INTERACTION OF HIGH CYCLE FATIGUE WITH HIGH-TEMPERATURE CREEP IN STEELS

The interaction of high cycle fatigue with high temperature creep was studied on austenitic steel of the type AISI 304 at 700-degrees-C and on bainitic steel of the type 2.25 Cr - 1 Mo (pressure vessel steel) at 600-degrees-C. The cyclic stress component affects strongly both the minimum creep rate and the time to fracture. For a constant maximum stress in stress cycle sigma-max, the creep rate and the time to fracture depend on the stress ratio R = sigma-min/sigma-max in a nonmonotonic way. From the practical point of view it is important that even small vibrations superimposed on the static load increase the time to fracture substantially. The explanation of the effect of cyclic stress component on deformation processes is based on composite model of dislocation structure.