JVD surface treatment

Abstract

This patent relates to a method for depositing a metal coating onto a substrate, including: - an annealing step of forming, in an annealing furnace, a ferrite surface layer having a thickness of 10 μm to 50 μm on the base material, the surface fraction of which is up to 10% and includes accumulated amounts of martensite and bainite, the remainder being ferrite, and the like; - Skin pass process, - a coating step in a vacuum chamber, in which metal vapor is ejected towards at least one side of the substrate to form at least one surface layer of metal.

Description

[Technical Field]

[0001] The present invention relates to a method for depositing a metal coating on a substrate. The present invention also relates to a coated steel strip.

[0002] The present invention is particularly intended for, but not limited to, depositing an anticorrosive metal coating such as a zinc or zinc-magnesium based coating onto a traveling steel strip. Such coated steel strips can then be cut and formed, for example by stamping, bending, or forming, to produce components, which can subsequently be painted to form a coating film over the coating. [Background Art]

[0003] There exist several coating methods such as hot-dip plating and electrodeposition coating. However, these conventional methods do not provide satisfactory coatings for steel grades containing high levels of oxidizing elements such as Si, Mn, Al, P, Cr or B. As a result, new methods have been developed, for example vacuum deposition techniques such as JVD (Jet Vapor Deposition).

[0004] In JVD, as described in WO97 / 47782 and WO2009 / 047333, a metal vapor spray propelled at supersonic velocity contacts a substrate in a vacuum chamber. [Prior Art Documents] [Patent Documents]

[0005] [Patent Document 1] WO 97 / 47782 [Patent Document 2] WO 2009 / 047333 [Summary of the Invention]

[0006] Nevertheless, it has been observed that such processes sometimes result in coating degradation particularly during forming processes. It is an object of the present invention to ameliorate this drawback.

[0007] Other features and advantages will become apparent from the following detailed description of the present invention.

[0008] To illustrate the present invention, various embodiments will be described with particular reference to the following figures. [Brief explanation of the drawing]

[0009] [Figure 1] The present invention provides a concrete example of a steel substrate layer after an annealing process. [Figure 2] The present invention provides a concrete example of a steel substrate layer after a coating process. [Figure 3] This document outlines the different steps involved in a three-stage flanging test. [Modes for carrying out the invention]

[0010] The present invention relates to a method for depositing a metal film on a steel substrate, and further details are provided below. i. An annealing process in an annealing furnace, a. A preheating step of heating the steel substrate to a temperature T1 lower than 600°C. b. A heating step in which the steel substrate is heated from T1 to a recrystallization temperature T2 of 720°C to 1000°C in an atmosphere containing 0.1 to 90 volume% H2, with the remainder being inert gas and unavoidable impurities, and having a dew point of -25°C to 10°C. c. A soaking process in which the steel substrate is maintained at a temperature range of 720°C to 1000°C in an atmosphere containing 0.1 to 90 volume% H2, with the remainder being inert gas and unavoidable impurities, and having a dew point of -25°C to 10°C. An annealing process that enables the formation of a ferrite surface layer having a thickness of 10 μm to 50 μm on the steel substrate, and a microstructure consisting of up to 10% by surface fraction of martensite, austenite, bainite, and carbides, with the remainder being ferrite. ii. A skin pass process in a temper mill, wherein the steel substrate is rolled in a skin pass process with a reduction ratio of 0.02% to 2%. iii. A coating step in a vacuum chamber, wherein at least one metal vapor is ejected toward at least one side of the substrate to form a metal film. Regarding methods including

[0011] The steel base material can be rolled before the annealing process. For example, it is preferable to hot-roll the base material and then cold-roll it.

[0012] Preferably, the present method relates to a method for depositing a metal film on a steel running substrate. Preferably, in the coating step, the at least metal vapor is ejected toward at least one side of the steel running substrate.

[0013] Preferably, the annealing process is carried out in a continuous annealing furnace.

[0014] During preheating, the steel plate is typically heated from room temperature to a temperature T1 of less than 600°C. Preheating can be carried out by any means. For example, preheating can be performed in an RTF (radiating furnace) using an induction device, or in a DFF (direct-fired furnace).

[0015] Limiting the preheating temperature to below 600°C is advantageous because it reduces oxidation of the steel sheet. Preferably, T1 is below 550°C. More preferably, T1 is below 500°C.

[0016] Preferably, the dew point is -20°C to -1°C during the heating process. Preferably, the dew point is -20°C to -1°C during the soaking process.

[0017] The atmosphere during the heating and soaking processes can be achieved by using preheated steam and introducing N2-H2 gas into the furnace, which is equipped with H2 detectors to monitor the dew point temperature of the atmosphere in different sections.

[0018] Preferably, in the heating step and / or soaking step, the atmosphere contains 0.1 to 10 volume percent of H2, with the remainder being inert gas and unavoidable impurities.

[0019] The ferrite surface layer is formed by changing the microstructure of steel according to the conditions in the annealing furnace, that is, through decarburization and phase transformation. Actually, oxygen present in the annealing atmosphere reacts with carbon from the steel to form gases such as CO₂ and CO, resulting in the depletion of carbon atoms under the steel surface, which is favorable for the formation of ferrite. For example, martensitic steel can be converted into ferrite under conditions well known to those skilled in the art. The ferrite surface layer can be formed on the base material by any means known to those skilled in the art. Preferably, water injection is performed during annealing to form the desired ferrite surface layer.

[0020] As shown in Figure 1, the steel base material exiting the annealing furnace comprises at least two layers, namely a steel bulk layer 10 and a ferrite surface layer 11 on the steel bulk 10. An iron oxide layer of 5 to 15 nm can be present on the ferrite layer.

[0021] In the coating step, the coating layer can be formed by any possible means in a vacuum chamber, for example, by any PVD process. Preferably, the metal coating layer is formed by sputtering. Preferably, the coating step comprises at least one coating process, in which at least one metal vapor is ejected at ultrasonic velocity toward at least one side of the base material to form a metal coating.

[0022] The coating step may comprise one or several coating processes. For example, the coating step may comprise PVD of a first metal alloy, followed by JVD of a second metal alloy, wherein at least one metal vapor is ejected at supersonic velocity toward at least one side of the base material to form a metal coating. As a result, the metal coating may comprise several layers of different metals or metal alloys.

[0023] The coating step may comprise a pretreatment in which alkaline degreasing and a subsequent rinsing step can be performed.

[0024] For example, this process makes it possible to manufacture a coated strip as shown in Figure 2. This coated strip comprises a steel bulk 10, a ferrite layer 11, a first metal layer 12, and a second metal layer 13.

[0025] A 5-15 nm thick iron oxide layer may exist on the ferrite surface layer between the ferrite layer 11 and the first metal layer 12.

[0026] After studying the causes of coating degradation during molding, the inventors found that many of the damages occur inside the top layer of coating, for example, inside the metal coating.

[0027] After confirming that damage mostly occurred in the topmost coating layer, we found that the surface morphology of the steel substrate significantly influences the occurrence of coating degradation. This is due, in particular, to the fact that non-uniform surfaces, including deep holes and gaps, affect the surface affinity with the rinse water in the pretreatment section of the vacuum deposition process.

[0028] The claimed method allows the annealing conditions to enable the formation of a ferrite layer by decarburizing the steel bulk. The ductile ferrite allows at least partially to seal the holes and gaps during the skin pass. As a result, the presence or at least the severity of holes and gaps on the surface is reduced, and the amount of residual water on the surface of the steel substrate before coating is reduced. Finally, the coated steel strip by this method is less prone to deterioration, especially during its forming process.

[0029] Preferably, the steel base material is a strip, band, or plate.

[0030] Preferably, the steel base material has a thickness of 0.5 mm to 5 mm. More preferably, the base material has a thickness of 1 to 3 mm.

[0031] Preferably, the steel base material comprises, in weight percent, 0.15<Si<0.4, 0.5<Mn<2.5, 0.1<C<0.4, P≦0.03, S≦0.02, 0.01<Al≦0.1, Cu≦0.2, Ti+Nb≦0.20, Cr+Mo≦1, with the balance being Fe and unavoidable impurities. Preferably, the steel base material has a bulk microstructure comprising a cumulative amount of ferrite, austenite, bainite and carbides of at most 10% by area fraction, with the balance consisting of martensite. Even more preferably, the steel base material has a bulk microstructure comprising a cumulative amount of ferrite, austenite, bainite and carbides of up to 5% by area fraction, with the balance consisting of martensite. Such a steel base material is advantageous for automotive applications.

[0032] These steels are known as martensitic steels.

[0033] Preferably, the steel base material comprises, in weight percent, 0.15<Si<0.6, 0.17<Mn<2.3, 0.1<C<0.4, P≦0.05, S≦0.01, 0.015<Al≦1.0, Cu≦0.2, B≦0.005, Ti+Nb≦0.15, Cr+Mo≦1.4, with the balance being Fe and unavoidable impurities. Preferably, the steel base material has a microstructure comprising austenite, ferrite and carbides of at most 10% by area fraction, with the balance consisting of bainite and martensite. Even more preferably, the steel base material has a microstructure comprising a cumulative amount of ferrite, austenite and carbides of up to 5% by area fraction, with the balance consisting of bainite and martensite. Such a steel base material is advantageous for automotive applications.

[0034] These steels are known as dual-phase steels.

[0035] Preferably, in the annealing step, the base material is maintained in a temperature range of 820°C to 930°C.

[0036] Preferably, the ferrite layer has a microstructure containing a cumulative amount of martensite, austenite, bainite and carbides of up to 5% by surface fraction, with the balance being ferrite.

[0037] Preferably, the ferrite layer has a thickness of 20 μm to 40 μm.

[0038] Preferably, the steel base material is rolled at a reduction ratio of 0.02% to 0.5%.

[0039] Preferably, in the coating step iii., the metal coating is - a first metal layer comprising at least 8% by weight of nickel and at least 10% by weight of chromium, with the balance being iron and impurities resulting from the manufacturing process, the first metal layer being formed on at least one side of the base material by physical vapor deposition, - a second metal layer of at least one metal formed on the first metal layer by jet vapor deposition.

[0040] Preferably, the second metal layer is a corrosion-resistant metal coating.

[0041] Preferably, in the coating step iii., the metal coating is - a first metal layer comprising Fe, Ni, Cr and Ti, wherein the amount of Ti is ≥5% by weight, satisfying the following formula: 8% by weight < Cr+Ti < 40% by weight, with the balance being Fe and Ni, the first metal layer being formed on at least one side of the base material by physical vapor deposition, - a second metal layer of at least one metal formed on the first metal layer by jet vapor deposition.

[0042] Preferably, the second metal layer is a corrosion-resistant metal coating.

[0043] Preferably, the first metal layer is formed by sputtering.

[0044] For example, the first metal layer may comprise, in percent by weight, 0.02<C<0.2, 15<Cr<25, 5<Ni<22, Mo<3, 0.5<Si<1.5, 1.5<Mn<2.5, P<0.1, S<0.05, with the balance consisting of Fe and unavoidable impurities.

[0045] For example, the first metal layer may comprise, in percent by weight, 0.02<C<0.5, 15<Cr<20, 9<Ni<15, 1.5<Mo<3, 0.5<Si<1.5, 1.5<Mn<2.5, P<0.1, S<0.05, with the balance consisting of Fe and unavoidable impurities.

[0046] Preferably, the second metal layer comprises aluminum and magnesium, or zinc, or magnesium and zinc.

[0047] Preferably, the second metal layer is formed from a coating process in which at least metal vapor is injected toward a base material at supersonic speed to form a metal coating. Even more preferably, the second metal layer is formed from a jet vapor deposition process.

[0048] Preferably, the second metal layer comprises, in percent by weight, 0≦Mg<20 and 80<Zn≦100, with the balance consisting of unavoidable impurities. Even more preferably, the second metal layer comprises, in percent by weight, 0≦Mg<10 and 90<Zn≦100, with the balance consisting of unavoidable impurities.

[0049] Preferably, the second metal layer is an anticorrosion layer. Preferably, the second metal layer comprises 100% Zn by weight percent. Preferably, the second metal layer comprises, in percent by weight, 0<Mg<10 and 90<Zn<100, with the balance consisting of unavoidable impurities.

[0050] Preferably, the second metal layer comprises, in percent by weight, 0<Mg<4 and 96<Zn<100, with the balance consisting of unavoidable impurities.

[0051] As shown in Figure 2, the present invention provides a coated steel strip, - Steel bulk 10 - A ferrite layer 11 provided on said steel bulk, having a thickness of 10 µm to 50 µm, wherein the cumulative amount of martensite, austenite, bainite and carbides accounts for up to 10% by surface fraction, and the remainder is a microstructure constituted of ferrite - An iron oxide layer 12 having a thickness of 5 to 15 nm provided on said ferrite layer, - A first metal layer 12 provided on said iron oxide layer, - The present invention relates to a coated steel strip comprising a second metal layer 13 having a thickness of 5 to 10 µm provided on said first metal layer.

[0052] Preferably, said coated steel strip is manufactured according to the aforementioned method in which the first and second metal layers are coated.

[0053] Preferably, said coated steel strip has a thickness of 0.5 mm to 5 mm. Even more preferably, said coated steel strip has a thickness of 1 mm to 3 mm.

[0054] One possibility is that, in percent by weight, said steel bulk 10 contains 0.15<Si<0.4, 0.5<Mn<2.5, 0.1<C<0.4, P≦0.03, S≦0.02, 0.01<Al≦0.1, Cu≦0.2, Ti+Nb≦0.20, Cr+Mo≦1, with the remainder being Fe and unavoidable impurities. Preferably, said steel base material contains up to 10% by surface fraction of ferrite, austenite, bainite and carbides, and the remainder has a microstructure constituted of martensite. Even more preferably, said steel base material contains up to 5% by surface fraction of ferrite, austenite, bainite and carbides, and the remainder has a microstructure constituted of martensite. Such a steel base material is advantageous for automotive applications. These steels are known as martensitic steels.

[0055] According to another possibility, the steel bulk 10 comprises, by weight percent: 0.15<Si<0.6, 0.17<Mn<2.3, 0.1<C<0.4, P≦0.05, S≦0.01, 0.015<Al≦1.0, Cu≦0.2, B≦0.005, Ti+Nb≦0.15, Cr+Mo≦1.4, with the balance consisting of Fe and unavoidable impurities. The steel bulk 10 has a microstructure comprising austenite, ferrite and carbides in a surface fraction of at most 10%, with the balance consisting of bainite and martensite.

[0056] Preferably, the steel bulk has a strength of 450 MPa or more.

[0057] An iron oxide layer of 5 to 10 nm may be present on the ferrite surface layer.

[0058] Preferably, the ferrite layer has a microstructure comprising a cumulative amount of martensite, austenite, bainite and carbides in a surface fraction of up to 5%, with the balance consisting of ferrite.

[0059] Preferably, the ferrite layer has a thickness of 20 µm to 40 µm.

[0060] Preferably, the first metal layer has a thickness of 2 to 15 nm.

[0061] Preferably, the first metal layer comprises at least 8% by weight of nickel and at least 10% by weight of chromium, with the balance being iron and impurities.

[0062] For example, the first metal layer comprises, by weight percent: 0.02<C<0.2, 15<Cr<25, 5<Ni<22, Mo<3, 0.5<Si<1.5, 1.5<Mn<2.5, P<0.1, S<0.05, with the balance consisting of Fe and unavoidable impurities.

[0063] For example, the first metal layer comprises, in percent by weight, 0.02<C<0.5, 15<Cr<20, 9<Ni<15, 1.5<Mo<3, 0.5<Si<1.5, 1.5<Mn<2.5, P<0.1, S<0.05, with the balance consisting of Fe and unavoidable impurities.

[0064] Preferably, said second metal vapor forms a corrosion protection layer. Preferably, the second metal vapor comprises 100% Zn by weight percent. Preferably, the second metal vapor comprises, in percent by weight, 0<Mg<3, 97<Zn<100, with the balance consisting of unavoidable impurities.

Example

[0065] [Experiment] The purpose of the experiment is to evaluate the effect of the claimed method on coating film damage of coated steel strip.

[0066] A first series of five samples of MS1500 steel sheet having a thickness of 1.5 to 2.0 mm, of the type sold under the brand MartINsite(R) 1500 by ArcelorMittal, were prepared. The exact composition of the steel used for the samples is 0.22% C, 1.8% Mn, 0.26% Si, 0.17% Cr, 0.03% Al. Percentages are by weight, the balance being iron and potential impurities resulting from manufacturing.

[0067] All samples were subjected to the following steps.

[0068] The annealing step comprises a heating step and a soaking step.

[0069] The heating step has a temperature T2 of 860°C to 870°C in an atmosphere containing 5 volume% of H2, with the balance being N2 and unavoidable impurities. The dew point of the heating step was either -40°C to -30°C (dry annealing) or -20°C to -1°C (wet annealing).

[0070] The soaking process was performed in an atmosphere containing 5% by volume of H2, with the remainder being N2 and unavoidable impurities, at a temperature of 860°C to 870°C. The dew point during the soaking process was either -40°C to -30°C (dry annealing) or -20°C to -1°C (wet annealing).

[0071] Next, skin passes were performed on several samples (n°1, 3, 4, 5) with a reduction ratio of 0.1%, while skin passes were not performed on one sample (n°2).

[0072] After skinning, the material contained 0.02% C, 16-18% Cr, 10.5-13% Ni, 2-2.5% Mo, 1% Si, 2% Mn, 0.04% P, and 0.03% S, with the remainder being iron and metal vapor, which are potential impurities arising from the manufacturing process. A 15 nm first layer of PVD and a 7.5 μm second layer of Zn JVD were then performed.

[0073] Next, as shown in Figure 3, all samples were tested using a three-stage flanging test.

[0074] In the first step, a sample having a thickness "t" is bent in the first bending zone B1 to form an angle of 130° on a given punch radius R. In the first series, all samples had a punch radius-to-sample thickness ratio of 2.5, i.e., R / t = 2.5.

[0075] Next, in the second step, the sample is moved so that a bending die perpendicular to the second bending zone B2 is positioned.

[0076] In the third step, the strip is bent in the second bending zone B2 to form a 90° angle, while the first bending zone B1 is bent again to become flat.

[0077] This test demonstrates that the coated steel strip can be deformed in the first step, and then compressed in the first bending zone by releasing the bending of the first bending section in the third step.

[0078] Finally, the adhesive is pressed into the first bending zone, and the quality is classified into two categories, "OK" or "NOK," depending on the amount of material that adheres to the adhesive.

[0079] The characteristics of each test specimen are shown in the table below.

[0080] [Table 1]

[0081] Samples 1 and 2 are not according to the present invention. Samples 3 to 5 are according to the present invention.

[0082] It is clear that when a steel sheet undergoes the process according to the present invention, good quality of the coating can be achieved. It is also clear that if at least one of the two processes preceding the coating process, for example, the annealing process or the skin pass process, is not performed according to the present invention, good coating quality cannot be reliably ensured.

[0083] Therefore, only the method according to the present invention makes it possible to reliably obtain a coating that is particularly resistant to deterioration during the molding process.

Claims

1. A method for depositing a metal film on a steel substrate, the following: i. An annealing process in an annealing furnace, a. A preheating step of heating the steel substrate to a temperature T1 lower than 600°C. b. The steel substrate is given 0.1 to 90 volume% H ２ A heating step of heating from T1 to a recrystallization temperature T2 of 720°C to 1000°C in an atmosphere containing, with the remainder being an inert gas and unavoidable impurities, and having a dew point of -25°C to 10°C, and then, c. The steel substrate is given 0.1 to 90 volume% H ２ A soaking process that includes a substance, with the remainder being an inert gas and unavoidable impurities, and maintains a temperature range of 720°C to 1000°C in an atmosphere with a dew point of -25°C to 10°C. An annealing process that includes forming a ferrite layer having a thickness of 10 μm to 50 μm on the steel substrate and a microstructure consisting of up to 10% by surface fraction of martensite, austenite, bainite, and carbides, with the remainder being ferrite. ii. A skin pass process in a temper mill, wherein the steel substrate is rolled in a skin pass process with a reduction ratio of 0.02% to 2%. iii. A coating step in a vacuum chamber, wherein at least one metal vapor is ejected toward at least one side of the steel substrate to form a metal film. Includes, The steel substrate has a composition consisting of, by weight percent, 0.15 < Si < 0.4, 0.5 < Mn < 2.5, 0.1 < C < 0.4, P ≤ 0.03, S ≤ 0.02, 0.01 < Al ≤ 0.1, Cu ≤ 0.2, Ti + Nb ≤ 0.20, Cr + Mo ≤ 1, with the remainder being Fe and unavoidable impurities. method.

2. The method according to claim 1, wherein the steel substrate has a thickness of 0.5 mm to 5 mm.

3. The method according to claim 1, wherein the steel substrate has a bulk microstructure consisting of a cumulative amount of ferrite, austenite, bainite, and carbides, with a maximum surface fraction of 10%, and the remainder being martensite.

4. A method for depositing a metal film on a steel substrate, the following: i. An annealing process in an annealing furnace, a. A preheating step of heating the steel substrate to a temperature T1 lower than 600°C. b. The steel substrate is given 0.1 to 90 volume% H ２ A heating step of heating from T1 to a recrystallization temperature T2 of 720°C to 1000°C in an atmosphere containing, with the remainder being an inert gas and unavoidable impurities, and having a dew point of -25°C to 10°C, and then, c. The steel substrate is given 0.1 to 90 volume% H ２ A soaking process that includes a substance, with the remainder being an inert gas and unavoidable impurities, and maintains a temperature range of 720°C to 1000°C in an atmosphere with a dew point of -25°C to 10°C. An annealing process that includes forming a ferrite layer having a thickness of 10 μm to 50 μm on the steel substrate and a microstructure consisting of up to 10% by surface fraction of martensite, austenite, bainite, and carbides, with the remainder being ferrite. ii. A skin pass process in a temper mill, wherein the steel substrate is rolled in a skin pass process with a reduction ratio of 0.02% to 2%. iii. A coating step in a vacuum chamber, wherein at least one metal vapor is ejected toward at least one side of the steel substrate to form a metal film. Includes, A method wherein the steel substrate has a composition comprising, by weight percent, 0.15 < Si < 0.6, 0.17 < Mn < 2.3, 0.1 < C < 0.4, P ≤ 0.05, S ≤ 0.01, 0.015 < Al ≤ 1.0, Cu ≤ 0.2, B ≤ 0.005, Ti + Nb ≤ 0.15, Cr + Mo ≤ 1.4, with the remainder being Fe and unavoidable impurities.

5. The method according to claim 4, wherein the steel substrate has a thickness of 0.5 mm to 5 mm.

6. The method according to claim 4, wherein the steel substrate has a bulk microstructure consisting of a maximum of 5% ferrite in surface fraction and the remainder consisting of martensite and bainite.

7. The method according to any one of claims 1 to 6, wherein in the annealing step, the steel substrate is maintained in a temperature range of 820°C to 930°C.

8. The method according to any one of claims 1 to 6, wherein the ferrite layer has a microstructure in which it contains up to 5% by surface fraction of martensite, austenite, bainite, and carbides, with the remainder being composed of ferrite.

9. The method according to any one of claims 1 to 6, wherein the ferrite layer has a thickness of 20 μm to 40 μm.

10. In the coating process, - A first metal layer, comprising at least 8% nickel and at least 10% chromium by weight, with the remainder being iron and impurities arising from the manufacturing process, is formed on at least one side of the steel substrate by physical vapor deposition. The method according to claim 1 or 4, wherein a vapor of the second metal is ejected toward at least the aforementioned side of the steel substrate to form at least one second metal layer on the first metal layer.

11. The method according to claim 10, wherein the second metal layer is a corrosion-resistant layer.

12. The method according to claim 10, wherein in the coating step, the second metal layer is formed by JVD.

13. It is a coated steel strip, - Steel Bulk 10 - A ferrite layer 11 on the steel bulk having a thickness of 10 μm to 50 μm and a microstructure comprising up to 10% of martensite, austenite, bainite, and carbides in surface fraction, with the remainder being ferrite. - An iron oxide layer having a thickness of 5 to 15 nm on the ferrite layer, - The first metal layer on the iron oxide layer, - A second metal layer having a thickness of 5 to 10 μm on the first metal layer. Includes, The steel bulk is a coated steel strip containing, by weight percentage, 0.15 < Si < 0.4, 0.5 < Mn < 2.5, 0.1 < C < 0.4, P ≤ 0.03, S ≤ 0.02, 0.01 < Al ≤ 0.1, Cu ≤ 0.2, Ti + Nb ≤ 0.20, Cr + Mo ≤ 1, with the remainder being Fe and unavoidable impurities.

14. It is a coated steel strip, - Steel Bulk 10 - A ferrite layer 11 on the steel bulk having a thickness of 10 μm to 50 μm and a microstructure comprising up to 10% of martensite, austenite, bainite, and carbides in surface fraction, with the remainder being ferrite. - An iron oxide layer having a thickness of 5 to 15 nm on the ferrite layer, - The first metal layer on the iron oxide layer, - A second metal layer having a thickness of 5 to 10 μm on the first metal layer. Includes, The steel bulk is a coated steel strip containing, by weight percentage, 0.15 < Si < 0.6, 0.17 < Mn < 2.3, 0.1 < C < 0.4, P ≤ 0.05, S ≤ 0.01, 0.015 < Al ≤ 1.0, Cu ≤ 0.2, B ≤ 0.005, Ti + Nb ≤ 0.15, Cr + Mo ≤ 1.4, with the remainder being Fe and unavoidable impurities.

15. A coated steel strip according to claim 13, wherein the first metal layer comprises at least 8% by weight of nickel and at least 10% by weight of chromium, with the remainder being iron and impurities arising from the manufacturing process. The second metal layer is a corrosion-resistant layer, a coated steel strip.

16. A coated steel strip according to claim 14, wherein the first metal layer comprises at least 8% by weight of nickel and at least 10% by weight of chromium, with the remainder being iron and impurities arising from the manufacturing process. The second metal layer is a corrosion-resistant layer, a coated steel strip.

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