Nb Microalloying Enhances the Grain Stability of SAE8620H Gear Steel During High-Temperature Carburizing
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe experimantal part of the work seems accurate and reasonable. At other hand it seems imposrtant to mention that one of the important parameter is number of particles. as for other remarks, they are below:
The pick (at 700 -750 C) on figure 1 must be discussed. It seems no thermodynamic reason for such pick exists.
In spite of high quality of the picture the change of grain sizes can hardly be demonstrated by figures 2 and 3. The authors must describe how they measure the grain size in this study.
What is sigma in equation (1)
Figure 11 demonstrates the coarsening kinetics and it is clearly seen the contradiction between theory and experiments. I can suggest to use logarithmic coordinates and to check if Ostwald ripening theory can be applied (I believe it is not).
Can the author indicate the ref. for interface energy value for (Nb-C-Fe) 0.54 J/m2.
Text in line 364 -366 and further is not correct at all. Temperature increasing mainly influence to the diffusion coefficient, kinetic parameter, as for thermodynamic driving force – it is quite difficult to say, but typically, it decreases with temperature…. As for increasing of the size with increasing of Nb content, it is also incorrect interpretation. I believe the Zener (or Ham) theory can be applied for the first stages. They are well described and can be used for steels (see e.g. V.A. Dub et al. / Materials Letters 215 (2018) 134–136). Increasing of the particle number leads to decreasing of their size.
This part (starting with table 2 must be completely rewritten). It is also important to add the particle density data (e.g. number of the particles per unit volume).
Author Response
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Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsPlease find attached below my review of this article.
Comments for author File: Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe article requires significant improvement. Despite the interesting topic, the entire article is difficult to read. Many of the experiments described are not described clearly enough and some of the drawings are difficult to read. Below are detailed guidelines for improving the article:
- The method used to determine the composition of the alloys in Table 1 should be indicated.
- TEM/EDS microstructure imaging parameters should be provided.
- Chapter 3.1 does not indicate how the data in Figure 1 were calculated. This should be supplemented.
- Figures 2 to 7 are of poor quality. In the caption of Fig. 2, the subitem "(a)" is missing. In the caption of Figure 6 there is "nitrogen" instead of "niobium"
- What software was used to calculate grain size in chapter 3.3
- How or with what software were the grain sizes calculated in section 3.4 and table 2?
- There is no "(a)" in the caption of Figure 8 and Figure 8c is not completely illegible.
- What are the time values ​​in Figure 11. Previously there was no information about times of the order of 30 hours. This should be explained.
- There are 22 references in this article, and they are up-to-date and appropriate. Generally, 40% of references are older than 10 years, and 45% are from the last 5 years. The number of cited publications seems to be small, considering the number of items that appear in Google Scholar. Additionally, in Chapter 3.4. Analysis and Discussion, the Authors do not enter into any discussion with other Authors and do not cite any publications.
The language used could be clearer.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsAccept in present form
