Method for reducing internal suspended sludge in pure zinc plating solution

Abstract

The application provides a method for reducing internal suspended slags of pure zinc plating solution, and belongs to the field of steel rolling. The method comprises the following steps: cold rolling a hot-rolled plate and controlling the surface roughness of the hot-rolled plate to obtain a steel base plate with a set surface roughness; plating nickel element to at least part of the surface of the steel base plate with the set surface roughness, and then annealing to obtain a pre-plated nickel plate; the thickness of the nickel layer of the pre-plated nickel plate is 300 mg / m 2 ~ 1000 mg / m 2 ; and the pre-plated nickel plate is hot-dip plated in a pure zinc plating solution with a set aluminum content to obtain a galvanized plate. By plating a nickel layer with a certain thickness on the surface of the strip steel, the nickel layer hinders the iron element from entering the zinc pot to a certain extent; the aluminum content in the zinc pot is controlled to avoid the high aluminum content from causing the solubility of the iron element in the zinc solution to decrease. The technical problem of the existing technology that there are many internal suspended slags in the pure zinc plating solution is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel rolling, in particular to a method for reducing internal suspended slag in pure zinc plating solution. BACKGROUND

[0002] In recent years, with the proposal of carbon emission and carbon peak policies, automobile production lines often use a free intermediate coating process instead of the traditional coating process. The free intermediate coating process puts higher requirements on the surface quality of automobile sheets, and one key defect affecting the coating quality is zinc slag defects on the surface of galvanized sheets. The zinc slag defects on the surface of galvanized sheets are evolved from the suspended slag defects inside the zinc pot. The main component of the suspended slag defects is Fe2Al5Zn X , which is caused by the iron element in the strip steel exceeding the saturation solubility and co-precipitating with the aluminum element inside the zinc pot.

[0003] However, the suspended slag is difficult to remove due to its similar density to the zinc solution and is easy to adhere to the coating to form zinc slag defects. Therefore, it is urgent to develop a method for reducing the internal suspended slag in pure zinc plating solution, so as to reduce the formation of zinc slag defects in the coating. SUMMARY

[0004] The present application provides a method for reducing internal suspended slag in pure zinc plating solution to solve the technical problem that there are many suspended slags in the pure zinc plating solution in the prior art, thereby causing many zinc slag defects in the coating.

[0005] The present application provides a method for reducing internal suspended slag in pure zinc plating solution, which comprises:

[0006] cold rolling the hot-rolled sheet and controlling the surface roughness of the hot-rolled sheet to obtain a steel substrate with a set surface roughness;

[0007] coating nickel element to at least part of the surface of the steel substrate with a set surface roughness, and then annealing to obtain a pre-plated nickel sheet; the thickness of the nickel layer of the pre-plated nickel sheet is 300 mg / m 2 ~ 1000 mg / m 2 ;

[0008] hot-dip plating the pre-plated nickel sheet in a pure zinc plating solution with a set aluminum content to obtain a galvanized sheet.

[0009] Optionally, the set surface roughness is 0.4 um ~ 0.8 um.

[0010] Optionally, the set surface roughness is 0.5 um ~ 0.7 um.

[0011] Optionally, before the cold rolling of the hot-rolled sheet to obtain a steel substrate and the control of the surface roughness of the steel substrate to a set surface roughness, the method further comprises:

[0012] The cast blank is hot-rolled and coiled, and the temperature of the coiling is controlled to obtain a hot-rolled plate.

[0013] Optionally, the temperature of the coiling and the type of the steel base plate satisfy the following relationship:

[0014] If the steel base plate is IF steel or BH steel, the temperature of the coiling is ≤620℃;

[0015] If the steel base plate is high-strength steel outer plate, the temperature of the coiling is ≤550℃.

[0016] Optionally, the thickness of the nickel layer of the pre-plated nickel plate is 600mg / m 2 ~900mg / m 2 .

[0017] Optionally, in the annealing process, the dew point of each section of the furnace zone inside the annealing furnace is ≤-45℃.

[0018] Optionally, the set aluminum content is 0.19%~0.21% by mass fraction.

[0019] Optionally, the temperature of the hot-dip plating is 450℃~460℃.

[0020] The above technical solution provided by the embodiments of the present application has the following advantages compared with the prior art:

[0021] The present application provides a method for reducing the suspended sludge in pure zinc plating solution, by controlling the roughness of the strip surface, improving the surface cleanliness of the strip in the cleaning section, and reducing the residual oil and residual iron content on the surface of the strip; by plating a certain thickness of nickel layer on the surface of the strip, the nickel layer formed to some extent hinders the iron element from entering the zinc pot; the aluminum content in the zinc pot is controlled to avoid the excessive aluminum content causing the solubility of the iron element in the zinc solution to decrease. The technical problem of the prior art that there are many suspended slags in the pure zinc plating solution, thereby causing many zinc slag defects in the plating layer is solved. BRIEF DESCRIPTION OF DRAWINGS

[0022] The drawings incorporated into the specification and forming a part thereof, illustrate embodiments consistent with the present application and, together with the specification, serve to explain the principles of the application.

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows, and obviously, other drawings can also be obtained by those skilled in the art without creative labor under the premise of not paying the creative labor.

[0024] Figure 1A flowchart of a method for reducing internal suspended sludge in a pure zinc plating solution provided by an embodiment of the present application is shown in FIG. 1.

[0025] Figure 2 A particle distribution diagram of internal suspended sludge in a pure zinc plating solution provided by Example 1 of the present application is shown in FIG. 2.

[0026] Figure 3 A particle distribution diagram of internal suspended sludge in a pure zinc plating solution provided by Comparative Example 1 of the present application is shown in FIG. 3. DETAILED DESCRIPTION

[0027] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0028] Various embodiments of the present application can exist in the form of a range; it should be understood that the description in the form of a range is merely for the convenience and brevity, and should not be understood as a hard limitation on the scope of the present application; therefore, it should be considered that the described range has specifically disclosed all possible sub-ranges and single values in the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers in the described range, such as 1, 2, 3, 4, 5 and 6, which is applicable to any range. In addition, whenever a numerical range is indicated in the present application, it refers to any cited number (fraction or integer) in the indicated range.

[0029] In addition, in the description of the present application, the terms "comprise", "contain" and the like are intended to mean "including but not limited to". In this document, relational terms such as "first" and "second", and the like can be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. In this document, "and / or" describes the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B can represent: A exists alone, A and B exist together, and B exists alone. Where A and B can be singular or plural. In this document, "at least one" means one or more, and "multiple" means two or more. "At least one", "at least one of the following" or the like means any combination of these items, including single item or combination of multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can mean a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

[0030] Unless otherwise specifically stated, the various raw materials, reagents, instruments and equipment used in the present application can be purchased on the market or can be prepared by existing methods.

[0031] The present application provides a method for reducing the internal suspended slag of pure zinc plating solution, the method comprising:

[0032] S1, cold rolling the hot-rolled plate and controlling the surface roughness of the hot-rolled plate to obtain a steel substrate with a set surface roughness;

[0033] In some embodiments, the set surface roughness is 0.4um-0.8um.

[0034] The surface roughness of the steel substrate is limited to the set surface roughness, and the set surface roughness is limited to 0.4um-0.8um, in order to control the small roughness of the surface of the cold-rolled steel plate, reduce the amount of residual oil and iron on the surface of the steel strip, and significantly improve the cleaning effect, so that the residual iron elements on the surface of the steel strip do not enter the zinc pot. For example, the set surface roughness can be 0.4um, 0.5um, 0.6um, 0.7um, 0.8um, etc.

[0035] In some embodiments, the set surface roughness is 0.5um-0.7um.

[0036] In some embodiments, before the hot-rolled plate is cold-rolled to obtain a steel substrate and the surface roughness of the steel substrate is controlled to be a set surface roughness, the method further comprises:

[0037] The cast slab is hot-rolled and coiled, and the coiling temperature is controlled to obtain a hot-rolled plate.

[0038] In some embodiments, the coiling temperature and the type of steel substrate satisfy the following relationship:

[0039] If the steel substrate is IF steel or BH steel, the coiling temperature is ≤620℃;

[0040] If the steel substrate is high-strength steel outer plate, the coiling temperature is ≤550℃.

[0041] The relationship between the coiling temperature and the type of steel substrate is limited to the above relationship, in order to: high-strength steel alloy element content is high, and intergranular oxidation is prone to occur, so the coiling temperature needs to be reduced. Soft steel needs to be coiled at high temperature in order to ensure low strength.

[0042] The coiling temperature of IF steel or BH steel is limited to ≤620℃, and the coiling temperature of high-strength steel outer plate is limited to ≤550℃, in order to: avoid the increase of the specific surface area of the strip surface after cold rolling caused by intergranular oxidation during hot rolling, which increases the contact area between the strip and the zinc liquid, thereby increasing the dissolution of iron elements in the zinc pot. Exemplarily, the coiling temperature of the IF steel or BH steel can be 500℃, 520℃, 550℃, 580℃, 600℃, 620℃, etc., and the coiling temperature of the high-strength steel outer plate can be 450℃, 480℃, 500℃, 520℃, 550℃, etc.

[0043] S2, plating nickel element to at least part of the surface of the steel substrate with a set surface roughness, and then annealing to obtain a pre-plated nickel plate; the thickness of the nickel layer of the pre-plated nickel plate is 300mg / m 2 ~1000mg / m 2 ;

[0044] The nickel layer of the pre-plated nickel plate is limited to 300mg / m 2 ~1000mg / m 2 , in order to: the formed nickel layer can significantly block the diffusion of iron elements into the zinc pot. Exemplarily, the thickness of the nickel layer of the pre-plated nickel plate is 300mg / m 2 , 400mg / m 2 , 500mg / m 2 , 600mg / m 2 , 800mg / m 2 , 1000mg / m 2 , etc.

[0045] In some embodiments, the thickness of the nickel layer of the pre-plated nickel plate is 600mg / m 2 ~900mg / m2 .

[0046] In some embodiments, during the annealing, the dew point of each section of the furnace zone inside the annealing furnace is ≤-45℃.

[0047] The dew point of each section of the furnace zone inside the annealing furnace is ≤-45℃, so that low dew point control can significantly reduce the oxidation of the surface of the strip steel, avoiding the formation of sponge iron or ferrous oxide by oxidation-reduction. For example, the dew point of each section of the furnace zone inside the annealing furnace can be -20℃, -25℃, -30℃, -35℃, -40℃, -45℃, etc.

[0048] S3, hot-dip plating the pre-plated nickel plate in a pure zinc plating solution with a set aluminum content to obtain a galvanized plate.

[0049] In some embodiments, the set aluminum content is 0.19%-0.21% by mass fraction.

[0050] The pure zinc plating solution with a set aluminum content is used for hot-dip plating, and the mass fraction of the set aluminum is 0.19%-0.21%, so that the solubility of iron elements in the zinc solution is reduced due to the excessive aluminum content. For example, the mass fraction of the set aluminum can be 0.19%, 0.195%, 0.20%, 0.205%, 0.21%, etc.

[0051] In some embodiments, the temperature of the hot-dip plating is 450℃-460℃.

[0052] The temperature of the hot-dip plating is 450℃-460℃, so that the temperature of the strip steel entering the zinc pot is between 450℃ and 460℃, reducing the diffusion of iron atoms on the surface of the strip steel into the zinc pot. For example, the temperature of the hot-dip plating can be 450℃, 452℃, 454℃, 456℃, 458℃, 460℃, etc.

[0053] In some embodiments, a pre-melted pot is used to melt zinc ingots, so as to avoid the precipitation of suspended slag caused by temperature fluctuations.

[0054] The present application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present application and not used to limit the scope of the present application. The experimental methods in the following examples are not specified, and are generally determined according to the industry standards. If there is no corresponding industry standard, the general international standards, conventional conditions, or the conditions recommended by the manufacturer are used.

[0055] The present application provides a method for reducing the suspended slag in a pure zinc plating solution, comprising the following steps:

[0056] S11, hot-rolling and coiling the cast slab and controlling the temperature of the coiling to obtain a hot-rolled plate;

[0057] S21, cold-rolling the hot-rolled plate and controlling the surface roughness of the hot-rolled plate to obtain a steel substrate with a set surface roughness;

[0058] S31, plating nickel element to at least part of the surface of the steel substrate with a set surface roughness, and then annealing to obtain a pre-plated nickel plate; the thickness of the nickel layer of the pre-plated nickel plate is 300 mg / m 2 ~1000 mg / m 2 ;

[0059] S41, hot-dipping the pre-plated nickel plate in a pure zinc plating solution with a set aluminum content to obtain a zinc-plated plate, a method for reducing the suspended sludge in the pure zinc plating solution, and the process parameters of the method for reducing the suspended sludge in the pure zinc plating solution are shown in Table 1.

[0060] Table 1 Process parameters of the method for reducing the suspended sludge in the pure zinc plating solution

[0061]

[0062] The number of suspended sludge on the surface of the zinc liquid in the furnace nose of Examples 1-4 and Comparative Examples 1-6 was tested, and the results are shown in Table 2. The counting range is 400x300um under a scanning electron microscope, the size of the suspended sludge is more than 5um, and the number of suspended sludge is the average value.

[0063] Table 2 Number of suspended sludge on the surface of the zinc liquid in the furnace nose

[0064] Group Number of Suspended Slag, pieces Example 1 12 Example 2 22 Example 3 18 Example 4 21 Comparative Example 1 89 Comparative Example 2 95 Comparative Example 3 46 Comparative Example 4 52 Comparative Example 5 78 Comparative Example 6 66

[0065] As shown in Table 1 and Table 2, if the key control points proposed by the present application are not properly controlled, the number of suspended sludge in the zinc liquid will significantly increase.

[0066] Figure 2 The particle distribution diagram of the suspended sludge in the pure zinc plating solution provided for Example 1 of the present application.

[0067] As Figure 2 can be seen, by using the method proposed by the present application, the number of suspended sludge in the zinc industry can be controlled at a lower level.

[0068] Figure 3 The particle distribution diagram of the suspended sludge in the pure zinc plating solution provided for Comparative Example 1 of the present application.

[0069] As Figure 3 can be seen, if the key control points proposed by the present application are not properly controlled, the number of suspended sludge in the zinc liquid will significantly increase.

[0070] The foregoing detailed description of the application has been presented for purposes of illustration and description. Various modifications and changes can be made to these embodiments without departing from the spirit and scope of the application. It is intended that the scope of the application should not be limited by the particular representative embodiments described above.

Claims

1. A method of reducing internal suspended sludge in a pure zinc plating solution, characterized by, The method comprises: carrying out cold rolling on the hot-rolled plate and controlling surface roughness of the hot-rolled plate to obtain a steel base plate with a set surface roughness; The nickel element is plated to at least part of the surface of the steel substrate with a set surface roughness, and then annealed to obtain a pre-plated nickel plate; the thickness of the nickel layer of the pre-plated nickel plate is 300 mg / m 2 1000 mg / m 2 ; carrying out hot-dip plating on the pre-plated nickel plate in a pure zinc plating solution with a set aluminum content to obtain a galvanized plate; the set surface roughness is 0.4um-0.6um, and the set aluminum content is 0.19%-0.21%.

2. The method of claim 1, wherein, Before the cold rolling on the hot-rolled plate to obtain the steel base plate and the controlling of the surface roughness of the steel base plate to the set surface roughness, the method further comprises: carrying out hot rolling and coiling on a cast blank and controlling a coiling temperature to obtain the hot-rolled plate.

3. The method of claim 2, wherein, The coiling temperature and the type of the steel base plate satisfy the following relationship: if the steel base plate is IF steel or BH steel, the coiling temperature is ≤620℃; if the steel base plate is high-strength steel outer plate, the coiling temperature is ≤550℃.

4. The method of claim 1, wherein, The nickel layer thickness of the pre-plated nickel plate is 600 mg / m 2 900 mg / m 2 .

5. The method of claim 1, wherein, During the annealing, the dew point of each section of the furnace zone inside the annealing furnace is ≤-45℃.

6. The method of claim 1, wherein, The hot-dip plating temperature is 450℃-460℃.

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