Hot-dip coated, flattened rolled steel sheet

Abstract

The invention relates to a hot-dip coated, flattened rolled steel sheet.

Description

Technical Field

[0001] The invention relates to a temper rolled hot dip coated steel sheet. Background Art

[0002] In the temper rolling process for hot-dip coated flat steel according to the prior art, the profile elements of the temper rolling roller are usually distributed on the roller surface in a random / random distribution, in which case no significant visible transfer effect of the profile elements via the coating into the substrate layer is observed to be evenly distributed over the entire surface. Confocal reflected light microscopy known in the prior art can be used to provide a proof of the uniformity and / or quality of the occurrence of indentations. For this purpose, such samples are usually provided, which are measured in the surface coated state and in the uncoated state, for example after chemical stripping. With the help of the visual appearance of these surfaces, the indentations of the punching elements of the temper rolling roller on the substrate surface can already be identified, which can serve as an indicator for judging the uniformity and / or quality of the indentations. This situation is particularly evident in the mathematical correlation evaluation of the surface morphology data after coating and stripping. Due to the random / random nature of the morphology / texture distribution, the spatial correspondence of the measurement points of the coated and stripped surfaces is mandatory. The correlation diagram of the corresponding coated and stripped surfaces shows that there are almost no related metal sheet areas, so that even regularly repeated related metal sheet areas cannot be identified. Summary of the invention

[0003] Therefore, the object of the present invention is to provide a temper-rolled hot-dip coated steel sheet which overcomes the drawbacks of the prior art, in particular improves the uniformity and / or quality of the indentation.

[0004] This object is achieved by the features of claim 1 .

[0005] The invention provides a temper-rolled hot-dip coated steel sheet, wherein at least one surface of the temper-rolled hot-dip coated steel sheet has deterministically arranged indentations, wherein a cross-correlation function r is used to compare different areas. z,u Height value z measured on the steel plate in the hot-dip coated state i and the height u of the steel plate measured in the uncoated state i , and by the cross-correlation function r z,u The obtained correlation coefficient r was at least 0.40.

[0006] The correlation coefficient r is calculated from the cross-correlation function r z,u The formula is: r z,u =s z,u / (s z *s u ), where s z,u is the covariance, determined by the following formula:

[0007] The average and And the standard deviation as well as

[0009] The measurement or evaluation area should be at least 0.5 x 0.5 mm 2 . More than 1.5 x 1.5 mm 2 When the shape and ripples are removed, filtering measures can be used. The determination of the correlation coefficient and its formula are part of the prior art.

[0010] In contrast to the prior art, the indentation punch elements of the surface of the tempered roller are evenly distributed both in the plane of the metal sheet and in the vertical direction, especially in the layer structure, and can be found / proven, for example, by means of a confocal reflected light microscope. Samples are created from coated steel sheets tempered according to the invention, which are measured in different areas in the surface coated state and in the decoated state after chemical removal of the coating. Therefore, there is no overlap in the observation of the coated area and the decoated area, that is, within a prescribed measurement area of ​​the first area, the measured sample is observed in the coated state, and within a prescribed measurement area of ​​the second area that does not correspond to the first area, the measured sample is observed after decoating. The size of the measurement areas is preferably the same. This can indicate, in particular, the uniformity and / or quality of the indentation. If the correlation coefficient is high, at least 0.40, it can be concluded that the uniformity and / or quality of the indentation is improved compared to the prior art.

[0011] In particular, the correlation coefficient r is at least 0.450, preferably at least 0.480, more preferably at least 0.50, particularly preferably at least 0.520, further preferably 0.550, 0.560, 0.570, 0.580, 0.590, 0.60, 0.610, 0.620, 0.630, 0.640, 0.650, 0.660, 0.670, 0.680, 0.690, 0.70, 0.710, 0.720, 0.730, 0.740. In theory, a correlation coefficient of 1 is possible, but it is difficult to achieve in practical applications, and therefore, the correlation coefficient can be close to 1, in particular a maximum of 0.90, preferably a maximum of 0.850. It can be assumed that as the correlation coefficient increases, the quality and / or uniformity of the indentation will also improve.

[0012] The term "steel plate" generally refers to a flat steel product, which can be in sheet form (sheet metal) or in slab form (slab) or in strip form (strip).

[0013] The steel sheet is coated with a hot-dip coating. Therefore, temper rolling of the steel sheet with a hot-dip coating is performed after the coating is completed in order to achieve better adhesion properties at the coating / substrate interface by means of the punch element designed according to the invention.

[0014] For example, steel sheets have been hot-dip coated with zinc based coatings.

[0015] In particular, the coating contains, in addition to zinc and unavoidable impurities, further elements, such as aluminum in an amount of at least 0.1 to 8.0% by weight and / or magnesium in an amount of at least 0.1 to 8.0% by weight. Steel sheets with a zinc-based coating have very good cathodic corrosion protection, which has been used for many years in automobile construction. If improved corrosion protection is required, the coating additionally contains at least 0.3% by weight of magnesium, in particular at least 0.6% by weight, preferably at least 0.9% by weight. Aluminum can be present as a substitute or in addition to magnesium in an amount of at least 0.3% by weight, in particular at least 0.6% by weight, for example to improve the bonding of the coating to the steel sheet, in particular to substantially avoid the diffusion of iron from the steel sheet into the coating during heat treatment of the coated steel sheet, thereby, for example, ensuring good adhesion adaptability. The total amount of unavoidable impurities and optional further components is limited to not more than 2.0% by weight.

[0016] The thickness of the coating can be between 1.5 and 15 μm, in particular between 2 and 12 μm, preferably between 3 and 10 μm.

[0017] In an alternative variant, the steel sheet has been hot-dip coated with an aluminum-based coating. In this case, the thickness of the coating may be between 1.5 and 15 μm, in particular between 2 and 12 μm, preferably between 3 and 10 μm.

[0018] In particular, the coating contains, in addition to aluminum and unavoidable impurities, further elements such as silicon in a content of maximum 15% by weight, optionally iron in a content of maximum 4% by weight, optionally alkali metals or alkaline earth metals in a content of maximum 1.0% by weight, and optionally other components, the total content of which is limited to not more than 2.0% by weight.

[0019] In a preferred variant, the silicon content is 0.2 to 4.5% by weight or 7 to 13% by weight, in particular 8 to 11% by weight. In a preferred variant, the optional iron content is 0.2 to 4.5% by weight, in particular 1 to 4% by weight, preferably 1.5 to 3.5% by weight. In a preferred variant, the optional alkali metal or alkaline earth metal content is 0.01 to 1.0% by weight of magnesium, in particular 0.1 to 0.7% by weight of magnesium, preferably 0.1 to 0.5% by weight of magnesium. In addition, the optional alkali metal or alkaline earth metal content may in particular contain at least 0.0015% by weight of calcium.

[0020] For example, in an alternative variant, the aluminum-based coating contains, in addition to aluminum and unavoidable impurities, further elements such as 2 to 24 wt. % zinc, 1 to 7 wt. % silicon, optionally 1 to 8 wt. % magnesium (when the silicon content should be between 1 and 4 wt. %), optionally a total amount of up to 0.3 wt. % Pb, Ni, Zr or Hf.

[0021] The temper rolling of the hot-dip coated steel sheet is carried out in a temper rolling stand, wherein a steel substrate with a hot-dip coated layer is provided, the steel sheet is introduced into the temper rolling mill and passes between two temper rolling rollers. At least one temper rolling roller has a defined arrangement of punch elements on its surface, wherein each punch element has an area A on the temper rolling roller surface P Between 12.4 and 32400 μm 2 between.

[0022] The deterministically arranged punch elements formed on the surface of the tempering roller, usually by laser ablation, form a "positive" shape, which acts on the surface of the coated steel sheet during the tempering rolling process and embosses a "negative" surface structure on the surface of the coated steel sheet. Since the complete embossing / immersion of the punch elements is not possible in practice, the degree of transfer of the geometric shape of the punch elements into or on the surface of the coated steel sheet is greater than 0%, in particular greater than 10%, more preferably greater than 20%, and less than 100%, in particular less than 90%, more preferably less than 85%.

[0023] Methods and devices for producing laser-textured smooth rolls are known from the prior art, see EP 2 892 663 B1 etc. Deterministic surface topography / surface structure or deterministic arrangement of punch elements refers to a recurring surface structure with a defined shape and / or configuration, see EP 2 892 663 B1.

[0024] By means of a laser, a defined arrangement of punch elements is introduced into or onto the surface of a smooth roller by removing material, in that a positive influence can be exerted by purposefully controlling the energy and pulse duration and selecting a suitable laser wavelength acting on the smooth roller surface. At a higher or higher pulse duration, the interaction time between the laser beam and the smooth roller surface increases, so that more material on the smooth roller surface can be removed. Each pulse leaves a substantially circular depression on the smooth roller surface. A reduction in the pulse duration influences the formation of the depression, in particular the diameter of the depression can be reduced. The punch elements are thus the remaining raised areas on the smooth roller surface that are not affected by the laser. In particular, the bombardment pattern to be formed can be carried out on the smooth roller surface by means of a laser in a computer-aided manner.

[0025] The skin-pass roll is thus endowed with a large number of raised punch elements. Each (partial) reference surface A refThe number n of punch elements within gives the number to area ratio Snr = n / A ref .

[0026] The area A of each punch element P (n) between 12.4 and 32400 μm 2 Area A P In particular, at least 50 μm 2 , more preferably at least 150 μm 2 , more preferably at least 300 μm 2 , and preferably at least 500 μm 2 , and in particular a maximum of 30000 μm 2 , preferably up to 25000 μm 2 , more preferably up to 20000 μm 2 , preferably up to 15000μm 2 .

[0027] The area of ​​the punch element in the section plane c p Measured in, where d 2 Smr(c o ) / dc 2 , the second derivative of the Firestone-Abbott curve Smr(c) has a maximum value:

[0028] d 2 Smr(c o ) / dc 2 ≈(Smr(c o +Δc)–2Smr(c o )+Smr(c o –Δc)) / (Δc)2

[0029] d 2 Smr(c P ) / dc 2 = Maximum value

[0030] c is the distance of the profile plane, ie the depth, below the reference plane, for example a height value. To suppress noise, the Smr(c) function can advantageously be smoothed by a mean value filter with a width of 1 μm. The discretization spacing Δc considered can be less than 0.1 μm.

[0031] Average area of ​​punch element A P,m By material ratio Smr(c P ) divided by the number of punch elements per unit area Snr(c P ) is determined by the ratio:

[0032] A P,m =Smr(c P ) / Snr(cP ).

[0033] For example, the area A of each punch element on the flat roller surface is P Can be between 500 and 20000μm 2 Between, especially between 750 and 15000 μm 2 between.

[0034] For example, the area A of each punch element on the flat roller surface is P Can be between 1001 and 5000μm 2 between.

[0035] Alternatively, the area A of each punch element of the flattened roll surface P For example, it can be between 5001 and 10000 μm 2 between.

[0036] For example, two flat rollers are respectively formed with deterministically arranged punch elements on their surfaces, wherein the area A of each punch element on the flat roller surface is P Between 12.4 and 32400 μm 2 between.

[0037] The hot-dip coated steel sheet is tempered by one or more tempering rolls, and the tempering rate is set to at least 0.1% and a maximum of 2.5%, wherein the tempering rate is particularly set to at least 0.3%, preferably at least 0.5%. If the tempering rate exceeds 2.5%, it will have a negative impact on the mechanical properties of the material. In order to optimize dimensional accuracy and surface quality, the tempering rate is particularly set to not more than 2.0%, preferably not more than 1.7%. The tempering rolling process and the adjustment of the tempering rate belong to the scope of the prior art. DETAILED DESCRIPTION

[0038] In the actual tests, three steel sheets (strips) coated with zinc-based coatings were tempered (EDT1, LT1, LT3). The thickness and composition of all three steel strips as well as the thickness and composition of the zinc-based coating were identical. Three other steel sheets (strips) coated with aluminum-based coatings were likewise tempered (EDT2, LT2, LT4). The thickness and composition of all three steel strips as well as the thickness and composition of the aluminum-based coating were identical. Tempering was carried out on two of the strips using two pairs of EDT tempering rollers with different random structures (EDT1, EDT2) in a tempering stand, while the remaining four strips were processed in a tempering stand using tempering roller pairs with laser-textured, differently deterministically arranged punch elements (LT1, LT2, LT3, LT4). The tempering reduction was the same in all tests. Further parameters are listed in Table 1.

[0039] EDT1 EDT2 LT1 LT2 LT3 LT4 Smr[%] 45 30 31 34 46 40 <![CDATA[Snr[1 / mm 2 ]]]> 16 288 195 95 52 61 <![CDATA[A ref [mm 2 ]]]> 4 0.16 1.0 0.22 0.81 0.51 n[-] 62 46 195 21 42 31 <![CDATA[A P,m [μm 2 ]]]> 29 000 1000 1589 3599 8841 6570

[0040] Table 1

[0041] Ten samples from each of six temper-rolled coated steel strips were investigated in detail. Confocal reflected light microscopy and a 0.8 x 0.8 mm 2 The height values ​​of the coated sample and the height values ​​of the chemically de-coated sample were measured in the measurement area. The de-coating process was as follows: rinse the sample with ethanol and dry; de-zincify with inhibited hydrochloric acid (essentially complete removal of the coating); rinse with ethanol and dry. The mathematical correlation evaluation of the topographic data of the measured surfaces of the coated sample and the de-coated sample was performed (μsoft analysis premium 6.2.6967) and the correlation coefficient r was determined, see

[0042] Table 2.

[0043]

[0044]

[0045] Table 2

[0046] exist Figure 1 In the figure, the results of the cross-correlation function were measured in the measurement area by reflected light microscopy during EDT1 and the height values ​​in the coated and uncoated state are shown compared to each other. The light-colored center points again represent local main maxima, which only appear in the case of perfect agreement, meaning that the area of ​​height values ​​measured in the coated and uncoated state is the same. It is obvious that there is no uniformity and / or quality of the indentation throughout the illustration. Therefore, no repetitive patterns are evident. In contrast, in Figure 2 In the figure, when performing LT1, local maxima appear in the form of secondary maxima, especially due to the shift of the observed area, that is, the first area in the coated state does not coincide with the second area observed in the uncoated state, which appears repeatedly in the figure, indicating the uniformity and / or quality of the indentation.

Claims

1. A temper-rolled hot-dip coated steel sheet, wherein at least one surface of the temper-rolled hot-dip coated steel sheet has indentations arranged in a defined manner, characterized in that: Comparison of cross-correlation function r in different regions z,u Height value z measured on the steel plate in the hot-dip coated state i and the height u of the steel plate measured in the uncoated state i , where the cross-correlation function r z,u The obtained correlation coefficient r was at least 0.

40.

2. The steel sheet according to claim 1, wherein the steel sheet is hot dip coated with a zinc based coating.

3. Steel sheet according to any of the preceding claims, wherein the coating contains, besides zinc and unavoidable impurities, further elements, such as aluminum in an amount of at least 0.1 to 8.0% by weight and / or magnesium in an amount of at least 0.1 to 8.0% by weight.

4. The steel sheet according to claim 1, wherein the steel sheet is hot dip coated with an aluminum based coating.

5. Steel sheet according to claim 4, wherein the coating contains, in addition to aluminum and unavoidable impurities, other elements such as silicon in an amount of maximum 15% by weight, optionally iron in an amount of maximum 4% by weight, optionally alkali metals or alkaline earth metals in an amount of maximum 1.0% by weight, and optionally other components, the total amount of which is limited to not more than 2.0% by weight.

6. The steel sheet according to claim 4, wherein the coating contains, in addition to aluminum and unavoidable impurities, further elements such as 2 to 24% by weight of zinc, 1 to 7% by weight of silicon, optionally 1 to 8% by weight of magnesium when the silicon content is between 1 and 4% by weight, and optionally a total of up to 0.3% by weight of Pb, Ni, Zr or Hf.

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