Development of Alloyed Pipe Steel Composition for Oil and Gas Production in the Arctic Region
Round 1
Reviewer 1 Report
The authors have done a good job on outlining the importance of bainitic steels low temperature conditions. The topic of bainite identification is very interesting and the results are often contradictory (depending on the author). Their experimental approach to the topic was a sound classic metallurgical methodology. The metallography is interesting and informative, a rare quality in papers. When doing a dilatometric study of a bainitic steel, the martensite transformation is often hidden and cannot be determined by the curve, the martensite is only visible in the microstructure.
However there are a few issues that need to be addressed.
Add references:
some of the data sources need to be cited: ... forecast is extra 100-140 billion tons of oil and gas resources (in oil equivalent).
...Northern Sea Route will increase from 49 7.5 million tons to 60 million tons (Figure 1)
Figure 2
Figure 3
...growth in gas production is expected (by 1.1 % in 2017, by 2.0 % in 2018)...
...2016 to 2018 more than 813 billion rubles...
Citation order!! The first three sources are 28-30! They should be 1-3! This is a problem that occurs throughout the whole paper.
"As noted in papers [9-14, 38]..." There is nos need for as noted..., just add the citations at the end of the sentences.
When using sentences like: A similar structure was found by the authors... use the actual author manes, because otherwise it reads like you wrote the papers yourself (as you are the authors).
... bainite was described in paper [26].- ref [26] is a book, maybe use ...decscribed by Bhadeshia...
Some expressions or sentences are odd. Like: "to achieve austenitic state of steel - this is austenitisation." or " To study the microstructure, the grinding surface was etched in four percent nital by dipping the polished surface in the sink with the chemical agent." -The samples were ground polished and etched by 4% nital. also "Hardness was measured using Buchler Mikromet hardness145 measuring instrument by indenting a 136 degrees square-based diamond pyramid in accordance146 with the ASTM E-384." I assume it was Vickers hardness, just say was it HV10 or something different.
Figure 4 (a-e), the scale bar is too small and μm is in cirilic. Please improve this! Also I suggest that you add the cooling speed to (a)-(e) markers (this can also be used in fig 6), for example (a)0,05 °C/s, do not ad the magnification (500x)
Figure 7, the microstructures seem verty similar it is not clear what you wanted to show, maybe mark it on the micrograph.
I suggest you add a table with the steel composition, not just in the text. Also what does and other element mean Al, Cu, V, Nb, Ti?
"Bainite also occurs in this range of cooling rates, its crystals have an elongated..." It is not clear which cooling rate.
A few other suggestions: page 4 line 102 .. cystalline ordered bainitic structure - bainitic microstructure, p4 line 104 ... in these crystals... - in bainite, p.6 line 172 ... one - bainite
Author Response
Authors appreciate the Reviewer for the attention. All corrections were inserted in the text. References were changed in accordance with the citation order. |
All citations are added to the text at the end of the sentences. |
Authors appreciate for the remark. All necessary corrections were made. |
The correction was made. |
The correction was made. |
The Reviewer is absolutely right. The Vickers microhardness НV1 was measured at the load of 1 kg. The peculiarities of the used method were described in details in the paper.
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Authors agree with the Reviewer. The scales in Fig. 4 and Fig. 6 were increased. The cooling rates were added in Fig. 4 and Fig. 6. The magnification x500 was deleted. |
The additional symbols for microstructure parameters were applied in Fig. 5 which identify the presence in steel structure perlite (P), martensite-austenite (MA), and “islands of the second phase” of mixed type consisted from both perlite and MA- constituent (P+MA) |
The Table with chemical composition of the investigated steel was inserted into the part “Materials and Methods”. |
Other elements (Al, Cu, V, Nb, Ti) means the quantity of microalloyed elements in steel which have a great affect on the properties of the studied steel. But it is impossible to specify the definite quantity of each element because all investigations were performed in the frame of complex project with PJSC “Magnitogorsk Iron and Steel Works” and all results are in the process of implementation to the industrial technologies, and are obligatory to the priority patenting. |
In this case it means the cooling rate in the range which was mentioned in the text above - it is the cooling rate from 0.05 to 60C/s. |
Authors agree with the Reviewer. All necessary corrections were made.
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
I think it is useful and necessary to give a more in-depth discussion on the possible reasons for the influence of the different cooling rates on the interpretations of figures 4 to 6. The authors do not indicate the origin of the steel used and it is also not clear how they avoided the formation of martensite. It seems to me that the justification for not detecting volumetric changes is insufficient. I really enjoyed reading the introduction text, it's very interesting and well written; would almost give a second article on the importance of the Arctic's natural resources. However, in the context of the present work I believe to be excessive. There is too much text in the introduction of the paper and little discussion of the results. The experimental section needs to be better described and the discussion should be further explored and enriched with more scientific content. In my opinion, this is the greatest weakness of this work.
In general, the work addresses a very interesting topic with immediate practical effects. After major revisions, I believe will be able to be published.
Author Response
Widely used low carbon alloyed pipe steel was taken as the basics for the investigation. But as practice has shown this steel (with ferrite-pearlite microstructure) does not have strength level higher than the class K60 (X70) together with necessary toughness, cold resistance, and weldability. It predetermines the necessity to find new technological decisions by improving the technology at metallurgical stage, particularly by optimization of chemical composition using alloyed and microalloyed elements. It is the explanation for the presence in the investigated steel the abnormal for pipe steel quantity of nickel (0.90%). It is well known that injection of nickel into the steel melt ensures its cold resistance. At the same time nickel strengthens ferrite simultaneously increasing its toughness. After inserting of 1% nickel the level of cold brittleness decreases to 60-800C. Also the steel melt was additionally alloyed by microalloyed additives (Al, Cu, V, Nb, Ti) in the total quantity to 0.53%. But all investigations were performed in the frame of complex project with PJSC “Magnitogorsk Iron and Steel Works” and all results are in the process of implementation to the industrial technologies, and are obligatory to the priority patenting. That is why it is impossible to show in details the percentage of several chemical elements (microalloyed additives) in the investigated steel. |
Authors fully agree with the Reviewer. It is impossible to deny the martensite formation at high cooling rates. But in the presented research the martensite transformation point was not fixed both by metallographic and dilatometric testing which can be apparently connected either with low volume quantity of MA or with limited sensivities of the used devices. |
Authors appreciate the Reviewer for this remark and agree with him. But on this stage of the research in the frame of investigation the aim of the study was to investigate the peculiarities of undercooled austenite disintegration and to study the morphological features of structural components (bainite) in steel with the indicated chemical composition. The next stage of the study will be the direct application of the obtained continuous cooling transformation diagram in practice at the industrial scale and determination of new properties important for pipe steels which predetermines the additional investigations and broad scientific data. |
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
After reread the manuscript with the suggested comments in mind, I agree with the publication of it in the form presented (there may be a need to correct some minor grammar errors)
