Effect of Cerium Content on the Evolution of Inclusions and Formation of Acicular Ferrite in Ti-Mg-Killed EH36 Steel

Round 1

Reviewer 1 Report

According to the reviewer, the text should be supplemented with the following issues:

1. EU (US) standard HHIW steel (composition of such steel), line: (30).
2. Introduction. Authors state: “dispersed non-metallic inclusions or precipitates to induce AF nucleation…….- what kind of inclusion???
3. Author discusses process of the formation inclusion in liquid steel. The text should be supplemented with equations of reactions of the inclusions formation, equations for the equilibrium constant (K) and Gibbs energy (ΔG), line (43-48).
4. The phase systems Ti-Mg-Ce-(O,S,N) should be analyzed, what kind of non-metallic inclusions are possible to form ????? depending on the sulfur, oxygen and nitrogen content ????, line (56)
5. Fig. 1. Samples were taken in stages, temperature was constant, but calculations in thermodynamic equilibrium conditions (Fig. 2) were made for cooling conditions, comment needed. Fig. 2 does not correspond to the conditions in Fig. 1. Fig. 2. should be supplemented with drawings showing the course of change in the oxygen, sulfur and nitrogen content in steel.
6. The Authors conclude that the addition of Ti titanium-containing inclusions are not formed, or certainly? No information about TiN formation. Carefully analyze the conditions for inclusion formation after move in next additive. It is necessary to perform additional simulations of inclusions after introduction of alloying additions. That is, a thorough analysis of the conditions of inclusion formation in subsequent stages of calculations (FactSage), line (128).
7. Table 1 shows the composition of steel after refining? What, was the initial composition, before  introductions of alloy to the steel, including oxygen, nitrogen and sulfur content???
8. line 134-137 should accurately describe the effect of oxygen and sulfur on the formation of inclusions containing Ce.

 

Author Response

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Reviewer 2 Report

The design of the work is fine for me. The results are good. In general, I suggest to present the work in a more scientific way: clear line and target of each part to lead the reader, smooth connection between each part. The following changes are suggested:

Line 63-66: in this work, Al was also added as deoxidizer? Al also contributed the main type of inclusions in some samples. Please reconsider and present your alloy system.

Figure1: it is a nice schematic to display the experimental results. It is suggested to further describe the figure step by step, especially the sample name which are frequently used later, otherwise it takes time to understand.

Line 71 to 76, how did you design the experiments should be detailed described: the scale of your furnace, mass of raw materials, alloys, crucible...... and why it was designed like this, why Al was added (you would like to study influence of Ti-Mg-Ce), your sampling methods

The rules of the experimental description is to be repeated by others

Line 78-79: the title of the figure should be simplified. the explain of the samples should be in the text. Also the present sampling name is not clear for me. please clarify it.

Line 82-90, please explain what is the aim for analyzing the samples using different methods. You checked the inclusions in the as cast samples using automated SEM, How about the process samples? Please describe it in a step-wise way

Line 88, what datbase you used for the thermodynamic calculation

Line 94, why did you present this thermo-calculation results first, what is aim the calculation. As I understand, it is for confirming your experimental results? Then please present it when you needed. The later on paragraph has no relationship or connection with this part

For the presentation, maybe you needs to first introduce the Figure 2. Then tell the reader the detail content.

Figure 3, is it from automated EDS? please clarify it? you offer a percentage of the different types of inclusions, how did you produce it? based on number density? I suggest to offer the exact value instead or percentage, the same for the figure 7, 9, 13

Line 131-132, the content of 0.024% Ce is not included

Line 159-161, 2#, 3# has a lower number density but 4# has larger one, hence it is not always reduced in number, please revise it; please separate the long sentence to simple ones

Figures 7 and 9 have the exact same title, please offer a clarified name

Line 165, please offer a proportion figure to display the different phases in the different samples

Line 172, why does the FSP increase in 4#_?

Line 177 to 178, does the highest amount of AF lead to the highest content of HAGBs? please explain it.

Line 198, can you please also add mismatch of MnS?

Line210 to 214, please separate into short sentences

Line 219 please indicate it is as cast sample

 

Author Response

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Reviewer 3 Report

The manuscript presents a laboratory scale investigation on the formation of AF by considering the characteristics of non-metallic inclusions in Ti-Mg killed treated with varied amounts of Ce.

Authors have provided an adequate background, highlighting the knowledge gap in literature. Laboratory scale experiments are systematically conducted to address the proposed research. However, the obtained results are not well presented and are difficult to follow by reader. Moreover, the paper doesn’t sufficiently explains the obtained results.

Following are some specific comments.

1. The experimental method should be more descriptive. Perhaps a text description of the Figure 1 would be helpful. How was the metal chemistry obtained? How much area of analyzed for INCA analysis? What number of inclusions were detected?
2. Throughout the manuscript, the commentary on the figures is insufficient which makes it difficult for reader to grasp the presented results. For instance, Figure 4 is indirectly referred to in line 113 without any further description. Similar thing for Figure 7 in line 138.
3. It is claimed based on Figure 6 that inclusion in melt change from MgOAl2O3 to multi-phase CeAlO3/Ce2O2S-MgO to single-phase Ce2O2S. This is based on selective inclusions. It’s in necessary to present complete inclusion analysis showing the fractions of different types of inclusions present in each sample.
4. Does Figure 9 present data for as-cast samples or melt? A correction is needed in caption and secondary Y-axis.
5. Figure 9 shows that as-cast sample from steel #4 contains over 200 mm-2 inclusions and Figure 3 indicates that 11% of total inclusions in steel #4 are MnS. That means the number density of MnS is over 20mm-2. But according to Figure 3 it is less than 10 mm-2. Similar data for other samples is inconsistent. Please check for this discrepancy.
6. Line 160 indicates that the inclusion density of as-cast sample of steel #4 is half than that in its melt. What’s the implication of this?
7. The inclusion density of steel #1 in as-cast samples is higher than steel # 2 and #3, whereas in case of melt samples it is less for steel #1 than that of #2 and #3. What’s the reason for this?
8. Figure 9: the fraction of inclusions larger than 2um is almost similar for all samples. Considering high coagulation tendency of Ce-containing inclusions, one can expect that steel #4 would contain a larger fraction of large sized inclusions? Please comment on this.
9. How is the density of effective inclusions evaluated for Figure 13? It’s not described in the paper.
10. From Figure 13, authors suggest that inclusions having size larger than 2um are more effective for AF but don’t explain this behavior.
11. The highest density of effective inclusions for sample #3 is justified by low MnS inclusions. Following that logic steel #4 should have a high density.

Author Response

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Reviewer 4 Report

It is impossible to understand the content of this paper becasue of the following reasons.

1) The name of sample is hardly understandable. What is the meaning of 1-Ti, 2-Ce etc?  What is the differnce with the "as cast sample". The meaning is only shown in Fig.1.  The authors should describe the meaning of each sample in detail.

2) What kind of heat treatment was conducted to analyse the metalographic structure? Please explain the scientific meaning to observe the structure of as cast sample.

3) The description of the experimental method is insufficient. Experimental method has to be described so as to conduct the same experiment by other researcher. Especially, the smapling method, area of analysis, crucible etc should be written.    

4) Calculation method of Fig.2 &4 should be written.

5) The color of each part of bar shown in Fig. 7,9 and 13 indicates the inclusion size?  For exapmle, what is the meaning of "2.0-3.0" of blue part?  

6) What is the meaning of "effective inclusion"?

7) Line 59-62: The authors described that Ti-Mg-Ce deoxidation "is " effective to AF nucleation. If this potency has already shown, please show some references. In this case, the scientific importance of this study should be clarified by the comparision of the previous study.  

Author Response

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Round 2

Reviewer 3 Report

Thank you for considering reviewer’s suggestions and clarifying the ambiguities. Major improvements can be seen in the revised version. However, authors need to work on the quality of presentation.

1. Please reword the wording in line 93-100 to make it clear that point counting method refers to counting the number of inclusions on OM images using Image J.
2. Line 164-190: The text provides description in following sequence: Figure 6(a), Figure 7 and Figure 6(b). It’s not a good flow of text and causes confusion. Perhaps describing switching position of Fig 6 and Fig 7 would help.
3. Since two different methods have been used for determining the number of inclusions, it is recommended to mention to clearly specify how the presented data is obtained. For instance, it’s not reported that which measurement method was used for the data in Figure 11? Is it from Automated SEM?

Author Response

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Reviewer 4 Report

All questions are solved.