Review Reports - Mechanistic Study of Surface Nanocrystallization for Surface Modification in High-Strength Low-Alloy Steel

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript investigates “Mechanistic Study of Surface Nanocrystallization for Surface 2 Modification in High-Strength Low-Alloy Steel”. The authors investigateing the surface nanocrystallization mechanism of 35CrMo high-strength low-alloy (HSLA) steel induced by ultrasonic surface rolling pro- cessing (USRP), with particular emphasis on elucidating its optimization effects on surface integrity, mechanical properties, and wear resistance. Through USRP treatment with varying static pressure parameters combined with multi-scale characterization techniques, they demonstrate that high-frequency impact and rolling effects promote martensite lath fragmentation and dislocation multiplication, thereby forming a gradient nanostructured layer composed of equiaxed nanocrystals and high-density dislocations in the surface region. The topic is interested, however, a few points the authors should take into account:

Comment 1:

As far as originality is concerned, there have been many similar publications.

https://doi.org/10.1016/S1359-6454(02)00310-5

https://doi.org/10.1016/j.matchar.2025.115332

https://doi.org/10.1016/j.jmrt.2024.04.178

https://doi.org/10.1016/j.jma.2025.07.005

https://doi.org/10.1016/j.surfcoat.2025.132525

It would be clearer if the authors focused more on novelty (as well as advancement) in comparison with existing literature

Comment 2:

The abstract is very long and should highlight the novelety and some key results derived from the Surface Nanocrystallization process.

Comment 3:

In order to make the introduction section more interesting, authors should include new references. The current form is very short, and the most important ones are already outdated.

Comment 4:

The introduction should be logical and include a paragraph outlining the paper's organization. Moreover, for research conducted by others, it is recommended that the authors provide a comprehensive analysis and summary, identifying the resolved and unresolved problems while highlighting the contributions and innovations of the current research.

Comment 5:

Some figures (Fig. 3.1, 3.6, 3.7 ). are very fuzzy ,the resolution need to be improved.

Comment 6:

Lines 208-215, “Residual compressive stress effectively inhibits crack initiation and propagation, whereas residual tensile stress may reduce the load-bearing capacity of the material. Therefore, the high compressive residual stress layer introduced by USRP can significantly enhance the load-carrying capacity of 35CrMo steel and prolong the service life of components. It should be noted, however, that excessive rolling pressure may not further increase the compressive residual stress but instead impair surface integrity through the introduction of microcracks or other defects, thereby diminishing the overall strengthening effect.” Please provide more details about this status.

Comment 7:

Could you please provide a comparison with other surface treatments or an analysis of the scalability and industrial applicability of surface nanocrystallization?

Comment 8:

In particular, what are the surface stability and thermal characteristics of 35CrMo high-strength low-alloy (HSLA) steel? (The thermal degradation of the nanostructured surface has been adequately addressed, particularly for high-temperature applications).

Comment 9:

It would be helpful if the authors explained in detail how the nanocrystalline surface layer relates to improvements in mechanical, tribological, or corrosion properties in comparison with other alloys.

Comment 10:

The conclusion section should be in spertaed section and include some key results focusing on the mprovement gradient structure modification properties, and wear surface of 35CrMo before and after surface treatment.

Comments 11:

Although the work presented by the researchers is very fascinating, I hope that the Optimial design Manufacturing parameters, Weight and Cost-Effectiveness concerns will be addressed.

Comment 12:

As far as nanostructure is concerned, I suggest that advanced techniques (such as TEM, XRD, EBSD) should be employed alongside SEM imaging in order to ensure a sufficient confirmation of nanocrystalline structure, grain size distribution, and depth of nanocrystalline layers?

Comments 13.

The reference list needs to be updated, as many papers have been published in the last three years.

Actually I am very interested in this research direction. However, these amendments will enhance the overall clarity and impact of the document.

Author Response

Thank you for your professional suggestion, the responses are in the document attached below.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript "Mechanistic Study of Surface Nanocrystallization for Surface Modification in High-Strength Low-Alloy Steel" refers to new research and the presented results are useful for manufacturing. I did not have any critical comments regarding the overall performance of the work. However, the work has some shortcomings and I had the following comments while reviewing it:

I suggest that the authors modify the title of the manuscript and make it something like this: "Study of mechanical properties for 35CrMo steel modified by ultrasonic surface treatment by rolling."
I propose to simplify the numbering of tables and figures. Just make a passing numbering.
In Fig. 1, the authors need to increase the size of the scales.
In Fig. 4, the transition layers are very poorly visible. SEM images at higher magnifications of this layer should be included. These can also be added to Figure 5 instead of Figure 4 (however, the same areas are needed as for EBSD). Authors need to introduce additional SEM so that the main illustration of their result is more accurate and understandable.
Remove the text "4. Discussion" on line 366.
The value for all 35CrMo samples is somewhat less than the value indicated in another literary source for untreated steel of this grade. Could the authors provide a short comment on this? Have the authors reviewed studies that include microhardness studies of this steel?
Lines 395-401 require a supporting literature reference or other evidence of the presence of an oxide film on the wear track after 200-300 seconds of testing.

Author Response

Thank you for your professional suggestion, the responses are in the document attached below.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

In this manuscript by Yiyang Jin and colleagues the authors perform a mechanistic study of the crystallization process after applying ultrasonic surface rolling processing to the surface. The static and dynamic rolling pressure induces grain refinement which strengths the top layer of the alloy, in this case 35CrMo. The abstract and introduction are well written, and the results are solid. However, there are several points the authors must address before being considered publication in the journal Coatings:

1) In the introduction, very little information is given about the state of the art of the technique. Only a very few works are reference through the introduction. For example: “The reciprocating vibration of the rolling head (amplitude: 10–50 μm) 55 induces cyclic plastic deformation, leading to martensite latheral fragmentation and the formation of equiaxed nanocrystals.” All these statements, if not proved by the authors through the paper, must be accompanied by the proper reference.

2) The ordering of the tables and figures must be fixed. The first table is Table 2.1 and the first figure is 3.1. Please correct the numbering through the text.

3) The authors study three different cylinder pressures 0.2, 0.35 and 0.5 MPa. These numbers seem a little arbitrary, what was the reasoning behind this choice. In addition, I believe this choice weakens the generality of the article as very little difference is observed from these variations. Why not use a wider range of values like 0.1 and 1.0 MPa or even more?

4) In figure 3.1 the text is not readable. Please increase present the results in accordance to the guidelines of the journal.

5) How is residual stress measured. It is not clear to me and it is not explained in the materials and methods section.

6) In fig 3.3 there is reference to caption (a)(b)(c) and (d) but I believe this is not needed has it is only a graph. Please correct this caption accordingly.

7) In figure 3.4 the width of the transition layer is measured. In the image only a line drawn by the authors is presented and if it is not clear to me if the results are conclusive. For this reason, I kindly ask the authors to include a cross section of the brightness of the image or any other methods that quantifies in any way the thickness of the transition layer.

8) What is the meaning of figure 3.6 b), how is it relevant to the manuscript?

9) Please remove the section “Authors should discuss the results and how…..”.

10) How is hardness measured at different depths?

Author Response

Thank you for your professional suggestion, the responses are in the document attached below.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The paper devoted for mechanistic study of surface nanocrystallization for surface modification in high-strength low-alloy steel. The topic is generally interesting, however the paper contain unexplained places and need major revisions.

Fig. 3.1 should be more commented. Particularly, line 145 ‘’under different parameters’’ which parameters You mean there?

Line 148, a ‘’peak removing and valey-filling ‘’effect, the term should be explained or corresponding reference should be added.

The part 4. Discussion should be rewritten in more informative way.

Lines 223-224, sentence ‘’This transformation directly reflects a fundamental shift in the deformation mechanism of the surface layer.’’ should be more explained.

It is difficult to see differences in Fig. 3.4 a, b, c and d parts.

All misprints should be corrected. For example, line 217 “This The”.

Author Response

Thank you for your professional suggestion, the responses are in the document attached below.