Correlation between Microstructure and Mechanical Properties of Welded Joint of X70 Submarine Pipeline Steel with Heavy Wall Thickness

Round 1

Reviewer 1 Report

The manuscript “Correlations of Microstructural and Mechanical Properties in X70 Submarine Pipeline Steel with Heavy Wall Thickness” presents investigation of the relationship between the structure of weld metal zones and a set of mechanical properties of thick walled submarine HSLA steel using standard characterization methods. The contents of current work should be useful for the field. However, the following comments should be addressed:

 

• The main subject of the research is a weld metal zone should be mentioned in the title.
• Materials and Methods do not specify the region through thickness where the tensile specimens were cut out.
• Line 128 – What do authors mean in “which ensures ductile fracture will not occur in the WM”. While Table 1 shows the 41% elongation on WM vs. 45% in BM.
• Please indicate the “ductile fracture” zone in Fig. 2b or doted boundaries of the zones can be highlighted in the figure.
• The accuracy of volume fraction in Table 2 seems to be overestimated. Could you explain the details of the method of its determining?
• Section “Results and Discussion” is followed by “Discussion”. Please check, if is it ok.
• Line 298 - «although cracks may from in HAZ» Please check, if is it ok.
• Section 4.2 needs major revision. The analysis of grain orientation on delamination using EBSD is incomplete. First, Figure 9a is not an “inverse pole figure”, but “orientation map”.

From the Fig. 9a it is impossible to determine the orientations of the grains: plane + direction. At least two orientation maps are needed. However, the connection between the external coordinates of the plate and grain orientation is not given in the figure. Moreover, one cannot unambiguously define the plane of the delamination relative to external coordinates. Another well-known fact is that crack in BCC metals propagate along {001} planes [R. Chang. An Atomistic Study of Fracture. International Journal of Fracture Mechanics, Vol. 6, No. 2, June 1970] was demonstrated for HSLA pipeline steel [https://doi.org/10.1016/j.msea.2019.138746].

• Figure 9 c,d do not demonstrate the statement given in the text. The crack in 9d should not be the same color as the deformed grains.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

This manuscript deals with a detail microstructural and mechanical characterisations of the different regions generated during the welding process of a 40 mm thick pipeline steel.

The paper is well written and structured, and conclusions are supported by the experimental results.

There are still some issues that might need further attention.

Abstract should not contain abbreviations

Pag 2 Line 53. A reference to those rigorous requirements mentioned in the text might be useful, also, are those requirements fulfil in the present case?

Pag 2 line 89. It is difficult to envision if 0.5 mm is suffice to avoid the plastic region generated by other close indentations.

How many tensile and charpy tests were performed at the same condition?. An estimation of the error in the relevant measured magnitudes is needed.

Acicular ferrite is understood as bainite (plate/lath like) nucleated in inclusion/precipitates, considering the magnification of your micrographs is difficult to assess the appearance of that particular phase. Please note that in none of the micrographs in Figure 4, the authors made identification of such phase. Only in Fig 8, which is far too small to make any identification.

Figure 7 is also far too small.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have made an extensive revision and most comments were considered. 

Though the main point of the review, namely the Section 4.2 EBSD Analysis of Delamination Crack, is still to be improved. To analyze the crack propagation path through the grain, one should define the orientation of the grain (plane and direction). From the Figure 9b only the plane can be defined. It means multiple variants of crack propagation in the grain. To demonstrate the orientation, the IPF colored maps (orinetation maps) from at least two perpendicular directions are needed or one can provide the orientation of each grain adjacent to the crack plane using unit cell like it is made in the following example. 

Author Response

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Author Response File: Author Response.pdf