Abstract
A Fe-0.75% Mn alloy was creep tested at 500°C to examine the following three points: (1) whether or not the steady state creep of the alloy was in a thermodynamical steady state, (2) which configuration of the dislocation network was contributing to the creep strength, and (3) which change in the dislocation network was the cause of the creep recovery. Specimens were furnace-cooled under stress and then observed by transmission electron microscopy. The creep stress was reduced during the test and the recovery of the creep rate was found to consist of two stages. The decrease in dislocation density was not connected with the rapid and extensive first stage recovery, but with the second stage recovery. The subgrain size changed during steady state creep, indicating that the subgrain boundary was not controlling the creep strength. Though not by a single stage, the recovery was completed; i.e. the history effect disappeared in the true steady state. The structure factor, therefore, did not exist as an independent variable during the true steady state creep of the present simple and stable alloy. This suggests that the thermodynamical steady state was realized at least for the factors controlling the creep strength.
