Tribological and Mechanical Behavior of Automotive Crankshaft Steel Superficially Modified Using the Boriding Hardening Process

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The study investigated the application of boriding surface hardening treatment on automotive steel, successfully forming a boride layers with excellent hardness and wear resistance. The research systematically studied the effects of boriding process, including the influence of treatment time on the characteristics of the boride layer, and comprehensively compared the improvement in friction performance of the boronized layer on steel. I suggest that your paper needs some necessary modifications. The main comments are given below:

1.       The introduction section requires some logical adjustments and should be appropriately simplified. It should begin with a brief introduction to wear and its hazards, followed by an overview of areas where wear issues exist, and conclude with methods for controlling wear.

2.       Why can it be argued that the presence of cracks in the indentation marks on samples treated for 6 hours is due to their higher hardness compared to other samples? Is it necessary to also provide the fracture toughness of samples treated at other times?

3.       The article needs to explain why 950°C was chosen as the treatment temperature. Is it because only at this temperature will the Fe₂B phase form? Or is this temperature most conducive to the formation of the Fe₂B phase? Or for other reasons.

4.       The English expression in the article is quite standard and may require some polishing.

Comments on the Quality of English Language

The English expressions in the article are pretty standard and could use some polishing.

Author Response

Dear reviewer,

The authors would like to thank you for your careful and thorough reading of our manuscript. All of your comments are valuable and helpful for improving our paper. The revision has been made according to your suggestions and highlighted in green in the text. We would like to express our gratitude to you for your valuable contributions to enhancing our manuscript. Of course, if you consider we have to do something else to improve the manuscript, please let us know.

Probably you will notice some other modifications in the manuscript, it is due to the comments of the other reviewers

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In this article, the authors attempted to enhance the surface wear resistance of the undefined grade of 'automotive steel' by applying a boriding thermochemical process. This is a well-known method of increasing the wear resistance of steel. The boride layers were analyzed by X-ray diffraction, tribological test and hardness measurements.

The experimental design is appropriate and treatments used are also appropriate.

The cited references are relevant. Only 30% of the cited literature was published in the last 5 years.

The figures and tables are appropriate and they properly show the data.

The conclusions are consistent with the evidence presented.

The ethics statements and data availability statements are adequate.

Generally, I do not find any novelty in this manuscript. Protective coatings that reproduce the conditions of steel in a lubricated environment have been used for many decades. So, 'the hypothesis of the present work because the tribological behavior of the boride layers reproduces the conditions of steel in a lubricated environment.' (lines 229-341) has been obvious for a long time. The results do not provide an advancement of the current knowledge. Moreover, sentence: 'Also, studying the tribological pair steel/Babbitt metal is important for reproducing the real conditions in the automotive engine.' confirms that this work examined a friction pair that does not correspond to the operation of the crankshaft in the engine.

In the Introduction section, the authors presented what will be explored in this article. However, the novelty based on published works has not been determined.

Dozens of steel grades are used in the automotive industry. The title suggests that the authors tested or the results apply to every grades of steel used in the automotive industry in auto bodies, rims, crumple zones, side members, etc.

line 78: A solid with dimensions of 12 x 12 x 5 is quboid, not square.

Which material standard defines the group of materials: 'automotive steel'?

Figure 1. Was the crankshaft taken from a specific engine?

Citation should be added in 'Shetty et al. model'.

The formula for determining CoF has not been provided.

Figure 3d: Boriding was carried out at 950°C. The layer thickness was measured at 900°C (Fig. 3d). It is not clear what the temperature marked in Fig. 3d refers to.

Figure 6b and Table 3 present the same data. In this case, either a Table or a Figure should be presented.

Subfigures (e)-(h) are not identified in Figure 7.

Table 5. Contact pressure changed during tests due to the change in contact area. So, it seems reasonable to ask how the contact pressure value presented in Table 3 was determined. Moreover, is the crankshaft loaded during real operation with such high contact pressures of 60-100 GPa? I suggest discussing this with the help of literature.

l. 338: 'The coefficient of friction on the surface of the automotive steel was reduced from 4.3 to 0.121.' This conclusion is not confirmed by the results obtained.

A lot of editing errors were found.

Author Response

Dear reviewer,

The authors would like to thank you for your careful and thorough reading of our manuscript. All of your comments are valuable and helpful for improving our paper. The revision has been made according to your suggestions and highlighted in yellow in the text. We would like to express our gratitude to you for your valuable contributions to enhancing our manuscript. Of course, if you consider we have to do something else to improve the manuscript, please let us know.

Probably notice some other modifications in the manuscript, it is due to the comments of the other reviewers

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have provided acceptable solutions to all the issues raised by the reviewer. I am satisfied with the answers. Therefore, I consider the paper suitable for publication in the Coatings journal.