The hot working behavior of a 38Ni-21Cr based superalloy was studied. Torsion tests at strain rates between 2 and 20 s-1and temperatures between 1123 and 1473 K were conducted. A fine microstructure of about 6-10 lm grain size and small TiC particles were observed after torsion tests at 1473 K and 4 s-1. The results of these tests were analyzed usingMATLAB and MS EXCEL programs to obtain the parameters of the Garofalo equation able to correlate the experimental data with a single equation. Stress exponent values much higher than 5 and a high activation energy for deformation suggest that the deformation is controlled by a slip creep mechanism characteristic of reinforced materials. The optimum forming temperatures at different strain rates were determined by means of the second Lyapunov stability equation. An optimum stability temperature of 1643 K (13708C) at 10 s-1is determined.

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°C were conducted. Results of these tests were correlated by means of the Garofalo hyperbolic sine creep relation. An optimum forming temperature of 1260°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.