DISLOCATION CONTRIBUTION TO THE FLOW STRESS OF POLYCRYSTALLINE IRON

Abstract

New information confirms the existing evidence that, after subtracting any friction stress, the flow stress during cold work and creep of polycrystalline iron is determined mainly by the attractive junctions and general stress field of the three-dimensional dislocation network. Thus, recent experiments show none of the preference among the dislocations for the screw orientation that would be expected if jogs in screw dislocations were a main factor, and the grain boundaries during cold work and the subboundaries during creep also have no direct influence. On the other hand, the three-dimensional network is of the tightly linked type envisaged by this theory, and therefore contains a concentration of attractive junctions as well as of dislocations which fits the theory. The unevenness of the three-dimensional network, when the well-known cellular dislocation pattern has developed, does not affect the quantitative relationship between flow stress and network density, probably because it is the average density which is always measured and the weakest links which always determine the flow stress. The average proportionate contributions to the flow stress from the various sources are more or less calculable, but the actual contributions at individual weak links must vary greatly.