Cold-worked state and annealing behaviour of austenitic stainless steel

Abstract

An investigation was made into the structural changes accompanying cold working and annealing treatments in seven austenitic stainless steels. The materials studied included five laboratory alloys and two commercial grades of austenitic stainless steels (types 304 and 316). X-ray line profile analysis showed that the stacking-fault energies of the seven steels ranged from 8 MJ m⁻² to 68 MJ m⁻². Transmission electron microscopy (TEM) was used extensively to characterize the cold-worked and annealed states, Measurements of the resistivity change were performed to characterize the recovery and recrystallization behaviours. The cold-worked structure was found to be related to the stacking-fault energy. Dislocations tended to be arranged in planar arrays and to be confined in the original slip planes in alloys of low stacking-fault energy. Dislocation arrangement was less uniform and more random for steel of high stacking-fault energy. In none of the cases studied was the stacking-fault energy high enough to allow the cross-slip necessary to generate the dislocation cell structure often seen in other metals. Isochronal annealing of the steels reveals a distinguishable stage of resistivity recovery prior to recrystallization, which was attributed to the annihilation of vacancies and removal of carbon from the solid solution. A second stage of resistivity drop (above 500° C) resulted from recrystallization. The temperature for the start of recrystallization was found to be related to stacking-fault energy.