METHOD FOR PRODUCING A HOT-DIP-COATED STEEL SHEET AND HOT-DIP-COATED STEEL SHEET

Abstract

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

Claims

1-11. (canceled)

12. 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; and coating on one or both sides with a zinc-based coating by hot dip coating, in order to obtain a hot-dip-coated steel sheet.

13. The method as claimed in claim 12, wherein the deterministic surface texture has a closed texture with embossments.

14. The method as claimed in claim 12, wherein the deterministic surface texture has an open texture with elevations.

15. The method as claimed in claim 12, wherein the deterministic surface texture has at least one embossment or at least one elevation that occupies an area between 100 and 25 000 m.sup.2.

16. The method as claimed in claim 15, 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 m.

17. The method as claimed in claim 12, 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.

18. The method as claimed in claim 12, further comprising: subjecting the hot-dip-coated steel sheet to skin pass rolling.

19. A hot-dip-coated steel sheet comprising a steel substrate with a zinc-based coating applied to one or both sides, wherein the steel substrate has a deterministic surface texture on one or both sides.

20. The steel sheet as claimed in claim 19, wherein the coating includes, in addition to zinc and unavoidable impurities, additional elements including 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.

21. The steel sheet as claimed in claim 19, wherein zinc grain sizes of the zinc-based coating are between 20 and 250 m.

22. The steel sheet as claimed in any of claim 19, wherein the hot-dip-coated steel sheet has been subjected to skin pass rolling with a stochastic or deterministic surface texture.

Description

[0044] The sole FIG. 1 shows scanning electron micrographs (SEM) of two surface-textured steel substrates before and after hot dip coating with a zinc-based coating in top view. The deterministic surface texture imparted was embossments into the surface of the steel substrate, for example in the form of a double-I texture in accordance with EP 2 892 663 B1. The deterministic surface texture was thus in both cases a closed texture. The texture differed merely in the dimensioning of the embossed I texture: in the image top left with 80 m25 m and hence an area of 2000 m.sup.2 per embossed I, and in the image top right with 210 m70 m and hence an area of 14 700 m.sup.2 per embossed I in FIG. 1. In the case of the embossed Is, it is easily possible in each case to ascertain the centroid for each area, where the distance between at least two adjacent centroids for the left-hand image was 50-70 m, for example, and for the right-hand image 120-150 m, for example. The grain sizes in the left-hand image are up to a maximum of 200 m and in the right-hand image up to a maximum of 900 m. Using the example for different configurations or dimensions of the deterministic surface texture of a steel substrate, the lower left-hand image by comparison with the lower right-hand image in FIG. 1 illustrates that finer textures (top left) on the surface of the steel substrate give rise to smaller zinc grains (bottom left). The crystallization seeds form preferentially at the transitions where the embossments adjoin the surface of the steel substrate.

[0045] The density of the crystallization seeds is accordingly dependent on the dimension of the texture or on the number of textures per unit area. In all tests, it was found that those steel substrates with a higher number of structures based on a constant area always had smaller zinc grains after hot dip coating. Comparable results (not shown here) were also found in the case of ZnAlMg coatings. In the case of assessment of hot-dip-coated coatings with eutectic phases (ZnAlMg coating), a finer grain structure at the surface of the steel substrate is advantageous for corrosion resistance. Based on the ZnAlMg coating, MgZn.sub.2 in the eutectic phase is a sacrificial anode for the zinc grains. This means that, under corrosive stress on the coating, there is firstly attack on the MgZn.sub.2 phases, for example in the case of acidic pretreatments or aftertreatments of the hot-dip-coated steel sheets (pickling), or on the Al phases, for example in the case of alkaline pretreatments or aftertreatments of the hot-dip-coated steel sheets (degreasing and/or cleaning, especially prior to pickling), in the eutectic and subsequently on the zinc grains. Under air, such a protective effect (anodic sacrificial mechanism) is essentially dependent on the distance between the less base and more base metallic phase. If the phases are spatially too far removed from one another, cathodic corrosion protection can no longer be assured. Accordingly, smaller zinc grains surrounded by eutectic are advantageous for corrosion resistance since the distance of eutectic from the middle of the zinc grain is smaller and hence anodic sacrifice of the phases in the eutectic for protection of the zinc can be better enabled.