What turbine blade alloy did the Jendrassik Cs-1 use?
Jendrassik's own patent from 1939 does not go in-depth into the alloys. However, for the turbine blade legs he mentions "austenitic [stainless] steel" as preferable (see PDF page 3).

From that era, a Swiss patent from 1937 on the materials of gas turbine parts also discusses austenitic steel, in particular (translated from German):


  Alloy of an austenitic steel containing 25 to 35% of chromium, 25 to 35% of at least one of austenite-forming metal [e.g. nickel], 1 to 4% of titanium and 0.3 to 0.8 (preferably 0.4 to 0.6%) containing carbon, optionally up to 3% silicon and up to 10% molybdenum.


It is close to the composition of the 316 stainless steel (source), which has a mechanical maximum temperature of 590°C (source).