SOME ASPECTS OF THERMOMECHANICAL FATIGUE OF AISI-304L STAINLESS-STEEL.1. CREEP-FATIGUE DAMAGE

Thermomechanical fatigue (TMF) tests on the austenitic stainless steel AISI 304L have been conducted under ''true'' plastic-strain control i n vacuum. This report considers the damage occurring during TMF loadin g. It is shown how the temperature interval and the phasing (in-phase, out-of-phase) determine the mechanical response and the lifetime of t he specimens. If creep-fatigue interaction takes place during in-phase cycling, the damage occurs inside the material, leading to intergranu lar cracks which reduce the lifetime considerably. Out-of-phase cyclin g inhibits creep-induced damage, and no lifetime reduction occurs, eve n if the material is exposed periodically to temperatures in the creep regime. A formula is proposed which allows prediction of the failure mode, depending on whether creep-fatigue damage occurs or not. At a gi ven strain rate, the formula is able to estimate the temperature of tr ansition between pure fatigue and creep-fatigue damage.