Cyclic hardening and softening of annealed and 9%-prestrained AISI 304 stainless steel during high strain cycling at room temperature

Testpieces of annealed and 9%-prestrained AISI 304 stainless steel were subjected to high strain cycling at room temperature. The material did not obey the rule of the unique stress/strain curve. The saturation stress levels in the stress response curves were different for the annealed and the prestrained steel. The dislocation substructures developing during cycling were studied by high-voltage electron microscopy. In both the annealed and the 9%-prestrained material the main components of the substructure were dislocation cell structures, which formed within the first few % of fatigue life. In the prestrained material bands probably containing stacking faults and/or ε-martensite plates were also observed that were not removed by the strain cycling. The cell structures of the prestrained material were less regular and less well defined than those of the annealed material.