In this paper, pulse laser cleaning and angle grinder polishing were used to clean the surface rust of carbon steel, and the cleaning effects of different cleaning methods for carbon steel surface rust were studied. The change of the micro-region morphology and element composition of the cleaned surface was analyzed. Comparative experiments were conducted on the corrosion resistance and paint anticorrosion ability of cleaned metal surfaces. Through comparison and analysis, the use of laser cleaning technology can improve the surface cleanliness and corrosion resistance of metals, reduce maintenance times, and extend service life. Laser cleaning machines with a power of 100 W or above can effectively perform precision cleaning and can be widely promoted in the field of power systems.

Topics
Surface states, Electric power, Power electronics, Corrosion, Materials treatment, Cement, Electrical conductor, Lasers, Solvents

A large number of metal materials are used in power systems. Due to the influence of the natural environment, these metal materials are corroded under the influence of various factors.1–3 Surface oxidation rust will seriously affect the quality and performance of metal materials. For outdoor steel structural parts, the traditional rust removal methods, such as grinding, require a large amount of manual work; the rust cleaning is uneven and incomplete and easily damages the substrate.4–6 Compared with the traditional rust removal methods, laser rust removal technology has more advantages in flexibility and accuracy, which is of great significance for reducing maintenance times and increasing the service life of steel structural parts.7,8

The samples used in the experiment are seriously corroded Q235 carbon steel. The main components of Q235 are Fe, C, Mn, and Si and also contain a small amount of impurity elements. The test sample sizes are 25 × 25 mm2 and 50 × 50 mm2, respectively.

Laser cleaning equipment is mainly composed of a laser, cleaning head, and control system. The laser output wavelength is 1064 nm, the output power is 25–250 W, and the power stability is ≥97%. The focal length of the laser field mirror is 330 mm, and the focal spot diameter is 0.1 mm. The surface of rusted carbon steel is cleaned by laser cleaning and angle grinder grinding. The parameters of the cleaning process and the effect after cleaning are shown in Table I.

TABLE I.

Cleaning process parameters and cleaning effect of the corroded Q235 steel plate.

Cleaning parametersBefore cleaningAfter cleaningRemarks
Power: 100 W   Cleaning time is about 30 s 
Speed: 5000 mm/s 
Frequency: 100 KHz 
Pulse width: 350 ns 
Power: 200 W   Cleaning time is about 16 s 
Speed: 5000 mm/s 
Frequency: 170 KHz 
Pulse width: 350 ns 
Power: 250 W   Cleaning time is about 10 s 
Speed: 5000 mm/s 
Frequency: 170 KHz 
Pulse width: 350 ns 
Angle grinder grinding treatment    
Cleaning parametersBefore cleaningAfter cleaningRemarks
Power: 100 W   Cleaning time is about 30 s 
Speed: 5000 mm/s 
Frequency: 100 KHz 
Pulse width: 350 ns 
Power: 200 W   Cleaning time is about 16 s 
Speed: 5000 mm/s 
Frequency: 170 KHz 
Pulse width: 350 ns 
Power: 250 W   Cleaning time is about 10 s 
Speed: 5000 mm/s 
Frequency: 170 KHz 
Pulse width: 350 ns 
Angle grinder grinding treatment    
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The carbon steel sample is taken from scrap steel. The surface is seriously rusted, and the large area of pitting corrosion is very serious. It can be seen from Table I that most of the surface after laser cleaning can expose the substrate, and only the deeper part of pitting corrosion (the black spot area after cleaning) is not completely cleaned. However, the surface of the sample grinded by the angle grinder is grayish black, and it is easy to damage the substrate by trying to grind it to a metallic color during the grinding process.

The SEM used in this paper has an error of 0.0054 µm and an uncertainty of 15.2 nm. Because the sample magnification is 100 µm, SEM errors and uncertainties can be ignored. There are several test samples, which can meet the test needs, and the state of each test sample is consistent. The image obtained by using a scanning electron microscope is the SEM image, and the image obtained by accompanying element analysis is the energy dispersive spectroscopy (EDS) image.

Figure 1 shows the SEM image of the corroded surface of carbon steel at a magnification of 100 µm. The sample is seriously rusted, and the surface is brittle and porous. Figure 2 shows the SEM image amplified by 100 µm after grinding by the angle grinder. Compared with the original state, it can be seen that the surface rust layer has been grinded off, and there are still large loose tissues after magnification, which is the reason why the rust layer has not been cleaned up.

FIG. 1.
SEM of the corroded surface of carbon steel.
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SEM of the corroded surface of carbon steel.

FIG. 1.
SEM of the corroded surface of carbon steel.
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SEM of the corroded surface of carbon steel.

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FIG. 2.
SEM of the corroded surface of carbon steel after grinding by using an angle grinder.
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SEM of the corroded surface of carbon steel after grinding by using an angle grinder.

FIG. 2.
SEM of the corroded surface of carbon steel after grinding by using an angle grinder.
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SEM of the corroded surface of carbon steel after grinding by using an angle grinder.

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Figures 3–5 show the SEM images amplified by 100 µm after laser cleaning of the corroded surface of carbon steel. It can be seen that there are very obvious laser spot traces on the rusted surface of the laser cleaning. There are some micro-pits in the laser spot traces, which may be caused by the multiple pulse laser irradiations at the overlap of the laser spot, causing the temperature of the overlap to increase, resulting in melting and rapid cooling. In addition, there are very few non-uniform areas, which should be the deeper part of pitting corrosion, so that they are not cleaned up.

FIG. 3.
SEM of the corroded surface of carbon steel after laser cleaning (100 W).
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SEM of the corroded surface of carbon steel after laser cleaning (100 W).

FIG. 3.
SEM of the corroded surface of carbon steel after laser cleaning (100 W).
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SEM of the corroded surface of carbon steel after laser cleaning (100 W).

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FIG. 4.
SEM of the corroded surface of carbon steel after laser cleaning (200 W).
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SEM of the corroded surface of carbon steel after laser cleaning (200 W).

FIG. 4.
SEM of the corroded surface of carbon steel after laser cleaning (200 W).
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SEM of the corroded surface of carbon steel after laser cleaning (200 W).

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FIG. 5.
SEM of the corroded carbon steel surface after laser cleaning (250 W).
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SEM of the corroded carbon steel surface after laser cleaning (250 W).

FIG. 5.
SEM of the corroded carbon steel surface after laser cleaning (250 W).
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SEM of the corroded carbon steel surface after laser cleaning (250 W).

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Figure 6 shows the SEM image of the original rust sample amplified by 100 µm, and Fig. 7 shows the element composition and relative content analysis image of the surface of the original rust sample. Among them, Fe, C, Mn, and Si are the elements contained in the carbon steel itself, while S, Cl, and Ca are all harmful impurities. The content of the Fe element on the surface of the rust sample is 62.59%, and the content of the O element is 29.57%. The main reason is that the rust mainly consists of Fe2O3 · nH2O and [FeO(OH), Fe(OH)3], resulting in a high O content.

FIG. 6.
The SEM diagram of the original rust sample.
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The SEM diagram of the original rust sample.

FIG. 6.
The SEM diagram of the original rust sample.
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The SEM diagram of the original rust sample.

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FIG. 7.
The element composition and relative content EDS analysis diagram.
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The element composition and relative content EDS analysis diagram.

FIG. 7.
The element composition and relative content EDS analysis diagram.
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The element composition and relative content EDS analysis diagram.

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Figure 8 shows the SEM image of the carbon steel rust amplified by 100 µm after grinding by using an angle grinder, and Fig. 9 shows the element composition and relative content of the carbon steel surface. The content of the Fe element is 67.53%, and the content of the O element is 27.04%. Compared with the original rust sample, the content of the Fe element is slightly increased, and the content of the O element is slightly decreased, which proves that the angle grinder only removes the surface rust layer, but the grinding is not thorough.

FIG. 8.
The SEM image of the carbon steel rust amplified by 100 µm after grinding by using an angle grinder.
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The SEM image of the carbon steel rust amplified by 100 µm after grinding by using an angle grinder.

FIG. 8.
The SEM image of the carbon steel rust amplified by 100 µm after grinding by using an angle grinder.
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The SEM image of the carbon steel rust amplified by 100 µm after grinding by using an angle grinder.

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FIG. 9.
The EDS element composition and relative content of the carbon steel surface.
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The EDS element composition and relative content of the carbon steel surface.

FIG. 9.
The EDS element composition and relative content of the carbon steel surface.
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The EDS element composition and relative content of the carbon steel surface.

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Figures 10–15 show the composition and relative content of the elements on the rust surface cleaned by laser. It can be seen that the surface rust of carbon steel is mainly composed of Fe, C, Mn, and Si elements after laser cleaning. The O element content is 3.78% (Fig. 11), 2.45% (Fig. 13) and 2.27% (Fig. 15), respectively. Compared with the original rust sample and the angle grinder grinding sample, the O content is greatly decreased, while the remaining 2%–3% O content may be a few deeper rust layers that have not been cleaned, and an oxide film may be formed on the surface of the sample after laser cleaning.

FIG. 10.
The SEM image of the carbon steel rust amplified by 100 µm after 100 W laser cleaning.
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The SEM image of the carbon steel rust amplified by 100 µm after 100 W laser cleaning.

FIG. 10.
The SEM image of the carbon steel rust amplified by 100 µm after 100 W laser cleaning.
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The SEM image of the carbon steel rust amplified by 100 µm after 100 W laser cleaning.

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FIG. 11.
The EDS element composition and relative content of the carbon steel surface after 100 W laser cleaning.
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The EDS element composition and relative content of the carbon steel surface after 100 W laser cleaning.

FIG. 11.
The EDS element composition and relative content of the carbon steel surface after 100 W laser cleaning.
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The EDS element composition and relative content of the carbon steel surface after 100 W laser cleaning.

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FIG. 12.
The SEM image of the carbon steel rust amplified by 100 µm after 200 W laser cleaning.
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The SEM image of the carbon steel rust amplified by 100 µm after 200 W laser cleaning.

FIG. 12.
The SEM image of the carbon steel rust amplified by 100 µm after 200 W laser cleaning.
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The SEM image of the carbon steel rust amplified by 100 µm after 200 W laser cleaning.

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FIG. 13.
The EDS element composition and relative content of the carbon steel surface after 200 W laser cleaning.
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The EDS element composition and relative content of the carbon steel surface after 200 W laser cleaning.

FIG. 13.
The EDS element composition and relative content of the carbon steel surface after 200 W laser cleaning.
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The EDS element composition and relative content of the carbon steel surface after 200 W laser cleaning.

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FIG. 14.
The SEM image of the carbon steel rust amplified by 100 µm after 250 W laser cleaning.
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The SEM image of the carbon steel rust amplified by 100 µm after 250 W laser cleaning.

FIG. 14.
The SEM image of the carbon steel rust amplified by 100 µm after 250 W laser cleaning.
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The SEM image of the carbon steel rust amplified by 100 µm after 250 W laser cleaning.

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FIG. 15.
The EDS element composition and relative content of the carbon steel surface after 250 W laser cleaning.
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The EDS element composition and relative content of the carbon steel surface after 250 W laser cleaning.

FIG. 15.
The EDS element composition and relative content of the carbon steel surface after 250 W laser cleaning.
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The EDS element composition and relative content of the carbon steel surface after 250 W laser cleaning.

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Figure 16 shows the columnar comparison of the content of Fe and O elements on the surface of the samples under different states. There are five samples for each type of experiment. After the experiment, the content of Fe and O elements in each sample is shown in Fig. 16. It can be seen from Fig. 16 that all three power laser cleaning methods can greatly reduce the oxygen content of the sample surface, increase the iron content, and expose the true color of the metal. Compared to angle grinder grinding, laser cleaning rust is more thorough.

FIG. 16.
The columnar comparison of the content of Fe and O elements on the surface of the samples under different states.
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The columnar comparison of the content of Fe and O elements on the surface of the samples under different states.

FIG. 16.
The columnar comparison of the content of Fe and O elements on the surface of the samples under different states.
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The columnar comparison of the content of Fe and O elements on the surface of the samples under different states.

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In order to compare the corrosion resistance performance of the cleaned metal surface, the test is carried out in two methods. The first method is that the sample is placed in a natural state, the angle grinder grinding sample and the laser cleaning sample are placed in the same natural environment, and the sample is sprayed with water mist at the same time every day. The water mist is the non-salt “spray fog” composed of distilled water.

Figure 17 shows the comparison of the corrosion status of the samples with different cleaning methods after one week in the natural environment. The surface of the sample cleaned by laser is partially rusted, but most of it still maintains the true color of the metal. The surface of the sample grinded by using the angle grinder has more corroded parts, and the degree of corrosion is larger, showing a flaky oxidation state. The electronic scanning mirror can only scan a local point, and the surface of the re-corroded sample presents a non-uniform corrosion state, which cannot accurately obtain the overall corrosion state of the sample through component analysis. Therefore, image analysis is used for qualitative judgment.

FIG. 17.
The comparison of the corrosion status of the samples: (a) Laser cleaning sample. (b) Angle grinder grinding the sample.
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The comparison of the corrosion status of the samples: (a) Laser cleaning sample. (b) Angle grinder grinding the sample.

FIG. 17.
The comparison of the corrosion status of the samples: (a) Laser cleaning sample. (b) Angle grinder grinding the sample.
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The comparison of the corrosion status of the samples: (a) Laser cleaning sample. (b) Angle grinder grinding the sample.

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Another method is to use a salt spray testing machine for the salt spray test. The spray solution concentration is 50 g/l NaCl solution. The grinding sample of angle grinder and the laser cleaning sample are put into the salt spray testing machine at the same time for the spray corrosion test. The 24 h salt spray test is equivalent to one year in the natural environment. Figure 18 shows the image of samples with different cleaning methods after 4 and 8 h salt spray tests, respectively. It can be seen from Fig. 18 that the surface of samples has been rusted, but the corrosion degree is different. After the salt spray test, the surface of the laser cleaned sample is basically in a floating rust state. The surface rust of the angle grinder grinded sample is flaky, and the surface oxide is about to be peeled off or scraped off.

FIG. 18.
Comparison of the surface state: (a) Laser cleaning sample. (b) Angle grinder grinded sample. (c) Laser cleaning sample after the 4 h salt spray test. (d) Angle grinder grinded sample after the 4 h salt spray test. (e) Laser cleaning sample after the 8 h salt spray test. (f) Angle grinder grinded sample after the 8 h salt spray test.
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Comparison of the surface state: (a) Laser cleaning sample. (b) Angle grinder grinded sample. (c) Laser cleaning sample after the 4 h salt spray test. (d) Angle grinder grinded sample after the 4 h salt spray test. (e) Laser cleaning sample after the 8 h salt spray test. (f) Angle grinder grinded sample after the 8 h salt spray test.

FIG. 18.
Comparison of the surface state: (a) Laser cleaning sample. (b) Angle grinder grinded sample. (c) Laser cleaning sample after the 4 h salt spray test. (d) Angle grinder grinded sample after the 4 h salt spray test. (e) Laser cleaning sample after the 8 h salt spray test. (f) Angle grinder grinded sample after the 8 h salt spray test.
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Comparison of the surface state: (a) Laser cleaning sample. (b) Angle grinder grinded sample. (c) Laser cleaning sample after the 4 h salt spray test. (d) Angle grinder grinded sample after the 4 h salt spray test. (e) Laser cleaning sample after the 8 h salt spray test. (f) Angle grinder grinded sample after the 8 h salt spray test.

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After cleaning the rusted surface of carbon steel, it is necessary to spray paint. According to ISO 12944 and the application environment requirements, a coating system with C3 corrosion environment and medium anticorrosion life (5–15 years) is selected. The coating method of epoxy zinc-rich primer + polyurethane top paint is used for spray painting. Two scratches are made on the surface of the painted sample, which are in the shape of “X.” The scratches penetrate through the coating to the substrate, and then, the salt spray test is carried out. Figure 19 shows the images of samples with different cleaning methods after 4, 8, and 12 h salt spray tests, respectively.

FIG. 19.
The images of paint samples with different cleaning methods after 4, 8, and 12 h salt spray tests: (a) angle grinder after 4 h; (b) angle grinder after 8 h; (c) angle grinder after 12 h; (d) laser cleaning after 4 h; (e) laser cleaning after 8 h; and (f) laser cleaning after 12 h.
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The images of paint samples with different cleaning methods after 4, 8, and 12 h salt spray tests: (a) angle grinder after 4 h; (b) angle grinder after 8 h; (c) angle grinder after 12 h; (d) laser cleaning after 4 h; (e) laser cleaning after 8 h; and (f) laser cleaning after 12 h.

FIG. 19.
The images of paint samples with different cleaning methods after 4, 8, and 12 h salt spray tests: (a) angle grinder after 4 h; (b) angle grinder after 8 h; (c) angle grinder after 12 h; (d) laser cleaning after 4 h; (e) laser cleaning after 8 h; and (f) laser cleaning after 12 h.
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The images of paint samples with different cleaning methods after 4, 8, and 12 h salt spray tests: (a) angle grinder after 4 h; (b) angle grinder after 8 h; (c) angle grinder after 12 h; (d) laser cleaning after 4 h; (e) laser cleaning after 8 h; and (f) laser cleaning after 12 h.

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Comparing the surface state of the two groups of samples after the salt spray test, it can be found that the corrosion rate of the paint sample after laser cleaning is significantly lower than that of the sample treated by the angle grinder, and the corrosion degree is also smaller, indicating that the sample after laser cleaning has better corrosion resistance performance.

  1. Pulse lasers can effectively clean the rust on the surface of carbon steel. The relative content of the Fe element on the surface of the sample after cleaning is very high, reaching over 90% from 62% before cleaning, and the relative content of the oxygen element is reduced from 29% to 2%–3%, which means that the rust on the surface of carbon steel can be cleaned by laser. The angle grinder can only grind the floating rust on the surface of the sample, and the content of Fe and oxygen on the surface of the grinded sample is about 68% and 27%, respectively.

  2. The corrosion resistance of the cleaned carbon steel samples was tested by the natural environment corrosion test and artificial salt spray corrosion test, respectively. Compared with the samples cleaned by laser, the samples grinded by using the angle grinder rusted faster and more seriously.

  3. The cleaned carbon steel surface is sprayed with matching paint according to the corrosion environment of class C3 and medium life (5–15 years), and then the salt spray test is carried out. Similarly, compared with the samples after laser cleaning, the paint samples after angle grinder grinding are rusted faster and more seriously, indicating that the corrosion resistance performance of the samples after laser cleaning has been significantly improved.

This work was supported by The Operation and Maintenance Cost Project of State Grid Hubei Electric Power Co., Ltd. (Project No. SGTYHT/21-JS-226).

The authors have no conflicts to disclose.

Yuhang He: Conceptualization (equal). Xuan Cai: Data curation (equal). JianfengYe: Formal analysis (equal).

The data that support the findings of this study are available from the corresponding author upon reasonable request.

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