Workability of commercial-purity titanium and 4340 steel during equal channel angular extrusion at cold-working temperatures

Abstract

The deformation and failure of commercial-purity (CP) titanium (grade 2) and AISI 4340 steel (tempered to Rc35) during equal channel angular extrusion were determined at temperatures between 25 °C and 325 °C and effective strain rates between 0.002 and 2.0 s−1. The CP titanium alloy underwent segmented failure under all conditions except at low strain rates and high temperatures. By contrast, the 4340 steel deformed uniformly except at the highest temperature and strain rate, at which it also exhibited segmented failure. Using flow curves and fracture data from uniaxial compression and tension tests, workability analysis was conducted to establish that the failures were a result of flow localization prior to the onset of fracture. This conclusion was confirmed by metallographic examination of the failed extrusion specimens.