Alternative Approach for the Intercritical Annealing of (Cr, Mo, V)-Alloyed TRIP-Assisted Steel before Austempering
, Mattia Franceschi 3, Kaiming Wu 4, František Kováč 2, Yuliia Chabak 1,2, Viktor Puchy 2 and Michail Brykov 5
Round 1
Reviewer 1 Report
The research paper is good, and the results are clear. I recommend accepting this paper after making the following modifications:
1- In Figure 2, the description of the relationships is placed inside the figure.
2- The loading rate should be written in the tensile test.
3- Add a figure for the tensile test specimen that was described in lines 133 and 134.
4- In line 262 correct the numbers of the figures “5i and 5k”.
5- Figure 3 shows the inverse of the result written in lines 203 to 205. Review the text carefully.
Comments for author File: 
Comments.pdf
Author Response
Dear Reviewer,
We appreciate your valuable comments which allowed us to improve our paper. We tried to address all your comments. The appropriate modifications in the text are denoted by blue lettering. Our responses please see below.
Comment 1: In Figure 2, the description of the relationships is placed inside the figure.
Response: The description of the relationships is added to the Figure 2 caption.
Comment 2: The loading rate should be written in the tensile test.
Response: The information on loading rate is added to the “Materials and Methods” (section 2.3).
Comment 3: Add a figure for the tensile test specimen that was described in lines 133 and 134.
Response: The information on the shape/size of the tensile and impact specimens is added to the “Materials and Methods” (section 2.3).
Comment 4: In line 262 correct the numbers of the figures “5i and 5k”.
Response: Corrected.
Comment 5: Figure 3 shows the inverse of the result written in lines 203 to 205. Review the text carefully.
Response: A thorough check of the indicated part of the text showed that it is correct corresponding. to the data presented in Figure 3. The point is that after reaching the maximum load, the stress-strain curve goes down, which corresponds to an area of non-uniform deformation (necking). If we compare all curves, we can see that for 770 °C, 830 oC, 900 oC and 950 °C the stress decreases (until the moment of rupture) by 24 MPa, 219 MPa, 316 MPa, and 361 MPa, accordingly. Thus, with an increase in the austenitization temperature (TA), a greater decrease in stress is observed, which is associated with a larger area reduction (AR). The increase in AR with an increase in TA is confirmed by the data, presented in Fig. 4.
Reviewer 2 Report
In this paper, the mechanism and kinetics of bainitic transformation of a (Cr, Mo, V)-added TRIP-assisted steel, the "structure/mechanical properties" relationships of the TRIP steel treated by the heat treatment method of intercritical annealing + austempering were investigated. The results are new and most points here are well-claimed. However, several concerns and flaws must be clarified before publication. Please see them below:
1. In figure.5, the positions of proeutectoid ferrite and bainite areas should be clearly marked. The full names and abbreviations of bainite morphology should appear in the paper.
2. Is the element composition analysis of the nanoscale precipitates reliable by EDX? In addition, is the EDX analysis result from a single point or three points in figure.5(d)?
3. The y-axis in the XRD patterns should not have an accurate scale.
4. The structure and quantitative analysis of the reference sample after Q+T treatment do not appear, then there is no reference to the effect of heat treatment on the structure.
5. What is the calculation method of bainite width in the TEM images? The positions of dislocation clots, nano-scaled carbide particles, and sub-grains should be clearly marked in the TEM images.
6. Should the paper make qualitative and quantitative analyses of the TRIP effect of the different specimens?
7. The necking degrees of the different specimens are different, there is no explanation given during the discussion.
8. This study only has a single-component alloy, and there is no reference component without complex alloys, then is the effect of Cr, Mo, and V elements on hardenability persuasive in the conclusion?
9. The only variable in this paper is the temperature of intercritical annealing. Is it appropriate to use a large amount of space to explain the influence of elements on structure in the discussion? The addition of Cr and Mo elements leads to the decline of the mechanical properties of steel, and the adverse effects are eliminated by adjusting the temperature of intercritical annealing. Does this contradict the so-called " alternative approach for intercritical annealing " of the title?
10. An additional "n" appears in line 301. In line 372, "Figure 1" should be "Figure 2".
Author Response
Dear Reviewer,
We appreciate your valuable comments which allowed us to improve our paper. We tried to address all your comments. The appropriate modifications in the text are denoted by blue lettering. Our responses please see below.
Comment 1: In figure.5, the positions of proeutectoid ferrite and bainite areas should be clearly marked. The full names and abbreviations of bainite morphology should appear in the paper.
Response: The positions of proeutectoid ferrite and bainite areas are designated in Figs. 5a and 5f. The abbreviations of the structural components (proeutectoid ferrite – PF, lamellar bainite – LB, granular bainite – GB) are added to the text (the first paragraph of section 3.2).
Comment 2: Is the element composition analysis of the nanoscale precipitates reliable by EDX? In addition, is the EDX analysis result from a single point or three points in figure.5(d)?
Response: The Reviewer is absolutely right that EDX analysis is not quite appropriate for the nano-scaled precipitates because the spatial resolution of EDS is higher than the particle size. However, the EDX allowed to reveal in precipitates the increased amount of Nb, V, Mo (higher than their total content in the steel) confirming the carbide nature of these particles. EDX analysis was performed at ten points in different sights averaging the results. The appropriate information and discussion are added to the “Materials and Methods” (section 2.3) and to section 3.2 (the first paragraph).
Comment 3: The y-axis in the XRD patterns should not have an accurate scale.
Response: Figure 6a is modified.
Comment 4: The structure and quantitative analysis of the reference sample after Q+T treatment do not appear, then there is no reference to the effect of heat treatment on the structure.
Response: The heat treatment (Q+T) was used as a reference as a standard treatment for the constructive steels. The aim was a revealing the advantage of austempering over the routing heat treatment in the mechanical properties. Therefore the structure of (Q+T)-treated specimen was not the focus of the present study. However, according to the comment, the image of (Q+T) specimen was added (Fig.1b) and its structure was commented on (section 2.1).
Comment 5: What is the calculation method of bainite width in the TEM images? The positions of dislocation clots, nano-scaled carbide particles, and sub-grains should be clearly marked in the TEM images.
Response: The bainite width was calculated using four TEM images of the same specimen. The width of each bainite lath was measured along three random crossing lines with further averaging the results for all images. Figure 7 is modified according to the comment (New Fig.7b is added).
Comment 6: Should the paper make qualitative and quantitative analyses of the TRIP effect of the different specimens?
Response: The qualitative assessment of the TRIP effect was made based on the strain hardening rate behaviour, presented in Fig. 11. The according discussion is added to the Discussion section (page 17).
Comment 7: The necking degrees of the different specimens are different, there is no explanation given during the discussion.
Response: An explanation of the different necking degrees is added to the Discussion section (page 18).
Comment 8: This study only has a single-component alloy, and there is no reference component without complex alloys, then is the effect of Cr, Mo, and V elements on hardenability persuasive in the conclusion?
Response: The results obtained in this study for (Cr,Mo,V)-alloyed steel were compared with the reference which is similar steel (without these elements) earlier described in Ref. [42]. The hardenability was assessed using a TTT diagram (Fig. 2) where the line of the transformation start for the reference (Cr,Mo,V)-free steel is designated by black colour. After assessing the maximal thickness of the plate which can gain a thorough hardening for both steels, the conclusion on the positive effect of Cr and Mo on hardenability was formulated.
Comment 9: The only variable in this paper is the temperature of intercritical annealing. Is it appropriate to use a large amount of space to explain the influence of elements on structure in the discussion? The addition of Cr and Mo elements leads to the decline of the mechanical properties of steel, and the adverse effects are eliminated by adjusting the temperature of intercritical annealing. Does this contradict the so-called " alternative approach for intercritical annealing " of the title?
Response: The addition of Cr and Mo was aimed at increasing the hardenability of TRIP-assisted steel, which is important for expanding its industrial application for the plates of heavier sections. The study showed that in this case, the usual approach in selecting the heat treatment regime actually leads to a decrease in the mechanical properties of the steel. However, changing this approach to an alternative one provides the steel with a high complex of mechanical properties in combination with increased hardenability. Thus, the (Cr+Mo) addition can give an advanced result if its effect on the structure formation is properly taken into account. This was the main outcome of the present study. We believe that the influence of Cr and Mo elements on the structure of steel is described in rather detail in the “Discussion” section, including the thermodynamic calculations (please see pages 14-16).
Comment 10: An additional "n" appears in line 301. In line 372, "Figure 1" should be "Figure 2".
Response: Additional “n” is deleted. The number of the figure is corrected.
Comment 11: Extensive editing of English language and style required.
Response: The editing of the English language and style was performed by a professional proofreading service. The certificate of editing is attached to the revised article.
