Study on the Deformation Behavior and Mechanical Properties of Lightweight Economic Stainless Steels with Varying Al and Mn Contents

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript is well written and easily accessible to a broad technical audience. This work expands our understanding of the subject. The reviewer was unable to identify any glaring deficiency in this work and it is recommended for publication as is.

Author Response

comment:The manuscript is well written and easily accessible to a broad technical audience. This work expands our understanding of the subject. The reviewer was unable to identify any glaring deficiency in this work and it is recommended for publication as is.

response:Thanks for your time and work on our manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

The article submitted for review presents interesting research results on the effect of Al and Mn on the mechanical properties of stainless steels. In my opinion, the article is scientifically sound but requires several revisions to enhance its quality. I have a few comments, which I include below:

1. Line 96 – I propose to quote the standard "GB/T 228-2002" with its full title in "References".
2. Line 102 – I propose to cite the standard “ASTM E23” with its full title in “References”.
3. Table 1 gives the percentages of Al and Mn. I propose to explain in Chapter 2 why the tests were performed for these and not other percentages. Why was the planned experiment not used, which would allow the construction of an appropriate mathematical model? The additions of Al and Mn are important, as indicated by the obtained results.
4. Figure 5 – Are the individual curves shown averaged from several curves, or are they curves for individual selected samples? How many samples were used in the measurement series?
5. Table 2 – deviations were given, e.g., ±8, ±15, etc. Are these the values ​​of the standard deviation or other errors? Please explain in the article.
6. Line 223 – Please provide in “References” the number and title of the standard according to which the “ISO evaluation” was performed.
7. Please add DIM to the abbreviations at the end of the article
8. Figure 6 shows red and black color curves. Red curves are "smoothed". Black curves show characteristic "oscillations". If possible, I would like to ask for an explanation in the article of the cause of these "oscillations". Why are the "oscillations" in Figure 6d greater than in the other figures?
9. In Chapter 5, it is written "The deformation behavior and mechanical properties ...". Deformations are the result of stresses; they do not arise by themselves. Therefore, I propose not to separate deformations from mechanical properties. This phrase should start "The mechanical properties of lightweight economic stainless steels ..."

Kind regards

Reviewer

Author Response

comments 1: Line 96 – I propose to quote the standard "GB/T 228-2002" with its full title in "References".

responses 1: Thanks for your comment. The standard "GB/T 228-2002" was replaced by "GB/T 228.1-2021", which was cited as ref. [22] in the revised manuscript.

 

comments 2: Line 102 – I propose to cite the standard "ASTM E23" with its full title in "References".

responses 2 :Thanks for your suggestion. The standard was cited as ref. [23] in the revised manuscript.

 

comments 3: Table 1 gives the percentages of Al and Mn. I propose to explain in Chapter 2 why the tests were performed for these and not other percentages. Why was the planned experiment not used, which would allow the construction of an appropriate mathematical model? The additions of Al and Mn are important, as indicated by the obtained results.

responses 3: We appreciate you sincerely for your comment. We intended to smelt four experimental steels (6 wt.% Mn + 0 wt.% Al, 6 wt.% Mn + 2 wt.% Al, 6 wt.% Mn + 4 wt.% Al, and 10 wt.% Mn + 4 wt.% Al). The 6Mn0Al steel serves as the control group. The addition of 2 wt.% and 4 wt.% Al is for studying the effect of Al content. Insufficient Al fails to effectively reduce density, while excessive Al leads to an increasing ferrite potential, which compromises the ductility of stainless steel. Increasing Mn content to 10 wt.% is to suppress ferrite formation. However, during the smelting process, the actual alloying composition may deviate from the planned composition. This is primarily due to the inherent variability in the composition of raw materials, potential dendritic segregation during smelting, and possible elemental loss during subsequent forging process. Consequently, the measured alloying composition (Table 1) may differ from the planned composition. It is important to note that such deviations commonly happen. The effect of this deviation on experimental results can be ignored.

 

comments 4: Figure 5 – Are the individual curves shown averaged from several curves, or are they curves for individual selected samples? How many samples were used in the measurement series?

responses 4: Thanks for your comment. For each steel, at least three samples were used for tensile test. Subsequently, the stress-strain curve that exhibited the highest overlap degree with the others was presented in Figure 5.

comments 5: Table 2 – deviations were given, e.g., ±8, ±15, etc. Are these the values of the standard deviation or other errors? Please explain in the article.

responses 5: Thanks for your comment. These values are mean deviations. This statement was added in the caption of Table 2, highlighted in red color.

 

comments 6: Line 223 – Please provide in “References” the number and title of the standard according to which the “ISO evaluation” was performed.

responses 6:  Thanks for your comment. What needs to be clarified is that "ISO evaluation" is a method for analyzing the load-deflection curves of standard impact samples as introduced in the refs. [1,2]. To avoid any misunderstanding, we have rephrased this sentence in page 7, lines 239-241, highlighted in red color.

"These curves were subsequently analyzed using the “ISO evaluation” procedure introduced in refs. [30,31] to identify characteristic events and their corresponding values". 

References:

[1] Alexopoulos, N.D.; Stylianos, A.; Campbell, J. Dynamic fracture toughness of Al–7Si–Mg (A357) aluminum alloy. Mechanics of Materials 2013, 58, 55–68,

[2]   Alexopoulos, N.D.; Stylianos, A. Impact mechanical behaviour of Al–7Si–Mg (A357) cast aluminum alloy. The effect of arti-ficial aging. Materials Science and Engineering: A 2011,528, 6303–6312, doi:10.1016/j.msea.2011.04.086.

 

comments 7: Please add DIM to the abbreviations at the end of the article

responses 7: The abbreviation of DIM was added.

comments 8: Figure 6 shows red and black color curves. Red curves are "smoothed". Black curves show characteristic "oscillations". If possible, I would like to ask for an explanation in the article of the cause of these "oscillations". Why are the "oscillations" in Figure 6d greater than in the other figures?

responses 8: Thank you for your comments. The black line represents the raw data. The smooth red line is the idealized load-deflection curve after processing by "ISO evaluation" procedure. The "oscillations" of the raw data curve is a common phenomenon, as seen in refs. [1,2]. Since the experimental steels are polycrystalline material, their internal structure are non-uniform, including grain boundaries, carbides, inclusions, and ferrite. When a crack propagates through these areas, load fluctuations may occur. Additionally, the sensitivity and accuracy of the load and displacement sensors of the impact tester are limited, which may result in errors. All these factors may lead to the "oscillations" of the raw load-deflection curve. The larger fluctuations observed in Figure 6d are very likely to be a coincidence.

References:

[1] Alexopoulos, N.D.; Stylianos, A.; Campbell, J. Dynamic fracture toughness of Al–7Si–Mg (A357) aluminum alloy. Mechanics of Materials 2013, 58, 55–68,

[2]   Alexopoulos, N.D.; Stylianos, A. Impact mechanical behaviour of Al–7Si–Mg (A357) cast aluminum alloy. The effect of arti-ficial aging. Materials Science and Engineering: A 2011,528, 6303–6312, doi:10.1016/j.msea.2011.04.086.

 

comments 9: In Chapter 5, it is written "The deformation behavior and mechanical properties ...". Deformations are the result of stresses; they do not arise by themselves. Therefore, I propose not to separate deformations from mechanical properties. This phrase should start "The mechanical properties of lightweight economic stainless steels ..."

responses 9: We totally agree with your point. The corresponding description was revised in page 9, lines 297-299, highlighted in red color.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

Deat Authors,
Congratulations on a well performed research and well written manuscript. My only comments are related to terminology issues.

Line 20-21: "The presence of ferrite led to cleavage at the fracture surface, which deteriorated the elongation and toughness" - I would suggest rephrasing, as formulated it results that cleavage causes this behavior, not that it is a consequence of crack growth.

Line 50: "...a fully austenitic to a duplex austenite-ferrite constituent" - here, and in other places, instead of "constituent" the term "structure" would be more appropriate.

Line 120 "network carbides" - I think that a network of carbides is exagerated. There is a high phase fraction of carbides, but they do not seem to be arranged as a network. A network of hard and brittle carbides would result in very poor mechanical properties. I suggest avoiding the use of "carbide network".

Line 124 "fully austenitic constituent " - same as for Line 50

Line 178 " ductile fracture and brittle fracture occurred simultaneously " - I think that this statement is very difficult to prove, if true. As austenite is more ductile than ferrite and it strain hardens more, it should deform more, the ferrite would fail first and redistribute stresses to the austenite and would fail later. Anyway, they surely do not fail simultaneously, rephrasing is advised. See line 245.

Line 203 "brittle ferrite" - I think it is improper to say that ferrite is brittle. It is less ductile than austenite, but definetly it is not brittle. 

line 206-207 -"the work hardening caused by ferritic constituent becomes weaker" - rephrasing is advised

 line 210 - "the brittle fracture occurrence of 6Mn4Al steel" - rephrasing woul we advised, it is nor really a brittle failure

line 232 "descripted " - altough correct, it is an old term, use "described"

line 252 "on the cotract, TWIP ..." - check, please

My best regards.

 

Author Response

comments 1: Line 20-21: "The presence of ferrite led to cleavage at the fracture surface, which deteriorated the elongation and toughness" - I would suggest rephrasing, as formulated it results that cleavage causes this behavior, not that it is a consequence of crack growth.

responses 1: Thanks for your suggestion. We rewrote this sentence in page 1, lines 20-22, highlighted in red color.

"The presence of ferrite led to cleavage at the fracture surface. The cleavage fracture explained the low elongation and toughness of duplex stainless steels".

 

comments 2: Line 50: "...a fully austenitic to a duplex austenite-ferrite constituent" - here, and in other places, instead of "constituent" the term "structure" would be more appropriate.

responses 2: Thanks for your suggestion. We revised the term "constituent" to "structure" throughout the revised manuscript.

 

comments 3: Line 120 "network carbides" - I think that a network of carbides is exagerated. There is a high phase fraction of carbides, but they do not seem to be arranged as a network. A network of hard and brittle carbides would result in very poor mechanical properties. I suggest avoiding the use of "carbide network".

responses 3: We agree with your point. We revised the related description.

 

comments 4: Line 124 "fully austenitic constituent " - same as for Line 50.

response 4: We changed the term "constituent" to "structure".

 

comments 5: Line 178 " ductile fracture and brittle fracture occurred simultaneously " - I think that this statement is very difficult to prove, if true. As austenite is more ductile than ferrite and it strain hardens more, it should deform more, the ferrite would fail first and redistribute stresses to the austenite and would fail later. Anyway, they surely do not fail simultaneously, rephrasing is advised. See line 245.

responses 5: We appreciate you sincerely for your comment. Therefore, we revised this description in page 5, lines 191-195, highlighted in red color.

“In contrast, Figures 4c and 4d show the coexistence of dimples and cleavage. This indicates that in 6Mn4Al and 10Mn4Al steels, the ferrite fractured first due to lower capacity for plastic deformation. Subsequently, stress was redistributed, and the austenite underwent plastic deformation until fractures”.

 

comments 6: Line 203 "brittle ferrite" - I think it is improper to say that ferrite is brittle. It is less ductile than austenite, but definetly it is not brittle. 

response 6: We totally agree with your point. We revised the term "brittle ferrite" as "ferrite".

 

comments 7: line 206-207 -"the work hardening caused by ferritic constituent becomes weaker" - rephrasing is advised.

responses 7: Thanks for your suggestion. We revised this sentence in page 6, lines 222-223, highlighted in red color.

"However, because the fraction of harder ferrite structure decreased, the work hardening rate and UTS of 10Mn4Al steel decreased".

 

comments 8: line 210 - "the brittle fracture occurrence of 6Mn4Al steel" - rephrasing would be advised, it is nor really a brittle failure.

responses 8: Thanks for your suggestion. We revised this sentence in page 6, lines 224-226, highlighted in red color.

"PSE decreases with the increasing Al content because the weaker work hardening of 6Mn2Al steel and the cleavage occurrence of 6Mn4Al steel".

 

comments 9: line 232 "descripted " - altough correct, it is an old term, use "described".

responses 9: We changed the term “descripted” to “described”.

 

comments 10: line 252 "on the cotract, TWIP ..." - check, please.

responses 10: Thanks for your comment. We revised this sentence in page 8, lines 269-270, highlighted in red color.

"Different from 6Mn0Al steel, TWIP effect in 6Mn2Al steel could absorb impact energy".

 

Author Response File: Author Response.docx

Reviewer 4 Report

Comments and Suggestions for Authors

The authors discuss the effect of Al and Mn additions to stainless steels to reduce their weight on the physical properties of the alloys. Some readers will be interested in these data. However, the following questions remain:

・The authors state that it is important to reduce the weight (specific gravity of the alloy) by adding lightweight elements while maintaining the essential properties of stainless steels, but they do not mention the specific gravity of the samples.
・Does the addition of Al cause a decrease in the machinability of the alloy used this study?
・Was no segregation observed in this study? (Al has low solubility in steel materials, so segregation sometimes can affect the homogeneity and mechanical properties of the stainless steels.) 

Author Response

Please refer to the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,
I appreciate your clarifications and corrections according to my comments. I'd like to recommend your article for publication.
Kind regards
Reviewer