High-peak-value thick-zinc-layer electro-galvanized steel plate and manufacturing method thereof

Abstract

The invention discloses a high peak number thick zinc layer electro-galvanized steel plate which comprises a steel substrate and an electro-galvanized layer plated on the surface of the steel substrate, the surface roughness profile skewness Rskb of the steel substrate is larger than or equal to 0.1, and the surface peak number Pcs of the electro-galvanized layer is larger than or equal to 75 / cm. The invention further discloses a manufacturing method of the high-peak-number thick-zinc-layer electro-galvanized steel plate, and the manufacturing method comprises the following steps: carrying out peak removal treatment on the roughened surface of the roller of a temper mill, so that the profile skewness parameter Rsk of the roller is less than or equal to-0.5; flattening and rolling the steel substrate by using a roller; and the leveled steel base plate is subjected to electrogalvanizing, and the high-peak-number thick-zinc-layer electrogalvanized steel plate is obtained. According to the high-peak-number thick-zinc-layer electro-galvanized steel plate and the manufacturing method thereof, the problem that surface topography parameters are too large in attenuation is solved, it can be effectively guaranteed that the surface topography parameters still have a high peak number index after electro-galvanizing, and therefore the stamping and coating use effects of the thick-zinc-layer electro-galvanized steel plate at a user side are improved.

Description

Technical Field

[0001] This invention relates to a steel plate and a method for manufacturing the same, and more particularly to a coated steel plate and a method for manufacturing the same. Background Technology

[0002] Electro-galvanized steel sheets are often used in automotive exterior panels with high surface quality requirements due to their good stamping stability and few surface defects.

[0003] The surface morphology of electro-galvanized steel sheets has a significant impact on their stamping and coating effects. To maintain good stamping stability and coating appearance, steel sheets are typically required to have a roughened surface with a certain degree of roughness and a high peak count. Appropriate roughness facilitates the formation of a good lubrication interface between the steel sheet and the die, while a higher peak count indicates a finer surface texture and better surface quality after coating.

[0004] The surface microstructure of electro-galvanized steel sheets primarily originates from the preceding rolling and leveling process, where rolls imprint a roughened texture onto the steel substrate before electro-galvanizing. During electro-galvanizing, due to the leveling effect of zinc deposition, the surface morphology of the steel sheet typically exhibits some degree of degradation after galvanizing. Some high-end automotive steel sheets require high surface peak counts to ensure good coating results; however, steel sheets with high peak counts have finer surface microstructures, leading to greater degradation after electroplating. Simultaneously, high-end automotive steel sheets often require thicker zinc plating to ensure good corrosion resistance; however, thicker zinc plating results in more severe degradation of the roughened surface morphology after electroplating.

[0005] Therefore, producing high peak zinc number thick zinc layer electroplated steel sheets presents significant production challenges. Existing technologies include Chinese patent literature on suppressing the surface morphology degradation of high peak zinc number thick zinc layer electroplated steel sheets during the electroplating process, among which:

[0006] For example, Chinese patent document CN115976597A, published on April 18, 2023, entitled "A Steel for Automobile Outer Panels and Its Preparation Method," discloses a steel for automobile outer panels and its preparation method. It mentions suppressing the attenuation of surface morphology parameters during the electroplating process by controlling parameters such as the pH value of the electroplating solution, the temperature of the electroplating solution, the zinc ion concentration, the electroplating speed, and the roughness of the leveling roller. Although this improves the morphology parameters of the electroplated galvanized steel sheet to some extent, it does not completely solve the attenuation problem of high peak number thick zinc layer electroplated steel sheets. Compared with conventional electroplated steel sheets, high peak number thick zinc layer electroplated steel sheets have a high peak number and a large zinc coating amount. It is still difficult to fully solve the attenuation problem during the electroplating process by simply adjusting the electroplating process and the roughness of the leveling roller. Summary of the Invention

[0007] One of the objectives of this invention is to provide a high peak value thick zinc layer electro-galvanized steel sheet. This high peak value thick zinc layer electro-galvanized steel sheet solves the problem of excessive attenuation of surface morphology parameters in previous thick zinc layer electro-galvanized steel sheets. It can effectively ensure that the surface morphology parameters still have a high peak value index after electro-galvanizing, thereby improving the performance of thick zinc layer electro-galvanized steel sheets in stamping and coating.

[0008] To achieve the above objectives, the present invention provides a high peak value thick zinc-coated electroplated steel sheet, comprising a steel substrate and an electroplated zinc layer coated on the surface of the steel substrate, wherein the surface roughness profile skewness Rsk of the steel substrate is specified. b ≥0.1, the surface peak number Pc of the electroplated zinc layer s ≥75 pieces / cm.

[0009] Through extensive experimental observation, the inventors discovered that the surface profile skewness parameter Rsk, a key characteristic parameter of the steel plate substrate surface morphology, plays a crucial role. b The profile skewness Rsk has a significant impact on the attenuation effect during the electroplating process. b The larger the parameter, i.e., the more peaks on the steel plate surface morphology, the smaller the decrease in surface roughness and peak number after electroplating. This is because peaks, compared to pits, are less easily filled during the electroplating process, thus more effectively suppressing the decrease in morphology parameters during electroplating. Furthermore, the inventors have verified through extensive experiments that improving the Rsk parameter on the steel plate surface... b When the value is controlled at 0.1 or above, the attenuation of steel plate surface roughness and peak number parameters during the electroplating process can be effectively suppressed.

[0010] Furthermore, in the high peak number thick zinc layer electroplated steel sheet of the present invention, the surface roughness Ra of the electroplated zinc layer is 0.9μm-1.4μm.

[0011] Furthermore, in the high peak value thick zinc layer electro-galvanized steel sheet described in this invention, the surface roughness Ra of the electro-galvanized layer... s The surface roughness Ra of the steel substrate at the corresponding position b Satisfying Ra b -Ra s ≤0.1μm.

[0012] Furthermore, in the high peak number thick zinc layer electro-galvanized steel sheet described in this invention, the surface peak number Pc of the electro-galvanized layer... s The surface peak number Pc of the steel substrate at the corresponding position b With satisfying Pc b -Pc s ≤10 pieces / cm.

[0013] Furthermore, in the high peak value thick zinc layer electro-galvanized steel sheet described in this invention, the average zinc coating weight on a single side of the steel substrate is ≥40g / m². 2 .

[0014] Furthermore, in the high peak number thick zinc layer electro-galvanized steel sheet described in this invention, the surface roughness profile skewness Rsk of the steel substrate is... b ≥0.2.

[0015] In this invention, the surface roughness profile skewness Rsk of the steel substrate is controlled. b ≥0.2 can further weaken the attenuation effect of thick zinc-coated steel sheets during the galvanizing process.

[0016] Another objective of this invention is to provide a method for manufacturing a high peak number thick zinc layer electro-galvanized steel sheet. This method can provide a high peak number thick zinc layer electro-galvanized steel sheet, which solves the problem of excessive attenuation of surface morphology parameters in previous thick zinc layer electro-galvanized steel sheets. It can effectively ensure that the surface morphology parameters still have a high peak number index after electro-galvanizing, thereby improving the performance of thick zinc layer electro-galvanized steel sheets in stamping and coating.

[0017] To achieve the above objectives, the present invention provides a method for manufacturing a high peak value thick zinc-coated electrogalvanized steel sheet, comprising the following steps:

[0018] (1) The surface of the roughened leveling mill roll is subjected to de-peaking treatment so that the roll profile skewness parameter Rsk≤-0.5;

[0019] (2) The steel substrate is leveled by rolling with rolls: the leveling elongation is controlled to be ≥0.6%;

[0020] (3) The flattened steel substrate is electro-galvanized to obtain a high peak value thick zinc layer electro-galvanized steel sheet.

[0021] Peak removal treatment refers to polishing and reducing the peaks on the surface contour of a roughened roll using physical or chemical methods.

[0022] Since the surface morphology of the steel sheet is achieved through texturing rolls, and the unevenness of the roll and strip surface contours is complementary, controlling the roll surface contour skewness Rsk to a negative value can make the Rsk value of the strip surface tend to be positive. Simultaneously, de-spiking the roll surface helps remove small, ineffective spikes, slowing down the roughness decay during roll use.

[0023] In this invention, the de-peaking treatment can make the roll surface obtain a more negative Rsk value. Combined with a larger flattening elongation, a higher profile skewness Rsk value can be imprinted on the steel plate surface. Combined with the control of electroplating process parameters, the morphology attenuation during the electroplating zinc process can be controlled, resulting in a high peak number thick zinc layer electroplated galvanized steel plate with a small attenuation.

[0024] In this invention, when the leveling elongation is too low, the transfer and replication ratio of the surface morphology of the leveling machine's work roll to the steel plate surface will be insufficient, making it difficult to guarantee the Rsk of the steel plate surface. b Therefore, in this invention, the flattening elongation is controlled to be ≥0.6%.

[0025] The key to the manufacturing method described in this invention lies in the de-peaking treatment of the roll surface and the use of a large flattening elongation. The de-peaking treatment can make the roll surface obtain a more negative Rsk value. Combined with the large flattening elongation, a higher profile skewness Rsk value can be imprinted on the steel plate surface. Furthermore, by controlling the electroplating process parameters, the morphology attenuation during the electroplating zinc process can be controlled, resulting in a high peak value electroplated zinc steel plate with a small attenuation.

[0026] Furthermore, in step (1) of the manufacturing method described in this invention, the surface roughness of the roll after the de-peaking treatment is 2.0-4.0 μm.

[0027] Furthermore, in step (1) of the manufacturing method described in this invention, the number of surface peaks of the roll after the de-peaking treatment is ≥95 / cm.

[0028] In this invention, by controlling the surface roughness and the number of surface peaks of the roll after the de-peaking treatment, it is further beneficial to control the surface roughness Ra of the electro-galvanized steel sheet between 0.9μm and 1.4μm, and the number of surface peaks Pc ≥ 75 / cm.

[0029] Furthermore, in step (3) of the manufacturing method described in this invention, the temperature of the electroplating solution is controlled at 48-53°C.

[0030] Through data statistics and numerous experiments, the inventors discovered a significant inverse correlation between the temperature of the electroplating solution and the amount of roughness reduction after electroplating. Further research revealed that as the temperature of the electroplating solution increases, the zinc layer deposited on the steel plate surface tends to grow more laterally, causing the coating to shift from rough to glossy. This results in increased surface morphology degradation during electroplating. Therefore, under suitable process conditions, appropriately lowering the electroplating solution temperature can effectively suppress morphology degradation after electroplating. When the electroplating solution temperature is too low, it can cause defects such as streaks on the steel plate surface. Therefore, preferably, in step (3) of the manufacturing method described in this invention, the electroplating solution temperature can be controlled between 48-53°C.

[0031] Compared with the prior art, the high peak value thick zinc layer electro-galvanized steel sheet and its manufacturing method described in this invention have the following advantages and beneficial effects:

[0032] The high peak value thick zinc layer electro-galvanized steel sheet and its manufacturing method described in this invention solve the problem of excessive attenuation of surface morphology parameters in previous thick zinc layer electro-galvanized steel sheets. It can effectively ensure that the surface morphology parameters still have a high peak value index after electro-galvanizing, thereby improving the stamping and coating performance of thick zinc layer electro-galvanized steel sheets at the user end. Attached Figure Description

[0033] Figure 1 The three-dimensional profile of the surface of the steel substrate in Embodiment 1 of the present invention is shown. Detailed Implementation

[0034] The high peak value thick zinc layer electroplated steel sheet and its manufacturing method described in this invention will be further explained and described below with reference to the specific drawings and embodiments. However, this explanation and description do not constitute an improper limitation on the technical solution of this invention.

[0035] Examples 1-5 and Comparative Examples 1-4

[0036] The high peak value thick zinc-coated electrogalvanized steel sheets described in Examples 1-5 of this invention are all prepared using the following steps:

[0037] (1) Roll surface treatment: The roll is roughened, and then the roughened surface of the leveling roll is de-peaked (e.g., using a sand belt polishing) so that the roll profile skew parameter Rsk≤-0.5.

[0038] In some implementations, the surface roughness Ra of the roll after de-peaking treatment can be controlled to be 2.0-4.0 μm, and the number of surface peaks Pc ≥ 95 / cm.

[0039] (2) The steel substrate is leveled by rolling with rolls: the leveling elongation is controlled to be ≥0.6%.

[0040] (3) The flattened steel substrate is electro-galvanized to obtain a high peak value thick zinc layer electro-galvanized steel sheet.

[0041] In some implementations, the temperature of the electroplating solution can be controlled between 48-53°C.

[0042] The rolls of Comparative Examples 1-3 were not subjected to de-peaking treatment after texturing, and the flattening elongation of Comparative Example 4 did not meet the design requirements of this invention.

[0043] Table 1 lists the specific process parameters of the high peak number thick zinc layer electroplated steel sheets of Examples 1-5 of the present invention and the comparative steels of Comparative Examples 1-4.

[0044] Table 1.

[0045]

[0046] The high peak value thick zinc-coated electrogalvanized steel sheets of Examples 1-5 of the present invention and the comparative steel sheets of Comparative Examples 1-4 were tested, and the test results are listed in Table 2. Wherein:

[0047] The roughness, peak count, and roughness profile skewness described in this invention are defined in GB / T 3505 and GB / T2523 standards. The sampling length for roughness measurement is specified as 2.5 mm, and the upper and lower cutoff lines for peak count are ±0.5 μm.

[0048] The surface morphology parameters of the corresponding steel substrate described in this invention are obtained by removing zinc from the surface of the electro-galvanized steel plate. The zinc removal method is to dissolve the zinc layer with an acid solution. The acid solution is prepared by a 5-20% concentration of dilute hydrochloric acid solution and a hexamethylenetetramine corrosion inhibitor added at a ratio of 2-5 g / L. The role of hydrochloric acid is to dissolve the zinc layer on the surface of the steel plate, and the role of the corrosion inhibitor is to weaken the corrosive effect of hydrochloric acid on the steel plate substrate.

[0049] The surface of the steel substrate after removing the zinc plating layer was cleaned and dried, and its roughness, peak number, and roughness profile skew were measured using a Mar PS10 roughness tester.

[0050] Table 2 lists the implementation effects of the high peak value thick zinc layer electroplated steel sheets of Examples 1-5 of the present invention and the comparative steels of Comparative Examples 1-4.

[0051] Table 2.

[0052]

[0053] As can be seen from Table 2 above, the surface roughness profile skewness Rsk of the steel substrate in each embodiment of the present invention is... b All are greater than 0.2. Meanwhile, the electro-galvanized steel sheets of Examples 1-5 of this invention all have an average zinc coating weight greater than or equal to 40 g / m². 2 In the case of a thick zinc coating, the peak number Pc on the surface of the zinc coating. s ≥75 particles / cm, the surface roughness Ra of the electroplated zinc layer is between 0.9μm and 1.4μm. s The surface roughness Ra of the steel substrate at the corresponding position b Satisfying Ra b -Ra s All are less than 0.1 μm, and the surface peak number Pc of the electroplated zinc layers The surface peak number Pc of the steel substrate at the corresponding position b With satisfying Pc b -Pc s ≤4 particles / cm, with no significant decrease in peak count or surface roughness.

[0054] Furthermore, the three-dimensional contour of the steel substrate surface in Example 1 was observed using an Olympus OLS4100 three-dimensional laser confocal microscope with a field of view of 640μm*640μm, yielding the following results: Figure 1 The three-dimensional morphological profile of the steel substrate surface is shown.

[0055] from Figure 1 As can be seen, the three-dimensional morphological structure of the steel plate surface mostly presents the shape of mountain peaks, with few valleys. This surface structure feature makes it less likely to be filled by the zinc layer after galvanizing, thus effectively reducing the attenuation of surface morphology parameters during the electroplating process.

[0056] It should be noted that the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0057] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A high peak value, thick zinc-coated electroplated steel sheet, comprising a steel substrate and an electroplated zinc layer coated on the surface of the steel substrate, characterized in that, The surface roughness profile skewness Rsk of the steel substrate b ≥0.1, the surface peak number Pc of the electroplated zinc layer s ≥75 pieces / cm.

2. The high peak value thick zinc-coated electrogalvanized steel sheet as described in claim 1, characterized in that, The surface roughness Ra of the electroplated zinc layer is 0.9μm-1.4μm.

3. The high peak value thick zinc-coated electrogalvanized steel sheet as described in claim 1, characterized in that, The surface roughness Ra of the electroplated zinc layer s The surface roughness Ra of the steel substrate at the corresponding position b satisfy Ra b -Ra s ≤0.1μm.

4. The high peak value thick zinc-coated electrogalvanized steel sheet as described in claim 1, characterized in that, The surface peak number Pc of the electroplated zinc layer s The surface peak number Pc of the steel substrate at the corresponding position b With satisfaction Pc b -Pc s ≤10 pieces / cm.

5. The high peak value thick zinc-coated electrogalvanized steel sheet as described in claim 1, characterized in that, The average zinc plating weight on one side of the steel substrate is ≥40g / m². 2 .

6. The high peak value thick zinc-coated electrogalvanized steel sheet as described in claim 1, characterized in that, The surface roughness profile skewness Rsk of the steel substrate b ≥0.

2.

7. The method for manufacturing high peak value thick zinc-coated electrogalvanized steel sheet according to any one of claims 1-6, characterized in that, Including the following steps: (1) The surface of the roughened leveling mill roll is subjected to de-peaking treatment so that the roll profile skewness parameter Rsk≤-0.5; (2) The steel substrate is leveled by rolling with rolls: the leveling elongation is controlled to be ≥0.6%; (3) The flattened steel substrate is electro-galvanized to obtain a high peak value thick zinc layer electro-galvanized steel sheet.

8. The manufacturing method as described in claim 7, characterized in that, In step (1), the surface roughness of the roll after the de-peaking treatment is 2.0-4.0 μm.

9. The manufacturing method as described in claim 7, characterized in that, In step (1), the number of surface peaks of the roll after the de-peaking treatment is ≥95 / cm.

10. The manufacturing method as described in claim 7, characterized in that, In step (3), the temperature of the electroplating solution is controlled at 48-53℃.

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