Influence of Dynamic Strain Aging on Ratcheting Deformation Behavior of SA333 Gr-6 Steel

SA333 Gr-6 steel is a candidate material for the primary cooling system in nuclear power plants. During service, piping components experience asymmetrical stress or strain cycling, resulting in plastic strain accumulation and a drastic reduction in fatigue life compared to symmetrical loading. This investigated steel is prone to the dynamic strain aging phenomenon. The present investigation deals with DSA and its influence on ratcheting deformation. Ratcheting tests were conducted at fixed load (σ_m= 50 & σ_a= 400 MPa) with varying temperatures from room temperature to 350 °C and stress rates (20-700 MPa s⁻¹). Result reveals that the steel shows greater resistance to ratcheting strain and increased fatigue life at DSA dominant temperature regimes. The DSA is active at a temperature between 250 and 350 °C and the DSA regime gets shifted to a higher temperature with the increase in stress rate. Transmission electron microscopy (TEM) studies reveal severe dislocations activities and dislocation forest at DSA dominant specimen, whereas the arrangement of dislocations into well-developed cell structures at the non-DSA regime. TEM result is corroborated by calculating dislocation density from x-ray diffraction analysis, and it was found greater dislocation density at DSA dominant and lower at the non-DSA regime.