A Novel Cyclic-Quenching-ART for Stabilizing Austenite in Nb–Mo Micro-Alloyed Medium-Mn Steel

Round 1

Reviewer 1 Report

The paper discusses about a novel cyclic-quenching-art for stabilizing austenite in Nb–Mo micro-alloyed medium-Mn steel. The paper has been well organized and can be considered for publication by metal. However, the following comments should be considered before publication.
1) In abstract section, the authors should bring some key results and findings. There are no results there.
2) The authors used a novel cyclic quenching and austenite reverse transformation to get better mechanical properties. The authors should explain how they reached such a novel method?
3) The chemical composition of tested specimens is missing. It should be represented in a table.
4) In the results and discussion section, the authors should talk about the microstructure evolution in treated steels and their role on mechanical properties. Please use and cite the following articles.
[1] Microstructure evolution and mechanical behavior of a new microalloyed high Mn austenitic steel during compressive deformation, Materials Science and Engineering A, 615 (2014) 424-435.
[2] Effect of arisen dislocation density and texture components during cold rolling and annealing treatments on hydrogen induced cracking susceptibility in pipeline steel, Journal of Materials Research, 31 (2016) 3390-3400.
5)In page 6, first line, it should be more explained that how austenite grains are refined by the increase of cyclic quenching.
6) Based on Fig. 4d, page 7, the tensile properties of CQ1, CQ2 and CQ3 specimens have not a considerable difference. How many times did the authors repeat this test?
7) It should be also discussed if there are any inclusions in the microstructure of treated specimens. They can be considered as crack nucleation site during tensile testing and decrease the mechanical properties.
8) The English of paper is fine.

Author Response

Response to Reviewer 1 Comments

 

Dear Reviewer

Thank you very much for your detailed and insightful comments concerning our manuscript entitled “A Novel Cyclic-Quenching-ART for Stabilizing Austenite in Nb–Mo Micro-alloyed Medium-Mn Steel” (ID: metals-611780). For your convenience to follow our changes, we usethe word track-change function. Our responses to your comments are listed point-by-point below and the changes we have made in response to your comments are all highlighted in green.

 

 

Point 1: In abstract section, the authors should bring some key results and findings. There are no results there.

 

Response 1: Thanks very much for your kind suggestion. We added some key results and findings in abstract section.

 

Point 2: The authors used a novel cyclic quenching and austenite reverse transformation to get better mechanical properties. The authors should explain how they reached such a novel method?

 

Response 2: Thanks very much for your kind suggestion. We draw on relevant references: “Grange, R.A. Strengthening Steel by Austenite Grain Refinement. ASM Trans Quart. 1966, 59, 26–48. ”   and      “L. Zhang, X.M. Huang, Y.H. Wang, Y.B. Guo, G.Z. Dai, D.S. Li, J. Mater. Eng. Perform. (2018) 1–9. ” . We draws on rapidly heating and cyclic quenching heat treatment technology, attempts to use cyclic quenching to destroy the orientation relationship between the new and original phase before intercritical annealing to refine the martensite structure, and then generate finer strip austenite in the subsequent reverse transformation process, thereby further increasing the content and stability of austenite in medium Mn steel to improving the comprehensive mechanical (paragraphs 1 of the introduction.)

 

Point 3: The chemical composition of tested specimens is missing. It should be represented in a table.

 

Response 3: Thanks very much for your kind suggestion. We have listed the chemical composition of the test samples in the table 1.

 

 

Point 4: In the results and discussion section, the authors should talk about the microstructure evolution in treated steels and their role on mechanical properties. Please use and cite the following articles.

[1] Microstructure evolution and mechanical behavior of a new microalloyed high Mn austenitic steel during compressive deformation, Materials Science and Engineering A, 615 (2014) 424-435.

[2] Effect of arisen dislocation density and texture components during cold rolling and annealing treatments on hydrogen induced cracking susceptibility in pipeline steel, Journal of Materials Research, 31 (2016) 3390-3400.

 

Response 4: Thanks very much for your kind suggestion. We added a discussion of the evolution of microstructure and its effect on mechanical properties and cited the two articles above (3.4 section).

 

Point 5: In page 6, first line, it should be more explained that how austenite grains are refined by the increase of cyclic quenching.

 

Response 5: Thanks very much for your kind suggestion. We discussed it in detail in the first paragraph of Section 3.2. “The sheets were repeatedly heated rapidly to near the austenitizing temperature, isothermal holding for a short time, and then rapidly cooled, causing the recrystallized austenite grains were forcibly interrupted before they could grow up and then producing finer lath martensite during subsequent quenching process [13]. At the same time, in the subsequent ART process, the reverted RA readily nucleation along the lath martensite boundary, and finally, a strip-shaped RA having a relatively small size can be obtained at ambient temperature. As reported by Morsdorf et al. [18] the reverse transformed strip-shaped RA readily nucleation along the lath martensite or original austenite grain boundary, thus, the finer strip-shaped RA at ambient temperature can be obtained by refining the size of the martensite lath.”

 

Point 6: Based on Fig. 4d, page 7, the tensile properties of CQ1, CQ2 and CQ3 specimens have not a considerable difference. How many times did the authors repeat this test?

 

Response 6: Thanks very much for your kind suggestion. We repeated the test twice. The excellent comprehensive performance of medium Mn steel strongly depend on the high RA content with appropriate stability. In we study, the estimated austenite fraction of CQ1-ART, CQ2-ART and CQ3-ART samples before tensile tests were ~49.2 vol.%, ~62.0 vol.% and ~64.8 vol.% respectively. The cyclic quenching is equivalent to providing a longer holding time to promoting the enrichment of Mn in prior austenite, which results in more Mn content in the austenite after multiple cyclic quenching, thereby improving the stability of austenite and obtaining more RA at ambient temperature (The preceding paragraph of 3.4 section).

 

Point 7: It should be also discussed if there are any inclusions in the microstructure of treated specimens. They can be considered as crack nucleation site during tensile testing and decrease the mechanical properties.

 

Response 7: This is a thought-provoking question. This paper mainly discusses how to obtain more content and more stable austenite by cyclic quenching-ART heat treatment process. But, as you said, we should also discuss whether the microstructure of the treated specimen contains any inclusions. They can be considered as crack nucleation site during tensile testing and decrease the mechanical properties. For the question, further research is needed. We mentioned this in last paragraph of section 3.2.

 

Point 8: The English of paper is fine.

 

Response 8: Thanks very much for your kind suggestion.

 

 

Once again, thank you very much for reviewing this manuscript and giving us detailed and helpful your comments.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

The present manuscript deals with the effects of “a novel cyclic quenching and austenite reverse transformation” on retained austenite stability and tensile properties of Nb-Mo microalloyed medium Mn steel. The topic of this manuscript, especially retained austenite stability, is of great interest and will bring the attention of the scientific community.　 Reviewer’s comments are as follows,

 

Figure 3

　

In the following highlighted sentence, average Mn concentration in RA are different from those in Table 2.

 

3.3. Mn and C partitioning behavior

Partitioning of Mn and C leads to difference of retained austenite content at ambient temperature after austenite reverse transformation [20–22]. The Mn concentration in RA of experimental steel at ambient temperature was quantitatively characterized by TEM-EDS. As shown in Table 2, the average Mn concentration in RA was 6.16 wt-% for CQ1-ART sample, and 7.31 w-t% and 7.19 w-t% for CQ2-ART and CQ3-ART samples, respectively.

 

Reference 37

 

Please follow the instructions in the manual of metals.

                              

                                                          That’s all

 

Author Response

Response to Reviewer 2 Comments

 

 

Dear Reviewer,

Thank you very much for your detailed and insightful comments concerning our manuscript entitled “A Novel Cyclic-Quenching-ART for Stabilizing Austenite in Nb–Mo Micro-alloyed Medium-Mn Steel” (ID: metals-611780). For your convenience to follow our changes, we use the word track-change function. Our responses to your comments are listed point-by-point below and the changes we have made in response to your comments are all highlighted in yellow.

 

Point 1: In the following highlighted sentence, average Mn concentration in RA are different from those in Table 2.3.3. Mn and C partitioning behavior

Partitioning of Mn and C leads to difference of retained austenite content at ambient temperature after austenite reverse transformation [20–22]. The Mn concentration in RA of experimental steel at ambient temperature was quantitatively characterized by TEM-EDS. As shown in Table 2, the average Mn concentration in RA was 6.16 wt-% for CQ1-ART sample, and 7.31 w-t% and 7.19 w-t% for CQ2-ART and CQ3-ART samples, respectively.

 

Response 1: We are terribly sorry for the carelessness. The average Mn concentration of a single austenite obtained by TEM-EDS in Figure 5a is 6.87 w-t%, while the average Mn content of multiple austenites in multiple TEM images of a CQ1-ART sample is 6.16 w-t%. Thus, the average Mn concentration in RA was 6.16 wt-% for CQ1-ART sample, and 7.31 w-t% and 7.19 w-t% for CQ2-ART and CQ3-ART samples, respectively. (Table 3)

 

Point 2: Reference 37. Please follow the instructions in the manual of metals.

 

Response 2: Thanks very much for your kind suggestion. We have made correction according to your comments. (Reference 37)

 

Once again, thank you very much for reviewing this manuscript and giving us detailed and helpful your comments.

 

 

 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The revisions are satisfactory. The paper can be considered for publication in the current format.

Author Response

Response to Reviewer 1 Comments

(Round 2)

Dear Reviewer

Thank you very much for your detailed and insightful comments concerning our manuscript entitled “A Novel Cyclic-Quenching-ART for Stabilizing Austenite in Nb–Mo Micro-alloyed Medium-Mn Steel” (ID: metals-611780).

Point 1: The revisions are satisfactory. The paper can be considered for publication in the current format.

 

Response 1: Once again, thank you very much for reviewing this manuscript and giving us detailed and helpful your comments.