Effect of Nitrogen Content on the Cavitation Erosion Resistance of 316LN Stainless Steel

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors presented the cavitation erosion of 316LN Stainless Steel with different Nitrogen content. The topic is  relevant to the current research trend in cavitation erosion resistance of steels. The work demonstrates solid experimental effort and attempts to correlate experimental observations with a regressions equations. The manuscript scope is appropriate to the aim of the journal. The conclusions are supported by experimental results. The structure of the manuscript is proper. The reader will discover the meaning behind the title. The references are chosen correctly. However, there are some shortcomings as follows:

1. Line 77. The abbreviation EDM should be explained.
2. Line 88. The equation in the text should be written separately with a number.
3. Chapter 3.1. More information about the estimating regression equation. What is the mean square error? What statistical method was used? For which ranges of N can the formula be used? Is there a minimum of mass loss?
4. Chapter 3.2. More information about the estimating regression equation. What is the mean square error? What statistical method was used? For which ranges of N can the formula be used? Is there a minimum of surface roughness?
5. Chapter 4. More information about the estimating regression equation. What is the mean square error? What statistical method was used? For which ranges of N can the formula be used?

Author Response

Manuscript No.: metals-3962773  

Response to Reviewers

Thanks to editor and reviewers for the thoughtful and thorough review. Their comments are most helpful in revising the paper and our future work. We have studied their comments carefully and have made correction which we hope meet with their approval. Below are our responses to the comments. The section, figure and paragraph numbers refer to our revised manuscript.

 

Reviewer #1:

 

The authors presented the cavitation erosion of 316LN Stainless Steel with different Nitrogen content. The structure of the manuscript is proper. The reader will discover the meaning behind the title. The references are chosen correctly.

Response: Thanks！

 

 

1.Line 77. The abbreviation EDM should be explained.

Response: we have added the corresponding explanations to the revised manuscript. (Section 2.2, line 96)

 

 

2.Line 88. The equation in the text should be written separately with a number.

Response: We have numbered the equation in the revised manuscript. (Section 2.2, line 117)

 

 

3.Chapter 3.1. More information about the estimating regression equation. What is the mean square error? What statistical method was used? For which ranges of N can the formula be used? Is there a minimum of mass loss?

 

Response: We appreciate the reviewer’s insightful comment. In the revised manuscript, we have added detailed information regarding the regression method, fitting accuracy, and applicability range. Specifically, the cumulative mass loss versus nitrogen content was fitted using a nonlinear least-squares exponential regression method. The regression equation, coefficient of determination (R²), and mean square error (MSE) have now been provided. We also clarified that the model is valid within the investigated nitrogen content range (0.008–0.34 wt.%), and that the exponential function reflects the experimental trend rather than indicating a theoretical minimum mass loss. These additions can be found in Section 3.1 (lines 171–175).

 

 

4.Chapter 3.2. More information about the estimating regression equation. What is the mean square error? What statistical method was used? For which ranges of N can the formula be used? Is there a minimum of surface roughness?

 

Response: We have added additional details on the regression analysis in Section 3.2. The Ra–N relationship was fitted using a nonlinear least-squares exponential regression model, The goodness-of-fit was high (R² = 0.99), with a mean square error of approximately 0.27 μm². The equation is applicable within the experimental nitrogen range of 0.008–0.34 wt.%. Within this range, no minimum surface roughness value was reached, as Ra continuously decreased with increasing nitrogen content. The corresponding clarification has been incorporated into the revised manuscript. (Section 3.2, line 200-205)

 

 

5.Chapter 4. More information about the estimating regression equation. What is the mean square error? What statistical method was used? For which ranges of N can the formula be used?

 

Response: We appreciate the reviewer’s comment. Additional statistical details have now been provided in the revised manuscript. The nitrogen–hardness regression was obtained using a nonlinear least-squares fitting method. The fitted model exhibits a high coefficient of determination (R²=0.99) and a mean square error of approximately

12 HV². The equation is valid within the experimental nitrogen range of 0.008–0.34 wt.%. These clarifications have been added in Chapter 4. (Section 4, line 306-308)

 

 

Hopefully we have addressed all of your concerns.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors.

The paper titled “Effect of Nitrogen Content on the Cavitation Erosion Resistance of 316LN Stainless Steel" presents the original paper but the revision should be done. The paper must be revised to improve the quality of presentation and understanding based on the following comments that also written in the pdf of the paper:

1. Please add information and references to support why the authors chose the variation of nitrogen from 0.008 to 0.34 wt.% not 0.5% [Line 61]
2. It should be written as (30 mm x 30 mm x 30 mm) [Line 72]
3. Please explain in detail hot to obtain total reduction of 60%, how many % reduction made for each pass of rolling process. [Line 73]
4. Please write the procedures to perform solution-treatment on the specimens. [Line 73]
5. Please write as diameter symbol 10 mm x 3 mm [Line 77]
6. Why did the authors select the certain values of the variables? Are there any supporting references? [Line 78-80]
7. This section should written before section after 24 h cavitation. [Line 192-235]
8. Please explain in the method section, how to do low-strain tensile deformation with 2.5% strain. Why was 2.5% chosen? Was it done in the TEM chamber? [Line 258]
9. Why did twin boundaries come out in this state? [Line 263]
10. Please make contrast on legend in the photographs to be easily seen. [Line 268]
11. From Figure 8, please explain more detail how to evaluate that the martensite fraction increased with nitrogen content [Line 282-286]
12. Please add discussion about the position of Nitrogen in the materials based on EDS or other observation and its role to improve the properties of 316LN steels, and add it in the conclusion section. [Line 236-314]
13. Please add conclusion about the position and role of Nitrogen to improve 316LN stainless steel. [Line 315-332]
14. Please revise the paper based on the above comments and in the paper. Please highlight the revised part with green color and to be resubmitted again.

 

Kind regards,

Comments for author File: Comments.pdf

Author Response

Manuscript No.: metals-3962773  

Response to Reviewers

Thanks to editor and reviewers for the thoughtful and thorough review. Their comments are most helpful in revising the paper and our future work. We have studied their comments carefully and have made correction which we hope meet with their approval. Below are our responses to the comments. The section, figure and paragraph numbers refer to our revised manuscript.

 

Reviewer #2:

 

1.Please add information and references to support why the authors chose the variation of nitrogen from 0.008 to 0.34 wt.% not 0.5% [Line 61]

 

Response: We appreciate the reviewer’s insightful comment. The upper limit of nitrogen content (0.34 wt.%) was selected based on the solid solubility limit of nitrogen in Fe–Cr–Ni austenitic steels under pressurized melting conditions. When the nitrogen content exceeds approximately 0.35–0.40 wt.%, Cr₂N precipitates easily during solidification or subsequent thermal processing, leading to chromium depletion along grain boundaries and deterioration in corrosion and mechanical properties. Therefore, 0.34 wt.% was selected as the upper nitrogen level to avoid nitride precipitation and ensure a fully austenitic matrix. Corresponding explanation and references have been added to the revised manuscript. (Section 1, line 60-64)

 

 

2.It should be written as (30 mm x 30 mm x 30 mm) [Line 72]

 

Response: The dimensions of the cast billets have been revised to “30 mm × 30 mm × 30 mm”. (Section 2.1, line 86)

 

 

3.Please explain in detail hot to obtain total reduction of 60%, how many % reduction made for each pass of rolling process. [Line 73]

 

Response: In this study, the total thickness reduction of approximately 60% was achieved through multiple passes. Specifically, the steel billet was heated to 1100 °C and hot-rolled in four passes, with approximate thickness reductions of 20%, 15%, 15%, and 10% in sequence. This information has now been added to the revised manuscript. (Section 2.1, line 87-88)

 

 

4.Please write the procedures to perform solution-treatment on the specimens. [Line 73]

 

Response: We have revised the manuscript to clarify the solution-treatment process. Specifically, all specimens were solution-treated using corresponding temperatures and holding times to obtain a fully austenitic microstructure and uniform initial grain size. The detailed heating parameters are provided in Table 2. (Section 2.1, line 93)

 

 

5.Please write as diameter symbol 10 mm x 3 mm [Line 77]

 

Response: The notation has been revised accordingly in the revised manuscript. (Section 2.2, line 96)

 

 

6.Why did the authors select the certain values of the variables? Are there any supporting references? [Line 78-80]

 

Response: We have clarified the basis for selecting the cavitation testing parameters in the revised manuscript. The vibration frequency (20 kHz), amplitude (20 μm), specimen–horn distance (0.5 mm), and controlled temperature (25 ± 1 °C) were chosen according to the standard vibratory cavitation erosion testing procedure, ASTM G32-2016. These conditions are widely used to evaluate the cavitation erosion resistance of metallic materials and ensure reproducibility of results. Additionally, related supporting references have now been included. (Section 2.2, line107-111).

 

 

7.This section should written before section after 24 h cavitation. [Line 192-235]

 

Response: We agree that the short-term cavitation results should precede the 24 h cavitation morphology for better logical flow. Therefore, the original Section 3.4 has been moved before the original Section 3.3, and section numbering has been updated accordingly in the revised manuscript.

 

 

8.Please explain in the method section, how to do low-strain tensile deformation with 2.5% strain. Why was 2.5% chosen? Was it done in the TEM chamber? [Line 258]

 

Response: The 2.5% tensile deformation was performed ex-situ using a standard uniaxial tensile testing machine (not in the TEM chamber). The strain value of 2.5% was selected to introduce early-stage dislocation structures while avoiding significant strain-induced martensite formation. The corresponding experimental details have now been added to the Methods section. (Section 2.3, line 128-133).

 

 

9.Why did twin boundaries come out in this state? [Line 263]

 

Response: Thank you for pointing this out. The use of “twin boundaries” in this sentence was incorrect. No deformation twins were observed in the micrographs at this deformation level. The intended description refers to dislocation pile-up at grain boundaries, not twin boundaries. (Section 4, line 326).

 

 

10.Please make contrast on legend in the photographs to be easily seen. [Line 268]

 

Response: We have improved the contrast and visibility of the legends in the relevant figures to ensure clearer identification. (Section 4, line 331).

 

 

11.From Figure 8, please explain more detail how to evaluate that the martensite fraction increased with nitrogen content [Line 282-286]

 

Response: We have now clarified how the martensite fraction was evaluated. Specifically, the martensite fraction in Figure 8 was quantified based on the area percentage of the martensitic phase in the EBSD phase maps, where austenite and martensite are distinguished by color contrast. This explanation has been added to the revised manuscript. (Section 4, line 358-360).

 

 

12.Please add discussion about the position of Nitrogen in the materials based on EDS or other observation and its role to improve the properties of 316LN steels, and add it in the conclusion section. [Line 236-314]

 

Response: Thank you for the suggestion. Nitrogen could not be directly detected by EDS due to its low atomic number, and no Cr₂N precipitation was observed in TEM, confirming that nitrogen remains in interstitial solid solution. We have now added a detailed discussion explaining that nitrogen forms Cr–N short-range ordered clusters, reduces stacking fault energy, promotes planar slip, and strengthens dislocation pinning. A corresponding statement has also been added to the conclusion. These revisions appear in the Discussion section. (Section 4, line 338-350).

 

 

13.Please add conclusion about the position and role of Nitrogen to improve 316LN stainless steel. [Line 315-332]

 

Response: We have added a concise conclusion paragraph summarizing nitrogen’s interstitial position, SFE reduction, planar slip/stacking-fault promotion, and strengthening via interstitial–dislocation interactions, which collectively increase hardness and improve cavitation resistance. Lines updated accordingly in the revised manuscript. (Section 5, line 411-413).

 

 

14.Please revise the paper based on the above comments and in the paper. Please highlight the revised part with green color and to be resubmitted again.

 

Response: We have revised the manuscript according to your suggestions and highlighted all changes in green. Thank you again for your valuable comments.

 

Hopefully we have addressed all of your concerns.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript “Effect of Nitrogen Content on the Cavitation Erosion Resistance of 316LN Stainless Steel” presents a cavitation performance improvement of 316L stainless steel by adding N as an alloying element. The performance improvement was supported by the material characterization which showed a microstructural evolution with the N content. The work is a scholar contribution, but, before recommending its acceptance, the reviewer lists some points that the authors should consider to improve its quality:

 

Line 41: The reviewer recommends “susceptible to damages due to cavitation phenomenon” instead of “susceptible to cavitation damage”

 

Line 44: The reviewer recommends adding “erosion wear” to this list “…plastic deformation, fatigue crack initiation and propagation, and ultimately pit formation [7–9].” [https://doi.org/10.1179/imtr.1986.31.1.1].

 

Line 46-48: “Previous studies have shown that austenitic stainless steels exhibit better cavitation resistance than some copper alloys and high-strength steels due to their high plasticity and energy absorption capacity [10].” The reference cited does not compare stainless steel to copper alloys. Please choose properly the references to support the statements. E.g., Vaz et al. really presented cavitation performance of martensitic stainless steel to austenitic stainless steel and a C-steel among others [https://doi.org/10.1016/j.hybadv.2023.100125].

 

Line 59-60: “…especially in chloride-containing environments where the synergy between mechanical impact and corrosion is not yet fully clarified.” Even it is not fully understood, the reviewer recommends adding some comments on the synergy corrosion-cavitation, as evaluated experimentally and discussed in [https://doi.org/10.1016/j.ultsonch.2020.105271].

 

Line 73-74: “The rolled plates were solution-treated 73 to obtain comparable grain sizes for all alloys.” The reviewer recommends adding more details about this treatment.

 

In the section 2.1., it is imperative to present the technique and experimental details that the authors used to measure the material chemical composition.

 

Line 78: The reviewer recommends “2.5 μm diamond suspension” instead of “2.5 μm diamond slurry”

 

Line 109: Why was a low load (25gf) employed for microhardness? Normally, for bulk materials higher loads would give more accurate results.

Author Response

Manuscript No.: metals-3962773  

Response to Reviewers

Thanks to editor and reviewers for the thoughtful and thorough review. Their comments are most helpful in revising the paper and our future work. We have studied their comments carefully and have made correction which we hope meet with their approval. Below are our responses to the comments. The section, figure and paragraph numbers refer to our revised manuscript.

 

Reviewer #3:

 

The manuscript “Effect of Nitrogen Content on the Cavitation Erosion Resistance of 316LN Stainless Steel” presents a cavitation performance improvement of 316L stainless steel by adding N as an alloying element. The performance improvement was supported by the material characterization which showed a microstructural evolution with the N content. The work is a scholar contribution.

 

Response: Thanks！

 

 

1.Line 41: The reviewer recommends “susceptible to damages due to cavitation phenomenon” instead of “susceptible to cavitation damage”

 

Response: Thank you. We have made the suggested change and highlighted it in green. (Section 1, line 41).

 

 

2.Line 44: The reviewer recommends adding “erosion wear” to this list “…plastic deformation, fatigue crack initiation and propagation, and ultimately pit formation [7–9].” [https://doi.org/10.1179/imtr.1986.31.1.1].

 

Response: We have added “erosion wear” to the sentence at Line 44 and cited the suggested reference. (Section 1, line 44).

 

 

3.Line 46-48: “Previous studies have shown that austenitic stainless steels exhibit better cavitation resistance than some copper alloys and high-strength steels due to their high plasticity and energy absorption capacity [10].” The reference cited does not compare stainless steel to copper alloys. Please choose properly the references to support the statements. E.g., Vaz et al. really presented cavitation performance of martensitic stainless steel to austenitic stainless steel and a C-steel among others [https://doi.org/10.1016/j.hybadv.2023.100125].

 

Response: We have replaced the reference with a more appropriate one which indeed compares austenitic stainless steel with other metallic materials. (Section 1, line 49).

 

 

4.Line 59-60: “…especially in chloride-containing environments where the synergy between mechanical impact and corrosion is not yet fully clarified.” Even it is not fully understood, the reviewer recommends adding some comments on the synergy corrosion-cavitation, as evaluated experimentally and discussed in [https://doi.org/10.1016/j.ultsonch.2020.105271].

 

Response: We agree that the synergistic effect between mechanical impact and corrosion is relevant to cavitation behavior in chloride-containing environments. We have added a short discussion to acknowledge the possible cavitation–corrosion synergy, citing the recommended reference. The revised text has been inserted in the Introduction, and the reference has been added to the reference list. (Section 1, line 59-63).

 

 

5.Line 73-74: “The rolled plates were solution-treated 73 to obtain comparable grain sizes for all alloys.” The reviewer recommends adding more details about this treatment.

 

Response: We have now added the detailed solution-treatment procedures to the revised manuscript to clarify how comparable initial grain sizes were obtained for all alloys. (Section 2.1, line 80-85).

 

 

6.In the section 2.1., it is imperative to present the technique and experimental details that the authors used to measure the material chemical composition.

 

Response: Thank you for the valuable comment. The chemical composition of all alloys was measured prior to processing. In the revised manuscript, we have added a description of the analytical techniques used to determine the elemental composition in Section 2.1. Specifically, nitrogen content was analyzed using an ON/H/N elemental analyzer, while metallic elements (Fe, Cr, Ni, Mo, Mn, etc.) were measured by ICP-OES. The corresponding text has been added as suggested. (Section 2.1, line 78-81).

 

 

7.Line 78: The reviewer recommends “2.5 μm diamond suspension” instead of “2.5 μm diamond slurry”

 

Response: We have made the corresponding revisions in the revised manuscript. (Section 2.2, line 97).

 

 

8.Line 109: Why was a low load (25gf) employed for microhardness? Normally, for bulk materials higher loads would give more accurate results.

 

Response: Thank you for the constructive comment. A low load of 25 gf was selected to ensure measurement consistency across the five alloys. Because the nitrogen content varies significantly, the hardness of the specimens also differs markedly. Using a higher load would cause large differences in indentation size and potential substrate influence, reducing the comparability of the hardness values. Therefore, a load of 25 gf was chosen to ensure that all indentations remained within a comparable depth range and thus allow valid comparison among the samples. This clarification has been added to Section 2.3 in the revised manuscript. (Section 2.3, line 151-152).

 

 

Hopefully we have addressed all of your concerns.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript "Effect of nitrogen content on the cavitation erosion resistance of 316LN stainless steel" (metals-3962773-peer-review-v1) is devoted to a systematic investigation of the effect of nitrogen content (0.008-0.34 wt.% N) on the cavitation erosion resistance of 316LN stainless steels, using a combination of experimental methods including 2 h and 24 h cavitation tests, SEM, 3D profilometry, TEM, EBSD, and microhardness measurements. Among the positive aspects of the study are the broad experimental coverage of various nitrogen contents, the use of multiple complementary microstructural characterization techniques, and the clear correlation established between hardness, microstructure, and mass loss. However, several issues should be addressed before the paper can be accepted for publication.

1. 1. The empirical equations presented in the manuscript require clarification and correction, along with statistical details of the fitting procedure. The expressions given, such as "Dm(N)=2.6+9.2x6.7N" and “Ra=1.6+3.9x2.2N," appear typographically distorted or incorrectly formatted (what exactly does the multiplier/exponent mean? No explanation is provided), making their meaning unclear. The authors should specify the functional form of the dependence (linear, exponential, polynomial, etc.), provide all coefficients with their errors, and include indicators of the fitting quality (R², RMSE). Units in all formulas (mg cm^–2, µm, etc.) should be consistent throughout.
2. The characterization of the base material should be expanded. The manuscript lacks a complete table of the chemical composition (except for nitrogen) for each alloy, although even small differences in Cr, Ni, Mo, Mn, and other elements may influence corrosion and mechanical properties. A table with the chemical composition (wt. %) including errors, initial grain sizes (average ± σ), and the type and parameters of the applied heat treatment should be provided.
3. The description of the cavitation test conditions and the verification of the testing setup should also be more detailed. Although ASTM G32 and parameters such as frequency (20 kHz), amplitude (20 µm), and intermittent mode are mentioned, the manuscript should include information on the measurement of power or intensity at the horn tip, calibration of the distance r between the horn and specimen in different series, dissolved gas/oxygen content in the water, and the temperature control procedure during testing. A description of sample positioning and reproducibility of geometry is also important for ensuring the reliability of the experiments.
4. The determination of martensite content and its distribution requires a more detailed description. The authors report an increase in martensite fraction with nitrogen content, but the methodology is not sufficiently described. EBSD parameters, phase identification criteria, noise filtering procedures, and the minimum area considered for phase assignment should be specified. Since EBSD analysis on a rough post-cavitation surface may be problematic, it is recommended to provide additional cross-sections, depth maps, or quasi-dynamic analyses to confirm the findings. Representative EBSD maps with indexed grains and phase histograms would be useful for illustration.
5. The TEM and dislocation analysis should be deepened. The manuscript presents TEM images showing planar slips and stacking faults, but lacks information about the sampling location (distance from the cavitated surface), imaging conditions (contrast mode, g-vector), and the use of EDS or EDS mapping to confirm or exclude the presence of Cr₂N or other carbides/nitrides at high nitrogen levels. Including SAED patterns and EDS maps as supplements to the TEM data is recommended.
6. The discussion of the strengthening mechanism should be expanded with consideration of hardness gradients and possible layer formation. While the authors correctly link increased hardness and modified dislocation structure with enhanced cavitation resistance, it would be beneficial to present hardness profiles versus depth (before and after cavitation) or nanohardness maps to demonstrate whether strengthening is limited to the surface or extends deeper. The potential negative effects of excessive nitrogen, such as Cr depletion or local corrosion susceptibility, should also be discussed, and the limitations of the conclusions (experiments conducted in deionized water) should be explicitly stated.
7. The presentation of surface profiling results could be improved. For the reported pit depths and roughness (Ra), the authors should show histograms of depth distribution, cross-sectional views of critical zones, and specify the sampling area for each profile. Figure captions should include precise scale bars, legends, and the analyzed area used for Ra calculation.
8. The conclusions should be adjusted to reflect the limitations of the study, for example by indicating that the results apply to tests performed in deionized water under the specific cavitation conditions employed.
9. Several stylistic and editorial issues require attention. Some references contain incomplete bibliographic data or inconsistent numbering and formatting. Notations (e.g., N, wt.% N, 34N) should be unified. There are also minor grammatical and stylistic errors in English; therefore, thorough language editing is recommended before resubmission.

Comments on the Quality of English Language

Several stylistic and editorial issues require attention. There are also minor grammatical and stylistic errors in English; therefore, thorough language editing is recommended before resubmission.

Author Response

Manuscript No.: metals-3962773  

Response to Reviewers

Thanks to editor and reviewers for the thoughtful and thorough review. Their comments are most helpful in revising the paper and our future work. We have studied their comments carefully and have made correction which we hope meet with their approval. Below are our responses to the comments. The section, figure and paragraph numbers refer to our revised manuscript.

 

Reviewer #4:

 

The manuscript "Effect of nitrogen content on the cavitation erosion resistance of 316LN stainless steel" (metals-3962773-peer-review-v1) is devoted to a systematic investigation of the effect of nitrogen content (0.008-0.34 wt.% N) on the cavitation erosion resistance of 316LN stainless steels, using a combination of experimental methods including 2 h and 24 h cavitation tests, SEM, 3D profilometry, TEM, EBSD, and microhardness measurements. Among the positive aspects of the study are the broad experimental coverage of various nitrogen contents, the use of multiple complementary microstructural characterization techniques, and the clear correlation established between hardness, microstructure, and mass loss. However, several issues should be addressed before the paper can be accepted for publication.

 

Response: Thanks！

 

 

1. The empirical equations presented in the manuscript require clarification and correction, along with statistical details of the fitting procedure. The expressions given, such as "Dm(N)=2.6+9.2x6.7N" and “Ra=1.6+3.9x2.2N," appear typographically distorted or incorrectly formatted (what exactly does the multiplier/exponent mean? No explanation is provided), making their meaning unclear. The authors should specify the functional form of the dependence (linear, exponential, polynomial, etc.), provide all coefficients with their errors, and include indicators of the fitting quality (R2, RMSE). Units in all formulas (mg cm–2, µm, etc.) should be consistent throughout.

 

Response: Thank you for pointing this out. We agree that the empirical equations required clearer presentation. In the revised manuscript, the fitting relationships in Sections 3.1 and 3.2 have been fully corrected and reformatted to avoid ambiguity. Specifically: All coefficients are now presented with consistent units (mg·cm⁻² for cumulative mass loss and µm for roughness, respectively). The statistical indicators have been added, including the coefficient of determination (R²) and mean square error (MSE) for each fitting. The applicable nitrogen content range (0.008–0.34 wt.%) has been clearly stated. These revisions clarify the physical meaning of the parameters and ensure that the regression equations are both interpretable and reproducible. The corrected equations and statistical details now appear in Lines XX–XX of the revised manuscript. (Section 3.1, line 167-175; Section 3.2, line 200-205; Section 4, line 306-308).

 

 

2.The characterization of the base material should be expanded. The manuscript lacks a complete table of the chemical composition (except for nitrogen) for each alloy, although even small differences in Cr, Ni, Mo, Mn, and other elements may influence corrosion and mechanical properties. A table with the chemical composition (wt. %) including errors, initial grain sizes (average ± σ), and the type and parameters of the applied heat treatment should be provided.

 

Response: We have added Table 1 (chemical composition for each alloy, wt.% ± analytical error for Cr, Ni, Mo, Mn, N, etc.) and Table 2 (initial grain size, average ± σ, and the heat-treatment type and parameters). (Section 2.1, line 92-94).

 

 

3.The description of the cavitation test conditions and the verification of the testing setup should also be more detailed. Although ASTM G32 and parameters such as frequency (20 kHz), amplitude (20 µm), and intermittent mode are mentioned, the manuscript should include information on the measurement of power or intensity at the horn tip, calibration of the distance r between the horn and specimen in different series, dissolved gas/oxygen content in the water, and the temperature control procedure during testing. A description of sample positioning and reproducibility of geometry is also important for ensuring the reliability of the experiments.

 

Response: We have expanded the experimental description accordingly. The revised text now details (i) calorimetric determination of effective acoustic power and intensity at the horn tip, with routine setup checks; (ii) calibration of the horn–specimen gap r for each series; (iii) monitoring of dissolved oxygen and temperature-controlled testing at 25 ± 1 °C; and (iv) specimen positioning with a dedicated jig and geometry reproducibility limits. These additions are highlighted in green in the revised manuscript. (Section 2.2, line 100-111).

 

 

4.The determination of martensite content and its distribution requires a more detailed description. The authors report an increase in martensite fraction with nitrogen content, but the methodology is not sufficiently described. EBSD parameters, phase identification criteria, noise filtering procedures, and the minimum area considered for phase assignment should be specified. Since EBSD analysis on a rough post-cavitation surface may be problematic, it is recommended to provide additional cross-sections, depth maps, or quasi-dynamic analyses to confirm the findings. Representative EBSD maps with indexed grains and phase histograms would be useful for illustration.

 

Response: We appreciate the reviewer’s insightful suggestion. In the revised manuscript, we have provided detailed EBSD parameters, including the scanning step size (0.1 µm), accelerating voltage (20 kV), and noise reduction procedure (grain dilation and neighbor orientation averaging). A minimum area threshold of five pixels was used for phase identification to minimize false indexing. (Section 2.3, line 141-145).

As mentioned, EBSD analysis was performed on samples subjected to 50% tensile deformation rather than post-cavitation surfaces to avoid interference from surface roughness. The EBSD results were only used qualitatively to confirm the occurrence of strain-induced martensitic transformation during deformation, which supports the discussion on strengthening and cavitation resistance mechanisms in Section 4. (Section 4, line 346-348)

Since quantifying martensite is not the main objective of this study, additional EBSD phase histograms or cross-sectional analyses are not included here but will be addressed in our follow-up work focusing on deformation-induced transformations.

 

 

5.The TEM and dislocation analysis should be deepened. The manuscript presents TEM images showing planar slips and stacking faults, but lacks information about the sampling location (distance from the cavitated surface), imaging conditions (contrast mode, g-vector), and the use of EDS or EDS mapping to confirm or exclude the presence of Cr2N or other carbides/nitrides at high nitrogen levels. Including SAED patterns and EDS maps as supplements to the TEM data is recommended.

 

Response: We thank the reviewer for the suggestion to deepen the TEM analysis. We would like to clarify that the TEM observations reported in this manuscript were performed on tensile-deformed specimens (2.5% engineering strain) and not on post-cavitation surfaces. The purpose of these TEM data is therefore qualitative and supportive: to demonstrate how increasing nitrogen alters dislocation configurations and slip modes during plastic deformation, which helps to interpret the enhanced cavitation resistance discussed in the manuscript.

To address the reviewer’s technical concerns, we have added details in the revised Methods section about the TEM sampling location and imaging conditions. Multiple representative fields at different magnifications were examined for each alloy. Despite these efforts, no discrete nitride or carbide precipitates were observed in any of the fields. We therefore judged EDS mapping of limited value for this work: (i) no candidate precipitates were apparent in any TEM field or in SAED patterns (ii) our earlier study on high-N steels (Wang, Y., Wang, Y., & Wang, Z. (2021). Enhancing yield strength of high nitrogen austenitic stainless steel. Journal of Constructional Steel Research, 187, 106927.) shows that nano-scale nitrides, when present, are detectable at comparable magnifications — none were seen here. (Section 2.3, line 136-139; Section 4, 329-333)

 

 

6.The discussion of the strengthening mechanism should be expanded with consideration of hardness gradients and possible layer formation. While the authors correctly link increased hardness and modified dislocation structure with enhanced cavitation resistance, it would be beneficial to present hardness profiles versus depth (before and after cavitation) or nanohardness maps to demonstrate whether strengthening is limited to the surface or extends deeper. The potential negative effects of excessive nitrogen, such as Cr depletion or local corrosion susceptibility, should also be discussed, and the limitations of the conclusions (experiments conducted in deionized water) should be explicitly stated.

 

Response: In this study, the microhardness values presented in Figure 6 were measured on the polished, undeformed surfaces of the solution-treated samples to reflect the intrinsic strengthening effect of nitrogen, rather than post-cavitation hardening. The purpose was to correlate bulk hardness and dislocation structure with the overall cavitation resistance. Therefore, hardness gradients or nanohardness maps were not measured, as the cavitation process mainly induces surface fatigue and microplastic deformation rather than extensive subsurface work hardening under the present test conditions. We have added the necessary descriptions to the revised manuscript to avoid misunderstandings.

In addition, deionized water was selected as the test medium following the ASTM G32 standard, in order to maintain a unified and reproducible environment for evaluating the intrinsic effect of nitrogen content on the cavitation resistance of 316LN stainless steel. This setup isolates mechanical damage from electrochemical effects, allowing the role of nitrogen in strengthening and microstructural evolution to be more clearly assessed.

As correctly pointed out, further exploration of hardness gradients and corrosion–cavitation coupling effects will be an important direction for future work. In our experiments, no corrosion products were observed on the specimen surfaces after either 2 h or 24 h cavitation, even under multiple magnifications in SEM. This result is consistent with the high corrosion resistance of 316LN stainless steel and the well-established role of nitrogen in enhancing passivity. Although excessive nitrogen can, in some cases, cause local Cr depletion and sensitization, our previous research (Wang, Y., Wang, Z., Wang, W., & Qu, M. (2024). Effect of nitrogen content on grain boundary engineering and corrosion resistance of 316LN stainless steel. Journal of Materials Research and Technology, 29, 3976-3989.) confirmed that within the studied range (0.008–0.34 wt.% N), nitrogen markedly improves corrosion resistance rather than degrading it. (Section 4, line 312-318; Section 2.2, line 108-111)

 

 

7.The presentation of surface profiling results could be improved. For the reported pit depths and roughness (Ra), the authors should show histograms of depth distribution, cross-sectional views of critical zones, and specify the sampling area for each profile. Figure captions should include precise scale bars, legends, and the analyzed area used for Ra calculation.

 

Response: We appreciate the reviewer’s suggestion to clarify the presentation of the surface profiling results. In the revised manuscript, detailed information about the scanned area and Ra calculation has been added to the figure captions. Each 3D surface morphology covers an area of 1.25 mm × 1.0 mm, which is large enough to minimize local selection bias. The analyzed zones correspond to the regions of most severe cavitation damage. The color scale in the 3D images represents pit depth (-80–0 µm), and surface roughness (Ra) was calculated from the entire scanned area using Vision software. Scale bars and legends have been added to improve readability. In addition, we also added a histograms of depth distribution to clearly demonstrate the surface differences caused by cavitation between samples. We believe these additions sufficiently clarify the measurement details and visualization of surface features. (Section 3.2, line 178-180; line 181-194; line 196)

 

 

8.The conclusions should be adjusted to reflect the limitations of the study, for example by indicating that the results apply to tests performed in deionized water under the specific cavitation conditions employed.

 

Response: In the revised manuscript, we have added a clarifying statement to specify the limitation of this study. The results were obtained under deionized-water cavitation conditions, aiming to isolate mechanical and fatigue effects from corrosion coupling. (Section 4, line 397-400)

 

 

9.Several stylistic and editorial issues require attention. Some references contain incomplete bibliographic data or inconsistent numbering and formatting. Notations (e.g., N, wt.% N, 34N) should be unified. There are also minor grammatical and stylistic errors in English; therefore, thorough language editing is recommended before resubmission.

 

Response: we have checked the entire manuscript, including the references and symbols, and meticulously examined the English grammar and style. Thank you again to the reviewers for their insightful suggestions.

 

Hopefully we have addressed all of your concerns.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors.

The paper titled “Effect of Nitrogen Content on the Cavitation Erosion Resistance of 316LN Stainless Steel" has been revised by the authors based on my comments. However, there are minor revisions based on the following comments that also written in the pdf of the paper:

1. "Dissolved oxygen (DO)" must be written. [Line 104]It should be written as (30 mm x 30 mm x 30 mm) [Line 72]
2. Please add the indentation time in this sentence about Vickers microhardness testing. [Line 151-152]
3. Please add captions for each figure (a)....(b)....in the title of Figure 1. Please do the same in Figures 2, 4, 5, 7 and 8. [Line176]
4. Please explain or write correctly about pit depth (-80-0 micron). Is it from -80 to 0 micron? [Line 181]

Kind regards,

Comments for author File: Comments.pdf

Author Response

Manuscript No.: metals-3962773  

Response to Reviewers

Thanks to editor and reviewers for the thoughtful and thorough review. Their comments are most helpful in revising the paper and our future work. We have studied their comments carefully and have made correction which we hope meet with their approval. Below are our responses to the comments. The section, figure and paragraph numbers refer to our revised manuscript.

 

 

1. "Dissolved oxygen (DO)" must be written. [Line 104]It should be written as (30 mm x 30 mm x 30 mm) [Line 72].

 

Response: We have revised the manuscript accordingly and now explicitly write “dissolved oxygen (DO)” at its first occurrence. The sample dimensions have been corrected to “30 mm × 30 mm × 30 mm” in the revised manuscript. (Section 2.1, line 86; Section 2.2, line 105)

 

 

2. Please add the indentation time in this sentence about Vickers microhardness testing. [Line 151-152].

 

Response: The indentation dwell time for the Vickers microhardness test has now been added in the revised manuscript. (Section 2.3, line 152-153)

 

 

3. Please add captions for each figure (a)....(b)....in the title of Figure 1. Please do the same in Figures 2, 4, 5, 7 and 8. [Line176]

 

Response: We have revised the captions of Figures 1, 2, 4, 5, 7, and 8 by adding explicit subfigure labels (e.g., (a), (b), (c), etc.) in the figure titles to improve clarity and consistency. The updated captions now clearly describe the content of each subfigure.

 

 

4. Please explain or write correctly about pit depth (-80–0 micron). Is it from −80 to 0 micron? [Line 181]

 

Response: Yes, the pit depth range refers to values from −80 μm to 0 μm (with the reference surface defined as 0 μm). This has now been clarified in the revised manuscript.

 

 

Hopefully we have addressed all of your concerns.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors improved the manuscript quality by accepting the reviewer's recommendations and suggestions. The reviewer recommends its acceptance for publication in Metals.

Author Response

Manuscript No.: metals-3962773  

Response to Reviewers

The authors improved the manuscript quality by accepting the reviewer's recommendations and suggestions. The reviewer recommends its acceptance for publication in Metals.

 

Response: Thanks!

 

Reviewer 4 Report

Comments and Suggestions for Authors

The authors have provided satisfactory responses to all questions and suggestions and made appropriate revisions to the manuscript. I believe the revised manuscript can be recommended for publication in its current form.

Author Response

Manuscript No.: metals-3962773  

Response to Reviewers

 

Reviewer #4: The authors have provided satisfactory responses to all questions and suggestions and made appropriate revisions to the manuscript. I believe the revised manuscript can be recommended for publication in its current form.

 

Response: Thanks!