The worse case is when nichel content lays in the range 8-10% i.e. AISI 304-316. Put the term Copson curve in google and look at it..

interesting question, initial thought is a high PREN (1 x %Cr + 3.3 x %Mo + 16 x %N (w/w)) is more likely to promote a BCC structure to be the stable phase and not austenite?

i.e. austenite stabilisers are not so useful for enhancing corrosion resistance

Major difference is in chemical composition. You can see that the presence of Cr, Mo, Ni are much higher in austenitic stainless steels in comparison with ferritic steels. Cr, Mo are most important alloying elements for increased corrosion resistance properties inside the steel. Simultaneous presence of Ni enhanced the corrosion resistance properties of austenitic stainless steels and it is also acts as an austenitic stabilizer.

Now for the case of SCC, you have to mention which method you are using. Say, if SSRT technique (most famous technique) you used in your work then you must receive the values of YS, UTS and ductility which is degraded due to the presence of corrosive environments with respect to the original values. Here one thing you have to remember that austenite phase (fcc) has more ductility rather than the ferritic (bcc) one. That is why you can easily accept good results in case of austenitic stainless steels. 

Make sure that you have done the testing as per the standard. For the cases of austenitic steels you have to fixed your strain  rate with in 10^-6 to 10^-7. 

One thing you must do that the fracture surface analysis after the SCC testing, where you can easily observ the SCC cracks in transgranular or intergranular or mixed mode. Most of the cases in austenitic stainless steels SCC cracks are appeared transgranular in surface but intergranular in deep, that indicate mixed mode of failure. And for ferritic steels, it is quite expected that the crack will be visible more in nature and in transgranular mode. Material chemistry (alloying effect) can be a more important reason for this. 

Any way, hope this will be helpful for you. If you need any further queries related this, you can message me directly or mail me: [email protected]

Thanks and regrads

Soumyabrata