Effect of Oxygen Content on Microstructure and Tensile Properties of a 22Cr-5Al ODS Steel

Round 1

Reviewer 1 Report

The manuscript compares two ODS alloys with different oxygen content with respect to microstructure and mechanical properties. The topic is of great interest and the presented results appear interesting, thus I can generally recommend publication. However, there are points and questions that require a major revision. While the experimental and result sections require mostly formal supplements, the discussion needs significant improvement by answering several questions given below.

General remarks:

G1)

I strongly recommend a thorough review of the English language by a native speaker.

G2)

Particularly the first two paragraphs on page 3 and throughout the manuscript a change is required:

The term "Figure.X" should be changed to "Figure X". Whenever "Figure" is not the first word of a sentence, "Fig." should be used instead.

Experimental part:

E1)

The author should state the dimensions of the tensile test samples and the machine which was used in tensile testing.

Furthermore, how many samples of each alloy were tested?

Results:

R1)

In all SEM and TEM figures the technique/detector type should be stated (e.g. "SEM secondary electron micrograph..." or "TEM bright field image...").

R2)

The first line in section 3.1 states "... images of microstructures..." plural is used while showing only one image. It should be changed to singular expression.

R3)

The author should briefly explain the methodology for grain size determination, since generally, different approaches can lead to different results. Furthermore, the stated values for the grain size should be rounded appropriately.

R4)

In Fig. 3 (c) the scale bar of the reciprocal space is missing.

R5)

On page 4 the authors state that "...SAD (selective area diffraction) patterns confirmed that the precipitate was cubic Y2O3...". It would be very helpful to state the space group and lattice constant of Y2O3, thus allowing a critical reader to easily follow the interpretation of Fig. 3(c).

R6)

In section 3.2 the authors state: "We then used SEM analysis to analyze the fracture surface morphology of the tensile tested samples...".

The term "Fractography" should be used (and later in the manuscript as well).

R7)

Can the authors clarify, if the fractography results presented in Figs. 5 and 6 are representable? How many samples were inspected in the SEM with respect to the fracture surface?

R8)

On page 4 the authors state: "...Tensile test results revealed that there was also occurrence of a brittle fracture in the as-HIPed alloy B (Fig.6 (c))..."

There is no Fig. 6(c) in the manuscript.

Discussion and Conclusions:

D1)

Can the authors comment on the influence of grain size with respect to embrittlement? - How does the observed grain size of about 100 µm compare with other ODS alloys?

D2)

In conclusion (1) it is stated that "The precipitates in the as-HIPed alloys were mainly Y-rich oxides..."

What other oxides were observed in the alloys and were there any differences between alloys A and B?

The questions can be extended: How exactly is the extra oxygen accommodated in alloy B?

It appears to me that based on the given ratio between O and Y inside the alloys, an increase of the number density of Y2O3 alone is not sufficient as an explanation.

D3)

Furthermore, conclusions (1) states that "...An increase of the oxygen content from 0.04wt% to 0.16wt% led to an increase in the number and density of precipitates in the as-HIPed alloys..."

Could the authors please provide specific numbers in the result section of the manuscript?

Author Response

The manuscript compares two ODS alloys with different oxygen content with respect to microstructure and mechanical properties. The topic is of great interest and the presented results appear interesting, thus I can generally recommend publication. However, there are points and questions that require a major revision. While the experimental and result sections require mostly formal supplements, the discussion needs significant improvement by answering several questions given below. 

Response: Thank you for your recommendation and suggestions. We have carefully revised the paper to improve the quality of the paper according to your suggestions.

G1) I strongly recommend a thorough review of the English language by a native speaker.

Response: The language has been reviewed under the help of the native speaker.  

G2) Particularly the first two paragraphs on page 3 and throughout the manuscript a change is required: The term "Figure.X" should be changed to "Figure X". Whenever "Figure" is not the first word of a sentence, "Fig." should be used instead.

Response: We have revised them in the manuscript according to your suggestions.

Experimental part:

E1) The author should state the dimensions of the tensile test samples and the machine which was used in tensile testing. Furthermore, how many samples of each alloy were tested?

Response: We have added the dimensions of the tensile test samples and the machine used in tensile testing in the manuscript according to your suggestions. i.e. “The samples with a gauge length of 15 mm and gauge diameter of 3 mm were used for the tensile strength testing by testing machine (AGS-X300). Three tensile samples of each alloy were tested.”

Results:

R1) In all SEM and TEM figures the technique/detector type should be stated (e.g. "SEM secondary electron micrograph..." or "TEM bright field image...").

Response: We have stated the technique/detector in all SEM and TEM figures according to your suggestions in the manuscript.

R2) The first line in section 3.1 states "... images of microstructures..." plural is used while showing only one image. It should be changed to singular expression.

Response: We have revised it according to your suggestions. i.e. “images” has been revised as “image”.

R3) The author should briefly explain the methodology for grain size determination, since generally, different approaches can lead to different results. Furthermore, the stated values for the grain size should be rounded appropriately.

Response: We have added the method for grain size determination according to your suggestions in the manuscript. i.e. “The grain size of the steel was calculated by the average length of the long axis and the short axis of the grains.”

R4) In Fig. 3 (c) the scale bar of the reciprocal space is missing.

Response: We have added it into the picture according to your suggestions.

R5) On page 4 the authors state that "...SAD (selective area diffraction) patterns confirmed that the precipitate was cubic Y₂O₃...". It would be very helpful to state the space group and lattice constant of Y₂O₃, thus allowing a critical reader to easily follow the interpretation of Fig. 3(c).

Response: We have added the space group and lattice constant of Y₂O₃ according to your suggestions. i.e. “Moreover, EDS results (Fig.4 (b)) indicated that the spherical precipitates (diameter about 150 nm, pointed by black arrows) had high Y and O content, while SAD (selective area diffraction) patterns confirmed that the precipitate (Fig.4 (c)) was cubic Y₂O₃ with a space group: Ia-3 (206) with a=b=c=0.1062 nm, α=β=γ=90°.”

R6) In section 3.2 the authors state: "We then used SEM analysis to analyze the fracture surface morphology of the tensile tested samples...". The term "Fractography" should be used (and later in the manuscript as well).

Response: We revised it in the manuscript according to your suggestions.

R7) Can the authors clarify, if the fractography results presented in Figs. 5 and 6 are representable? How many samples were inspected in the SEM with respect to the fracture surface?

Response: Three samples of each alloy were inspected in the SEM with respect to the fracture surface. The fractography results of as-HIPed B are representable. On the fracture surfaces of three as-HIPed A tested samples, the aggregated oxide particles were observed on two of them. We have revised the fractography picture of both as-HIPed A and B alloys in Fig.6 and Fig.7, respectively.

R8) On page 4 the authors state: "...Tensile test results revealed that there was also occurrence of a brittle fracture in the as-HIPed alloy B (Fig.6 (c))..."There is no Fig. 6(c) in the manuscript.

Response: It is a mistake. We have revised it in the manuscript according to your suggestions. i.e. “Fig.6 (c)” has been revised into “Fig.7 (a)”.

Discussion and Conclusions:

D1) Can the authors comment on the influence of grain size with respect to embrittlement? - How does the observed grain size of about 100 µm compare with other ODS alloys?

Response: The larger grain size is detrimental to the toughness of the alloys. The grain size of about 100 µm is larger than other ODS alloys prepared by mechanical alloying. Refining the grain size can improve the toughness and strength of alloy. The grain size can be refined by decreasing the powder size and thermomechanical processing after HIP.

D2) In conclusion (1) it is stated that "The precipitates in the as-HIPed alloys were mainly Y-rich oxides...". What other oxides were observed in the alloys and were there any differences between alloys A and B? The questions can be extended: How exactly is the extra oxygen accommodated in alloy B? It appears to me that based on the given ratio between O and Y inside the alloys, an increase of the number density of Y₂O₃ alone is not sufficient as an explanation.

Response: In the two as-HIPed alloys, not only Y-rich oxides were formed, but also a little number of Zr-rich and Ti-rich oxides were found. In addition, Y could react with O and Ti/Al/Zr to form more stable ternary Y-Ti/Al/Zr-O oxides (Y₂Ti₂O₇, Y₂TiO₅, Y₃Al₅O₁₂, Y₄Al₂O₉, YAlO₃, Y₄Zr₃O₁₂). Formation of these ternary Y-containing oxides need to consume more oxygen compared to the formation of Y₂O₃. Considering these oxides containing Y, these oxides are collectively referred as Y-rich oxides in this paper.

D3) Furthermore, conclusions (1) states that "...An increase of the oxygen content from 0.04wt% to 0.16wt% led to an increase in the number and density of precipitates in the as-HIPed alloys...". Could the authors please provide specific numbers in the result section of the manuscript?

Response: The increase of the number and density of precipitates mainly describes a trend. And due to the existence of strip precipitates and enrichment of precipitates at and near the grain boundaries, it is not easy to objectively and accurately count the numbers of precipitates.

Reviewer 2 Report

The paper reports on the investigation of the effect of oxygen content of HIPed ODS steel alloys on their tensile properties. A few additional details would be welcome as described below in the comments for authors. Other than that, it is a neat study. The paper is concise and rather well written, and it might be considered suitable for publication in Materials pending minor revision.

Detailed comments for the authors:

3. Results

3.2. Tensile test and fracture surface analysis

- I must say that I am puzzled by the EDS results shown in figure 5(b), and more particularly by the very high C content. While small amount of C are commonly found in EDS analyses due to minor contamination issues during samples preparation, 33.9% is too high a concentration not to require some deeper comments. In particular, please comment on the following. Where does this high C content come from? More generally, what is the origin of such large aggregated particles? How often would you see this kind of particles in ODS steels elaborated by GARS+HIP? In other terms, is it a major issue with these alloys, and rather an incidental phenomenon?

Author Response

The paper reports on the investigation of the effect of oxygen content of HIPed ODS steel alloys on their tensile properties. A few additional details would be welcome as described below in the comments for authors. Other than that, it is a neat study. The paper is concise and rather well written, and it might be considered suitable for publication in Materials pending minor revision.

Response: Thank you for your approval and suggestions. We have carefully revised the paper to improve the quality of the paper according to your suggestions.

1. I must say that I am puzzled by the EDS results shown in figure 5(b), and more particularly by the very high C content. While small amount of C are commonly found in EDS analyses due to minor contamination issues during samples preparation, 33.9% is too high a concentration not to require some deeper comments. In particular, please comment on the following. Where does this high C content come from? More generally, what is the origin of such large aggregated particles? How often would you see this kind of particles in ODS steels elaborated by GARS+HIP? In other terms, is it a major issue with these alloys, and rather an incidental phenomenon?

Response: We think the high C content of large aggregated particles may come from two sources: one is organisms deposited on the powder surfaces during the process of materials preparation; another is residual impurities, just like the carbide or dust, which was introduced during the preparation and collection of powders. On the fracture surfaces of three tested samples, the aggregated oxide particles were observed on two of them. Although the aggregated oxide particles was not the major issue, it is one reason for the instability of tensile strength and should be avoided.

Reviewer 3 Report

This study investigates the microstructure and tensile properties of two 22Cr-5Al oxide dispersion
strengthened steels with different oxygen content. I highly recommend considering the following points since the manuscript has serious flaws.

atomization reactive synthesis and hot isostatic pressing (HIP) to fabricate

„The excellent mechanical performance“ – please specify which properties are referred

“Results showed Y-rich precipitates at and near grain boundaries of the as-HIPed alloys. Moreover, higher oxygen content resulted in more precipitates in as-HIPed alloys, and the ultimate tensile strength of the alloys was improved. However, increasing the oxygen content led to formation of stripe and chain precipitates at and near grain boundaries, which caused partial intergranular fracture of as-HIPed alloys.” --- the approach used i.e. the mechanisms observed must be linked to the particular amounts of oxygen used since this is ambiguous here.

“Oxide dispersion strengthened (ODS) steels are key candidate structural materials for advanced nuclear systems” --- the introduction must discuss compare the approach used using HIP to other references using other manufacturing techniques: see DOI: 10.1017/S1431927617004135…

Figure points to the formation of Y, Zr, rich precipitates and Ti rich oxide. EDX / element analysis are required to provide such evidences.

Figure 4: To provide the tensile curves studied and explain how may tests have been performed for each condition.

“the distribution of grain size” --- the methodology of this is not described

The discussion is too short. It is required to explain the effect of precipitation in the grain boundaries and in the matrix.

“The excellent mechanical property of ODS steels is attributed to the fine and stable dispersed oxides.” --- no evidence of stable dispersed oxides is presented.

“An increase of the oxygen content from 0.04wt% to 0.16wt% led to an increase in the number and density of precipitates in the as-HIPed alloys.”

The phase identification requires XRD to give an overview of the phases present.

“increasing the oxygen content increased the ultimate tensile strength of as-HIPed alloy” --- no measurements of the oxygen content are provided.

The presentation of results and the discussion are poor.

Author Response

Materials-1191792                                            2021/4/20

Editor, Materials

Dear Ms. Adela Liu

Thank you for the reviewers’ comments for our manuscript “Effect of oxygen content on microstructure and tensile properties of a 22Cr-5Al ODS steel” (Materials-1191792) which was submitted to Materials for publication. Thanks for your approval and suggestions. We have carefully reviewed and prepared the changes for each question. Attached are our response and revised manuscript. The revised part has been marked by blue color.

We would appreciate your efforts in reviewing our manuscript and shall look forward to hearing from your final decision when it is made.

Sincerely

Yingjie Yan

Lanzhou University of Technology

This study investigates the microstructure and tensile properties of two 22Cr-5Al oxide dispersion strengthened steels with different oxygen content. I highly recommend considering the following points since the manuscript has serious flaws.

Response: Thank you for your recommendation and suggestions. We have carefully revised the paper to improve the quality of the paper according to your suggestions.

1. atomization reactive synthesis and hot isostatic pressing (HIP) to fabricate

Response: We have revised it. i.e. “Herein, we employed gas atomization reactive synthesis to prepare pre-alloy powders and following hot isostatic pressing (HIP) to consolidate two 22Cr-5Al ODS steels with different oxygen content.”.

2. „The excellent mechanical performance“ – please specify which properties are referred

Response: We have revised it according to your suggestions. i.e. “The high tensile strength and irradiation resistance of oxide dispersion strengthened (ODS) ferritic steels is attributed to the ultrafine and dispersed oxides within the matrix.”.

3. “Results showed Y-rich precipitates at and near grain boundaries of the as-HIPed alloys. Moreover, higher oxygen content resulted in more precipitates in as-HIPed alloys, and the ultimate tensile strength of the alloys was improved. However, increasing the oxygen content led to formation of stripe and chain precipitates at and near grain boundaries, which caused partial intergranular fracture of as-HIPed alloys.” --- the approach used i.e. the mechanisms observed must be linked to the particular amounts of oxygen used since this is ambiguous here.

Response: We have revised it according to your suggestions. i.e. “Results showed Y-rich precipitates at and near grain boundaries of the as-HIPed alloys. Moreover,

with the oxygen content increasing from 0.04 wt% to 0.16 wt%, more precipitates precipitated in as-HIPed alloy, and the ultimate tensile strength of the alloy was improved. However, the increasing of the oxygen content to 0.16 wt% led to formation of stripe and chain precipitates at and near grain boundaries, which caused partial intergranular fracture of as-HIPed alloy.”

4. “Oxide dispersion strengthened (ODS) steels are key candidate structural materials for advanced nuclear systems” --- the introduction must discuss compare the approach used using HIP to other references using other manufacturing techniques: see DOI: 10.1017/S1431927617004135…

Response: We have added the introduction according to your suggestions. i.e. “The common processes to fabricate ODS steels were powder metallurgy (PM) consisted of mechanical alloying (MA) and heat consolidation, like hot isostatic pressure (HIP), hot extrusion (HE) and spark plasma sintering (SPS), and ODS steels had a high density and excellent tensile strength. Constrast to HIP and HE, laser additive manufacturing (LAM) without the MA process, is a method to manufacture the ODS Fe-matrix alloys due to its low cost and flexibility. Yingnan Shi et al fabricated a Zr-containing ODS-FeCrAl alloy by LAM which presented anisotropic tensile properties.”.

5. Figure points to the formation of Y, Zr, rich precipitates and Ti rich oxide. EDX / element analysis are required to provide such evidences.

Response: We have added EDX / element analysis results according to your suggestions.

6. Figure 4: To provide the tensile curves studied and explain how may tests have been performed for each condition.

Response: We have added the dimensions of the tensile test samples and the machine used in tensile testing in the manuscript according to your suggestions. i.e. “The samples with a gauge length of 15 mm and gauge diameter of 3 mm were used for the tensile strength testing by testing machine (AGS-X300). Three tensile samples of each alloy were tested.” And also the representative curves are provided at below. The histograms with error bars in manuscript contribute to accurately understand the difference of tensile properties for two alloys.

7. “the distribution of grain size” --- the methodology of this is not described

Response: We have added the method for grain size determination according to your suggestions in the manuscript. i.e. “The grain size of the alloy was calculated by the average length of the long axis and the short axis of the grains.”.

8. The discussion is too short. It is required to explain the effect of precipitation in the grain boundaries and in the matrix.

Response: We have explained the effect of precipitation in the grain boundaries and in the matrix according to your suggestions. i.e. “The dispersided precipitates in grain boundaries and matrix are the main reasons for the high tensile and creep strength of ODS steels. With the increasing of precipitates density and decreasing of precipitates size, the yield strength and tensile strength increasing, but the elongation of ODS steels would be decreased and occurred brittle fracture.”.

9. “The excellent mechanical property of ODS steels is attributed to the fine and stable dispersed oxides.” --- no evidence of stable dispersed oxides is presented.

Response: We have added the reference according to your suggestions. i.e. “S.F. Li et al. reported that the average size of nano-sized oxide particles in 16Cr ODS steel slightly increased with a percentage of 15.7% when the aging time up to 5000 h at 973 K.”.

10. “An increase of the oxygen content from 0.04wt% to 0.16wt% led to an increase in the number and density of precipitates in the as-HIPed alloys.”

Response: The increase of the number and density of precipitates mainly describes a trend. And due to the existence of strip precipitates and enrichment of precipitates at and near the grain boundaries, it is not easy to objectively and accurately count the numbers of precipitates.

11. The phase identification requires XRD to give an overview of the phases present.

Response: We have added XRD results according to your suggestions. i.e. “Next, the phase analysis of as-HIPed alloys were carried out by X-ray diffraction (XRD) using a D/max-2400 X-ray diffractometer with Cu Kα and scan rate was 10° min^-1”. “Figure 2 shows the XRD profiles of as-HIPed alloy A and B. It can be seen that the matrix of as-HIPed A and B mainly were α-Fe phase due to the high Cr-content.”.

12. “increasing the oxygen content increased the ultimate tensile strength of as-HIPed alloy” --- no measurements of the oxygen content are provided.

Response: We have revised it according to your suggestions. i.e. “The oxygen content of the alloys were tested by LECO TCH600 Combined Determination Apparatus for Oxygen Nitrogen and Hydrogen.”. “ Moreover, with the increasing of the oxygen content from 0.04 wt% to 0.16 wt%, the ultimate tensile strength of as-HIPed alloy increased from 604 MPa to 669 MPa, and the yield strength increased from 468 MPa to 506 MPa.”

13. The presentation of results and the discussion are poor.

Response: We have added more results and also discussed in detail according to your suggestions.

Author Response File: Author Response.pdf

Reviewer 4 Report

Dear Authors,

The paper is well written but the results are not so good. There are many other works with more promising results, nevertheless the scientific method is clear and well done.

Please consider the following suggestions:

1. add a paragraph with the starting powders size after GARS.

2.Three lines below Section Materials and Experiments: You disclose the HIP parameters. These parameters (1220°C+150 MPa+3h) suggest that probably some typo occurs. In fact, according to my personal experience with powder consolidation under isostatic pressing at 150MPa and 1220°C there is the risk of a possible incipient melting and an important grain growth. Do you have some evidence of it? Why You select such hard and not optimised parameters’ set? Any HIP cycle with temperature above 1100°C will work at 150MPa and 3 h. Please, explain the reasons for these set selection. Moreover, the grain size will be affected by this high temperature, as well shown by the 100 and higher, microns recorded (Fig. 1 and 2).

3. Do you have the mechanical properties of not-Oxigen added Fe22CrAl steel? In fact the mechanical Yield you have shown, are almost in the lower band of mechanical strength for a structural steel.

4. Please, add details about powder can before HIP: dimension, vacuum level reached before HIP.

5. Fig5: Is this is quite an oxide “inclusion” the manufaturing route should avoids these defects.

Author Response

The paper is well written but the results are not so good. There are many other works with more promising results, nevertheless the scientific method is clear and well done.

Response: Thank you for your approval and suggestions. We have carefully revised the paper to improve the quality of the paper according to your suggestions.

1. Add a paragraph with the starting powders size after GARS.

Response: We have added powders size in the manuscript according to your suggestions. i.e. “The powders size ranges from 50 μm to 350 μm.”

2. Three lines below Section Materials and Experiments: You disclose the HIP parameters. These parameters (1220°C+150 MPa+3h) suggest that probably some typo occurs. In fact, according to my personal experience with powder consolidation under isostatic pressing at 150 MPa and 1220°C there is the risk of a possible incipient melting and an important grain growth. Do you have some evidence of it? Why You select such hard and not optimised parameters’ set? Any HIP cycle with temperature above 1100°C will work at 150 MPa and 3 h. Please, explain the reasons for these set selection. Moreover, the grain size will be affected by this high temperature, as well shown by the 100 and higher, microns recorded (Fig. 1 and 2).

Response: We have checked the HIP parameters and the parameters are accurate.

The melting point of FeCrAl alloy is near to 1500℃ and the formation of dispersed oxide at grain boundaries could suppress the grain growth during the HIP. Qian Zhao et al. (Materials science and engineering A, 680 (2017) 347-350) and Liye Zhang et al. (Materials science and engineering A, 695 (2017) 66-73) have also reported that the 14Cr ODS steel were consolidated by HIP at 1150°C under a pressure of 150 MPa for 3 h. High temperature and high pressure contribute to improve the density of the alloys. N. Ordás et al. (Reference [26]) reported that, with raising HIP temperature from 900℃ to 1320℃, part of the PPBs at grain boundaries could be dissolved and the fully dense ferritic steel could be obtained at 1220℃ and 1320℃. When HIP temperature was equal or higher than 1220℃, moderate grain growth took place.

3. Do you have the mechanical properties of not-Oxygen added Fe22CrAl steel? In fact the mechanical Yield you have shown, are almost in the lower band of mechanical strength for a structural steel.

Response: Thank you for your recommendation and suggestions. We currently don’t have the mechanical properties of not-Oxygen added 22Cr-5Al steel. Jiyun Zheng et al. (Materials, 12 (2019) 2939) reported a Fe-13Cr-4.5Al-2Mo alloys prepared by vacuum induction melting and hot forging, which can be a refer for the mechanical properties of not-Oxygen added FeCrAl steel, and it has a yield strength about 560-593 MPa. The low yield strength of the alloy is mainly because of the coarse precipitates and large grain size compared to the alloy prepared by mechanical alloying. The yield strength could be further improved by the addition of solid solution elements and refining the size of precipitates and grains of as-HIPed alloy through thermomechanical processing.   

4. Please, add details about powder can before HIP: dimension, vacuum level reached before HIP.

Response: We have added the details about powder can before HIP in the manuscript according to your suggestions. i.e. “The powder cans were 100 mm high, the inner diameter was 50 mm and the can wall thickness was 5 mm. The vacuum within the can was 10^-2 Pa before HIP.”

5. Fig5: Is this is quite an oxide “inclusion” the manufacturing route should avoids these defects.

Response: Yes, these defects should be avoided during the manufacturing process.

Round 2

Reviewer 1 Report

The manuscript was clearly improved with respect to experimental details, the presentation of results and some additions to the discussion have been contributed as well.

I still think that the English needs some improvement. Some examples are given below.

Experimental part:

E1)

Page 2, last sentence “…And the fracture surfaces of tensile sampleswere using SEM and EDS.”

Has to be rewritten, e.g:

“Fractography and EDS on the fracture surfaces has been done by SEM.”

Results:

R1)

Page 3, last line: “…a=b=c=0.1062 nm …”

The lattice spacing is larger by a factor of 10.

R2)

Page 6:

“…We then used SEM analysis to analyze the fractography of the tensile tested samples in order to …“ should be changed into:

“… Afterwards, the SEM was used for fractography on the tensile tested samples in order to…”

R3)

Page 6:

“Intergrular fracture were observed on all the fractography of tested sample.”

should be changed into:

“Intergranular fracture was observed on the fracture surfaces of all three tested samples.”

Author Response

The manuscript was clearly improved with respect to experimental details, the presentation of results and some additions to the discussion have been contributed as well.

Response: Thank you for your approval.

I still think that the English needs some improvement. Some examples are given below.

Experimental part:

E1) Page 2, last sentence “…And the fracture surfaces of tensile sampleswere using SEM and EDS.”

Has to be rewritten, e.g: “Fractography and EDS on the fracture surfaces has been done by SEM.”

 Response: We have revised it according to your suggestions.

Results:

R1) Page 3, last line: “…a=b=c=0.1062 nm …”

The lattice spacing is larger by a factor of 10.

Response: We have revised it according to your suggestions. i.e. “a=b=c=1.062 nm, α=β=γ=90°.”

R2) Page 6: “…We then used SEM analysis to analyze the fractography of the tensile tested samples in order to …“ should be changed into: “… Afterwards, the SEM was used for fractography on the tensile tested samples in order to…”

 Response: We have revised it according to your suggestions.

R3) Page 6: “Intergrular fracture were observed on all the fractography of tested sample.” should be changed into: “Intergranular fracture was observed on the fracture surfaces of all three tested samples.”

Response: We have revised it according to your suggestions.

Reviewer 3 Report

The authors addressed the reviewer's comments.

Author Response

The authors addressed the reviewer's comments.

Response: Thank you for your approval.

Reviewer 4 Report

The paper has been improved with further addition of experimental details and can be recommended for publication.

The main concern remain the low performances obtained. This fact has not been discussed and no route for improvment has been presented by Authors. I really invite the Authors to add some "perspective" for improving the quality of the final material: HIP parameters, HIP vacuum? etc.

Author Response

The paper has been improved with further addition of experimental details and can be recommended for publication.

Response: Thank you for your approval.

1. The main concern remain the low performances obtained. This fact has not been discussed and no route for improvment has been presented by Authors. I really invite the Authors to add some "perspective" for improving the quality of the final material: HIP parameters, HIP vacuum? etc.

Response: Thank you for your recommendation and suggestions.

Comparing to the Fe-based ODS steels prepared by MA following HIP with grain size less than 10 μm (YS more than 700 MPa, UTS more than 900 MPa, reference [43, 45, 46]), the yield strength and ultimate tensile strength of the alloys in this study are low. We think that there are three reasons for the low strength of the as-HIPed alloys: the large size grains, the big impurity particles and the low density of the precipitates within grains. On the one hand, the strength of alloys can be improved by optimizing HIP parameters and reducing as-atomized powders size. The high temperature and long time of HIP will lead to slight grain growth during HIP. Lower HIP temperature and shortening time from 1220 ℃ and 3 h to 1150 ℃ and 2 h (even to 1 h) (reference [45]), respectively, may be a effective method to prevent the grain growth during HIP process. And, improving powder purity and reduce the impurity particles in powders can improve the strength of alloy. In addition, appropriately increasing content of Y, Zr and Ti, can increase the denity of the precipitates and promote the formation of Y-Zr-O and Y-Ti-O oxides, which had smaller size than Y₂O₃, ZrO₂ and TiO₂ oxides (reference [8, 28-29] ). Meanwhile the addition of solid solution elements like Mo and W (reference [32, 47]), can also effectively improve the strength of alloy. Furthermore, a thermomechanical process after the HIP can refine the grains and dispere precipiates enriched at grain boundaries. At last, using hot extrusion to consolidate as-atomized powders can also obtain the dense alloy and improve the yield strength (reference [16]).

We have revised the manuscript according to your suggestions. i.e. “Notably, comparing to the FeCrAl-ODS steels prepared by MA following HIP with grain size less than 10 μm [45, 46], the strength of the alloys in this study is low. There are three factors for the low strength of as-HIPed alloys: the large grain size, the big impurity particles in matrix and the low density of the precipitates within grains.”. “Lower HIP temperature and shortening HIP time can prevent the grain growth during HIP process [34]. Optimizing composition of powders, reducing as-atomized powder size and avoiding the impurity particles in powders can effectively improve the strength and ductility of alloy [32, 47].”