Effect of Solidification Variables on the Tensile Property of 2.8 wt% C–26 wt% Cr White Iron
Round 1
Reviewer 1 Report
In this study, the tensile properties of 2.8wt%C-26wt%Cr white iron at different solidification rates were investigated; meanwhile, some valuable information is obtained, which can be accepted after major revisions. The following are my detailed comments:
1. The English level of the manuscript needs to be improved. It is recommended to simplify some long sentences.
2. In line 101, “ Figure 3d-f ” should be “ Figure 3c-e ” because there is no Figure 3f in Figure 3.
3. I would like to know why the primary austenite with a solidification rate of 50um/s cannot grow directionally.
4. Generally, a large number of dendrites and a small grain size are beneficial to improve the strength of the alloy. Figures 4 and 5 show that an increase in the number of dendrites in the primary austenite would lead to a decrease in the tensile strength of the 2.8wt%C-26wt%Cr white iron; I wonder why?
5. What heating equipment is used in directional solidification in this study? Is it induction heating? In the case of induction heating, the effect of electromagnetic force on grains and dendrites cannot be ignored.
6. Figure 8 shows the difference in orientation of M7C3 carbides in the eutectic in situ composite and in the interdendritic region. I would like to know the effect of this difference on the strength of the casting.
Author Response
Response to the Reviewer 1.
Thank you for your kind comments! I revised the indicated points as followings:
- The English level of the manuscript needs to be improved. It is recommended to simplify some long sentences.
Response: several sentences were divided into a few ones. Several were deleted.
- In line 101, “ Figure 3d-f ” should be “ Figure 3c-e ” because there is no Figure 3f in Figure 3.
Response: deleted Figure 3.
- I would like to know why the primary austenite with a solidification rate of 50um/s cannot grow directionally.
Response: It does not meet directional solidification criteria which were drawn by calculation of liquidus temperature and thermal gradient at the solidification rate.
- Generally, a large number of dendrites and a small grain size are beneficial to improve the strength of the alloy. Figures 4 and 5 show that an increase in the number of dendrites in the primary austenite would lead to a decrease in the tensile strength of the 2.8wt%C-26wt%Cr white iron; I wonder why?
Response: Generally, it is true, and we also found the same results in the ordinary equiaxed castings. However, in the present study, directionally solidified materials have M7C3/austenite eutectic structure in the interdendritic region.the M7C3/austenite eutectic structure contains randomly oriented M7C3 carbide particles. Thus the more dendrites (fine) have the more randomly oriented M7C3 which cause early crack initiation under tensile stress.
- What heating equipment is used in directional solidification in this study? Is it induction heating? In the case of induction heating, the effect of electromagnetic force on grains and dendrites cannot be ignored.
Response: Directional solidification and quenching unit (DSQ) were used for the experiment which was mentioned in the previous study (Oh J.S.; Song Y.G.; Choi B.G.; Bhamonsut C; Nakkuntod R.; Jo C.Y.; Lee J.H. Effect of dendrite fraction on the M23C6 precipitation behavior and the mechanical properties of high Cr white irons. Metals 2021, 11, 1576). We adopted Super Kanthal heating element. Thus, we did not have such effect.
- Figure 8 shows the difference in orientation of M7C3carbides in the eutectic in situ composite and in the interdendritic region. I would like to know the effect of this difference on the strength of the casting.
Response: M7C3 particles in the in situ composite aligned along the growth direction which is parallel to the tensile stress direction, however those in the interdendritic region have random orientation as well as their interface meets normal or a certain degree to the tensile stress axis. Thus, those in the interdendritic region deteriorate tensile property.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Dear Authors,
The possibility of the formation of an 'austenite-graphite' composite eutectic microstructure in grey iron with a chemical composition significantly different from the stoichiometric one (similar to the 'austenite-carbide' eutectic considered in your article) is described in:
· Kurz,W.; Fisher, D.J. Dendrite growth in eutectic alloys: The coupled zone. Int. Metals Rev. 1979, 24, 177–204.
· Burden, M.H.; Hunt, J.D. The extent of the eutectic range. J. Cryst. Growth 1974, 22, 328.
· Stefanescu, D.M. Science and Engineering of Casting Solidification, 3rd ed.; Springer: Berlin, Germany, 2015.
I believe that citing this work will enhance the scientific merit of the manuscript.
I hope that the following comments will also serve this purpose.
Lines 24-46. „Generally, most of the wear resistance high Cr white irons have hypoeutectic composition because of the combination of solidified phases. Microstructure of hypoeutectic high Cr white irons is composed of primary austenite and eutectic structure…”
This text in my opinion, not correct from the point of view of the nomenclature used in physical metallurgy. I propose to reduce it to: „Generally, most of the wear resistance high Cr white irons of different chemical composition have hypoeutectic microstructure [1-5] that composed of primary austenite and austenite-carbide eutectic”.
Lines 33-34
The very high hardness of such cast irons is not due to the entire eutectic structure, but mostly to the presence of one of the phases, namely carbide.
Line 37
You don’t take into account the possibility of using of different molding composition and chill blocks used in the foundry technology to vary the cooling intensity.
Line 52
There are different sizes of Y-blocks. Please indicate, what size was used.
Line 57
The EDM abbreviation was not described.
Lines 73-75
What does this mean: ”Specimens … were prepared metallurgically”?
Line 74.
A lower-case letter should be used to indicate the unit 'litre'.
Lines 98-99. “Only austenite/M7C3 eutectic phase existed…”
Calling the eutectic component of the microstructure a phase is a mistake. Please check the definition of the term "phase". A eutectic is a microstructure component that consists in this alloy of two phases.
Lines 131-132. “It means …”
This conclusion is not obvious. It would need to be clarified.
Line 152. Typo.
Use dashes instead of semicolon.
Lines 198-199.
The arrows in Figure 10b are supposed to indicate 'deformation bands (or slip bands)'. Unfortunately, the deformation bands / slip bands are not visible in the photo. A higher contrast photo should be used or the text should be corrected to match the features visible in the microstructure.
Author Response
Response to Reviewer 2
Thank you for your kind comments! I revised the indicated points as followings:
The possibility of the formation of an 'austenite-graphite' composite eutectic microstructure in grey iron with a chemical composition significantly different from the stoichiometric one (similar to the 'austenite-carbide' eutectic considered in your article) is described in:
- Kurz,W.; Fisher, D.J. Dendrite growth in eutectic alloys: The coupled zone. Int. Metals Rev. 1979, 24, 177–204.
- Burden, M.H.; Hunt, J.D. The extent of the eutectic range. J. Cryst. Growth 1974, 22, 328.
- Stefanescu, D.M. Science and Engineering of Casting Solidification, 3rd ed.; Springer: Berlin, Germany, 2015.
I believe that citing this work will enhance the scientific merit of the manuscript.
I hope that the following comments will also serve this purpose.
Thank you for the references! The references would be helpful for the study. We are preparing another paper, we will cite those in the next article. (unfortunately, I am on business trip in US, thus, it is not easy to meet the date for the revised manuscript with those references.)
Lines 24-46. „Generally, most of the wear resistance high Cr white irons have hypoeutectic composition because of the combination of solidified phases. Microstructure of hypoeutectic high Cr white irons is composed of primary austenite and eutectic structure…”
This text in my opinion, not correct from the point of view of the nomenclature used in physical metallurgy. I propose to reduce it to: „Generally, most of the wear resistance high Cr white irons of different chemical composition have hypoeutectic microstructure [1-5] that composed of primary austenite and austenite-carbide eutectic”.
Response: Revised in the text. And deleted reference [6] due to withdrawal of the submitted article
Lines 33-34
The very high hardness of such cast irons is not due to the entire eutectic structure, but mostly to the presence of one of the phases, namely carbide.
Response: It is not easy to understand that you pointed. Anyhow, it is right. Especially, M7C3 in eutectic structure improve hardness, but not directly related to this article.
Line 37
You don’t take into account the possibility of using of different molding composition and chill blocks used in the foundry technology to vary the cooling intensity.
Response: Casting of the equiaxed mother alloy was carried out in a Y-block sand mold. The ‘solidification variables’ in the text covers the comments.
Line 52
There are different sizes of Y-blocks. Please indicate, what size was used.
Response: we adopted the following scheme of Y block
Line 57
The EDM abbreviation was not described.
Response: EDM abbreviation is not important, because the rods were remelted during DSQ.
Lines 73-75
What does this mean: ”Specimens … were prepared metallurgically”?
Response: It is generally accepted in the UK where I worked before. ‘Metallurgically’ means all the procedure for microstructural observation. I published many papers with the same terminology.
Line 74.
A lower-case letter should be used to indicate the unit 'litre'.
Response: revised
Lines 98-99. “Only austenite/M7C3 eutectic phase existed…”
Calling the eutectic component of the microstructure a phase is a mistake. Please check the definition of the term "phase". A eutectic is a microstructure component that consists in this alloy of two phases.
Response: Right, revised from ‘phase’ to ‘structure’
Lines 131-132. “It means …”
This conclusion is not obvious. It would need to be clarified.
Response: revised in the text as ultimate tensile fracture strength
Line 152. Typo.
Use dashes instead of semicolon.
Response: I think dashed line instead of semi colon is not proper to indicated the hardness value of the phases. Semi colon looks proper. And it is not important point.
Lines 198-199.
The arrows in Figure 10b are supposed to indicate 'deformation bands (or slip bands)'. Unfortunately, the deformation bands / slip bands are not visible in the photo. A higher contrast photo should be used or the text should be corrected to match the features visible in the microstructure.
Response: Yes, I agree to your opinion. However, observation of slip band in the alloy was not easy. We found the Slip bands occasionally during analysis of the microstructure. The photo was the best quality in the present study.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The author's response is correct and the manuscript can be accepted.
Author Response
Thank you for reviewing the revised version of the manuscript.
