Superplastic behaviour of commercial duplex stainless steel SAF 2304

The superplasticity of duplex stainless steel SAF 2304 was investigated at temperatures from 900 to 1050 degrees C and strain rates from 10(-4) to 10(-2) s(-1) using uniaxial tensile tests. Within the range of temperature 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 microstuctural evolution was investigated using optical, scanning electron, and transmission electron microscopes. During superplastic deformation, the initially banned two phase structure progressively broke up and evolved into a homogeneously distributed structure. Also, the strain rate sensitivity index initially rose with str ain. Two possible models were consirdered for this behaviour, one based on slip, and the other a more conventional grain boundary sliding/grain switching model. MST/4307.