Abstract
In order to obtain a fundamental knowledge for the study of austenitic heat resisting steels, the strengthening factors affecting high temperature creep of nickel-copper alloys, representative of face-centered cubic alloys, is discussed using Sherby’s equation: \dotεs=Aγ3.5(σ⁄E)nD, where \dotεs is the steady state creep rate, γ is the stacking fault energy, σ is the applied stress, E is Young’s modulus, D is a diffusion constant. Although it is shown that the steady state creep rate of these alloys can be expressed approximately with the above equation, it is necessary to consider a third strengthening factor. A possible factor seems to be the friction stress to dislocations, induced by dragging the Suzuki or the Cottrell atmosphere. To ascertain this assumption, the anomalous strengthening by annealing at about 300°C was measured for the 5% cold worked alloy. On the other hand, dislocation structures of the cold worked alloys were continuously observed at elevated temperatures by means of 500 kV electron microscope, and it was confirmed that the dislocation arrangement does not change up to 350°C. This indicates that the anomalous strengthening is due to the segregation of solute atoms to dislocations. From these results, the contributions from the solute segregation to dislocations on the strength are considered to be about 1/5 those estimated by Suzuki. These values support the assumption that the third strengthening factor at high temperature may be the interaction between dislocations and the solute atmosphere.
