Abstract
The superplasticity of duplex stainless steel SAF 2304 was investigated at temperatures from 900 to 1050°C and strain rates from 10-4 to 10-2 s-1 using uniaxial tensile tests. Within the range of temperatures and strain rates at which superplasticity occurred, the flow stress was under 20 MPa, and the instantaneous strain rate sensitivity was between 0·45 and 0·75. The microstructural evolution was investigated using optical, scanning electron, and transmission electron microscopes. During superplastic deformation, the initially banded two phase structure progressively broke up and evolved into a homogeneously distributed structure. Also, the strain rate sensitivity index initially rose with strain. Two possible models were considered for this behaviour, one based on slip, and the other a more conventional grain boundary sliding/grain switching model.
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