Review Reports - Continuous Cooling Transformation of Tool Steels X153CrMoV12 and 100MnCrW4: Analysis of Microstructure and Hardness Changes

Round 1

Reviewer 1 Report

The work is of very good quality and it is also important for the practitioners who are interested in correlating microstructure with mechanical properties of different grades of tool steels. However, the objective and novelty of the work is not presented clearly (neither in abstract nor in conclusions).

The phase diagrams have been obtained from Thermocalc software. These softwares use chemical composition to evaluate phase diagrams. However, the microstructure depends upon the thermos-mechanical heat treatment followed during manufacturing. Hence, it is not clear why you are showing initial microstructure along with predicted phase diagram. It is suggested that initial microstructures should be shown separately from phase diagrams.

The heat treatments for each microstructure should be clearly mentioned in the text. Please provide the full form of PAGB in the text. The normalizing annealing conditions should be mentioned.

Fig. 9 and 14 should be plotted together at the end in a separate section. The variations in hardness values with cooling rates for the two grades of steel should be compared and the reason for the difference should be elaborated.

Fig. 9: It is mentioned that hardness change from 302 to 650 is because of presence of bainite in the microstructure. Can you provide some relative hardness of pearlite and bainite phases and their fraction in the microstructure so that the above data can be justified?

It is mentioned that the microstructure and hardness values change significantly when cooling rates change from 0.2 to 0.1 deg.C/s. Please show the corresponding microstructure to support this point. You have only shown the microstructures for 0.1 and 1 deg.C/s. Moreover, whether the Thermocalc software calculation supports this conclusion? If yes, please mention the fraction of these phases as calculated by the software and as measured in the microstructure. Please include a Table and associated discussion in the text.

Comments on the manuscript ‘Dilatometric Analysis of Continuous Cooling Transformation (CCT): Comparison of Simulation Diagrams with Physical Experiments on Tool Steels’ (Ref: applmech-3436049)

In this work, the authors have experimentally derived the continuous cooling transformation data for two kinds of tool steels. Various phase transition temperatures have been derived for these grades of steel. In addition, the microstructure and microhardness of the above grades of steels have been evaluated and the data have been correlated with the cooling rates. The reviewer has the following comments.

1. The work is of very good quality and it is also important for the practitioners who are interested in correlating microstructure with mechanical properties of different grades of tool steels. However, the objective and novelty of the work is not presented clearly (neither in abstract nor in conclusions).

2. The statement (Page-1) ‘The results clearly demonstrate that increasing the weight percent content of alloying elements has a substantial effect on the accuracy of the simulation results’, is not clear. Here, what are the specific alloying elements you are referring to? Please mention. On the other hand, it is not clear why the accuracy of simulation software depends on the composition. Is there any specific limitation in the software? Please elaborate.

3. Fig. 1: The schematic diagram is not fully described. What is ‘20 mm’ in tempering region? What are solid lines and dashed lines? The figure should be self-explanatory and details should be explained in the text. Moreover, the temperature range and time scales should be mentioned approximately in the figure.

4. Fig. 2 is taken from Ref. [9]. However, the temperature and time scales for the two grades of tool steels used in this work should be mentioned. The caption mentions ‘thermo-mechanical factors’. Please mention what are these factors and show their effect (schematically) in the figure. Similarly, include a brief description of the figure in the text.

5. First paragraph of section-2: Please check the sentence “The reason why these three tool steels were chosen is their different chemical composition”. Are you using three grades or two grades of steel? The results are for two grades. Please check.

6. Table-1: Are these compositions taken from literature? Please mention the appropriate reference. Moreover, the range of compositions have been specified here. This range is used in standards. However, for your work, you have used some particular composition. Please mention composition of your materials.

7. Table-2: Tensile strength is measured by two properties, yield strength and ultimate tensile strength. Please mention both data. For 100MnCrW4, why is it mentioned as >612? Please mention the value correctly. How do you measure modulus of elasticity here? Are these taken from literature? If yes, please mention source. Similar is the case for thermal conductivity and specific heat values. Why are hardness values mentioned as 890 and 810 HV respectively? Your work is to find hardness as a function of cooling rate. Hence, please mention the cooling rate here. Otherwise, please leave this data and refer to subsequent results.

8. Page-4 (last paragraph): The phase diagrams have been obtained from Thermocalc software. These softwares use chemical composition to evaluate phase diagrams. However, the microstructure depends upon the thermos-mechanical heat treatment followed during manufacturing. Hence, it is not clear why you are showing initial microstructure along with predicted phase diagram. It is suggested that initial microstructures should be shown separately from phase diagrams. The heat treatments for each microstructure should be clearly mentioned in the text. Please provide the full form of PAGB in the text. The normalizing annealing conditions should be mentioned.

9. Fig. 3(a) and (b): The microstructure length scale is different. One is 5 micron and the other is 10 micron. Please use same scale so that the relative carbide and grain sizes can be interpreted clearly.

10. You have mentioned names of instruments and softwares in the text. It looks like commercially promoting a particular instrument. Is it required here?

11. Page-5, 4th line from end: Please check the sentence “Depending on the type of experimental material examined, the range of cooling rates ranged from 20 °C/s to 0.01 °C/s.”. The actual heating rate used is 0.1 to 10 in one case and 0.1 to 20 in another. Why do you mention lowest as 0.01 deg.C/s. Please check.

12. Fig. 4 is very obvious and it is not needed. Just mention the sample size, heating and cooling rates and holding times in the text.

13. Fig. 8 and 13: Please mention abbreviations for ‘A’ as austenite, ‘B’ for bainite etc. in the figure and in the text. Similarly, for M, P etc.

14. Figure numbers have been mentioned incorrectly. Please check. In page-14, the figure 4 should be Fig. 11. Similarly, check other figure numbers.

15. Figs. 5, 6 and other figures: You are using two axes. Left for dilation curve and right for deviation curve. Please mark the curves to the corresponding axes using arrows. Moreover, it is not clear how deviation is measured here? Please include a brief description in the text. It seems like strain derivative here. What is the physical significance? Why are deviations show oscillations in Fig. 6, whereas, the oscillations are nearly zero in Fig. 5?

16. Fig. 9 and 14 should be plotted together at the end in a separate section. The variations in hardness values with cooling rates for the two grades of steel should be compared and the reason for the difference should be elaborated.

17. Fig. 9: It is mentioned that hardness change from 302 to 650 is because of presence of bainite in the microstructure. Can you provide some relative hardness of pearlite and bainite phases and their fraction in the microstructure so that the above data can be justified?

18. It is mentioned that the microstructure and hardness values change significantly when cooling rates change from 0.2 to 0.1 deg.C/s. Please show the corresponding microstructure to support this point. You have only shown the microstructures for 0.1 and 1 deg.C/s. Moreover, whether the Thermocalc software calculation supports this conclusion? If yes, please mention the fraction of these phases as calculated by the software and as measured in the microstructure. Please include a Table and associated discussion in the text.

19. Fig. 14: For the cooling rates of 0.1 and 0.5, pearlite is present in the microstructure. However, the hardness values increase drastically from 298 to 384 HV even in the absence of bainite formation. Please explain. This is opposite to the observation for the other grade of steel.

20. Conclusions: This section should be rewritten completely. Lot of descriptions are being repeated here and hence, these are not needed. Please include some of the important conclusions in brief (one to two lines for each) and present in bulleted points. Conclusion-2 is just a general statement and it is not a conclusion from your work. This may be removed.

21. Some of the references are very old, i.e., of 1979 and 1982 respectively. Moreover, there are abundant recent literature regarding prediction of phase transformation and associated mechanical properties. Hence, it is suggested that the authors should include some recent works in this area and modify the sections appropriately.

22. The style of reference is not proper and information is not complete. For example, volume and page or article numbers are not provided for Ref. 22, 23, 29 and 30. Similarly, there are mistakes in other references. Please check and rectify. Ref. 18 is a web page, which may change and hence, these types of references may be avoided.

23. The title is not appropriate. It doesn’t reflect the content of work presented. What is physical experiment here? Are you mentioning hardness values and microstructure? Please rephrase the title accordingly. Abbreviation in title, such as ‘CCT’ should be avoided.

24. The abstract should be shortened and modified. The generalized descriptions should be avoided. Some of the important conclusions should be mentioned. The objective and novelty of the work should also be mentioned.

25. There are a lot of grammatical and sentence construction errors in the paper. Please check the manuscript thoroughly and rectify the same in the revised version.

Author Response

Please see attached document.

Author Response File: Author Response.pdf

Reviewer 2 Report

This study analyzes the decomposition of austenite during cooling using experimentally derived continuous cooling transformation (CCT) diagrams for two tool steels, X153CrMoV12 and 100MnCrW4. The dilatation curves were compared with metallographic evaluations using scanning electron microscopy (SEM) and hardness measurements. The accuracy and reliability of the CCT diagrams were validated by comparing them with theoretical diagrams computed using JMatPro simulation software. The cooling rates varied from 20°C/s to 0.01°C/s, depending on the steel type. The weight percentage of alloying elements significantly influenced the CCT diagrams, with increasing the weight percent content affecting the simulation results.

The researchers used the DIL 805A quenching dilatometer. The dilatometer measures the change in size of the steel as it cools. To understand how the steel changes at the microscopic level, they also used scanning electron microscopy (SEM).

The paper is within the scope of the journal but its current state does reach a level allowing its recommendation for publication

- The quality of figures 1 and 4 must be improved with more explanation of information given in these figures.

- Some references are out of date and must be updated. Moreover, all the references must be given in the same format.

- The introduction failed to show a gap in the actual knowledge to motivate the present research

- figure numbering needs to be revised because something is wrong in the numbering

- It would have been interesting to binarize the images to extract more information such as defects or microcracks. Free tools are available for this type of analysis.

- The conclusion is very long and must be shortened

Author Response

Please see attached document.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have addressed many of the concerns raised during the first review of the manuscript. However, some of the major comments have not been considered adequately during the process of these revision. These are listed as follows.

1. One of the major concerns was regarding the microstructure-property correlations between the two grades of steel as obtained during the cooling process. The rate of cooling is between 0.1 and 20 degC/s. For the X135Cr steel, the hardness increases from 302 to 1138 HV5 as the rate of cooling increases, whereas for the 100MnCr steel, the hardness changes from 298 to 789 HV5 with increased rate of cooling. The dominant microstructures for both the tool steels have been classified as P, P+B, M+B etc. It is suggested that the hardness values should be plotted as a function of rate of cooling (in terms of curves, not in terms of bar charts as presented now) for both grades of tool steels so that the effect of cooling on hardness can be compared directly. It would have been preferable to evaluate the change in mechanical properties such yield strength, UTS and ductility for both steels in terms of rate of cooling. However, at least the hardness values should be compared. Moreover, the authors mention that the hardness is due to the presence of different types of phases (M, B) and carbides in the matrix. The carbide volume fraction should be mentioned as a function of cooling rates and these should be plotted as a function of cooling rates along with the hardness data. The bar charts only show M+B, M+B+P etc. These are mere qualitative information. It is recommended that the authors quantify the microstructure in terms of different phase fractions like, pearlite, bainite, martensite etc. and report these for different cooling rates for both grades of steel and compare the same through appropriate graphs. Without these information, the results look very qualitative in nature.

2. The authors have used simulation software to calculate different phase fractions and carbide fractions and their size as a function of cooling rates. Hence, the computed information regarding these parameters should be provided along with the measured data. The results and discussion section should be modified accordingly by considering the above points.

3. In the first grade of steel, i.e., X135Cr steel, Cr, Mo and V are significant, whereas in the second grade of tool steel (100MnCr), there is no Mo, very less Cr, less V and some W. Carbon content is also less in second grade of steel. So, the carbide compositions and their fractions shall be very different upon processing and upon subjecting these to various cooling rates. The authors should provide a table highlighting different carbide phases and their composition in as-received state as well as after the heat treatment process. This information is very crucial in order to understand the reason for change in mechanical properties of both the grades of steels as a function of cooling rates. Moreover, the results of simulation software can be presented for this purpose and their comparison with experimental data shall provide confidence in the accuracy of these softwares.

4. The similarity check indicates that the percentage of similarity of the revised version of the manuscript with existing literature has increased from 25% to 33%. It seems the authors have used some significant text from other publications. The authors should remove the content taken from other sources and check the manuscript thoroughly to reduce the similarity to bare minimum percentage.. Here is one of the source with which the content matches to a large extent.

Physical modeling of CCT diagram of tool steel 1.2343 Procedia Structural Integrity, Volume 43, 2023, Pages 270-275.The authors have addressed many of the concerns raised during the first review of the manuscript. However, some of the major comments have not been considered adequately during the process of these revision. These are listed as follows.

Here is one of the source with which the content matches to a large extent.

Physical modeling of CCT diagram of tool steel 1.2343 Procedia Structural Integrity, Volume 43, 2023, Pages 270-275.

It is suggested that the authors should consider these points while revising the manuscript

Here is one of the source with which the content matches to a large extent.

Physical modeling of CCT diagram of tool steel 1.2343 Procedia Structural Integrity, Volume 43, 2023, Pages 270-275.

It is suggested that the authors should consider these points while revising the manuscript.

Author Response

Please see the attached document.

Author Response File: Author Response.docx

Reviewer 2 Report

The authors have successfully addressed all comments. The revised manuscript can be accepted.

Author Response

Thank you once again for your valuable questions, advice and comments, which will certainly raise our publication to a higher level, and with your help, we will be able to present our contribution to a wide professional public.

Round 3

Reviewer 1 Report

The authors have now addressed all the comments and the manuscript has been revised accordingly. The revised version of the manuscript may be accepted for publication.