Strain Hardening and Ductility of Iron: Axisymmetric Vs Plane-Strain Elongation. Final Report

摘要

The strain hardening of interstitial-free iron at high strains in plane-strain elongation (strip drawing) falls increasingly below that of drawn iron wires at true strains (epsilon = ln l/l/sub o/) above 2, going through zero strain hardening at epsilon = 3, and becoming strongly negative thereafter. High-resolution selected-area electron diffraction maps show no textural instability or change in orientation associated with the shear bands. The only instability seen in these shear bands is microstructural. Flow properties of Fe-0.17 w/o Ti has been characterized for monotonic plane-strain elongation, monotonic axisymmetric elongation, and completely reversed deformation. Strip drawn wire (i.e., initially wire drawn to epsilon = 3.3, then converted to a rectangular cross section and strip drawn by another epsilon = 2.6, a total elongation of epsilon = 5.9) shows a good deal of strain hardening during the strip drawing in spite of the fact that it is now stronger than the monotonically drawn strip at the same total elongation. The wire drawn strip (i.e., initially strip drawn to epsilon = 2.2, then converted to a circular cross section and wire drawn by another epsilon = 1.3, a total elongation of epsilon = 3.5) shows strain hardening much the same as the strip drawn wire, but it still tends to become elliptical in cross section throughout the subsequent tensile tests. (ERA citation 08:010198)