DE1408975A1 - Process for the production of fiber texture and cube texture sheets from iron and iron alloys - Google Patents

Description

WESTIHGHOTJSE ELECTRIC Hanau, the ~ 7.0KT. 196 0 CORPORATION Dr "Fr / K

^{East Plttrtursh} ' ^{PA / USA} 59/9249 1408975

Process for the production of fiber texture and cube texture sheets from iron and Iron alloys

The invention relates to magnetic materials and the production of polycrystalline iron or iron-based sheets, especially those made of iron-silicon, Iron-aluminum, iron-molybdenum, with a highly developed paser or cube texture «

V / calibrating magnetic materials, such as iron and alloys of iron and SiIiZiUm ₅ iron and aluminum, iron and molybdenum, have found wide industrial use as core matorial for transformers, motors, generator parts and other applications. These cores are usually made of lamellas of relatively thin magnetic , punched or cut sheet metal or wound from long strips »Usually the laminated cores form one or more closed magnetic circles»

Because of the anisotropic character of the magnetic properties of single crystals made of iron or iron-based alloys, much work has been done to obtain a preferential orientation of the crystals in the polycrystalline material »Iron and the iron alloys under consideration here have a body-centered cubic crystal lattice at low temperatures and maintain this over a wide temperature range, which extends to several 10O ⁰ C, for pure iron z, B <> to 91O ⁰ Co Body-centered cubic materials have a direction of easiest magnetizability parallel to an edge of the unit cube -

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A sheet of material in which a large number of grains are arranged in such a way that they have favorable magnetic properties in several directions can be described by the orientation indication (10O) / ÖOjJ . (ίΟΟ) means that a (100) crystallographic plane or die surface lies in or parallel to the sheet plane, and / öO'i / means that a / UOi / crystallographic direction or 4 cube edges lie parallel to the rolling direction of the sheet. . Such a sheet is referred to as a cube-layer sheet or sheet with a cube texture.

An oriented magnetic sheet that has somewhat less good magnetic properties, but is still widely used commercially, is one such, ZcB. . of silicon-iron, in which the majority of the grains of the material have a ( 'MO) _j / Ü0_1_7 ~ 0 ^r i ^s "ti ^{to chan} S This orientation is referred to as Goss texture; 4 cube edge parallel to the rolling direction 4 of the The faces of the cube form on average an angle of 45 ° with the sheet surface ο Goss material is usually produced by secondary recrystallization, The Goss material in sheet form has superior magnetic properties in the rolling direction, s, 3. highest magnetic induction (flux density) at a given magnetic Field strength and maximum saturation “On the other hand, the magnetic properties perpendicular to the rolling direction are relatively poor, which means that if the magnetic flux path coincides with the whale direction .; .good magnetic properties are obtained, but if the flux v / eg in a direction perpendicular to Rolling direction changes, like ZoBo at a 90 ° corner in an I- or U-shaped punched part, this part is relatively bad has real magnetic properties with a corresponding reduction in the performance of the core.

It has long been recognized that a polycrystalline sheet of iron or iron-based alloys with cubic body-centered lattice with favorable magnetic properties both in the longitudinal and in the transverse direction, which the

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Goss-I.iaterial is only comparable in the direction of rolling are, "especially useful in the field of electrical apparatus would be, for example, annular magnetic stampings were made for motors and generators would be greatly improved if such magnetic sheets were available »

A practical method for developing cube texture in iron and iron-based alloys is through effort Numerous Inventors Escaped »Most of the processes which have been disclosed have been made to achieve the desired

to produce the effect are based on / secondary recrystallization phenomena ,

Purely secondary recrystallization is a typical characteristic that the amount of .Y / ure layer grains η in the primarily recrystallized structure is very small. As many examples show, the proportion of primary curling grains is only a few percent of the total volume, e.g. Ί0 to 20 ia. V / ecause the driving force for the subsequent growth of the cube layer grains during Selcundärrekristallisation of small differences in the surface energy of the different crystallographic surfaces depends _s is a critical control the furnace atmosphere or vacuum, if one is used, is required even if the annealing conditions carefully can be controlled _} the growth of these cube-shaped grains can be completely hindered by difficulties, the nature of which has not yet been fully clarified. Once the axis of a cube grain has stopped, further glowing to restore the ability to grow has little effect. On the contrary, its prolonged annealing treatment can often cause the (nO) grains to grow at the expense of the cube-ply grains (100). This difficulty can be overcome by repeated cleaning, which means etching or electrolytic polishing of the surface of the sample between repeated annealing treatments. ¹ = - and G-annealing can prevent the continuous growth of the grains by 809803/0493 BAD ORIGINAL - 4 -

almost the entire volume of the sheet can be caused ο Cube texture material produced by secondary recrystallization has been produced, but is characterized by an extraordinary grain size, which in the is generally not associated with an optimum of magnetic or mechanical properties -

The terms primary recrystallization and secondary recrystallization are used here in the same sense as they are generally applied and understood. (See ζΌβ. Acta Metallurgica, Volume 2, March 1954, Pages 174 to 183 and Acta Metallurgica, Volume 2, May 1954, pages 386 to 393) »

The cube texture can also be obtained by cold rolling and annealing grain-oriented bars or plates cut from them are produced in which columnar crystals are produced, which have a preferred direction which is essentially parallel to the axis of the columnar crystals. Such Grain-oriented bars are made by solidifying slowly and carefully in one direction of the metal bar in a specially designed form, in which precisely controlled heating and Cooling devices are attached.

All of the above methods require special and complicated apparatus and must be critical be controlled »The invention is mainly based on an economical and simple method of manufacture directed by cube texture in magnetic materials.

The invention relates to a method of production a fiber texture sheet made of iron or a body-centered cubic iron alloy, which may be added can serve to produce a soft-magenta polycrystalline sheet from it by primary recrystallization, da's has essentially high magnetic properties in the rolling direction and in the direction transverse to it »The '· / ÜCnJ fiber texture is a texture in which the

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/ ÜOjlJ direction lies in the rolling direction. In the / p pasertexture there are a large number of surfaces which are oriented in such a way that they lie between the extremes (100) '/ GOjJ and (110) / ÜOf /.

The invention also relates to a method which has at least one cycle of two cold rolling steps and

■ comprises two Primärrekristallisationsglühungen and allowed to generate from a sheet of iron or a body-centered cubic Bisenlegierung with / Ü0jf7-I'asertextur a soft--magnetisches polycrystalline sheet having a high proportion of Vi ^r · ürfellagekörnern>

As a special case, a sheet with a large number of cube-layer grains can be produced according to the invention by primary recrystallization by at least one cold rolling of a ferrous sheet that has predominantly grains with orientations (210) / pof / to (100) / 0027, the sheet after cold rolling, primary recrystallization takes place first at a low temperature and then at a high temperature *

Finally, a special case of the invention relates to a method for producing a primarily recrystallized sheet made of iron or a body-centered cubic iron alloy with over 50 ^c / o Y / ole layer grains. The process consists of cold rolling a sheet in which the grains predominantly have an orientation (410) / jSOiJ ^ is (100) / ÖOJy ⁷ , and annealing at low temperature with subsequent annealing at high temperature for primary recrystallization.

According to the invention, sheets of iron or from body-centered cubic iron alloys with primary recrystallization generated cube texture from hot rolled Plates produced that have a substantially disordered structure, but with a very weak eye preferred orientation. An intermediate product in the manufacture of the sheets with a cube texture is a new one

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_i / Ö0f7-5 ¹ aserteitur sheet, which is produced from a hot-rolled plate.

A hot rolled plate with an essentially disordered structure .; but with a caused by the hot rolling weak orientation, comprising the steps of subjecting t

1, annealing the plate at 800 to HOO ⁰ C for a period of up to 1 hour ο

2 .. Pickling the plate in acid solution to remove the surface scale.

(The goal of these first steps is to produce a clean sheet of crystallized ferrous material supply = sine annealing of 1 hour / 25 ram thickness is in generally sufficient).

ο cold rolling the plate to reduce the plate thickness from 40 to 80 pounds for the formation of the sheet too cause ο

ο Annealing the sheet in a moist hydrogen atmosphere at 700 to 1000 ⁰ C for 1 to 5 hours in order to bring about recrystallization and decarburization.

5 »Annealing of the recrystallized sheet at 1100 to 1300 C for 6 to 48 hours in dry hydrogen, to cause secondary recrystallization.

The above steps are intended to produce a new sheet material with a / tKDiT fiber texture with the rolling direction as the fiber axis - The following additional process steps convert the / pOf / '-' FaseT texture of the sheet into an end product with V / ürfelteztur.

6. Cold rolling of the pasertextur sheet with a "reduction in thickness." from 40 to 80 #.

7- annealing of the sheet material at 400 to 600 ⁰ C for 4 to 48 hours, & llisation to partially Priuierrekrist

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to reach.

8, the completion of the G-lühung of the sheet material "at 700 ⁰ C for MS 1000 r / 2 to 12 hours, to obtain au substantially complete primary recrystallization.

9 »Repeat the cold rolling and annealing steps 6, 7 and 8 at least once in the specified order in order to produce a primary recrystallized sheet that has at least 40 fo cube layer grains» If increased grain size is desired, an additional final annealing of the sheet at a temperature in the range from 1100 to 1300 ⁰ C can be used.

After steps 6, 7 and 8, up to 25 ^c ;> or more of the grains have a. Texture (100) / ÜOJ_7 "the majority of the remaining grains predominantly orientations between (210) / ÜOJ_7 and (100) / Po] ~ / 'N ^ac h the second cold rolling and Primärrekristallisationsglühen (step 9) shows the sheet 40 to 45 ^c! ° cube layer grains, the majority of the remaining grains is predominantly between (410) / pOf / and (100) / ÖOf7 "Hach a third cold rolling and Primärrekristallisationsglühen have 70 to 75 ^c / -> or more of the grains have an orientation (100) / Ö0J [ 7 on. Highly larger proportions of cube-shaped grains can be obtained by applying 4 of the cycles mentioned v / ground =

The Pasertextur / Ü0V7 sheets are an industrially usable intermediate product in the manufacture of the cube texture sheet _? The intermediate product can also be used directly for the production of magnetic cores =.

It is noteworthy that so far, the term fiber texture nur'für material has been applied in the form of wire, which is formed by drawing or extruding ο The / pOf / - fiber texture material is produced in sheet form for the first time using the inventive method =

The following materials are required to carry out the

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driving useful! Iron .. Iron with silicon up to 6 %, iron with aluminum "up to 8 % and iron with molybdenum up to 5% = iron can also be alloyed with 2 or more of the elements silicon, aluminum or molybdenum, for example with 3? ' Silicon and 0.5 * p molybdenum ·. A small amount of carbon (preferably less than 0.005 fo) may be present. More carbon may be allowed, but at the expense of magnetic properties. Small amounts of manganese up to 1 ^c / o will ordinarily be present. Incidental impurities and small amounts of other elements may be present.

The following example illustrates how to make a

Example I.

The material used was a 7 _? 7 mm thick, hot rolled plate of a commercially available silicon iron with 3 i ° silicon of the following composition in percent by weight «

Si 3.10 C. 0.026 Mn 0.087 P. 0.007 S. 0.023 Ou 0.012 Sn 0.007 ° 2. 0.005 Solved Al 0.005 Unresolved Al 0.0029 Pe rest

The plate was ^{in hydrogen at 1000 °} C. for 20 minutes. annealed and then pickled in sulfuric acid solution to remove the surface scale. This was followed by cold rolling to about 2.5 mm. The cold rolled sheet

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was strip in an oven at 85O ⁰ C for 2 hours annealing in a humid hydrogen atmosphere (ca. 27 ⁰ C dew point), decarburizing to the metal and to recrystallize The recrystallized sheet strip was then annealed at 1200 ⁰ C in dry hydrogen for 8 hours. The effect of the glow was complete secondary recrystallization. The grain sizes of the annealed metal strips were very uniform, the average size was approximately 2 mm in diameter »

Over the approximately 50 mm width of the sheet metal strip, 30 grains were arbitrarily selected and their orientation was determined by an optical goniometer. As the pole figure (Fig. I) shows, these grains have an orientation of the surfaces in the range from (100) to (TiO) and essentially parallel to the rolling plane, and the / 00J_7 ~ axis almost parallel to the rolling direction Sheet metal strip can be described as a / ÜOf / ~ fiber texture with the rolling direction as the fiber axis.

The orientation (TiO) is at the equator of the Pole figure denoted by the symbol (), the (210) -orientation by the symbol x, the (410) -orientation by the symbol 0 and the cube orientation by the symbol Q

The process for the production of 'ÖOiT' fiber texture can be varied. Preferably, a hot-rolled plate is used as the starting material with a thickness of about 1.3 to 15 mm. The first anneal may be at 800 to 110o ⁰ C for a period up to an hour or longer run, and for etching the surface oxides, other acids, ZJ, hydrochloric acid and nitric acid, are used. The cold rolling of the annealed and cleaned material should bring about a reduction of 40 to 80 $ = the annealing in moist hydrogen with a dew point of up to 65 ^° C. can take place at 700 to 1000 ^{° C. for 1 to 5 hours.} The secondary recrystallization anneal can last 6 to 48 hours in dry hydrogen

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Π00 to 13OO ° C. In this example a Average grain size of 2 mm in diameter reached, what is considered good, an acceptable range for the average size is within the limits of 0.5 up to 5 mm,

The following example illustrates the production of Y / cube sheet metal according to the invention using a Initial blsches with a / ÜO_1_7 fiber texture < >

Example II

A _j /.OOj/-Ii ¹ asertextur sheet with a thickness of about 2.5, which was obtained as described above, was cold- rolled at 40 ° p to a thickness of about 1.5 mm. Thereafter, the sheet was annealed for 24 hours at 55O ⁰ C, ο to initiate primary recrystallization the strips were then annealed for a further 2 hours at 700 ⁰ C, to complete the primary recrystallization "The amount of cube texture grains after this annealing, was approximately $ 17 *

The metal strips were ^{annealed at 80O 0} C for 2 hours. The proportion of V, ^r ürfellagekörner increased from. 17 to 25 ° A ° The rest of the structure mainly comprised grains with an orientation from (210) / jÖOf / to (100) / ßOjJ ■ ·

The sheet metal strips were then cold-rolled for the second time with a reduction in thickness of 70 ^c / o to a thickness of about 0.45 ram, compartment annealing for 24 hours at 55O ⁰ C and completion of the primary ^{recrystallization by annealing at 800 0} C for ₃ 2 hours, - the proportion of Y / ole layer grains was now 40 fo compared to previously 25 ^C , L The rest of the grains had a predominant orientation of (410) ß) 0f / to (100) / 0027-

The 0.45 mm thick strip was then cold rolled for the third time with a reduction of 70 ^c / o to a thickness of about 0.15 mm. The sample was back first at 24 hours

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55O ⁰ C and then for 2 hours "annealed at 800 ⁰ C, ο to develop a complete primary recrystallization All anneals were carried out so that the samples were placed in the furnace and the furnace was brought together with the sample to the desired temperature. The The structure consisted of uniformly fine grains with an average diameter of 0.04- mm. The proportion of cube-shaped grains was $ 70 and almost all cube-shaped grains had two of their faces within 5 of the sheet plane The rolling direction was such that 62 fj of the cube grains were within ί 5 °? 85 $ of the grains within Z 10 °, and 90 io of the grains were within ± 15 ° ..

In the reproduction of a microphotograph (Fig. 2), the bright areas mean the grains oriented in the cube position. Un to obtain a product with excellent magnetic properties that are completely primary recrystallized sheet in addition more than 800 ⁰ C, preferably annealed in the range of TI00 to 1300 C, a growth of the grains and an improvement to obtain the degree of orientation of the cube layer grains .. An annealing at ζ B "1200 ⁰ C for 2 hours produces a growth of the grains. However, little or no secondary recrystallized grains form during this last annealing

All firings were carried out in a kiln with a ITickel chrome tube in a dry hydrogen atmosphere with a dew point of about -60 ⁰ C <> The samples were taken at room temperature in the oven and then heated to the temperature indicated * After the samples at If the temperature was kept for the specified time, they were brought to the cold zone inside the furnace tube to cool down ο

Example III

A procedure similar to that in Example II was used o The procedure differs only in

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that the amount of deformation "is increased during the first cold rolling". The same, approximately 2.5 mm thick fiber texture sheet with / ÖOj_7 texture was used. «The fiber texture sheet was 60 ° ß> cold rolled to a thickness of about first ram Then 24 hours at 55O ⁰ C was annealed and Prirnärrekristallisation was completed by further annealing 2 hours · at 700 ⁰ C ο Thereafter, the sheet was annealed for a further 2 hours at 800 ⁰ C.

This was followed by a second cold rolling at a deformation of 70 io "to about 0.3 mm in thickness was then carried out for 24 hours at 55O ⁰ C and 2 hours at 800 ⁰ C annealed.

The sheet metal strip is / o cold-rolled m for the third time by 70 ° to about 0.1. The final annealing was similar to that of Example II "The proportion of the" cube layer grains was approximately 70 to 75 ^c / ° and were the other structural components of the sheet essentially the same as in Example II »As stated in Example II, a product with optimal magnetic properties ^{can be obtained by additional annealing at 1100 to 1300 0 C»}

The conditions and measures described in Examples II and III for producing cube texture material / ÜO ^ fiber texture material can be used within 'certain Limits are varied »

For example, the cold deformation can be varied within the range of $ 40 to $ 80.

An essential feature of the invention is the primary recrystallization annealing. This comprises the initial annealing at a low temperature in order to initiate the recrystallization, and the subsequent annealing at 700 to 1000 ^° C. in order to complete the primary recrystallization. The first annealing to initiate, the primary recrystallization, can take place at 400 to 600 ^° C. for 4 to 48 hours or longer. At higher temperatures, the shorter ones are sufficient. Duration .. ■ ■

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Since the low temperature annealing initiates the desired primary recrystallization, some comments should be made on the associated phenomenon ο When studying the recrystallization of single crystals it has been observed that a (110) / 5017-ICr is all after cold rolling and primary recrystallization annealing either (110) / ßOf / or (210) / 00i7 can be oriented according to the level of the annealing temperature rird, on the other hand, the orientation arises (210)

Similarly, after cold rolling and primary recrystallization annealing, a (210) / 50j [7 crystal can be converted into either the (210) / OOjT 'orientation if a high temperature is used or the (410) / UOff reflection if a low temperature is used.

If a cold rolling and a Primärrekristallisationsglühung on a crystal with an orientation (410) / 00j7 applied the Primärrekristallisationsprodukt werfer.wird usually a (ίΟΟ) / ÜO27-O ^r ientierung have, because the (410) / ^{ri-orientation} Ü027-0 already very close the (100) / 50j7 orientation comes «The (lOO) / ÜOjJ orientation is the cube position ο

From the above experimental observations it can be seen that a crystal with an original orientation of (110) / D "0j7 by successive cycles can be converted into a product with a cube layer by cold rolling and primary recrystallization annealing. pre-condition is here at least during the beginning a low annealing temperature. If a high temperature alone is applied, the product after cold rolling and primary recrystallization annealing is essentially the have the same orientation as the original crystal.

In the method according to the invention, the above are Principles on polycrystalline material that is a fiber

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texture from / OOjJ has applied. As stated above, the material comprises an orientation range from (110) / OOjy to (100) £ Ö0_17> including the orientations (210) / pOf /, (410) / ÜOjf countless other orientations. The / OQiJ-las er texturMaterial is cold-rolled and in this state can have numerous components of a deformation texture that have different recrystallization temperatures. The low temperature of Primärrekristallisationsglühung promotes the recrystallization of certain deformation texture components, resulting in an increase of those grains ₅ a desired preferred direction have "At the same time the low Temperaturglühung aims to suppress the recrystallization of other deformation texture components with after recrystallization an increase in grains would cause undesired orientation o The crystals in the polycrystalline material with the orientations (110) / OOjJ, (210) / ÜOjJ and (410) / ÜOj / correspond to the effects of cold rolling and primary recrystallization annealing, that is, predicted from the experiments on single crystals , the grains rotate around an axis parallel to the rolling direction and approach the cube position with each cycle of cold rolling and annealing n have, strive to approach the cube position after recrystallization. When a grain has reached a cube, it retains this orientation during further cold rolling and annealing steps »

Once the growth of the desired grain nucleus has been well initiated by annealing at a low temperature, a higher temperature promotes rapid growth of the grains with the desired orientation. This last temperature can be 700 to 1000 ⁰ O and is maintained for 1/2 to 12 hours until complete primary recrystallization is achieved. The final annealing temperature can vary. For example, the label sheet 2 hours at 800 ⁰ C ₃ followed by 2 hours at 900 ⁰ C, are annealed.

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A special feature of the method of the invention is that the furnace atmosphere is not critical »In the Examples have been used as "dry hydrogen" atmosphere for convenience, but can be without adverse effects on the texture of the material also moist hydrogen, ammonia and inert gases such as argon, and even air must be used = of course, if the atmosphere used has an undesirable. Degree of oxidation causes the oxidation product to be removed from the material before the sheet can be used. To get that extra This step is to be avoided, and because hydrogen gas is mostly readily available, is for practical reasons uses a hydrogen atmosphere »

The thickness of the sheet metal strip can also be made much larger than indicated in the examples _? The limitation in sheet thickness is mainly due to the practical difficulties associated with cold rolling very thick plates =

As described, a hot-rolled plate is treated with a substantially disordered structure to '"/ ürfeltextur material to produce" As an essential Zwirchenprodukt a / OQfZ-lPasertextUT sheet is first generated "When a! Fiber texture plate is available, be only the new cold rolling and annealing steps applied to it »

As indicated above, the first cold rolling step and primary recrystallization annealing of the / OOjJ fiber texture material produces a material which contains 17 "to 25 <$> cube-ply grains with a remainder of grains whose orientation predominantly is in the range of (210) JSO ₁ I / Ms (100) / ÜOjJ lies »(see Fig. I)« When a material having this final orientation region, no matter how it is produced, is subjected to the cold rolling annealing cycle of this invention, a sheet material is produced which has 40 ° /> or more cube gel grains and a remainder of grains whose orientation is predominantly in the range between (410) / ßOf / to (100) / OOjJ ο when the latter material is subjected to the cold-rolling annealing cycle you have a material with

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prevailing cube position.

Materials with an orientation essentially from (210) / 0027 to (100) / jSOtf, which have been produced by casting technique or by single crystal technique or by rolling and annealing applications, only need to be subjected to two cold rolling and annealing cycles in order to produce a material which has a predominantly cube texture, similarly, a material that has been given an orientation (410) £ Ü0j7 ^to (100) / ÜOjJ by this last technique only needs to be subjected to one cold rolling and annealing cycle in order to become a material that has a substantial litter texture.,

The primary recrystallization technique is therefore advantageous v / o you a comparatively easy control of the grain size and avoids a critical furnace atmosphere, reduces the required annealing temperature and allows thicker sheet material to be produced. Farther Soft annealing can be carried out after punching, depending on the process conditions according to the invention Procedures are less critical than in previous procedures »

Claims (1)

Claims A process for preparing ^ 00J ^[7-l-n asertextur sheets of iron and, in particular body-centered cubic iron alloys such as Eisensilizium-, Eisenaluminium- and Sis.enmolybdän-1-egierungen, from hot-rolled plates having a substantially disordered structure, characterized by the following Work steps: (a) Cold rolling the plates by 40 to 80 ^C , O to sheet metal (b) recrystallizing and decarburizing the sheet by · annealing in wet hydrogen for 1 to 5 hours at 700 to 100O ⁰ C (c) Annealing the recrystallized sheet for 6 to 48 hours Dis 1300 ⁰ C in dry hydrogen: 809803 / 0A93 _{ßAn ηο} , _{Λ (Μ4 (} "-7- Hours at 1100 to 1300 ⁰ C in dry hydrogen " ο Method for creating cube texture in sheet metal Iron or, in particular, iron alloys centered in cubic form, such as iron silicon, iron aluminum and Iron molybdenum alloys, from / Ü0J_7 fiber texture sheets, characterized by the following work steps: (d) Cold rolling the fiber texture 31ech.es by 40 to 80 # (e) introducing a primary recrystallization by annealing for 4 to 48 hours at 400 to 600 ⁰ C. (f) Complete the primary recrystallization by annealing for 1/2 to 12 hours at 700 to 1000 ^° C (g) if necessary, repeating work steps (d) at least once _? (e) and (f) * 3- The method according to claim 2, characterized in that if, after method step (f), the sheet metal contains a predominant proportion of grains with orientations in the range from (210) / UOY / to (100) / T) Oj / -, repeat the processing steps (d) to (f) at least twice. Method according to claim 2, characterized in that if the milling texture sheet has predominantly grains with orientations in the range between (210) / ÜOy / to (100) / ÖOiJ, process steps (d) to (f) are repeated once will" Method according to claim 2, characterized in that if the fiber texture sheet predominantly has grains with orientations in the range (410) / ÜOf / to (100) / O ~ Öj7, only method steps (d) to (f) are used » 6, method naoh claims ^ .to 5, characterized by a final ^{annealing at 1100 to 1300 0} Co BATH ORIGINAL '809803/0493