Effect of Cu Content on Microstructure and Mechanical Properties for High-Strength Deposited Metals Strengthened by Nano-Precipitation
Wolfgang Löser
Round 1
Reviewer 1 Report
This paper studies the Effect of Cu content on microstructure and mechanical properties for deposited metals prepared by TIG welding. Even though the article's subject and content are interesting, I am reluctant to recommend this manuscript version for publication in Metals. The text flow is generally not straightforward, and some parts are difficult to follow. Besides, the authors should address some significant issues with the novelty and conclusions before the paper could be considered for publication. Please consider the following comments and open questions.
1- I have a serious concern about the novelty of this research. In 'Introduction,' the effect of Cu additions on strength and ductility was explained well. Likewise, a few published studies already exist on the same subject, which the authors also cited. The current paper in the present form lacks sufficient novelty. The authors should explain the novelty of their work in the paper and how their findings add to the existing literature results.
2- In many parts, the spaces between the words are missing, e.g., lines 32, 34, 37, 44, 49, 52, etc. Please check the whole manuscript and add the missing spaces.
3- Several times, the capital letters were misused in the lines, e.g., in lines 28, 342, etc. Please check the entire text and correct it.
4- The word 'And' was often used at the beginning of a sentence, which is grammatically wrong, for example, in lines 61, 142, and 282. Check the whole text and correct the mistakes.
5- In the title, 'GPa deposited metals, ' – What does GPa mean?
6- There are multiple grammatic errors, which make the text difficult to understand. I firmly ask the authors to check their manuscript thoroughly concerning grammar.
7- In line 55, define HSLA and YS for the first time you mention them.
8- In line 81, emphatically?
9- Line 121, the strain rate has the dimension of 1/s. I guess the authors mean deformation speed instead.
10- In Fig. 2, dimensions are missing and define what A and F refer to.
11- The reasonable discussion in Fig. 3 is missing. Besides, the IPF color key is missing.
12- In line 171, the authors mentioned that with the increase of Cu, the RA increases. However, the RA increases first up to Cu content of 1.79 and then decreases. A related discussion is required here.
13- Section 3.2 explains how the crack initiation and propagation energies are calculated or measured.
14- Fig 7 a does not show tensile properties but stress-strain curves.
15- In Fig8, a discussion is required on the mechanism of the fracture mode changing from ductile to quasi-cleavage with the increase of Cu content to 2.32.
16- Section 4.3 should be written clearly, and the influence of Cu addition on toughness should be clearly explained. I could not understand the text even after several times reading.
17- The authors mentioned that the M-A constituents refine from strip to granular morphology. However, they did not discuss the influence of this morphology change on the mechanical properties.
18- A discussion is needed to rationalize why Ei reduces significantly for Cu2.32.
19- What is the effect of lath size (Fig .4) and the amount of RA on strength and ductility?
20. Conclusions are too long and difficult to follow. Summarize them.
Author Response
Dear Editor,
Re: Manuscript “Effect of Cu content on microstructure and mechanical properties for GPa deposited metals strengthened by nano-precipitation”
Thank you for your letter and the reviewers’ comments concerning our manuscript. Those comments are valuable and very helpful. We have read through comments carefully and have made corrections. Based on the instructions provided in your letter, we uploaded the file of the revised manuscript. The responses to the comments are presented following.
We would love to thank you for allowing us to resubmit a revised copy of the manuscript and we highly appreciate your time and consideration.
Sincerely.
Xinjie Di
Author Response File: 
Author Response.pdf
Reviewer 2 Report
1. The uppercase and lowercase of the title should be revised according to MDPI format.
2. In line 7, the email of the authors should use black color without an underline.
3. Keywords need to be reordered based on alphabetical order.
4. What is the novelty of the present study? GPa deposited metallic materials have been widely studied in the past. Nothing something really new that cutting edge based on the evaluation from the reviewer. This issue should be addressed seriously by the Authors. Highlighted in the introduction section is needed.
5. In lines 41-44, to support this sentence, additional references published by MDPI should be adopted as follows: Computational Contact Pressure Prediction of CoCrMo, SS 316L and Ti6Al4V Femoral Head against UHMWPE Acetabular Cup under Gait Cycle. J. Funct. Biomater. 2022, 13, 64. https://doi.org/10.3390/jfb13020064
6. Research workflow needs to be explained in the materials and methods section.
7. Experimental testing information including its manufacturer should be given in more detail.
8. Information on tools' accuracy and the error should be provided for better understanding regarding different results in further time.
9. Results comparison with previous identical study needs to be performed.
10. The limitation of the present study should be explained before the conclusion section.
11. The conclusion is not solid, further elaboration is needed. Also, not make it by point as present form, but by paragraph.
12. Further research needs to be stated in the conclusion section.
13. Please recheck MDPI format in the present manuscript.
Author Response
Dear Editor,
Re: Manuscript “Effect of Cu content on microstructure and mechanical properties for GPa deposited metals strengthened by nano-precipitation”
Thank you for your letter and the reviewers’ comments concerning our manuscript. Those comments are valuable and very helpful. We have read through comments carefully and have made corrections. Based on the instructions provided in your letter, we uploaded the file of the revised manuscript. The responses to the comments are presented following.
We would love to thank you for allowing us to resubmit a revised copy of the manuscript and we highly appreciate your time and consideration.
Sincerely.
Xinjie Di
Author Response File: Author Response.pdf
Reviewer 3 Report
The work is devoted to the development of novel welding consumables with high strength and good ductility. The influence of different Cu contents on deposited metals prepared from metal cored wires via tungsten inert gas welding was studied. The effects of microstructure and the fractions of various phase constituents on the mechanical characteristics are revealed. The impact of Cu precipitates on solid-state phase transformations during cooling of the steel samples is analyzed. It is found out that Cu precipitation can improve the strengths of the deposited metals, but it degrades their toughness. On this basis, steels with optimized Cu contents are predicted.
The article contains many valuable results for optimizing the composition of Cu bearing steels for welding consumables. However, before publication considerable improvement is necessary.
(1) What means ‘GPa deposited metals’ in the headline?
(2) In Sec. 2.1 a sketch of the experimental arrangement of the layer deposition is helpful for the reader’s understanding.
(3) The compositions of Cu precipitates shown in Fig. 6 are seemingly a scientific flaw! The high Fe concentrations rather hint that the authors have analyzed a part of the surrounding steel matrix. Please, repeat the measurements, correct the results, and provide a correct description of the image. (Are the dark objects Cu precipitates?)
(4) All the figure captions need some more details for the reader’s better understanding.
(5) In the EBSD image, Figure 3, a color scale bar is necessary, which corresponds to the various grades of misorientation.
(6) In Table 3 the symbol Et(J) is not explained. (Total impact energy?)
(7) The temperature differences (lines 16 and 225) must be given in K but not in °C!
(8) Please, correct typos and the English grammar: Line 28: ‘The introduction For…’=> ‘For…’; Line 342: ’This The multiphase…’ => The multiphase…; Line 324: ‘Results shows’ => ‘Results show’; Do not begin a sentence with: ‘And …’!
Author Response
Dear Editor,
Re: Manuscript “Effect of Cu content on microstructure and mechanical properties for GPa deposited metals strengthened by nano-precipitation”
Thank you for your letter and the reviewers’ comments concerning our manuscript. Those comments are valuable and very helpful. We have read through comments carefully and have made corrections. Based on the instructions provided in your letter, we uploaded the file of the revised manuscript. The responses to the comments are presented following.
We would love to thank you for allowing us to resubmit a revised copy of the manuscript and we highly appreciate your time and consideration.
Sincerely.
Xinjie Di
Author Response File: Author Response.pdf
Reviewer 4 Report
General review: This author explains the deposited metals with 0.62‒2.32% Cu addition in low carbon steel prepared by tungsten inert gas welding via metal cored wire. The effect of Cu element on microstructure and mechanical properties of deposited metals were investigated. The multiphase microstructure of deposited metals consists of bainite, martensite, residual austenite, and martensite-austenite constituents. It is found that Cu decreases the start temperature of martensite (Ms) and enlarges the temperature range of bainite from 99 to 143 ℃, improving the formation of bainite. With the increase of Cu content, the fraction of martensite decreases and the shape of M-A constituent changes from strip into granular. There are BCC and FCC Cu precipitates in the deposited metals. The diameter of Cu precipitates is 14‒28 nm, and the volume fraction of it increases with the increase of Cu content. Meanwhile, the deposited metals with 1.79% Cu can achieve a 10% enhancement in strength (yield strength, 873‒961 MPa, ultimate tensile strength, 1173‒1286 MPa) at little expense of impact toughness (64.56‒56.39 J at ‒20 ℃). Cu precipitation can effectively improve the strength of the deposited metals, but it degrades toughness because of lower crack initiation energy. The deposited metal with 1.79% Cu addition shows an excellent strength‒toughness balance. However, before it can be published, I have some questions about this article and some suggestions:
Minor revision:
1. Everything is well explained except that the shape of M-A constituents changes from strip into granular with the increase of Cu content. Could you explain why?
2. How can the changes of the morphological features affect the mechanical properties?
3. I know that the size of Cu precipitates is important for the mechanical properties of the low carbon steel. In addition, the shape of the Cu nano-precipitates is considered to affect the mechanical properties. Thus, you should read and cite this paper entitled, “Additive manufacturing of a shift block via laser powder bed fusion: the simultaneous utilisation of optimised topology and a lattice structure”.
Author Response
Dear Editor,
Re: Manuscript “Effect of Cu content on microstructure and mechanical properties for GPa deposited metals strengthened by nano-precipitation”
Thank you for your letter and the reviewers’ comments concerning our manuscript. Those comments are valuable and very helpful. We have read through comments carefully and have made corrections. Based on the instructions provided in your letter, we uploaded the file of the revised manuscript. The responses to the comments are presented following.
We would love to thank you for allowing us to resubmit a revised copy of the manuscript and we highly appreciate your time and consideration.
Sincerely.
Xinjie Di
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors sufficiently addressed most of the issues raised by me. However, several minor corrections/additions are still necessary before acceptance.
Please consider the following comments and open questions.
5- In the title, 'GPa deposited metals, ' – What does GPa mean?
I would recommend replacing 'GPa deposited metals' with, e.g., 'deposited high-strength metals.' The word 'GPa' might not be easily understood by the public.
10- In Fig. 2, dimensions are missing; 'Counts' for Y-axis and 'degrees' for the X-axis.
11- The IPF color key is still missing.
P.S.
There are still many spaces (-) missing between the words, particularly in the figure captions. Please recheck the whole manuscript and correct them.
Author Response
The point-by-point responses are as following.
Reviewers’ comments:
Reviewer #1
5- In the title, 'GPa deposited metals, ' – What does GPa mean?
I would recommend replacing 'GPa deposited metals' with, e.g., 'deposited high-strength metals.' The word 'GPa' might not be easily understood by the public.
Response: Thank you for your valuable comments and kind suggestions.
The revised content (Title, In page1, line 1-3)
Effect of Cu Content on Microstructure and Mechanical Properties for High-Strength Deposited Metals Strengthened by Nano-precipitation
10- In Fig. 2, dimensions are missing; 'Counts' for Y-axis and 'degrees' for the X-axis.
Response: Thank you for your kind comments. We will modify them in the text.
The revised content (Results, In page4,5, line 202-218)
Figure 2. Multiphase microstructure of deposited metals with different Cu addition. (a) Cu0.62, (b) Cu1.38, (c)Cu1.79, (d) Cu2.32.
Figure 3. XRD patterns of deposited metals with different Cu addition. A means γ-Fe, F means α-Fe.
11- The IPF color key is still missing.
Response: Thank you for your strict comments. We will modify them in the text.
The revised content (Results, In page6,5, line 233-235)
Figure 4. EBSD IPF maps(a-d), misorientation angle maps(e-h), and area fraction of misorientation degree(i) of deposited metals. (a,e) Cu0.62, (b,f) Cu1.38, (c,g)Cu1.79, (d,h) Cu2.32.
P.S.
There are still many spaces (-) missing between the words, particularly in the figure captions. Please recheck the whole manuscript and correct them.
Response: Thanks again for your helpful advice. We will revise the whole manuscript carefully.
Author Response File: Author Response.pdf
Reviewer 2 Report
Good job to the authors. I belie it is suitable for publication in the present form.
Author Response
Thank you for your review and the recognition of our work.
Reviewer 3 Report
The authors have followed the amendments of the referees and considerably improved the article. In particular the experiments are more comprehensively explained and the figure captions were supplemented.
However, there is one necessary correction before publication.
(1) Although the caption of Fig. 7 (formerly Fig.6) has been complemented there is still no realistic explanation for compositions shown in the images (e.g. 3.91 wt.% Ni 6.04 wt.% Cu 83.47 wt.% Fe in Fig 7a). The text phrase, ‘… the components of nano-Cu precipitates are mainly Fe, Cu, and Ni’ (line 207) is apparently not correct. Obviously, the EDS results can only show an enhancement of the Cu concentration around the anticipated Cu-precipitates, because the objects themselves are too small for an exact analysis. Please, provide a precise description for the meaning of the composition values.
Please, correct typos in the revised text: Line 224: ‘starin’=> ‘strain’; Line 374: ’ The M-A constituents is…’ => The M-A constituent is…;
Do not use digits for the temperature differences: 372.15 K => 372 K; 416.15 K => 416 K.
Author Response
The point-by-point responses are as following.
Reviewers’ comments:
Reviewer #3
The authors have followed the amendments of the referees and considerably improved the article. In particular the experiments are more comprehensively explained and the figure captions were supplemented.
However, there is one necessary correction before publication.
- Although the caption of Fig. 7 (formerly Fig.6) has been complemented there is still no realistic explanation for compositions shown in the images (e.g. 3.91 wt.% Ni 6.04 wt.% Cu 83.47 wt.% Fe in Fig 7a). The text phrase, ‘… the components of nano-Cu precipitates are mainly Fe, Cu, and Ni’ (line 207) is apparently not correct. Obviously, the EDS results can only show an enhancement of the Cu concentration around the anticipated Cu-precipitates, because the objects themselves are too small for an exact analysis. Please, provide a precise description for the meaning of the composition values.
Response: Thank you for your scientific comments. We couldn't agree more with your comments. Due to the small size of precipitates, EDS results could not accurately characterize the chemical composition of precipitates, and it could indicate that enhancement of Cu occurred near precipitates. We have rigorously revised it in the manuscript. Then, we characterized the crystal structure of Cu precipitated by HRTEM test in the discussion section, which is consistent with the current research literature. Cu precipitated mainly exists in BCC and FCC structures. In particular, the precipitation of BCC-Cu is typical fishbone shape. This proves that the precipitates are Cu precipitates.
The revised content (Result, In page8, line 269-276)
The components of α-Fe marix are C, Cr, Mn, Fe, and Ni. There is no Cu element detected in the matrix. According to chemical composition of deposited metals, the Cu precipitation will occur. Due to the nanoscale size of black precipitates, the chemical composition of particles will be deviated during EDS analysis. It can be seen from the results that the content of Cu increases significantly near precipitates, which were 6.54wt%(Cu0.62), 3.54wt% (Cu1.38), 5.05wt% (Cu1.79) and 11.94wt% (Cu2.32), respectively. So, the ellipse precipitates were identified as Cu precipitation.
- Please, correct typos in the revised text: Line 224: ‘starin’=> ‘strain’; Line 374: ’ The M-A constituents is…’ => The M-A constituent is…;
Response: Thank you for your valuable comments. We will modify them in text.
The revised content (Mechanical properties and Toughening mechanism of deposited metals, In page10,15, line 324,489)
- Engineering strength-strain curves. The Cu79 obtains the maximum strength value.
The M-A constituent is a brittle phase, which is detrimental to toughness.
- Do not use digits for the temperature differences: 372.15 K => 372 K; 416.15 K => 416 K.
Response: Thank you for your valuable comments. We will modify them in text.
The revised content (In page1,11, line 16,355)
It is found that Cu decreases the start temperature of martensite (Ms) and enlarges the temperature range of bainite from 372K to 416K, improving the formation of bainite.
The difference values(Δ) of Bs and Ms point increases from 372K to 416K with increase of Cu addition.
Author Response File: Author Response.pdf
