Official Answer
Answer
302 Stainless Steel is metastable and can transform from austenite to martensite when cold-worked (during the coiling process) or when exposed to cryogenic temperatures. This transformation causes a volume expansion (approx. 4%). For precision retaining rings used in aerospace liquid oxygen ($LOX$) systems, this can cause the ring to 'grow' and lose its grip on the groove. 'Cryogenic Treatment' (soaking at $-320^{\circ}F$) is used to force this transformation to completion during manufacturing. After the transformation, the ring is stress-relieved. This ensures that the ring's dimensions remain stable during actual cryogenic service, preventing the ring from expanding and failing to retain the assembly.
