Deformation Induced Soft and Hard Lath Packets Enhance Ductility in Martensitic Steels

Round 1

Reviewer 1 Report

The manuscript is well written and the obtained results are clearly demonstrated and evaluated. Similar results and deductions have been previously reported in a specific martensitic steel, partially by the present author(s). Thus, the novelty here is more like an extension of a phenomenon to another steel composition. Although the presented composite-like behaviour of lath martensite steel is probably a general characteristic, it cannot be firmly stated that it is general based on the results of two compositions. Therefore, the sentence on page 2, lines 85-86, should be refined to something like "...we show that the composite behaviour .. is not unique to one composition, and is probably a general feature of low-carbon lath martensite steels."

Further minor points:

On page 1, lines 41-42: "consisting of a single martensite blocks" single here is singular

page 3, Experimental: It is not described that tensile tests were carried out to 6 different strains, it becomes clear only from Figure 1.

page 3, Fig. 1: The dash-dot line cannot be distinguished from dashed lines; other mode of highlighting should be used

Author Response

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Reviewer 2 Report

In this MS, the authors explored the deformation mechanism of the low carbon martensitic using high-resolution x-ray diffraction. The analysis and discussions of this paper are quite similar to ref. [22, 23], which verifies that the composite model of low carbon lath martensite originally proposed by Ungar et al. ref. [22] ( one of the authors of this MS).The study is useful for researchers both in industry and academia and should be considered for publication. However, it is suggested to clarify the points describe below:

1. (page 3: line 99): Is there any microstructural difference (e.g., size of PAG, block, lath, etc.) between the lath martensite used in this study and used in ref. [22, 23]?
2.  (Page 10: Figure 8): M decreases to ~2.0 in this study compare to ~1 in ref. [23], how much is this due to variations in experimental techniques employed (neutron vs. x-ray) vs. materials used? Is it expected that higher carbon martensite will show stronger dipole characteristics?
3. (page 6: Figure 5): It is hard to see the prior austenite grain boundaries from figure 5. The micrographs need to be improved.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

In general, the work reported in the manuscript is rather interesting and worth to be published in Crystal, however, several points are needed to be clarified and some parts of the manuscript is recommended to be restructured.

• The introduction was written in a rather confusing way. Authors stated the first objective in Line 63 and in Line 85. The reviewer highly recommends authors to restructure this section in a way that the objectives of this work is one paragraph and highly the purpose of each experiment conducted and how they are connected.
• In reference mentioned between Line 40-67, what does [N] stand for? Furthermore, why did authors discuss Figure from the reference in the introduction because this really makes the reviewer confusing. It would be better to summarize the main finding from the reference.
• In section 2.1, the reviewer assumed that authors performed 6 uniaxial tensile tests with different applied strain to investigate the change in the microstructure. However, description of experimental set up is unclear and unstructured, which make it difficult to understand. Please considering revising this section and also describe the purpose of this experiment in detail.
• In Line 103, please provide information on configuration of tensile specimen with respect to the sample axis (along RD or TD).
• The fracture strain reported in Line 106, is plastic strain or total strain?
• In section 2.3, it is really difficult to extract useful meaning from Figure 3. The only thing the reviewer could understand is with larger applied strain, nano hardness would be higher, which is a common understanding in the materials science community. Would it be possible to perform either SEM or EBSD exactly at these locations where authors performed nanoindentation so that we could understand a bit more about the microstructure deformation?
• In section 2.4, if this would be possible, the reviewer highly recommends authors to perform an EBSD analysis on this microstructure and use MTEX to analyze the hierarchical structure and properly reconstruct the prior austenite grains. By using only SEM, the results would still be only qualitative.
• In section 4.2, analysis of SEM was rather an approximation, as already suggested in previous comments, it would be better to analyze the hierarchical structure of martensite from EBSD. In line 311-312, how did authors define q-value for screw and edge dislocations of the martensitic steel?
• For the sake of completeness of Figure 9a, please also add SO result into the plot and discuss. It would also be great if the author could also compare the flow curve (true stress-plastic strain) calculated from Eqs.(9) with experimental tensile testing result for validation.
• Unless authors can provide EBSD maps or SEM picture of the area where nanoindentation had been performed and are able to identify which area was SO and HO, discussion in section 4.4 is too approximation. Furthermore, property mapping, only 400 indentations were far too less.

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

The revised manuscript is now in a much better shape and almost ready to be published. The referee has only one remark.

Because of the COVID-19 outbreak, authors stated that they could not perform further SEM/EBSD as suggested by the referee, which is understandable.

Therefore, the referee suggests that authors should mention about further EBSD investigation as outlook in the conclusion of the manuscript.

Author Response

Reviewer #3:

"Therefore, the referee suggests that authors should mention about further EBSD investigation as outlook in the conclusion of the manuscript."

We inserted into the "Conclusions and Summary" chapter the following new point:

"6) Further SEM or EBSD  investigations should be carried out in the future on new specimens at the same locations where nanoindentation is performed in order to better understand the evolution of microstructure during plastic straining of lath martensite."

Thank you very much for the comments.

Yours Sncerely,

P. J. Szabó and co-authors