Influence of Alpha/Gamma-Stabilizing Elements on the Hot Deformation Behaviour of Ferritic Stainless Steel

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The tested materials designed are mainly focused on the different C and N contents together. Both are interstitial elements in steel materials. They are slightly various in some properties such as diffusion in steels. Such design of experimented materials could not divide the different influences of each element on DRV, DRX etc. It would be meaningful for further study. 

1.Main question is that the influences of C and N elements are not divided. Both are interstitial elements for steel material but different properties. It would be better if this difference could be divided.

2.The original topic "Optimal Hot Rolling Conditions to Improve the Forming Properties of Ferritic Stainless Steel" seems not really suitable for this good quality research work because this research focuses on the comparison of 2 materials with different C and N element contents.

3.As mentioned the influence of separate element C and N should be divided.

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding corrections highlighted in track changes attached.  

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Comment 1: Main question is that the influences of C and N elements are not divided. Both are interstitial elements for steel material but different properties. It would be better if this difference could be divided.

Response 1: We thank the reviewer for pointing out this issue, and we agree with the reviewer's observation regarding the individual contributions of carbon and nitrogen. While we agree that a detailed separation of their effects would be valuable, the materials for this study were sourced directly from an integral stainless steel mill. The inherent cost and practicalities associated with producing alloys with specific, isolated variations in C and N content in such a setting were prohibitive for this particular work. Nevertheless, our study provides valuable insights by investigating the combined influence of these interstitial elements along with the varied substitutional elements, silicon and chromium, on the hot deformation behavior of ferritic stainless steel. We recognize the importance of differentiating C and N effects and plan to address this in future research through dedicated alloy design and characterization.

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Comment 2: The original topic "Optimal Hot Rolling Conditions to Improve the Forming Properties of Ferritic Stainless Steel" seems not really suitable for this good quality research work because this research focuses on the comparison of 2 materials with different C and N element contents. 

Response 2: We agree with the reviewer's observation and a new title has been considered, taking into account not only C and N but also the influence of alpha/gamma elements. The title has been modified to a new one: "Influence of alpha/gamma stabilizing elements on the hot deformation behavior of ferritic stainless steel".

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Comment 3: As mentioned the influence of separate element C and N should be divided.

Response 3: As mentioned in Comment 1 / Response 1: We thank the reviewer for pointing out this issue, and we agree with the reviewer's observation regarding the individual contributions of carbon and nitrogen. While we agree that a detailed separation of their effects would be valuable, the materials for this study were sourced directly from an integral stainless steel mill. The inherent cost and practicalities associated with producing alloys with specific, isolated variations in C and N content in such a setting were prohibitive for this particular work. Nevertheless, our study provides valuable insights by investigating the combined influence of these interstitial elements along with the varied substitutional elements, silicon and chromium, on the hot deformation behavior of ferritic stainless steel. We recognize the importance of differentiating C and N effects and plan to address this in future research through dedicated alloy design and characterization.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript investigates the hot deformation behavior of two AISI 430 ferritic stainless steel variants, with a focus on microstructural evolution using EBSD characterization and texture analysis. The study reveals distinct DRX and DRV behaviors attributed to differences in chemical composition. Overall, the work is interesting and contributes meaningfully to the field. However, several issues need to be addressed before the manuscript can be considered for publication. Detailed comments are as follows:

 

1. Page 2, Lines 57–63, the authors highlight the importance of advanced microscopy techniques and thermodynamic simulation software in understanding the interplay between hot rolling conditions and microstructural evolution. However, this section lacks specificity. Please elaborate on the types of advanced microscopy techniques (e.g., TEM, EBSD) and simulation tools (e.g., Thermo-Calc), and provide examples demonstrating their relevance. Additional references would strengthen this discussion.

 

2. Page 2, Lines 67–68, the authors claim that the hot compression test used in this study more accurately simulates industrial hot rolling finishing mill conditions compared to previous studies. To support this claim, please provide a brief overview of typical industrial finishing mill parameters (e.g., strain rate, temperature range, reduction schedule) and compare them with the test conditions used in this work. A short review of relevant literature would also be helpful.

 

3. Page 3, Table 1, the chemical composition table for 0A and 1C is incomplete. Key alloying elements such as Ni are missing. Additionally, the annealing times are vaguely described as "short" and "long." Please include the full chemical composition and specify the actual annealing durations in the table for clarity and reproducibility.

 

4. Page 3, Figure 1, figure caption is loosely written and lacks subfigure labeling. Please divide Figure 1 into clearly labeled subfigures (e.g., 1a, 1b, etc.) and revise the caption to describe each panel concisely and clearly.

 

5. Page 4, Figure 2a, it is clear that the 0A sample tested at 930 °C exhibits a noticeably different modulus compared to other temperatures. Please explain the reason for this deviation. Additionally, clarify how many samples were tested under each condition to assess the reliability and repeatability of the results.

 

6. Page 8, Figure 4a–d, numerous white lines are shown in the grain boundary maps. Please clarify the meaning of these lines in the color code. If they represent noise or artifacts, consider cleaning up the maps to improve visual clarity.

 

7. Page 13, Lines 366–367, the authors state that the 0A composition inhibits DRX compared to 1C, but the supporting discussion is insufficient. Please provide theoretical calculations or cite relevant literature to substantiate this conclusion.

 

8. Title and Conclusion, this manuscript is titled “Optimal Hot Rolling Conditions to Improve the Forming Properties of Ferritic Stainless Steel”, yet the conclusion section does not address optimal hot rolling conditions. Instead, it emphasizes the influence of chemical composition on DRX behavior. Please revise the conclusion to better align with the title, or consider modifying the title to more accurately reflect the study’s main findings.

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding corrections highlighted in track changes attached.  

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Comment 1: Page 2, Lines 57–63, the authors highlight the importance of advanced microscopy techniques and thermodynamic simulation software in understanding the interplay between hot rolling conditions and microstructural evolution. However, this section lacks specificity. Please elaborate on the types of advanced microscopy techniques (e.g., TEM, EBSD) and simulation tools (e.g., Thermo-Calc), and provide examples demonstrating their relevance. Additional references would strengthen this discussion.

Response 1: Page 2, Lines 54-77: Thanks for suggesting strengthening the Introduction section by adding specific references on advanced electron microscopy and thermodynamic simulation tools. We have extended the mentioned paragraph accordingly, including four new references.

The advancement of knowledge regarding the interplay between hot rolling conditions and the resulting microstructural characteristics is essential for the optimization of FSS. The continuous evolution of methodologies aimed at characterizing these relationships significantly contributes to the effective manufacturing of high-performance FSS components. In this regard, electron backscatter diffraction (EBSD), coupled with scanning electron microscopy (SEM), is indispensable for quantitatively analyzing crystallographic orientation, grain size and shape distributions, grain boundary character (e.g., high-angle vs. low-angle boundaries), and texture evolution during hot rolling, which are critical to understanding how variations in hot rolling conditions affect material drawability \cite{Carneiro2020}. In this regard, while Schneider et al. investigated the influence of hot rolling conditions on the microstructure and texture of the hot band in Ferritic FeSi Steels, Kisko et al. specifically observed how hot rolling and coiling temperatures affect the formation of structures and substructures (low-angle boundaries) to enhance drawability and resist ridging in FSS.

Furthermore, the use of thermodynamic simulation software provides crucial insights into phase transformations, equilibrium compositions, and precipitate formation at various temperatures, complementing experimental investigations by predicting microstructural constituents and stability during processing \cite{Andersson2002}. In this regard, Zhang et al. predicted the formation of (Cr,Fe)₂₃C₆ and AlN precipitates in hot-formed ferritic stainless steel that was later evidenced by advanced electron microscopy techniques. Nabiran et al. demonstrated the use of CALPHAD modeling in designing FSS for high-temperature applications, specifically to stabilize the microstructure through solid-state precipitation of MX carbonitrides, by calculating phase equilibria and evaluating phase stabilities to determine the influence of alloying elements.

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Comment 2: Page 2, Lines 67–68, the authors claim that the hot compression test used in this study more accurately simulates industrial hot rolling finishing mill conditions compared to previous studies. To support this claim, please provide a brief overview of typical industrial finishing mill parameters (e.g., strain rate, temperature range, reduction schedule) and compare them with the test conditions used in this work. A short review of relevant literature would also be helpful.

Response 2: Page 3, Lines 87-90: The paragraph mentioned by the reviewer has been expanded to include what was requested:

The industrial finisher pass program consists of four passes at 990, 960, 930, and 850°C, with an average reduction of 45% per pass and an average speed of 220 m/min. Each pass was simulated individually, not perform in a multi-pass way, at these same temperatures and conditions.

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Comment 3: Page 3, Table 1, the chemical composition table for 0A and 1C is incomplete. Key alloying elements such as Ni are missing. Additionally, the annealing times are vaguely described as "short" and "long." Please include the full chemical composition and specify the actual annealing durations in the table for clarity and reproducibility.

Response 3: Page 3, Table 1: Thank you for pointing this out. We agree with this comment. Although the Ni content is low and it does not changed significantly in the two steel variants under study, we have included the Ni content in Table 1 to complete the chemical composition of the alloys.

With respect to annealing times, this is a mistake because it is refered to material after cold rolling, so it does not correspond and this description has been removed from the Table 1. In the FM simulation being performed in the current article, the conditions are the same in both materials (so that the results can be compared), and are already described in the text: temperature and strain rate.

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Comment 4: Page 3, Figure 1, figure caption is loosely written and lacks subfigure labeling. Please divide Figure 1 into clearly labeled subfigures (e.g., 1a, 1b, etc.) and revise the caption to describe each panel concisely and clearly.

Response 4: Page 4, Figure 1: Thanks for pointing this out. We have modified Figure 1 and its caption accordingly.

Figure 1: Schematic representation of the plane-stress compression test reproduced by the Gleeble thermo-mechanical testing system as a simulation of the hot-rolling process (a), showing normal, rolling, and transversal directions (ND, RD, TD), and F, the applied load. A prismatic specimen is positioned in the testing chamber (b), the sample is heated and then compressed (c) according to the curve shown in (d). A slice of the compressed sample (e) is prepared for microscopy analysis as shown in (f), where the studied region is highlighted with a red square.

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Comment 5: Page 4, Figure 2a, it is clear that the 0A sample tested at 930 °C exhibits a noticeably different modulus compared to other temperatures. Please explain the reason for this deviation. Additionally, clarify how many samples were tested under each condition to assess the reliability and repeatability of the results.

Response 5: Page 5, Figure 2a: We thank the reviewer the comment. The seemingly "distinct" slope of the curve at 930 °C could be the result of a more complex interaction between work hardening and dynamic softening processes (recovery and recrystallisation). Due to the phase transformations experienced by this type of steel, it might be a temperature where the ferrite-austenite transformation and the subsequent deformation of the austenite, or its later transformation during deformation, contribute in a particular way to the mechanical response, differentiating it from temperatures where the microstructure is more stable (predominantly ferritic at 850 °C) or where dynamic softening is more dominant (at 960 °C and 990 °C).

The tests were replicated three times, without discrepancies in the results obtained in them.

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Comment 6: Page 8, Figure 4a–d, numerous white lines are shown in the grain boundary maps. Please clarify the meaning of these lines in the color code. If they represent noise or artifacts, consider cleaning up the maps to improve visual clarity.

Response 6: Page 9, Figure 4 a-f, lines 205-208: Thank you for pointing this out. We have revised the description to clarify the meaning of this concept.

The following text has been included: "where it was found that for the grain size analysis by EBSD (Figure 4e), CSLs were considered special boundaries and not as regular grain boundaries, specially the well-known Σ3 twin boundary in face-centred cubic materials, which appeared as concentrated red lines in sample 0A (Figure 4a and Figure 4b) and represented the martensite fraction".

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Comment 7: Page 13, Lines 366–367, the authors state that the 0A composition inhibits DRX compared to 1C, but the supporting discussion is insufficient. Please provide theoretical calculations or cite relevant literature to substantiate this conclusion.

Response 7: Page 14, Lines 382-393: We have rewritten the text accounting for the concerns raised by the reviewer:

The results of this article demonstrated that the composition of material 1C improves the plastic deformation response, leading to significant grain refinement and efficient DRX at hot rolling temperatures. For material 0A, DRX is almost entirely inhibited due to a higher fraction of transformed austenite. This causes the mechanical response to work hardening to differ from that of material 1C, notably at lower temperatures of 850 and 930 °C. At these temperatures, the mobility of dislocations is observed to be lower in 0A, with a reduced tendency for recovery and recrystallisation. In contrast, for material 1C, DRX continues to be favoured despite the decrease in temperature. All these phenomena can be clearly seen in the flow curves from the high-temperature compression tests. The control of the temperature and the strain level is crucial in 0A for managing the final texture and grain size, directly influencing mechanical properties and product performance.

While there is no existing literature to directly support this statement, our experimental evidence strongly supports this conclusion.

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Comment 8: Title and Conclusion, this manuscript is titled “Optimal Hot Rolling Conditions to Improve the Forming Properties of Ferritic Stainless Steel”, yet the conclusion section does not address optimal hot rolling conditions. Instead, it emphasizes the influence of chemical composition on DRX behavior. Please revise the conclusion to better align with the title, or consider modifying the title to more accurately reflect the study’s main findings.

Response 8: We agree with the reviewer comment. The title has been changed to better align with the conclusions:

"Influence of Alpha/Gamma-Stabilizing Elements on the Hot Deformation Behaviour of Ferritic Stainless Steel".

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript deals with investigations into the microstructure formation of a ferritic stainless-steel alloy with different fractions of austenite-stabilizing elements by hot forming. The results are of scientific and practical interest, the work is well documented with well comprehensible conclusions from the analyses carried out. Publication of the manuscript is recommended, whereby the following points should still be checked and amended:

(1) Line 90, Table 1: The authors indicate the elements "... (C, N, Ni) ..." as a component of alloy 0A, but Ni is not listed in Table 1 (and typically not common in the alloy under investigation). Has Ni been omitted from the table or should “Ni” be removed from line 90?

(2) Line 97: Is “… 20 x 15 x 10mm …” the dimension of the overall workpiece or the size/part of the workpiece that is compressed? This should be specified more precisely.

(3) Line 215: The expression “… (1504 and 32.58, …” is not clear.

(4) The font size in Figures 1 and 5 is partly very small and should be made more readable.

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding corrections highlighted in track changes attached.  

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Comment 1: Line 90, Table 1: The authors indicate the elements "... (C, N, Ni) ..." as a component of alloy 0A, but Ni is not listed in Table 1 (and typically not common in the alloy under investigation). Has Ni been omitted from the table or should “Ni” be removed from line 90

Response 1: Line 106, Table 1: Thank you for pointing this out. We agree with this comment. Although the Ni content is low and it does not changed significantly in the two steel variants under study, we have included the Ni content in Table 1 to complete the chemical composition of the alloys.

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Comment 2: Line 97: Is “… 20 x 15 x 10mm …” the dimension of the overall workpiece or the size/part of the workpiece that is compressed? This should be specified more precisely.

Response 2: Lines 113-114: Thank you for pointing this out. We have changed the description of the specimens in section 2, paragraph 4.

«Rectangular specimens with overall dimensions of 20 x 15 x 10 mm, featuring a compressed surface of 20 x 5 mm with the compression axis aligned with the normal direction, were taken from the industrial process transfer bar. »

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Comment 3: Line 215: The expression “… (1504 and 32.58, …” is not clear.

Response 3: Lines 232-236: Thank you for pointing this out. We have revised the sentence to improve clarity.

«For sample 0A at 960 ºC, the grain size distribution exhibits a sharp peak and a long tail towards larger grain sizes. This is quantitatively supported by the high kurtosis value of 1504 and a skewness value of 32.58, respectively, even though these characteristics are less visually apparent in the normalized frequency plot.»

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Comment 4: The font size in Figures 1 and 5 is partly very small and should be made more readable.

Response 4: Thanks for your suggestions. We have increased the font sizes in both Figures.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have addressed all my comments adequately, therefore, I recommend this manuscript for publication.