High-Temperature Precipitation Design-of-Experiments Simulation in Low-Alloy Cr–Mo–Ni Hot Forging Steel

Round 1

Reviewer 1 Report

The research work is an initiative attempt to analyze the role of alloying elements such as Cr, Mo and Mn in low alloy 8620 steel during hot forging operations by using Thermocalc simulations combine with Design of Experiments. In order to make the proof more rational, some suggesting are as follows: 1, As the paper mentioned, the precipitation simulation of M₇C₃, M₂₃C₆ or MnS were carried out using TC-PRISMA precipitation module to tracing the precipitation of these phases in a 1000 s period. Please present how to consider the role of stress or strain on the precipitation as hot forging manufacturing operations performing at high speed. The calculate model parameters should be elucidated for the thermodynamic or kinetic analysis in order to make the simulation more rational. 2. As well known, carbon replica extraction can be conducted on the steel samples and the replicas can be observed by TEM to study the morphology and size of particles. In addition, M₇C₃, M₂₃C₆carbide particles were extracted from the samples because they can be dissolved in phosphoric acid. Then the particles can be determined by XRD analysis. So the TEM analysis in this work was not evident to support the explanation of the precipitation the second phase in experimental sample. 3. In line 292, “the roll of Cr, Mo and Mn as precipitate forming elements” should be “the role of ……”, please noted these writing error to avoid ambiguity.

Author Response

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Reviewer 2 Report

This manuscript has described that the alloying elements on the precipitation behavior in low alloy 8620 steels during deformation at 1000~1100 C. The research topic is interesting, which contains many valuable points to clarify. In addition, plenty of experimental results are also listed in the manuscript. However, the authors should spend considerable effort to improve the present manuscript, such as the whole structure of the manuscript especially the introduction is not clear, and the content is highly recommended to modify to meet the requirement of Metals. Details comments are given:

 

• In the title “DOE “ the DOE should give the full name or change it to a professional way when it appears the first time.
• The writing is needs to be polished to a level that the readers could interpreter, some but more are not listed here.

For instance: Page 1 Line 22  “The values of alloying elements percentage The values of alloying elements percentage were drastically modified, as nominal values will not produce precipitation and segregation at the austenite matrix may be responsible for short term, nanometric precipitates producing grain growth inhibition.” What is the meaning here?

The format for figures is not fixed, such as fig. X,  Figure X, figure X.

 

• Page 1 Line 14 “The role of alloying elements such as Cr, Mo and Mn y low alloy 8620 steel during hot……” What is the “y” here?
• Page 2 Line 46 “Comparison between Thermocalc calculations and experimental data ”

What is “Thermocalc calculations”? Is it thermodynamic or kinetic modeling or something else? You also mentioned it late in some way around like “Calphad method” “Thermocalc simulations”, please keep it consistent in the text.

• Page 2 Line 84 “”merged in cold water in order to produce martensite”

What is the temperature for “cold water” since the temperature will affect the phase transformation/ volume fraction?

• Page 3 Line 113 “Simulations were carried out using Thermocalc TC-PRISMA precipitation module, by feeding the program with the corresponding amount (weight %) of alloying element, ….”

The details for the simulation such as nucleation interfacial energy, nucleation type, and number density are missed. Which database is applied? Thus, I am wondering how reliable the calculated results. The authors are recommended to include and discuss this point.

• Page 7 Line 189: “Yet, fig. 2 shows that the variation of hardness is larger in the upper zone, which means lamellar spacing is not the only factor to determine mechanical properties and PAS is also important. “

Ref is missed.

• Page 8 Line 210 “As expected, nucleation rate for this precipitate is extremely low at 1100 C and higher as temperature decreases (fig 10). This temperature interval, in which static and dynamic recrystallization phenomena may occur during hot forging, is highly modified by nanometric size precipitation which prevents grain growth.

Is this conclusion true? How to reach this？ Please add comments on this.

Author Response

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Reviewer 3 Report

1. The current study investigates the influence of high temperature in the precipitation of Cr-Mo-Ni hot forging steel. For this the authors conduct design of experiment study to analyse a deformed bar to study the hardness at different regions and use of scanning electron microscopy and TEM to study the formed microstructure. The authors also conduct simulation to model thermo elasticity to determine the significant variable.
2. Please consider reviewing the abstract and highlight the novelty, major findings and conclusions. Especially the findings, it seems like there is a lot of work that has been done but the findings do not reflect that.
3. Literature review is minimal and must be improved. Please try to expand your introduction and discuss in more details about previous studies similar to your current work. Perhaps if you find work related on forging at high temperature of this alloy or similar alloys or make a table which summarises past studies, what they looked for and what were their main findings.
4. After line 72 the authors should answer the following question: What is the research gap did you find from the previous researchers in your field? Mention it properly. It will improve the strength of the article.
5. Table 1 is so far from where you first mention it please bring it closer to the top
6. Please reference table 1 if you did not create/prepare the material by yourselves
7. The manuscript is not organised at all. The authors suddenly jump to FE modelling within the materials and method section. The details on the FE model is limited and it is not clear what was setup in it. The authors need to expand and give detailed information about their FE model and also their experimental setup. For example what is the design matrix used in the study for DoE. Why it was chose, how many parameters were involved and what were their levels. you said nine factors and then you used 32 runs only due to larger number of required trials but you didn’t mention which method you used? Was it partial factorial?
8. Mesh study, elements details, boundary conditions, limitations  in the model…etc all missing
9.  This work is more suitable to be as a communication not as an article many details are missing
10. This paper needs significant work and can not be accepted in its current state.
11. The title of the manuscript does not reflect that there was an FE modelling in it, this must be highlighted clearly in the abstract and the title of the manuscript
12. Please combine figures 6 and 7 into one larger figure
13. The authors focus a lot of the DoE model results but not the scientific logic behind the phenomena they describe from their findings
14. Please support the claim you made in lines 289-290 with a reference
15. Line 203-204 the authors make a very generic statement here, it is not followed by any explanation or discussion or comparison with previous literature
16. I am afraid the current paper does not read well, it feels more like a simple study that uses simple design of experiment and SEM to make some very generic and simple conclusions which are already known in the literature. The work must be significantly improved to qualify for a scientific journal article.
17. The results are not well described, they are limited to comparing the experimental observation and focused so much on the DoE analysis. The authors are encouraged to include detailed scientific discussion and analysis of their findings and compare their work with past literature when possible.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors have addressed most part of the comments mentioned, which is great! However, as I said in Point 2, “……some but more are not listed here.” Thus, the following comments should be considered as well in the updated version.

 

• Page 1 line 16 : “1000~1100 C”, the unit should be “^oC”, please check through this;

Page 11 Line 327 “ deformation at 1100 C and cooling in air at a 50~100 327

C/min rate. ”  Check the cooling rate unit and modify the writing.

 

• Page 1 Line 40: for the Fe-C-Cr ternary alloys, there are several workers published in recent years for tempered martensite at 700^oC, which contains M₇C₃ M₂₃C₆ and M₃C, see refs.: Coarsening of M23C6 Precipitates in a Fe-Cr-C Ternary Alloy (2012), Quantitative modeling and experimental verification of carbide precipitation in a martensitic Fe–0.16wt%C–4.0wt%Cr alloy(2016), Early stages of cementite precipitation during tempering of 1C–1Cr martensitic steel (2019), and other relevant refs should be also be mentioned at somewhere such as at Table 1. In addition, some necessary work on the comparison of the calculated precipitation behavior using TC-PRISMA, DICTRA software and experiments results are should be also mentioned in the discussion part to give a more confidential conclusion.

 

• Page 4 Line 128: the key parameters such as interfacial energy are still missed for the TC-PRISMA simulations, even though the authors have added a short paragraph, which is very known sensitive parameters see refs as the mentioned above group, the interfacial energy are recommended to give for each type precipitate, otherwise it is meaningless to discuss the calculated results.

 

• Figure 15, please give the index for each type of precipitates and specify where the diffraction patterns come from. Furthermore, in the conclusion part “The presence of small precipitates of the M7C3 and M23C6 in Figure 15” isn’t a proper way to present, and thus recommend rewriting it.

 

Best regards,

 

Author Response

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Reviewer 3 Report

First of all the authors have modified the manuscript and now it reads better but still it need major revisions: please see below my comment. 

The article presents a series of experimental and simulation results of low alloy Cr-Mo-Ni hot forging steel and a subsequent analysis using design of experiments techniques. In reviewer's opinion, the article does not analyze the influence of the process on the parts and does not discuss the results of the experimental tests, limiting the analysis to statistical results. Furthermore, alloy Cr-Mo-Ni steel alloy may show significant change in grain growth inhibition due to temperature during forging, but this issue is not deeply analyzed, which could be of scientific interest. Therefore, in the reviewer's opinion, the article focuses more on a practical-experimental analysis of material forging process of the material, which is very useful from a practical point of view, but does not go into sufficient depth from a scientific point of view.

Author Response

Response to reviewer is attached

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Round 3

Reviewer 3 Report

No further comments