Effect of Plasma Nitriding and Oxidation on the Corrosion Resistance of 304 Stainless Steel in LiBr/H2O and CaCl2-LiBr-LiNO3-H2O Mixtures
, E. Vazquez-Velez 1, H. Martinez-Valencia 1 and J. G. Gonzalez-Rodriguez 2
Round 1
Reviewer 1 Report
1. In the whole manuscript I suggest that the authors to revisit formatting issues such as first-line indentation, and spaces before units.
2. The author only characterized the formation of CrN layer by nitriding treatment, so does the nitriding treatment also change the structure and composition of the surface passivation film? There is no such description. It is recommended to add relevant tests for the structure and composition of the passivation film.
3. On page 7 of the manuscript, lines 221 to 227, whether it is nitriding or pre-oxidation treatment, an oxide film appears on the surface, and the oxidation treatment is to generate corrosion-resistant Cr2O3, how to explain that the oxide film does not protect the base steel.
4. The corrosion resistance results of LiBr/H2O and CaCl2-LiBr-LiNO3/H2O solutions are different, what factors lead to this situation, which are not described.
5. On page 5 of the manuscript, lines 166 to 170, This is contrary to the description of the whole manuscript, how to explain?
6. The vertical range of the test curve is suggested to be unified for readers to compare.
Author Response
Thank you very much, we be grateful for the time and careful reading of the manuscript. We addressed the comments listed and have made corresponding changes to our revised manuscript. Details of our replies to the comments are the following:
- In the whole manuscript I suggest that the authors to revisit formatting issues such as first-line indentation, and spaces before units.
It has been corrected.
- The author only characterized the formation of CrN layer by nitriding treatment, so does the nitriding treatment also change the structure and composition of the surface passivation film? There is no such description. It is recommended to add relevant tests for the structure and composition of the passivation film.
Answer: we add EDS analysis
Lines 148-159: Energy dispersive X-ray analysis (EDS) is shown in figure 4, it can observe the presence of elements such as Fe, Cr, O, Si, Mn and Ni for 304 type stainless steel sample at different atmospheres. The N element observed in plasma nitrided steel sample treated at 20% N2 + 80% H2 (Fig. 4b) atmosphere and pure N2 (Fig. 4c) confirmed the presence of the chromium nitride layer (CrN).
Table 2 shows EDS quantitative analysis of 304 stainless steel samples at different atmospheres, the O percentage increased in pre-oxidized steel by plasma from 3.45% to 23.00 % (wt.), which indicates that the oxide layer formed on the surface of the steel treated is higher than in the untreated steel. On the other hand, the percentage of N in the sample treated with pure N2 is slightly higher that nitrided steel sample treated at 20% N2 + 80% H2 atmosphere. However, the O percentage is higher in plasma nitrided steel sample treated with pure N2, which is more susceptible to corrosion
Figure 4. EDS analysis obtained for 304 type stainless steel under the different atmospheres.
Table 2. EDS quantification analysis for 304 type stainless steel under the different atmospheres.
- On page 7 of the manuscript, lines 221 to 227, whether it is nitriding or pre-oxidation treatment, an oxide film appears on the surface, and the oxidation treatment is to generate corrosion-resistant Cr2O3, how to explain that the oxide film does not protect the base steel.
(Answer: Stainless steel forms a passive film, which provide the key to their high resistance to corrosive attack, however, it is affected by an environment containing chloride and bromide ions at 80 ºC.)
- The corrosion resistance results of LiBr/H2O and CaCl2-LiBr-LiNO3/H2O solutions are different, what factors lead to this situation, which are not described.
Answer: One of the factors lead to this situation is the presence of chloride and bromide ions in the CaCl2-LiBr-LiNO3/H2O solution. On the other hand, LiNO3 is a kind of anode inhibitor. Thus, in the LiBr/H2O solution, we have only the effects of bromide ions, whereas in the CaCl2-LiBr-LiNO3/H2O solution we have two opposite effects that for chloride and bromide ions and that for LiNO3
Line 181-185: The most active OCP value was for the untreated steel sample, which exhibited a more active value than that in the LiBr/H2O solution, one of the factors that lead to this situation is the presence of chloride and bromide ions in the CaCl2-LiBr-LiNO3/H2O solution. On the other hand, LiNO3 is a kind of anode inhibitor. Thus, in the LiBr/H2O solution, we have only the effects of bromide ions, whereas in the CaCl2-LiBr-LiNO3/H2O solution we have two opposite effects that for chloride and bromide ions and that for LiNO3.
- On page 5 of the manuscript, lines 166 to 170, This is contrary to the description of the whole manuscript, how to explain?
Answer: the sentence was corrected, that is: (lines 187-191: the OCP values for nitrided steel sample at a 20% N2 + 80% H2 atmosphere as well as the pre-oxidized specimen rapidly moved towards more noble values, indicating a lower susceptibility to be corroded, whereas the OCP value exhibited by the untreated steel sample shifted towards more active values, indicating the formation of a less protective layer of corrosion products.
- The vertical range of the test curve is suggested to be unified for readers to compare
They have been corrected.
Reviewer 2 Report
In the abstract: line 15: X - ray analysis. It is XRD analysis (diffraction)
page 2, line 45: cero potential??
page 2, line 75: They were abraded - grinded is a more common term
page 3, line 101: corking or working?
page 4, Fig. : Presence of CrN was confirmed only from 1 peak? For 20% N2 + 80% H2 the peak at cca 50 degrees in not marked
page 6, line 188-190: sentence On the other hand..... Rephrase the sentence!
page 6, line 195, , Fig. 4b or Fig. 5b?
page 6, line 205 N2[30-32] or N2 [30-32]? - insert a space
page 7, line 229-231 Is this statement true? (the highest corrosion....)
page 8, line 234-235 The sentence must be corrected.
page 8, line 272 -275 Is this statement correct?
page 10, Fig. 9 or line 306 - State, that it is surface a surface observation
Author Response
Thank you very much, we be grateful for the time and careful reading of the manuscript. We addressed the comments listed and have made corresponding changes to our revised manuscript. Details of our replies to the comments are the following:
In the abstract: line 15: X - ray analysis. It is XRD analysis (diffraction)
It has been corrected.
page 2, line 45: cero potential?? It has been corrected.
page 2, line 75: They were abraded - grinded is a more common term
It has been corrected.
page 3, line 101: corking or working?
It has been corrected.
page 4, Fig. : Presence of CrN was confirmed only from 1 peak? For 20% N2 + 80% H2 the peak at cca 50 degrees in not marked
The XRD patterns of steel nitrided in the 20% N2 + 80% H2 and pure N2 atmospheres were compared with the ICDD card pattern: PDF#11-0065, CrN presents a characteristic diffraction peak at 43.737°.
So, we corrected lines 122-124: The presence of phase corresponding to chromium nitride, CrN is present for steel nitrided in the 20% N2 + 80% H2 and pure N2 atmospheres at 2 theta values of 43.71° and 43.62° respectively (ICDD PDF#11-0065)
page 6, line 188-190: sentence On the other hand..... Rephrase the sentence!
It has been corrected, that is: lines 208 – 210 On the other hand, by nitriding the steel either in pure N2 or in the 20% N2 + 80% H2 mixture, the Icorr value decreased slightly, whereas for pre-oxidized steel the value of Icorr increase.)
page 6, line 195, , Fig. 4b or Fig. 5b?
It has been corrected.
page 6, line 205 N2[30-32] or N2 [30-32]? - insert a space
It has been corrected.
page 7, line 229-231 Is this statement true? (the highest corrosion....)
It has been corrected, that is (lines 246-248): As can be seen in the Fig. 8a, the biggest semicircle diameter was observed for the sample nitrided in pure N2, followed for the semicircle of the steel nitrided in 20% N2 + 80% H2, this means that the highest corrosion resistance was obtained by nitrided steels.
page 8, line 234-235 The sentence must be corrected.
It has been corrected, that is (lines 251-253): because the oxide layer formed on the surface of the steel is thicker than the formed on the untreated steel, the pre-oxidation treatment improve the steel corrosion resistance [33].
page 8, line 272 -275 Is this statement correct?
It has been corrected, that is (lines 290-296): Similarly, for the tests carried out in the CaCl2-LiBr-LiNO3/H2O solution, the maximum Rox value was, once again, for steel nitride in pure N2 followed by the steel nitride in 20% N2 + 80% H2 and the pre-oxidized specimen. Conversely to this, in the LiBr solution, the CPEox value was lowest for steel nitride in the 20% N2 + 80% H2 atmosphere whereas in the CaCl2-LiBr-LiNO3/H2O solution, the CPEox value was lowest for the pre-oxidized steel in 100% O2. In both corrosive solutions the highest value was obtained for untreated steel
page 10, Fig. 9 or line 306 - State, that it is surface a surface observation
It has been corrected.
Reviewer 3 Report
This manuscript shows a thin layer of CrN can be formed on stainless steel using N2 or N2 + H2 plasma treatment. The electrochemical impedance and pitting inspection results show an improvement in corrosion resistance. The manuscript is interesting and shows a technique for nitridation on steel surfaces that helps to prevent corrosion. Using plasma to modify surfaces is not new and had been applied to other industries. This manuscript demonstrates the nitridation process can be performed on stainless steel parts and improve corrosion resistance.
The XRD results show the presence of the CrN signal on the specimens. This steel contains different metal elements and the reviewer wonders if another form of nitride is created by the plasma process.
Both the N2 and N2+H2 plasma treatments can create nitride film but with different thicknesses. Is the poorer performance of the N2 plasma-treated sample because of the thinner nitride film or the lower quality of the CrN films?
The oxygen-plasma-created film is the thinnest. Is the poor Cr2O3 film corrosion resistance performance because this specimen has the thinnest film, or the oxide material is more reactive?
Since the protective films created by different plasma processes have different thicknesses. It is difficult to conclude that CrN provided better protection than Cr2O3. We need to compare films with similar thicknesses
Another round of proof reading will be useful.
Author Response
Thank you very much, we be grateful for the time and careful reading of the manuscript. We addressed the comments listed and have made corresponding changes to our revised manuscript. Details of our replies to the comments are the following:
The XRD results show the presence of the CrN signal on the specimens. This steel contains different metal elements and the reviewer wonders if another form of nitride is created by the plasma process.
Answer: From the present XRD results, CrN is only present signal in the samples, of course it may be possible that another nitrate could be formed which would depend of the composition of the gases, pressure, temperature, and treatment time. But in the present condition, we only observe CrN.
Both the N2 and N2+H2 plasma treatments can create nitride film but with different thicknesses. Is the poorer performance of the N2 plasma-treated sample because of the thinner nitride film or the lower quality of the CrN films?
Answer lines 134-137: A thicker film provides a better corrosion resistance to the surrounding environment because it will create a longer diffusion barrier and restrict corrosive ions from interacting with the metal causing its degradation.
The oxygen-plasma-created film is the thinnest. Is the poor Cr2O3 film corrosion resistance performance because this specimen has the thinnest film, or the oxide material is more reactive?
Answer: it is due to both reasons, because the Cr2O3 is the thinnest film and the oxide material is more reactive
Since the protective films created by different plasma processes have different thicknesses. It is difficult to conclude that CrN provided better protection than Cr2O3. We need to compare films with similar thicknesses
Answer: In the present work, the conclusion made about of the comparation of the protection of CrN and Cr2O3 was make taken into de account the same experimental conditions in the treatments done in this work. However, the comparison with similar thicknesses can be done in future works.
