An iron alloy is provided which exhibits excellent strength and toughness characteristics at cryogenic temperatures. The alloy consists essentially of about 10 to 16 percent by weight nickel, about 0. 1 to 1.0 percent by weight aluminum, and 0 to about 3 percent by weight copper, with the balance being essentially iron. The iron alloy is produced by a process which includes using cold rolling at room temperature and subsequent heat treatment at temperatures ranging from 400° to 650. degree. C., and possesses a fracture toughness ranging from 200 to 230 ksi {square root}in. and yield strengths up to 230 ksi.
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