Evaluation of Microstructural and Mechanical Behavior of AHSS CP780 Steel Welded by GMAW-Pulsed and GMAW-Pulsed-Brazing Processes

Round 1

Reviewer 1 Report

The authors in their article made CP-780 steel joints using an ER-CuAl-2 filler metal for the GMAW-P brazing process and ER-80S-D2 for the GMAW-P process. They determined the contribution of individual phases to the created joints with a scanning electron microscope (SEM) in the course of their research. In my opinion, it is not enough to determine the participation of individual phases on the basis of SEM micrographs. I believe that to improve the quality of the results, an additional analytical technique should be used, which will be a complementary technique to SEM like XRD or TEM. Additionally, the work contains many stylistic errors. The authors did not pay enough attention to the preparation of the article. It is necessary to improve the work according to comments before it is accepted for publication in Metals.

COMMENT #1:

Line 5: No affiliation for Víctor Hugo.

COMMENT #2:

Line 38: Is written: “All of them offer attractive properties such as strength, formability, weldability, durability and impact resistance, making them very attractive for the automotive sector [4].” The sentence is too general. They are more attractive than which other alloys? Maybe you can provide some parameters, something that distinguishes them?

COMMENT #3:

Line 45: Please add literature references to the new welding technologies listed.

COMMENT #4:

Table 1: Are the data in the table provided by the manufacturer or have you measured the chemical composition of the BM CP-780 and the electrodes? In which units are these data (at%, wt%)?

COMMENT #5:

Table 2: change "voltaje" to "voltage", “Kj/mm” to “kJ/mm”.

COMMENT #6:

Line 104: Decipher EDS acronym.

COMMENT #7:

Lines 128-131: Please add literature references to the equations if you are not the author of them.

COMMENT #8:

Subchapter 3.1 - The contribution of the individual phases from the SEM micrographs was determined. In my opinion, SEM images are not readable. Use a higher magnification (Fig. 3). Otherwise, one can only guess that such phases really exist in this microstructure. Second, SEM is some method of determining the proportion of phases, but a qualitative one. You don't write anything about the number of SEM images that you used for the image analysis. How large was the area of analysis made of? Another method to confirm the phase participation should be used, e.g. XRD. Always in good quality publication, you should confirm the results with at least 2 techniques.

COMMENT #9:

Line 167: change "macro structural" to "macrostructural" or “macro-structural”.

COMMENT #10:

Line 171: Mark the cracks in Fig 4. Can you add a higher magnification in the corner?

COMMENT #11:

Line 173: change "4.9b" to “4b”.

COMMENT #12:

How was HAZ determined? Is it a single measurement or is it an average of several? Add standard deviation?

COMMENT #13:

Fig 4: Are you sure the OM images were recorded at the same magnification? Fig. 4 c and d have the same databar, but the joint appears to be larger in Fig. 4d.

Referring to line 199, I don't see a dendritic structure. The images are too much contrasted.

COMMENT #14:

Line 188: remove "de" before “welds”.

COMMENT #15:

Additionally, the description should be based on other analyzes such as XRD. I understand that you can have a great eye and identify all phases based on literature [9, 10, 18]. Singht et al. comment on the presence of ferrite and martensite. Although add some EDS analyzes.

J.J. Guzman-Aguilera, C.J. Martinez-Gonzalez, V.H. Baltazar-Hernandez, S. Basak, S.K. Panda, M.H. Razmpoosh, A. Gerlich, Y. Zhou, “Influence of SC-HAZ microstructure on the mechanical behavior of Si-TRIP steel welds”, Materials Science and Engineering: A 718 (2018) 216-227, https://doi.org/10.1016/j.msea.2018.01.108

COMMENT #16:

Line 181: Decipher ZAT acronym.

COMMENT #17:

Line 182: Decipher TAZ acronym.

COMMENT #18:

Fig. 5: Add a higher magnification of the connection in Fig. 5 c and d. Add a comment in the text regarding the grain size.

COMMENT #19:

Fig. 6: An interesting combination would be to make the EDS linescan from the same area as the microhardness profiles. Please standardize the descriptions of what elements were measured in the charts.

COMMENT #20:

Line 218: Correct the measurement units of Vickers microhardness which is HV.

COMMENT #21:

Line 229: How do you know that there is a Fe-Cu-Al phase if you have not confirmed its presence by any analytical technique?

COMMENT #22:

Fig. 7: Is measurement distance in good units? Because you will definitely exceed the connection width.

COMMENT #23:

Line 236: change "Fig. 9" to “Fig. 8”.

COMMENT #24:

In the commentary on the tensile tests, you do not mention anything about the crack effect which you wrote about in line 171 for C.1 and C.2. How many samples have the tensile test been performed? Are there any statistics here?

COMMENT #25:

Fig. 10 illustrates the load vs elongation plot. You got very interesting results and I miss a comment on the difference in curves. Their plastic behavior. A longer plastic region for samples C.1-B and C.2-B and a different elongation are observed. This can help you describe fractography.

COMMENT #26:

Fig. 11: change "c) EDS" to “d) EDS spectrum”.

COMMENT #27:

Can you add to the description in Section 3.4, how do spherical particles present in C.2 affect toughness?

Author Response

Dear reviewer, the pertinent corrections have been made according to the observations framed in the manuscript, we hope that this meets your demand.
Regards

Please find the attachment

Response to Reviewer 1 Comments

Point 1: Line 5: No affiliation for Víctor Hugo.

Response 1: The affiliation for Víctor Hugo has been aded.

Point 2: T Is written: “All of them offer attractive properties such as strength, formability, weldability, durability and impact resistance, making them very attractive for the automotive sector [4].” The sentence is too general. They are more attractive than which other alloys? Maybe you can provide some parameters, something that distinguishes them?

Response 2: New text was aded comparing the steels: All of them offer attractive properties such as strength, formability, weldability, durability and impact resistance compared with High Strength Steels (HSS), making them very at-tractive for the automotive sector

Point 3: Line 45: Please add literature references to the new welding technologies listed.

Response 3: New references have been added according to the different technologies developed in pulsed GMAW welding.

Point 4: Table 1: Are the data in the table provided by the manufacturer or have you measured the chemical composition of the BM CP-780 and the electrodes? In which units are these data (at%, wt%)?

Response 4: The CP-780 base metal was analyzed in the laboratory and the results are shown in Table 1. For the ER80S-D2 and ERCuAl-2 electrodes, the chemical composition was provided by the manufacturer. There was an error in the table (units are % wt) which has been corrected.

Point 5: Table 2: change "voltaje" to "voltage", “Kj/mm” to “kJ/mm”.

Response 5: Table 2 was corrected.

Point 6: Line 104: Decipher EDS acronym.

Response 6: The acronym EDS was aded for Energy Dispersive Spectroscopy (EDS).  

Point 7: Lines 128-131: Please add literature references to the equations if you are not the author of them.

Response 7: References has been aded for the equations listed.

Point 8: Subchapter 3.1 - The contribution of the individual phases from the SEM micrographs was determined. In my opinion, SEM images are not readable. Use a higher magnification (Fig. 3). Otherwise, one can only guess that such phases really exist in this microstructure. Second, SEM is some method of determining the proportion of phases, but a qualitative one. You don't write anything about the number of SEM images that you used for the image analysis. How large was the area of analysis made of? Another method to confirm the phase participation should be used, e.g. XRD. Always in good quality publication, you should confirm the results with at least 2 techniques.

Response 8: SEM image of the base metal and EDS was aded as well as a description.

Point 9: Line 167: change "macro structural" to "macrostructural" or “macro-structural”.

Response 9: The text has been changed to macro structural for macrostructural.

Point 10: Line 171: Mark the cracks in Fig 4. Can you add a higher magnification in the corner?

Response 10: A magnification image was aded indicating the crack in the corner of the weldments. 

Point 11: Line 173: change "4.9b" to “4b”.

Response 11: The text has been corrected. 

Point 12: How was HAZ determined? Is it a single measurement or is it an average of several? Add standard deviation?

Response 12: Measurements in the HAZ were performed with the Karl Zeiss microscope image analysis software. Standard deviation was aded.

Point 13: Fig 4: Are you sure the OM images were recorded at the same magnification? Fig. 4 c and d have the same databar, but the joint appears to be larger in Fig. 4d.

Response 13: The same magnification conditions were used in the 4 joints, however in welding 4d a higher electrode feed was used, so the dimension of the deposited metal is larger. 

Point 14: Line 188: remove "de" before “welds”.

Response 14: The text has been corrected.

Point 15: Additionally, the description should be based on other analyzes such as XRD. I understand that you can have a great eye and identify all phases based on literature [9, 10, 18]. Singht et al. comment on the presence of ferrite and martensite. Although add some EDS analyzes.

J.J. Guzman-Aguilera, C.J. Martinez-Gonzalez, V.H. Baltazar-Hernandez, S. Basak, S.K. Panda, M.H. Razmpoosh, A. Gerlich, Y. Zhou, “Influence of SC-HAZ microstructure on the mechanical behavior of Si-TRIP steel welds”, Materials Science and Engineering: A 718 (2018) 216-227, https://doi.org/10.1016/j.msea.2018.01.108 

Response 15: New tex as has been aded to the manuscript as well as the reference cited.

Point 16: Line 181: Decipher ZAT acronym.

Response 16: It was a typo mistake, the acronym was corrected by HAZ.

Point 17: Line 182: Decipher TAZ acronym.

Response 17: It was a typo mistake, the acronym was corrected by HAZ.

Point 18: Fig. 5: Add a higher magnification of the connection in Fig. 5 c and d. Add a comment in the text regarding the grain size.

Response 18: New coment was added in the text. In the heat-affected zone, a lath-type martensitic transformation is observed, with upper bainite and a low percentage of ferrite, the grain size at the interface did not undergo coalescence and growth as occurs in the fusion process, as a consequence of the low energy necessary to melt the filler metal

Point 19: Fig. 6: An interesting combination would be to make the EDS linescan from the same area as the microhardness profiles. Please standardize the descriptions of what elements were measured in the charts.

Response 19: The masured elements are mentioned in the text and more description was aded.

Point 20: Line 218: Correct the measurement units of Vickers microhardness which is HV.

Response 20: The units were corrected to HV in the manuscript.

Point 21: Line 229: How do you know that there is a Fe-Cu-Al phase if you have not confirmed its presence by any analytical technique?

Response 21: Such text was ereased from the manuscrip because is not part of the mechanical discussion. 

Point 22: Fig. 7: Is measurement distance in good units? Because you will definitely exceed the connection width.

Response 22: The purpose of such a hardness scan is to determine the extent to which the hardness undergoes any change including the molten zone, heat affected zone, and base metal. It is not indicated with any figure, but the profile includes each section of the base material as well as the cross-sectional profile of the melted zone.

Point 23: Line 236: change "Fig. 9" to “Fig. 8”.

Response 23: The text was corrected.

Point 24: In the commentary on the tensile tests, you do not mention anything about the crack effect which you wrote about in line 171 for C.1 and C.2. How many samples have the tensile test been performed? Are there any statistics here?

Response 24: New tex as has been aded to the manuscript: ¨It can be seen that in both cases, in conditions C1 and C2 for the GMAW P and GMAW -B joints, the fracture occurs at 45° with respect to the load application, since this direction presented the maximum stress during the test¨  

Point 25: Fig. 10 illustrates the load vs elongation plot. You got very interesting results and I miss a comment on the difference in curves. Their plastic behavior. A longer plastic region for samples C.1-B and C.2-B and a different elongation are observed. This can help you describe fractography.

Response 25: New tex as has been aded to the manuscript: ¨ rimary cavities and secondary microcavities with a great deformation are observed, this corre-lates with the ductility observed in the tension tests, where the joints presented a greater elon-gation compared to the joints welded with the ER80S electrode.¨  

Point 26: Fig. 11: change "c) EDS" to “d) EDS spectrum”.

Response 26: The text was corrected.

Point 27: Can you add to the description in Section 3.4, how do spherical particles present in C.2 affect toughness?

Response 27: A Comment was aded in the manuscript.

Author Response File: Author Response.pdf

Reviewer 2 Report

Although the authors provided microstructural characteristics and mechanical properties of welded CP780 steel, the scientific attractions and discussions are relatively poor. Thus, we dont reccommend this work published in Metals.

Some revision have been highlighted in the pdf file.

Comments for author File: Comments.pdf

Author Response

Dear reviewer, the pertinent corrections have been made according to the observations framed in the manuscript, we hope that this meets your demand.

Regards

Please find the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

In this paper, experiment and observation methods were carried out to evaluate the microstructural and mechanical behavior of AHSS CP780 steel welded by GMAW-Pulsed and GMAW-Pulsed-brazing process. The research is comprehensive and the result is valuable. However, the following points need to be addressed before the publishing:

• Fig.3, 4 and 6 are blurred image, which makes the information hard to capture from the whole pictures. I suggest that the authors should provide the original format.
• In Fig.7, the points, both blue and orange, are so large that they interrupt the view from the curves.
• In addition, the microhardness in Fig.7(a) varies from 200~450 HV_0.1 , which is less than half of the range of longitudinal axis(0~600 HV_0.1). Situation like this would make the curves too compact to capture the details. The problem in Fig.7(b) is similar to this one. I suggest that the authors should modified the range of longitudinal axis to solve these problems.
• In Fig.10, Fig.14, etc. Some curves are extremely close to each other, which makes the curves hard to tell. I suggest that the authors should use partial enlargement or zoom of the necessary part to make them easy to see.

• In 2.1Microstuctural Characterization, what is the meaning of this sentence?

“The metallographic preparation was carried out in 3 stages…by immersion with 5% nital)… ”

• In 2.3Free fall impact tests, The letter v should be lowercase in this sentence in order to stay consistent with equation(3).

“V is the velocity of the mass reached during the test.”

• Indentations can be seen in most of the paragraphs. However, some paragraphs in 2.2, 3.2, 3.3 and 3.4 are typed without any indenting.
• Please explain why the two curves(C2 and C1-B in fig.14) have similar trends and explain the reasons for this trend.

Author Response

Dear reviewer, the pertinent corrections have been made according to the observations framed in the manuscript, we hope that this meets your demand.

Regards

Please find the attachment

Response to Reviewer 3 Comments

Point 1: Fig.3, 4 and 6 are blurred image, which makes the information hard to capture from the whole pictures. I suggest that the authors should provide the original format.

Response 1: Figures were improved with actual format.

Point 2: In Fig.7, the points, both blue and orange, are so large that they interrupt the view from the curves.

Response 2: Figure 7 was change to figure 8 and the dots were improved.

Point 3: In addition, the microhardness in Fig.7(a) varies from 200~450 HV0.1 , which is less than half of the range of longitudinal axis(0~600 HV0.1). Situation like this would make the curves too compact to capture the details. The problem in Fig.7(b) is similar to this one. I suggest that the authors should modified the range of longitudinal axis to solve these problems.

Response 3: The microhardness axis was to the same scale.

Point 4: In Fig.10, Fig.14, etc. Some curves are extremely close to each other, which makes the curves hard to tell. I suggest that the authors should use partial enlargement or zoom of the necessary part to make them easy to see.

Response 4: New image was aded in figure 14 wich changes to figure 15. The new image is a larger portion of the initial test.

Point 5: In 2.1Microstuctural Characterization, what is the meaning of this sentence? “The metallographic preparation was carried out in 3 stages…by immersion with 5% nital)… ”

Response 5: The text refers to the preparation process of the samples:

1. I) mechanical grinding with abrasive silicon carbide paper of different granulometry,
2. II) mirror polishing of specimens using 5 and 1 µm alumina (Al2O3), and III) chemical etch-ing by immersion with 5% nital

Point 6: In 2.3Free fall impact tests, The letter v should be lowercase in this sentence in order to stay consistent with equation(3). “V is the velocity of the mass reached during the test.”

Response 6: The text was corrected.

Point 7: Indentations can be seen in most of the paragraphs. However, some paragraphs in 2.2, 3.2, 3.3 and 3.4 are typed without any indenting.

Response 7: Indents were corrected throughout the manuscript.

Point 8: Please explain why the two curves(C2 and C1-B in fig.14) have similar trends and explain the reasons for this trend.

Response 8: At this respect, new text was aded in the manuscrip. ¨the loss of ductility in GMAW-P welding can also be associated with the presence of Ti micro-spheres, since during welding, acicular ferrite is a precursor for the formation of this type of in-clusion at high temperatures¨

Author Response File: Author Response.pdf

Reviewer 4 Report

1. The amount of increased tensile strength for GMAW-P brazing compared to GMAW-P process is to be added in the abstract.
2. Further, the reasons for improving is also to be addressed (short one or two lines) in the abstract
3. The language of the entire manuscript is to be improved. For example, in Introduction part, “Therefore, having financial environmental impact, which affects the vehicle’s design and the materials selection for its manufacture”. This sentence, there is no subject and verb.
4. “12% are used commercially…”. Here, 12% of which steel?
5. The novelty of the present work is to be highlighted. Further, some literature related to GMAW-P brazing is to be added.
6. The main objectives of the present work is to be written elaborately at the end of introduction part. The present one is like a paper title only.
7. The first sentence of “Materials and Method” section is too long. It has to be made as simple sentences.
8. Why the torch angle was fixed to 20 degree?. It has to be addressed
9. There is no meaning full information from Fig2 as the sample information mentioned in the text is clear. Hence, it is recommended to remove it.
10. The conditions related to C1 and C2 are to be addressed.
11. The experimental procedure related to GAMA-P brazing is not addressed.
12. How the distance of 0.3, 0.15, and 0.1 mm were controlled while measuring the hardness?
13. “For the vertical impact test, welded samples of 16 x 20cm2”. Here, check the sample size
14. Based on Figure 3, the grain size of each observed phases can be measured using any software, and it has to be reported with distribution.
15. How the macrostructure (Figure 4) was captured? It has to be addressed
16. The acronym of “ZAT” is to be incorporated at least once in beginning.
17. Figure 6 is not clear
18. There is no scale marker in Figure 9
19. Why GMAW-P Brazing sample under C2 condition has produced high strength with the same strain like GMAW-P under the same C2 condition
20. The mechanism behind the strength improvement is also to be addressed
21. Scale bar should be added in Figure 13
22. The conclusion is to be revised

Author Response

Dear reviewer, the pertinent corrections have been made according to the observations framed in the manuscript, we hope that this meets your demand.

Regards

Please find the attachment

Response to Reviewer 4 Comments

Point 1:   The amount of increased tensile strength for GMAW-P brazing compared to GMAW-P process is to be added in the abstract.

Response 1: New text was aded in the abstract indicating the increasing in % of mechanical properties.

Point 2: Further, the reasons for improving is also to be addressed (short one or two lines) in the abstract

Response 2: The text is addressed at the end of the abstract.

Point 3: The language of the entire manuscript is to be improved. For example, in Introduction part, “Therefore, having financial environmental impact, which affects the vehicle’s design and the materials selection for its manufacture”. This sentence, there is no subject and verb.

Response 3: The text was improved in the introduction. 

Point 4: “12% are used commercially…”. Here, 12% of which steel?

Response 4: Resonpes has been aded.

Point 5: The novelty of the present work is to be highlighted. Further, some literature related to GMAW-P brazing is to be added.

Response 5: Literaure related to the GMAW –P Brazing has been aded in the manuscrip.

Point 6: The main objectives of the present work is to be written elaborately at the end of introduction part. The present one is like a paper title only.

Response 6: The objetives were extended in the manuscript in order to explain with more detail the work.  

Point 7: The first sentence of “Materials and Method” section is too long. It has to be made as simple sentences.

Response 7: The sentence was divided in short sentences.

Point 8: Why the torch angle was fixed to 20 degree?. It has to be addressed

Response 8: The objetive of the torch angle was to fulfill the fillet weld during the application of the filler, such text was aded in the manuscript.

Point 9: There is no meaning full information from Fig2 as the sample information mentioned in the text is clear. Hence, it is recommended to remove it

Response 9: The authors beleved that figure 2 is important to show where the samples were cut. 

Point 10: The conditions related to C1 and C2 are to be addressed.

Response 10: Conditions C1 and C2 are mentioned in the manuscript as low heat input and high heat input respectively.

Point 11: The experimental procedure related to GMAW-P brazing is not addressed.

Response 11: The welding parameters are mentioned in table 2 for both GMAW-P and GMAW-P Brazing.

Point 12: How the distance of 0.3, 0.15, and 0.1 mm were controlled while measuring the hardness?

Response 12: Measurements in the HAZ were performed manually with a micrometer.

Point 13: “For the vertical impact test, welded samples of 16 x 20cm2”. Here, check the sample size

Response 13: The size was checked.

Point 14: Based on Figure 3, the grain size of each observed phases can be measured using any software, and it has to be reported with distribution.

Response 14: In this regard, grain size distribution was not part of the research to be carried out, so it is considered for future work.

Point 15: How the macrostructure (Figure 4) was captured? It has to be addressed

Response 15: The text of optical microscopy (OM) was aded.

Point 16: The acronym of “ZAT” is to be incorporated at least once in beginning.

Response 16: The acronym ZAT is a typo mistake, it was corrected.

Point 17: Figure 6 is not clear.

Response 17: The image was improved.

Point 18: 18.       There is no scale marker in Figure 9

Response 18: The scale marker was aded.

Point 19: Why GMAW-P Brazing sample under C2 condition has produced high strength with the same strain like GMAW-P under the same C2 condition

Response 19: At this respect, new text was aded in the manuscrip. ¨the loss of ductility in GMAW-P welding can also be associated with the presence of Ti micro-spheres, since during welding, acicular ferrite is a precursor for the formation of this type of in-clusion at high temperatures

Point 20:  The mechanism behind the strength improvement is also to be addressed

Response 20: The text was addressed.

Point 21: Scale bar should be added in Figure 13

Response 21: The scale marker was aded.

Point 22: 22.       The conclusion is to be revised

Response 22: The conclusions were revised.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear Authors,

thank you for your review. However, I believe that not all of them have been answered sufficiently. I perceive this as the fact that it is impossible to perform XRD tests in your research unit. I accept the article for printing as it is.

Reviewer 2 Report

Accepted

Reviewer 4 Report

The authors have worked based on my previous comments and hence, I am recommending to accept the revised verison. Thanks