂SiO₄) bildet.

A method according to the invention for producing a grain-oriented electrical strip that is covered with a forsterite layer comprises at least the following work steps:

1. a) Provision of two or more 0.10 - 0.35 mm thick, decarburization annealed and primary recrystallized cold-rolled steel strips, which consist of, in % by mass, 2.5 - 4.0% Si, ≤ 0.30% Mn, ≤ 0 .50% Cu, ≤ 0.065% Al, 0.005 - 0.1% N, ≤ 0.2% Sn and optionally one or more elements from the group "Cr, Ni, Mo, P, As, S, Sb, Se, Te, B or Bi" with the proviso that the contents of the elements of this group are ≤ 0.2%, the remainder being iron and unavoidable impurities, with the steel strips containing at least 0.05% by mass Cu or at least 0.005% by mass %Sn included.
2. b) Selecting that steel strip or those steel strips from the steel strips provided in step a) for which or for which the result of a ToF-SIMS examination is carried out in which the surface of the respective steel strip is treated with Cs ions with an acceleration voltage of 2keV as sputtering material and Bi-ions are bombarded with an acceleration voltage of 25keV as analysis ions, the following condition 1 is met:

   Condition 1:

   The value of the quotient "Al bound to Cs" / "Al not bound to Cs" formed from the signal "Al bound to Cs" and the signal "Al not bound to Cs" is in one of the Surface of the steel strip down to a depth of 8 µm depth range less than 0.01.

3. c) Application of an anti-adhesive layer formed from an aqueous sludge, the solids content of which consists of 90 - 100% by mass of MgO particles, also TiO ₂ particles, optionally added further additives with a total content of at most 0.5% by mass steel strip selected in step b), the composition of the slime fulfilling the following requirements (i) and (ii):
   1. (i) For the %TiO/%MgO ratio formed from the %TiO content of TiO ₂ in the sludge and the %MgO content of MgO in the sludge: $$0<\%\mathrm{TiO}/\%\mathrm{MgO}<0.12$$
      
   2. (ii) The mixing ratio %TiO_Anatase/%TiO_Rutil of the shares %TiO_Anatase and %TiO_Rutil of the two TiO ₂ structures anatase and rutile in the TiO ₂ content of the sludge satisfies the following condition 2: $$\%\mathrm{TiO}\_\mathrm{anatase/}\%\mathrm{TiO}\_\mathrm{rutile}>\%\mathrm{N}\times {\mathrm{AlCs/Al}}_{\mathrm{ToF}-\mathrm{SIMS}}$$
      
      with

      %N:

      respective N content of the steel strip provided in step a) in mass ppm and

      AlCs/AlToF SIMS:

      Quotient of the in a ToF-SIMS examination, in which the surface of the respective steel strip is bombarded with Cs ions with an acceleration voltage of 2keV as sputtering material and Bi ions with an acceleration voltage of 25keV as analysis ions, in a starting from the surface of the steel strip measured sputter depth of 3 µm the signals "Al bonded to Cs" and "Al not bonded to Cs"

4. d) annealing of the steel strip, the forsterite layer (Mg ₂ SiO ₄ ) being formed from the anti-adhesive layer applied in step c) via the annealing.

The intermediate product provided in step a) of the method according to the invention as a cold-rolled and decarburization-annealed steel strip can be produced in accordance with the manner established in the prior art for the production of grain-oriented electrical steel sheets. It is crucial that the steel strip is produced with a composition that is typical for grain-oriented electrical steel sheets and that it is decarburized and primary recrystallized annealed. The alloy of the steel strip is also optimized to optimize the adhesion of the forsterite layer. For this purpose, the invention provides, on the one hand, that in the standard base alloy of the steel strip, which is known per se, contents of 0.05-0.50% copper ("Cu") or 0.005-0.2% tin ("Sn") are preferred grades of 0.05 - 0.50% copper ("Cu") and 0.005 - 0.2% tin ("Sn") are present. As is known per se, the presence of copper and/or tin not only refines the secondary recrystallization grains, but also promotes the formation of the forsterite layer. In this context, it has proven to be advantageous if the composition of the steel strip contains a minimum content of 0.05% by weight of Cu. According to a preferred embodiment of the invention, the composition of the steel strip contains 0.05-0.3% Cu, particularly preferably 0.05-0.2% Cu. By limiting the Cu content to at most 0.50% by mass, in particular at most 0.3% by mass, particularly preferably at most 0.2% by mass, negative effects on the magnetic properties of a grain-oriented electrical strip according to the invention are avoided. Of the other elements from the group "Cr, Ni, Mo, P, As, S, Sn, Sb, Se, Te, B or Bi" optionally occurring in the composition, the addition of at least 0.005% Sn in particular has proven to be practical . According to another preferred embodiment According to the invention, the composition of the steel strip contains 0.005 - 0.1% Sn, particularly preferably 0.005 - 0.08% Sn. Limiting the Sn content to at most 0.1% by mass, in particular 0.08% by mass, advantageously ensures good workability of the steel strip when it is produced. In a particularly advantageous manner, both Cu and Sn can be present in the composition of the steel strip in the aforementioned contents.

In step b) of the method according to the invention, it is then decided on the basis of the criteria specified according to the invention whether or not the steel strips provided have the potential for the formation of an optimally adhering forsterite layer. If the steel strip in question does not meet the requirements, it is no longer processed, but recycled as scrap and fed back into the steel strip production cycle for the manufacture of grain-oriented electrical steel strips. With the procedure according to the invention, only those cold-rolled steel strips reach the high-temperature annealing (step d)) in which it can be expected that the forsterite layer produced on them will meet the highest requirements with regard to their adhesion to the steel substrate of the electrical strip.

The invention is based on the knowledge that by time-of-flight secondary ion mass spectroscopy (English "Time of Flight Secondary Ion Mass Spectrometry", short "ToF-SIMS"), in which the surface to be examined of the intermediate product present after the decarburizing annealing with Cs Ions with an acceleration voltage of 2keV and for analysis with Bi+ ions with an acceleration voltage of 25keV is bombarded, the adhesive strength of the forsterite layer produced in the following work steps can be predicted if at the same time a sludge is used to produce the anti-adhesive layer, the composition of which is determined by the invention specified requirements are met.

ToF-SIMS is an analytical method for the chemical characterization of surfaces. It is based on the time-resolved detection of secondary ions, which are generated from the examined surface by bombardment with high-energy primary ions (e.g. Bi). These primary ions, directed at the surface to be examined in a short ion pulse, penetrate the upper atomic layers of the surface and release so-called "secondary ions" from it. The kinetic energy of the primary ions is transferred to the released secondary ions, so that the secondary ions are accelerated and run through a drift path until they hit a detector system that records the intensity of the secondary ions as a function of the flight time with high time resolution. Since ions of different masses have different velocities for a given kinetic energy, their mass can be deduced from the measured flight time. The individual elements of the surface to be examined can be detected by mass separation (see https://tazgmbh.de/tof---sims.html; https://de.wikipedia.org/wiki/Sekundär ionen-Massenspektrometrie, https ://en.wikipedia.org/wiki/Static_secondary-ion_mass_spectrometry, accessed December 7, 2019).

In order to obtain a depth profile, the material to be examined is bombarded with sputter ions (e.g. Cs) in addition to the primary ions, so that material is continuously removed. The inventors found that a part of the secondary ions combines with the sputtering ions (Cs) and passes through the drift path as a total mass. The depth-resolved degree of affinity for this binding is the basis of the invention.

By using the "ToF-SIMS" characterization method according to the invention in the state after the decarburization annealing, i.e. before the high-temperature annealing (step e)), it can thus be reliably predicted if the result of the ToF-SIMS measurement satisfies condition 1 that the forsterite layer is optimally firm on the surface after step d) The finished material obtained adheres if the sludge applied in step c) to produce the anti-adhesive layer is not only composed in accordance with requirement (i), but the forms in which the TiO ₂ particles are contained in the sludge correspond to requirement (ii). .

Requirement (ii) is of particular importance because it takes into account the connection between the presence of TiO ₂ in the anti-adhesive layer and the presence of N, which is unavoidable for production reasons. This prevents the formation of brittle TiN during the high-temperature anneal, which, if present in the forsterite layer after the high-temperature anneal, would significantly deteriorate the bond strength of the forsterite layer to the steel substrate of the resulting grain-oriented electrical steel. In addition, the investigations carried out by the inventors indicate that the ToF-SIMS quotient "Al bound to Cs" / "Al not bound to Cs" of the steel strip provided in step a) is related to the release temperature of nitrogen from aluminum nitride. The nitrogen released by the aluminum nitrate contained in the steel substrate in the course of the high-temperature annealing should not be released at the same time as the TiO ₂ is also decomposing, in order to also make TiN formation more difficult in this way.

The cold-rolled steel strip, which forms the steel substrate of a grain-oriented electrical strip according to the invention and which is provided in step a), has an N content of at least 0.005% by mass.

Grain-oriented electrical steel according to the invention, in which the forsterite film formed on its cold-rolled steel strip adheres excellently and which is obtained by the method according to the invention, is characterized in that in a ToF-SIMS examination by bombarding the forsterite layer with Cs ions with an acceleration voltage of 2keV as

Sputtering material and bi-ions with an acceleration voltage of 25keV as analysis ions criterion A) the curve of the quotient "Al bound to Cs" / "Al not bound to Cs" formed from the signal "Al bound to Cs" and the signal "Al not bound to Cs" at a sputtering depth of 6 measured from the surface of the forsterite layer µm is greater than a sputtering depth of 2 µm, also measured from the surface of the forsterite layer, and criterion B) the quotient "Al bound to Cs"/"Al not bound to Cs" is less than 0.01 in the sputtering depth of 2 µm and greater than 0.02 in the sputtering depth of 6 µm.

Criteria A) and B) developed according to the invention as criteria for evaluating the adhesive strength of the forsterite layer on the steel substrate of a completely processed grain-oriented electrical strip according to the invention can be achieved by selecting the appropriate cold-rolled steel strip in accordance with the requirements of the invention (step b) of the method according to the invention). and an adjustment of the composition of the sludge which also corresponds to the specifications of the invention, from which the anti-adhesion layer is formed in step c) of the method according to the invention.

Typically, the TiO ₂ content of the sludge is 2-10% by mass of the solids content, in particular 5-8% by mass.

The sum of the contents of the other additives that can optionally be added to the sludge is at most 0.5% by mass of the solids content. Additives that can be added to the sludge include ammonium chloride or antimony chloride, which increase the density of the later forsterite layer and the gas exchange between Annealing atmosphere during high temperature annealing and metal is controlled.

The annealing of the steel strip, which is finally completed in step d), during which the forsterite layer (Mg2SiO4) forms, can also be carried out in a manner known per se. For this purpose, the cold-rolled steel strip obtained after step d) and coated with the anti-tack layer formed from the MgO powder can be wound into a coil and kept in a hood furnace for 10-200 hours at a temperature of 1000-1600 K under an atmosphere that consists of at least 50% H ₂ consists.

The grain-oriented electrical strips according to the invention, produced by the method according to the invention, have a bending radius of less than 15 mm, in particular less than 12 mm, particularly preferably less than 10 mm.

The invention is explained in more detail below using exemplary embodiments.

In 1 the course of the quotient "Al bound to Cs" / "Al not bound to Cs" is shown as an example over the sputtering depth.

In order to check whether grain-oriented electrical steel strips can be reliably created on the basis of the criteria, specifications and measures developed by the invention, in which an optimized adhesive strength of the forsterite layer on the respective steel substrate is given, samples P1 - P7 been divided.

The samples P1 - P7 separated from the cold strips produced in this way and made available for further processing are to be examined by ToF-SIMS, in which the surface of the respective steel strip is treated with Cs ions with a acceleration voltage of 2keV as sputtering material and Bi-ions with an acceleration voltage of 25keV as analysis ions, up to a depth of 10 µm measured from the surface of the respective sample, the curve of the from the signal "Al bound to Cs" and the signal "Al not bound to Cs" was determined and the resulting course of the quotient "Al bound to Cs"/"Al not bound to Cs" was determined.

In 1 For sample 1, the course of the quotient "Al bonded to Cs"/"Al not bonded to Cs" is shown as an example, plotted against the sputtering depth.

Based on the curves determined for the samples P1 - P7 of the respective quotient "Al bound to Cs" / "Al not bound to Cs" it was checked whether these curves meet condition 1 "the value of the quotient "Al bound to Cs" / "Al not bonded to Cs" is satisfied in a depth range ranging from the surface of the steel strip to a depth of 8 µm less than 0.01". The results of this evaluation are summarized in Table 2.

The surfaces of samples P1-P7 examined in this way were then coated with an anti-tack layer. For this purpose, a slurry containing %MgO solids content of MgO particles and %TiO content of TiO particles was applied to the surface to be coated of the respective cold-rolled, decarburization-annealed and primary-recrystallized steel strip. The contents of the MgO particles and the TiO ₂ particles are shown in Table 3 as the %TiO ₂ /%MgO ratio

The TiO ₂ particles were present in the respective sludge as anatase and rutile structures with %TiO_anatase and %TiO-rutile contents. The respective mixing ratio % TiO _anatase/% TiO rutile is listed in Table 4. In addition, for samples P1 - P7 in Table 4, the N content is %N des cold-rolled steel strips of the respective sample as well as the AlCs/Al _ToF-SIMS value of the quotient that was obtained in a ToF-SIMS investigation in which the surface of the respective steel strip was sputtered with Cs ions with an acceleration voltage of 2keV and Bi ions with an acceleration voltage of 25keV as analysis ions, signals "Al bonded to Cs" and "Al not bonded to Cs" have been determined at a sputtering depth of 3 µm measured from the surface of the steel strip.

The samples coated in this way were subjected to high-temperature annealing, during which they were kept in a top hat furnace for a period of 24 h at a temperature of 1450 K under a dry atmosphere of pure hydrogen.

For each of the samples P1 - P7, after cooling, a further ToF-SIMS examination by bombarding the forsterite layer with Cs ions with an acceleration voltage of 2keV as sputtering material and Bi ions with an acceleration voltage of 25keV as analysis ions was checked to determine whether the on the curves of the quotients "Al bonded to Cs" / "Al not bonded to Cs" determined after high-temperature annealing from the samples P1 - P7 formed grain-oriented electrical sheets, criterion A) "the quotient 'Al bonded to Cs'/ ,Al not bonded to Cs' is greater at a sputter depth of 6 µm measured from the surface of the forsterite layer than at a sputter depth of 2 µm also measured from the surface of the forsterite layer" and criterion B) "the quotient 'Al bonded to Cs' / 'Al not bound to Cs' is less than 0.01" in the sputtering depth of 2 µm and greater than 0.02" in the sputtering depth of 6 µm. The result of these investigations is summarized in Table 5.

Finally, on the samples P1 - P7 produced and tested in the manner explained above, the strength of the adhesion of the forsterite layer is shown determined by the initially provided cold rolled steel substrate. For this purpose, a sample was clamped in a cone mandrel bending device. The sample was bent 180° around a cone mandrel ranging continuously from a bending radius of 5 mm (cone apex) to 30 mm (cone base). After removal, the bending radius from which the coating flaked off was checked. The smaller this bending radius, the better the adhesion.

The results of this review are summarized in Table 6.

It turns out that the samples P2 and P3, which meet the conditions and specifications formulated by the invention, adhere optimally to the respective steel substrate, while this is not the case with the samples P1, P4-P7 not according to the invention. Table 1: Contents in % by mass Steel of the cold strip sample si Mn Cr Al S N Cu sn P1 3.25 0.15 0.05 0.020 0.003 0.009 0.20 0.052 p2 3.25 0.09 0.12 0.041 0.003 0.015 0.15 0.027 P3 3.07 0.25 0.10 0.033 0.004 0.025 0.05 0.009 P4 3:12 0.21 0.10 0.055 0.005 0.022 0.30 0.055 P5 3:19 0.13 0.06 0.025 0.009 0.037 0.11 0.020 P6 3.07 0.05 0.03 0.017 0.005 0.044 0.22 0.058 P7 3.25 0.11 0.05 0.031 0.006 0.013 0.04 0.016 sample condition 1 P1 Fulfills p2 Fulfills P3 Fulfills P4 not fulfilled P5 Fulfills P6 Fulfills P7 not fulfilled sample %MgO %TiO ₂ %TiO ₂ /%MgO Requirement (i) fulfilled? [Dimensions-%] P1 92.5 7.5 0.08 YES p2 95.0 5.0 0.05 YES P3 98.0 2.0 0.02 YES P4 95.0 5.0 0.05 YES P5 88.0 12.0 0.14 NO P6 94.0 6.0 0.06 YES P7 97.0 3.0 0.03 YES sample %TiO_anatase / %TiO rutile %N AlCs/Al _{ToF SIMS} : Requirement (ii) fulfilled? [mass ppm] P1 3 200 0.005 3 > 1 ⇒ YES p2 2 150 0.003 2 > 0.45 ⇒ YES P3 1.2 120 0.009 1.2 > 1.08 ⇒ YES P4 7 160 0.002 7 > 0.32 ⇒ YES P5 1 155 0.005 1 > 0.775 ⇒ YES P6 0 95 0.007 0 < 0.665 ⇒ NO P7 4 112 0.03 4 > 3.36 ⇒ YES sample Quotient "Al bound to Cs" / "Al not bound to Cs" Criterion A fulfilled? Criterion B fulfilled? According to the invention? at a depth of 6 µm at a depth of 2 µm P1 0.03 0.007 NO YES NO p2 0.05 0.005 YES YES YES P3 0.08 0.009 YES YES YES P4 0.01 0.005 NO YES NO P5 0.008 0.009 NO NO NO P6 0.05 0.07 YES NO NO P7 0.03 0.04 YES NO NO sample Bond strength of the forsterite layer [chipping from bend radius] P1 16.5mm p2 6.0mm P3 7.5mm P4 18.5mm P5 15.0mm P6 17.0mm P7 19.5mm P7 22.0mm

Claims (2)

Process for producing a grain-oriented electrical strip that is covered with a forsterite layer, comprising the following work steps: a) Provision of two or more 0.10 - 0.35 mm thick, decarburization annealed and primary recrystallized cold-rolled steel strips, which consist of, in % by mass, 2.5 - 4.0% Si, ≤ 0.30% Mn, ≤ 0 .50% Cu, ≤ 0.065% Al, 0.005 - 0.1% N, ≤ 0.2% Sn and optionally one or more elements from the group "Cr, Ni, Mo, P, As, S, Sb, Se, Te, B or Bi" with the proviso that the contents of the elements of this group are ≤ 0.2%, the remainder being iron and unavoidable impurities, with the steel strips containing at least 0.05% by mass Cu or at least 0.005% by mass -% Sn included. b) Selecting that steel strip or those steel strips from the steel strips provided in step a) for which or for which the result of a ToF-SIMS examination is carried out in which the surface of the respective steel strip is treated with Cs ions with an acceleration voltage of 2keV as sputtering material and Bi-ions are bombarded with an acceleration voltage of 25keV as analysis ions, the following condition 1 is met: Condition 1: The value of the formed from the signal "Al bound to Cs" and the signal "Al not bound to Cs". The quotient "Al bonded to Cs"/"Al not bonded to Cs" is less than 0.01 in a depth range extending from the surface of the steel strip to a depth of 8 µm. c) Application of an anti-adhesive layer formed from an aqueous sludge, the solids content of which consists of 90 - 100% by mass of MgO particles, also TiO ₂ particles, optionally added further additives with a total content of at most 0.5% by mass steel strip selected in step b), the composition of the slime fulfilling the following requirements (i) and (ii): (i) For the %TiO/%MgO ratio formed from the %TiO content of TiOa in the sludge and the %MgO content of MgO in the sludge: $$0<\%\mathrm{TiO}/\%\mathrm{MgO}<0.12$$

(ii) The mixing ratio %TiO_Anatase/%TiO_Rutil of the shares %TiO_Anatase and %TiO_Rutil of the two TiO ₂ structures anatase and rutile in the TiO ₂ content of the sludge satisfies the following condition 2: $$\%\mathrm{TiO\_Anatase/}\%\mathrm{TiO\_rutile}>\%\mathrm{N}\times {\mathrm{AlCs/Al}}_{\mathrm{ToF}-\mathrm{SIMS}}$$

with %N: respective N content of the steel strip in mass ppm and AlCs/Al _ToF-SIMS : quotient of the ToF-SIMS examination in which the surface of the respective steel strip is sputtered with Cs ions with an acceleration voltage of 2keV and Bi ions with an acceleration voltage of 25keV as analysis ions is bombarded, the signals "Al bonded to Cs" and "Al not bonded to Cs" obtained at a sputtering depth of 3 µm measured from the surface of the steel strip d) annealing of the steel strip, the forsterite layer (Mg ₂ SiO ₄ ) being formed from the anti-adhesive layer applied in step c) via the annealing. Grain-oriented electrical strip with very good adhesion of a forsterite layer formed on it, produced according to claim 1, characterized in that in a ToF-SIMS examination by bombarding the forsterite layer with Cs ions with an acceleration voltage of 2keV as sputtering material and Bi ions with an acceleration voltage of 25keV as analysis ions A) the curve of the quotient "Al bound to Cs" / "Al not bound to Cs" formed from the signal "Al bound to Cs" and the signal "Al not bound to Cs" at a sputtering depth measured from the surface of the forsterite layer of 6 µm is greater than at a sputtering depth of 2 µm, also measured from the surface of the forsterite layer, and B) the quotient "Al bound to Cs"/"Al not bound to Cs" is less than 0.01 at the sputtering depth of 2 µm and greater than 0.02 at the sputtering depth of 6 µm.

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