Work hardening in a steel containing a coarse dispersion of cementite particles

Abstract

The contribution of long range stresses to work hardening has been investigated in a high carbon (1.1 wt.%) steel containing a coarse dispersion of spheroidal cementite particles. X-ray diffraction measurements of lattice strains showed that the internal stress system developed by plastic deformation was of the kind envisaged in the theory of Fisher, Hart and Pry: back stresses in the ferrite being mainly balanced by larger stresses of the opposite sign in the cementite. The inter-phase stresses increased rapidly during the first few per cent of plastic extension. While this occurred the rate of work hardening was much higher than that of a low carbon steel, but the additional work hardening due to the presence of the particles approached a limiting value after 6–8 per cent strain. At this stage the average stress in the cementite had reached about 10 5 p.s.i.; thus it is likely that the inter-phase stresses were limited by slip processes within the matrix rather than by deformation or fracture of the cementite particles. Estimates of the magnitude of the back stresses in the ferrite show that they account for a major part of the additional work hardening due to the dispersed particles. It is expected that this result will be generally true of dispersion hardened alloys having a similarly large volume fraction of strong, noncoherent particles.