SUPERPLASTIC GAS-PRESSURE DEFORMATION OF IRON CARBIDE SHEET

The superplastic now characteristics of iron carbide under conditions of biaxial gas-pressure forming are described. Forming experiments wer e conducted at 1050 degrees C on a fine-grained (7-8 mu m) Fe-5.25%C-1 .5%Cr material. Flow stresses in the range of 6-22 MPa were applied an d 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 stre ss-strain rate data and the strain analysis show that iron carbide def orms with an apparent strain rate sensitivity exponent value of about 0.4 with deformation rates lower than those observed in uniaxial tensi le tests. The difference between uniaxial and biaxial test results is attributable to grain size effects. Microstructural observations and f racture behavior are also discussed.