Reversibility in the work hardening of spheroidised steels

Abstract Estimates of the contributions made by directional and non-directional components of work hardening, to the flow strengths of two spheroidised steels in monotonic and reversed axisymmetric deformation, have been based on measurements in X-ray diffraction, indentation hardness and shapechange tests. The results show that, in monotonic deformation of a 1.1% carbon steel, the directional component of internal stress made the dominant contribution to work hardening with applied strains up to ~ 0.02 and it accounted for about half the hardening increment with ~ 0.05 strain. In reversed deformation, the directional mean stress was fully reversed at the reverse strains required to give near-parallelism between the “forward” and “reverse” stress-strain curves. Thus the directional component of internal stress had little direct influence on the magnitude of permanent softening observed in Bauschinger tests. To a close approximation, permanent softening was a measure of the extent to which non-directional hardening was wiped out in reversed deformation. Comparison with the behaviour of a low-carbon steel showed that the extent of this reversibility in work hardening increased with an increasing volume fraction of non-deforming particles. Some implications of these findings are discussed.