Compositional Optimization of High-Performance Ferritic (HiperFer) Steels—Effect of Niobium and Tungsten Content
Round 1
Reviewer 1 Report
Line 19: “elevated temperature” is a very generic statement. In fact depending from the industrial sector “elevated temperature” can be understood ….from boiling water up to 1000°C and over.
Looking at the YS and UTS such steel is not suited for elevated temperatures, at least in the main industrial application fields such us: boilers and shell and tube heat exchangers. Probably in some chemical-reactors where the creep properties are not so demanding.
It is suggested to improve the introduction indicating the expected industrial sector of spplication and temperature-range you intend to find an application for HiperFer steel.
Line 17: Please check, because “10 N” are ~equivalent to 1 kg and from a hardness engineering system this load is frequently labelled as: HV1 not HV10. Anyway it is clear that you have used 10 N, so does not care if it is not a type.
Line 170: Creep is interesting when investigated by mean of tensile tests. This data are more similar to constant-load compression tests. In fact when reading "creep" some misunderstanding can arise and it is suggested to add “Compression creep” to the 3.3.3 header. A general concern:The addition of Nb and W have a clear hardening effect. You show it and the ageing curves are clear. From a scientific and metallurgical point of view your paper is acceptable.The elevated temperature application needs some more deeper tests. i.e: tensile creep with the record of creep-curve and time to rupture or to 0,1 % and 0,2 % deformation.
In fact, your compression data does not give any “industrial interesting news” because are not related to duration-life in service.
In conclusion:
1. is it suggested to specify the fact that you have carried on constant-load compression tests avoiding confusion with the “creep” that is the acting deformation phenomenon during the compression tests.
2. It is suggested to add some detail about temperature application range you believe this steel is suited.
3. If you have, please add the tensile-creep curve, if you do not have this date please add a sentence for fhurther full development of the material.
Author Response
Thank you very much for you review, which helped to increase the quality of the manuscript.
Please refer to the attached document for our comments.
Regards
Bernd Kuhn
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript under review examined the effect of niobium and tungsten compositions on the mechanical properties of HiperFer steels. The manuscript is recommended to publish if the following comments could be considered:
- The introduction section could be expanded, by explaining why W and Nb are selected as strengthening elements rather others, etc.
- Addition of one more alloy such as 2.4W1Nb or 2.6W0.6Nb could be more complete, considering both the contents of W and Nb are increased from the reference alloy to the next close alloy of 2.6W1Nb.
- Any comment can be provided regarding the effect of Nb content above 1.0wt%?
- Could the authors make it clear that all (or most) particles in Fig. 2 are precipitates of the LTL- and HTL-Laves phases? Based on the paragraphs from Line 101 to Line 121, it seems to the readers that these particles are Laves phases only.
- Are the authors sure that the first composition in Line 110 is (2.6W0.6Nb), rather than (2.4W0.6Nb) which belongs to the reference alloy? Maybe the variation of the content ±0.2wt% is allowed?
Author Response
Thank you very much for you review, which helped to increase the quality of the manuscript.
Please refer to the attached document for our comments.
Regards
Bernd Kuhn
Author Response File: Author Response.pdf
Reviewer 3 Report
Authors, in my opinion, presented interesting results of investigations of 4 alloys, with the different content of W and Nb. The increase of content of W and Nb increase hardness, favorably improve creep and decrease mean Laves phase precipitation size. The graphical presentation of such results as: volume fraction and ECD (fig.3) and hardness (fig.4) shows point-to-point plot connection. In my opinion it would be more transparent to determine the trend of changes if the graph fit was presented, for example, with a polynomial function. Statistically there may be scattering of results, which has not been shown. In fig.4 I see lack of last point at 17Cr2 graph.
In my opinion after this minor revision the article could be ready for publication as is.
Author Response
Thank you very much for you review, which helped to increase the quality of the manuscript.
Please refer to the attached document for our comments.
Regards
Bernd Kuhn
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Dear Authors thanks for your updated revision and for take in account the suggestions.
The specification about solid solution hardening effect and comparison with grade92 surely will increase the interest in the readers.
