The effect of stress changes on creep induced dislocation subgrain arrangements in ferrite

Abstract

The effect of stress changes on the final dislocation subgrain sizes developed in specimens containing ferrite is examined. Uniaxial, constant load, creep tests were carried out on α-iron (ferrite) specimens at 873 K over the stress range 13–22 MPa. The tests were interrupted at a prescribed proportion of the specimen strain within the steady state creep range and then continued at either a higher or lower stress. The dislocation arrangements developed within the specimens were examined using optical and electron microscopy and the subgrain sizes were established using an X-ray back reflection technique. The range of subgrain sizes over which this technique may be realistically applied is also critically considered. The results are discussed with regard to models describing the role of pre-existing dislocation arrangements on the steady state creep rate of metals.