Influence of the C Content on the Fatigue Crack Initiation and Short Crack Behavior of Cu Alloyed Steels
Round 1
Reviewer 1 Report
The authors presented results of a study concerning the influence of C content on the fatigue crack initiation and short crack behavior of Cu alloyed steels. They revealed the proportion of crack initiation and short crack propagation along grain boundaries vs. within grain interior, which is interesting. The major deficiency the reviewer found is that it lacks EBSD analysis of the microcracking behavior reported in Figs 3, 4, 6, 7. EBSD is quite popular for this kind of study. The authors statement like "The role of the grain boundaries for crack propagations seems to depend on the orientation of the grain boundaries to the crack and possibly also on the crystallographic orientation of the grains" should be strengthened/supported by EBSD analysis. Also, EBSD may also reveal the orientation of grain within which the crack initiated, and what orientations of the adjacent grains where the crack initiated along the boundaries in between. The conclusion that inter- and transgranular crack initiation and growth occurred in both steels is too generic to be of particular meaning as new understanding. Some other minor distracting points are given below.
1. The reviewer does not understand this sentence: "The specimens used in this study were manufactured from the shafts of fatigue specimens, which failed in the investigations described in [22, 28]". It sounds like the specimens were hogged out from a fatigue-failed shaft, is it true?
2. The authors mentioned several times of the "Cu precipitation state" but never give details of what precipitate and what "state" they are in exactly. Better give detailed information.
3. Line 194 on page 6. Figure 4 or 3?
Some minor English typos, e.g., in some sentences, "for X05" and "for X21" better be "in X05" and "in X21"
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript studies the influence of the C content on the fatigue crack initiation and 2 short crack behavior of Cu alloyed steels. The results and discussion are well-written and consistent. I recommend publication with minor revisons.
1- The conclusion should be represented in bullet points and should be shortened. Only the important results should be summarized.
2- Regarding the intergranular mechanism, the discussion is not enough. More in-depth discussion and evidence are required to prove this mechanism.
None
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
The work is interesting, convincing, and well described. A few minor improvements can be suggested.
* the abstract could be condensed
* Provide the mean grain size + tensile stress and yield stress (their ratio is indicative of their cyclic hardening capacity) for each of the investigated steels and heat treatment.
* do the annealing treatments modify the hardness and/or texture, and if so, do these modifications paly a role in crack nucleation and growth ?
* the shift of crack initiation from PSBs towards GBs when the stress range increases might perhaps be discussed in terms of dislocation arrangements (dislocation cells are more favorable to intergranular crack initiation than PSBs)
* The effect of the carbon content on the preferential crack initiation sites might perhaps be discussed in terms of relative mobility of edge and screw dislocation segments, and thus the type of dislocation structures formed (PSBs or cells, see Magnin & Driver 1982)
* error bars should be added on figure 5 and 8
* Was any difference in crack growth rate noticed between transgranular and intergranular paths ?
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
