Official Answer
Answer
At cryogenic temperatures (below $-300^{\circ}F$), most carbon steels and some stainless steels undergo a ductile-to-brittle transition, becoming susceptible to impact failure. 302 and 304 Stainless Steels maintain their face-centered cubic (FCC) lattice structure, which does not exhibit this transition. These materials retain high ductility and toughness at liquid nitrogen temperatures. For aerospace liquid oxygen (LOX) systems, these rings are often passivated per ASTM A967 to remove free iron from the surface and enhance the protective oxide layer.
