It is shown that characteristics of plastic strain in the case of delayed fracture (DFPS) under creep conditions reflect fundamental laws governing the temperature- and time-dependent fracture of metallic materials if these characteristics are functions of stress and temperature. The laws governing the change in DFPS are different for different classes of metallic materials. For the unalloyed steels studied in the present investigation, DFPS characteristics increase with a decrease in stress and then — if the time to fracture is very long — decrease. In the case of chromium-nickel steels, a decrease in stress (an increase in time to fracture) is accompanied by a decrease in these characteristics. However, this decrease slows after the passage of certain stress regions which exist for each test temperature. Two laws of development of DFPS are established for the above steels in tests lasting 100,000 h or more. The rupture strength of these steels for times greater than 100,000–200,000 h can be reliably predicted only with allowance for the kinetics of damage accumulation in the material, which is qualitatively reflected by the laws which govern DFPS development in relation to stress and temperature. Numerical solutions are presented for prediction problems for periods of 300,000 h or more. The reliability of the solutions is evaluated.