Currently have conflicting interpretations of the timing of a sub-zero step during treatment of 440C to AMS 2759/5F.
Below is reference from the specification:
1. Req. of 440C:
After hardening quench, sub zero cool at -90 °F (-68 °C) or colder for not less than 2 hours.
2. General req. AMS...
Yes after annealing, would re-austenitize at ~1900F.
For annealing:
Ideally, would equalize ~1300F (process anneal temp.) + Full anneal ~1560F
Economically, would process anneal >1400F
My main concern is the final grain structure not recovering enough from the anneal + re-austenitize, resulting...
Would annealing and re-hardening 440B (0.9C) that was austenitized above 1950F not refine the coarse grained structure?
Train of thought is coarseness of the prior austenite grains and out of matrix carbides from the high austenitization and subsequent coarse martensitic structure would...
