Mechanical equation of state analysis of elevated temperature cyclic deformation of austenitic stainless steels

The present work considers load relaxation data reported by Conway, Stentz and Berling, for 304 and 316 stainless steels during cyclic deformation with various hold times. The experiments were conducted at 650 and 5380C, temperatures sufficiently high so that recovery is likely to occur during the experiment. The experimental data are analyzed to determine if a power law suggested as an equation of state can represent the observed behavior. In 304 at 6500C short hold times and large cyclic strain amplitudes inhibit recovery. Conversely, long hold times and small cyclic strains promote recovery. At 5380C for 304 no evidence of recovery was found. Likewise in 316 at 6500C no recovery was found. These observations can be explained on the basis of thermal and strain induced recovery of the microstructure developed by cyclic deformation. When recovery occurs, stress relaxation no longer prescribes the loci of rate dependent behavior at a constant state; rather the material passes through a continuous succession of states. The results of this analysis indicate that the power law may provide an equation of states for the stainless steels