The Effects of Recrystallization on Strength and Impact Toughness of Cold-Worked High-Mn Austenitic Steels

Round 1

Reviewer 1 Report

The authors studied the toughness behavior of a high Manganese steel processed in different ways. The study shows a comprehensive investigation, which itself is of interest for the community. Unfortunately, the discussion and the presentation of the results is rather poor and rudimentary.

To begin with, the manuscript is not well written and plagued by numerous grammatical errors and nonsensical sentences. For example, the sentence “The high-Mn steels have been used chemical composition of 24%Mn, 0.44%C, 0.27%Si, 3.4%Cr, 0.013%P, 0.0023%S, 0.429%Cu and balance Fe (in wt%). The dimension of the high-Mn steels plate was in the width of 1500 mm, the length of 200 mm, and the thickness of 20 mm” left me confused.

These errors were not that problematic with a bit of imagination I can infer what the authors meant. There are, however, other mistakes that are misleading or plain incorrect. For example, in page 7 the authors wrote “It is indicated that work hardening by a cold working process is entirely induced by twinning mechanism of deformation”. This sentence is simply wrong for any FCC metal.

The next sentence “However, the elongation of cold-worked steels decreased dislocations density [23] and other strengthening mechanisms such as TRIP and TWIP [37]” is impossible to understand. How is it physically possible that deformation (elongation) could ever decrease the dislocation density?

In the same page 7, the authors note that “elongation increased due to increased ductility”, which besides being obvious is a good example why the discussion is very rudimentary.

We continue with page 7, the authors wrote “ductility was not recovered due to the presence of mechanical twin within the grain boundary”. The sentence is not only grammatically wrong but also nonsensical because a twin cannot be within a grain boundary. A twin is a special case of a grain boundary.

In the same manner, in page 8 the authors state: “the grain boundary was not completely recrystallized”. This is wrong again. The grain boundaries do not recrystallize.

Figure 11a, what was the previous processing of the as-received sample. To me it looks like a poorly prepared sample. You must mention the pre-processing otherwise the reader would suppose a as-cast condition, in which case the high fraction of LAGB is not expected.

Substantial contribution by the German group on high manganese steel were not cited. It comes to my mind the works by Haase et al in similar investigations that were not even considered.

Author Response

We are most grateful for the reviewers' helpful and detailed comments. We agree that the original manuscript should be revised to address the justified comments given by the reviewers. Accordingly, the revised manuscript has been systematically improved with new information and additional interpretations. We enclose the correspondingly revised version of the paper. Below, we describe how the paper was modified to address and comply with the reviewers’ comments. We sincerely hope that these changes and additional explanations render the article acceptable for publication in Metals.

The authors studied the toughness behavior of a high Manganese steel processed in different ways. The study shows a comprehensive investigation, which itself is of interest for the community. Unfortunately, the discussion and the presentation of the results is rather poor and rudimentary.

To begin with, the manuscript is not well written and plagued by numerous grammatical errors and nonsensical sentences. For example, the sentence “The high-Mn steels have been used chemical composition of 24%Mn, 0.44%C, 0.27%Si, 3.4%Cr, 0.013%P, 0.0023%S, 0.429%Cu and balance Fe (in wt%). The dimension of the high-Mn steels plate was in the width of 1500 mm, the length of 200 mm, and the thickness of 20 mm” left me confused.

>>>Thanks for the valuable comments. We've added a table.1 to our manuscript to explain the method more clearly.

These errors were not that problematic with a bit of imagination I can infer what the authors meant. There are, however, other mistakes that are misleading or plain incorrect. For example, in page 7 the authors wrote “It is indicated that work hardening by a cold working process is entirely induced by twinning mechanism of deformation”. This sentence is simply wrong for any FCC metal.

>>> Thanks for your comments. We modified our manuscript as follows.

‘It is indicated that work hardening by a cold working process is not induced by TRIP effects but twinning mechanism of deformation’

The next sentence “However, the elongation of cold-worked steels decreased dislocations density [23] and other strengthening mechanisms such as TRIP and TWIP [37]” is impossible to understand. How is it physically possible that deformation (elongation) could ever decrease the dislocation density?

>>> We are much grateful for these comments. We have modified the manuscript to reflect your comments.

‘However, the elongation of cold-worked steels decreased due to an increase in dislocations density.

In the same page 7, the authors note that “elongation increased due to increased ductility”, which besides being obvious is a good example why the discussion is very rudimentary.

>>> We thank for this suggestion. It has been clarified in the manuscript with this statement.

‘Tensile strength and yield strength decreased with increasing annealing temperature from 600℃ to 1000℃, but the elongation increased.’

We continue with page 7, the authors wrote “ductility was not recovered due to the presence of mechanical twin within the grain boundary”. The sentence is not only grammatically wrong but also nonsensical because a twin cannot be within a grain boundary. A twin is a special case of a grain boundary.

>>> Thanks for your comments. Mechanical twin observed within the grains, not grain boundary. It has been clarified in the manuscript with this statement.

‘In addition, ductility was not recovered due to the still presence of mechanical twin within the grains’

In the same manner, in page 8 the authors state: “the grain boundary was not completely recrystallized”. This is wrong again. The grain boundaries do not recrystallize.

>>> Thanks for this comments. I have selected the wrong word. Recrystallization is occurred within the grains, not grain boundary. It has been revised in the manuscript with this sentence.

‘Below 800℃, the grains were not completely recrystallized despite annealing, which maintained high twinning and high dislocation density.’

Figure 11a, what was the previous processing of the as-received sample. To me it looks like a poorly prepared sample. You must mention the pre-processing otherwise the reader would suppose a as-cast condition, in which case the high fraction of LAGB is not expected.

>>> Thanks for your comments. We prepared a test specimen and experimented again. We also added the new data in Figure 11a. We prepared that the EBSD sample was grinded with #320, #600, #1200, #2000 SiC paper, polished with 3㎛, 1㎛, 0.25㎛ suspension and colloidal silica using auto-polisher (STRUERS, Labosystem ). We obtained the EBSD grain boundary map of as-received samples. This result shows that the fraction of LAGBs is higher than that of HAGBs.

Substantial contribution by the German group on high manganese steel were not cited. It comes to my mind the works by Haase et al in similar investigations that were not even considered.

>>> We are much grateful for these comments. Based on the reference you recommended, we added the two references by Haase et al .

Haase, C.; Kühbach, M.; Barrales-Mora, L.A.; Wong, S.L.; Roters, F.; Molodov, D.A.; Gottstein, G. Recrystallization behavior of a high-manganese steel: Experiments and simulations. Acta Materialia 2015, 100, 155-168. Haase, C.; Barrales-Mora, L.A.; Roters, F.; Molodov, D.A.; Gottstein, G. Applying the texture analysis for optimizing thermomechanical treatment of high manganese twinning-induced plasticity steel. Acta Materialia 2014,80, 327-340.

Reviewer 2 Report

This paper well describes the relationship between cold-worked/annealed microstructures and mechanical properties. Here are the minor suggestion before accepting the paper. 

1) Overall English and grammar should be improved.

For instance,

2) How did you measure the tensile elongation? It seems that the elongation is transformed from the load-line displacement, not the strain gage. If so, the experimental details should be modified.

3) Does the annealing time, 15min, contain the heating or just mean the holding time? Because usually, the recrystallization in high-Mn steels is enough by a few minutes.

4) The dimension of tensile specimen is a bit weird, please check '6 mm in diameter, and 2 mm in thickness'.

5) In the section 3.1., 'deformation twin and slip band were observed in the grain boundary': It is better to revise it to 'near', 'around', or others, or inside grain etc.

6) "but the elongation increased due to increased ductility." This should be revised.

7) In the manuscript, 'Figure 10' should be Figure 11.

8) "In particular, the effect of grain refinement was maximized by most of the recrystallized grains containing abundant annealing twin boundaries." Please re-write this sentence.

9) Regarding fractographs, the authors described aforementioned there is no DBTT in these kinds of steels; however, they stated the fracture surface of the as-received or cold-worked specimens is brittle mode. Fig. 12a-d seems to show enlarged dimple rather than the cleavage or similar. This should be cheked.

Author Response

We are most grateful for the reviewers' helpful and detailed comments. We agree that the original manuscript should be revised to address the justified comments given by the reviewers. Accordingly, the revised manuscript has been systematically improved with new information and additional interpretations. We enclose the correspondingly revised version of the paper. Below, we describe how the paper was modified to address and comply with the reviewers’ comments. We sincerely hope that these changes and additional explanations render the article acceptable for publication in Metals.

This paper well describes the relationship between cold-worked/annealed microstructures and mechanical properties. Here are the minor suggestion before accepting the paper. 

1) Overall English and grammar should be improved.

For instance,

"Microstructure and mechanical properties~" in Abstract,  twining It is indicate etc.

>>> Thanks for your comments. It has been clarified in the manuscript with this statement.

‘Microstructure and mechanical properties were performed to evaluate the influence of cold worked and annealed high-Mn austenitic steels’

2) How did you measure the tensile elongation? It seems that the elongation is transformed from the load-line displacement, not the strain gage. If so, the experimental details should be modified.

>>> Thanks for your comments. We determined the elongation by the travel distance of crosshead. It has been clarified in the manuscript with this statement.

‘The 0.2 % offset stress was determined to be the yield strength in the specimens showing continuous yielding behavior and the elongation determined by the travel distance of crosshead.’

3) Does the annealing time, 15min, contain the heating or just mean the holding time? Because usually, the recrystallization in high-Mn steels is enough by a few minutes.

>>> We are grateful for these important comments. Generally, annealing time recrystallized of high-Mn steels is a few minutes, but we determined that the annealing time is 15 minutes which mean the holding time in this study. In order to achieve sufficient heat transfer to the plate, the heat treatment time was determined to be 15minutes (holding time). We changed the Fig.1 (adding a holding time).

4) The dimension of tensile specimen is a bit weird, please check '6 mm in diameter, and 2 mm in thickness'.

>>>We thank for this suggestion. We have changed it from “diameter” to “width” in the manuscript.

‘The dimensions of the plate-type sub-sized tensile specimens were 25 mm in gauge length, 6 mm in width , and 2 mm in thickness in ASTM-E8.’

5) In the section 3.1., 'deformation twin and slip band were observed in the grain boundary': It is better to revise it to 'near', 'around', or others, or inside grain etc.

>>>Many thanks for this comment. Generally, deformation twins and slip band were observed inside grain, not grain boundary. We have revised the sentence with this statement.

‘After the cold working process, deformation twin and slip band were observed inside grains in Figure 2b-d’

6) "but the elongation increased due to increased ductility." This should be revised.

>>> We are grateful for these important comments. It has been clarified in the manuscript with this statement

‘Tensile strength and yield strength decreased with increasing annealing temperature from 600℃ to 1000℃, but the elongation increased.’

7) In the manuscript, 'Figure 10' should be Figure 11.

>>>Thanks for your comments. It has modified from “Figure 10” to “Figure 11” in page 10, line 291.

8) "In particular, the effect of grain refinement was maximized by most of the recrystallized grains containing abundant annealing twin boundaries." Please re-write this sentence.

>>>We are much grateful for comment. It has been clarified in the manuscript with this statement.

‘In particular, grain refinement occurred due to recrystallization and grain subdivision by the annealing twins’

9) Regarding fractographs, the authors described aforementioned there is no DBTT in these kinds of steels; however, they stated the fracture surface of the as-received or cold-worked specimens is brittle mode. Fig. 12a-d seems to show enlarged dimple rather than the cleavage or similar. This should be cheked.

>>> Many thanks for these helpful comments. It has revised from “brittle” to “quasi-brittle”

Reviewer 3 Report

Do all mandatory changes defined in attached file

Comments for author File: Comments.pdf

Author Response

We are most grateful for the reviewers' helpful and detailed comments. We agree that the original manuscript should be revised to address the justified comments given by the reviewers. Accordingly, the revised manuscript has been systematically improved with new information and additional interpretations. We enclose the correspondingly revised version of the paper. Below, we describe how the paper was modified to address and comply with the reviewers’ comments. We sincerely hope that these changes and additional explanations render the article acceptable for publication in Metals.

Paper formally well organized, in whcich several flaws can be solved easy:

1- State of the art, recently in Metals was a new contribution about Mn is steel, and how

it affected the propierties, Metals 2019, 9(5), 556; https://doi.org/10.3390/met9050556,

and in others.

2- Script material works seems to be your main source of information, please reduce and eliminate 1-2 references. The same with Materials Characterization. The general idea of that the paper could be previously in other journal consideration must be eliminated at all.

>>> Thanks for your suggestion. It’s removed some of references of scripta matierial and Materials characterization.

Klimova, M.; Zherebtsov, S.; Stepanov, N.; Salishchev, G.; Haase, C.; Molodov, D.J.M.C. Microstructure and texture evolution of a high manganese TWIP steel during cryo-rolling. Materials Characterization 2017, 132, 20-30. Saha, R.; Ueji, R.; Tsuji, N.J.S.M. Fully recrystallized nanostructure fabricated without severe plastic deformation in high-Mn austenitic steel. Scripta Materialia 2013, 68, 813-816. Yanushkevich, Z.; Belyakov, A.; Kaibyshev, R.; Haase, C.; Molodov, D. Effect of cold rolling on recrystallization and tensile behavior of a high-Mn steel. Materials Characterization 2016, 112, 180-187.

3- Your Conclusion 2 define exact numbers when you have not too many samples to make

statistical analysis. In this case:

How can you make sure the value of data. My guess is that you tested twice or

three times several samples, under the microscope, or other analytical ways.

>>> We are much grateful for comments. The microstructures were checked as a whole according to each condition, and a representative microstructure photograph was included in the manuscript. Vickers hardness tests were performed at room temperature with a load of 4.903 N with 10s of dwell time. At least 7 measurements were made to calculate the average micro-hardness values by excluding the minimum value and maximum value. We performed the Charpy impact test at one specimen test for each condition.

Make you’re a original work. The properties of intermetallic phases are in direct link with secondary process performances, as it was shown by several authors, including Beranoagirre, in Metals 2018, 8(7), 543; https://doi.org/10.3390/met8070543 you can find several Works more in this line of thinking, including several works by Suarez and Polvorosa about the effects of grain size and heat treatment in several supaeralloys. Cryogenic cooling is under big discussion. The International Journal of Advanced Manufacturing Technology, January 2016, Volume 82, Issue 1–4, pp 303–314 for instance is a good example. My opinion is not very good, however please extend a little this discussion.

Figure 9: please make it bigger…the values are not well defined.

>>>Thank you for your suggestion. We read the two reference you recommended Metals 2019, 9(5), 556 and Metals 2018, 8(7), but we think that it’s less relevant reference of this paper. Instead of, we added the reference related to high-Mn steels of this study. We have added the references below to the manuscript.

Haase, C.; Kühbach, M.; Barrales-Mora, L.A.; Wong, S.L.; Roters, F.; Molodov, D.A.; Gottstein, G. Recrystallization behavior of a high-manganese steel: Experiments and simulations. Acta Materialia 2015, 100, 155-168. Haase, C.; Barrales-Mora, L.A.; Roters, F.; Molodov, D.A.; Gottstein, G. Applying the texture analysis for optimizing thermomechanical treatment of high manganese twinning-induced plasticity steel. Acta Materialia 2014, 80, 327-340.

>>> And, size of Figure 9 was reduced to be width of 13cm

Reviewer 4 Report

The present manuscript describes the effect of the recrystallization caused by annealing heat treatments after cold-working on the impact toughness of high-Mn austenitic steels for cryogenic applications. Overall, the manuscript is appropriately organized with some grammatical and word-choice errors that detract from the main message, moderate English check required. The research design is appropriate, the conclusions are supported by results, which were thoroughly discussed and adequately connected by citation of prior and current work in this area.

Some aspects should to be addressed before publication:

Line 47-48: please add a quote after the sentence, since SFE not always increases with higher Mn content – it depends on chemical composition, i.e. interaction of all alloying elements.

Line 305-307, fractographic investigations: the fracture surface doesn’t show any cleavage, which is the main characteristic of brittle mode, large dimples are still present. With only one exception, namely high-nitrogen austenitic steels, the austenitic steel in general doesn’t show embrittlement at low temperatures. The fracture mode presented in SEM images may be characterized as “quasi-brittle” which points out the decreased contraction of fracture surface sides due to low toughness.

Author Response

We are most grateful for the reviewers' helpful and detailed comments. We agree that the original manuscript should be revised to address the justified comments given by the reviewers. Accordingly, the revised manuscript has been systematically improved with new information and additional interpretations. We enclose the correspondingly revised version of the paper. Below, we describe how the paper was modified to address and comply with the reviewers’ comments. We sincerely hope that these changes and additional explanations render the article acceptable for publication in Metals.

Some aspects should to be addressed before publication:

Line 47-48: please add a quote after the sentence, since SFE not always increases with higher Mn content – it depends on chemical composition, i.e. interaction of all alloying elements.

>>> We are grateful for these important comments. Generally, SFE depends on the chemical composition. In general, SFE increases as Mn, Cr, Ni and Mo increase. The material tested in this study depends mainly on the SFE content of Mn. It has been clarified in the manuscript with this statement.

“These mechanisms depend on stacking fault energy (SFE), and the SFE generally increases as Mn, Cr and Ni content increase in TWIP steels.”

Line 305-307, fractographic investigations: the fracture surface doesn’t show any cleavage, which is the main characteristic of brittle mode, large dimples are still present. With only one exception, namely high-nitrogen austenitic steels, the austenitic steel in general doesn’t show embrittlement at low temperatures. The fracture mode presented in SEM images may be characterized as “quasi-brittle” which points out the decreased contraction of fracture surface sides due to low toughness.

>>> We are much grateful for comments. We have changed it from “brittle” to “quasi-brittle”.