MIL-S-23009C, MILITARY SPECIFICATION, STEEL FORGINGS, ALLOY, HIGH YIELD STRENGTH (HY-80 AND HY-100) (10 DEC 1987) [SEE NOTICE 1 FOR REPLACEMENT INFORMATION]., This specification covers grade HY-80 and grade HY-100 alloy steel forgings intended for critical structural applications where a weldable, high-strength, high-toughness material is required.