Microstructural and Mechanical Assessment of Camshafts Produced by Ductile Cast Iron Low Alloyed with Vanadium

Round 1

Reviewer 1 Report

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Reviewer 2 Report

The authors have analyzed microstructure and mechanical properties of as-cast camshafts used in the automotive industry. Metallographic techniques and optical microscopy are applied for quantitative examination of the various microstructure constituents.

The change of local cooling rate leads to local variation of number and size of graphite nodules. A smaller number and larger size of nodules were detected in the middle region of lobes, where the lowest cooling rate is expected. The effect of microalloying with V on the constitution of gray cast iron was revealed. An increase of V content from 0.2 to 0.3 wt.% leads to enhanced carbide formation. The tensile strength rises on the cost of a slight reduction of toughness.

The paper offers a couple of interesting aspects for optimizing the microstructure of camshafts for automotive industry. However, English grammar and a few typos must be corrected. Some examples:

Line 34: in used => used in; Line 57: the lowest hardness results than… => lower hardness than…(?); Line 73: mm-2 =>  mm^-2; Line 99: lloys => alloys; Line 196: micro constituents => microconstituents; Lines 280/282: Mpa => MPa; Line 198: figure 6a => Figure 6a.

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Reviewer 3 Report

The paper presents an interesting issue regarding alloying of the cast iron with vanadium. Authors investigated a camshaft microstructure and compared its development in various casting areas. The paper has a publication potential however a few improvements should be done before its acceptance. I have some methodological remarks and "results discussion" related comments which should be answered and improved. Summing up, the comparison of the results with the "standard" cast iron used for camshafts should be added, the structure after the austempering heat treatment should be shown, and statistic should be used for results comparison. Detailed comments bellow:

1. The statistic is missing in the paper. Authors made a quantitative analysis of the results and some statistics should be added to accurately compare and discuss the results. So add to figs 6, 7, 8 and 9 the SD or/and max-min and average or/median
2. From my point of view, to show and discuss the properties changes of the V-rich cast iron, the comparison between standard camshaft cast iron and your 0.2% and 0.3% of V should be included in the paper. Authors should reconsider adding it.
3. The results from figures 6, 7, 8 and 9 should be compared with the data for standard camshaft cast iron.
4. 4. Literature references are old-and most of them is older than 10 years. The up-to-date references should be added.
5. In the material and methods should be clearly stated that the investigated cast irons will be used for ADI cast iron production. 
6. In the line 96 the ADI should be added eg. "...heat treatment of ADI camshaft production".
7. Can you add some results after ADI-treatment? Now, the paper describes only a half product. How this V-addition behaves during the ADI cast iron heat treatment - is it beneficial for structure or not? It should be added in the paper. Now, it is unclear how the V-addition and heat treatment affects the final cast properties. 
8. L99 - should be written "alloys" not "lloys" 
9. I think that authors meant hardness tester rather than "durometer" see line 147. Please improve it.
10. Please explain the formula used for CE calculations (see tab.1) There are many attempts for calculating the CE. Also, compare your CE with those calculated for "standard cast iron" used for camshafts.
11. The microstructures in Fig 4 are unclear. Please add some higher magnification photos of selected areas.
12. Why only the 0.3%V microstructures were shown in this paper?

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Reviewer 4 Report

Line 280: MPa instead of Mpa

Line 282: MPa instead of Mpa

Lines 355, 356, 358, 359, 361: Capital letters

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Round 2

Reviewer 3 Report

Thank you for your improvements. Now, the paper looks better and it is much more suitable for publication. 

Generally, I accept your explanations, however, still, I have a few remarks:

A. regarding my previous comment no. 11. "Please add some higher magnification
photos of selected areas" - can you provide one figure for each of "0.3 and 0.2%" and mark the most important phases. The figure from your response could be adapted. Or you should add the SEM microstructure. Mark the mentioned phases such as carbides, ferrite, pearlite etc.

B. Regarding: "no. 12. Why only the 0.3%V microstructures were shown in this paper?" - please add the microstructures from your response to the manuscript as an Appendix. Include in the appendix both 0.3%V and  0.2%V. It improves the readability of the paper. 

C. Fig.7 - it is not justified to present such high accuracy. Use only integers. Instead of the eg. 348.65 HV write 349 HV - and improve all the average in each bar. 

D. In conclusions compare the cast iron without and with the V addition. How the V addition affects the properties of the cast iron?.

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Round 3

Reviewer 3 Report

Dear Authors,

Thank you for your improvements.  I think that in fig. 5 Authors explained quite well the microstructure of the casts.

The paper, in my opinion, needs one more minor improvements - the figs. 3,4 and 5 should be transferred to the Appendix. Additionally, fig. A4 should be moved from Appendix into the manuscript text.

In the future, I suggest you study the types of carbides with the usage of XRD methods and focusing on statistical testing (e.g Anova testing ect.) to properly compare/investigate the differences between samples' areas.

Good luck in your future works,

Reviewer

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