Carbides in Austenite phase
Carbides in Austenite phase
(OP)
Hi I have a samples of F55 duplex stainless steel that appears to have a high percentage of carbide/intermetallic phase in the austenite grains, could this be down to a poor solution treat after forging?





RE: Carbides in Austenite phase
RE: Carbides in Austenite phase
RE: Carbides in Austenite phase
My hunch is that at higher magnification you will find a lot of secondary phases along the ferrite/austenite boundaries as well.
You really need to cool fast, under 1000F in less than 30 sec, and under 600F in less than 4 min. are the values that I use.
It is going to take a good soak to get rid of this stuff.
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Plymouth Tube
RE: Carbides in Austenite phase
I have not done impacts yet, I have not actually produced the forgings so I do not know the exact parameters used for ST. I am just carrying out some further testing and noticed them when I have prepared the sample for ferrite count. No deleterious 3rd phases appear at the boundaries, etchant used was 40% aqueous NAOH electrolytically.
RE: Carbides in Austenite phase
RE: Carbides in Austenite phase
RE: Carbides in Austenite phase
RE: Carbides in Austenite phase
I agree that it looks like a solution anneal temp/time issue.
My hunch is that they finished forge a bit low, formed carbides, and then didn't fully re-solution them.
From high temp to lower the order of preferential formation is: sigma, chi, nitride, carbide.
If it sat for a few min in the range of 600C-700C you would preferentially form carbides
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Plymouth Tube
RE: Carbides in Austenite phase
Also with regard to carrying out the austenite spacing - what is the calc used to actually work out the austenite spacing? ASTM E112 states at a magnification suitable to count 50 fields, also it would depend how many lines are superimposed on the image.