Microstructure and stability conditions for hot deformation of a modified iron-based superalloy

A modified iron-based superalloy is studied regarding its hot formability. The microstructure contained particles of titanium carbides, carbonitrides and nitrates. Torsion tests at high strain rate at temperatures ranging from 800 to 1200 degrees C were conducted. Results of these tests were correlated by means of the Garofalo hyperbolic sine creep relation. An optimum forming temperature of 1260 degrees C at 10 s(-1) is obtained. This temperature is strongly dependent on the strain rate. An activation energy for plastic deformation close to that for the activation energy for lattice diffusion in austenitic stainless steels and a stress exponent near 5 were obtained. These values suggest that plastic deformation is controlled by a dislocation climb mechanism.