Ultra-fined/nano structure after HOT FORGING

[seep555]

Hello everyone!
Is it possible to obtain an ultra-fined/nano structure (single grains of 200nm in the structure) just after hot forging?
I have to steels with slightly different compositions. Both of them are rich in Ni and Co, there is also a big amount of Cr and Mn. In one (after the same conditions of rolling) I obtained, let's say, standard structure, and in the other the grains are very small (and mechanical properties are also different).
What could be the reason for that?
Should I focus on the as-cast state to see the difference maybe? Do you have any ideas how could I analyse the alloys to explain different structure and properties? Of course there is a difference in chemical composition but it's not very big.

 

[metengr]

You would need to evaluate several different areas;

1. What was the thermal processing history of each heat of metal before forging.
2. What were the forging conditions? Work reduction ratio, sequence, temperature of the work piece before and after forging, geometry, etc.
3. The answers from 1 and 2 would be used in conjunction with chemical composition differences especially looking at grain refining elements.

 

[EdStainless]

If the alloys are different then the critical temperatures for phase changes, recrystallization and grain growth will all be different. This will change the conditions.

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P.E. Metallurgy, Plymouth Tube

 

[seep555]

Thank you!
Anyway, it's quite interesting from the theoretical point of view, don't you think? As far as I know obtaining UFG structure is possible only by high deformation techniques, and forging (hot, so also recovery and recrystallization occur) is rather not one of them...