Superplastic gas-pressure deformation of iron carbide sheet

The superplastic flow characteristics of iron carbide under conditions of biaxial gas-pressure forming are described. Forming experiments were conducted a 1050 °C on a fine-grained (7–8 μm) Fe5.25%C-1.5%Cr material. Flow stresses in the range of 6–22 MPa were applied and deformation strain rates approaching 10−3 s−1 were achieved. The strain distribution in as-formed hemispherical caps was examined for comparison with a previously developed analytical model. Both the stress-strain rate data and the strain analysis show that iron carbide deforms with an apparent strain rate sensitivity exponent value of about 0.4 with deformation rates lower than those observed in uniaxial tensile tests. The difference between uniaxial and biaxial test results is attributable to grain size effects. Microstructural observations and fracture behavior are also discussed.