bruv- I have some thoughts about your problem that might be helpfull but I am not familiar with this particular alloy. Somewhere on this site I found a thread to a site called "About metals Guide." When I searched using keyword of ASTM, it gave me 38000+ choices. Cannot zero in on chemistry, properties, heat treat, etc for ASTM A352 CA6NM and when I search under that same site under 'ASM's Alloys Online', I come to a choice of 4 categories of S.S. cast alloys and then I am stuck again. For example; what is the the Mf (Martensite finish)temperature for this alloy which is a very important factor for analyzing your problem since it bears heavily on the question of retention/transformation of Retained Austenite especially since you are testing cryogenically.
Can anyone give me a step-by-step method to find specific info for a particular ASTM designation?