Evolution of the Fretting Wear Damage of a Complex Phase Compound Layer for a Nitrided High-Carbon High-Chromium Steel

Round 1

Reviewer 1 Report

The first sentence is very ambiguous? I suggest to remove it

Overall the abstract should be reformulated as is difficult to follow its message

The abstract is very poor too. There are mentioned few time “the sliding wear characteristics of this type of compound layer have been 40 extensively studied” and “and has been widely used in tribological applications as 58 the engineering components”. So my question, which is novelty of this study? There is any industrial application, if so which components ? Please make an introduction easy readable for readers. Despite of all statements there are only around 21 ref for a field which authors claim that are plenty study.   

The nitriding process corresponds to any standard ? why this set up was sued for 500C and 70 h ?

Why 35 N and 70N ? is there any physical meaning ?

“which was measured after the removal of pores on the top surface of the compound layer” how was removed the pores ?

Details of caption a, b, and c for Figure 2?

OK but which is the difference in Figure 4 b and figure 4c ? because both are nitrided specimen ?

OK , but why is contrary as per your statement “This finding is in contrast with the results reported by many other investigators”. Also for me is something unclear… please provide your thoughts. Apart how many test were conducted to obtain these assumption ?

The font size for Figure 7 a, d, g is very small

The sacle for Figure 10 c, f, I should be the same otherwise is confusion

The overall work should be improved in terms of quality

There are no much details about physical explanation of some results .

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

General Evaluation

The paper constitutes an experimental study concerning the fretting wear behaviour of gas nitrided high alloy steel under two different loading cases. The research was undertaken mainly by employing ball-on-disk tribotesting and surface characterization by SEM/EDS and optical profilometry. The results formulate a general preliminary hypothesis regarding the emergent wear mechanisms governed the entire degradation process of the thermochemically treated surface. Although additional investigation (e.g. high resolution electron microscopy at cross sections, more loading cases) could be deemed valuable, ascertaining the stated wear processes, the paper is considered as well written and organized and provides a first view and discussion on the already performed research. Therefore, it can be accepted for publication, provided some further suggestions and comments.

Technical/Scientific Comments

1. Some Figures need enlargement to enhance readership; for instance Figure 2, 3, 4, 5 and 6.
2. Please round the EDS quantitative results keeping one decimal digit, as the most significant.
3. Please write the caption of Figures 4 (b), (c) in higher detail (what is the difference between them as it was referred in the text).
4. Please check the references of Figures in the text; e.g. in Line 127 Figure 3c does not exist; probably it should be Figure 4c.
5. In caption of Figure 6 there are no (a) and (b) sub-figures. Please correct.
6. In Figure 9 caption please write the loading conditions.
7. Are there cross-sectional profile measurements for low load case as they were presented in Figure 10? It is advised to be added for comparison reasons, if they were available.
8. Please check whether Figures 10f and 10i are inversed; profile depth seems to be higher in the lower fretting cycles period compared to the highest!
9. A schematic representation highlighting the induced wear micro-mechanisms is recommended (e.g. using a Table or a flow chart) underlining also the main differences between the two loading cases tested.

Language/Grammar Comments

The language seems sufficient. However, a final proofreading is recommended to avoid minor typographical errors. For instance:

1. Please check syntax in the sentence between lines 57 and 59. Maybe the phrase is better to be separated to shorter sentences.
2. Please check the chemical and mathematical formulae and expression to be written in a standard way, using subscripts or superscripts, capital or lower case letters (see L27, 104, 117-118, 192, etc.).
3. Please keep one space separation between the numerical part and the units of a physical entity (e.g. L154, 156 should be 70 N instead of 70N).   

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

REVIEW COMMENTS

Manuscript ID: metals-965363

Evolution of the Fretting Wear Damage of a Complex Phase Compound Layer for a Nitrided High-Carbon High-Chromium Steel

A very interesting work. In addition, it is presented clearly, which makes it very pleasant to read.

The manuscript analyzes the fretting wear behavior of a tool steel subjected to a gas nitriding in order to obtain a complex phase compound layer with limited porosity. The experimental methodology used is described in detail and the results are presented and discussed clearly. However, some minor errors have been observed and some aspects could perhaps be better explained. For this reason, I would appreciate you consider the following suggestions:

1. Line 67. What is the hardness of the steel after quenching and tempering?
2. Line 82. When the authors say that "The normal load parameters were optimized", what do they mean? How was the optimization done? What criteria were taken into account? Explain it, please.
3. Line 84: How many tests were performed for each set of test parameters (load, frequency, stroke, duration)? Indicate it, please.
4. Line 96: Typographic error. Write "Stroke" instead of "Stoke"
5. Lines 127: Typographic error. Write "Figure 4c" instead of "Figure 3c"
6. Line 130: In figure 2 it is observed that the hardness value it is lower near the surface than at a point further away. Why this behavior? Is it a consequence of surface decarburization? Explain it please.
7. Line 133: It would be advisable to explain in the caption that the diffraction patterns 4b and 4c refer to the nitrided sample before and after being polished, respectively

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

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Author Response

Sorry, we can't find any new comments.