Does anyone have a suggestion for pump/motor shafting that will be exposed to "low temperature" (-130°C) fluid? Is there any reason to be concerned with using AISI 1045 or 4150?
Go to any pump website and inquire about cryogenic pumps.
They are always constructed from austenitic stainless material (or better)
Carbon steel(s) all exhibit a "nil ductility transition temperature" where material toughness drops away quickly with lower temperatures. (Do a web search on any of these terms, or pick up an elementary materials text book)
I agree with RICH2001, if you uses these materials, you may be heading for a disaster.