High-surface cold-rolling hot-dip aluminum-zinc plating control method

Abstract

The invention relates to a high-surface cold-rolling hot-dip aluminum-zinc plating control method. The method comprises the following steps of 1, a degreasing process, 2, an annealing process, 3, a zinc pot process, 4, a cooling process after plating and 5, a leveling process. According to the scheme, residual oil and oxide on the surface of the steel plate are completely removed through degreasing, annealing and zinc pot processes, meanwhile, the content of generated slag elements is reduced, and zinc slag is effectively inhibited from being generated. The temperature field is accurately controlled by adjusting the zinc pot process, and zinc ash and zinc slag are prevented from being enriched. Large and deep pores of a plating layer are eliminated through an ultra-fast cooling process at the front section of cooling after plating. And through the post-plating large leveling process, the surface kurtosis / sharpness is effectively improved, and finally, the surface leveling property of the steel plate is greatly improved.

Description

TECHNICAL FIELD

[0001] The application relates to a control method, in particular to a high-surface cold-rolled hot-dip aluminum-zinc control method, and belongs to the technical field of alloy production control. BACKGROUND

[0002] The aluminum-zinc plated steel plate for electric cabinet purposes is often sprayed on the surface before use to coat an organic coating layer to improve the corrosion resistance of the product. During the coating process, a type of coating defect, i.e., a pimple, often occurs. This defect is mainly caused by poor leveling of the organic coating layer on the surface of the steel plate and is closely related to the state of the surface of the steel plate.

[0003] The main reasons for poor leveling include two aspects. On the one hand, zinc ash and zinc residue defects in the zinc pot during hot-dip plating adhere to the surface of the plated layer, resulting in poor leveling of the coating at this position and further forming a pimple. On the other hand, during the solidification process of the plated layer after being taken out of the zinc pot, the solidification time of the aluminum-rich phase and the zinc-rich phase is too long, forming a large pore in the plated layer, causing air to be trapped in the pore, and the air cannot be effectively discharged during the subsequent coating, baking and solidification of the coating, thereby lifting the coating above to form a pimple.

[0004] Therefore, improving the surface leveling of the aluminum-silicon-zinc plated product is a technical problem in the development of cold-rolled hot-dip aluminum-zinc products.

[0005] After preliminary search, the related schemes in the prior art are as follows: A method for eliminating zinc residue defects on the surface of a zinc-aluminum-magnesium plated product is disclosed in Chinese Patent Publication No. CN111235509A. On the one hand, the patent controls the zinc residue by controlling the humidity of the furnace nose, and on the other hand, the patent controls the zinc residue by adjusting the cooling air volume after plating. The strip steel temperature entering the zinc pot is 453-465 DEG C, and the control fluctuation range is large. A large temperature fluctuation range will lead to an increase in the amount of zinc ash and zinc residue. Meanwhile, the patent uses four cooling fans for cooling. The first cooling fan power is controlled at 10%, the second cooling fan power is controlled at 30%, and the third and fourth cooling fan powers are controlled at 80% respectively. This cooling method is too slow at the initial stage, which can easily cause large shrinkage holes in the plated layer, thereby causing poor surface quality.

[0006] Chinese Patent Publication No. CN114318201A discloses a method for controlling zinc residue in the molten pool of an aluminum-zinc pot in a continuous hot-dip aluminum-zinc production line. The Ti element content in the zinc ingot is 0.001-0.020%, which is too high and can easily lead to an increase in zinc residue precipitation during production. Meanwhile, the method does not control the rare earth elements, thereby further increasing the risk of zinc residue precipitation. The zinc pot temperature fluctuation range in the method is 590-610 DEG C. Such a large temperature fluctuation will cause a large amount of zinc residue to be produced, which can cause great damage to the surface quality of the produced steel plate. Therefore, there is an urgent need for a new scheme to solve this technical problem. SUMMARY

[0007] The present application is just for the technical problems existing in the prior art, provide a kind of high surface cold rolling hot-dip aluminum zinc control method, this scheme is designed to product overall, including steel base plate, coating, post-processing film, overall improve the corrosion resistance of product.

[0008] In order to achieve the above object, the technical scheme of the present application is as follows, a kind of high surface cold rolling hot-dip aluminum zinc control method, the method comprises the following steps:

[0009] Step 1: degreasing process,

[0010] Step 2: annealing process,

[0011] Step 3: zinc pot process,

[0012] Step 4: post-coating cooling process,

[0013] Step 5: leveling process.

[0014] Among them, step 1: degreasing process, as follows: degreasing temperature 80~85 ℃, NaOH concentration in degreasing agent 3~5%. Because paint is difficult to flow in the zinc residue defect place on the surface of coating, therefore, the more zinc residue defects in coating, the more easily form pitting defects. The less residual oil and carbon on the surface of steel plate, the cleaner the surface of steel plate, the less likely to produce zinc residue defects, reasonable degreasing process can effectively eliminate the residual oil and carbon on the surface of steel plate. When degreasing temperature is lower than 80 ℃, NaOH concentration in degreasing agent is lower than 3%, degreasing efficiency is insufficient, residual oil and carbon on the surface of steel plate cannot be completely removed; when degreasing temperature is higher than 85 ℃, NaOH concentration in degreasing agent is higher than 5%, cause energy and raw material cost increase, at the same time, degreasing efficiency does not increase significantly. Therefore, process is preferably degreasing temperature 80~85 ℃, NaOH concentration in degreasing agent 3~5%

[0015] Step 2: annealing process, as follows, the annealing furnace is a horizontal annealing furnace, the dew point of the soaking section: -35 to -50℃, H2 content ≥ 28%, the furnace temperature of the soaking section ≥ 1000℃. Since the coating is difficult to flow on the zinc residue defect on the surface of the coating, the more the zinc residue defects in the coating, the more likely to form the pitting defects. The less the oxide on the surface of the steel plate, the cleaner the surface of the steel plate, the less likely to produce zinc residue defects, and a reasonable annealing process can effectively eliminate the oxide on the surface of the steel plate. When the dew point of the soaking section is higher than -35℃, the H2 content is less than 28%, and the furnace temperature of the soaking section is lower than 1000℃, the reduction capacity of the annealing section is insufficient, and the oxide film on the surface of the strip steel is difficult to be completely reduced, causing the oxide to remain, the cleanliness of the surface of the steel plate to be poor, and the zinc residue defects to increase. When the dew point of the soaking section is lower than -50℃, it takes a long time to completely remove the water vapor in the furnace, resulting in an increase in cost. Therefore, the process is preferably the dew point of the soaking section: -35 to -50℃, H2 content ≥ 28%, the furnace temperature of the soaking section ≥ 1000℃

[0016] Step 3: Zinc pot process, as follows, is regulated. The strip steel temperature entering the zinc pot is 596-598℃, the zinc liquid temperature is 589-591℃, the furnace nose temperature is 586-588℃, the zinc liquid Ti element content in the zinc pot is ≤0.0005%, and the zinc liquid V+La+Ce element content is ≤0.002%. Since the coating is difficult to flow on the zinc ash and zinc slag defects on the surface of the coating, the more zinc ash and zinc slag defects in the coating, the more likely to form pitting defects. The zinc ash in the coating is related to the evaporation and condensation of the zinc liquid at the zinc liquid surface at the furnace nose entering the zinc pot position, and the zinc slag is related to the Fe element precipitation after the strip steel enters the pot. The greater the temperature fluctuation, the more frequent the evaporation and condensation of the zinc liquid, and the more zinc ash defects; the greater the temperature fluctuation, the more Fe element precipitation, and the more zinc slag defects. When the temperature fluctuation exceeds 3℃, both will cause a significant increase in zinc ash and zinc slag defects. Therefore, the process preferably controls the fluctuation range of the entering pot temperature, the zinc liquid temperature, and the furnace nose temperature within 3℃. Based on the zinc liquid temperature, when the strip steel entering temperature is 5-10℃ higher than the zinc liquid temperature, the energy input by the strip steel can be balanced with the energy dissipated by the zinc liquid, and when the furnace nose temperature is 10℃ lower than the entering pot temperature, the energy loss of the strip steel in the furnace nose section can be effectively compensated. In summary, the process preferably controls the strip steel entering temperature to be 596-598℃, the zinc liquid temperature to be 589-591℃, and the furnace nose temperature to be 586-588℃. In addition to the temperature fluctuation, the zinc slag is also related to the cleanliness of the zinc liquid. The cleaner the zinc liquid, the less likely to produce slag. When the Ti, V, La, and Ce impurity elements in the zinc liquid increase, the Al element in the zinc liquid and the Fe on the surface of the steel plate will react with the impurity elements to form slag. When the Ti element content is greater than 0.0005%, the Al3Ti slag content in the plating solution increases significantly, and when the V+La+Ce element content is greater than 0.002%, the Al3V, La, and Ce slag content in the plating solution increases significantly. Therefore, the process preferably controls the zinc liquid Ti element content to be ≤0.0005% and the zinc liquid V+La+Ce element content to be ≤0.002%.

[0017] Step 4: post-plating cooling process, specifically as follows, the post-plating cooling air box lower edge is 1.5-2 m from the zinc liquid surface, the post-plating cooling rate gradually decreases from the position where the strip steel enters the post-plating cooling air box to the position where the strip steel exits the cooling air box, the cooling rate at the position where the strip steel enters the cooling air box is 40-50℃, the cooling rate at the position where the strip steel exits the cooling air box is 10-15℃, and the strip steel temperature at the top roll position is ≤180℃. The more large and deep pores in the plated layer, the worse the leveling property of the paint on the plated layer surface due to the influence of the pores, the more difficult the paint flows into the pores, and the more difficult the air in the pores is discharged, and the more likely the surface pitting defects of the steel plate are caused. The large and deep pores in the plated layer are mainly related to the post-plating cooling rate, the lower the cooling rate and the longer the cooling time, the larger and deeper the pores formed. When the cooling rate at the position where the strip steel enters the cooling air box is less than 40℃, the cooling rate at the position where the strip steel exits the cooling air box is less than 10℃, and the top roll temperature is greater than 180℃, the skeleton segmentation molten pool of the Al-rich phase solidification is large, the volume shrinkage of the Zn-rich phase liquid in the skeleton is obvious when it solidifies, and the large and deep pores significantly increase. When the cooling rate at the position where the strip steel enters the cooling air box is greater than 50℃, the cooling rate at the position where the strip steel exits the cooling air box is greater than 15℃, and the on-site cooling air box power is too high, on the one hand, the energy consumption is large, leading to cost increase, and on the other hand, the high air volume can cause the strip steel to shake, causing safety hazards. Therefore, the process is preferably selected as follows: the cooling rate at the position where the strip steel enters the cooling air box is 40-50℃, the cooling rate at the position where the strip steel exits the cooling air box is 10-15℃, and the strip steel temperature at the top roll position is ≤180℃.

[0018] Step 5: smoothing process, specifically as follows, the smoothing process is controlled as follows: the smoothing elongation is 1.0-1.2%.

[0019] In the above scheme, the thickness of the aluminum-zinc-silicon plated steel plate is 1.0-2.0 mm, the plated layer weight is 60-80 g / m 2 , and the surface SKu value of the steel plate is 1.0-2.5. The SKu value reflects the sharpness of the steel plate surface, the larger the value, the more the number of sharp peaks and valleys on the steel plate surface, the worse the leveling property of the paint on the surface, and the more likely the surface pitting defects of the steel plate are caused. The SKu value can be achieved by controlling the smoothing elongation, the higher the smoothing elongation, the lower the SKu value. When the SKu is greater than 2.5, corresponding to the smoothing elongation being less than 1.0%, the number of sharp peaks and valleys significantly increases, and the paint on the surface is difficult to level; when the SKu is less than 1.0, corresponding to the smoothing elongation being greater than 1.2%, a certain work hardening is caused, leading to the material mechanical properties not meeting the requirements. Therefore, the process is preferably selected as follows: the smoothing elongation is 1.0-1.2%, and the surface SKu value of the steel plate is 1.0-2.5.

[0020] The inventors have found through long-term research that the zinc ash defects in the coating are mainly related to the evaporation and condensation of the zinc liquid at the position of the furnace nose entering the zinc pot, and the greater the temperature fluctuation, the more frequent the evaporation and condensation of the zinc liquid, and the more zinc ash defects.

[0021] The zinc slag defects in the coating are mainly related to three factors, namely, the cleanliness of the steel plate, the cleanliness of the zinc liquid, and the stability of the zinc pot temperature. The cleaner the steel plate, the fewer impurities such as oxides brought into the zinc pot, and the less likely the zinc slag defects are to occur; the cleaner the zinc liquid, the lower the Ti, V, La, and Ce content in the pot, and the less likely the point slag containing Ti, V, La, and Ce is to form; the more stable the zinc liquid temperature, the less fluctuation, and the less Fe element precipitates after the steel strip enters the pot, and the less likely the zinc slag is to form. When the strip entering temperature is 5-10 DEG C higher than the zinc liquid temperature, the energy input by the strip and the energy dissipated by the zinc liquid can be balanced. Therefore, by increasing the cleaning capacity of the degreasing process and the reduction capacity of the annealing process for the oxides on the surface of the strip, the inventors effectively ensure the cleanliness of the surface of the steel plate, effectively reduce the occurrence rate of the point slag by controlling the upper limit of the Ti, V, La, and Ce element content in the zinc liquid, and effectively reduce the occurrence of the zinc slag defects by ensuring the stability of the zinc liquid temperature and reducing the precipitation of Fe element.

[0022] The large and deep pores in the coating are mainly related to the cooling rate after plating, especially the cooling rate at the beginning of the strip leaving the zinc pot. The lower the cooling rate and the longer the cooling time, the larger the melt pool divided by the skeleton when the aluminum-rich phase solidifies, and the more obvious the volume shrinkage when the zinc-rich phase liquid in the skeleton solidifies, resulting in large and deep pores. Therefore, by increasing the cooling rate after plating, especially the cooling rate at the beginning of the strip leaving the zinc pot, the inventors effectively eliminate the large and deep pores generated during the solidification of the aluminum-zinc coating.

[0023] Using a larger flattening extension rate can effectively improve the Sku (acuteness / sharpness) value of the coating surface of the steel plate, make the height distribution of the steel plate surface tend to be flat, reduce the number of sharp peaks and valleys, enhance the leveling of the paint, and further reduce the pitting defects caused by poor leveling of the coating due to sharp peaks and valleys.

[0024] Compared with the prior art, the present application has the following advantages:

[0025] 1. The production method of the high-surface cold-rolled hot-dip aluminum-zinc-silicon steel plate provided by the present application effectively reduces the occurrence rate of zinc ash defects by controlling the strip entering temperature, the zinc liquid temperature, and the furnace nose holding temperature to fluctuate within a small range, compared with the traditional strip entering temperature, zinc liquid temperature, and furnace nose holding temperature fluctuation process.

[0026] 2. The application provides a production method of high-surface cold-rolled hot-dip aluminum-zinc-silicon steel plate, through implementation of high-efficiency degreasing process and annealing process, high-KOH concentration process is adopted for degreasing, high-reducing atmosphere and high-furnace temperature process are adopted for annealing, compared with traditional low-alkali concentration, low-reducing atmosphere and low-furnace temperature process, residual oil and oxides on the surface of the steel plate are effectively removed, and the problem that residual oil and oxides on the surface of the steel plate are not clean enough before entering the zinc pot to react with zinc liquid to form slag is solved.

[0027] 3. The application provides a production method of high-surface cold-rolled hot-dip aluminum-zinc-silicon steel plate, through reduction of Ti, V, La and Ce content in the pot, compared with traditional process with high Ti, V, La and Ce impurity content in the pot, the production rate of spot slag is effectively reduced, and the problem of too much spot slag caused by impurity elements in the zinc pot is solved.

[0028] 4. The application provides a production method of high-surface cold-rolled hot-dip aluminum-zinc-silicon steel plate, through control of the process that the strip steel enters the pot at a temperature 5-10 DEG C higher than the temperature of the zinc liquid, compared with traditional process with too high or too low difference between the temperature of the strip steel and the temperature of the zinc pot, the ability of the strip steel to input energy and the zinc liquid to emit energy to maintain balance is effectively increased, and the problem of too much Fe dissolution caused by large temperature fluctuation of the zinc pot in traditional process is solved.

[0029] 5. The application provides a production method of high-surface cold-rolled hot-dip aluminum-zinc-silicon steel plate, through the mode of increasing the cooling rate of the steel plate at the initial stage after the steel plate leaves the zinc pot, compared with traditional process with slow cooling rate at the initial stage after the steel plate leaves the zinc pot, the size of the molten pool caused by skeleton segmentation when the Al-rich phase solidifies is effectively reduced, the volume shrinkage when the Zn-rich phase liquid in the skeleton solidifies is eliminated, large and deep pores generated in the solidification process of the aluminum-zinc coating are eliminated, and the problem that air residues cause the coating on the top to be lifted up in the baking and curing process is eliminated.

[0030] 6. The application provides a production method of high-surface cold-rolled hot-dip aluminum-zinc-silicon steel plate, through adoption of a large flattening process path, compared with traditional small flattening mode, the height distribution of the surface of the steel plate tends to be gentle, the number of sharp peaks and valleys is reduced, and the flow flatness of the coating is further enhanced. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The surface macro photograph before implementation of the application,

[0032] Figure 2 The surface macro photograph after implementation of the application,

[0033] Figure 3 The coating surface metallographic photograph before implementation of the application,

[0034] Figure 4 The coating surface metallographic photograph after implementation of the application. DETAILED DESCRIPTION

[0035] In order to deepen the understanding of the present application, the following detailed description of the present embodiment is made in conjunction with the accompanying drawings.

[0036] The production method of the high surface cold-rolled aluminum-zinc-silicon plated steel sheet of the present embodiment comprises a hot aluminum-zinc plating process, characterized in that the degreasing process, annealing process, zinc pot process, post-plating cooling process and flattening process in the aluminum-zinc plating process are regulated.

[0037] The degreasing process is regulated, and the degreasing temperature is 80-85℃, and the NaOH concentration in the degreasing agent is 3-5%.

[0038] The annealing process is regulated, and the annealing furnace is a horizontal annealing furnace, the dew point of the soaking section is -35 to -50℃, the H2 content in the soaking section is ≥28%, and the furnace temperature in the soaking section is ≥1000℃.

[0039] The zinc pot process is regulated, and the strip steel entering temperature into the zinc pot is 596-598℃, the zinc liquid temperature is 589-591℃, the furnace nose insulation temperature is 586-588℃, the Ti element content in the zinc liquid in the zinc pot is ≤0.0005%, and the V+La+Ce element content in the zinc liquid is ≤0.002%.

[0040] The post-plating cooling process is regulated, and the lower edge of the post-plating cooling air box is 1.5-2m away from the zinc liquid surface, the post-plating cooling rate gradually decreases from the position where the strip steel enters the post-plating cooling air box to the position where it exits the cooling air box, the cooling rate at the position where the strip steel enters the cooling air box is 40-50℃, the cooling rate at the position where the strip steel exits the cooling air box is 10-15℃, and the strip steel temperature at the top roll position is ≤180℃.

[0041] The flattening process is regulated, and the characteristic is that the flattening elongation is 1.0-1.2%.

[0042] The aluminum-zinc-silicon plated steel sheet has a thickness of 1.0-2.0mm, and the coating weight is 60-80g / m 2 , and the steel sheet surface SKu value is 1.0-2.5.

[0043] The product obtained by the production method of the high surface cold-rolled aluminum-zinc-silicon plated steel sheet of the present embodiment has the following characteristics:

[0044] The following five embodiments are described.

[0045] Table 1: Degreasing process control parameters of the present embodiment

[0046] Parameter Defatting temperature / °C NaOH concentration in defatting agent / % The present invention 80～85 3～5 Example 1 82 4 Example 2 83 4 Example 3 85 3 Example 4 80 5 Example 5 82 5

[0047] Table 2: Annealing process control parameters of the present embodiment

[0048] Parameter Soaking section dew point / °C H2 content / % Soaking section furnace temperature / °C The present invention -35～-50 ≥28 ≥1000 Example 1 -45 28 1050 Example 2 -38 30 1029 Example 3 -50 28 1053 Example 4 -40 30 1058 Example 5 -45 30 1021

[0049] Table 3 Process control parameters of zinc pot in the embodiment of the present application

[0050]

[0051] Table 4 Process control parameters of post-plating cooling in the embodiment of the present application

[0052]

[0053] Table 5 Process control parameters of flattening and performance indexes of steel plate in the embodiment of the present application

[0054]

[0055]

[0056] It should be noted that the above embodiments are not intended to limit the protection scope of the present application, and equivalent transformations or substitutions made on the basis of the above technical solutions all fall within the protection scope of the claims of the present application.

Claims

1. A method of controlling high surface cold rolled hot dip aluminium zinc, characterized in that, The method comprises the following steps: Step 1: degreasing process, Step 2: annealing process, Step 3: zinc pot process, Step 4: post-plating cooling process, Step 5: leveling process.

2. The high surface cold rolled hot dip aluminium zinc process control method according to claim 1, characterized in that, Step 1: degreasing process, specifically as follows: degreasing temperature 80-85 DEG C, NaOH concentration in degreasing agent 3-5%.

3. The high surface cold rolled hot dip aluminium zinc process according to claim 2, characterized in that, Step 2: annealing process, specifically as follows: the annealing furnace is a horizontal annealing furnace, the dew point of the soaking section is -35 to -50 DEG C, the H2 content is greater than or equal to 28%, and the temperature of the soaking section is greater than or equal to 1000 DEG C.

4. The high surface cold rolled hot dip aluminum zinc process control method according to claim 1 wherein, Step 3: zinc pot process, specifically as follows: the zinc pot process is controlled, the strip steel enters the zinc pot at a temperature of 596-598 DEG C, the zinc liquid temperature is 589-591 DEG C, the furnace nose insulation temperature is 586-588 DEG C, the zinc liquid Ti element content in the zinc pot is less than or equal to 0.0005%, and the zinc liquid V+La+Ce element content is less than or equal to 0.002%.

5. The high surface cold rolled hot dip aluminum zinc process control method according to claim 1 wherein, Step 4: post-plating cooling process, specifically as follows: the post-plating cooling process is controlled, the lower edge of the post-plating cooling air box is 1.5-2 m away from the zinc liquid surface, the post-plating cooling rate gradually decreases from the position where the strip steel enters the post-plating cooling air box to the position where it exits the cooling air box, the cooling rate at the position where the strip steel enters the cooling air box is 40-50 DEG C, the cooling rate at the position where the strip steel exits the cooling air box is 10-15 DEG C, and the strip steel temperature at the top roll position is less than or equal to 180 DEG C.

6. The high surface cold rolled hot dip aluminum zinc process control method according to claim 1 wherein, Step 5: leveling process, specifically as follows: the leveling process is controlled, and the leveling elongation is 1.0-1.2%.

7. The high surface cold rolled hot dip aluminum zinc process control method according to claim 1 wherein, The aluminized zinc-silicon steel plate has a thickness of 1.0-2.0 mm, a plated layer weight of 60-80 g / m 2 , and a steel plate surface SKu value of 1.0-2.5.

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