DE2900333A1 - CLAD METAL PRODUCT AND METHOD FOR MANUFACTURING IT - Google Patents

Description

KRAUS & WEfSERT 2300333

PATENT LAWYERS

DR. WALTER KRAUS DIPLOMA CHEMIST DR.-ING. ANNEKÄTE WEISERT DIPL-ING. SPECIALIZATION CHEMISTRY IRMGARDSTRASSE 15 ■ D-8OOO MUNICH 71 · TELEPHONE 089 / 797077-797078 - TELEX O5-2T2156 kpat d

TELEGRAM CRAUS PATENT -

Ϊ ■■■ '■' ■■■■

1983 WK / left

CLAD METALS, INC. , Canonsburg. (V. St. A.)

Clad metal product and process for its manufacture

2800333 - ϊ -

Description

The invention relates to plated metal products having a plurality of Elements and processes for their manufacture. More particularly, the invention relates to clad copper core aluminum and Stainless steel product. '

The use of laminated or clad metal products with three layers or less is well known. So are e.g. stainless steel utensils with a copper bottom layer and also those made of stainless steel with an aluminum core well known. These products have been available for some time; they are widely used in the manufacture of cooking utensils used. One of the persistent problems with these known materials is that these materials fail to do so are to achieve rapid and even heat transfer over the entire pan surface. The known materials While far superior to single-layer metal products, they are still far from perfect to be.

It is already a clad metal product based on a copper clad aluminum core or a copper core between two layers of aluminum clad with one or more layers of stainless steel has been proposed. This product eliminates some of the basic problems described above known materials. For example, heat is distributed quickly and evenly and that The problem of invisible oxidation of copper is eliminated that occurs when it is used in known copper-clad Stainless steel utensils. Compared to popular aluminum clad with stainless steel a superior heat distribution is achieved. The material has all the unique thermal properties in combination of copper and aluminum along with the corrosion and abrasion resistance of stainless steel.

& 9982Θ / 0946

ORIGINAL INSPECTED

A unique and completely unexpected characteristic of the proposed metal products and those made therefrom Cooking utensils are characteristic of reducing food sticking to the surface. The problem with all metallic cooking utensils is that food sticks to the surface when these are subjected to heat occurred. Teflon and other synthetic coatings are a thing of the past has already been applied to prevent this phenomenon. However, the material of the present invention is of concern practically equivalent to preventing sticking with Teflon-coated everyday objects.

Tests have been carried out to determine the various thermal properties of many metals on this Area used to be carried out to identify differences in uniform heat transfer capability to determine. The following test procedures were applied to materials for use in such cooking utensils to rate.

A single gas-heated heat source, similar to a Bunsen burner, was placed equidistantly under each device arranged. The amount of gas available to the burner was constant. The flame hit right in the middle of the The outer bottom of the article and created a 3 inch circular contact. Thermocouples were attached to the Added to the inner center of the pan, which extends to the outer edge including the side wall in lengths of 1.27 cm stretched. All objects had a similar shape, i.e. it was a grill or frying pan with 25.4 cm.

The excellent heat transfer properties of products made of solid aluminum; copper / aluminum-clad stainless steel; stainless steel-clad aluminum / copper core pro-

9 * 9828/0946

products and a two-layer stainless steel clad aluminum product is notable. Because copper is considered the ultimate in thermal conductivity and because its thermal conductivity is generally considered to be 100%, its ability to transfer heat is well known. In its pure state, aluminum is generally considered to be the second best metal for heat transfer and it has a conductivity of about 57% that of copper. Cast iron, also used for cooking utensils becomes, has about 16.6% of the thermal conductivity of copper, while mild steel, as it does for the core of stainless steel clad mild steel in U.S. Patents 2,718,690 and 2,758,368 is 15.1% of the conductivity of pure copper. owns. Type 304 stainless steel (18% chromium, 8% nickel) has approximately 3.83% thermal conductivity of pure copper. Ceramic materials similar to glass are total resistances to heat transfer and they have a conductivity of about 1% that of pure copper.

A direct calculation of the percentages of each metal that is used in the cross section of a clad metal which may be suitable for cooking utensils, in combination with the thermal conductivity relative to copper would give the heat transfer values that are required to determine the thermal conductivity of bonded, plated metal. The thickness or the mass The metals used in the body of a commodity are also of importance when one takes into account cooking behavior. According to the earlier proposal, a minimum thickness of 1.2 mm is therefore recommended.

Tests were carried out to determine the food release properties of different materials to determine. Utility objects with similar dimensions were made on a gas or electrically heated kitchen stove

909828/0946

ORIGINAL INSPECTED

■ Μ-

that had a central thermocouple capable of doing so was exactly the center of the outer bottom of the cooking appliance to feel. The inside of the commodity was prepared by lightly coating it with a cooking oil. Then there was flour on the covered with the cooking oil Surface of the cooking object sprinkled on excess Flour quantities were removed by dropping them off. Of the The resulting thin coating of flour on the surface of the commodity was then observed for color. The utensil was placed on the burner with the thermostat and heated by turning the burner setting was set to 177 C. The cooking utensils were about a Heated for a period of 2 1/2 minutes. Then they were taken away from the burner. Tried the heated Remove flour from the surface of the cooking utensil by placing the cooking utensil under a tap with a pressure of 15.9 kg was brought. Water was used for rinsing at a temperature of approximately 43.3 ° C. The length of time it took for the flour to go through the described Rinsing process was removed was recorded. The tack resistance was directly related to time the removal by rinsing with water is determined. The color of the flour is affected by the concentration of heat. The greater the heat concentration, the darker the burnt appearance of the flour. Cooking appliances with high conductivity resulted in little or no heat discoloration on the surface of the flour. Below the results obtained corrected to a uniform basis of 3.2 mm in thickness are reported.

909828/0946

product

Color appearance distance

of the flour

opening time

1.Cu / Al / ES (thickness 3.2 mm)

2. Teflon-coated Al (thickness 3.2 mm)

3.Al (thickness 3.2 mm)

4. ES-clad Al (thickness 3.2mm)

5.ES / Al / Cu / Al / ES (thickness 2.8 mm)

6.ES / AI / ES (thickness 2.8mm)

7. ES / Al bottom (0.9 mm ES / 2.3 mm Al)

8. Porcelain-coated steel (thickness 2.2mm)

9. SS unalloyed steel (iron core)

(Thickness 1.4 mm)

10. High temperature glass

cream colored
cream colored

cream colored
cream colored
cream colored
tan

tan brown

22 sec.

23 sec.

25 sec. 29 sec. 33 sec. 37 sec. 48 sec.

tan brown

3 9.4 sec, dark brown 63.0 sec,

dark brown 105 sec.

The food release properties of stainless steel / aluminum / copper cooking utensils were superior to all other metal and glass surfaces. The release properties of synthetic surfaces are improved with increasing thickness and are the same when using an aluminum thickness of 3.2 mm. Cooking devices with the same thickness made of copper / aluminum / stainless steel showed release properties that were superior to those made of Teflon-coated aluminum of the same thickness. Cooking appliances made of stainless steel _r aluminum-copper, aluminum, stainless steel were in the same area as Teflon-coated aluminum. The excellent thermal properties of the plated metals are described herein. These properties are of the greatest importance for the superiority of the metal combinations according to the invention.

It has been found that when pure aluminum is used alone as a cladding for copper, there are cases where a Orange peel effect takes place. This effect cannot be achieved by any known mechanical or thermal treatments to be controlled. It has now been found that this orange peel effect can be switched off if one

909628/0946

ORIGINAL INSPECTED

Aluminum alloy base with a thin coating of pure Applies aluminum on the sides bonded to the copper and / or stainless steel. This creates the orange peel problem while maintaining these excellent bonding properties of pure aluminum. It was determined, that the base is an aluminum alloy, e.g. 3003, 3004, 5005 or any other such aluminum product that is considered in the art to be an alloy instead of pure aluminum, can be. As a thin pure aluminum coating on the aluminum alloy e.g. the aluminum grades EC, Π00, 1130, 1230, 1145, 1175, or 7072 can be used. This pure aluminum should be on the surfaces of the aluminum alloy clad to be bonded to the copper and stainless steel.

The invention provides an aluminum clad copper product in which the aluminum can be clad on one or both sides of the copper. The aluminum-clad copper or copper-core aluminum can then be clad with stainless steel (ES) on one or both sides of the aluminum. The aluminum must be substantially pure aluminum (for example of the 1100, 1130, 1230, 1145, 1175 or 7072), which is coated on an aluminum alloy such as type 3003, 3004, 5005th Preferably, an aluminum, for example of the 1145 type, is used which is coated as a layer cladding on one or both sides of an aluminum alloy, for example of the 3003, 3004 and 5005 types. All elements or components of the composite material are preferably cleaned and their surfaces conditioned by sanding them to remove any oxides. However, this stage can be omitted with the stainless steel, but must be with a pure aluminum plate.

! © 9828/0946

ORIGINAL INSPECTED

application surface of the aluminum alloy. Preferably, the product can be made by forming a composite precursor of aluminum and copper, which precursor can be copper clad on one side of the pure aluminum clad aluminum alloy or aluminum clad on both sides of a copper core whereupon a stainless steel clad is bonded to one or both sides of the aluminum clad aluminum alloy. This preformed cladding or core is preferably cleaned and conditioned on the surface (s) of the bare aluminum by abrading it or subjecting it to a wire brush treatment or any other suitable mechanical method to remove any oxides. However, this stage can be omitted for stainless steel. In this procedure, the copper clad with an aluminum alloy which is in turn clad with pure aluminum or the copper core which is clad with an aluminum alloy which in turn is clad with pure aluminum is cleaned, cold-bonded under pressure in the manner described above, for example by severely reducing from 40 to 70% in one or more passes through a roller mill and then, if desired, post heat treated to increase the strength of the interlayer bond. , Heating the pre-formed plating or the preformed core consisting of an aluminum alloy, which is plated with pure aluminum, and copper with the stainless steel to a temperature of about 149 to 427 ° C (300 to 800 ⁰ F) to 20 to 70% reduced in a single pass, or alternatively up to 5% reduced in a rolling stand, and then reduced in a second stand by 10 to 25% and then to about 316 to 427 ° C, preferably about 371 ° C (600 to 800 ⁰ F, preferably 700 ⁰ F) is reheated to allow diffusion between adjacent layers of the metals to take place. The diffusion process increases the bond strength between the three dissimilar metals. It also causes a certain amount of tension relief. The re-

999828 / 094S-

Resulting product can easily be thermoformed into cooking vessels will.

According to a second alternative, the product can be made by forming a composite pre-cladding or core of an aluminum alloy clad with pure aluminum and copper and then applying the stainless steel cladding to one or both sides of the surface of the pure aluminum . In this procedure, the aluminum alloy and copper sheets clad with pure aluminum are cleaned by grinding and conditioned, brought into contact with one another, heated to 149 to 371 ° C and subjected to a reduction of 30 to 70%. The composite preform of pure aluminum clad aluminum alloy and copper can be post-heated to increase the strength of the union. The resulting copper / aluminum compact product is then abraded on the surface or surfaces of the pure aluminum and then used as a cladding or core for a stainless steel cladding process. In this stage, the assembly of cladding or core and stainless steel is reheated to about 316 to 427 C, preferably subjected to a first reduction or cross-sectional reduction of about 2 to 5% and then a second reduction or cross-sectional reduction in the range of 5 to 25%. subject. Alternatively, the composition can also be reduced or reduced in cross-section by about 20 to 70% in a single reduction pass. The product is then ^{heat-treated at about 371 °} C. in order to bring about tempering and diffusion, as described above.

According to a third alternative, one or two sheets of pure aluminum clad aluminum alloy are mechanical cleaned, heated to 316 to 427 ° C and sealed with one or both surfaces of a copper sheet at room temperature

989 82 8/0948

ORIGINAL INSPECTED

door contacted and either through a single stage or two-stage reduction, as described above, reduced or reduced cross-section. The composite preliminary product Made of pure aluminum clad aluminum alloy and copper, can be heat treated if desired, to increase the strength of the union between the layers. This cladding or this core is then between Brought stainless steel sheets and reduced or reduced cross-section according to the procedures given above and remunerated.

A fourth alternative could be to make a preform jaus., An aluminum alloy clad with pure aluminum on one or both sides of the copper, a cold or hot bond as in connection with the first Alternatives discussed include followed by cold bonding this preform from clad with pure aluminum Aluminum alloy and copper on one or both sides with stainless steel using a severity reduction stage with 30 to 70% could be done in one or two passes. The resulting compound Product made of stainless steel, copper and aluminum is made, as in Related to the first alternative discussed, heat treated.

According to a fifth alternative, all the elements, i.e. the copper, become the aluminum alloy clad with pure aluminum and the stainless steel of the composite material, preferably cleaned and on their exposed surfaces conditioned by abrasion to remove all oxides, but this can be omitted in the case of stainless steel can. The pieces are heated separately or brought together before heating. You will be on a temperature heated from about 149 to 427 ° C, reduced by 20 to 70% in one pass or reduced cross-section or up to about 5% reduced in one roll stand or reduced cross-section and then in a second roll stand by 10 to

9 * 9828/0946

25% reduced or decreased cross-section and finally again heated to about 316-427 ° C (preferably at 371 ⁰ C), so that a diffusion may take place between adjacent metal layers. The diffusion process increases the bond strength between the three dissimilar metals.

The invention is based on the following examples and the attached figure, which shows the cross section of an inventive composite product shows, explained in more detail.

example 1

A copper sheet with a thickness of 0.3 mm was cleaned by grinding with a wire brush and placed between two sheets of aluminum of type 3003 each with a thickness of 1.8 mm, which were coated on both sides with a thin layer of aluminum of type 1145 and similarly cleaned by abrasion. The copper and pure aluminum clad aluminum alloy were reduced in section by about 50 to 65% to bond them together. The 1.3 mm thick aluminum clad copper preform was abraded clean of the exposed surface of pure aluminum and then brought into contact with two sheets of 304 stainless steel 0.3 mm thick and against the stainless steel cleaned surfaces made of pure aluminum. The assembly of metals was heated to 371 ° C and passed through a rolling mill to reduce the thickness to 1.7 mm. The assembly was then passed through a second mill and reduced in cross section to a thickness of 1.3 mm. The resulting product was then reheated to 371 ^° C. for a sufficient time to obtain diffusion between the adjacent metal layers throughout the interfaces. The remunerated end product was deep-drawn into cooking vessels such as frying or grill pans.

98-9828 / 0948

ORIGINAL INSPECTED

If it is desired to have one surface made of stainless steel and the other made of copper, then follow the steps outlined above Procedures a preform consisting of a copper clad aluminum material, formed, whereupon only one Side of the copper being plated.

Example 2

A copper sheet having a thickness of ₇ O 3 mm was cleaned by sanding and between two purified by grinding sheets of 3.2 mm thick made of aluminum alloy Alclad 3004, which had been coated with aluminum of the type 1145 made. The metals were heated to 232 ° C. and then subjected to a first rolling pass with a reduction of about 2%. They were then rolled to a thickness of about 2.8 mm in one final pass. The rolled product was then reheated to 371 ^° C. in order to allow diffusion between the metal layers to take place. The end product was cut into blanks and deep-drawn into cooking vessels.

If it is desired that one surface be stainless steel and the other aluminum or copper, then the the same procedures as described above can be carried out, except that the coating is not used is omitted.

Example 3

A copper sheet 0.3 mm thick was cleaned with a wire brush by grinding and between two Each 1.9 mm thick sheet made of the aluminum alloy type 3003, coated with aluminum 1145 and similar Way that had been cleaned by grinding. Two sheets of 304 stainless steel with a thickness of 0.3 mm was cleaned by abrasion and applied to each side of the aluminum alloy sheet clad with pure aluminum.

8/0 9.48

ORIGINAL INSPECTED

marriage brought. The assembly was ^{heated to 371 °} C. and passed through a rolling mill to reduce the thickness to 3.0 mm. The resulting product was then reheated to 371 ^° C. for a sufficient time so that diffusion could take place between adjacent metal layers in their interfaces. The remunerated end product was deep-drawn into cooking vessels.

It has been found that the products of the invention for the manufacture of cooking vessels in a variety of ways and can be used in a variety of combinations. For example, a 9-layer material such as it is shown in the figure consisting of a copper core 10 connected on each side with an aluminum alloy sheet

11, which in turn is made of pure aluminum on each side

12 is coated, which in turn is coated on both sides with stainless steel 13, can be used to Manufacture cooking vessels that have the desired properties of stainless steel on the exposed surfaces, which, however, have a uniformity of heat transfer that is not available with all known materials is.

A 7 or 8 layer material with a copper core clad with pure aluminum on each side Aluminum alloy is coated and which has an outer layer made of stainless steel, is used to manufacture cooking vessels very satisfactory, which porcelainized on the exposed surface of pure aluminum after molding or coated or intended to be used as discs to be attached to the bottom of cooking utensils which are made in a conventional manner from solid or clad metal »Here too, again obtain high heat transfer effects. In the event that disks are used, the coating can be made of pure Aluminum can be omitted from the surface to be exposed.

Finally, a 5-layer material can be used according to the above Procedures are produced that has a copper layer on one side with a pure. Aluminum clad aluminum alloy is coated and that has an outer layer of stainless steel bonded to the surface of pure aluminum, thereby providing a product that can be deformed into cooking utensils which have a copper outer surface for decorative purposes and for heat transfer, the other being The outer surface of the stainless steel is provided with an aluminum core.

The invention has been described above mainly on the basis of cooking appliances because this is the technical field in which the greatest amounts of such metals are used will. However, the material of the invention can be used for a wide variety of technical purposes, where heat transfer is important and where resistance to discoloration, oxidation, etc. it is asked for.

End of description.

PAD ORIGINAL

Claims (27)

PATENTANWÄLTE DR WALTER KRAUS DIPLOMAL CHEMIST DR-ING. ANNEKÄTE WEISERT DIPL-ING. SPECIALIZATION CHEMICALS IRMGARDSTRASSE 15 ■ D-8OOO MUNICH 71 · TELEPHONE 089 / 797077-797078 ■ TELEX 05-212156 kpatd TELEGRAM CRAUSPATENT 1983 WK / li Patent claims 1. Clad metal product characterized by a core made of copper or a copper alloy and a layer of a Aluminum alloy coated with essentially pure aluminum, the core being the major part of the thickness of the composite product is formed by at least one stainless steel cladding layer opposite the copper, which is bound to the aluminum. 2. Metal product according to claim 1, characterized by a layer of an aluminum alloy which .on the sides dc- _; : Aluminum's bonded to the copper on either side of the copper, coated with essentially pure aluminum, by an outer plating layer of stainless steel on one of the aluminum layers. 3. Metal product according to claim 2, characterized in that the core is made of a layer of copper and layers of an aluminum alloy, which is coated with substantially pure aluminum on each side, and that the core on each side with a layer of stainless steel is plated. 4. Metal product according to claim 1, characterized by a core of an aluminum alloy, which is based on pure aluminum coated on both sides, and by outer claddings of copper and stainless steel. 5. A process for the manufacture of a composite clad metal product , characterized in that first a copper sheet and a sheet of an aluminum alloy , which with essentially pure aluminum on the to be joined 909828/0945 BATH ORIGINAL _ ₂ _ 2300333 The sides are coated with one another under a pressure sufficient to achieve a reduction to 80%, the product obtained is subjected to a post-heat treatment, the aluminum surface is mechanically cleaned> the mechanically cleaned, pre-bonded, composite material is applied to a stainless steel sheet, the metals stacked on top of one another heated to a temperature from 149 to 4 27 ° C (300 to 800 ⁰ F) and the stacked metals enough pressure to a first reduction or cross-sectional reduction of about 2%, followed by a reduction or cross-sectional reduction of about 5 to 25%, subject. 6. The method according to Anr .uch 5, characterized in that the sheets are combined under a pressure sufficient to cause a reduction in cross-section from about 20 to 70% is obtained. 7. The method according to claim 5, characterized in that the sheets to be combined from a central copper sheet and an aluminum alloy sheet with substantially pure aluminum on each facing the copper sheet Side is coated, and a stainless steel sheet on at least one side of the pre-formed copper aluminum core exist. 8. The method according to claim 5, characterized in that one connects the plates to one another in such a manner that passing it through a rolling mill. 9. The method according to claim 5, characterized in that the metal sheets are subjected to a post-heat treatment at about 371 C (700 ⁰ F). 10. A method for producing a composite clad metal product, characterized in that there is a copper sheet and an aluminum alloy sheet, the 009828/0946 ^Λ: = - BAD ORIGINAL with essentially pure aluminum, coated on the sides to be united, first connects with one another under sufficient pressure that a reduction or cross-section reduction to 80% is obtained, the material obtained is subjected to a post-heat treatment, the aluminum surface is mechanically cleaned, the mechanically cleaned ,
pre-bound, composite product on a sheet
Stainless steel brings and the stacked metals
subjected to an initial reduction or reduction in area of about 2% followed by a reduction or reduction in area of about 5 to 25%. 11. The method according to claim 10, characterized in that the metal sheets are connected to one another under sufficient pressure that a reduction or cross-section reduction from about 20 to 70% is obtained. 12. The method according to claim 10, characterized in that the sheets to be combined from a central copper sheet and a sheet made of an aluminum alloy which ^{is coated with essentially pure aluminum on each side facing the} copper sheet and a stainless steel sheet on at least one side of the preformed copper aluminum core exist. 13. The method according to claim 10, characterized in that the sheets are combined with one another by passing them through
a. Rolling mill directs. 14. The method according to claim 10, characterized in that post heat treatment at about 371 F 1700 ⁰ F). 15. A method of manufacturing a composite clad metal product, characterized in that a copper sheet and a sheet of an aluminum alloy, which on the sides to be connected with substantially pure
Aluminum is coated, initially to 149 to 427 ° C (300 6 ** 828/0046 ORIGINAL INSPECTED 2SOQ333 -A- to 80 (J ⁰ F), then bonded together under a pressure sufficient to obtain a reduction or cross-sectional reduction of 20 to 70%, the material obtained is subjected to a post-heat treatment, the aluminum surface is mechanically cleaned, the mechanically cleaned , prebonded _t composite product on a sheet of stainless steel hangs up, heats the piled materials to a temperature of 149 to 427 ° C f300 to 800 ⁰ F) and the stacked metals enough pressure for a first reduction or cross-sectional reduction of about 2%, followed by a reduction in cross section of about 5 to 25%. 16. The method according to claim 15, characterized in that the sheets are connected to one another under a pressure that it is sufficient that a reduction or reduction in cross section of about 20 to 70% is obtained. 17. The method according to claim 15, characterized in that the sheets to be joined from a central copper sheet and a sheet of an aluminum alloy, which is coated with substantially pure aluminum on each of the copper sheet facing., Side, and a stainless steel sheet on at least one side of the pre-formed copper aluminum core. 18. The method according to claim 15, characterized in that the sheets are joined together by passing them through a rolling mill. 19. The method according to claim 15, characterized in that one the lead subject. heat treatment of the sheets at about 371 C (700 F) 20. A method of making a composite clad metal product, characterized in that one Copper sheet and an aluminum alloy sheet, the is coated with substantially pure aluminum on the sides to be connected, first at 149-427 ° C heated (300 to 800 ⁰ F), then connects at a sufficient pressure that a reduction or cross-sectional reduction is obtained of 20 to 70%, Subjecting the product obtained to an after-treatment, mechanically cleaning the aluminum surface, applying the mechanically cleaned, pre-bonded, composite product to a sheet of stainless steel and the coated metals to a first reduction or cross-sectional reduction of about 2%, followed by a reduction or cross-sectional reduction of about 5 to 25%, subject. 21. The method according to claim 20, characterized in that the metal sheets are connected to one another under a pressure which it is sufficient that a reduction or reduction in cross section of about 20 to 70% is obtained. 22. The method according to claim 20, characterized in that the sheets to be joined together from a middle Copper sheet and an aluminum alloy sheet with essentially pure aluminum on each side of the Copper sheet is coated, and a stainless steel sheet on at least one side of the pre-formed copper aluminum core exist. 23. The method according to claim 20, characterized in that the sheets are connected to one another by passing them through directs a rolling mill. 24. The method according to claim 20, characterized in that the metal sheets are subjected to a post-heat treatment at about 371 C (700 ⁰ F). 25. A method of manufacturing a clad metal product with a high rate of thermal transfer and high corrosion resistance, characterized by 2300333 - 6 - ■ the following stages: a) the surfaces of a sheet of copper or a Copper alloy and a sheet made of an aluminum alloy with essentially pure aluminum is coated are mechanically cleaned; b) the mechanically cleaned sheets are placed on top of one another and a sheet is made on the aluminum Stainless steel applied; c) the sheets are brought to a temperature of about 149 heated to 427 ° C (300 to 800 ° F); d) the sheets are joined together under sufficient pressure that the total thickness of the sheets is reduced by 25 to 60%, and e) the sheets connected to one another are subjected to a stress reduction ^{treatment at a temperature of about 371 °} C. (700 ^{° F.).} 26. The method according to claim 25, characterized in that the stacked metals in a first reduction stage be reduced or reduced in cross-section by approximately 2% and in a second reduction stage by can be reduced by up to 25% or reduced in cross-section. 27. The method according to claim 25, characterized in that the sheets are connected to one another by passing them through directs a rolling mill. 28/0 ORIGINAL INSPECTED