Creep and Creep Recovery of 304 Stainless Steel at Low Stresses With Effects of Aging on Creep and Plastic Strains

Creep and creep recovery data of 304 stainless steel are reported for experiments at low stress levels under combined tension and torsion at 593°C (1100°F). The data were represented by a viscous-viscoelastic model in which the strain was resolved into five components—elastic, plastic (time-independent), viscoelastic (time-dependent recoverable), and viscous (time-dependent nonrecoverable) which has separate positive and negative components. Only part of the creep strain at low stresses was recovered upon complete unloading following creep (as also found at high stresses), and each time-dependent strain data was well represented by a power function of time. But the stress dependence below a transition stress was approximately a linear relation with no creep limits and no cross effects such as were found in a previous analysis for higher stress levels above a transition stress. The transition stress for nonrecoverable strains agrees with the Frost-Ashby boundary between diffusional flow and dislocation creep. Aging decreased the creep rate and plastic strain. Results for different times of aging at 593°C (1100°F) under pure tension stresses were well represented by power functions of aging time up to 1000 h for each creep component and plastic strain.