Mechanical Properties and Microstructural Aspects of Two High-Manganese Steels with TWIP/TRIP Effects: A Comparative Study

Round 1

Reviewer 1 Report

Will the authors please provide more description of their SFE calculation and how composition was incorporated?

It must be my downloaded version of the .pdf, but images/scale bars are missing in Figure 1.

 

Discussion 4.1: I would think the residual stresses in Steel C (from epsilon martensite that formed upon cooling) are the reason behind the unusual yielding behavior?

There does not appear to be anything technically wrong with this paper, but given my understanding of the literature encompassing high-Mn TRIP and TWIP steels, I'm having trouble understanding what this paper's unique contribution to the literature is. Is it a new chemistry? Is it the Charpy results? Is it the high value of true stress or product of stress and elongation? Based on the current Conclusions and Discussion, I don't know if the paper warrants publication. Please emphasize the unique contributions.

 

Author Response

Dear Referee 1:

 

Due to the complexity of equations in the answer to your comments, please find attached a file with our responses.

 

Thank you very much for your suggestions.

Author Response File: Author Response.pdf

Reviewer 2 Report

Review of paper titled Mechanical properties and microstructural aspects of two high-manganese steels with TWIP/TRIP effects: a comparative study' by Matías Bordone et al.

 

This manuscript mainly explores the relationship between the mechanical properties and microstructure of high manganese TWIP/TRIP steel. The author analyzed and discussed the experimental results in detail. In view of this, the reviewers recommend that they be published on Metal, but a certain degree of modification is required.

 

General Comments:

Before the academic evaluation, the reviewer recommends that the authors carefully draw the figures in this manuscript.

• Please place the labels “(a)” and “(b)” et al. upper left corner of the figure.
• Please carefully supplement the scale label in the figure, such as Fig.1(a), (c), (d) and (e); Currently, the word "cleavage" in Figure 8(d).
• Line 110 “(a strain rate of 8.33 10-4 s-1)”, "-4" and "-1" should be superscripts.

Specific comments:

• Line 80. During the homogenization process at 1200°C for 2 hours, is the steel ingot in a protective atmosphere or coated with anti-oxidation coating on the surface? Because the carbon content in B steel is relatively high, decarburization behavior easily occurs during the homogenization process, which will affect the stability of the austenite phase. Similar work such as: Fu, et al. Appl. Surf. Sci. 470 (2019) 870-881; Y.S. Chun, et al., Mat. Sci. Eng: A 533 (2012)87–95; H. Fu, et al., Corros. Sci. (2019) 108191; So the reviewer asked the authors to explain in the experimental part.
• Why does the fractured specimen of steel B in Fig. 6(a) appear necking? Usually in high-manganese TWIP steel, no necking fracture occurs due to the presence of deformation twins.
• Line 206 “Figure 7(a) and Figure 7(b) clearly show transgranular nature of fracture profiles…” The reviewer did not believe that there is a transgranular fracture profile here. If there is a transgranular fracture profile, cleavage or quasi-dissociation fracture characteristics will appear on the fracture surface. This does not correspond to the ductile fracture morphology in Figure 8 (a and b).
• In Table 5, for tensile samples, why is the microhardness of B steel greater than that of C steel? It is generally believed that the hardness of martensite is higher than that of austenite. Even though there are a large number of deformation twins in B steel, because the ε-martensite is a close-packed hexagonal structure, it is not necessarily that its microhardness is greater than that of ε-martensite.
• Can you consider placing Lines 249-257 in the " Materials and Methods" section?

Author Response

Comments of Reviewer 2

 

General Comments:

• Before the academic evaluation, the reviewer recommends that the authors carefully draw the figures in this manuscript.
• Please place the labels “(a)” and “(b)” et al. upper left corner of the figure.
• Please carefully supplement the scale label in the figure, such as Fig.1(a), (c), (d) and (e); Currently, the word "cleavage" in Figure 8(d).
• Line 110 “(a strain rate of 8.33 10-4 s-1)”, "-4" and "-1" should be superscripts.

 

ANSWER or COMMENT: All indicated observations were introduced in the paper.

 

 

Specific comments:

Line 80. During the homogenization process at 1200°C for 2 hours, is the steel ingot in a protective atmosphere or coated with anti-oxidation coating on the surface? Because the carbon content in B steel is relatively high, decarburization behavior easily occurs during the homogenization process, which will affect the stability of the austenite phase. Similar work such as: Fu, et al. Appl. Surf. Sci. 470 (2019) 870-881; Y.S. Chun, et al., Mat. Sci. Eng: A 533 (2012)87–95; H. Fu, et al., Corros. Sci. (2019) 108191; So the reviewer asked the authors to explain in the experimental part.

 

ANSWER or COMMENT: Homogenization processes were carried out without the use of a protective atmosphere. The superficial layer with oxide films and eventual decarburization was mechanically removed to obtain the test specimens (removed thickness was higher than 3 mm).

 

Why does the fractured specimen of steel B in Fig. 6(a) appear necking? Usually in high-manganese TWIP steel, no necking fracture occurs due to the presence of deformation twins.

 

ANSWER or COMMENT: We agree that in high-manganese TWIP steels necking observed in tensile broken specimens is imperceptible. In fact, this is in agreement with our observations as shown in next figures (omitted in the paper).

 

Figure 6 corresponds to the Charpy V-notch tested specimens, and shows considerable lateral contraction and expansion, which are consistent with the high absorbed energy values measured.

 

 

Line 206 “Figure 7(a) and Figure 7(b) clearly show transgranular nature of fracture profiles…” The reviewer did not believe that there is a transgranular fracture profile here. If there is a transgranular fracture profile, cleavage or quasi-dissociation fracture characteristics will appear on the fracture surface. This does not correspond to the ductile fracture morphology in Figure 8 (a and b).

 

ANSWER or COMMENT: We admit that in the figures 7(a) and 7(b) cannot be recognized a fracture pattern, and propose to modify the sentence as follows: “Samples were taken from tensile tests specimens for microstructural observations on RD-TD plane, perpendicular to the fracture surface. Figure 7(a) and Figure 7(b) show the microstructures close to the fracture surfaces where cavities can be observed.”. We do not agree with the reviewer that there are no transgranular ductile fracture. SEM observations in figures 8(a) and (b) reveal this kind of fracture. This is also shown by Mills in “Fracture toughness of type 304 and 316 stainless steels and their welds”.

 

 

In Table 5, for tensile samples, why is the microhardness of B steel greater than that of C steel? It is generally believed that the hardness of martensite is higher than that of austenite. Even though there are a large number of deformation twins in B steel, because the ε-martensite is a close-packed hexagonal structure, it is not necessarily that its microhardness is greater than that of ε-martensite.

 

ANSWER or COMMENT: The presence of 45 % v/v of ε-martensite in steel C in the non-tested material is the reason of its higher microhardness values in comparison to Steel B, which even has a higher carbon content. So, ε-martensite effect on microhardness in Steel C prevails over the solid solution strengthening due to carbon in the other alloy. However, trends are reversed in tensile and Charpy specimens, since the values of microhardness in Steel B resulted higher than those obtained in Steel C. The larger amount of plastic deformation due to the TWIP effect developed in Steel B could explain the fact that the local microhardness close to the fractured surfaces resulted higher than in Steel C, in which TRIP effect took place.

 

 

Can you consider placing Lines 249-257 in the " Materials and Methods" section?

 

Lines 249-257 were placed in the “Materials and Methods” section, continuing last paragraph.

 

Yours faithfully,

On behalf of all the authors,

Alberto Monsalve González

Author Response File: Author Response.pdf