Temperature zone to avoid IGA in Duplex material

[limey1]

Im looking through previous trials to assertain the best quenching process to avoid IGA in the material. The Temp ranges i see are anywhere between 1900-900f in 30 seconds (This seems like a wide range). Can anyone point me in the right direction?

 

[MikeMet]

The wide range is valid. Sigma phase formation in DSS can occur between 1000 - 1800 deg. F. Formation is time/temp dependent, but one still wants to cool quickly through that range to prevent any sigma formation. Super duplex alloys, i.e. UNS S32750 at more susceptible to sigma formation in a shorter time compared to UNS 32205. Depending on whose TTT diagram you choose to use, in 30 - 60 seconds you can get 1 - 5% sigma in super duplex at the higher end of the temperature range. At the same temperature it would take S32205 about 3 times a long for sigma formation.

 

[limey1]

Thanks Mike. Ive been looking online for TTT diagrams for both IGA and Sigma phase and there seems to be alot of, can I say, "crappy information". The graphs I have seen are all Logarithmic and I want to find a real-time analysis, if one exists!!

 

[MikeMet]

The log curves are from real time tests. You would have to ask one of the duplex producers for more specific data. If you don't think you can cool quickly through the temperature range you can always take a sample of your chemistry material, heat treat and then do a corrosion evaluation test per ASTM A923 to determine if there are any detrimental effects.