Review Reports

Round 1

Reviewer 1 Report

Quenching and partitioning (Q&P) process was proposed to obtain a good combination of strength and ductility in multiphase high strength low alloy (HSLA) steels. The authors have carried out a fairly large amount of experimental work. However, there are still quite a few questions that need clarification.

 

 

Lines 86, 92, 125, etc. / Unfortunately the pdf file for checking the publication contains many errors. Part of the text is missing, figures and tables are displaced, references to figures and tables in the text are practically absent.

Lines 105,138 / Authors mention light microscopy, however all structure and fracture images in the article are from SEM. Perhaps there were still OM photos from previous versions?

Lines 128-132 / cyclic load increase tests (LIT) in this work is the most interesting method for the analysis of functional properties (CSLA) of steel in the low-cycle fatigue load region. However, there is no information about the statistics of the studies performed for each condition and previous experiences of using this method (Why was this step and the number of cycles for each step chosen?).

Lines 234, 239, 254-256. This section raises questions related to test statistics. To limit the scope for interpretation, DIN 50100: 2016 (Line 135) contains numerical and graphical examples for the evaluation and representation of fatigue tests with constant amplitudes. For test evaluation, it is assumed that test results are subject to a logarithmic normal distribution in the direction of the cycles and in the direction of the load. LLF strength is determined using a modified staircase method. In this method, the test results concentrate around the mean of LLF strength automatically. No precise prior knowledge of the position of LLF strength is required. Although the mean value of LLF strength can be estimated well by means of just a few specimens (n ≥ 15). In this article, a maximum of 6 samples is given for one condition, which is not enough to substantiate the fourth conclusion (Lines 314-317). And the values obtained on the basis of 10^6 cycles are approximately at the same level as in the work [16] from the presented references.

Author Response

Dear Reviewer 1,

I want to thank you for the review of the manuscript and the valuable and constructive comments that helped to improve this work! I answered the comments in the uploaded document and highlighted the changes made in the revised manuscript.

 

Best regards

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors studied the monotonic and fatigue behavior of 42SiCr steel after two types of quenching and partitioning heat treatments. The effect of the heat treatments on the fatigue limit was evaluated. The method to determine the fatigue limit should be clearly explained.

1. Please correct the formats for the reference citation.

2. How to measure the plastic strain during the cyclic fatigue testing? Did the author use the total strain and the elastic strain? Since the ratcheting strain is included in the total strain, how to justify the obtained plastic strain?

3. Was the method to estimate the fatigue limit is influenced justified? How to determine the start points and the points of tangency of two tangent lines?

4. The fatigue lifetime data in Fig. 9 is not enough for the determination of the fatigue limit. The data “fatigue strength of 900 MPa (QP1) and 850 MPa (QP2)” is not convincible.

Author Response

Dear Reviewer 2,

I want to thank you for the review of the manuscript and the valuable and constructive comments that helped to improve this work! I answered the comments in the uploaded document and highlighted the changes made in the revised manuscript.

 

Best regards

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The article can be accepted in its current form. It would be interesting to compare your "short" methods with the standard methods for a more accurate presentation of the results.

Reviewer 2 Report

 Can be accepted in thi form.