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US-12624436-B2 - Method for producing a hot-dip-coated steel sheet and hot-dip-coated steel sheet

US12624436B2US 12624436 B2US12624436 B2US 12624436B2US-12624436-B2

Abstract

This disclosure relates to a method of producing a hot-dip-coated steel sheet and to a hot-dip-coated steel sheet.

Inventors

  • Burak William Cetinkaya
  • Fabian Junge

Assignees

  • THYSSENKRUPP STEEL EUROPE AG

Dates

Publication Date
20260512
Application Date
20221110
Priority Date
20211117

Claims (14)

  1. 1 . A method of producing a hot-dip-coated steel sheet, the method comprising: providing a cold-rolled steel substrate, having a deterministic surface structure on one or both sides; subsequent to the providing, coating on the cold-rolled steel substrate having a deterministic surface structure on one or both sides with a zinc-based coating by hot dip coating, in order to obtain the hot-dip-coated steel sheet, wherein the deterministic surface structure is applied to the steel substrate prior to the hot dip coating to influence a crystallization nuclei density of the zinc-based coating during solidification; and subjecting the hot-dip-coated steel sheet to skin pass rolling.
  2. 2 . The method as claimed in claim 1 , wherein the deterministic surface texture has a closed texture with embossments.
  3. 3 . The method as claimed in claim 2 , wherein the closed texture comprises two or more embossments each occupying an area between 100 and 25,000 μm 2 and each having a centroid, wherein the distance between at least two adjacent centroids is between 10 and 1,000 μm.
  4. 4 . The method as claimed in claim 1 , wherein the deterministic surface texture has an open texture with elevations.
  5. 5 . The method as claimed in claim 4 , wherein the open texture comprises two or more elevations each occupying an area between 100 and 25,000 μm 2 and each having a centroid, wherein the distance between at least two adjacent centroids is between 10 and 1,000 μm.
  6. 6 . The method as claimed in claim 1 , wherein the deterministic surface texture has at least one embossment or at least one elevation that occupies an area between 100 and 25 000 μm 2 .
  7. 7 . The method as claimed in claim 6 , wherein two or more embossments or two or more elevations are present, each of which has an area each with a centroid, where the distance between at least two adjacent centroids is between 10 and 1000 μm.
  8. 8 . The method as claimed in claim 1 , wherein the zinc-based coating, in addition to zinc and unavoidable impurities, contains additional elements such as aluminum with a content of up to 10.0% by weight and/or magnesium with a content of up to 10.0% by weight in the coating.
  9. 9 . The method as claimed in claim 1 , wherein the deterministic surface structure on the cold-rolled steel substrate provides nucleation sites at an interface between a liquid zinc-based melt and the cold-rolled steel substrate during the hot dip coating, thereby controlling a distribution and density of crystallization nuclei of zinc grains in the zinc-based coating upon solidification.
  10. 10 . The method of claim 1 , wherein the deterministic surface structure on the cold-rolled steel substrate increases a density of crystallization nuclei of zinc grains at the interface between the liquid zinc-based melt and the cold-rolled steel substrate relative to a cold-rolled steel substrate lacking the deterministic surface structure, resulting in a finer-grained zinc-based coating.
  11. 11 . The method of claim 1 , wherein the deterministic surface structure is imparted to the one or both sides of the cold-rolled steel substrate in the course of a cold rolling process, wherein at least one roll of a last roll stand of a cold rolling train is provided with a corresponding deterministic structure.
  12. 12 . The method of claim 11 , wherein the deterministic structure on the at least one roll is introduced by laser material removal.
  13. 13 . The method as claimed in claim 1 , wherein the deterministic surface structure is imparted to the one or both sides of the cold-rolled steel substrate in a separate rolling process conducted after cold rolling and before the hot dip coating, by means of at least one roll having a corresponding deterministic structure.
  14. 14 . The method as claimed in claim 1 , wherein the cold-rolled steel substrate has a chemical composition comprising, in percent by weight: C up to 0.1%; Mn up to 2.0%; Si up to 0.3%; P up to 0.1%; S up to 0.1%; N up to 0.1%; and balance iron and unavoidable impurities.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a 371 U.S. National Stage of International Application No. PCT/EP2022/081502 filed Nov. 10, 2022 which claims the benefit of German Patent Application No. 10 2021 129 934.9 filed Nov. 17, 2021. The disclosures of each of the above applications are incorporated herein by reference in their entirety. The invention relates to a method of producing a hot-dip-coated steel sheet and to a hot-dip-coated steel sheet. Ever more complex forming processes in the production of components in sheet design are leading to ever higher material stresses, and are in some cases accompanied by cracking within the coating of a hot-dip-coated sheet, especially steel sheet. This is manifested in particular in regions of acute radii and (steel) sheet component regions that undergo a high degree of forming in the processing operation. Examples of these include steel components for the vehicle industry, the shaping of which is characterized by locally high deforming stress, or sheets in the industrial sector, for example trapezoidal sheets. Conventionally, hot-dip-coated steel sheets having a zinc-based coating are employed, so that cathodic corrosion protection can be ensured. Although cracks in the zinc-based coating do not necessarily disrupt cathodic corrosion protection, the risk of a corrosion attack nevertheless rises with the possibility of air humidity penetrating up to the steel material (substrate). In the case of the vehicle industry, the coated surface of the steel sheet is treated by conversion chemistry only after forming/shaping, for example by phosphation, such that areas of the steel material that have been exposed in the forming/shaping operation are also closed again. However, the presence of cracks in the coating and/or at the surface of the coating can have the effect that these are filled by a process medium, for example an (alkaline) cleaner, an (alkaline) activation or an (acidic) phosphation and cannot be fully cleaned/dried. One effect of this can be that there is outgassing of these constituents (of the process medium) in the process of a heat treatment, for example in the baking operation in cathodic electrocoating. It is also additionally or alternatively conceivable for the constituents (of the process medium) that get stuck in the crack to remain, such that there can be formation of an alkaline or acidic solution within the cracks in the event of later contact with water, for example via diffusion through an applied paint layer, and these can attack the coating and hence adversely affect cathodic corrosion protection. It is also possible for pretreatment or aftertreatment applied via what is called coil coating to locally break up the coating via cracks and cause it to locally lose its passivating action. For instance, in these applications, it is possible, for example, for the conversion layer to be undermined by moisture, which can lead to corrosion and in particular loss of paint adhesion. It is thus known that cracking can damage the zinc-based coating so as to be able to result in loss of adhesion of the layer and/or at least of parts of the layer. Crack propagation is promoted in the coating by the structure thereof. For instance, in the zinc-based coating which is applied in the liquid state to a steel substrate (steel sheet) in the hot dip operation and is then cooled and hence solidified, a small number of “large” zinc grains with the same orientation are formed, which extend throughout the coating thickness. When these crystals are stressed, there is the fracture in a preferential direction, depending on the orientation of the crystal. In the case of different crystal sizes, large crystals are less stable to mechanical stresses than small crystals. In order to be able to influence and hence vary the crystal sizes, it is either necessary to alter the process conditions, for example the cooling rate to bring about the solidification of the liquid coating, for example via accelerated cooling for achievement of small zinc flowers in the coating, or to enrich the zinc-based melt with additional elements, for example by addition of lead as nucleator. Changes to the process conditions in conventionally operated continuous strip galvanization processes are achievable only to a very limited degree: for example, cooling rates are technically limited or high cooling rates are possible at additional costs (high capital costs), and additions of further elements as grain refiners/nucleating agents can affect the coating system, which is complex in any case, not just economically, for example via the additional expenditure on the addition and the monitoring, but also in an adverse manner, for example via a negative influence on secondary metallurgy and the process regime, and also on the environment. It is therefore the object of the invention to specify not only a method of producing a hot-dip-coated steel sheet but also a hot-dip-coated steel she