Generally, 9% nickel steel pressure vessel plates may be furnished in double-normalized and tempered condition (ASTM A353), quenched and tempered condition (ASTM A553), or direct-quenched and tempered condition (ASTM A844). The microstructure of 9% nickel steel after heat treatment consist of fine tempered-martensite and appreciable retained austenite (about 5% to 15% structure size) which contributes to the excellent cryogenic toughness of this steel. Since the alloying addition of approximate 9% nickel also suppresses the formation of ferrite/pearlite high-temp transformation phases, relatively higher strength is also attained.