Correct option is B
For cryogenic applications (temperatures below −150°C/−238°F), the preferred steel materials must retain toughness, ductility, and strength despite extreme cold. The top choices are:
1. Austenitic Stainless Steels
Best for temperatures down to −269°C (−452°F).
Grades:
304/304L, 316/316L: Standard choices for most cryogenic systems (e.g., LNG tanks, superconducting magnets).
Nitrogen-enhanced grades (e.g., 304LN, 316LN): Higher strength and toughness.
Why?
Austenitic structure (FCC crystal) resists brittle fracture.
Low carbon content avoids sensitization (carbide precipitation).
2. Nickel-Alloyed Steels
For ultra-low temperatures (−196°C/−321°F and below).
Grades:
9% Nickel Steel (ASTM A353, A553): Used in LNG storage tanks (−196°C).
Invar (Fe-36% Ni): Near-zero thermal expansion for precision instruments.
