No. Spinodal decomposition is a specific transformation that needs unstable thermodynamic conditions for the phase. I've never read anything about this condition for austenite phase. Ferrite experience spinodal decomposition, generating Cr-rich alpha prime and Fe-rich ferrite. I did not read the "Chung" work mentioned in one of the answers to this topic. The other answer describes transformations that are not spinodal decomposition, except for the decomposition of ferrite (item 3).

I have the phase diagram of Fe-Cr system where there are three very wide miscibility gabs.  The first miscibility domain  is between Fe- Rich ferrite and  Cr-Rich  ferrite which ends up at 800 K. The second and third miscibility domains are between Fe-Rich ferrite and Sigma intermetallic, and Sigma intermetallic and Cr-Rich ferrite regions, respectively. These last two domains lie in the temperature range of 800K-1100K .  There would be eutectoid decomposition of sigma phase at   50at % around 800oK. One expects any composition which lie down in these there miscibility gaps to show some type of spinodal  of transformation having essentially ferrite matrix  based on the  iron rich and  chromium rich terminal solid solutions,  which are caled BCC1 and   BCC2, respectively.  But austenite _as Dr. Magnabosco pointed out above_  doesn't have any chance  to decomposed as spinodal.

Unless an austenite sample having high concentration of chromium content ,  if it  can be quenched down below the temperature dictated by the Fe-rich terminal solid solution line (500K-800K) as a  supercooled state then there might be possibility to have spinodal decomposition having BCC1 ferrite matrix and  BCC2 second phase showing periodic  concentration undulations as advocated by John Cahn (1961). This is of course completely hypothetical case.

Only the ferrite.  See recent work

https://www.researchgate.net/publication/269275099_Assessment_of_Thermal_Embrittlement_in_Duplex_Stainless_Steels_2003_and_2205_for_Nuclear_Applications?ev=prf_pub

Article Assessment of Thermal Embrittlement in Duplex Stainless Stee...

Dear guys, thank your very much for your inputs.

@ A. Chennakesava Reddy: you say "yes" to my answer but I do not see any "evidence". This topic is highly crucial and most researchers believe that nothing goes on in the austenite, although it does! It is true that alloying elements can affect the equilibrium phase fields in the TTT diagram, however, be careful in saying that intermetallics is spinodal decomposition because this is not true. Alpha prime, however, can be precipitated by nucleation and growth mechanism but this was not my question. I am aware about (all) precipitation occurring in ferrite, and I am aware that nitride and carbides can be formed in austenite in the 475C embrittlement temperature window, but the point is spinodal decomposition in austenite. Nevertheless, thanks for your comments! All appreciated.

@ Rodrigo: I am unsure about that. The spinodal decomposition in ferrite has been well-assessed but I can tell you that I am about publishing a paper dealing with this issue, and indeed I see "something" in austenite with similar appearance to a "spinodal-like decomposition". This terminology was first used by Chung from the States. There are several reports which you can find online. In the early 80's he interestingly used this terminology several times in different reports but without showing any evidence. Then, interestingly, he published a paper calling "Spinodal decomposition in austenite ...)" but again without showing convincing evidence. Miller used the same term in his work. Nevertheless, I appreciated your input, thank you.

@ Tarik Omer: It is a very interesting point from you to mention that spinodal decomposition can be formed in austenite by the formation of bcc-alpha prime + bcc alpha double prime, albeit theoretically only. There are some people saying that in duplex stainless steels containing >8wt.% Ni spinodal decomposition in austenite can occur such in the case for hyper duplex alloys. Well, people always "just say that" I haven't seen any evidence so far, that's why I opened this discussion. It seems to be that significantly more discussion is needed. Thanks for your time comments. All appreciated!

@ George: I have seen your paper. Great work! But not "seen" anything in austenite does not necessarily mean nothing happened :). Thanks for sharing your work. I will read it carefully and may come back to you for questions when some arise. Thanks.

Gamma-gamma prime spinodal decomposition in superalloys are supposed to occur: however some authors defend gamma prime as nucleation and growth process. Remember that compositions in superalloys are quite different than composition of austenite in DSS. If there is not a d2G