A Comparative Study of the Corrosion Behavior of 30CrMnSiNi2A in Artificial Seawater and Salt Spray Environments

Round 1

Reviewer 1 Report

1. Similarity index is more than 35% excluding references. It is not acceptable at all. Reduce the plagiarism in the entire manuscript.

2. It is recommended to revise the manuscript for grammatical and typo errors.

3. Introduction seems weak, it is recommended to write the motivation for the present work. Few lines about the corrosion test, elaborate applications, and properties of the alloy used.

4. It is recommended to cite more articles in the introduction part or insert a table to discuss the comparison.

5.   The surface dimension of the alloy used for both the test are different, how can the authors compare them? Differences in the surface area can directly affect the rate of corrosion.

6. If the authors has adopted any of the figures or tables from the published sorces, it is recommended to obtain copyright.

Author Response

1. Similarity index is more than 35% excluding references. It is not acceptable at all. Reduce the plagiarism in the entire manuscript.

Response: Dear reviewer, we are sorry for the high similarity index. As seen in the report, the most similar part is some description that similar with our previous work. To overcome this problem, we revise the manuscript carefully and reduce the similarity. We have checked it use the same software and the similarity index has been reduced. Thank you.

2. It is recommended to revise the manuscript for grammatical and typo errors.

Response: Dear reviewer, the grammatical and typo errors throughout the manuscript have been checked and revised in the new manuscript.

3. Introduction seems weak, it is recommended to write the motivation for the present work. Few lines about the corrosion test, elaborate applications, and properties of the alloy used.

Response: Dear reviewer, the introduction section has been re-written in the revised manuscript. The main revisions are summarized as follows:

(1) The background is explained for the investigated. This steel is used in the landing gear of the amphibious aircraft, which suffers atmospheric corrosion and seawater corrosion because its takeoff and landing at sea. Therefore, the corrosion behavior of the steel used for the landing gear in the atmospheric and immersion environment should be considered and understood.

(2) The brief literature review about the corrosion behavior differences in different environments are given. During service in the real environment, the differences in the marine atmosphere and full-immersion environments cause the distinct corrosion behavior of the steel, which should be considered. In the atmospheric environment, corrosion is determined by the environmental parameters including temperature, relative humidity, and ion deposition [1], yielding the corrosion under adsorbed thin electrolyte layer [2]. In the full-immersion environment, the limited dissolved oxygen is the most significant factor that differs with the atmospheric environment. Meanwhile, the sediment and accumulation of the organisms also affect the corrosion process beneath the attached layer [3]. To distinguish the different corrosion behavior, some studies have been conducted. Trough simulation test, Yu et al. [4] reported that the γ-FeOOH and Fe₃O₄ were the main corrosion product during the wet-dry cycling exposure, while additional α-FeOOH emerges in full-immersion test. Liang et al. [5] found the most severe pitting corrosion in the immersion test as compared to other environments on Al-Mg-Si aluminum alloy in marine environment because of the lack of dissolved oxygen in the former case. In our previous work [6], the corrosion behavior of E690 steel in different simulated marine zones are investigated and the results demonstrated that the oxygen diffusion, drying period, scour stress, and water holding ability determined the corrosion behavior.

(3) The purpose of this manuscript is given in the last paragraph of this section. From the above analysis, it can be found that the different service environment will definitely affect the corrosion behavior of the steel for the landing gear of the amphibious aircraft. However, the response of the 30CrMnSiNi2A steel to the environment variation is not clear.

The above revision can be found in the introduction section (Line 27-31, Line 38-43, Line 45-67) in the revised manuscript.

4. It is recommended to cite more articles in the introduction part or insert a table to discuss the comparison.

Response: Thank you for your advice. The introduction section has been re-written and more articles are added.

5. The surface dimension of the alloy used for both the test are different, how can the authors compare them? Differences in the surface area can directly affect the rate of corrosion.

Response: Dear reviewer, thank you for your constructive suggestion about the sample dimension sued in this work. Indeed, the sample surface area has a considerable effect on the corrosion behavior. In the present work, the samples for the immersion test were cut into dimensions of 30 mm × 20 mm × 3 mm. The ratio of the sample surface area to the solution volume was kept at 50 mL/cm². In the salt spray test, the samples with dimensions of 60 mm × 40 mm × 3 mm were used. However, because the salt spray environment contributes to the formation of adsorbed thin electrolyte layer on the sample surface. Therefore, the ratio between the electrolyte and surface area is not considered. In this case, the sample surface area will not significantly affect the corrosion processes and the comparison is reliable. Even so, in our following works, we will use the samples with the same dimensions to ensure the rigorous results.

    The brief description is added in section 2.3 (Line 107-108) in the revised manuscript.

6. If the authors has adopted any of the figures or tables from the published sources, it is recommended to obtain copyright.

Response: Dear reviewer, there is no figure or table in from the published sources in the present work. Thank you.

References

[1] D. de la Fuente, I. Diaz, J. Simancas, B. Chico, M. Morcillo, Long-term atmospheric corrosion of mild steel, Corrosion Science 53 (2011) 604-617.

[2] L. Wang, J. Liang, H. Li, L. Cheng, Z. Cui, Quantitative study of the corrosion evolution and stress corrosion cracking of high strength aluminum alloys in solution and thin electrolyte layer containing Cl, Corrosion Science 178 (2021) 109076.

[3] H. Tian, X. Wang, Z. Cui, Q. Lu, L. Wang, L. Lei, Y. Li, D. Zhang, Electrochemical corrosion, hydrogen permeation and stress corrosion cracking behavior of E690 steel in thiosulfate-containing artificial seawater, Corrosion Science 144 (2018) 145-162.

[4] J. Yu, H. Wang, Y. Yu, Z. Luo, W. Liu, C. Wang, Corrosion behavior of X65 pipeline steel: Comparison of wet–Dry cycle and full immersion, Corrosion Science 133 (2018) 276-287.

[5] M. Liang, R. Melchers, I. Chaves, Corrosion and pitting of 6060 series aluminium after 2 years exposure in seawater splash, tidal and immersion zones, Corrosion Science 140 (2018) 286-296.

[6] H. Tian, Z. Cui, H. Ma, P. Zhao, M. Yan, X. Wang, H. Cui, Corrosion evolution and stress corrosion cracking behavior of a low carbon bainite steel in the marine environments: Effect of the marine zones, Corrosion Science 206 (2022) 110490.

Author Response File: Author Response.pdf

Reviewer 2 Report

Page 2 – Line 54. Observation: the Si composition (wt. %) is missing.

Page 2 – Line 80: Before the test, a potential of -1.2 VSCE is applied 80 for cathodic polarization to ensure the same surface test state. Question: How long was the potential applied?

Page 4 – Line 162; EIS is conducted after the OCP monitoring of 30 min.

Question: Why do the authors only make one single measurement of EIS at time equal to 30 minutes? Why don’t the authors analyse the evolution of the system with time? The information regarding to 30 minutes of immersion is not enough for making an analysis. The dependence of the temperature with the pH is only made for 30 ºC, but not with 20 ºC and 40 ºC, why?

Page 5 – Line 181: The equivalent circuits shown in Figure 4a and 4b are selected to fit EIS results under various conditions, and the fitting results are shown in Table 1.

Question: Why the authors select electrical equivalent circuits with two constants of time? It is well known that there is an induction associated with a corroding uncoated metal. This system exhibits a single time constant with induction. However, other authors use different equivalent circuits for modelling similar systems, but in this case, the inductive loop is clear for pHs 3.0 and 4.5.

Page 6 – Line 201: 3.1.3. Potentiodynamic polarization behavior analysis 201.

The discussion of this section is too qualitative. There is not an analysis of the obtained data, shown in table 2. The results for pH 8.2 at different temperatures are very similar for 30 ºC and 40 ºC and there is not a clear difference between the icorr for pH 6.0 an 8.2 at 30 ºC. The authors only make a theoretical discussion in the text.

 

Page 7 – Line 229: 3.2. Comparison of the corrosion behavior in salt spray and immersion test. 3.2.1. Corrosion rate.

Question: The test period for the Immersion test and salt spray test is set to 3, 7, 14 and 28 days, but there is only data for 14 days and 28 days. Why?

 

Page 12 – Line 314: 3.2.3. Corrosion process and mechanism.

Observation: There are two different systems under study, but only one mechanism. How can it be possible? The proposed mechanism is too theoretical and not supported by the set of experimental data.

 

Page 13 – Line 330: This process also can be explained by energy level diagram of the rust thermodynamics data.

Question: Can the authors develop this affirmation? There are good references about this fact, with the elementary thermodynamic data of various iron oxides, carbon oxides, hydrogen and water vapor that are used to calculate the changes of thermodynamic quantities such as enthalpy, entropy and Gibbs free energy of the redox reactions (1) to (10).

Author Response

1. Page 2 – Line 54. Observation: the Si composition (wt. %) is missing.

Response: Dear reviewer, thank you for your reminder. The Si content (1.18 wt.%) has been added in the revised manuscript (Line 78).

2. Page 2 – Line 80: Before the test, a potential of -1.2 VSCE is applied for cathodic polarization to ensure the same surface test state.

Question: How long was the potential applied?

Response: Dear reviewer, thank you for your suggestion. The pre-polarization at -1.2 V_SCE is kept for 1 min to ensure the same surface state. With long-term cathodic polarization, the surface alkalization could affect the polarization curves. Therefore, the duration of 1 min is used.

    This has been added in section 2.2 (Line 100) in the revised manuscript.

3. Page 4 – Line 162; EIS is conducted after the OCP monitoring of 30 min.

Question: Why do the authors only make one single measurement of EIS at time equal to 30 minutes? Why don’t the authors analyse the evolution of the system with time? The information regarding to 30 minutes of immersion is not enough for making an analysis. The dependence of the temperature with the pH is only made for 30 ºC, but not with 20 ºC and 40 ºC, why?sed.

Response: Dear reviewer, thank you for your constructive suggestion about the EIS. Indeed, the long-term monitoring of the EIS could provide insights for the evolution of the corrosion behavior. However, the main purpose of this manuscript is to study the effect of some parameters and compare the corrosion behavior in salt spray environments. Therefore, the long-term EIS tests are not considered. In our future work, this will be taken into account to monitor the long-term degradation behavior of metals.

In addition, the variables for the electrochemical tests include the temperature and pH. To reduce the number of the experiments, only one pH is considered when studying the effect of temperature, and only one temperature is considered when probing the effect of pH. This method is scientific because the effect of the pH or temperature on the corrosion process is similar under different temperature or pH, respectively. Therefore, only one temperature is considered.

The above explanation has been added in section 3.1.3 (Line 254-257) in the revised manuscript.

4. Page 5 – Line 181: The equivalent circuits shown in Figure 4a and 4b are selected to fit EIS results under various conditions, and the fitting results are shown in Table 1.

Question: Why the authors select electrical equivalent circuits with two constants of time? It is well known that there is an induction associated with a corroding uncoated metal. This system exhibits a single time constant with induction. However, other authors use different equivalent circuits for modelling similar systems, but in this case, the inductive loop is clear for pHs 3.0 and 4.5.

Response: Dear reviewer, thank you for your suggestion about the EIS data. Actually, during the 30 min short-term immersion, the rust layer has not completely covered the steel surface and the corrosion proceeds with the dissolution of the uncoated steel, yielding one time constant. In some cases, the induction loop is observed, which is attributed to the adsorption/desorption process in the acidic environment. However, at pH 4.5, a tail is also found within the low frequency range. After a close check, the values within this range are also higher than zero, which can not be ascribed to the induction loop. As reported in literature, it is resulted from the unsteady state of the system. According to the above analysis, the two equivalent circuits shown in Fig. R1 are used and the Nyquist diagrams are shown in Fig. R2.

    According to the above analysis, the EIS section is re-written in the revised manuscript, including the qualitative description and quantitative calculation. This can be found in section 3.1.2 (Line 173-215) in the revised manuscript.

Fig. R1. Equivalent circuit for the fitting of EIS data: (a) Model A for the spectrum at pH 3.0, (b) Model B for the other spectra.

 

Fig. R2. Nyquist diagrams of the 30CrMnSiNi2A steel in the ASW at 30 ºC with different pH (a) and at pH 8.2 with different temperatures (b).

5. Page 6 – Line 201: 3.1.3. Potentiodynamic polarization behavior analysis 201.

The discussion of this section is too qualitative. There is not an analysis of the obtained data, shown in table 2. The results for pH 8.2 at different temperatures are very similar for 30 ºC and 40 ºC and there is not a clear difference between the icorr for pH 6.0 an 8.2 at 30 ºC. The authors only make a theoretical discussion in the text.

Response: Dear reviewer, thank you for your advice. It is known that there are three strict prerequisites for the Tafel fitting, i.e., only one electrochemical reaction on the anodic and cathodic process, respectively, no protective film covered on the metal surface, and no diffusion for the cathodic process [1, 2]. However, the system in the present work is complex and the i vs. E is not a simple exponential. Therefore, Tafel fitting is abandoned and only the qualitative analysis is conducted.

    For the effect of pH, the description has been revised to the following form:

When the solution pH is 3.0, the corrosion potential is -0.559 V_SCE, which is much positive than that in the solutions with other pH values. The remarkable acceleration of cathodic reaction kinetics is responsible for the noble shift of the corrosion potential. At pH 4.5, the cathodic reaction kinetics is obviously retarded, and the current density decreases about two orders even though the pH only decreases 1.5. This may be attributed to the variation of the dominant reaction pathways. As reported by Davydov et al. [3], the hydrogen evolution reaction (HER) occurred via two basic ways: the reduction of H⁺ at pH < 4 and the reduction of H₂O at higher pH values. Therefore, it can be deduced that cathodic reaction is dominated by H⁺ reduction at pH 3.0 and H₂O reduction at pH 4.5. In addition, the oxygen reduction also participates the cathodic reactions when the solution pH is 4.5, yielding the diffusion-controlled behavior within the cathodic potential range. When the solution pH is increased from 4.5 to 8.2, cathodic current density decreases, and cathodic reaction is controlled by oxygen reduction at pH 8.2. As for the anodic branch, decreasing pH from 8.2 to 4.5 accelerates the anodic dissolution as indicated by the higher anodic current density at higher pH values.  The co-promotion of cathodic and anodic processes yields the unnoticeable change of the corrosion potential within this potential range.

As for the effect of temperature, the following analysis is added:

In the present work, it is perceived that the cure at 30 ℃ shows the most obvious diffusion-controlled behavior, revealing the balance of the above two effects. Even so, corrosion occurs faster at high temperatures. In addition, it should be noted that the effect of temperature on the corrosion behavior is similar at different temperatures, and the same criterion is also found for the effect of pH at different temperatures. Therefore, only one pH and one temperature are selected when studying the effect of variables.

The above revision can be found in section 3.1.3 (Line 219-240, Line 251-254) in the revised manuscript.

6. Page 7 – Line 229: 3.2. Comparison of the corrosion behavior in salt spray and immersion test. 3.2.1. Corrosion rate.

Question: The test period for the Immersion test and salt spray test is set to 3, 7, 14 and 28 days, but there is only data for 14 days and 28 days. Why?

Response: Dear reviewer, thank you for your reminder. In the present work, the samples after corrosion for 3 and 7 days are only used to take the macro-morphologies. After that, they are put back to the environmental chamber to continue the tests. After 14 and 28 days, the samples are rinsed with the rust-cleaning solution and then the corrosion rates are calculated.

    Two aspects are considered for this method. Firstly, the weight loss after corrosion for 3 and 7 days is not so high and the results are questionable. Secondly, the corrosion rate after exposure for a long time is enough to compare the differences between the tow environments and the short-term corrosion period is neglected.

7. Page 12 – Line 314: 3.2.3. Corrosion process and mechanism.

Observation: There are two different systems under study, but only one mechanism. How can it be possible? The proposed mechanism is too theoretical and not supported by the set of experimental data.

Response: Dear reviewer, thank you for your constructive comment. Indeed, in the original form, the effect of environment on the corrosion behavior is not discussed even though it is the emphasis of the present work. In the revised manuscript, this part is re-written with the following outlines.

(i) Firstly, the controlling factor is analyzed. In the two environments, the essential reason for the different corrosion behavior is the difference in the electrolyte presence form. This has been pointed out.

(ii) The corrosion rate difference in the two environments is discussed with considering the oxygen availability.

(iii) The differences in corrosion products are analyzed with providing the reaction pathways and the reason for the phase content differences in different environments.

(iv) The differences in corrosion morphologies after removing corrosion products are discussed.

    The above revision can be found in section 3.2.3 (Line 345-393) in the revised manuscript.

8. Page 13 – Line 330: This process also can be explained by energy level diagram of the rust thermodynamics data.

Question: Can the authors develop this affirmation? There are good references about this fact, with the elementary thermodynamic data of various iron oxides, carbon oxides, hydrogen and water vapor that are used to calculate the changes of thermodynamic quantities such as enthalpy, entropy and Gibbs free energy of the redox reactions (1) to (10).

Response: Dear reviewer, thank you for your professional comment. Indeed, some reference give the thermodynamic data of the redox reactions shown in the present work. In the revised version, the analysis emphasis is put on the effect of electrolyte presence form. The effect of the electrolyte presence form on the corrosion rate, corrosion product, and corrosion morphologies are discussed (as described in the comment 7). Therefore, the thermodynamic data of the reactions are not considered. In our future works, the detailed calculation will be considered. Thank you once again for your advice.

    The analysis about the corrosion product formation can be found in section 3.2.3 (Lin 358-372) in the revised manuscript.

References

[1] H. Pan, K. Pang, F. Cui, F. Ge, C. Man, X. Wang, Z. Cui, Effect of alloyed Sr on the microstructure and corrosion behavior of biodegradable Mg-Zn-Mn alloy in Hanks’ solution, Corrosion Science 157 (2019) 420-437.

[2] M.A. Amin, K.F. Khaled, S.A. Fadl-Allah, Testing validity of the Tafel extrapolation method for monitoring corrosion of cold rolled steel in HCl solutions – Experimental and theoretical studies, Corrosion Science 52 (2010) 140-151.

[3] A. Davydov, K.V. Rybalka, L.A. Beketaeva, G.R. Engelhardt, P. Jayaweera, D.D. Macdonald, The kinetics of hydrogen evolution and oxygen reduction on Alloy 22, Corrosion Science 47 (2005) 195-215.

 

 

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript is devoted to study of the corrosion behavior of 30CrMnSiNi2A in simulated marine environment and can be published after a minor revision. There are a number of points that authors should take into account.

i. Table 1. What is R_f, CPE_f? In the text R_a, CPE_a are present (183 line), but the values of R_а, CPE_а are absent in Table 1.

Why is R_ct in a medium with pH=8.2 at 30^o higher than at 20^o, and at 40^o lower by 3 orders of magnitude. Doesn't an increase in temperature contribute to a decrease in R_ct?

 

ii. Page 14, Lines 368-370: "The SCC of 30CrMnSiNi2A in ASW is related to 368 anodic dissolution.  Due to pitting corrosion on the surface of the sample, the stress in the 369 bottom of the pit is concentrated, and the crack initiation is promoted" 

However, the authors write earlier : Lines 302-303: "No pit is observed on 30CrMnSiNi2A after 14 and 28 days of corrosion in immersion and salt spray environment, and uniform corrosion is observed." How do you explain this contradiction?

 

iii. Lines 385-391: "Meanwhile, the acidic environment beneath the corrosion product layer facilitates the hydrogen evolution reaction which can promote the hydrogen related failure processes. Stress corrosion is the anodic dissolution mechanism of ultra high strength steel in alkaline environment, but hydrogen embrittlement (HE) mechnism may also exist. Hydrogen atoms are preferentially concentrated in and around the corrosion pits that have been formed, and partial H atoms are permeated into lattice gaps or other crystal defects, resulting in local embrittle and crack initiation".

However, the authors write earlier: Lines 203-204: "The anodic curve shows active dissolution, and the cathodic process is controlled by oxygen reduction and water reduction". If the cathodic process is controlled by the reduction of oxygen, then an alkaline environment arises there, and not acidic. Where will the hydrogen atoms come from?

In addition, you yourself wrote in the lines 302-303:"No pit is observed on 30CrMnSiNi2A after 14 and 28 days of corrosion in immersion and salt spray environment, and uniform corrosion is observed." Authors should explain the inconsistency.

 

Comments for author File: Comments.pdf

Author Response

1. Table 1. What is R_f, CPE_f? In the text R_a, CPE_a are present (183 line), but the values of R_а, CPE_а are absent in Table 1.

Response: Dear reviewer, thank you for your reminder. We are sorry for the wrong presentation of the fitting parameters, In the revised manuscript, the equivalent circuits are changed and the EIS data is re-fitted. The change of the circuit is based on the physical characteristics of the interfacial system of the steel/electrolyte. It is associated with the dissolution of the uncoated steel, which exhibits one time constant. At pH 3.0, an inductive loop is observed because of the adsorption/desorption behavior. This section has been revised as follows:

EIS is conducted after the OCP monitoring for 30 min. Figure 3a shows the Nyquist plots in artificial seawater at 30 ℃ with different pH values. When the pH is 6.0 and 8.2, the impedance spectrum shows a capacitive reactance arc, while when the pH is 4.5, a tail is observed within the low frequency range. However, the impedance values are all within the first quadrant and it thus this tail is not the inductive loop. It can be attributed to the unsteady state of the system, which induces the low frequency disturbance [1]. At pH 3.0, an inductive tail is perceived within the low frequency range, which can be ascribed to the adsorption/desorption processes occurring in acidic environment [2]. Meanwhile, the diameter of the capacitive loops decreases with decreasing solution pH.

Fig. 3b shows the Nyquist diagrams in artificial seawater at pH 8.2 with different temperatures. All the spectra exhibit depressed semicircles without inductive or diffusion tails, suggesting the capacitive behavior of the material/electrolyte interface. The diameter of the capacitive loop at 30 ℃ is slightly higher than that at 20 ℃, while it decreases dramatically as the temperature increases to 40 ℃.

 

Figure 3. Nyquist plot of 30CrMnSiNi2A in artificial seawater at 30 ºC with different pH (a) and at pH 8.2 with different temperatures (b).

Fig. 4 shows the equivalent circuits used for fitting the EIS data and the fitting results are included in Fig. 3 as solid lines. As the pre-immersion time of the EIS test is only 30 min, it is speculated that the sample surface has not been covered by the rust layer completely. Therefore, the capacitive loop with one time constant is used, denoting the charge transfer process occurring at the uncoated steel surface (Fig. 4a). At pH 3.2, the addition inductive elements are supplemented to describe the adsorption/desorption behavior. In the circuits, R_s is the solution resistance, R_ct is the charge transfer resistance, CPE_dl is the double layer capacitance, and R_L and L represent the inductance. Due to the non-uniformity of the electrode surface, the capacitive arc will deviate from the regular semicircle due to the dispersion effect, so the constant phase element (CPE) is used instead of the pure capacitance (C) [3].

   

Figure 4. Equivalent circuit for the fitting of EIS data: (a) Model A for the spectrum at pH 3.0, (b) Model B for the other spectra.

    The above revision can be found in section 3.1.2 (Line 173-209) in the revised manuscript.

 

2. Why is R_ct in a medium with pH=8.2 at 30° higher than at 20°, and at 40° lower by 3 orders of magnitude. Doesn't an increase in temperature contribute to a decrease in R_ct?

Response: Dear reviewer, we have re-checked the EIS data and the spectra measured at 30 ℃ is indeed slightly higher than that obtained at 20 ℃. The increase of the charge transfer resistance with increasing temperature from 20 to 30 ℃ may be attributed to two aspects. On one hand, the increase of temperature decreases the oxygen concentration in the solution, especially at the electrode/solution interface, thus decelerating the corrosion process [4]. On the other hand, the increase of temperature facilitates the local deposition of protective corrosion products or aragonite which impedes the attack of Cl^-. At 40 ℃, the above tow processes are overshadowed by the increased dissolution process and thus the charge transfer resistance decreases.

    The above description can be found in section 3.1.2 (Line 201-209) in the revised manuscript.

3. Page 14, Lines 368-370: "The SCC of 30CrMnSiNi2A in ASW is related to anodic dissolution. Due to pitting corrosion on the surface of the sample, the stress in the bottom of the pit is concentrated, and the crack initiation is promoted"

However, the authors write earlier: Lines 302-303: "No pit is observed on 30CrMnSiNi2A after 14 and 28 days of corrosion in immersion and salt spray environment, and uniform corrosion is observed." How do you explain this contradiction?

Response: Dear reviewer, thank you for your suggestion. Indeed, Fig. 12a and b shows that uniform corrosion occurs on 30CrMnSiNi2A steel in artificial seawater after immersion for 14 and 28 days. However, the immersion time of the SSRT tests only lasts for less than 72 hours, which is still in the initial corrosion period of the steel. Lu et al. [5] reported the corrosion evolution processes of low alloy steel in artificial seawater and suggested that corrosion evolved from pitting corrosion to uniform corrosion. Liu et al. [6] also found the pitting corrosion in the initial period of the low alloy steel. The macro-morphologies shown in Fig. 7a reveal that obvious localized corrosion occurs after immersion for 72 hours, which is close to the duration of the SSRT test. Therefore, it can be speculated that the pitting corrosion occurs and promotes the crack initiation during the SCC process. The absence of pitting corrosion after 14 and 28 days immersion does not contradict with the presence of pitting corrosion during the SSRT test. In addition, the SCC mechanism is re-analyzed according to the next comment.

    The above analysis has been added in section 3.2.2 (Line 278) and section 3.3.3 (Line 427-441) in the revised manuscript.

4. Lines 385-391: "Meanwhile, the acidic environment beneath the corrosion product layer facilitates the hydrogen evolution reaction which can promote the hydrogen related failure processes. Stress corrosion is the anodic dissolution mechanism of ultra high strength steel in alkaline environment, but hydrogen embrittlement (HE) mechnism may also exist. Hydrogen atoms are preferentially concentrated in and around the corrosion pits that have been formed, and partial H atoms are permeated into lattice gaps or other crystal defects, resulting in local embrittle and crack initiation".

However, the authors write earlier: Lines 203-204: "The anodic curve shows active dissolution, and the cathodic process is controlled by oxygen reduction and water reduction". If the cathodic process is controlled by the reduction of oxygen, then an alkaline environment arises there, and not acidic. Where will the hydrogen atoms come from?

In addition, you yourself wrote in the lines 302-303:"No pit is observed on 30CrMnSiNi2A after 14 and 28 days of corrosion in immersion and salt spray environment, and uniform corrosion is observed." Authors should explain the inconsistency.

Response: Dear reviewer, thank you for your professional comment about our manuscript. Indeed, the analysis of the hydrogen related mechanism is doubtful to support the SCC mechanism. Firstly, the cathodic reactions are dominated by the oxygen reduction reaction in the ASW, which contributes to the formation of local alkaline environment. Even so, the local acidic area can be found in some cases where thick and cracked rust layer is formed. This local occluded cell can generate the environment with a low pH and high concentration of Cl^- and facilitate the formation of H_ads. Huang et al. [7] demonstrated that pH beneath the rust layer could be lower than 4.5 and the hydrogen permeation current could be detected immediately after the sample surface was wet [8].

Even so, the hydrogen effect can not be taken as the factor that affects the SCC behavior in the present work. As indicated in Fig. 13, the SCC susceptibility I_δ calculated by elongation loss is lower than 5%, while that determined by reduction in area I_φ attains 25%. The I_δ, which mainly characterizes the dislocation and deformation of a specimen, is influenced by hydrogen content inside the steel [9]. Instead, I_φ is mainly affected by cracks and defects in the steel as it reflects the sensitivity of SCC at crack propagation stage [10]. The low I_δ suggests that hydrogen paly a negligible role in the SCC degradation, while anodic dissolution, which provides the defects, controls the deterioration process.

In addition, the effect of pitting corrosion is responded in the previous comment, which is not contradictory.

    The above analysis can be found in section 3.3.3 (Line 427-442) in the revised manuscript.

References

[1] R. Ren, S. Zhang, X. Pang, K. Gao, A novel observation of the interaction between the macroelastic stress and electrochemical corrosion of low carbon steel in 3.5 wt% NaCl solution, Electrochimica Acta 85 (2012) 283-294.

[2] Z. Cui, Z. Liu, L. Wang, H. Ma, C. Du, X. Li, X. Wang, Effect of pH value on the electrochemical and stress corrosion cracking behavior of X70 pipeline steel in the dilute bicarbonate solutions, Journal of Materials Engineering and Performance 24 (2015) 4400-4408.

[3] L. Wang, J. Liang, H. Li, L. Cheng, Z. Cui, Quantitative study of the corrosion evolution and stress corrosion cracking of high strength aluminum alloys in solution and thin electrolyte layer containing Cl, Corrosion Science 178 (2021) 109076.

[4] M. Pour-Ghaz, O.B. Isgor, P. Ghods, The effect of temperature on the corrosion of steel in concrete. Part 1: Simulated polarization resistance tests and model development, Corrosion Science 51 (2009) 415-425.

[5] Q. Lu, L. Wang, J. Xin, H. Tian, X. Wang, Z. Cui, Corrosion evolution and stress corrosion cracking of E690 steel for marine construction in artificial seawater under potentiostatic anodic polarization, Construction and Building Materials 238 (2020) 117763.

[6] Z.Y. Liu, W.K. Hao, W. Wu, H. Luo, X.G. Li, Fundamental investigation of stress corrosion cracking of E690 steel in simulated marine thin electrolyte layer, Corrosion Science 148 (2019) 388-396.

[7] Y. Huang, Y. Zhu, Hydrogen ion reduction in the process of iron rusting, Corrosion Science 47 (2005) 1545-1554.

[8] T. Tsuru, Y. Huang, M.R. Ali, A. Nishikata, Hydrogen entry into steel during atmospheric corrosion process, Corrosion Science 47 (2005) 2431-2440.

[9] D. Hardie, E.A. Charles, A.H. Lopez, Hydrogen embrittlement of high strength pipeline steels, Corrosion Science 48 (2006) 4378-4385.

[10] Z.Y. Liu, X.Z. Wang, C.W. Du, J.K. Li, X.G. Li, Effect of hydrogen-induced plasticity on the stress corrosion cracking of X70 pipeline steel in simulated soil environments, Materials Science and Engineering: A 658 (2016) 348-354.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear author, the revised manuscript is in good shape now after considering my comments

Author Response

Dear reviewer, Thank you for your advice to improve this manuscript.