Hydrogen Embrittlement Susceptibility of Corrosion-Resistant Spring Rod Used in High-Speed Railway
Round 1
Reviewer 1 Report
The manuscript studies the hydrogen embrittlement susceptibility of corrosion-resistant spring steel used in high-speed railway. The manuscript has serious flaws and could not be published in its current form:
1- The English language of the manuscript is not appropriate, and should be improved with the help of a native English speaker who is an expert in the field.
2- The story of the paper is not in good order and the different parts of the paper are not connected very well.
3- Most of the reported conclusions are known even without testing from the other references. however, there are some interesting results that can be analysed and discussed.
4- Please add the reference for equation (7). If you want to measure the plasticity by this calculation, please explain how it can be related to the work hardening (UTS-YS) from your stress-strain curve.
5- In Table 1, please add the exact composition, not the range of composition coming from the standard. The chemical compositions should be reported based on the chemical analysis results.
6- There are many punctuality problems in the manuscript.
7- There is no explanation for the trapping behaviour of the Nb as a carbide former.
8- The title includes the corrosion-resistant spring, however, it is not clear why it was used. Please remove that and have a better title that is representative of the manuscript.
9- Please add more references about the hydrogen embrittlement in martensitic steels. Why there is hydrogen embrittlement in the material and what are the hydrogen embrittlement mechanisms in martensitic steels? You should improve the introduction of the manuscript. Please cite the following important reference about the hydrogen embrittlement in martensitic steels. https://doi.org/10.1016/j.vacuum.2022.111187, https://doi.org/10.2355/isijinternational.52.198
10- The mechanisms of hydrogen embrittlement based on the fracture surface observations should be explained and extended carefully in the discussion part to reveal the role of Nb addition.
Author Response
Point 1: The English language of the manuscript is not appropriate, and should be improved with the help of a native English speaker who is an expert in the field.
Response 1:The English language of the manuscript has been adjusted and improved in tense, grammar and word use.
Point 2: The story of the paper is not in good order and the different parts of the paper are not connected very well.
Response 2:Added experimental steps to the Abstract,It can make the logic of the manuscript clearer.As shown:For this study, the following steps were performed:Firstly, the material composition has been designed, and the experimental materials that meet the experimental design have been prepared according to the corresponding deformation and heat treatment process; Secondly, the experimental materials were charged with hydrogen; Finally, conventional tensile testing, slow tensile testing and fracture morphology testing were carried out; On the other hand, hydrogen permeation experiment is carried out for materials.
Point 3: Most of the reported conclusions are known even without testing from the other references. however, there are some interesting results that can be analyzed and discussed.
Response 3:In view of the hydrogen embrittlement problem of conventional spring steel, many related studies have been carried out, and the above research conclusions have been taken as a reference in this paper. However, the hydrogen embrittlement problem of elastic elements of railway spring rod has not been reported so far. Through this study, it has been verified that the corrosion resistance and hydrogen embrittlement resistance of this special part under special working conditions have similar conclusions with the original research. Therefore, the conclusions in this manuscript have always been the direction of the previous researchers' conclusions, and even have similarities, which can be used for reference to improve the performance of this part.
Point 4: Please add the reference for equation (7). If you want to measure the plasticity by this calculation, please explain how it can be related to the work hardening (UTS-YS) from your stress-strain curve.
Response 4: The corrosion resistance index (I) is quoted from the following references：1.ISO 5952-2019 steel sheet , hot-rolled, of structural quality with improved atmospheric corrosion resistance(Annex A A.3.2) ;2.ASTM G101-04 (Reapproved 2010) standard guide for estimating the atmospheric corrosion resistance of low alloy steels( 6.3.1.1 Legault-Leckie equation)
It has been added to the manuscript.
Point 5: In Table 1, please add the exact composition, not the range of composition coming from the standard. The chemical compositions should be reported based on the chemical analysis results.
Response 5:The ingredients in Table 1 have been modified, and a narrow range of ingredients has been added.
Point 6: There are many punctuality problems in the manuscript.
Response 6:The punctuality problems has been modified
Point 7: There is no explanation for the trapping behaviour of the Nb as a carbide former.
Response 7:On the research of hydrogen trap and hydrogen capture, many scholars have carried out relevant research before, and have formed mature theories, which have been successfully applied and verified in many steel products. This manuscript belongs to the research on application. On the basis of previous researchers' research results, the application type research on hydrogen embrittlement resistance of special parts (i.e. railway spring rod) is carried out. Therefore, the focus of this manuscript is to apply the mature theory (or micro aspect) to specific products. Therefore, the micro precipitates are hydrogen trapped without too much characterization,There is no explanation for the trapping behaviour of the Nb as a carbide former in the manuscript. However, I think the comments of the judges are of great benefit to the manuscript, so the content of this part of references has been added to the manuscript.
References 1:SI Y,TANG Y S,ZHOU X,et a1．Research Progress of Microalloy Elements on Hydrogen-Induced Delayed Cracking in High Strength Martensitie Steels[J].Automobile Technology＆Material，2022(6)：16-26．
The development of high strength martensitic steels can control the precipitation of C,N and other nano compounds by optimizing the composition design of micro alloy and matching reasonable heat treatment，and form a benign“hydrogen trap”,thus reducing the risk of delayed cracking caused by hydrogen in the process of application. This paper compared the precipitation forms and hydrogen trapping sites of Ti,Nb and Cu alloy elements in martensitic steels under different heat treatment processes,and evaluated the hydrogen trapping ability of precipitated phases in high strength martensitic steels.The results show that the hydrogen capture capacity is ranked as follows:NbC>TiC>grain boundary>e-Cu>dislocation,and the compound addition of microalloying elements can play a better anti-hydrogen embrittlement effect．
References 2：SHIN J H，KONG B S，EOM H J,et a1.Dynamic evolution of nanosized NbC precipitates in austenite matrix during deformation and its contribution to strengthening [J].Materials Science and Engineering:A,2021(806): 140816．
References 3:SHI R,MA Y,WANG Z,et a1.Atomic-scale investigation of deep hydrogen trapping in NbC／αFe semi-coherent interfaces[J].Acta Materialia,2020(200):686-698．
Point 8: The title includes the corrosion-resistant spring, however, it is not clear why it was used. Please remove that and have a better title that is representative of the manuscript.
Response 8:The title of the manuscript involving spring steel is really not targeted, and the comments of the judges have been changed to spring rod
Point 9: Please add more references about the hydrogen embrittlement in martensitic steels. Why there is hydrogen embrittlement in the material and what are the hydrogen embrittlement mechanisms in martensitic steels? You should improve the introduction of the manuscript. Please cite the following important reference about the hydrogen embrittlement in martensitic steels. https://doi.org/10.1016/j.vacuum.2022.111187, https://doi.org/10.2355/isijinternational.52.198
Response 9:After referring to the above two references, the revised version of the manuscript has been revised.
Masoud Moshtaghi and Tomoki DOSHIDA et al. have conducted relevant research to show that:The joint effect of temperature and strain rate on hydrogen embrittlement properties of martensitic steel was investigated. At 50 ◦C, the elongation loss first increases and then, decreases with decreasing the strain rate. It was firstly reported that at the low strain rates, hydrogen embrittlement susceptibility was mitigated by temperature due to an increase in the hydrogen effusion to the surface of the material and the release of a significant amount of hydrogen before the yield point by temperature effect. At 25 ◦C, elongation loss increase with decreasing the strain rate, since in lower strain rates, the hydrogen can interact with mobile dislocations, which finally leads to H-induced fracture. The specimen fractured under elastic stress in the presence of hydrogen macroscopically showed brittle fracture without necking. Whereas fracture surface was attributed to localized plastic deformation, since the morphology of the microscopic fracture surface was mostly quasi-cleavage fracture. The increased lattice defects in the near-fracture area were subsequently removed by annealing at 200°C. The mean positron annihilation lifetime measured with the PPMA for a fractured specimen was longer in the near-fracture area than in other areas. Thus, the most probable reason for the increase in the amount of lattice defects can be ascribed to an increase in the amount of vacancies or vacancy clusters. Regarding hydrogen embrittlement involving microscopic plastic deformation, the localized enhanced vacancies due to interactions between dislocations and hydrogen under elastic stress directly caused ductility loss, because ductility loss occurred even though hydrogen was completely removed by degassing before the tensile test. Besides hydrogen content and applied stress, the time of formation and accumulation of vacancies are also concluded to be important factors causing hydrogen embrittlement.[26,27].There is no report on the application of the above research results to the Railway spring rod.
Point 10: The mechanisms of hydrogen embrittlement based on the fracture surface observations should be explained and extended carefully in the discussion part to reveal the role of Nb addition.
Response 10:same as Point 7
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Dear authors,
Hydrogen embrittlement is a general problem in many applications. Therefore, it is very important to improve materials resistance against hydrogen systematically. If you cannot prohibit the hydrogen to penetrate a material, the idea to trap the hydrogen is consequent. Thereby, adding alloying elements to precipitate hydrogen traps during a heat treatment as described in the paper by NbC nanoprecipitates is a promising approach.
However, here are the major concerns about the paper:
- The improvement seems marginal, at least at the longest charging time.
- There is no proof, that the NbC nano-precipitates exist
This means that neither the hypothesis of improvement is validated nor the mechanism to get this.
To the first point: In figure 3 there a no error bars provided. Therefore, it cannot be evaluated if this is a real effect. There is no information, how many specimens have been tested for each charging time to check the reproducibility. In the discussion, this figure is described as three stages of changes. In my view this is just an exponential decrease of ductility. If you would take charging times in between and test more specimens, this might be clearly visible. You should also try to fit an exponential decrease in these curves. And finally: For the longest charging time, there is no difference anymore. However, the problem for the spring steel as used for railway tracks is the long-time resistance. Even if there may be any improvement for the short times, this will not solve the problem during service.
And the fracture surfaces are not related to the mechanical test results: For material B, the strongest differences are visible between 1.5 and 2 hours charging. However, in the mechanical test, the strongest differences are found between no charging and 0.5 hours. To evaluate this quantitatively, you should measure the percentage of dimple fracture and that of cleavage fracture. This should be done for a representative area, which is much larger than the areas shown in the figures (The magnification of the figures is fine, however, it can not be estimated, if this is representative. But the percentage would give this information.)
And: Why do you use normal strain rate tensile tests for the non-charged but slow strain rate tests for the charged specimens. This makes the results incomparable.
To the second point: You do not show any TEM-image to prove, that you have NbC nanoprecipitates ion material B and that in material A these are missing. Or any other influence on the microstructure development during the heat treatment as assumed in your discussion. Therefore, micrographs are mandatory.
Minor concerns:
Lines 94-98: several times “stain rate” instead of “strain rate”
Fig. 2: Is the specimen identical with the cathode? Which is the nickel-plated side?
Lines 152-153: Check the English syntax
Lines 237-244: Whole paragraph not organized very well.
Fig: 7: You should use the same scale for both diagrams. Then the differences would be clearly visible.
Best regards
Your reviewer
Author Response
Point 1:The improvement seems marginal, at least at the longest charging time.
Response 1:In the process, the experimental results show significant differences under different parameters. Under the condition of tending to infinity, the two tend to be consistent.So,the improvement seems marginal, at the longest charging time.
Point 2:There is no proof, that the NbC nano-precipitates exist。This means that neither the hypothesis of improvement is validated nor the mechanism to get this.To the second point: You do not show any TEM-image to prove, that you have NbC nanoprecipitates ion material B and that in material A these are missing. Or any other influence on the microstructure development during the heat treatment as assumed in your discussion. Therefore, micrographs are mandatory.
Response 2:On the research of hydrogen trap and hydrogen capture, many scholars have carried out relevant research before, and have formed mature theories, which have been successfully applied and verified in many steel products. This manuscript belongs to the research on application. On the basis of previous researchers' research results, the application type research on hydrogen embrittlement resistance of special parts (i.e. railway spring rod) is carried out. Therefore, the focus of this manuscript is to apply the mature theory (or micro aspect) to specific products. Therefore, the micro precipitates are hydrogen trapped without too much characterization,There is no explanation for the trapping behaviour of the Nb as a carbide former in the manuscript. However, I think the comments of the judges are of great benefit to the manuscript, so the content of this part of references has been added to the manuscript.
References 1:SI Y,TANG Y S,ZHOU X,et a1．Research Progress of Microalloy Elements on Hydrogen-Induced Delayed Cracking in High Strength Martensitie Steels[J].Automobile Technology＆Material，2022(6)：16-26．
The development of high strength martensitic steels can control the precipitation of C,N and other nano compounds by optimizing the composition design of micro alloy and matching reasonable heat treatment，and form a benign“hydrogen trap”,thus reducing the risk of delayed cracking caused by hydrogen in the process of application. This paper compared the precipitation forms and hydrogen trapping sites of Ti,Nb and Cu alloy elements in martensitic steels under different heat treatment processes,and evaluated the hydrogen trapping ability of precipitated phases in high strength martensitic steels.The results show that the hydrogen capture capacity is ranked as follows:NbC>TiC>grain boundary>e-Cu>dislocation,and the compound addition of microalloying elements can play a better anti-hydrogen embrittlement effect．
References 2：SHIN J H，KONG B S，EOM H J,et a1.Dynamic evolution of nanosized NbC precipitates in austenite matrix during deformation and its contribution to strengthening [J].Materials Science and Engineering:A,2021(806): 140816．
References 3:SHI R,MA Y,WANG Z,et a1.Atomic-scale investigation of deep hydrogen trapping in NbC／αFe semi-coherent interfaces[J].Acta Materialia,2020(200):686-698．
Point 3:Lines 94-98: several times “stain rate” instead of “strain rate”
Response 3:This error was caused by a clerical error and has been corrected.
Point 4:Fig. 2:Is the specimen identical with the cathode? Which is the nickel-plated side?
Response 4:The sample in the hydrogen charging electrolytic cell is connected with the cathode of the constant current source as the cathode; In the hydrogen releasing electrolytic cell, the sample is connected to the positive pole of the potentiostat as the anode; The contact surface between the sample and the hydrogen release cell on the right side is nickel plated.
Point 5:Lines 152-153: Check the English syntax
Response 5:The error has been corrected according to the expert's opinion.
Point 6:Lines 237-244: Whole paragraph not organized very well.
Response 6:This paragraph has been reorganized and references have been added.
Point 7:Fig: 7: You should use the same scale for both diagrams. Then the differences would be clearly visible.
Response 7:The error has been corrected according to the expert's opinion.
Author Response File: Author Response.pdf
Reviewer 3 Report
The article Hydrogen Embrittlement Susceptibility of Corrosion-resistant Spring Steel Used in High Speed Railway is devoted to the study of the mechanisms and processes of corrosion in 60Si2Mn springs that have been improved by adding chromium, copper and nickel to them in order to create a multi-component composite alloy. This direction is quite promising and interesting, since it considers one of the most important issues in modern materials science related to determining the resistance of materials to external influences, including corrosion, as well as hydrogen embrittlement processes. This article is quite new and contains a number of experimental data, as well as their interpretation. The material of the article corresponds to the subject of the declared journal, and the article itself is well written and maintains a balance between experimental data and their interpretation. The article can be accepted for publication after the authors answer a number of questions that have arisen during its reading and analysis.
1. Firstly, the authors should provide in the abstract data on how exactly the experiments on hydrogen enrichment of the selected objects of study were carried out, as well as how exactly the multicomponent composite alloy was created.
2. Choice of the watch range for hydrogen enrichment The authors should explain the reason for such a condition of the experiments, and how the hydrogen enrichment processes were evaluated.
3. The presented SEM images of the surface of the samples require a better representation, indicating the observed changes in the form of pores or defective inclusions.
4. The data presented in Table 3 require correction and the introduction of measurement errors, so that it is clear that such experiments were carried out more than once. The authors are also invited to compare their data with other works in this direction.
5. Authors are encouraged to provide data on structural changes in samples as a result of hydrogenation and degradation.
6. The conclusion needs to be revised, since it is just a listing of facts, and not a presentation of conclusions and main conclusions.
Author Response
Point 1: Firstly, the authors should provide in the abstract data on how exactly the experiments on hydrogen enrichment of the selected objects of study were carried out, as well as how exactly the multicomponent composite alloy was created.
Response 1:In the "2. Materials and Methods" and "2.3. Hydrogen permeation test" link of the manuscript, the composition and process of the experimental materials have been described.As shown below:
The experimental sample materials are corrosion-resistant 60Si2Mn NH spring steel (referred to as material A) and conventional 60Si2Mn spring steel (referred to as material B). Their chemical compositions are listed in Table 1. Based on material B, the atmospheric corrosion of material A is improved by adding elements such as Cu, Ni, Cr that can improve the corrosion resistance of the material. And the trace Nb is added forming the second phase of NbC to refine the grains. The relevant samples are prepared by hot rolling and heat treatment. The heat treatment process of material A is 960℃ for 0.5h, 847℃ - 860℃ for oil quenching, 485℃ for tempering, and 1.5h for holding; The heat treatment process of material B is 960℃ for 0.5h, 860℃ - 880℃ for oil quenching, 440℃ for tempering and 1.5h for holding.
Point 2: Choice of the watch range for hydrogen enrichment The authors should explain the reason for such a condition of the experiments, and how the hydrogen enrichment processes were evaluated.
Response 2:A constant current is applied to the hydrogen charging electrolytic cell, and hydrogen ions are produced by electrolysis of water in the solution. The sample is connected to the cathode of the constant current source as the cathode. The hydrogen ion moves towards the cathode, and the electrochemical reaction takes place at the interface between the electrolyte and the cathode, that is, the electrons on the surface of the steel plate become hydrogen atoms, and the hydrogen atoms diffuse to the nickel plated side through the interior of the steel plate. Electrode reaction of hydrogen charging electrolytic cell is as follows:
Cathodic reaction：4H++4e-=4H=2H2↑
Anodic reaction：4OH--4e-=O2↑+2H2O
In the hydrogen releasing electrolytic cell, the sample is connected to the positive pole of the potentiostat as the anode. Apply a constant potential of 0.2~0.3V, and when the residual anode current drops to steady (less than 2 μ A/cm2), turn on the hydrogen charging current and keep it constant. When the hydrogen atom does not diffuse to the surface of the steel plate anode, a stable circuit is formed by the potentiostat and the hydrogen releasing electrolytic cell, and a stable ground state current is generated. When the hydrogen atom diffuses to the anode surface through the steel plate, the hydrogen atom loses electrons and becomes hydrogen ions, which will generate a current increment based on the ground state current, which will be measured by the instrument and converted into hydrogen permeation flux J until it reaches stability. Electrode reaction of hydrogen releasing electrolytic cell is as follows:
Cathodic reaction：4H++4e-=4H=2H2↑
Anodic reaction：4OH--4e-=O2↑+2H2O
Point 3: The presented SEM images of the surface of the samples require a better representation, indicating the observed changes in the form of pores or defective inclusions.
Response 3:The experimental equipment used can only take 4000 times pictures at most, and the 4000 times pictures are somewhat blurred after being taken, so only 2000 times pictures can be selected.
Point 4: The data presented in Table 3 require correction and the introduction of measurement errors, so that it is clear that such experiments were carried out more than once. The authors are also invited to compare their data with other works in this direction.
Response 4:The hydrogen diffusion efficiency coefficient (Deff) and other parameters are calculated by formula. The main experimental data used is the steady state current density iss. The current density has reached the steady state, so the error is extremely small; In the hydrogen permeation experiment, the current stability is easily affected by the external environment, so the data obtained by using the same device are more comparable.
Point 5: Authors are encouraged to provide data on structural changes in samples as a result of hydrogenation and degradation.
Response 5:This manuscript belongs to applied research. At present, there is no much research on microstructure. The reasons are as follows. However, I accept the experts' opinions. In the next step, the work will continue to be in-depth, and the verification of microstructure characterization will be carried out.
On the research of hydrogen trap and hydrogen capture, many scholars have carried out relevant research before, and have formed mature theories, which have been successfully applied and verified in many steel products. This manuscript belongs to the research on application. On the basis of previous researchers' research results, the application type research on hydrogen embrittlement resistance of special parts (i.e. railway spring rod) is carried out. Therefore, the focus of this manuscript is to apply the mature theory (or micro aspect) to specific products. Therefore, the micro precipitates are hydrogen trapped without too much characterization,There is no explanation for the trapping behaviour of the Nb as a carbide former in the manuscript. However, I think the comments of the judges are of great benefit to the manuscript, so the content of this part of references has been added to the manuscript.
Masoud Moshtaghi and Tomoki DOSHIDA et al. have conducted relevant research to show that:The joint effect of temperature and strain rate on hydrogen embrittlement properties of martensitic steel was investigated. At 50 ◦C, the elongation loss first increases and then, decreases with decreasing the strain rate. It was firstly reported that at the low strain rates, hydrogen embrittlement susceptibility was mitigated by temperature due to an increase in the hydrogen effusion to the surface of the material and the release of a significant amount of hydrogen before the yield point by temperature effect. At 25 ◦C, elongation loss increase with decreasing the strain rate, since in lower strain rates, the hydrogen can interact with mobile dislocations, which finally leads to H-induced fracture. The specimen fractured under elastic stress in the presence of hydrogen macroscopically showed brittle fracture without necking. Whereas fracture surface was attributed to localized plastic deformation, since the morphology of the microscopic fracture surface was mostly quasi-cleavage fracture. The increased lattice defects in the near-fracture area were subsequently removed by annealing at 200°C. The mean positron annihilation lifetime measured with the PPMA for a fractured specimen was longer in the near-fracture area than in other areas. Thus, the most probable reason for the increase in the amount of lattice defects can be ascribed to an increase in the amount of vacancies or vacancy clusters. Regarding hydrogen embrittlement involving microscopic plastic deformation, the localized enhanced vacancies due to interactions between dislocations and hydrogen under elastic stress directly caused ductility loss, because ductility loss occurred even though hydrogen was completely removed by degassing before the tensile test. Besides hydrogen content and applied stress, the time of formation and accumulation of vacancies are also concluded to be important factors causing hydrogen embrittlement.[26,27].There is no report on the application of the above research results to the Railway spring rod.
Point 6: The conclusion needs to be revised, since it is just a listing of facts, and not a presentation of conclusions and main conclusions.
Response 6:According to the experts' suggestions, the conclusions are modified accordingly.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The revised manuscript seems much bettert han the previous version and the authors could answer the comments. I recommend publication with one round of English language ans style revision.
Reviewer 3 Report
The authors answered all the questions, the article can be accepted for publication.
