Review Reports - Optimization of Heat Treatment Process and Strengthening–Toughening and Mechanism for H13 Steel

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper is devoted to the study of the effect of quenching and tempering modes within the Q-P-T process on the structure and properties of H13 steel, which is widely used for the manufacture of toolholders and stamping tools. High operational loads and temperature conditions require this material to simultaneously have high strength, hardness and toughness, but existing heat treatment technologies do not always provide an optimal balance of properties. The article shows that the correct selection of heating parameters allows controlling phase transformations, carbide dispersion and distribution of residual austenite, which directly affects the mechanical behavior of steel. It was found that quenching at 1020 °C followed by tempering at 530–560 °C provides a combination of high strength, hardness and satisfactory ductility, reducing the risk of brittle fracture and increasing the reliability of the tool. The obtained results are of high practical importance for the development of technological modes for processing H13 steel, since they allow increasing the service life and reliability of working elements used under conditions of dynamic loads and intense wear. The paper needs correction:
1. The text (lines 120–138) describes problems with carbide dissolution during quenching. However, later in the experimental section, the data on specific phases (M6C, M23C6, M2C, MC) are not supported by X-ray diffraction or TEM analysis, but only by SEM. This makes the explanation too theoretical. Either the phase analysis should have been provided or the redundant details should have been removed.
2. At the end of the introductory section (lines 164–172), it is stated that existing heat treatment methods do not provide high hardness and toughness at the same time. However, in the discussion of the conclusions, it is clear that even the optimal parameters are also accompanied by a compromise - a decrease in ductility with an increase in strength. It should be acknowledged that this limitation remains, rather than talking about a complete solution to the problem.
3. In the Research Contents section (lines 174–185), it is stated that the paper will provide quantitative correlations between heat treatment parameters and properties. However, such correlations are not presented in the results in the form of regression models or equations. Everything is limited to descriptive analysis and comparison.
4. Table 1 (lines 197–197) gives the composition of H13 steel, but the range of carbon content of 0.32–0.45% is quite wide. The question arises: what was the real concentration in the studied sample? Small changes in carbon can significantly affect the microstructure and properties. An exact value for the applied batch should be indicated.
5. The microstructural analysis section (lines 239–261) talks about the dissolution of carbides and the formation of mixed structures, but does not provide a quantitative assessment, for example, of the proportion of residual austenite. Since the purpose of the work is to show the relationship between phases and properties, without such data the conclusions remain partly speculative.
6. Table 2 (lines 267–267) gives the results of mechanical tests, but the strength and relative elongation values are not always consistent. For example, at 1000°C + 530°C the strength is higher than at 1020°C + 530°C, but the elongation is lower. This contradicts the statement in the text that the 1020°C + 530°C regime provides a better balance of properties.
7. The section on "Reduction of area" (lines 304–312) shows that the effect of tempering temperature is insignificant. However, Table 2 shows that at 560°C the value increases significantly. The authors should have used stricter criteria so as not to discount the visible differences.
8. The section on "Strengthening and Toughening Mechanism" (lines 377–389) provides generalized explanations and hardly relies on the authors' own data. It seems as if the description is from a textbook rather than unique analytical results.
9. The Conclusions section (lines 397–410) states that increasing the tempering temperature always increases hardness. However, according to Figure 9, the hardness increases at 500–530°C, and decreases in some cases at 560°C. This means that the conclusions do not fully agree with the graphs.

10. The conclusion (lines 405–409) states that lower processing temperatures are preferable to prevent brittleness. However, the main recommendation of the article (1020°C + 560°C) refers to relatively high tempering temperatures. This is an internal contradiction that needs to be resolved.

Author Response

Response to Reviewer#1:

Comment 1: The text (lines 120–138) describes problems with carbide dissolution during quenching. However, later in the experimental section, the data on specific phases (M6C, M23C6, M2C, MC) are not supported by X-ray diffraction or TEM analysis, but only by SEM. This makes the explanation too theoretical. Either the phase analysis should have been provided or the redundant details should have been removed.

Answer: Thanks for your constructive suggestion. We have removed redundant details from the existing problematic sections of the main text.

Changes: “Some carbides have high hardness and are not easily melted at high temperatures, which has a significant impact on cutting performance and may even cause problems such as edge chipping.”

Comment 2: At the end of the introductory section (lines 164–172), it is stated that existing heat treatment methods do not provide high hardness and toughness at the same time. However, in the discussion of the conclusions, it is clear that even the optimal parameters are also accompanied by a compromise - a decrease in ductility with an increase in strength. It should be acknowledged that this limitation remains, rather than talking about a complete solution to the problem.

Answer: Thank you for pointing this out. We have added the limitations of the research in the research content section of the main text.

Changes: “Although the obtained heat treatment process parameters are difficult to provide both high hardness and toughness, and have certain limitations, they have guiding significance for optimizing the heat treatment process of H13 steel tool holder perfor-mance.”

Comment 3: In the Research Contents section (lines 174–185), it is stated that the paper will provide quantitative correlations between heat treatment parameters and properties. However, such correlations are not presented in the results in the form of regression models or equations. Everything is limited to descriptive analysis and comparison.

Answer: Thanks for your insightful suggestion. We have made revisions to the inaccurate description in that area.

Changes: “These analyses aim to explore the influence of heat treatment parameters on the me-chanical properties of H13 steel tool holders, in order to reveal the microstructural mechanisms that control the hardness toughness balance.”

Comment 4: Table 1 (lines 197–197) gives the composition of H13 steel, but the range of carbon content of 0.32–0.45% is quite wide. The question arises: what was the real concentration in the studied sample? Small changes in carbon can significantly affect the microstructure and properties. An exact value for the applied batch should be indicated.

Answer: Thanks for your constructive suggestion. According to the Chinese standard GB/T 1299-2014, the carbon content of H13 steel is 0.32% to 0.45%, and high-quality H13 steel can reach a carbon content of 0.37% to 0.40%. The H13 steel used in this study meets the national standard, and the fluctuation value of carbon content is within a reasonable range, with little impact on the microstructure and properties.

Comment 5: The microstructural analysis section (lines 239–261) talks about the dissolution of carbides and the formation of mixed structures, but does not provide a quantitative assessment, for example, of the proportion of residual austenite. Since the purpose of the work is to show the relationship between phases and properties, without such data the conclusions remain partly speculative.

Answer: Thank you for pointing this out. In our current work, we mainly rely on SEM analysis to evaluate the dissolution of carbides and the formation of mixed structures. Due to limitations in research conditions, XRD analysis was not performed. According to other literature reports, under similar H13 steel heat treatment processes, it was found through quantitative measurements that the residual austenite content is usually between 2-8%, which mainly enhances toughness. Thank you for your insightful feedback. We have identified it as a key focus for our future work.

Comment 6: Table 2 (lines 267–267) gives the results of mechanical tests, but the strength and relative elongation values are not always consistent. For example, at 1000°C + 530°C the strength is higher than at 1020°C + 530°C, but the elongation is lower. This contradicts the statement in the text that the 1020°C + 530°C regime provides a better balance of properties.

Answer: Thanks for your constructive suggestion. Due to the fact that the stretching process of the stretching part involves yielding first and then breaking, and for optimizing the strength of the tool holder, we prefer to remain in the elastic stage throughout use without yielding. Therefore, when the difference between tensile strength and yield strength is small, yield strength is the main selection criterion. Although the tensile strength at 1020 ° C+530 ° C is lower than that at 1000 ° C+530 ° C, the yield strength is higher, so the performance is better at 1020 ° C+530 ° C.

Comment 7: The section on "Reduction of area" (lines 304–312) shows that the effect of tempering temperature is insignificant. However, Table 2 shows that at 560°C the value increases significantly. The authors should have used stricter criteria so as not to discount the visible differences.

Answer: We sincerely appreciate your constructive comments. We apologize for the inaccurate description here. What we want to express is that the effect of tempering temperature on the reduction of cross-sectional area is not obvious, and the non effect can be almost ignored. The description has been modified in the text.

Changes: “… the variation in tempering temperature has no obvious pattern of influence on the re-duction of area.”

Comment 8: The section on "Strengthening and Toughening Mechanism" (lines 377–389) provides generalized explanations and hardly relies on the authors' own data. It seems as if the description is from a textbook rather than unique analytical results.

Answer: Thanks for your professional suggestion. The quenching and tempering processes can cause microstructural evolution, thereby affecting the toughness of H13 steel. This part is summarized based on the SEM and other reference materials mentioned earlier. The relationship between post fracture elongation, cross-sectional shrinkage, strength, and toughness is further discussed in conjunction with tensile experiments, with the aim of selecting the optimal heat treatment temperature.

Comment 9: The Conclusions section (lines 397–410) states that increasing the tempering temperature always increases hardness. However, according to Figure 9, the hardness increases at 500–530°C, and decreases in some cases at 560°C. This means that the conclusions do not fully agree with the graphs.

Answer: Thanks for your professional suggestion. From Fig. 9, it can be seen that the hardness only decreases from 49.8 to 49.7 when the tempering temperature increases from 1020 ° C to 1040 ° C at a tempering temperature of 500 ° C. This decrease is almost negligible. Therefore, we believe that overall, the hardness will increase with the increase of quenching temperature and tempering temperature.

Comment 10: The conclusion (lines 405–409) states that lower processing temperatures are preferable to prevent brittleness. However, the main recommendation of the article (1020°C + 560°C) refers to relatively high tempering temperatures. This is an internal contradiction that needs to be resolved.

Answer: Thank you for pointing this out. We apologize for the incomplete description here. As mentioned in the description of Figure 10, the optimal temperature for heat treatment is 1020 ℃ quenching+530 ℃ tempering, and 1020 ℃ quenching+560 ℃ tempering. Both have their own advantages and disadvantages, and in practical applications, the best choice should be made according to the needs. The corresponding parts in the conclusion have been modified.

Changes: “At 1020°C quenching + 530°C tempering, as well as at 1020°C quenching + 560°C tempering, H13 steel has good toughness and hardness matching and tensile properties. In actual processing, the choice between the two should be made ac-cording to the requirements.”

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The presented study "Optimization of Heat Treatment Process and Strengthening-Toughening Mechanism for H13 Steel" focuses on the optimization of the Q-P-T (quenching–partitioning–tempering) process for H13 steel. The authors investigate the influence of various combinations of quenching and tempering on the microstructure and mechanical properties in order to achieve an optimal balance between strength and toughness. The work presents the results of systematic experiments, microstructural analyses, strength and hardness tests, as well as the interpretation of the strengthening and toughness improvement mechanisms.

Strengths:

Relevance of the topic: H13 steel is widely used in toolmaking and in environments with high temperatures and mechanical loads. Optimization of its heat treatment has a direct impact on extending the service life of tools and increasing their reliability.
Comprehensive experimental approach: The authors tested several combinations of quenching and tempering and evaluated their influence on mechanical properties (strength, ductility, hardness). Thanks to this, they provide an overview of the behavior of steel at different parameters and give industrially applicable recommendations.
Detailed microstructural analysis: SEM observations and interpretation of carbide precipitation are processed at a high level. The text explains the mechanisms behind the changes in strength and toughness at different combinations of parameters.
Practical benefit: The study identifies optimal parameters (e.g. quenching at 1020 °C + tempering at 530–560 °C) that lead to a balanced ratio between strength, toughness and hardness. The recommendations formulated in this way have immediate application significance.

Weaknesses and recommendations for improvement:

Discussion of results: o Although the text is rich in experimental data, the discussion remains predominantly descriptive. I recommend expanding the analytical level – for example, emphasizing why the differences between 1020 °C and 1040 °C are crucial for practical applications. o It would be appropriate to deepen the comparison with other published works on the topic of Q-T or Q-P-T processes in H13 steel and explicitly state what makes this work different or what is new.
Limits and transferability of results: o The article focuses on laboratory conditions. It would be appropriate to mention the limits of applicability of the findings on an industrial scale - e.g. the influence of the size of the component, different cooling rates or operating conditions. o The discussion could also reflect the extent to which the results are applicable to other types of tool steels.
Data presentation: o The graphs and tables are informative, but readability could be increased by clearer description of the axes and more uniform formatting. o A synthetic table would be helpful in the conclusion, summarizing the best combinations of parameters for different scenarios (e.g. toughness preference vs. hardness preference).
Conclusion and perspectives: o The conclusion could be more extensive – explicitly formulate what this work brings compared to previous research, and indicate future directions (e.g. the influence of other alloying elements, the combination of Q-P-T with surface treatments or validation in industrial tests).

The article represents a high-quality and practically beneficial contribution to the issue of optimizing the heat treatment of H13 steel. It is methodologically robust and brings recommendations that can be used in industry. However, before acceptance, it should be supplemented with a deeper discussion, an explicit comparison with the existing literature and a clearer formulation of the limits and future perspectives. Therefore, I recommend accepting the article after modifications.

Author Response

Response to Reviewer#2:

Strengths:

Relevance of the topic: H13 steel is widely used in toolmaking and in environments with high temperatures and mechanical loads. Optimization of its heat treatment has a direct impact on extending the service life of tools and increasing their reliability.

Comprehensive experimental approach: The authors tested several combinations of quenching and tempering and evaluated their influence on mechanical properties (strength, ductility, hardness). Thanks to this, they provide an overview of the behavior of steel at different parameters and give industrially applicable recommendations.

Detailed microstructural analysis: SEM observations and interpretation of carbide precipitation are processed at a high level. The text explains the mechanisms behind the changes in strength and toughness at different combinations of parameters.

Practical benefit: The study identifies optimal parameters (e.g. quenching at 1020 °C + tempering at 530–560 °C) that lead to a balanced ratio between strength, toughness and hardness. The recommendations formulated in this way have immediate application significance.

Comment 1: Discussion of results: Although the text is rich in experimental data, the discussion remains predominantly descriptive. I recommend expanding the analytical level – for example, emphasizing why the differences between 1020 °C and 1040 °C are crucial for practical applications. It would be appropriate to deepen the comparison with other published works on the topic of Q-T or Q-P-T processes in H13 steel and explicitly state what makes this work different or what is new.

Answer: We appreciate your suggestion. We emphasize the difference in quenching temperature because the 20 ° C range has a significant impact on the properties of H13 steel. Compared to the literature related to the Q-P-T heat treatment process that has been published, other scholars have mainly focused on selecting the process path and controlling the temperature within a reasonable range. This study, on the other hand, selects the optimal temperature through experiments within a reasonable temperature range.

Comment 2: Limits and transferability of results: The article focuses on laboratory conditions. It would be appropriate to mention the limits of applicability of the findings on an industrial scale - e.g. the influence of the size of the component, different cooling rates or operating conditions. The discussion could also reflect the extent to which the results are applicable to other types of tool steels.

Answer: Thanks for your constructive suggestion. This article mainly focuses on the selection of heat treatment process parameters for H13 steel tool holders. The applicability in industry and other tool steels is our future research direction, and we will further deepen it in future research.

Comment 3: Data presentation: The graphs and tables are informative, but readability could be increased by clearer description of the axes and more uniform formatting. o A synthetic table would be helpful in the conclusion, summarizing the best combinations of parameters for different scenarios (e.g. toughness preference vs. hardness preference).

Answer: We sincerely appreciate your careful reading and constructive comments. We have optimized the clarity of Fig. 10.

Figure 10. Various indicators of H13 steel at different quenching and tempering temperatures. Tensile strength (TS); Yield strength (YS); Elongation after fracture (El.); Reduction of area (RA); Hardness (HRC)

Comment 4: Conclusion and perspectives: The conclusion could be more extensive – explicitly formulate what this work brings compared to previous research, and indicate future directions (e.g. the influence of other alloying elements, the combination of Q-P-T with surface treatments or validation in industrial tests).

Answer: We sincerely appreciate your careful reading and constructive comments. Compared to previous work, this study optimized the process parameters for heat treatment of H13 steel and selected quenching and tempering temperatures with better matching hardness and toughness. In the future, we will conduct TEM and other analyses to further reveal the influence of heat treatment processes on the microstructure of H13 steel.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Comment in the attachment.

Comments for author File: Comments.pdf

Author Response

Response to Reviewer#3:

The article is written in a clear and accessible manner. The illustrations facilitate understanding of the topics discussed in the article. Below are my comments on the article. I believe that your responses to my comments will improve the quality of the article.

Comment 1: Please, emphasize more precisely in Introduction novelty as well as potential industrial and practical contribution of your paper in comparison with other papers in this area.

Answer: Thanks for your constructive suggestion. We have added the significance and limitations of this study in the introduction section.

Comment 2: I propose to take into account the hardness of the tested steel tempered at a temperature of 530°C for different heating times.

Answer: Thank you for pointing this out. We will make it a research target in future studies.

Comment 3: In Figure 1, I suggest marking the temperature values.

Answer: We sincerely appreciate your careful reading and constructive comments. We have added annotations in Figure 1.

Comment 4: Figure 2: Please indicate according to which standard (recommendations) the authors prepared the sample for the static tensile test?

Answer: Thanks for your constructive suggestion. The static tensile test was conducted using ASTM E8 and GB/T 228.1 standards for sample preparation.

Comment 5: In figures 5 to 9, I suggest inserting markers of standard deviations of the measurements taken.

Answer: Thank you for pointing this out. The experiments in this study were conducted under strictly controlled conditions, ensuring the accuracy and reproducibility of individual experimental results, therefore no standard deviation was added.

Comment 6: What is the lattice distortion of samples hardened at 1020°C and tempered at 530°C?

Answer: We sincerely appreciate your careful reading and constructive comments. In the H13 sample hardened at 1020 ° C and tempered at 530 ° C, the lattice distortion is no longer the macroscopic, severe distortion caused by carbon supersaturation in the quenched state, but rather a microscopic, highly dispersed, coherent elastic strain field caused by nanoscale alloy carbide precipitates. Although this distortion is not as strong as the quenched state, its distribution is more uniform and stable. It can effectively hinder the movement of dislocations, thereby endowing the material with high strength and red hardness. This specific and controlled lattice distortion is the key to the excellent performance of H13 steel as a hot work die steel.

Comment 7: I suggest including impact tests on the samples in the article. This would enhance the scientific value of the article.

Answer: Thanks for your constructive suggestion. We will make it a research target in future studies.

Comment 8: How were the hardness measurements performed? How were the samples prepared for hardness measurement?

Answer: Thank you for pointing this out. The sample preparation and measurement method for hardness measurement have been described in Section 2.2.

Comment 9: The finer grains could not only improve the hardness of the steel but also guaranteed toughness. Please describe in more detail the process and causes of grain refinement of H13 steel during the heating process.

Answer: We sincerely appreciate your careful reading and constructive comments. H13 steel grain refinement is caused by undissolved alloy carbides pinning austenite grain boundaries, strongly hindering their migration.

Comment 10: Transmission electron micrographs of the microstructure of the precipitates in samples at 1020°C quenching temperature. I suggest including it in the article.

Answer: Thanks for your constructive suggestion. TEM images were not taken in this study, and we will add them in future research.

Comment 11: This article presents the results of research conducted by the authors. Similar studies are described in the literature. I propose that the article describe what constitutes novelty.

Answer: Thank you for pointing this out. This article takes H13 steel as the research object and conducts Q-P-T (quenching distribution tempering) heat treatment process experiments to study the effects of quenching temperature and tempering temperature on the microstructure and mechanical properties of H13 steel. Optimized the heat treatment process of H13 steel and improved the problem of easy breakage of the tool holder.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Unsubstantiated, general statements about specific carbides have been removed; the style has become more precise. Limitations and tradeoffs ("not all at once" for hardness/toughness) have been clearly added. A statistical analysis of hardness (ANOVA) has been added, confirming the significant influence of temperature. The wording has been corrected, limitations have been acknowledged, an ANOVA for hardness has been introduced, and the selection of modes has been better structured.

Reviewer 3 Report

Comments and Suggestions for Authors The authors have made the necessary corrections to the article. I propose publishing the article.