Effect of Cooling Mode on the Microstructure of High-Strength Steel during Hot Rolling
Round 1
Reviewer 1 Report
Comments and specific questions requiring clarification:
1. I reccomend to use full names first, then shortcut in brackets. It will be more readable (undersandle) It reffers to whole manuscript. Please correct it. For example LF, RH, TMCP, FCC, BCC, (line no 62, 63, 205, 206).
2. Line no 18 – in my opinion “It helps…” – will be better from the grammar point of view.
3. Reffers to the fig no. 2, 3, 9 and 10 – if it is possible add full names of phase component: ferrite, pearlite, etc.
4. Reffers to the fig no. 8 and 10 - Are the figures no 8 and 10 presented in the manuscript are your authorship. If not, please provide the appropriate sources from the technical literature.
5. In my opinion the analyzed process ( Chapter 2.2, fig no 1) must be described more précised. Add these information to Your paper please. For example explain please:
- on what basis was the holding time of 3 minutes selected?
- on what basis was the heating rate of 20C/s selected?
- on what basis was the strain parameters (strain value and strain rate) selected? What they are supposed to represent?
6. You prepare TTT diagrams or DTTT diagrams?? If it is TTT type diagrams my question is Why You didn’t use DTTT diagram? It mean diagram of phase transformation after deformation process. Deformation (strain) has influence on the time of beginning and ending of particular phase transformations? – Add these explanation to Your paper please.
7. Description of the cooling process in some part of the manuscript is not very precise – “slow or high” – is not precise description. Please correct it. Use cooling rate value (C/s).
8. In line no 135-137 – You wrote that for sample no 2 martensite structure was found in some places. Explain it please – how it is possible if this sample was cooled slowly?
9. Between line no 138-141 You wrote that the variation of ferrite proportion in industrial test results are consistent with that in the laboratory simulation results, but the grain size and the uniformity of the structure are quite different, which is related to the sample size during actual industrial production and the time after coiling. In my opinion the main idea of physical modeling of the real technological process is to ensure (similar) values of time, temperature and strain parameters and cooling conditions. So the results of grains size must be similar also. Explain this problem for me please.
Comments for author File: 
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Author Response
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Reviewer 2 Report
In their study, the authors raise an interesting subject, concerning the phenomena occurring during hot rolling of steel and the influence of cooling on the microstructure of the material. Obtaining the proper structure when rolling high-strength steels is of key importance for the subsequent properties of the semi-finished products. As the authors point out, the method of cooling during the technological process has a great influence on the steel microstructure. Therefore, conducting research in this area is purposeful and fully justified.
Despite the rather interesting topic, there are some ambiguities that need to be clarified.
1. What grade of steel has been rolled? It is true that the chemical composition of the steel is presented in Table 1, but judging by the content of carbon and alloying elements as well as admixtures, it is difficult to call this high-strength steel.
2. Is the increase in the strength of the analyzed steel due to the hardening as a result of cold deformation?
3. On what basis was the heating and cooling cycle shown in Fig. 1 selected? How does the characteristic presented in Fig. 1 compare to the real conditions?
4. Were the mechanical properties of the rolled material analyzed during the research? What were the following parameters: Rm, Re, A?
5. Can the obtained results be applied to steels with a higher content of carbon and alloying elements?
Author Response
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Reviewer 3 Report
I have some remarks for authors:
- It is not appropriate to use abbreviations in the abstract, I recommend replacing it with a phrase.
- I recommend expanding the introduction section with articles dealing with the researched issues.
- Chapter 2.2, I recommend to state the value of the cooling rate from 900 ° C to 600 ° C for both samples.
- It is necessary to add the meaning of the abbreviations used (i.e. SEM, etc.), for example in the nomenclature form.
Author Response
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Reviewer 4 Report
Coil collapse in high-strength steels is a production-relevant issue. As pointed out by the authors, this is a materials technology problem. The topic is well outlined. Unfortunately, relevant information for a more detailed consideration and use of the results are missing.
Thus, more detailed information on the chemical composition is missing, which would allow to establish the connection to the precipitation state of the steel. Data on N, Al, Mo, V and B contents are missing.
In general, there is a lack of information on precipitation behavior, grain size before transformation and effective forming. All of these have a significant influence on the position of the transformation lines.
The TTT- diagrams are only suitable for describing isothermal phase transformations. To show the influence of cooling conditions, CCT or better DCCT - diagrams are necessary. CCT -diagrams can be easily calculated from ttt diagrams. In particular, Fig. 9 is completely unacceptable in this representation.
In the discussion, the relationship between microstructure and resulting longitudinal expansion would be valuable. This would quantify the effect on coil behavior more clearly.
There are numerous typos and knowingly unusual phrases in the text. Please correct this and check with a native speaker.
Author Response
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