Hydrogen Trapping in Laser Powder Bed Fusion 316L Stainless Steel
Round 1
Reviewer 1 Report
Dear Editor, dear author,
In this manuscript, the influence of hydrogen on martensite formation is compared by loading tests on AISI 316L steel in the PBF and cast+formed tempers. The manuscript is well written, and the results are interesting. However, I have the following essential comments that must be implemented before publication:
- Please name all parameters when describing the experimental section. A test procedure is written correctly if all parameters are named so that a third party can repeat the results and get the same results.
- Later in the text, reference is made to the chemical composition and the associated austenitic stability. The correct and not the nominal chemical composition of the PBF bulk samples should be reported here.
- There are no measured values ​​for the H2 content introduced by the loading tests.
- How can it be ensured during the loading tests that at 600°C, there is no drop in the dislocation density in PBF-processed steel, which affects the hydrogen absorption? That should be described.
- The results and the discussion are separated. Unfortunately, the results in the results section are discussed using a variety of references. Here the author should restructure the manuscript accordingly and make a summary or strictly separate presentation of the findings and their discussion
Other minor annotations can be found in the manuscript. Despite the criticism, however, it is an interesting paper and should be published after adjustment.
Comments for author File: 
Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Reviewer 2 Report
In this paper, the authors systematically investigated the correlation between microstructure, hydrogen traps’ characteristics and susceptibility to HE of SLM 316L SS and compared them to the CR316L SS. This work is interesting and inspirational for the readers of Metals. So, I recommend it to publish in Metals after a minor revision as follows:
1. The authors study the effect of hydrogen traps and initial microstructure on the HE susceptibility of SLM 316L SS. Nevertheless, the introduction provides too little information on the effect of the unique microstructures on the HE behavior of SLM 316L SS. Please revise the Introduction section by adding some related research literature.
2. What is the necessity to list the same XRD patterns in Figure 1,since these results can be seen in Figure 3 and Figure 4?
3. It is suggested to adjust the order of Figure 5, which may be more logical to put Figure 5 after Figure 2.
4. In Section “Results”, the author said, “…, we were able to identify different hydrogen traps within the material and to estimate the activation energy, Ea, for hydrogen release…”. It is better to give a Table of activation energies for relatively hydrogen traps, which is useful to the readers.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
The manuscript studies the trapping behaviour of the selective laser melted 316L stainless steel. The manuscript has serious flaws and open questions that could be answered:
1- There are many typing errors and language problems which should be revised by an English native speaker who is an expert in the field.
2- You chose Lee and Lee's model. Could you explain in the manuscript why the authors chose that? There are other models, which can be considered.
3- The detail of the TDS machine should be added to the manuscript.
4- In the SLM sample, it seems that the XTD pattern also contains the bcc structure (110 peak).
5- In Fig. 6, for 72 (h).
6- In Fig. 7, the fitting is not accurate. It should be improved with the addition of one more heating rate.
7- What is the meaning of a weak irreversible trap? Also, I do not agree with the discussion about the trap sites (dislocations for the first peak).
8- The application of equation 1 is not for the phase transformation due to hydrogenation. The equation is mainly used for deformation-induced phase transformation.
9- According to the composition, it seems the equations which were used for the instability of the austenite are not accurate. Since the Nickel content is lower in the CR specimen, it is recommended to use the other empirical equations and use the Md30 parameter instead. Please use the following references to calculate the Md30 accurately. Also, please calculate the SFE and compare the alloys together. https://doi.org/10.1002/srin.202000242 https://doi.org/10.1007/s11661-013-1943-0
10- Please do not use informal sentence structures such as [’].
11- It seems that the trapping site energy differences are not too much. the discussion based on these differences is not accurate.
12- There is no SSRT results for the estimation of HR sensitivity. Also, the comparison between two alloys (one with a higher content of martensite and the other very low) cannot be a good base for comparison.
14- Regarding the study of hydrogen trapping in the SLM alloy, more evidence is needed to reach a conclusion.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
While the authors answered the comments, the answers are not complete.
Comment 2- In some of the other references Choo and Lee were used not Lee and Lee. Please describe the difference.
Comment 8- The explanation is not satisfactory. The authors claimed that there was a good correlation between the calculated austenite stability factor and the amounts of martensite phases induced by internal stresses, which accompany the absorption of hydrogen. However, there is not clear explanation for the effect of hydrogen on phase transformation vs the usual phase transformation due to deformaiton. Also, the conclusion No. 3 is not proven based on the observed results. More explanation is needed.
Comment 9- Please add the results of Md30 and SFE to the manuscript with the equations from the reference. Add the agreement of the results with your findign to the mansucript with a proper discussion.
comment 10- The explanation is not convincing. If the authors cannot add the results of SSRT, the authors could explain how they can response the negetive comment about the comparison between two alloys (one with a higher content of martensite and the other very low).
Comments 11,14- The comments were not answered properly. The identification of the trap site is not clear and the comparison of the two alloys are not clear. Also, the complementary validation of the traps were not presented.
Author Response
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Author Response File: Author Response.pdf
Round 3
Reviewer 3 Report
The answers to the comments seem satisfactory and I recommend considering it for publication.
