WO2019096735A1

WO2019096735A1 - Grain-oriented electrical steel strip and method for the production of such an electrical steel strip

Info

Publication number: WO2019096735A1
Application number: PCT/EP2018/080926
Authority: WO
Inventors: Christian Hecht; Carsten Schepers; Andreas Allwardt; Ludger Lahn; Heiner Schrapers
Original assignee: Thyssenkrupp Electrical Steel Gmbh; Thyssenkrupp Ag
Priority date: 2017-11-20
Filing date: 2018-11-12
Publication date: 2019-05-23
Also published as: DE102017220721A1

Abstract

The present invention relates to a grain-oriented electrical steel strip, wherein, during the production thereof, high-temperature annealing takes place in a temperature range of 700 to 900°C and the electrical steel strip, during this high-temperature annealing, has a particular nitrogen concentration N, a method for the production thereof and the use of such an electrical steel strip.

Description

Grain-oriented electrical steel strip and method for producing such

electrical steel

The present invention relates to a grain-oriented electrical steel, wherein during its production, a high-temperature annealing in a

Temperature range of 700 to 900 ° C and the electrical steel during this high temperature annealing has a certain nitrogen content N, a process for its preparation and the use of such an electrical tape.

With the invention, an optimization of the Stickstoffleveis succeeds during a bell annealing carried out in the course of the method according to the invention.

Process for the production of grain oriented electrical tapes and

corresponding electrical tapes are already known from the prior art.

EP 1 025 268 B1 discloses a method for the production of grain-oriented electrical steel sheet, which after a hot rolling step and a

Cold rolling step recrystallizing and decarburizing is annealed, then provided with a Glühseparator and finally final annealing. The setting of a certain Giühatmosphäre is not disclosed in this document.

WO 2017/037019 A1 likewise discloses a method for the production of grain-oriented electrical steel strip. This method comprises an annealing step after the cold rolling of the electrical strip, in which an oxide layer is formed on the surface. This oxide layer is determined by means of FTIR spectroscopy examined. From the FTIR investigation it is then determined how the

Area ratio between Fe ₂ Si0 ₄ and aSi0 ₂ in the layer is. In the annealing step disclosed in this document, a certain ratio of the maximum temperature attained in the annealing step and the dew point of the atmosphere in the annealing step is to be maintained.

EP 1752548 A1 and EP 1752549 A1 disclose processes for the production of grain-oriented electrical steel. These methods also each comprise an annealing step in which the cold-rolled electrical steel is annealed recrystallizing and decarburizing, and which preferably takes place in an ammonia atmosphere.

In the production of grain-oriented electrical steel, the control of the nitridic phase during the annealing is important because it already at temperatures below the secondary crystallization temperature with the

Annealing atmosphere can interact. Too low a set nitridic phase manifests itself in too low an inhibition effect and, consequently, in higher core losses, while an over-adjusted nitridic phase can both shift the secondary crystallization temperature above the inhibitor dissolution temperature and produce an inhomogeneous forsterite layer, resulting in insufficient

Gearing and thus may lead to a deteriorated adhesion of the glass layer on the base material.

The object of the present invention is therefore to a

To provide grain-oriented electrical steel, which is an optimized

Combination of low core losses and good

Adhesive strength of Forsterit layer has on the surface, in particular, the interlocking of the glass layer is to be improved with the base material. Furthermore, it is an object of the present invention to provide a method for To provide a corresponding grain-oriented electrical tape.

These objects are achieved by a grain-oriented electrical steel strip, during which a high-temperature annealing step is carried out in which the electrical steel strip has a nitrogen content N according to the following formula (1):

in which

Al _si Aluminum content (acid-soluble) in the preparation of the

Electro tapes used melt in ppm,

DP dew point in high temperature annealing step in ° C and

N (melt) nitrogen content in the production of electrical tape

Mean melt used in ppm.

Furthermore, the objects are achieved by the method according to the invention for producing a grain-oriented electrical strip, comprising at least the following steps:

(A) melting a molten steel containing (in wt% in each case) 2.0 to 4.0 Si, 0.010 to 0.100 C, up to 0.065 Al and up to 0.02 N, and each optionally up to 0.5 Cu, up to 0.060 S and also optionally in each case up to 0.3 Cr, Mn, Ni, Mo, P, As, Sn, Sb, Se, Te, B or Bi, the remainder contains iron and unavoidable impurities, (B) casting the molten steel into a starting material, for example into a slab, thin slab or a cast strip,

(C) hot rolling the primary material into a hot strip,

(D) coiling the hot strip into a coil,

(E) optional annealing of the hot strip,

(F) cold rolling the hot strip in one or more cold rolling steps to a cold strip,

(G) annealing the cold strip from step (F) at a temperature of 700 to 900

° C,

(H) optional application of an annealing separator layer to at least one

Surface of the cold strip from step (G),

(I) high-temperature annealing of optionally with the Glühseparator

coated cold-rolled strips to form a forsterite layer on the surface of the annealed cold-rolled strip,

(J) Optional application of an insulating layer on the forsterite layer

having surface of cold strip, and

(K) optional final annealing of the cold strip wherein in step (I) the electrical steel has a nitrogen content N according to the following formula (1):

in which

Al _si Aluminum content (acid-soluble) in the preparation of the

Electro tapes used melt in ppm,

DP dew point in high temperature annealing step in ° C and

N (melt) nitrogen content in the production of electrical tape

Mean melt used in ppm.

According to the invention, "electrical steel" is understood to mean an electrical steel produced by rolling suitably composed steel and blanks divided therefrom and intended for the production of parts for electrotechnical applications. Grain-oriented electrical tapes of the type in question are particularly suitable for applications in which a particularly low loss of magnetization is in the foreground and high demands are placed on the permeability or polarization. Such requirements exist in particular for parts for

Power transformers, distribution transformers, higher quality

Small transformers or in rotating electrical machines.

In the following, the method according to the invention will be described in detail. The method according to the invention may comprise, in addition to the further steps explicitly described herein, which are carried out in the conventional production of electrical tapes in order to achieve optimized magnetic properties or properties which are important for practical use. These include, for example, reheating the precursor obtained after the casting of the steel, descaling the hot strip before cold rolling or, in the case of multi-stage cold rolling, respectively performed between the cold rolling stages in a conventional manner

Intermediate annealing.

Step (A) of the process according to the invention comprises the melting of a molten steel containing (in each case in% by weight)

2.0 to 4.0 Si,

0.010 to 0.100 C,

up to 0.065 AI and

up to 0.02 N,

and optionally up to 0.5 Cu each, up to 0.060 S and

also optionally up to 0.3 Cr, Mn, Ni, Mo, P, As, Sn, Sb, Se, Te,

B or Bi,

Contains residual iron and unavoidable impurities.

In step (A) of the process according to the invention, preference is given to

Melted molten steel containing (in wt .-%) 2 to 4 Si, 0.01 to 0.1 C, 0.01 to 0.065 Al and 0.002 to 0.02 N, and in each case optionally 0.005 to 0.5 Cu, 0.005 to 0.060 S and also optionally each 0 to 0.3 Cr, Mn, Ni, Mo, P, As, Sn, Sb, Se, Te, B or Bi, the remainder contains iron and unavoidable impurities.

Step (A) of the process according to the invention can be carried out by all methods known to the person skilled in the art. For this purpose, a molten steel of known composition is preferably melted. This melt is then treated by secondary metallurgy. This treatment is first preferably carried out in a vacuum plant in order to adjust the chemical composition of the steel in the required narrow analysis margins and preferably to achieve low hydrogen contents of at most 10 ppm in order to reduce the risk of To minimize the occurrence of strand breakthroughs when casting the molten steel to a minimum.

Following treatment in the vacuum plant, use in a ladle furnace is desirable to ensure the casting temperature required in the case of casting delays, and by adding slag conditioning to clog the scoop casts in the mold during thin slab continuous casting and thus to avoid a cast-iron demolition.

According to the invention in step (A), the use of a ladle furnace for slag conditioning would also be possible, followed by treatment in a vacuum system for adjusting the chemical composition of the molten steel within narrow analytical limits. However, this combination is associated with the disadvantage that in the case of casting delays the

Temperature of the melt drops so far that the molten steel can not be poured.

It is also possible in step (A) to use only the ladle furnace. However, this has the disadvantage that the analysis accuracy is not as good as in the treatment in a vacuum system and also high

Hydrogen contents in the casting melt can occur with the risk of strand breakthroughs.

According to the invention, it is further preferred in step (A) to use only the vacuum system. On the one hand, however, this involves the risk that, in the case of casting delays, the temperature of the melt drops to such an extent that the molten steel can no longer be cast. On the other hand, there is a risk that the immersion spouts clog in the sequence and thus the sequence must be canceled. In step (B) of the process according to the invention, the molten steel produced in step (A) is then cast into a starting material. This starting material may according to the invention be for example a slab, a thin slab or a cast strip. For this purpose, preferably according to the invention, a strand is first produced from the melt by casting.

For the production of thin slabs, a strand is preferably poured for this purpose, which has a thickness of, for example, 25 mm to 150 mm.

According to the invention, the aim is to avoid the formation of nitridic precipitates prior to hot rolling and during hot rolling as much as possible in order to make extensive use of the possibility of a controlled production of such precipitates during the cooling of the hot strip. To support this, it is preferred according to an advantageous embodiment of the invention to make an inline thickness reduction of cast from the melt, but still core liquid strand.

As a known method for reducing the thickness offer the so-called "Liquid Core Reduction", hereinafter "LCR", and the so-called "Soft Reduction", hereinafter "SR" to. These possibilities of

Thickness reduction of a cast strand can be used alone or in combination. In the LCR, the strand thickness is reduced at the core liquid inside the strand just below the mold. LCR is used in the prior art in thin slab continuous casters primarily to achieve lower hot strip thicknesses, especially for higher strength steels. In addition, LCR can reduce the reduction in the number of passes or the rolling forces in the rolling mills of the hot strip mill with the result that the work roll wear of the rolling mills and the scale porosity of the rolling mills

Hot bands can be reduced and the tape can be improved. The thickness reduction achieved by LCR according to the invention is preferably in the range of 5 mm to 30 mm. Under SR is meant the targeted reduction in thickness of the strand in the swamp tip near Enderstarrung. The SR aims to reduce mitigation and core porosity. The achievable by the SR reduction, in particular the silicon Mitsenigerung in the subsequently hot-rolled precursors allows a homogenization of the chemical

Composition over the tape thickness, which is beneficial for the magnetic values. Good results of the SR are obtained when the at the

Application of SR achieved thickness reduction, for example 0.5 to 5 mm. As an indication of the time at which the SR is used in connection with the continuous casting carried out according to the invention, the following specification can be used: start of the SR zone at a solidification rate f _s of 0.2 and end of the SR zone at f _s equal to 0 , 7 to 0.8.

According to the invention, thin slabs are preferably produced in step (B) of the process according to the invention. In thin slab continuous casting the usually emerging from the casting mold strand is bent at lower points and guided in a horizontal direction. Characterized in that in an advantageous embodiment of the invention, the strand cast from the melt at a temperature of 700 to 1000 ° C, preferably 850 to 950 ° C, bent and directed, cracks can be avoided on the surface of the separated from the strand thin slabs which may otherwise be due, in particular, to edge cracks in the strand. In the temperature range mentioned, the steel used according to the invention has a good ductility at the strand surface or in the edge region, so that it can follow well the deformations occurring during bending and straightening. Of the thus cast strand thin slabs are divided in a conventional manner.

Step (C) of the process according to the invention comprises the hot rolling of the starting material from step (B), in particular the thin slabs produced a hot strip. For this purpose, the starting material obtained in step (B),

in particular a thin slab, preferably heated in an oven to the appropriate hot rolling start temperature and then fed to the hot rolling. The temperature at which the starting material, in particular a thin slab, enter the furnace is preferably above 650 ° C. The residence time in the oven should be less than 60 minutes in order to avoid adhesive scale.

The hot rolling is preferably carried out in step (C) following the first forming pass in the two-phase region (a / g). Also, this measure has the goal of reducing the formation of nitridic precipitates in the course of hot rolling as far as possible in order to control these excretions via the cooling conditions on the outlet roller table behind the last

To be able to control the roll stand of the hot strip mill. In order to ensure this, according to the invention, it is preferred to hot-roll at temperatures at which austenitic and ferritic components are mixed in the microstructure of the hot strip. Typical temperatures, for which this is given for the steel alloys used according to the invention, lie above approximately 800 ° C.,

especially in the range of 850 to 1150 ° C. In the g-phase, the AIN is kept in solution at these temperatures. Another positive aspect of hot rolling in the two-phase mixed area is the grain refining effect. By converting the austenite into ferrite following the hot rolling passes, a finer grained and more homogeneous hot strip structure is obtained, which has a positive effect on the magnetic properties of the

End product affects. Furthermore, the avoidance of nitridic precipitations during hot rolling is further supported, for example, in that a degree of deformation of at least 40% is achieved in the first forming pass, in order to have only relatively small stitch reductions in the last stands for achieving the desired end strip thickness. In this respect, therefore, preferred is the scored over the first two Umformstiche

Gesamtumformgrad over 60%, wherein in a further advantageous embodiment of the invention in the first stand of the finishing train a degree of deformation of more than 40% is reached and in the second stand of the finishing train the reduction is more than 30%.

The preferred application of high stitch reductions (forming degrees) in the first two stands effects the required conversion of the

coarse-grained solidification microstructure into a fine rolling structure, what a

Prerequisite for good magnetic properties of the final product to be produced is. Accordingly, the reduction in stitching in the last stand should preferably be limited to a maximum of 30%, more preferably less than 20%, and it is also favorable for an optimum warm rolling result in view of the desired properties if the reduction in the penultimate stand of the finishing train is less than 25 % is.

To avoid a coarse uneven texture or coarse

Hot strip precipitations, which would adversely affect the magnetic properties of the final product, benefit from early cooling of the hot strip behind the last mill stand of the finishing train. According to a practical embodiment of the invention, it is therefore preferable to start with the water cooling within a maximum of five seconds after leaving the last mill stand. The aim is to have the shortest possible break times, for example, of one second and less.

The cooling of the hot strip can be known to the expert

Process carried out, for example by water and / or air.

Step (D) of the process of the invention comprises coiling the hot strip obtained in step (C) into a coil. Corresponding methods for coiling a hot strip are known per se to those skilled in the art. The reel temperature should preferably be in the temperature range of 500 to 780 ° C. Overlying temperatures would on the one hand lead to undesirably coarse precipitates and on the other hand the Beizbarkeit

deteriorate. For setting higher reel temperatures of over 700 ° C, a so-called short-distance reel is preferably used, which is arranged directly after the compact cooling zone.

Within the limits given by the invention, the

inventive method in the production of the hot strip preferably carried out so that the hot strip obtained sulfide and / or nitridic precipitates having an average particle diameter less than 150 nm and an average density of at least 0.05 microns ^{-2 is} achieved. Such a hot strip has optimal conditions for the effective control of grain growth during the subsequent process steps. The thickness of the hot strip obtained according to the invention is preferably 1.5 to 3.5 mm, more preferably 2 to 2.7 mm.

In the optional step (E) of the method according to the invention, to further optimize the microstructure, the hot strip thus produced can optionally be annealed after reeling or before cold rolling.

In step (F), the hot strip is rolled in one or more cold rolling steps to a cold strip. In this case, in the case of a multi-stage, multi-stage cold rolling between the cold rolling steps

if necessary, an intermediate annealing. The thickness of the cold strip obtained according to the invention is preferably 0.10 to 0.35 mm, more preferably 0.15 to 0.23 mm.

Step (G) of the process of the invention comprises annealing the cold strip at a temperature of 700 to 900 ° C, preferably 800 to 900 ° C. Step (G) of the process according to the invention can in principle be carried out in all devices known to the person skilled in the art.

In a preferred embodiment of the method according to the invention, step (G) is carried out such that a dew point DP corresponds to the following equation (2)

is present, and thus the nitrogen concentration in the material after step (G) is adjusted so that the following equation (1)

is satisfied, where

Al _si aluminum content (acid-soluble) in the melt in ppm,

N (melt) nitrogen content in the melt in ppm,

DP dew point in ° C and

N mean nitrogen content in the material after process step G in ppm.

According to the invention, the annealing in step (G) is preferably carried out in an atmosphere in which the dew point DP indicated in ° C corresponds to the equation (2) mentioned above. Here, Al _{si means} the content of aluminum in the melt, which has been used in step (A) of the method according to the invention. The unit of Al _si is ppm. According to the invention, values for Al _si are preferably 100 to 650 ppm, particularly preferably 150 to 550 ppm, very particularly preferably 200 to 400 ppm. N (melt) means the nitrogen content in the melt which has been used in step (A) of the process according to the invention. The unit of N (melt) is ppm. Values for N (melt) according to the invention are preferably from 20 to 200 ppm, more preferably from 40 to 150 ppm, most preferably from 60 to 120 ppm.

The present invention preferably relates to the process according to the invention, wherein step (G) takes place at a dew point DP of from 20 to 90 ° C., more preferably from 30 to 70 ° C.

By the dew point DP, which is preferably set in step (G), the nitrogen concentration N in the material results after step (G) according to equation (1).

Here, Al _si and N (melt) have the meanings mentioned above. N means the nitrogen content in the material after process step G in ppm. The unit of N is ppm. The nitrogen content N is preferably from 70 to 180 ppm, more preferably from 90 to 160 ppm.

In step (G) of the process according to the invention is preferably a

Nitrogen content in the furnace atmosphere N (atmosphere) before, which favors the formation of the content of the invention N in the material after step (G).

Because step (G) of the process according to the invention is preferably carried out under certain conditions with regard to the dew point of the furnace atmosphere and the nitrogen concentration in the material after step (G), it is possible according to the invention to provide a grain-oriented electrical steel which is characterized by particularly low remagnetization losses and a particularly good Liability of the forsterite layer (magnesium silicate layer), which is formed in step (I) of the method according to the invention is characterized. This can be done by one DRIFT spectrum of the magnesium silicate layer are detected, preferably containing at least one peak in the range 960 to 975 cm ^-1 (A) and at least one peak in the range of 976 to 990 cm ^-1 , more preferably the peak height of the at least one peak in Range (A) is higher than the peak height of the at least one peak in the range (B).

In the optional step (H) of the process of the invention, an annealing separator layer may be applied to at least one surface of the cold strip of step (G), preferably such an annealing separator layer is applied to both surfaces of the cold strip of step (G).

The annealing separator is typically MgO. The

Annealing separator prevents the turns of a coil wound from the cold strip from welding together during subsequent high-temperature annealing.

Step (I) of the method according to the invention comprises

High-temperature annealing, if necessary with the Glühseparator

coated cold tapes to form a forsterite layer on the surface of the annealed cold strip, wherein in step (I) the electrical steel has a nitrogen content N according to the following formula (1):

in which

Al _si Aluminum content (acid-soluble) in the preparation of the

Electro tapes used melt in ppm,

DP dew point in high temperature annealing step in ° C and

N (melt) nitrogen content in the production of electrical tape

used melt in ppm mean.

Step (!) Of the method according to the invention is under certain

Conditions are carried out, which show that the nitrogen content N assume certain values, which are pending according to equation (1) of the

Aluminum content in the melt, which was used in process step (A).

Step (I) of the process according to the invention is preferably carried out at a temperature of 700 to 900 ° C.

Step (I) of the process according to the invention is typically carried out in a hood furnace under protective gas. As a result, selective texture growth in the cold strip results in a structural texture which contributes significantly to the magnetic properties. At the same time, during the high-temperature annealing, a forsterite layer is formed on the strip surfaces, often referred to in technical literature as "glass film." In addition, the steel material is cleaned by diffusion processes occurring during the high-temperature annealing.

By the step (I) according to the invention, a grain-oriented electrical steel is obtained in which the toothing of the glass film with the

Base material is surprisingly improved. The shows in particular in an improved adhesive strength. This improved adhesive strength can be determined, for example, according to the method disclosed in EP 2 022 874 A1 by bending over conical mandrels with different diameters. The use of a conical mandrel allows all bending radii to be measured in one step. The grain-oriented electrical strip according to the invention preferably exhibits a bending radius of less than 7.5 mm, preferably less than 5 mm. The optional step (J) of the method according to the invention comprises applying an insulating layer to the surface of the cold strip having the forsterite layer. Suitable materials which can act as an insulating layer are, for example, phosphates, silicates or mixtures thereof. Corresponding processes are known per se to the person skilled in the art. Characterized in that in the high-temperature treatment in step (I) a certain

Nitrogen content was set, succeeds in step (J) of

inventive method to apply in a single pass a thicker and more uniform insulation layer. The present invention therefore preferably relates to the method according to the invention, wherein in step (J) an insulating layer is applied in a single pass.

Furthermore, the cold strip obtained from step (J) of the method according to the invention can be thermally directed. Corresponding methods for this purpose are likewise known to the person skilled in the art.

The optional step (K) of the process according to the invention comprises a final annealing of the cold strip according to the invention. In the so-called "stress relief annealing", the cold strip is stress relieved. This final annealing can be carried out before or after the assembly of the steel flat product produced in the manner described above into the blanks required for further processing. By a

Final annealing, which is carried out after the blanks have been cut, may be supplemented by the additional costs incurred during the division process

Tensions are reduced.

The grain-oriented electrical strip produced according to the invention is characterized by the fact that it has low core losses and, due to a high degree of toothing of the forsterite layer with the surface of the electrical strip, good adhesion of the forsterite layer. In particular, the grain-oriented electrical steel produced according to the invention shows a bending radius smaller than 7.5 mm, preferably smaller than 5 mm. The present invention therefore also relates to a grain-oriented electrical steel produced by the

inventive method.

The present invention also relates to a grain oriented electrical steel, wherein a high temperature annealing step is carried out during its production in which the electrical steel has a nitrogen content N according to the following formula (1):

in which

Al _si Aluminum content (acid-soluble) in the preparation of the

Electro tapes used melt in ppm,

DP dew point in high temperature annealing step in ° C and

N (melt) nitrogen content in the production of electrical tape

Mean melt used in ppm.

The grain-oriented electrical strip according to the invention is subjected to high-temperature annealing during its production. At this

High-temperature annealing must be ensured according to the invention that in a temperature range of 700 to 900 ° C, the electrical steel has a nitrogen content according to equation (1). This preserves that

inventive electrical steel surprising technical properties. For example, the grain-oriented electrical strip according to the invention has a glass film (magnesium silicate layer), which is connected to the base material by a particularly high toothing and therefore the adhesive strength of the glass film is markedly increased. In particular, the invention shows produced komoriented electrical steel a bending radius of less than 7.5 mm, preferably less than 5 mm. The electrical strip according to the invention is preferably obtained by the method according to the invention.

The grain-oriented electrical strip according to the present invention preferably has a magnesium silicate layer on at least one surface, wherein in a DRIFT spectrum of the magnesium silicate layer at least one peak in the range 960 to 975 cm ^-1 (A) and at least one peak in the range of 976 to 990 cm ^-1 , wherein the peak height of the at least one peak in the region (A) is higher than the peak height of the at least one peak in the region (B).

The so-called DRIFT method (Diffuse Reflection Fourier Transform Infrared Spectroscopy) is known per se to the person skilled in the art. In the DRIFT method, an IR light beam is directed onto the sample surface by means of concave mirrors and the reflected light is also detected by means of concave mirrors, see, for example, Beasley et al., "Comparison of

Transmission FTIR, ATR and DRIFT sprecta ", Journal of Archeological Science, Vol. 46, June 2014, pages 16 to 2). This allows the evaluation of deeper oxide layers and thus a deeper analysis of the molecular components in the oxide layer.

The electrical strip according to the invention is characterized in that it has a magnesium silicate layer, ie a so-called forsterite layer, which has at least two peaks in a DRIFT spectrum of this layer, at least one peak in a wavenumber range of 960 to 975 cm ^-1 (range (A)), and at least one peak in one

Wavelength range from 976 to 990 cm ^-1 . Furthermore, the peak height of the at least one peak in the region (A) is higher than the peak height of the

at least one peak in the range (B). In the context of the present

Invention means "higher" that the at least one peak in the range (A) to at least 5%, preferably at least 30%, is higher than the at least one peak in the region (B).

According to the invention, the ratio of the peak height of the at least one peak in the region (A) to the peak height of the at least one peak in the region (B) is greater than 1, 0, preferably greater than or equal to 1, 1, particularly preferably greater than or equal to 1.3 ,

The electrical strip according to the invention is particularly suitable in

Power transformers, distribution transformers, small transformers or to be used in rotating electrical machines.

The present invention therefore further relates to the use of the electrical strip according to the invention in power transformers,

Distribution transformers, small transformers or in rotating electrical machines.

Examples

The following embodiments serve to illustrate the invention.

Grain-oriented electrical tapes 1 to 14 according to the present invention were obtained by the steps of melting a molten steel containing the alloying elements shown in Table 1, casting the molten steel into a thin slab, hot rolling the thin slab at a temperature of 1050 ° C. into a hot strip, and tumbling the hot strip at a temperature from 700 ° C to a coil, cold rolling the hot strip in 5 steps to a thickness between 0.23 and 0.3 mm, annealing the cold strip at a temperature of 700 to 900 ° C according to those given in Table 2

Process parameters. The surfaces of the obtained grain-oriented electrical tapes were measured by means of DRIFT spectroscopy. The results for the peaks at 977 and 985 ppm are shown in Table 2. Furthermore, the

Polarizability at 1, 7 Tesla and the adhesion of the glass film with the base material according to EP 2 022 874 A1 determined. These results are also shown in Table 2.

For comparison, Comparative Examples V15 to V28 were prepared. These differ from the examples according to the invention in that equations (1) and (2) are not satisfied.

Table 1: Compositions of the melts used, remainder Fe and unavoidable impurities

Table 2: Results

Table 2: Results

Claims

PATENT APPLICATIONS

A grain-oriented electrical steel characterized in that a high temperature annealing step is carried out during its production, wherein the electrical steel has a nitrogen content N according to the following formula (1):

in which

Al _si Aluminum content (acid-soluble) in the preparation of the

Electro tapes used melt in ppm,

DP dew point in high temperature annealing step in ° C and

N (melt) Nitrogen content in the melt used to produce the electrical strip in ppm

mean.

2. Electrical strip according to claim 1, characterized in that the

underlying molten steel (each in wt .-%) 2.0 to 4.0 Si, 0.010 to 0.100 C, up to 0.065 Al and up to 0.02 N, and each optionally up to 0.5 Cu, up to 0.060 S and also optionally each up to 0.3 Cr, Mn, Ni, Mo, P, As, Sn, Sb, Se, Te, B or Bi, the remainder iron and unavoidable impurities.

3. Electrical strip according to claim 1 or 2, characterized in that it has a bending radius of less than 7.5 mm, preferably less than 5 mm.

4. Electrical strip according to one of claims 1 to 3, characterized in that it comprises a magnesium silicate layer on at least one surface, wherein in a DRIFT spectrum of the magnesium silicate layer at least one peak in the range 960 to 975 cm ^-1 (A) and at least one peak in the range of 976 to 990 cm ^-1 , wherein the peak height of the at least one peak in the region (A) is higher than the peak height of the at least one peak in the region (B).

5. A method for producing a grain-oriented electrical tape, comprising at least the following steps:

(A) melting a molten steel containing (in wt% in each case) 2.0 to 4.0 Si, 0.010 to 0.100 C, up to 0.065 Al and up to 0.02 N, and each optionally up to 0.5 Cu, up to 0.060 S and also optionally in each case up to 0.3 Cr, Mn, Ni, Mo, P, As, Sn, Sb, Se, Te, B or Bi, the remainder contains iron and unavoidable impurities,

(B) casting the molten steel into a starting material, for example into a slab, thin slab or a cast strip,

(C) hot rolling the primary material into a hot strip,

(D) coiling the hot strip into a coil,

(E) optional annealing of the hot strip (F) cold rolling the hot strip in one or more cold rolling steps to a cold strip,

(G) annealing the cold strip from step (F) at a temperature of 700 to 900 ° C,

(H) optionally applying an annealing separator layer to at least one surface of the cold strip of step (G),

(I) high-temperature annealing of the optional annealing separator-coated cold-rolled strip to form a forsterite layer on the surface of the annealed cold-rolled strip,

(J) optionally applying an insulating layer to the forsterite layer surface of the cold strip, and

(K) optional final annealing of the cold strip, characterized in that in step (I) the electrical steel has a nitrogen content N according to the following formula (1):

in which

AI _{S |} Aluminum content (acid-soluble) in the preparation of the

Electro tapes used melt in ppm,

DP dew point in high temperature annealing step in ° C and

mean.

6. The method according to claim 5, characterized in that the

Aluminum content Al _si at 100 to 650 ppm, preferably at 150 to 550 ppm, more preferably at 200 to 400 ppm.

7. The method according to claim 5 or 6, characterized in that the nitrogen content N (melt) at 20 to 200 ppm, preferably 40 to 150 ppm, more preferably 60 to 120 ppm).

8. The method according to any one of claims 5 to 7, characterized in that step (G) at a dew point DP of 20 to 90 ° C, particularly preferably 30 to 70 ° C, takes place.

9. Grain-oriented electrical steel, producible by the method according to one of claims 5 to 8.

10. Use of a grain-oriented electrical tape according to one of

Claims 1 to 4 or 9 in power transformers,