Method for accurately detecting adhesion of zinc layer of advanced high-strength steel

Abstract

This invention relates to the field of steel testing technology, specifically disclosing a method for accurately detecting the adhesion of zinc coatings on advanced high-strength steel. The method includes sampling and sample preparation: a sample is cut from a galvanized steel coil and a metallographic sample is prepared; precise measurement of the reduced iron layer thickness: the thickness *d* of the reduced iron layer on the metallographic sample is measured using a microscopic analysis instrument; a zinc coating adhesion determination system is established, and a preset logic relating the reduced iron layer thickness range threshold to the zinc coating adhesion level is used; the measured reduced iron layer thickness *d* is input into the zinc coating determination system; the system calculates the zinc coating adhesion level and indicates the processing scenario for product application; the zinc coating determination result is then obtained. This invention utilizes a high-precision microscopic analysis instrument to measure the thickness of the reduced iron layer at the interface between the steel plate substrate and the zinc layer. The zinc coating adhesion determination system pre-sets a threshold range for the reduced iron layer thickness and a corresponding relationship with the zinc coating adhesion, classifying the zinc coating adhesion into multiple levels, thus achieving an objective, quantifiable, and highly accurate assessment of the zinc coating adhesion.

Description

Technical Field

[0001] This invention relates to the field of steel testing technology, specifically to a method for accurately testing the adhesion of zinc coatings on advanced high-strength steel. Background Technology

[0002] Hot-dip galvanized high-strength steel is widely used in automobiles and other fields, and the adhesion of its zinc coating is a key indicator of coating quality. Traditional adhesion testing methods (such as tape peeling, bending tests, and impact tests) are mostly subjective qualitative or semi-quantitative methods, which are difficult to accurately reflect the actual situation of high-strength steel, especially in terms of accurately addressing the adhesion quality of high-strength steel in different application scenarios. In practical applications, high-strength steel with zinc coating adhesion that meets the standards tested by traditional methods may experience zinc peeling problems during user operation, leading to significant economic losses and user complaints.

[0003] The invention patent CN107505260A discloses a device and method for testing the adhesion of galvanized steel sheet coatings. This method primarily provides a destructive, results-oriented qualitative testing device and method for adhesion. Its core principle is to use high-strength sealant to bond the zinc layer, followed by mechanical peeling (bending). The "qualified" or "unqualified" result is determined by observing whether zinc residue remains on the peeled surface. However, this method cannot accurately assess the adhesion of high-strength steel in different application scenarios.

[0004] Invention patent CN111537437B discloses a bending die operation method for graded testing of the adhesion of DP980 high-strength steel. For high-strength steel, by designing bending dies with different angles (30° to 120°), a semi-quantitative, graded adhesion testing method is established. The smaller the deformation angle, the higher the adhesion requirement, thus achieving graded evaluation. However, it is still an indirect, empirical inference based on macroscopic deformation results.

[0005] Invention patent CN120967124A discloses a production process for stabilizing and controlling the adhesion of zinc coatings on DP steel. This patent ensures adhesion by optimizing production process parameters, precisely controlling the dew point of the annealing furnace in stages, and utilizing the principle of "selective oxidation" to remove surface-enriched Si and Mn elements. The patent aims to achieve good adhesion in high-strength steel, but it fails to accurately reflect the actual condition of high-strength steel. Therefore, a method for accurately detecting the adhesion of zinc coatings on advanced high-strength steel is needed to solve the problems of low accuracy and difficulty in adapting to different materials and application environments in existing technologies. Summary of the Invention

[0006] To address the problems existing in the prior art, the purpose of this invention is to provide a method for accurately detecting the adhesion of advanced high-strength steel zinc coating.

[0007] The technical solution adopted by this invention to solve its technical problem is: a method for accurately detecting the adhesion of advanced high-strength steel zinc coating, comprising the following steps:

[0008] S1. Sampling and Sample Preparation: Cut samples from galvanized steel coils and prepare metallographic samples;

[0009] S2. Precise measurement of reduced iron layer thickness: The thickness d of the reduced iron layer in the metallographic sample is determined using a microscopic analysis instrument;

[0010] S3. Establish a zinc layer adhesion determination system and preset the logic of the relationship between the threshold of the iron layer thickness range and the zinc layer adhesion level.

[0011] S4. Input the measured thickness d of the reduced iron layer into the zinc layer determination system;

[0012] S5. The system calculates the zinc coating adhesion level and indicates the processing scenario for product application;

[0013] S6. Zinc layer determination results complete.

[0014] Specifically, in step S1, the steel coil sample is cut to create a cross-sectional metallographic sample for observing the complete interface between the steel plate substrate and the coating.

[0015] Specifically, in step S2, the microscopic analysis instrument measures the reduced iron layer at the interface between the steel plate substrate and the zinc layer of the metallographic sample.

[0016] Specifically, the microscopic analysis instrument used in step S2 is either SEM / EDS or FIB-SEM.

[0017] Specifically, the logic relating the reduced iron layer thickness range threshold and the zinc layer adhesion level in step S3 is as follows:

[0018] The zinc coating adhesion rating is excellent: d<100nm, allowing for the stamping of complex parts, with the deformation of the stamped parts within 180°;

[0019] The zinc coating adhesion grade is good: 100≤d<200nm, allowing for the stamping of relatively complex parts, with the deformation of the stamped parts within 150°;

[0020] The zinc coating adhesion grade is qualified: 200≤d<300nm, allowing for simple stamping of parts, with deformation of stamped parts within 120°;

[0021] The zinc coating adhesion rating is unacceptable: d≥300nm.

[0022] Specifically, the processing scenario for the product application in step S5 is the complexity of the part stamping process. The complexity of the part stamping process includes complex parts, relatively complex parts, simple parts, and parts that cannot be stamped.

[0023] The present invention has the following beneficial effects:

[0024] This invention presents a method for accurately detecting the adhesion of zinc coatings on advanced high-strength steel. It utilizes a high-precision microscopic analysis instrument to measure the thickness of the reduced iron layer at the interface between the steel substrate and the zinc coating. Simultaneously, a zinc coating adhesion assessment system is established, pre-setting a threshold range for reduced iron layer thickness and its correlation with zinc coating adhesion. The zinc coating adhesion is categorized into multiple levels (e.g., excellent, good, acceptable, unacceptable). The reduced iron layer thickness is input into the zinc coating adhesion assessment system, which calculates the zinc coating adhesion level and indicates the applicable scenarios for the steel coil. This quantitative criterion enables an objective, quantifiable, and highly accurate evaluation of zinc coating adhesion.

[0025] This invention presents a method for accurately detecting the adhesion of zinc coatings in advanced high-strength steel. The measured thickness of the reduced iron layer directly reflects the degree of pre-oxidation in the annealing furnace of advanced high-strength steel, providing a clear direction for optimizing process parameters such as dew point and temperature in the pre-oxidation chamber to improve zinc coating adhesion. This method not only significantly outperforms traditional methods in terms of detection accuracy but also has process guidance value, demonstrating outstanding practicality and broad prospects for widespread application. Attached Figure Description

[0026] Figure 1 Screenshot of the parameter settings for the zinc coating adhesion determination system.

[0027] In the diagram: EHT represents the electric field strength; Signal A indicates that the signal A channel uses NTS BSD; WD represents the working distance; Mag represents the amplification factor. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] Example 1

[0030] Background: A steel mill's 1.4mm HC440 / 780DHD product exhibited slight zinc depletion during the stamping process for battery pack casings, drawing significant customer complaints. A review of the steel coil production process revealed that the annealing furnace temperature, unit speed, and pre-oxidation control were all within the process range. Samples were subjected to a 1-ton bending test (bending angle approximately 120-180°) and no zinc depletion was observed, meeting the high-strength steel release standards. Therefore, the specific cause of the zinc depletion could not be identified, leading to a stalemate in rectification efforts.

[0031] Diagnosis using the technical solution of this invention: The dezincified sample is sampled and prepared according to requirements, and the thickness of the reduced iron layer at the interface between the steel plate substrate and the zinc layer is measured using a high-precision microscopic analysis instrument. The measurement results show that the thickness of the reduced iron layer is 115nm. The measurement results are input into the zinc layer adhesion judgment system. The system shows that the zinc layer adhesion is good, allowing for the stamping of more complex parts, and the deformation of the stamped parts is within 150°.

[0032] Therefore, it was determined that the dezincification was caused by the excessive thickness of the reduced iron layer. By adjusting the process, the thickness of the reduced iron layer in the high-strength steel produced in subsequent batches was reduced to 90nm, and the user did not experience any further dezincification issues after using the product.

[0033] Example 2

[0034] Background: When a steel plant was producing 2.5mm HC440 / 780DPD products, a sudden speed reduction occurred due to a machine malfunction. After the speed reduction, the steel coils were sampled and bent on-site for testing. The sample showed slight zinc peeling after 1T bending, but no zinc peeling was found after 2T bending. However, this result did not meet the release standard for zinc coating adhesion of conventional high-strength steel. Therefore, the on-site operators had to downgrade 50 tons of this batch of high-strength steel, resulting in a loss of about 50,000 yuan.

[0035] However, technicians used the method of this invention for diagnosis: after sampling and sample preparation, the thickness of the reduced iron layer was measured to be 230nm, and the measured thickness of the reduced iron layer was input into the zinc layer adhesion judgment system. The system showed that the judgment result was qualified, allowing for simple stamping of parts, and the deformation of the stamped parts was within 90°. Through user identification, it was found that the stamping of thick high-strength steel was extremely simple. Therefore, the technicians released the batch of products as qualified products. Subsequent user follow-up observation showed no zinc dezincification. This method saved approximately 50,000 yuan from the loss.

[0036] Example 3

[0037] A large number of samples were taken on-site for analysis, and the relationship between the thickness of the reduced iron layer and the bending of the zinc layer was measured. The results are shown in Table 1.

[0038] Table 1. Comparison of the relationship between the thickness of the reduced iron layer and the bending of the zinc layer.

[0039] Serial Number Reduced iron layer thickness / nm degree of bending Zinc layer determination results Determine the level 1 66 180° Unzinc excellent 2 99 180° Unzinc excellent 3 110 180° Dezinc / 4 110 1T（150°-180°） Unzinc good 5 196 180° Dezinc / 6 196 1T（150°-180°） Unzinc good 7 220 1T（150°-180°） Dezinc / 8 220 2T（120°-150°） Unzinc qualified 9 310 2T（120°-150°） Dezinc Unqualified 10 400 2T（120°-150°） Dezinc Unqualified

[0040] like Figure 1 As shown, the zinc coating adhesion assessment system parameters are set. This invention utilizes high-precision microscopic analysis instruments (such as SEM / EDS, FIB, etc.) to measure the thickness of the reduced iron layer at the interface between the steel plate substrate and the zinc layer. Simultaneously, a zinc coating adhesion assessment system is established. The system pre-sets a threshold range for the reduced iron layer thickness and its correspondence with zinc coating adhesion, classifying zinc coating adhesion into multiple levels (e.g., excellent, good, acceptable, unacceptable). The reduced iron layer thickness is input into the zinc coating adhesion assessment system, which calculates the zinc coating adhesion level and indicates the applicable scenarios for the steel coil. Through this quantitative criterion, an objective, quantifiable, and highly accurate assessment of zinc coating adhesion can be achieved.

[0041] This invention is not limited to the above-described embodiments. Anyone should know that any structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention.

[0042] The technologies, shapes, and structures not described in detail in this invention are all known technologies.

Claims

1. A method for accurately detecting the adhesion of zinc coatings on advanced high-strength steel, characterized in that, Includes the following steps: S1. Sampling and Sample Preparation: Cut samples from galvanized steel coils and prepare metallographic samples; S2. Precise measurement of reduced iron layer thickness: The thickness d of the reduced iron layer in the metallographic sample is determined using a microscopic analysis instrument; S3. Establish a zinc layer adhesion determination system and preset the logic of the relationship between the threshold of the iron layer thickness range and the zinc layer adhesion level. S4. Input the measured thickness d of the reduced iron layer into the zinc layer determination system; S5. The system calculates the zinc coating adhesion level and indicates the processing scenario for product application; S6. Zinc layer determination results complete.

2. The method for accurately detecting the adhesion of advanced high-strength steel zinc coating according to claim 1, characterized in that, In step S1, the steel coil sample is cut to create a cross-sectional metallographic sample for observing the complete interface between the steel plate substrate and the coating.

3. The method for accurately detecting the adhesion of advanced high-strength steel zinc coating according to claim 2, characterized in that, In step S2, a microscopic analysis instrument is used to measure the reduced iron layer at the interface between the steel plate matrix and the zinc layer of the metallographic sample.

4. The method for accurately detecting the adhesion of advanced high-strength steel zinc coating according to claim 1, characterized in that, The microscopic analysis instrument used in step S2 is either SEM / EDS or FIB-SEM.

5. The method for accurately detecting the adhesion of advanced high-strength steel zinc coating according to claim 1, characterized in that, The specific logic relating the reduced iron layer thickness range threshold and the zinc layer adhesion level in step S3 is as follows: The zinc coating adhesion rating is excellent: d<100nm, allowing for the stamping of complex parts, with the deformation of the stamped parts within 180°; The zinc coating adhesion grade is good: 100≤d<200nm, allowing for the stamping of relatively complex parts, with the deformation of the stamped parts within 150°; The zinc coating adhesion grade is qualified: 200≤d<300nm, allowing for simple stamping of parts, with deformation of stamped parts within 120°; The zinc coating adhesion rating is unacceptable: d≥300nm.

6. The method for accurately detecting the adhesion of advanced high-strength steel zinc coating according to claim 5, characterized in that, The processing scenario for the product application in step S5 is the complexity of the part stamping. The complexity of the part stamping includes complex parts, relatively complex parts, simple parts, and parts that cannot be stamped.

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