The effects of thermomechanical history on the microstructure of a nickel-base superalloy during forging

The effect of thermo-mechanical history on hot compression behaviour and resulting microstructures of a nickel base superalloy is presented. Hot compression tests were carried out on HAYNES® 282® specimens to varying strains from 0.1 to 0.8. Both single pass and multi-pass tests were completed. 60 minute inter-pass times were utilized to accurately replicate industrial forging practices. The effect of dynamic, metadynamic and static recrystallization during inter-pass times on flow stress was investigated. The study showed the presence of yield peaks in the flow stress data which have been identified in previous studies and thought to be due to solute atoms pinning dislocations, but in this work are shown to be due to friction. The resulting microstructures were analysed using scanning electron, optical microscopy and EBSD to relate grain size and homogeneity with flow stress data. The study showed a negligible difference between multi-pass and single pass tests for strain increments above 0.2. Therefore, when modelling similar low strain and strain rate forging processes inHAYNES® 282®, previous forging steps can be ignored