Abstract
The present work was concerned with an experimental study of Lüders band propagations in the blue-brittleness range and its analysis of some parameters, that is, dislocation structures, stress dependence of the propagation velocity, and others. The specimen used was an α-iron containing 0.006 wt% carbon. The correlation between the stress drop and the decay time during the band propagation was obtained by using an oscillographic recorder. Also, dislocation structures were observed by means of transmission electron microscopy.
Dislocation structures were tangled and the average dislocation density was about 8×109/cm2 in the temperature range from 160 to 250°C. The magnitude of the stress drop did not directly depend on the amount of dislocation generated and its multiplication rate, but on the width of Lüders band propagated. The propagation velocity of Lüders band could be expressed by the same relation as the stress dependence of dislocation velocity. The dislocation velocity exponent, m, derived from the relation between the stress drop and the decay time was approximately 18 in the temperature range investigated. With increasing temperature, initial velocities of Lüders propagation became higher, i.e. about 55.6 cm/sec at 160°C, 312.4 cm/sec at 200°C, and 595.5 cm/sec at 250°C. This temperature dependence of the velocity could be associated with that of the stress concentration factor caused by dynamical strain ageing near the Lüders band front.
