Duplex and Superduplex Stainless Steels: Microstructure and Property Evolution by Surface Modification Processes
Round 1
Reviewer 1 Report
The paper is classified as a “Review”. However, Authors provide some results of their own study. Unfortunately, the results are incomplete and the discussion is irrelevant and not reliable. The review part does provide any important information. Other comments are listed below.
The image in Fig. 2 is very low quality. It could easily redraw.
“Hence, the main differences observed between austenite and ferrite structures regarding nitriding process are the result of ...”
Comment: “are the results“ ?
“...plasma nitride specimens...”
Comment: “plasma nitrided” ?
The drawing in Fig. 2 doesn’t bring anything new or important. It is explained in the text, so there is no reason to put such simple drawing.
First of all the quality of the Fig. 3 is bad. It is just a screenshot. Moreover, the three curves presented in the graph reached the temperature level little over 500 Celsius degree. Contrary, the legend indicates temperature 660 Celsius for T1, T2, and T3.
“Presence of a brighter phase among the grain boundaries of the expanded austenite and expanded ferrite is detected.”
Comment: Haw was it detected ? Regarding the Fig. 4. the ferrite and austenite zones may be indicated. However, you do not provide any phase identification for the other constituents. The EDS is not reliable for phase identification.
“Such phase is associated to the sigma precipitate characteristic of duplex stainless steels after thermal treatments in the range of 600 ºC and 850 ºC.”
Comment: According to previous information the treatment was carried out at 520 Celsius. So the sigma phase should not be predicated.
“The nitriding-substrate interface on austenite and ferrite phases, shown in fig. 4b, is very irregular.”
Comment: What do you mean “very irregular” ? What is the deviation in your case, and what is for the case when it is regular ?
“Instead, DSS nitride layer has more black spots, identified as nitrides.”
Comment: How did you identify the black spots as nitrites ?
“Hardness of the nitride layer was measured in order to analyze the resistance obtained at higher temperature of plasma nitriding process.”
Comment: What resistance were you going to analyse ?
“As observed in the images from backscattered electron microscopy (BSE) cross-section of SDSS plate in Fig. 5a and 5b, precipitates of chromium nitride are identified inside expanded ferrite phase.”
Comment: How the chromium nitrides were identified ?
Author Response
Response to Reviewer 1 Comments
Point 1: The image in Fig. 2 is very low quality. It could easily redraw.“Hence, the main differences observed between austenite and ferrite structures regarding nitriding process are the result of ...”Comment: “are the results“ ?
“...plasma nitride specimens...”Comment: “plasma nitrided” ?
Response 1: “Hence, the main differences observed between austenite and ferrite structures regarding nitriding process are the result of the thermodynamic conditions during nitrogen diffusion”. In this sentence it is said that austenite and ferrite present different morphology after nitriding process because of the different nitrogen diffusion during the process into ferrite or austenite.
“Plasma nitride specimens” refers to the specimens under the process we did that is explained by fig.3
M. Bobadilla and A. Tschiptschin, “On the Nitrogen Diffusion in a Duplex Stainless Steel”, Mater. Res., vol. 18, no. 2, pp. 390–394, 2015.
Christiansen, T. L., & Somers, M. A., “Determination of the concentration dependent diffusion coefficient of nitrogen in expanded austenite”, International Journal of Materials Research, vol. 99, no. 9, pp. 999-1005, 2008.
Parascandola, S., Möller, W., & Williamson, D. L., “The nitrogen transport in austenitic stainless steel at moderate temperatures”, Applied Physics Letters, vol. 76,no. 16, pp. 2194-2196, 2000.
Please find in yellow the update in the manuscript as follows:
Hence, the main differences observed between austenite and ferrite structures regarding nitriding process are the result of the thermodynamic conditions, since both phases present different nitrogen diffusion rate.
Point 2:The drawing in Fig. 2 doesn’t bring anything new or important. It is explained in the text, so there is no reason to put such simple drawing.
Response 2:It was introduced for a better compression of the explanation.
Point 3:First of all the quality of the Fig. 3 is bad. It is just a screenshot. Moreover, the three curves presented in the graph reached the temperature level little over 500 Celsius degree. Contrary, the legend indicates temperature 660 Celsius for T1, T2, and T3.
“Presence of a brighter phase among the grain boundaries of the expanded austenite and expanded ferrite is detected.”
Comment: Haw was it detected ? Regarding the Fig. 4. the ferrite and austenite zones may be indicated. However, you do not provide any phase identification for the other constituents. The EDS is not reliable for phase identification.
Response 3:Phases were identified by the microanalysis technique (EDS) used in conjunction with SEM. Different chemical composition (such as differences in Mo, Cr) lead to identify each phase. The composition of the different phases was determined using JEOL J-7100 field emission scanning electron microscope (FE-SEM) with energy-dispersive X-ray spectroscopy system (EDS) INCA PentaFETx3 detector. In addition, a JEOL JXA-8230 microprobe (with five WDS spectrometers) allowed us to obtain a higher chemical composition accuracy.
There are a lot of references in which it can been seen that EDS is enough for element distribution.
N. Llorca-Isern, H. López-Luque, I. López-Jiménez, and M. V. Biezma, “Identification of sigma and chi phases in duplex stainless steels,” Mater. Charact., vol. 112, pp. 20–29, 2016.
D. M. Escriba, E. Materna-Morris, R. L. Plaut, and A. F. Padilha, “Chi-phase precipitation in a duplex stainless steel,” Mater. Charact., vol. 60, pp. 1214–1219, 2009.
B. Zhang, Z. Jiang, H. Li, S. Zhang, H. Feng, and H. Li, “Precipitation behavior and phase transformation of hyper duplex stainless steel UNS S32707 at nose temperature,” Mater. Charact., vol. 129, pp. 31–39, 2017.
Please find in yellow the update in the manuscript as follows:
Presence of a brighter phase among the grain boundaries of the expanded austenite and expanded ferrite is detected. Such phase is associated to the sigma precipitate characteristic of duplex stainless steels after thermal treatments in the range of 600 ºC and 850 ºC. This phase was identified through the EDS microanalyses showing a higher content of Mo than that of the ferrite phase. Precipitates of chromium nitrides (black dots) are also present and can be seen in fig 4b as expected after nitriding at a temperature of 520ºC. These chromium nitride precipitates are apparently distributed only in the expanded austenite. Fig. 4c and d show the microstructure of SDSS samples extracted from SDSS plate. Fig. 4d shows the sigma precipitation linking expanded austenite phase within expanded ferrite phase. Chromium nitrides are also noticed inside both phases. The composition of the different phases was determined using JEOL J-7100 field emission scanning electron microscope (FE-SEM) with energy-dispersive X-ray spectroscopy system (EDS) INCA PentaFETx3 detector. In addition, a JEOL JXA-8230 microprobe (with five WDS spectrometers) allowed us to obtain a higher chemical composition accuracy. Different chemical composition (such as differences in Mo, Cr) led to identify each phase.
Point 4:“Such phase is associated to the sigma precipitate characteristic of duplex stainless steels after thermal treatments in the range of 600 ºC and 850 ºC.”
Comment: According to previous information the treatment was carried out at 520 Celsius. So the sigma phase should not be predicated.
Response 4:Sigma phase should not be predicted, but as we explain later, such behaviour could not only happen within temperature, but it can be due to the high nitrogen ferrite and austenite that help to induce its formation even at temperature as low as 520ºC.
Point 5:“The nitriding-substrate interface on austenite and ferrite phases, shown in fig. 4b, is very irregular.”
Comment: What do you mean “very irregular” ? What is the deviation in your case, and what is for the case when it is regular ?
Response 5:It was defined as “very irregular” the shape of the thickness over the ferrite and austenite phases as it is not similar for both of them. In contrast, similar thickness over both phases was described after treatments above 500ºC as explained in Fig.2
Please find in yellow the update in the manuscript as follows:
The nitriding-substrate interface on austenite and ferrite phases, shown in fig. 4b, is dissimilar for both phases
Point 6:“Instead, DSS nitride layer has more black spots, identified as nitrides.”
Comment: How did you identify the black spots as nitrites ?
Response 6:The composition of the different phases was determined using JEOL J-7100 field emission scanning electron microscope (FE-SEM) with energy-dispersive X-ray spectroscopy system (EDS) INCA PentaFETx3 detector. In addition, a JEOL JXA-8230 microprobe (with five WDS spectrometers) allowed us to obtain a higher chemical composition accuracy. Different chemical composition (such as differences in Mo, Cr) lead to identify each phase.
There are a lot of references in which it can been seen that EDS is enough for element distribution.
N. Llorca-Isern, H. López-Luque, I. López-Jiménez, and M. V. Biezma, “Identification of sigma and chi phases in duplex stainless steels,” Mater. Charact., vol. 112, pp. 20–29, 2016.
D. M. Escriba, E. Materna-Morris, R. L. Plaut, and A. F. Padilha, “Chi-phase precipitation in a duplex stainless steel,” Mater. Charact., vol. 60, pp. 1214–1219, 2009.
B. Zhang, Z. Jiang, H. Li, S. Zhang, H. Feng, and H. Li, “Precipitation behavior and phase transformation of hyper duplex stainless steel UNS S32707 at nose temperature,” Mater. Charact., vol. 129, pp. 31–39, 2017.
Point 7:“Hardness of the nitride layer was measured in order to analyze the resistance obtained at higher temperature of plasma nitriding process.”
Comment: What resistance were you going to analyse
Response 7:Hardness analyses was meant to see how increases when higher temperature of nitriding is applied.
Please find in yellow the update in the manuscript as follows:
Hardness of the nitride layer was measured in order to see the improvement of the resistance obtained at higher temperature of plasma nitriding process.
Point 8:“As observed in the images from backscattered electron microscopy (BSE) cross-section of SDSS plate in Fig. 5a and 5b, precipitates of chromium nitride are identified inside expanded ferrite phase.”
Comment: How the chromium nitrides were identified ?
Response 8:The composition of the different phases was determined using JEOL J-7100 field emission scanning electron microscope (FE-SEM) with energy-dispersive X-ray spectroscopy system (EDS) INCA PentaFETx3 detector. In addition, a JEOL JXA-8230 microprobe (with five WDS spectrometers) allowed us to obtain a higher chemical composition accuracy. Different chemical composition (such as differences in Mo, Cr) led to identify each phase.
There are a lot of references in which it can been seen that EDS is enough for element distribution.
N. Llorca-Isern, H. López-Luque, I. López-Jiménez, and M. V. Biezma, “Identification of sigma and chi phases in duplex stainless steels,” Mater. Charact., vol. 112, pp. 20–29, 2016.
D. M. Escriba, E. Materna-Morris, R. L. Plaut, and A. F. Padilha, “Chi-phase precipitation in a duplex stainless steel,” Mater. Charact., vol. 60, pp. 1214–1219, 2009.
B. Zhang, Z. Jiang, H. Li, S. Zhang, H. Feng, and H. Li, “Precipitation behavior and phase transformation of hyper duplex stainless steel UNS S32707 at nose temperature,” Mater. Charact., vol. 129, pp. 31–39, 2017.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Dear authors, the manuscript should be re-written.
In general, the organization of manuscript is misleading: it starts as a short review and transforms into unstructured research article without any clear division between chapters. The review does not provide sufficient background of duplex stainless steels, which can be seen on citation mostly from 90´s-2000´s, without citing of prior works on phase transformation of DSS or recent publications on N-induced transformations. Therefore, basic knowledge about duplex stainless steels and understanding of solid state phase transformation are missing.
Since the research methods are not accurately described due to misleading organization of document, the research design is not clear. Phase analysis by means of backscatter electron detector seems to be inadequate considering conclusion about crystallographic nature of occurring phases. As a result, the formed microstructures cannot be adequately described and their discussion is not relevant.
Overall, the literature research, design of experiment, interpretation of results, discussion and conclusions do not reach an appropriate scientific level neither for review nor for research article.
Author Response
Response to Reviewer 2 Comments
Dear authors, the manuscript should be re-written.
In general, the organization of manuscript is misleading: it starts as a short review and transforms into unstructured research article without any clear division between chapters. The review does not provide sufficient background of duplex stainless steels, which can be seen on citation mostly from 90´s-2000´s, without citing of prior works on phase transformation of DSS or recent publications on N-induced transformations. Therefore, basic knowledge about duplex stainless steels and understanding of solid state phase transformation are missing.
Since the research methods are not accurately described due to misleading organization of document, the research design is not clear. Phase analysis by means of backscatter electron detector seems to be inadequate considering conclusion about crystallographic nature of occurring phases. As a result, the formed microstructures cannot be adequately described and their discussion is not relevant.
Overall, the literature research, design of experiment, interpretation of results, discussion and conclusions do not reach an appropriate scientific level neither for review nor for research article.
Response:
Dear reviewer, the manuscript has not been meant to provide background on the phase transformation and/or solid state phase transformation but a mini review on the most relevant surface treatment and nitriding processes.
As far we concern, the research methods do not need to be specified if preferred by authors for such type of manuscript.
Additional references were added as shown in yellow in the manuscript.
[10] J. Wan, H. Ruan, J. Wang, and S. Shi, “The Kinetic diagram of sigma phase and its precipitation hardening effect on 15Cr-2Ni duplex stainless steel,” Mater. Sci. Eng. A, vol. 711, pp. 571–578, 2017.
[11] S. Atamert and J. E. King, “Sigma-phase formation and its prevention in duplex stainless steels,” J. Mater. Sci. Lett., vol. 12, no. 14, pp. 1144–1147, 1993.
[12] T. H. Chen, K. L. Weng, and J. R. Yang, “The effect of high-temperature exposure on the microstructural stability and toughness property in a 2205 duplex stainless steel.”
[13] R. Magnabosco and D. Caluscio dos Santos, “Intermetallic Phases Formation During Short Aging between 850°C and 950°C of a Superduplex Stainless Steel,” 2012.
[14] Y.-L. He, N.-Q. Zhu, X.-G. Lu, and L. Li, “Experimental and computational study on microstructural evolution in 2205 duplex stainless steel during high temperature aging,” Mater. Sci. Eng. A, vol. 528, pp. 721–729, 2010.
[15] D. M. Escriba, E. Materna-Morris, R. L. Plaut, and A. F. Padilha, “Chi-phase precipitation in a duplex stainless steel,” Mater. Charact., vol. 60, pp. 1214–1219, 2009.
[16] M. Pohl, O. Storz, and T. Glogowski, “Effect of intermetallic precipitations on the properties of duplex stainless steel ☆,” 2006.
Reviewer 3 Report
"Secondary phases, mostly sigma phase, were already formed within the nitriding process before any heat treatment"
The sigma phase effected on forming the nitride layer significently.
Therefore, it is recommended that the rate of sigma phase of DSS, SDSS, tube and plate effecteing on the nitride layer are discussed.
Author Response
Response to Reviewer 3 Comments
"Secondary phases, mostly sigma phase, were already formed within the nitriding process before any heat treatment"
The sigma phase effected on forming the nitride layer significently.
Therefore, it is recommended that the rate of sigma phase of DSS, SDSS, tube and plate effecteing on the nitride layer are discussed.
Response:
Due to the higher amount of nitrogen diffused into ferrite and austenite phases after the nitriding process, σ-phase is formed even at lower temperature. The nucleation and growth kinetics could be influenced by the previous forming process history of the specimen related to the texture and anisotropy developed in each case, as for SDSS plate and SDSS tube.
Moreover, chromium nitrides act as a favourable site for the nucleation of σ-phase. However, after treatment σ-phase is enhanced, whereas the chromium nitrides remain stable and their location is kept from their original nucleation site.
Please find in yellow the update in the manuscript as follows:
Secondary phases, mostly sigma phase, were already formed within the nitriding process before any heat treatment applied to the SDSS samples. Such behaviour could not only be due to the temperature, but it can be regarded as high nitrogen ferrite and austenite help to induce its formation even at temperature as low as 520ºC. The nucleation and growth kinetics could be influenced by the previous forming process history of the specimen related to the texture and anisotropy developed in each case, as for SDSS plate and SDSS tube. Moreover, chromium nitrides act as a favourable site for the nucleation of σ-phase.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The article has been corrected, but some of the previous comments are still valid (e.g. regarding low quality of the images).
Author Response
Dear reviewer,
Due to the quality of both Fig. 2 and 3 and that their contribution to the text is not relevant as commented previously, they were removed and the quality of the rest of the images was improved.
Reviewer 2 Report
I appreciate the changes done by authors and extension of citations. Unfortunately, I couldn´t detect a significant improvement of manuscript. The main critic point was the unappropriate organisation of manuscript, which pretend to be a review, but as a matter of fact, is a research article.
Author Response
Dear reviewer,
The manuscript was changed from Review to Research Article as required. However, it has its own structure.
Round 3
Reviewer 1 Report
Since you have provide revised third version of the manuscript, I accept it for publication.
Reviewer 2 Report
The new organisation of manuscript meets the requirements for research article and therefore can be accepted for publication.
