Improving the Surface Properties of an API 5L Grade B Pipeline Steel by Applying the Boriding Process—Part II: On the Changes in the Mechanical Properties

Round 1

Reviewer 1 Report

The study provides an experimental assessment of the mechanical characteristics, wear resistance, corrosion resistance of  API 5L grade B pipeline  steel after the boriding process of different duration and temperature. The motivation of the authors is quite obvious. The topic is relevant, the study seems complete, and the conclusions are justified. However, a number of points need to be clarified or improved according to the comments below.

1. What is x100 in Eq(3)?

2. Why is P introduced after (4) if it is not used there?

3.  A in (5) and (6) obviously refers to different quantities. Please correct.

4. There is no discussion about the relationship between hardness and abrasive wear resistance. Why then measure hardness?

5. A decrease in hardness with depth should lead to a change in the wear rate, this is not written.

6. In equation (6), with negative C at large distances from the surface, the hardness of the pure steel should be obtained (which is A). Why then are the values of A different even for the same temperature regime?

7. What is the "level" in the caption in Figures 4-6 and why is it measured in hours? In its present form, these figures are not informative.

Author Response

1. What is x100 in Eq(3)?-
2. In equations 2 and 3, the part “x 100” represents the factor to show the result in percentage. The equation was modified according to this explanation.
3. Why is P introduced after (4) if it is not used there?-
4. the authors agree with and thank for the observation of the reviewer; P was removed from the text.
5. A in (5) and (6) obviously refers to different quantities. Please correct.
6. The authors agree with the reviewer, A was changed to A_w, in Equation 5
7. There is no discussion about the relationship between hardness and abrasive wear resistance. Why then measure hardness?
8. The authors disagree with the reviewer. The answer of the next question explains this issue
9. A decrease in hardness with depth should lead to a change in the wear rate, this is not written.
10. The authors have already described the relationship between hardness and wear rate:

“This apparent contradictory behavior can be explained because as the treatment temperature increase, the boride layers tend to be thicker and thicker and their hardness increase too, which should be beneficial for the wear resistance [37, 38,39]. Nevertheless, the loss of volume during the wear tests is also related to the brittleness of the material and it is clear that the higher the temperature, the more brittle the layers are. Similar results were reported in our previous work[]”

6. In equation (6), with negative C at large distances from the surface, the hardness of the pure steel should be obtained (which is A). Why then are the values of A different even for the same temperature regime?

1. Equation (6) is only valid the boride layer hardness. It does not take into consideration the “pure steel hardness”. The following sentence was modified in the manuscript to avoid misunderstandings:

“Where () is the boride layer microhardness”

This is a good comment, to portray a model with physical meaning. The nonlinear regression was obtained constraining the parameter A to the hardness minimum value measured.

In Equation (6), parameter A represents the minimum value of the hardness and it was obtained in the boride layer formed. In the specific case of the boride layer obtained at 1000°C and 6h was not possible to portray this meaning. This is because one found a lot of observation data with greater values of hardness. This is because at higher temperatures the layer becomes more stable and tougher. The following sentences are included in the manuscript to explain this issue and the possible reason of the layer behavior observed:

“This behavior can be explained because the layers tend to be very thick at high temperatures. So, the hardness is almost constant in all the layer thickness. However, once it is on the layer limit, the hardness decreases drastically until reaches the substrate hardness. Parameter A, that is a constant, was obtained constraining its value to those greater than the lowest hardness value measured in the boride layer in the non-linear regression. This process allows to obtain at least the minimum value recorded”

7. What is the "level" in the caption in Figures 4-6 and why is it measured in hours? In its present form, these figures are not informative.
8. In the Figures 4-6 “level” is referred to hardness profile measurements which are depicted in Figure 3. To help to future readers to facilitate this explanation, the following sentence is included in the manuscript:

“The hardness evolution is depicted in Figures 4, 5, 6 and 7 for each condition and for different levels (hardness profile measurements illustrated in Figure 3)”

Author Response File: Author Response.docx

Reviewer 2 Report

Dear collage

The article contains useful information especially for industrial applications. However, the writing of the article needs to be improved. The discussion section of the features should be enriched, and collective references such as [32, 31, 28, 40, 41, 42] should be avoided. References should be shown one by one and the similarities and differences with the study should be emphasized. I'm in favor of publishing the article, but only after the following corrections have been made.

1- A non-standard introduction was written between Line 61-74. In this section, the definitions of boriding should be made and the publications dealing with the alloys to which it is applied, especially bending and drawing, should be mentioned.

The importance of the method should be introduced by using sentences such as "Boring is a method introduced into the literature in 1895 and is currently applied to carbon steels, stainless steels, superalloys and even high entropy alloys […..]".

Moreover, it should be added what effect boriding can have on the yield and tensile strengths of boronized steels. There are limited studies in the literature examining the tensile strengh and bending behaviors. The following articles can be used in this regard.

a- https://doi.org/10.1134/S0031918X15090021

b- Calik, A., Sahin, O., & Ucar, N. (2009). Mechanical properties of boronized AISI 316, AISI 1040, AISI 1045 and AISI 4140 steels. Acta Physica Polonica A, 115(3), 694-698.

2- The content of the powders used in boriding is decisive on the boride layer. Detail the construction of the boriding process. Boron powders used, activator, cooling etc. should given in detail.

3- In Figure 3, the hardness traces are taken clearly and it looks very nice. However, it is very difficult to determine that the Boride layer is composed of Fe2B without taking EDS and/or XRD. Give XRD or EDS or explain this Fe₂B formation.

4- In the stress-strain graph in Figure 11, it is seen that the 850-6h sample shows higher elongation than the untreated sample. This is not very likely. Because, with boronizing, a hardness in the form of a crust is formed on the surface. Explain the reason why it is higher than the untreated sample. Were samples taken in at least 3 replicates?

Corrosion and wear results are given without discussion.

5- Compare the corrosion results obtained with boride coatings with the results obtained in different liquids.

https://doi.org/10.18280/acsm.450109

https://doi.org/10.1007/s11661-018-4862-2

 https://doi.org/10.30544/829.

6- In the same way, compare the wear results with the literature. As a matter of fact, boriding is characterized by their wear resistance.

https://doi.org/10.1016/j.wear.2020.203277

Kumaravel, D., & Arunkumar, K. (2019). Improve the Wear Property of En19 Steel by Boronizing Process. In Advances in Manufacturing Processes (pp. 123-131). Springer, Singapore.

Gunen, A., Ulutan, M., Gok, M., Kurt, B., & Orhan, N. (2014). Friction and wear behavior of borided aisi 304 stainless steel with nano particle and micro particle size of boriding agents. Journal of the Balkan Tribological Association, 20(3).

Author Response

Dear collage

The article contains useful information especially for industrial applications. However, the writing of the article needs to be improved. The discussion section of the features should be enriched, and collective references such as [32, 31, 28, 40, 41, 42] should be avoided. References should be shown one by one and the similarities and differences with the study should be emphasized. I'm in favor of publishing the article, but only after the following corrections have been made.

1. Great comment of the reviewer. The authors will avoid collective references. The following sentences were included after applying this comment:

“For example, to consider the amount of matter exposed to the thermochemical process helps to determine boride layers thickness in function of simple size []. Wear resistance can be studied after undergoing the boriding process in AISI 1018 steel with successful results []. Significant hardness improvements also were detected in carbon steel []. In all these cases, it was formed layers that contain FeB and Fe₂B”

1- A non-standard introduction was written between Line 61-74. In this section, the definitions of boriding should be made and the publications dealing with the alloys to which it is applied, especially bending and drawing, should be mentioned. AMBOS

1. The authors want to remind you that this paper is the Part II of the research work. Part I [i] give details about boriding definitions and schematizations and it was already accepted for publication by Coatings Journal. The authors pretend to avoid repeatability in Part II. However, the authors also consider it necessary to facilitate some background knowledge to the readers. Hence, the authors want to incorporate the following sentence to indicate that is suggested to the readers to study Part I to complement the understanding of this work:

“In the first part of this investigation (Improving the surface properties of an API 5L grade B pipeline steel by applying the boriding process. Part I: Kinetics and layer characterization []), it is detailed some basic concepts about the boriding process. Likewise, it is described and analyzed the boriding process, kinetics, layer thickness measurement, X-ray diffraction, morphology by SEM and the changes in the grain size provoked by the thermochemical treatment. The authors recommend prior reading of Part I [] to facilitate understanding of the full scope of the research work.”

The importance of the method should be introduced by using sentences such as "Boring is a method introduced into the literature in 1895 and is currently applied to carbon steels, stainless steels, superalloys and even high entropy alloys […..]". AMBOS

1. The authors consider that the modified paragraph in the introduction section is enough to explain this issue.

Moreover, it should be added what effect boriding can have on the yield and tensile strengths of boronized steels. There are limited studies in the literature examining the tensile strengh and bending behaviors. The following articles can be used in this regard.

a- https://doi.org/10.1134/S0031918X15090021

b- Calik, A., Sahin, O., & Ucar, N. (2009). Mechanical properties of boronized AISI 316, AISI 1040, AISI 1045 and AISI 4140 steels. Acta Physica Polonica A, 115(3), 694-698.

1. The authors agree with the reviewer. It is necessary to add a kind of comparison regarding other works found in the Literature. For this reason, the authors include the following sentence in the Manuscript:

 “The results are in sync with others found in the literature, in which a decrease of up to 10% of the yield strength, UTS and % elongation [.].That is, the engineering strength characteristics are highly affected by the treatment thermal conditions”.

2- The content of the powders used in boriding is decisive on the boride layer. Detail the construction of the boriding process. Boron powders used, activator, cooling etc. should given in detail. ENRIQUE

The authors agree with the reviewer. However, the explanation for this point is in the page 4, lines 122-123 as follows: “Details of the surface finishing of each specimen and the boriding process conditions are detailed in the Part I of the present research work”. Nevertheless, deails of the boriding process were added to the manuscript to more clarification (lines 124 to 132)

3- In Figure 3, the hardness traces are taken clearly and it looks very nice. However, it is very difficult to determine that the Boride layer is composed of Fe2B without taking EDS and/or XRD. Give XRD or EDS or explain this Fe₂B formation. ENRIQUE

R3: The nature of the boride layers obtained on the API 5L grade B steel was described in the first part of this research work [i]. An extensive XRD analysis was done to all the samples at the different treatment conditions.  

4- In the stress-strain graph in Figure 11, it is seen that the 850-6h sample shows higher elongation than the untreated sample. This is not very likely. Because, with boronizing, a hardness in the form of a crust is formed on the surface. Explain the reason why it is higher than the untreated sample. Were samples taken in at least 3 replicates? JULIO

1. The reviewer is right. Figure 11 was reviewed and corrected. The samples were taken in at least 3 replicates. It is only depicted the most representative. To provide a better explanation of this issue the following paragraph was included in the manuscript:

“Additionally, yield strength and ultimate tensile strength also tend to decrease for all the treated specimens except those treated at 850 °C for 6 h. This effect of the partial improvement of yield strength has been observed in some cases when the pipeline steel is exposed to high temperatures, like the isothermical aging process because it is caused by possible carbide precipitations []. This tendency of diminish the material strength is in sync with the information found in the literature, in which a decrease of up to 10% of the yield strength, UTS and % elongation []. That is, the engineering strength characteristics are highly affected by the treatment thermal conditions”

Corrosion and wear results are given without discussion.

1. The authors agree to include this suggestion in the new version of the manuscript.

R4. In fact, an extensive discussion about to corrosion results is presented in page 16, lines 363 to 388. Additionally, new information was added in this part. The authors consider that it could be enough for the understanding of this issue.

On the other hand, results of wear were discussed in pages 18 and 19, lines 415 to 441.

Additionally, the new discussion was added to the manuscript (lines 428 to 441), for more understanding of the results.

5- Compare the corrosion results obtained with boride coatings with the results obtained in different liquids. JULIO

https://doi.org/10.18280/acsm.450109

https://doi.org/10.1007/s11661-018-4862-2

 https://doi.org/10.30544/829.

1. The authors agree with this comment. For this reason, the following texts are inserted in the manuscript:

“This type of behavior has been also found in titanized carbon steels immerse into HF []. It means that some of surface hardening could not be resistant to corrosion in some acids. This poor corrosion resistance to HNO3 of the borided API 5L grade B steel is not really a bad result because neither crude oil nor sour gas tends to contain enough HNO3 concentrations when they are transmitted by pipelines”

“The improvement in the corrosion resistance in API 5L steels immersed in acids was also assessed by electrochemical techniques []. These studies confirmed that the corrosion resistance of API 5L steels against HCl and H₂SO₄ can be improved when it is boride the surface.”

6- In the same way, compare the wear results with the literature. As a matter of fact, boriding is characterized by their wear resistance. ENRIQUE

R6. This observation was attended with the response to the observation 4, new references were added for more clarification

https://doi.org/10.1016/j.wear.2020.203277

Kumaravel, D., & Arunkumar, K. (2019). Improve the Wear Property of En19 Steel by Boronizing Process. In Advances in Manufacturing Processes (pp. 123-131). Springer, Singapore.

Gunen, A., Ulutan, M., Gok, M., Kurt, B., & Orhan, N. (2014). Friction and wear behavior of borided aisi 304 stainless steel with nano particle and micro particle size of boriding agents. Journal of the Balkan Tribological Association, 20(3).

1. According to the suggestions, the following sentences were included:

“The boriding process tends to be suitable for materials that are exposed to wear due to metal friction, such as gear and shaft []. Nonetheless, in the oil and gas industry, this erosion and wear resistance can be appropriate for pipes, elbows, tees and other fittings. Similar findings were done by Eugene Medvedovski and Maksim Antonov [] for Carbon steels J55 and L80, but with a bi-phasic boride layer formed (FeB + Fe₂B) over this material”

REFERENCE

[i] Alcantar-Martínez, L.M.; Ruiz-Trabolsi, P.A.; Tadeo-Rosas, R.; Miranda-Hernández, J.G.; Terán-Méndez, G.; Velázquez, J.C.; Hernández-Sánchez, E. Improving the Surface Properties of an API 5L Grade B Pipeline Steel by Applying the Boriding Process. Part I: Kinetics and Layer Characterization. Coatings 2023,13, 298. https://doi.org/10.3390/coatings13020298

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The paper can be accepted

Reviewer 2 Report

All the shortcoming done. Therefore the paper can be published as current stage.