Method for detecting carbon content on the surface of hot-rolled organic coated sheet

Abstract

The application discloses a kind of detection methods of hot-rolled coating plate surface carbon content, first using degreasing gauze with organic solvent to wipe and extract the organic coating of hot-rolled plate surface;Ultrasonic treatment is carried out in organic solvent, then take out gauze, rinse, dry, obtain organic coating film;Magnetic flux guide, combustion improver, cosolvent are sequentially added to heating container, measure blank C content value under the condition of not introducing organic coating film;The obtained organic coating film is added to heating container, magnetic flux guide, combustion improver and cosolvent are sequentially added, then it is placed in infrared combustion carbon sulfur instrument, and the C content in sample is determined;The obtained C content is subtracted from the blank value obtained in 4), and converted into the content in unit area, and finally the carbon content of unit area with coating surface is obtained.The application can realize efficient separation of hot-rolled plate surface coating and quantitative analysis of C element in hot-rolled coating plate surface coating, and realize rapid evaluation of corrosion resistance of hot-rolled plate with coating.

Description

Technical Field

[0001] This invention belongs to the field of metal material testing technology, specifically relating to a method for detecting the carbon content on the surface of hot-rolled organic coated plates. Background Technology

[0002] Steel is widely used in industry and the automotive sector due to its high machinability and low manufacturing cost, for example, in compressor crankshafts, guide rails, and rolling mill rolls. However, ordinary steel is prone to wear and corrosion failure due to its poor wear resistance, relatively low hardness, or poor corrosion resistance, severely impacting its service life. Applying a functional coating to the surface of steel is the most effective protective method. Using surface coating technology to process and repair various parts can provide pre-protection, repair, and reuse, and further extend the service life of equipment.

[0003] Coating hot-rolled steel plates effectively prevents the diffusion of oxygen and metal ions, thereby achieving anti-oxidation and anti-decarburization effects during billet heat treatment, and enabling surface functional differentiation of hot-rolled high-strength steel. Coating the surface of hot-rolled plates significantly improves corrosion resistance and extends the service life of workpieces. Therefore, the ability to quickly and accurately evaluate the corrosion resistance of hot-rolled coated products is of paramount importance. Currently, methods for evaluating product corrosion resistance mainly include outdoor hanging test, salt spray test, and weekly immersion test. The outdoor hanging test typically requires 1-4 years of hanging time, with samples retrieved annually from the base station for weight loss analysis to obtain the corrosion rate and evaluate the sample's corrosion resistance. The salt spray test primarily examines the differences in corrosion resistance under simulated chloride ion conditions. This method simulates an environment where chloride ions are present in the air, resulting in a harsh service environment that cannot accurately reflect the product's inherent corrosion resistance. The weekly immersion test primarily examines the differences in corrosion resistance of samples under simulated industrial atmospheric conditions. Both salt spray and immersion methods require cutting samples at the production site and bringing them back to the laboratory for analysis. They also necessitate simulating extremely harsh service conditions to assess the corrosion resistance of samples, or examining the corrosion resistance of samples over a long period (more than 2 years). These methods cannot effectively evaluate the corrosion resistance of newly produced samples. The salt spray method examines the corrosion resistance of samples in the presence of chloride ions, while the immersion method simulates the corrosion resistance of samples after at least 2 years. None of these three methods can be used for rapidly evaluating the amount of coating on the surface of products and their corrosion resistance. Therefore, there is an urgent need to develop a method suitable for on-site testing of the coating content on hot-rolled steel plates. Summary of the Invention

[0004] The main objective of this invention is to address the problems and shortcomings of existing corrosion resistance testing methods by providing a method for detecting the carbon content on the surface of coated hot-rolled steel sheets, thereby enabling rapid evaluation of the corrosion resistance of coated hot-rolled steel sheets.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for detecting the carbon content on the surface of a hot-rolled coated steel sheet includes the following steps:

[0007] 1) Use degreased gauze soaked in organic solvent to wipe and extract the organic coating from the surface of the hot-rolled plate;

[0008] 2) Immerse the degreased gauze with the organic coating in an organic solvent and sonicate it to separate the degreased gauze from the organic coating, and then remove the gauze.

[0009] 3) The remaining mixture obtained in step 2) is rinsed with an organic solvent and dried to obtain an organic coating film;

[0010] 4) Add magnetic agent, combustion aid, and solvent to the heating container in sequence, and measure the blank C content value under the condition of no organic coating being introduced;

[0011] 5) Add the organic coating film obtained in step 3) into a heating container, add a magnetic agent, a combustion aid and a solvent in sequence, and then put it into an infrared combustion carbon-sulfur analyzer to determine the C content in the sample;

[0012] 6) Convert the obtained C content into the content per unit area, subtract the blank value obtained in 4), and finally obtain the carbon content per unit area of ​​the coated surface.

[0013] In the above scheme, the thickness of the organic coating on the surface of the hot-rolled plate is less than 20 μm.

[0014] In the above scheme, the wiping extraction area of ​​the organic coating on the surface of the hot-rolled plate is >1600mm². 2 .

[0015] In the above scheme, the organic solvent can be an alcohol solvent or a ketone solvent, etc.; specifically, one or more of ethanol, methanol, propanol, acetone, etc. can be selected.

[0016] In the above scheme, the ultrasonic treatment step 2) uses a power of 30-50W / L and a time of 10-15min.

[0017] In the above scheme, the magnetic agent can be iron powder; the combustion aid can be tungsten granules, etc.; and the flux can be tin granules, etc.

[0018] In the above scheme, the drying step in step 3) uses a temperature of 30-40℃.

[0019] In the above scheme, the heating container can be a ceramic crucible or the like.

[0020] Further, in step 4), each material and its weight percentage includes: 1.000-2.500 parts of magnetic agent, 1.5000-3.000 parts of combustion accelerator, and 0.15-0.40 parts of tin granules.

[0021] In the above scheme, the present invention does not have any special restrictions on the type of organic coating on the surface of hot-rolled plate, and the detection method described in the present invention is applicable to conventional organic coating systems in the steel industry.

[0022] The detection method described in this invention involves wiping the surface of a hot-rolled steel plate with an organic coating using degreased gauze containing an organic solvent until the dark gray iron oxide scale is completely exposed, ensuring the complete extraction of the organic coating. This method achieves complete peeling of the coating from the hot-rolled steel plate surface and has no special requirements regarding the location and structural characteristics of the area where the organic coating was extracted, making it widely applicable. The degreased gauze and organic coating are then further separated. Finally, the carbon dioxide infrared combustion method is used to detect the carbon content in the degreased gauze. Ensuring complete combustion of carbon is crucial in this method. Since the organic coating sample itself is non-conductive, magnetic and fluxing materials are added to aid in complete combustion and ensure the accuracy of the results. By detecting the difference in carbon content before and after wiping the hot-rolled steel plate with degreased gauze, the carbon content per unit area of ​​the coating is calculated, thus inferring the level of coating content on the hot-rolled steel plate surface. This method enables precise surface location detection and analysis, is simple to operate, time-efficient, and can accurately determine the carbon content in the coating of hot-rolled steel plates, providing an objective basis for judging the corrosion resistance of hot-rolled steel plates.

[0023] The detection method described in this invention can basically achieve rapid judgment of the surface corrosion resistance of any part of the product surface. It is simple to operate, time-saving, and can accurately obtain the C content in the coating of hot-rolled plate, providing an objective basis for judging the corrosion resistance of hot-rolled plate.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1) This invention proposes for the first time to use degreased gauze to wipe the coating on the surface of hot-rolled plate (the coating cannot be effectively separated by mechanical peeling, warm water soaking, hair dryer or cleaning agent), and then separate the coating film by ultrasonic and low temperature drying. Then, the C content in the sample is detected by infrared carbon-sulfur analyzer, which can realize the quantitative analysis of C element in the coating on the surface of hot-rolled plate.

[0026] 2) The detection method described in this invention can provide objective basis and detailed data for the subsequent determination of the corrosion resistance of hot-rolled coated plates, provide objective basis for screening whether products meet customer requirements, and provide strong technical support for product segmentation and providing different products for different needs. Attached Figure Description

[0027] Figure 1After sealing the edges of samples 3# and 4# obtained in Example 2, they were placed in an outdoor exposure area, and photos of the samples were taken at 0, 2, and 4 weeks to track their progress.

[0028] Figure 2 This is the standard curve plotted for Example 1 based on C content and C element intensity of the standard sample;

[0029] Figure 3 After sealing the edges of samples 1# and 2# obtained in Example 1, they were placed in an outdoor exposure area, and photos of the samples were taken at 0, 2, 4, and 6 weeks to track their progress.

[0030] Figure 4 The standard curve for Example 2 is plotted based on C content and C element intensity of standard sample. Detailed Implementation

[0031] The technical solution of the present invention will be described in full and clear below with reference to the embodiments. However, the described embodiments are only some embodiments of the present invention. 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.

[0032] In the following embodiments, the hot-rolled sheet with organic coating is a hot-rolled sheet with a conventional water-based epoxy resin coating on the surface, with an average thickness of 10 μm; the coating system bonds more tightly to the substrate after being heated in hot water, making it difficult to wipe off effectively.

[0033] In the following examples, the infrared carbon-sulfur analyzer was preheated at 900°C for about 30 minutes before testing; the tin granules were ultrasonically cleaned with acetone for 1-3 minutes, then removed and dried; the ceramic crucible was preheated for 15 minutes and then set aside for use.

[0034] Example 1

[0035] A method for detecting the carbon content on the surface of a hot-rolled steel plate with an organic coating, comprising the following steps:

[0036] 1) Sample 1# is a coated hot-rolled plate and sample 2# is an uncoated hot-rolled plate. The sample size is 50mm×50mm. Use degreased gauze soaked in anhydrous ethanol to wipe the organic coating on the surface of sample 1# and sample 2# until the gray substrate is completely exposed on the sample surface. Weigh sample 1# and sample 2# before and after the organic coating is applied. The results are shown in Table 1.

[0037] 2) After wiping off the organic coating, black substances were found on the sample surface after wiping with degreased gauze. The degreased gauze was then placed in 30 mL of anhydrous ethanol and sonicated for 5-10 minutes until the color of the degreased gauze remained unchanged. The degreased gauze was then removed.

[0038] 3) Rinse the degreased gauze 3-5 times with anhydrous ethanol, pour all the solution into a petri dish, place the petri dish on an alcohol lamp and heat until all the solution evaporates, tap the edge of the petri dish with a clean brush, and pour the collected sample into a ceramic crucible.

[0039] 4) Preheat the infrared carbon-sulfur analyzer for about 30 minutes before testing. Clean the tin granules with acetone using ultrasonic cleaning for 1-3 minutes, remove and dry them. Preheat the ceramic crucible for 15 minutes and set it aside after heating. Transfer the collected sample to the ceramic crucible and add 1.000g of magnetic agent (iron powder), about 0.2g of flux tin granules and 1.2000g of combustion aid to the ceramic crucible. Measure the blank C content value under the condition of no organic coating.

[0040] 5) Add 0.5000g of standard sample C obtained in step 3) to a heating container, and then add 1.000g of magnetic agent (iron powder), 1.5000g of combustion aid (tungsten granules), and 0.25g of flux (tin granules) sequentially. Place the container in an infrared combustion carbon-sulfur analyzer to determine the C content in the standard sample (the instrument can automatically subtract blank C content values ​​after setup). Select standard samples to establish a working curve. The C content ranges in the working curve are 0mg, 1mg, 5.3mg, 8.31mg, 11.31mg, and 30mg. Measure the intensity of C element in all standard samples using the carbon-sulfur analyzer, and plot a standard curve based on C content and the intensity of C element in the standard samples (see...). Figure 2 The relationship between intensity and concentration was obtained as y = -0.428 + 1.90x, R = 0.9997. The sample collected in step 3) was placed in a carbon-sulfur analyzer to measure the intensity of C element in the same way. Then, based on the constructed standard curve, the content of C element in different samples was calculated.

[0041] Table 1 Carbon content on the surface of hot-rolled steel plate

[0042]

[0043] Table 1 shows that sample #1 has an organic coating on its surface, while sample #2 does not. The carbon content in the coating of sample #1 is 7.5 g / m³. 2 .

[0044] Both sample #1 and sample #2 were suspended in an outdoor, sun-exposed area in Wuhan. The results are shown below. Figure 3 Within the same time period, the area of ​​rust spots on sample #1 with organic coating was significantly smaller than that on sample #2 without organic coating. Starting from week 4, almost the entire surface of sample #2 was corroded. However, under the protection of organic coating, the degree of corrosion on sample #1 increased slightly from week 4 to week 6, with the corrosion area being almost the same. The corrosion resistance of sample #1 was significantly better than that of sample #2.

[0045] Example 2

[0046] A method for detecting the carbon content on the surface of a hot-rolled steel plate with an organic coating, comprising the following steps:

[0047] 1) Provide two types of coated hot-rolled plates, No. 1 and No. 2. No. 1 sample uses coating A and No. 2 sample uses coating B. The sample size is 80mm×40mm. Use degreased gauze soaked in anhydrous ethanol to wipe the organic coating on the surface of No. 1 and No. 2 samples until the gray substrate is completely exposed on the sample surface. Weigh the No. 1 and No. 2 samples before and after the organic coating is applied. The results are shown in Table 2.

[0048] 2) After wiping off the organic coating, black substances were found on the sample surface after wiping with degreased gauze. The degreased gauze was then placed in 30 mL of anhydrous ethanol and sonicated for 5-10 minutes until the color of the degreased gauze remained unchanged. The degreased gauze was then removed.

[0049] 3) Rinse the degreased gauze 3-5 times with anhydrous ethanol, pour all the solution into a petri dish, place the petri dish on an alcohol lamp and heat until all the solution evaporates, tap the edge of the petri dish with a clean brush, and pour the collected sample into a ceramic crucible.

[0050] 4) Preheat the infrared carbon-sulfur analyzer for about 30 minutes before testing. Clean the tin granules with acetone using ultrasonic cleaning for 1-3 minutes, remove and dry them. Preheat the ceramic crucible for 15 minutes and set it aside after heating. Transfer the collected sample to the ceramic crucible and add about 1.000g of magnetic agent (iron powder), 0.2g of flux tin granules and 1.2000g of combustion aid to the ceramic crucible. Measure the blank C content value under the condition of no organic coating.

[0051] 5) Add 0.5000g of standard sample C obtained in step 3) to a heating container, and then add 1.000g of magnetic agent (iron powder), 1.2000g of combustion aid (tungsten granules), and 0.2g of flux (tin granules) sequentially. Place the container in an infrared combustion carbon-sulfur analyzer to determine the C content in the standard sample (the instrument can automatically subtract blank C content values ​​after setup). Select standard samples to establish a working curve. The C content ranges in the working curve are 0, 1mg, 5mg, 7mg, 10mg, and 15mg. Measure the intensity of C element in all standard samples using the carbon-sulfur analyzer, and plot a standard curve based on the C content and the C element intensity of the standard samples (see [link to standard curve]). Figure 4 The samples collected in step 3) were placed in a carbon-sulfur analyzer to measure the intensity of C element, and the content of C element in different samples was calculated based on the constructed standard curve.

[0052] Table 2 Carbon content on the surface of hot-rolled steel plates

[0053]

[0054] Table 2 shows that the carbon content in the coating of sample #3 is 3.081 g / m³. 2 The carbon content in the coating of sample #4 was 1.369 g / m³. 2 By comparing the C element content per unit area, it can be seen that the corrosion resistance of sample 1 is better than that of sample 2.

[0055] After sealing the edges of samples #3 and #4, they were placed in an outdoor drying area. Photos were taken at 0, 2, and 4 weeks to track the samples. The results are shown below. Figure 1 ,like Figure 1 As shown, after four weeks of outdoor exposure, sample #1 showed almost no obvious corrosion, while sample #2 showed noticeable rust spots starting from the second week of outdoor exposure, and by the fourth week, the rust spots were very prominent across the entire surface. This indicates that sample #1 exhibits better corrosion resistance than sample #2, which is consistent with the measured C content in the coating.

[0056] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concept, should be covered within the scope of protection of the present invention.

Claims

1. A method for detecting the carbon content on the surface of a hot-rolled coated steel plate, characterized in that, Includes the following steps: 1) Wipe the surface of the hot-rolled plate with degreased gauze containing organic solvent to remove the organic coating; the organic coating is a water-based epoxy resin coating; 2) Immerse the degreased gauze with the organic coating in an organic solvent and sonicate it to separate the degreased gauze from the organic coating, and then remove the gauze. 3) The remaining mixture obtained in step 2) is rinsed with an organic solvent and dried to obtain an organic coating film; 4) Add magnetic agent, combustion aid, and solvent to the heating container in sequence, and measure the blank carbon content value under the condition of no organic coating film introduction; 5) Place the organic coating film obtained in step 3) in a heating container, add a magnetic agent, a combustion aid and a solvent in sequence, and then place it in an infrared combustion carbon-sulfur analyzer to determine the carbon content in the sample; 6) Subtract the blank value obtained in step 4) from the carbon content obtained, and convert it into the content per unit area to obtain the carbon content per unit area of ​​the coated surface, and further determine the corrosion resistance of the hot-rolled coated plate. The organic solvent is an alcohol solvent or a ketone solvent; Step 3) The drying step uses a temperature of 30-40 ℃.

2. The detection method according to claim 1, characterized in that, Wipe-off extraction area of ​​organic coating on hot-rolled steel plate surface >1600 mm 2 .

3. The detection method according to claim 1, characterized in that, Step 2) The ultrasonic treatment step uses a power of 30-50 W / L and a time of 10-15 min.

4. The detection method according to claim 1, characterized in that, In step 4), the materials and their weight percentages include: 1.000-2.500 parts of magnetic agent, 1.5000-3.000 parts of combustion accelerator, and 0.15-0.40 parts of flux.

5. The detection method according to claim 1, characterized in that, The magnetic agent is iron powder; the combustion aid is tungsten granules; and the flux is tin granules.

6. The detection method according to claim 1, characterized in that, The thickness of the organic coating on the surface of the hot-rolled plate is less than 20 μm.

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