EP4202067A1 - Grain-oriented electrical tape and method of producing a grain-oriented electrical tape - Google Patents

Abstract

The invention enables the production of grain-oriented electrical strips with an optimally developed forsterite layer that adheres to the steel substrate. For this purpose, a) at least two 0.10 - 0.35 mm thick, decarburization annealed, primary recrystallized, cold-rolled steel strips made of, in % by mass, 2.5 - 4.0 % Si, ≤ 0.30 % Mn, ≤ 0, 50% Cu, ≦0.065% Al, ≦0.1% N, and optionally at least one element from the group “Cr, Ni, Mo, P, As, S, Sn, Sb, Se, Te, B or Bi” with contents of ≤ 0.2% each, remainder iron and unavoidable impurities, b) those selected for which the result of a ToF-SIMS investigation, in which the steel strip surface was 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 conditions are met: - The curve of the quotient "Si bonded to Cs" / "Si not bonded to Cs" has exactly a local maximum in the depth profile of 0.5 - 5.0 µm .- The value of the quotient "Si bonded to Cs" / "Si not bonded to Cs" is consistently <0.01 down to a depth of 2 µm. c) An anti-adhesive layer is applied to at least one of the surfaces of one of the steel strips selected in this way , which consists of MgO powder and ≤ 10% by mass of additives. The steel strip coated in this way is d) annealed to form the forsterite layer (Mg2SiO4).

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 cold-rolled, decarburization-annealed and primary recrystallized 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"), ≤ 0.30% 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% in each case, 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, 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 strip is wound into a coil and annealed again in the coil in order to effect secondary recrystallization and subsequent purification of the steel from precipitate-forming elements.

During this high-temperature annealing step, which typically takes place at 1100° C. to 1300° C., the anti-adhesive layer, which essentially consists of MgO, reacts with the surface of the steel substrate existing oxides, consisting mainly of silicon oxide, and thus forms the desired forsterite layer ("Mg2SiO4"), which is also referred to as a "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. Because during this period the production continues to run, larger quantities of defective electrical steel may be produced until the cause of the defect has been rectified.

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

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 that achieves the above-specified object according to the invention has at least the features specified in claim 5 .

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, during the production of grain-oriented electrical steel, it is possible to use fixed criteria to decide at one point in time whether an intermediate product obtained before high-temperature annealing is suitable for forming a forsterite layer that optimally adheres to the steel substrate of the electrical steel. 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 kaltgewalzten Stahlbändern, welche aus, in Masse-%, 2,5 - 4,0 % Si, ≤ 0,30 % Mn, ≤ 0,50 % Cu, ≤ 0,065 % Al, ≤ 0,1 % N sowie jeweils optional einem Element oder mehreren Elementen aus der Gruppe "Cr, Ni, Mo, P, As, S, Sn, 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 und primärrekristallisierend sowie entkohlend geglüht worden sind;
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 Bedingungen erfüllt:

   Bedingung 1:

   Der Kurvenverlauf des aus dem Signal "Si an Cs gebunden" und dem Signal "Si nicht an Cs gebunden" gebildeten Quotienten "Si an Cs gebunden" / "Si nicht an Cs gebunden" weist im Tiefenverlauf von 0,5 - 5,0 µm genau ein lokales Maximum auf.

   Bedingung 2:

   Der Wert des Quotienten "Si an Cs gebunden" / "Si nicht an Cs gebunden" ist in einem an der Oberfläche des Stahlbands beginnenden und bis in eine Tiefe von 2 µm reichenden Tiefenbereich durchgehend kleiner als 0,01.

3. c) Auftragen einer Klebschutzschicht auf mindestens eine der Oberflächen eines Stahlbands, das im Arbeitsschritt b) jeweils ausgewählt worden ist, wobei die Klebschutzschicht aus einem MgO-Pulver gebildet wird, das aus MgO-Partikeln und optional bis zu 10 Masse-% Additiven besteht;
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 cold-rolled steel strips, which consist of, in % by mass, 2.5 - 4.0% Si, ≤ 0.30% Mn, ≤ 0.50% Cu , ≦0.065% Al, ≦0.1% N and optionally one or more elements from the group “Cr, Ni, Mo, P, As, S, Sn, Sb, Se, Te, B or Bi” with the Provided that the content of the elements in this group is ≤ 0.2%, the remainder is iron and unavoidable impurities and has undergone primary recrystallization and decarburization annealing;
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 conditions are met:

   Condition 1:

   The curve of the formed from the "Si bound to Cs" signal and the "Si not bound to Cs" signal The quotient "Si bonded to Cs" / "Si not bonded to Cs" shows a local maximum in the depth profile of 0.5 - 5.0 µm.

   Condition 2:

   The value of the quotient "Si bonded to Cs"/"Si not bonded to Cs" is consistently less than 0.01 in a depth range beginning at the surface of the steel strip and extending to a depth of 2 μm.

3. c) applying an anti-tack layer to at least one of the surfaces of a steel strip selected in step b), the anti-tack layer being formed from an MgO powder consisting of MgO particles and optionally up to 10% by mass of additives;
4. d) Annealing of the steel strip, with the forsterite layer (Mg2SiO4) being formed from the anti-adhesive layer applied in step c) through the annealing.

The invention is based on the knowledge that by time-of-flight secondary ion mass spectroscopy (English "Time of Flight Secondary Ions Mass Spectrometry", short "ToF-SIMS"), in which the surface to be examined of the intermediate product present after the decarburizing annealing with Cs Ions are bombarded with an acceleration voltage of 2keV and for analysis with Bi+ ions with an acceleration voltage of 25keV, the adhesive strength of the forsterite layer produced in the following work steps can be predicted. This prediction is based on an evaluation of the proportion of the element Si on the examined surface of the steel substrate which is bound with the element Cs in relation to the proportion of the element Si which is not bound with Cs. The larger this relation is for the examined surface before the annealing step, the better the adhesion of the forsterite layer after the annealing step (step e)).

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.

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 and decarburized with a composition that is typical for grain-oriented electrical steel sheets.

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 e)) 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.

1. (1) Der Kurvenverlauf des Quotienten aus dem Signal "Si an Cs gebunden" zum Signal "Si nicht an Cs gebunden" weist im Tiefenverlauf von 0,5 µm bis 5,0 µm genau ein lokales Maximum auf.
2. (2) Der Wert des Quotienten aus dem Signal "Si an Cs gebunden" zum Signal "Si nicht an Cs gebunden" ist im Tiefenbereich von der Oberfläche bis 2 µm Tiefe durchgehend kleiner als 0,01.

The requirements that are checked in the intermediate state "after decarburization annealing" in step b) and qualify the steel strip provided in step a) for further processing are therefore:

1. (1) The curve of the quotient of the signal "Si bound to Cs" to the signal "Si not bound to Cs" shows exactly one local maximum in the depth range from 0.5 µm to 5.0 µm.
2. (2) The value of the quotient of the "Si bound to Cs" signal to the "Si not bound to Cs" signal is consistently less than 0.01 in the depth range from the surface to a depth of 2 µm.

Due to the reaction of the element Si present on the surface of the steel substrate with Mg, which occurs in the course of the high-temperature annealing (step e)), and which is applied to the material in the form of MgO, a similar reaction is found in the grain-oriented electrical strip processed according to the invention Relationship, which, however, is then based on the corresponding signal ratio of the element Mg.

1. A) der Kurvenverlauf des aus dem Signal "Mg an Cs gebunden" und dem Signal "Mg nicht an Cs gebunden" gebildeten Quotienten "Mg an Cs gebunden" / "Mg nicht an Cs gebunden" in einer ausgehend von der Oberfläche der Forsteritschicht gemessenen Sputtertiefe von 1 µm bis 2 µm niedriger ist als in einer ebenfalls ausgehend von der Oberfläche der Forsteritschicht gemessenen Sputtertiefe von 5 µm bis 6 µm, und
2. B) der Quotient "Mg an Cs gebunden" / "Mg nicht an Cs gebunden" im ausgehend von der Oberfläche der Forsteritschicht gemessenen Tiefenbereich von 1 - 2 µm unter 0,05 liegt, während er im ebenfalls ausgehend von der Oberfläche der Forsteritschicht gemessenen Tiefenbereich von 5 - 6 µm über 0,05 liegt.

Accordingly, a grain-oriented electrical strip according to the invention with very good adhesion of the forsterite film formed on it 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

1. A) The curve of the quotient "Mg bound to Cs" / "Mg not bound to Cs" formed from the signal "Mg bound to Cs" and the signal "Mg not bound to Cs" at a sputtering depth measured from the surface of the forsterite layer 1 µm to 2 µm lower than a sputtering depth of 5 µm to 6 µm, also measured from the surface of the forsterite layer, and
2. B) the quotient "Mg bound to Cs" / "Mg not bound to Cs" in the depth range of 1 - 2 µm measured from the surface of the forsterite layer is below 0.05, while it is in the depth range also measured from the surface of the forsterite layer of 5 - 6 µm is above 0.05.

Typically, the steel substrate of a grain-oriented electrical steel sheet according to the invention consists of a steel which has the alloy specified above for step a) of the method according to the invention.

The stipulations A) and B) developed according to the invention as criteria for evaluating the adhesion of the forsterite layer on the steel substrate of a completely processed grain-oriented electrical strip according to the invention can be

Meet the powder that is applied in step c) of the method according to the invention to the previously provided (step a)) and selected (step b)) steel strip. This MgO powder consists of at least 90% by mass of MgO, it being possible for the optionally remaining remainder of the powder to be filled with at least one additive. The sum of the contents of the additives is at most 10% by mass. Additives that can be added to the MgO powder include, for example, titanium oxide, ammonium chloride or antimony chloride, the addition of which controls the density of the later forsterite layer and the gas exchange between the annealing atmosphere during high-temperature annealing and the metal.

1. i) für den für die Partikelgrößenverteilung des im Arbeitsschritt c) aufgetragenen MgO-Pulvers ermittelte D50-Wert gilt: 2 µm < D50 < 7 µm;
2. ii) das MgO-Pulver im Arbeitsschritt c) mit einem Flächengewicht FG_MGO aufgetragen wird, für das gilt: 4 g/m² < FG_MgO < 18 g/m^2;
3. iii) das im Arbeitsschritt c) aufgetragene MgO-Pulver eine Zitronensäureaktivität CAA aufweist, welche so groß ist, dass der pH-Wert von 200 ml einer auf 30 °C erwärmten Zitronensäurelösung innerhalb von 600 s nach der Zugabe von 2,0 g des MgO-Pulvers den Wert 7 übersteigt, wobei die Zitronensäurelösung angesetzt wird, indem 56 g Zitronensäure (C8H8O7 * 1H2O), 0,5 g Natriumbenzoat (NaC7H5O2) und 4 ml Phenolphthalein (1% in Ethanol) in destilliertem Wasser gelöst und auf 2 Liter aufgefüllt werden.

The stipulations A) and B) mentioned by the invention as a criterion for the selection of cold-rolled steel sheets that are particularly suitable for the production of grain-oriented electrical steel sheet and the associated strictest requirements for optimal adhesion of the forsterite layer can be met with particular certainty that in the method according to the invention

1. i) the following applies to the D50 value determined for the particle size distribution of the MgO powder applied in step c): 2 µm < D50 < 7 µm;
2. ii) the MgO powder in step c) is applied with a basis weight FG_MGO for which the following applies: 4 g/m ² <FG_MgO <18 g/m ^2;
3. iii) the MgO powder applied in step c) has a citric acid activity CAA, which is so great that the pH of 200 ml of a citric acid solution heated to 30 °C within 600 s after the addition of 2.0 g of the MgO -Powder exceeds the value 7, the citric acid solution is prepared by dissolving 56 g of citric acid (C8H8O7 * 1H2O), 0.5 g of sodium benzoate (NaC7H5O2) and 4 ml of phenolphthalein (1% in ethanol) in distilled water and making up to 2 liters become.

Each of the measures i) - iii) can, seen alone, contribute to a grain-oriented electrical sheet according to the invention with optimal adhesion To generate forsterite layer, this succeeds particularly safely if all three measures i) - iii) are carried out.

The particle size distribution of the MgO powder can be determined in measure i) using methods known per se. For example, there are measuring instruments available on the market, such as the Mastersizer 2000 (see https://www.malvernpanalytical.com/de/support/productsupport/mastersizer-range/mastersizer-2000, accessed on December 7, 2019). Disposal.

In measure iii), the pH value can be recorded with any pH measuring device available on the market for this purpose, which enables a continuously updated measurement over a period beginning with the addition of the MgO powder to the citric acid solution.

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.

Surprisingly, it was shown here that, as long as conditions 1 and 2 were met, the high-temperature anneal itself has no influence on the predicted adhesion behavior of the forsterite layer if the maximum temperature of the high-temperature anneal is above 1300 K.

Even if this has not yet been conclusively researched, it is assumed that near-surface Si, which preferentially binds to the sputtering material Cs in the ToF-SIMS process, does not contribute to the formation of a well-interlocked forsterite layer. Therefore, it should be on the surfaces of steel strips for the production of grain-oriented electrical steel strips, which are to be covered with a forsterite layer, can be avoided as far as possible. This can be achieved by annealing under an annealing atmosphere with a low dew point, at least in the last section of the annealing, during the decarburization annealing, which is carried out in a conventional manner and which the steel strip provided according to the invention runs through.

Fig. 1

ein Diagramm, mit dem Verlauf des Quotienten "Si an Cs" / "Si nicht an Cs" der an dem für die Erzeugung des Beispiels 1 bereit gestellten kaltgewalzten und entkohlungsgeglühten Stahlband aus einer ToF-SIMS-Messung gewonnenen Signale "Si an Cs" zu "Si nicht an Cs", Wert < 0,01 im Bereich von der Oberfläche bis 2 µm Tiefe (Achseneinheit x-Achse: 1 nm = 1/1000 µm)

Fig. 2

ein Diagramm mit den Ergebnissen der Ermittlung der Zitronensäureaktivität CAA für drei Beispiele;

Fig. 3

ein Diagramm mit dem Verlauf des Quotienten "Mg an Cs" / "Mg nicht an Cs" der an dem gemäß Beispiel 1 erzeugten kornorientierten Elektroblech aus einer ToF-SIMS-Messung gewonnenen Signale "Mg an Cs" zu "Mg nicht an Cs" mit einem durchschnittlichen Wert zwischen 1 µm und 2 µm, welcher niedriger ist als der Verlauf des Quotienten "Mg an Cs" / "Mg nicht an Cs" in einer Tiefe von 5 µm und 6 µm (Achseneinheit x-Achse: 1 nm = 1/1000 µm)

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

1

a diagram showing the course of the quotient "Si to Cs" / "Si not to Cs" of the signals "Si to Cs" obtained from a ToF-SIMS measurement on the cold-rolled and decarburization-annealed steel strip provided for the production of Example 1 "Si not on Cs", value < 0.01 in the range from the surface to a depth of 2 µm (axis unit x-axis: 1 nm = 1/1000 µm)

2

a diagram with the results of the determination of the citric acid activity CAA for three examples;

3

a diagram with the course of the quotient "Mg on Cs" / "Mg not on Cs" of the signals "Mg on Cs" to "Mg not on Cs" obtained from a ToF-SIMS measurement on the grain-oriented electrical sheet produced according to Example 1 an average value between 1 µm and 2 µm, which is lower than the course of the quotient "Mg on Cs" / "Mg not on Cs" at a depth of 5 µm and 6 µm (axis unit x-axis: 1 nm = 1/ 1000 µm)

To check whether grain-oriented electrical steel strips can be reliably created on the basis of the conditions, requirements and measures developed by the invention, in which an optimized adhesion of the If there is a forsterite layer on the respective steel substrate, samples P1 - P7 were divided from eight cold-rolled steel strips originating from the normal production process, the respective composition of which is given in Table 1.

On the cold-rolled samples P1 - P8 provided in this way, by ToF-SIMS examination, in which the surface of the respective steel strip was 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, up to a depth of 10 µm measured from the surface of the respective sample, the course of the curve from the signal "Si bonded to Cs" and the signal "Si not bonded to Cs" is determined and the resulting course of the quotient "Si to Cs bound" / "Si not bound to Cs".

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

Based on the curves determined for the samples P1 - P8 of the respective quotient "Si bound to Cs" / "Si not bound to Cs" it was checked whether these curves meet condition 1 "the curve of the quotient "Si bound to Cs" / "Si not bonded to Cs" has exactly one local maximum in the depth profile of 0.5 - 5.0 µm and condition 2 "the value of the quotient "Si bonded to Cs" / "Si not bonded to Cs" is in one consistently below 0.01" starting at the surface of the steel strip and extending down to a depth of 2 µm. The results of this evaluation are summarized in Table 2.

The surfaces of samples P1 - P8 examined in this way were then coated with an aqueous MgO suspension, the mass of which was adjusted by means of squeezing rollers.

The MgO powder used consisted of 94% by mass MgO and 6% by mass TiO ₂ .

For each of the MgO powders used in samples P1 - P8, it was checked whether the requirements i) "for the D50 value determined for the particle size distribution of the MgO powder applied in step c) apply: 2 µm < D50 < 7 µm", ii) "the MgO powder is applied with a basis weight FG_MGO, for which the following applies: 4 g/m ² <FG_MgO <18g/m ² " and iii) "the MgO powder has a citric acid activity CAA, which is large that the pH value of 200 ml of a citric acid solution heated to 30 °C exceeds the value 7 within 600 s after the addition of 2.0 g of MgO powder, the citric acid solution is prepared by mixing 56 g of citric acid ( C8H8O7 * 1H2O), 0.5 g sodium benzoate (NaC7H5O2) and 4 ml phenolphthalein (1% in ethanol) dissolved in distilled water and made up to 2 liters" are met. The result of this review is summarized in Table 3. 2 shows an example of the result of the investigation of the citric acid activity CAA for samples 1, 2 and 7, with the MgO powder used in samples 1 and 2 complying with requirement iii) of the invention, whereas this is the case with the MgO powder used in sample 7 has been used is not the case.

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.

After cooling, a ToF-SIMS investigation 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 for the samples P1 - P8 in the course of the high-temperature annealing, the curve of the forsterite layers formed from the signal "Mg bound to Cs" and the signal "Mg not to Cs bound" formed quotients "Mg bound to Cs" / "Mg not bound to Cs". In 3 the corresponding course of the quotient "Mg bound to Cs" / "Mg not bound to Cs" over the sputtering depth is shown as an example for sample 1.

For each of the samples P1 - P8, 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 then used to check whether the The curves of the quotients "Mg bonded to Cs" / "Mg not bonded to Cs" determined from the high-temperature annealing of the grain-oriented electrical sheets formed from samples P1 - P8 required A "the curve profile of the quotient "Mg bonded to Cs" / "Mg not bonded to Cs bound" is lower at a sputtering depth of 1 µm to 2 µm, measured from the surface of the forsterite layer, than at a sputtering depth of 5 µm to 6 µm, also measured from the surface of the forsterite layer", and requirement B "the quotient "Mg bound to Cs" / "Mg not bound to Cs" is below 0.05 in the depth range of 1 - 2 µm measured from the surface of the forsterite layer, while it is above 0.05 in the depth range of 5 - 6 µm, also measured from the surface of the forsterite layer 0.05. The result of these investigations is summarized in Table 4.

Finally, the strength of the adhesion of the forsterite layer on the initially provided, cold-rolled steel substrate was determined on the samples P1 - P8 produced and tested in the manner explained above. 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 5.

It is found that the samples P1-P4, 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 P5-P8 not according to the invention. Table 1 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 condition 2 P1 Fulfills Fulfills p2 Fulfills Fulfills P3 Fulfills Fulfills P4 Fulfills Fulfills P5 2x Max Fulfills P6 not fulfilled Fulfills P7 not fulfilled Fulfills P8 Fulfills not fulfilled sample D50 according to measure i) FG_MgO according to measure ii) Increase in pH within 600 s after adding MgO according to measure iii) According to the invention? P1 3.7 µm 7.7 g/m2 Fulfills YES p2 2.5 µm 10.9 g/m2 Fulfills YES P3 6.6 µm 17.1 gsm Fulfills YES P4 3.7 µm 13.4 gsm Fulfills YES P5 3.7 µm 13.4 ^gsm Fulfills NO P6 1.5 µm 13.4 gsm Fulfills NO P7 5.2 µm 11.0 g/m2 not fulfilled NO P8 6.6 µm 11.5 g/m2 Fulfills NO sample Condition A Condition B P1 Fulfills Fulfills p2 Fulfills Fulfills P3 Fulfills Fulfills P4 Fulfills Fulfills P5 Fulfills Fulfills P6 not fulfilled not fulfilled P7 not fulfilled not fulfilled P8 Fulfills Fulfills sample Bond strength of the forsterite layer [Spalling from bending radius ] P1 7.5mm p2 9.0mm P3 11.0mm P4 10.5mm P5 16.0mm P6 22.5mm P7 16.5mm P8 21.0mm

Claims (5)

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, ≦0.1% N and optionally one or more elements from the group “Cr, Ni, Mo, P, As, S, Sn, 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; 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 conditions are met: Condition 1: The curve of the quotient "Si bound to Cs" / "Si not bound to Cs" formed from the signal "Si bound to Cs" and the signal "Si not bound to Cs" has a depth range of 0.5 - 5 .0 µm exactly a local maximum. Condition 2: The value of the quotient "Si bonded to Cs"/"Si not bonded to Cs" is consistently less than 0.01 in a depth range starting at the surface of the steel strip and extending to a depth of 2 µm. c) applying an anti-tack layer to at least one of the surfaces of a steel strip selected in step b), the anti-tack layer being formed from an MgO powder consisting of MgO particles and optionally up to 10% by mass of additives; d) Annealing of the steel strip, with the forsterite layer (Mg2SiO4) being formed from the anti-adhesive layer applied in step c) through the annealing. Method according to Claim 1, characterized in that the following applies to the D50 value determined for the particle size distribution of the MgO powder applied in step c): $$2\mathrm{\mu }\mathrm{m}<\mathrm{D50}<7\mathrm{\mu }\mathrm{m}.$$

Method according to one of the preceding claims, characterized in that the MgO powder is applied in step c) with a basis weight FG_MGO for which applies: $$4\mathrm{G}/{\mathrm{m}}^2<\mathrm{FG\_MgO}<18\mathrm{G}/{\mathrm{m}}^2$$

Method according to one of the preceding claims, characterized in that the MgO powder applied in step c) has a citric acid activity CAA which is so great that the pH value of 200 ml of a heated to 30 °C Citric acid solution exceeds the value 7 within 600 s after adding 2.0 g of the MgO powder, the citric acid solution is prepared by adding 56 g of citric acid (C8H8O7-*1H2O), 0.5 g of sodium benzoate (NaC7H5O2) and 4 ml Dissolve phenolphthalein (1% in ethanol) in distilled water and make up to 2 liters. Grain-oriented electrical steel with very. good adhesion of a forsterite layer formed on it, 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 "Mg bound to Cs" / "Mg not bound to Cs" formed from the signal "Mg bound to Cs" and the signal "Mg not bound to Cs" at a sputtering depth measured from the surface of the forsterite layer 1 µm to 2 µm lower than a sputtering depth of 5 µm to 6 µm, also measured from the surface of the forsterite layer, and B) the quotient "Mg bound to Cs" / "Mg not bound to Cs" in the depth range of 1 - 2 µm measured from the surface of the forsterite layer is below 0.05, while it is in the depth range also measured from the surface of the forsterite layer of 5 - 6 µm is above 0.05.

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