Temperature-Dependent Martensitic Transformation in Cold-Rolled AISI 304 Stainless Steel

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 

This work dealt with the influence of plastic deformation and temperature on the formation of mechanically induced martensite and the associated changes in hardness in AISI 304 austenitic stainless steel. The findings provide insights into optimizing the mechanical properties of AISI 304 stainless steel through controlled deformation and temperature conditions. Accordingly, the obtained results appear reasonable and can attract numerous readers. However, some suggestions and revisions to improve the quality of the manuscript should be considered before acceptance:

1) All abbreviations should be defined on the first use after the abstract.
2) Include the most quantitatively significant results in the abstract. It seems that the abstract is not well presented.
3) How does it expand the subject area compared to other published materials?
4) Some articles should be added to the introduction and/or results. It seems that the following papers may be useful to complete the introduction section:
https://doi.org/10.1016/j.ijheatmasstransfer.2025.126864
https://doi.org/10.1016/j.mser.2025.100936
5) The conclusion is wordy. It needs to be condensed.
6) The grain refinement mechanism should be explained with a schematic representation.
7) It would be great if the authors could add the KAM maps for each processing condition. In addition, the fraction of recrystallized grains should be discussed.

Author Response

Firstly, we would like to thank the reviewer for his time, effort and valuable comments, we have implemented them to the best of our ability.

This work dealt with the influence of plastic deformation and temperature on the formation of mechanically induced martensite and the associated changes in hardness in AISI 304 austenitic stainless steel. The findings provide insights into optimizing the mechanical properties of AISI 304 stainless steel through controlled deformation and temperature conditions. Accordingly, the obtained results appear reasonable and can attract numerous readers. However, some suggestions and revisions to improve the quality of the manuscript should be considered before acceptance:

 

1) All abbreviations should be defined on the first use after the abstract.

We have improved the text accordingly.

2) Include the most quantitatively significant results in the abstract. It seems that the abstract is not well presented.

We have added text within the limitations of the abstract format.

 

3) How does it expand the subject area compared to other published materials?

 

We would like to highlight the following key contributions and expansion compared to other publications:

 

The paper systematically investigates the effect of a wide range of temperatures (20 °C, 0 °C, and -196 °C) on the martensitic transformation in cold-rolled AISI 304. Many studies focus on either room temperature or cryogenic temperatures, but our work provides a more complete picture by including intermediate temperatures. This allows for a more nuanced understanding of the temperature dependence.

Quantification of Martensite Formation: The study uses EBSD and XRD to detect and  quantify the volume fractions of austenite, ε-martensite, and α'-martensite at different temperatures and deformation levels. This detailed quantification provides valuable data for modeling and predicting the behavior of AISI 304 under various processing conditions.

Correlation of Microstructure and Hardness: Our paper establishes a clear correlation between the martensite content (specifically α'-martensite) and the hardness of the steel. This is consistent with other research, but the detailed analysis, including the calculation of martensite formation rates and their relation to hardness changes, offers a deeper insight into the hardening mechanisms.

Emphasis on the γ → ε → α' Transformation Pathway: The paper confirms that the martensitic transformation proceeds via the γ → ε → α' sequence in AISI 304, which aligns with existing literature. However, the detailed microstructural analysis, particularly the EBSD results, provides strong evidence for this pathway and clarifies the role of ε-martensite as an intermediate phase.

Stacking Fault Energy Calculation: The paper calculates the stacking fault energy (SFE) and relates it to the observed transformation pathway. This reinforces the understanding that SFE is a critical parameter influencing martensitic transformation in these steels.

Practical Implications: The findings provide practical insights for optimizing the mechanical properties of AISI 304 stainless steel through controlled deformation and temperature conditions. This could be valuable for industrial applications where specific strength and ductility requirements must be met.

 

4) Some articles should be added to the introduction and/or results. It seems that the following papers may be useful to complete the introduction section:

https://doi.org/10.1016/j.ijheatmasstransfer.2025.126864

https://doi.org/10.1016/j.mser.2025.100936

 

Thank you for the suggestions. We have added papers.

 

5) The conclusion is wordy. It needs to be condensed.

 

We have formed new more concise conclusions and replaced the conclusion section with the following:

 

This study effectively demonstrates the significant influence of cold rolling temperature and deformation degree on the mechanically induced martensitic transformation in AISI 304 stainless steel.

 

Our findings confirm that the initial microstructure consists of austenite and δ-ferrite. Upon deformation, shear bands form, increasing with strain. These bands, particularly their intersections, act as nucleation sites for martensite. Martensite (both ε and α') forms at lower deformation levels with decreasing temperature (e.g., at 10% deformation at 0°C and -196°C, versus 30% at 20°C).

 

The transformation primarily follows the γ → ε → α' pathway. Lower temperatures and higher deformation degrees accelerate the formation and increase the fraction of both ε and α' martensite, with α' martensite showing a more rapid increase.

 

Critically, hardness directly correlates with martensite content. Initial hardening at lower deformations is due to strain hardening. However, as martensite forms, it becomes the dominant hardening mechanism. The highest hardness (551 HV) was achieved at -196°C and 70% deformation, where martensite formation was maximized. The rate of martensite formation significantly influences the hardening effect, with faster transformation leading to greater hardness increases.

 

6) The grain refinement mechanism should be explained with a schematic representation.

We do not feel comfortable discussing grain refining as this is cold deformation, and does not involve recrystallization, only deformation induced transformation, that is military in nature, and involves structutres that would be destroyed if recrystallization was involved.

 

7) It would be great if the authors could add the KAM maps for each processing condition. In addition, the fraction of recrystallized grains should be discussed.

We have added figure 6 that addresses this issue, showing image quality and KAM maps for all processing conditions investigated. Regarding recrystalisation, we would like to point out that this process does not involve recrystalisation but only deformation-induced transformations.

Reviewer 2 Report

Comments and Suggestions for Authors

This study systematically investigates the effects of cold rolling temperature (20°C, 0°C, -196°C) and deformation degree (10%-70%) on martensitic transformation and hardness in AISI 304 stainless steel, confirming the γ→ε→α′ transformation pathway and establishing correlations between ε/α′ martensite fractions and hardness. While the experimental design is robust and data are comprehensive, the novelty is somewhat limited due to overlap with existing literature (e.g., References 23, 24). To enhance originality, emphasize unique contributions such as SFE calculations or phase transformation kinetics analysis.

The quantitative analysis of cryogenic deformation-induced martensite (e.g., phase fraction vs. hardness) holds value. However, deeper discussion on engineering implications (e.g., TRIP effect optimization) is needed to strengthen practical relevance.

The manuscript presents a well-structured study with valuable data on martensitic transformation in AISI 304. However, revisions are required to address:

1.Provide more detailed experimental parameters, such as the cold-rolling experiment and the EBSD detection method,Specify rolling speed, roller dimensions, and cooling protocols (e.g., liquid nitrogen immersion time) for reproducibility.

2. The author conducted cold-rolling experiments with deformation levels of 10%, 30%, 50%, and 70%. It is imperative to provide all experimental data to Lauren, especially the results obtained from the EBSD detection.
3. The primary reason for the increase of material hardness is the α′ martensite content, and the ε→α′ transformation process is crucial. The paper should provide the discussions of ε→α′ martensitic transformation under different temperatures and deformation levels.
4. The author should provide the EBSD detection results under different deformation levels at 0°C and -196°C to substantiate the variation in the content of ε/α′ martensite.
5. The author should increase the number of references from the past five years to enhance the reliability of the research conclusions,
6. The author should adjust the formatting of all figures and tables throughout the manuscript to ensure consistency.

Author Response

The review has provided helpful guidelines to improve the paper, the authors would like to express our gratitude.

1.Provide more detailed experimental parameters, such as the cold-rolling experiment and the EBSD detection method,Specify rolling speed, roller dimensions, and cooling protocols (e.g., liquid nitrogen immersion time) for reproducibility.

We have added text to clarify the experiment.

1. The author conducted cold-rolling experiments with deformation levels of 10%, 30%, 50%, and 70%. It is imperative to provide all experimental data to Lauren, especially the results obtained from the EBSD detection.

We have added data regarding experimental process and also added a new figure tto the paper.

1. The primary reason for the increase of material hardness is the α′ martensite content, and the ε→α′ transformation process is crucial. The paper should provide the discussions of ε→α′ martensitic transformation under different temperatures and deformation levels.

We have added the discussion on this matter.

While α′ martensite is indeed the primary phase responsible for the significant increase in hardness, the γ→ϵ→α′ transformation sequence is not merely a pathway but an intrinsic and crucial mechanism that enables and enhances this hardening, especially at lower temperatures.

In materials with SFE > 18 mJ/m² (AISI 304 with 25.9 mJ/m²), ε martensite forms first from stacking faults in the austenite. These ε martensite plates, particularly their intersections with each other or with mechanical twins, act as preferential nucleation sites for the harder α′ martensite.[24,27]

Without this preceding ε martensite phase, the nucleation of α′ directly from austenite would be much more difficult, requiring higher driving forces (more deformation, lower temperatures) or a different crystallographic mechanism, thus affecting the efficiency of α′ formation and subsequently the hardening rate.

The formation of ε-martensite itself induces local stresses and lattice distortions, which contribute to the overall work hardening.[28]

The transformation from ε to α′ involves additional lattice shear and rearrangements. This dynamic process during deformation continuously introduces new defects (dislocations, boundaries) and refines the microstructure, further increasing the steel's resistance to plastic flow. This "dynamic" aspect of transformation is key to the TRIP effect.

1. The author should provide the EBSD detection results under different deformation levels at 0°C and -196°C to substantiate the variation in the content of ε/α′ martensite.

We have added a new figure (Figure 6) to the paper, showing image quality and KAM maps for all processing conditions, As can be seen, the quality of the EBSD measurements significantly decreases with lower temperatures and deformation levels.

 

1. The author should increase the number of references from the past five years to enhance the reliability of the research conclusions,

We have improved the text accordingly.

1. The author should adjust the formatting of all figures and tables throughout the manuscript to ensure consistency.

We have adjusted the formatting.

Reviewer 3 Report

Comments and Suggestions for Authors

No comments

Comments for author File: Comments.pdf

Author Response

1. Refence was not complete we have corrected the issue.
2. Terminology  was improved.
3. Proper solution treatment  eliminates most of the delta ferrite content. Furthermore, we believe that adding measurement uncertainties would not contribute to the interpretation of the results. These are hard to asses in for example EBSD measurements, where a limited number of fields can be acquired. Missing Vickers hardness measurement data has been added.
4. There was a mistake with the markings BCC, FCC and HCP are correct. We have now changed the XRD measurements Figures and belive that they are easier to read and compare now.
5. The stacking fault energy (SFE) of the as-received AISI 304 was calculated to be 25.9 mJ/m² using. We acknowledge that calculating SFE in complex multicomponent alloys like AISI 304 often involves inherent uncertainties due to the empirical nature of many models, the strong dependence on exact chemical composition, and variations in material properties with temperature. Indeed, the reported SFE values for AISI 304 in literature vary significantly. Nevertheless, our calculated value of 25.9 mJ/m² is consistent with the established understanding that SFE values in this range are conducive to the observed γ→ε→α’ martensitic transformation pathway, supporting our experimental findings regarding strain-induced martensite formation.
6. We kindly disagree.
7. They do, but this is an application of cold rolling.
8. This is a text editing issue. While ε symbols are used, these are standard ways of using them. We have emphasized ε-martensite, to avoid confusion.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The author has made careful revisions to the paper as per the reviewers' requests. The paper has now reached the publication standard for the journal.

Reviewer 3 Report

Comments and Suggestions for Authors

The present reviewer does not wish to repeat his comments, as most of them were not taken into account. But the reviewer repeats his previous conclusion: the paper should be rejected.