Forming and Oxidation Behavior During Forging with Consideration of Carbon Content of Steel

Round  1

Reviewer 1 Report

The paper is clear and well written. It well fits the Metals Journal purposes.

Author Response

Thank you.

Reviewer 2 Report

The authors present mathematical expressions to model the high-temperature forming of steels. The model takes into account the flow stress, the recrystallization behavior and oxidation as a function of the carbon content. I think that before accepting publication of this paper the authors should clarify in a revised version the following points:

1. What is the novelty of the paper? It is not clear to me if the models presented are ‘new’ or adopted from previous works. The authors should clarify what are exactly the new modifications they introduced in the models.

2. What is the effect of composition in the forming process? The authors show results for C15 steel in figure 3 and C60 steel in figure 4, but they do not compare or discuss the differences obtained for the different compositions. This comparison should be fully developed in a revised version.

Author Response

Dear reviewer,

all your comments as well as from a second reviewer are considered and highligthed in the document.

Best regards,

Marcel

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear authors,

You present a very interesting and comprehensive work. Indeed numerical simulation needs to be adjusted to the very material properties and, thus, the microstructure is the most critical parameter. Of course, the microstructure in steels is set as a result of chemical composition, thermal history and deformation sequences (both overall and stepwise reductions are important). Considering the chemical composition effect first is correct.  The effects of Carbon and other important alloying elements such as Chromium, Nickel, Molybdenum, Boron, Manganese, Silicon, Aluminium and micro-alloying elements e.g. Niobium, Vanadium, Titanium, that rule transformation temperatures and phase transformation kinetics, must be put into the equation. Therefore, embedding the effect of Carbon into the simulation, which significantly alters the microstructure, is a good starting point.

Congratulations on your work. Reading through a clearly presented manuscript helps the reader to understand the topic.

Prior to publication, I would like to underline a few points and ask you to improve the text accordingly for the benefit of the readers. These are the following points:

·     In line 104, you refer to heat treatment, but you don’t show this in the text. Please put the needed information to complete the information provided. 
Also correct “than” with “then” in line 103.

·     According to my understanding reference [17] is of immense significance for your work. Thus, please elucidate in your manuscript the basic model parameters and the way you utilize them in your study so that the reader won’t need at first to seek for the German reference in order to understand the procedure followed. (please see lines 118-119). The model as you write takes into consideration the austenitization temperature, the strain rate and the forming temperature. The Carbon content influences directly the transformation temperatures. However, the strain rate and the heating rate influence as well the occurrence of phase transformations shifting the A3 temperature for instance to higher temperatures. Thus, I believe that providing more information and references regarding this can be extremely helpful for the reader to gain a deeper understanding on the complex phenomena occurring simultaneously.  

Regarding the strain rate effect, I would expect you to precisely explain how this influences crucial parameters. The dislocation density and dislocation mobility are of significance. According to my understanding forging can proceed at lower, but also at higher strain rates. Thus, the reader must raise awareness on the strain hardening effect and its effect on the process. The microstructure plays here again a very important role. During high hot deformations the material is significantly heated. This can affect the microstructure, especially when Carbides are included. Of course in your original work you do not consider alloyed steels (that contain Cr, Mo, Nb, V, Ti, B), but only Carbon steels (C45, C60 etc.). Still, the heating rate influences phase transformations. High heating rates shift the A1 and A3 temperatures. High heating rates can result also from high strain rates in hot deformations. With regard to the effect of heating rate you can take a look on the following references:

1.     Papaefthymiou, S. , Goulas, C. , Castro Cerda, F. M., Geerlofs, N. and Petrov, R. (2017), The Effect of Heating Rate on the Microstructure of a Soft‐Annealed Medium Carbon Steel. steel research int., 88: 1700158. doi:10.1002/srin.201700158

2.    Papaefthymiou S.; Bouzouni M.; Petrov R. H.: Study of Carbide Dissolution and Austenite Formation during Ultra – Fast Heating in Medium Carbon Chromium Molybdenum Steel, Metals (2018), 8, 646; doi:10.3390/met8080646

3.    Castro Cerda F., Schulz B., Papaefthymiou S., Artigas A., Monsalve A., Petrov R. H.: The effect of ultrafast heating on cold-rolled low carbon steel: Formation and decomposition of austenite, Metals 6 (2016) No.12, pp. 321

4.    Castro Cerda F., Goulas C., Sabirov I., Papaefthymiou S., Monsalve A., Petrov R.H.: Microstructure, texture and mechanical properties in a low carbon steel after ultrafast heating, Materials Science and Engineering A 672 (2016), pp. 108-120

5.     Felipe Manuel Castro Cerda, Florian Vercruysse, Constantinos Goulas, Bernd Schulz and Roumen H. Petrov, ‘Flash’ Annealing in a Cold‐Rolled Low Carbon Steel Alloyed With Cr, Mn, Mo, and Nb: Part I ‐Continuous Phase Transformations, steel research international, (2018)

6.    Sajad Ghaemifar and Hamed Mirzadeh, Refinement of Banded Structure via Thermal Cycling and Its Effects on Mechanical Properties of Dual Phase Steel, steel research international, 89, 6, (2018).

7.     Bouzouni M., Papaefthymiou S.: Modeling of the Steel Microstructure Gained after the Application of an Ultra-Fast Heat Treatment, J Nanosci Adv Tech 2 (2017) No.1, pp. 15-19

8.     Bouzouni M., Papaefthymiou S.: Preliminary Study of Carbide Dissolution during an Ultra-Fast Heat Treatment in Chromium Molybdenum Steel, Int J Metall Met Phys 2 (2017) No.5.

·     In lines 169-170 you correctly refer to the influence of Carbon content on scale thickness. Also, you refer to the positive effect of Silicon in preventing scale formation. Perhaps you could explain shortly the mechanism to the reader. In the case of Si, the formation of mixed Fe-Si-oxides (fayalite) in the proximity of the metal/scale interface is of significance as it delays the further oxidation of the iron substructure. Please elucidate similarly the effect of Carbon. Pointing out the sequence of the oxidation reactions might be helpful. Just for your consideration. This way the reader can better understand what you mean when writing “oxidation rate decreases with increasing carbon content”.

·     In lines 240-241 I think you should elucidate more on the reasons for the observed deviations in Figure 2(a). Neglecting the machine stiffness in the numerical simulation how much deviation could have caused and why? Please explain. Also provide the % of the expected deviation as you do in Table 9 (line 250).

·     In lines 271-273 you describe the occurrence of a high stress difference in the oxide layer during the forging process. It is not so clear to me how the cracks will form. Please give some additional explanations. It might be helpful if you also refer to the way the oxide layers are removed from the metal/die interface.

·     In section 4, conclusions, lines 291-292, you write that “…the influence of

this alloying element on the forming, recrystallisation and oxidation behaviour could be investigated.” Perhaps you mean that it was “simulated successfully”. If you just write “investigated”, it is non conclusive. In general I recommend that you try to write in a more conclusive manner this paragraph. Finally, the last three lines (297-299) refer to further investigations and should not be part of the conclusions.

·     In your manuscript you refer to several German articles. It might not be a problem for me as I do speak and write in German, but it could be troubling a lot of readers. Please check the availability of English references. I am sure, your co-authors and/or Prof. Kawalla can suggest a suitable alternative English article for references [1], [13], [15], [17] respectively.           

·     In line 4 please superscript “a, b, c”

·     In the text when you refer to a researcher, please provide after the “name et. al.” the reference number. Example in line 58: “A study of Kawalla et. al. compared…” You don’t provide [ref]. Please correct this all over the manuscript.

·     Please put the [refs] before of the full stops of the sentences. Example in line 68: “…among others. [1] Especially…” Please do so all over the manuscript.

Herewith I accept the publication of your manuscript after a minor revision in order for you to improve the aforementioned points and to perform some minor corrections pointed out to you.

Sincerely,

The reviewer

Author Response

Dear reviewer,

thank you for your comments. I try to answer/consider all, which is highligthed in the document.

Only the comment for the ref. number is not possible, because if I write Kawalla et al. follows a whole paragraph and after the last sentence must be the ref. behind the full stop. If I quoted only one sentence the reference must be inside the.

Author Response File: Author Response.pdf

Round  2

Reviewer 2 Report

I recommend the resubmitted version of the manuscript to be accepted for publication in Metals.