Yield Points and Transient Creeps in Polycrystalline Iron of Very Low Carbon Content

Abstract

The time-dependent plastic properties in wet-hydrogen-treated iron were observed at −78°C. The stress-strain curves at various strain rates showed gradual yield drops at yield point and no inhomogeneous deformation i. e. Lüders band. The creep curves showed an exponential rise of plastic strain at an early period of creep. Observed results were analysed by the strain rate equation, \dotε=bnv. The magnitude m in the dislocation velocity-stress relation, v^∞σ^m, is obtained to be about 10 from the stress sensitivity of strain rate at a constant strain. It is concluded that the upper yield stresses in the present experiment are not closely relatated to the stress required to unpin dislocations.