Creep of Metals and Recrystallization

Abstract

THERE has been a certain amount of dispute as to the fundamental laws of creep of polycrystalline metals1. I have advanced the view that the normal creep of a rod extending longitudinally under constant stress can always be represented fairly closely by the formula where l is the length at time t, l0 is approximately the initial length and β and k are constants. This gives a final rate of extension per unit length which tends to become approximately constant. On the other hand, it has been contended that there is a final state of accelerated creep, called2 by some metallurgists Stage 4. When the total extension is of some per cent, this stage is often obtained in tests at constant load and can then, on my view, be attributed to increasing stress, consequent upon the thinning of the specimen. As argument against this, it has been pointed out that the increasing rate of creep has been obtained with extensions of less than 1 per cent in the case of certain steels at high temperature (see Fig. 1)3. This I have, however, attributed to recrystallization during the process of creep, recrystallization having been shown to produce increased rate of flow in certain cases4.