EP4202066A1 - Method for producing a grain-oriented electrical strip, cold-rolled steel strip and grain-oriented electrical strip - Google Patents

Abstract

The invention proposes a method for producing grain-oriented electrical steel with an optimally adhering forsterite film. For this purpose, a) a 1 - 3 mm thick hot-rolled steel strip made of, in % by mass, 2.5 - 4.0% Si, ≤ 0.30% Mn, ≤ 0.50% Cu, ≤ 0.1% Sn, ≤ 0.065% Al, ≤ 0.0150% N, ≤ 0.10% C and optionally at least one element from the group "Cr, Ni, Mo, P, As, S, Sb, Se, Te, B, Bi" in Content of ≤ 0.2% each, remainder iron and unavoidable impurities, the steel strip containing at least 0.01% by mass Cu or at least 0.003% by mass Sn, b) cold-rolled to form a cold-rolled steel strip, with the over the last pass of the cold rolling, the degree of deformation is adjusted in such a way that the cold-rolled steel strip is heated to a material temperature T_aging of 340 K < T_aging < 675 K. The cold-rolled steel strip is c) annealed under an annealing atmosphere of 40-90% vol Annealing temperature in the temperature range of 300 - 1000 K with > 40 Kls. On one of the surfaces of the cold-rolled steel strip, d) an anti-adhesive layer is formed from an MgO powder, which consists of MgO particles and optionally up to 10% by mass of additives. A forsterite layer (Mg2SiO4) is formed from the anti-adhesive layer applied in step d) by annealing. The invention also specifies a criterion for determining a cold-rolled steel strip that is suitable for the production of grain-oriented electrical steel with a forsterite layer that adheres particularly well to its steel substrate, and criteria for determining grain-oriented electrical steel with a forsterite layer that adheres particularly well.

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 below, "electrical steel" or "plates" are meant in the same way, which can be separated from such an electrical steel or have widths or lengths that deviate from the dimensions typical for electrical steel.

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

The cold-rolled steel substrate of grain-oriented electrical steels 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%, the remainder being iron and unavoidable impurities Ein An example of a steel alloy intended for the production of grain-oriented electrical strips with low core loss and high magnetic flux density is from DE 32 29 295 C2 known. This steel contains (in mass %) 2.5 to less than 4.0% Si, 0.03 to less than 0.15% Mn, 0.03 to less than 0.5% Sn, 0.02 to less 0.3% Cu and the balance Fe and unavoidable impurities, the %Cu/%Sn ratio of the %Cu content of Cu to the %Sn content of Sn being in the range of 0.5 - 1.

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 is wound into a coil and annealed again in the coil to create a To bring about secondary recrystallization and subsequent cleaning 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 consists essentially of MgO, reacts with the oxides present on the surface of the steel substrate, which mainly consist of silicon oxide, and thus forms the desired forsterite layer ("Mg2SiO4"), which also referred to 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, it is possible that larger quantities of defective electrical steel are 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 cold-rolled steel strip should be mentioned that is suitable for the production of a grain-oriented electrical steel sheet in which the forsterite layer adheres particularly well to the steel substrate.

Finally, 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 when carrying out the method according to the invention and its expansion options explained here, a person skilled in the art adds those work steps not explicitly mentioned here that he knows from 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 and is produced by the method according to the invention has at least the features specified in claim 3 .

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

1. a) Bereitstellen eines 1 - 3 mm dicken warmgewalzten Stahlbands, welches aus, in Masse-%, 2,5 - 4,0 % Si, ≤ 0,30 % Mn, ≤ 0,50 % Cu, ≤- 0,1% Sn, ≤ 0,065 % AI, ≤ 0,0150 % N, ≤ 0,10 % C sowie jeweils optional einem Element oder mehreren Elementen aus der Gruppe "Cr, Ni, Mo, P, As, S, Sb, Se, Te, B oder Bi", Rest Eisen und unvermeidbaren Verunreinigungen mit der Maßgabe besteht, dass die Gehalte der optional vorhandenen Elemente der Gruppe "Cr, Ni, Mo, P, As, S, Sb, Se, Te, B oder Bi" jeweils ≤ 0,2 % betragen, wobei das Stahlband mindestens 0,01 Masse-% Cu oder mindestens 0,003 Masse-% Sn enthält;
2. b) Kaltwalzen des warmgewalzten Stahlbands zu einem kaltgewalzten Stahlband in mehreren Stichen, wobei der über den letzten Stich des Kaltwalzens eingestellte Umformgrad so eingestellt wird, dass das kaltgewalzte Stahlband in Folge seiner über den letzten Walzstich eintretenden Erwärmung auf eine Materialtemperatur T_aging erwärmt wird, für die gilt 340 K < T_aging < 675 K;
3. c) entkohlendes Glühen des erhaltenen kaltgewalzten Stahlbands unter einer Glühatmosphäre, die aus (in Vol.-%) 40 - 90% H₂, Rest N₂, besteht, bei einer Glühtemperatur von 900 K bis 1200 K, wobei das kaltgewalzte Stahlband bei der Erwärmung auf die Glühtemperatur im Temperaturbereich von 300 - 1000 K mit einer Erwärmungsgeschwindigkeit dR erwärmt wird, die mehr als 40 Kls beträgt;
4. d) Auftragen einer Klebschutzschicht auf mindestens eine der Oberflächen des kaltgewalzten Stahlbands, wobei die Klebschutzschicht aus einem MgO-Pulver gebildet wird, das aus MgO-Partikeln und optional bis zu 10 Masse-% Additiven besteht;
5. e) Glühen des mit der Klebschutzschicht versehenen Stahlbands, wobei sich über das Glühen aus der im Arbeitsschritt d) 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 a 1 - 3 mm thick hot-rolled steel strip consisting of, in % by mass, 2.5 - 4.0% Si, ≤ 0.30% Mn, ≤ 0.50% Cu, ≤- 0.1% Sn, ≤ 0.065% Al, ≤ 0.0150% N, ≤ 0.10% C and optionally one or more elements from the group "Cr, Ni, Mo, P, As, S, Sb, Se, Te, B or Bi", remainder iron and unavoidable impurities with the proviso that the contents of the optionally present elements of the group "Cr, Ni, Mo, P, As, S, Sb, Se, Te, B or Bi" are ≤ 0 .2%, the steel strip containing at least 0.01% by mass Cu or at least 0.003% by mass Sn;
2. b) Cold rolling of the hot-rolled steel strip into a cold-rolled steel strip in several passes, with the degree of deformation set over the last pass of the cold rolling being adjusted in such a way that the cold-rolled steel strip is heated to a material temperature T _aging as a result of its heating occurring over the last rolling pass, for which holds 340K < T _aging <675K;
3. c) decarburizing annealing of the cold-rolled steel strip obtained under an annealing atmosphere consisting of (in vol%) 40-90% H ₂ , remainder N ₂ , at an annealing temperature of 900 K to 1200 K, the cold-rolled steel strip at the Heating to the annealing temperature in temperature range of 300 - 1000 K is heated with a heating rate dR, which is more than 40 Kls;
4. d) applying an anti-tack layer to at least one of the surfaces of the cold-rolled steel strip, the anti-tack layer being formed from an MgO powder consisting of MgO particles and optionally up to 10% by mass of additives;
5. e) Annealing of the steel strip provided with the anti-adhesive layer, the forsterite layer (Mg2SiO4) being formed from the anti-adhesive layer applied in step d) during the annealing.

The invention is based on the finding that the formation of an optimally adhering Forster film on the steel substrate of a grain-oriented electrical strip according to the invention can be ensured beyond the procedure known from the prior art by three measures that are already required during the production of the cold-rolled steel strip , which forms the steel substrate of the electrical strip according to the invention and is then covered with the forsterite layer.

The invention makes use of the fact that there is an accumulation of Si in the outer surface layers that adjoin the surfaces of a cold-rolled steel strip processed according to the invention, since the steel strip and the preliminary products from which it was produced not only hot-rolled but also annealed. This is accompanied by oxidation, in particular of the edge region of the steel strip close to the surface, with Si already oxidizing at temperatures which are lower than the temperatures at which oxidation of iron ("Fe") occurs. These Si enrichments contribute to the formation of the forsterite layer and its connection to the steel substrate.

The first measure provided by the invention for the development of an optimally adhering forsterite film is that, based on the conventional Procedure the cold rolling of the steel strip, which is completed in several stages, is carried out according to the invention in such a way that the reduction in thickness brought about in the last stage of cold rolling is so great and, as a result, the forming heat generated in the cold-rolled steel strip as a result of the forming work is so great that the cold strip as a result of its over the last rolling pass is heated to a material temperature T _aging for which applies 340 K < T _aging < 675 K Suitable degrees of deformation ΔU = ([thickness of the cold strip before the last cold rolling stage] - [thickness of the cold strip after the last cold rolling stage]) / [thickness of the cold strip before the last cold rolling stage] are typically in the range of 20% to 50%.

As a second measure, the invention provides that during the decarburizing annealing, which is carried out in the usual way, in which the cold-rolled steel strip is heated in an annealing atmosphere consisting of (in vol. %) 40-90% H _2, , remainder N ₂ in particular 50-80% H ₂ , remainder N ₂ , is heated at an annealing temperature of 900-1200 K, in particular 1100-1200 K, the cold-rolled steel strip being heated to the annealing temperature in the temperature range of 300-1000 K with a Heating rate dR is heated, which is more than 40 Kls in particular more than 50 K / s. In practice, the maximum set heating rates are up to 1000 K/s. The decarburizing annealing can be combined with a recrystallizing annealing in a manner known per se, it being possible for the decarburizing and the recrystallizing annealing to be carried out in one go. Typically, in practice, the decarburizing annealing and the recrystallizing annealing optionally carried out in combination therewith, optionally simultaneously taking place, are carried out continuously through a continuous furnace.

The heating of the material during cold rolling results in a near-surface enrichment of Si. The goal of rapid heating during decarburization annealing is then not to change or destroy this layer containing the Si enrichments.

As a third measure of the measures according to the invention for optimizing the adhesion of the forsterite layer, the alloy of the steel strip, which forms the basis of a grain-oriented electrical strip according to the invention, is additionally optimized. 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 0.01-0.50% copper ("Cu") or 0.003-0.1% tin ("Sn") are preferred Concentrations of 0.01 - 0.50% copper ("Cu") and 0.003 - 0.1% 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. According to the findings of the invention, however, the presence of both Cu and Sn in the specified contents is particularly favorable for an optimized connection of the forsterite layer to the steel substrate, with the steel substrate requiring a Cu content that is significantly higher than the content of Sn in the steel substrate. Accordingly, in this embodiment, which is particularly advantageous with regard to the result of the measures according to the invention, the invention stipulates that the %Cu content of Cu must be more than three times greater than the tin content, with particularly good effects being achieved by the presence of Cu and Sn if the mass ratio %Cu/%Sn of the %Cu content of Cu and the %Sn content of Sn of the steel strip applies: %Cu/%Sn > 4. The Cu content is limited to a maximum of 0.5% by mass, in particular at most 0.3% by mass, in order to avoid negative effects on the magnetic properties of a grain-oriented electrical strip according to the invention. It has proven to be particularly practical if the base alloy of the steel strip contains at least 0.05% by weight Cu. Likewise, at least 0.003% by mass, in particular at least 0.005% by mass, of Sn is required in order to achieve the effects used according to the invention. At the same time, the content of Sn is limited to at most 0.1% by mass, in particular at most 0.08% by mass, in order to ensure good workability of the steel strip when it is produced.

The setting of the contents of Cu and Sn, which is set in relation to a preferred embodiment, also serves to To protect the Si-enriched layer formed by cold rolling from being altered. If the Cu content is lower in relation to the Sn content, there would be a risk that Sn would displace Si as a surface-sensitive element, so that only limited amounts of Si would be available on the surface of the steel strip for the formation and bonding of the forsterite layer.

The combination of measures according to the invention in the production of the cold-rolled steel strip, on which the MgO layer is then applied and the forsterite layer is formed in the subsequent high-temperature annealing (step e) of the method according to the invention), enables an optimized adhesive strength of the forsterite layer to be reliably achieved .

The powder applied to the cold-rolled steel strip to produce the forsterite layer consists of at least 90% by mass of MgO and can contain up to 10% by mass of additives in a manner known per se. These additives can be, for example, titanium oxide, ammonium chloride or antimony chloride, the addition of which controls the density of the subsequent forsterite layer and the gas exchange between the annealing atmosphere during high-temperature annealing and the metal.

The annealing of the steel strip, which is finally completed in step e), 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 invention also proposes a criterion that enables a precise assessment of the suitability of a 0.10-0.35 mm thick cold-rolled steel strip, provided in the decarburized annealed state, for the production of a grain-oriented electrical strip that has a forsterite layer that adheres optimally to the cold-rolled steel strip .

Such a cold-rolled steel strip which is suitable according to the invention for use in the production of grain-oriented electrical strip consists in a conventional manner of, in % by mass, 2.5-4.0% Si, ≦0.30% Mn, ≦0.50% Cu , ≤ 0.1% Sn, ≤ 0.065% Al, ≤ 0.1% N 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, the steel strip containing at least 0.01% by mass Cu or at least 0.003% by mass Sn. For the reasons already explained above, the cold-rolled steel strip intended for use according to the invention for the production of a grain-oriented electrical strip has an Sn content of at least 0.003% by mass or a Cu content of at least 0.01% by mass, preferably a Sn -Content of at least 0.003% by mass and a Cu content of at least 0.01% by mass, provided here also preferred for the mass ratio %Cu/% formed from the %Cu content of Cu and the %Sn content of Sn Sn is %Cu/%Sn>3. Here, too, the configurations of the Cu and Sn contents which have already been explained above in connection with the method according to the invention have proven to be particularly practical.

According to the findings of the invention, a steel strip obtained as an intermediate product in the production of a grain-oriented electrical strip after decarburizing annealing is suitable for the reliable production of a grain-oriented electrical strip in which particularly good adhesion of the forsterite layer formed on it is guaranteed if it is 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, the following condition 1 is met:
Condition 1: The curve of the quotient "Si on" formed from the signal "Si bound to Cs" and the signal "Si not bound to Cs". Cs bound" / "Si not bound to Cs" shows exactly a local maximum in the depth profile of 0.5 - 3.0 µm.

Cold-rolled steel strips produced according to the invention and available after completion of work step c) reliably meet this requirement.

However, condition 1 defined by the invention also opens up the possibility of using a measurement to precisely predict whether a steel strip produced in any other way, which has a composition typical of grain-oriented electrical strips and is intended for coating with the MgO layer, the potential for the development of an optimally adhering forsterite layer.

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 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 further work steps on the steel strip provided in each case 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 "proportion of the element Si which is not bonded to Cs" is understood to mean only atomic Si, ie Si which is not bonded to other atoms such as Cs, O etc., but is completely unbound.

ToF-SIMS is an analytical method for the chemical characterization of surfaces. It is based on the time-resolved detection of secondary ions, which escape from the surface under investigation by bombardment with high-energy primary ions (e.g. Bi) are generated. 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.

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 (work step e)), and which is applied to the material in the form of MgO, a similar relationship is found in the finished grain-oriented electrical strip processed according to the invention.

• Maßgabe A) 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 in einer ausgehend von der Oberfläche der Forsteritschicht gemessenen Sputtertiefe von 2 µm bis 8 µm genau ein lokales Maximum auf, und
• Maßgabe B) das gemäß Maßgabe A) bestimmte Maximum des Verlaufs des Quotienten "Si an Cs gebunden" / "Si nicht an Cs gebunden" hat einen Maximalwert von 0,01 - 0,3.

Accordingly, a grain-oriented electrical strip according to the invention is characterized by very good adhesion of the forsterite film formed on it, produced by the method according to the invention, 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, the following provisions A) and B) are fulfilled:

• Requirement A) 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" points in a starting from the surface of the forsterite layer measured sputtering depth of 2 µm to 8 µm exactly a local maximum, and
• Requirement B) the maximum of the course of the quotient "Si bonded to Cs"/"Si not bonded to Cs" determined according to requirement A) has a maximum value of 0.01-0.3.

The steel substrate of a grain-oriented electrical strip according to the invention that is produced in this way typically consists of a steel produced above in connection with the step a) of the method according to the invention. The use of the method according to the invention reliably results in electrical steel strips whose forsterite film satisfies requirements A and B in an examination carried out in the manner indicated above.

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

1 shows an example of the course of the quotient "Si bonded to Cs"/"Si not bonded to Cs" for a sample produced according to the invention.

To check whether grain orientation is reliable based on the conditions, provisions and measures developed by the invention In order to create electrical steel strips with an optimized adhesive strength of the forsterite layer on the respective steel substrate, samples P1 - P6 were divided from seven cold-rolled steel strips originating from the normal manufacturing process.

The production of the cold-rolled steel strips, from which the samples P1 - P6 originated, was carried out in a conventional manner in that seven steels, the composition of which is given in Table 1, were melted and cast and rolled to form hot strips. The components of the alloy of the steels of the samples P1 - P6 not specified in Table 1 are to be assigned to the unavoidable impurities, the individual contents and total content of which are so severely limited according to the standard that they have no influence on the properties of the grain-oriented electrical steel sheets produced from the samples P1 - P6 have.

The hot strips were cold-rolled in 5 cold-rolling passes to form cold-rolled steel strip. The respective last stage of cold rolling was carried out in such a way that the cold-rolled strips were heated to a temperature T _aging by the forming work carried out in the course of this forming stage. The associated degree of deformation ΔU and the temperature T _aging are given in Table 2 for samples P1-P6.

The cold-rolled steel strips thus obtained then passed through an annealing furnace in which they were heated under an annealing atmosphere consisting of 60% by volume H2 and 40% by volume _N2 at a heating rate dR to an annealing temperature TG, at which they annealing time tG have been held in order to anneal them recrystallizing and decarburizing. The heating rate dR, the annealing temperature TG and the annealing time tG are also given in Table 2 for the samples P1 - P6.

On the samples P1 - P6 cut off from the cold strips produced in this way and made available for further processing, there is a ToF-SIMS examination at 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 curve of the determined from the signal "Si bound to Cs" and the signal "Si not bound to Cs" and the resulting course of the quotient "Si bound to Cs" / "Si not bound to Cs" determined. The ToF-SIMS investigation was carried out with the device "TOF.SIMS 5-300" from the company IONTOF, using the standard parameters of this device and an angle of incidence of 45°C. As described, so-called "dual-beam depth profiling" was used for depth measurement.

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

Based on the curves determined for samples P1 - P6 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 from the signal "Si bound to Cs " and the signal "Si not bound to Cs" formed quotients "Si bound to Cs" / "Si not bound to Cs" shows exactly a local maximum in the depth profile of 0.5 - 3.0 µm'. The result is fulfilled of this review is summarized in Table 3.

The surfaces of samples P1 - P6 examined in this way were then coated with an aqueous MgO suspension, the thickness 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 .

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 - P6 in the course of the high-temperature annealing, the condition A) "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 in an outgoing a local maximum at a sputtering depth of 2 µm to 8 µm measured from the surface of the forsterite layer', and B) "the maximum of the course of the quotient "Si bonded to Cs" / "Si not bonded to Cs" determined according to requirement A) has a maximum value of 0.01 - 0.3". The results of this test are also listed in Table 3.

Finally, the strength of the adhesion of the forsterite layer on the initially provided, cold-rolled steel substrate was determined on the samples P1 - P6 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 4.

It turns out that the samples P1 - P3, which meet the conditions and stipulations formulated by the invention, optimally on the respective Adhere steel substrate, while this is not the case with the non-inventive samples P4 - P6. Contents in % by mass, remainder iron and unavoidable impurities Table 1 Steel of the cold strip sample si Mn Cr Al S N Cu sn %Cu/%Sn P1 3.25 0.15 0.05 0.020 0.003 0.009 0.20 0.052 3.8 p2 3.25 0.09 0.12 0.041 0.003 0.015 0.15 0.027 5.5 P3 3.07 0.25 0.10 0.033 0.004 0.025 0.05 0.009 5.5 P4 3:12 0.21 0.10 0.055 0.005 0.022 0.30 0.055 5.5 P5 3:19 0.13 0.06 0.025. 0.009 0.037 0.11 0.020 5.5 P6 3.07 0.05 0.03 0.017 0.005 0.044 0.22 0.058 3.8 sample ΔU tagging dr TG tG [%] [K] [K/s] [K] [n] P1 33 493 220 1100 170 p2 27 360 55 1150 150 P3 29 410 42 1200 120 P4 22 310 50 1150 150 P5 47 700 55 1150 150 P6 33 493 30 1150 150 sample condition 1 requirement A) requirement B) According to the invention? P1 1 max 0.27 1 max YES p2 1 max 0.14 1 maxirrium YES P3 1 max 0.02 1 max YES P4 No max --- No max NO P5 3 maximums 0.09 3 maximums NO P6 No max --- No max NO sample Bond strength of the forsterite layer [Spalling from bending radius ] P1 9.0mm p2 10.0mm P3 8.0mm P4 19.5mm P5 15.0mm P6 18.0mm

Claims (5)

Process for producing a grain-oriented electrical strip that is covered with a forsterite layer, comprising the following work steps: a) Providing a 1 - 3 mm thick hot-rolled steel strip, which consists of, in % by mass, 2.5 - 4.0% Si, ≤ 0.30% Mn, ≤ 0.50% Cu, ≤ 0.1% Sn , ≤ 0.065% Al, ≤ 0.0150% N, ≤ 0.10% C and optionally one or more elements from the group "Cr, Ni, Mo, P, As, S, Sb, Se, Te, B or Bi", remainder iron and unavoidable impurities with the proviso that the contents of the optionally present elements of the group "Cr, Ni, Mo, P, As, S, Sb, Se, Te, B or Bi" are each ≤ 0, 2%, the steel strip containing at least 0.01% by mass Cu or at least 0.003% by mass Sn; b) Cold rolling of the hot-rolled steel strip into a cold-rolled steel strip in several passes, with the degree of deformation set over the last pass of the cold rolling being adjusted in such a way that the cold-rolled steel strip is heated to a material temperature T _aging as a result of its heating occurring over the last rolling pass, for which holds 340K < T _aging <675K; c) decarburizing annealing of _{the cold} -rolled steel strip obtained under an annealing atmosphere consisting of, in vol cold-rolled steel strip is heated to the annealing temperature in the temperature range of 300 - 1000 K with a heating rate dR, which is more than 40 Kls; d) applying an anti-tack layer to at least one of the surfaces of the cold-rolled steel strip, the anti-tack layer being formed from an MgO powder consisting of MgO particles and optionally up to 10% by mass of additives; e) Annealing of the steel strip provided with the anti-adhesive layer, the forsterite layer (Mg2SiO4) being formed from the anti-adhesive layer applied in step d) during the annealing. Method according to Claim 1, characterized in that the steel of the steel strip provided in step a) contains at least 0.01% by mass of Cu and at least 0.003% by mass of Sn and that for the %Cu content of Cu and the %Sn content The mass ratio %Cu/%Sn determined on the Sn of the steel of the steel strip is %Cu/%Sn > 3. Cold-rolled steel strip, 0.10 mm to 0.35 mm thick and provided in the decarburization-annealed condition, for the production of a grain-oriented electrical strip, the steel strip comprising, in % by mass, 2.5 - 4.0% Si, ≤ 0.30 % Mn, ≤ 0.50% Cu, ≤ 0.1% Sn, ≤ 0.065% Al, ≤ 0.1% N 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% in each case, with the steel strip containing at least 0.01% by mass Cu or at least 0.003% by mass Sn contains, characterized in that the steel strip in a ToF-SIMS analysis, 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, the following condition 1 is 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 - 3 .0 µm exactly a local maximum. Cold-rolled steel strip according to claim 3, characterized in that the steel of the steel strip contains at least 0.01% by mass of Cu and at least 0.003% by mass of Sn and that for the %Cu content of Cu and the %Sn content of Sn of the steel The mass ratio %Cu/%Sn determined for the steel strip is %Cu/%Sn > 3. 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 the following requirements A) and B) are met: Requirement A) 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 in a starting from the surface of Forsterite layer measured sputtering depth of 2 µm to 8 µm exactly a local maximum, and Requirement B) the maximum of the course of the quotient "Si bonded to Cs"/"Si not bonded to Cs" determined according to requirement A) has a maximum value of 0.01-0.3.

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