Powder Particle Size Effects on Microstructure and Mechanical Properties of Mechanically Alloyed ODS Ferritic Steels

Round 1

Reviewer 1 Report

It is considered that the sufficient analysis and evaluation for the RAF ODS steel samples have been carried out in this manuscript.  

Author Response

The authors appreciate the reviewer’s comments.

Reviewer 2 Report

Introduction:

"row 80, Several consolidated batches were obtained following this method and were 79 subsequently hot cross rolled."

Add immediately (HCR).

Experimental:

Because authors use Powder Metallurgy, in the experimental condition missing information related to the density measurement. Why authors do not measure porosity?

3.2 Grain microstructure

row 165: .. characterized by regions of elongated grains 165 sized up to 4 μm and 0.2 aspect ratio, and equiaxed grains, ....

row 171: ... the initial powder particle sizes; however ...

row 365: Although the prior particle boundaries are not visible anymore after the consolidation and hot cross rolling, they could still be playing a role on (should be authors change to "in") the impact properties observed.

Authors start from metal powders, then my question, where you disappear your powder and get only grains.
Please, write information about small black points in Figure 3. It is porosity?
Give a better explanation of what readers see in the Figures.

3.4 Mechanical properties

row 312: to a change in the deformation mechanism induced by tempera-312 ture [25]. This ..

Which mechanism?

Remarks:

Roughly, grain refinement can be considered as the most effective strengthening mechanism to yield strength. The final diameter of the grain size strongly depends on the processing conditions of metal powders, such as ball-milling, HIP; grain refinement during hot plastic deformation and phase transformations during material cooling.

The increase of the average size of the grains is accompanied by a reduction in the total grain boundary energy per unit volume. The grain boundary migration cannot involve the nucleation of new grains but only the growth of the existing grains.

Moreover, rapid cooling had to prevent the ferrite grains growth to achieve a fine-grained final structure. The authors need to add cooling information.

Rolling is classified according to the temperature of the metal rolled. If the temperature of the metal is above its recrystallization temperature.

Therefore, authors must see grain grow in the present microstructures..

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

The paper is interesting and deserves publication. I have the following comments and recommendations to the manuscript as well as to the following work of the authors.

I am wondering that the temperature of 1403–1473 K was necessary for HCR with very low influence on the coarsening of Ti-Y nanooxides. How long the batches were held at that temperature?

The paper clearly indicates the role of Y in the system. In both ODS-L and ODS-S the Y/O ratio is to low, and that is why some O must be bond in much less stable Ti2CrO7. To avoid precipitation a certain amount of metallic Y can be added.  

Clear warning must be given against bimodal grain microstructures which cause significant deterioration in mechanical properties and the possibilities of avoiding such grain microstructures should be discussed.

There is evidently no advantage of using fine prealloyed powders, this only introduces more O into the system. The use of prealloyed powders of size about 0.2-0.4 mm could be much more advantageous. 

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Authors satisfy the comments of the reviewer.