Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper explores the influence of cold-working on the radiation resistance of reactor steels – a topic important to explore. The introduction is clear and succinct. Experimental methods and materials are described in detail. The results are presented clearly (with some figures requiring some improvement) and discussed with caution.

The English is fine and clear.

I recommend the publication of the paper after some minor revisions.

Detailed comments:

Figure 2 a: The green inset “Dislocation” is okay on the screen but in print it is hardly readable. Could you change it to lighter shade of green?

Page 7, Table 2: Should be Table 3.

Figure 7: The right-hand side of figure should be changed in order to improve the visibility of the bar charts. I would recommend to format them to two columns of plots occupying the space on the right and the height of the corresponding EBSD IPF maps.

Text corresponding to Figures 9 and 11: Could you indicate the numbers or orders of magnitude of bubbles and dislocation loops that where analysed to yield the bar graphs?

General: In reactor applications the damage is introduced mainly by the neutrons which will cause similar damage but no He bubble formation. Can you comment on how this influences your conclusions on the radiation hardness for these applications?

General: You have investigated three cases (in great detail) indicating a beneficial effect for “moderate cold working”. Do you have any estimate where an optimum for this could be located – on the side between 0 and 5% or between 10 and 50%. Do you plan to investigate this issue further?

Author Response

Ref. No.: metals-3917359

Title: Exploring complex pattern: How Cold Work Modulates Defect Evolution and Radiation Resistance in CLF-1 Steels under Multi-beam Ion Irradiations

Metals

 

We would like to thank the editor and reviewers for the valuable comments and suggestions that gave us the opportunity to improve the manuscript. We've revised the manuscript carefully according to the comments. Detailed changes made to the manuscript were highlighted in the revised version and the responses to the reviewers’ questions/suggestions are given as follows.

 

• Comments:

To Reviewer #1:

1. Figure 2 a: The green inset “Dislocation” is okay on the screen but in print it is hardly readable. Could you change it to lighter shade of green?

Response: Thank you for the suggestion. The color of “Dislocation” has been changed to lighter shade of green.

Fig. 2.  a) Bright-field (BF) TEM image of CLF-1 steels. b) EDS image of the matrix. c) EDS image of the M23C6phase. d)EDS image of the MX phase.

 

 

 

 

 

2. Page 7, Table 2: Should be Table 3.

Response: Thanks for your kind reminder. Table 2 has been modified to Table 3.

Table 3 NI-hardness calculated using the Nix-Gao model for samples before and after irradiation.

Samples	Hunirra (GPa)	Hirra (GPa)	Hback (GPa)	Hirra -Hunirra (GPa)	Hardening rate
CW 0%	3.18±0.06	4.40±0.03	3.17±0.02	1.22	38.46%
CW 10%	3.50±0.07	3.43±0.02	3.41±0.01	-0.07	-2.00%
CW 50%	3.94±0.09	4.01±0.08	3.26±0.01	0.07	1.78%

3. Figure 7: The right-hand side of figure should be changed in order to improve the visibility of the bar charts. I would recommend to format them to two columns of plots occupying the space on the right and the height of the corresponding EBSD IPF maps.

Response: Thank you for the suggestion. Fig.7 has been correct according to your nice suggestion.

Fig. 7.  The EBSD IPF maps and grain size distribution of CW 0%, CW 10% and CW 50% before and after irradiation.

4. Text corresponding to Figures 9 and 11: Could you indicate the numbers or orders of magnitude of bubbles and dislocation loops that where analysed to yield the bar graphs?

Response: Thanks for the comment. Figures 9 and 11 illustrate the statistical results of He bubbles and dislocation loops, respectively. A statistical analysis was performed on five such different areas, revealing a total of about 250 He bubbles and 200 dislocation loops. We clarified the description in the Section 2.

5. General: In reactor applications the damage is introduced mainly by the neutrons which will cause similar damage but no He bubble formation. Can you comment on how this influences your conclusions on the radiation hardness for these applications?

Response: We thank the reviewer for raising this important point. While He generation is negligible in conventional fission reactors, it is a defining feature of the fusion neutron spectrum and a significant concern in advanced Generation-IV fission systems due to (n,α) transmutation. Our multi-beam ion irradiation, which includes a dedicated He⁺ implantation step, is specifically designed to simulate this combined effect of displacement damage and simultaneous He production, which is a critical concern for fusion structural materials. Therefore, the key mechanism identified in our study—that a moderate density of pre-existing dislocations (from 10% cold work) acts as effective sinks for both point defects and He atoms, thereby suppressing the growth of large dislocation loops and He bubbles—remains directly relevant to reactor conditions. While the specific kinetics of He accumulation and bubble nucleation may differ between ion irradiation and neutron irradiation, the fundamental role of engineered microstructures (like dislocation networks) in managing both displacement damage and transmutation He is universally applicable. Our conclusions on the benefit of moderate cold work remain valid and particularly critical for the performance of RAFM steels in fusion and Gen-IV systems.

6. General: You have investigated three cases (in great detail) indicating a beneficial effect for “moderate cold working”. Do you have any estimate where an optimum for this could be located – on the side between 0 and 5% or between 10 and 50%. Do you plan to investigate this issue further?

Response：We thank the reviewer for this valuable question. Our current data with three deformation levels (0%, 10%, 50%) clearly reveals a non-monotonic relationship, where moderate cold work (10%) significantly enhances irradiation resistance. However, these relatively discrete points are insufficient to pinpoint the precise optimum. Therefore, we fully agree that systematically mapping this parameter space is a critical and logical next step. We plan to conduct a follow-up study investigating a finer series of cold work levels to precisely determine the optimal deformation window. This work will provide essential scientific data for establishing quantitative microstructure design guidelines to maximize the radiation tolerance of RAFM steels.

Relevant description has been added in Section 4.1: “systematically mapping this parameter space is a critical and logical next step. We plan to conduct a follow-up study investigating a finer series of cold work levels to precisely determine the optimal deformation window. This work will provide essential scientific data for establishing quantitative microstructure design guidelines to maximize the radiation tolerance of RAFM steels.”

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This study investigated the irradiation response of cold worked steels in terms of irradiation hardening and bubble swelling. Nanoindentation and TEM were performed to quantify the irradiation hardening and characterize irradiation induced defects. The questions that need to be answered before the work can published include:

1. The irradiation response of cold worked steels has been studied before. It is not clear how the findings from this study can advanced the current understanding in nuclear/radiation community on how to improve irradiation resistance via microstructure design. The manuscript discussed the possible reasons for seeing almost no difference in irradiation hardening between 10% and 50% cold worked samples, but a more in-depth discussion on how microstructure can be tailored to improve irradiation resistance while maintaining microstructure stability should be provided.
2. How did the author calculate the bubble/loop size and density? How many bubbles/loops were measured to get the statistics?
3. The estimation of different contributors to irradiation hardening could not explain the observed hardness difference before and after irradiation. In fact, although the authors mentioned that there might be statistics errors, these deviations (underestimation of bubble/loop density etc.) would underestimate the amount of hardening and cannot explain why 10% and 50% CW steels have almost no hardening. The influence of stress relaxation, recrystallization should be discussed. Otherwise these calculations can be misleading.

Author Response

Ref. No.: metals-3917359

Title: Exploring complex pattern: How Cold Work Modulates Defect Evolution and Radiation Resistance in CLF-1 Steels under Multi-beam Ion Irradiations

Metals

 

We would like to thank the editor and reviewers for the valuable comments and suggestions that gave us the opportunity to improve the manuscript. We've revised the manuscript carefully according to the comments. Detailed changes made to the manuscript were highlighted in the revised version and the responses to the reviewers’ questions/suggestions are given as follows.

 

• Comments:

To Reviewer #2:

1. The irradiation response of cold worked steels has been studied before. It is not clear how the findings from this study can advance the current understanding in nuclear/radiation community on how to improve irradiation resistance via microstructure design. The manuscript discussed the possible reasons for seeing almost no difference in irradiation hardening between 10% and 50% cold worked samples, but a more in-depth discussion on how microstructure can be tailored to improve irradiation resistance while maintaining microstructure stability should be provided.

Response: We sincerely appreciate your valuable feedback. The present results provide an important clarification for microstructural tailoring to enhance radiation resistance: a threshold of pre-existing sink density may exist. The key finding is that despite significantly different initial dislocation densities, the 10% and 50% cold-worked samples exhibit remarkably similar final irradiation hardening. This counterintuitive result is central to our contribution: it demonstrates that a moderate dislocation network (10% CW) offers a high sink strength that effectively suppresses defect accumulation and hardening. However, this study reveals that excessive cold work (50% CW) triggers partial recrystallization under relatively long-time multi-beam irradiation, as directly evidenced by the grain refinement observed in the EBSD results (Fig. 7f, l), and the sink structure is not retained. The triggered recrystallization annihilates dislocations, thereby reducing the very sink density intended for improvement.

Therefore, the design principle is is not merely about increasing sink density, but about optimizing it to ensure both high initial sink strength and long-term microstructural stability under specific service conditions, such as temperature and dose. 

Relevant description is as follows in Section 4.1: “In summary, the design principle is not merely about increasing sink density, but about optimizing it to ensure both high initial sink strength and long-term microstructural stability under specific service conditions, such as temperature and dose.”

 

2. How did the author calculate the bubble/loop size and density? How many bubbles/loops were measured to get the statistics?

Response: As detailed in Section 2, size and density were calculated from 5 different TEM regions per sample, with ~250 He bubbles and ~200 dislocation loops counted for each. Statistical errors are included in the Fig. 9, Fig. 11 and Table 4.

 

3. The estimation of different contributors to irradiation hardening could not explain the observed hardness difference before and after irradiation. In fact, although the authors mentioned that there might be statistics errors, these deviations (underestimation of bubble/loop density etc.) would underestimate the amount of hardening and cannot explain why 10% and 50% CW steels have almost no hardening. The influence of stress relaxation, recrystallization should be discussed. Otherwise these calculations can be misleading.

Response: We thank the reviewer for this critical observation. The reviewer is correct that the DBH and FKH models, which quantify hardening from irradiation-induced defects alone, cannot fully explain the negligible hardening observed in the CW 10% and CW 50% samples, as the two models estimate a relatively significant hardening effect.

The key to resolving this discrepancy lies in acknowledging the competing effect of irradiation-induced microstructural evolution, which encompasses stress relaxation, defect recovery and partial recrystallization. For all cold-worked samples, the thermal and irradiation-enhanced diffusion at 723 K facilitates dislocation rearrangement and annihilation, leading to a softening that counteracts the hardening from new defect clusters. This stress relaxation effect occurs in both the CW 10% and CW 50% samples. However, in the CW 50% sample, this recovery is drastically accelerated into partial recrystallization, as directly evidenced by the EBSD results (Fig. 7f, l), which creates new, strain-free grains and drastically reduces the initial dislocation density.

Therefore, the final hardening is a balance: ΔH = (Hardening from defects) - (Softening from recovery/ partial recrystallization). In the CW 10% and CW 50% samples, this competition results in the two opposing factors largely canceling each other out. We have revised Section 4.1 to integrate this discussion comprehensively, explicitly describing the role of stress relaxation and recrystallization to provide a complete and accurate interpretation of the hardening behavior.

Relevant description is as follows in Section 4.1: “Note that DBH and FKH models, which quantify hardening from irradiation-induced defects alone, cannot fully explain the negligible hardening observed in the CW 10% and CW 50% samples, as the two models predict a relatively significant hardening effect.

The key to resolving this discrepancy lies in acknowledging the competing effect of irradiation-induced microstructural evolution, which encompasses stress relaxation, defect recovery and partial recrystallization. For all cold-worked samples, the thermal and irradiation-enhanced diffusion at 723 K facilitates dislocation rearrangement and annihilation, leading to a softening that counteracts the hardening from new defect clusters. This stress relaxation effect occurs in both the CW 10% and CW 50% samples. However, in the CW 50% sample, this recovery is drastically accelerated into partial recrystallization, as directly evidenced by the EBSD results (Fig. 7f, l), which creates new, strain-free grains and drastically reduces the initial dislocation density.

Therefore, the final hardening is a balance: ΔH = (Hardening from defects) - (Softening from recovery/ partial recrystallization). In the CW 10% and CW 50% samples, this competition results in the two opposing factors largely canceling each other out.”

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

In this study, cooled-worked CLF-1 steels were irradiated with dual ion beams of Fe2+ and H+ followed by single ions He+ at 723 K to explore the complex relationship between cold work and defect evolution as well as irradiation hardening.

                                                                                           

Each experiment is good, but it is not organized well to convey its purpose. For example, the injection of hydrogen is not clear. I cannot understand why the irradiation of He occurs after the irradiation of Fe and H. The synergetic effect between damage and He is important for bubble growth. What is the purpose of hydrogen irradiation? Why did the authors choose 723 K?

 

For the development of irradiation defects, the grain size is important(3.3). On the other hand, by deformation, many point defects are introduced. These defects play an important role in the grain growth and annihilation of dislocations. The authors need to take this point into the discussion. To obtain the irradiation effects, it is important to know the structures before irradiation; you should obtain the dislocation density and TEM after annealing at 723 K.

 

Other points

-Line 118.  HZ ---> Hz?

-Line 92.  Write the dpa of He peak position, including He and H damage.

-Line 134.  Fig. 24 ?

-Eq. (3)  The Burgers vector of a dislocation does not depend on Miller index.

-Line 268.  What kind of defects do authors consider?

-Line 307.  Eqn.(7)?

Author Response

Ref. No.: metals-3917359

Title: Exploring complex pattern: How Cold Work Modulates Defect Evolution and Radiation Resistance in CLF-1 Steels under Multi-beam Ion Irradiations

Metals

 

We would like to thank the editor and reviewers for the valuable comments and suggestions that gave us the opportunity to improve the manuscript. We've revised the manuscript carefully according to the comments. Detailed changes made to the manuscript were highlighted in the revised version and the responses to the reviewers’ questions/suggestions are given as follows.

 

• Comments:

To Reviewer #3:

1. Each experiment is good, but it is not organized well to convey its purpose. For example, the injection of hydrogen is not clear. I cannot understand why the irradiation of He occurs after the irradiation of Fe and H. The synergetic effect between damage and He is important for bubble growth. What is the purpose of hydrogen irradiation? Why did the authors choose 723 K?

Response: We sincerely appreciate your critical inquiry. The primary objective of this study is to systematically investigate the influence of cold work pre-treatment (0%, 10%, 50%) on the defect evolution and irradiation hardening of CLF-1 steel, with (Fe²⁺+H⁺)-He⁺ irradiation serving solely as a single variable to produce defects. The aim is to elucidate the correlation mechanism among deformation amount, sink density, and irradiation hardening, rather than concentrating on the synergistic effects of hydrogen and helium.

Our future work will involve a comparative study between simultaneous and sequential irradiations such as (Fe²⁺+H⁺) and (Fe²⁺+H⁺+He⁺) to investigate the mechanistic aspects of the H-He synergistic effect. We greatly appreciate your valuable comments, and studies of ion irradiation sequence are important and highly meaningful.

Temperature (723 K): The temperature of 723 K was selected as it is a relevant intermediate operating temperature for RAFM steels and falls within the range where pronounced void swelling is typically observed, making the microstructural evolution particularly significant.

 

2. For the development of irradiation defects, the grain size is important(3.3). On the other hand, by deformation, many point defects are introduced. These defects play an important role in the grain growth and annihilation of dislocations. The authors need to take this point into the discussion. To obtain the irradiation effects, it is important to know the structures before irradiation; you should obtain the dislocation density and TEM after annealing at 723 K.

Response: Thank you for this valuable technical point. The pre-existing defects introduced by deformation do indeed influence the grain growth and annihilation of dislocations.

The pre-irradiation dislocation density was measured via XRD (Table 2), and EBSD has captured the grain changes before and after irradiation (Fig. 7). As we emphasized in the manuscript, it is the triple factors (synergistic effect) of cold working deformation, irradiation temperature of 723K and relatively long-time multi-beam irradiation (4.8 h based on the dose rate of 1.09 dpa/h for Fe) that promote the microstructure evolution. Therefore, assessing the isolated effect of pre-existing defects is challenging. It is unlikely that a single annealing at 723 K can explain the evolution of defect dynamics under the synergistic effect of ion irradiation, temperature and dose rate (time). Especially noteworthy are the irradiation-enhanced recovery processes, which drastically accelerate microstructural changes, such as dislocation rearrangement and recrystallization. Different levels of cold working deformation and ion irradiation at a certain temperature with controlled dose rates synergistically drive defect evolution pathways differently, thus, their collective impact on radiation resistance requires systematic investigation.

 

3. -Line 118.  HZ ---> Hz?

-Line 92.  Write the dpa of He peak position, including He and H damage.

-Line 134.  Fig. 24 ?

-Eq. (3) The Burgers vector of a dislocation does not depend on Miller index.

-Line 268.  What kind of defects do authors consider?

-Line 307. Eqn. (7)?

Response: Thank you for the suggestions.

• Line 118: "HZ" corrected to "Hz".
• Line 92: The dpa at the He peak position (~5.1 dpa, including He and H damage) is now explicitly stated.

Relevant description has been added in Section 2: “The displacement damage caused by H and He is negligible (only ~0.0046 dpa and ~0.032 dpa, respectively) compared to Fe.”

• Line 134: "Fig. 24" corrected to "Fig. 3".
• (3): We sincerely thank the reviewer for catching this critical error. The reviewer is absolutely correct. The Burgers vector is a fixed crystallographic vector defining the displacement caused by a dislocation, and its magnitude and direction are intrinsic properties of the crystal structure. We have corrected the manuscript by removing the erroneous Eq. (3) and explicitly stating the used Burgers vector value with its crystallographic justification.
• Line 268: Defects considered include point defects (vacancies, interstitials) and He atoms.
• Line 307: "Eqn. (7)" corrected to "Eqn. (9)".
  All corrections have been implemented in the revised manuscript.

 

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The revised version of the article can be accepted in present form.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 5 Report

Comments and Suggestions for Authors

The paper “Exploring complex pattern: How Cold Work Modulates Defect Evolution and Radiation Resistance in CLF-1 Steels under Multi-beam Ion Irradiations” study the effect of cold working on the irradiation toughness.
Several company name and equipment name used in the paper. Please delete them, due advertisement should not be included into scientific papers. Of course, the name of the co-operating instates and universities can remain.
On figures please use sharply different colours. E.g. in Figure 4a and Figure 5a hardly can recognise the blue and the green lines (irrad and unirrad)
The basic idea to study the effect of cold work on the radiation toughness are  interesting.
It is recommended to extend the conclusion that this work is an initiating step in the direction of use of cold work to increase the radiation toughness due to the following arguments:
Radiation embrittlement is the sum of 3 main components: precipitations occurs, some alloying and polluting elements segregate at the grain boundaries, and the dislocation structure is changed. The paper deals with the last one, and hardness test result depends on the dislocation structure and precipitations. Grain boundary segregations cannot be measured by the applied testing methods.
Very short time irradiation applied (3-5 hours). During and after irradiation diffusion recovery, and precipitations , segregations occur for long time. It can change the material structure and hardness too. (Called as flux effect in the literature). The blanket module of the fusion devices planned to operate years. 
I recommend the extended paper for publication.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The authors did not revise the manuscript satisfactorily for me. But it may be OK for the publication.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf