Fabrication method for a multi-layer substrate

Abstract

A method for fabricating a substrate provided with a plurality of layers, includes: providing a steel substrate with an oxide layer including metal oxides on the steel substrate; providing a metal coating layer directly on the oxide layer, the metal coating layer including: at least 8% by weight nickel; at least 10% by weight chromium; and a remainder being iron and impurities from a fabrication process; and providing an anti-corrosion coating layer directly on the metal coating layer.

Claims

1. A method for fabricating a substrate provided with a plurality of layers, the method comprising: providing a steel substrate with an oxide layer including metal oxides on the steel substrate; providing a metal coating layer directly on the oxide layer, the metal coating layer including: at least 8% by weight nickel; at least 10% by weight chromium; and a remainder being iron and impurities from a fabrication process; and providing an anti-corrosion coating layer directly on the metal coating layer; wherein the providing of the anti-corrosion layer includes depositing the anti-corrosion layer by an electro-deposition process.

2. The method as recited in claim 1 wherein the providing of the metal coating layer includes depositing the metal coating layer by a vacuum deposition process.

3. The method as recited in claim 1 wherein the providing of the metal coating layer includes depositing the metal coating layer by an electro-deposition process.

4. The method as recited in claim 1 wherein the providing of the metal coating layer occurs includes a magnetron cathode pulverization process.

5. The method as recited in claim 1 wherein the steel substrate with the oxide layer is provided without pickling the oxide layer.

6. The method as recited in claim 1 wherein the oxide layer is in direct contact with the steel substrate.

7. A method for fabricating a substrate provided with a plurality of layers, the method comprising: providing a steel substrate depositing an aluminum-based coating on the steel substrate, an oxide layer being directly on the aluminum-based coating, the oxide layer including metal oxides; providing a metal coating layer directly on the oxide layer, the metal coating layer including: at least 8% by weight nickel; at least 10% by weight chromium; and a remainder being iron and impurities from a fabrication process; and providing an anti-corrosion coating layer directly on the metal coating layer.

8. The method as recited in claim 7 wherein the aluminum-based coating is deposited by hot dipping.

9. The method as recited in claim 7 wherein the aluminum-based coating has a thickness of between 10 and 30 μm.

10. The method as recited in claim 7, wherein the providing of the anti-corrosion layer includes depositing the anti-corrosion layer by an electro-deposition process.

11. The method as recited in claim 7 wherein the providing of the metal coating layer includes depositing the metal coating layer by a vacuum deposition process.

12. The method as recited in claim 7 wherein the providing of the metal coating layer includes depositing the metal coating layer by an electro-deposition process.

13. The method as recited in claim 7 wherein the providing of the metal coating layer includes a magnetron cathode pulverization process.

14. A method for fabricating a substrate provided with a plurality of layers, the method comprising: providing a steel substrate with an oxide layer including metal oxides on the steel substrate; providing a metal coating layer directly on the oxide layer, the metal coating layer including: at least 8% by weight nickel; at least 10% by weight chromium; and a remainder being iron and impurities from a fabrication process; and providing an anti-corrosion coating layer directly on the metal coating layer; and providing a further metal oxide layer directly on the anti-corrosion coating layer, a further metal coating layer directly on the further metal oxide layer; and a further anti-corrosion coating layer directly on the further metal coating layer.

15. The method according to claim 14, wherein the further metal coating layer includes at least 8% by weight nickel; at least 10% by weight chromium; and a remainder being iron and impurities from a fabrication process.

16. The method as recited in claim 14, wherein the providing of the anti-corrosion layer includes depositing the anti-corrosion layer by an electro-deposition process.

17. The method as recited in claim 14 wherein the providing of the metal coating layer includes depositing the metal coating layer by an electro-deposition process.

18. A method for fabricating a substrate provided with a plurality of layers, the method comprising: providing a steel substrate with an oxide layer including metal oxides on the steel substrate; providing a metal coating layer directly on the oxide layer, the metal coating layer including: at least 8% by weight nickel; at least 10% by weight chromium; and a remainder being iron and impurities from a fabrication process; and providing an anti-corrosion coating layer directly on the metal coating layer; wherein the providing of the metal coating layer includes depositing the metal coating layer by an electro-deposition process.

19. The method as recited in claim 18 wherein the providing of the anti-corrosion layer includes depositing the anti-corrosion layer by a vacuum deposition process.

20. The method as recited in claim 18 wherein the steel substrate with the oxide layer is provided without pickling the oxide layer.

21. The method as recited in claim 18 wherein the oxide layer is in direct contact with the steel substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) To illustrate the invention, tests have been performed and will be described in the form of non-limiting examples, in particular with reference to the accompanying figures, in which:

(2) FIG. 1 is a schematic illustration of a substrate in a first embodiment of the invention.

(3) FIG. 2 is a schematic illustration of the substrate in a second embodiment of the invention.

(4) FIG. 3 is a schematic illustration of a substrate in a third embodiment of the invention.

DETAILED DESCRIPTION

(5) FIGS. 1 to 3 illustrate different embodiments of the invention. The thickness of the layers represented is exclusively for purposes of illustration and cannot be considered to be a representation of the different layers to scale.

(6) For all of the FIGS. 1 to 3, the term “steel” as used here includes all known grades of steel and can be, for example, one of the following grades of THR (Very High Strength, generally between 450 and 900 MPa) or UHR (Ultra High Strength, generally greater than 900 MPa), steel which contain large quantities of oxidizable elements: Steels without interstitial elements (IF—Interstitial Free), which can contain up to 0.1% by weight Ti; Dual-phase steels such as DP 500 steels up to DP 1200 steels which can contain up to 3% by weight Mn in association with up to 1% by weight Si, Cr and/or Al, TRIP (TRansformation Induced Plasticity) steels such as TRIP 780, which contains, for example, approximately 1.6% by weight Mn and 1.5% by weight Si; TRIP or dual-phase steels containing phosphorus; TWIP (TWinning-Induced Plasticity) steels—steels that have a high content of Mn (generally 17-25% by weight), Low-density steels such as the Fe—Al steels which can contain, for example, up to 10% by weight Al; Stainless steels, which have a high content of chromium (generally 13-35% by weight), in association with other alloy elements (Si, Mn, Al etc.).

(7) FIG. 1 illustrates a first embodiment of a substrate provided with several layers in accordance with the present invention. This substrate includes a steel sheet 1 that has a layer of oxides 2 on at least one of its surfaces. This layer 2 can be continuous or discontinuous on the steel surface 1 in question and includes metal oxides from the group that includes the iron oxides, chromium oxides, manganese oxides, aluminum oxides, silicon oxides or one or more mixed oxides containing steel alloy elements such as mixed Mn—Si or Al—Si oxides. The thickness of this layer of metal oxides 2 can vary, in general, from 3 to approximately 60 nanometers, for example, and preferably from 3 to approximately 20 nm.

(8) This oxide layer 2 is therefore not removed by pickling and is covered with a layer of a metal coating 3 that contains at least 8% by weight nickel and at least 10% by weight chromium, the remainder including iron, additional elements such as carbon, molybdenum, silicon, manganese, phosphorus or sulfur and the impurities resulting from the fabrication process. This coating 3 can be, for example, stainless steel, and preferably 316 stainless steel (16-18% by weight Cr, 10-14% by weight Ni) its thickness can be, for example, greater than or equal to 2 nm. This metal coating 3 can be applied by any known coating method, and in particular, for example, by magnetron cathodic pulverization or by electro-deposition.

(9) The method for the formation of a coating on a substrate by magnetron cathodic pulverization, which is generally called “sputtering”, is carried out in a closed enclosure in which a vacuum has been established and in which are installed a target and a substrate located opposite the target at a certain distance from the latter. The target has a surface layer which is oriented toward the face of the substrate on which a coating is to be formed. This surface layer contains at last one of the elements of which the coating to be deposited on the substrate by sputtering is constituted.

(10) The enclosure contains a plasma of an inert gas such as argon.

(11) In one sputtering method, atoms are ejected from the surface of the surface layer and are deposited in the form of a coating on the substrate. A negative voltage is applied to the target and consequently to the material of the surface layer to be ejected. As a result, a discharge is generated which creates the plasma formed by ions, electrons and inert gas particles. Positively charged ions are accelerated toward the target, which is at a negative potential, so that they reach the target with sufficient energy to cause the ejection of atoms from the surface layer. These detached atoms move toward the substrate and are deposited on the substrate in the form of a reproducible and essentially uniform coating which adheres well to the face of the substrate.

(12) In this first embodiment, the layer 3 of Fe—Ni—Cr metal coating is covered with a layer of anticorrosion metal coating 4. This anticorrosion metal coating layer 4 can include, for example, pure zinc (including the potential impurities resulting from the fabrication process), or zinc alloys such as Zn—Al, Zn—Al—Mg, Zn—Mg, Zn—Fe or Zn—Ni. It can also include aluminum, copper, magnesium, titanium, nickel, chromium, pure manganese (including the potential impurities resulting from the fabrication method), or their alloys, such as Al—Si or Mg—Al, for example. This anti-corrosion metal coating 4 can be applied by any known coating method such as, for example, a sonic vapor jet deposition process, which is also called JVD (Jet Vapor Deposition), an electron gun deposition method or plasma-assisted evaporation, which is also called SIP (Self-Induced Plating) and is described in particular in patent EP0780486.

(13) The JVD method is a vacuum deposition method in which metal vapor is generated by inductively heating a crucible containing a bath of the coating metal in a vacuum enclosure. The steam escapes from the crucible via a conduit that transports it to an exit orifice, which is preferably calibrated, to form a jet at the speed of sound directed at the surface of the substrate to be coated.

(14) FIG. 2 illustrates a second embodiment of the present invention. In this embodiment, the substrate includes as in FIG. 1 a steel sheet 21. This steel sheet 21 is coated with a layer of an aluminum-based anti-corrosion coating 25, such as, for example, an aluminum-silicon coating (10-12% by weight Si). This aluminum-based coating 25 can be deposited by hot dipping, and can have a thickness of between 10 and 30 μm, for example. This aluminum-based coating layer 25 is topped by a layer of metal oxides 22. This layer 22 can be continuous or discontinuous over the surface of the aluminum-based coating 25 in question and can include aluminum oxides and/or mixed aluminum oxides such as Al—Si oxides. The thickness of this layer of metal oxides 22 can in general vary from 3 to approximately 60 nanometers, preferably from 3 to approximately 20 nm.

(15) This layer of oxides 22 is therefore not removed by pickling and is covered by a layer of a metal coating 23 that contains at least 8% by weight nickel and at least 10% by weight chromium, with the remainder including iron, additional elements as disclosed above and the impurities resulting from the fabrication process. This metal coating 23 can be stainless steel, for example, and preferably stainless steel 316 (16-18% by weight Cr, 10-14% weight Ni). This metal coating 23 can be applied by any known coating method and can have a thickness, for example, greater than or equal to 2 nm.

(16) This layer of metal coating 23 in this second embodiment is topped by a layer of anti-corrosion metal coating 24 selected from among the anti-corrosion metal coatings described with reference to the first embodiment. This anti-corrosion metal coating 24 can be applied by any known coating process, such as, for example, a vacuum method or a hot dip method, optionally followed by a post-diffusion treatment.

(17) Coatings that can be considered, for example, include a layer of steel 21 coated by an Al—Si-base coating 25, whereby this coating 25 is topped by a layer of oxides 22 composed of mixed Al—Si oxides, the oxides layer 22 being coated by a layer 23 of stainless steel 316, this layer 23 of stainless steel being coated with a Zn—Mg alloy anti-corrosion coating 24.

(18) FIG. 3 illustrates a third embodiment of the present invention. In this third embodiment, the substrate includes, as in the first embodiment, a steel sheet 31 with a first layer of oxides 32 on at least one of its surfaces. This first layer 32 can be continuous or discontinuous over the surface of the steel 31 and contain metal oxides from the group comprising of, for example, the iron oxides, chromium oxides, manganese oxides, aluminum oxides, silicon oxides or one of the mixed oxides containing the alloy elements of the steel such as mixed Al—Si or Mn—Si oxides. The thickness of this first layer of metal oxides 32 can vary, in general, from 3 to approximately 60 nm, for example, and preferably from 3 to approximately 20 nm.

(19) As in the first embodiment, this layer of oxides 32 is therefore not removed by pickling and is covered by a layer of a metal coating 33 that contains at least 8% by weight nickel and at least 10% by weight chromium, whereby the remainder includes iron, additional elements as disclosed above and the impurities resulting from the fabrication process. This coating 33 can be, for example, stainless steel, and preferably stainless 316 (16-18% by weight Cr, 10-14% by weight Ni). The thickness of this layer of metal coating 33 can, for example, be greater than or equal to 2 nm. This metal coating 33 can be applied by any known coating process, and in particular, for example, by magnetron cathodic pulverization or by electro-deposition. In this embodiment, the layer 33 of Fe—Ni—Cr metal coating is covered by a first layer of anti-corrosion metal coating 34. This first layer of anti-corrosion metal coating 34 can include, for example, pure zinc (containing the potential impurities resulting from the fabrication process), or zinc alloys such as Zn—Al, Zn—Al—Mg, Zn—Mg or Zn—Ni. It can also include aluminum, copper, magnesium, titanium, nickel, chromium, pure manganese (containing the potential impurities resulting from the fabrication process) or their alloys, such as, for example, Al—Si or Mg—Al. This first layer of anti-corrosion metal coating 34 can be applied by any known coating method, such as, for example, a process carried out in a vacuum or a hot-dip process.

(20) In this third embodiment, the first layer of anti-corrosion metal coating 34 is topped by a second layer of metal oxides 36. This layer 36 can be continuous or discontinuous on the surface of the anti-corrosion metallic coating 34 and can include oxides, the composition of which depends on the constituent material of the anti-corrosion metal coating 34. For example, these oxides can be zinc oxides, aluminum oxides or mixed Al—Si, Zn—Mg or Zn—Al oxides. The thickness of this layer of metal oxides 36 can vary, in general, from 3 to approximately 60 nm, for example, and preferably from 3 to approximately 20 nm.

(21) This second layer of oxides 36 is not eliminated by pickling and is covered by a layer of a metal coating 37 that contains at least 8% by weight nickel and at least 10% by weight chromium, with the remainder being iron, additional elements as disclosed above and the impurities resulting from the fabrication process. This coating 37 can, for example, be stainless steel, and preferably stainless steel 316 (16-18% by weight Cr, 10-14% by weight Ni). This metal coating 37 can be applied by any known coating process and can but need not be identical to the metal coating 33. The thickness of this layer of metal coating 37 can, for example, be greater than or equal to 2 nm.

(22) In this third embodiment, this layer of metal coating 37 is topped by a second layer of anti-corrosion metal coating 38 selected from among the anti-corrosion metal coatings described with reference to the first embodiment. This anti-corrosion metal coating 38 can be applied by any known coating method, such as for example a vacuum method or a hot-dip method, optionally followed by a post-diffusion treatment. This anti-corrosion metal coating 38 can but need not be identical to the first anti-corrosion metal coating 34.

(23) For example, consideration can be given to a layer of steel 31, a first layer of iron oxides 32, a first metal coating 33 consisting of stainless steel 316, a first anti-corrosion metal coating 34 consisting of an Al—Si alloy, a second layer of oxides 36 consisting of mixed Al—Si oxides, a second metal coating 37 consisting of stainless steel 316 and the second anti-corrosion metal coating 38 consisting of a Zn—Al—Mg alloy.

(24) The present invention will now be explained on the basis of tests performed for purposes of illustration only and not intended to be limiting.

(25) Tests

(26) Acceptance Criteria

(27) T-Bend Test

(28) The purpose of this test is to determine the adherence of the coatings by bending the coated sheet at an angle of 180°. The bending radius applied is equal to twice the thickness of the substrate used (which corresponds to a “2T” bend). The adherence of the coating is verified by the application of an adhesive tape. The result of the test is judged positive if the coating remains on the tested sheet and does not appear on the adhesive tape after the tape is removed.

(29) The adhesive tape used for the performance of this test in the tests described below is a commercial adhesive, TESA4104.

(30) Cup Test

(31) This method consists of performing a stamping test during which a cup is formed. This deformation of the material as well as of the metal coating identifies potential problems relating to the adherence of the metal deposit on the substrate. The loss of adherence (or dusting) is expressed in a reduction of the weight of the cup, which is weighed before and after stamping, in g/m.sup.2.

(32) Daimler Bending

(33) The first stage of this test consists of applying a punch to the coated steel sheet and measuring the bending angle at which a reduction in strength greater than or equal to 30 kN is observed. This drop in strength corresponds to the cracking of the substrate. The adhesion test of the metal coating then consists of bending the coated sheet at an angle close to but less than this cracking point and checking the adherence of the zinc by the application of an adhesive coating. The test result is judged positive if the zinc coating remains on the sheet and does not appear on the adhesive tape after the tape is removed.

(34) The adhesive tape used to perform the tests described below has an adhesive strength between 400 and 460 N/m, e.g. Scotch® 3M595.

(35) Tests—1—Adhesion

(36) For all of the tests the composition of the stainless steel 316L used is 0.02% C, 16-18% Cr, 10.5-13% Ni, 2-2.5% Mo, 1% Si, 2% Mn, 0.04% P, 0.03% S. The percentages are percentages by weight, with the remainder being iron and potential impurities resulting from fabrication.

(37) A series of 8 specimens of DP1180 steel sheet of the type sold by ArcelorMittal was prepared. The exact composition of the steel used for the samples is 0.15% C, 1.9% Mn, 0.2% Si, 0.2% Cr, and 0.013% Ti. The percentages are percentages by weight, with the remainder being iron and potential impurities resulting from fabrication.

(38) All of the samples were subjected to the steps described below: Brightening of the steel sheet by passing it through a bath containing formic acid HCOOH or sulfuric acid H.sub.2SO.sub.4 held at a temperature below 50° C. The purpose of this step is to remove the upper layer of iron oxides of type FeO, but it does not remove the underlying layer of oxides. Rinsing with water. Drying to remove the water adsorbed during the rinsing step. Insertion of the strip into a vacuum chamber having a pressure P<10.sup.−3 mbar. Vacuum evaporation deposition of a layer of 5 μm of zinc.

(39) Specimens 2 and 6 which are of the type described by the prior art are subjected after this drying step to an etching step to remove the metal oxides that are present on the surface of the steel sheet.

(40) Specimens 1, 5 and 9 in accordance with preferred embodiments of the present invention are then subjected after the step of insertion into the vacuum chamber to a step in which they are coated with a layer of 10 nm of stainless steel 316L by magnetron cathodic pulverization (see description of this method above).

(41) Specimens 4 and 8 are subjected after the insertion into the vacuum chamber to a step in which they are coated with a layer of 10 nm of titanium by magnetron cathodic pulverization (see description of this method above).

(42) Specimen 9 was not subjected to the brightening step.

(43) The characteristics of each specimen are presented in the table below:

(44) TABLE-US-00001 Specimen number Brightening Etching Coating 1* H2SO4 No Stainless 316 2 H2SO4 Yes No 3 H2SO4 No No 4 H2SO4 No Ti 5* HCOOH No Stainless 316 6 HCOOH Yes No 7 HCOOH No No 8 HCOOH No Ti 9* None No Stainless 316 *Specimen according to the present invention

(45) All of these specimens were then subjected to the T-bend and cup tests described above.

(46) The results of the “Cup test” are expressed as a percentage of loss of zinc compared to the initial weight of zinc of the cup.

(47) The results are presented in the table below.

(48) TABLE-US-00002 Cup test Specimen number T-bend % loss Conclusion 1* OK 4.5 OK 2 OK 8.4 OK 3 NOK 79.8 NOK 4 OK 42 NOK 5* OK 5.9 OK 6 OK 3.3 OK 7 NOK 67 NOK 8 OK 29 NOK 9* OK 10.5 OK

(49) Specimens 2 and 6 as described by the prior art had positive results for both tests. This result is not surprising because these two specimens of the prior art were subjected to an etching step which makes it possible to remove the metal oxides present on the surface and therefore guarantees a good surface condition before coating to obtain a proper adherence of the zinc coating.

(50) For the specimens 1, 5 and 9 according to the present invention, the two tests are conclusive and indicated a good adherence of the zinc, equivalent to that which could be obtained with an etching step, regardless of the acid used for the brightening and even without a prior brightening step (specimen 9).

(51) In addition, specimens 4 and 8 which had a titanium coating instead of the stainless steel 316 coating did not provide any conclusive results in the two tests performed because the adherence of the zinc coating was insufficient.

(52) Tests—2

(53) A series of 12 specimens was prepared with different grades of steel and different process parameters. The set of specimens was manufactured according to the invention and was subjected to the following process steps: Alkaline degreasing to eliminate potential organic residues present on the surface of the steel sheet. This degreasing was performed by dipping the strip in a bath of a basic solution held at 60° C. The dip time as well as the characteristics of the bath used for each specimen are indicated in the table below. Rinsing with water. Drying to eliminate the water adsorbed during the rinsing step. Insertion of the strip into a vacuum chamber which is at a pressure P<10.sup.−3 mbar. Preheating of the strip to a temperature of approximately 120° C. Depositing of a layer of stainless steel 316L by magnetron cathodic pulverization (see description of this method above). The thickness of this layer of stainless steel 316L varies from one specimen to another and is indicated in the table below. Deposition of a layer of zinc by JVD (See description of this process above).

(54) The characteristics of each specimen are listed in the table below:

(55) TABLE-US-00003 Thickness Thick- Sheet of ness thick- Type of stainless of Zn No. Steel (mm) oxides Degreasing steel (nm) (μm) 10 DP1180 1.22 mm Chromium Novaclean ™ 2.5 nm   8 μm 11 oxides and 300M 2% +   5 nm 12 iron oxides Ridosol ®  10 nm 13 MS1500  1.1 mm Iron oxides 0.2% 2.5 nm   8 μm 14 60° C.-10   5 nm 15 sec  10 nm 16 Trip  0.8 m  Mixed Mn- pH = 12 2.5 nm   8 μm 17 Dual Si   5 nm 18 1200 oxides  10 nm 19 Usibor ® 1.5 mm Mixed S5183   3 nm 4.5 μm 20 AS150 Al-Si 60° C.-15  15 nm oxides sec pH = 14

(56) Novaclean™ and Ridosol® are products sold by Henkel. Gardoclean S5183 is sold by Chemetall.

(57) Specimens 10 to 12 were prepared starting with DP1180 steel sheets as sold by ArcelorMittal. The exact composition of the steel used for the specimens was 0.15% C, 1.9% Mn, 0.2% Si, 0.2% Cr, and 0.013% Ti. The percentages are percentages by weight, the remainder being iron and potential impurities resulting from fabrication. The majority of the metal oxides present on the surface of the steel sheet are chromium oxides and iron oxides. The oxidized steel sheet was coated with a layer of stainless steel 316L, the thickness of which varied from one specimen to another, and then a layer of zinc with a thickness between 7.5 and 8 μm.

(58) The specimens 13 to 15 were prepared starting with MS1500 steel sheets as sold by ArcelorMittal. MS stands for martensitic steel. The exact composition of the steel used for the specimens is 0.225% C, 1.75% Mn, 0.25% Si, 0.2% Cr, 0.035% Ti. The percentages are percentages by weight, the remainder being iron and potential impurities resulting from fabrication. The majority of the metal oxides present on the surface of the steel sheet are iron oxides. The oxidized steel sheet was coated with a layer of stainless steel 316L, the thickness of which varied from one specimen to another, and then a layer of zinc with a thickness between 7.5 and 8 μm.

(59) Specimens 16 to 18 were prepared starting with Trip Dual 1200 steel sheets as sold by ArcelorMittal. The exact composition of the steel used for the specimens is 0.2% C, 2.2% Mn, 1.5% Si, and 0.2% Cr. The percentages are percentages by weight, the remainder being iron and potential impurities resulting from fabrication. The majority of the metal oxides present on the surface of the steel sheet are mixed manganese and silicon oxides. The oxidized steel sheet was coated with a layer of 316L stainless steel, the thickness of which varied from one specimen to another, followed by a layer of zinc with a thickness between 7.5 and 8 μm.

(60) Specimens 19 and 20 were prepared starting with Usibor® AS150 steel sheets. The steel in question is a Usibor® steel coated with a layer of 150 g/m.sup.2 of AluSi@, an aluminum- and silicon-based coating. The exact composition of the AluSi@ coating used for these specimens was 90% Al, 10% Si. The percentages are expressed by weight. The majority of the metal oxides present on the surface of the steel sheet are mixed aluminum and silicon oxides. The oxidized steel sheet was covered with a layer of stainless steel 316L, the thickness of which varied from one specimen to another, followed by a layer of zinc in a thickness between 4 and 5 μm.

(61) This set of specimens was then subjected to the T-bend and Daimler Bending tests as described above.

(62) The results are presented in the table below:

(63) TABLE-US-00004 Daimler Bending No. T-Bend Angle Result 10 OK 108° OK 11 OK 108° OK 12 OK 108° OK 13 OK 137° OK 14 OK 137° OK 15 OK 137° OK 16 OK  89° OK 17 OK  89° OK 18 OK  89° OK 19 OK Not tested 20 OK Not tested

(64) These results prove that with the substrate in accordance with a preferred embodiment of the present invention, the zinc coating is adherent regardless of the composition of the metal oxides present on the surface or of the pH of the solution used for degreasing. In addition, the results of the adhesion tests of the zinc coating are positive beginning with the application of a thickness of 2.5 nm of stainless steel 316.

(65) Test—3

(66) A series of 2 specimens was prepared starting with Usibor® steel. The 2 specimens were subjected to the following process steps: Alkaline degreasing to remove any potential organic residue that may be present on the surface of the steel sheet. This degreasing is performed by dipping the strip in a bath of a basic solution held at 60° C. The dip time as well as the characteristics of the bath used for each specimen are indicated in the table below. Rinsing with water. Drying to remove the water adsorbed during the rinsing step. Insertion of the strip into a vacuum chamber which is at a pressure of P<10.sup.−3 mbar. Deposition of a metal coating.

(67) Specimen 31 as described by the prior art is subjected after the drying step to an etching step to remove the metal oxides present on the surface of the steel sheet.

(68) Specimen 32 as claimed by the invention is then subjected after the step of the insertion into a vacuum chamber to a step in which it is coated with a layer of stainless steel 316L by magnetron cathodic pulverization (see description of this process above).

(69) The thickness of this coating is 10 nm.

(70) Following the etching step or following the step of the deposition of a layer of stainless steel 316L, the specimens were coated with a layer of 5 μm of aluminum by magnetron cathodic pulverization.

(71) The characteristics of each specimen are presented in the table below:

(72) TABLE-US-00005 Coating stainless Metal Number Steel sheet Etching steel 316 coating 31 Usibor ® Yes No 5 μm Al 32* Usibor ® No 10 nm 5 μm Al *Specimen as claimed by the invention.
* Specimen as claimed by the invention.

(73) The adhesion of the top metal coating of each specimen was then tested by means of an adhesive tape applied to the flat specimen and then removed. The adhesive tape used has an adhesive strength between 400 and 460 N/m, e.g. Scotch® 3M595.

(74) The result is positive if the coating remains on the surface of the specimen and does not appear on the adhesive tape when the tape is removed. For all of the specimens tested, the adhesive tape did not contain any coating after the test, which means that the coating is adherent. This result was expected for specimen 31 of the prior art because it had been subjected to an etching step which removed the metal oxides that were present on the surface of the steel sheet, whether or not it was coated. On the other hand, these results show that this step of removing the oxides can be eliminated by the deposition of a layer of stainless steel 316L directly on the oxidized surface, because the results of the adhesion test are also positive with the configuration of a preferred embodiment of the present invention.