Galvanizing process of electrogalvanized steel sheet with high surface quality

Abstract

The invention relates to a galvanizing process for an electrogalvanized steel plate with high surface quality, and the steps are as follows: degreasing a base steel plate, and then washing it with desalted water to obtain a degreased steel plate; pickling the degreased steel plate, and then washing it with desalted water to obtain a pickled steel plate; electroplating the pickled steel plate with iron, and the plating amount is 250-12000C / m 2 , and then washed with desalted water to obtain an electroplated iron-treated steel plate; electrogalvanizing the electroplated iron-treated steel plate and forming a 10-60g / m 2 The zinc adhesion is reduced by 0.1%, and then washed with desalted water to obtain a steel plate treated with electrogalvanizing. The present invention can make the crystal nucleation, growth rate and coating crystal orientation of zinc electrodeposited on the surface of the steel plate uniform during electrogalvanizing, and can effectively inhibit the transfer of filamentary streak defects on the surface of the base steel plate to the surface of the galvanized layer.

Description

Technical Field

[0001] The invention relates to a galvanizing process for an electro-galvanized steel plate, in particular to a galvanizing process for an electro-galvanized steel plate with high surface quality. Background Art

[0002] Electrogalvanized steel sheets have excellent processing performance and corrosion resistance, and have been widely used in automobiles, home appliances, offices and other application fields. These fields usually have very high requirements for the surface quality of materials used, and any surface defects will cause the appearance of degraded products. Electrogalvanized steel sheets, especially fingerprint-resistant electrogalvanized steel sheets, often have more harmful surface defects such as filamentous streaks on their surfaces. Such surface defects will have a serious impact on the quality of the finished product and need to be strictly controlled and avoided.

[0003] The surface quality of electrogalvanized steel sheets is affected not only by the galvanizing process, but also by the surface quality of the base steel sheet (e.g., cold-rolled steel sheet). Certain defects on the base steel sheet surface will be transferred to the surface of the electrogalvanized layer. For example, when there are filamentary streak defects on the surface of the cold-rolled steel sheet, after electrogalvanizing, especially after being treated with a fingerprint-resistant film, the filamentary streak defects on the surface of the cold-rolled steel sheet will be transferred to the surface of the galvanized layer, and finally the filamentary streak defects will be very obvious on the surface of the galvanized layer of the electrogalvanized steel sheet. The mechanism of this type of defect is as follows: the iron oxide scale is pressed into the hot rolling process, resulting in iron oxide scale defects on the surface of the hot-rolled steel plate. After the pickling and cold rolling processes, the iron oxide scale defects still exist on the surface of the cold-rolled steel plate, and with the cold rolling, they become long strip-shaped filamentary streak defects, which makes the electrochemical properties of the surface of the cold-rolled steel plate uneven, that is, the electrochemical properties at the filamentary streak defects are different from those at other parts, resulting in differences in the crystallization nucleation, growth rate, and crystal orientation of zinc during electrogalvanizing. As a result, there are differences in the microscopic morphology of the galvanized layer surface, which is manifested macroscopically as color difference, that is, the observed filamentary streak defects.

[0004] In order to obtain high surface quality electrogalvanized steel sheets, the existing solution is generally to improve the surface quality of electrogalvanized steel sheets by adding additives to the galvanizing solution. Chinese Patent 90103672.2 discloses a synthesis and application process of a galvanizing additive, which can be applied to an alkaline zincate zinc plating solution to obtain a flat, bright, and well-bonded zinc coating. However, the alkaline zincate zinc plating process using the additive not only has low electroplating efficiency, is not suitable for high-speed galvanizing of steel sheets, but also cannot effectively inhibit the transfer of filamentary streak defects on the surface of the base steel sheet to the coating surface. In addition, Chinese Patent 95109682.6 discloses an electrogalvanized steel sheet and a method for preparing the same. The method comprises adding an appropriate amount of tin sulfate to a pickling solution, and then electrogalvanizing the steel sheet after pickling to form a tin layer, thereby improving the surface quality of the galvanized layer, especially improving the whiteness of the galvanized layer. However, experiments have shown that if defects such as filamentary streaks exist on the surface of the base steel sheet, the filamentary streak defects can still be seen on the surface of the base steel sheet after the base steel sheet is electrogalvanized according to the method. Therefore, the method has limited effect on inhibiting the filamentary streak defects on the surface of the steel sheet from being transmitted to the surface of the galvanized layer. Summary of the invention

[0005] The object of the present invention is to provide a galvanizing process for high surface quality electrogalvanized steel sheets, in which the base steel sheet is pre-galvanized with iron before electrogalvanizing, and the electrochemical properties of the steel sheet surface are homogenized after the iron electroplating treatment, so that the crystal nucleation, growth rate and crystal orientation of the zinc electrodeposited on the steel sheet surface during electrogalvanizing are homogenized, and the filamentous streak defects existing on the surface of the base steel sheet are effectively suppressed from being transmitted to the surface of the galvanized layer.

[0006] The present invention is achieved in that:

[0007] A galvanizing process for an electrogalvanized steel sheet with high surface quality, comprising the following steps:

[0008] Step 1, degreasing the base steel plate, and then washing it with desalted water to obtain a degreased steel plate;

[0009] Step 2, pickling the degreased steel plate, and then washing it with desalted water to obtain a pickled steel plate;

[0010] Step 3: Electroplating the pickled steel plate with iron, and the plating amount is 250-12000C / m 2 , and then washed with desalted water to obtain a steel plate treated with electroplating iron;

[0011] Step 4: Electroplated iron treated steel plate

[0012] Electrogalvanizing is performed to form a 10-60g / m 2 The zinc adhesion is then removed and washed with desalted water to obtain an electro-galvanized steel sheet.

[0013] In the step 1, the degreasing treatment is one or a combination of chemical degreasing and electrolytic degreasing.

[0014] In the step 2, the pickling treatment uses a sulfuric acid aqueous solution.

[0015] In step 3, the iron plating solution used for iron electroplating contains FeSO with a concentration of 100 to 300 g / L. 4 7H 2 O and HBF with a concentration of 1 to 50 g / L 4 The pH value of the iron plating solution is 1.0-3.0, the temperature of the iron plating solution is 10-50°C, and the current density of the electroplating iron is 500-10000A / m 2 , the plating time is 0.1~5s.

[0016] In step 4, the zinc plating solution used for electrogalvanizing contains ZnSO with a concentration of 450-550 g / L. 4 7H 2 O and H at a concentration of 5 to 15 g / L 2 SO 4 The temperature of the zinc plating solution is 45-55°C, and the current density of the electrogalvanizing is 3000-15000A / m 2 The flow rate of the galvanizing solution relative to the steel plate is 0.5 to 4 m / s.

[0017] The galvanizing process of the electrogalvanized steel sheet with high surface quality of the present invention, firstly, according to the mechanism of the generation of surface defects of the base steel sheet, a pre-electrogalvanizing iron treatment is added before the electrogalvanizing treatment, and the electrochemical characteristics of the steel sheet surface after the electrogalvanizing iron treatment are uniformized, so that the crystal nucleation, growth rate and crystal orientation of the coating layer of zinc electrodeposited on the steel sheet surface during the electrogalvanizing treatment are also uniformized, thereby effectively inhibiting the transmission of the filamentary stripe defects existing on the surface of the original base steel sheet to the surface of the galvanized layer, ensuring the acquisition of the electrogalvanized steel sheet with high surface quality. Secondly, the plating amount of the pre-electrogalvanizing iron is controlled within a suitable amount range, which can not only ensure that the iron coating layer can meet the requirements of the uniformization of the electrochemical characteristics of the steel sheet surface, but also reasonably control the manufacturing cost.

[0018] Compared with the prior art, the present invention has the following beneficial effects: the electrochemical characteristics of the steel plate surface are homogenized by pre-electroplating iron, thereby achieving homogenization of the crystal nucleation, growth rate and crystal orientation of the coating during electrogalvanizing of zinc on the steel plate surface, and can effectively inhibit the surface defects of the base steel plate from being transmitted to the surface of the zinc-plated layer, thereby ensuring high surface quality of the electrogalvanized steel plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic flow chart of the galvanizing process of the electro-galvanized steel sheet with high surface quality according to the present invention;

[0020] Figure 2 The surface image of the zinc coating layer in Example 1 of the present invention;

[0021] Figure 3 This is the surface image of the zinc coating of Comparative Example 12 of the present invention;

[0022] Figure 4 This is a scanning electron microscope image of the zinc coating surface of Example 1 of the present invention;

[0023] Figure 5 This is a scanning electron microscope image of the zinc coating surface of Comparative Example 12 of the present invention. DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with specific embodiments.

[0025] See also Figure 1 A galvanizing process for high surface quality electrogalvanized steel sheet comprises the following steps:

[0026] Step 1: Degrease the base steel plate and then wash it with desalted water to obtain a degreased steel plate. The purpose of this step is to remove grease and other pollutants (such as dust particles) on the surface of the base steel plate. The degreasing agent is an alkaline degreasing agent aqueous solution. The degreasing treatment is one or a combination of chemical degreasing and electrolytic degreasing.

[0027] Step 2: pickling the degreased steel plate, and then washing it with desalted water to obtain a pickled steel plate. The purpose of this step is to remove the oxide film on the surface of the steel plate and activate the surface of the steel plate. Preferably, the pickling treatment uses a sulfuric acid aqueous solution, and the H 2 SO 4 The concentration is 2 to 200 g / L, the solution temperature is 5 to 50°C, and the processing time is 0.5 to 10 seconds.

[0028] Step 3: Electroplating the pickled steel plate with iron, and the plating amount is 250-12000C / m 2 , and then washed with desalted water to obtain a steel plate treated with electroplating iron.

[0029] The purpose of this step is to treat the surface of the steel plate to make its electrochemical properties uniform, so as to make the crystal nucleation, growth rate and coating crystal orientation of zinc electrodeposited on the steel plate surface uniform during the subsequent electrogalvanizing step, thereby inhibiting the filamentary streak defects existing on the surface of the base steel plate from being transferred to the surface of the galvanized layer.

[0030] Specifically, the iron plating solution used in the electroplating process contains FeSO at a concentration of 100 to 300 g / L. 4 7H 2 O and HBF with a concentration of 1 to 50 g / L 4The pH value of the iron plating solution is 1.0-3.0, the temperature of the iron plating solution is 10-50°C, and the current density of the electroplating iron is 500-10000A / m 2 The plating time is 0.1 to 5 seconds.

[0031] In this step, the steel plate is pre-galvanized before being treated with galvanized steel. Iron is electroplated instead of other substances because the iron formed by electroplating is the same substance as the iron of the base steel plate, which can more effectively achieve the uniformity of the electrochemical properties of the surface of the base steel plate. Compared with the existing technology, for example, a tin layer is pre-formed on the surface of the base steel plate. Although it can improve the surface quality of the steel plate to a certain extent, the tin layer and the iron of the base steel plate are different substances and have great differences in electrochemical properties. Therefore, it is difficult to achieve the effect of uniformity of the electrochemical properties of the base steel plate surface by pre-forming a small amount of tin layer on the surface of the base steel plate, so it is impossible to effectively inhibit the transmission of filamentary streak defects on the surface of the steel plate to the surface of the galvanized layer.

[0032] In addition, the amount of electroplated iron should be controlled within a reasonable range. If the amount is too little, the surface treatment effect of the steel plate will not be achieved. If the amount is too much, it will not affect the treatment effect, but it will increase the manufacturing cost of the electrogalvanized steel plate. The amount of electroplated iron is 250-12000C / m 2 In order to obtain better treatment effect and lower manufacturing cost, the optimal range of plating amount is 1000~6000C / m 2 The optimal range of plating amount is 2000~6000C / m 2 .

[0033] Step 4: Electrogalvanize the steel sheet treated with electroplating iron, and form a 10-60g / m 2 The zinc adhesion is then washed with desalted water to obtain the electro-galvanized steel sheet. Generally speaking, the zinc adhesion requirement for electro-galvanized steel sheets used in the home appliance industry is 10 to 30 g / m 2 For electro-galvanized steel sheets used in the automotive industry, the zinc adhesion requirement is 50-60 g / m 2 .

[0034] Specifically, the zinc plating solution used in the electrogalvanizing process contains 450-550 g / L of ZnSO4·7H 2 O and H at a concentration of 5 to 15 g / L 2 SO 4 The temperature of the zinc plating solution is 45-55°C. The current density of the electrogalvanizing is 3000-15000A / m 2 The flow rate of the galvanizing solution relative to the steel plate is 0.5 to 4 m / s.

[0035] According to the galvanizing process, the cold-rolled steel sheets after annealing were selected as the base steel sheet samples of Examples 1 to 11 and Comparative Examples 12 to 14, wherein the process steps of Comparative Example 12 do not include step 3, i.e., electroplating iron treatment. Specifically, in step 2, the H 2 SO 4 The concentration is 50g / L, the solution temperature is 30℃, and the treatment time is 2s.

[0036] Table 1 lists the component concentrations, pH values ​​and temperatures of the iron plating solutions of Examples 1 to 11 of the present invention and the corresponding electroplating iron process parameters, and lists the corresponding specific parameters of Comparative Examples 12 to 14. Table 2 lists the component concentrations, temperatures and corresponding electroplating zinc process parameters of the zinc plating solutions of Examples 1 to 11 of the present invention and lists the corresponding specific parameters of Comparative Examples 12 to 14.

[0037] Table 1

[0038]

[0039] It can be seen from Table 1 that Examples 1 to 11 increase the iron electroplating process steps and ensure that the plating amount is 250 to 12000 C / m 2 In the numerical range of , a better treatment effect can be obtained, among which the treatment effects of Examples 1 to 5 are excellent, but Examples 3 and 5 have higher manufacturing costs than other examples due to the higher plating amount. Therefore, the optimal numerical range of the plating amount according to the electricity meter is 2000-6000C / m 2 .

[0040] Table 2

[0041]

[0042] Combining Table 1 and Table 2, it can be concluded that although Comparative Examples 12 to 14 also used the same composition of the galvanizing solution and similar process parameters, since Comparative Example 12 did not use the electroplating iron process step and the plating power of Comparative Examples 13 and 14 was not controlled within a reasonable amount range, Comparative Examples 12 to 14 did not achieve the effect of suppressing the transmission of the filamentary streak defects on the surface of the steel plate to the surface of the galvanized layer.

[0043] See also Figure 2 and Figure 3 The surface appearance of the zinc coating of Example 1 is uniform, and no filamentous streak defects are visible, while the surface of the zinc coating of Comparative Example 12 has obvious filamentous streak defects. Figure 4 and Figure 5The parameters for taking the scanning electron microscope images are acceleration voltage EHT=20.00kV, working distance WD=10.5m, magnification Mag=1.00KX, and SE1 detector is used. The scanning electron microscope images of the surface micromorphology of the galvanized layer of Example 1 and Comparative Example 12 respectively show that the surface crystallization of the galvanized layer of Example 1 is uniform, while the surface of the galvanized layer of Comparative Example 12 has strip-shaped uneven crystallization. Therefore, after the galvanizing process, the surface defects of the base steel plate can be effectively suppressed from being transmitted to the surface of the galvanized layer.

[0044] The galvanizing process of the high surface quality electrogalvanized steel sheet of the present invention performs pre-electrogalvanizing iron treatment on the steel sheet to homogenize the electrochemical characteristics of its surface, thereby improving the electrogalvanizing electrodeposition effect and effectively inhibiting the surface defects of the base steel sheet from being transmitted to the surface of the galvanized layer, thereby ensuring that the electrogalvanized steel sheet with high surface quality is obtained.

[0045] The above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A galvanizing process for electrogalvanized steel sheet with high surface quality, characterized in that: The steps include: Step 1, degreasing the base steel plate, and then washing it with desalted water to obtain a degreased steel plate; Step 2, pickling the degreased steel plate, and then washing it with desalted water to obtain a pickled steel plate; Step 3: Electroplating the pickled steel plate with iron, and the amount of plating is 1000-6000C / m 2 , and then washed with desalted water to obtain a steel plate treated with electroplating iron; In the step 3, the iron plating solution used for the iron plating contains FeSO4·7H2O with a concentration of 100-300 g / L and HBF4 with a concentration of 1-50 g / L, the pH value of the iron plating solution is 1.0-3.0, the temperature of the iron plating solution is 10-50°C, and the current density of the iron plating is 500-10000 A / m 2 , plating time is 0.1~5s; Step 4: Electrogalvanize the steel sheet treated with electroplating iron and form a 10-60g / m 2 The zinc adhesion is then washed with desalted water to obtain a steel plate treated with electrogalvanizing; In the step 4, the zinc plating solution used for electrogalvanizing contains ZnSO4·7H2O with a concentration of 450-550 g / L and H2SO4 with a concentration of 5-15 g / L, the temperature of the zinc plating solution is 45-55°C, and the current density of the electrogalvanizing is 3000-15000 A / m 2 The flow rate of the galvanizing solution relative to the steel plate is 0.5 to 4 m / s.

2. The galvanizing process for high surface quality electrogalvanized steel sheet according to claim 1, characterized in that: In the step 1, the degreasing treatment is one or a combination of chemical degreasing and electrolytic degreasing.

3. The galvanizing process for high surface quality electrogalvanized steel sheet according to claim 1, characterized in that: In the step 2, the pickling treatment uses a sulfuric acid aqueous solution.

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