Mechanical Properties of σ-Phase and Its Effect on the Mechanical Properties of Austenitic Stainless Steel
Round 1
Reviewer 1 Report
The article refers to the σ-phase and its influence on the mechanical properties of austenitic stainless steel.
In the introduction, the σ-phase was characterized in terms of hardness, brittleness and metal content. However, the authors did not present a hypothesis for the presented research - information about what research was carried out is not a hypothesis.
Experimental details:
- information on service conditions should be completed. Information that "after servicing for 8 years at 680-720 oC" is insufficient
- complete the information on the accuracy of measurements, the number of samples
Results/Discussion:
- it should be clarified what means: "The Cr and Fe element content of iron" (line: 102)
- the authors indicate servicing at room temperature and compare it to servicing at a higher temperature - the methodology does not indicate that the sample serviced at room temperature will also be analyzed; this should be clarified
- the authors in the discussion of the results refer to image pro plus software, while in the methodology there is no information on this subject - it should be clarified
Author Response
First of all, we would like to thank the reviewers for their very useful comments, which helped us improve the manuscript. We have replied to your comments one by one and revised the manuscript. The revised manuscript and the reply to your review comments have been uploaded to the attachment. Please check it.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Manuscript ID: coatings-2028797
Manuscript Title: Mechanical properties of σ-phase and its effect on the mechanical properties of austenitic stainless steel
The manuscript discusses mainly two important things.
(i) mechanical properties of σ-phase (such as Young’s modulus, yield strength, etc.) through the long term.
(i) The effect of the presence of σ-phase on the mechanical proper- 55 ties of this 304H austenitic stainless steel was also studied.
The study is carried out after servicing for 8 years at 680-720 ℃ was investigated. This article presents lots of innovative information with respect to the study. I appreciate the authors for this wonderful work. Especially, the discussion part (Section 4) is highly informative.
I have gone through the manuscript thoroughly and suggest the following queries.
1. During the experimentation, how did you observe the repetitive nature of tensile properties of the 304H austenitic stainless steel? Is it less or more repeatable compared to other engineering structural alloys?
2. How do you compare the properties of 304H austenitic stainless steel compared to other structural alloys made by additive manufacturing?
3. Could you have an insight into the anisotropy of the mechanical properties of the 304H austenitic stainless steel?
4. Could you provide the figure of the specimen for the experimentation with its configuration and orientation for the various tests conducted? It will be more convincing if the authors provide a photo of the set-up of various tests.
5. Whether the cracks in the σ-phase are susceptible to propagating along or across these interfaces? Whether these cracks deteriorate the mechanical properties.
6. Discuss the embrittlement effect of the σ-phase.
7. How does the volume fraction of the sigma phase affect impact toughness?
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Comments for author File: Comments.pdf
Author Response
Response to the comments of Reviewers 2
coatings-2028797: Mechanical properties of σ-phase and its effect on the mechanical properties of austenitic stainless steel
By Peiheng Qiao, Jinyang Xie, Yong Jiang, Pengjie Tang, Bin Liang, Yilan Lu, Jianming Gong
Dear Editor and Reviewers:
First of all, we would like to express our thanks to the editor for providing a chance to review our work and to the reviewers for their very useful comments, which have helped us to improve the manuscript. Therefore, we have made corrections/ modifications in order to improve the content of the manuscript. Revised portions are marked in red in the revised manuscript. The following are the reply to each point of reviewer 2, please check.
Reviewer #2:
- During the experimentation, how did you observe the repetitive nature of tensile properties of the 304H austenitic stainless steel? Is it less or more repeatable compared to other engineering structural alloys?
- How do you compare the properties of 304H austenitic stainless steel compared to other structural alloys made by additive manufacturing?
- Could you have an insight into the anisotropy of the mechanical properties of the 304H austenitic stainless steel?
- Could you provide the figure of the specimen for the experimentation with its configuration and orientation for the various tests conducted? It will be more convincing if the authors provide a photo of the set-up of various tests.
- Whether the cracks in the σ-phase are susceptible to propagating along or across these interfaces? Whether these cracks deteriorate the mechanical properties.
- Discuss the embrittlement effect of the σ-phase.
- How does the volume fraction of the sigma phase affect impact toughness?
We extracted all the concerns involved in these comments and addressed them item by item as follows.
Comment 1:
During the experimentation, how did you observe the repetitive nature of tensile properties of the 304H austenitic stainless steel? Is it less or more repeatable compared to other engineering structural alloys?
Answer:
In order to verify the repeatability of the tests results, we have carried out three times of tensile test and impact test, respectively, and took the average value as the test result. We also gave the error of test results, as shown in Table 1. It can be seen that the test results have good repeatability.
Comment 2:
How do you compare the properties of 304H austenitic stainless steel compared to other structural alloys made by additive manufacturing?
Answer:
Our study focuses on the changes associated with the long-term high-temperature service of 304H stainless steel processed by conventional methods, so it is not compared with the structural alloy made by additive manufacturing. However, we believe that with the development and maturity of additive manufacturing technology, additive manufacturing structural alloys will be more and more widely used in industrial production.
Comment 3:
Could you have an insight into the anisotropy of the mechanical properties of the 304H austenitic stainless steel?
Answer:
The anisotropy of stainless steel processed by traditional methods is mainly caused by the different degrees of deformation in different directions (that is, the different degrees of deformation strengthening). The stainless steel made by additive manufacturing will also show a certain degree of anisotropy. We think it is mainly due to the cooling rate in the additive manufacturing process, the direction of grain growth, the stress and stress redistribution caused by many cold and hot changes and so on.
Comment 4:
Could you provide the figure of the specimen for the experimentation with its configuration and orientation for the various tests conducted? It will be more convincing if the authors provide a photo of the set-up of various tests.
Answer:
Thanks for your comments. According to the reviewer's suggestion, we have added the photos of the nanoindentation instrument, and the modified part has been marked in red in Section 2.4.
Comment 5:
Whether the cracks in the σ-phase are susceptible to propagating along or across these interfaces? Whether these cracks deteriorate the mechanical properties.
Answer:
According to our study, the cracks in the σ-phase are susceptible to propagating along these interfaces. At the initial stage of tensile deformation, cracks did not extend into the austenite phase. This is why the material still retains the elongation of 39 %. At the later stage of the tensile test, with the increase of tensile load, these micro-cracks became an important reason for the reduction of elongation from 59% to 39%.
Comment 6:
Discuss the embrittlement effect of the σ-phase.
Answer:
Thanks for your kind and valuable comments. As suggested by the reviewer, we have improved the related texts of discussion in Section 4.4. These changes are marked as red in this paper. For the convenience of reviewers, improvements are listed here. " About half a century ago, it has been accepted that the impact toughness in steel is strongly dependent on the cracking of precipitates, inclusion and the second phases [61]. in the particle cracking progress, the initiation sites of cracks are highly related to the distribution, size, volume fraction and morphology of these particles [62]. In addition, according to the fracture model of precipitated phase by Smith et al. [63], the larger the size of precipitated phase is, the lower the critical fracture stress of a precipitated phase / matrix interface is. The dramatic decreased impact toughness of 304H stainless steel after long-term service should be attributed to the precipitation and coarsening of σ-phase. The dislocation pile-up at a σ / σ and σ / matrix interface and thus initiate the microcrack. In Fig.4 and Fig.5, large amount of micro-cracks are observed between the σ / σ and σ / matrix interface, which shows that these interfaces are the main source of the micro-cracks initiation. The easy generation of microcracks leads to a sharp decrease in the toughness of 304H studied in this paper."
References
[61] Curry D A, Knott J F. Effect of microstructure on cleavage fracture toughness of quenched and tempered steels[J]. Metal Science, 1979, 13(6): 341-345. http://dx.doi.org/10.1179/msc.1979.13.6.341
[62] Li Z, Xiao N, Li D, et al. Effect of microstructure evolution on strength and impact toughness of G18CrMo2-6 heat-resistant steel during tempering[J]. Materials Science and Engineering: A, 2014, 604: 103-110. http://dx.doi.org/10.1016/j.msea.2014.03.013
[63] Curry D A, Knott J F. Effects of microstructure on cleavage fracture stress in steel[J]. Metal Science, 1978, 12(11): 511-514. http://dx.doi.org/10.1179/msc.1978.12.11.511
Comment 7:
How does the volume fraction of the sigma phase affect impact toughness?
Answer:
Dispersion strengthening is one of the important strengthening methods for metals. For example, due to the pinning effect, the small carbide in steel can greatly improve the strength of materials without reducing the plastic toughness. If these dispersed precipitated strengthening phases grow (such as carbide aggregation and growth), the plastic toughness will be reduced. The influence of Sigma on the mechanical properties of 304H stainless steel is similar to that of carbide. If the size of Sigma phase is small and the content is low, the strength of 304H can be improved without affecting the plastic toughness. However, if the Sigma phase is coarsened and the volume fraction increased, the plastic toughness of 304H stainless steel will be greatly reduced.
Author Response File: Author Response.pdf
Reviewer 3 Report
The paper is interesting to researchers.
Author Response
Response to the comments of Reviewers 3
coatings-2028797: Mechanical properties of σ-phase and its effect on the mechanical properties of austenitic stainless steel
By Peiheng Qiao, Jinyang Xie, Yong Jiang, Pengjie Tang, Bin Liang, Yilan Lu, Jianming Gong
Dear Editor and Reviewers:
Thank you for taking time out of your busy schedule to review our manuscripts, and thank you for your recognition of our research content. At the same time, we will work harder to write more excellent articles.
Author Response File: Author Response.pdf
Reviewer 4 Report
Through the review, I think this is a very nicely written paper, and the author analyzed and discussed the results in detail and correctly. The analysis developed in this paper is correct and the obtained results are interesting. The paper has sufficient novelty and covers the scope of the Coatings journal. Therefore, the manuscript may consider for publication in the Coatings journal after responding to the following comments and revising the manuscript properly.
1. The novelty of the work is missing in the introduction section. Explain it properly.
2. Improve language throughout the manuscript.
3. Reduce similarity, check attached report.
Comments for author File: Comments.pdf
Author Response
Response to the comments of Reviewers 4
coatings-2028797: Mechanical properties of σ-phase and its effect on the mechanical properties of austenitic stainless steel
By Peiheng Qiao, Jinyang Xie, Yong Jiang, Pengjie Tang, Bin Liang, Yilan Lu, Jianming Gong
Dear Editor and Reviewers:
First of all, we would like to express our thanks to the editor for providing a chance to review our work and to the reviewers for their very useful comments, which have helped us to improve the manuscript. Therefore, we have made corrections/ modifications in order to improve the content of the manuscript. Revised portions are marked in red in the revised manuscript. The following are the reply to each point of reviewer 4, please check.
Reviewer #4:
- The novelty of the work is missing in the introduction section. Explain it properly.
- Improve language throughout the manuscript.
- Reduce similarity, check attached report.
We extracted all the concerns involved in these comments and addressed them item by item as follows.
Comment 1:
The novelty of the work is missing in the introduction section. Explain it properly.
Answer:
Many studies have shown that sigma phase has high hardness and its precipitation has a great impact on the mechanical properties of materials. The mechanical properties of Sigma phase itself can help to understand its impact on the overall mechanical properties of the matrix. However, due to the small size of Sigma phase, it is difficult to directly measure its mechanical properties with conventional methods. Therefore, we studied the mechanical properties of Sigma phase itself through nano indentation test.
As suggested by the reviewer, we have improved the related texts in Section 1 as following: “Because of size of σ phase is too small, it is difficult to obtain the true mechanical properties of σ phase directly. So except for several articles on the hardness of σ-phase [16,17], there are no reports on other mechanical properties of σ-phase (such as Young’s modulus, yield strength, etc.). However, these mechanical properties of σ phase itself are valuable for further understanding the mechanical properties degradation due to σ phase precipitation. Therefore, it is necessary to study the mechanical properties of σ phase.”
References
[16] You D, Yang G, Choa Y H, Kim J K. Crack-resistant σ/FCC interfaces in the Fe40Mn40Co10Cr10 high entropy alloy with the dispersed σ-phase[J]. Materials Science and Engineering: A, 2022, 831: 142039. https://doi.org/10.1016/j.msea.2021.142039
[17] Minami Y, Kimura H, Ihara Y. Microstructural changes in austenitic stainless steels during long-term aging[J]. Materials Science and Technology, 1986, 2(8): 795-806. https://doi.org/10.1179/mst.1986.2.8.795
Comment 2:
Improve language throughout the manuscript.
Answer:
Thank you for your comment. The manuscript has been revised carefully and some grammar errors have been corrected as well. We hope this can meet your requirements.
Comment 3:
Reduce similarity, check attached report.
Answer:
Thank you for your valuable comments. We have modified the expressions that can be modified, except for some common fixed expressions such as "yield strength and tensile strength", "the elongation", and so on.
Author Response File: Author Response.pdf
Reviewer 5 Report
The paper as a research paper is excellent. However, I can’t understand where it fits into the scope of the Special Issue. What has the hardness of the σ-phase to do with coatings? Certainly the technique of microhardness testing might be very useful when it comes to assessing the hardness of thin surface coatings but it is not at all clear why this is being used here. Could the authors explain why it is being submitted to this Journal and not to a more appropriate Journal?
I myself have often found microhardness testing can give you a lot of information on the properties of hard fine particles and your paper illustrates very well the sensitivity of the technique when the right corrections are made to the data.
I suggest some very minor corrections to make the paper a little clearer but again I do not understand your choice of Journal.
Fig. 1 Metallographic images showing the distribution and size of the sigma Fe-Cr precipitates -- line 105
Fig 2. Scanning electron microscopy (SEM) images of the 304H stainless steel showing the variation in the proportion of Cr and Fe in the sigma phase in the nine Fe-Cr precipitates examined -- line 110
line 113 -- meet the standard requirements although the elongation is reduced.
Line 117-- However, the impact energy --
line 127. Cracking characteristics on the side
line 135. the dimple size is very shallow which is consistent with the low impact energy? Do you have a reference for this?
line 143. Fig.4 Fracture character of impact test specimen tested at room temperature.
line 212. Fig.9 Linear regression of (a) nano-hardness and (b) Young's Modulus against inverse of the dislacement
Author Response
Response to the comments of Reviewers 5
coatings-2028797: Mechanical properties of σ-phase and its effect on the mechanical properties of austenitic stainless steel
By Peiheng Qiao, Jinyang Xie, Yong Jiang, Pengjie Tang, Bin Liang, Yilan Lu, Jianming Gong
Dear Editor and Reviewers:
First of all, we would like to express our thanks to the editor for providing a chance to review our work and to the reviewers for their very useful comments, which have helped us to improve the manuscript. Therefore, we have made corrections/ modifications in order to improve the content of the manuscript. Revised portions are marked in red in the revised manuscript. The following are the reply to each point of reviewer 5, please check.
Reviewer # 5:
The paper as a research paper is excellent. However, I can’t understand where it fits into the scope of the Special Issue. What has the hardness of the σ-phase to do with coatings? Certainly the technique of microhardness testing might be very useful when it comes to assessing the hardness of thin surface coatings but it is not at all clear why this is being used here. Could the authors explain why it is being submitted to this Journal and not to a more appropriate Journal?
I myself have often found microhardness testing can give you a lot of information on the properties of hard fine particles and your paper illustrates very well the sensitivity of the technique when the right corrections are made to the data.
I suggest some very minor corrections to make the paper a little clearer but again I do not understand your choice of Journal.
Fig. 1 Metallographic images showing the distribution and size of the sigma Fe-Cr precipitates -- line 105
Fig 2. Scanning electron microscopy (SEM) images of the 304H stainless steel showing the variation in the proportion of Cr and Fe in the sigma phase in the nine Fe-Cr precipitates examined -- line 110
line 113 -- meet the standard requirements although the elongation is reduced.
Line 117-- However, the impact energy --
line 127. Cracking characteristics on the side
line 135. the dimple size is very shallow which is consistent with the low impact energy? Do you have a reference for this?
line 143. Fig.4 Fracture character of impact test specimen tested at room temperature.
line 212. Fig.9 Linear regression of (a) nano-hardness and (b) Young's Modulus against inverse of the dislacement
We extracted all the concerns involved in these comments and addressed them item by item as follows.
Comment 1:
The paper as a research paper is excellent. However, I can’t understand where it fits into the scope of the Special Issue. What has the hardness of the σ-phase to do with coatings? Certainly the technique of microhardness testing might be very useful when it comes to assessing the hardness of thin surface coatings but it is not at all clear why this is being used here. Could the authors explain why it is being submitted to this Journal and not to a more appropriate Journal?
Answer:
Coatings is a relatively comprehensive journal. Indeed, as the reviewer said, nano indentation method is a good method to characterize the mechanical properties of thin coatings. In fact, we have used this method to characterize the mechanical properties of carburized layer [Mechanical properties of low-temperature gaseous carburizated layer in 316L stainless steel based on nano-indentation and four-point bending tests] and oxygen layer [Study on the mechanical properties gradient in surface oxygen diffusion hardened layer of Ti6Al4V alloy]. The main reasons why we submitted this manuscript to coating are as follows: 1. One scope of the Coatings journal is Characterization, and the relevant content of our manuscript is consistent with this scope. 2. The journal has got a large readership, and we hope that if this manuscript can be published in this journal, more researchers can focus on nano-indentation test method.
Comment 2:
Fig. 1 Metallographic images showing the distribution and size of the sigma Fe-Cr precipitates -- line 105
Answer:
Thanks for your valuable comments. As suggested by the reviewer, we have changed the relevant part of the manuscript to "Metallographic images showing the distribution and size of the sigma Fe-Cr precipitates ".
Comment 3:
Fig 2. Scanning electron microscopy (SEM) images of the 304H stainless steel showing the variation in the proportion of Cr and Fe in the sigma phase in the nine Fe-Cr precipitates examined
Answer:
Thanks for your valuable comments. As suggested by the reviewer, we have changed the relevant part of the manuscript to " Scanning electron microscopy (SEM) images of the 304H stainless steel showing the variation in the proportion of Cr and Fe in the sigma phase in the nine Fe-Cr precipitates examined ".
Comment 4:
line 113 -- meet the standard requirements although the elongation is reduced.
Answer:
Thanks for your valuable comments. As suggested by the reviewer, we have changed the relevant part of the manuscript to " The room temperature mechanical properties of serviced 304H are listed in Table 1, meet the standard requirements although the elongation is reduced ".
Comment 5:
Line 117-- However, the impact energy --
Answer:
Thanks for your valuable comments. As suggested by the reviewer, we have changed the relevant part of the manuscript to " However, the impact energy declined greatly from 258 J to only 25 J ".
Comment 6:
line 127. Cracking characteristics on the side
Answer:
Thanks for your valuable comments. As suggested by the reviewer, we have changed the relevant part of the manuscript to " Cracking characters on the side of tensile specimen are shown in Fig. 4 (b) ".
Comment 7:
line 135. the dimple size is very shallow which is consistent with the low impact energy? Do you have a reference for this?
Answer:
The depth of dimple is closely related to the degree of deformation and the start of slip. Generally speaking, the more sufficient the slip and greater the degree of deformation are, the deeper the dimple is. This conclusion is consistent with the conclusion of such as Shokuhfar A et al [1].
References
[1] Shokuhfar A, Nejadseyfi O. A comparison of the effects of severe plastic deformation and heat treatment on the tensile properties and impact toughness of aluminum alloy 6061[J]. Materials Science & Engineering A, 2014, 594(jan.31):140-148.
Comment 8
line 143. Fig.4 Fracture character of impact test specimen tested at room temperature.
Answer:
Thanks for your valuable comments. As suggested by the reviewer, we have changed the relevant part of the manuscript to " Fracture character of impact test specimen tested at room temperature. (a) Fracture surface, (b) Partial magnification ".
Comment 9
line 212. Fig.9 Linear regression of (a) nano-hardness and (b) Young's Modulus against inverse of the displacement
Answer:
Thanks for your valuable comments. As suggested by the reviewer, we have changed the relevant part of the manuscript to " Linear regression of (a) nano-hardness and (b) Young's Modulus against inverse of the displacement ".
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors supplemented most of the comments indicated in the review. However, in terms of the hypothesis, they pointed to only two publications: one from 1986 and the other from 2022, and wrote that there are "several articles on the hardness of σ-phase". The reference to the 1986 publication is a misunderstanding. The authors should refer to the current publications in the field of σ phase hardness. This aspect must be completed both in the area of hypothesis and in the area of discussion of results.
Author Response
Response to the comments of Reviewers 1
coatings-2028797: Mechanical properties of σ-phase and its effect on the mechanical properties of austenitic stainless steel
By Peiheng Qiao, Jinyang Xie, Yong Jiang, Pengjie Tang, Bin Liang, Yilan Lu, Jianming Gong
Dear Editor and Reviewers:
First of all, we would like to express our thanks to the editor for providing a chance to review our work and to the reviewers for this very useful comment, which have helped us to improve the manuscript. Therefore, we have made corrections/ modifications in order to improve the content of the manuscript. Revised portions are marked in blue in the revised manuscript. The following are the reply to this point of reviewer 1, please check.
Reviewer #1:
Comments and Suggestions for Authors
The authors supplemented most of the comments indicated in the review. However, in terms of the hypothesis, they pointed to only two publications: one from 1986 and the other from 2022, and wrote that there are "several articles on the hardness of σ-phase". The reference to the 1986 publication is a misunderstanding. The authors should refer to the current publications in the field of σ phase hardness. This aspect must be completed both in the area of hypothesis and in the area of discussion of results.
We extracted all the concerns involved in these comments and addressed them item by item as follows.
Comment 1:
In the introduction, the σ-phase was characterized in terms of hardness, brittleness and metal content. However, the authors did not present a hypothesis for the presented research - information about what research was carried out is not a hypothesis.
Answer:
Thank the reviewers for their valuable comments. Indeed, as the reviewer said, we should pay attention to the current research on σ-phase hardness. We replaced the original reference 17 [Minami Y, Kimura H, Ihara Y. Microstructural changes in austenitic stainless steels during long-term aging[J]. Materials Science and Technology, 1986, 2(8): 795-806. https://doi.org/10.1179/mst.1986.2.8.795] and added several literature from newer years studying σ-phase hardness. The added references are highlighted in blue in the manuscript.
For the convenience of reviewers, the relevant sections we will change are listed:
“Because of size of σ phase is too small, it is difficult to obtain the true mechanical properties of σ phase directly. So except for several articles on the hardness of σ-phase [16,26,27,28], there are no reports on other mechanical properties of σ-phase (such as Young’s modulus, yield strength, etc.). However, these mechanical properties of σ-phase itself are valuable for further understanding the mechanical properties degradation due to σ-phase precipitation. Therefore, it is necessary to study the mechanical properties of σ-phase. “
References
[16] You D, Yang G, Choa Y H, Kim J K. Crack-resistant σ/FCC interfaces in the Fe40Mn40Co10Cr10 high entropy alloy with the dispersed σ-phase[J]. Materials Science and Engineering: A, 2022, 831: 142039. https://doi.org/10.1016/j.msea.2021.142039
[26] Kumar S, Krisam S, Jacob A, et al. Microstructures and element distributions in an aged hyper duplex stainless steel and corresponding hardness variation[J]. Materials & Design, 2020, 194: 108951. https://doi.org/10.1016/j.matdes.2020.108951
[27] Ohmura T, Tsuzaki K, Sawada K, et al. Inhomogeneous nano-mechanical properties in the multi-phase microstructure of long-term aged type 316 stainless steel[J]. Journal of Materials research, 2006, 21(5): 1229-1236. https://doi.org/10.1557/jmr.2006.0143
[28] Badji R, Cheniti B, Kahloun C, et al. Microstructure, mechanical behavior, and crystallographic texture in a hot forged dual-phase stainless steel[J]. The International Journal of Advanced Manufacturing Technology, 2021, 116(3): 1115-1132. https://doi.org/10.1007/s00170-021-07502-8
Author Response File: Author Response.pdf
