Low Temperature Deformation Induced Microstructure Refinement and Consequent Ultrahigh Toughness of a 20Mn2SiCrNi Bainitic Steel
Round 1
Reviewer 1 Report
Paper is written straight forward and results are clearly descript. However there are some minor improvements necessary.
Grain refinement is the key effect of the work, but there is no clear quantification the degree of refinement given. Change in Prior Austenite Grain Size (PAGS) is given in chapter 3.3, but only comparing two different degrees of deformation. Please give the PAGS for the undeformed state too. Please quantify the refinement of the resulting microstructure in chapter 3.5 in terms of block or packet size as well. Change in amount of Blocky and Filmy RA is stated and an EBSD analysis given as proof (Fig 10). In Fig 11 you show the dimension of Filmy RA in TEM micrographs. The area indicated as Filmy RA in Fig are not Filmy RA in the sense of Fig 11. In chapter 3.4 it is stated that the amount of RA is different for both deformation grades. RA of 9.2% and 9.4% is no difference, esp. if determined with XRD. In chapter 3.5 you state the difference in high angle grain boundaries (HAGB) for both deformation grades. Please also indicted the scatter of the determination due to EBSD indexing. Please indicate the three different stages, mentioned in Line 115 in Fig. 4 or a separate Fig. with a plot of work hardening rate.Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The authors optimized the temperature treatment of 20Mn2SiCrNi steel and show how different deformation temperatures and deformation rates affect the stress-strain curves. After selecting optimal conditions, different amounts of total deformation were applied and differences in strength and toughness are related to the grain structure.
Even though a large amount of experiments were performed there are some observations that are missing.
Nothing is stated about any carbides/cementite that was formed. For example in the TEM images of figure 11: are the elongated structures all austenite or are they elongated carbides? Are there carbides? Are they affected by the amount of deformation? Some diffraction analysis could be useful here.
Similar question about martensite: is there any twinned martensite present? for example in the blocky RA parts (which are not shown in the TEM images) is that austenite or is it twinned martensite.
Not all images are well explained: specifically figure 6. what do the authors call the fibrous zone? if it is the area within the red lines, the statement that the fibrous zone of the 20% deformed sample is small, does not seem to be correct. What do the authors mean with a homogeneous and a tortuous crack? And where does the Ni coating inf figures 6c and 6d come from, that is not explained.
Similar comment for the EBSD images in figure 12: correctly explain the results that are represented here. Is there any austenite or martensite present in this area.
Line 137: it is concluded that ... but there are at that point no arguments for such a conclusion
Lines 171-176: the aim of the discussion of the dislocations is not clear, please reformulate
Line 192-193: is a volume fraction of 9.4% RA significantly different from 9.2% or should it be concluded that the total amount of RA is not affected by the higher amount of deformation?
Line 217-... the model of the microstructure is not well explained and it seems to contain a much higher amount of RA than in the real steel. A decent discussion of all results should be presented here leading to an accurate description of the microstructure.
The use of English language needs to be reviewed, some suggestions are given in the attached file.
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Title: It should read “microstructural refinement”?. Please omit the word “unique”
Is the investigated 20Mn2SiCrNi steel an ASTM grade? DIN grade? etc
Line 42: is “alloying” or “microalloying”…if microalloying, then it may not increase the cost that much?
Section 2: Please give the steel specification grade
Line 54: What is the orientation of the 8 mm x 12 mm with respect to the forged 35mm thick x 70 mm wide.
Line 58: Please specific the hot deformation temperatures.
Please include subsections in Section 2.
Please give more details regarding the gauge length dimensions, U notch dimensions?
Lines 81 and 83: please define γ and γ’ α and α’
Line 97: In line with images and text it should be discussed “ As deformation temperature increases,”…
Figure 4: Please mark using lines Stages I, II and III in Figure 4.
Lines 116-117 and 121-122: “Stage II: The rate of increase of stress decreases with the increase of deformation.”
Stage III: After dynamic recrystallization of all austenite, the stress value remains unchanged with the increase of deformation [25,26]
The two above statements are not need in Figure 4.
Line 130: …”with different degree of deformation.” Please specify 20% and 60%.
Lines 130-139: Those should be rewritten as it not only improves the strength but also elongation and toughness
Grain refinement not only improves toughness but also strength.
Figure 6: Higher magnifications? Is the term “fibrous” or “ductile”?
If the 20% deformation sample has less fibrous zone than the 60% deformation sample, what would be the fracture mode for the rest of the sample?
Lines 161-163: “Compared with 20% deformation, the original austenite grain size and microstructure of 60% deformation is refined, and the size of retained austenite is reduced.” Where are those results?
Errors should be given through the manuscript. For example:
Lines 169-170: 32 μm +- STDEV 14.5 μm +- STDEV
Lines 192-193: 9.4% +- STDEV 9.2% +- STDEV
And so on…
Lines 179-185: Please mark GB, LB and MA in Figure 8.
Figure 13: Schematic images for 20% and 60% deformation
Please include a separate legend for the 60% deformation image.
Symbols should have representative equivalent sizes from the representative images. For example, the oval symbols are too big relative to the pentagon symbols
The Conclusion section should be rewritten. Small equiaxed grains were also seen at 900oC.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
This article reveals the effect of microstructural refinement on toughness of a 20Mn2SiCrNi steel. The experimental result showing that the refinement improves the toughness is reasonable. However, the manuscript is difficult to read and understand, due to somehow strange and non-logical descriptions. In addition, grammatical mistakes were found throughout the text. To improve this manuscript, revisions should be required as suggest below.
Line 58: Please note how the "strain" of the specimen was measured.
1. Line 74: The expression "impact fracture was nickel plated" is strange. "fracture surface was nickel plated" would make sense. Similar strange expressions were seen throughout the manuscript, which should be corrected.
2. Line 102: "Deformation resistance" sounds somehow strange, since Figure 3 shows stress and strain. Just "flow stress" or other suitable terms would be used.
3. Line 104: "which can case work hardening" seems wrong grammatically.
4. Figure 2: Please note the strain rate.
5. Line 118: The authors mention the dynamic recrystallization, but the reviewer feels that the s-s curves in Fig.4 do not show the feature of dynamic recrystallization. On the other hand, dynamic recovery is mentioned afterward, which is confusing. Please consider the use of suitable terms.
7. Fig.5: This figure shows the properties of the hot-rolled plate specimens, which should be described in the text, as well as the testing temperature.
8. Line 135: "Toughness of room temperature" would be corrected to be "toughness at room temperature".
9. Line 137: The authors concluded that the grain refinement improved the toughness, but this is confusing because any data for the grain refinement was not shown there.
10. Caption of Fig. 5(a): The caption does not describe the all contents in the figure (not only strength value). Please correct.
11. Line 143: Please define the term "fibrous zone", and indicate where it exists in the SEM photographs.
12. Line 147: Please explain how the "single crack propagation path" was measured from the micrograph.
13, Line 150: Please note how the deformation amount was judged from the SEM micrograph.
14. Figure 6: The red text characters could not be read.
15. Line 162: How the retained austenite distinguished in the micrograph?
16. Line 164: "refines the grain size and microstructure" is confusing. Please note the difference between the "grain size" and "microstructure", if the authors wish to use both terms. In addition, "refines the grain size" seems strange, and it would be corrected to be "refines the grain" or “refines the microstructure”.
17. Line 169: "original austenite grain" seems not be used generally. "Prior austenite grain" would be suitable.
18. Line 171: "Grain size is fine" is strang. "Grain is fine" or "grain size is small" would be suitable.
19: Caption of Figure.12: The title "EBSD analysis" is not suitable. As other figures, please indicate such as grain boundary map, IPF map or misorientation angle distribution with using characters (a), (b), etc.
20. Line 183: The authors concluded that there is no difference in microstructures between the specimens deformed by 20% and 60%. However, this seems overstatement since some differences (prior austenite grain size, size and volume of carbides, as well as size and shape of retained austenite) are found in the SEM micrographs in Fig. 8.
21. Line 199: “Lath bainite” is a term to express the microstructure. “Between lath bainite” would be corrected to be “between bainite laths” or “between the laths of bainte”.
22. Fig. 12: Please define the colors of line in the grain boundary maps and the cut-off misorientation angle in the misorientation distribution.
23. It is recommended that whole text body would be spell-checked and also be checked by a native English speaker.
24. Please confirm the use of unit. For example, both /s and s-1 exit, and -1 should be subscript.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
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Author Response
We are glad to appreciate the affirmation of this article.Thanks so much again. Meanwhile, we have improved the English language and style.
Reviewer 2 Report
The comments of my first review are adequately answered and the paper can be published after a few editorial corrections. Most are indicated in the attached PDF file, but I recommend a final review of the English language.
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
The authors have addressed most of my comments. However, there are still a number of comments:
Errors should be given through the manuscript.
For example: lines 212-213: 5 microns and 2 microns
Please mark GB, LB and MA in Figure 8.
Figure 13: Schematic images for 20% and 60% deformation
Please include a separate legend for the 60% deformation image.
Symbols should have representative equivalent sizes from the representative images. For example, the oval symbols are too big relative to the pentagon symbols
In addition:
Is the investigated steel an Advance High-Strength Steel (AHSS)?
Line 12: please omit “for the first time”
Line 16: Please specific the lower temperature.
Line 47: …”a limited number of studies [Reference(s)?]…
Line 74: U-notch dimensions?
Lines 93-94: ?? is not the same symbol as ?? as shown in the text.
Lines 95-96: Cohen’s method [Reference(s)?]
Lines 102-103: “6.8 μm ± 2.1, 21.72 μm ± 2.5, 24.3 μm ± 102 size increases”
Standard Deviation missing?
Which deformation temperatures correspond to?
Line 140: “increased”
Line 157: A crack is not homogeneous
English corrections:
Line 2: “induce”
Line 32: “strength”
Lines 33-34: “processing parameters”
Line 47: “Q690E steel”
Lines 59-60: …”extensometer which the gauge length was 25 mm”…
Line 72: …”the dimensions of extensometer is 25 mm.”??. Should be rewritten.
Line 63: “The austenite grain pictures…” should be rewritten.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
Although the manuscript was revised, grammatical mistakes and somehow strange expressions still remain in the text, even in the revised or added part (for example, tensile strenght).
Due to poor English, this manuscript is difficult to read.
The reviewer strongly recommends the authors to ask a native speaker or a professional technical translator to correct the whole text, and submit again.
In addition, in Fig.12, the definition of the colors of lines and cut-off misorientation angle were not found. Please confirm again.
Author Response
Please see the attachment.
Firstly, we are very grateful to the reviewers for the valuable comments. We have carefully considered the comments and made modifications in the manuscript accordingly as listed below.
All the modifications which have been done are highlighted with in BLUE colour in the revised manuscript.
Then, if there are another some unsatisfactory expressions and standardizations in this article, please point out patiently and we are glad to revise it again.
Author Response File: Author Response.pdf
Round 3
Reviewer 4 Report
The manuscript was significantly improved in language.
However, there still are mistakes in Figs. 12 and 13.
The revised captions indicate that the blue line corresponds to low angle boundaries, but it should be high angle ones since they contain containing prior austenite boundaries and block boundaries. Please confirm and correct.
Author Response
Dear reviewer
Thanks for the constructive suggestion. We have revised the sentence to"the red lines are low-angle boundaries with misorientation angles between 2° and 15° while the blue lines are high-angle boundaries with misorientation angles over 15°", according to EBSD data.
Thanks again for your attention to the manuscript.
