Hot working characteristics of nickel-base superalloy 740H during compression

The hot deformation behavior of nickel-based superalloy 740H has been investigated by hot compression experiments. The tests were carried out in the temperature range of 1050-1200 °C with strain rates of 0.1-20 s−1 to a total strain of 0.6. True stress-true strain curves and deformation microstructures were studied. The results show that dynamic recrystallization, which is the principal softening mechanism in the hot working of 740H, determines the shape of flow curves. The fraction of DRX grains at the strain of 0.6 is increased by deformation temperature while at a particular temperature, it is lower at strain rate of 1 s−1 than at other strain rates. A hyperbolic-sine type equation has been established between peak stress and deformation conditions through Z parameter, giving activation energy value of 357.3 kJ/mol. The hot working windows of alloy 740H was briefly discussed using the processing map. Temperature range of 1160-1200 °C with strain rate larger than 10 s−1 is the probable domain for hot extrusion of 740H.