EP4388144A1 - Produit plat en acier à revêtement de zinc amélioré - Google Patents

Produit plat en acier à revêtement de zinc amélioré

Info

Publication number
EP4388144A1
EP4388144A1 EP22764666.8A EP22764666A EP4388144A1 EP 4388144 A1 EP4388144 A1 EP 4388144A1 EP 22764666 A EP22764666 A EP 22764666A EP 4388144 A1 EP4388144 A1 EP 4388144A1
Authority
EP
European Patent Office
Prior art keywords
coating
steel substrate
zinc
corrosion coating
steel
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP22764666.8A
Other languages
German (de)
English (en)
Inventor
Stefan BIENHOLZ
Sebastian STILLE
Stefan Krebs
Luis Fernando PIEDRA-GARZA
Bernd Schuhmacher
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
ThyssenKrupp Steel Europe AG
Original Assignee
ThyssenKrupp Steel Europe AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by ThyssenKrupp Steel Europe AG filed Critical ThyssenKrupp Steel Europe AG
Publication of EP4388144A1 publication Critical patent/EP4388144A1/fr
Pending legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
    • C23C14/14—Metallic material, boron or silicon
    • C23C14/16—Metallic material, boron or silicon on metallic substrates or on substrates of boron or silicon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/02—Pretreatment of the material to be coated
    • C23C14/021—Cleaning or etching treatments
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/24—Vacuum evaporation
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/54—Controlling or regulating the coating process
    • C23C14/542—Controlling the film thickness or evaporation rate
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/56—Apparatus specially adapted for continuous coating; Arrangements for maintaining the vacuum, e.g. vacuum locks
    • C23C14/562—Apparatus specially adapted for continuous coating; Arrangements for maintaining the vacuum, e.g. vacuum locks for coating elongated substrates

Definitions

  • the invention relates to a flat steel product comprising a steel substrate with an anti-corrosion coating of zinc or a zinc alloy present on at least one side of the steel substrate.
  • the invention also relates to a method for producing such a flat steel product.
  • flat steel products are understood to mean rolled products whose length and width are each significantly greater than their thickness. These include, in particular, steel strips and steel sheets or blanks.
  • Galvanized steel flat products When used in automobile construction, such flat steel products are typically galvanized nowadays in order to ensure protection against corrosion.
  • the galvanizing is applied by hot-dip coating, electrolytically or by means of vapor deposition.
  • Galvanized steel flat products have the disadvantage, however, that they have poor paint adhesion without post-treatment. For this reason, post-treatment is usually carried out, for example phosphating, to ensure good paint adhesion.
  • the object of the present invention is to provide a galvanizing with improved surface properties.
  • a flat steel product comprising a steel substrate with an anti-corrosion coating of zinc or a zinc alloy present on at least one side of the steel substrate.
  • the anti-corrosion coating has zinc nanocrystals with an average diameter of less than 500 nm on the surface facing away from the steel substrate.
  • the mean diameter is more than 50 nm, preferably more than 70 nm, particularly preferably more than 80 nm, in particular more than 100 nm.
  • a “corrosion protection coating made of zinc” is to be understood as meaning a corrosion protection coating which, in addition to zinc, only contains unavoidable impurities, ie which consists of zinc and unavoidable impurities.
  • a “corrosion protection coating made of a zinc alloy” is to be understood as meaning a corrosion protection coating that consists of a maximum of 50% by weight of additional alloying elements, the remainder being zinc and unavoidable impurities.
  • Such an anti-corrosion coating particularly preferably consists of a maximum of 40% by weight, in particular a maximum of 30% by weight, preferably a maximum of 10% by weight, of additional alloying elements, the remainder being zinc and unavoidable impurities.
  • the alloying elements are preferably selected from the group consisting of aluminum, alkaline earth metals and semimetals.
  • a percentage by weight of addition elements is to be understood as the sum of the weight % of all addition elements.
  • unavoidable impurities in a steel, zinc or other alloy refer to technically unavoidable impurities that get into the steel or the coating during production or cannot be completely removed, but whose contents are so low in any case that they have no influence on the properties of the steel or the coating.
  • alloying components e.g. the zinc alloy
  • the average diameter of the zinc nanocrystals is determined using computer-aided image analysis. For this purpose, a scanning electron micrograph of a measuring field of 5 pmx5 pm of the surface is created at a magnification of 15000x. The edges of the zinc nanocrystals are determined by means of image analysis and a diameter is determined for each crystal. The average of all diameters in the measuring field is the mean diameter of the zinc nanocrystals. Occasionally, image analysis can lead to misidentifications when individual nodules (see below) are identified as zinc nanocrystals and are also considered. A histogram of the determined diameters is used to rule this out. In the case of misidentifications, a second peak occurs in the histogram for the larger tuber diameters.
  • This data can then be sorted out using the histogram by choosing an appropriate cut-off in the histogram.
  • the arrangement according to the invention of zinc nanocrystals with an average diameter of less than 500 nm on the surface facing away from the steel substrate has various positive effects.
  • the zinc nanocrystals result in an irregular surface on a very small scale. This leads to improved wettability and direct coatability without the need for additional phosphating.
  • the anti-corrosion layer according to the invention has a more positive potential in a mildly corrosive environment than conventional zinc layers.
  • the anti-corrosion layer thus behaves more noble due to an oxide layer leading to passivity and is therefore less prone to corrosion.
  • this means that the active corrosion protection is reduced compared to the steel substrate.
  • the extremely increased size of the surface caused by zinc nanocrystals leads to increased surface reactivity compared to conventional zinc layers. In the event of damage to the surface, the active corrosion protection of the zinc for the underlying steel is even greater than with conventional zinc layers.
  • the flat steel product is further developed in such a way that the surface of the anti-corrosion coating facing away from the steel substrate has a nodular microstructure with an average nodule size between 1 pm and 5 pm and a nanostructure, the nanostructure being formed by the zinc nanocrystals.
  • the mean tuber size is determined using computer-assisted image analysis. For this purpose, a scanning electron micrograph of a measuring field of 50 pm ⁇ 50 pm of the surface is created at a magnification of 1000. The edges of the nodules are determined by means of image analysis and a diameter is determined for each nodule. The average of all diameters in the measuring field is the mean nodule size.
  • the surface of the anti-corrosion coating facing away from the steel substrate thus has two essential structures; a coarser micron-scale structure with bulbous Structures and an overlying finer nanometer-scale structure formed by zinc nanocrystals.
  • the nodules of the nodular microstructure are arranged side by side in the direction of extension of the steel substrate.
  • This arrangement has the further advantage that continuous microchannels result between the nodules of the microstructure, through which diffusible hydrogen can escape from the steel substrate.
  • the microchannels ensure that diffusible hydrogen, which has diffused into the steel substrate, for example during a pre-treatment before the zinc coating, can exit again through the anti-corrosion coating and does not remain enclosed in the steel substrate.
  • pre-treatment is necessary.
  • the pretreatment is in particular a deoiling (for example an alkaline degreasing in combination with an electrolytic degreasing) and a surface preparation or activation step (for example a desmutting).
  • diffusible hydrogen can be absorbed by the steel substrate.
  • Ordinary zinc coating would prevent this hydrogen from outgassing, leaving it bound in the steel substrate and leading to hydrogen embrittlement.
  • the microstructure of the advanced anti-corrosion coating with microchannels allows the absorbed hydrogen to be degassed.
  • the nodules of the nodular microstructure are each designed as an agglomeration of zinc nanocrystals.
  • zinc nanocrystals are formed during the deposition of zinc from the gas phase. However, due to the high coating rate, these do not continue to grow into larger crystals, but instead more and more nanocrystals are formed, which attach themselves to the existing crystals.
  • the first nanocrystals act as condensation nuclei. This results in agglomerations of zinc nanocrystals arranged next to one another on the steel substrate. These agglomerations form the nodules of the nodular microstructure.
  • at least 70%, preferably 80%, in particular 90% of the surface of the anti-corrosion coating facing away from the steel substrate is covered with the zinc nanocrystals.
  • the proportion of the covered surface is determined using computer-aided image analysis. For this purpose, a scanning electron micrograph of a measuring field of 5 pmx5 pm of the surface is created at a magnification of 15000x. The edges of the zinc nanocrystals are determined by means of image analysis. Furthermore, the recording is divided into a square grid with a grid width of 0.5pm. The edges of the determined zinc nanocrystals are aligned with the grid. If one of the edges falls at least partially within a grid element, that grid element is classified as covered by zinc nanocrystals. In this way, it can be clearly defined for each grid element whether it is covered by zinc nanocrystals or not. The proportion of the covered raster elements then corresponds to the proportion of the covered surface.
  • the surface energy is greater than 50 mN/m, preferably greater than 60 mN/m.
  • the surface energy has a dispersive fraction that is greater than 40 mN/m, in particular greater than 45 mN/m, preferably greater than 50 mN/m, in particular greater than 55 mN/m.
  • the wettability of the surface with a liquid results from the interaction of the surface energy of the substrate and the surface tension of the liquid.
  • a particularly high surface energy is therefore advantageous.
  • the surface energy of the anti-corrosion coating is determined by measuring the contact angle in accordance with DIN EN ISO 19403-2 (2020.04). Drops of a test liquid are deposited on the surface. The contact angle, which characterizes the wetting behavior of the surface with the liquid, is measured on these deposited drops. The surface energy of the corresponding relevant solid body (here the anti-corrosion layer).
  • the measuring device used was the OCA 20 contact angle measuring device from Dataphysics, including the associated software.
  • the determination of the surface energy is carried out on samples with stable surface properties in air, in particular a stable native oxide layer, i.e. after storage in ambient air has resulted in a stable state in which the surface has a natural oxide layer and the surface properties no longer change over time due to reactions change with the surrounding atmosphere.
  • This state is achieved, for example, by storage at room temperature (untempered storage) in an air atmosphere for at least 7 days with at least 50% atmospheric humidity.
  • -0.7 V preferably at least -0.65 V, ie at least -0.7 V or more positive, or at least -0.65 V or more positive.
  • the electrochemical potential was determined in accordance with DIN standard DIN 50918 (2018.09) (“resting potential measurement on homogeneous mixed electrodes”). Insofar as absolute instead of difference values for the electrochemical potential are given, this refers to the reference to the standard hydrogen electrode.
  • the anti-corrosion layer according to the invention therefore has a more positive potential in a mildly corrosive environment than conventional zinc layers.
  • Zinc layers that have been applied electrolytically or by means of hot-dip coating typically have an electrochemical potential of about -0.8 V.
  • the anti-corrosion layer according to the invention therefore behaves more noble due to its passive properties and is therefore less prone to corrosion.
  • the surface reactivity of the anti-corrosion coating in an aqueous solution with a pH of 8.4 is greater than 800 pW/cm 2 , preferably greater than 1000 pW/cm 2 , in particular greater than 1200 pW/cm 2 , particularly preferably greater than 1400 pW/cm 2 .
  • the surface reactivity is determined by means of cyclic voltammetry.
  • the size of this area is proportional to the electrochemically accessible and active surface and reflects the gradual penetration of the electrolyte into the "inner" surface through pores and due to the high roughness within the framework of the 20 consecutive cycles.
  • the higher the surface reactivity the stronger the active corrosion protection of the steel substrate in the event of damage to the anti-corrosion layer.
  • the ability of the electrolyte to penetrate into the interior of the zinc layer is related to the good wettability described above.
  • the anti-corrosion coating preferably has an average infiltration U/2 which is less than 15 mm, preferably less than 10 mm, particularly preferably less than 5 mm, in particular less than 3 mm, preferably less than 2 mm, particularly preferably less than 1.5mm
  • the infiltration is measured by providing the coated steel flat product with a Clemen score down to the base material in order to simulate damage.
  • the sample prepared in this way is then immersed in a sodium sulfate solution with a concentration of 0.1 mol/L at 40°C for 24 hours.
  • a current of -1.8 mA/mm 2 (relative to the scratched area) is applied in order to accelerate the paint delamination, starting from the scratch.
  • the infiltration is now measured on the sample prepared in this way.
  • the infiltrated varnish is removed with a scalpel. To do this, hold the knife blade at a slight angle and carefully remove the coating from the scored edge to the zone that is still firmly attached.
  • the surface structure according to the invention described also exhibits low abrasion. This was determined using a modified multi-terry test.
  • a sheet metal strip measuring 50 x 700 mm is pulled through a tool at high surface pressure.
  • the tool is a flat jaw with a 20 mm diameter cylinder on top, through which the strip is pulled.
  • the tool material used 1.3342, has a hardness of HRC > 60.
  • the test speed is 5 mm/min with a constant normal force FN of 5 kN.
  • the test length is 500 mm
  • the sample geometry is 50 x 700 mm, with the strip sample being cleaned and de-oiled in an ultrasonic bath beforehand.
  • the strip sample is then oiled in a defined manner with FUCHS Anticorit PL 3802-39 S oil and 1.5 g/m 2 per side.
  • the tool is cleaned, and then the sheet metal strip is pulled through the tool over a length of 500 mm at a speed of 5 mm/s. After drawing, the surface is visually assessed for abrasion and damage. In the case of the anti-corrosion layer according to the invention, there is no damage and only slight abrasion.
  • the anti-corrosion coating has a thickness of 1-20 ⁇ m, preferably 1-10 ⁇ m.
  • the thickness is particularly preferably 3-10 ⁇ m.
  • the thickness is at least 5 pm.
  • the thickness is in particular up to 8 pm.
  • Layers below 1 pm typically do not provide adequate protection against corrosion.
  • a layer thickness of 3 pm or more will provide adequate corrosion protection until the end of the product's service life.
  • Up to a thickness of 20 pm there is improved protection against corrosion. From this thickness there is no more significant improvement.
  • excessively thick layers are not preferred because of the correspondingly longer coating time and the higher material costs.
  • the anti-corrosion coating made of zinc or a zinc alloy is directly adjacent to the steel substrate. Between the layer of zinc or No further layers are arranged between the zinc alloy and the steel substrate. Zinc or the zinc alloy is therefore directly adjacent to the steel substrate. As a result, the active corrosion protection of the anti-corrosion coating comes into its own.
  • the steel substrate of the steel flat product is preferably carbon steel, in particular with a carbon content of up to 0.5% by weight
  • the steel substrate of the flat steel product is, in particular, a high-strength, preferably an ultra-high-strength steel. That means the tensile strength is more than 590 MPa, especially more than 780 MPa. The tensile strength is particularly preferably more than 1000 MPa, in particular more than 1200 MPa.
  • the coating according to the invention is all the more relevant the higher the tensile strength of the substrate, since the susceptibility to hydrogen embrittlement and thus to brittle fractures also increases with the tensile strength.
  • the steel substrate in this variant is formed from a multi-phase steel, in particular from a complex-phase steel (CP) or a dual-phase steel (DP) or a martensite-phase steel (MS).
  • Complex-phase steels have a structure that consists largely of bainite.
  • CP steels have high tensile strength, but suffer from relatively low deformability, which prevents the design of geometrically complex components.
  • Dual-phase steels have a structure consisting of a combination of hard components (e.g. martensite or bainite) and soft components (e.g. ferrite).
  • DP steels are suitable for complex components due to their combination of high strength and good formability.
  • the steel substrate consists of a multi-phase steel with the following analysis (data in % by weight):
  • Si 0.01 - 2.00% by weight, preferably up to 1.80% by weight
  • Mn 1.00 - 3.00 wt%, preferably 1.2 - 2.6 wt%
  • Al up to 1.60% by weight, preferably up to 1.00% by weight
  • Cr up to 1.00% by weight, preferably up to 0.85% by weight
  • Cu up to 0.20% by weight, preferably up to 0.15% by weight
  • N up to 0.01% by weight, preferably up to 0.010% by weight
  • Ni up to 0.30% by weight, preferably up to 0.01% by weight
  • Nb up to 0.08% by weight, preferably up to 0.050% by weight
  • V up to 0.15% by weight, preferably up to 0.020% by weight
  • Ca up to 0.01% by weight, preferably up to 0.005% by weight
  • the steel substrate is made of a deep-drawing steel with the following analysis (data in % by weight):
  • Si up to 0.70% by weight, preferably up to 0.50% by weight, in particular up to 0.12% by weight
  • Mn 0.01 wt% - 1.20 wt%, preferably up to 0.60 wt%
  • P up to 0.12% by weight, preferably up to 0.07% by weight, in particular up to 0.05% by weight
  • Cu up to 0.20% by weight, preferably up to 0.15% by weight
  • N up to 0.03% by weight, preferably up to 0.01% by weight
  • Ni up to 0.50% by weight, preferably up to 0.10% by weight
  • Nb up to 0.01% by weight, preferably up to 0.005% by weight
  • Ti up to 0.20% by weight, preferably up to 0.12% by weight
  • V up to 0.050% by weight, preferably up to 0.015% by weight
  • Sn up to 0.05% by weight, preferably up to 0.030% by weight
  • Ca up to 0.01% by weight, preferably up to 0.005% by weight, balance iron and unavoidable impurities.
  • the anti-corrosion coating is applied by physical vapor deposition (PVD). It has been shown that the surface structure according to the invention can be easily achieved in this way.
  • PVD physical vapor deposition
  • a coating material which is initially in solid or liquid form, is usually vaporized by physical processes. This can be done, for example, thermally by directly heating the coating material (for example via an electric arc), by bombarding it with an electron or ion beam, or by illuminating it with a laser beam. To ensure that the vapor particles of the vaporized coating material can reach the workpiece to be coated and are not lost through collision with gas particles in the ambient atmosphere for the coating, the PVD coating process is carried out in a coating chamber under reduced pressure.
  • This coating process has several advantages. On the one hand, such methods are known for the fact that, due to the process, they do not introduce any or only very little hydrogen into the starting substrate. On the other hand, it is not necessary to heat the steel substrate too much. In hot-dip galvanizing, for example, the steel substrate is inevitably heated to temperatures in excess of 460°C (the zinc bath temperature). At these temperatures, however, a hard component of the substrate structure, in particular martensite, is tempered, as a result of which the characteristics of the steel substrate are lost. This is particularly relevant in the case of DP steels as the steel substrate. Overall, tests have shown that all the steel substrates described above with a correspondingly high tensile strength can be coated without errors by means of gas phase deposition.
  • the object according to the invention is also achieved by a method for producing a flat steel product as described, having at least the following steps:
  • the coating rate when applying the anti-corrosion coating is preferably at least 0.5 ⁇ m/s. It has been shown that the surface structure consists of zinc nanocrystals due to the higher coating rate. The condensation takes place so quickly that it is not possible to grow into larger crystals, but instead more and more nanocrystals are formed, which attach themselves to the existing crystals. The first nanocrystals act as condensation nuclei. This results in agglomerations of zinc nanocrystals arranged next to one another on the steel substrate. These agglomerations form the nodules of the nodular microstructure. However, if the coating rates are too high, instabilities can occur in the coating process. The desired surface structure can be achieved in a particularly process-reliable manner at coating rates between 1.0 ⁇ m/s and 100 ⁇ m/s, preferably between 2 ⁇ m/s and 20 ⁇ m/s.
  • the continuous feeding of the steel substrate into the coating chamber and the continuous discharge of the steel substrate from the coating chamber has the advantage that in this way steel strips can be treated and coated continuously as a steel substrate.
  • steel strips wound into coils would have to be introduced into the coating chamber, the coating chamber evacuated and, after coating, ventilated again in order to remove the steel strips. This would be significantly more complex than continuous inward and outward smuggling.
  • a coating chamber with a negative pressure is understood to mean a coating chamber whose pressure is at least 10% below the atmospheric pressure of the environment.
  • the continuous inward and/or outward transfer is implemented by means of at least one barometric fluid lock, which is described in WO 2019/122131 A1.
  • the continuous smuggling in and/or ejecting is realized by means of at least one roller sluice.
  • the continuous inward and/or outward transfer takes place via two or more locks in the form of lock stages, which reduce the pressure in stages (during inward transfer) or increase it in stages (during exit).
  • the temperature of the steel substrate when applying the anti-corrosion coating is between 70°C and 300°C. This also enables process-reliable condensation of zinc nanocrystals with the desired topography.
  • the anti-corrosion coating is applied in a protective gas atmosphere with a pressure of between 1 mbar and 100 mbar, in particular between 10 mbar and 100 mbar.
  • the negative pressure in the coating chamber is therefore between 1 mbar and 100 mbar, in particular between 10 mbar and 100 mbar. This ensures that little coating material is lost for coating due to scattering on particles in the coating chamber.
  • the pressure is in a range that can be achieved with reasonable effort in large-scale industrial applications, for example in the coating of steel strips.
  • the protective gas atmosphere has an oxygen content of less than 5% by volume, preferably less than 2% by volume, in particular less than 1% by volume. This ensures that there is no undesirable oxidation of the hot steel substrate.
  • the protective gas atmosphere is preferably an inert gas atmosphere, in particular a nitrogen atmosphere and/or an argon atmosphere, ie the protective gas atmosphere consists exclusively of an inert gas, in particular nitrogen or argon or a mixture of nitrogen and argon and technically unavoidable impurities .
  • the protective gas atmosphere is an inert gas atmosphere with an admixture of hydrogen. In this case, the protective gas atmosphere consists of up to 8% by volume hydrogen, the remainder inert gas (especially nitrogen or argon or a mixture of nitrogen and argon) and technically unavoidable impurities.
  • the application of the anti-corrosion coating to the steel substrate is carried out by means of physical vapor deposition. follows by providing the steel substrate in a coating chamber, the pressure in the coating chamber being regulated. Zinc or a zinc alloy is flowed into the coating chamber as a coating material at an inflow point, with the zinc or zinc alloy being tempered to a certain temperature.
  • pressure and temperature are set in such a way that the temperature is above the dew point of the coating material. At a temperature above the dew point of the coating material, it is in its gaseous phase. If the pressure is adjusted, for example increased, the dew point shifts, in the example towards higher temperatures. Appropriate readjustment of the temperature ensures that the coating material is in gaseous form.
  • FIG. 1 shows a scanning electron microscopic representation of the anti-corrosion coating (magnification 1000x);
  • FIG. 2 shows a scanning electron microscopic representation of the anti-corrosion coating (magnification 3000x);
  • FIG. 3 shows a scanning electron microscopic representation of the anti-corrosion coating (magnification 15000x);
  • FIG. 4 shows a light microscopic representation of the anti-corrosion coating in a vertical section (magnification 1000x);
  • FIG. 5 shows a scanning electron micrograph of the anti-corrosion coating of a hot-dip coated comparison sample (magnification 5000x);
  • FIG. 6 shows a scanning electron microscopic representation of the anti-corrosion coating of an electrolytically coated comparative sample (magnification 5000x).
  • FIGS. 1 to 4 show different representations of the same flat steel product 13.
  • FIGS. 1 to 3 each show scanning electron micrographs of the surface of the flat steel product 13 at different magnifications.
  • FIG. 4 shows a light micrograph of a vertical section. All of the recordings relate to exemplary embodiment no. 2 in the tables explained below.
  • the flat steel product 13 comprises a steel substrate 15 with an anti-corrosion coating 17 present at least on one side of the steel substrate 15.
  • the anti-corrosion coating consists of zinc and avoidable impurities.
  • the anti-corrosion coating has zinc nanocrystals 19 with an average diameter of less than 500 nm. It can be clearly seen in FIG. 3 that the surface is essentially completely covered with zinc nanocrystals 19 .
  • the zinc nanocrystals are the honeycomb structures in FIG. 3. For the sake of clarity, only two selected zinc nanocrystals 19 have been provided with reference symbols.
  • the steel flat product 13 comprises a steel substrate 15 with a thickness of 1.8 mm from a cold-rolled multi-phase steel with the analysis A, which is given in the following:
  • the anti-corrosion coating 17 has the nanostructure described, which is formed by the zinc nanocrystals 19, on the one hand, and a nodular microstructure on the other.
  • two exemplary tubers are provided with the reference numeral 21.
  • the Tubers 21 the tuberous Microstructure have a mean nodule size between 1pm and 5pm.
  • the nodules 21 of the nodular microstructure are arranged next to one another in the direction in which the steel substrate extends. Therefore, continuous microchannels 23 result between the nodules 21 of the microstructure, through which diffusible hydrogen can escape from the steel substrate 15.
  • the surface of the anti-corrosion coating 17 facing away from the steel substrate 15 thus has two essential structures.
  • the nodules of the nodular microstructure are arranged side by side in the direction of extension of the steel substrate.
  • This arrangement has the further advantage that continuous microchannels result between the nodules of the microstructure, through which diffusible hydrogen can escape from the steel substrate.
  • FIG. 3 shows that the nodules 21 of the nodular microstructure are each designed as an agglomeration of zinc nanocrystals 19 .
  • FIG. 5 shows the surface structure after hot-dip coating
  • FIG. 6 shows the surface structure after electrolytic coating. No evidence of zinc nanocrystals or nodular microstructure is seen in either.
  • Table 1 below shows the characteristics of the surface produced and process parameters during their production for several exemplary embodiments.
  • Samples 1 and 2 were produced according to the invention by means of physical vapor deposition (PVD). The coating rate was 4 pm/s in each case. Only the temperature of the steel substrate was different. In both cases, the coating took place in a nitrogen atmosphere, with the technically unavoidable impurities (including oxygen) being below 3% by volume. The pressure in the protective gas atmosphere was 50 mbar.
  • a hot-dip coated sample 3 and an electrolytically coated sample 4 were produced as comparative samples.
  • Table 2 below shows the surface properties of the two samples 1 and 2 according to the invention and some of the reference samples 3 and 4.
  • the surface energy of the samples according to the invention is significantly greater than that of the reference samples.
  • Sample 2 even has twice the surface energy. The same applies to the dominant, dispersive part of the surface energy. This achieves better wettability.
  • the surface energy was determined on samples with surface properties that were stable in air. There were no longer any changes in the surface properties over time. The samples were previously stored for 7 days without temperature in an air atmosphere for at least 7 days with at least 50% humidity.
  • the electrochemical potential of the samples according to the invention is about 20% higher and is therefore more positive than the electrochemical potential of the two reference samples.
  • the potential was determined relative to the standard hydrogen electrode.
  • the anti-corrosion layer according to the invention therefore has a more positive potential in a mildly corrosive environment than conventional zinc layers which have been applied electrolytically or by means of hot-dip coating.
  • the anti-corrosion layer according to the invention therefore behaves more elegantly and is therefore less prone to corrosion or shows passive behavior.
  • both samples according to the invention show an extremely increased surface reactivity of the anti-corrosion coating in the aforementioned mildly corrosive environment of 1285 pW/cm 2 and 1600 pW/cm 2 . This results from the extremely enlarged surface in the surface structure described.
  • Samples 1 and 2 according to the invention thus show very good active protection against corrosion of the steel substrate in the event of damage to the anti-corrosion layer.
  • the samples according to the invention show very good direct paintability. This can be seen from the measured infiltration U/2.
  • Samples 1 and 2 according to the invention show an average infiltration of 1-2 mm. On the other hand, it is 19mm in the comparative sample 4. The infiltration of 1-2 mm is similarly low as in a sample phosphated before painting.
  • the penultimate column of Table 2 indicates how great the undermining is when a typical automotive phosphating has been carried out before painting.
  • the undercutting U/2 can be reduced from 19 mm to 1.3 mm by phosphating.
  • Samples 1 and 2 already have this magnitude without phosphating.
  • the two samples 1 and 2 according to the invention also exhibit low abrasion, which was confirmed with the modified multi-frottement test described.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Other Surface Treatments For Metallic Materials (AREA)
  • Physical Vapour Deposition (AREA)

Abstract

L'invention concerne un produit plat en acier comprenant un substrat en acier avec un revêtement anticorrosion en zinc ou en alliage de zinc disposé sur au moins un côté du substrat en acier. Le revêtement anticorrosion comporte des nanocristaux de zinc (19) d'un diamètre moyen inférieur à 500 nm sur la surface tournée à l'opposé du substrat en acier. L'invention concerne également un procédé de fabrication d'un tel revêtement anticorrosion.
EP22764666.8A 2021-08-17 2022-08-08 Produit plat en acier à revêtement de zinc amélioré Pending EP4388144A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102021121343.6A DE102021121343A1 (de) 2021-08-17 2021-08-17 Stahlflachprodukt mit verbesserter Zinkbeschichtung
PCT/EP2022/072237 WO2023020874A1 (fr) 2021-08-17 2022-08-08 Produit plat en acier à revêtement de zinc amélioré

Publications (1)

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EP4388144A1 true EP4388144A1 (fr) 2024-06-26

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EP22764666.8A Pending EP4388144A1 (fr) 2021-08-17 2022-08-08 Produit plat en acier à revêtement de zinc amélioré

Country Status (5)

Country Link
US (1) US20240200184A1 (fr)
EP (1) EP4388144A1 (fr)
CN (1) CN117836462A (fr)
DE (1) DE102021121343A1 (fr)
WO (1) WO2023020874A1 (fr)

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6473070A (en) 1987-09-11 1989-03-17 Nisshin Steel Co Ltd Galvanized steel sheet formed by phosphate treatment and vacuum deposition and production thereof
TW359688B (en) * 1995-02-28 1999-06-01 Nisshin Steel Co Ltd High anticorrosion Zn-Mg series-plated steel sheet and method of manufacture it
GB2340131A (en) 1998-07-29 2000-02-16 Ford Motor Co Corrosion resistant surface coating based on zinc
UA117592C2 (uk) * 2013-08-01 2018-08-27 Арселорміттал Пофарбований оцинкований сталевий лист та спосіб його виготовлення
KR101867732B1 (ko) 2016-12-22 2018-06-14 주식회사 포스코 다층구조의 도금강판 및 그 제조방법
DE102017127987A1 (de) 2017-11-27 2019-05-29 Muhr Und Bender Kg Beschichtetes Stahlsubstrat und Verfahren zum Herstellen eines gehärteten Bauteils aus einem beschichteten Stahlsubstrat
DE102017223778B4 (de) 2017-12-22 2022-06-09 Thyssenkrupp Ag Barometrische Flüssigkeitsschleusen und Verfahren zum kontinuierlichen Einschleusen oder Ausschleusen von Materialbändern

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DE102021121343A1 (de) 2023-02-23
CN117836462A (zh) 2024-04-05
US20240200184A1 (en) 2024-06-20

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