Effect of Multiple-Pass Friction Stir Processing on Hardness and Corrosion Resistance of Martensitic Stainless Steel

Round 1

Reviewer 1 Report

The authors investigated the influence of multi-pass friction stir processing (FSP) of AISI 420 martensitic stainless steel on the microstructure, hardness and corrosion behavior. The work is straightforward and objective.

 

I make the following comments:

 

The authors compare different conditions, for example, AR 420, AQ 420, FSD in certain sections of the article and in others not, it's not clear how this was decided. The authors need to make it clearer.

 

The symbols did not appear in the PDF version. Please check it out.

 

In some points of the article the authors wrote “matensite” instead of “martensite”

 

The authors wrote in line 148 “ The grain sizes of AR420 and AQ420 were found to be 4 μm and 2 μm “. But what phase?

 

Please improve Fig 2b. Some characters are missing.

 

Line 164- 165. The authors wrote “ Overlap ratio of 75% produced a larger overlapped area but promoted a FSPed layer with more uniform hardened depth (Fig. 2b). On the contrary, the specimen processed with an overlap ratio of 25% showed a small overlapped area with a non-unform hardened depth (Fig. 2d).” Please indicate in the figure

 

Line 173 – the authors wrote “Compared with AQ420, the average grain size of FSP250 was reduced from 2 μm to 0.75 μm. e 173.” Compared? Where?

 

What is the reason for showing the micrographs of the sample 75%, Figure 5? And others no?

 

Line 189 – The authors do not call the figure in the text.

 

In the Figure captions, of figure 5, I t could be clear what are the phases present in the micrographs and their coloration.

 

In line 241-244, the authors wrote “Compared with AQ420, the average grain size of FSP250 was reduced from 2 μm to 0.75 μm.” Compared? Where?

In line 255- 257, the authors wrote “ The lower hardness detected at C1 of FSP50% is due to back-tempering. Softening occurred because the diffusion of carbons, reduction of dislocation density and martensite becomes less tetragonal”. This is the possible cause, because the authors did not measure the dislocation density. Make it clear in the text that is a hypothesis.

 

In line 257 – 260, the authors wrote “ From Fig. 8c, the hardness profiles along C2 for the three multi-pass FSPed specimens demonstrate similar profiles (with surface hardness of 705-720 HV1) as that of the single-pass FSPed specimens (at C2) because the 259 microstructure at C2 consists of mainly martensite.” Please, called the figure

 

What is the need for equation 2 in the text? So the explanation wasn't enough?

 

Please correct the Figure caption 11

Author Response

Please see the attached file.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper investigates the effect of friction stir processing on microstructure, hardness and corrosion performance of martensitic stainless steel AISI 420. In particular, it focuses on multi-pass processing of the material. Although the multi-pass processing did not lead to any improvement in the studied properties, the data will be useful for future investigators. The manuscript is well written and structured. The experiments were performed systematically and are carefully documented. All conclusions are supported by experimental data, which are thoroughly discussed. There are only few minor shortcomings listed below. I recommend the paper to be published in Coatings.

All abbreviations need to be introduced. E.g., FSW in line 23 and BCT and BCC in Fig. 7. Line 57-58. … no report … CAN be found …. Line 94. … reported elsewhere. Line 112, 143, 146, 316 and further. Greek symbols are missing. Line 131. … rods served as … Line 127-133. Please, describe better the measurement procedure. What potential the measurement started at? Where it was terminated? What about stabilization procedure (exposure duration before the start of potential scanning). Line 211. …, which LEADS TO the reduction … Line 214-216. The sentence should be improved. Line 221. … to their nano-SIZE. Line 286. … activities occurred. Line 288 and further. It is open circuit potential or free corrosion potential, not corrosion potential. According to an appropriate ISO standard, corrosion potential is any potential a corroding system can achieve. Table 2. Put 4 mV instead of 4.0. Such precision is not possible in this case. Table 2. It is mentioned in the experimental that each experiment was repeated at least three times. Can you state the error of measurement or standard deviation then? Line 308. … by an order of magnitude of three. Can you re-phrase the statement? Line 324. … martensite POSSESSING poor … Line 333. Corrosion morphology. Figure 11 and 12. Reproduction right for images from an earlier published paper has to be granted by the current copyright owner. If not possible, these need to be removed. Line 339. … the FOLLOWING can be …

Author Response

Please see the attached file.

Author Response File: Author Response.pdf

Reviewer 3 Report

Line 35 - replace existing with presence

Line 48 - remove the word with

Line 66 - change "higher in AS" to "higher in the AS"

Line 88 - Table 1, include the standard deviation values for the wt% values in the table.

Line 112 - The theta symbol was missing.

Line 114 - The EBSD acronym was used with explanation until line 116.

Line 144 and 146 - the symbol in front of -ferrite was missing.

Line 158 - straighten up the labels on Figure 2.

Line 221 - change "nano-sized" to "presumed nano size"

Line 222 - change "was" to "were"

Line 257 - change "carbons" to "carbon atoms"

Line 286 - change "occurred" to "occurring" 

Line 316 and 317 - missing the symbol before the m (meters)

Line 321 - change "mouth" to "mouths"

Line 323 - change "to high" to " to a high"

Line 325 - change "possesses" to "possessing"

Line 331 - change "region" to "regions"

Author Response

Please see the attached file.

Author Response File: Author Response.pdf