Method for carrying out pretreatment on hot-rolled strip steel and judging pickling end point in hydrochloric acid

Abstract

The invention belongs to the technical field of steel plate pickling, and relates to a method for carrying out pretreatment and pickling end point judgment on hot-rolled strip steel in hydrochloric acid. The method specifically comprises the following steps: taking a to-be-used hydrochloric acid liquid for testing, heating the hydrochloric acid liquid, adding a wetting reagent A and a potential stabilizing reagent B, and putting a to-be-measured hot-rolled strip steel into the hydrochloric acid liquid; and measuring the pickling process of the hot-rolled strip steel by adopting a dual-electrode detection system and a constant potential rectifier, synchronously recording electrode potential values in different time periods in the process, and taking a time point when a potential first-order derivative value is basically unchanged as the pickling end point time of the hot-rolled strip steel. According to the method, the implementation process is simple, only certain manpower needs to be input for manual operation, and analysis instruments related to related work are mature; the method can effectively measure the pickling end point of the hot-rolled strip steel, especially the ultra-high-strength hot-rolled steel plate in the acid liquor, eliminates the effects of various influence factors in pickling, and has extremely high practical application value.

Description

Technical Field

[0001] The invention belongs to the technical field of steel plate pickling, and specifically relates to a detection method for performing relevant pre-treatment and research and determination of the pickling endpoint in a hot-rolled steel plate pickling experiment using a hydrochloric acid solution. Background Art

[0002] Modern steel manufacturers typically implement a pickling process during the cold rolling process. Pickling involves placing the hot-rolled strip in a strong acid (commonly concentrated hydrochloric acid) at the cold rolling entrance to chemically dissolve the oxide scale on the strip's surface, eliminating the hot-rolled oxide scale and revealing the steel base material. Pickling the strip at the cold rolling entrance is essential for achieving high-quality surface quality. Oxide scale forms during the hot rolling process, and its composition and thickness are directly determined by the alloy and the hot rolling process (finishing rolling and coiling temperature). Insufficient cold-rolling pickling time often results in residual scale defects. Excessive cold-rolling pickling time removes the oxide scale, but over-pickling can occur, resulting in excessive surface roughness over large areas of the strip, high acid consumption, and high iron loss.

[0003] Therefore, the primary focus of research on the pickling process is determining the pickling endpoint in the laboratory—the point at which the acid completely dissolves the hot-rolled scale. Traditionally, this endpoint determination is done visually. Hot-rolled specimens are placed in the acid solution, removed at various times, and visually observed. The pickling endpoint is determined when a bright silver base material appears. This method is subject to the influence of visual observation, resulting in varying times. Furthermore, accurately determining the time at which the scale is completely removed during the pickling process can be difficult, resulting in significant errors in the final results.

[0004] In recent years, with the continuous development of steel materials, especially the continuous research and development breakthroughs of high-strength steel products, a large amount of alloy elements have been added to the materials, and the amount of alloys has become increasingly higher, which has led to the increasing complexity of the oxide scale structure. The simple oxide scale structure of carbon steel in the past no longer exists. The surface of hot-rolled strip will have many oxide scales with different thicknesses and very different structural compositions. There will even be many oxide scales with different structural compositions intertwined on the surface.

[0005] Figure 1 This is a typical modern high-strength steel with higher alloys. The complex multi-layer oxide scale composition is formed on the hot-rolled surface. It can be seen that there are multiple oxide scale structures intertwined together, and it can also be found that the thickness of different layers of oxide scale in different areas is also different. Therefore, it is difficult to determine the end point of this type of steel during pickling.

[0006] Based on the above situation, relevant technical literature and patent documents on pickling endpoint detection methods were searched in this field, mainly focusing on the following aspects:

[0007] Accurate determination of the end point of pickling of strip steel (G. Hubmer, A. Osterkom, K. Rendl and R. Puntigam, "World Steel", September 2003) proposed a method for measuring the end point of pickling using electrode potential method. The difference between the change in the chemical reaction potential when the acid solution and the oxide scale are dissolved and the change in the potential of the reaction between the acid solution and the steel substrate is used to determine the end point of pickling. The method used is as follows: Figure 2 As shown in the figure, the intersection of the tangent lines of the third and fourth stages of the potential change during the pickling period is taken as the pickling end point in the cold rolling pickling production process.

[0008] This method has the advantages of good repeatability and high measurement accuracy. However, in actual use, the potential needs to show the above-mentioned multi-stage change pattern. In the actual production process, the composition of the oxide scale of the hot-rolled strip will change a lot due to the influence of the hot rolling process. Therefore, it is difficult to show the multi-stage obvious change pattern of the potential in the actual pickling experiment. Therefore, the use of the potential method to measure the pickling endpoint time has very limited application adaptability.

[0009] CN201721390294.9 (A device for measuring the end point of turbulent pickling time) proposes a measuring device and method that can measure the pickling end point of strip steel under different acid flow rate conditions (turbulence), wherein the hot-rolled strip steel sheet to be tested is placed in an acid tank equipment, and then the flow rate of the acid solution is adjusted with an acid pump to obtain different turbulences. At the same time, electrodes are installed on the hot-rolled strip steel to measure the online pickling potential change, and the time point when this potential is basically unchanged (the difference in potential value before and after the time is approximately zero) is defined as the pickling end point. This method still uses the change of electrode potential to calibrate the pickling end point, but the difference is that the time point when the potential remains unchanged is used as the pickling end point.

[0010] However, in actual pickling, especially when simulating the pickling of the high-alloy high-strength steel mentioned above, the overly complex reasons for the oxide scale will lead to multi-segment and fluctuating characteristics of the potential change. For example, the potential method is used to measure the pickling of a high-strength steel. Figure 3 As shown in the left figure, the potential at point I shows a significant inflection point, while the actual potential change is approximately zero at point II, indicating that point II is the clock point. When the steel strip is removed from the acid solution, the right figure shows that the oxide scale on the strip surface has been removed near point I, effectively meeting the pickling endpoint. However, the hot-rolled steel strip removed at point II is visually indistinguishable from that at point I, indicating localized over-pickling. This phenomenon is due to the complex oxide scale morphology of high-strength steel, as previously mentioned. The presence of fine oxide scale at the microscopic level causes small fluctuations in the acid solution potential between points I and II. Using this method for determination clearly indicates over-pickling. Figure 3Diagram of potential variation (left) and images of actual pickling point I (center) and point II (right) of the strip.

[0011] CN200910047971.0 (An electrochemical method for determining the pickling endpoint of hot-rolled carbon steel in a hydrochloric acid system) proposes a method suitable for use in hydrochloric acid systems and capable of determining the pickling endpoint. This method also uses potential measurement to determine the pickling endpoint. This method finds the lowest potential point during the pickling process and then uses the corresponding time point as the final pickling endpoint. This method is based on the principle that at the pickling endpoint, all oxide scale is dissolved and eliminated. At this point, the iron matrix reacts with the acid solution to produce hydrogen and ferrous ions. Because the standard potential of this reaction is relatively low (approximately -0.447 V), this is used as the pickling endpoint.

[0012] However, with the development of modern high-strength steel, as analyzed above, the composition of hot-rolled oxide scale is very complex, and metal elements are easily enriched on the surface of the strip. Some alloy elements are enriched to the surface of the strip during hot rolling, which will greatly change the composition and ingredients of the oxide scale. At the same time, the adjustment of the hot rolling coiling temperature may even cause microcracks in some oxide layers on the surface of the strip, resulting in the generation of a large amount of hydrogen in the early stage of pickling. In addition, the large-scale use of elements such as Al and Mn, the use of these alloys will cause the potential in the pickling process to change to a lower value. In summary, the lowest point of the pickling potential changes greatly. Using this method to determine the pickling end point may often result in under-pickling. Figure 4 This is a graph of the potential change of a certain high-strength steel measured using this method. At points I and II where the potential is the lowest, a large amount of oxide scale can be found on the surface, so the use of this method has great limitations. Figure 4 Potential variation diagram of a high-strength steel during pickling (left) and images of the actual pickling point I (center) and point II (right) of the strip.

[0013] Therefore, judging from the contents of the above-mentioned patents and articles, in addition to the traditional visual method of determining pickling, the focus is usually on using potential measurement to determine the pickling endpoint. The biggest advantage of this method is that it overcomes visual influences, has good repeatability, and eliminates the measurement error and operational error of the measurer. However, the problem with the previous potential-based method is that the selection of the judgment standard cannot meet the current determination of the effects of scale residue, large amounts of hydrogen, and alloy components on the pickling potential that occur in the pickling production process of high-alloy and high-strength steel. Summary of the Invention

[0014] In order to solve the above technical problems, the present invention proposes a determination method specifically for treating and measuring the pickling endpoint of hot-rolled strip steel in a hydrochloric acid solution.

[0015] The technical solution of the present invention:

[0016] A method for pre-treating a hot-rolled strip and determining the pickling endpoint in hydrochloric acid comprises the following steps:

[0017] The hydrochloric acid liquid to be tested is heated, and a wetting agent A and a potential stabilizing agent B are added. The hot-rolled steel strip to be measured is then placed in the hydrochloric acid liquid. As the hydrochloric acid solution pickles, dissolves, and corrodes the oxide scale on the surface of the hot-rolled steel strip, a dual-electrode detection system and a constant potentiostat are used to measure the pickling process of the hot-rolled steel strip. The electrode potential values ​​at different time periods during this process are simultaneously recorded, and the time point at which the first-order derivative value of the potential remains substantially unchanged is taken as the pickling endpoint time of the hot-rolled steel strip.

[0018] Furthermore, the hot-rolled steel strip refers to a steel strip material that has undergone hot rolling and has an original surface oxide scale and has not undergone any oxide scale treatment.

[0019] Furthermore, the hydrochloric acid liquid to be used is a hydrochloric acid solution with a total acid concentration of 160-220 g / L, preferably a total acid concentration of 180-190 g / L, and the Fe content in the hydrochloric acid liquid is controlled. 2+ The concentration is not higher than 50g / L, Fe 3+ The concentration is not higher than 6g / L.

[0020] Furthermore, the heating temperature is 60-85°C, preferably 75-80°C.

[0021] Furthermore, the hot-rolled strip to be measured is connected to a constant potential instrument via a wire; at the same time, the reference electrode in the dual-electrode system is connected to the constant potential instrument via a wire; during measurement, the detection end of the reference electrode is placed in hydrochloric acid, and the hot-rolled strip is also placed in hydrochloric acid. The hydrochloric acid solution begins to corrode the oxide scale on the surface of the hot-rolled strip, and the changing values ​​of the electrode potential and time are synchronously recorded.

[0022] More preferably, the reference electrode of the two-electrode system is a standard Ag / AgCl electrode.

[0023] Furthermore, the wetting agent A is sodium lauryl sulfate, and the potential stabilizing agent B is hexamethylenetetramine and / or methylpentynol.

[0024] More preferably, the concentration of sodium lauryl sulfate is 0.01 to 0.2 g / L, more preferably 0.08 to 0.1 g / L.

[0025] Furthermore, the concentration of hexamethylenetetramine is 0.5-2.5 g / L, and the concentration of methylpentynol is 0.5-2.5 g / L; more preferably, the concentration of hexamethylenetetramine is 1.2-1.5 g / L, and the concentration of methylpentynol is 0.6-0.8 g / L;

[0026] Furthermore, a dual-electrode detection system and a constant potentiostat were used to measure the pickling process of the hot-rolled strip, and the electrode potential values ​​at different time periods during the process were recorded simultaneously. The first-order derivative calculation operation was performed on the obtained time-potential relationship diagram (t~E) to obtain E at different time points. div (t) value; the "time point at which the value of the first-order derivative of the potential remains substantially unchanged" is determined by the following method:

[0027] d. For the obtained E div (t) data values ​​are compared, and E at a certain time n div (t n ) point data≤1×10 -5 V / s;

[0028] e. Judge the data in the subsequent Δt period. When E in this period div (t n+Δt )Point data average

[0029] ≤1×10 -5 When V / s is reached, the moment n is considered the end point of pickling.

[0030] The Δt time period is preferably ≥ (800-1800) ms, and more preferably the Δt time period is 800-1800 ms. Detailed description of the invention:

[0032] A method for pre-treating hot-rolled strip steel and determining the pickling endpoint in hydrochloric acid, the specific method process is as follows:

[0033] (1) taking a hydrochloric acid liquid with the required concentration to be tested, heating it to the temperature to be tested, adding the required amount of wetting agent A and potential stabilizing agent B to the hydrochloric acid, and then placing the hot-rolled steel strip to be measured into the hydrochloric acid liquid; while the hydrochloric acid solution pickles, dissolves and corrodes the oxide scale on the surface of the hot-rolled steel strip, a dual-electrode detection system and a constant potentiostat are used to measure the pickling process of the hot-rolled steel strip, and the electrode potential values ​​at different time periods during the process are simultaneously recorded, and the time point at which the first-order derivative value of the potential remains substantially unchanged is taken as the pickling end time of the hot-rolled steel strip;

[0034] (2) Furthermore, in the method for determining the end point of pickling of steel strips described in the above invention (1), the hot-rolled steel strips refer to steel strips that have undergone hot rolling and have an original surface oxide scale and have not undergone any oxide scale treatment;

[0035] (3) Furthermore, the hydrochloric acid liquid to be used as described in the above invention (1) is controlled at a temperature of 60-85°C, and a hydrochloric acid solution with a total acid concentration of 160-220 g / L is used to control the Fe content in the hydrochloric acid liquid. 2+The concentration is not higher than 50g / L, Fe 3+ The concentration is not higher than 6g / L;

[0036] (4) Furthermore, the hot-rolled steel strip to be measured as described in the above invention (1) is connected to a constant potential instrument via a wire; at the same time, the reference electrode in the dual-electrode system is connected to the constant potential instrument via a wire; during measurement, the detection end of the reference electrode is placed in hydrochloric acid, and the hot-rolled steel strip is also placed in hydrochloric acid, and the hydrochloric acid solution begins to corrode the oxide scale on the surface of the hot-rolled steel strip, and the change in electrode potential with time is synchronously recorded;

[0037] (5) Furthermore, the reference electrode of the two-electrode system described in the above invention contents (1) to (4) is preferably a standard Ag / AgCl electrode;

[0038] (6) Furthermore, in the above invention (1), the wetting agent A added is sodium lauryl sulfate, the potential stabilizing agent B is hexamethylenetetramine and / or methylpentynol, the concentration of sodium lauryl sulfate is 0.01 to 0.2 g / L, the concentration of hexamethylenetetramine is 0.5 to 2.5 g / L, and the concentration of methylpentynol is 0.5 to 2.5 g / L;

[0039] (7) Furthermore, in the pickling process of the hot-rolled strip steel after the contents of the above invention (1) to (6) are processed, the obtained time-potential relationship diagram (t~E) is preferably subjected to a first-order derivative calculation operation to obtain E at different time points. div (t) value; the "time point at which the value of the first-order derivative of the potential is substantially unchanged" described in the Summary of the Invention (1) is determined by the following method:

[0040] f. E obtained div (t) data values ​​are compared, and E at a certain time n div (t n ) point data≤1×10 -5 V / s;

[0041] g. Judge the data in the subsequent Δt period. When E in this period div (t n+Δt )Point data average

[0042] ≤1×10 -5 When V / s is reached, the moment n is considered the end point of pickling.

[0043] h. The Δt time period is preferably 800 to 1800 ms.

[0044] The present invention takes into account the properties of alloying elements and oxide scale in modern high-strength steel. The hot-rolled oxide scale of high-strength steel contains a unique structure of multiple complex layers of oxide scale, which is rich in microcracks and contains many alloying elements. When the steel strip is placed in acid, the acid often reacts directly with the substrate iron through the cracks, generating large amounts of hydrogen, which can cause dramatic fluctuations in the measured potential. Furthermore, the presence of very fine oxide scale remaining locally on the surface of ultra-high-strength steel can also cause the acid to continuously corrode the oxide, resulting in small fluctuations in the measured potential and affecting the determination of the pickling endpoint. Taking these characteristics into account, the present invention adds chemical substances to the acid solution, utilizing the strong wettability of sodium lauryl sulfate to prevent the formation of large amounts of hydrogen accumulation on the surface of the hot-rolled steel strip, eliminating its influence on the measured potential during the pickling process. Furthermore, the use of hexamethylenetetramine and methylpentynol can rapidly adsorb on the surface of the substrate after pickling, shielding the fine oxide scale residue on the surface, significantly slowing the corrosive chemical effects of the acid solution. This reduces dramatic fluctuations in the potential during the experiment and achieves a stable potential value. The accuracy of the potential determination pickling method is greatly improved, the use process is relatively simple, the selected substances and the addition amount will not affect the end point of the pickling process, the technology used is uncomplicated and relatively easy to implement, and it has broad practical prospects and high detection accuracy. Description of the drawings:

[0045] Figure 1 This is the structure diagram of the hot-rolled surface oxide scale of a typical high-alloy high-strength steel;

[0046] Figure 2 This is a schematic diagram of a method for determining the end point of pickling using a potential measurement method;

[0047] Figure 3 The potential change diagram of different high-strength steel pickling and the pickling effect diagram of the actual strip steel at different points in the actual pickling process (actual pickling point I strip steel (center) point II (right) image);

[0048] Figure 4 The potential change diagram of different high-strength steel pickling and the pickling effect diagram of the actual strip steel at different points in the actual pickling process (actual pickling point I strip steel (center) point II (right) image);

[0049] Figure 5 The effect diagram of the implementation of Example 1 is shown in the figure on the left, wherein the curve of the potential change of a hot-rolled strip in a conventional hydrochloric acid solution is shown, and the figure on the right is the potential curve and first-order derivative diagram obtained after the treatment of this embodiment according to the content of the present invention;

[0050] Figure 6 The pickling surface condition of a hot-rolled steel strip at the pickling endpoint time point obtained in Example 1;

[0051] Figure 71 is a graph showing the effect of the implementation of Example 2, wherein the left figure is a curve showing the change in potential of a hot-rolled strip during pickling in a conventional hydrochloric acid solution, and the right figure is a potential curve and first-order derivative graph obtained after treatment in accordance with the present invention in this example;

[0052] Figure 8 This is the pickling surface condition of a hot-rolled strip at the pickling endpoint time point obtained in Example 2. Specific embodiments

[0053] Example 1

[0054] According to the method of the present invention, a hot-rolled sample of a certain ultra-high-strength steel is sampled in a certain cold rolling mill on site, processed into the size required for the experimental process, and then:

[0055] (1) Take unused hydrochloric acid solution with a total acid concentration of 184g / L and Fe 2+ At a concentration of 10 g / L, Fe 3 + The concentration is 2.5g / L. Heat the acid solution and keep it at a constant temperature of 75℃. Place it in a standard chemical laboratory beaker.

[0056] (2) adding sodium lauryl sulfate and hexamethylenetetramine to the acid solution, adjusting the concentration of the former to 0.08 g / L and the concentration of the latter to 1.5 g / L;

[0057] (3) Connect one end of the sample prepared by processing the hot-rolled steel strip to be measured to the constant potential instrument through a wire; at the same time, connect the standard Ag / AgCl reference electrode to the constant potential instrument through a wire;

[0058] (4) During the measurement, the hot-rolled steel strip is placed in hydrochloric acid. The hydrochloric acid solution begins to corrode the oxide scale on the surface of the hot-rolled steel strip, and the change in electrode potential and time is recorded synchronously;

[0059] (5) The pickling potential and the corresponding first-order derivative value of the hot-rolled strip sample are plotted as follows: Figure 5 As shown in the figure on the right:

[0060] (6) According to the method of the present invention, the Δt time period is set to 1200 ms. At this time, it is found that the pickling end point n time point is 110.4 s.

[0061] A hot-rolled sample of a certain ultra-high strength steel treated by the method of the present invention, Figure 5The left figure is a potential-time curve of a hot-rolled sample pickled in a hydrochloric acid solution under the same conditions. Due to the influence of hydrogen and the avoidance of residual complex scale components, if the conventional method of determining the end point of pickling potential is used, the end time of pickling will be 3.1s or 315.9s, which is obviously inconsistent with the actual time point. The potential curve and first-order derivative diagram obtained after treatment with the method of the present invention are shown in FIG. Figure 5 In the right figure, the time point is 110.4s. After taking out the sample, it is observed that Figure 6 It can be seen that the oxide scale on the surface has been effectively removed and there are no pickling defects.

[0062] Example 2

[0063] According to the method of the present invention, a hot-rolled sample of a certain ultra-high-strength steel is sampled in a certain cold rolling mill on site, processed into the size required for the experimental process, and then:

[0064] (1) Take unused hydrochloric acid solution with a total acid concentration of 188g / L and Fe 2+ The concentration is 8g / L, Fe 3+ The concentration is 3g / L. Heat the acid solution and keep it at a constant temperature of 80℃. Place it in a standard chemical laboratory beaker.

[0065] (2) adding sodium lauryl sulfate, hexamethylenetetramine, and methylpentynol to the acid solution, adjusting the concentration of sodium lauryl sulfate to 0.08 g / L, the concentration of hexamethylenetetramine to 1.2 g / L, and the concentration of methylpentynol to 0.6 g / L;

[0066] (3) Connect one end of the sample prepared by processing the hot-rolled steel strip to be measured to the constant potential instrument through a wire; at the same time, connect the standard Ag / AgCl reference electrode to the constant potential instrument through a wire;

[0067] (4) During the measurement, the hot-rolled steel strip is placed in hydrochloric acid. The hydrochloric acid solution begins to corrode the oxide scale on the surface of the hot-rolled steel strip, and the change in electrode potential and time is recorded synchronously;

[0068] (5) The pickling potential and the corresponding first-order derivative value of the hot-rolled strip sample are plotted as follows: Figure 7 As shown in the figure on the right:

[0069] (6) According to the method of the present invention, the Δt time period is set to 1000 ms. At this time, it is found that the pickling end point n time point is 209.79 s.

[0070] A hot-rolled sample of a certain ultra-high strength steel treated by the method of the present invention, Figure 7The left figure is a potential-time curve of a hot-rolled sample pickled in a hydrochloric acid solution under the same conditions. It is also affected by hydrogen and the alloy composition of the oxide scale. According to the previous method of determining the end point of the pickling potential, the pickling end time will be 4.2s or 71.9s. At this time point, obvious oxide scale residue will be found when the hot-rolled sample is taken out. The potential curve and first-order derivative diagram obtained after treatment with the method of the present invention are shown as follows: Figure 7 In the right figure, the time point is 209.79s. When the sample is taken out at this time, it is observed that Figure 8 It can be seen that the oxide scale on the surface has been effectively removed and there are no pickling defects.

[0071] The present invention is simple to implement, requiring only a limited amount of manual labor. The analytical instrumentation required for this work is also mature. It can effectively measure the pickling endpoint of hot-rolled steel strip, especially ultra-high-strength hot-rolled steel plate, in acid solution, eliminating the effects of various factors affecting the pickling process and possessing extremely high practical application value.

[0072] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention fall within the scope of the technical solution of the present invention.

Claims

1. A method for pre-treating hot-rolled strip and determining the pickling endpoint in hydrochloric acid, characterized in that: The steps include: Take the hydrochloric acid liquid to be tested, heat it, add the wetting agent A and the potential stabilizing agent B, and then put the hot-rolled steel strip to be measured into the hydrochloric acid liquid; along with the pickling, dissolution and corrosion of the oxide scale on the surface of the hot-rolled steel strip by the hydrochloric acid solution, use a double-electrode detection system and a constant potentiostat to measure the pickling process of the hot-rolled steel strip, and simultaneously record the electrode potential values ​​at different time periods in this process, and take the time point when the first-order derivative value of the potential is basically unchanged as the pickling end time of the hot-rolled steel strip.

2. A method for pre-treatment of hot-rolled strip and determination of pickling endpoint in hydrochloric acid according to claim 1, characterized in that: The hot-rolled steel strip refers to a steel strip material that has undergone hot rolling and has an original surface oxide scale and has not undergone any oxide scale treatment.

3. A method for pre-treatment of hot-rolled strip and determination of pickling endpoint in hydrochloric acid according to claim 1, characterized in that: The hydrochloric acid liquid to be used is a hydrochloric acid solution with a total acid concentration of 160-220 g / L. The Fe 2+ Concentration is not higher than 50g / L, Fe 3+ The concentration is not higher than 6g / L.

4. A method for pre-treatment of hot-rolled strip and determination of pickling endpoint in hydrochloric acid according to claim 1, characterized in that: The heating temperature is 60-85°C.

5. The method for pre-treating hot-rolled strip and determining the pickling endpoint in hydrochloric acid according to claim 1, characterized in that: The hot-rolled steel strip to be measured is connected to the constant potential instrument through a wire; at the same time, the reference electrode in the dual-electrode system is connected to the constant potential instrument through a wire; during measurement, the detection end of the reference electrode is placed in hydrochloric acid, and the hot-rolled steel strip is also placed in the hydrochloric acid, the hydrochloric acid solution begins to corrode the oxide scale on the surface of the hot-rolled steel strip, and the change value of the electrode potential and time is synchronously recorded.

6. A method for pre-treatment of hot-rolled strip and determination of pickling endpoint in hydrochloric acid according to claim 5, characterized in that: The reference electrode of the dual-electrode system is a standard Ag / AgCl electrode.

7. A method for pre-treatment of hot-rolled strip and determination of pickling endpoint in hydrochloric acid according to claim 1, characterized in that: The wetting agent A is sodium dodecyl sulfate, and the potential stabilizing agent B is hexamethylenetetramine and / or methylpentynol.

8. A method for pre-treatment of hot-rolled strip and determination of pickling endpoint in hydrochloric acid according to claim 7, characterized in that: The concentration of sodium dodecyl sulfate is 0.01-0.2 g / L.

9. A method for pre-treatment of hot-rolled strip and determination of pickling endpoint in hydrochloric acid according to claim 7, characterized in that: The concentration of hexamethylenetetramine is 0.5-2.5 g / L, and the concentration of methylpentynol is 0.5-2.5 g / L.

10. The method for pre-treating hot-rolled strip and determining the pickling endpoint in hydrochloric acid according to claim 1, characterized in that: The pickling process of the hot-rolled strip was measured by a dual-electrode detection system and a constant potentiostat, and the electrode potential values ​​at different time periods in the process were recorded synchronously. The first-order derivative calculation operation was performed on the obtained time-potential relationship diagram (t~E) to obtain E at different time points. div (t) value; the "time point at which the value of the first-order derivative of the potential remains substantially unchanged" is determined by the following method: a. For the obtained E div (t) data value is compared, E at a certain time n div (t n ) point data≤1×10 -5 V / s; b. Judge the data in the subsequent Δt period. When E in this period div (t n+Δt ) point data are all ≤1×10 - 5 V / s, the moment n is considered as the pickling end point; c. The Δt time period is preferably 800 to 1800 ms.

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