STRESS RESPONSE UNDER THERMAL-MECHANICAL STRAIN CYCLING FOR A 1 CrMoV FERRITIC STEEL AND TWO 316 STAINLESS STEELS

Abstract— Isothermal and thermal-mechanical strain fatigue tests were conducted in air on representative service alloys; a 1 CrMoV steel, and two batches of 316 stainless steel. Data was obtained for thermal-mechanical in-phase and out-of-phase cycles, and also for isothermal tests at the maximum, minimum, and mid-temperature of the thermal-mechanical cycle. Dwell periods were also incorporated in the cycle to assess their effects.
A comparative evaluation has been made on the basis of the materials' cyclic stress response. In general, the results have shown that the thermal-mechanical strain cycling tests cause a large increase in stress range over those tested under isothermal conditions at maximum temperature. In addition, mean stress and strain offsets were developed in continuous cycle thermal-mechanical tests, whereas negligible offsets occurred in isothermal tests.
It appears that the response of the materials could not always simply be explained by reference to the temperature change itself.