WO2013004747A1 - Method for producing a grain-oriented electrical steel flat product intended for electrotechnical applications - Google Patents

Abstract

The invention relates to a method for producing a grain-oriented flat steel product for electrotechnical applications, in which a melt is cast into a strand, a thin slab is divided from the cast strand, the thin slab is heated and hot-rolled into a warm strip, the warm strip is cooled, coiled and cold-rolled into a cold strip, the cold strip undergoes decarburizing and nitriding annealing, an annealing separator is applied to the surface of the cold strip and the cold strip undergoes final annealing to obtain a distinctive cast texture. The working step of "decarburizing and nitriding annealing" is carried out in two stages, wherein the first annealing stage, which comprises heating the cold strip from a starting temperature to a first desired annealing temperature and keeping it at this desired annealing temperature, extends over a first time interval and the second annealing stage, in which the cold strip is heated to a second desired annealing temperature and is subsequently kept at this desired annealing temperature, extends over a second time interval. The first desired annealing temperature is 10 - 50°C lower than the second desired annealing temperature and the duration of the first time interval is 30 - 70% of the overall duration of the annealing treatment comprising the first and second time intervals.

Description

 Method for producing a grain-oriented, intended for electrical applications

 Electric steel salmon product

The invention relates to a method for producing grain-oriented electrical steel flat products intended for electrotechnical applications.

 Electrical steel flat products of this type are also known in practice as grain-oriented "electric sheets" or

grain-oriented "electrical bands" called.

Grain-oriented electrical steel flat products have special magnetic properties and are produced by a complex manufacturing process. Base material for electrical steel flat products is a silicon steel sheet. The metallurgical properties of the material, the

 Forming degrees of the rolling processes and the parameters of

 Heat treatment steps are so on each other

 coordinated that targeted recrystallization processes take place. These recrystallization processes lead to a material typical "Goss texture", in which the direction of the easiest magnetization in

 Rolling direction of the finished strips lies.

To be distinguished from grain-oriented electrical sheet or strip of the type in question here

Electric steel flat products in which the grains do not have pronounced orientation. In such non-grain oriented electrical steel or sheet, the magnetic flux is not fixed to any particular direction so that the same magnetic flux in all directions

Form properties (isotropic magnetization).

Grain-oriented electrical steel or sheet of the type in question here, however, has a strong anisotropic

magnetic behavior on. This is on one

uniform orientation of the grains (crystallites) of the structure attributed. This crystallographic texture is replaced by an appropriate action in the

 Manufacturing process effective

 Grain growth selection achieved. The aim is, after one at the end of the manufacturing process

 Final annealing to obtain an electrical steel flat product, in which the grains have a slight misalignment and consequently an almost ideal texture.

Grain-oriented electrical steel is particularly suitable for applications in which particularly high demands are placed on the magnetic properties, as is the case, for example, in the construction of transformers.

Method of producing high quality

 grain-oriented electrical steel are known in greater numbers.

With that described in EP 0 910 676 Bl, so

 mentioned "low-heating method" can be

 produce highly permeable, grain-oriented electrical sheets with an optimized distribution of properties.

Characteristic of this method is a Slab heating temperature below 1250 ° C. Due to this comparably low temperature

Aluminum nitrides, which at the conclusion of the

Whole-temperature annealing step take place completely dissolved in solution, only partially dissolved and excreted again. As a result, produced by the low-heating process

Electrical tape weaker inherent inhibition than via the conventional process via

High temperature slab heating produced material.

The purpose of the particle inhibition is to control the grain growth in the primary structure of the cold strip after and during the

To suppress decarburization annealing. Only during the final annealing, during which the cold strips are annealed at temperatures of up to 1200 ° C, a controlled abnormal grain growth in the temperature range of 950 - 1100 ° C to a high

Texture sharpness with Goss orientation [001] (110) too

enable .

In order for optimal, abnormal grain growth with high texture sharpness to begin, it is necessary to set an ideal equilibrium state between driving and restoring forces after decarburization annealing. The driving force for grain growth during annealing is the grain boundary energy stored in the microstructure. This is essentially due to the grain size after the

 Primary recrystallization determined.

Due to the weaker inherent inhibition in the low-heating process is the average primary particle size after decarburization annealing greater than

conventional methods and is subject to larger

Variations due to the cold process. The driving force for abnormal grain growth is thus generally lower. On the other hand, a restraining force opposing the abnormal grain growth by the non-magnetic precipitated in the cold strip

Excretions (inhibitors) determined. Therefore, it is important to have many finely divided particles. In the low-heating process, however, the relevant particles are not in the hot strip but before, after or during the decarburization annealing or during the

Heating phase of the final annealing in the course of various nitriding produced.

In the course of the process described in EP 0 950 119 Bl and EP 0 950 120 Bl, an inhibition strength Iz is adjusted by nitrides and sulfides via the hot rolling process in such a way that the primary grain growth during the

Cold process is inhibited even at higher temperatures. The slabs become hot prior to hot rolling

Temperatures heated from 1100 ° C to 1320 ° C. A simultaneously carried out for decarburization annealing

Nitriding treatment at temperatures between 850 and 1050 ° C in an ammonia-containing atmosphere allows the direct formation of aluminum nitrides. The

subsequent annealing must be opposite to the

conventional manufacturing way of manufacturing

grain-oriented electrical steel can not be modified.

In contrast, when in EP 0 219 611 Bl

Nitriding after the Primary recrystallization, but before onset of

abnormal grain growth. The nitration can be carried out here by an atmosphere with nitriding capability or by a nitrogen-donating adhesive protection additive.

Especially in the case of the process with an ammonia-containing atmosphere in which the nitriding temperature is below 850 ° C., the nitration is close to

Surface silicon manganese nitrides (Materials Science Forum 204-206 (1996), 143-154). Due to their lower thermodynamic stability they dissolve during the heating of the annealing. The nitrogen

then diffuses into the steel matrix and recombines with the free aluminum present there to aluminum nitride (Materials Science Forum 204-206 (1996), 593-598). The resulting aluminum nitrides are then the inhibitors effective for secondary grain growth. The

Inhibition is indeed in comparison to the

conventional process used for the production of grain-oriented electrical steel weaker, but allows complete secondary recrystallization at higher temperatures with a larger secondary grain size in the finished strip (TMS Proceedings 3 (2008), 49-54).

A disadvantage of this approach, however, is that a modified time-temperature cycle of the

High annealing is required. The dissolution of the silicon-manganese nitrides and the formation of new A1N

Nitrogen diffusion occurs at temperatures between 700 to 800 ° C. To make this crucial process step completely possible, is in the implementation of the previously explained method an isothermal

Halt level of at least four hours during the

Heating phase of the annealing required. This not only requires a significant extension of the entire

Process duration, but also leads to increased costs in the production.

In addition to the above-described prior art, EP 1 752 549 A1 discloses a process for the production of high-quality grain-oriented electrical steel based on thin-slab continuous casting, in which the

Steps are coordinated so that using conventional aggregates

Electrical sheet with optimized magnetic properties is obtained. The aim is to avoid the formation of nitridic precipitates before hot rolling and during hot rolling as possible to the possibility of a controlled generation of such

To be able to use excrements during the cooling of the hot strip on a large scale. Specifically, a steel is melted first, next to iron and

unavoidable impurities (in mass%) Si: 2.5-4.0%, C: 0.02-0.10%, Al: 0.01-0.065% N: 0.003-0.015% optionally up to 0.30 % Mn, up to 0.05% Ti, up to 0.3% P, one or more elements from the group S, Se in contents whose sum is at most 0.04%, one or more elements from the group As, Sn, Sb, Te, Bi with contents of up to 0.2% each, one or more elements from the group consisting of Cu, Ni, Cr, Co, Mo with contents of in each case up to 0, 5% and one or more elements of Group B, V, Nb at levels of up to 0.012% each. The composite Melt then becomes secondary metallurgical in one

Vacuum system or a ladle furnace treated and

then continuously shed to a strand. From the strand thus obtained become thin slabs

divided, which are subsequently heated in a standing oven to a temperature between 1050 ° C and 1300 ° C. The residence time in the oven is at most 60 min. Following the warming of the

Thin slabs are hot rolled into a hot strip 0.5 to 4.0 mm thick in a multi-stand hot rolling mill in line. During hot rolling, the first forming pass will be at a

Temperature of 900 - 1200 ° C performed with a degree of deformation of more than 40%. Furthermore, during hot rolling, at least the two forming passes subsequent to rolling at 900 - 1200 ° C in the

Two-phase mixed area (α-γ) rolled. Finally, in the last cold forming of hot rolling, the reduction is not more than 30%. Following the

Hot rolling, the hot strip thus obtained is cooled and coiled into a coil. Optionally, then annealing of the hot strip after reeling or before the

Cold rolling can be performed. Subsequently, the hot strip is cold rolled to a cold strip having a final thickness of 0.15 mm to 0.50 mm. The resulting cold strip is then annealed recrystallizing and decarburizing. In addition to the decarburization annealing, nitriding of the strip in a NH ₃ -containing atmosphere can also be carried out at temperatures above 850 ° C. After this

Subsequently, an annealing separator has been applied to the surface of the annealed cold strip, the thus coated cold-rolled strip to the expression of Gosstextur recrystallizing final annealed. Also optionally, the finally annealed cold strip can then be provided with an electrical insulation and

finally annealed stress-free.

In EP 0 378 131 B1 attention is drawn to the significance of the mean grain size but also its variance. In addition to an optimal average grain size is therefore of particular importance that the deviation from the mean grain size in the sheet is low. This results from the fact that grain growth processes are more uncontrolled due to the lower inhibition

 (Materials Science Forum 204-206 (1996), 623-628).

As a result, under unfavorable process conditions, grains that are not goss-oriented but can not grow at high temperatures can contribute to fine grain formation.

Finally, EP 0 392 534 B1 describes in detail the atmospheres of decarburization annealing which may be considered. In this context will be on it

noted that at the beginning of the decarburization and

Nitrierglühung the partial pressure p _H 2o P _H 2 must be lowered to adjust a suitable oxide layer. The result of this process is a satisfactory formation of the glass film during the annealing.

Against the background of the prior art explained above, the object of the invention was to provide a method with which it is possible to carry out grain-oriented electrical steel flat products in a simple manner to produce an optimally uniform distribution of the grain size.

This object has been achieved by a method which comprises the measures and features specified in claim 1.

Advantageous embodiments of the invention are specified in the dependent claims and are explained below as the general inventive concept in detail.

In accordance with the prior art described above, a method according to the invention for producing a grain-oriented electrical steel flat product intended for electrotechnical applications comprises the following steps: a) producing a molten steel next to iron and

 unavoidable impurities (in% by weight) Si: 2.5-4.0%, C: 0.02-0.1%, Al: 0.01-0.065%, N: 0.003-0.015%, and optionally up to to 0.30% Mn, up to 0.05% Ti, up to 0.3% P, one or more

 Elements of the group S, Se in contents whose sum is at most 0.04%, one or more elements from the group As, Sn, Sb, Te, Bi with contents of up to 0.2%, one or more elements from the group Cu, Ni, Cr, Co, Mo with contents of in each case up to 0, 5%, one or more elements from the group B, V, Nb with contents of in each case up to 0,012%, contains, b) casting the Melt into a strand in one

Continuous casting machine, c) separating at least one thin slab from the cast strand, d) heating the thin slab to a temperature between 1050 ° C and 1300 ° C, e) hot rolling the thin slab in a hot rolling mill to a hot strip having a thickness of 0.5-4.0 (f) cooling the hot strip, (g) coiling the hot strip into a coil, (h) cold rolling the hot strip to a cold strip having a final thickness of 0,15 to 0,50 mm, (i) decarburizing and nitriding annealing the cold strip obtained, (j) Applying an annealing separator to the surface of the annealed cold-rolled strip, and k) final annealing the annealing separator

 Cold bands for the expression of a Gosstextur.

Of course, in the generation of the

Elektrostahlflachprodukts additional work steps are carried out in the conventional

Preparation of grain-oriented electrical tapes or sheets are usually required. These include, for example, between steps g) and h) one - or multi - stage hot strip annealing, thermal straightening of the cold - rolled strip and application of an insulating layer carried out as part of the

inventive method using and

Considering the known from the prior art parameters can be performed.

Essential for the invention is that the cold strip in the course of the process step i) "decarburizing and nitriding annealing of the obtained cold strip" in at least two stages decarburizing and nitriding annealed.

The first stage of this annealing extends according to the invention over a first time interval, which is a heating of the cold strip, starting from a

Start temperature to a first target annealing temperature and then holding at this target annealing temperature includes.

The second stage of annealing extends into

corresponding manner according to the invention over a second time interval, within which the cold strip is first heated to a second target annealing temperature and then maintained at this target annealing temperature.

According to the invention, the first target annealing temperature is lower by 10 to 50 ° C. than the second target annealing temperature. At the same time, according to the invention, the duration of the first time interval is 30-70% of the total duration of the annealing treatment comprising the first time interval and the second time interval. The invention is based on the recognition that can be produced by an at least two-stage "step annealing" during the step i) a cold strip in which on the one hand the grains have an optimal mean grain size and on the other hand, the deviation of the grain size of the individual grains of the average grain size is low.

In practice, this can be achieved by subjecting the cold strip for decarburizing and nitriding annealing, obtained after cold rolling, to a continuous flow through at least two zones

Continuous annealing furnace is passed in the first

passed through the front zone in accordance with the invention, a target annealing temperature is set to

10-50 ° C is lower than the target annealing temperature in the subsequently passed by the cold strip second zone of the furnace, wherein the duration of the time interval within which the first stage of the annealing is 30 to 70% of the total duration of the decarburizing and nitriding Annealing , By the invention predetermined

Temperature difference between the first and second stages of the decarburizing and nitriding annealing and the

According to the invention provided for the two stages of this annealing times, excessive grain growth is suppressed the unfavorable for the Gosstexturausbildung orientations. The cold-rolled strip structure obtained after annealing thus has the same mean grain size as that achieved by the higher annealing temperature

Glowing in the rear furnace zone is set to a significantly smaller variance, thus enabling during the final, at a high temperature final annealing achieved a homogeneous secondary grain growth.

With the method according to the invention, it is thus possible to achieve a variance in the course of the cold rolling process

To minimize grain sizes. Overall, the result of the previous cold process is stabilized against fluctuations in the particle size distribution. An electric flat steel product produced according to the invention thus has a crystallographic texture after the annealing treatment carried out after at least two stages following the cold rolling, by means of which a homogeneous secondary grain growth during the final heat treatment

Hochtemperaturglühung is ensured in an optimal manner.

The invention combines in this way the known from the low-heating process approach with a modern thin-slab production, which takes place according to the known, characterized by a continuous production process casting-rolling process. The result is at

A procedure according to the invention

 Electric flat steel product having optimum magnetic properties relative to the uses typical of grain-oriented electrical sheets or tapes.

If a nitriding and decarburizing annealing (working step i) carried out according to the invention in at least two stages is mentioned here, this does not mean that a combined nitriding and decarburization always necessarily has to take place in both stages of this annealing. Instead, the first stage of this annealing carried out according to the invention can also be carried out as a pure heating stage and the decarburization and nitration take place in the second stage. It is also conceivable to carry out a decarburization over the two annealing stages and then in a further annealing step

To carry out residual decarburization and nitration. Alternatively, the decarburization and nitriding can take place in succession distributed over the at least two stages of the annealing carried out according to the invention. Finally, it is also conceivable to let at least one of the completed annealing stages according to the invention take place without decarburization or nitration and only in a subsequent to the two stages of the annealing according to the invention

Annealing step to complete the decarburization and nitriding.

Accordingly, in the context of the invention in practice in step i) l.i) the first and second stages of

Annealed after each other and then another annealing step are carried out in which the cold strip of a decarburizing and nitriding

Annealing is subjected. The first and second stage of the annealing in step i) can under

Considering the invention for these annealing stages in terms of the location of the temperature levels and the

Time portion of the first annealing stage based on the

Total time of annealing stages are performed.

Subsequently, a further annealing step takes place in which decarburization and nitriding are carried out in a conventional manner.

Overall, in this variant of the invention in the course of the work step i) so at least three Teilglühschritte completed successively, with the invention for the first two annealing steps

Specifications apply and the third, the nitriding comprehensive step is completed in a conventional manner.

Practical experiments have shown that optimal properties of a generated according to the invention

Elektrostahlflachprodukts result when the

Target annealing temperature of the first stage by 10 - 30 ° C

is lower than the target annealing temperature of the second stage annealing.

Likewise, it has a favorable effect on the result of

According to the invention carried out at least two stages

Firing step off when the duration of the first time interval to 30 - 60% of the total duration of the annealing treatment

is limited.

The heating of the cold strip to the desired temperature of the first annealing stage should be as fast as possible.

During the heating phase of the decarburization and

Nitrierungsglühung passes through the cold-worked band initially a recovery. Then set the

 Primary recrystallization. At higher temperatures and longer annealing times, grain growth processes are added. To save as much stored energy as possible

To provide recrystallization, the temperature range of the recovery should be run through quickly. For this purpose, an advantageous embodiment of the invention provides that the heating rate with which the cold strip is heated in the first stage of the annealing from the start temperature to the first target annealing temperature, 25 - 500 ° C / s. In a conventional heating, the heating rate is typically 30-70 ° C / s. In terms of a particularly good

 However, primary recrystallization and, consequently, optimal work results may also be advantageous for setting particularly fast heating rates of 200-500 ° C./s. In practice, such a rapid heating rate can be achieved, in particular in the case of a production that takes place in a continuous pass, by virtue of the fact that at the entrance of the respective continuous furnace

inductive rapid heating takes place, in which the cold strip is heated by the action of an induced electromagnetic field in the band.

The invention is based on

Embodiments explained in more detail. Show it:

Diag. 1 is a schematic representation of the

 Temperature profile T over the annealing time t for a conventionally annealed electrical steel strip (curve A) and an inventive

 Electrical steel strip (curve B);

Diag. 2 the polarization at 800 A / m in Tesla for two differently composed

Electrical steel sheets S1, S2, plotted over the ratio t _x / t _{2 of} the duration of the

annealing according to the invention for the first annealing stage provided time interval ti to the total duration t _{2 of} the annealing.

In a conventional continuous casting machine, four steel melts Sl - S4 are given in Table 1 After a secondary metallurgical treatment carried out in a ladle furnace and a vacuum plant, compositions were continuously poured off into a 63 mm thick strand.

From the strand thin slabs have also been divided in a conventional manner. After a compensation annealing in a compensation furnace at 1165 ° C, these thin slabs were descaled and hot rolled in the finishing train to a final thickness of 2.34 mm and coiled into a coil.

Example 1:

The hot strips produced in the manner described above are a two-stage hot strip annealing

been subjected. The annealing temperature in the first stage of the hot strip annealing was 1090 ° C, while the

Annealing temperature in the second stage was 850 ° C.

Instead of a two-stage hot strip annealing, a single-stage hot strip annealing with a uniform uniform annealing temperature could have been carried out.

After hot strip annealing, the annealed hot strip is

cold rolled in one stage with a degree of deformation of 87% to a final thickness of 0.285 mm. Sheet samples have been separated from the cold strips thus obtained.

A comparison group A of these sheet samples is in

Passed in a continuous annealing furnace annealed. In this case, in a first furnace section which has been passed through first, an annealing step of 150 seconds at a temperature of 860 ° C. under a moist mixture formed from a hydrogen / nitrogen mixture (p _H 2o / pH 2 = 0.50) Atmosphere has been carried out. Then, in a second furnace section passed through after the first furnace section, a second annealing step lasting 30 seconds was carried out under a moist, from a

Ammonia / hydrogen / nitrogen mixture existing

Atmosphere to effect a Restent carbonization and nitration. The temperature of the annealing was always 910 ° C. Corresponding to the above-mentioned embodiment of the invention which is important for practice, the annealing in step i) of the method according to the invention was hereby subdivided into two annealing steps, of which the first annealing step is according to the invention

Subsequent division has been carried out again in two annealing stages, following the second as follows

Annealing step a conventional decarburizing and

nitriding annealing has been completed. All in all, the work i) has been completed here in three consecutive parts.

A second group B of the sheet samples is in one

corresponding sequence of operations initially in the course of the first annealing step in accordance with the invention in two

annealed successive annealing stages and then restenciated and nitrided in a second annealing step. There are five variants B.a) - B.e) the

According to the invention, two-stage annealing has been investigated. In the first over a first duration t _x expiring

Annealing stage is in each case a target annealing temperature χ and in the second annealing stage in each case a target annealing temperature T _{2 has been} set. The total duration t _{2 of} the two consecutively completed annealing stages was also 150 s in this case. The first stage of the first glow section also included one with a

Heating rate of 40 ° C / sec taking place rapid heating to the respective target annealing temperature Ii.

In Diag. 1, the temperature curve during the annealing in the first annealing step is shown in a dashed line over the annealing time t on the one hand for the group A electrical sheet samples produced for comparison in a solid line and on the other hand for one of the variants B.a) - B.e).

Accordingly, the first two annealing stages of the variant exemplified here of the inventive method are mainly used for decarburization and are in this regard with respect to gas composition and

Temperature optimized. The Entkohlungsglühung takes place in two stages with respect to the temperature control in such a way that in the first passed first section is first gently decarburized to avoid grain enlargements as possible, and in the subsequently passed section at the optimal temperature for the effectiveness of the decarburization decarburization is continued and terminated.

In contrast, the third annealing stage of

inventive method optimized in terms of nitriding. At the same time a residual decarburization occurs here to a small extent. The optimization of the third annealing stage in relation to the nitriding is done essentially by the choice of an optimized gas composition, but may also mean a temperature adjustment. In Diag. 1 is an example carried out accordingly Temperature control to detect a small temperature jump, which occurs after the end of the annealing time t ₂ .

Specifically, for carrying out the inventive heat treatment variants B.a) - B.e) is the first

Furnace section of the continuous annealing furnace has been divided into two equal-length temperature zones, for their passage each of the glowing sheet metal samples so each 75 s

required. Accordingly, in these experiments, the duration ti of the first annealing stage was 50% of the total duration t ₂ of 150 s.

In the first temperature zone of the first furnace section first passed through by the respective sample, the desired annealing temperature has been changed from variant to variant when carrying out the experiments according to the invention, while in the second temperature zone when carrying out the second annealing stage a constant amount of 860 ° C. is in each case Target annealing temperature has been set. The in the first furnace section of the continuous annealing furnace

According to the invention performed two annealing stages are respectively as in the processing of the sheet metal samples of

Group A under a damp, out of one

Hydrogen / nitrogen mixture (P _H2O P _H2 = 0.50) formed atmosphere has been carried out.

Then, as in the case of the treatment of the comparative samples of group A, the first furnace section was taken

followed by a decarburizing and nitriding annealing for 30 seconds under a moist, from an ammonia / hydrogen / nitrogen mixture existing atmosphere. In the meantime, the target annealing temperature in the second annealing step was 910 ° C.

After annealing, the samples were subsequently taken with

Magnesium oxide coated and final annealed under a to 50 vol .-% of H2 and 50 vol .-% of N2 existing Glühzmosphäre.

Table 2 shows for each variant a) - e) the

Heat treatment according to the invention in the first

Annealing stage respectively set target annealing temperature Ti, the difference ΔΤ between the first target annealing temperature and the target annealing temperature of the second annealing stage and the polarization J ₈₀ o at 800 A / m, indicated in Tesla, and the specified in W / kg Ummagnetisierungsverlust Pi , ₇ at a polarization of 1.7 T and a respective frequency of 50 Hz enumerated. It turns out that the

Irrespective of which of the variants a) - e) they are produced, electrical steel sheets produced according to the invention have better properties than those in

conventionally annealed specimens.

Example 2:

Hot strips produced from the melt 1 in the above-described manner were subjected to a two-stage hot strip annealing at 1130 ° C./900 ° C., hot strips of the melt 2

single-stage hot strip annealing at 980 ° C subjected.

, 45 ) geglüht worden. Anschließend erfolgte bei 860 °C für 30 Sekunden eine Glühung in einem feuchten Ammoniak/Wasserstoff /Stickstoff-Gemisch wobei restentkohlt und nitriert wurde. Anschließend wurde wie beim Beispiel 1 bei 910 °C nitriert und restentkohlt. Subsequently, the hot-rolled strip was cold rolled with a degree of deformation of 87% in one stage to 0.285 mm thick cold strips. From the obtained cold tapes sheet samples have been divided. In this case as well, for comparison, a group A of electric-wire samples obtained from the cold-rolled tapes is held for a period of 150 seconds at a temperature of 840 ° C in a wet hydrogen / nitrogen mixed atmosphere

, 45). This was followed by annealing in a humid ammonia / hydrogen / nitrogen mixture at 860 ° C. for 30 seconds, with residual decarburization and nitriding. Subsequently, as in Example 1, nitrided at 910 ° C and restentarbohlt.

A second group B of samples was in the same

Atmosphere according to the invention in two stages in the first

Process part of the used continuous furnace annealed. The temperature of the first furnace zone was set at 810 ° C (ΔΤ = 30 ° C). Also in this case were five

Variants B.a) - B.e). The annealing time ti to increase the target annealing temperature in the second part of

Annealing at 840 ° C for the variant Ba) was 120 s (annealing time ratio ti / t ₂ = 80%), for variant Bb) 90 s (ti / t ₂ = 60%), for variant Bc) 75 s

(ti / t ₂ = 50%), for variant Bd) 45 s (ti / t ₂ = 30%) and for variant Be) 30 s (ti / t ₂ = 20%).

Subsequently, as in Example 1, nitriding and residual decarburization were also carried out at 910.degree.

The electric sheet samples were then subsequently coated with magnesium oxide and finally annealed under an annealing atmosphere consisting of 50% by volume of H2 and 50% by volume of N2.

In Diag. 2 is for the samples prepared from the melts 1 and 2 in accordance with the invention Polarization Jsoo applied over the annealing time ti the first stage of the inventive annealing.

Example 3:

Hot melts of melts 1 and 2 were subjected to a single-stage hot strip annealing at 950 ° C. This was followed by one-stage cold rolling to cold-rolled strip with a final thickness of 0.165 mm. From the obtained cold tapes sheet samples have been divided.

A first group A of the separated from the cold strip

Sample panels were placed in a humidified at a temperature of 880 ° C for a period of 130 seconds

Hydrogen / nitrogen mixture atmosphere (PH2O / PH2 = 0.44) annealed. Subsequently, at 900 ° C for 30 seconds, a Giühung in a humid ammonia / hydrogen

Nitrogen atmosphere. In the course of this second annealing step, on the one hand, residual carbon was used and, on the other hand, nitrided.

A second group B of sheet metal samples was annealed in the same atmosphere in the first part of the process used in the experiments reported here in two stages, wherein during the first, to 70.

Second (ti / t ₂ ~ 55%) annealing stage annealing a set annealing temperature of 850 ° C and then in the second, from the 70th to the 130th second annealing stage a target annealing temperature of 880 ° C was set , Subsequently, as in Example 1, nitriding and residual decarburization were also carried out at 900 ° C. in each case.

After this annealing treatment of the electric sheet samples, they are each subsequently coated with magnesium oxide and finally annealed under an annealing atmosphere consisting of 50% by volume of H2 and 50% by volume of N2.

The magnetic properties J ₈₀ o and Ρ χ, _{7 of} the

Inventive and comparative samples are summarized in Table 3. It also shows here the superiority of the products produced according to the invention.

Example 4:

In the manner described above from the melt 3 produced hot strips are subjected to a two-stage hot strip annealing at 1070 ° C / 950 ° C and one-stage to a

Cold strip was cold rolled to a final thickness of 0.215 mm. From the obtained cold tapes sheet samples have been divided.

A first group A of the sheet samples was heated for 120 seconds at a temperature of 870 ° C in one of a wet hydrogen / nitrogen mixture

existing atmosphere (P _H2O / P _H2 = 0, 51) annealed.

This was followed by annealing at 910 ° C. for 30 seconds under one of a moist

Ammonia / hydrogen / nitrogen mixture existing

Atmosphere, where on the one hand a residual decarburization and on the other a nitration has taken place.

, 51 A second group B of sheet samples is in a wet hydrogen / nitrogen mixture with

, 51

 According to the invention in a first annealing step in the first invention, divided into two stages according to the invention

Furnace section of the continuous annealing furnace used here has been annealed. It is in a first to 65. The annealing temperature has been set to 850 ° C during the second annealing stage, while the target annealing temperature in the second annealing stage, which is from the 70th to the 120th.

Second lasted, was at 870 ° C. After completion of the first, in the first furnace section in this way completed two-stage annealing the sheet samples were at

910 ° C nitrated in a humid ammonia / hydrogen / nitrogen mixture and Entkkohlt.

All sheets were subsequently treated with magnesia

and finally annealed under an annealing atmosphere consisting of 50% by volume of H2 and 50% by volume of N2.

In the present example, the first annealing stage of the first annealing step included as in the preceding

Examples described a rapid warming of

Sheet metal samples to the target annealing temperature of the first

Annealing. In order to show the influence of the heating rates "AHR", in the present example 4 are in four

In various experimental runs, the heating rates AHR have been varied under otherwise unchanged conditions.

 (Experiment 4.1: AHR = 70 ° C / s Experiment 4.2: AHR = 150 ° C / s, Experiment 4.3: AHR = 300 ° C / s, Experiment 4.4: AHR = 500 ° C / s).

The magnetic characteristics of the thus obtained

Electrical steel sheets are summarized in Table 4. Melt Si C Al N Mn S Cu Sn Cr

[ppm] [ppm] [ppm] [ppm] [ppm] [ppm] [ppm] [ppm]

Sl 3, 10 470 260 93 1470 78 1950 580 1140

S2 3, 32 580 287 105 1390 82 1810 720 780

S3 3.24 720 320 87 1580 92 1470 630 820

S4 2, 90 450 348 112 1420 85 1610 1050 930

In wt.% Or wt. Ppm;

 Remaining iron and unavoidable impurities

Table 1

Table 2 Reference 880 ° C invention

J800 [T] P _{1; 7} [W / kg] ^ 800 [T] Pi, 7 [W / kg]

Melt 1 1, 867 0.882 1.899 0, 803

Melt 2 1,873 0, 853 1, 901 0,779

Table 3

 Table 4

Claims

PATENT APPLICATIONS 1. A method for producing a grain-oriented intended for electrical applications  Electric flat steel product comprising the following  Steps: a) Generating a molten steel, containing iron and unavoidable impurities (in% by weight) Si: 2.5-4.0%,  C: 0.02 - 0.1%,  AI: 0.01-0.065%,  N: 0.003-0.015%,  optionally  - up to 0.30% n,  - up to 0, 05% Ti,  - up to 0.3% P,  - one or more elements of the group S, Se in concentrations of not more than 0,04%,  one or more elements of the group As, Sn, Sb, Te, Bi, each containing up to 0.2%, one or more elements from the group Cu, Ni, Cr, Co, Mo with contents of in each case up to 0, 5%, one or more elements from group B, V, Nb, each containing up to 0.012%, contains Casting the melt into a strand in a continuous casting machine, At least one thin slab from the cast strand, Heating the thin slab to a temperature between 1050 ° C and 1300 ° C, Hot rolling the thin slab in a hot rolling mill to a hot strip with a thickness of  0.5-4.0 mm, Cooling the hot strip, Coiling the hot strip into a coil, Cold rolling of the hot strip to a cold strip with a final thickness of 0.15 - 0.50 mm, decarburizing and nitriding annealing of  obtained cold bands, Applying an annealing separator to the surface of the annealed cold-rolled strip, Final annealing of the annealing separator  provided cold bands to the expression of a Gosstextur, adurchgekennzeichnet, that the cold-rolled strip is annealed in at least two stages in the course of step i), - That the first stage of this annealing extends over a first time interval and a heating of the cold strip from a starting temperature to a first target annealing temperature and a  comprising subsequently holding the heated cold strip at the desired annealing temperature, - That the second stage of the annealing extends over a second time interval, within which the cold strip is first heated to a second target annealing temperature and then maintained at this target annealing temperature, - d a s s the first target annealing temperature to  10 - 50 ° C is lower than the second target annealing temperature, and - d a s s the duration of the first time interval  30-70% of the total duration of the annealing treatment comprising the first time interval and the second time interval. 2. The method of claim 1, d a d u r c h characterized in that the first target annealing temperature is lower by 10 - 30 ° C than the second target annealing temperature. 3. Method according to one of the preceding claims, characterized in that the duration of the first time interval is 30-60% of the total duration of the annealing treatment. 4. Method according to one of the preceding claims, characterized in that the heating rate at which the cold strip is heated in the first stage of the annealing from the start temperature to the first target annealing temperature, d a s s e c h e c e  25 - 500 ° C / s. 5. The method of claim 4, d a d u r c h  e n c ia n, the s  Heating rate is at least 200 ° C. 6. The method of claim 5, d a d u r c h  The heating of the cold strip is inductive. 7. The method according to any one of the preceding claims, characterized in that in step 1) 1. i) the first and second stages of the annealing are completed after each other and subsequently a further annealing step is carried out, in which the cold strip is subjected to a decarburizing and nitriding annealing. Method according to claim 7, characterized The first second stage of the annealing in the working step i) can be carried out as pure decarburization annealing.