Structure and Mechanical Behavior of Heat-Resistant Steel Manufactured by Multilayer Arc Deposition
, Antonina I. Gordienko, Aleksandr V. Eremin, Vyacheslav M. Semenchuk and Anastasia E. Kuznetsova
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors1. There are still some type-errors and hard expressions. Please check it carefully.
2. Why GMAW has thinner layers Compared to coldArc mode?
3. How about the defined elongation rate of the static tensile tests. Why the strain is so small? How do you achieve the stress 463MPa? Why the strain in top zone is larger? A stress-strain curve is needed.
4. Allotriomorphic ferrite and acicular ferrite should be labeled in the observation pictures. In Fig.7 a slight increase in microhardness is due to the formation of an acicular ferrite structure and a small proportion of ferrite layers. Please illustrate the observation pictures.
Comments on the Quality of English Language1. There are still some type-errors and hard expressions. Please check it carefully.
Author Response
The authors would like to thank the Reviewer for their careful reading of the manuscript and comments which help to improve the paper. Changes in the manuscript are highlighted in yellow.
- There are still some type-errors and hard expressions. Please check it carefully.
The English language has been revised and corrected.
- Why GMAW has thinner layers Compared to coldArc mode?
The higher layer height in coldArc mode is caused by less metal spreading due to lower heat input – 0.388 kJ/mm in coldArc mode versus 0.425 kJ/mm in GMAW mode. This explains the difference in the geometric dimensions of the walls and contributes to the formation of a higher and narrower wall in the coldArc printing mode. This discussion of possible reasons for the difference in layer thicknesses has been added to the section “3.1. Wall appearance".
- How about the defined elongation rate of the static tensile tests. Why the strain is so small? How do you achieve the stress 463MPa? Why the strain in top zone is larger? A stress-strain curve is needed.
Static tensile tests were carried out on an Instron 5582 electromechanical machine with a crosshead travel speed of 1.5 mm/min. It is written in the manuscript in the section “Materials and methods” (line 213).
The printed walls have a structure of acicular ferrite, which is characterized by higher hardness compared to the ferrite-pearlite structure of the substrate. Therefore the plasticity (and strain at break as well) of specimens cut from the walls is lower than specimens cut from the substrate. An additional factor in reducing plasticity is the layer boundaries, which increase the strain localization.
The authors found this question unclear. The only one place where stress of 463 MPa is mentioned is a first DIC image for codlArc mode. In general mechanical stress was calculated using the following equation σ=P/A, where P – applied load, measured by load cell of testing machine and A – cross-section of the specimen at the beginning of the test.
Specimens cut from the printed walls were placed in a tensile tests the same as they were located in the printed wall. Since the lowest value of microhardness was in the upper part of the wall, the strain localization occurs in the upper part. This is visible in DIC strain fields.
Stress-strain curves were presented in the initial paper in Figure 8a, while in the revised version the diagram is shown in Figure 9. Only one curve for each type of the specimen was drawn to demonstrate general shape for each tested material.
- Allotriomorphic ferrite and acicular ferrite should be labeled in the observation pictures. In Fig.7 a slight increase in microhardness is due to the formation of an acicular ferrite structure and a small proportion of ferrite layers. Please illustrate the observation pictures.
The designation of the phases has been added for all metallography in Figures 4-6 of the revised version of the manuscript. To make the explanation more intelligible, the authors slightly rephrase it and note the L coordinate in brackets. It would help to find the described region in the graph of microhardness.
Reviewer 2 Report
Comments and Suggestions for AuthorsThis review report has been removed from the review record as it did not meet MDPI’s review report standards (https://www.mdpi.com/reviewers#_bookmark11).
Comments on the Quality of English Language
NA
Author Response
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors have analyzed the mesoscopic structure, hardness and behavior under tensile stress of two differently fabricated specimens. The samples were both produced by multilayer arc deposition, but with different heat inputs, which consequently leads to different structural and mechanical properties. Overall, the procedure and results are well presented. However, the conclusions lack a classification in the current state of research, which would enhance the manuscript enormously. I therefore recommend adding this to the manuscript. Thus, the manuscript would be publishable in Metals with minor modifications.
Other comments:
Does the OK Autrod 13.14 material contain copper as a cover material?
Can the authors provide a porosity of the fabricated materials?
In Fig. 2 b the unit [mm/mm] can be omitted.
Do the authors give an average layer height (I may have overlooked this)?
Figure 7. it would be good to measure the hardness with higher lateral resolution. For example, in the transition areas between layers.
Table 3: Two other materials ‘Russia GOST’ are mentioned here, but they have no reference in the text. This must be added.
For Chernov-Luders band a citation is missing.
Embedding of the Conclusion in the current state of the literature.
Comments on the Quality of English LanguageThere are some spelling errors
Author Response
The authors would like to thank the Reviewer for their careful reading of the manuscript and comments which help to improve the paper. Changes in the manuscript are highlighted in yellow.
- However, the conclusions lack a classification in the current state of research, which would enhance the manuscript enormously. I therefore recommend adding this to the manuscript.
An additional analysis of the literature has been carried out in the introduction. A classification of welding method and the main problems in the study area were reviewed and this information was added to the paper. The list of relevant literature has been increased.
- Does the OK Autrod 13.14 material contain copper as a cover material?
Copper is used as a protective coating on OK Autrod 13.14 wire. However, handbooks usually indicate the composition of the uncoated wire without copper. To evaluate the copper content, an additional analysis of the chemical composition was carried out using a portable Niton xL 3t spectrometer. On the surface of the wire, the copper content is 14%. In the process of 3D printing, a significant evaporation of copper occurs and its content does not exceed 0.3% (measurements were made on the surface of the wall). The authors believe that Cu will not play an important role in the structure formation during printing. This comments were added to the revised manuscript.
- Can the authors provide a porosity of the fabricated materials?
Porosity has not been measured for the printed materials, because pores are rare on SEM images. Thus it can be concluded, that the material is quite homogenous and additional porosity measurements are not obligatory.
- In Fig. 2 b the unit [mm/mm] can be omitted.
The units [mm/mm] in Figures 3b and 10a,b,c, have been removed
- Do the authors give an average layer height (I may have overlooked this)?
The layers height was mentioned in the paragraphs, where strain localization obtained via DIC was discussed. The authors considered that it also would be good to write the layers thickness in the section “3.1. Wall appearance”. “The average vertical travel of the welding torch after each layer deposition was 1.6 and 1.8 mm for the GMAW and coldArc modes, respectively.”
- Figure 7. it would be good to measure the hardness with higher lateral resolution. For example, in the transition areas between layers.
Measurements of microhardness along the wall height were carried out with a step of 5 mm. However, in the lower part of the wall and HAZ, where microhardness changes significantly, additional indentations were made. The step of measurements in these regions was less than 1 mm. Some of the points in Figure 8 were excluded in order to make the graph clearly visible and not overloaded with excessive data points. Microhardness measurement were also made at layers boundaries. It has been shown that microhardness in these regions is lower by 15% than in the layer. These explanations were added to the revised version of the manuscript.
- Table 3: Two other materials ‘Russia GOST’ are mentioned here, but they have no reference in the text. This must be added.
Russian GOST references were added in Tables 1 and 3 as well as mentioned in the text where materials are described.
- For Chernov-Luders band a citation is missing.
The citation for Chernov-Luders band was added in the sentence where it mentioned.
- Embedding of the Conclusion in the current state of the literature.
As far as literature review of the recent papers in the field of arc welding were extended and sufficiently improved, the authors prefer not to overload conclusion and leave a numerated structure to highlight the key results.
A sixth point has been added to the Conclusion, in order to highlight the key result of the article, which can contribute to the development of modern ideas about 3D printing.
- There are some spelling errors
The English language has been revised and corrected.
