The Effect of Immersion Corrosion Time on Electrochemical Corrosion Behavior and the Corrosion Mechanism of EH47 Ship Steel in Seawater

Round 1

Reviewer 1 Report

The manuscript entitled „The effect of immersion corrosion time on the Electrochemical Corrosion Behavior and corrosion mechanism of EH47 ship steel in seawater” is relevant to the scope of this journal.

This is an interesting study that can provide interesting information to specialists.

However, several points need to be addressed prior to publication of this manuscript. My comments/suggestions are given:

1. Pay attention to how the title is written.
2. In my opinion, the introductory chapter is too broad, it could have been written a little more concisely.
3. In Materials chapter, the authors must specify how the chemical composition of the sample was determined.
4. Line 127 “Electrochemical impedance spectroscopy (EIS) was measured at an electrochemical workstation.” I think all the electrochemical tests were done on the electrochemical workstation. The authors must specify the type of potentiostat / galvanostat or electrochemical workstation was used.
5. Has no mechanical processing of the samples been performed before the electrochemical tests? Just “wiped with alcohol and acetone and washed with distilled water”? Then this must be specified. Is it safe to say "wiped"?
6. Line 131 “The test was carried out under the condition of open circuit potential, the scanning range was -200 ~ 200 mV relative to the open circuit potential” Must be reformulated! It cannot be understood! I think that at open circuit potential the EIS tests were done, and the scanning range is for the polarization curves…
7. Line 148 “Nyquist diagram of electrochemical impedance spectroscopy were measured”. I think the Zre and Zim values were measured and then represented as a Nyquist diagram. Reformulate.
8. Please explain how the corrosion value of the metal sample can influence the value of the open circuit potential. In electrochemistry, the notion of smaller or larger is not used for potential, but more electronegative or electropositive. The authors must correct.
9. How do you explain the shift to more electropositive values of the potential in open circuit from 28 to 49 days? Do you think that after this period the trend would continue?
10. Line 168 “cathodic polarization curve of 0 immersion day (no corrosion) is the shortest” ??? Please explain what you meant!
11. Line 172 “curves of the no corrosion sample”? Is it a non-corroded sample?
12. Line 177 “The polarization curve of the anode”? Explain!
13. Line 178 “passivation range is about 0.5 V” For whom? For the 14-day immersion test is shorter. Please reformulate!
14. The explanations given in 3.2.3 Nyquist diagram are insufficient and unclear. The data resulting from the electrochemical impedance spectroscopy tests must also be presented in the form of Bode diagrams because as they are in the Nyquist diagram, they do not seem to correlate with the results obtained from the polarization curves.
15. The experimental results from the EIS tests must be fitted with electrical equivalent circuits, obtained the specific parameters to each sample and, in this way, the behavior of the samples and the different interfaces that appear can be better understood and explained.
16. I think that XRD patterns for the other studied samples should be presented, because changes in composition could be observed…
17. In the legend of Figure 6 it must be explained what a, b, c and d mean respectively. Figure 6 shows optical microscopy or SEM images? Please specify!
18. Why were the immersion tests not performed at the same time intervals as the electrochemical ones?
19. In order to better elucidate which products appear on the surface of the samples after immersion and in the form of what salt the calcium ions appear, several analyzes should be made. Maybe XRD…
20. Conclusion 1 must be completed.
21. Where did the second conclusion come from? XRD tests were done only on the 49-day immersion test!
22. Some of the bibliographic references are a bit old and could be replaced with more recent ones.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

In the present manuscript Zhang et al. evaluate the effect of immersion corrosion time on the electrochemical corrosion behaviour and mechanism of EH47 steel in seawater. The topic is solid and of interest to the general readearship, and the presented data supports the conclusion. There are some points that need improvement, as follows:

1. Improvement of the figures. For example fig1 EDS spectra, replot to show only up to 10keV and make sure text is readable, or fig 7 (the different annotations below the SEM images or the EDS line scans are not required).
2. The XRD of the full immersion sample (fig 5) is quite noisy, so it is difficult to annotate the peaks. Authors should measure with a lower step.
3. No experimental data is provided for ALL the different characterization techniques (SEM, EDS, XRD, how were the cross-sections achieved, etc.), except from the electrochemical characterization.
4. Minor English corrections

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

1. Line 72: "increase of" should be "increase in"

- Please thoroughly check English for the manuscript.

2. Line 122: Author mention “marginal” Fe. Fe is the dominant element in steel. Why the author uses the word “marginal”?

3. The author mentions that the samples were immersed in the seawater for 0, 7, 14, and 49  days in Line 139. By the way, the author mentions that the samples were immersed in the seawater for 0, 14, 28, and 49 days. What is the correct information? It is confusing.

4. Line 174:, English is poor for this sentence. Please re-write it.

5. Line 183: How the author specifies the corrosion product (FeOOH) without the appropriate analysis? This should be mentioned with or after Figure 5.

6. Figure 6 should be placed before Figure 2. Therefore, it can support the author’s opinion in Line 200-206. Moreover, if the author can present the microstructural images for the porous corrosion layer, it might be helpful.

- Moreover, Figure 5 also should be place before Figure 2.

7. The author should present the Nyquist plot with full semicircle arcs.
- Is there any reason the author does not show the perfect semicircle arcs?
- At least, the author should give the information of Z values.

8. Thorough analysis is absent to characterize the corrosion products, which will support the corrosion mechanism.

9. Line 205: The author should present SEM or OM images for the pitting corrosion. 
- Moreover, the author should indicate black holes and cracks in the image.

 

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors made most of the required corrections, but there are still a few points that need to be resolved.

1. The explanation given for the question Q9 “How do you explain the shift to more electropositive values of the potential in open circuit from 28 to 49 days? Do you think that after this period the trend would continue?” from the previous review, it must be introduced in the text, with bibliographical references possibly.
   
   
2. The explanation given for question Q10 is not sufficient. “Line 168 “cathodic polarization curve of 0 immersion day (no corrosion) is the shortest” The scan could have started from much more electronegative potentials and then it was not the shortest…
   
   This statement must be removed!
   
   
3. Line 169 “the polarization curve of the anode zone”. I think it's the anodic polarization curve or the anodic branch of the polarization curve.
   
   
4. “The passivation range is about 0.5 V from -0.8 V to -0.3 V, and the polarization curve of the anode zone is obtained under 0, 7, 14, 49 immersion days tests.” The explanation is not enough. The authors must clearly specify the value of the passive domain for each immersion time because they are different. I recommend adding these values in Table 1.
   
   
5. I appreciate that the authors have fitted the experimental data with the proposed equivalent circuit. The error obtained should be added to the Table 2. You must also specify the software with which the data was fitted. The two proposed constant phase elements must be denoted CPE1 and CPE2 in order to avoid confusion. Attention line 223 Hz not HZ.

Author Response

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Reviewer 3 Report

1. Please clarify the meaning of Line 292
   - cannot understand the authors' intention.
   
   
2. Please present the low magnification of SEM images in Figure 9.
   - In high magnification of SEM images, it is difficult to define which one is a crack or hole.
   - Moreover, it is hard to insist those are occurred by the corrosion.
   
   
3. Please define the crevice corrosion in Line 302.
   
   
4. Microstructure characterization should be presented before the corrosion test.
    - First, the microstructure result should be presented, then the result of the corrosion test should be analyzed based on the microstructure characterization. the corrosion result should be 

Author Response

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Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

Thank you for your kind revision. The manuscript is well organized.

Author Response

Thank you.