Hardening interaction in cyclic creep of a type 316 stainless steel at 20 degrees C and 500 degrees C

The development of anisotropic material properties due to torsional cyclic plastic straining of tubes with sustained axial loads was examined for a type 316 stainless steel at room temperature and at 500 degrees C. The effect of the cyclic strains and the cumulative ratchetting strains on the axial tensile properties was determined and the results show a significant increase in the tensile strength at both 20 degrees C and 500 degrees C, with more pronounced hardening at the higher temperature. The cyclic shear stress-strain response of the material is shown to be extremely temperature dependent and the hardening ratio is much greater at 500 degrees C, which is consistent with the dynamic strain ageing observed previously for this material. The ratchetting strains are controlled by the cyclic shear strain hardening, by the axial hardening resulting from the cyclic shear and the cumulative axial strains, and by the ratio of the secondary shear stress to the primary axial stress.