Corrosion Behavior of AISI 904L Austenitic Stainless Steel in High-Temperature and High-Pressure Water Environment

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The study (metals-4114443) addresses a relevant topic for nuclear materials; however, key conclusions particularly regarding SCC susceptibility are not completely supported by the presented data. Significant clarification, additional quantitative analysis, and revision of over-stated claims are required before the manuscript can be considered for publication.

 

The English is generally understandable and suitable for technical communication; however, it requires moderate language polishing. Issues include repetitive phrasing, long sentences, occasional grammatical errors, and inconsistent terminology. Professional language editing is recommended to improve clarity and conciseness.

 

1. The manuscript repeatedly discusses stress corrosion cracking (SCC) susceptibility; however, no actual cracks are observed in the U-bend tests after 1500 h. The conclusions on SCC resistance are therefore not sufficiently supported. Quantitative SCC metrics (crack density, crack length, crack depth, or time-to-failure) are required, or the claims must be significantly softened.
2. Despite stating “varying degrees of SCC susceptibility,” the U-bend results explicitly show no visible cracks for all microstructures. This internal inconsistency must be resolved, either by redefining SCC susceptibility indicators or by revising the interpretation.
3. The applied stress level in the U-bend specimens is not quantified (like strain level, stress calculation, or standard followed). Without stress quantification, SCC relevance and comparison with literature data are limited.
4. Fast-scan polarization curves are interpreted as representative of crack-tip chemistry, yet no direct validation (for example: fractured samples, in-situ crack monitoring, or literature justification specific to 904L) is provided. This extrapolation requires stronger justification or should be toned down.
5. Sensitization is inferred mainly from grain boundary corrosion appearance and general arguments. There is no direct evidence of chromium depletion or carbide/σ-phase formation (like TEM, EDS line scans, DL-EPR, or EBSD). This weakens the mechanistic conclusions.
6. Several fitted parameters such as extremely large or very small resistance values and n ≈ 1 in multiple cases are reported without discussing their physical meaning or fitting quality (χ², residuals). The robustness of the EIS modeling must be addressed.
7. The stated polarization range (-1.5 to +2 V vs. Ag/AgCl) at high temperature and pressure is unusually wide and may induce non-relevant reactions (water decomposition, severe trans-passive effects). The rationale for this range must be justified.
8. While 904L is less studied than 304/316, the experimental approach (polarization + EIS + U-bend) and conclusions largely confirm well-known trends (temperature effect, sensitization degradation). The manuscript needs a clearer statement of what is new compared with prior studies.
9. The discussion of passive films relies only on SEM morphology and thickness observations. No chemical or phase analysis (XPS, Raman, TEM-EDS) is provided to support claims about oxide composition or protectiveness.
10. Although tests are said to be repeated three times, no error bars, standard deviations, or statistical analysis are presented in figures or tables. This limits confidence in comparisons between microstructures.
11. Make sure all figures are well-presented and clear. Pay attention to captions to include all necessary data and information.

Comments on the Quality of English Language

The English is generally understandable and suitable for technical communication; however, it requires moderate language polishing. Issues include repetitive phrasing, long sentences, occasional grammatical errors, and inconsistent terminology. Professional language editing is recommended to improve clarity and conciseness.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript presents an interesting and potentially original study; however, substantial revisions are required before it can be considered for publication. My detailed comments are provided below.

 

First, 904L appears to be an AISI designation. Please clearly state the corresponding standard designation in the title and consistently throughout the manuscript.

 

The email address format will be specified by the Editor. Nevertheless, the authors are advised to revise it in advance according to the journal’s standard formatting used in previously published papers.

 

The abstract currently describes mainly the authors’ intentions. An abstract should concisely summarize the background, experimental methodology, and main results. Please revise the abstract accordingly so that readers can clearly understand the purpose, methods, and key findings of this study.

 

Although the application fields of 904L stainless steel can be inferred, the introduction lacks logical structure and contains mixed statements. The introduction should be reorganized in the following order:

(1) service environments and industrial necessity of 904L,

(2) differences between conventional materials and 904L,

(3) key characteristics of 904L,

(4) limitations and technical issues of this alloy, and

(5) alternative design strategies and research direction addressed in this study.

 

Please present the chemical composition of 904L in a table using standard notation.

 

The experimental procedure should be illustrated as a schematic diagram arranged in chronological order. The figure should clearly indicate what was done, how it was performed, and for what purpose at each step.

 

In the experimental methods section, the manuscript only describes how the experiments were conducted. Please add an explanation of why each analysis was selected before describing the experimental procedures.

 

The manuscript states that a three-electrode cell was used at 325 °C. This is not clear. Was the electrochemical experiment actually performed at this temperature? If so, please explain in detail how this was technically achieved and under what conditions.

 

A non-conventional electrolyte solution was used in this study. Please clearly justify why this solution was selected and explain its relevance to the research objective.

 

The frequency unit used in the EIS analysis is incorrect and must be corrected.

 

Figure 1 should be replaced with a properly etched microstructure. In its current form, grain boundaries are not distinguishable, which significantly reduces the scientific value of the image.

 

All figure captions should be strengthened to clearly specify experimental conditions and observation details.

 

At sensitization temperatures, secondary phase precipitation is generally expected. However, no secondary phases are observed in the XRD results. Please explain the reason for this and revise the discussion based on a correct understanding of sensitization temperature and precipitation behavior.

 

The heat-treatment effect images lack explanation. Please describe why the observed differences occur and which mechanisms are responsible.

 

The caption of Figure 3 is unclear and should be completely rewritten for proper understanding.

 

Several chemical equations contain significant errors. Although Mn and Mo have low electrochemical potentials, they are not included in the reaction expressions. If chemical equations are used to support the discussion, all major alloying elements must be considered.

 

Please clarify the numbering and structure of Table 2, as it is currently confusing.

 

The interpretation of EIS results is incorrect. The manuscript does not clearly explain why Rs appears multiple times, nor does it define the physical meaning of Qf. The EIS analysis must be fundamentally revised.

 

Please specify which area was observed in Figure 5.

 

The Results and Discussion section is not logically developed, and the Conclusion section is incomplete. Both sections require substantial revision to clearly interpret the results and summarize the study.

Comments on the Quality of English Language

The authors are strongly encouraged to revise the manuscript with careful reference to existing literature and to seek guidance from an experienced supervisor or senior researcher.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

In this paper, the authors studied the corrosion resistance of 904L austenitic stainless steel in as-received, sensitized, and solution-treated states. Corrosion was studied electrochemically in pressurized aqueous solutions of LiOH and H₃BO₃ at 25-325 ° C. The results are interesting and worthy of publication subject to revision. The following comments should be considered:

1.It would help to provide the chemical composition of 904L austenitic stainless steel in tabular form.

2.The sentences on lines 80-82 should be rewritten in past tense.

3.The authors measured open-circuit potentials (line 103); however, data is not presented. The OCP results should be included in the manuscript.

4.The potentiodynamic curves given in Fig. 3 are indicated as “slow-scan” and “fast-scan”. However, the scanning rate is not indicated. You should specify it in the figure caption.

5.Similarly, it is not clear to which data the parameters in Table 2 belong. It must be specified.

6.Since you measured the corrosion current density at different temperatures, you should estimate the activation energy of the corrosion reaction.

7.The corrosion products indicated in Equations 1 – 6 should be verified using XRD and/or XPS.

8.You should provide EDS line scans/maps of the elements in addition to Figs. 5g-i to verify the corrosion products.

9.Scale bars in Figs. 5g-i should be enlarged as they are difficult to read.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

See attached file

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Professional language editing is recommended to improve clarity and conciseness.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Please check whether the grammar of the title is appropriate and revise it.

 

In the first sentence of the abstract, please add a statement explaining why this research is necessary. What you have written describes only the objective of what you intend to do, not the motivation or necessity of the study.

 

In the experimental section, you mention several analytical tools. Please add an analysis explaining why each of these techniques is required. Statements such as “SEM was conducted” or “XRD was performed” do not provide any scientific value on their own.

 

In Figure 4, your corrosion test results are terminated at different applied voltages. What is the reason for this? Please clearly explain why the experiments were terminated at different voltages and add this explanation to the manuscript.

 

Please revise the figure captions properly. Clearly describe what each subfigure ((a), (b), etc.) represents. Do not describe them as ranges.

 

You included chemical formulas for Fe, Mn, and Ni. However, there is no alloy element that corrodes faster than Cr except for Mn, and stainless steels are protected by a Cr-based oxide layer. Nevertheless, you excluded Cr from your discussion. Please provide an appropriate explanation for this choice and add it to the manuscript.

 

Please add a Bode plot to the EIS results.

 

Your conclusion does not appear to be a conclusion. This is a result of insufficient discussion. Please strengthen the discussion section. Review existing literature and refer to how other authors structure and write their discussion sections.

Comments on the Quality of English Language

The authors are strongly encouraged to revise the manuscript with careful reference to existing literature and to seek guidance from an experienced supervisor or senior researcher.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors partially answered my previous comments. The paper has been improved. However, few amendments are still necessary:

1.Some corrosion potentials (E_corr) in Table 2 are apparently not correct as they do not correspond to Fig. 4. The values in Table 2 are all positive. However, E_corr values for 250 and 325 °C should be negative, see Figs. 4b and 4c. You should double check the signs of E_corr in Table 2.

2.The scanning rate must be specified in the caption of Table 2. You should use slow scan data (Figs. 4a-c) to obtain the E_corr, j_corr and E_tp (Table 2). The fast scan data (Figs. 4d-e) have been measured at 50 mV/s, which is an extremely large sweeping rate. The fast scan data do not correspond to steady state.

3.The red and blue dots in Fig. 5 are invisible. Furthermore, the green dots are too high. They do not correspond to the green fitting line. Double-check the figure.

4.Corrosion products have not been verified since you have not included any XRD, EDS, XPS data of the corrosion products in the manuscript. Therefore, you should be careful with equations (5) – (11). You should either provide a solid experimental evidence or remove the equations.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 3

Reviewer 1 Report

Comments and Suggestions for Authors

Authors replied to most comments in a good way.

The equations on page 10 lines 293 onward need attention. Discuss in the text. refer to. and improve the chemical writing! For example Fe -2e is strangely reported!

Comments on the Quality of English Language

Professional language editing is recommended to improve clarity and conciseness.

Author Response

Dear Editors and Reviewers:

     Thank you for your letter and for your comments concerning our manuscript entitled “Corrosion behavior of AISI 904L austenitic stainless steel in high-temperature and high-pressure water environment” (metals-4114443-re). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied these comments carefully and have made corrections which we hope meet with approval. Changes are highlighted with yellow background in the revised version again. The main corrections in the paper and the responses to the reviewers’ comments are as following: 

The equations on page 10 lines 293 onward need attention. Discuss in the text. refer to. and improve the chemical writing! For example Fe -2e is strangely reported!

Reply: Thank you for your comment. Based on the formula you mentioned, we have elaborated, cited, and explained it in the manuscript in conjunction with our electrochemical test results, so that the formula serves to logically connect and interpret the results. In addition, we have also optimized the relevant chemical formulas to make their notation more standardized.

 

Reviewer 2 Report

Comments and Suggestions for Authors

No review has been carried out, and the identified issues have not been resolved; therefore, this is difficult to accept.

Comments on the Quality of English Language

The authors are strongly encouraged to revise the manuscript with careful reference to existing literature and to seek guidance from an experienced supervisor or senior researcher.

Author Response

Dear Reviewer:

     Thank you for your letter and for your comments concerning our manuscript entitled “Corrosion behavior of AISI 904L austenitic stainless steel in high-temperature and high-pressure water environment” (metals-4114443-re). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied these comments carefully and have made corrections which we hope meet with approval. Changes are highlighted with yellow background in the revised version again. The main corrections in the paper and the responses to the reviewers’ comments are as following: 

 

No review has been carried out, and the identified issues have not been resolved; therefore, this is difficult to accept.

Reply: Thank you for your comment. Regarding the issues you mentioned that “the problems identified have not yet been resolved,” we have re-examined and reflected on the suggestions you provided in the previous version and have revised the manuscript again based on your advice, mainly involving the following content:

 

1. You mentioned, “In the first sentence of the abstract, please add a statement explaining why this research is necessary. What you have written describes only the objective of what you intend to do, not the motivation or necessity of the study.” Based on this, we have added a statement to the first sentence of the abstract to explain the necessity of this research. The added content is: “AISI 904L stainless steel (904L SS) is a promising material for nuclear power plant primary circuits due to its superior corrosion resistance, but its behavior under simulated high-temperature, high-pressure water environments with different microstructures remains poorly understood.”
2. You mentioned, “Clearly describe what each subfigure ((a), (b), etc.) represents. Do not describe them as ranges.” Based on this, we have revised the descriptions of Figures 4 and 8. The description of Figure 4 has been changed to: “Figure 4. The slow-scan (0.5 mV/s) polarization curves of (a) solid solution treated samples, (b) as-received state samples, and (c) sensitized samples, and the fast-scan (50 mV/s) polarization curves of (d) solid solution treated samples, (e) as-received state samples, and (f) sensitized samples in the test solution at four different temperatures.” The description of Figure 8 has been changed to: “Figure 8. Macroscopic morphologies of U-bend specimens of (a) as-received, (b) sensitized, and (c) solution-treated, and microscopic surface morphologies of specimens of (d) as-received, (e) sensitized, and (f) solution-treated, and microscopic cross-sectional morphologies of specimens of (g) as-received, (h) sensitized, and (i) solution-treated of AISI 904L stainless steel after immersion in the test solution for 1500 h.”
3. You mentioned, “The discussion is insufficient. Please strengthen the discussion section.” Based on this, we have combined the electrochemical results, the characterization results after immersion, and the kinetic calculation results to discuss the main point that “AISI 904L stainless steel, although its corrosion resistance decreases with temperature after solution treatment, still has the capability to serve in the high-temperature and high-pressure environment of nuclear power plant primary circuit piping.” In addition to the previous version of the manuscript, we have also added a comparison discussion between AISI 904L stainless steel and 304 and 316/316L stainless steels to enhance the sufficiency of the discussion.

In addition to the revisions made to the discussion section, we have also thoroughly revised the conclusion section to ensure that it corresponds with the discussion section and maintains logical consistency.