Effects of solutionizing cooling processing on γ″ (Ni3Nb) phase and work hardening characteristics of a Ni-Fe-Cr-base superalloy

The effects of solutionizing cooling processing (the interrupted water-cooling and direct water-cooling) on the number and size distribution of γ″ (Ni3Nb) phase, as well as work hardening characteristics during hot tensile deformation, of a Ni-Fe-Cr-base superalloy are investigated. It is found that γ″ phase and work hardening characteristics are sensitive to the solutionizing cooling processing. For the superalloy treated by the interrupted water-cooling, the size and number of γ″ phase significantly decrease with raising the interrupted temperature (Tin). The strain hardening exponent rapidly increases when Tin are higher than 705 °C. When Tin are below 755 °C, the tensile curves exhibit parabolic shape, showing a typical work hardening-dynamic recovery behavior. With the increase of true plastic strain (εp), the work hardening rate (θ=dσ/dε) firstly increases and then decreases after elastic-plastic transient stage. However, when Tin are higher than 755 °C, flow stress linearly increases, and the obvious linear hardening occurs. The value of θ remains almost constant with the further increase of true plastic strain (εp) after elastic-plastic transient stage. In addition, the flow characteristics of the superalloy treated by the direct water-cooling are similar to those of the superalloy treated by the interrupted water-cooling.