Phase Transformations During Softening of Iron Ore Sinter of Varying Basicity in the CaO–SiO₂–FeO System

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript presents a systematic and well‑structured study on the influence of basicity and reduction degree on the phase composition and softening behaviour of iron ore sinter. The work is technically sound, clearly written, and supported by a comprehensive experimental program including XRD (Rietveld), SEM‑EDS, and softening tests. The results are coherent and relevant for blast furnace process optimization. Overall, the manuscript is suitable for publication after a minor revision to account for the followings:

1. Table 1: A comment is needed to explain why the sum of components is not yielding 100%.
2. Table 2: The table presents crystalline phases, what about the content of amorphous (vitreous) components?

• Conclusions: The conclusions are supported by data of manuscript. However, there shall be noted also the formation of liquid phase consisting of calcium-alumina-silicate components which on cooling form non-crystalline (vitreous) phases. Sinter is actually composed of both crystalline and amorphous (melt and glass) phases.... Can these be somehow noted as well?

The manuscript is scientifically solid and well executed. After addressing the minor points above, it will be fully suitable for publication.

Author Response

Dear Expert!

We, the authors of the article “Phase Transformations during the Softening of Iron Ore Sinter of Varying Basicity”, Elena A. Vyaznikova, Andrey N. Dmitriev, Galina Yu. Vitkina and Vladimir V. Katayev, would like to express our gratitude for your meticulous review of our article and for your constructive comments and suggestions. We are immensely grateful for your invaluable feedback, which has enabled us to enhance the quality of our work to a considerable extent. The following section presents a comprehensive response to the issues raised, accompanied by a detailed description of the corrections made to the manuscript.

Comments 1.  The manuscript presents a systematic and well‑structured study on the influence of basicity and reduction degree on the phase composition and softening behaviour of iron ore sinter. The work is technically sound, clearly written, and supported by a comprehensive experimental program including XRD (Rietveld), SEM‑EDS, and softening tests. The results are coherent and relevant for blast furnace process optimization. Overall, the manuscript is suitable for publication after a minor revision to account for the followings:

A comment is needed to explain why the sum of components is not yielding 100%.

Response 1. We would like to express our gratitude to the reviewer for their comment. The discrepancy of the component sum from 100% is attributable to the inherent heterogeneity of the sinter composition and the fact that the table lists only the major elements determined by titrimetric analysis, whereas certain components (impurities present at low concentrations) were not taken into account. To avoid misunderstanding, we have added a note below Table 1.

Comments 2. The table presents crystalline phases, what about the content of amorphous (vitreous) components?

Response 2. We would like to express our gratitude to the reviewer for their comment. We agree that Table 2 lists only the crystalline phases identified by X-ray diffraction analysis. The silicate matrix of the sinter indeed contains a glassy phase, which cannot be determined by the standard Rietveld method without the introduction of an internal standard. The amount of the X-ray amorphous phase was determined separately using the internal standard method (Si) and was found to be up to 20%; however, within the scope of this work, the primary focus was on the evolution of the crystalline iron-bearing phases (Fe₃O₄, Fe₂O₃, FeO, SFCA), which govern the softening process. The presence of the amorphous phase is indirectly accounted for during the interpretation of the results as part of the silicate matrix. Nevertheless, we have added a mention of the presence of an amorphous phase and its possible role in Section 2.2. The quantitative determination of the glass phase requires separate research and does not affect the main conclusions about phase transformations during the recovery process.

Comments 3. Conclusions: The conclusions are supported by data of manuscript. However, there shall be noted also the formation of liquid phase consisting of calcium-alumina-silicate components which on cooling form non-crystalline (vitreous) phases. Sinter is actually composed of both crystalline and amorphous (melt and glass) phases.... Can these be somehow noted as well?

The manuscript is scientifically solid and well executed. After addressing the minor points above, it will be fully suitable for publication.

Response 3. We added in Conclusions an appropriate explanation in the revised version of the manuscript, noting that the quantitative determination of the amorphous phase requires a separate methodology (e.g., using an internal standard).

It is asserted that the alterations made fully address all of the reviewer's comments and significantly enhance the scientific and practical value of the article. We would like to express our gratitude for your assistance in enhancing the quality of our work.

Best regards, authors.

Reviewer 2 Report

Comments and Suggestions for Authors

In the paper “Phase Transformations During the Softening of Iron Ore Agglomerates with Different Basicities” by Elena A. Vyaznikova, Andrei N. Dmitriev, Galina Yu. Vitkina*, and Vladimir V. Kataev, presents the results of a study of sintered ore with basicity (CaO/SiO₂) in the range of 1.2 to 3.0, conducted using a combination of methods.
I have the following comments on the paper:
1. Introduction
The sentence: “The sampling procedure was carried out in accordance with the guidelines set forth in Russian State Standard 15054-80” requires a citation and reference to the cited standard. A better option would be to seek a European equivalent, as most Russian standards are inaccessible.
2. Methods
The sentence “The chemical composition was determined by titrimetric analysis and atomic emission spectroscopy” raises questions regarding the methodology of the titrimetric analysis and the description of the equipment and operating conditions for the atomic emission spectroscopy. It is unclear which data are emission data and which are titrimetric data, as well as the measurement error.
Section 2.4 The reference to ISO 7998 requires a citation

3. Results and Discussion
Section 3.1. Phase Composition of the Initial Sinter
The diffractograms presented in Fig. 2 are overly stylized. The intensities of the diffraction lines are greatly reduced to the point of insignificance. Many diffraction lines are unidentified. Overall, the figure is of poor quality and the identified phases have a low degree of reliability. The authors claim that a quantitative phase analysis was performed using the Rietveld method, but the results of the analysis are missing. Data from the Rietveld refinement would provide insight into the quality of the processing performed and the reliability of the results obtained. It is necessary to include this in the text along with figures and tabular data.
Section 3.2: The authors need to explain the meaning of the term “Basicity.” 
Fig. 2 presents the processing of the experimental results using mathematical equations. Information is missing regarding the type of equations and the physical meaning of the obtained coefficients. In the first model, R² is low. What is the reason for this? Additional processing should be performed to increase R².

Fig. 4 – The labels in the figure are completely unclear. The figure must be revised so that the labels are visible and informative.
Fig. 5 – What is the value of R on the x-axis? The graph as presented is unclear.

In conclusion, the research results provided as evidence are too general and insufficiently explained. Results from the analyses used, such as Rietveld refinements data and data and analysis from an energy-dispersive microanalyzer, are missing. In its current form, the article is not suitable for publication.

Author Response

Dear Expert!

We, the authors of the article “Phase Transformations during the Softening of Iron Ore Sinter of Varying Basicity”, Elena A. Vyaznikova, Andrey N. Dmitriev, Galina Yu. Vitkina and Vladimir V. Katayev, would like to express our gratitude for your meticulous review of our article and for your constructive comments and suggestions. We are immensely grateful for your invaluable feedback, which has enabled us to enhance the quality of our work to a considerable extent. The following section presents a comprehensive response to the issues raised, accompanied by a detailed description of the corrections made to the manuscript.

Comments 1.  

1. Introduction

The sentence: “The sampling procedure was carried out in accordance with the guidelines set forth in Russian State Standard 15054-80” requires a citation and reference to the cited standard. A better option would be to seek a European equivalent, as most Russian standards are inaccessible.

Response 1. We would like to express our gratitude to the reviewer for comment. The reference was incomplete. We have replaced it with the full citation: the Russian State Standard 15054‑80 “Iron ores, concentrates, agglomerates, and pellets. Methods for sampling and preparing samples for chemical analysis and moisture content determination”. In addition, we added the international equivalent ISO 3082:2017 “Iron ores – Sampling and sample preparation procedures” to ensure accessibility for an international audience.

Comments 2.

2. Methods

The sentence “The chemical composition was determined by titrimetric analysis and atomic emission spectroscopy” raises questions regarding the methodology of the titrimetric analysis and the description of the equipment and operating conditions for the atomic emission spectroscopy. It is unclear which data are emission data and which are titrimetric data, as well as the measurement error.

Section 2.4 The reference to ISO 7998 requires a citation.

Response 2. We thank the reviewer for raising these important methodological concerns.

1. On the phrase “titrimetric analysis and atomic emission spectroscopy”

We acknowledge that the mention of atomic emission spectroscopy was an inadvertent error. The chemical composition was actually determined by titrimetric analysis (using standard procedures) and by scanning electron microscopy (SEM) coupled with energy‑dispersive X‑ray spectroscopy (EDS). The latter was employed for the elemental characterization of individual phases in the agglomerates and to corroborate the results of X‑ray diffraction analysis. In the revised manuscript, the sentence corrected accordingly. The manuscript has been corrected.

2. On the distinction between the two methods and measurement uncertainty

The titrimetric method was used to determine the major element concentrations (e.g., total iron, FeO, SiO₂, CaO, etc.), as presented in the main elemental composition table. Minor impurities present at low concentrations were not quantified. The SEM‑EDS data were used qualitatively and semi‑quantitatively for phase‑specific elemental analysis, not for bulk composition.

Regarding measurement uncertainty, we provided appropriate values based on our previous publications (cited in the revised manuscript). These uncertainty estimates were derived from replicate analyses and routine quality control procedures.

3. On the ISO 7998 reference in Section 2.4

We thank the reviewer for pointing this out. Upon re‑examination, we were unable to locate the specific reference to ISO 7998 in the original manuscript. It appears to have been included erroneously. We removed the reference. In the revised version, Section 2.4 contains a complete and accurate description of the experimental conditions without unsupported references.

Comments 3.

3. Results and Discussion

Section 3.1. Phase Composition of the Initial Sinter

The diffractograms presented in Fig. 2 are overly stylized. The intensities of the diffraction lines are greatly reduced to the point of insignificance. Many diffraction lines are unidentified. Overall, the figure is of poor quality and the identified phases have a low degree of reliability. The authors claim that a quantitative phase analysis was performed using the Rietveld method, but the results of the analysis are missing. Data from the Rietveld refinement would provide insight into the quality of the processing performed and the reliability of the results obtained. It is necessary to include this in the text along with figures and tabular data.

Section 3.2: The authors need to explain the meaning of the term “Basicity.”

Fig. 2 presents the processing of the experimental results using mathematical equations. Information is missing regarding the type of equations and the physical meaning of the obtained coefficients. In the first model, R² is low. What is the reason for this? Additional processing should be performed to increase R².

Fig. 4 – The labels in the figure are completely unclear. The figure must be revised so that the labels are visible and informative.

Fig. 5 – What is the value of R on the x-axis? The graph as presented is unclear.

Response 3.

Section 3.1. We thank the reviewer for this important observation. We acknowledge that the diffractograms in the original figure were deliberately simplified to serve a specific illustrative purpose – namely, to demonstrate that the phase assemblage of the agglomerates remains qualitatively the same as the basicity increases from 1.2 to 3.0, with only the phase quantities changing. However, we agree that the resulting figure quality is inadequate for a research publication.

In the revised manuscript, we:

– provide improved diffractogram with higher resolution and without excessive reduction of peak intensities (Fig. 1).

– performed a complete identification of all major diffraction lines, with corresponding phase labels clearly indicated.

The estimated error in phase quantification does not exceed 2–3%, and the obtained data are in good agreement with the results of microstructural analysis (SEM‑EDS).

Section 3.2. We apologize for the omission. In this work, “basicity” is defined as the ratio CaO/SiO₂ (by mass). This parameter governs the composition of the silicate bonding phase in the agglomerates and, consequently, serves as an indicator of the slag fluidity during the softening process. A clear definition added in the revised manuscript.

Figure 2. We appreciate the reviewer’s scrutiny of the mathematical treatment. The dependence of the softening temperature of agglomerates on their basicity was described by a quadratic function. The coefficient of the x² term determines the direction and rate of change of the onset and end‑point softening temperatures as basicity increases. For low‑basicity agglomerates, where the amount of SFCA phases is small, the softening temperatures are lowest. The absolute value of this coefficient indicates how rapidly the material transitions to a liquid phase with changing basicity. The coefficient of the x term reflects the intensity of formation of the silicoferrite bonding matrix, which raises the softening temperature.

Regarding the low R² value for the end‑point softening temperature: this is attributable to the inherently non‑linear nature of the processes occurring during softening. The present approximation was intended to be illustrative, serving to identify the optimal basicity of agglomerates for minimizing the cohesive zone. We acknowledge that a higher R² would be desirable; however, the physical complexity of the softening behavior makes a simple quadratic fit only approximate. The previous quadratic fit with low R² has been replaced by a polynomial regression (of 3 degrees): for T_end R² = 0.84.

Figure 4. We agree with the reviewer. The figure enlarged and the labels revised to ensure legibility. All annotations clearly visible and appropriately informative. A revised figure provided in the updated manuscript.

Figure 5. We thank the reviewer for pointing out this ambiguity. The symbol R on the x‑axis denotes the degree of reduction (in percent). In the revised figure, the axis label will be explicitly written as “Degree of reduction, %” to avoid any confusion.

Comments 4. In conclusion, the research results provided as evidence are too general and insufficiently explained. Results from the analyses used, such as Rietveld refinements data and data and analysis from an energy-dispersive microanalyzer, are missing. In its current form, the article is not suitable for publication.

Response 4. We accept this judgement. The original version indeed lacked essential data. All the above‑described corrections have been made. We believe the revised manuscript now meets the standards of the journal and respectfully ask you to consider it for publication.

It is asserted that the alterations made fully address all of the reviewer's comments and significantly enhance the scientific and practical value of the article. We would like to express our gratitude for your assistance in enhancing the quality of our work.

Best regards, authors.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The research addresses a topic of considerable industrial relevance, systematically investigating the effects of basicity (1.2–3.0) and reduction degree (0–95%) on the softening and melting behavior of iron ore sinter, and seeking to correlate these macroscopic properties with microstructural evolution via quantitative XRD phase analysis and SEM-EDS. Nevertheless, several issues concerning the experimental design and the reliability of the characterization methods must be satisfactorily resolved.

1. While reporting the total iron content in Table 1 is standard practice, the rationale for listing FeO as a separate component is unclear and requires clarification.
2. In line 201, the elemental proportions of the SFCA phase are stated to have been derived from EDS. EDS is inherently semi-quantitative and cannot provide reliable stoichiometric ratios for complex phases, particularly at the spatial resolution reported. The Fe content of 8.5 appears substantially higher than typical values for SFCA-type phases. The conclusions drawn from this composition are therefore insufficiently justified; even bulk ICP analysis could not fully exclude the influence of finely intermixed iron oxide impurities.
3. The discussion in lines 262–268 lacks supporting citations and experimental evidence, making the arguments appear largely speculative. If supporting literature is available, it should be cited; otherwise, this passage should be removed.
4. Figure 4a is of low quality and the black annotations on the SEM micrograph are difficult to read. It is recommended to use a more contrasting color and to increase the font size and weight. Since SEM images are already available, the addition of EDS element mapping would significantly improve the interpretability of the microstructures. Furthermore, “gelenite” in line 231 appears to be a typographical error, the correct spelling is likely “gehlenite.”
5. The degree of reduction is determined from mass loss. The exact formula used for this calculation should be provided explicitly, or the authors should consider whether reporting the mass loss directly would be more transparent and reproducible. Moreover, the potential variation in the final mass losses among the different formulations tested does not appear to have been taken into account. This aspect requires careful consideration and justification.
6. Lines 147–149 state that an optical microscope was used “for quantitative phase distribution analysis”. However, no corresponding quantitative data or analysis appears anywhere in the subsequent text. This discrepancy should be checked and corrected.

Author Response

Dear Expert!

We, the authors of the article “Phase Transformations during the Softening of Iron Ore Sinter of Varying Basicity”, Elena A. Vyaznikova, Andrey N. Dmitriev, Galina Yu. Vitkina and Vladimir V. Katayev, would like to express our gratitude for your meticulous review of our article and for your constructive comments and suggestions. We are immensely grateful for your invaluable feedback, which has enabled us to enhance the quality of our work to a considerable extent. The following section presents a comprehensive response to the issues raised, accompanied by a detailed description of the corrections made to the manuscript.

Comments 1.  While reporting the total iron content in Table 1 is standard practice, the rationale for listing FeO as a separate component is unclear and requires clarification.

Response 1. We report FeO separately because it is a critical phase in the reduction process. FeO content directly affects the formation of low‑melting eutectics in the FeO–CaO–SiO₂ system, which determines the softening behavior. Moreover, the initial FeO content in sinter influences the rate of wustite accumulation during reduction. We have added a brief explanation in the text when introducing Table 1.

Comments 2. In line 201, the elemental proportions of the SFCA phase are stated to have been derived from EDS. EDS is inherently semi-quantitative and cannot provide reliable stoichiometric ratios for complex phases, particularly at the spatial resolution reported. The Fe content of 8.5 appears substantially higher than typical values for SFCA-type phases. The conclusions drawn from this composition are therefore insufficiently justified; even bulk ICP analysis could not fully exclude the influence of finely intermixed iron oxide impurities.

Response 2. We agree that EDS is semi‑quantitative. The formula provided (Ca_2.3Mg_0.8Al_1.5Fe_8.3Si_1.2O₂₀) was intended as an approximate representation based on multiple point analyses on clearly identified SFCA grains free of visible magnetite inclusions. Nevertheless, we acknowledge that the exact stoichiometry may vary. We have therefore rephrased the statement to avoid overinterpretation, added the range of measured values, and cited literature references for typical SFCA compositions [10, 11, 32]. A footnote has been added that EDS provides semi‑quantitative data.

Comments 3. The discussion in lines 262–268 lacks supporting citations and experimental evidence, making the arguments appear largely speculative. If supporting literature is available, it should be cited; otherwise, this passage should be removed.

Response 3. We would like to express our gratitude to the reviewer. We have shortened Section 3.5, removed speculative wording. The section now focuses on the mechanism of cohesion zone formation based on the experimental data.

Comments 4. Figure 4a is of low quality and the black annotations on the SEM micrograph are difficult to read. It is recommended to use a more contrasting color and to increase the font size and weight. Since SEM images are already available, the addition of EDS element mapping would significantly improve the interpretability of the microstructures. Furthermore, “gelenite” in line 231 appears to be a typographical error, the correct spelling is likely “gehlenite.”

Response 4. We agree with the reviewer. The figure 4 enlarged and the labels revised to ensure legibility. All annotations clearly visible and appropriately informative. A revised figure provided in the updated manuscript. The typo “gelenite” has been corrected to “gehlenite” throughout the manuscript.

Comments 5. The degree of reduction is determined from mass loss. The exact formula used for this calculation should be provided explicitly, or the authors should consider whether reporting the mass loss directly would be more transparent and reproducible. Moreover, the potential variation in the final mass losses among the different formulations tested does not appear to have been taken into account. This aspect requires careful consideration and justification.

Response 5. The method for calculating the degree of reduction was based on the change in the sample's mass after reduction and the data from the chemical analysis:

where R is the degree of reduction, %; FeO’ is the mass fraction of wustite (before reduction), %; Fe’_met is the mass fraction of metallic iron (before reduction), %; Fe’_total is the mass fraction of total iron (before reduction), %; m’ is the mass of the material (before reduction), g; m is the mass of the material (after reduction), g.

Comments 6. Lines 147–149 state that an optical microscope was used “for quantitative phase distribution analysis”. However, no corresponding quantitative data or analysis appears anywhere in the subsequent text. This discrepancy should be checked and corrected.

Response 6. We apologize for this oversight. An Olympus GX-51 optical microscope with SIAMS 700 software for quantitative assessment of phase distribution was used for preliminary analysis of the micro and macro structure of agglomerates and selection of representative samples for SEM analysis. The revised text reflects this.

It is asserted that the alterations made fully address all of the reviewer's comments and significantly enhance the scientific and practical value of the article. We would like to express our gratitude for your assistance in enhancing the quality of our work.

Best regards, authors.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

This study explores the phase transition of iron ore sintered ore during the softening process. Research has found that regardless of alkalinity, when iron ore undergoes softening, a viscous region is formed, which plays a key role in gas dynamics and reducing coke consumption.

This is a iron ore research and fits scope of journal Metals more than this Materials.

This is a short paper and the results are clearly presented.

Below are comments for revision:

1. The tittle is too in general, the iron ore sinter or slag system need to be specified in tittle.
2. This should also be mentioned in abstract section. For the studied sinter and slag systems.
3. Key words are too many! Should be reduced with numbers of about 5 to 8 according to the journal requirement.
4. Introduction section also need to be more focused on the research status on the softening of iron ores in the specific slag system. There are many studies on this topic. The literature review should be more specific. A good paper on sinering is recommended: Super-high bed homogeneous sintering for iron ores with low carbon emissions. https://doi.org/10.1016/j.jclepro.2025.146848
5. Definition of basicity need to be given as a formula.
6. The lab setup as described in section 2.3 need to be more clear. Is this mixture with coal means pre-reduction in this experiment?
7. Besides, what is this reduction furnace in lab? For example type, name of the equipment.
8. The parameter settings for XRD analysis are quite strange: 'tube voltage of 22kV and current of 30mA'. The working voltage of a copper target X-ray tube is usually around 40kV, which is lower than the conventional voltage of 22kV. This may lead to insufficient peak intensity and poor signal-to-noise ratio.
9. How about the repentance of the experiments? The errors need to be evaluated.
10. The section 3.5 need to be revised, the descriptions on the upper part of the blast furnace can be shortened. Those are inference but not conclusions.

Author Response

Dear Expert!

We, the authors of the article “Phase Transformations during the Softening of Iron Ore Sinter of Varying Basicity”, Elena A. Vyaznikova, Andrey N. Dmitriev, Galina Yu. Vitkina and Vladimir V. Katayev, would like to express our gratitude for your meticulous review of our article and for your constructive comments and suggestions. We are immensely grateful for your invaluable feedback, which has enabled us to enhance the quality of our work to a considerable extent. The following section presents a comprehensive response to the issues raised, accompanied by a detailed description of the corrections made to the manuscript.

General comment about scope: This is an iron ore research and fits scope of journal Metals more than this Materials.

Response. We appreciate your remark. While iron ore sinter is indeed a ferrous material, the focus of our work is on phase transformations (solid‑state and liquid‑phase evolution) and their influence on the softening behavior, which falls within the scope of Materials as a journal covering the structure and properties of inorganic materials. For now, we have revised the manuscript according to your suggestions to strengthen its suitability for Materials.

Comments 1. The tittle is too in general; the iron ore sinter or slag system need to be specified in tittle.

Response 1. We would like to express our gratitude to the reviewer. We have changed the title to “Phase Transformations during Softening of Iron Ore Sinter of Varying Basicity in the CaO–SiO₂–FeO System”.

Comments 2. This should also be mentioned in abstract section. For the studied sinter and slag systems.

Response 2. We would like to express our gratitude to the reviewer. We have added a sentence in the abstract specifying that the sinter belongs to the CaO–SiO₂–FeO–Al₂O₃–MgO system and that the liquid phase formed during softening lies in the FeO–CaO–SiO₂ system.

Comments 3. Key words are too many! Should be reduced with numbers of about 5 to 8 according to the journal requirement.

Response 3. We would like to express our gratitude to the reviewer. We have reduced the keywords to 8: blast furnace; iron ore sinter; softening; phase composition; SFCA; wustite; basicity; reduction.

Comments 4. Introduction section also need to be more focused on the research status on the softening of iron ores in the specific slag system. There are many studies on this topic. The literature review should be more specific. A good paper on sintering is recommended: Super-high bed homogeneous sintering for iron ores with low carbon emissions. https://doi.org/10.1016/j.jclepro.2025.146848

Response 4. We would like to express our gratitude to the reviewer. We have revised the introduction, focusing on studies of softening/melting in the FeO–CaO–SiO₂ system and the role of basicity. We have also added the recommended reference: Super‑high bed homogeneous sintering for iron ores with low carbon emissions, J. Clean. Prod. 2025, 146848.

Comments 5. Definition of basicity need to be given as a formula.

Response 5. We would like to express our gratitude to the reviewer. We have added the formula CaO/SiO₂ in Section 2.1.

Comments 6. The lab setup as described in section 2.3 need to be clearer. Is this mixture with coal means pre-reduction in this experiment?

Response 6. We would like to express our gratitude to the reviewer. Yes, the second method (sinter + pulverized coal) was used to achieve controlled pre‑reduction at lower temperatures. We have clarified this in the text. Section 2.3, added: “This second method was used to simulate pre‑reduction of sinter by carbonaceous materials before the softening zone.”

Comments 7. Besides, what is this reduction furnace in lab? For example, type, name of the equipment.

Response 7. We would like to express our gratitude to the reviewer. We have added the description: vertical detachable tube furnace (PTVR-1.25-70, JSC "Aramil Plant of advanced technologies" (JSC "AZPT"), Russia, Aramil) with a gas‑tight retort, equipped with a mass‑flow controller for CO/N₂.

Comments 8. The parameter settings for XRD analysis are quite strange: 'tube voltage of 22kV and current of 30mA'. The working voltage of a copper target X-ray tube is usually around 40kV, which is lower than the conventional voltage of 22kV. This may lead to insufficient peak intensity and poor signal-to-noise ratio.

Response 8. We would like to express our gratitude to the reviewer. The parameters for X-ray diffraction analysis were chosen consciously, taking into account the research objectives and the characteristics of the instrument. The measurements were performed using a Shimadzu XRD-7000 diffractometer with Cu-Kα radiation, and the primary goal was to perform quantitative phase analysis using the Rietveld method, rather than simply obtaining the maximum peak intensity. The sufficient amount of data was confirmed by the fact that the error in determining the phase composition did not exceed 2-3 wt. %, and the results were in good agreement with the microstructural analysis. Therefore, the chosen measurement parameters ensured an acceptable signal-to-noise ratio and reliable quantitative analysis.

Comments 9. How about the repentance of the experiments? The errors need to be evaluated.

Response 9. We would like to express our gratitude to the reviewer. Due to the specific features of the material (heterogeneity of the sinter in terms of structure), all experiments were conducted several times for statistical reliability. Only the repeated results are presented in the paper. For X-ray phase analysis, at least two parallel samples were analyzed for each point, and the error of quantitative phase analysis was 2-3 wt. %. For softening tests, several parallel tests were conducted, and the temperature difference did not exceed ±10°C.

Comments 10. The section 3.5 need to be revised, the descriptions on the upper part of the blast furnace can be shortened. Those are inference but not conclusions.

Response 10. We would like to express our gratitude to the reviewer. We have shortened Section 3.5, removed speculative wording. The section now focuses on the mechanism of cohesion zone formation based on the experimental data.

It is asserted that the alterations made fully address all of the reviewer's comments and significantly enhance the scientific and practical value of the article. We would like to express our gratitude for your assistance in enhancing the quality of our work.

Best regards, authors.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The revised version of the article is much better than the original. The comments provided have been taken into account, and the quality of the work and the figures have now been improved.

The article is ready for publication.

Author Response

Dear Reviewer, thank you so much for your encouraging feedback and for taking the time to review our revised manuscript. We are truly delighted to hear that you find the new version much improved and that the quality of both the work and the figures now meets your expectations. Your thoughtful comments and guidance have been invaluable throughout this process, and we sincerely appreciate your support.

Best regards, the Authors.

Reviewer 3 Report

Comments and Suggestions for Authors

All issues have been properly addressed. 

Author Response

Dear Reviewer, thank you so much for your kind words and for taking the time to look at our revised manuscript. We are truly glad to hear that everything is now in order - your feedback was incredibly helpful, and we really appreciate the thoughtful suggestions you shared with us.

Best regards, the Authors.