Shock Hugoniot of Forged and Additively Manufactured 304L Stainless Steel

Round 1

Reviewer 1 Report

 

The authors exclusively provide the chemical composition of the powder used to produce the AM plate. A product analysis of the manufactured plates, including O content, should be provided.

Moreover, no information is provided on the product analysis of the forged product which is used for comparison. The detail comparison of the compositions is an important basis for a critical discussion of the different behaviour of the two products, namely in terms of austenite stability.

In addition, no information is provided about the thermomechanical process that the respective products have undergone: does the AM product has been submitted to a final solution annealing? The forged product, if procured according to standards in force, has most probably be solution annealed as a last stage of manufacturing. This information is relevant for the comparison of the products and should be provided.

Finally, in the discussion the authors confirm that the effect of even relatively small amounts of porosity can be relevant on shock velocity, however no results of volumetric inspection by Non-Destructive Testing of the AM plates (e.g. by Ultrasonic Testing, or Computed Microtomography) is provided in the paper to confirm the internal soundness of the products tested. This information on possibly applied quality control tests should be provided.

Author Response

Comment: The authors exclusively provide the chemical composition of the powder used to produce the AM plate. A product analysis of the manufactured plates, including O content, should be provided.

Reply:  Thank you for your comment.  We have added this information in the paper in a modified Table 1.  This shows the chemistry of the forged 304L SS, powder and the final built plate.

Table 1. The measured chemical composition of the 304L SS wrought plate, powder used in the AM process and the as build AM plate in weight percent.

	C	Si	Mn	P	S	Cr	Ni	Mo	Cu	N	O	Fe
Wrought	0.015	0.57	1.47	0.019	0.002	18.47	10.02	0.11	0.18	0.05	<0.01	Bal
AM Powder	0.015	0.53	1.5	0.012	0.003	18.4	9.8	0.0	0.0	0.05	0.019	Bal
AM Plate	0.20	0.63	1.43	0.007	0.004	18.32	10.03	0.015	0.008	0.05	0.03	Bal

Comment: Moreover, no information is provided on the product analysis of the forged product which is used for comparison. The detail comparison of the compositions is an important basis for a critical discussion of the different behaviour of the two products, namely in terms of austenite stability.

Reply:  We have added the chemistry of the wrought material in the paper.  We have also added a reference to the process used to manufacture the 304L SS.  We already had included microstructure and texture information in the paper.  

The following text and reference were added to the manuscript:

The chemical composition from the final plate build was also measured using an outside vendor and is shown in Table 1.  The wrought material used in this study was processed by high energy rate forging [*].

[*]M.C. Mataya, et al., Processing and Structure of High-Energy-Rate-Forged 21-6-9 and 304L Forgings, Rockwell International Corp., Golden, CO (USA), 1981(Rocky Flats Plant).

Comment:  In addition, no information is provided about the thermomechanical process that the respective products have undergone: does the AM product has been submitted to a final solution annealing? The forged product, if procured according to standards in force, has most probably be solution annealed as a last stage of manufacturing. This information is relevant for the comparison of the products and should be provided.

Reply:   We agree with the reviewer and hence we extensively characterized the microstructure and texture of the AM and forged materials.  To clarify the point about any post-processing, we have added the following text to clarify this point:  “It is important to note that no post-build heat treatment was performed on the AM plates”.

Comment: Finally, in the discussion the authors confirm that the effect of even relatively small amounts of porosity can be relevant on shock velocity, however no results of volumetric inspection by Non-Destructive Testing of the AM plates (e.g. by Ultrasonic Testing, or Computed Microtomography) is provided in the paper to confirm the internal soundness of the products tested. This information on possibly applied quality control tests should be provided.

Reply:  Thank you for your comment.  We had performed an extensive number of non-destructive testing – use of optical micrographs, X-Ray tomography to also measure porosity in the samples.  These techniques showed a <1% porosity in all samples and the amount of porosity did not trend with the shock velocity.  We have added the following text to clarify this point:

It is important to note that it has been documented in the literature that accurately measuring the density of AM samples, especially with porosity, can be complicated especially using standard immersion techniques [].  In presence of porosity, liquid can fill the “pores” and cause a larger error in the density measurements [].  Hence, additional analysis using optical micrographs and X-Ray tomography was also performed on the samples to measure porosity in the samples.  This analysis showed a <1% porosity in the samples. 

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear authors, the manuscript “Shock Hugoniot of Forged and Additively Manufactured 304L stainless steel” have some issues that must be improved, as follows:

• Revise the abstract. Add more quantitative findings.
• Keyword: replace 304L SS with Stainless steel 304L
• In the entire article, authors were claiming about only about additive manufacturing. It is necessary to mention which type of additive manufacturing process is used and why?
• Considering the “introduction’ section, it contains many valuable information to put the reader in a good requirements of the results presented. Motivation is clear but please try to emphasize the lack of knowledge that are improved in the manuscript.
• Authors may consider citing the following references which are relevant to justify the use of additive manufacturing for Stainless steel alloys. https://doi.org/10.1016/j.jmrt.2022.08.074
• Add summary of your work in last paragraph of introduction section.
• Specify the limits of this study. State in more detail the respective advantages and disadvantages.
• Line 156-157: Authors claimed about microstructure findings. However, I did not observed any microstructures in the manuscript. Add those details.
• In results and discussion section, compare your findings with past studies and give reasonable agreement from literature
• Revise conclusion section. Firstly, add summary of your work in 2-3 sentences and then mention the outcomes with key results.
• Comparison of your results with past work is not required in conclusion. Move it in discussion section.
• References are not as per the journal format. Correct it

Author Response

Comment:  Revise the abstract. Add more quantitative findings.

Reply:  Thank you for your comment.  Our abstract already is quantitative and shows that the measured shock velocity in AM samples is 3% lower than the forged counterpart. 

Comment: Keyword: replace 304L SS with Stainless steel 304L

Reply:  We have made the change.

Comment:  In the entire article, authors were claiming about only about additive manufacturing. It is necessary to mention which type of additive manufacturing process is used and why?

Reply:  We apologize that the manufacturing method was not clear from the manuscript.   We have added the following the methodology section:

“In this work, we used powder bed laser fusion to manufacture the samples.”

The details of the method were already included in the section.

Comment: Considering the “introduction’ section, it contains many valuable information to put the reader in a good requirements of the results presented. Motivation is clear but please try to emphasize the lack of knowledge that are improved in the manuscript.

Reply:  Thank you for your comment.  We have the following sentence in the introduction to clarify the lack of knowledge:

“While many studies exist to understand the specific microstructure and the resulting properties at low strain rates, there are only a handful of studies on the dynamic behavior of AM materials”

Along with the following:

“As shown above, the majority of the published work has focused on investigating failure in AM materials. To our knowledge the only previously published study to investigate the equation of state of AM metal under dynamic loading is that of Wise et al. [8] which investigated the equation of state of AM 304L and found no measurable differences in the shock stress of AM vs. wrought 304L. However, Wise et al. did not report directly measured or calculated shock velocity in the stainless samples. This scarcity in experiments investigating the equation of state of AM materials is possibly related to the fact that prior research has shown that equation of state is fairly insensitive to changes in grain size [23], texture and orientation [21, 24].

The goal of this work is to fill this gap in knowledge by performing systematic experiments on AM 304L SS. The rest of the paper is organized as follows.”

Comment: Authors may consider citing the following references which are relevant to justify the use of additive manufacturing for Stainless steel alloys. https://doi.org/10.1016/j.jmrt.2022.08.074

Reply:  We have added this to the reference list.

Comment: Add summary of your work in last paragraph of introduction section.

Reply: Thank you for your comment.  I think this is more a style issue.  I have usually never added a summary in the introduction section and find that having a summary in the abstract and conclusion section is usually enough.

Comment: Specify the limits of this study. State in more detail the respective advantages and disadvantages.

Reply:  Thank you for your comment.  We have several sections in the manuscript that discuss the limits of the study.  I am not sure I understand what else the reviewer wants added.

Comment: Line 156-157: Authors claimed about microstructure findings. However, I did not observed any microstructures in the manuscript. Add those details.

Reply: Figures 2 and 3 in the manuscript show the micrographs and texture plots showing the microstructure of the material. 

Comment: In results and discussion section, compare your findings with past studies and give reasonable agreement from literature

Reply:  We have already included a comparison with literature in the discussion section including points where we agree or not.  I am not sure I understand what else the reviewer wants added.

Comment: Revise conclusion section. Firstly, add summary of your work in 2-3 sentences and then mention the outcomes with key results.

Reply:  We already have the following in the conclusion, “The results from this work showed that the shock velocities in AM 304L were up to 3% lower than its forged counterpart. This difference was determined to be outside the estimated uncertainties for this type of experiment.” I am wondering if the reviewer read a corrupted version of the paper, as the requested information is already there in the suggested format.

Comment: Comparison of your results with past work is not required in conclusion. Move it in discussion section.

Reply:  We have removed this information. 

Comment: References are not as per the journal format. Correct it

Reply:  We have corrected the format.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have provided the product analysis of the AM plate, however it is surprising that the C content is as high as 0.20%, which would mean that the plate is no longer a 304L grade, but a 304 and the text should be revised in function. This value should be checked and confirmed.

Author Response

The reviewer is correct.  It was a typo and should have been 0.020.  We have corrected that in the manuscript.

 

Thanks

-Saryu

Reviewer 2 Report

Accept in the present form 

Author Response

Thanks