Technology for stably controlling iron content in zinc liquid of continuous hot galvanizing line

Abstract

The invention relates to the technical field of galvanized plates, and discloses a technology for stably controlling the iron content in zinc liquid of a continuous hot galvanizing line, which comprises the following steps: carrying out surface treatment on rolled hard strip steel, carrying out alkali immersion cleaning, alkali scrubbing, electrolytic cleaning, hot water scrubbing and hot water rinsing treatment, carrying out annealing treatment, and putting into a zinc pot for galvanizing, slag salvaging is conducted on the liquid level in a zinc pot according to the frequency of one time / 4 h, rolled hard strip steel is subjected to the surface residual iron removal procedure before continuous hot galvanizing, the cleanliness of the surface of the rolled hard strip steel is guaranteed, the rolled hard strip steel enters the zinc pot after annealing, the mechanical property of the strip steel is improved, slag salvaging can guarantee that surface zinc slag is removed in time, the zinc slag is prevented from suspending in zinc liquid, and the service life of the strip steel is prolonged. The method can realize stable control of the iron content in the zinc liquid of the continuous hot galvanizing line, and has the characteristics of simple operation and stable realization.

Description

Technical Field

[0001] The invention relates to the technical field of galvanized sheets, and in particular to a technology for stabilizing and controlling the iron content in zinc liquid of a continuous hot-dip galvanizing line. Background Art

[0002] At present, with the rapid development of new energy vehicles in China, the demand and quality requirements for galvanized sheets are getting higher and higher. The zinc slag and zinc particle defects on the surface of the pure zinc coating have a huge impact on the surface quality of hot-dip galvanized automotive sheets, affecting the production efficiency during the stamping process and the surface quality after stamping. The generation of zinc slag is directly related to the Fe in the zinc pot. If there is no Fe or the Fe content is low in the zinc pot, the generation of zinc slag will be greatly reduced. Controlling the Fe content in the zinc pot becomes the key to controlling the generation of zinc slag on the surface of the pure zinc coating. In actual production, in order to control the Fe content in the zinc liquid, more preparation work needs to be done. At the same time, the time to have stable production conditions is short, generally about 2-4 days. The iron content in the zinc liquid at other times is generally controlled at more than 0.01%, which will lead to more zinc slag defects in the zinc pot.

[0003] Chinese patent application CN108559937A discloses a method for removing iron from zinc liquid before the production of continuous hot-dip galvanized sheet for automobile exterior and its production method, comprising the following steps: adjusting the aluminum content in the zinc liquid to 0.28-0.35wt%, and adjusting the temperature to 430-450°C; introducing inert gas for stirring to react iron with aluminum, precipitating Fe2Al5 solid particles, standing, and removing slag; the patent controls the solubility of Fe in the zinc liquid by the methods of "reducing aluminum" and "raising temperature", creates a slag-free process window for producing automobile outer panels, and controls the surface quality extremely well, but the patent also has strict requirements on the production conditions of automobile outer panels, and the continuous stable production time is also about 2-4 days. At this time, the Fe content in the zinc liquid can be controlled between 0.003% and 0.006%, but the Fe content outside this condition will reach more than 0.01%.

[0004] The present invention controls the cleaning method, the temperature of the steel strip entering the zinc pot, the temperature of the zinc liquid and the composition of the zinc liquid, etc., without the need for a series of special preparations, and can ultimately stably control the Fe content in the zinc liquid to below 0.01%, thereby achieving stable production of automobile steel. Summary of the invention

[0005] 1. Technical issues to be resolved

[0006] In order to solve the above technical problems, the present invention provides a technology for stabilizing the iron content in the zinc liquid of a continuous hot-dip galvanizing line. The technology has the advantages of simple operation, and can stably control the Fe content in the zinc liquid to below 0.01%, thereby solving the problem of zinc slag on the surface of the pure zinc coating.

[0007] (II) Technical solution

[0008] In order to achieve the above object, the present invention discloses a technology for stabilizing the iron content in zinc liquid of a continuous hot-dip galvanizing line, comprising the following steps:

[0009] (1) performing surface treatment on the hardened steel strip, and performing alkali leaching, alkali brushing, electrolytic cleaning, hot water brushing, and hot water rinsing to obtain the surface treated hardened steel strip;

[0010] (2) After annealing, the hardened steel strip treated in step (1) is placed in a zinc pot for galvanizing, and the slag is removed from the liquid level in the zinc pot at a frequency of once every 4 hours.

[0011] Preferably, the specific treatment steps for the hardened steel strip in step (1) are as follows: surface treatment is performed on the hardened steel strip before continuous hot-dip galvanizing to remove residual iron on the surface of the hardened steel strip, and the hardened steel strip is treated by alkali immersion, alkali scrubbing, electrolytic cleaning, hot water scrubbing and hot water rinsing, wherein the alkali concentration during alkali immersion and alkali scrubbing is 1.0-2.5 g / L, the alkali temperature is 50-90°C, and the alkali immersion time is 5-10S; during electrolytic cleaning, the current is 0.5-1.0A; during hot water scrubbing and hot water rinsing, the hot water temperature is 80-90°C, to obtain the surface treated hardened steel strip.

[0012] Preferably, after the residual iron on the surface of the hardened steel strip is removed, the reflectivity of the surface of the hardened steel strip after treatment is ≥90%.

[0013] Preferably, the alkali solution in the alkali leaching and alkali scrubbing process is a sodium hydroxide solution.

[0014] Preferably, the hardened steel strip after surface treatment in step (2) is subjected to annealing treatment, wherein during the annealing treatment, the heating rate is 2-5°C / min, the annealing temperature is 720-840°C, and the annealing time is 12-15min.

[0015] Preferably, after annealing, the hardened strip steel treated in step (2) is cooled to 430-450°C by a staged cooling method of first slow cooling and then fast cooling, and then put into a zinc pot for galvanizing, and the temperature of the zinc liquid in the zinc pot is controlled at 454±1°C.

[0016] Preferably, in step (2), the Al content in the zinc liquid in the zinc pot is 0.22% to 0.26%.

[0017] (III) Beneficial technical effects

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) In the present invention, the hardened steel strip needs to go through a process of removing residual iron on the surface before continuous hot-dip galvanizing, and undergoes alkali immersion, alkali brushing, electrolytic cleaning, hot water brushing, and hot water rinsing. The residual iron on the surface of the steel strip is first removed by alkali immersion followed by alkali brushing. At the same time, after the surface is cleaned by electrolytic reaction, the residual iron on the surface of the steel strip will be further removed. During the electrolytic cleaning process, there are two pairs of electrodes in the electrolytic reaction. The first pair of electrodes uses the steel strip as an anode and the electrode as a cathode. After the electrolytic reaction between the two, O2 is generated. The second pair of electrodes uses the steel strip as a cathode and the electrode as an anode. After the electrolytic reaction between the two, H2 is generated. The gas generated by the electrolytic reaction will diffuse outward from the surface of the steel strip, and the residual iron attached to the surface of the steel strip will be peeled off or loosened, and will be cleaned in the subsequent hot brushing process. After hot water brushing and rinsing, the pollutants and oxides on the surface of the hardened strip are effectively removed, ensuring that the surface reflectivity of the strip is ≥90%, ensuring the cleanliness of the surface of the hardened strip, providing a clean and rough base for the zinc layer, thereby improving the adhesion of the galvanized layer, and avoiding the defects such as zinc particles and zinc scars that are easily formed during the galvanizing process, which is conducive to the uniform adhesion and flow of the zinc liquid, thereby forming a galvanized layer with uniform thickness and good quality.

[0020] (2) In the present invention, the hardened steel strip is annealed before entering the zinc pot. The annealing treatment can heat the steel strip to a temperature above the recrystallization temperature and below the transformation temperature from ferrite to austenite, thereby eliminating the strong internal stress generated by cold rolling deformation, restoring the equiaxed grain structure before deformation, optimizing the organization structure of the steel strip, removing some defects on the surface of the steel strip, and making it easier to form a uniform zinc coating during galvanizing. Annealing treatment can improve the mechanical properties of the steel strip, such as tensile strength, yield strength, etc., thereby improving the overall performance of the galvanized sheet. The plate temperature of the hardened strip is lower than the zinc liquid temperature, which can reduce the dissolution of iron on the strip surface in the zinc liquid. Controlling the zinc liquid temperature can reduce the zinc slag produced by the change of iron solubility in the zinc liquid due to the temperature fluctuation of the zinc liquid. The Al content in the zinc liquid is controlled between 0.22% and 0.26%. The Al in the zinc liquid can react with iron to produce Fe2Al5, which is formed in the form of zinc slag and suspended on the surface of the zinc liquid, thus reducing the iron content in the zinc liquid. The zinc pot liquid surface is slaged at a frequency of once every 4 hours, which can ensure that the surface zinc slag is removed in time to prevent the zinc slag from being suspended in the zinc liquid.

[0021] (3) The present invention can realize the stable control of the iron content in the zinc liquid of the continuous hot-dip galvanizing line, and has the characteristics of simple operation and stable realization. It only needs to remove the slag and adjust the zinc liquid composition during the maintenance before each production. No special production preparation cycle is required during the normal galvanizing production process. The process measures taken can realize the stable control of the iron content in the zinc liquid during the entire production cycle of the zinc pot roller, and the iron content is controlled below 0.01% during the entire production cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0023] Figure 1 It is a schematic diagram of the electrolytic cleaning of the steel strip before continuous hot-dip galvanizing in the present invention;

[0024] Figure 2 It is a schematic diagram of electrolytic cleaning of steel strip before continuous hot-dip galvanizing in the present invention;

[0025] Figure 3 The phase diagram of the influence of the zinc liquid temperature and the effective aluminum content of the zinc liquid on the generation of zinc slag in the present invention;

[0026] Figure 4 This is a graph showing the actual control results of the aluminum content in the zinc liquid on the iron content in the present invention. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] Example 1

[0029] A technology for stabilizing the iron content in zinc liquid of a continuous hot-dip galvanizing line comprises the following steps:

[0030] (1) before continuous hot-dip galvanizing, the hardened steel strip is subjected to surface treatment to remove residual iron on the surface of the hardened steel strip, and then subjected to alkali leaching, alkali scrubbing, electrolytic cleaning, hot water scrubbing, and hot water rinsing treatments, wherein the alkali solution concentration during the alkali leaching and alkali scrubbing is 1.0 g / L, the alkali solution temperature is 50° C., and the alkali leaching time is 10 s; during the electrolytic cleaning process, the current is 0.5 A; during the hot water scrubbing and hot water rinsing process, the hot water temperature is 80° C., and the surface of the hardened steel strip after the surface treatment is obtained, and the surface reflectivity of the hardened steel strip after the treatment is ≥90%;

[0031] (2) The hardened steel strip treated in step (1) is subjected to annealing treatment, wherein during the annealing treatment, the heating rate is 2°C / min, the annealing temperature is 720°C, and the annealing time is 15min. After the annealing treatment, the hardened steel strip is cooled to 430°C by a staged cooling method of first slow cooling and then fast cooling, and then put into a zinc pot for galvanizing. The Al content of the zinc liquid in the zinc pot is 0.22%, the temperature of the zinc liquid in the zinc pot is controlled at 454±1°C, and the liquid level in the zinc pot is slag removed at a frequency of once every 4 hours.

[0032] Example 2

[0033] A technology for stabilizing the iron content in zinc liquid of a continuous hot-dip galvanizing line comprises the following steps:

[0034] (1) before continuous hot-dip galvanizing, the hardened steel strip is subjected to surface treatment to remove residual iron on the surface of the hardened steel strip, and then subjected to alkali leaching, alkali scrubbing, electrolytic cleaning, hot water scrubbing, and hot water rinsing treatment, wherein the alkali solution concentration during the alkali leaching and alkali scrubbing is 1.5 g / L, the alkali solution temperature is 70° C., and the alkali leaching time is 7 seconds; during the electrolytic cleaning process, the current is 0.6 A; during the hot water scrubbing and hot water rinsing process, the hot water temperature is 85° C., and the surface reflectivity of the hardened steel strip after the surface treatment is obtained, and the surface reflectivity of the hardened steel strip after the treatment is ≥90%;

[0035] (2) The hardened steel strip treated in step (1) is subjected to annealing treatment, wherein during the annealing treatment, the heating rate is 4°C / min, the annealing temperature is 750°C, and the annealing time is 14min. After the annealing treatment, the hardened steel strip is cooled to 435°C by a staged cooling method of first slow cooling and then fast cooling, and then put into a zinc pot for galvanizing. The Al content in the zinc liquid in the zinc pot is 0.23%, the temperature of the zinc liquid in the zinc pot is controlled at 454±1°C, and the liquid level in the zinc pot is slag removed at a frequency of once / 4h.

[0036] Example 3

[0037] A technology for stabilizing the iron content in zinc liquid of a continuous hot-dip galvanizing line comprises the following steps:

[0038] (1) before continuous hot-dip galvanizing, the hardened steel strip is subjected to surface treatment to remove residual iron on the surface of the hardened steel strip, and then subjected to alkali leaching, alkali scrubbing, electrolytic cleaning, hot water scrubbing, and hot water rinsing treatments, wherein the alkali concentration during alkali leaching and alkali scrubbing is 2 g / L, the alkali temperature is 80° C., and the alkali leaching time is 8 seconds; during electrolytic cleaning, the current is 0.8 A; during hot water scrubbing and hot water rinsing, the hot water temperature is 85° C., and the surface-treated hardened steel strip is obtained, and the surface reflectivity of the treated hardened steel strip is ≥90%;

[0039] (2) The hardened steel strip treated in step (1) is subjected to annealing treatment, wherein during the annealing treatment, the heating rate is 3°C / min, the annealing temperature is 820°C, and the annealing time is 14min. After the annealing treatment, the hardened steel strip is cooled to 445°C by a staged cooling method of first slow cooling and then fast cooling, and then put into a zinc pot for galvanizing. The Al content of the zinc liquid in the zinc pot is 0.25%, the temperature of the zinc liquid in the zinc pot is controlled at 454±1°C, and the liquid level in the zinc pot is slag removed at a frequency of once every 4 hours.

[0040] Example 3

[0041] A technology for stabilizing the iron content in zinc liquid of a continuous hot-dip galvanizing line comprises the following steps:

[0042] (1) before continuous hot-dip galvanizing, the hardened steel strip is subjected to surface treatment to remove residual iron on the surface of the hardened steel strip, and then subjected to alkali leaching, alkali scrubbing, electrolytic cleaning, hot water scrubbing, and hot water rinsing treatments, wherein the alkali concentration during alkali leaching and alkali scrubbing is 2.5 g / L, the alkali temperature is 90° C., and the alkali leaching time is 5 seconds; during electrolytic cleaning, the current is 1.0 A; during hot water scrubbing and hot water rinsing, the hot water temperature is 90° C., and the surface of the hardened steel strip after surface treatment is obtained, and the surface reflectivity of the hardened steel strip after treatment is ≥90%;

[0043] (2) The hardened steel strip treated in step (1) is subjected to annealing treatment, wherein during the annealing treatment, the heating rate is 5°C / min, the annealing temperature is 840°C, and the annealing time is 12 min. After the hardened steel strip is subjected to annealing treatment, the strip is cooled to 450°C by a staged cooling method of first slow cooling and then fast cooling, and then placed in a zinc pot for galvanizing. The Al content in the zinc liquid in the zinc pot is 0.26%, the temperature of the zinc liquid in the zinc pot is controlled at 454±1°C, and the slag is removed from the zinc pot at a frequency of once every 4 hours.

[0044] In the present invention, from Figure 3 It can be seen that the solubility of iron in zinc liquid increases with the increase of temperature. When the temperature of zinc liquid increases from low temperature to high temperature, the dissolution of iron in zinc liquid will increase. When the temperature decreases, the iron saturation will precipitate to form zinc slag. When the temperature rises again, the zinc slag will not dissolve back, which will produce zinc slag and lead to an increase in suspended iron in the zinc liquid. Therefore, the stability of the zinc liquid temperature is crucial to controlling the iron content in the zinc liquid.

[0045] In the present invention, from Figure 4 It can be seen that the control method of the present invention can achieve stable control of the iron content in the zinc liquid during the entire production cycle of the zinc pot roller, and the iron content can be stably controlled below 0.01% during the entire production cycle.

[0046] Although the embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that all equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A technology for stabilizing the iron content in zinc liquid of a continuous hot-dip galvanizing line, characterized in that: The steps include: (1) performing surface treatment on the hardened steel strip, and performing alkali leaching, alkali brushing, electrolytic cleaning, hot water brushing, and hot water rinsing to obtain the surface treated hardened steel strip; (2) After annealing, the hardened steel strip treated in step (1) is placed in a zinc pot for galvanizing, and the slag is removed from the liquid level in the zinc pot at a frequency of once every 4 hours.

2. The technology for stabilizing the iron content in the zinc solution of a continuous hot-dip galvanizing line according to claim 1 is characterized by: The specific processing steps for the hardened steel strip in step (1) are as follows: surface treatment is performed on the hardened steel strip before continuous hot-dip galvanizing to remove residual iron on the surface of the hardened steel strip, and the hardened steel strip is subjected to alkaline immersion, alkaline brushing, electrolytic cleaning, hot water brushing, and hot water rinsing to obtain the surface-treated hardened steel strip.

3. The technology for stabilizing the iron content in the zinc solution of a continuous hot-dip galvanizing line according to claim 2 is characterized by: During the alkali leaching and alkali scrubbing process, the alkali solution concentration is 1.0-2.5 g / L, the alkali solution temperature is 50-90° C., and the alkali leaching time is 5-10 seconds.

4. The technology for stabilizing the iron content in the zinc solution of a continuous hot-dip galvanizing line according to claim 2 is characterized by: During the electrolytic cleaning process, the current is 0.5-1.0A.

5. The technology for stabilizing the iron content in the zinc solution of a continuous hot-dip galvanizing line according to claim 2 is characterized by: During the hot water scrubbing and hot water rinsing process, the hot water temperature is 80-90°C.

6. The technology for stabilizing the iron content in the zinc solution of a continuous hot-dip galvanizing line according to claim 2 is characterized by: After the residual iron on the surface of the hardened steel strip is removed, the surface reflectivity of the processed hardened steel strip is ≥90%.

7. The technology for stabilizing the iron content in the zinc solution of a continuous hot-dip galvanizing line according to claim 2 is characterized by: The alkali solution in the alkali leaching and alkali scrubbing process is a sodium hydroxide solution.

8. The technology for stabilizing the iron content in zinc solution of a continuous hot-dip galvanizing line according to claim 1 is characterized by: The hardened steel strip after surface treatment in step (2) is subjected to annealing treatment, wherein during the annealing treatment, the heating rate is 2-5°C / min, the annealing temperature is 720-840°C, and the annealing time is 12-15min.

9. The technology for stabilizing the iron content in zinc liquid of a continuous hot-dip galvanizing line according to claim 1 is characterized by: After annealing, the hardened strip steel treated in step (2) is cooled to 430-450° C. by a staged cooling method of first slow cooling and then fast cooling, and then put into a zinc pot for galvanizing, and the temperature of the zinc liquid in the zinc pot is controlled at 454±1° C.

10. The technology for stabilizing the iron content in the zinc solution of a continuous hot-dip galvanizing line according to claim 9 is characterized in that: The Al content in the zinc liquid in the zinc pot is 0.22% to 0.26%.

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