MIL-S-16216
MIL-S-16216 is the US Navy specification governing HY-80 and HY-100 quenched-and-tempered high-yield-strength alloy steel plate for submarine pressure hull construction, naval structural applications, and specialized deep-sea equipment. HY-80 (Grade A) provides 80,000 psi minimum yield with exceptional Charpy toughness at −120°F; HY-100 (Grade B) provides 100,000 psi minimum yield with toughness at −60°F. Both grades use a Ni-Cr-Mo-V composition specifically developed to combine high yield strength with the subzero fracture toughness required to survive underwater explosive shock loading.
HY-80 has been the primary US submarine pressure hull material since the USS Albacore (AGSS-569) in the 1950s. MIL-S-16216 imposes stringent chemistry, toughness, and cleanliness requirements that exceed civilian structural steel standards, with NAVSEA qualification required for all producers. Controlled preheat, low-hydrogen electrodes, and strict weld procedure qualification are mandatory for welding.
Mechanical Properties — MIL-S-16216
- HY-80 (Grade A): Min yield 80,000 psi (552 MPa), Min UTS 100,000 psi, Min elongation 20%, CVN ≥ 80 ft-lb at −120°F
- HY-100 (Grade B): Min yield 100,000 psi (690 MPa), Min UTS 115,000 psi, Min elongation 18%, CVN ≥ 80 ft-lb at −60°F
- Plate thickness: 0.188–8.000 inch (HY-80), 0.188–5.000 inch (HY-100)
- Condition: Quenched and tempered
- Preheat for welding: 50–200°F (HY-80), 200–400°F (HY-100) by thickness
MIL-S-16216 plate is produced in the quenched and tempered condition. HY-80: austenitize 1600–1700°F, water or polymer quench, temper 1100–1200°F for 80 ksi yield with excellent subzero toughness. HY-100: temper at 1050–1150°F for 100 ksi yield. Post-weld stress relief (PWSR) is required for all critical joints. Welding consumables must be NAVSEA-approved low-hydrogen types achieving equivalent or superior toughness to the base metal. WPS (Weld Procedure Specification) qualification per NAVSEA Technical Publications is mandatory for submarine hull construction.
- US Navy submarine pressure hull plating and structural frames
- Submarine sail (conning tower) structure
- Torpedo room pressure bulkheads and watertight closures
- Deep-diving research vessel and bathyscaphe pressure hulls
- Naval ship hull structure in areas requiring guaranteed subzero impact toughness
- Oceanographic equipment housings for deep-sea applications
- Specialized naval deep-submergence vehicle structural components
HY-80 Steel
80 ksi yield quench-and-tempered naval steel — the primary US submarine pressure hull material since the 1950s, governed by MIL-S-16216 Grade A.
HY-100 Steel
100 ksi yield HY-grade steel for deeper-diving submarine hulls — MIL-S-16216 Grade B with more demanding weld procedure requirements than HY-80.
MIL-S-24645 - HSLA-80/100
Age-hardening weldable alternatives to HY-80/100 for naval surface combatant construction — same yield classes without mandatory preheat.
Certified Material for Critical Service
MIL-S-16216 requires full chemistry traceability, yield strength, tensile strength, elongation, reduction of area, and Charpy V-notch impact energy documentation for each plate. HY-80 impact testing at −120°F; HY-100 at −60°F. NAVSEA approval is required for all producers supplying submarine pressure hull material. Material must be procured from the NAVSEA Qualified Products List and accompanied by a Qualified Products Certificate along with the CMTR. Plate identification and heat number marking are mandatory for submarine hull material traceability.