The Geometric Surface Structure of EN X153CrMoV12 Tool Steel after Finish Turning Using PCBN Cutting Tools

Round 1

Reviewer 1 Report

The authors reported the research on the influence of finish turning parameters with PCBN coated tools of EN X153CrMoV12 steel on the quality of the technological surface. The volume ratio of Polycrystalline cubic boron nitride (PCBN), types of coatings, and finish turning parameters influence the geometric structure of the machined surfaces. And the authors summarized the best parameters attained in this analysis. But the currently selected contrast factors have no exact rules, and the comparisons of different tools and parameters are insufficient. Therefore, I disagree the publication in coatings. It is better to modify the manuscript according to the following suggestions:

1. Please increase the types of coated tools according to a certain volume ratio gradient, and explain how the coated tools are obtained.
2. If possible, please add the morphological characterization of different cutting tools.
3. If possible, please provide the pictures of the steel surface structures obtained by different cutting tools and finish turning parameters.
4. Feed f₃=0.3 mm/rev is the best value of feed in this analysis, but if the value of feed is increased to 0.35 or 0.4 mm/rev, can you get a better result by this way?
5. Please explain why the feed f₃=0.3 mm/rev is the upper limit of the working range for T3 tools.
6. In figure 9, the identification of T4 and T5 tools is missing.

Author Response

Dear Reviewer,
Thank you so much for taking the time to read the article we prepared. Any corrections to the text are highlighted in yellow.
We would like to respond to the comments as follows:
1. Please increase the types of coated tools according to a certain volume ratio gradient, and explain how the coated tools are obtained.
The introduction to the article was extended by theoretical issues related to e.g. coatings applied on cutting tools with PCBN (e.g. lines 58 – 67).
2. If possible, please add the morphological characterization of different cutting tools.
We included more detailed characteristics of the tools used for this study in Table 2 (row 148).
3. If possible, please provide the pictures of the steel surface structures obtained by different cutting tools and finish turning parameters.
The results of the study were extended with Table 5b, which shows actual images of surfaces machined with coated tools and relates them to the condition of a surface machined with an uncoated tools (Table 5a).
4. Feed f3=0.3 mm/rev is the best value of feed in this analysis, but if the value of feed is increased to 0.35 or 0.4 mm/rev, can you get a better result by this way?
All the tools used in this study are commercially available. Their manufacturers have set a feed rate of 0.3 mm/rev for each tool as the upper limit (an appropriate note was added in line 223). The authors of the study decided not to go beyond the acceptable machining parameter range for individual tools.
5. Please explain why the feed f3=0.3 mm/rev is the upper limit of the working range for T3 tools.
According to the answer to item 4: this is the maximum feed rate allowed by the tool manufacturer for the studied tool.
6. In figure 9, the identification of T4 and T5 tools is missing.
The figure was corrected according to the comment.
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We hope that the changes made and the response to the comments will allow the article to be accepted for publication.

Sincerely Yours, Authors

Author Response File: Author Response.pdf

Reviewer 2 Report

The present manuscript by Michal Ociepa, Mariusz Jenek and Piotr Kurylo, entitled "The geometric surface structure of EN X153CrMoV12 tool steel after finish turning using PCBN cutting tools", focuses mainly on the influence of the coating type and, on the other hand, of the machining feed on the surface roughness of the specimens of the hardened and tempered steel X153CrMoV12, turned by the uncoated and coated cutting tools, which are manufactured from polycrystalline cubic boron nitride. The manuscript seems to be once revised, however, the reviewer hasn't evaluated it yet.
The manuscript definitely has its strong sides, such as a practical outcome of the study, a large number of references (it is worth noting that 39% of them (twelve out of 31) are from 2018 or later years, what is a good indication of the relevance of this research) and nearly errorless English. At the same time, the manuscript also has a large number of drawbacks to be considered for publishing. The reviewer's critisism is explained below.

1. The contents of the manuscript don't entirely match the scope of the journal, as the authors focus mainly on the effect of machining feed, not the one of the coatings.
2. The manuscript strongly lacks novelty. There are plenty of studies, which handle the influence of the machining parameters on the surface roughness of a steel (e. g., [1-3]). The mentioned coatings (TiN and TiAlN) have been applied for the protection of cutting tools for decades. Cubic boron nitride (further c-BN) has been used as a tool cutting material for a long time, as well.
3. The abstract isn't informative at all. It is quite impossible to understand, what was the object of the research (the term 'quality of technological surface' is too general), what experimental methods were used, and what was the outcome of this research. By the way, the coatings aren't mentioned in the abstract at all.
4. Literature overview, brought in the chapter 'Introduction', isn't connected with the object of the study (as it mainly highlights the aspects of the wear of the tools from c-BN, while it wasn't studied at all).
5. The aims of the research weren't formulated, thus it is quite impossible to understand, what the authors actually study.
6. The amount of the experiments done is too small for a research article (in general, only surface roughness and microhardness distribution in the turned steel are presented). Moreover, the experiments seem to have been done unsystematically (e. g., the wear of the uncoated tool is analysed, and the wear of the coated tools isn't).
7. The description of the experimental procedure is unclear and incomplete. For example, the parameters, measured by the three-axis optical measurement system, aren't mentioned in the chapter 'Materials and Methods' at all. The determination procedure of the microhardness distribution isn't described there, as well. The cutting length, etc., isn't specified.
8. The analysis of the results sometimes seems to be based on wrong assumptions. For example, the claimed adhesive wear of the uncoated tool, which is said to be depicted at Fig. 4, is just a built-up edge, formed by the material, which stack to the surface of the cutting tool during the machining process. It is not clear, what was the evidence that [citation] "... All the average measurement results of the roughness parameters Ra and Rz for the f1 feed significantly exceeded the theoretical values given by the manufacturers of individual tools ..." (Results, paragraph 7), etc.
9. A lot of text and figures actually contain too general, too uninformative or duplicative information and must therefore be deleted:
a) Introduction, paragraph 1, lines 3-4: the sentence starting with "It can be stated ...".
b) Introduction, the entire paragraphs 2-5;
c) left part of Fig. 5;
d) Results, the entire paragraph 6;
e) Results, the entire paragraph 8;
f) Figs. 6-8.
10. There should be 3-5 conclusions, and they should summarize the findings in a more concise way.
11. References must be formatted in a strict accordance with the journal guidelines.
12. In addition to that, there is a number of formatting issues that must also be corrected:
a) The reference numbers should be written like [1-5], not [1;2;3;4;5];
b) The measuring units must be written without square brackets;
c) The measuring units must be splitted from the numerical values;
d) Table 1: the decimal parts of the numbers should be separated by dots, not by commas;
e) Fig. 9: the legend must entirely fit the chart; the reviewer strongly recommends to use squares, crosses, triangles, etc., to designate the points on the curves;
f) Etc.

[1] Khorasani, A. M., Yazdi, M. R. S., & Safizadeh, M. S. (2012). Analysis of machining parameters effects on surface roughness: a review. International Journal of Computational Materials Science and Surface Engineering, 5(1), 68-84.
[2] Bartarya, G., & Choudhury, S. K. (2014). Influence of machining parameters on forces and surface roughness during finish hard turning of EN 31 steel. Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture, 228(9), 1068-1080.
[3] Čep, R., Janásek, A., Petrů, J., Sadilek, M., Mohyla, P., Valíček, J., ... & Czán, A. (2014). Surface roughness after machining and influence of feed rate on process. In Key Engineering Materials (Vol. 581, pp. 341-347). Trans Tech Publications Ltd.

Author Response

Dear Reviewer,
Thank you so much for taking the time to read the article we prepared. Any corrections to the text are highlighted in yellow.
We would like to respond to the comments as follows:
1. The contents of the manuscript don't entirely match the scope of the journal, as the authors focus mainly on the effect of machining feed, not the one of the coatings.
The introduction to the article was extended by theoretical issues related to e.g. coatings applied on PCBN - cutting tools. We included more detailed characteristics of the tools used in this study in Table 2 (row 131), including those concerning the wear protection coatings applied. The results of the study were extended with Table 5b, which shows actual images of surfaces machined with coated tools and relates them to the condition of a surface machined with an uncoated tool (Table 5a).
2. The manuscript strongly lacks novelty. There are plenty of studies, which handle the influence of the machining parameters on the surface roughness of a steel (e. g., [1-3]). The mentioned coatings (TiN and TiAlN) have been applied for the protection of cutting tools for decades. Cubic boron nitride (further c-BN) has been used as a tool cutting material for a long time, as well.
The article comprehensively describes the effect of TiN- and TiAlN coatings applied on PCBN - cutting tools on the condition of surface layer and the condition of cutting tools after hard turning of thermally toughened X153CrMoV12 steel. It shows a number of disadvantages of using uncoated blades for turning of a given material, e.g. related to shorter blade life or the occurrence of adverse phenomena on the machined surfaces (chip adhesion, the side flow phenomenon), which negatively affect the shape of the bearing area curves, and thus – the operational properties of the machined surfaces. The subject of the article is relevant and up to date, which is indicated, among others, by the number of cited literature items published in the last three year.
3. The abstract isn't informative at all. It is quite impossible to understand, what was the object of the research (the term 'quality of technological surface' is too general), what experimental methods were used, and what was the outcome of this research. By the way, the coatings aren't mentioned in the abstract at all.
The article abstract was updated according to the comments.
4. Literature overview, brought in the chapter 'Introduction', isn't connected with the object of the study (as it mainly highlights the aspects of the wear of the tools from c-BN, while it wasn't studied at all).
The literature review was updated. Some content unrelated to the subject of the study was removed. Lines 29-64 were added to address issues specifically related to the scope of the study (include the machining of hardened materials, and the role of wear protection coatings on CBN tools).
5. The aims of the research weren't formulated, thus it is quite impossible to understand, what the authors actually study.
The purpose of the study was detailed both in the abstract of the article and in the summary of the introduction (lines 122-126). It concerned studying the possibility of replacing the grinding of a given material in its toughened condition by turning and achieving comparable properties of the surface layer for both machining methods.
6. The amount of the experiments done is too small for a research article (in general, only surface roughness and microhardness distribution in the turned steel are presented). Moreover, the experiments seem to have been done unsystematically (e. g., the wear of the uncoated tool is analysed, and the wear of the coated tools isn't).
A a new cutting tool and a new material sample was used for each operation. The graphs of roughness and microhardness distribution show the average values of measurements for these parameters. According to the comment made, the content of the article was extended to include a comparative analysis of phenomena occurring on coated cutting tools (Figure 4b was added). The results were extended by adding Fig. 5b, which shows actual images of surfaces machined with coated tools and relates them to the condition of a surface machined with an uncoated tool (Fig. 5a).
7. The description of the experimental procedure is unclear and incomplete. For example, the parameters, measured by the three-axis optical measurement system, aren't mentioned in the chapter 'Materials and Methods' at all. The determination procedure of the microhardness distribution isn't described there, as well. The cutting length, etc., isn't specified.
Appropriate changes were made. The geometric dimensions of the test specimens were added in line 130. Line 152 refers to the parameters tested with the 3D optical system. Lines 155-147 characterize the parameters and the testing method of material microhardness distribution.
8. The analysis of the results sometimes seems to be based on wrong assumptions. For example, the claimed adhesive wear of the uncoated tool, which is said to be depicted at Fig. 4, is just a built-up edge, formed by the material, which stack to the surface of the cutting tool during the machining process. It is not clear, what was the evidence that [citation] "... All the average measurement results of the roughness parameters Ra and Rz for the f1 feed significantly exceeded the theoretical values given by the manufacturers of individual tools ..." (Results, paragraph 7), etc.
We believe that BUE (built-up edge) refers to the machined material that builds up in the area of the cutting edge, rather than the flank face. An example of BUE is presented below (authors’ original research).
The phenomena shown in Figs. 4a and 4b represent the adhesive wear of the analyzed tools, with the adhesion wear for the uncoated T1 tool being much more intense than for the coated tools.
As far as the second comment is concerned – the presented conclusion is based on the comparison of test results obtained with the predicted values of Ra and Rz parameters provided in information materials from various tool manufacturers.
9. A lot of text and figures actually contain too general, too uninformative or duplicative information and must therefore be deleted.
Some content unrelated to the subject of the study was removed. The results of the research were expanded, expressing, e.g. no negative phenomena occurring on coated cutting blades in comparison with uncoated (fig. 4a, b) and machined surfaces (fig. 5a, 5b). We would like to emphasize, that some reviewers asked for that kind of comparison. Please accept the proposed method of presenting the cutting blades and machined screens.
10. There should be 3-5 conclusions, and they should summarize the findings in a more concise way.
Corrected according to the comment.
11. References must be formatted in a strict accordance with the journal guidelines.
Corrected according to the comment.
12. In addition to that, there is a number of formatting issues that must also be corrected: a) The reference numbers should be written like [1-5], not [1;2;3;4;5]; b) The measuring units must be written without square brackets; c) The measuring units must be splitted from the numerical values; d) Table 1: the decimal parts of the numbers should be separated by dots, not by commas; e) Fig. 9: the legend must entirely fit the chart; the reviewer strongly recommends to use squares, crosses, triangles, etc., to designate the points on the curves;
Corrected according to the comments.
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We hope that the changes made and the response to the comments will allow the article to be accepted for publication.

Sincerely Yours, Authors

Author Response File: Author Response.pdf

Reviewer 3 Report

I would like to note that the article corresponds to the subject of the "Coatings" journal. Simultaneously, the relevance of the chosen direction of research and research experience and the authors' high level of competence is beyond doubt.

Nevertheless, there are several comments on the article that I hope the author will take note of and eliminate.

1. The introduction is more like some "mess" and verbiage. I got the impression that the purpose of the introduction was not to introduce the reader to the course of the matter but to confuse him and ensure an increase in the number of manuscript pages. It is given basically about the durability of mechanical engineering products; general phrases are given about the importance of cutting tools quality in the manufacture of products. It is entirely out of place and has little to do concerning the present work. Why do you cite Figure 1 from the work of other authors "... an example of a" white layer" on the chip surface after processing improved steel [13]". What does the white layer have to do with your experiments? Why do you bring a macro photo of shavings because you are not considering similar questions? I would like to recommend the authors rewrite the introduction and introduce the article's readers to the specific problems you were engaged in. You mentioned that PCBN-based cutting could replace and eliminate grinding. That is right, it is. Thus, you can develop this topic, which is critical here, considering that you did nothing apart from studying the surface quality (and this is OK because this is also an important problem for finishing).

1. Provide a statement that the problem of machining high-hardness steels and alloys in mechanical engineering in the vast majority of cases is solved by grinding. At the same time, abrasive processing can negatively affect the workpiece's surface layer, residual tensile stresses are often formed, etc. (refer to relevant works). Next, it can be logically moved on to the PCBN tool since blade machining is devoid of abrasive machining's main disadvantages.
2. PCBN with different structures should be considered (you have it), be sure to indicate what quantitative values ​​of the surface roughness of the products are achieved when machining with a PCBN tool and show that they are comparable to grinding (refer to the relevant work).
3. Further note that coating is an additional tool and direction to improve tool performance (refer to relevant work). Be sure to note how the effect of the coating is manifested? After all, the role of coating for PCBN is radically different from that of coating for carbide tools. You mentioned the thermal barrier in passing but did not develop this idea. The known works that show ways that coatings can increase the blade cutting efficiency with PCBN tools should be summarized and cited.
4. The introduction should be completed by the formulation of your research tasks, describe the purpose, differences from similar work already performed. Be sure to indicate why the object of research was the processing of steel X153CrMoV12. What parts are made of it in mechanical engineering, and what are the requirements for the roughness (also indicate the hardness, since you are evaluating it in the process) of the surface layer, it is better to indicate the range (I hope it will correlate with the topic with the roughness values ​​that the authors received during the experiments).

If you follow these recommendations, it will at least be clear why you did all this.

2. However, let us not forget that you write your manuscript for publication in Coatings Journal with a dedicated readership. You are considering and testing a coated tool. It is necessary to clarify somehow the conditions for obtaining these coatings. If you decide not to touch upon the issue of informing readers about the physical and mechanical properties of coatings at all, then at least specify by what technology the coatings are applied to the PCBN tool and what their thickness is. Otherwise, your results will be of little practical value.

3. Figures 6-8 present the roughness profilograms for various machining conditions (with varying feed values). Unfortunately, profilograms are poorly readable, and they definitely should not be so blurry. The scale showing quantitative values ​​should also be made more apparent. Besides, the scale appears to exist separately from the profilograms. Then what informational load does the presented profilograms carry, are they presented for decoration? Furthermore, what do you mean by the term "Bearing area" (in charts 6-8, this area is highlighted in lilac). To which section of the workpiece does this area belong? Please clarify this in the text! Also, increase the font and add clarity to the scales and profilograms. Profilograms may eventually overlap these areas, which you have highlighted in lilac, but they should correlate with the scales. There is one more point regarding the presented roughness data (Fig. 3, Fig. 6-8). Everyone knows that surface roughness changes over time and increases with tool wear. At what point in time (cutting) the roughness measurements were carried out? What was the cutting tool state at that moment (how much the edge and working surfaces were worn out)? Please, clarify it at least in section 2, where you describe the measurement procedure.

4. Concerning Figure 9 "Microhardness of the material processed," firstly, the figure shows five curves, and an explanation of what each of the curves means is given only for 3 cases (look carefully at the lower right corner of the figure). Concerning the obtained hardness values, the requirements for hardness for parts made of steel of the X153CrMoV12 type are provided nowhere; in the article's text, you simply state the measurement results. For example, I do not understand what values ​​of the surface layer's hardness should be strived for and what will happen if the required hardness is exceeded and the so-called work hardening is obtained? It is no coincidence that in Remark 1d of the current review, it was recommended to indicate the types of parts so that you can understand the nature of the operating loads during operation. In the current version of the manuscript, the reader can not understand which of the presented curves is "good" and which is "bad" (Fig. 9). High hardness does not mean increased workability of the part during operation. It must be clarified by presenting at least a brief analysis of the obtained hardness measurement results.

5. During acquaintance with the article, the feeling does not leave that the authors were in a hurry somewhere, and they did not bother themselves with additional explanations and analysis. They give the results of all experiments in section 3, Results. Then immediately follows section 4, Conclusions. Why isn't there a Discussion of Results section? If it is so difficult to add, then reformat at least section 3 and provide the results and their discussion. You can also title section 3 as Results and discussion and add inferences about the obtained results. The article has a lot of omissions and even oddities. For example, why the roughness of the processed workpiece for a specific tool is more than 1.5 times the corresponding value obtained with a feed of 0.3 mm / rev at a feed value of 0.2 mm / rev (Fig. 3)? Usually, as the feed increases, the roughness also increases. In your case, on the contrary - in some cases, the roughness when feeding 0.3 is less than when feeding 0.1. It is all extraordinary. Moreover, you do not consider it necessary to explain anything. Understand that conclusions are a summary of your research, and they consist of several meaningful sentences that reveal the essence and the results obtained. All analysis that deeply explains the results obtained should be in section 3 Results and discussion (or in a separate section of the article).

The article needs some revision and to be shaped up. It can then be published in Coatings. 

Author Response

Dear Reviewer,
Thank you so much for taking the time to read the article we prepared. Any corrections to the text are highlighted in yellow.
We would like to respond to the comments as follows:
1. The introduction is more like some "mess" and verbiage. I got the impression that the purpose of the introduction was not to introduce the reader to the course of the matter but to confuse him and ensure an increase in the number of manuscript pages. It is given basically about the durability of mechanical engineering products; general phrases are given about the importance of cutting tools quality in the manufacture of products. It is entirely out of place and has little to do concerning the present work. Why do you cite Figure 1 from the work of other authors "... an example of a" white layer" on the chip surface after processing improved steel [13]". What does the white layer have to do with your experiments? Why do you bring a macro photo of shavings because you are not considering similar questions? I would like to recommend the authors rewrite the introduction and introduce the article's readers to the specific problems you were engaged in. You mentioned that PCBN-based cutting could replace and eliminate grinding. That is right, it is. Thus, you can develop this topic, which is critical here, considering that you did nothing apart from studying the surface quality (and this is OK because this is also an important problem for finishing).
a. Provide a statement that the problem of machining high-hardness steels and alloys in mechanical engineering in the vast majority of cases is solved by grinding. At the same time, abrasive processing can negatively affect the workpiece's surface layer, residual tensile stresses are often formed, etc. (refer to relevant works). Next, it can be logically moved on to the PCBN tool since blade machining is devoid of abrasive machining's main disadvantages.
b. PCBN with different structures should be considered (you have it), be sure to indicate what quantitative values of the surface roughness of the products are achieved when machining with a PCBN tool and show that they are comparable to grinding (refer to the relevant work).
c. Further note that coating is an additional tool and direction to improve tool performance (refer to relevant work). Be sure to note how the effect of the coating is manifested? After all, the role of coating for PCBN is radically different from that of coating for carbide tools. You mentioned the thermal barrier in passing but did not develop this idea. The known works that show ways that coatings can increase the blade cutting efficiency with PCBN tools should be summarized and cited.
d. The introduction should be completed by the formulation of your research tasks, describe the purpose, differences from similar work already performed. Be sure to indicate why the object of research was the processing of steel X153CrMoV12. What parts are made of it in mechanical engineering, and what are the requirements for the roughness (also indicate the hardness, since you are evaluating it in the process) of the surface layer, it is better to indicate the range (I hope it will correlate with the topic with the roughness values that the authors received during the experiments).
If you follow these recommendations, it will at least be clear why you did all this.
The introduction to the article was updated. Some content unrelated to the subject of the study was removed. The introduction was extended by theoretical issues related to e.g. coatings applied on PCBN - cutting tools. Lines 32-67 were added to address issues specifically related to the scope of the study. We included more detailed characteristics of the tools used in this study in Table 2 (row 148), including those concerning the coatings applied. The results of the study were extended, e.g. with Table 5b, which shows actual images of surfaces machined with coated blades and relates them to the condition of a surface machined with an uncoated blade (Table 5a). We would like to emphasize, that some reviewers asked for that kind of comparison.
2. However, let us not forget that you write your manuscript for publication in Coatings Journal with a dedicated readership. You are considering and testing a coated tool. It is necessary to clarify somehow the conditions for obtaining these coatings. If you decide not to touch upon the issue of informing readers about the physical and mechanical properties of coatings at all, then at least specify by what technology the coatings are applied to the PCBN tool and what their thickness is. Otherwise, your results will be of little practical value.
The introduction to the article was extended to include content specifically related to coatings used on PCBN tools (lines 58-67), referring to current literature. Table 2 contains detailed characteristics of the cutting tools, including the description extended by the parameters of the coatings used. We would like to emphasize that the blades used in this study are commercially available on the market. The coatings were applied by the manufacturers of the respective tools, and their parameters (described in Tab. 2) provided at our direct request.
3. Figures 6-8 present the roughness profilograms for various machining conditions (with varying feed values). Unfortunately, profilograms are poorly readable, and they definitely should not be so blurry. The scale showing quantitative values should also be made more apparent. Besides, the scale appears to exist separately from the profilograms. Then what informational load does the presented profilograms carry, are they presented for decoration? Furthermore, what do you mean by the term "Bearing area" (in charts 6-8, this area is highlighted in lilac). To which section of the workpiece does this area belong? Please clarify this in the text! Also, increase the font and add clarity to the scales and profilograms. Profilograms may eventually overlap these areas, which you have highlighted in lilac, but they should correlate with the scales. There is one more point regarding the presented roughness data (Fig. 3, Fig. 6-8). Everyone knows that surface roughness changes over time and increases with tool wear. At what point in time (cutting) the roughness measurements were carried out? What was the cutting tool state at that moment (how much the edge and working surfaces were worn out)? Please, clarify it at least in section 2, where you describe the measurement procedure.
Figures 6-8 show the change in the shape of the bearing area curves, and thus the operating properties of the machined surfaces, depending on the feed rate f and the type of tool being used. By evaluating the shape form, we are able to determine the overall surface susceptibility to wear. Visualization of this data allowed us to assess the effect of the feed rate and the type of tool being used on the operational properties of the machined surfaces.
As noted, the legibility of these figures was improved. Due to the low resolution of the profilograms, it was decided to remove them.
As to the last observation in the specific section – a new cutting tool and a new material sample was used for each operation (as described in line 160).
4. Concerning Figure 9 "Microhardness of the material processed," firstly, the figure shows five curves, and an explanation of what each of the curves means is given only for 3 cases (look carefully at the lower right corner of the figure). Concerning the obtained hardness values, the requirements for hardness for parts made of steel of the X153CrMoV12 type are provided nowhere; in the article's text, you simply state the measurement results. For example, I do not understand what values of the surface layer's hardness should be strived for and what will happen if the required hardness is exceeded and the so-called work hardening is obtained? It is no coincidence that in Remark 1d of the current review, it was recommended to indicate the types of parts so that you can understand the nature of the operating loads during operation. In the current version of the manuscript, the reader can not understand which of the presented curves is "good" and which is "bad" (Fig. 9). High hardness does not mean increased workability of the part during operation. It must be clarified by presenting at least a brief analysis of the obtained hardness measurement results.
Figure was corrected as noted (an error in the graph’s legend description was overlooked). The range of the X-axis has also been changed to increase the readability of the data presented. We, as the authors, were interested in the course of microhardness of the obtained surfaces after machining, i.e. determining whether the material hardened or tempered during machining as a result of high temperatures in the machining zone.
We are not looking for a specific value or range of values for a specific parameter. The aim of the specific analysis was to obtain information whether the machined element did not lose its properties (microhardness) during processing. Figure 10 was added showing the microhardness test results in numerical format.
5. During acquaintance with the article, the feeling does not leave that the authors were in a hurry somewhere, and they did not bother themselves with additional explanations and analysis. They give the results of all experiments in section 3, Results. Then immediately follows section 4, Conclusions. Why isn't there a Discussion of Results section? If it is so difficult to add, then reformat at least section 3 and provide the results and their discussion. You can also title section 3 as Results and discussion and add inferences about the obtained results. The article has a lot of omissions and even oddities. For example, why the roughness of the processed workpiece for a specific tool is more than 1.5 times the corresponding value obtained with a feed of 0.3 mm / rev at a feed value of 0.2 mm / rev (Fig. 3)? Usually, as the feed increases, the roughness also increases. In your case, on the contrary - in some cases, the roughness when feeding 0.3 is less than when feeding 0.1. It is all extraordinary. Moreover, you do not consider it necessary to explain anything. Understand that conclusions are a summary of your research, and they consist of several meaningful sentences that reveal the essence and the results obtained. All analysis that deeply explains the results obtained should be in section 3 Results and discussion (or in a separate section of the article).
As noted, Article 3 was entitled "Results and Discussion", and new content was added to the section.
The unnatural course of roughness change with increasing feed rate f for tool T1 (the only uncoated one among the studied tools) is caused mainly by numerous chip adhesions on the machined surface, as well as the occurrence of the phenomenon of the material side flow, which was described in lines 192 - 200. The authors decided to extend the results with Figures 4b and 5b in order to show that the aforementioned phenomena do not occur after turning with coated tools, further confirming the validity of CBN-coated tools for “hard” machining.
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We hope that the changes made and the response to the comments will allow the article to be accepted for publication.

Sincerely Yours, Authors

Author Response File: Author Response.pdf

Reviewer 4 Report

Dear Authors,

Congratulations on your work, which is about an interesting issue.

However, I've some deep concerns about it, suggesting below some mandatory actions to become this paper publishable. The suggestions are as follows:

1. The paper must be rewritten, using clear scientific language and where the message naturally flows. This is not the case in the ciurrent version.
2. The Abstract is short and doesn't focus on the main goals and results of your work. Please do it again. Moreover, please correct X153CRMOV12 to X153 CrMoV12, please, as in the title.
3. The keywords should be improved. Add "Roughness", "Coatings", "Turning", "Pre-treated steel", "Heat-treated steel", "Tool wear".
4. Please remove the 5 first paragraphs of the Introduction.
5. Please don't use groups of 5 references for just one idea.
6. Please organize your Introduction, talking about: Hardened steels -Turning process - Turning parameters - Tools geometry - Tools coatings - Tool wear - Surface finishing. Please leave to flow your text in a smooth manner. Be straight-to-the-point. Refer what others have been made in recent works in a direct speech, as you start doing in the second page of your paper (after bullets).
7. Please do not refer "Poulachon and co-authors" but "Poulachon et al.".
8. When you start a sentence by "Coelho et al. ...", please immediately add the reference [20].
9. In the introduction, please use more MDPI papers, such as these ones: doi:10.3390/met10020170 + doi: 10.3390/cryst11020180 + doi: 10.3390/coatings10080731 + doi:10.3390/coatings8110402 + doi: 10.3390/met11020260 + doi: 10.3390/surfaces2020024, doi: 10.3390/met8080582, for example.
10. Please highlight the coatings function in the yools, because it is not clear in the current version.
11. Please use "balance" instead of "the rest" in Table 1.
12. Please clearly state the number of samples used for each test condition.
13. Please provide the results with standard deviation, even in the graphs.
14. Please include a blank space between the units and the values (after Figure 2: 160m/min ......160 m/min).
15. Please explain the reasoning behind the selection of test condition in Table 2.
16. Please properly characterize the coatings used in terms of thickness, topography, structure, composition, etc.
17. Please properly characterize the hardness of the machined material.
18. Please include information about the lathe used, as well as the tool holder and other equipment used in turning process.
19. Please include information about the equipment used, brand, model, features and so on, namely the Profilometer.
20. Please include information about the selected roughness variables and corresponding definition. Please include the measurement procedures.
21. Please include scale in Figure 4 and point out the observation technique used.
22. Please contextualize some figures as Figure 5.
23. Please deeply revise the sentence after Figure 5.
24. Please comment the assymetry observed in some roughness profiles, which doesn't match with the feed rate used in the turning process.
25. Please comment on the vibration of the equipment and tool holder.
26. After the Results presentation, please include a DISCUSSION section where you must compare your results with the results btained by others. 
27. Please improve the Conclusion, talking about the relation of the coatings used with the surface roughness obtained, and so on.

Good luck for the rework.

Kind regards,

Francisco Silva

Author Response

Dear Reviewer,
Thank you so much for taking the time to read the article we prepared. Any corrections to the text are highlighted in yellow.
We would like to respond to the comments sent as follows:
- Respond to comment nr 1.
The content of the summary was updated. Changes were made in accordance with the comment.
- Respond to comment nr 2.
The key words was updated. Changes were made in accordance with the comment.
- Respond to comment nr 3.
The introduction to the article was updated in accordance with the comment.
- Respond to comment nr 4.
Changes were made in accordance with the comment.
- Respond to comment nr 5.
The introduction to the article was updated. Some content unrelated to the subject of the study was removed. The introduction was extended by theoretical issues related to e.g. coatings applied on PCBN – cutting tools. Lines 32-67 were added to address issues specifically related to the scope of the study. We included more detailed characteristics of the tools used in this study in Table 2 (row 148), including those concerning coatings applied. The results of the study were extended, e.g. with Table 5b, which shows actual images of surfaces machined with coated blades and relates them to the condition of a surface machined with an uncoated blade (Table 5a). We would like to emphasize, that some reviewers asked for that kind of comparison.
- Respond to comment nr 6.
Changes were made in accordance with the comment.
- Respond to comment nr 7.
Changes were made in accordance with the comment.
- Respond to comment nr 8.
The introduction to the article was updated in accordance with the comment.
- Respond to comment nr 9.
The introduction to the article was extended to include content specifically related to coatings used on PCBN tools (lines 58-67), referring to current literature. Table 2 contains detailed characteristics of the cutting tools, including the description extended by the parameters of the coatings used. We would like to emphasize that the blades used in this study are commercially available on the market. The coatings were applied by the manufacturers of the respective tools, and their parameters (described in Tab. 2) provided at our direct request.
- Respond to comment nr 10.
Changes were made in accordance with the comment.
- Respond to comment nr 11.
For each test (variable feed rate), a new cutting tool and a new material sample (described in line 160) were used.
- Respond to comment nr 12.
Changes were made in accordance with the comment.
- Respond to comment nr 13.
Changes were made in accordance with the comment.
- Respond to comment nr 14.
The tools used in this study are commercially available on the market. The coatings were applied by the manufacturers of the respective tools, and their parameters (described in Tab. 2) provided at our direct request. Tools manufacturers have specified a feed rate of 0.3 mm/rev for each blade as a upper limit value (an appropriate note was added in lines 223-224). The authors of the study decided not to go beyond the acceptable machining parameter range for individual tools.
- Respond to comment nr 15.
We included more detailed characteristics of the tools used for this study in Table 2 (row 131).
- Respond to comment nr 16.
The hardness of studied samples was 63 ± 2 HRC (row 132).
- Respond to comment nr 17.
The machining was performed using the CTX 510 machining centre (DMG Mori) with the following cutting parameters: Vc = 160 m/min, ap = 0.2 mm, f = 0.1; 0.2; 0.3 mm/rev. The PDJNR2020K11 holder knife was used in the research (r = 93°, α = 6°, γ = -6°) with DNGA 110408 replaceable inserts (re = 0.8 mm) – rows 133-136.
- Respond to comment nr 18.
Roughness was measured using an Alicona Infinite SL optical measurement system, as reported in the article, lines 152-154. In addition, information about the microhardness tester used for the tests was added in lines 155-157.
- Respond to comment nr 19.
The data is included in lines 164-166.
- Respond to comment nr 20.
The unnatural course of roughness change with increasing feed rate f for tool T1 (the only uncoated one among the studied tools) is caused mainly by numerous chip adhesions on the machined surface, as well as the occurrence of the phenomenon of the material side flow, which was described in lines 192 - 200.
The authors decided to extend the results with Figures 4b and 5b in order to show that the aforementioned phenomena do not occur after turning with coated tools, further confirming the validity of CBN-coated tools for “hard” machining.
- Respond to comment nr 21.
We are unable to address the issue related to the vibrations. We did not record them during the study. However, taking into account the class of the machining center used during the tests, we believe that the vibrations were negligible and did not affect the obtained results.
- Respond to comment nr 22.
Article 3 was entitled "Results and discussion" (acceptable by the Publisher) and new content was added to the section.
- Respond to comment nr 23.
Changes were made in accordance with the comment.
---
We hope that the changes made and the response to the comments will allow the article to be accepted for publication.

Sincerely Yours, Authors

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The author revised the manuscript, and the paper can be accepted now.

Author Response

Dear Reviewer,
Thank you so much for taking the time to read the corrected article we prepared.
We are happy, that the article can now be accepted for publication. ----- Sincerely Yours, Authors

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear colleagues!
You are slowly but surely moving forward so that your manuscript is eventually published in Coatings.
Many comments were taken into account. However, there remain questions about the manuscript in its current form.
1. It is not customary to name pictures as you did:
Figure 5a. The surface treated with ……
Figure 5b. The example of surfaces….
Either you have to sequentially number these figures Figure 5, Figure 6
Alternatively, you have to accept the numbering of this picture under position 5, and each picture inside this picture will be under the letters - a, b, c, d, etc.
The same criticism is about Figure 4.
If you have any doubts, take other authors' published articles in Coatings and study how they are organized.

2. You have not yet revised the comments on Figures 6, 7, 8, which illustrate the "Bearing area ....". They are entirely unreadable. What are the Z and X axes, and what are the values? It is clear that a specialized program formed these graphs, and you "pulled" them out of there just as it is. Nevertheless, such graphs are always processed in the most straightforward editors (such as Paint and so on), in which readable values and axis names are superimposed (for respect to the readers).

3. Many questions remain for Figure 9. Microhardness of the material ...

In the description of the graph, you write (lines 269 - 270): "For all tested surfaces, the hardness of the material core was achieved at a depth of 400÷500 µm from the outer border of the processed material". What is it all about? Indeed, you have the maximum value on the X-axis - 200 µm on the graph. The graph that you "stuck" on top is generally unconvincing since nothing is readable. Well, since you are all scientists, think of how to convey information to the reader clearly. For example, you can make a break in the line of the graph or something else. However, all data must be readable.
Lines 270 - 271: "The lowest degree of tempering was obtained for the material treated with the T1 uncoated tool…." Are you sure this statement matches the data on the chart? In my opinion, not for T1, but for T4 - The lowest degree of tempering…. This is not a discussion, but this is how it is depicted on your graph. Please align all markers on the curves.

4. A new graph to the manuscript's current revision, Figure 10, Surface hardening rate of the material processed ..., was added.  It raises even more questions so far. What does the Surface hardening rate mean in %? Why does this degree have negative values "-"? What would be taken as a base (the starting point or reference point) concerning what you count the degree? Why is there no correlation with the data in Graph 9? Are you showing softening (tempering) or hardening (hardening) here? Finally, what does it mean under each column in Fig. 10, the sign that usually denotes a scatter of values?

5. Why in the conclusions on the work the surface layer's hardness was not mentioned? You added this material to the article, so it is essential. Furthermore, since it is important, then something from your observations or original patterns should be presented in the conclusions (at least 1 point would be enough).
6. To complete the study with the section of Discussion is recommended.

7. The novelty of the work should be highlighted at the end of the Introduction. The description of formulated study tasks is recommended to complete the Introduction.

Author Response

Dear Reviewer,
Thank you so much for taking the time to read the corrected article we prepared. We hope, that new corrections will make it much more attractive for readers.
Please note, that any new corrections to the text are highlighted in yellow.
We would like to respond to the comments sent as follows:
- Respond to comment nr 1.
Changes were made in accordance with the comment.
- Respond to comment nr 2.
Changes were made in accordance with the comment.
- Respond to comment nr 3 and 4.
Changes were made in accordance with the comment.
The new graph (fig. 10) shows the degree of tempering of the surface. It indicates the ratio of the microhardness of the material core to the microhardness of the surface layer. The percentage values show us by how many % less hard the WW is in comparison to the core of the material. However, according to Your comment, the graph has been updated – now it shows a degree of tempering, not hardening. The content of the article related to this figure has also been corrected.
- Respond to comment nr 5.
Changes were made in accordance with the comment.
- Respond to comment nr 6.
Changes were made in accordance with the comment.
---
We hope that the changes made and the response to the comments will allow the article to be accepted for publication. Sincerely Yours, Authors

Author Response File: Author Response.pdf

Reviewer 4 Report

Dear Authors,

Thank you so much for properly addressing the Reviewers' comments and suggestion. 

Congratulations, because the quality of your paper is nor, much better.

However, there are two topics that can be improved, in order to make your paper more valuable for the readers. Thus, please consider:

1. Your Introduction is good, but should be improved. Because you are using mainly TiAlN coatings, I'm suggesting you include more information in your Introduction about this coating widely used in machining tools. I'm also suggesting a very recent REVIEW about this subject (https://doi.org/10.3390/met11020260), in open access, which could be complemented with others, like the following ones: https://doi.org/10.1016/j.wear.2020.203329; https://doi.org/10.1016/j.wear.2013.08.025; https://doi.org/10.1016/j.ijrmhm.2017.12.011; https://doi.org/10.1016/j.wear.2013.01.074; https://doi.org/10.1016/j.wear.2018.10.007; https://doi.org/10.1016/j.jmatprotec.2005.06.079.
2. Please avoid the use of references from Proceedings and journals without impact factor.
3. Please complete some references information, like in [33].
4. Please make clear the source of references [23] (date is missing) and [26] (Language? Thesis? Degree?)], among others.
5. The discussion about your results is poor yet. Please try to discuss what is going on with your Tool T5, the main reasons of the drop reported in Figure 9, after an initial raise.
6. Please improve the information in the axes of your graphs.
7. Please try to compare your results with similar works previously performed.

These improvements are crucial to make your paper stronger and more cited in the future.

Kind regards,

Reviewer

Author Response

Dear Reviewer,
Thank you so much for taking the time to read the corrected article we prepared. We hope, that new corrections will make it much more attractive for readers.
Please note, that any new corrections to the text are highlighted in yellow.
We would like to respond to the comments sent as follows:
- Respond to comment nr 1.
Changes were made in accordance with the comment. The introduction to the article was updated. Some new informations about properties of TiAlN have been added. However, it should be taken into account that the article focuses on the machining processes. That is why the introduction describes mainly the experience on this issue.
- Respond to comment nr 2.
Changes were made in accordance with the comment. Also - some new references has been added.
- Respond to comment nr 3 – 7.
Changes were made in accordance with the comment.
---
We hope that the changes made and the response to the comments will allow the article to be accepted for publication. Sincerely Yours, Authors

Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

Most of the comments are taken into account. Meanwhile, there are still issues that must be solved before publication. 
You have written that the smallest tempering corresponds to the T1 tool without coating (green on the graph, Figure 9). Could you kindly explain why it is not for the T4 tool (black line on the graph)? And why, in general, the black color of T4 shows more significant hardness? Do you recommend working without coating? It is the most important since there is the lowest tempering value is for the T1 tool without coating.

Author Response

Dear Reviewer,
Thank you so much for taking the time to read the corrected article we prepared. We would like to comment on Your last review as follows:
The hardness of all samples used in the tests was 63 +/- 2 HRC. Analyzing fig. 9, especially the microhardness of the material core, it can be concluded that among the tested samples, the material treated with the T4 tool had the highest hardness after the heat treatment process. There can be many reasons for the different hardness of samples - it can even be influenced by their location in the quenching furnace or tempering furnace or even the temperature distribution inside those furnaces.
While describing the test reresults, we focused on the percentage difference of microhardness between the material core and the sample surface. The smallest percentage difference was obtained for the material processed with the T1 tool. Not much more - for the material processed with the T4 tool.
Regarding the Reviewer's question - why the black line for the T4 tool shows greater hardness - we believe that a given sample after the quenching process had the highest hardness among those presented in Fig. 9. What is more, we would like pay attention to the comment in lines 269-271 of the article, describing what could disrupt the accuracy of the microhardness measurement.
Regarding the Reviewer's question - whether we recommend using cutting tools without coatings- considering the results of microhardness tests - we believe that the results of the tests presented leave no doubt that the use of coated cutting tools brings many benefits, including the durability of tools (lower wear degree than in the case of uncoated blades), or the parameters of the machined surfaces (no negative effects on the surface, e.g. material side flow or chip sticking). We belive, that the obtained results of microhardness may constitute the basis for the appropriate selection of material heat treatment conditions - so that the final component has the assumed microhardness of the surface layer after machining.
Dear Reviewer,
We hope that the presented arguments will allow You to accept the article and consent to its publication.
-- Sincerely Yours, Authors

Author Response File: Author Response.pdf

Reviewer 4 Report

Dear Authors,

Thanks for addressing the Reviwers' comments and suggestions.

some minor amendments need to be done regarding English and formatting, but the Publisher will improve this.

kind regards, 

Reviewer

Author Response

Dear Reviewer,
Thank you so much for taking the time to read the corrected article we prepared.
We are happy, that the article can now be accepted for publication.

Sincerely Yours, Authors

Author Response File: Author Response.pdf

Round 4

Reviewer 3 Report

Although the article has many shortcomings, the main comments to the graphs and pictures have not been taken into account during revision, the conclusions are contradictory and do not correspond to the tasks set in the work, the section of discussion is still absent, the article can be accepted for publication in its current form with the hope that the main remarks will be eliminated during the preparation of the manuscript for publication.