Impact of Processing on the Creep Properties of High Performance Ferritic (HiperFer) Steels

Round 1

Reviewer 1 Report

This is an excellent paper, concisely describing the impact of processing parameters on the fatigue performance of a ferritic stainless steel. The logic in the selection of processing parameters is clearly reasoned and related to the creep performance. The conclusions are sound and potential applications are indicated.

I would propose a few changes in wording as follows:

line 95: fcc -> bct instead of gamma iron -> alpha iron

lines 98 and 261: dedicated heat treatment instead of quality heat treatment

line 99: addressed instead of tackled

Author Response

Thank you for your comments.

The few changes you indicated were implemented.

Reviewer 2 Report

Thanks for the author's contribution to the metals.

This manuscript shows the impact of processing on the creep properties of High performance Ferritic steels.

In general, the outcome obtained by the present study is well organised and summerized but it can still be available to improve the quality based on the following comments.

[Abstract] This is a condensed version of your whole study. So, you must give your conclusions, 2 or 3 sentences. 

ex.1) Impact of processing on initial microstructure.

ex.2) Impact of processing on creep properties.

ex.3) Microsctructure evolution during high temperature application. etc.

[4. Conclusions and Outlook] If appropriate, outlook or suggestions for future work may be placed in a separate section.

Author Response

Thank you very much for you remarks.

The abstract has been amended.

Regarding comments

ex1: The impact of processing on initial microstructure is described in detail in lines 124 to 156 with exemplary micrographs included and the impact of the various TMT procedure steps on microstructural features indicated. Because initial dislocation density is the most important issue for creep strength in the TMT state we added hardness levels as an indicator for dislocation density for clarity.

ex2: The impact of processing on creep properties is outlined in detail in section 3.2.1 (line 161 to 198) with explanations of the impact of initial dislocations density and grain size on precipitation kinetics, creep curve shape (exemplary 100 MPa curves of differently treated materials) and achievable creep rupture time and creep deformation (i.e. ductility). There is not a lot more we think we can describe.

ex3: Microstructure evolution during high temperature application is addressed in section 3.3 with an exemplary comparison of microstructures after 3 and 3500 h at 650 °C (Fig. 7). The changes are clearly indicated and described starting from line 252. Because the microstructural issues governing creep deformation and failure of this type of steel was already published in several other papers we decided to not repeat them here and just referenced these publications for people who are interested in the details.

We decided to not prepare a separate section for the outlook, because it would just consist of a few sentences. We like the way it is more, because the outlook comes like a natural consequence and rounds up the conclusion of the current paper. It like: Mission accomplished for this time, but we know there is something more to do...

Reviewer 3 Report

This paper studies the influence of processing technology on creep properties in high performance ferritic (HiperFer）steels, which has certain theoretical significance and engineering value.

1.Using only figure 2 and figure 3, it is impossible to observe the dislocation  and judge the dislocation density and morphology under different processes. From Fig. 2 and Fig. 3, the small angle grain boundary and large angle grain boundary can not be clearly distinguished. It is suggested to use TEM to analyze dislocations and EBSD to analyze grain boundary types.

2. In Table 2, the process parameters are not clearly stated, so the table is redesigned.

3. The characterization of the precipitation structure changes after high temperature application is insufficient. It is suggested that supplementary tests should be carried out to compare the precipitates and PFZ zone at different creep times, so as to reveal the evolution of precipitated structure with creep time; The effects of different processes on the precipitation structure after high temperature application were compared.

Author Response

Thank you very much for your comments.

Regarding issue

1. Fig. 3 and the descriptive text passage (lines 154 - 159) has been changed. We added a band contrast image (now Fig. 3b) and another image with the high angle grain boundaries added (now Fig. 3c) to clarify the difference. TEM observations are quite expensive. As differences precipitate microstructure are not great the only significant difference in the as-rolled state is dislocation density. We added hardness information as an indicator for different dislocation density and hope this better signifies the differences between the processing parameter sets.
2. We are aware that the table is not easy to understand from a first glance, but it contains all the necessary information in one table. We (and the majority of reviewers) believe that it can be well understood in combination with the schematic representation of the processing procedure in Figure 1. So, we preferred to not change Table 2.
3. The changes in microstructure of this type of steel under high temperature creep loading are well documented in our other publications, which we referenced [21. 28, 30, 34, 35, 36] in the paper.

Round 2

Reviewer 3 Report

This paper studies the influence of processing technology on creep properties in high performance ferritic (HiperFer）steels, which has certain theoretical significance and engineering value.I think the revised manuscript is a good article.

Author Response

Thank you very much for the time you invested in reviewing our paper.