Sorry this is rather fractured.
I have always found great difficulty getting negative temperature properties for metals unless they have been specifically designed for that purpose i.e. 17.4 ph 1150MM.
In the years I have been in Cryogenics we have always had to approach the manufacturer for more information.
The physical property testing at these temperatures is obviously a lot harder to under take a great deal more expensive for what must be seen as a minority of users.
B